Adaptive array antenna combined with tapped delay line using processing gain for direct‐sequence/spread‐spectrum multiple‐access system

Abstract

AbstractAs countermeasures for co‐channel interference from simultaneously accessing users in the spread spectrum multiple access (SSMA), co‐channel interference cancellers using the adaptive digital filters, and array antennas and their combinations have been proposed. However, in these systems, it is necessary to generate a reference signal with a large correlation with the desired wave in receiver so that their coefficients can be updated adaptively. In the SSMA, a method has been proposed in which the reference signal generated by respreading of the demodulated data is used for the updating of the weight coefficient of the array antenna. However, as the input interference and the noise power increase, the convergence of the array antenna becomes difficult. Also, in the conventional method, most of the discussions have been limited to an array antenna in which one weight coefficient corresponds to an array element. However, as the interference signal bandwidth increases, the wideband interference signals cannot sufficiently be removed from the antenna output.In this paper, from the viewpoint of improving the co‐channel interference elimination capability of the array antenna in the space domain, the reduction of the noise component and the co‐channel interference in the error signal for the array antenna updating is considered and an updating method for an adaptive array antenna using the spread spectrum processing gain is proposed. Further, from the viewpoint of increasing the co‐channel interference elimination capability of the array antenna in the time domain, a receiving system using a TDL (tapped delay line) adaptive array antenna is proposed to increase the frequency characteristics of the bandstop filter for a wideband spread spectrum signal.Finally, by means of a computer simulation, the basic characteristics of the updating method and the performance of the receiving system are evaluated. It is shown that good characteristics can be obtained under an environment with co‐channel interference and noise power higher than in the conventional system.