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Code division multiple access
 

Code division multiple access

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you can be friend with me on orkut

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"mangalforyou@gmail.com" : i belive in sharing the knowledge so please send project reports ,seminar and ppt. to me .

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    Code division multiple access Code division multiple access Presentation Transcript

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