Analytical bit error rate performance of DS-CDMA ad hoc networks using large area synchronous spreading sequences

Abstract

The performance of large area synchronous (LAS) direct sequence code division multiple access (DS-CDMA) assisted ad hoc networks is investigated in the context of a single-hop infinite mesh of rectilinearly located ad hoc nodes. It is shown that LAS DS-CDMA exhibits a significantly better performance than the family of traditional spreading sequences used in a quasisynchronous DS-CDMA scenario having a low number of resolvable multipath components and a sufficiently high number of RAKE receiver branches. The benefits of LAS codes in ad hoc networks are multifold: (i) Their performance is noise-limited, rather than interference-limited, provided that the multipath and multi-user interference arrives within their interference free window. (ii) Under the same conditions LAS codes are robust against the 'near -far' effects imposed by ad hoc networks operating without base-station-aided power control, without accurate synchronisation and without implementationally complex interference cancellers. IntroductionThe family of large area synchronous (LAS) [1] spreading codes exhibits an interference free window (IFW), where the off-peak aperiodic auto-correlations and crosscorrelations become zero [2]. These attractive correlation properties assist us in eliminating the effects of both the multipath interference (MPI) and multiple access interference (MAI). Initial comparative studies between LAS-CDMA and traditional code division multiple access (CDMA) were presented, for example in [1]. LAS codes are generated by combining large area (LA) [3,4] codes and loosely synchronous (LS) [4,5] codes. Li [3] proposed various construction schemes for LA codes and analysed the performance of LA-CDMA, which exhibited higher spectral efficiency than traditional CDMA. Stanczak et al. [5] focused their attention on contriving systematic methods for the construction of LS codes. Choi and Hanzo [6] investigated the design of efficient and flexible LAS codes having an increased duty ratio, which resulted in a higher number of codes and hence a higher number of supported users than previous designs. An entire LAS-CDMA network was studied in [7]. For the detailed construction methods of LA, LS and LAS codes please refer to [3 -5].Again, as a benefit of having an IFW, LAS codes have the ability to support asynchronous operation in ad hoc networks, provided that both the propagation delay and the multipath-induced dispersion are limited to the duration of the IFW. If this condition is satisfied, the system's performance becomes essentially noise-limited, rather than interference-limited. Ad hoc networks have been studied for decades and have evolved to sensor networks and mesh networks [8,9], both of which potentially support a large number of nodes in the network. Although the application of LAS codes in cellular networks is limited by the low number of available spreading codes, this impediment is less restrictive in ad hoc networks, since the nodes only communicate with their neighbours. In this paper, we will focus our attention...

On the performance of the Code Division Duplex system using interference rejection codes

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