An Investigation on Efficient Spreading Codes for Transmitter Based Techniques to Mitigate MAI and ISI in TDD/CDMA Downlink

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The authors investigate efficient spreading codes for transmitter based techniques of Code Division Multiple Access (CDMA) systems. The channel is considered to be known at the transmitter which is usual in a Time Division Duplex (TDD) system where the channel is assumed to be the same on uplink and downlink. For such a TDD/CDMA system, both bitwise and block-wise multiuser transmission schemes are taken up where complexity is transferred to the transmitter side so that the receiver has minimum complexity. Different spreading codes are considered at the transmitter to spread the signal efficiently over the entire spectrum. The Bit Error Rate (BER) curves portray the efficiency of the codes in presence of Multiple Access Interference (MAI) as well as Inter Symbol Interference (ISI).