Smart Antenna Based OVSF Code Assignment for WCDMA Networks

Abstract

This paper presents a new method for dynamic allocation of orthogonal variable spreading factor (OVSF) codes in WCDMA networks where each base station is equipped with an adaptive antenna array (AAA). Previous works about OVSF code assignment problem deal with the code limited case. Here, we investigate the feasibility to turn the problem into the SIR limited case. With our scheme, the new call request is allocated an OVSF code that may be currently used by an active user whose downlink beam has the smallest spatial correlation with the channel vector of the requesting user, as long as desired SIR level is achieved. The performance of the new scheme is justified through computer simulations under different traffic load conditions.

Performance of Adaptive Antenna Array Based Dynamic OVSF Code Assignment for Multipath Propagation and Multicell Environment

“…It is clear that AAA-DCA is more effective for higher traffic loads achieving up to 30% less blocking at traffic load of 16 Erlang. Blocking probability performance of the AAA-DCA for non-ideal channel conditions studied in this paper is slightly worse than that for ideal channel conditions studied in [10]. As traffic load gets higher, the difference between ideal and nonideal case becomes prominent.…”

“…The common ground of above mentioned OVSF code assignment schemes is that they are constrained by code limited case in which the system can not assign more than available code rates. An OVSF code assignment technique based on employing an adaptive antenna array (AAA) at the BS of a WCDMA network, which is referred as AAA-DCA, has been recently proposed in [10]. The idea with the AAA-DCA is to exploit spatial diversity of users which fall in different downlink beams of the AAA.…”

“…Hence, rather than code limitation, SINR limitation becomes important issue for the AAA-DCA. The performance of AAA-DCA scheme in [10] is, however, evaluated for ideal and simple scenario where there is no multipath propagation and only single cell exists. In this work, we extend this work for more realistic wireless scenario where multipath and multicell environment is considered.…”

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An OVSF code assignment method using adaptive antenna (AAA) array in WCDMA network has been previously proposed [10] and it has been shown that AAA based dynamic code assignment (AAA-DCA) significantly reduces call blocking probability and increases spectral efficiency in the system when compared to conventional code assignment (CCA) and widely known dynamic code assignment (DCA). In AAA-DCA, OVSF code of an existing user can be reused for the new user as long as downlink weight vector of the existing user and channel vector of the new user have the smallest spatial correlation, and estimated SINR of the new user remains above threshold.

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“…In AAA-DCA, OVSF code of an existing user can be reused for the new user as long as downlink weight vector of the existing user and channel vector of the new user have the smallest spatial correlation, and estimated SINR of the new user remains above threshold. However, ideal propagation conditions having a single cell with no multipath propagation were considered in [10]. In this work, performance of the AAA-DCA is investigated under more realistic wireless scenario where there is multicell environment and multipath propagation exists.…”