This paper presents a method of reducing excitation error in sidelobe canceller without increasing the resolution of the digital phase shifters and the digital attenuators. In general sidelobe canceller, the null direction is shifted because of the excitation error (quantization error and random error, etc.) and the suppression capability degrades. The proposed method can alleviate the influence of the excitation error by vector composition of some quantized excitation weights. Computer simulation results show that the output signal to interference and noise power ratio (SINR) using the proposed method can improve greatly in comparison with that using conventional quantized excitation weight.

In this paper, we propose a novel spatial filtering technique for orthogonal frequency division multiplexing (OFDM) signals called "VIrtual Subcarrier Assignment (VISA)." Here, virtual subcarrier is a subcarrier which is not used for data transmission. When a wireless terminal is equipped with multiple antennas, VISA can easily achieve a space division multiple access (SDMA) by assigning a different spectral position of virtual subcarrier to a different user. To realize VISA in an already-existing OFDM-based wireless local area network (WLAN), we discuss an antenna weight control method in the preamble of a signal burst format designed for the IEEE802.11a standard and evaluate the bit error rate (BER) performance in typical indoor wireless environments.

We have proposed a novel spatial filtering technique named "VIrtual Subcarrier Assignment (VISA)" for orthogonal frequency division multiplexing (OFDM) signals, which enables the transceiver equipped with an adaptive array antenna (AAA) to selectively receive or reject OFDM signals through coloring them with different virtual subcarrier positions in their frequency spectra. In this paper, we develop the VISA to use multiple virtual subcarrier assignment, which assigns a different combination of multiple virtual subcarrier positions in the frequency spectrum to each OFDM signal. Furthermore, we present two kinds of recursive least square (RLS)-based array weight control methods to support the VISA with multiple subcarrier puncturing in an IEEE802.11a-based system and evaluate the link-level performance in typical indoor wireless environments by computer simulations.

MBF (Microwave Beam Forming) antennas are beam forming antennas that perform pattern control in RF, for a low-cost design suitable for mobile terminals. An MBF antenna has only a single output port, since this antenna consists of an array antenna, microwave phase shifters, and a power combiner. Because of this simple configuration, MBF antennas cannot adopt conventional beam forming algorithms that require both phase and amplitude control, and signal observation of each antenna element. In this paper, mutual coupling matrix estimation and null forming methods are presented for MBF antennas. It is shown that the mutual coupling matrix can be estimated by changing the antenna weight instead of signal observation of each antenna element. It is also shown that phase-only null forming, including mutual coupling effect, can be done by the optimum phase perturbations. Numerical and experimental results show the performance of these algorithms.