Frequency correlation characteristics for broadband MIMO systems in indoor NLOS propagation environment

1. INTRODUCTION Due to the recent popularity of mobile phones and broadband wireless LANs, broadband wireless systems employing Orthogonal Frequency Division Multiplexing (OFDM) signals were introduced to combat the effects of multi-path fading in indoor wireless LAN systems. Moreover, Multiple Input Multiple Output (MIMO) is incorporated into these broadband wireless systems using OFDM signals to achieve higher transmission speeds without expanding the frequency band [1]. Since the channel capacity of a MIMO channel greatly depends on the fading environment between the transmission and reception antennas, the difference in radio frequency also affects the capacity of the broadband MIMO channels. The channel capacity of MIMO channels based on the antenna arrangements and the element spacing in an actual non-line-of-sight (NLOS) indoor environment was investigated to clarify the relationship between the antenna configuration and the propagation channels in MIMO systems [2]. Although it is well known that the frequency correlation characteristics can be used to judge the transmission quality in conventional broadband propagation channels [3], no research has been done regarding the effect of the capacity of broadband MIMO channels. This paper investigates the frequency correlation characteristics of the channel capacity for broadband MIMO channels in NLOS indoor environments. Particularly, we focus on the dependency of the element spacing on the frequency correlation characteristics. Based on simulation and measurement results in NLOS indoor environments, we show that the calculation results agree well with the measured results. ENVIRONMENT 2.1 Analysis Model Figure 1 shows the propagation model considered in this paper. The height of this room is 3 m. We assume that the walls, partitions, ceiling, and floor are all constructed of metal. We used the ray-tracing method to analyze the propagation channels, and the numbers of reflections and diffractions are set to 20 and 2, respectively. As shown in Fig. 1, a transmission antenna is placed at Location X (x = 14 m, y = 2 m), at the height of 0.7 m and a reception antenna is placed inside the partitions. The number of receiving points is 100. We employ four transmission and four reception antennas. The element spacing of the array is changed from 0.1 to 1.5 wavelengths. The carrier frequency, fc, is 5,200 MHz, and we use the frequencies fc+0.5×α (α = 1 to 10) to calculate the frequency correlation of the channel capacity in the MIMO channels. In this paper, the frequency correlation is obtained by using the …