Experiments on throughput performance above 100-Mbps in forward link for VSF-OFCDM broadband wireless access

This paper presents experimental evaluations on the throughput performance of the recently proposed variable spreading factor (VSF)- orthogonal frequency and code division multiplexing (OFCDM) broadband packet wireless access associated with adaptive modulation and channel coding (AMC) in the forward link multipath Rayleigh fading channel. 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 in 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 employing time domain spreading with the spreading factor of SF = 16 in the forward link with a 100-MHz bandwidth, in a six-path Rayleigh fading channel with the fading maximum Doppler frequency of f_D = 20 Hz. Furthermore, we elucidate that the throughput of more than 100 Mbps is achieved at the average received E_s/N₀ of approximately 8-10 dB even for the root mean squared delay spread of 0.6 μsec (i.e., the maximum time delay of the path is 2 μsec) and for f_D = 400 Hz (corresponding moving speed of approximately 90 km/h assuming a 5-GHz carrier frequency).