Analog Decoding Method for Simplified Short-Range MIMO Transmission

Abstract

A novel analog decoding method using only 90-degree phase shifters is proposed to simplify the decoding method for short-range multiple-input multiple-output (MIMO) transmission. In a short-range MIMO transmission, an optimal element spacing that maximizes the channel capacity exists for a given transmit distance between the transmitter and receiver. We focus on the fact that the weight matrix by zero forcing (ZF) at the optimal element spacing can be obtained by using dividers and 90degree phase shifters because it can be expressed by a unitary matrix. The channel capacity by the proposed method is next derived for the evaluation of the exact limitation of the channel capacity. Moreover, it is shown that an optimal weight when using directional antennas can be expressed by using only dividers, 90-degree phase shifters, and attenuators, regardless of the beam width of the directional antenna. Finally, bit error rate and channel capacity evaluations by both simulation and measurement confirm the effectiveness of the proposed method.

Broadband transmission performance and antenna displacement tolerance in 4×4 short-range MIMO simple decoding

“…Because the computational complexity required for weight multiplication in MIMO detection increases in proportion to the square of the number of elements, the power consumption also increases when the number of elements is increased to achieve higher transmission rate. To solve the problem, we have proposed a simple decoding method [6] that reduces the complexity by performing MIMO detection with an analog circuit. The principle of the method is as follows.…”

“…In SR-MIMO transmission, there is an optimum element spacing that maximizes the channel capacity [8] [9]. With the optimum spacing, a channel matrix with the optimum element spacing is approximated by (1) [6].…”

“…As shown in (1), phase differences between propagation channels with the optimum element spacing are and . In this case, the ZF weight matrix for MIMO detection is approximated by (2) [6].…”

“…To solve the problem, we have proposed a simple decoding method [6] that reduces the complexity by performing MIMO detection with an analog circuit. In the above applications, Tx and Rx array antennas are fixedly installed; the propagation channels between Tx and Rx array antennas are static.…”

“…The method's performance in 4x4 SR-MIMO transmission was also reported in [6]; however, the ideal analog circuit characteristics were assumed and no evaluations using an actual analog circuit have yet been performed. Although the evaluations in previous studies [6] [7] were performed under the condition that Tx and Rx array antennas are in the opposite position with no antenna displacement, it is assumed that displacement occurs when the array antennas are actually installed. In this paper, we show the broadband transmission performance and antenna displacement tolerance obtained by a 4x4 SR-MIMO prototype system for quasi-millimeter wave band (25 GHz band) when employing the method.…”