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Code division multiple access

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Code division multiple access

  1. 1. Code Division Multiple Access Prepared by: Christina Chiu Mar 24, 2004
  2. 2. Outline <ul><li>Spread Spectrum Communications </li></ul><ul><li>Multiple Access Technique </li></ul><ul><ul><li>Direct Sequence DS-CDMA </li></ul></ul><ul><li>CDMA standards </li></ul><ul><ul><li>CDMAOne (2G) – IS 95A, (2.5G) IS-95B </li></ul></ul><ul><ul><li>CDMA 2000 and WCDMA (3G) – IMT2000 </li></ul></ul><ul><li>4G in the future </li></ul><ul><li>Conclusions </li></ul>
  3. 3. Spread Spectrum Technique <ul><li>Low power spectral density </li></ul><ul><li>Rejection to jamming signal and interference </li></ul><ul><li>Pseudorandom sequence </li></ul><ul><ul><li>Randomness and noise properties </li></ul></ul><ul><ul><li>Walsh, M-sequence, Gold, Kasami, Z4 </li></ul></ul><ul><ul><li>Provide signal privacy </li></ul></ul>
  4. 4. Direct Sequence Spread Spectrum <ul><li>Spreading </li></ul><ul><ul><li>Source signal is multiplied by a PN signal </li></ul></ul><ul><li>Processing Gain: </li></ul><ul><li>Despreading </li></ul><ul><ul><li>Spread signal is multiplied by the spreading code </li></ul></ul>
  5. 5. System Block Diagram
  6. 6. Spreading & Despreading <ul><li>Polar {±1} signal representation </li></ul>
  7. 7. Spreading & Despreading
  8. 8. CDMA <ul><li>Unique code to differentiate all users </li></ul><ul><li>Sequence used for spreading have low cross-correlations </li></ul><ul><li>Allow many users to occupy all the frequency/bandwidth allocations at that same time </li></ul><ul><li>Processing gain is the system capacity </li></ul><ul><ul><li>How many users the system can support </li></ul></ul>
  9. 9. Demodulation (Correlator)
  10. 10. 2G: IS-95A (1995) <ul><li>Known as CDMAOne </li></ul><ul><li>Chip rate at 1.25Mbps </li></ul><ul><li>Convolutional codes, Viterbi Decoding </li></ul><ul><li>Downlink (Base station to mobile): </li></ul><ul><ul><li>Walsh code 64-bit for channel separation </li></ul></ul><ul><ul><li>M-sequence 2 15 for cell separation </li></ul></ul><ul><li>Uplink (Mobile to base station): </li></ul><ul><ul><li>M-sequence 2 41 for channel and user separation </li></ul></ul>
  11. 11. 2G: IS-95A (1995) 8~13 kbps Speech Rate Up to 14.4 kbps Data Rate 1.25 Mbps (chip rate) Channel Bit Rate 600 mW Maximum Tx Power 64 Number of Channel BPSK/QPSK Modulation Scheme 1.25 MHz Channel Separation 824-849 MHz Downlink Frequency 869-894 MHz Uplink Frequency CDMA Multiple Access IS-95, ANSI J-STD-008 Standard
  12. 12. 2.5G: IS-95B (1998) <ul><li>Increased data rate for internet applications </li></ul><ul><ul><li>Up to 115 kbps (8 times that of 2G) </li></ul></ul><ul><li>Support web browser format language </li></ul><ul><ul><li>Wireless Application Protocol (WAP) </li></ul></ul>
  13. 13. 3G Technology <ul><li>Ability to receive live music, interactive web sessions, voice and data with multimedia features </li></ul><ul><li>Global Standard IMT-2000 </li></ul><ul><ul><li>CDMA 2000, proposed by TIA </li></ul></ul><ul><ul><li>W-CDMA, proposed by ARIB/ETSI </li></ul></ul><ul><li>Issued by ITU (International Telecommunication Union) </li></ul>
  14. 14. 3G Specficiations <ul><li>Excellent voice quality </li></ul><ul><li>Data rate </li></ul><ul><ul><li>144 kbps in high mobility </li></ul></ul><ul><ul><li>384 kbps in limited mobility </li></ul></ul><ul><ul><li>2 Mbps in door </li></ul></ul><ul><li>Frequency Band 1885-2025 MHz </li></ul><ul><li>Convolutional Codes </li></ul><ul><li>Turbo Codes for high data rates </li></ul>
  15. 15. 3G: CDMA2000 (2000) <ul><li>CDMA 1xEV-DO </li></ul><ul><ul><li>peak data rate 2.4 Mbps </li></ul></ul><ul><ul><li>supports mp3 transfer and video conferencing </li></ul></ul><ul><li>CDMA 1xEV-DV </li></ul><ul><ul><li>Integrated voice and high-speed data multimedia service up to 3.1 Mbps </li></ul></ul><ul><li>Channel Bandwidth: </li></ul><ul><ul><li>1.25, 5, 10, 15 or 20 MHz </li></ul></ul><ul><li>Chip rate at 3.6864 Mbps </li></ul><ul><li>Modulation Scheme </li></ul><ul><ul><li>QPSK in downlink </li></ul></ul><ul><ul><li>BPSK in uplink </li></ul></ul>
  16. 16. 3G: CDMA2000 Spreading Codes <ul><li>Downlink </li></ul><ul><ul><li>Variable length orthogonal Walsh sequences for channel separation </li></ul></ul><ul><ul><li>M-sequences 3x2 15 for cell separation (different phase shifts) </li></ul></ul><ul><li>Uplink </li></ul><ul><ul><li>Variable length orthogonal Walsh sequences for channel separation </li></ul></ul><ul><ul><li>M-sequences 2 41 for user separation (different phase shifts) </li></ul></ul>
  17. 17. 3G: W-CDMA (2000) <ul><li>Stands for “wideband” CDMA </li></ul><ul><li>Channel Bandwidth: </li></ul><ul><ul><li>5, 10 or 20 MHz </li></ul></ul><ul><li>Chip rate at 4.096 Mbps </li></ul><ul><li>Modulation Scheme </li></ul><ul><ul><li>QPSK in downlink </li></ul></ul><ul><ul><li>BPSK in uplink </li></ul></ul>
  18. 18. 3G: W-CDMA Spreading Codes <ul><li>Downlink </li></ul><ul><ul><li>Variable length orthogonal sequences for channel separation </li></ul></ul><ul><ul><li>Gold sequences 2 18 for cell separation </li></ul></ul><ul><li>Uplink </li></ul><ul><ul><li>Variable length orthogonal sequences for channel separation </li></ul></ul><ul><ul><li>Gold sequences 2 41 for user separation </li></ul></ul>
  19. 19. 4G Technology (2010) <ul><li>High data rates => 100 Mbps </li></ul><ul><li>Multimedia data up to ~10 2 Mbps </li></ul><ul><li>IP-oriented network => Internet </li></ul><ul><li>MIMO using Multiple Antennas </li></ul><ul><li>Spreading code </li></ul><ul><ul><li>Non-binary sequences </li></ul></ul><ul><li>Multiple Access Technique </li></ul><ul><ul><li>MC-CDMA </li></ul></ul>
  20. 20. MC-CDMA
  21. 21. Conclusions <ul><li>CDMA can increase the capacity of mobile system </li></ul><ul><li>Goals of next generation cellular </li></ul><ul><ul><li>Further increase data rate </li></ul></ul><ul><ul><li>Reduce interference among users </li></ul></ul><ul><li>Future research: </li></ul><ul><ul><li>Search for good non-binary sequences </li></ul></ul><ul><ul><ul><li>Ideal 2-level autocorrelation </li></ul></ul></ul><ul><ul><ul><li>Low cross correlations </li></ul></ul></ul>

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