Elementary Concepts, Standards And CDMA Anjan.K III Sem M.Tech  Dept Of CSE M.S.R.I.T 10/03/09 MC: Elementary Concepts and...
Agenda <ul><li>Mobile Standards </li></ul><ul><li>Different Generations </li></ul><ul><li>CDMA </li></ul><ul><ul><li>Need ...
International Standardization <ul><li>ITU (International Telecommunication Union) </li></ul><ul><ul><li>Radio standards an...
IMT-2000 Radio Standards <ul><li>IMT-SC*  Single Carrier (UWC-136): EDGE </li></ul><ul><ul><li>GSM evolution (TDMA); 200 K...
10/03/09 MC: Elementary Concepts and CDMA
Mobile Standards Organizations <ul><li>European Technical Standard Institute (Europe): </li></ul><ul><ul><li>http://www.et...
First Generation <ul><li>Advanced Mobile Phone Service (AMPS) </li></ul><ul><ul><li>US trials 1978; deployed in Japan (’79...
Second Generation — 2G <ul><li>Digital systems </li></ul><ul><li>Leverage technology to increase capacity </li></ul><ul><u...
Need for CDMA Technology <ul><li>Higher capacity </li></ul><ul><li>Improved performance in multipath by diversity </li></u...
CDMA???? <ul><li>Both an access method and air-interface </li></ul><ul><li>Rest of the network is very similar </li></ul><...
CDMA Analogy <ul><li>10 people in a room. </li></ul><ul><ul><li>5 speak English, 2 speak Spanish, 2 speak Chinese, and 1 s...
CDMA Standards - IS-95 <ul><li>TIA standard Interim Standard (IS) -95 (ANSI-95) in 1993 </li></ul><ul><li>IS-95 deployed i...
CDMA Standards - IS-95A <ul><li>IS-95A is the CDMA-based second generation (2G) standard for mobile communication. The fol...
CDMA Standards - IS-95B <ul><li>IS-95B is the evolved version of IS-95A and is designated as 2.5G.  </li></ul><ul><li>IS-9...
IS-95 CDMA Features-(1) <ul><li>Bandwidth Recycling </li></ul><ul><ul><li>Enhancing the system capacity due to the increas...
IS-95 CDMA Features-(2) <ul><li>Diversity   </li></ul><ul><ul><li>Taking advantage of multiple levels of diversity: freque...
IS-95  Vs 2G Phone Systems 10/03/09 MC: Elementary Concepts and CDMA
IS – 95 Vocoders <ul><li>AMR: Adaptive multi-rate </li></ul><ul><ul><li>Defined for UMTS (W-CDMA) </li></ul></ul><ul><ul><...
Frequency Allocation GSM Vs CDMA 10/03/09 MC: Elementary Concepts and CDMA
10/03/09 MC: Elementary Concepts and CDMA
Mathematical Background – (1) <ul><li>Multiple users occupying the same band by having different codes is known as  CDMA -...
Mathematical Background – (2) What is the tolerable interference over desired signal power?
Mathematical Background – (3) <ul><li>In conventional systems W/R    1 which means, for satisfactory operation J/S < 1 </...
Mathematical Background – (4) <ul><li>JM can be used to accommodate multiple users in the same band </li></ul><ul><li>If (...
Spreading Codes <ul><li>A noise-like and random signal has to be generated at the transmitter. </li></ul><ul><li>The same ...
Desirable Randomness Properties <ul><li>Relative frequencies of  “0”  and  “1”  should be ½ (Balance property) </li></ul><...
Desirable Randomness Properties (contd…) <ul><li>If the random sequence is shifted by any nonzero </li></ul><ul><li>number...
PN Sequences <ul><li>A deterministically generated sequence that nearly satisfies these properties is referred to as a Pse...
PN Sequences (contd…) <ul><li>However, if the feedback connections satisfy a specific property, P = 2 r  - 1. Then the seq...
Randomness Properties of PN Sequences <ul><li>Balance property  -  Of the 2 r  - 1 terms, 2 r-1  are one and 2 r-1 –1 are ...
PN Sequences Specified in IS-95 <ul><li>A  “long”  PN sequence (r =42) is used to scramble the user data with a different ...
PN Sequences Specified in IS-95 (contd…) <ul><li>A short PN sequence (r = 15) is specific to a base station and its period...
Walsh Code <ul><li>There are some issues with Walsh Codes </li></ul><ul><ul><li>Synchronization of all users is required <...
Spread Spectrum <ul><li>A modulation system in which the modulated (spread spectrum) signal bandwidth is much greater than...
Advantages of Spread Spectrum <ul><li>It is Secure, difficult to intercept </li></ul><ul><li>A large number of codes can s...
Types Of Spread Spectrum <ul><li>Direct Sequence Spread Spectrum </li></ul><ul><li>Frequency Hoping </li></ul><ul><li>Hybr...
Direct Sequence Spread Sprectrum <ul><li>DS-SS is one popular way to make the noise-like waveforms for CDMA </li></ul><ul>...
10/03/09 MC: Elementary Concepts and CDMA
CDMA Forward Link <ul><li>The forward link uses the same frequency spectrum as AMPS  (824-849 Mhz) . Each carrier 1.25MHz ...
CDMA MUX 10/03/09 MC: Elementary Concepts and CDMA Copyright © Data Communication and Networking By Behrouz A Forozan
CDMA Reverse Channel <ul><li>Fundamentally different from the forward channels </li></ul><ul><li>Uses OQPSK for power effi...
CDMA DeMUX 10/03/09 MC: Elementary Concepts and CDMA Copyright © Data Communication and Networking By Behrouz A Forozan
3G Vision <ul><li>Universal global roaming </li></ul><ul><li>Multimedia (voice, data & video) </li></ul><ul><li>Increased ...
10/03/09 MC: Elementary Concepts and CDMA
IS 95 to CDMA 2000 3G Evolution  10/03/09 MC: Elementary Concepts and CDMA
CDMA2000 <ul><li>Evolution from original Qualcomm CDMA </li></ul><ul><li>Better migration story from 2G to 3G </li></ul><u...
10/03/09 MC: Elementary Concepts and CDMA
W-CDMA <ul><li>Wideband CDMA </li></ul><ul><ul><li>Standard for Universal Mobile Telephone Service (UMTS) </li></ul></ul><...
Need For WCDMA <ul><li>WCDMA is a step further in the CDMA technology.  </li></ul><ul><ul><li>Uses a 5 MHz wide radio sign...
W-CDMA Vs cdma2000 10/03/09 MC: Elementary Concepts and CDMA
TD-SCDMA <ul><li>Time division duplex (TDD) </li></ul><ul><li>Chinese development  - deployed in China </li></ul><ul><li>G...
Rake Receiver <ul><li>Mobile station receives multiple attenuated and delayed replicas of the original signal (multipath d...
Summary  <ul><li>Different mobile standard organization ITU, IMT 2000, TIA, IS </li></ul><ul><li>CDMA </li></ul><ul><ul><l...
References <ul><li>[1] T. S. Rappaport, “Wireless communications  </li></ul><ul><li>principles&practice”, Prentice Hall, 1...
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Cdma Anjan V1

  1. 1. Elementary Concepts, Standards And CDMA Anjan.K III Sem M.Tech Dept Of CSE M.S.R.I.T 10/03/09 MC: Elementary Concepts and CDMA
  2. 2. Agenda <ul><li>Mobile Standards </li></ul><ul><li>Different Generations </li></ul><ul><li>CDMA </li></ul><ul><ul><li>Need for CDMA Technology </li></ul></ul><ul><ul><li>cdmaOne IS-95 Architecture </li></ul></ul><ul><ul><ul><li>Features </li></ul></ul></ul><ul><ul><li>IS 95 Vs 2G systems </li></ul></ul><ul><ul><li>3G Vision </li></ul></ul><ul><ul><li>Migrating to 3G </li></ul></ul><ul><ul><li>CDMA 2000 </li></ul></ul><ul><ul><ul><li>Architecture </li></ul></ul></ul><ul><ul><li>WCDMA </li></ul></ul><ul><ul><li>TD-SCDMA </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  3. 3. International Standardization <ul><li>ITU (International Telecommunication Union) </li></ul><ul><ul><li>Radio standards and spectrum </li></ul></ul><ul><li>IMT-2000 </li></ul><ul><ul><li>ITU’s umbrella name for 3G which stands for International Mobile Telecommunications 2000 </li></ul></ul><ul><li>National and regional standards bodies are collaborating in 3G partnership projects </li></ul><ul><ul><li>ARIB, TIA, TTA, TTC, CWTS. T1, ETSI - refer to reference slides at the end for names and links </li></ul></ul><ul><li>3G Partnership Projects (3GPP & 3GPP2) </li></ul><ul><ul><li>Focused on evolution of access and core networks </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  4. 4. IMT-2000 Radio Standards <ul><li>IMT-SC* Single Carrier (UWC-136): EDGE </li></ul><ul><ul><li>GSM evolution (TDMA); 200 KHz channels; sometimes called “2.75G” </li></ul></ul><ul><li>IMT-MC* Multi Carrier CDMA: CDMA2000 </li></ul><ul><ul><li>Evolution of IS-95 CDMA, i.e. cdmaOne </li></ul></ul><ul><li>IMT-DS* Direct Spread CDMA: W-CDMA </li></ul><ul><ul><li>New from 3GPP; UTRAN FDD </li></ul></ul><ul><li>IMT-TC** Time Code CDMA </li></ul><ul><ul><li>New from 3GPP; UTRAN TDD </li></ul></ul><ul><ul><li>New from China; TD-SCDMA </li></ul></ul><ul><li>IMT-FT** FDMA/TDMA (DECT legacy) </li></ul>10/03/09 MC: Elementary Concepts and CDMA * Paired spectrum; ** Unpaired spectrum
  5. 5. 10/03/09 MC: Elementary Concepts and CDMA
  6. 6. Mobile Standards Organizations <ul><li>European Technical Standard Institute (Europe): </li></ul><ul><ul><li>http://www.etsi.org </li></ul></ul><ul><li>Telecommunication Industry Association (USA): </li></ul><ul><ul><li>http://www.tiaonline.org </li></ul></ul><ul><li>Standard Committee T1 (USA): </li></ul><ul><ul><li>http://www.t1.org </li></ul></ul><ul><li>China Wireless Telecommunication Standard (China): </li></ul><ul><ul><li>http://www.cwts.org </li></ul></ul><ul><li>The Association of Radio Industries and Businesses (Japan): </li></ul><ul><ul><li>http://www.arib.or.jp/arib/english/ </li></ul></ul><ul><li>The Telecommunication Technology Committee (Japan): </li></ul><ul><ul><li>http://www.ttc.or.jp/e/index.html </li></ul></ul><ul><li>The Telecommunication Technology Association (Korea): </li></ul><ul><ul><li>http://www.tta.or.kr/english/e_index.htm </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  7. 7. First Generation <ul><li>Advanced Mobile Phone Service (AMPS) </li></ul><ul><ul><li>US trials 1978; deployed in Japan (’79) & US (’83) </li></ul></ul><ul><ul><li>800 MHz band — two 20 MHz bands </li></ul></ul><ul><ul><li>TIA-553 </li></ul></ul><ul><ul><li>Still widely used in US and many parts of the world </li></ul></ul><ul><li>Nordic Mobile Telephony (NMT) </li></ul><ul><ul><li>Sweden, Norway, Demark & Finland </li></ul></ul><ul><ul><li>Launched 1981; now largely retired </li></ul></ul><ul><ul><li>450 MHz; later at 900 MHz (NMT900) </li></ul></ul><ul><li>Total Access Communications System (TACS) </li></ul><ul><ul><li>British design; similar to AMPS; deployed 1985 </li></ul></ul><ul><ul><li>Some TACS-900 systems still in use in Europe </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  8. 8. Second Generation — 2G <ul><li>Digital systems </li></ul><ul><li>Leverage technology to increase capacity </li></ul><ul><ul><li>Speech compression; digital signal processing </li></ul></ul><ul><li>Utilize/extend “Intelligent Network” concepts </li></ul><ul><li>Improve fraud prevention </li></ul><ul><li>Add new services </li></ul><ul><li>There are a wide diversity of 2G systems </li></ul><ul><ul><li>IS-54/ IS-136 North American TDMA; PDC (Japan) </li></ul></ul><ul><ul><li>iDEN </li></ul></ul><ul><ul><li>DECT and PHS </li></ul></ul><ul><ul><li>IS-95 CDMA (cdmaOne) </li></ul></ul><ul><ul><li>GSM </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  9. 9. Need for CDMA Technology <ul><li>Higher capacity </li></ul><ul><li>Improved performance in multipath by diversity </li></ul><ul><li>Lower mobile transmit power = longer battery life </li></ul><ul><ul><li>Power control </li></ul></ul><ul><ul><li>Variable transmission rate with voice activity detection </li></ul></ul><ul><li>Allows soft handoff </li></ul><ul><li>Sectorization gain </li></ul><ul><li>High peak data rates can be accommodated </li></ul><ul><li>Combats other-user interference = lower reuse factors </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  10. 10. CDMA???? <ul><li>Both an access method and air-interface </li></ul><ul><li>Rest of the network is very similar </li></ul><ul><ul><li>Radio resource management, mobility management, security are similar </li></ul></ul><ul><ul><li>Power control and handoffs are different </li></ul></ul><ul><li>Uses DSSS and ECC </li></ul><ul><li>Frequency reuse factor is 1 </li></ul><ul><li>Three CDMA systems </li></ul><ul><ul><li>IS-95 2G </li></ul></ul><ul><ul><li>CDMA2000 </li></ul></ul><ul><ul><li>W-CDMA </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  11. 11. CDMA Analogy <ul><li>10 people in a room. </li></ul><ul><ul><li>5 speak English, 2 speak Spanish, 2 speak Chinese, and 1 speaks Russian. </li></ul></ul><ul><li>Everyone is talking at relatively the same time over the same medium – the air. </li></ul><ul><li>Who can listen to whom and why? </li></ul><ul><li>Who can’t you understand? </li></ul><ul><li>Who can’t speak to anyone else? </li></ul>
  12. 12. CDMA Standards - IS-95 <ul><li>TIA standard Interim Standard (IS) -95 (ANSI-95) in 1993 </li></ul><ul><li>IS-95 deployed in the 800 MHz cellular band </li></ul><ul><ul><li>J-STD-08 variant deployed in 1900 MHz US “PCS” band </li></ul></ul><ul><li>Evolution fixes bugs and adds data </li></ul><ul><ul><li>IS-95A provides data rates up to 14.4 kbps </li></ul></ul><ul><ul><li>IS-95B provides rates up to 64 kbps (2.5G) </li></ul></ul><ul><ul><li>Both A and B are compatible with J-STD-08 </li></ul></ul><ul><li>All variants designed for TIA IS-41 core networks (ANSI 41) </li></ul><ul><li>CDMA was first commercialized by its founder </li></ul><ul><li>A.J Verterbi at Qualcomm in 1995. </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  13. 13. CDMA Standards - IS-95A <ul><li>IS-95A is the CDMA-based second generation (2G) standard for mobile communication. The following are the key aspects of this standard: </li></ul><ul><ul><li>Support for data rates of upto 14.4 kbps </li></ul></ul><ul><ul><li>IS-95A has been used exclusively for circuit-switched voice </li></ul></ul><ul><ul><li>Convolutional Channel coding used </li></ul></ul><ul><ul><li>Modulation technique used is BPSK </li></ul></ul>
  14. 14. CDMA Standards - IS-95B <ul><li>IS-95B is the evolved version of IS-95A and is designated as 2.5G. </li></ul><ul><li>IS-95B maintains the Physical Layer of IS-95A, but due to an enhanced MAC layer, is capable of providing for higher speed data services. The following are the key aspects of the standard: </li></ul><ul><ul><li>Theoretical data rates of upto 115 kbps, with generally experienced rates of 64 kbps </li></ul></ul><ul><ul><li>Additional Walsh codes and PN sequence masks, which enable a mobile user to be assigned up to eight forward or reverse code channels simultaneously, thus enabling a higher data rate </li></ul></ul><ul><ul><li>Code channels, which are transmitted at full data rates during a data burst </li></ul></ul><ul><ul><li>Convolutional Channel coding </li></ul></ul><ul><ul><li>Binary Phase Shift Keying (BPSK) as the Modulation technique used </li></ul></ul>
  15. 15. IS-95 CDMA Features-(1) <ul><li>Bandwidth Recycling </li></ul><ul><ul><li>Enhancing the system capacity due to the increase of reuse efficiency. </li></ul></ul><ul><ul><li>Achieving higher bandwidth efficiency (interference limited) and simplifying the system planning. </li></ul></ul><ul><ul><li>Achieving flexibility due to the bandwidth on demand. </li></ul></ul><ul><li>Power Control </li></ul><ul><ul><li>Reducing the interference and increasing the talk time of mobile </li></ul></ul><ul><li>station by using the efficient power control scheme. </li></ul><ul><li>Soft handoffs </li></ul><ul><ul><li>Contributing to the achievement of the diversity and reduce the </li></ul></ul><ul><li>chance of loss of link midway through the conversation. </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  16. 16. IS-95 CDMA Features-(2) <ul><li>Diversity </li></ul><ul><ul><li>Taking advantage of multiple levels of diversity: frequency diversity (spreading), spatial diversity (multiple antennas), path diversity (rake receiver) and time diversity (block interleaver), all of which reduce the interference and improve speech quality. </li></ul></ul><ul><li>Variable Rate Vocoder </li></ul><ul><ul><li>Offering high speed coding and reducing background noise and system interference based on the detection of the voice activity. </li></ul></ul><ul><li>Coding Technique </li></ul><ul><ul><li>Enhancing the privacy and security. </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  17. 17. IS-95 Vs 2G Phone Systems 10/03/09 MC: Elementary Concepts and CDMA
  18. 18. IS – 95 Vocoders <ul><li>AMR: Adaptive multi-rate </li></ul><ul><ul><li>Defined for UMTS (W-CDMA) </li></ul></ul><ul><ul><li>Being retrofitted for GSM </li></ul></ul><ul><li>SMV: Selectable mode vocoder </li></ul><ul><ul><li>Defined by 3GPP2 for CDMA2000 </li></ul></ul><ul><li>Many available coding rates </li></ul><ul><ul><li>AMR 8 rates: 12.2, 10.2, 7.95, 7.4, 6.7, 5.9, 5.15 & 4.75bps, plus silence frames (near 0 bps) </li></ul></ul><ul><ul><li>SMV 4 rates: 8.5, 4, 2 & 0.8kbps </li></ul></ul><ul><li>Lower bit rates allow more error correction </li></ul><ul><ul><li>Dynamically adjust to radio interference conditions </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  19. 19. Frequency Allocation GSM Vs CDMA 10/03/09 MC: Elementary Concepts and CDMA
  20. 20. 10/03/09 MC: Elementary Concepts and CDMA
  21. 21. Mathematical Background – (1) <ul><li>Multiple users occupying the same band by having different codes is known as CDMA - Code Division Multiple Access system </li></ul><ul><li>Let </li></ul><ul><li>W - spread bandwidth in Hz </li></ul><ul><li>R = 1/T b = Date Rate </li></ul><ul><li>S - received power of the desired signal in W </li></ul><ul><li>J - received power for undesired signals like multiple access users, multipath, jammers etc in W </li></ul><ul><li>E b - received energy per bit for the desired signal in W </li></ul><ul><li>N 0 - equivalent noise spectral density in W/Hz </li></ul>
  22. 22. Mathematical Background – (2) What is the tolerable interference over desired signal power?
  23. 23. Mathematical Background – (3) <ul><li>In conventional systems W/R  1 which means, for satisfactory operation J/S < 1 </li></ul><ul><li>Example Let R = 9600; W = 1.2288 MHz </li></ul><ul><li>(E b /N 0 ) min = 6 dB (values taken from IS-95) </li></ul><ul><li>Jamming margin (JM) = 10log 10 (1.2288*10 6 /9.6*10 3 ) - 6 </li></ul><ul><li> = 15.1 dB  32 </li></ul><ul><li>This antijam margin or JM arises from Processing Gain (PG) = W/R = 128 </li></ul><ul><li>If (E b /N 0 ) min is further decreased or PG is increased, JM can be further increased </li></ul>
  24. 24. Mathematical Background – (4) <ul><li>JM can be used to accommodate multiple users in the same band </li></ul><ul><li>If (E b /N 0 ) min and PG is fixed, number of users is maximized if perfect power control is employed. </li></ul><ul><li>Capacity of a CDMA system is proportional to PG. </li></ul>
  25. 25. Spreading Codes <ul><li>A noise-like and random signal has to be generated at the transmitter. </li></ul><ul><li>The same signal must be generated at the receiver in synchronization. </li></ul><ul><li>We limit the complexity by specifying only one bit per sample, i.e., a binary sequence. </li></ul>
  26. 26. Desirable Randomness Properties <ul><li>Relative frequencies of “0” and “1” should be ½ (Balance property) </li></ul><ul><li>Run lengths of zeros and ones should be (Run property): </li></ul><ul><ul><li>Half of all run lengths should be unity </li></ul></ul><ul><ul><li>One - quarter should be of length two </li></ul></ul><ul><ul><li>One - eighth should be of length three </li></ul></ul><ul><ul><li>A fraction 1/2 n of all run lengths should be of length n for all finite n </li></ul></ul>
  27. 27. Desirable Randomness Properties (contd…) <ul><li>If the random sequence is shifted by any nonzero </li></ul><ul><li>number of elements, the resulting sequence </li></ul><ul><li>should have an equal number of agreements and </li></ul><ul><li>disagreements with the original sequence </li></ul><ul><li>(Autocorrelation property) </li></ul>
  28. 28. PN Sequences <ul><li>A deterministically generated sequence that nearly satisfies these properties is referred to as a Pseudorandom Sequence (PN) </li></ul><ul><li>Periodic binary sequences can be conveniently generated using linear feedback shift registers (LFSR) </li></ul><ul><li>If the number of stages in the LFSR is r, P  2 r - 1 where P is the period of the sequence </li></ul>
  29. 29. PN Sequences (contd…) <ul><li>However, if the feedback connections satisfy a specific property, P = 2 r - 1. Then the sequence is called a Maximal Length Shift Register (MLSR) or a PN sequence. </li></ul><ul><li>Thus if r=15, P=32767. </li></ul><ul><li>MLSR satisfies the randomness properties stated before </li></ul>
  30. 30. Randomness Properties of PN Sequences <ul><li>Balance property - Of the 2 r - 1 terms, 2 r-1 are one and 2 r-1 –1 are zero. Thus the unbalance is 1/P. For r=50; 1/P  10 -15 </li></ul><ul><li>Run length property - Relative frequency of run length n (zero or ones) is 1/ 2 n for n  r-1 and 1/(2 r - 1) for n = r </li></ul><ul><li>One run length each of r-1 zeros and r ones occurs. There are no run lengths for n > r </li></ul><ul><li>Autocorrelation property - The number of disagreements exceeds the number of agreements by unity. Thus again the discrepancy is 1/p </li></ul>
  31. 31. PN Sequences Specified in IS-95 <ul><li>A “long” PN sequence (r =42) is used to scramble the user data with a different code shift for each user </li></ul><ul><li>The 42-degree characteristic polynomial is given by: </li></ul><ul><ul><li>x 42 +x 41 +x 40 +x 39 +x 37 +x 36 +x 35 +x 32 +x 26 +x 25 +x 24 +x 23 +x 21 +x 20 +x 17 +x 16 +x 15 +x 11 +x 9 +x 7 +1 </li></ul></ul><ul><li>The period of the long code is 2 42 - 1  4.4*10 2 chips and lasts over 41 days </li></ul>
  32. 32. PN Sequences Specified in IS-95 (contd…) <ul><li>A short PN sequence (r = 15) is specific to a base station and its period is (2 15 −1)Tc = 27ms. </li></ul><ul><li>Two “short” PN sequences (r=15) are used to spread the quadrature components of the forward and reverse link waveforms </li></ul>
  33. 33. Walsh Code <ul><li>There are some issues with Walsh Codes </li></ul><ul><ul><li>Synchronization of all users is required </li></ul></ul><ul><ul><li>In a multipath channel, delayed copies may be received which are not orthogonal any longer! </li></ul></ul><ul><ul><li>Only J codes exist with a bandwidth expansion of J, so as far as capacity, we are right back where we started with TDMA and FDMA! </li></ul></ul><ul><li>Advantages relative to TDMA and FDMA </li></ul><ul><ul><li>No guard bands or guard times are typically required </li></ul></ul><ul><ul><li>No equalizer is typically required, when a RAKE receiver is used </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  34. 34. Spread Spectrum <ul><li>A modulation system in which the modulated (spread spectrum) signal bandwidth is much greater than the message signal bandwidth. </li></ul><ul><li>The spectral spreading is performed by a code that is independent of the message signal. The same code is used at receiver to de spread the received signal and to recover the message signal. </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  35. 35. Advantages of Spread Spectrum <ul><li>It is Secure, difficult to intercept </li></ul><ul><li>A large number of codes can support a large number of users </li></ul><ul><li>As a large bandwidth is used the system is less prone to distortion </li></ul><ul><li>Resistant to jamming </li></ul><ul><li>Asynchronous multiple access technology </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  36. 36. Types Of Spread Spectrum <ul><li>Direct Sequence Spread Spectrum </li></ul><ul><li>Frequency Hoping </li></ul><ul><li>Hybrid System </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  37. 37. Direct Sequence Spread Sprectrum <ul><li>DS-SS is one popular way to make the noise-like waveforms for CDMA </li></ul><ul><li>Maximal-length shift registers make binary sequences that have noise-like properties </li></ul><ul><li>n-stage shift register produces a sequence with a period of length 2 n -1. </li></ul><ul><li>Codes for different users </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  38. 38. 10/03/09 MC: Elementary Concepts and CDMA
  39. 39. CDMA Forward Link <ul><li>The forward link uses the same frequency spectrum as AMPS (824-849 Mhz) . Each carrier 1.25MHz </li></ul><ul><li>Four types of logical channel </li></ul><ul><ul><li>Pilot, </li></ul></ul><ul><ul><li>Synchronization, </li></ul></ul><ul><ul><li>7 Paging, and </li></ul></ul><ul><ul><li>55 Traffic channels </li></ul></ul><ul><li>Channels are separated using different spreading codes </li></ul><ul><li>QPSK is the modulation scheme </li></ul><ul><li>Orthogonal Walsh codes are used (64 total) </li></ul><ul><li>After orthogonal codes, they are further spread by short PN spreading codes </li></ul><ul><li>Short PN spreading codes are M sequences generated by LFSRs of length 15 with a period of 32768 chips. </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  40. 40. CDMA MUX 10/03/09 MC: Elementary Concepts and CDMA Copyright © Data Communication and Networking By Behrouz A Forozan
  41. 41. CDMA Reverse Channel <ul><li>Fundamentally different from the forward channels </li></ul><ul><li>Uses OQPSK for power efficiency </li></ul><ul><li>QPSK demodulation is easy </li></ul><ul><li>869-894 MHz range. </li></ul><ul><li>No spreading of the data using orthogonal codes </li></ul><ul><li>Same orthogonal codes are used for WAVEFORM encoding </li></ul><ul><li>Two types of logical channels: </li></ul><ul><ul><li>Access channels </li></ul></ul><ul><ul><li>Reverse traffic channels </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  42. 42. CDMA DeMUX 10/03/09 MC: Elementary Concepts and CDMA Copyright © Data Communication and Networking By Behrouz A Forozan
  43. 43. 3G Vision <ul><li>Universal global roaming </li></ul><ul><li>Multimedia (voice, data & video) </li></ul><ul><li>Increased data rates </li></ul><ul><ul><li>384 kbps while moving </li></ul></ul><ul><ul><li>2 Mbps when stationary at specific locations </li></ul></ul><ul><li>Increased capacity (more spectrally efficient) </li></ul><ul><li>IP architecture </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  44. 44. 10/03/09 MC: Elementary Concepts and CDMA
  45. 45. IS 95 to CDMA 2000 3G Evolution 10/03/09 MC: Elementary Concepts and CDMA
  46. 46. CDMA2000 <ul><li>Evolution from original Qualcomm CDMA </li></ul><ul><li>Better migration story from 2G to 3G </li></ul><ul><ul><li>cdmaOne operators don’t need additional spectrum </li></ul></ul><ul><ul><li>1xEVD0 promises higher data rates than UMTS, i.e. W-CDMA </li></ul></ul><ul><li>Better spectral efficiency </li></ul><ul><li>CDMA2000 core network less mature </li></ul><ul><ul><li>cdmaOne interfaces were vendor-specific </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  47. 47. 10/03/09 MC: Elementary Concepts and CDMA
  48. 48. W-CDMA <ul><li>Wideband CDMA </li></ul><ul><ul><li>Standard for Universal Mobile Telephone Service (UMTS) </li></ul></ul><ul><li>Committed standard for Europe and likely migration path for other GSM operators </li></ul><ul><ul><li>Leverages GSM’s dominant position </li></ul></ul><ul><li>Requires substantial new spectrum </li></ul><ul><ul><li>5 MHz each way (symmetric) </li></ul></ul><ul><li>Legally mandated in Europe and elsewhere </li></ul><ul><li>Sales of new spectrum completed in Europe </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  49. 49. Need For WCDMA <ul><li>WCDMA is a step further in the CDMA technology. </li></ul><ul><ul><li>Uses a 5 MHz wide radio signal and </li></ul></ul><ul><ul><li>chip rate of 3.84 Mcps, which is about three times higher than the chip rate of CDMA2000 (1.22 Mcps) </li></ul></ul><ul><ul><li>QPSK Modulation </li></ul></ul><ul><li>Migration from 3G to 4G </li></ul><ul><li>Higher spectrum efficiency </li></ul><ul><li>Higher QoS </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  50. 50. W-CDMA Vs cdma2000 10/03/09 MC: Elementary Concepts and CDMA
  51. 51. TD-SCDMA <ul><li>Time division duplex (TDD) </li></ul><ul><li>Chinese development - deployed in China </li></ul><ul><li>Good match for asymmetrical traffic! </li></ul><ul><li>Single spectral band (1.6 MHz) possible </li></ul><ul><li>Costs relatively low </li></ul><ul><ul><li>Handset smaller and may cost less </li></ul></ul><ul><ul><li>Power consumption lower </li></ul></ul><ul><ul><li>TDD has the highest spectrum efficiency </li></ul></ul><ul><li>Power amplifiers must be very linear </li></ul><ul><ul><li>Relatively hard to meet specifications </li></ul></ul><ul><li>35MHz for downlink and uplink </li></ul>10/03/09 MC: Elementary Concepts and CDMA
  52. 52. Rake Receiver <ul><li>Mobile station receives multiple attenuated and delayed replicas of the original signal (multipath diversity channels). </li></ul><ul><li>Two multipath signals are resolvable only if their relative delay exceeds the chip period Tc </li></ul><ul><li>Amplitudes and phases of multipath components are found by correlating the received waveform with multiple delayed versions of the signal (delay = nTc). </li></ul><ul><li>Searcher performs the above task for up to 3 different multipath signals. </li></ul><ul><li>3 parallel demodulators (RAKE fingers) isolate the multipath components and the RAKE receiver combines them. </li></ul>
  53. 53. Summary <ul><li>Different mobile standard organization ITU, IMT 2000, TIA, IS </li></ul><ul><li>CDMA </li></ul><ul><ul><li>IS 95 , IS95A,IS95B </li></ul></ul><ul><ul><li>Codes –Walsh,Autocorrelation, PN </li></ul></ul><ul><ul><li>Rake Receiver </li></ul></ul><ul><ul><li>Forward and Reverse Link </li></ul></ul><ul><ul><li>CDMA 2000 </li></ul></ul><ul><ul><li>WCDMA </li></ul></ul>10/03/09 MC: Elementary Concepts and CDMA
  54. 54. References <ul><li>[1] T. S. Rappaport, “Wireless communications </li></ul><ul><li>principles&practice”, Prentice Hall, 1996 </li></ul><ul><li>[2] C. Y. Lin and J. Shieh, “IS-95 North American </li></ul><ul><li>standard-a CDMA based digital cellular system”, IEEE </li></ul><ul><li>Website. </li></ul><ul><li>[3] A. J. Viterbi, “CDMA principles of spread spectrum </li></ul><ul><li>communication”, Addison-Wesley Publishing Company, 1995. </li></ul><ul><li>[4] R. Paul and K. V. Shah, “An objective comprison of second </li></ul><ul><li>generation cellular systems - GSM, IS-136 and IS-95”, IEEE, 1997. </li></ul><ul><li>[5] Dr.V.K Ananthashayana , “Lecture Notes on CDMA” </li></ul><ul><li>[6] Motorola, Inc. “CDMA Technology & Benefits: An </li></ul><ul><li>introduction to the benefits of CDMA for wireless </li></ul><ul><li>technology”, 1996. </li></ul>
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