Evaluation of throughput employing hybrid ARQ packet combining in forward link OFCDM broadband wireless access

The paper presents the throughput performance when employing hybrid automatic repeat request packet combining, i.e., Chase combining and incremental redundancy, in forward-link orthogonal frequency and code division multiplexing (OFCDM) broadband packet wireless access achieving a peak throughput above 100 Mbps. Simulation results elucidate that the achievable throughput at the average received signal energy per symbol-to-background noise power spectrum density ratio (E_s/N₀) of 4 dB and 10 dB, employing incremental redundancy, is increased by approximately 50% and 70% in a 12-path exponentially decayed fading channel compared to that using Chase combining for QPSK and 16QAM data modulation, respectively. However, we show that despite the superiority of incremental redundancy to Chase combining in the achievable throughput for the respective modulation and coding schemes (MCSs), the total throughput when employing incremental redundancy associated with a near optimum MCS set in an actual adaptive modulation and coding (AMC) operation becomes almost identical to that using Chase combining in a low maximum Doppler frequency, f_D, channel. Finally, we show that incremental redundancy coupled with a higher channel coding rate is still more effective than Chase combining in improving the throughput for a high f_D channel owing to its large coding gain.