INTERFERENCE CANCELLATION FOR COMMON CODE MULTIPLE-ACCESS TRANSMISSION

In this paper, we propose a multiple access technique using a simple i nterference canceller for common code transmission. In the proposed sy stem, we adopt a common code for a receiver oriented system. All the t ransmitters utilize the same pseudo noise (PN) code to communicate wit h a receiver. Here the receiver structure becomes very simple with onl y one matched filter (MF). The proposed system has two very important merits. One is to avoid packet collisions by means of an interference cancellation method based on a common code chip shift transmission tec hnique. That is, in order to avoid interference, which occurs because all the received signals have the same PN code, the same data with dif ferent timing are transmitted in two channels. In this study, we defin e and evaluate three types of packet collision which can be reduced by the canceller. The other merit is to reduce the system degradation du e to the correlation side-lobes by means of a side-lobe canceller. In spread spectrum (SS) communication systems with PN codes like M-sequen ces, the correlation side-lobes appear at the detector in the case of the polarity data changing from +/-1 to -/+ 1. The side-lobes degrade the system quality. Therefore in this system a interference canceller operates to cancel the correlation side-lobes and attempts to reduce t he system degradation. Finally, by our cancellation method it becomes possible to realize a simple multiple access using only one PN code un der the condition of a receiver oriented system without a base station .