Yoshihiro Ichikawa

A design methodology of a tapped delay line adaptive array antenna

Unlike the basic adaptive array antenna (AAA) , a tapped delay line adaptive array antenna (TDL-AAA) is effective in mitigating interference from user signals or multipath waves which impinge on the array close to the direct wave. This is also useful for reducing the number of antenna elements under a multipath propagation environment. Furthermore, this adaptive antenna system is also effective for multi-input multi-output (MIMO) spatial multiplexing techniques under frequency selective fading channels. However, a method of designing the required number of antenna elements or tap stages has not been studied. We propose a design equation for TDL-AAA when a number of users and maximum delay time are given. We assume that multipath waves impinge on the array successively with symbol period interval and individual waves have a different direction of arrival (DoA). The influence of the roll-off factor of a cosine roll-off filter is also studied by computer simulation. Simulation results show that the proposed design equation is applicable in case of a roll-off factor of 1.0. On the other hand, simulation results of a roll-off factor of 0.5 show that one can determine the number of antenna elements.

Computational complexity reduced MMSE adaptive array antenna with space-temporal joint equalization

A tapped-delay-line adaptive array antenna (TDL-AAA) is proposed for the method of space and temporal (frequency) equalization. However, this method has a drawback that requires many variable taps (AAA elements /spl times/ LE (linear equalizer) taps) and many multiplications. In this paper, in order to reduce the computational complexity, we propose the cascade connection of one adaptive array antenna and one linear equalizer with space and temporal joint equalization. The LE mitigates multipath waves close to the direct wave. The AAA removes only interference users waves. The effectiveness of the proposed method is confirmed by theoretical consideration and computer simulation.

Pattern synthesis of an array antenna with maximum directivity and nulls at specified directions

In order to solve a problem of maximizing a directivity of a transmitting array antenna with nulls at specified directions, we intended to utilize an adaptive antenna algorithm which enables the SNR to be maximum under the incidence of interferences. However, we encountered the discrepancy between transmitting antenna patterns and receiving ones. We investigated why this discrepancy arises, although a reciprocity theorem is effective between the transmitting pattern and the receiving one. Through these investigations, we derived the equation which determines the matched load impedances of the array elements and solved it numerically up to five elements. We also derived an equation to evaluate output voltages which are summed up into an output of the array and confirmed the coincidence between the transmitting pattern and the receiving one.

Dual-Mode Space-Temporal Simultaneous Processing Equalizer

A tapped delayed line adaptive array antenna (TDL-AAA) and a space-temporal simultaneous processing equalizer (ST-SPE) are proposed as simple space-temporal equalizers based on minimum mean square error (MMSE) criterion. The ST-SPE has a compact hardware with a small number of taps compared to that of the TDL-AAA. The ST-SPE can reduce the computational complexity of the space-temporal joint equalization and it works effectively under the minimum phase condition such as appeared at line-of-sight (LOS) propagation environments at a high antenna height base station. However the ST-SPE cannot work under a non-minimum phase condition caused under N-LOS (non-line-of-sight). On the other hand, the TDL-AAA whose reference signal is synchronized at the center tap (TDL-AAAC) can work even in the non-minimum phase condition. In this paper, we propose a dual-mode space-temporal simultaneous processing equalizer (Dual-mode ST-SPE) which has a simple configuration and also works in non-minimum phase condition. The Dual-mode ST-SPE can reduce the computational complexity compared to the TDL-AAAC.