Subband Adaptive Array for DS-CDMA Mobile Radio
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Subband Adaptive Array for DS-CDMA Mobile Radio Xuan Nam Tran Department of Electronic Engineering, The University of Electro-Communications, Chofugaoka 1-5-1, Chofu-shi, Tokyo 182-8585, Japan Email: [email protected]
Takanori Omata Department of Electronic Engineering, The University of Electro-Communications, Chofugaoka 1-5-1, Chofu-shi, Tokyo 182-8585, Japan Core Network Planning Department and Switching Network Planning Department, Vodafone K.K., Atago 2-5-1, Minato-ku, Tokyo 105-6205, Japan Email: [email protected]
Tetsuki Taniguchi Department of Electronic Engineering, The University of Electro-Communications, Chofugaoka 1-5-1, Chofu-shi, Tokyo 182-8585, Japan Email: [email protected]
Yoshio Karasawa Department of Electronic Engineering, The University of Electro-Communications, Chofugaoka 1-5-1, Chofu-shi, Tokyo 182-8585, Japan Email: [email protected] Received 15 April 2003; Revised 24 September 2003; Recommended for Publication by Mukund Padmanabhan We propose a novel scheme of subband adaptive array (SBAA) for direct-sequence code division multiple access (DS-CDMA). The scheme exploits the spreading code and pilot signal as the reference signal to estimate the propagation channel. Moreover, instead of combining the array outputs at each output tap using a synthesis filter and then despreading them, we despread directly the array outputs at each output tap by the desired user’s code to save the synthesis filter. Although its configuration is far different from that of 2D RAKEs, the proposed scheme exhibits relatively equivalent performance of 2D RAKEs while having less computation load due to utilising adaptive signal processing in subbands. Simulation programs are carried out to explore the performance of the scheme and compare its performance with that of the standard 2D RAKE. Keywords and phrases: subband adaptive array, CDMA, RAKE, multipath fading.
1.
INTRODUCTION
Digital mobile communications are affected by multipath fading and interference causing reduced channel capacity and impaired signal quality. One approach to overcome the problem is to use the spread spectrum or specifically code division multiple access (CDMA). The use of orthogonal codes with large processing gain can help to reduce the cochannel interference (CCI) and prevent users from interfering with each other, that is, reduce the multiple access interference (MAI) [1]. Another approach to cancelling interference and increasing channel capacity is to employ array antenna at the base station. The use of an array antenna with an appropriate adaptive algorithm adds another dimension, namely,
spatial dimension to channel estimation resulting in spatiotemporal signal processing which has been realised as an efficient scheme for improvement of capacity and interference suppression [2]. The combination of an array antenna and CDMA to maximise performance benefits was first presented by Compton in [3] and studied further in [4, 5, 6, 7, 8, 9]. It was clearly shown that this combination helps to greatly reduce inte
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