Experimental evaluation of coherent rake combining for broadband single-carrier DS-CDMA wireless communications

This paper experimentally evaluates the bit error rate (BER) performance of single-carrier broadband DS-CDMA (B-CDMA) scheme using a 100-MHz bandwidth (chip rate of 81.92 Mcps) in frequency-selective multipath fading channels. The achievable information bit rate is 20.36 (2.5) Mbps when the spreading factor (SF) is SF = 4 (32). In order to achieve a high data-rate transmission with high quality (i.e., average BER is below 10^-6), we apply pilot symbol-assisted coherent Rake receiving with a large number of Rake fingers (maximum number of Rake fingers is SF × 2), 2-branch antenna diversity reception, convolutional coding, and signal-to-interference power ratio (SIR) measurement-based fast closed-loop transmit power control (TPC). Experimental results show that the average BER of 10^-6 for the 20.36 (2.5)-Mbps transmission is achieved at the required average transmit E_b/N_O of approximately 6.7 (5.0) dB when the number of multipaths is L = 2 and the maximum fading Doppler frequency is f_D = 20 Hz. We also show that Rake time diversity and fast TPC are effective in a broadband propagation channel where many resolvable paths (such as 12 paths) are observed.