A MUSIC-Based Algorithm for Blind User Identification in Multiuser DS-CDMA
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A MUSIC-Based Algorithm for Blind User Identification in Multiuser DS-CDMA Afshin Haghighat Department of Electrical Engineering, Concordia University, Montreal, Quebec, Canada H3G 1M8 Email: [email protected]
M. Reza Soleymani Department of Electrical Engineering, Concordia University, Montreal, Quebec, Canada H3G 1M8 Email: [email protected] Received 29 July 2003; Revised 21 April 2004 A blind scheme based on multiple-signal classification (MUSIC) algorithm for user identification in a synchronous multiuser code-division multiple-access (CDMA) system is suggested. The scheme is blind in the sense that it does not require prior knowledge of the spreading codes. Spreading codes and users’ power are acquired by the scheme. Eigenvalue decomposition (EVD) is performed on the received signal, and then all the valid possible signature sequences are projected onto the subspaces. However, as a result of this process, some false solutions are also produced and the ambiguity seems unresolvable. Our approach is to apply a transformation derived from the results of the subspace decomposition on the received signal and then to inspect their statistics. It is shown that the second-order statistics of the transformed signal provides a reliable means for removing the false solutions. Keywords and phrases: blind, user identification, CDMA, MUSIC, multiuser.
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INTRODUCTION
CDMA-based systems are widely used in various wireless applications. In order to exploit the capacity of a CDMA system, multiuser detection techniques are essential. A large number of schemes and algorithms have been devised to enhance the performance and also to reduce the complexity of a CDMA receiver in a multiuser environment. In most cases, some prior knowledge of the user parameters, for example, the spreading code, timing, and power, is assumed. However, in a real system, this may not be the case. Users enter and exit the system irregularly and the base station has to keep track of the status of each user. Various methods could be used to transfer users parameters to the base station, however, one way or the other, they impose some overhead and reduce system capacity. Therefore, another important aspect of the CDMA reception is to assist multiuser detection schemes by user identification. In other words, it is desired to know how many active users are operating at any given time and who they are. This enables the receiver to dynamically adapt itself to the multiuser environment. This capability has a twofold benefit for a CDMA multiuser system. First, the receiver will be able to maximize the cancellation of multiple-access interference (MAI), since it has the updated information on other active users. Second, the degree of complexity, which is almost directly proportional to the performance of the re-
ceiver, can be optimized against the number of active users. In other words, when there are a small number of users, the receiver will be able to select a more complex detection algorithm to achieve a lower bit error rate. This is an attrac
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