Cdma system


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Cdma system

  1. 1. CDMA System Course Name cdma2000 Systems
  2. 2. Contents The characteristics of mobile communications CDMA migration from 2G to 3G CDMA spectrum usage CDMA Codes CDMA Channels The advantage of CDMA cdma2000 -1x
  3. 3. Characteristics of Mobile Communication • Mobility: – flexible and convenient , global personal communication • Poor environment and conditions : – Co-channel interference, multi-path(space and time)shadow effect and delay, power change and other noise • Multiple MS and channels: – Interference, near and far effect • Limit of frequency resources • Reliability is important – registration, handoff, switching
  4. 4. Communications System AMPS: Advanced Mobile Phone System TACS: Total Access Communication System GPRS: General Packet Radio Services 11GG 22GG 33GG Analog cellular DDiiggiittaall cceelllluullaarr DDiiggiittaall cceelllluullaarr VVooiiccee VVooiiccee //ddaattaa VViiooccee // hhiigghh ssppeeeedd ddaattaa AAMMPPSS CCDDMMAA 11XXRRtttt CCDDMMAA22000000 TTAACCSS GGSSMM GGPPRRSS WW__CCDDMMAA 8800’’ 11999922 11999999 22000011 22000033
  5. 5. CDMA 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
  6. 6. CDMA-Its History & Status
  7. 7. CDMA-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.
  8. 8. CDMA Subscriber Growth History: Sept.1997 through Sept.2003
  9. 9. CDMA 800 MHz Cellular Spectrum Usage Possible CDMA Center Freq. Assignments Channel Numbers Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)824 MHz 849 MHz 869 MHz 894 MHz other usesA” A”A B A’ B’ 1 10 10 1.5 2.5 A B A’ B’ 1 10 10 1.5 2.5 991 1023 1 333 334 666 667 716 717 799 991 1023 1 333 334 666 667 716 717 799 ~300 kHz. “guard bands” possibly required if adjacent- frequency signals are non-CDMA (AMPS, TDMA, ESMR, etc.) • All CDMA RF carriers are 1.25 MHz. wide – Can serve ~20 users /8 kb vocoder
  10. 10. CDMA PCS 1900 MHz Spectrum Usage Guard Bands Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits) 1850 MHz B T A B T A B T A B T A B T A B T A Paired Bands MTA BTAMTABTA MTAMTA 1910 MHz 1930 MHz 1990 MHz Data Voice A D B E F C A D B E F C 15 51010 1515151515 555 55 Licensed Licensed Unlicensed 0 Channel Numbers 299 300 400 699 700 800 900 1199 0 299 300 400 699 700 800 900 1199
  11. 11. CDMA Frequency Channel Assignment at 800 MHz Cellular 1 334 667 991 1023 333 666 715 799 716 Channel Numbers A Band B Band A’A” B’ 1019 37 78 119 160 201 242 283 384 425 466 507 548 589 630 691 777 CDMA A-Band Carriers CDMA B-Band Carriers 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 9 9 8 * *** * Requires frequency coordination with non-cellular interferers ** Requires frequency coordination with A-band carrier A Band Primary Channel 283 A Band Secondary Channel 691 B Band Primary Channel 384 B Band Secondary Channel 777 736
  12. 12. Multiple Access Each pair of users enjoys a dedicated, private circuit through the transmission medium, unaware that the other users exist. Since the beginning of telephony and radio, system operators have tried to squeeze the maximum amount of traffic over each circuit. Transmission Medium• Types of Media -- Examples: – Twisted pair - copper – Coaxial cable – Fiber optic cable – Air interface (radio signals) Advantages of Multiple Access –Increased capacity: serve more users –Reduced capital requirements since fewer media can carry the traffic –Decreased per-user expense –Easier to manage and administer
  13. 13. Multiple Access Schemes Power Power Power FDMA TDMA CDMA • FDMA Frequency Division Multiple Access – Each user on a different frequency – A channel is a frequency • TDMA Time Division Multiple Access – Each user on a different window period in time (“time slot”) – A channel is a specific time slot on a specific frequency • CDMA Code Division Multiple Access – A channel is a unique code pattern – Each user uses the same frequency all the time, but mixed with different distinguishing code patterns
  14. 14. Frequency Reuse CDMA (IS-95) frequency reuse = 1 TDMA (IS-136) frequency reuse = 7
  15. 15. Terms & Definitions • 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 • 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 45 or 80 MHz CDMA CHANNEL CDMA Reverse Channel 1.25 MHz CDMA Forward Channel 1.25 MHz
  16. 16. Walsh 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
  17. 17. Short PN Sequences • The two Short PN Sequences, I and Q, are 32,768 chips long • Together, they can be considered a two-dimensional binary “vector” with distinct I and Q component sequences, each 32,768 chips long • Each Short PN Sequence (and, as a matter of fact, any sequence) correlates with itself perfectly if compared at a timing offset of 0 chips • Each Short PN Sequence is special: Orthogonal to a copy of itself that has been offset by any number of chips (other than 0)
  18. 18. The Long PN Sequence • Each mobile station uses a unique User Long Code Sequence generated by applying a mask, based on its 32-bit ESN, to the 42-bit Long Code Generator which was synchronized with the CDMA system during the mobile station initialization. • Generated at 1.2288 Mcps, this sequence requires 41 days, 10 hours, 12 minutes and 19.4 seconds to complete. Long Code Register (@ 1.2288 MCPS) Public Long Code Mask (STATIC) User Long Code Sequence (@1.2288 MCPS) 1 1 0 0 0 1 1 0 0 0 P E RMU T E D E S N AND =S UM Modulo-2 Addition
  19. 19. Coding Process on CDMA Forward Channels WALSH 19 BTSPilot Walsh 0 Walsh 19 Paging Walsh 1 Walsh 6 Walsh 11 Walsh 20 Sync Walsh 32 Walsh 42 Walsh 37 Walsh 41 Walsh 56 Walsh 60 Walsh 55 PN OFFSET 116BTS PN OFFSET 226BTS PN OFFSET 510BTS S PN 372 x x x PN OFFSET ANALOG SUM/MUX PN OFFSET 372
  20. 20. CDMA Code Summary Walsh Codes Short PN Sequences Long PN Sequences Type of Sequence Mutually Orthogonal Orthogonal with itself at any time shift value except 0 near-orthogonal if shifted Special Properties 64 2 1 How Many 64 chips 1/19,200 sec. 32,768 chips 26-2/3 ms 75x in 2 sec. 242 chips ~41 days Length Orthogonal Modulation (information carrier) Quadrature Spreading (Zero offset) Distinguish users Reverse Link Function User identity within cell’s signal Distinguish Cells & Sectors Data Scrambling to avoid strings of 1’s or 0’s Forward Link Function
  21. 21. CDMA 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
  22. 22. 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
  23. 23. 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
  24. 24. Spreading Spectrum (3) “Principle of Using Multiple Codes” 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
  25. 25. Spread Spectrum (4)
  26. 26. Advantages of Spread Spectrum Avoid interference arising from jamming signal or multi-path effects. Covert operation:Difficult to detect Achieve Privacy: Difficult to demodulate, Noise like signal. Impossible to Eavesdrops on the signal expect using the same PN sequence
  27. 27. Soft & Softer Handoff Connection first and disconnection afterwards in handoff. High quality of service and effective reduction of call drops. Softer handoff: same BS & frequency, between different sectors. Soft handoff: adjacent cells of the same frequency. BSC BSC MSC
  28. 28. Rake Receiver (1) d1 d2 t t t d3 transmission receiving Raker combination noise
  29. 29. Rake Receiver (2) Correlator 1 Correlator 2 Correlator 3 Search Correlator Combiner To De-Interleaver, Viterbi Decoder Multipath Delay Components ( 150 ms > Dt > 1ms) Rake receiver can isolate multipath spaced > 1 chip length.
  30. 30. Rake Receiver (3) • 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
  31. 31. Intelligent Vocoder
  32. 32. High Quality Voice(1) Voice quality 64k PCM present GSM 8k CDMA 13k CDMA 8k EVRC CDMA
  33. 33. High Quality Voice(2) High quality Voice?? Voice activity Technology
  34. 34. Power Control Autonomous power control On the Uplink tells the MS to vary it’s transmitted power inversely with the power level it receive from the BS. Direct power control On the Uplink measures Eb/No at the base station and sends power Control Bits over the Downlink to the MS to instruct the MS to either increase or decrease its transmit power. Downlink power control Attempts to use minimum power needed to meet to a Frame Error Rate (FER) threshold at the MS s.
  35. 35. Coverage • The coverage radius is 2 times of standard GSM. • Coverage of 1000 km2: GSM needs 200 BTS 's, while CDMA requires only 50. • Under the same coverage conditions, the number of BTS 's is greatly decreased
  36. 36. Simple Network Planning Simple project design & convenient capacity expansion 1 3 2 4 3 2 4 2 4 4 1 2 3 1 4 2 3 1 4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Simple project design & convenient capacity expansion
  37. 37. Green Handset Systems M ean transmission power M ax transmission power GSM 125 mW 2W CDM A 2 mW 200mW Low transmission power: Accurate power control, handoff control, voice activation
  38. 38. Functions of the CDMA Reverse Channels • There are two types of CDMA Reverse Channels: – TRAFFIC CHANNELS are used by individual users during their actual calls to transmit traffic to the BTS. – ACCESS CHANNELS are used by mobile stations not yet in a call to transmit registration requests, call setup requests, page responses, order responses, and other signaling information
  39. 39. Coding Process on CDMA Reverse Channels • Each mobile is uniquely identified by the User Long Code, which it generates internally. • All mobile stations transmit simultaneously on the same 1.25 MHz wide frequency band. • Any nearby BTS can dedicate a channel element to the mobile station and successfully extract its signal. • Mobile stations also use the other CDMA spreading sequences, but not for channel-identifying purposes. • Short PN Sequences are used to achieve phase modulation. • Walsh Codes are used as Orthogonal Modulation to give ultra-reliable communications recovery at the BTS.
  40. 40. Benefits 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
  41. 41. Backward Compatible with IS-95 Air Interface IS-95 mobiles are supported in the IS- 2000 standard for 1xRTT: • No need to change any RF infrastructure • Capacity improvements will not be realized until most IS-95 subscribers disappear
  42. 42. Channel List: 1xRTT vs. IS-95 • IS-95B built on the IS-95A channels, and introduced two new channels – Fundamental channel was the same as IS-9A traffic channel – Supplemental code channels assigned to support rates above 14.4Kbps • IS-2000 1xRTT continue to build on the IS-95 channels – IS-95 channels continue to be supported in IS-2000 to support IS-95 mobiles Pilot channel Sync channel Paging channel Access channel Forward Traffic Channel Reverse Traffic Channel Fundamental channel Fundamental channel Supplemental Code channel (F-SCCH) Supplemental Code channel (R-SCCH) Supplemental channel (F-SCH) Supplemental channel (R-SCH) Quick Paging channel (F-QPCH) Reverse Pilot channel (R-PICH) IS-95B 1xRTT IS-95A Forward Reverse
  43. 43. Discriminating Among Forward Code Channels • A Mobile Station receives a Forward Channel from a sector in a Base Station. • The Forward Channel carries a composite signal of up to 64 forward code channels. • Some code channels are traffic channels and others are overhead channels. • A set of 64 mathematical codes is needed to differentiate the 64 possible forward code channels. – The codes in this set are called “Walsh Codes” SyncPilot FW Traffic (for user #1) Paging FW Traffic (for user #2) FW Traffic (for user #3)
  44. 44. Discriminating Among Base Station • A mobile Station is surrounded by Base Stations, all of them transmitting on the same CDMA Frequency. • Each Sector in each Base Station is transmitting a Forward Traffic Channel containing up to 64 forward code channels. • A Mobile Station must be able to discriminate between different Sectors of different Base Stations. • Two binary digit sequences called the I and Q Short PN Sequences (or Short PN Codes) are defined for the purpose of identifying sectors of different base stations. • These Short PN Sequences can be used in 512 different ways in a CDMA system. Each one of them constitutes a mathematical code which can be used to identify a particular sector. A B Up to 64 Code Channels Up to 64 Code Channels
  45. 45. Example of cdma2000 1x Network
  46. 46. Structure of a Typical CDMA system