EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS Euro. Trans. Telecomms. 2007; 18:803–810 Published online 23 April 2007 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ett.1215 Letter Wireless Systems New quasi-orthogonal BCH-derived sequences for CDMA applications Cesaltina N. E. Ricardo 1 , Manuel D. Ortigueira 1 * and Jose ´ Anto ´nio B. Gerald 2 1 UNINOVA/DEE Campus da FCT da UNL, Quinta da Torre, 2825-114 Monte da Caparica, Portugal 2 Instituto Superior Te ´cnico and INESC, R. Alves Redol, 9, 2  1000-029 Lisboa, Portugal SUMMARY Based on two methods recently proposed—the ‘Ranging Criterion’ (RC) and the ‘Generators Ranging Criterion’ (GRC)—new (quasi-orthogonal) even BCH-derived sequences are generated which are very attractive for synchronous or quasi-synchronous Code Division Multiple-Access (CDMA) systems. Numerical results show that the new family of BCH-derived sequences can contain a higher number of quasi-orthogonal sequences with lower correlation values and higher processing gains (PGs) than the spreading sequences typically used in the third generation of mobile communications system, UMTS or in the recent large area synchronised CDMA (LAS-CDMA) technology. It is shown that the even BCH- derived sequences are easily generated by a linear shift register generator, allowing the construction of systems with receiver structures of low complexity as compared with those of quasi-synchronous systems using low correlation zone sequences, as for instance the LAS-CDMA system. Copyright # 2007 John Wiley & Sons, Ltd. 1. INTRODUCTION In recent years, the Code Division Multiple-Access (CDMA) technology has been used in cellular mobile communication systems (for instance, UMTS/IMT-2000 and IS-95) with two aims: (1) to counterbalance the pro- blem of spectrum overload due to the excessive growth of the number of users; (2) to follow the new tendencies of the telecommunications market in providing a large variety of services, including broadband applications, with identical quality of service of wired networks. These requirements are completely satisfied by the current UMTS system, that uses the wideband CDMA (W-CDMA) tech- nique to provide higher capacity, coverage, and spectral and power efficiencies, than the systems based on TDMA, FDMA or narrowband CDMA (as IS-95) [1–4]. Additionally, the Direct Sequence CDMA (DS-CDMA) form provides some other important features such as resis- tance against multipath fading and low interference. In these systems, each user is identified by a specific pseudo-noise (PN) code [5–9]. So, the average perfor- mance of these systems can degrade significantly when the number of active users increases, due to the increase in the level of multiple-access interference (MAI) in the channel [7, 9–14]. This depends on the (out-of-phase auto and cross) correlation properties of the PN spreading sequences [13, 14]. Hence, reduced values of out-of-phase autocorrelation and cross-correlation should be required, respectively, to make easier the synchronisation and to minimise (or eliminate) the MAI. This issue is very impor- tant, because it allows the capacity of CDMA systems to increase [7, 9, 11, 13]. For instance, the well-known Received 19 June 2005 Copyright # 2007 John Wiley & Sons, Ltd. Revised 3 February 2006 Accepted 23 October 2006 *Correspondence to: Manuel D. Ortigueira, UNINOVA/DEE Campus da FCT da UNL, Quinta da Torre, 2825-114 Monte da Caparica, Portugal. E-mail: mdortigueira@uninova.pt