Code acquisition of a DS-CDMA receiver with antenna arrays and blind adaptation for air traffic control

Abstract

Code-Division Multiple-Access (CDMA) [1] is widely used in both civil and military applications. It does take advantages from the system characteristics. For example, higher data rate and user capacity, better multipath resolution [2] and resistance to jamming, low probability of interception, accurate timing and ranging, and more importantly, stronger ability to suppress interference and jamming. To airborne applications, such as air traffic control, the use of CDMA as an alternative is highly suggested [3]. The reasons to do so are as follows. First, radio systems are spectrum sensitive, especially to the airborne environments. Careful spectrum regulation is needed. Second, most of current systems available are narrowband. Adding new system to limited spectrum resources is very difficult. Third, CDMA is wideband in nature. The signal power is spread and hides below the white noise level. As a result, its interference to narrowband systems is marginal. Fourth, CDMA receivers [4] by proper design have the ability of suppressing narrowband interference and Multiple Access Interference (MAI). Fifth, adaptive filter algorithms can provide excellent tracking performance to airborne dynamics. Sixth, incorporating the use of antenna arrays [5] may further improve the performance to interference suppression and user capacity. In this paper, proposed is an adaptive DS-CDMA receiver with antenna arrays and blind adaptation. This receiver structure assumes the same amount of information as the conventional matched filter receiver, namely, the signature sequence and the synchronization information (the timing and the carrier phase) of the desired user. In reality, the signature sequence is usually available at the receiver, while the code timing [6] and the carrier phase have to be estimated. As a consequence, the development of reliable and efficient code acquisition algorithm to the proposed receiver structure is important. The novelty of this algorithm is that the estimator is based on processing the weight vector of the adaptive receiver and the only side information the receiver requires in order to form its estimate is the spreading sequence of the desired user.