Improving the direction-of-arrival resolution via double code filtering in WCDMA

This paper presents a new method for improving the azimuthal resolution at the base station of the WCDMA system employing antenna array. The method uses two covariance matrices resulting from double code filtering. The first matrix is extracted by the traditional de-spreading and results in noisy signal estimate. The other matrix is extracted by an orthogonal re-spread method. The orthogonal re-spread (OR) is a new extraction method for the spatial correlation matrix of interference and noise only. The method uses one of the remaining orthogonal variable spreading factor code (OVSF) that is orthogonal to all traffic and control channels to spread energy form the desired user while attempting to maintain the same level of multiple access interference. In the presented method information obtained from OR correlation matrix is used to suppress interference and improve the signal resolution via the whitening (Mahalanobis) transform. Since the proposed method operates as additional transform on the sample covariance matrix, it can be used in conjunction with all DoA estimation methods.