Multi-Stage RLS OFDM Adaptive Array Antenna with Short Pilot Symbols

Takeo FUJII  Yukihiro KAMIYA  Yasuo SUZUKI  

IEICE TRANSACTIONS on Communications   Vol.E89-B    No.5    pp.1589-1597
Publication Date: 2006/05/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e89-b.5.1589
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
OFDM,  adaptive array antenna,  RLS,  packet communication,  

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Post-FFT type orthogonal frequency division multiplexing (OFDM) adaptive array antennas can reduce the co-channel interference with a few antenna elements under multi-path fading environments. However, the Post-FFT type OFDM adaptive array antennas require a lot of pilot symbols in order to determine the optimal weights in each subcarrier. In packet communication systems, since the data are transmitted burst by burst, the ratio of the effective data in a channel decreases when the long pilot symbols are used. Recursive least squares (RLS) algorithm is one of the weight optimization algorithm with fast convergence based on minimum mean square errors (MMSE). However, the optimal weight determination with a few pilot symbols is difficult. Therefore, in this paper, we propose a novel multi-stage RLS OFDM adaptive array antenna for realizing weight determination with a few pilot symbols. In the proposed method, the weights are optimized by using a multiple stage structure with the stored pilot symbols. Here, the initial weights and the initial inverse matrix of correlation matrix are decided by the results of the weight determination in the adjacent subcarriers of the previous stage. As a result, the weight determination with a few pilot symbols can be achieved.