BER Performance Evaluation of Tail-Biting Convolution Coding Applied to Companded QPSK Mobile WiMax

Abstract

A Bit-Error-Rate (BER) performance evaluation is presented for mu-Law companded QPSK modulated Mobile WiMax (IEEE802.16e) employing tail-biting convolutional coding (TBCC). The Down Link (DL) Partially Used Subcarrier (PUSC) deployment has been considered for this investigation. Equalized symbol power transmissions for uncompanded and mu-Law companded WiMax scenarios employing mu = 0.1, 1, 3, 10, 30, 100, 255, 1000, and 3000 has been undertaken. It is shown that for 30 clusters each carrying 48 bits of random data, the improvement in SNR for TBCC using the convolutional code (7, 171, 133) is best for uncompanded WiMax and deteriorates slightly for companded WiMax situations. The maximum improvement in SNR at the 0.001 BER probability level is ~1.7 dB, whilst at the 0.0001 BER probability level the improvement is ~2.9 dB. As companded BER rates for smaller values of mu are only slightly degraded over normal WiMax BER rates, then TBCC for small values of mu may be used to provide improved SNR performance over normal convolutional coding (CC) WiMax situations. Importantly, small values of mu can also provide improved Peak-to-Average Power Ratio (PAPR) but for larger values of mu, where significant PAPR reduction can be obtained, the improved performance of TBCC does not provide sufficient SNR gain to improve upon the standard CC WiMax performance.