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3 g training by luca

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3 g training by luca

  1. 1. Part I 3G Overview 1 Company Confidential
  2. 2. What’s New in WCDMA? Characteristic to WCDMA • RAKE receiver takes advantage of multipath propagation • Fast power control keeps system stable by using minimum power necessary for links • Soft handover ensures smooth handovers 2 Company Confidential Multiservice Environment • Data speed – In RAN1 bit rate varies from 8 kbps up to 384 kbps – Variable bit rate also available – Bit rate gradually grows up to 2 Mbps • Service delivery type – Real-time (RT) & non real-time (NRT) • Quality classes for user to choose – Different error rates and delays • Traffic asymmetric in uplink & downlink • Common channel data traffic (FACH) • Inter-system handovers Air Interface • Capacity and coverage coupled - “cell breathing” • Neighbor cells coupled via interference • Soft handover • Fast power control • Interference limited system (e.g. GSM frequency limited)
  3. 3. 3 Company Confidential UMTS network architecture BSS BSC RNS RNC CN Node B Node B A IuPS Iur Iubis USIM ME MS Cu Uu MSC SGSN Gs GGSNGMSC Gn HLR Gr Gc C D E AuC H EIR F Gf GiPSTN IuCSGb VLR B Gp VLR G BTSBTS Um RNC Abis SIM SIM-ME i/f or MSC B PSTNPSTN cell Ref. 3GPP TS23.002 Microsoft Word Document
  4. 4. 3G Spectrum Allocation 4 Company Confidential
  5. 5. IMT2000 Frequency Allocation for UMTS 1900 1920 1980 2010 2025 2110 2170 2200 MSS UL TDD UL/DL TDD UL/DL FDD UL MSS DL FDD DL MHz 5 Company Confidential FDL FDL/UL FUL FDD Mode TDD Mode
  6. 6. 3G Terms 6 Company Confidential • IMT 2000 – Third generation mobile systems as defined by ITU – Global recommendation • 3GPP – 3rd Generation Partnership Project (Forum for a WCDMA standardization) – Involved: ETSI (Europe), ARIB (Japan), TTA (Korea), T1P1 (USA), TTC (Japan) and CWTS (China) • 3GPP2 – 3rd Generation Partnership Project (Forum for a CDMA2000) • UMTS – Third generation telecommunication system, that is subject to specifications produced by 3GPP • WCDMA – Air Interface technology adapted for UMTS Terrestrial Radio Access (UTRA) • UTRA-FDD – WCDMA in 3GPP, FDD mode • UTRA-TDD – WCDMA in 3GPP, TDD mode • CDMA2000 – Air Interface technology proposal from TR45.5 (USA) on evolution of IS-95 (CDMA) • TD-SCDMA – Time Division Synchronous CDMA (TD-SCDMA) was proposed by China Wireless Telecommunication Standards group (CWTS) and approved by the ITU in 1999 • MSS – Mobile Satellite System
  7. 7. 3G Standards 7 Company Confidential
  8. 8. UMTS System Characteristics • W-CDMA : 5 MHz • Carrier Spacing : multiples of 200 kHz • W-CDMA spreading rate = 3.84 Mchip/s • Chip Rate = 3.84 MHz • Raised cosine filtering with roll-off 0.22 • Information bit rate: between 8 kbit/s and 2 Mbit/s (currently up to 384 Kbit/s) • Spreading Factor (SF): 4 -256 • Multiple Access Scheme : Wideband DS-CDMA • Duplex Scheme : FDD and TDD modes • Carrier Spacing : 4.4 – 5.4 MHz • 10 ms frame with 15 time slots • NodeB synchronization: asynchronous • Highly variable data rates, data rate constant within 10 ms frame • Bandwidth on demand, efficient resource usage • Multiple services with different variable data rates over one physical channel • DL Transmission diversity 8 Company Confidential
  9. 9. Key features of WCDMA •Soft handoff: user equipment (UE) and base stations use special rake receivers that allow each UE to simultaneously communicate with multiple base stations. The diversity gain associated with soft handoff is known as the "soft handoff gain factor". – Soft handover (links from different NodeB) is performed at RNC level using Selection Combination (RNC choose the best link) – Softer handover (links from same NodeB) is performed at NodeB using Maximum Ratio Combination (NodeB combines the signals). Softer handover usually is higher then soft •Multi-path reception: the rake receivers also allow the UE to decode multiple signals that have traveled over different physical paths from the base station. For example, one signal may travel directly from the base station to the UE, and another may reflect off a large building and then travel to the UE. This phenomenon, "multi-path propagation", also provides a diversity gain. The same effect occurs on the uplink from the UE to the base station. •Power control: transmissions by the UE must be carefully controlled so that all transmissions are received with roughly the same power at the base station. If power control is not used, a “near-far” problem, where mobiles close to the base station over- power signals from mobiles farther away, occurs. The base station uses a fast power control system to direct the mobile to power up or power down as its received signal level varies due to changes in the propagation environment. Likewise, on the downlink, transmissions from the base stations are power-controlled to minimize the overall interference throughout the system and to ensure a good received signal by the UE. 9 Company Confidential
  10. 10. Key features of WCDMA Frequency reuse of 1: every base station in the CDMA system operates on the same frequency for a given carrier, so no frequency planning is required. As every site causes interference to every other site, careful attention must be paid to each site's radio propagation. Soft capacity: capacity and coverage are intertwined in CDMA, depending on the number of users in the system and the amount of interference allowed before access is blocked for new users. By setting the allowed interference threshold lower, coverage will improve at the expense of capacity. By setting the threshold higher, capacity will increase at the expense of coverage. Because of the fundamental link between coverage and capacity, cells with light traffic loads inherently share some of their latent capacity with more highly loaded surrounding cells. 10 Company Confidential
  11. 11. WCDMA Compared to GSM and CDMA IS-95 WCDMA vs. GSM WCDMA has some similarities with GSM technology, however, it is a fundamentally different technique for allowing multiple users to share the same spectrum and as a result it has many differences. 11 Company Confidential
  12. 12. 12 Company Confidential WCDMA Compared to GSM and IS-95 CDMA
  13. 13. 13 Company Confidential • TD-SCDMA Technical Summary Frequency band: 2010 MHz - 2025 MHz in China (WLL 1900 MHz - 1920 MHz) Minimum frequency band required: 1.6MHz Frequency re-use: 1 (or 3) Chip rate: 1.28 Mcps Frame length: 10ms Number of slots: 7 Modulation: QPSK or 8-PSK Voice data rate: 8kbit/s Circuit switched services: 12.2 kbits/s, 64 kbits/s, 144 kbits/s, 384 kbits/s, 2048 kbits/s Packet data: 9.6kbits/s, 64kbits/s, 144kbits/s, 384kbits/s, 2048kbits/s Receiver: Joint Detection, (mobile: Rake) Power control period: 200 Hz Number of slots / frame: 7 Frame length: 5ms Multi carrier option Handovers: Hard Smart antennas Uplink synchronization Physical layer spreading factors: 1, 2, 4, 8, 16 TD-SCDMA System Characteristics Time Division Synchronous CDMA (TD-SCDMA) was proposed by China Wireless Telecommunication Standards group (CWTS) and approved by the ITU in 1999 and technology is being developed by the Chinese Academy of Telecommunications Technology and Siemens. TD-SCDMA uses the Time Division Duplex (TDD) mode, which transmits uplink traffic (traffic from the mobile terminal to the base station) and downlink traffic (traffic from the base station to the terminal) in the same frame in different time slots. That means that the uplink and downlink spectrum is assigned flexibly, dependent on the type of information being transmitted. When asymmetrical data like e-mail and internet are transmitted from the base station, more time slots are used for downlink than for uplink. A symmetrical split in the uplink and downlink takes place with symmetrical services like telephony.
  14. 14. QoS for different services Real time Non Real time 14 Company Confidential
  15. 15. Conversational services • Speech service: – Real time conversational service require the low time delay from end to end , and the uplink and the downlink service bandwidth is symmetrical – Adopt AMR ( adaptive multi rate ) technique (WCDMA). • 12.2 (GSM), 10.2, 7.95, 7.40(IS-41), 6.70(PDC), 5.90, 5.15 and 4.75kbps • The bit rate of AMR voice can be controlled by the RAN according to the payload of air interface and the quality of voice service • According to the requirement of the operator ,AMR technique can balance the relationship among the network capacity, coverage and the service quality • Video phone (WCDMA) – The requirement of time delay is similar to the voice service. – The CS connection :adopt ITU-T Rec.H.324M – The PS connection :adopt IETF SIP or H.323 15 Company Confidential
  16. 16. Streaming services • Multimedia data streaming: – Preserve time relation between information entities of the data streaming – Data is processed into stable and continuous streaming – Non-symmetry service • Services example : – Telemetry ( monitoring ) 16 Company Confidential
  17. 17. Interactive services • Interactive traffic - fundamental characteristics for QoS: – request response pattern – preserve payload content • Services example : – Location based services – Online game – Web browsing 17 Company Confidential
  18. 18. Background services • Background traffic - fundamental characteristics for QoS: – the destination is not expecting the data within a certain time – preserve payload content • Service example: – E-mail ( server to server ) – SMS – Download of database – Reception of measurement records 18 Company Confidential
  19. 19. Transmission diversity - STTD • Space Time Transmit Diversity 19 Company Confidential
  20. 20. Transmission diversity - TSTD Time Switch Transmit Diversity, used in Synchronization physical channels P-SCH and S-SCH P-SCH S-SCH P-SCH S-SCH 20 Company Confidential
  21. 21. Part II WCDMA Fundamentals 21 Company Confidential
  22. 22. WCDMA = DS-CDMA •WCDMA is a code-division multiple access technology which separates each user’s voice or data information by multiplying the information by pseudo-random bits called "chips". •Direct sequence (DS): with DS, a binary modulated signal is ‘directly’ multiplied by a code. The code is a pseudo-random sequence of ±1, where the bit rate of the code (Chip Rate) is higher than the rate of the signal, usually considerably higher. This has the effect of spreading the signal to a wideband. At the receiver, the same code is used to extract the original signal from the incoming wideband signal. A bit of the code is referred to as a chip, and the defining parameter for such a system is the chip rate. •The pseudo-random bit sequences have a rate of 3.84 Mcps (millions of chips per second), resulting in the narrowband information bits of the user being spread across a much wider bandwidth of approximately 5 MHz. • For this reason, CDMA technology is sometimes referred to as “spread spectrum.” •Spread spectrum describes any system in which a signal is modulated so that its energy is spread across a frequency range that is greater than that of the original signal •The user data (signal) is first spread by the channelisation code (based on Hadamard matrix) called Orthogonal Variable Spreading Factor (OVSF) Code. •OVSF code has the property that two different codes from the family are perfectly orthogonal if in phase 22 Company Confidential
  23. 23. TDMA based System 23 Company Confidential
  24. 24. 24 Company Confidential W-CDMA based System
  25. 25. Processing Gain and Spreading 25 Company Confidential According to information theory, as the frequency spectrum a signal occupies is expanded, the overall power level decreases. In CDMA, the user signals are spread up to a wideband by multiplication by a code. Consider a narrowband signal, say, for example, a voice call. When viewed in the frequency spectrum, it occupies some frequency and has some power level. Once the frequency is spread across a wideband, the total power of this signal is substantially reduced. Now consider that another user has the same procedure performed on it and is also spread to the same wideband. The total system power is increased by a small amount as the two users are transmitted at the same time. Therefore, each new user entering the system will cause the power of the wideband to increase.
  26. 26. Spreading and Despreading • At the receiver, the process of extracting one user is performed (DESPREADING) • The regenerated signal needs to be retrieved with enough power that it can be perceived aboveabove the level of the remaining spread signals. That is, it needs to be of a sufficient strength, or margin, above the rest of the signals so that the signal can be accurately interpreted. • Considering this as a signal to interference ratio (SIR), or carrier to interference (C/I) ratio, the noise affecting one signal is the remaining spread signals that are transmitting at that frequency. This SIR is classified in CDMA as Eb/No. • For mobile device measurements of the quality of the signals from the network, it uses a pilot channel (CPICH), which is broadcast by each cell. The mobile device measures Ec/Io, the energy level of this pilot channel, Ec, compared to the total energy received, Io • Another important characteristic is the rejection of unwanted narrowband noise signals. If a wideband signal is affected by a narrowband noise signal, then since the spreading function is commutative, the despreading operation while extracting the wanted signal will in turn spread the narrowband noise to the wideband, and reduce its power level ••The lower the power that the original signals are transmitted wiThe lower the power that the original signals are transmitted with, the lower theth, the lower the noise in the system. It is therefore essential that each user innoise in the system. It is therefore essential that each user in the system transmitsthe system transmits with an optimum power level to reach the receiver with its requiwith an optimum power level to reach the receiver with its required power level. Ifred power level. If the power level is too high, then that user will generate noise,the power level is too high, then that user will generate noise, which in turn affectswhich in turn affects the performance of all the other users. If there is too littlethe performance of all the other users. If there is too little power, then the signalpower, then the signal which reaches the receiver is of too low quality, and it cannotwhich reaches the receiver is of too low quality, and it cannot be accurately ‘heard’be accurately ‘heard’ 26 Company Confidential
  27. 27. 27 Company Confidential • There are two solutions to the problem of noise levels: – First, an Admission Control policy is required that monitors the number of users and the noise level, and once it reaches some maximum tolerable level, refuses admission of further users. In a cellular system, such admission control needs to be considered not only for one cell, but also for the effects that noise levels within that cell have on neighboring cells. – The second solution is to implement Power Control. Each user needs to transmit with just enough power to provide a clear signal at the receiver above the noise floor. This should be maintained regardless of where the users are located with respect to the receiver, and how fast they are moving. Power control needs to be performed frequently to ensure that each user is transmitting at an optimum level. • The ratio of the original signal to the spread signal is referred to as the spreading factorspreading factor and is defined as: Spreading factor (SF) = chip rate/Spreading factor (SF) = chip rate/symbolsymbol raterate Spreading and Despreading WCDMAWCDMA 5 MHz, 1 carrier5 MHz, 1 carrier TDMA (GSM)TDMA (GSM) 5 MHz, 25 carriers5 MHz, 25 carriers
  28. 28. • In the next slides, the SF is 4. Hence, variable data rates can be supported by using variable length codes and variable SF to spread the data to a common chip rate • When considering CDMA systems, it is useful to define how the different signals interact with each other. Correlation is defined as the relationship or similarity between signals. For pulse-type waveforms, such as CDMA codes, the cross- correlation between two signals is defined as: where R12 is the correlation between two signals v1 and v2, and τ is their relative time offset. • For the code to be effective, the receiver must know the specific code (in this case 1,-1,1,-1, see next slides) which is being used for transmission and it must also be synchronized with this transmission. On reception the receiver can then simply reintroduce the correct code which is multiplied with the incoming signal and reproduce the actual symbol sent by the transmitter. • The receiver also needs to know the actual number of chips that represent a symbol (spreading factor) so that the chips can be regenerated to the sent symbol through averaging the value of the chips over the symbol time. This is achieved through integration, where the chips are summed over the total time period of the symbol they represent. • The principle of correlation is used at the receiver to retrieve the original signal out of the noise generated by all the other users’ wideband signal. Spreading and Despreading 28 Company Confidential
  29. 29. 29 Company Confidential • At the receiver, the received signal is multiplied by the code and the result is integrated over the period of each baseband bit to extract the original data. Since the receiver has four chips over which to integrate, the procedure yields a strong result at the output. • However, consider now that the receiver does not know the correct code. Then the integration process will result in a signal which averages to around zero. • For both of these, the relative strength of the desired signal and the rejection of other signals is proportionate to the number of chips over which the receiver has to integrate, which is the SF. Large SFs result in more processing gain and hence the original signals do not needdo not need so much transmission power to achieve a target quality level. • As can be seen, the longer the symbol time (i.e. lower data rate and higher chip rate), the longer the integration process, thus the higher the amplitude of the summed signal. This is referred to as processing gain (Gp) and is directly proportional to the SF used. • For example, if the symbols were spread over 8 chips then the Gp will be 8; if spread over 16 chips, Gp would be 16. This means that the processing gain is higher for lower data rates than for higher data rates, i.e. lower data rates can be sent with reduced power since it is easier to detect them at the receiver Spreading and Despreading
  30. 30. Spreading and Despreading 30 Company Confidential The spreading sequences must have good correlation properties to facilitate the separation of the wanted signal from all others: •One sharp and dominant peak of the autocorrelation function for zero phase shift •As small as possible values of the autocorrelation function for all out-of-phase shift •As small as possible values of the cross-correlation (different signals) function for all phase shift SF= chip rate/symbol rate = 4
  31. 31. Spreading and Despreading 31 Company Confidential
  32. 32. CDMA Multiple Access Advantages : Multiple Access Features 1. All Users’ Signals overlap in TIME and FREQUENCY 2. Correlating the Received Signal despreads ONLY the WANTED SIGNAL 32 Company Confidential p f f S1 p S1xC1 p f f S2 p S2xC2 f RECEIVER of USER 1 p S1 = S1 X C1 X C1p S2 X C2 X C1 f
  33. 33. CDMA Multiple Access Advantages : Interference Rejection p f f S1 p S1xC1 33 Company Confidential p f I f p S1 p f I IxC1 Correlation Narrowband Interference Spread the power Only a small portion of the interfering signal energy passes the filter and remain as residual interference
  34. 34. CDMA Principles 34 Company Confidential m1(t) Tb 2Tb 3Tb 1 -1 1 Tc : Chip Rate of the PN Code Tb : Information rate (voice/data) M1(f) f 1/Tb C1(f)c1(t) f 1/Tb 1/Tc Tc 4Tc C1(f)* M1(f)m1(t).c1(t) f 1/Tb 1/Tc
  35. 35. Processing gain (Gp) • Gp = Wc/Wi • Where – Wc: chip rate – Wi: user data rate • The more processing gain the system has, the more the power of uncorrelated interfering signals is suppressed in the despreading process • Thus, processing gain can be seen as an improvement factor in the SIR (Signal to Interference Ratio) of the signal after despreading • Example: Voice AMR 12.2 Kbps Gp = 10*log(3840000/12200)= 25 dB • After despreading the signal power has to be typically few dB above the interference and noise: Eb/No = 5dB; therefore the required wideband signal- to-interference ratio is 5dB – Gp = -20 dB. • In other words, the signal power can be 20 dB underunder the interference and the WCDMA receiver can still detect the signal • Wideband signal-to-interference ratio is also called carrier-to-interference ratio: C/I • Thanks to spreading and desporeading, C/I can be much lower in WCDMA than GSM (C/I = 9-12 dB) f Wi Wc 35 Company Confidential
  36. 36. Voice user (12,2 kbit/s) Packet data user (384 kbit/s) Powerdensity (W/Hz) W R Frequency (Hz) 36 Company Confidential Frequency (Hz) Unspread narrowband signal Spread wideband signal Processing Gain G=W/R=25 dB Powerdensity (W/Hz) W R Unspread "narrowband" signal Spread wideband signal Processing Gain G=W/R=10 dB •Spreading sequences of different length •Processing gain dependent on user data rate (User data rate) x (spreading ratio)= const.=W=3,84 Mcps Processing gain (Gp)
  37. 37. Spreading in WCDMA Consists of 2 operations: 1. Channelisation (OVSF: Orthogonal Variable SF) • Transforms each symbol (data bit) to the number of chips (increases bandwidth) • Number of chips per symbol = Spreading Factor (SF) 2. Scrambling (does not affect the signal bandwidth) • Scrambling code is applied (PN codes) TX 37 Company Confidential MOD Scrambling Code 3.84 Mcps 3.84 McpsData Channel codingChannel coding (CRC, Encoder, Interleaver, convoluter, Rate Matching) Bit Rate Symbol Rate Channelisation code (OVSF) Chip Rate Chip Rate
  38. 38. • Channel coding – CRC attachment • Check for error during transmission • Voice: if CRC check returns error discard information • Data: if CRC check returns error ask for retransmission – Convolutional or Turbo Coding • Convolution coding for voice and low speed signalling • Turbo coding for large data transmission, better performances than convolutional coding – Interleaving • Distribute error (burstly error) over data transmitted – Rate Matching • Match Symbol Rate to that accepted by spreading • Rate matching techniques: Repeat or Puncturing (remove) Spreading in WCDMA Channel coding Symbol Rate Chip Rate 3.84 Mcps 38 Company Confidential(OVSF) Rs Rb Example: voice 12.2 (SF 128) Rs=3.84/128= 30Ksps If the output of Channel cod is < 30Ksps, Rate matching repeats the info else uses puncturing (remove)
  39. 39. Spreading in WCDMA 12.2 Kbps Uplink Reference channel 39 Company Confidential 64 Kbps Uplink Reference channel
  40. 40. 40 Company Confidential OVSF properties • In the spreading process, information symbols, which occupy a relatively narrow bandwidth, are multiplied by a high-rate spreading code consisting of chips • The resulting spread signal has a wider bandwidth dependent on the number of chips per symbol • In the de-spreading process, the spreading code is multiplied by the spread signal to recover the original data symbols. The de-spreading process converts the wide bandwidth spread signal back to the original narrower bandwidth of the data symbols • Spreading codes (OVSF) are specially designed to allow the symbols from multiple users to occupy the same spectrum at the same time, while still allowing the original information to be retrieved. • Codes are allocated in RNC • OVSF code has the property that two different codes from the family are perfectly orthogonal if in phase • Restrictions: another physical channel may use a certain code in the tree if no other physical channel to be transmitted using the same code tree is using a code that is on an underlying branch, i.e. using a higher SF generated from the intended spreading code to be used. Neither can a smaller SF code on the path to the root of the tree be used SF4
  41. 41. OVSF properties • The signals that are all being transmitted at the same time and frequency must be separated out into those from individual users. This is the second role of the code. Considering the party analogy, if this was a GSM party, then the problem is solved easily. All guests must be quiet and each is then allowed to speak for a certain time period; no two guests speak at the same time. At a CDMA party, all users are allowed to speak simultaneously, and they are separated by speaking in different languages, which are the CDMA codes. All of the codes that are used must be unique and have ideally no relationship to each other. Mathematically speaking, this property is referred to as orthogonality. The system can support as many simultaneous users as it has unique or orthogonal codes. • Orthogonal codes are used in CDMA systems to provide signal separation. As long as the codes are perfectly synchronized, two users can be perfectly separated from each other. • To generate a tree of orthogonal codes, a Walsh–Hadamard matrix is used. For perfect orthogonality between two codes, for example, it is said that they have a cross- correlation of zero when τ = 0. Consider a simple example using the following two codes: 41 Company Confidential
  42. 42. OVSF properties 42 Company Confidential • To verify if two codes have a zero cross-correlation, they are tested in the below equation, first multiplied together and then integrated, as shown in Figure below. The result is zero, indicating that indeed they are orthogonal. • The number of chips which represent a symbol is known as the SF or the processing gain. To support different data rates within the system, codes are taken from an appropriate point in the tree. These types of orthogonal codes are known as orthogonal variable spreading factors (OVSF). • In the 3G WCDMA system the chip rate is constant at 3.84 Mchips/s. However, the number of chips that represent a symbol can vary. Within this system as laid down by the specifications, the minimum number of chips per symbol is 4 which would give a data rate of 3 840 000/4 = 960 000 symbols per second. The maximum SF or number of chips per symbol is 256,1 which would give a data rate of 3 840 000/256 = 15 000 symbols per second. Thus it can be seen that the fewer chips used to represent a symbol, the higher the user data rate. The actual user data rate must be rate matched to align with one of these SF symbol rates. • Although orthogonal codes demonstrate perfect signal separation, they MUST be perfectly synchronized to achieve this. Another drawback of orthogonal codes is that they do not evenly spread signals across the wide frequency band, but rather concentrate the signal at certain discrete frequencies. As an example, consider that the code ‘1 1 1 1’ will have no spreading effect on a symbol. To overcome these drawbacks the PN codes are introduced
  43. 43. 43 Company Confidential • Another code type used in CDMA systems is the pseudo-random noise (PN) sequence. This is a binary sequence of ±1 that exhibits characteristics of a purely random sequence, but is deterministic. Like a random sequence, a PN sequence has an equal number of +1s and −1s, with only ever a difference of 1. PN sequences are extremely useful as they fulfill two key roles in data transmission: 1. Even spreading of data: when multiplied by a PN sequence, the resultant signal is spread evenly across the wideband. To other users who do not know the code, this appears as white noise. 2. Signal separation: while PN sequences do not display perfect orthogonality properties, nevertheless they can be used to separate signals. At the receiver, the desired signal will show strong correlation, with the other user signals exhibiting weak correlation • Another property of PN sequences is that they exhibit what is known as autocorrelation. This is defined as the level of correlation between a signal and a time-shifted version of the same signal, measured for a given time shift. For a PN sequence, the autocorrelation is at a maximum value, N, when perfectly time aligned, i.e. τ = 0. N is the length in numbers of bits of the PN sequence. This single peak drops off quickly at ±Tc, where Tc is the width of a chip of the code. This allows a receiver to focus in on where the signal is, without a requirement for the transmitter and receiver to be synchronized. In comparison, the autocorrelation of time-shifted orthogonal codes results in several peaks, which means that this signal locking is much more problematic. Scrambling code properties
  44. 44. Scrambling code properties • The OVSF codes are effective only when the channels are perfectly synchronized at symbol level • The loss in cross-correlation, e.g. due to multipaths, is compensated by the additional scrambling operation • Scrambling codes are used to separate different cells in the downlink and different terminals in the uplink • They have good correlation properties (interference averaging) and are always used on top of the spreading codes, thus not affecting the transmission bandwidth • Gold sequence is used to generate scrambling codes • For downlink physical channels, a total of 218 = 262,143 scrambling codes can be generated • Only scrambling codes k = 0, 1, ..., 8191 are used • 8192 scrambling codes are divided into 512 groups each of which contains 16 scrambling codes • The first scrambling code of each group is called Primary Scrambling Code (PSC) and the other 15 are Secondary Scrambling Codes (SSC) 44 Company Confidential
  45. 45. Usage of the codes Channelization Code Scrambling Code Usage Uplink: separation of physical data (DPDCH) and control channels (DPCCH) for the same terminal Downlink: separation of downlink connections to different users within on cell Uplink: Separation of terminalsSeparation of terminals Downlink: Separation of sectorsSeparation of sectors (cells)(cells) Length 4-256 chips In downlink also 512 chips Uplink: 10ms = 38400 chips Downlink: 10ms = 38400 chips Number of codes Spreading Factor indicates the number of codes under one scrambling code Uplink: over 16 millions Downlink: 512 Code Family Orthogonal Variable Spreading Factor (OVSF) 10ms code: Gold Code 66.7µs code: Extended code family Spreading Yes, indicates bandwidth No, does not affect bandwidth 45 Company Confidential
  46. 46. Receivers • Both NodeB and Terminals use the same type of correlation receivers • Due to multipath propagation it’s necessary to use multiple correlation receivers (fingers) in order to recover (combine) the energy from all paths coherently and obtain multipath diversity 46 Company Confidential
  47. 47. 47 Company Confidential • A transmission from a mobile device is more or less omni directional, and this is also the case for base stations when they have only one cell. Base stations which are sectorized will have directional antennas, which will transmit only over a certain range. • For example, a three-sectored site will have three antennas which each transmit over the range of 120 degrees. From the point of view of the mobile device, it would be ideal if a transmission were unidirectional; however, this is impractical since it would mean that the antenna of the mobile device would need to point towards the base station at all times. • In this ideal situation the device could transmit with reduced power, thus causing less interference to other users and increasing the device’s battery life. In the cellular environment, much of the power transmitted is actually in the wrong direction. In urban areas there is considerable reflection of the signal from surrounding buildings. This is actually a reason why cellular systems work, since the mobile device can thus be out of direct line of sight of the BTS and its signal will still be received. • The reflected signals travel further distances than the direct line of sight transmission and therefore arrive slightly laterslightly later, with greater attenuation and possible phase difference. • It would be advantageous if these time-shifted versions in the multipath signal could be combined at the receiver with the effect that a much stronger signal is received. • Because this combined signal is stronger, it is possible that the BTS may tell the mobile device to reduce its transmitting power. Any process of combining multiple versions of the same signal to provide a more powerful, better quality signal is known as diversity. •• The autocorrelation property of the PN sequence is again used. SThe autocorrelation property of the PN sequence is again used. Since the received signalince the received signal resolves into a single peak around the chip width, then as longresolves into a single peak around the chip width, then as long as theas the multipathmultipath profile is ofprofile is of a duration longer than the chip width, a number of peaks will bea duration longer than the chip width, a number of peaks will be observed, each oneobserved, each one representing a particularrepresenting a particular multipathmultipath Multipath propagation and diversity
  48. 48. Wide Band Channel • Definition: • A channel is defined wide when its bandwidth (Bw) is greater than the Coherence Bandwidth: Bw >> ∆fc 48 Company Confidential τπS fc 2 1 =∆
  49. 49. Wide Band Channel – Delay Spread Channel impulse response (power delay profile) and delay spread Dominant Path 1τ 49 Company Confidential
  50. 50. Wide Band Channel – Narrow/Wide Band System 50 Company Confidential Microsoft Word Document
  51. 51. WCDMA and GSM in TU3 Channel 51 Company Confidential
  52. 52. Optimal Receiver for WCDMA signal • For a channel with only one signal path optimal receiver is one correlator (code de-spreading and integration 52 Company Confidential Basic unit of Rake Receiver
  53. 53. Optimal Receiver for WCDMA signal • In a multipath environment optimal receiver utilizes several correlators (Rake Fingers) tuned for dominant delays = Rake receiver Adobe Acrobat Document 53 Company Confidential
  54. 54. Rake Receiver • Rake finger delays tuned based on channel impulse response estimation • Code Matched Filter, Search Finger • Fingers combined with Maximal Ratio combining • Performance of Rake Receiver depends on the channel powers delay profile • Max path delay difference vs. chip time amount of multipath diversity 54 Company Confidential
  55. 55. Rake Receiver - Combining • Combined signal without and with phase estimation and correction (example 6 path channel) 55 Company Confidential
  56. 56. Maximal Ratio Combining of Symbols Transmitted signal Combined signal (+ residual noise) Received signal (+noise) Finger n.1 Finger n.2 Finger n.3 Time and phase adjustment WBTS UE 56 Company Confidential
  57. 57. Maximal Ratio Combining of Symbols Received symbol+noise Transmitted symbol Modified with channel estimate and relative delay compensation (for combining) Combined symbol + residual noise Finger n.1 Finger n.2 Finger n.3 WBTS UE 57 Company Confidential
  58. 58. WCDMA in TU Channel time Corr 1 Corr 2 Corr 3 Corr 4 Corr 5 Corr 6 Corr 7 • High level of multipath diversity 58 Company Confidential
  59. 59. WCDMA in Indoor Channel Rake Finger RESOLUTION = 0.26µs 78m Chip period = 1/3840000 s = 0.26µsCorr 1 • No multipath diversity 59 Company Confidential
  60. 60. Part III Scrambling Code Planning 60 Company Confidential
  61. 61. Scrambling Code Planning 61 Company Confidential
  62. 62. Scrambling Code Planning 62 Company Confidential
  63. 63. Scrambling Code Planning 63 Company Confidential
  64. 64. Scrambling Code Planning 64 Company Confidential
  65. 65. Scrambling Code Planning 65 Company Confidential
  66. 66. Scrambling Code Planning 66 Company Confidential
  67. 67. Scrambling Code Planning 67 Company Confidential
  68. 68. Scrambling Code Planning 68 Company Confidential
  69. 69. Scrambling Code Planning 69 Company Confidential
  70. 70. Scrambling Code Planning 70 Company Confidential
  71. 71. Scrambling Code Planning 71 Company Confidential
  72. 72. Part IV Physical Layer 72 Company Confidential
  73. 73. Channel Mapping 73 Company Confidential In GSM, we distinguish between logical and physical channels. In UMTS there are three different types of channels: • Logical Channels Logical Channels were created to transmit a specific content. There are for instance logical channel to transmit the cell system information, paging information, or user data. Logical channels are offered as data transfer service by the Medium Access Control (MAC) layer to the next higher layer. Consequently, logical channels are in use between the mobile phone and the RNC. • Transport Channels (TrCH) The MAC layer is using the transport service of the lower, the Physical layer. The MAC layer is responsible to organise the logical channel data on transport channels. This process is called mapping. In this context, the MAC layer is also responsible to determine the used transport format. The transport of logical channel data takes place between the UE and the RNC. • Physical Channels (PhyCH) The physical layer offers the transport of data to the higher layer. The characteristics of the physical transport have to be described. When we transmit information between the RNC and the UE, the physical medium is changing. Between the RNC and the Node B, where we talk about the interface Iub, the transport of information is physically organised in so-called Frames. Between the Node B and the UE, where we find the WCDMA radio interface Uu, the physical transmission is described by physical channels. A physical channel is defined by the UARFCN and the a spreading code in the FDD mode.
  74. 74. Radio Interface Channel Organisation 74 Company Confidential Logical Channels (define what type of data is transferred ) content is organised in separate channels, e.g. System information, paging, user data, link management Transport Channels define how and with which type of characteristics the data is transferred by the physical layer Physical Channels (UARFCN, spreading code) Frames Iub interface RLC Layer MAC Layer PHY Layer L2 L1
  75. 75. 75 Company Confidential L3 control control control control Logical Channels Transport Channels C-plane signalling U-plane information PHY L2/MAC L1 RLC DCNtGC L2/RLC MAC RLC RLC RLC RLC RLC RLC RLC Duplication avoidance UuS boundary BMC L2/BMC control PDCP PDCP L2/PDCP DCNtGC Radio Bearers RRC Radio Interface Protocol Architecture L1:Closed loop PC, Macrodiversity distribution/combining and soft handover execution; Error detection on transport channels and indication to higher layers; FEC encoding/decoding and interleaving/deinterleaving of transport channels; Multiplexing of transport channels and demultiplexing of coded composite transport channels; Rate matching; Mapping of coded composite transport channels on physical channels; Power weighting and combining of physical channels; Modulation and spreading/demodulation and despreading of physical channels; Frequency and time (chip, bit, slot, frame) synchronisation; Measurements and indication to higher layers (e.g. FER, SIR, interference power, transmit power, etc.); L2/MAC (Medium Access Control): Mapping Logical channels to transport Reporting of measurements.Chipering. Local measurements such as traffic volume and quality indication are reported to RRC L2/RLC (Radio Link Control): Segmentation (Reassembly), Retransmission, Error correction [Transparent (no overhead added, e.g. voice/video), Unack (add overhead but no retransmission, e.g. cell broadcast), Ack (add overhead and retransmission enable, e.g. PS)] L2/BMC (Broadcast/Multicast Control): Storage of Cell broadcast messages, dealing with CBS (Cell Broadcast Servises) L2/PDCP (Packet Data Convergence Protocol): Header compression and decompression, Support for lossless SRNS relocation L3 RRC (Radio Resource Control): Broadcast of information provided by the non-access stratum (Core Network). Broadcast of information related to the access stratum Establishment, re- establishment, maintenance and release of an RRC connection between the UE and UTRAN , Establishment, reconfiguration and release of Radio Bearers, Assignment, reconfiguration and release of radio resources for the RRC connection, RRC connection mobility functions, Paging/notification, Control of requested QoS, UE measurement reporting and control of the reporting, Outer loop power control
  76. 76. 76 Company Confidential Logical Channels There are two types of logical channels (FDD mode): Control Channels (CCH): • Broadcast Control Channel (BCCH) System information is made available on this channel. The system information informs the UE about the serving PLMN, the serving cell, neighbourhood lists, measurement parameters, etc. This information permanently broadcasted in the downlink. • Paging Control Channel (PCCH) Given the BCCH information the UE can determine, at what times it may be paged. Paging is required, when the RNC has no dedicated connection to the UE. PCCH is a downlink channel. • Common Control Channel (CCCH) Control information is transmitted on this channel. It is in use, when no RRC connection exists between the UE and the network. It is a bi-directional channel, i.e. it exists both uplink and downlink. • Dedicated Control Channel (DCCH) Dedicated resources were allocated to a UE. These resources require radio link management, and the control information is transmitted both uplink and downlink on DCCHs. Traffic Channels (TCH): • Dedicated Traffic Channel (DTCH) User data has to be transferred between the UE and the network. Therefore dedicated resources can be allocated to the UE for the uplink and downlink user data transmission. • Common Traffic Channel (CTCH) Dedicated user data can be transmitted point-to-multipoint to a group of UEs.
  77. 77. 77 Company Confidential Transport Channels (TrCH) Logical Channels are mapped onto Transport Channels. There are two types of Transport Channels (FDD mode): Common Transport Channels: • Broadcast Channel (BCH) It carries the BCCH information. • Paging Channel (PCH) It is in use to page a UE in the cell, thus it carries the PCCH information. It is also used to notify UEs about cell system information changes. • Forward Access Channel (FACH) The FACH is a downlink channel. Control information (FACH-c), but also small amounts of user data can be transmitted on this channel (FACH-u). • Downlink Shared Channel (DSCH) This channel is used downlink. Dedicated user data and control information for several mobile phones can be transmitted with one DSCH. • Random Access Channel (RACH) This uplink channel is used by the UE, when it wants to transmit small amounts of data, and when the UE has no RRC connection. It is often used to allocated dedicated signalling resources to the UE to establish a connection or to perform higher layer signalling. It is a contention based channel, i.e. several UE may attempt to access UTRAN simultaneously.
  78. 78. Transport Channels (TrCH) • Common Packet Channel (CPCH) Similar to the RACH, it is a contention based uplink channel. In contrast to the RACH, it can be used to transmit larger amounts of (bursty) traffic. Dedicated Transport Channels: • Dedicated Channel (DCH) Dedicated resources can be allocated both uplink and downlink to a UE. DedicatedDedicated resources are exclusively in use for the subscriber.resources are exclusively in use for the subscriber. On the following figures. you can see the mapping of logical channels onto transport channels, as well as the mapping of transport channels onto physical channels. 78 Company Confidential
  79. 79. Physical Channels (PhyCH) Physical Channels are characterised by •UARFCN, •scrambling code, •channelisation code (optional), •start and stop time, and •relative phase (in the uplink only, with relative phase being 0 or π/2) Transport channels can be mapped to physical channels. But there exist physical channels, which are generated at the Node B only, as can be seen on the next figures. In addition to the physical channels mapped from the transport channels, there exist physical channels for signaling purposes (blue color) to carry only information between network and the terminals. 79 Company Confidential
  80. 80. 80 Company Confidential Channel Mapping DL (Network Point of View) PCH BCH DCH FACH DSCH Logical Channels Transport Channels Physical Channels CTCH DCCH CCCH PCCH BCCH DTCH P-CCPCH CPICH S-SCH P-SCH CSICH CD/CA-ICH AICH PDSCH DPDCH S-CCPCH PICH DPCCH
  81. 81. Channel Mapping UL (Network Point of View) Physical Channels Logical Channels Transport Channels DCCH DCH DPDCHDTCH CPCH RACHCCCH PCPCH PRACH DPCCH I branch Q branch 81 Company Confidential
  82. 82. Transport Channels Physical Channels • Transport channels contain the data generated at the higher layers, which is carried over the air and are mapped in the physical layer to different physical channels. • The data is sent by transport block (TB) from MAC layer to physical layer and generated by MAC layer every 10 ms (TTI) • The transport format of each transport channel is identified by the Transport Format Indicator (TFI), which is used in the interlayer communication between the MAC layer and physical layer. • Several transport channels can be multiplexed together by physical layer to form a single Coded Composite Transport Channel (CCTrCh). 82 Company Confidential
  83. 83. Transport Formats 83 Company Confidential TB Transport Block TF Transport Format TBS Transport Block Set TFS Transport Format Set TFC Transport Format Combination TFCS Transport Format Combination Set DCH 2 TB TB TB TB TB TB TB TB TBS TF TFS TFC TFCS TTI TTI TTI TTI TTITTI TB TB TB DCH 1
  84. 84. 84 Company Confidential Cell Synchronisation When a UE is switched on, it starts to monitor the radio interface to find a suitable cell to camp on. But it has to determine, whether there is a WCDMA cell nearby. If a WCDMA cell is available, the UE has to be synchronised to the downlink transmission of the system information – transmitted on the physical channel P-CCPCH – before it can make a decision, in how far the available cell is suitable to camp on. Initial cell selection is not the only reason, why a UE wants to perform cell synchronisation. This process isThis process is also required for cell realso required for cell re--selection and the handover procedure.selection and the handover procedure. Cell synchronisation is achieved with the Synchronisation Channel (SCH). This channel divides up into two sub-channels, PP--SCH and SSCH and S--SCH are not under the cellSCH are not under the cell-- specific primary scrambling code (the UE must be able to synchrospecific primary scrambling code (the UE must be able to synchronize to the cellnize to the cell before knowing thebefore knowing the downlimkdownlimk scrambling code)scrambling code) •Primary Synchronisation Channel (P-SCH) (SLOT and CHIP SYNCHRONIZATION) A time slot lasts 2560 chips. The P-SCH only uses the first 10% of a time slot. A Primary Synchronisation Code (PSC) is transmitted the first 256 chips of a time slot. This is the case in every UMTS cell. If the UE detects the PSC, it has performed TS and chip synchronisation. •This is typically done with a single matched filter matched to the primary synchronization code which is common for all cells. The slot timing of the cell can be obtained by decoding peaks in the matched filter output (continued on the next text slide) Matched Filter
  85. 85. Synchronisation Channel (SCH) CP CP 2560 Chips 256 Chips Cs1 Cs2 Cs15 Slot 1 Slot 14Slot 0 CP CP CP Cs1 Primary Synchronisation Channel (P-SCH) Secondary Synchronisation Channel (S-SCH) Slot 0 85 Company Confidential Cp = Primary Synchronisation Code (Activity Factor 10%) Cs = Secondary Synchronisation Code (Activity Factor 10%) 10 ms Frame
  86. 86. • Secondary Synchronisation Channel (S-SCH) • (FRAME SYNCH and Scrambling Code Group DETECTION) The S-SCH also uses only the first 10% of a timeslot; Secondary Synchronisation Codes (SSC) are transmitted. There are 16 different SSCs, which are organised in a 10 ms frame (15 timeslots) in such a way, that • the beginning of a 10 ms frame can be determined, and • 64 different SSC combinations within a 10 ms frame are identified. There is a total of 512 primary scrambling codes, which are grouped in 64 scrambling code families, each family holding 8 scrambling code members. The 15 SSCs in one 10 ms frame identify the scrambling code family of the cell‘s downlink scrambling code. • The sequence permits downlink frame synchronization and indicate which of the code grouping the downlink scrambling code belongs to. • This is done by correlating the received signal with all possible secondary synchronization code sequences and identifying the maximum correlation value. Since the cyclic shifts of the sequences are unique, the code group as well as the frame synchronization is determined Cell Synchronisation 86 Company Confidential
  87. 87. SSC Allocation for S-SCH scrambling code group slot number 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 87 Company Confidential 15 15 group 05 group 04 group 62 group 63 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10 1 2 1 15 5 5 12 16 6 11 2 16 11 12 1 2 3 1 8 6 5 2 5 8 4 4 6 3 7 1 2 16 6 6 11 5 12 1 15 12 16 11 2 1 3 4 7 4 1 5 5 3 6 2 8 7 6 8 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10 group 00 group 01 group 02 group 03 11 11 11 11 11 11 11 11 11 15 15 15 15 15 15 15 15 15 15 15 5 5 I monitor the S-SCH
  88. 88. Common Pilot Channel (CPICH) 88 Company Confidential With the help of the SCH, the UE was capable to perform chip, TS, and frame synchronisation. Even the cell‘s scrambling code group is known to the UE. But in the initial cell selection process, it does not yet know the cell‘s primary scrambling code. There is one primary scrambling code in use over the entire cell, and in neighbouring cells, different scrambling codes are in use. There exists a total of 512 primary scrambling codes. The CPICH is used to transmit in every TS a pre-defined bit sequence (stream of 256 ‘1’) with a fixed data rate of 30 kbps, which corresponds to spreading factor 256. The CPICH divides up into a mandatory Primary Common Pilot Channel (P-CPICH) and optional Secondary CPICHs (S-CPICH). The P-CPICH is in use over the entire cell. And it is the first physical channel, where a spreading code is in use. A spreading code is the product of the cell‘s scrambling code and the channelisation code. The channelisation code is fixed: Cch,256,0. I.e., the UE knows the P-CPICH‘s channelisation code, and it uses the P-CPICH to determine the cell‘s primary scrambling code by trial and error (UE tries 8 SC Codes of the group identified). The P-CPICH is not only used to determine the primary scrambling code. It also acts as - phase reference for most of the physical channels, - measurement reference in the FDD mode (and partially in the TDD mode). There may be zero or several S-CPICHs. Either the cell‘s primary scrambling code or its secondary scrambling codes can be used. In contrast to the P-CPICH, it can be broadcasted just over a part of the cell. CPICH has activity factor of 100% (continuous transmission)
  89. 89. Primary Common Pilot Channel (P-CPICH) CP 2560 Chips 256 Chips Synchronisation Channel (SCH) P-CPICH 10 ms Frame applied spreading code = cell‘s primary scrambling code ⊗ Cch,256,0 89 Company Confidential P-CPICH Cell scrambling code? I get it with trial & error! • Phase reference • Measurement reference
  90. 90. CPICH as Measurement Reference 90 Company Confidential The UE has to perform a set of L1 measurements, some of them refer to the CPICH channel: • CPICH RSCP RSCP stands for Received Signal Code Power. The UE measures the RSCP on the Primary-CPICH. The reference point for the measurement is the antenna connector of the UE. The CPICH RSCP is a power measurement of the CPICH. The received code power may be high, but it does not yet indicate the quality of the received signal, which depends on the overall noise level. • UTRA carrier RSSI. RSSI stands for Received Signal Strength Indicator. The UE measures the received wide band power, which includes thermal noise and receiver generated noise. The reference point for the measurements is the antenna connector of the UE. • CPICH Ec/No The CPICH Ec/No is used to determine the „quality“ of the received signal. It gives the received energy per received chip divided by the band‘s power density. The „quality“ is the primary CPICH‘s signal strength in relation to the cell noise. (Please note, that transport channel quality is determined by BLER, BER, etc. ) If the UE supports GSM, then it must be capable to make measurements in the GSM bands, too. The measurements are based on the • GSM carrier RSSI The wideband measurements are conducted on GSM BCCH carriers.
  91. 91. P-CPICH as Measurement Reference Received Signal Code Power (in dBm)CPICH RSCP received energy per chip divided by the power density in the band (in dB)CPICH Ec/No received wide band power, including thermal noise and noise generated in the receiver (in dBm) UTRA carrier RSSI CPICH Ec/No = CPICH RSCP UTRA carrier RSSI CPICH Ec/No 91 Company Confidential CPICH RSCP 0: -115 1: -114 2: -113 : 88: -27 89: -26 RSCP values in dBm UTRA carrier RSSI 0: -110 1: -109 2: -108 : 71: -39 72: -38 73: -37 RSSI values in dBm 0: -24 1: -23.5 2: -23 3: -22.5 ... 47: -0.5 48: 0 Ec/No values in dB
  92. 92. Primary Common Control Physical Channel (P-CCPCH) The UE knows the cell‘s primary scrambling code. It now wants to gain the cell system information (MIB,SIB), which is transmitted on the physical channel P- CCPCH. The channelisation code of the P-CCPCH is also known to the UE, because it must be Cch,256,1 in every cell for every operator. By reading the cell system information on the P-CCPCH, the UE learns everything about the configuration of the remaining common physical channels in the cell, such as the physical channels for paging and random access. As can be seen from the P-CCPCH‘s channelisation code, the data rate for cell system information is fixed. The SCH is transmitted on the first 256 chips of a timeslot, thus creating here a peak load. The cell system information is transmitted in the timeslot except for the first 256 chips. By doing so, a high interference and load at the beginning of the timeslot is avoided. This leads to a net data rate of 27 kbps for the cell system information. Channel estimation is done with the CPICH, so that no pilot sequence is required in the P-CCPCH. (The use of the pilot sequence is explained in the context of the DPDCH later on in this document.) There are also no power control (TPC) bits transmitted to the UE‘s. P-CCPCH has activity factor of 90% 92 Company Confidential
  93. 93. Primary Common Control Physical Channel (P-CCPCH) 10 ms Frame CP 2560 Chips 256 Chips Synchronisation Channel (SCH) P-CCPCH 93 Company Confidential P-CCPCH Finally, I get the cell system information • channelisation code: Cch,256,1 • no TPC, no pilot sequence • 27 kbps (due to off period) • organised in MIBs and SIBs
  94. 94. 94 Company Confidential Primary Common Control Physical Channel (P-CCPCH) In GSM all common channels have the same power, there is no need to consider the power setting of common channels as all common channels are on full power. In GSM we have to decide how many TSLs to dedicate to common tasks, I.e. how many SDCCH TSL are required per cell
  95. 95. Nokia Parameters for Cell Search • WCEL: PtxPrimaryCPICH The parameter determines the transmission power of the primary CPICH channel. It is used as a reference for all common channels. [-20 dBm … 43 dBm], step 1 dB, default: 33dBm (WPA power = 43 dBm) • WCEL: PtxPrimarySCH Transmission power of the primary synchronization channel, the value is relative to primary CPICH transmission power. [-35 dB … 15 dB], step size 0.1 dB, default: -3 dB • WCEL: PtxSecSCH Transmission power of the secondary synchronization channel, the value is relative to primary CPICH transmission power. [-35 dB… 15 dB], step size 0.1 dB, default: -3 dB 95 Company Confidential
  96. 96. Nokia Parameters for Cell Search • WCEL: PtxPrimaryCCPCH This is the transmission power of the primary CCPCH channel, the value is relative to primary CPICH transmission power. [-35 dB … 15 dB], step size 0.1 dB, default: -5 dB • WCEL: PriScrCode Identifies the downlink scrambling code of the Primary CPICH (Common Pilot Channel) of the Cell. [0 ... 511], default: 0 dB 96 Company Confidential
  97. 97. Secondary Common Control Physical Channel (S-CCPCH) The S-CCPCH can be used to transmit the transport channels • Forward Access Channel (FACH) and • Paging Channel (PCH). More than one S-CCPCH can be deployed. The FACH and PCH information can multiplexed on one S-CCPCH – even on the same 10 ms frame -, or they can be carried on different S-CCPCH’s. When 2 S-CCPCH’s are broadcast, the first S-CCPCH has a spreading factor of 256 and carries PCH, while the spreading factor of the remaining S-CCPCH can range between 256 (30 Kbps or 15 Ksps) and 4 (1920 Kbps) and carries FACH. UTRAN determines, whether a S-CCPCH has the TFCI (Transport Format Combination Indicator) included (supports variable rates). Please note, that the UE must support both S-CCPCHs with and without TFCI. S-CCPCH is on air ONLY when there is data to transmit (FACH or Paging), however the TFCI bits are broadcast irrespective of whether or not there is any data to transmit (min activity factor 25%) Typical value is SF = 64 120 Kbps (60 Ksps) 97 Company Confidential
  98. 98. Secondary Common Control Physical Channel (S-CCPCH) 10 ms Frame Slot 0 Slot 1 Slot 2 Slot 14 98 Company Confidential S-CCPCH TFCI (optional) Data Pilot bits • carries PCH and FACH • Multiplexing of PCH and FACH on one S-CCPCH, even one frame possible • with and without TFCI (UTRAN set) • SF = 4..256 • (18 different slot formats) • no inner loop power control • a maximum of 1 paging message can be sent per 10 ms TTI
  99. 99. 99 Company Confidential S-CCPCH and the Paging Process • The network has detected, that there is data to be transmitted to the UE (MTC). Both in the RRC idle mode and in the RRC connected mode (e.g. in the sub-state CELL_PCH) a UE may get paged. But how does the mobile know, when it was paged ? And in order to save battery power, we don‘t want the UE to listen permanently to paging channel – instead, we want to have discontinuous reception (DRX) of paging messages. But WHEN and WHERE does the UE listen to the paging messages? • Cell system information is broadcasted via the P-CCPCH. The cell system information is organised in System Information Blocks (SIB). SIB5 informs the mobile phones about the common channel configuration, including a list of S- CCPCH descriptions. The first 1 to K entries transmit the (transport channel) PCH, while the remaining S-CCPCH in the list hold no paging information. • The UE determines the S-CCPCH, where it is paged, by its IMSI and the number of PCH carrying S-CCPCHs K. When paging the UE, the RNC knows the UE‘s IMSI, too, so that it can put the paging message on the correct PCH transport channel. • Discontinuous Reception (DRX) of paging messages is supported. A DRX cycle length k has to be set in the network planning process for the cs domain, ps domain, and UTRAN. k ranges between 3 and 9. If for instance k=6, then the UE can be paged every 2k = 640 ms. If the UE is in the idle mode, it takes the smaller k-value of either the cs- or ps-domain. If the UE is in the connected mode, it has to select the smallest k- value of UTRAN and the CN, it is not connected to.
  100. 100. S-CCPCH and the Paging Process 100 Company Confidential Node B UTRAN BCCH (SIB 5) common channel definition, including S-CCPCH carrying one PCH S-CCPCH carrying one PCH S-CCPCH carrying one PCH S-CCPCH without PCH S-CCPCH without PCH a lists of UE Index of S-CCPCHs 0 1 K-1 UE‘s paging channel: Index = IMSI mod K e.g. if IMSI mod K = 1 „my paging channel“ RNC
  101. 101. 101 Company Confidential The Paging Process Paging Indicator Channel (PICH) UMTS provides the terminals with an efficient sleep mode operation. The UEs do not have to read and process the content, transmitted during their paging occasion on their S-CCPCH. Each S-CCPCH, which is used for paging, has an associated Paging Indicator Channel (PICH). A PICH is a physical channel, which carries paging indicators. A set of (paging indicator) bits within the PICH indicate to a UE, whether there is a paging occasion for it. Only then, the UE listens to the S- CCPCH frame, which is transmitted 7680 chips after the PICH frame in order to see, whether there is indeed a paging message for it. The PICH is used with spreading factor 256. 300 bits are transmitted in a 10 ms frame, and 288 of them are used for paging indication (activity factor 96%). The UE was informed by the BCCH, how many paging indicators exist on a 10 ms frame. The number of paging indicator Np can be 18, 32, 72, and 144, and is set by the operator as part of the network planning process. The higher Np, the more paging indicators exist, the more paging groups exist, among which UEs can be distributed on. Consequently, the lower the probability, that a UE reacts on a paging indicator, while there is no paging message in the associated S-CCPCH frame (saving battery consumption). But a high number of paging indicators results in a comparatively high output power for the PICH (increase DL interference), because less bits exists within a paging indicator to indicate the paging event. The operator then also has to consider, if he has to increase the number of paging attempts.
  102. 102. S-CCPCH and its associated PICH PICH frame S-CCPCH frame, associated with PICH frame τPICH = 7680 chips b287 b288 b299b286b0 b1 for paging indication no transmission τS-CCPCH 10 ms 102 Company Confidential{b2q, b2q+1} = {1,1} {b2q, b2q+1} = {0,0} # of paging indicators per frame (Np) Subscribers with Pq indicator paged => 18 (16 bits) 32 (8 bits) 72 (4 bits) 144 (2 bits) Subscribers with Pq indicator not paged => {b4q, …, b4q+3} = {1,1,…,1} {b4q, …, b4q+3} = {0,0,…,0} {b8q, …, b8q+7} = {1,1,…,1} {b8q, …, b8q+7} = {0,0,…,0} {b16q, …,b16q+15} = {1,1,…,1} {b16q, …,b16q+15} = {0,0,…,0}
  103. 103. Nokia Parameters for S-CCPCH and Paging RAN 1 & RAN1.5 support data rates of 15, 30, and 60 ksym/s for the S-CCPCH. FACH Open Loop power control can be implemented only if the S-CCPCH is dedicated, uplink PC information through the RACH (RAN 2) • WCEL: NbrOfSCCPCHs The parameter defines how many S-CCPCH are configured for the given cell. Range: [1,2], step: 1; default = 1 (1 = FACH&PCH; 2 = FACH on 1st / PCH on 2nd) • WCEL: PtxSCCPCH1 (carries FACH & PCH) This is the transmission power of the 1st S-CCPCH channel, the value is relative to primary CPICH transmission power. Range: [-35 dB … 15 dB] , step size 0.1 dB, default: - 5dB • WCEL: PtxSCCPCH2 (carries PCH only) This is the transmission power of the 2nd S-CCPCH channel, the value is relative to primary CPICH transmission power. Range: [-35 dB … 15 dB] , step size 0.1 dB, default: - 5dB 103 Company Confidential
  104. 104. Nokia Parameters for S-CCPCH and Paging • WCEL: PtxPICH This is the transmission power of the PICH channel. It carries the paging indicators which tell the UE to read the paging message from the associated secondary CCPCH. This parameter is part of SIB 5. [-10 dB..5 dB]; step 1 dB; default: -8 dB (with Np =72) NP Repetition of PICH bits [18, 36, 72, 144] with relative power [-10, -10, -8, -5] dB • RNC: CNDRXLength The DRX cycle length used for CN domain to count paging occasions for discontinuous reception. This parameter is given for CS domain and PS domain separately. This parameter is part of SIB 1. [640, 1280, 2560, 5120] ms; default = 640 ms. • WCEL: UTRAN_DRX_length The DRX cycle length used by UTRAN to count paging occasions for discontinuous reception. [80, 160, 320, 640, 1280, 2560, 5120] ms; default = 320 ms 104 Company Confidential
  105. 105. 105 Company Confidential FACH and S-CCPCH • The transport channel Forward Access Channel (FACH) is used, when relatively small amounts of data have to be transmitted from the network to the UE. In-band signalling is used to indicate, which UE is the recipient of the transmitted data (see MAC PDU with UE-ID type). This common downlink channel is used without (fast) closed loop power control and is available all over the cell. FACH data is transmitted in one or several S-CCPCHs. FACH and PCH data can be multiplexed on one S-CCPCH, but they can also be be transmitted on different S-CCPCHs. • The FACH is only transmitted downlink. The FACH is organised in FACH Data Frames via the Iub-interface. Each FACH Data Frames holds the Transmission Blocks for one TFS. The used TFS is identified by the TFI. A TFI is associated with one Transmission Time Interval (TTI), which can be either 10, 20, 40 or 80 ms. The TTI identifies the interleaving time on the radio interface. A FACH Data Frame has header fields, which identify the CFN, TFI, and the Transmit Power Level. • The Transmit Power Level gives the preferred transmission power level for the FACH and for the TTI time. The values specified here range between 0 and 25.5 dB, with a step size of 0.1 dB. The value is taken as a negative offset to the maximum power configured for the S-CCPCHs, specified for the FACH. • The pilot bits and the TFCI-field may have a relative power offset to the power of the data field, which may vary in time. (The offset is determined by the network.) The power offsets are set by the NBAP message COMMON TRANSPORT CHANNEL SETUP REQUEST, which is sent from the RNC to the Node B. There are two power offset information included: • PO1:defines the power offset for the TFCI bits; it ranges between 0 and 6dB with a 0.25 step size. • PO3:defines the power offset for the pilot bits; it ranges between 0 and 6dB with a 0.25 step size. Another important parameter is the maximum allowed power on the FACH: MAX FACH Power.
  106. 106. FACH and S-CCPCH 106 Company Confidential Node B RNC FACH Data Frame CFNTFI Transmit Power Level TB TB Iub UE Uu TFCI (optional) Data Pilot bits max. transmit power for S-CCPCH 0..25.5 dB, step size 0.1 Transmit Power Level PO1 PO3 Power offsets for TFCI and TPC defined during channel setup
  107. 107. Nokia Parameters for S-CCPCH Power Setting Currently, either one or two S-CCPCHs are supported. • WCEL: PowerOffsetSCCPCHTFCI Defines the power offset for the TFCI symbols relative to the downlink transmission power of a Secondary CCPCH. This parameter is part of SIB 5. P01_15/30/60 15 ksps: [0..6 dB]; step 0.25 dB; default: 2 dB 30 ksps : [0..6 dB]; step 0.25 dB; default: 3 dB 60 ksps : [0..6 dB]; step 0.25 dB; default: 4 dB • WCEL: PowerOffsetSCCPCHPilot Defines the power offset for the pilot symbols relative to the downlink transmission power of a Secondary CCPCH. This parameter is part of SIB 5. P03_15/30/60 15 ksps : [0..6 dB]; step 0.25 dB; default: 2 dB 30 ksps : [0..6 dB]; step 0.25 dB; default: 3 dB 60 ksps : [0..6 dB]; step 0.25 dB; default: 4 dB 107 Company Confidential
  108. 108. Code Tree Capacity There are 5 CCH's (4 use SF256 and one uses SF64), they blocked (5 used + 13 not allowed) a total of 18 codes Note: there are not P-SCH and S-SCH !! PP--SCH and SSCH and S--SCHSCH are not under the cellare not under the cell--specific primary scrambling codespecific primary scrambling code (the UE must be able to synchronize to the cell before(the UE must be able to synchronize to the cell before knowing theknowing the downlimkdownlimk scrambling code)scrambling code) 108 Company Confidential
  109. 109. Part V Power Control 109 Company Confidential
  110. 110. Effect of TX & RX Powers on Interference Levels Downlink transmission power = Interference to the network Uplink received power = Interference to own cell users Uplink transmission power = Interference to other cells 110 Company Confidential Since every TX and RX power is causing interference to others, PC is necessary to limit the interference
  111. 111. CDMA Fundamentals : Power Control 111 Company Confidential MS2 Pr,2 Pr,1 MS1 P = 21 dBm P = 21 dBm Near-Far Problem PL1 = 100 dB PL2 = 90 dB Pr,1 = EIRP(MS1) - PL1 = 21 - 100 = -79 dBm Pr,2 = EIRP(MS2) - PL2 = 21 - 90 = -69 dBm (S/N)1 = Pr,1 - Pr,2 = -10 dB (S/N)2 = Pr,2 - Pr,1 = +10 dB MS2 must be Power Controlled by -10 dB to have the same S/N for both users MS1 and MS2
  112. 112. Near-Far Effect 112 Company Confidential
  113. 113. Purpose of Power Control in WCDMA 113 Company Confidential
  114. 114. Physical Random Access (Open loop Power Control) Outer Loop Power Control Fast Closed Loop (Inner) Power Control 114 Company Confidential
  115. 115. 115 Company Confidential Physical Random Access (Open loop Power Control) In the random access (based on Slotted ALOHA approach with fast acquisition indication) , initiated by the UE (MOC), two physical channels are involved: • Physical Random Access Channel (PRACH) The physical random access is decomposed into the transmission of preambles in the uplink. Each preamble is transmitted with a higher output power as the preceding one. After the transmission of a preamble, the UE waits for a response by the Node B. This response is sent with the physical channel Acquisition Indication Channel (AICH), telling the UE, that the Node B has acquired the preamble transmission of the random access. Thereafter, the UE sends the message itself, which is the RACH/CCCH of the higher layers. The preambles are used to allow the UE to start the access with a very low output power. If it had started with a too high transmission output power, it would have caused interference to the ongoing transmissions in the serving and neighbouring cells. Please note, that the PRACH is not only used to establish a signalling connection to UTRAN. It can be also used to transmit very small amounts of user data. • Acquisition Indication Channel (AICH) This physical channel indicates to the UE, that it has received the PRACH preamble and is now waiting for the PRACH message part.
  116. 116. 116 Company Confidential Random Access – the Working Principle Node BUE PRACH (preamble) PRACH (preamble) PRACH (preamble) PRACH (message part) AICH No response by the Node B No response by the Node B I just detected a PRACH preamble OLA!
  117. 117. Random Access Timing 117 Company Confidential The properties of the PRACH are broadcasted (SIB5, SIB6). The candidate PRACH is randomly selected (if there are several PRACH advertised in the cell) as well as the access slots (= 2 TIME SLOTS) within the PRACH. 15 access slots are given in a PRACH, each access slot lasting two timeslotstwo timeslots or 5120 chips. In other words, thethe access slots stretch over two 10 ms framesaccess slots stretch over two 10 ms frames. A PRACH preamble, which is transmitted in an access slot, has a length of 4096 chips. Also the AICH is organised in (AICH) access slots, which stretch over two timeslots. AICH access slots are time aligned with the P-CCPCH. (Activity factor 80%) The UE sends one preamble in uplink access slot n. It expects to receive a response from the Node B in the downlink (AICH) access slot n, τp-a chips later on. If there is no response, the UE sends the next preamble τp-p chips after the first one. The maximum numbers of preambles in one preamble access attempt can be set between 1 and 64. The number of PRACH preamble cycles can be set between 1 and 32. If the AICH_Transmission_Timing parameter in the SIB is set to BCCH SIB5 & SIB6 to •0, then, the minimum preamble-to-preamble distance is 3 access slots, the minimum preamble-to- message distance is 3 access slots, and the preamble-to-acquisition indication is 3 timeslots. •1, then, the minimum preamble-to-preamble distance is 4 access slots, the minimum preamble-to- message distance is 4 access slots, and the preamble-to-acquisition indication is 5 timeslots.
  118. 118. Random Access Timing SFN mod 2 = 0 SFN mod 2 = 0SFN mod 2 = 1 P-CCPCH 118 Company Confidential AICH access slots 0 1 1282 1175 964 13103 14 0 1 2 75 643 5120 chips Preamble 5120 chips Preamble AS # i 4096 chips preamble-to-preamble distance τp-p UE point of view PRACH access slots AICH access slots Message part preamble-to-message distance τp-m Acquisition Indication preamble-to-AI distance τp-a (distances depend on AICH_Transmission_Timing ) AS # i
  119. 119. PRACH Power Setting Preamble_Initial_Power = UL interference + Primary CPICH TX power – CPICH_RSCP + Constant Value UL interference at Node B 1st preamble: power setting attenuation in the DL estimated receive level Constant Value Pre- amble Message partPre- amble Pre- amble Pp-p Pp-m Pp-p 119 Company Confidential 1..8 dB -5..10 dB # of preambles: 1..64 # of preamble cycles: 1..32 “RRC Connection Request”
  120. 120. Nokia Parameters Related to the PRACH and AICH WCEL: PRACHRequiredReceivedCI This UL required received C/I value is used by the UE to calculate the initial output power on PRACH according to the Open loop power control procedure. This parameter is part of SIB 5. [-35 dB..-10 dB]; step 1 dB; default -25 dB. We use - 20 WCEL: PowerRampSteponPRACHPreamble UE increases the preamble transmission power when no acquisition indicator is received by UE in AICH channel. This parameter is part of SIB 5. [1dB..8dB]; step 1 dB; default: 2 dB. We use 1 • WCEL: PowerOffsetLastPreamblePrachMessage The power offset between the last transmitted preamble and the control part of the PRACH message. [-5 dB..10 dB]; step 1 dB; default 2dB • WCEL: PRACH_preamble_retrans The maximum number of preambles allowed in one preamble ramping cycle, which is part of SIB5/6. [1 ... 64]; step 1; default 8. We use 7 120 Company Confidential
  121. 121. Nokia Parameters Related to the PRACH and AICH 121 Company Confidential • WCEL: RACH_tx_Max Maximum number of RACH preamble cycles defines how many times the PRACH pre-amble ramping procedure can be repeated before UE MAC reports a failure on RACH transmission to higher layers. This message is part of SIB5/6. [1 ... 32]; default 8. We use 16 WCEL: PRACHScramblingCode The scrambling code for the preamble part and the message part of a PRACH Channel, which is part of SIB5/6. [0 ... 15]; default 0. • WCEL: AllowedPreambleSignatures The preamble part in a PRACH channel carries one of 16 different orthogonal complex signatures. Nokia Node B restrictions: A maximum of four signatures can be allowed (16 bit field). [0 ... 61440]; default 15. We use 4 • WCEL: AllowedRACHSubChannels A RACH sub-channel defines a sub-set of the total set of access slots (12 bit field). [0 ... 4095]; default 4095.
  122. 122. Nokia Parameters Related to the PRACH and AICH • WCEL: PtxAICH This is the transmission power of one Acquisition Indicator (AI) compared to CPICH power. This parameter is part of SIB 5. [-22 ... 5] dB, step 1 dB; default: -8 dB. • WCEL: AICHTraTime AICH transmission timing defines the delay between the reception of a PRACH access slot including a correctly detected preamble and the transmission of the Acquisition Indicator in the AICH. 0 ( Delay is 0 AS), 1 ( Delay is 1 AS) ;default 0. • WCEL: RACH_Tx_NB01min In case that a negative acknowledgement has been received by UE on AICH a backoff timer TBO1 is started to determine when the next RACH transmission attempt will be started. The backoff timer TBO1 is set to an integer number NBO1 of 10 ms time intervals, randomly drawn within an Interval 0 ≤ NB01min ≤ NBO1 ≤ NB01max (with uniform distribution). [0 ... 50]; default: 0. • WCEL: RACH_Tx_NB01max [0 ... 50]; default: 50. 122 Company Confidential
  123. 123. Outer Loop Power Control OL PC is needed to keep the quality of the communication at the required level (BLER, SIR, BER,…) by setting the target (SIR) for the fast power control. It aims at providing the required quality: no worse, no better. Too high quality would waste capacity. It is needed in both UL and DL since there is Fast PC (Closed Loop or Inner Loop) in both UL and DL “RRC Conn Request” “RRC Conn Setup” UL DPDCH “RRC Conn Setup Complete” 123 Company Confidential
  124. 124. Outer Loop Power Control In RADIO BEARER SETUP Message you can find the Target BLER (for the DL) For AMR and PS 128 = 1% BLER, CS T (VIDEO) = 0.1%, CS NT = 0.2% 124 Company Confidential
  125. 125. 125 Company Confidential UL Outer Loop Power Control Algorithm Case of Soft Handover
  126. 126. UL Outer Loop Power Control Algorithm When Max SIR Target is hit, RNC might force a hard handover 126 Company Confidential
  127. 127. UL OL PC: BLER Eb/No (Initial SIR Target, SIR Target Max, SIR Target Min) 127 Company Confidential
  128. 128. DL Outer Loop Power Control DeltaSIR(1,2), DeltaSIR after (1,2),….. 128 Company Confidential The adjustments of the SIR Target done by the UE is a proprietary algorithm that provides the same measured quality (BLER) as the quality target set by the RNC
  129. 129. Fast Closed Loop (Inner) Power Control 129 Company Confidential
  130. 130. Fast Closed Loop (Inner) Power Control • UL (Near-Far Problem): UE1 and UE2 operate within the same frequency, separable at the base station only by their respective spreading codes. It may happen that UE1 at the cell edge suffers a path loss, say 70 dB above that of UE2 which is near to NodeB. If there were no mechanism for UE1 and UE2 to be power-controlled to the SAME level at the NodeB, UE2 could easily overshoot UE1 and thus a large part of the cell. Power control tries to equalizes the Rx power per bit of all UE’s at NodeB. Since Fast Fading is uncorrelated between uplink and downlink (large freq separation between ul and dl bands in FDD) we can not use only a method based on Open Loop Power Control. Solution: Closed Loop PC: in UL the NodeB performs frequent (1.5 KHz) estimates of the received SIR and compares it to the SIR Target (calculated during Outer Loop PC). • DL: We do not have Near-Far Problem due to one-to-many scenario: all the signals within one cell originate from one NodeB to all mobiles. However it is desirable to provide a marginal amount of additional power to UE at the cellat the cell edge, as they suffer from increased otheredge, as they suffer from increased other--cellcell--interference.interference. 130 Company Confidential
  131. 131. 131 Company Confidential DL Fast Closed (Inner) Loop Power Control Inner loop power control is also often called (fast) closed loop power control. It takes place between the UE and the Node B. We talk about UL inner loop power control, when the Node B returns immediately after the reception of a UE‘s signal a power control command to the UE. By doing so, the UE‘s SIR ratio is kept at a certain level. DL inner loop power control control is more complex. When the UE receives the transmission of the Node B, the UE returns immediately a transmission power control command to the Node B, telling the Node B either to increase or decrease its output power for the UE‘s DPCH. The Node B‘s transmission power can be changed by 0.5, 1, 1.5 or 2 dB. 1 dB must be supported by the equipment. If other step sizes are supported or selected, depends on manufacturer or operator. The transmission output power for a DPCH has to be balanced for the PICH, which adds to the power step size. There are two downlink inner loop power control modes: • DPC_MODE = 0: Each timeslot, a unique TPC command is sent uplink. • DPC_MODE = 1: 3 consecutive timeslots (for DL), the same TPC commandsame TPC command is transmitted. One reason for the UE to request a higher output power is given, when the QoS target has not been met. It requests the Node B to transmit with a higher output power, hoping to increase the quality of the connection due to an increased SIR at the UE‘s receiver. But this also increases the interference level for other phones in the cell and neighbouring cells. The operator can decide, whether to set the parameter Limited Power Increase Used. If used, the operator can limit the output power raise within a time period.
  132. 132. DL Fast Closed (Inner) Loop PC Algorithm 132 Company Confidential Every 1500 Hz (time slot) UE measures SIR= (RSCP/ISCP)×SF
  133. 133. Downlink Inner Loop Power Control DPC_MODE = 0 unique TPC command per TS DPC_MODE = 1 same TPCsame TPC over 3 TS, then new command two modes cell TPC TPCest per 1 TS / 3 TS 500 times/s1500 times/s 133 Company Confidential
  134. 134. UL Inner Loop Power Control time SIRest SIRtarget TCP = 1 TCP = 1 TCP = 0 TCP = 0 TPC ⇒ TPC_cmd in FDD mode: 1500 times per second 134 Company Confidential
  135. 135. UL Fast Closed (Inner) Loop PC Algorithm 135 Company Confidential
  136. 136. UL Inner Loop Power Control Power Control Algorithm 1 is applied in medium speed environments. Here, the UE is commanded to modify its transmit power every timeslot. If the received TPC value is 1, the UE increases the transmission output at the DPCCH by ∆DPCCH, otherwise it decreases it by ∆DPCCH. The ∆DPCCH is either 1 or 2 dB, as set by the higher layer protocols. TPC values from the same radio link set represent one TLC_cmd. TPC_cmds from different radio link sets have to be weighted, if there is no reliable interpretation. Power Control Algorithm 2 (300 times/s) was specified to allow smaller step sizes in the power control in comparison to PCA1. This is necessary in very low and high speed environments. In these environments, PCA1 may result in oscillating around the target SIR. PCA2 changes only with every 5th timeslot, i.e. the TPC_cmd is set to 0 (do not do anything) the first 4 timeslots. In timeslot 5, the TPC_cmd is –1, 0, or 1. For each radio set (Radio set is combined radio links from same NodeB), the TPC_cmd is temporarily determined. This can be seen in the next figure. The temporary transmission power commands (TPC_temp) are combined as can be seen in the figure after the next one. Here you can see, how the final TPC_cmd is determined. 136 Company Confidential
  137. 137. UL Inner Loop Power Control Algorithms (1 and 2) 137 Company Confidential • The optimum PC step size varies depending on the UE speed. For a given quality target, the best UL PC step size is the one that results in the lowest target SIR. With an update rate of 1500 Hz, a PC step size of 1dB can effectively track a typical Rayleigh fading channel up to Doppler frequency of about 55 Hz (30 Km/h). At higher speeds, up to about 80 Km/h, a PC step size of 2dB gives better results. • For speeds greater than 80 Km/h the inner loop PC can no longer follow the fades and just introduces noise into the UL transmission. This adverse effect on the UL performance could be reduced if a PC step size smaller than 1 dB was employed. Also, for UE speeds lower than about 3 Km/h where the fading rate of the channel is very small, a smaller step size is more beneficial. • Algorithm 1 is used when the UE speed is sufficiently low to compensate for the fading of the channel (PC step size should be 1 or 2 dB) • Algorithm 2 was designed for emulating the effect of using a PC step size smaller than 1 dB and can be used to compensate for the slow fading trend of the propagation channel rather than rapid fluctuations. It performs better than Alg 1 when the UE moves faster than 80 Km/h or slower than 3 Km/h. The UE does not change its transmission power until it has received 5 consecutive TPC commands.
  138. 138. 138 Company Confidential UL Inner Loop Power Control PCA2 PCA1 PCA2 algorithms for processing power control commands TPC_cmd PCA1 TPC_cmd for each TS TPC_cmd values: +1, -1 step size ∆ TPC: 1dB or 2dB PCA2 TPC_cmd for 5th TS TPC_cmd values: +1, 0, -1 step size ∆ TPC: 1dB UL DPCCH power adjustment: ∆DPCCH = ∆ TPC × TPC_cmd km/h0 ≈ 3 ≈ 80 Rayleigh fading can be compensated
  139. 139. Soft Handover Case: UL Inner Loop Power Control Algorithm 1 139 Company Confidential Example: reliable transmission Cell 1 Cell 2 Cell 3 TPC1 = 1 TPC3 = 0 TPC3 = 1 ⇒ “Down” TPC_cmd = -1 At the mobile, a “power down” command has higher priority over “power up” command “Down”“UP” “UP”
  140. 140. 140 Company Confidential TPC = 1 TPC = 1 TPC = 1 TPC = 1 TPC = 1 TPC = 1 TPC = 0 TPC = 1 TPC = 0 TPC = 1 TPC = 0 TPC = 0 TPC = 0 TPC = 0 TPC = 0 TPC_temp 0 0 0 0 1 0 0 0 0 0 0 0 0 0 -1 • if all TPC-values = 1 ⇒ TPC_temp = +1 • if all TPC-values = 0 ⇒ TPC_temp = -1 • otherwise ⇒ TPC_temp = 0 No Soft Handover Case - UL Inner Loop Power Control Algorithm 2 (Part 1)
  141. 141. Soft Handover Case :UL Inner Loop Power Control Algorithm 2 (Part 2) TPC_temp1 TPC_temp2 TPC_temp3 Example: N = 3 cells ∑= N i i N 1 TPC_temp 1 -1 141 Company Confidential -0.5 0.50 1 -1 10TPC_cmd =
  142. 142. Part VI Dedicated Physical Channels 142 Company Confidential
  143. 143. 143 Company Confidential Downlink Dedicated Physical Channel (DPCH) The downlink DPCH is used to transmit the DCH data. Control information and user data are time multiplexed. The control data is associated with the Dedicated Physical ControlControl Channel (DPCCH), while the user data is associated with the Dedicated Physical DataData Channel (DPDCH). Data is not only User Traffic/Data but could be also High layer signalling (“Measurement control”, “RRC messages”,L3 Dedicated signalling) The transmission is organised in 10 ms radio frames, which are divided into 15 timeslots. The timeslot length is 2560 chips. Within each timeslot, following fields can be found: • Data field 1 and data field 2, which carry DPDCH information • Transmission Power Control (TPC) bit field • Transport Format Combination Indicator (TFCI) field, which is optional • Pilot bits The exact length of the fields depends on the slot format, which is determined by higher layers. The TFCI is optional, because it is not required for services with fixed data rates. Slot format are also defined for the compressed mode; hereby different slot formats are in used, when compression is archived by a changed spreading factor or a changed puncturing scheme. The pilot sequence is used for channel estimation as well as for the SIR ratio determination within the inner loop power control. The number of the pilot bits can be 2, 4, 8 and 16 – it is adjusted with the spreading factor. A similar adjustment is done for the TPC value; its bit numbers range between 2, 4 and 8. The spreading factor for a DPCH can range between 4 and 512. The spreading factor can be changed every TTI period. Superframes last 720 ms and were introduced for GSM-UMTS handover support.
  144. 144. Downlink Dedicated Physical Channel (DPCH) Superframe = 720 ms Radio Frame 0 Radio Frame 1 Radio Frame 2 Radio Frame 71 10 ms Frame Slot 0 Slot 1 Slot 2 Slot 14 TPC bits Pilot bits TFCI bits (optional) Data 2 bitsData 1 bits 144 Company Confidential DPDCHDPDCH DPCCH DPCCH • 17 different slot formats • Compressed mode slot format for changed SF & changed puncturing 2,4,8,16 bits (SIR estimation, phase estimation for Rake receiver)2,4,8 bits
  145. 145. Downlink Dedicated Physical Channel (DPCH) 145 Company Confidential Following features are supported in the downlink: • Blind rate detection, and • Discontinuous transmission. Rate matching is done to the maximum bit rate of the connection. Lower bit rates are possible, including the option of discontinuous transmission. Please note, that audible interference imposes no problem in the downlink, since Common Channels have continuous transmission. Multicode usage: Several physical channels can be allocated in the downlink to one UE. This can occur, when several DPCH are combined in one CCTrCH in the PHY layer, and the data rate of the CCTrCH exceeds the maximum data rates allowed for the physical channels. Then, on all downlink DPCHs, the same spreading factor is used. Also the downlink transmission of the DPCHs takes place synchronous. One DPCH carries DPDCH and DPCCH information, while on the remaining DPCHs, no DPCCH information is transmitted. But also in the case, when several DPCHs with different spreading factors are in use, the first DPCH carries the DPCCH information, while in the remaining DPCHs, this information is omitted (discontinuous transmission). Multicode usage is not implemented in RAN1.
  146. 146. Physical Layer Bit Rates (Downlink) Spreading factor Channel symbol rate (ksps) Channel bit rate (kbps) DPDCH channel bit rate range (kbps) Maximum user data rate with ½- rate coding (approx.) 512 7.5 15 3–6 1–3 kbps 256 15 30 12–24 6–12 kbps 128 30 60 42–51 20–24 kbps 64 60 120 90 45 kbps 32 120 240 210 105 kbps 16 240 480 432 215 kbps 8 480 960 912 456 kbps 4 960 1920 1872 936 kbps 4, with 3 parallel codes 2880 5760 5616 2.8 Mbps • The number of orthogonal channelization codes = Spreading factor Half rate speech Full rate speech 128 kbps 384 kbps 2 Mbps 146 Company Confidential
  147. 147. Downlink Dedicated Physical Channel (DPCH) TS TS maximum bit rate TS TS TS discontinuous transmission with lower bit rate Multicode usage: TS TS TS 147 Company Confidential TS TS TS DPCH 1 DPCH 2 DPCH 3
  148. 148. 148 Company Confidential Power Offsets for the DPCH Node B RNC DCH Data Frame Iub UE Uu PO1 NBAP: RADIO LINK SETUP REQUEST TPC bits Pilot bits TFCI bits (optional) Data 2 bitsData 1 bits PO3PO2 • Power offsets • TFCS • DL DPCH slot format • FDD DL TPC step size P0x: 0..6 dB step size: 0.25 dB
  149. 149. Nokia Parameters Related to DPCHs • RNC: PowerOffsetDLdpcchPilot The parameter defines the power offset for the pilot symbols in relative to the data symbols in dedicated downlink physical channel [0 … 6 dB]; step size 0.25 dB; default: 3 dB for 12.2 kbps • RNC: PowerOffsetDLdpcchTpc, The parameter defines the power offset for the TPC symbols relative to the data symbols in dedicated downlink physical channel [0 … 6 dB]; step size 0.25 dB; default: 3 dB for 12.2 kbps • RNC: PowerOffsetDLdpcchTfci, The parameter defines the power offset for the TFCI symbols relative to the data symbols in dedicated downlink physical channel. [0 … 6 dB], step size 0.25 dB; default: 3 dB for 12.2 kbps 149 Company Confidential
  150. 150. 150 Company Confidential Uplink Dedicated Physical Channels The uplink dedicated physical channel transmission, we identify two types of physical channels: Dedicated Physical Control Channel (DPCCH), which is always transmitted with spreading factor 256 (3840/256=15Ksps=15Kbps). Following fields are defined on the DPCCH: - Pilot bits for channel estimation. Their number can be 3, 4, 5, 6, 7 or 8. - Transmitter Power Control (TPC), with either one or two bits - Transport Format Combination Indicator (TFCI), which is optional, and a - Feedback Indicator (FBI). Bits can be set for the closed loop mode transmit diversity and site selection diversity transmission (SSDT) 6 different slot formats were specified for the DPCCH. Variations exist for the compressed mode. Dedicated Physical Data Channel (DPDCH), which is used for user data transfer (Data is not only User Traffic/Data but could be also High layer signalling (“Measurement Reports”, “RRC messages”,L3 signalling) . Its spreading factor ranges between 4 and 256. 7 different slot formats are defined, which are set by the higher layers. The DPCCH and DPDCH are combined by I/Q code multiplexing with each multiframe. Multicode usage is possible. If applied, additonal DPDCH are added to the uplink transmission, but no additional DPCCHs! The maximum number of DPDCH is 6; when more than one DPDCH is used (Multicodes) they all use SF = 4. The transmission itself is organised in 10 ms radio frames, which are divided into 15 timeslots. The timeslot length is 2560 chips.
  151. 151. Superframe = 720 ms Slot 0 Slot 1 Slot 2 Slot 14 10 ms Frame TPC bits Pilot bits TFCI bits (optional) Data 1 bits Radio Frame 0 Radio Frame 1 Radio Frame 2 Radio Frame 71 DPDCH 151 Company Confidential DPCCH FBI bits • 7 different slot formats • 6 different slot formats • Compressed mode slot format for changed SF & changed puncturing Feedback Indicator for • Closed loop mode transmit diversity, & • Site selection diversity transmission (SSDT) Uplink Dedicated Physical Channels
  152. 152. 152 Company Confidential Discontinuous Transmission and Power Offsets Discontinuous transmission (DTX) is supported for the DCH both uplink and downlink. If DTX is applied in the downlink – as it is done with speech – then 3000 bursts are generated in one second. (1500 times the pilot sequence, 1500 times the TPC bits) This causes two problems: • Inter-frequency interference, caused by the burst generation. At the Node B, the problem can be overcome with exquisite filter equipment. This filter equipment is expensive and heavy. Therefore it cannot be applied in the UE. The UE‘s solution is I/Q code multiplexing, with a continuous transmission for the DPCCH. DPDCH changes can still occur, but they are limited to the TTI period. The minimum TTI period is 10 ms. The same effects can be observed, then the DPDCH data rate and with it its output power is changing. • 3000 bursts causes audible interference with other equipment – just see for example GSM. By reducing the changes to the TTI period, the audible interference is reduced, too. Determination of the power difference between the DPCCH and DPDCH I/Q code multiplexing is done in the uplink, i.e. the DPCCH and DPDCH are transmitted with different codes (and possible with different spreading factors). Gain factors are specified: βc is the gain factor for the DPCCH, while βd is the gain factor for the DPDCH. The gain factors may vary for each TFC. There are two ways, how the UE may learn about the gain factors: • The gain factors are signalled for each TFC. If so, the nominal power relation Aj between the DPDCH and DPCCH is βd/βc. • The gain factor is calculated based on reference TFCs.
  153. 153. DPCCH DPDCH DPCCH DPDCH DPCCH DPDCH 153 Company Confidential TTI TTI TTI UL DPDCH/DPCH Power Difference: DPCCH DPDCH = βd βc =Nominal Power Relation Aj two methods to determine the gain factors: • signalled for each TFCs • calculation based on reference TFCs Discontinuous Transmission and Power Offsets
  154. 154. Transmit Diversity – Closed Loop Mode • Closed loop mode transmit diversity – Used in DPCH and PDSCH to improve DL performance based on feedback information from UE – Channel coding, interleaving and spreading are done as in non-diversity mode. The spread complex valued signal is fed to both TX antenna branches, and weighted with antenna specific weight factors w1 and w2. NodeB adjusts the phase of antenna 2 (as antenna 1 taken as reference), so as to maximize the power received by UE – The weight factors are determined by the UE, and signalled to the UTRAN access point (=cell transceiver) using the D-bits of the FBI field of uplink DPCCH – The calculation of weight factor is the key point of closed loop Tx diversity – There are two modes with different calculation methods of weight factor: 1. Mode 1 uses phase adjustment;the dedicated pilot symbols of two antennas are different (orthogonal) 2. Mode 2 uses phase/amplitude adjustment; the dedicated pilot symbols of two antennas are the same 154 Company Confidential
  155. 155. 155 Company Confidential Initial Uplink DCH Transmission When we look to the PRACH, we can see, that a preambles were used to avoid UEs to access UTRAN with a too high initial transmission power. The same principle is applied for the DPCH. After PRACH procedure the UE transmits between 0 to 7 radio frames only the DPCCH uplink (the period is called DPCCH power control Preamble), before the DPDCH is code multiplexed. The number of radio frames is set by the higher layers (RRC resp. the operator). Also for this period of time, only DPCCH can be found in the downlink. The UE can be also informed about a delay regarding RRC signalling – this is called SRB delay, which can also last 0 to 7 radio frames. The SRB delay follows after the DPCCH preamble. How to set the the transmission power of the first UL DPCCH preamble? Its power level is DPCCH_Initial_power = – CPICH_RSCP + DPCCH_Power_offset The DPCCH Power Offset is retrieved from RRC messages. It’s value ranges between –164 and –6 dB (step size 2 dB). CPICH_RSCP is the received signal code power on the P-CPICH, measured by the UE.
  156. 156. Initial Uplink DCH Transmission T0 DPCCH only DPCCH & DPDCH reception at UE trans- mission at UE 0 to 7 frames for power control preamble DPCCH only, always based on PCA1 DPCCH & DPDCH PCA based on RRC 156 Company Confidential DPCCH_Initial_power = – CPICH_RSCP + DPCCH_Power_offset
  157. 157. Radio frame timing and access slot timing of downlink physical channels 157 Company Confidential k:th S-CCPCH AICH access slots Secondary SCH Primary SCH τS-CCPCH,k 10 ms τPICH #0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4 Radio framewith(SFN modulo 2) = 0 Radio framewith(SFN modulo 2) = 1 τDPCH,n P-CCPCH Any CPICH PICH for k:th S-CCPCH Any PDSCH n:th DPCH 10 ms Subframe #0 HS-SCCH Subframes Subframe #1 Subframe #2 Subframe #3 Subframe #4
  158. 158. Part VII WCDMA Planning 158 Company Confidential

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