Combination between CMA and On-Off Algorithms for Adaptive Array Antenna

During the last decade, an adaptive antenna has considerable received the interest for mobile communication systems. This is because it can increase the system capacity by reducing interference. To achieve the interference reduction, an adaptive algorithm is necessary. There are a number of the adaptive algorithms proposed to improve the signal-to-interference plus noise ratio (SINR) in such the systems i.e. [1]. Recently, an adaptive on-off algorithm was introduced to achieve a high SINR [2]-[3]. This approach maximizes the array output power. The SINR improvement using the algorithm depends on the strength of received signals. Namely, the algorithm work well if the power of the desired signal is sufficiently stronger than that of interference. It is know that generally an adaptive antenna using on-off algorithm adjusts its main beam to the desired signal. Nevertheless, its nullity does not appear at the interference direction. Another popular adaptive algorithm recently proposed in [4] is a constant modulus algorithm (CMA) which is a blind algorithm. The algorithm does not need a training sequence for adaptation. It can eliminate interference with the condition that the transmitted signal has a constant envelope, for example, a frequencyor phase-modulated signal. This is because the interference signal involves the amplitude fluctuation on the received signal. The main drawback of applying the CMA to the adaptive antenna system is its slow convergence property. It was reported that the convergence behavior of CMA heavily depends on its initial condition [5]. Recently, the problem of CMA convergence property was resolved by using the concept of the digital beam-switching initialization for CMA [6]. However, it is still sensitive to convergence because there are only sixteen initial beams used for adaptation of CMA. Moreover, an adaptive antenna using CMA has a nullity at the interference signal but it does not guarantee whether its main beam directs to the desired signal. In this paper, we propose a combination between CMA and on-off algorithms. The on-off algorithm is utilized to generate an initial beam for CMA. Then, CMA is used for adaptation to eliminate interference. After introduction, a combination between CMA and on-off algorithms is presented via its derivation in Section 2. Simulation results are shown to validate the performance of the proposed technique in Section 3. Finally, the conclusions are drawn in Section 4.