Loosely Synchronised Spreading Code Aided Network Performance of Quasi-Synchronous UTRA-like TDD and FDD CDMA Systems

It is demonstrated that loosely synchronised (LS) spreading codes exhibit a so-called interference-free window, where both the autocorrelation and cross-correlation of the codes become zero. Therefore LS codes have the promise of mitigating the effects of both inter-symbolinterference and multiple-access-interference in time dispersive channels. Hence, LS codes have the potential of increasing the capacity of CDMA networks. The work reported has studied the achievable network performance and compared it to that of a UTRA-like time division duplex (TDD) and frequency division duplex (FDD) CDMA system using orthogonal variable rate spreading factor codes

Analytical BER Performance of DS-CDMA Ad Hoc Networks using Large Area Synchronized Spreading Codes

The family of operational CDMA systems is interference-limited owing to the Inter Symbol Interference (ISI) and the Multiple Access Interference (MAI) encountered. They are interference-limited, because the orthogonality of the spreading codes is typically destroyed by the frequency-selective fading channel and hence complex multiuser detectors have to be used for mitigating these impairments. By contrast, the family of Large Area Synchronous (LAS) codes exhibits an Interference Free Window (IFW), which renders them attractive for employment in cost-efficient quasi-synchronous ad hoc networks dispensing with power control. In this contribution we investigate the performance of LAS DS-CDMA assisted ad hoc networks in the context of a simple infinite mesh of rectilinear node topology and benchmark it against classic DS-CDMA using both random spreading sequences as well as Walsh-Hadamard and Orthogonal Gold codes. It is demonstrated that LAS DS-CDMA exhibits a significantly better performance than the family of classic DS-CDMA systems operating in a quasi-synchronous scenario associated with a high node density, a low number of resolvable paths and a sufficiently high number of RAKE receiver branches

Loosely synchronized spreading code aided network performance of quasi-synchronous UTRA-like TDD/CDMA systems

In this paper we investigate the achievable capacity of a UTRA-like Time Division Duplex (TDD) Code Division Multiple Access (CDMA) system employing Loosely Synchronized (LS) spreading codes. The family of operational CDMA systems is interference limited, suffering from Inter-Symbol-Interference (ISI), since the orthogonality of the spreading sequences is destroyed by the frequency selective channel. They also suffer from Multiple-Access-Interference (MAI) owing to the non-zero cross-correlations of the spreading codes. By contrast, the family of LS codes exhibits a so-called Interference Free Window (IFW), where both the auto-correlation and cross-correlation of the codes become zero. Therefore LS codes have the promise of mitigating the effects of both ISI and MAI in time dispersive channels. Hence, LS codes have the potential of increasing the capacity of CDMA networks. This contribution studies the achievable network performance in comparison to that of a UTRA-like TDD/CDMA system using Orthogonal Vari- MSO able Rate Spreading Factor (OVSF) codes

Interference-Free Broadband Single- and Multi-Carrier DS-CDMA

The choice of the direct sequence spreading code in DS-CDMA predetermines the properties of the system. This contribution demonstrates that the family of codes exhibiting an interference-free window (IFW) outperforms classic spreading codes, provided that the interfering multi-user and multipath components arrive within this IFW, which may be ensured with the aid of quasi-synchronous adaptive timing advance control. It is demonstrated that the IFW duration may be extended with the advent of multicarrier DS-CDMA proportionately to the number of subcarriers. Hence, the resultant MC DS-CDMA system is capable of exhibiting nearsingle-user performance without employing a multi-user detector. A limitation of the system is that the number of spreading codes exhibiting a certain IFW is limited, although this problem may be mitigated with the aid of novel code design principles