A novel CMA adaptive array antenna achieving asynchronous 2D-RAKE receiver for M-ary/SS signals

M-ary spread spectrum (M-ary/SS) is used as a high efficiency SS system and is employed in various systems such as IEEE 802.11b WLAN. Furthermore, it is being considered for use in DS-UWB as a candidate for a future PAN (personal area network). However, the acquisition of the bit timing requires additional preambles or separately-transmitted signals. These additional preambles are also used to estimate the transfer function of the channel in order to realize RAKE combining of delayed signals. We propose a novel algorithm based on CMA criteria that can not only detect the bit timing but also realize two-dimensional (2D), i.e., spatio-temporal, RAKE using an array antenna asynchronously, without any additional preamble or separate signals for synchronization. The proposed scheme achieves 2D-RAKE by processing only the Hadamard code employed by M-ary/SS. The performance is verified through computer simulations.