Dense deployments of wireless local area network (WLAN) access points (APs) are accelerating to accommodate the massive wireless traffic from various mobile devices. The AP densification improves the received power at mobile devices; however, total throughput in a target area is saturated by inter-cell interference (ICI) because of the limited number of frequency channels available for WLANs. To substantially mitigate ICI, we developed and described a distributed smart antenna system (D-SAS) proposed for dense WLAN AP deployment in this paper. We also describe a system configuration based on our D-SAS approach. In this approach, the distributed antennas externally attached to each AP can be switched so as to make the transmit power match the mobile device's conditions (received power and packet type). The gains obtained by the antenna switching effectively minimize the transmission power required of each AP. We also describe experimental measurements taken in a stadium using a system prototype, the results show that D-SAS offers double the total throughput attained by a centralized smart antenna system (C-SAS).

This letter presents a comprehensive analytical framework for average pairwise error probability (PEP) of decode-and-forward cooperative network based on various distributed space-time block codes (DSTBCs) with antenna switching (DDF-AS) technique over quasi-static Rayleigh fading channels. Utilizing the analytical framework, exact and asymptotic PEP expressions can be effectively formulated, which are based on the Lauricella multiplicative hypergeometric function, when various DSTBCs are adopted for the DDF-AS system. The derived asymptotic PEP formulas and some numerical results enable us to verify that the DDF-AS scheme outperforms the conventional cooperative schemes in terms of error rate performance. Furthermore, the asymptotic PEP formulas can also provide explicit and useful insights into the full diversity transmission achieved by the DDF-AS system.

For automatic repeat request (ARQ)-aided TSTD (Time Switched Transmit Diversity) system, a receiver sends the acknowledgement signal (ACK or NACK) to a transmitter in order to predict the condition of the channel. In this paper, two antenna switching schemes, in which the NACK trigger the transmit antenna switching in the proposed antenna switching patterns, are proposed for the TSTD with the ARQ in WCDMA LCR-TDD systems. In addition, the system performances are investigated. Simulation results demonstrate that the performances of the TSTD systems can be improved by applying the ARQ scheme. Furthermore, the performances of ARQ-aided TSTD systems may be significantly improved by applying the proposed antenna switching schemes, especially when the mobile's speed is low.

This paper investigates the performance of ARQ-aided downlink Time Switched Transmit Diversity (TSTD) in the WCDMA Low Chip Rate (LCR)-Time Division Duplex (TDD) system, when antenna switching and power ramping are applied. With the help of the ARQ signal, where the receiver sends the acknowledgement (ACK or NACK) to the transmitter, the proposed TSTD scheme switches the transmit antenna and ramps up the transmission power for the retransmitted data, when the transmitter receives a NACK signal. Simulation results demonstrate, that when the mobile speed is 3 km/h and a frame error rate (FER) is set to 1%, the antenna switching scheme yields 2 dB to 3 dB performance gain in terms of average Eb/N0, and the power ramping gives 0.7 dB to 1.6 dB gain, compared with the conventional ARQ-aided TSTD. In addition, 6% of throughput gain is shown by amalgamating the antennas switching as well as the power ramping, when the average Eb/N0 is equal to 0 dB.

In this paper, a simple subcarrier selection combining technique is proposed for orthogonal frequency-division multiplexing (OFDM) systems with multiple receive antennas. The subcarrier-based selection algorithm is developed in the frequency domain to achieve an optimal selection combining gain for OFDM systems, instead of the antenna-based selection algorithms in the time domain or frequency domain. The proposed technique selects an optimal subcarrier with a maximum channel gain among all the receive antennas with the same subcarrier position, based on the estimated channel frequency response during the training period. Hardware complexity for the proposed technique is minimal since it requires single front-end with multiple receive antennas and single baseband demodulator. It is shown by computer simulation that a significant gain can be achieved by the proposed technique over the conventional selection combining technique for OFDM systems in practical situations.