Low Rate Channel Coding with Complex-Valued Block Codes

Authors: A. Dekorsy, V. Kühn, K.-D. Kammeyer

This paper addresses aspects of channel coding in OFDM-CDMA uplink systems where each user occupies a bandwidth much larger than the information bit rate. This inherent bandwidth expansion allows the application of powerful low rate codes under the constraint of low decoding costs. Three different coding strategies are considered: the combination of convolutional and repetition codes, the code-spread system consisting of one single very low rate convolutional code and a serial concatenation of convolutional, Walsh-Hadamard and repetition code. The latter scheme is improved by combining the Walsh-Hadamard codes with an additional M-PSK modulation resulting in complex valued Walsh-Hadamard codes (CWCs). Analytical performance evaluations will be given for these codes for the first time. The application of CWCs as inner codes in a serial code concatenation is also addressed in this paper. We derive a symbol-by-symbol MAP decoding algorithm in the complex signal space in order to enable iterative decoding for the entire code. A comprehensive performance analysis by simulation of all the proposed coding schemes shows that the Walsh-Hadamard based schemes are the best choice for low up to medium system load. Note that even for fully loaded OFDM-CDMA systems the concatenation with an inner complex valued Walsh-Hadamard code leads to a bit-error-rate less than 10e-5 for an Eb/N0 of about 6dB.

Document type: Journal Paper
Publication: May 2003
Journal: IEEE Transactions on Communications
Pages: 800-809
Volume: 51
Number: 5
Index: 208
IEEETransComm_2003_kühn.pdf569 KBIEEETransComm_2003_kühn.gz496 KB
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