An adaptive array antenna with optimally formed beams for CDMA

Abstract

The adaptive antenna (AA) or smart antenna for mobile telecommunication especially for code division multiple access (CDMA) systems has developed at an extraordinary pace. Most professional people and related papers centered their attention on the so-called "optimum combining (OC)" AA which is represented by algorithms using least mean squares (LMS) and recursive least squares (RLS). These types of AA were able to provide an optimum signal to interference plus noise ratio (SINR), through the use of a desirable antenna radiation pattern whose mainlobe pointed towards the desired signal while the nulls pointed towards the source of interference. For computing these adaptive algorithms, the requirements of the CPU time and the memory usage are proportional to the number of antenna elements, and speed of computations depends on the velocity of the mobiles. Finally, there is a restriction on the number of users. In order to avoid the above shortcomings, this paper proposes a type of AA which is close to the category of "direction finding (DF)" AA, but it is a "beam forming in advance" array antenna with super low sidelobes. This AA possesses similar adaptive functions as found in the OCAA, but without the computation of complex weight vectors. When this AA is operating only a few computational procedures are needed. Another advantage of this AA is that it does not mind whether the number of users M is much larger than the number of antenna elements N or not.