Experimental evaluation of throughput performance in broadband packet wireless access based on VSF-OFCDM and VSF-CDMA

We recently proposed broadband packet wireless access based on variable spreading factor (VSF)-orthogonal frequency and code division multiplexing (OFCDM) in the forward link and variable spreading and chip repetition factors (VSCRF)-CDMA in the reverse link for the systems beyond IMT-2000. This paper presents experimental evaluations on the throughput performance of that proposed broadband packet wireless access scheme associated with adaptive modulation and channel coding (AMC) in a multipath Rayleigh fading channel employing the implemented base station (BS) and mobile station (MS) transceivers. The implemented OFCDM transceiver verifies the effectiveness of the combination of the OFCDM and AMC including QPSK and 16QAM data modulations with a fast round trip delay of 6 msec for improving the throughput performance by exploiting the frequency diversity effect in a broadband channel. The experimental results show that the throughput performance of 100 and 200 Mbps employing AMC is achieved at the average received signal energy per symbol-to-background noise power spectrum density ratio (E_s/N₀) of approximately 7.5 and 19 dB, respectively, for 15-code multiplexing for the spreading factor of SF=16 in the OFCDM forward link with a 100-MHz bandwidth, in a six-path fading channel with the fading maximum Doppler frequency of f_D=20 Hz. Furthermore, we elucidate that the peak throughput of 20 Mbps is achieved at the average received E_s/N₀of approximately 9 dB by employing QPSK data modulation with R = 1/2 for three-code multiplexing for SF= 4 in a four-path fading channel in the broadband CDMA reverse link with a 40-MHz bandwidth.