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Code Division Multiple Access- CDMA

CDMA is a digital cellular standard that allows multiple users to access the same radio frequency channel simultaneously through the use of unique code sequences. Users are separated by spreading their transmitted signals across the frequency band using pseudo-random codes. CDMA provides advantages over other multiple access techniques like FDMA and TDMA such as increased capacity, soft handoffs between cells, and covert operation due to its noise-like signals. The IS-95 standard introduced CDMA to cellular networks and specified the use of orthogonal codes to separate signals and a 1.25 MHz channel bandwidth to support multiple simultaneous voice calls.

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CDMA – CODE DIVISION MULTIPLE ACCESS VIVEK PATEL CWID- 10404232 17/30/2015 EE 583 Code Division Multiple Access
Outline:  History And Introduction  Multiple Access Method – FDMA/TDMA/CDMA  Comparison  Spread Spectrum  CDMA Introduction  IS 95-CDMA  General Specification  How CDMA Works?  Types Of CDMA  Architecture  CDMA Architecture  Spreading Codes  Walsh Codes  PN Sequences And Orthogonal  CDMA Frame Structure  CDMA Capacity  Power control  Rake receiver  Handoffs  Detection  Third Generation 3G  Commercial use  Advantage And Disadvantage Of CDMA  Conclusion  References 27/30/2015 EE 583 Code Division Multiple Access
1st.Generation (1980s) Analog NMT CT0 TACS CT1 AMPS 3rd. Generation (2000s)2nd. Generation (1990s) Digital GSM DECT DCS1800 CT2 PDC PHS IS-54 IS-95 IS-136 UP-PCS IMT-2000 CDMA2000 W-CDMA  Evolution of Cellular Systems : 7/30/2015 EE 583 Code Division Multiple Access 3
Time Time Time Freq Freq Freq PN Code FDMA TDMA CDMA  Access Technology : 7/30/2015 EE 583 Code Division Multiple Access 4
 FDMA : •In FDMA, the entire allocated cellular frequency spectrum is divided into a number of 30-kHz channels . •The power transmitted by a cell is only large enough to communicate with mobile stations located near the edge of the cell’s coverage area. •The radius of a cell might be one mile or less- referred to as a small cell. 7/30/2015 EE 583 Code Division Multiple Access 5
6  FDMA MS #1 MS #2 MS #n BS f1’ f2’ fn’ f1 f2 fn … … … Reverse channels (Uplink) Forward channels (Downlink) 7/30/2015 EE 583 Code Division Multiple Access
7  FDMA: Channel Structure 1 2 3 … N Frequency Total Bandwidth W=NWc Guard Band Wg 4 Sub Band Wc Frequency Protecting bandwidth … f1’ f2’ fn’ … f1 f2 fn Reverse channels Forward channels 7/30/2015 EE 583 Code Division Multiple Access
 TDMA : •TDMA is a digital wireless air interface . •It divides each carrier frequency into a number of time slots, each of which constitutes an independent telephone circuit. 7/30/2015 EE 583 Code Division Multiple Access 8 C B A C B A C B A C B A C A B Time f0 Frequency
9 MS #1 MS #2 MS #n BS … … Reverse channels (Uplink) Forward channels (Downlink) t Frequency f ’ #1 … #1 … Frame Slot … #1 … #1 Frame … t Frequency f Frame Frame … t #2 … #2 … … t #n … #n … … #2 … #2 … t … #n … #n … t  TDMA: 7/30/2015 EE 583 Code Division Multiple Access
10  TDMA: Channel Structure … t f #1 #2 #n #1 #2 #n … (a). Forward channel … #1 #2 #n Frame FrameFrame … t f ’ #1 #2 #n #1 #2 #n … (b). Reverse channel … #1 #2 #n Frame FrameFrame 7/30/2015 EE 583 Code Division Multiple Access
11  TDMA: Frame Structure (Cont’d) … Time Frequency f = f ’ #1 #2 #n #1 #2 #n … Forward channel Reverse channel … #1 #2 #n Forward channel Frame Frame #1 #2 #n … Reverse channel Channels in Simplex Mode 7/30/2015 EE 583 Code Division Multiple Access
12  TDMA: Frame Structure (Cont’d) … Time Frequency#1 #2 #n #1 #2 #n … … #1 #2 #n Frame FrameFrame Head Data Guard time 7/30/2015 EE 583 Code Division Multiple Access
 CDMA : •A digital multiple access technique specified by the Telecommunications Industry Association (TIA) as "IS-95.“ •One of the unique aspect of CDMA is that while there are certainly limits to the number of phone calls that can be handled by a carrier, this is not a fixed number . •Code division multiple access (CDMA) is a digital air interface standard, claiming eight to fifteen times the capacity of analog. 7/30/2015 EE 583 Code Division Multiple Access 13
14  Code Division Multiple Access (CDMA) MS #1 MS #2 MS #n BS C1’ C2’ Cn’ C1 C2 Cn … … … Reverse channels (Uplink) Forward channels (Downlink) Frequency f ’ Note: Ci’ x Cj’ = 0, i.e., Ci’ and Cj’ are orthogonal codes, Ci x Cj = 0, i.e., Ci and Cj are orthogonal codes Frequency f 7/30/2015 EE 583 Code Division Multiple Access
15  Comparisons of FDMA, TDMA, and CDMA Operation FDMA TDMA CDMA Allocated Bandwidth 12.5 MHz 12.5 MHz 12.5 MHz Frequency reuse 7 7 1 Required channel BW 0.03 MHz 0.03 MHz 1.25 MHz No. of RF channels 12.5/0.03=416 12.5/0.03=416 12.5/1.25=10 Channels/cell 416/7=59 416/7=59 12.5/1.25=10 Control channels/cell 2 2 2 Calls/RF Channel 1 4* 40** Voice channels/cell 57x1=57 57x4=228 8x40=320 Sectors/cell 3 3 3 Voice calls/sector 57/3=19 228/3=76 320 Capacity vs FDMA 1 4 16.8 7/30/2015 EE 583 Code Division Multiple Access
 Spread Spectrum Principles : 7/30/2015 16EE 583 Code Division Multiple Access •Does not attempt to allocate disjoint frequency or time slot resources •Instead, this approach allocates all resources to simultaneous users, controlling the power transmitted by each user to the minimum required to maintain a given SNR •Each user employs a noise-like wideband signal occupying the entire frequency allocation •Each user contributes to the background noise affecting all users, but to the least extent possible. •This restriction on interference limits capacity, but because time and bandwidth resource allocations are unrestricted, the resulting capacity is significantly higher than the conventional system
 Spread Spectrum Principles : •Suppose each user use a wideband Gaussian noise carrier •Suppose each user’s transmission is controlled so that all signals received at the BS are of equal power •Let Psbe the power of each user, and the background noise be negligible. •Then the total interference power, I, presented to each user’s demodulator is I = (K-1) Ps (1) where K is the number of users 7/30/2015 17EE 583 Code Division Multiple Access
 Spread Spectrum Principles : •Let’s say demodulator of each user operates at bit- energy-to-noise-density level of Eb/N0. •So the noise density received by each user’s demodulator is N0 = I/W (2), where W Hz is the bandwidth of the wideband noise carriers. •The received energy per bit is the received signal power divided by the data rate R (bits/s), i.e., Eb= Ps/R (3) 7/30/2015 18EE 583 Code Division Multiple Access
 Spread Spectrum Principles : •Combining (1), (2) and (3) we get K – 1 = I/Ps = (W/R) / (Eb/N0) (4) •If W >> R then the capacity of the system can be large i.e., transmission bandwidth should be much larger than the message bandwidth •If Eb/N0is small, then also the capacity can be large. (since Eb/N0 SNR, this means SNR should be as smallα as possible) 7/30/2015 EE 583 Code Division Multiple Access 19
 Spread Spectrum (1)Spread Spectrum (1) :: S(f) ff0 Before spreading Signal S(f) ff0 After spreading Signal S(f) ff0 After despreading signal Interfering noise f S(f) f0 Before despreading Signal Interfering noise 7/30/2015 EE 583 Code Division Multiple Access 20
 Spread Spectrum(2)Spread Spectrum(2) :: Radio Channel Channel Coding (SS) Carrier Modulation DS-PN Source Coding Transmit Antenna Radio Channel Channel Coding (SS) Carrier Modulation DS-PN Source Coding Transmit Channel Decoding Carrier Demodulation DS-PN Source Decoding Receive Channel Decoding Carrier Demodulation DS-PN Source Decoding Receive Antenna A B 7/30/2015 EE 583 Code Division Multiple Access 21
 Spreading Spectrum (3)Spreading Spectrum (3) “Principle of Using Multiple Codes”“Principle of Using Multiple Codes” 7/30/2015 EE 583 Code Division Multiple Access 22 Spreading Sequence A Spreading Sequence B Spreading Sequence C Spreading Sequence C Spreading Sequence B Spreading Sequence A Input Data X Recovered Data X X+A X+A+B X+A+B+C X+A+B X+A Spread-Spectrum Chip Streams ORIGINATING SITE DESTINATION
 Spread Spectrum (4)Spread Spectrum (4) 7/30/2015 EE 583 Code Division Multiple Access 23
 Advantages of Spread SpectrumAdvantages of Spread Spectrum:: 1. Avoid interference arising from jamming signal or multi-path effects. 2. Covert operation : Difficult to detect 3. Achieve Privacy: Difficult to demodulate, Noise like signal. 4. Impossible to Eavesdrops on the signal expect using the same PN sequence 7/30/2015 EE 583 Code Division Multiple Access 24
 CDMA: •Classification of CDMA Systems : CDMA one CDMA 2000 IS95 IS95B JSTD 008 Narrow Band Wide Band CDMA SYSTEMS 7/30/2015 EE 583 Code Division Multiple Access 25
7/30/2015 26 CDMA Evolution PathsCDMA Evolution Paths 2Mbps 153.6kbps CDMA 1xRTT CDMA 1xEV-DV CDMA IS-95 CDMA 1xEV-DO CDMA 3x 5x 2G 2.5G 3G 9.6kbps EE 583 Code Division Multiple Access
CDMA-Its History & StatusCDMA-Its History & Status 7/30/2015 27EE 583 Code Division Multiple Access
CDMA-Its History & StatusCDMA-Its History & Status 1993, the first CDMA standard IS-95 was issued; In 1995, CDMA technology was put into commercialization in Hong Kong and America on large scale; In April, 2001, China Unicom began to construct CDMA networks—the largest in the world (about 70Million line now); At present, CDMA commercial networks are established in about 40 countries or area, almost 20% of all users in the world. 7/30/2015 28EE 583 Code Division Multiple Access
CDMA Subscriber Growth History:CDMA Subscriber Growth History: Sept.1997 through Sept.2003Sept.1997 through Sept.2003 7/30/2015 29EE 583 Code Division Multiple Access
 IS-95 CDMA: •IS-95 (cdmaone) 2G digital cellular standard •Motivation –Intended as a new system (greenfield) or replacement for AMPS (not an upgrade) –Increase system capacity –Add new features/services 7/30/2015 EE 583 Code Division Multiple Access 30
 IS-95 CDMA: •History: –1990 Qualcomm proposed a code division multiple access (CDMA) digital cellular system claimed to increase capacity by factor 20 or more –Started debate about how CDMA should be implemented and the advantages vs. TDMA (religious tones to debate) –1992 TIA started study of spread spectrum cellular •Several alternative CDMA proposals floated – large debate in the CTIA –came down to Interdigital vs. Qualcomm –Qualcomm proposal won7/30/2015 EE 583 Code Division Multiple Access 31
 IS-95 CDMA: • 1993 TIA IS-95 code division multiple access • (CDMA) standards completed –1995 IS-95A enhanced revision –ANSI J-STD-008 (IS-95b) is standard up banded to 1900 MHz PCS band –1996 Commercial deployment in US (Sprint PCS) –Most popular system in U.S. and Korea –1997 IS-95 name changed to cdmaone • IS-95 evolves to cdma 2000 in 2.5 and 3G 7/30/2015 EE 583 Code Division Multiple Access 32
 IS-95 System Features: •Digital Voice –QCELP fixed rate 14.4Kbps coder –variable rate QCELP coder: 9.6, 4.8, 2.4, 1.2 Kbps •Use of voice activation to reduce interference •As data rate reduces, the transmitter can reduce the power to achieve the same error rates •Dual Mode (AMPS/CDMA), Dual Band (900, 1900 MHz bands) •Low power handsets (sleep mode supported) •Soft Handoff possible •Digital Data services (text, fax, circuit switched data) •Advanced Telephony Features (call waiting, voice mail, etc.) 7/30/2015 EE 583 Code Division Multiple Access 33
IS-95 System Features: •Security: CDMA signal + CAVE encryption •Air Interface Standard Only •Code Division Multiple Access/FDMA/FDD •Traffic Channel –Pair of 1.25 MHz radio channels (up/downlink) –Several users share a radio channel separated by a code not a timeslot or frequency! –Receiver performs a time correlation operation to detect only desired code word –All other code words appear as noise due to decorrelation –Receiver needs to know only codeword and frequency used by transmitter7/30/2015 EE 583 Code Division Multiple Access 34
IS-95 System Features: –Adjust power often to prevent near –far problem •Universal frequency reuse (frequency reuse cluster size K =1) –Simple planning –large capacity increase 7/30/2015 EE 583 Code Division Multiple Access 35
 IS-95 Radio Aspects: 7/30/2015 EE 583 Code Division Multiple Access 36
 Code Division Multiple Access – CDMA: •Multiple users occupying the same band by having different codes is known as CDMA - Code Division Multiple Access system Let W - spread bandwidth in Hz R = 1/Tb = Date Rate S - received power of the desired signal in W J - received power for undesired signals like multiple access users, multipath, jammers etc in W Eb - received energy per bit for the desired signal in W N0 - equivalent noise spectral density in W/Hz 7/30/2015 37EE 583 Code Division Multiple Access
 Code Division Multiple Access – CDMA: 7/30/2015 38 • What is the tolerable interference over desired signal power? ( )min0max NE RW S J b =      EE 583 Code Division Multiple Access 00 0 NE RW NE WT TE WN S J bb b bb === )()((db)marginJamming min0max db N E db R W S J b       −==     
 Code Division Multiple Access – CDMA: •In conventional systems W/R ≈ 1 which means, for satisfactory operation J/S < 1 •Example Let R = 9600; W = 1.2288 MHz (Eb/N0)min = 6 dB (values taken from IS- 95) Jamming margin (JM) = 10log10(1.2288*106 /9.6*103 ) - 6 = 15.1 dB ≡ 32 •This antijam margin or JM arises from Processing Gain (PG) = W/R = 128 •If (Eb/N0)minis further decreased or PG is increased, JM can be further increased 7/30/2015 39EE 583 Code Division Multiple Access
 Code Division Multiple Access – CDMA: •JM can be used to accommodate multiple users in the same band •If (Eb/N0)min and PG is fixed, number of users is maximized if perfect power control is employed. •Capacity of a CDMA system is proportional to PG. 7/30/2015 40EE 583 Code Division Multiple Access
 Code Division Multiple Access – CDMA: •Multiple Access in CDMA: oEach user is assigned a unique PN code. oEach user transmits its information by spreading with unique code. oDirect Sequence spread spectrum is used. oUsers are separated by code not by time slot and frequency slot. 7/30/2015 EE 583 Code Division Multiple Access 41
 Code Division Multiple Access – CDMA: •Concept of CDMA oUsers share same bandwidth oUser axis shows cumulative signal strength of all users Code 1 Code2 Code 3 Code 4 Freq User 7/30/2015 EE 583 Code Division Multiple Access 42
-5000 -4000 -3000 -2000 -1000 0 1000 2000 3000 4000 5000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 noise massege After SpredingChipDurationis0.4 ms. Bit Durationis 6.4 ms. ProcessingGainis 16  How CDMA works?: •Spectrum of the CDMA: 7/30/2015 EE 583 Code Division Multiple Access 43
 Types of CDMA: 1. Frequency hopping •Fixed sequence of frequency values & time is divided into slots . •In the first time slot, a given user transmit to the base station using the first frequency in its frequency hopping sequence. •In the next time interval, it transmits using the second frequency value in its frequency hopping sequence, and so on. •This way, the transmit frequency keeps changing in time. 7/30/2015 44EE 583 Code Division Multiple Access
 Types of CDMA: 2. Direct sequence •Each user transmits its message to the base station using the same frequency, at the same time. •Here signals from different users interfere with each other. •But the user distinguishes its message by using a special, unique code. This code serves as a special language that only the transmitter and receiver understand. 7/30/2015 45EE 583 Code Division Multiple Access
ME SI M BT S BT S BSC BSC MSC VLR EIR HLR AuC AUm Abis PSTN ISDN Mobile station Base Station Subsystem Network Subsystem MS BSS NS  Architecture Of CDMA: 7/30/2015 EE 583 Code Division Multiple Access 46
 Architecture Of CDMA: •Mobile Station (MS): Two Blocks oMobile Equipment (ME) oSubscribers Identity Module (SIM) •Function of Mobile Station: 1. Personal Mobility 2. IMEI (International Mobile Equipment Identity) 3. IMSI (International Mobile Subscriber Identity) 7/30/2015 EE 583 Code Division Multiple Access 47
BSC  Architecture Of CDMA: •Base Station Subsystem (BSS) oBase Transceiver Station (BTS) oBase Station Controller (BSC) 7/30/2015 EE 583 Code Division Multiple Access 48
 Architecture Of CDMA: •BTS : Base Transceiver station •1. It defines the cell . •2. It handles the radio link protocol with the mobile station BSC: Base station Controller •1. It manages radio resources for one or more BTS. •2. Allocation and Deallocation of channels. •3. Transmitter power control. •4. Handoff control 7/30/2015 EE 583 Code Division Multiple Access 49
BS C MSC VLR EIR HLR AuC PSTN ISDN  Architecture Of CDMA: •Network Subsystem oMSC: Mobile Switching Center oHLR: Home Location Register oVLR: Visitor Location register oAuC: Authentication Center oEIR: Equipment Identity Register 7/30/2015 EE 583 Code Division Multiple Access 50
 Architecture Of CDMA: •Mobile Switching center:(MSC) 1 Call set up/supervision/release 2 Call routing 3 Billing information collection 4 Mobility management 5 Paging, Echo cancellation connection to BSC, other MSC and other local exchange networks 6 Access to HLR and VLR 7/30/2015 EE 583 Code Division Multiple Access 51
 Architecture Of CDMA: •Home Location Register (HLR) 1 One HLR per CDMA operator 2 Contains permanent M database of all the subscribers in the network 3 Contains MSRN(mobile station routing no.) 4 It is referred for every incoming call 7/30/2015 EE 583 Code Division Multiple Access 52
 Architecture Of CDMA: •Visitor Location Register(VLR) 1. Temporary visitors database 2. One VLR per MSC •Authentication Center(AuC) 1. Provides security 2. Authentication and encryption •Equipment Identity Register: 1. Contains IMEI 7/30/2015 EE 583 Code Division Multiple Access 53
 Spreading Codes: •A noise-like and random signal has to be generated at the transmitter. •The same signal must be generated at the receiver in synchronization. •We limit the complexity by specifying only one bit per sample, i.E., A binary sequence. 7/30/2015 54EE 583 Code Division Multiple Access
 Desirable Randomness Properties Of SC: •Relative frequencies of “0” and “1” should be ½ (balance property) •Run lengths of zeros and ones should be (run property): •Half of all run lengths should be unity •One - quarter should be of length two •One - eighth should be of length three •A fraction 1/2n of all run lengths should be of length n for all finite n 7/30/2015 55EE 583 Code Division Multiple Access
 Desirable Randomness Properties Of SC: •If the random sequence is shifted by any nonzero number of elements, the resulting sequence should have an equal number of agreements and disagreements with the original sequence (Autocorrelation property) 7/30/2015 EE 583 Code Division Multiple Access 56
 Walsh CodesWalsh Codes:: •64 sequences, each 64 chips long •A chip is a binary digit (0 or 1) •Each Walsh code is orthogonal to all other Walsh codes •This means that it is possible to recognize and therefore extract a particular Walsh code from a mixture of other Walsh codes which are “filtered out” in the process •Two same-length binary strings are orthogonal if the result of xoring them has the same number of 0s as 1s 7/30/2015 EE 583 Code Division Multiple Access 57
 PN Sequences: •A deterministically generated sequence that nearly satisfies these properties is referred to as a Pseudorandom Sequence (PN) •Periodic binary sequences can be conveniently generated using linear feedback shift registers (LFSR) •If the number of stages in the LFSR is r, P ≤ 2r - 1 where P is the period of the sequence 7/30/2015 58EE 583 Code Division Multiple Access
 PN Sequences: •However, if the feedback connections satisfy a specific property, P = 2r - 1. Then the sequence is called a Maximal Length Shift Register (MLSR) or a PN sequence. •Thus if r=15, P=32767. •MLSR satisfies the randomness properties stated before 7/30/2015 59EE 583 Code Division Multiple Access
 Randomness Properties of PN Sequences: •Balance property - Of the 2r - 1 terms, 2r-1 are one and 2r-1 –1 are zero. Thus the unbalance is 1/P. For r=50; 1/P≅10-15 •Run length property - Relative frequency of run length n (zero or ones) is 1/ 2n for n ≤ r-1 and 1/(2r - 1) for n = r •One run length each of r-1 zeros and r ones occurs. There are no run lengths for n > r •Autocorrelation property - The number of disagreements exceeds the number of agreements by unity. Thus again the discrepancy is 1/p 7/30/2015 60EE 583 Code Division Multiple Access
 PN Sequences Specified in IS-95: •A “long” PN sequence (r =42) is used to scramble the user data with a different code shift for each user •The 42-degree characteristic polynomial is given by: •x42 +x41 +x40 +x39 +x37 +x36 +x35 +x32 +x26 +x25 +x24 +x23 +x21 +x20 +x17 +x16 + x15 +x11 +x9 +x7 +1 •The period of the long code is 242 - 1 ≈ 4.4*102 chips and lasts over 41 days 7/30/2015 61EE 583 Code Division Multiple Access
 PN Sequences Specified in IS-95: •A short PN sequence (r = 15) is specific to a base station and its period is (215 −1)Tc = 27ms. •Two “short” PN sequences (r=15) are used to spread the quadrature components of the forward and reverse link waveforms 7/30/2015 EE 583 Code Division Multiple Access 62
 CDMA Related Terms: •CDMA Channel or CDMA Carrier or CDMA Frequency: Duplex channel made of two 1.25 MHz-wide bands of electromagnetic spectrum, one for Base Station to Mobile Station communication (called the FORWARD LINK or the DOWNLINK) and another for Mobile Station to Base Station communication (called the REVERSE LINK or the UPLINK). •In 800 Cellular these two simplex 1.25 MHz bands are 45 MHz apart, •In 1900 MHz PCS they are 80 MHz apart 7/30/2015 63EE 583 Code Division Multiple Access
 CDMA Related Terms: •CDMA Forward & Reverse Channel 1.25 MHz Forward / Reverse Link CDMA Code Channel Each individual stream of 0’s and 1’s contained in either the CDMA Forward Channel or in the CDMA Reverse Channel •Code Channels are characterized (made unique) by mathematical codes Code channels in the forward link: Pilot, Sync, Paging and Forward Traffic channels Code channels in the reverse link: Access and Reverse Traffic channels 7/30/2015 EE 583 Code Division Multiple Access 64
 cdma2000 Uplink Frame Structure: • Radio Configuration 3 7/30/2015 65 CRC encoder tail bits Convolutional or Turbo Coder symbol repetition symbol puncture block interleaver modulation symbol C channel bits Bits/ Frame 16 40 80 172 350 744 1512 3048 6120 CRC bits 6 6 8 12 16 16 16 16 16 tail bits 8 8 8 8 8 8 8 8 8 Data Rate kbps 1.5 2.7 4.8 9.6 19.2 38.4 76.8 153.6 307.2 Code Rate 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/2 Repeats 16 8 4 2 1 1 1 1 1 Delete 1 of 5 1 of 9 none none none none none none none Symbols 1536 1536 1536 1536 1536 3072 6144 12288 12288 EE 583 Code Division Multiple Access
 cdma2000 Uplink Modulator: 7/30/2015 66 C C C A B Σ Σ dβ dβ dβ cβ )cos( tcω )sin( tcω Ilong,c Qlong,c + + + + Σ + _ sumsum 1Dw Cw 2Sw 1Sw Primary Traffic Secondary Traffic 1 Secondary Traffic 2 Control Pilot pulse shape pulse shape EE 583 Code Division Multiple Access
 cdma2000 Downlink Frame Structure: 7/30/2015 67 Bits/ Frame 21 55 125 267 552 1128 2280 4584 9192 20712 CRC bits 6 8 10 12 16 16 16 16 16 16 tail bits 8 8 8 8 8 8 8 8 8 8 Data Rate kbps 1.8 3.6 7.2 14.4 28.8 57.6 115.2 230.4 460.8 1036.8 Code Rate 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 Repeats 8 4 2 1 1 1 1 1 1 1 Delete none none none none none none none none none 2 of 18 Symbols 576 576 576 576 1152 2304 4608 9216 18432 36864 Radio Configuration 9 CRC encoder tail bits Convolutional or Turbo Coder symbol repetition symbol puncture block interleaver modulation symbol channel bits W EE 583 Code Division Multiple Access
 Benefits of the cdma2000 1x StandardsBenefits of the cdma2000 1x Standards:: •Increased mobile standby battery life (via Quick Paging Channel) •Total backward compatibility to reuse switch and call processing features •2-3 dB better coverage •High speed 153.6 kbps packet data capabilities •cdma2000 1x = 1.25 MHz Radio Transmission Technology 7/30/2015 EE 583 Code Division Multiple Access 68
 cdma2000 1X DL Modulation Processing: 7/30/2015 EE 583 Code Division Multiple Access 69 + long code 0  1 1  -1 channel gain fwd pwr ctrl gain powercontrol symbolpuncture DEMUX decimate pwr ctrl bit pos I/Q scrambling bit extract power control bits puncture timing 800 Hz W YQ YI modulation symbol rate
 cdma2000 1X Downlink Modulation: 7/30/2015 70 I channel pilot PN Q channel pilot PN Walsh code QOF code IY QY Σ Σ Σ Σ Σ pulse shape pulse shape + + + - )cos( tcω )sin( tcω other channels other channels phaserotateforQOF QX IX EE 583 Code Division Multiple Access
 CDMA Capacity: •CDMA Main Advantages –resistant to narrow band interference –resistant to multipath fading and ISI –no hard limit on number of users (soft capacity) 7/30/2015 EE 583 Code Division Multiple Access 71 .1 .01 .001 .0001 10 20 30 40 50 60 users BER of CDMA system with 128 cps.
 CDMA Capacity: –As number of users on a frequency increase the interference level increases and BER increases for all users –With proper limits all frequencies can be used in every cell 7/30/2015 EE 583 Code Division Multiple Access 72
 CDMA Capacity: •CDMA is a interference limited system –Must limit number of users on a frequency to limit interference within a cell and between cells using same frequency (All CDMA carriers can be assigned to each sector in each cell!) –Total Interference It=Ioc+ Io+ No •Ioc = other cell interference, Io= own cell interference, No= Noise •uplink not downlink in CDMA systems considered the constraining factor 7/30/2015 EE 583 Code Division Multiple Access 73
 CDMA Capacity: •Remember in direct sequence spread spectrum Processing Gain = bandwidth of the spread signal to the bandwidth of the data signal = W/R –In IS-95 W/R = 10 log (1.23.MHz/9.6 KHz) = 21.1 dB for rate set 1, for rate set two (14.4 kbps) => 19.3 db •Number of traffic channels per carrier and cell function of processing gain, interference, speech coder tolerance for errors, error control coding, etc. 7/30/2015 EE 583 Code Division Multiple Access 74
 CDMA Capacity: •The effect of more users in a cell on frequency is to degrade the channel for everyone – can be thought off as decreasing the usable cell size 7/30/2015 EE 583 Code Division Multiple Access 75
 Power Control in CDMA: •CDMA goal is to maximize the number of simultaneous users •Capacity is maximized by maintaining the signal to interference ratio at the minimum acceptable •Power transmitted by mobile station must be therefore controlled •Transmit power enough to achieve target BER: no less no more 7/30/2015 76EE 583 Code Division Multiple Access
 Power Control in CDMA: •Controlling transmitted power affects the CIR 7/30/2015 EE 583 Code Division Multiple Access 77 77 Pr Pt = 1        4πdf c α Pt = Transmitted power Pr = Received power in free space d = Distance between receiver and transmitter f = Frequency of transmission c = Speed of light a = Attenuation constant (2 to 4)
 Power Control: Open Loop vs. Closed Loop •Open loop: –Base station transmits at a known power level (a beacon) which mobile measures to estimate the path loss –Assumes path loss in both directions is the same –Not very accurate as uplink and downlink are separated in frequency –Useful for coarse initial estimates at mobile used in Access channel for signaling 7/30/2015 EE 583 Code Division Multiple Access 78
 Power Control: Open Loop vs. Closed Loop: •Closed loop: –Signal-to-Interference Ratio (SIR) measured at the receiver and compared to a target value for SIR –Receiver sends a power control command to transmitter to reduce or increase the power level - requires a bi-directional link –Used in TCH – power control sub channel operates at 800 bps by puncturing downlink data with periodic bits – each power command adjusted MS power in 1 dB increments 7/30/2015 EE 583 Code Division Multiple Access 79
 Closed Loop Power Control: Inner Loop vs. Outer Loop: •Inner Loop (or fast power control) –Measures received SIR, controls transmit power –Commands sent several times per frame (hence fast power control) 7/30/2015 EE 583 Code Division Multiple Access 80
 Closed Loop Power Control: Inner Loop vs. Outer Loop: •Outer Loop (or slow power control) –Measures packet error rate –Changes target SIR for inner loop –Directly modify transmit power based on FER –Commands sent once per frame (hence slow power control) 7/30/2015 EE 583 Code Division Multiple Access 81
 Two factors important for power control: •Propagation loss •due to propagation loss, power variations up to 80 dB •a high dynamic range of power control required •Channel Fading •average rate of fade is one fade per second per mile hour of mobile speed •power attenuated by more than 30 dB •power control must track the fade 7/30/2015 82EE 583 Code Division Multiple Access
 Power Control in IS-95A: •At 900 MHz and 120 km/hr mobile speed Doppler shift =100Hz •In IS 95-A closed loop power control is operated at 800 Hz update rate •Power control bits are inserted (‘punctured’) into the interleaved and encoded traffic data stream •Power control step size is +/- 1 dB •Power control bit errors do not affect performance much 7/30/2015 83EE 583 Code Division Multiple Access
 Rake Receiver: •Mobile station receives multiple attenuated and delayed replicas of the original signal (multipath diversity channels). •Two multipath signals are resolvable only if their relative delay exceeds the chip period Tc •Amplitudes and phases of multipath components are found by correlating the received waveform with multiple delayed versions of the signal (delay = nTc). •Searcher performs the above task for up to 3 different multipath signals. •3 parallel demodulators (RAKE fingers) isolate the multipath components and the RAKE receiver combines them. 7/30/2015 84EE 583 Code Division Multiple Access
d1 d2 t t t d3 transmission receiving Racer combination noise 7/30/2015 EE 583 Code Division Multiple Access 85  Rake Receiver:
Correlator 1 Correlator 2 Correlator 3 Search Correlator Combiner To De-Interleaver, Viterbi Decoder Multipath Delay Components ( 150 µs > ∆t > 1µs) Rake receiver can isolate multipath spaced > 1 chip length. 7/30/2015 EE 583 Code Division Multiple Access 86  Rake Receiver:
•Handset uses combined outputs of the three traffic correlators “rake fingers” •Each finger can independently recover a particular PN offset and Walsh code •Fingers can targeted on delayed multipath reflections, or even on different BTSs •Searcher continuously checks pilots 7/30/2015 EE 583 Code Division Multiple Access 87  Rake Receiver:
7/30/2015 88 88  Handoff in CDMA System: •In GSM hard handoff occurs at the cell boundary •Soft Handoff •Mobile commences Communication with a new BS without interrupting communication with old BS •same frequency assignment between old and new BS •provides different site selection diversity •Softer Handoff •Handoff between sectors in a cell •CDMA to CDMA hard handoff •Mobile transmits between two base stations with different frequency assignment EE 583 Code Division Multiple Access
Handoff is of 3 types 1. Intra BSC 2 Inter BSC 3. Inter MSC  Handoff in CDMA System: BSCBSC BSC MSC MSC GMS C 7/30/2015 EE 583 Code Division Multiple Access 89
 Soft Handoff- A unique feature of CDMA Mobile: Advantages •Contact with new base station is made before the call is switched •Diversity combining is used between multiple cell sites •Diversity combining is the process of combining information from multiple transmitted packets to increase the effective SNR of received packets • additional resistance to fading •If the new cell is loaded to capacity, handoff can still be performed for a small increase in BER •Neither the mobile nor the base station is required to change frequency 7/30/2015 90EE 583 Code Division Multiple Access
 Detection in the CDMA system: •Multi-Users Detection (MUD) •The capacity and the performance of the CDMA system increase when MUD is implemented. •The basic principle of MUD is the elimination of the negative effect of each user on the other. • MUD is also known as joint detection and interference cancellation . • Multi-user detection considers all users as signals for each other. 7/30/2015 91EE 583 Code Division Multiple Access
 Detection in the CDMA system: •Multi-Users Detection (MUD) •The ultimate technique for the MUD is the optimum receiver. •Optimum Receiver: •Very complex. So, it is unpractical solution to reduce the multiple access interference. Sup- optimum detector will be implemented. 7/30/2015 EE 583 Code Division Multiple Access 92
 Detection in the CDMA system: •Multi-Users Detection (MUD) •Sup-optimum solution: •Serial Interference cancellation (SIC): •SIC is preferred in the absence of power control. • Serial canceling the interference generated from the other users. •Cancel the strongest signal first (most negative effect ) 7/30/2015 93EE 583 Code Division Multiple Access
 Detection in the CDMA system: •Multi-Users Detection (MUD) •Parallel Interference Cancellation (PIC): •PIC would be preferred when the amount of interference from each user is similar. •In the initial detection stage, all active users are detected in parallel by a SUD technique. •Then, the obtained interference is subtracted from the received signal and data detection is performed again with reduced MAI 7/30/2015 EE 583 Code Division Multiple Access 94
 Detection in the CDMA system: Disadvantages: 1. Multiple Access Interference: •Require multi-user detection (MUD) algorithms to solve. 2. Near-far problem. •Where stronger (near to the Base Station) user masks the weaker user (far from the Base Station) 3. Requires wideband channel. 7/30/2015 95EE 583 Code Division Multiple Access
 What is Third Generation? : •Flexible support of multiple services •Voice •Messaging – email, fax, etc. •Medium-rate multimedia – Internet access, educational •High-rate multimedia – file transfer, video •High-rate interactive multimedia – video teleconferencing, telemedicine, etc. •Mobility: quasi-stationary to high-speed platforms •Global roaming: ubiquitous, seamless coverage •Evolution from second generation systems 7/30/2015 96EE 583 Code Division Multiple Access
 W-CDMA Versus cdma2000 : 7/30/2015 97 97 EE 583 Code Division Multiple Access
 cdma2000 vs WCDMA: •Chip rate •Coherent Pilot Channels •Transmit Diversity •Underlying Network •Single Carrier versus Multicarrier Spreading •Cell Site Synchronization 7/30/2015 98EE 583 Code Division Multiple Access
Commercial usage of CDMA: •CDMA was introduced in the 2nd Generation (early of the 1990s). •E.g. IS-95 standard, also known as cdma One which support up to 64 users that are orthogonally coded and at the same time transmitted over 1.25 MHz channel •Used for Cellular Communication System •(824-894 MHz in US Cellular) • 3rd Generation: cdma2000 •Allow high rate of packet transmitting in addition of voice transmitting. 7/30/2015 EE 583 Code Division Multiple Access 99
 CDMA AdvantagesCDMA Advantages:: •Spread Spectrum •Soft & Softer Handoff •Rake Receiver •Variable Rate Vocoder •High quality voice •Power Control •Coverage •Simple Network Planning •Green Handset •Smooth migration to 3G and the operator’s benefit is protected at the most 7/30/2015 100EE 583 Code Division Multiple Access
 DISADVANTAGES OF CDMA : • Near far problem. • CDMA is relatively low, and the network is not as mature as GSM. • CDMA can not offer international roaming, a large GSM advantage.
 Conclusion: •The CDMA will allow many signals to be transmitted at the same channel at the same time. This done by giving each user a Pseudo-Noise code which is a binary sequence. This code should have low cross- correlation between each other. •Multiple access interference has bad effect on the CDMA system so the multiple user detection is used to reduce the MAI. •CDMA cellular system is deemed superior to the FDMA and TDMA •cellular systems for the time being. 7/30/2015 102EE 583 Code Division Multiple Access
 Conclusion: • Therefore, CDMA technique becomes more important in radio • communication systems. •CDMA is based on the spread spectrum technique which has been used at military field. 7/30/2015 EE 583 Code Division Multiple Access 103
 References: •http://www.tubex.com/category/cdma/gsm •http://www.bsnl.co.in:cdma/architecture.html •http://www.cellular.co.za/technologies/cdma/cdma_w_paper •http://www.arcx.com/sites/CDMAvsTDMA.htm •Lee JS and Miller LM, CDMA System Engineering Handbook, Arttech Publishing House, 1998. •Viterbi A, CDMA-Spread Spectrum Communication, Addison Wesley 1995. • R. L. Peterson, “Third Generation Personal Communications: Physical Layer Status,” Presentation at Clemson University, Feb. 1, 2001 1047/30/2015 EE 583 Code Division Multiple Access
 References: • Manjit Singh and Manoneet Singh, “3G Wireless with Respect to IMT-2000 and Beyond,” Telecom 99 • Harri Holma and Antti Toskala, WCDMA for UMTS: Radio Access for Third Generation Mobile Communications, New York: Wiley, 2000 • “CDMA Evolution from IS-95, IS-2000, to 1XTREME,” Technology Transfer Training Class, Motorola, Inc., July 2000 7/30/2015 EE 583 Code Division Multiple Access 105

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Code Division Multiple Access- CDMA

  • 1.
    CDMA – CODEDIVISION MULTIPLE ACCESS VIVEK PATEL CWID- 10404232 17/30/2015 EE 583 Code Division Multiple Access
  • 2.
    Outline:  History AndIntroduction  Multiple Access Method – FDMA/TDMA/CDMA  Comparison  Spread Spectrum  CDMA Introduction  IS 95-CDMA  General Specification  How CDMA Works?  Types Of CDMA  Architecture  CDMA Architecture  Spreading Codes  Walsh Codes  PN Sequences And Orthogonal  CDMA Frame Structure  CDMA Capacity  Power control  Rake receiver  Handoffs  Detection  Third Generation 3G  Commercial use  Advantage And Disadvantage Of CDMA  Conclusion  References 27/30/2015 EE 583 Code Division Multiple Access
  • 3.
    1st.Generation (1980s) Analog NMT CT0 TACS CT1 AMPS 3rd. Generation (2000s)2nd. Generation (1990s) Digital GSMDECT DCS1800 CT2 PDC PHS IS-54 IS-95 IS-136 UP-PCS IMT-2000 CDMA2000 W-CDMA  Evolution of Cellular Systems : 7/30/2015 EE 583 Code Division Multiple Access 3
  • 4.
    Time Time Time FreqFreq Freq PN Code FDMA TDMA CDMA  Access Technology : 7/30/2015 EE 583 Code Division Multiple Access 4
  • 5.
     FDMA : •InFDMA, the entire allocated cellular frequency spectrum is divided into a number of 30-kHz channels . •The power transmitted by a cell is only large enough to communicate with mobile stations located near the edge of the cell’s coverage area. •The radius of a cell might be one mile or less- referred to as a small cell. 7/30/2015 EE 583 Code Division Multiple Access 5
  • 6.
    6  FDMA MS #1 MS#2 MS #n BS f1’ f2’ fn’ f1 f2 fn … … … Reverse channels (Uplink) Forward channels (Downlink) 7/30/2015 EE 583 Code Division Multiple Access
  • 7.
    7  FDMA: ChannelStructure 1 2 3 … N Frequency Total Bandwidth W=NWc Guard Band Wg 4 Sub Band Wc Frequency Protecting bandwidth … f1’ f2’ fn’ … f1 f2 fn Reverse channels Forward channels 7/30/2015 EE 583 Code Division Multiple Access
  • 8.
     TDMA : •TDMAis a digital wireless air interface . •It divides each carrier frequency into a number of time slots, each of which constitutes an independent telephone circuit. 7/30/2015 EE 583 Code Division Multiple Access 8 C B A C B A C B A C B A C A B Time f0 Frequency
  • 9.
    9 MS #1 MS #2 MS#n BS … … Reverse channels (Uplink) Forward channels (Downlink) t Frequency f ’ #1 … #1 … Frame Slot … #1 … #1 Frame … t Frequency f Frame Frame … t #2 … #2 … … t #n … #n … … #2 … #2 … t … #n … #n … t  TDMA: 7/30/2015 EE 583 Code Division Multiple Access
  • 10.
    10  TDMA: ChannelStructure … t f #1 #2 #n #1 #2 #n … (a). Forward channel … #1 #2 #n Frame FrameFrame … t f ’ #1 #2 #n #1 #2 #n … (b). Reverse channel … #1 #2 #n Frame FrameFrame 7/30/2015 EE 583 Code Division Multiple Access
  • 11.
    11  TDMA: FrameStructure (Cont’d) … Time Frequency f = f ’ #1 #2 #n #1 #2 #n … Forward channel Reverse channel … #1 #2 #n Forward channel Frame Frame #1 #2 #n … Reverse channel Channels in Simplex Mode 7/30/2015 EE 583 Code Division Multiple Access
  • 12.
    12  TDMA: FrameStructure (Cont’d) … Time Frequency#1 #2 #n #1 #2 #n … … #1 #2 #n Frame FrameFrame Head Data Guard time 7/30/2015 EE 583 Code Division Multiple Access
  • 13.
     CDMA : •Adigital multiple access technique specified by the Telecommunications Industry Association (TIA) as "IS-95.“ •One of the unique aspect of CDMA is that while there are certainly limits to the number of phone calls that can be handled by a carrier, this is not a fixed number . •Code division multiple access (CDMA) is a digital air interface standard, claiming eight to fifteen times the capacity of analog. 7/30/2015 EE 583 Code Division Multiple Access 13
  • 14.
    14  Code DivisionMultiple Access (CDMA) MS #1 MS #2 MS #n BS C1’ C2’ Cn’ C1 C2 Cn … … … Reverse channels (Uplink) Forward channels (Downlink) Frequency f ’ Note: Ci’ x Cj’ = 0, i.e., Ci’ and Cj’ are orthogonal codes, Ci x Cj = 0, i.e., Ci and Cj are orthogonal codes Frequency f 7/30/2015 EE 583 Code Division Multiple Access
  • 15.
    15  Comparisons ofFDMA, TDMA, and CDMA Operation FDMA TDMA CDMA Allocated Bandwidth 12.5 MHz 12.5 MHz 12.5 MHz Frequency reuse 7 7 1 Required channel BW 0.03 MHz 0.03 MHz 1.25 MHz No. of RF channels 12.5/0.03=416 12.5/0.03=416 12.5/1.25=10 Channels/cell 416/7=59 416/7=59 12.5/1.25=10 Control channels/cell 2 2 2 Calls/RF Channel 1 4* 40** Voice channels/cell 57x1=57 57x4=228 8x40=320 Sectors/cell 3 3 3 Voice calls/sector 57/3=19 228/3=76 320 Capacity vs FDMA 1 4 16.8 7/30/2015 EE 583 Code Division Multiple Access
  • 16.
     Spread SpectrumPrinciples : 7/30/2015 16EE 583 Code Division Multiple Access •Does not attempt to allocate disjoint frequency or time slot resources •Instead, this approach allocates all resources to simultaneous users, controlling the power transmitted by each user to the minimum required to maintain a given SNR •Each user employs a noise-like wideband signal occupying the entire frequency allocation •Each user contributes to the background noise affecting all users, but to the least extent possible. •This restriction on interference limits capacity, but because time and bandwidth resource allocations are unrestricted, the resulting capacity is significantly higher than the conventional system
  • 17.
     Spread SpectrumPrinciples : •Suppose each user use a wideband Gaussian noise carrier •Suppose each user’s transmission is controlled so that all signals received at the BS are of equal power •Let Psbe the power of each user, and the background noise be negligible. •Then the total interference power, I, presented to each user’s demodulator is I = (K-1) Ps (1) where K is the number of users 7/30/2015 17EE 583 Code Division Multiple Access
  • 18.
     Spread SpectrumPrinciples : •Let’s say demodulator of each user operates at bit- energy-to-noise-density level of Eb/N0. •So the noise density received by each user’s demodulator is N0 = I/W (2), where W Hz is the bandwidth of the wideband noise carriers. •The received energy per bit is the received signal power divided by the data rate R (bits/s), i.e., Eb= Ps/R (3) 7/30/2015 18EE 583 Code Division Multiple Access
  • 19.
     Spread SpectrumPrinciples : •Combining (1), (2) and (3) we get K – 1 = I/Ps = (W/R) / (Eb/N0) (4) •If W >> R then the capacity of the system can be large i.e., transmission bandwidth should be much larger than the message bandwidth •If Eb/N0is small, then also the capacity can be large. (since Eb/N0 SNR, this means SNR should be as smallα as possible) 7/30/2015 EE 583 Code Division Multiple Access 19
  • 20.
     Spread Spectrum(1)Spread Spectrum (1) :: S(f) ff0 Before spreading Signal S(f) ff0 After spreading Signal S(f) ff0 After despreading signal Interfering noise f S(f) f0 Before despreading Signal Interfering noise 7/30/2015 EE 583 Code Division Multiple Access 20
  • 21.
     Spread Spectrum(2)SpreadSpectrum(2) :: Radio Channel Channel Coding (SS) Carrier Modulation DS-PN Source Coding Transmit Antenna Radio Channel Channel Coding (SS) Carrier Modulation DS-PN Source Coding Transmit Channel Decoding Carrier Demodulation DS-PN Source Decoding Receive Channel Decoding Carrier Demodulation DS-PN Source Decoding Receive Antenna A B 7/30/2015 EE 583 Code Division Multiple Access 21
  • 22.
     Spreading Spectrum(3)Spreading Spectrum (3) “Principle of Using Multiple Codes”“Principle of Using Multiple Codes” 7/30/2015 EE 583 Code Division Multiple Access 22 Spreading Sequence A Spreading Sequence B Spreading Sequence C Spreading Sequence C Spreading Sequence B Spreading Sequence A Input Data X Recovered Data X X+A X+A+B X+A+B+C X+A+B X+A Spread-Spectrum Chip Streams ORIGINATING SITE DESTINATION
  • 23.
     Spread Spectrum(4)Spread Spectrum (4) 7/30/2015 EE 583 Code Division Multiple Access 23
  • 24.
     Advantages ofSpread SpectrumAdvantages of Spread Spectrum:: 1. Avoid interference arising from jamming signal or multi-path effects. 2. Covert operation : Difficult to detect 3. Achieve Privacy: Difficult to demodulate, Noise like signal. 4. Impossible to Eavesdrops on the signal expect using the same PN sequence 7/30/2015 EE 583 Code Division Multiple Access 24
  • 25.
     CDMA: •Classification ofCDMA Systems : CDMA one CDMA 2000 IS95 IS95B JSTD 008 Narrow Band Wide Band CDMA SYSTEMS 7/30/2015 EE 583 Code Division Multiple Access 25
  • 26.
    7/30/2015 26 CDMA EvolutionPathsCDMA Evolution Paths 2Mbps 153.6kbps CDMA 1xRTT CDMA 1xEV-DV CDMA IS-95 CDMA 1xEV-DO CDMA 3x 5x 2G 2.5G 3G 9.6kbps EE 583 Code Division Multiple Access
  • 27.
    CDMA-Its History &StatusCDMA-Its History & Status 7/30/2015 27EE 583 Code Division Multiple Access
  • 28.
    CDMA-Its History &StatusCDMA-Its History & Status 1993, the first CDMA standard IS-95 was issued; In 1995, CDMA technology was put into commercialization in Hong Kong and America on large scale; In April, 2001, China Unicom began to construct CDMA networks—the largest in the world (about 70Million line now); At present, CDMA commercial networks are established in about 40 countries or area, almost 20% of all users in the world. 7/30/2015 28EE 583 Code Division Multiple Access
  • 29.
    CDMA Subscriber GrowthHistory:CDMA Subscriber Growth History: Sept.1997 through Sept.2003Sept.1997 through Sept.2003 7/30/2015 29EE 583 Code Division Multiple Access
  • 30.
     IS-95 CDMA: •IS-95(cdmaone) 2G digital cellular standard •Motivation –Intended as a new system (greenfield) or replacement for AMPS (not an upgrade) –Increase system capacity –Add new features/services 7/30/2015 EE 583 Code Division Multiple Access 30
  • 31.
     IS-95 CDMA: •History: –1990Qualcomm proposed a code division multiple access (CDMA) digital cellular system claimed to increase capacity by factor 20 or more –Started debate about how CDMA should be implemented and the advantages vs. TDMA (religious tones to debate) –1992 TIA started study of spread spectrum cellular •Several alternative CDMA proposals floated – large debate in the CTIA –came down to Interdigital vs. Qualcomm –Qualcomm proposal won7/30/2015 EE 583 Code Division Multiple Access 31
  • 32.
     IS-95 CDMA: •1993 TIA IS-95 code division multiple access • (CDMA) standards completed –1995 IS-95A enhanced revision –ANSI J-STD-008 (IS-95b) is standard up banded to 1900 MHz PCS band –1996 Commercial deployment in US (Sprint PCS) –Most popular system in U.S. and Korea –1997 IS-95 name changed to cdmaone • IS-95 evolves to cdma 2000 in 2.5 and 3G 7/30/2015 EE 583 Code Division Multiple Access 32
  • 33.
     IS-95 SystemFeatures: •Digital Voice –QCELP fixed rate 14.4Kbps coder –variable rate QCELP coder: 9.6, 4.8, 2.4, 1.2 Kbps •Use of voice activation to reduce interference •As data rate reduces, the transmitter can reduce the power to achieve the same error rates •Dual Mode (AMPS/CDMA), Dual Band (900, 1900 MHz bands) •Low power handsets (sleep mode supported) •Soft Handoff possible •Digital Data services (text, fax, circuit switched data) •Advanced Telephony Features (call waiting, voice mail, etc.) 7/30/2015 EE 583 Code Division Multiple Access 33
  • 34.
    IS-95 System Features: •Security:CDMA signal + CAVE encryption •Air Interface Standard Only •Code Division Multiple Access/FDMA/FDD •Traffic Channel –Pair of 1.25 MHz radio channels (up/downlink) –Several users share a radio channel separated by a code not a timeslot or frequency! –Receiver performs a time correlation operation to detect only desired code word –All other code words appear as noise due to decorrelation –Receiver needs to know only codeword and frequency used by transmitter7/30/2015 EE 583 Code Division Multiple Access 34
  • 35.
    IS-95 System Features: –Adjustpower often to prevent near –far problem •Universal frequency reuse (frequency reuse cluster size K =1) –Simple planning –large capacity increase 7/30/2015 EE 583 Code Division Multiple Access 35
  • 36.
     IS-95 RadioAspects: 7/30/2015 EE 583 Code Division Multiple Access 36
  • 37.
     Code DivisionMultiple Access – CDMA: •Multiple users occupying the same band by having different codes is known as CDMA - Code Division Multiple Access system Let W - spread bandwidth in Hz R = 1/Tb = Date Rate S - received power of the desired signal in W J - received power for undesired signals like multiple access users, multipath, jammers etc in W Eb - received energy per bit for the desired signal in W N0 - equivalent noise spectral density in W/Hz 7/30/2015 37EE 583 Code Division Multiple Access
  • 38.
     Code DivisionMultiple Access – CDMA: 7/30/2015 38 • What is the tolerable interference over desired signal power? ( )min0max NE RW S J b =      EE 583 Code Division Multiple Access 00 0 NE RW NE WT TE WN S J bb b bb === )()((db)marginJamming min0max db N E db R W S J b       −==     
  • 39.
     Code DivisionMultiple Access – CDMA: •In conventional systems W/R ≈ 1 which means, for satisfactory operation J/S < 1 •Example Let R = 9600; W = 1.2288 MHz (Eb/N0)min = 6 dB (values taken from IS- 95) Jamming margin (JM) = 10log10(1.2288*106 /9.6*103 ) - 6 = 15.1 dB ≡ 32 •This antijam margin or JM arises from Processing Gain (PG) = W/R = 128 •If (Eb/N0)minis further decreased or PG is increased, JM can be further increased 7/30/2015 39EE 583 Code Division Multiple Access
  • 40.
     Code DivisionMultiple Access – CDMA: •JM can be used to accommodate multiple users in the same band •If (Eb/N0)min and PG is fixed, number of users is maximized if perfect power control is employed. •Capacity of a CDMA system is proportional to PG. 7/30/2015 40EE 583 Code Division Multiple Access
  • 41.
     Code DivisionMultiple Access – CDMA: •Multiple Access in CDMA: oEach user is assigned a unique PN code. oEach user transmits its information by spreading with unique code. oDirect Sequence spread spectrum is used. oUsers are separated by code not by time slot and frequency slot. 7/30/2015 EE 583 Code Division Multiple Access 41
  • 42.
     Code DivisionMultiple Access – CDMA: •Concept of CDMA oUsers share same bandwidth oUser axis shows cumulative signal strength of all users Code 1 Code2 Code 3 Code 4 Freq User 7/30/2015 EE 583 Code Division Multiple Access 42
  • 43.
    -5000 -4000 -3000-2000 -1000 0 1000 2000 3000 4000 5000 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 noise massege After SpredingChipDurationis0.4 ms. Bit Durationis 6.4 ms. ProcessingGainis 16  How CDMA works?: •Spectrum of the CDMA: 7/30/2015 EE 583 Code Division Multiple Access 43
  • 44.
     Types ofCDMA: 1. Frequency hopping •Fixed sequence of frequency values & time is divided into slots . •In the first time slot, a given user transmit to the base station using the first frequency in its frequency hopping sequence. •In the next time interval, it transmits using the second frequency value in its frequency hopping sequence, and so on. •This way, the transmit frequency keeps changing in time. 7/30/2015 44EE 583 Code Division Multiple Access
  • 45.
     Types ofCDMA: 2. Direct sequence •Each user transmits its message to the base station using the same frequency, at the same time. •Here signals from different users interfere with each other. •But the user distinguishes its message by using a special, unique code. This code serves as a special language that only the transmitter and receiver understand. 7/30/2015 45EE 583 Code Division Multiple Access
  • 46.
  • 47.
     Architecture OfCDMA: •Mobile Station (MS): Two Blocks oMobile Equipment (ME) oSubscribers Identity Module (SIM) •Function of Mobile Station: 1. Personal Mobility 2. IMEI (International Mobile Equipment Identity) 3. IMSI (International Mobile Subscriber Identity) 7/30/2015 EE 583 Code Division Multiple Access 47
  • 48.
    BSC  Architecture OfCDMA: •Base Station Subsystem (BSS) oBase Transceiver Station (BTS) oBase Station Controller (BSC) 7/30/2015 EE 583 Code Division Multiple Access 48
  • 49.
     Architecture OfCDMA: •BTS : Base Transceiver station •1. It defines the cell . •2. It handles the radio link protocol with the mobile station BSC: Base station Controller •1. It manages radio resources for one or more BTS. •2. Allocation and Deallocation of channels. •3. Transmitter power control. •4. Handoff control 7/30/2015 EE 583 Code Division Multiple Access 49
  • 50.
    BS C MSC VLR EIR HLR AuC PSTN ISDN  ArchitectureOf CDMA: •Network Subsystem oMSC: Mobile Switching Center oHLR: Home Location Register oVLR: Visitor Location register oAuC: Authentication Center oEIR: Equipment Identity Register 7/30/2015 EE 583 Code Division Multiple Access 50
  • 51.
     Architecture OfCDMA: •Mobile Switching center:(MSC) 1 Call set up/supervision/release 2 Call routing 3 Billing information collection 4 Mobility management 5 Paging, Echo cancellation connection to BSC, other MSC and other local exchange networks 6 Access to HLR and VLR 7/30/2015 EE 583 Code Division Multiple Access 51
  • 52.
     Architecture OfCDMA: •Home Location Register (HLR) 1 One HLR per CDMA operator 2 Contains permanent M database of all the subscribers in the network 3 Contains MSRN(mobile station routing no.) 4 It is referred for every incoming call 7/30/2015 EE 583 Code Division Multiple Access 52
  • 53.
     Architecture OfCDMA: •Visitor Location Register(VLR) 1. Temporary visitors database 2. One VLR per MSC •Authentication Center(AuC) 1. Provides security 2. Authentication and encryption •Equipment Identity Register: 1. Contains IMEI 7/30/2015 EE 583 Code Division Multiple Access 53
  • 54.
     Spreading Codes: •Anoise-like and random signal has to be generated at the transmitter. •The same signal must be generated at the receiver in synchronization. •We limit the complexity by specifying only one bit per sample, i.E., A binary sequence. 7/30/2015 54EE 583 Code Division Multiple Access
  • 55.
     Desirable RandomnessProperties Of SC: •Relative frequencies of “0” and “1” should be ½ (balance property) •Run lengths of zeros and ones should be (run property): •Half of all run lengths should be unity •One - quarter should be of length two •One - eighth should be of length three •A fraction 1/2n of all run lengths should be of length n for all finite n 7/30/2015 55EE 583 Code Division Multiple Access
  • 56.
     Desirable RandomnessProperties Of SC: •If the random sequence is shifted by any nonzero number of elements, the resulting sequence should have an equal number of agreements and disagreements with the original sequence (Autocorrelation property) 7/30/2015 EE 583 Code Division Multiple Access 56
  • 57.
     Walsh CodesWalshCodes:: •64 sequences, each 64 chips long •A chip is a binary digit (0 or 1) •Each Walsh code is orthogonal to all other Walsh codes •This means that it is possible to recognize and therefore extract a particular Walsh code from a mixture of other Walsh codes which are “filtered out” in the process •Two same-length binary strings are orthogonal if the result of xoring them has the same number of 0s as 1s 7/30/2015 EE 583 Code Division Multiple Access 57
  • 58.
     PN Sequences: •Adeterministically generated sequence that nearly satisfies these properties is referred to as a Pseudorandom Sequence (PN) •Periodic binary sequences can be conveniently generated using linear feedback shift registers (LFSR) •If the number of stages in the LFSR is r, P ≤ 2r - 1 where P is the period of the sequence 7/30/2015 58EE 583 Code Division Multiple Access
  • 59.
     PN Sequences: •However,if the feedback connections satisfy a specific property, P = 2r - 1. Then the sequence is called a Maximal Length Shift Register (MLSR) or a PN sequence. •Thus if r=15, P=32767. •MLSR satisfies the randomness properties stated before 7/30/2015 59EE 583 Code Division Multiple Access
  • 60.
     Randomness Propertiesof PN Sequences: •Balance property - Of the 2r - 1 terms, 2r-1 are one and 2r-1 –1 are zero. Thus the unbalance is 1/P. For r=50; 1/P≅10-15 •Run length property - Relative frequency of run length n (zero or ones) is 1/ 2n for n ≤ r-1 and 1/(2r - 1) for n = r •One run length each of r-1 zeros and r ones occurs. There are no run lengths for n > r •Autocorrelation property - The number of disagreements exceeds the number of agreements by unity. Thus again the discrepancy is 1/p 7/30/2015 60EE 583 Code Division Multiple Access
  • 61.
     PN SequencesSpecified in IS-95: •A “long” PN sequence (r =42) is used to scramble the user data with a different code shift for each user •The 42-degree characteristic polynomial is given by: •x42 +x41 +x40 +x39 +x37 +x36 +x35 +x32 +x26 +x25 +x24 +x23 +x21 +x20 +x17 +x16 + x15 +x11 +x9 +x7 +1 •The period of the long code is 242 - 1 ≈ 4.4*102 chips and lasts over 41 days 7/30/2015 61EE 583 Code Division Multiple Access
  • 62.
     PN SequencesSpecified in IS-95: •A short PN sequence (r = 15) is specific to a base station and its period is (215 −1)Tc = 27ms. •Two “short” PN sequences (r=15) are used to spread the quadrature components of the forward and reverse link waveforms 7/30/2015 EE 583 Code Division Multiple Access 62
  • 63.
     CDMA RelatedTerms: •CDMA Channel or CDMA Carrier or CDMA Frequency: Duplex channel made of two 1.25 MHz-wide bands of electromagnetic spectrum, one for Base Station to Mobile Station communication (called the FORWARD LINK or the DOWNLINK) and another for Mobile Station to Base Station communication (called the REVERSE LINK or the UPLINK). •In 800 Cellular these two simplex 1.25 MHz bands are 45 MHz apart, •In 1900 MHz PCS they are 80 MHz apart 7/30/2015 63EE 583 Code Division Multiple Access
  • 64.
     CDMA RelatedTerms: •CDMA Forward & Reverse Channel 1.25 MHz Forward / Reverse Link CDMA Code Channel Each individual stream of 0’s and 1’s contained in either the CDMA Forward Channel or in the CDMA Reverse Channel •Code Channels are characterized (made unique) by mathematical codes Code channels in the forward link: Pilot, Sync, Paging and Forward Traffic channels Code channels in the reverse link: Access and Reverse Traffic channels 7/30/2015 EE 583 Code Division Multiple Access 64
  • 65.
     cdma2000 UplinkFrame Structure: • Radio Configuration 3 7/30/2015 65 CRC encoder tail bits Convolutional or Turbo Coder symbol repetition symbol puncture block interleaver modulation symbol C channel bits Bits/ Frame 16 40 80 172 350 744 1512 3048 6120 CRC bits 6 6 8 12 16 16 16 16 16 tail bits 8 8 8 8 8 8 8 8 8 Data Rate kbps 1.5 2.7 4.8 9.6 19.2 38.4 76.8 153.6 307.2 Code Rate 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/2 Repeats 16 8 4 2 1 1 1 1 1 Delete 1 of 5 1 of 9 none none none none none none none Symbols 1536 1536 1536 1536 1536 3072 6144 12288 12288 EE 583 Code Division Multiple Access
  • 66.
     cdma2000 UplinkModulator: 7/30/2015 66 C C C A B Σ Σ dβ dβ dβ cβ )cos( tcω )sin( tcω Ilong,c Qlong,c + + + + Σ + _ sumsum 1Dw Cw 2Sw 1Sw Primary Traffic Secondary Traffic 1 Secondary Traffic 2 Control Pilot pulse shape pulse shape EE 583 Code Division Multiple Access
  • 67.
     cdma2000 DownlinkFrame Structure: 7/30/2015 67 Bits/ Frame 21 55 125 267 552 1128 2280 4584 9192 20712 CRC bits 6 8 10 12 16 16 16 16 16 16 tail bits 8 8 8 8 8 8 8 8 8 8 Data Rate kbps 1.8 3.6 7.2 14.4 28.8 57.6 115.2 230.4 460.8 1036.8 Code Rate 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 1/2 Repeats 8 4 2 1 1 1 1 1 1 1 Delete none none none none none none none none none 2 of 18 Symbols 576 576 576 576 1152 2304 4608 9216 18432 36864 Radio Configuration 9 CRC encoder tail bits Convolutional or Turbo Coder symbol repetition symbol puncture block interleaver modulation symbol channel bits W EE 583 Code Division Multiple Access
  • 68.
     Benefits ofthe cdma2000 1x StandardsBenefits of the cdma2000 1x Standards:: •Increased mobile standby battery life (via Quick Paging Channel) •Total backward compatibility to reuse switch and call processing features •2-3 dB better coverage •High speed 153.6 kbps packet data capabilities •cdma2000 1x = 1.25 MHz Radio Transmission Technology 7/30/2015 EE 583 Code Division Multiple Access 68
  • 69.
     cdma2000 1XDL Modulation Processing: 7/30/2015 EE 583 Code Division Multiple Access 69 + long code 0  1 1  -1 channel gain fwd pwr ctrl gain powercontrol symbolpuncture DEMUX decimate pwr ctrl bit pos I/Q scrambling bit extract power control bits puncture timing 800 Hz W YQ YI modulation symbol rate
  • 70.
     cdma2000 1XDownlink Modulation: 7/30/2015 70 I channel pilot PN Q channel pilot PN Walsh code QOF code IY QY Σ Σ Σ Σ Σ pulse shape pulse shape + + + - )cos( tcω )sin( tcω other channels other channels phaserotateforQOF QX IX EE 583 Code Division Multiple Access
  • 71.
     CDMA Capacity: •CDMAMain Advantages –resistant to narrow band interference –resistant to multipath fading and ISI –no hard limit on number of users (soft capacity) 7/30/2015 EE 583 Code Division Multiple Access 71 .1 .01 .001 .0001 10 20 30 40 50 60 users BER of CDMA system with 128 cps.
  • 72.
     CDMA Capacity: –Asnumber of users on a frequency increase the interference level increases and BER increases for all users –With proper limits all frequencies can be used in every cell 7/30/2015 EE 583 Code Division Multiple Access 72
  • 73.
     CDMA Capacity: •CDMAis a interference limited system –Must limit number of users on a frequency to limit interference within a cell and between cells using same frequency (All CDMA carriers can be assigned to each sector in each cell!) –Total Interference It=Ioc+ Io+ No •Ioc = other cell interference, Io= own cell interference, No= Noise •uplink not downlink in CDMA systems considered the constraining factor 7/30/2015 EE 583 Code Division Multiple Access 73
  • 74.
     CDMA Capacity: •Rememberin direct sequence spread spectrum Processing Gain = bandwidth of the spread signal to the bandwidth of the data signal = W/R –In IS-95 W/R = 10 log (1.23.MHz/9.6 KHz) = 21.1 dB for rate set 1, for rate set two (14.4 kbps) => 19.3 db •Number of traffic channels per carrier and cell function of processing gain, interference, speech coder tolerance for errors, error control coding, etc. 7/30/2015 EE 583 Code Division Multiple Access 74
  • 75.
     CDMA Capacity: •Theeffect of more users in a cell on frequency is to degrade the channel for everyone – can be thought off as decreasing the usable cell size 7/30/2015 EE 583 Code Division Multiple Access 75
  • 76.
     Power Controlin CDMA: •CDMA goal is to maximize the number of simultaneous users •Capacity is maximized by maintaining the signal to interference ratio at the minimum acceptable •Power transmitted by mobile station must be therefore controlled •Transmit power enough to achieve target BER: no less no more 7/30/2015 76EE 583 Code Division Multiple Access
  • 77.
     Power Controlin CDMA: •Controlling transmitted power affects the CIR 7/30/2015 EE 583 Code Division Multiple Access 77 77 Pr Pt = 1        4πdf c α Pt = Transmitted power Pr = Received power in free space d = Distance between receiver and transmitter f = Frequency of transmission c = Speed of light a = Attenuation constant (2 to 4)
  • 78.
     Power Control:Open Loop vs. Closed Loop •Open loop: –Base station transmits at a known power level (a beacon) which mobile measures to estimate the path loss –Assumes path loss in both directions is the same –Not very accurate as uplink and downlink are separated in frequency –Useful for coarse initial estimates at mobile used in Access channel for signaling 7/30/2015 EE 583 Code Division Multiple Access 78
  • 79.
     Power Control:Open Loop vs. Closed Loop: •Closed loop: –Signal-to-Interference Ratio (SIR) measured at the receiver and compared to a target value for SIR –Receiver sends a power control command to transmitter to reduce or increase the power level - requires a bi-directional link –Used in TCH – power control sub channel operates at 800 bps by puncturing downlink data with periodic bits – each power command adjusted MS power in 1 dB increments 7/30/2015 EE 583 Code Division Multiple Access 79
  • 80.
     Closed LoopPower Control: Inner Loop vs. Outer Loop: •Inner Loop (or fast power control) –Measures received SIR, controls transmit power –Commands sent several times per frame (hence fast power control) 7/30/2015 EE 583 Code Division Multiple Access 80
  • 81.
     Closed LoopPower Control: Inner Loop vs. Outer Loop: •Outer Loop (or slow power control) –Measures packet error rate –Changes target SIR for inner loop –Directly modify transmit power based on FER –Commands sent once per frame (hence slow power control) 7/30/2015 EE 583 Code Division Multiple Access 81
  • 82.
     Two factorsimportant for power control: •Propagation loss •due to propagation loss, power variations up to 80 dB •a high dynamic range of power control required •Channel Fading •average rate of fade is one fade per second per mile hour of mobile speed •power attenuated by more than 30 dB •power control must track the fade 7/30/2015 82EE 583 Code Division Multiple Access
  • 83.
     Power Controlin IS-95A: •At 900 MHz and 120 km/hr mobile speed Doppler shift =100Hz •In IS 95-A closed loop power control is operated at 800 Hz update rate •Power control bits are inserted (‘punctured’) into the interleaved and encoded traffic data stream •Power control step size is +/- 1 dB •Power control bit errors do not affect performance much 7/30/2015 83EE 583 Code Division Multiple Access
  • 84.
     Rake Receiver: •Mobilestation receives multiple attenuated and delayed replicas of the original signal (multipath diversity channels). •Two multipath signals are resolvable only if their relative delay exceeds the chip period Tc •Amplitudes and phases of multipath components are found by correlating the received waveform with multiple delayed versions of the signal (delay = nTc). •Searcher performs the above task for up to 3 different multipath signals. •3 parallel demodulators (RAKE fingers) isolate the multipath components and the RAKE receiver combines them. 7/30/2015 84EE 583 Code Division Multiple Access
  • 85.
    d1 d2 t t t d3 transmission receiving Racercombination noise 7/30/2015 EE 583 Code Division Multiple Access 85  Rake Receiver:
  • 86.
    Correlator 1 Correlator 2 Correlator3 Search Correlator Combiner To De-Interleaver, Viterbi Decoder Multipath Delay Components ( 150 µs > ∆t > 1µs) Rake receiver can isolate multipath spaced > 1 chip length. 7/30/2015 EE 583 Code Division Multiple Access 86  Rake Receiver:
  • 87.
    •Handset uses combinedoutputs of the three traffic correlators “rake fingers” •Each finger can independently recover a particular PN offset and Walsh code •Fingers can targeted on delayed multipath reflections, or even on different BTSs •Searcher continuously checks pilots 7/30/2015 EE 583 Code Division Multiple Access 87  Rake Receiver:
  • 88.
    7/30/2015 88 88  Handoffin CDMA System: •In GSM hard handoff occurs at the cell boundary •Soft Handoff •Mobile commences Communication with a new BS without interrupting communication with old BS •same frequency assignment between old and new BS •provides different site selection diversity •Softer Handoff •Handoff between sectors in a cell •CDMA to CDMA hard handoff •Mobile transmits between two base stations with different frequency assignment EE 583 Code Division Multiple Access
  • 89.
    Handoff is of 3types 1. Intra BSC 2 Inter BSC 3. Inter MSC  Handoff in CDMA System: BSCBSC BSC MSC MSC GMS C 7/30/2015 EE 583 Code Division Multiple Access 89
  • 90.
     Soft Handoff-A unique feature of CDMA Mobile: Advantages •Contact with new base station is made before the call is switched •Diversity combining is used between multiple cell sites •Diversity combining is the process of combining information from multiple transmitted packets to increase the effective SNR of received packets • additional resistance to fading •If the new cell is loaded to capacity, handoff can still be performed for a small increase in BER •Neither the mobile nor the base station is required to change frequency 7/30/2015 90EE 583 Code Division Multiple Access
  • 91.
     Detection inthe CDMA system: •Multi-Users Detection (MUD) •The capacity and the performance of the CDMA system increase when MUD is implemented. •The basic principle of MUD is the elimination of the negative effect of each user on the other. • MUD is also known as joint detection and interference cancellation . • Multi-user detection considers all users as signals for each other. 7/30/2015 91EE 583 Code Division Multiple Access
  • 92.
     Detection inthe CDMA system: •Multi-Users Detection (MUD) •The ultimate technique for the MUD is the optimum receiver. •Optimum Receiver: •Very complex. So, it is unpractical solution to reduce the multiple access interference. Sup- optimum detector will be implemented. 7/30/2015 EE 583 Code Division Multiple Access 92
  • 93.
     Detection inthe CDMA system: •Multi-Users Detection (MUD) •Sup-optimum solution: •Serial Interference cancellation (SIC): •SIC is preferred in the absence of power control. • Serial canceling the interference generated from the other users. •Cancel the strongest signal first (most negative effect ) 7/30/2015 93EE 583 Code Division Multiple Access
  • 94.
     Detection inthe CDMA system: •Multi-Users Detection (MUD) •Parallel Interference Cancellation (PIC): •PIC would be preferred when the amount of interference from each user is similar. •In the initial detection stage, all active users are detected in parallel by a SUD technique. •Then, the obtained interference is subtracted from the received signal and data detection is performed again with reduced MAI 7/30/2015 EE 583 Code Division Multiple Access 94
  • 95.
     Detection inthe CDMA system: Disadvantages: 1. Multiple Access Interference: •Require multi-user detection (MUD) algorithms to solve. 2. Near-far problem. •Where stronger (near to the Base Station) user masks the weaker user (far from the Base Station) 3. Requires wideband channel. 7/30/2015 95EE 583 Code Division Multiple Access
  • 96.
     What isThird Generation? : •Flexible support of multiple services •Voice •Messaging – email, fax, etc. •Medium-rate multimedia – Internet access, educational •High-rate multimedia – file transfer, video •High-rate interactive multimedia – video teleconferencing, telemedicine, etc. •Mobility: quasi-stationary to high-speed platforms •Global roaming: ubiquitous, seamless coverage •Evolution from second generation systems 7/30/2015 96EE 583 Code Division Multiple Access
  • 97.
     W-CDMA Versuscdma2000 : 7/30/2015 97 97 EE 583 Code Division Multiple Access
  • 98.
     cdma2000 vsWCDMA: •Chip rate •Coherent Pilot Channels •Transmit Diversity •Underlying Network •Single Carrier versus Multicarrier Spreading •Cell Site Synchronization 7/30/2015 98EE 583 Code Division Multiple Access
  • 99.
    Commercial usage ofCDMA: •CDMA was introduced in the 2nd Generation (early of the 1990s). •E.g. IS-95 standard, also known as cdma One which support up to 64 users that are orthogonally coded and at the same time transmitted over 1.25 MHz channel •Used for Cellular Communication System •(824-894 MHz in US Cellular) • 3rd Generation: cdma2000 •Allow high rate of packet transmitting in addition of voice transmitting. 7/30/2015 EE 583 Code Division Multiple Access 99
  • 100.
     CDMA AdvantagesCDMAAdvantages:: •Spread Spectrum •Soft & Softer Handoff •Rake Receiver •Variable Rate Vocoder •High quality voice •Power Control •Coverage •Simple Network Planning •Green Handset •Smooth migration to 3G and the operator’s benefit is protected at the most 7/30/2015 100EE 583 Code Division Multiple Access
  • 101.
     DISADVANTAGES OFCDMA : • Near far problem. • CDMA is relatively low, and the network is not as mature as GSM. • CDMA can not offer international roaming, a large GSM advantage.
  • 102.
     Conclusion: •The CDMAwill allow many signals to be transmitted at the same channel at the same time. This done by giving each user a Pseudo-Noise code which is a binary sequence. This code should have low cross- correlation between each other. •Multiple access interference has bad effect on the CDMA system so the multiple user detection is used to reduce the MAI. •CDMA cellular system is deemed superior to the FDMA and TDMA •cellular systems for the time being. 7/30/2015 102EE 583 Code Division Multiple Access
  • 103.
     Conclusion: • Therefore,CDMA technique becomes more important in radio • communication systems. •CDMA is based on the spread spectrum technique which has been used at military field. 7/30/2015 EE 583 Code Division Multiple Access 103
  • 104.
     References: •http://www.tubex.com/category/cdma/gsm •http://www.bsnl.co.in:cdma/architecture.html •http://www.cellular.co.za/technologies/cdma/cdma_w_paper •http://www.arcx.com/sites/CDMAvsTDMA.htm •Lee JSand Miller LM, CDMA System Engineering Handbook, Arttech Publishing House, 1998. •Viterbi A, CDMA-Spread Spectrum Communication, Addison Wesley 1995. • R. L. Peterson, “Third Generation Personal Communications: Physical Layer Status,” Presentation at Clemson University, Feb. 1, 2001 1047/30/2015 EE 583 Code Division Multiple Access
  • 105.
     References: • ManjitSingh and Manoneet Singh, “3G Wireless with Respect to IMT-2000 and Beyond,” Telecom 99 • Harri Holma and Antti Toskala, WCDMA for UMTS: Radio Access for Third Generation Mobile Communications, New York: Wiley, 2000 • “CDMA Evolution from IS-95, IS-2000, to 1XTREME,” Technology Transfer Training Class, Motorola, Inc., July 2000 7/30/2015 EE 583 Code Division Multiple Access 105