Experimental evaluation of coherent adaptive antenna array diversity receiver employing optical fiber interface in IF stage

Based on laboratory experiments, the paper investigates the multiuser interference suppression effect of the coherent adaptive antenna array diversity (CAAAD) receiver. An optical fiber feeder is employed in the intermediate frequency (IF) stage of a base transceiver station (BTS), aiming at the practical use of adaptive antenna array beamforming techniques in the W-CDMA air interface. We employ a configuration in which the optical fiber conversion, i.e., electrical-to-optical (E/O) or O/E conversion, is performed on a received signal amplified by an automatic gain control (AGC) amplifier in the IF stage in order to abate the impact of the noise component generated by the E/O (O/E) converters. We first show by computer simulation the superiority of the optical fiber conversion in the IF stage to that in the radio frequency (RF) stage from the viewpoint of reducing the bit error rate (BER) performance. Furthermore, experimental results elucidate that the loss in the required transmit signal energy per bit-to-background noise power spectrum density ratio (E_b/N₀) of the implemented CAAAD receiver at the average BER of 10^-3 employing the optical fiber feeders in the IF stage compared to that with coaxial cables is within a mere 0.2 dB for conditions of 6 antennas, 3 users, 2-path Rayleigh fading channel model, and the ratio of the target signal energy per bit-to-interference power spectrum density ratio (E_b/I₀) of the desired user to that of the interfering users for fast transmission power control is ΔE_b/I₀ = -15 dB.