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Compare SDMA, TDMA, FDMA, CDMA techniques.
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Approach SDMA TDMA FDMA CDMA
Idea Space is segmented into  cells or sectors. Sending time is segmented into time slots either demand fdriven or fixed patterns. Frequency band is segmented into subbands. Spectrum is spread by orthogonal codes.
Terminals Only one terminal can be active in one cell or one sector. All terminals are active for a small period of time on same frequency. Every terminal has its own frequency uninterrupted. All terminals can be active at the same place and same time uninterrupted.
Signal Separation Cell structure, directed antennas Synchronization in the time domain Fitering in the frequency domain Code plus special recievers
Transmission Scheme Continuous Discontinuous Continuous Continuous
Cell capacity Depends on cell area Limited Limited Interference limited system
Advantages simple, increases capacity flexible, fully digital simple, robust flexible, soft handover
Disadvantages inflexible, antennas are fixed Guard sppace needed, syynchronization is difficult inflexible complex recievers
Comment Used only with TDMA, CDMA and FDMA used with SDMA and FDMA used with TDMA and SDMA used with TDMA and FDMA
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