Statistical Modeling of Multiple Access Interference Power: a Nakagami-m Random Variable

This paper proposes a statistical model for the total multiple access interference (MAI) power for both Direct-Sequence Code Division Multiple Access (DS-CDMA) and Multicarrier Code Division Multiple Access (MC-CDMA) systems. We consider the use of both Walsh-Hadamard (WH) and Gold spreading codes transmitting over the asynchronous uplink channel. Detailed signal models of both CDMA systems are derived illustrating the production of MAI under asynchronous conditions. The paper demonstrates the Gaussian nature of the total MAI and shows that the probability density function (pdf) of the total MAI power can be very accurately characterized by the Nakagami-m distribution

MIMO-aided near-capacity turbo transceivers: taxonomy and performance versus complexity

In this treatise, we firstly review the associated Multiple-Input Multiple-Output (MIMO) system theory and review the family of hard-decision and soft-decision based detection algorithms in the context of Spatial Division Multiplexing (SDM) systems. Our discussions culminate in the introduction of a range of powerful novel MIMO detectors, such as for example Markov Chain assisted Minimum Bit-Error Rate (MC-MBER) detectors, which are capable of reliably operating in the challenging high-importance rank-deficient scenarios, where there are more transmitters than receivers and hence the resultant channel-matrix becomes non-invertible. As a result, conventional detectors would exhibit a high residual error floor. We then invoke the Soft-Input Soft-Output (SISO) MIMO detectors for creating turbo-detected two- or three-stage concatenated SDM schemes and investigate their attainable performance in the light of their computational complexity. Finally, we introduce the powerful design tools of EXtrinsic Information Transfer (EXIT)-charts and characterize the achievable performance of the diverse near- capacity SISO detectors with the aid of EXIT charts

Ant-Colony-Based Multiuser Detection for MC DS-CDMA Systems

In this contribution we present a novel ant colony optimization (ACO) based multi-user detector (MUD) designed for synchronous multi-carrier direct sequence code division multiple access (MC DSCDMA) systems. The operation of the ACO-based MUD is based on the behaviour of the ant colony in nature. The ACO-based MUD aims for achieving the same bit-error-rate (BER) performance as the optimum maximum likelihood (ML) MUD, without carrying out an exhaustive search of the entire MC DS-CDMA search space constituted by all possible combinations of the received multi-user vectors. We will demonstrate that the system is capable of supporting almost as many users as the number of chips in the spreading sequence, while searching only a small fraction of the entire ML search space. It will also be demonstrated that the number of floating point operations per second is a factor of 108 lower for the proposed ACO-based MUD than that of the ML MUD, when supporting K = 32 users in a MC DS-CDMA system employing 31-chip Gold codes as the T-domain spreading sequence

Implementable Wireless Access for B3G Networks - III: Complexity Reducing Transceiver Structures

This article presents a comprehensive overview of some of the research conducted within Mobile VCE’s Core Wireless Access Research Programme,1 a key focus of which has naturally been on MIMO transceivers. The series of articles offers a coherent view of how the work was structured and comprises a compilation of material that has been presented in detail elsewhere (see references within the article). In this article MIMO channel measurements, analysis, and modeling, which were presented previously in the first article in this series of four, are utilized to develop compact and distributed antenna arrays. Parallel activities led to research into low-complexity MIMO single-user spacetime coding techniques, as well as SISO and MIMO multi-user CDMA-based transceivers for B3G systems. As well as feeding into the industry’s in-house research program, significant extensions of this work are now in hand, within Mobile VCE’s own core activity, aiming toward securing major improvements in delivery efficiency in future wireless systems through crosslayer operation

Characterizing CDMA downlink feasibility via effective interference

This paper models and analyses downlink power assignment feasibility in Code Division Multiple Access (CDMA) mobile networks. By discretizing the area into small segments, the power requirements are characterized via a matrix representation that separates user and system characteristics. We obtain a closed-form analytical expression of the so-called Perron-Frobenius eigenvalue of that matrix, which provides a quick assessment of the feasibility of the power assignment for each distribution of calls over the segments. Although the obtained relation is non-linear, it basically provides an effective interference characterisation of downlink feasibility. Our results allow for a fast evaluation of outage and blocking probabilities, and enable a quick evaluation of feasibility that may be used for Call Acceptance Control. \u

Performance Analysis of OFDM-CDMA Systems with Doppler Spread

6 pagesInternational audienceMulti carrier modulation are very sensitive to rapid time-varying multi-path channel characterized by Doppler spread. Although progress has been made in the description of the time variation, there is still considerable gaps in its effect especially on diversity gain acquired by time selectivity. This paper models a general case of time-varying channel effect on the OFDM-CDMA performance. This performance is measured through the Signal to Interference and Noise Ratio SINR at the output of the detector and the Bit Error Rate BER at the output of the channel decoder. The originality of the paper is twofold. First, we propose a simple tool to evaluate an analytical expression of the SINR independently on the spreading codes while taking into account their orthogonality. Second, we adapt a new technique to predict the BER at the output of the channel decoder from the link level simulation expressed in terms of the SINRs. We show by simulation the validity of our analytical models. We show also that the time variation of the channel would be favourable for system performance in MC-DS-CDMA system and QPSK constellation however it is destructive with other simulation assumptions

SINR evaluation of OFDM-CDMA systems with constant timing offset: asymptotic analysis

5 pagesThis article presents the impact of a constant timing error on the performance of a downlink 2 dimensional spreading OFDM-CDMA system. This impact is measured by the Signal to Interference plus Noise Ratio (SINR) degradation after equalization and despreading. Using random matrix theory, an asymptotic evaluation of the SINR is obtained. It is independent of the value of users' spreading code while taking into account their orthogonality. Simulation results are provided to evaluate and discuss the validity of this model