Simulation of Third Generation CDMA Systems - Virginia Tech
Simulation of Third Generation CDMA Systems - Virginia Tech
Simulation of Third Generation CDMA Systems - Virginia Tech
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2.8 Channel CodingThe main purpose <strong>of</strong> channel coding is to selectively introduce redundancy into thetransmitted data and improve the wireless link performance in the process [9]. Channel codescan be used to detect as well as correct errors. The W<strong>CDMA</strong> systems have provision for botherror detection and error correction. Channel coding scheme at the W<strong>CDMA</strong> system is acombination <strong>of</strong> error detection, error correction, along with rate matching, interleaving andtransport channels mapping onto/splitting from physical channels [10]. This section gives abrief description on the error detection and error correction schemes recommended for theW<strong>CDMA</strong> systems.2.8.1 Error DetectionError detection is provided by a Cyclic Redundancy Check (CRC) code. The CRC is24,16,8 or 0 bits. The entire transmitted frame is used to compute the parity bits. Any <strong>of</strong> thefollowing cyclic generator polynomials can be used to construct the parity bits:24 23 6 5g ( D)= D + D + D + D + D+12416 12 5g ( D)= D + D + D + D+1168 7 4 3g ( D)= D + D + D + D + D+18(2.14)A detailed description <strong>of</strong> the error detection scheme is given in [10].2.8.2 Error CorrectionTwo alternative error correction schemes have been specified for the W<strong>CDMA</strong>system. They are• Convolutional Coding• Turbo Coding25
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