List of Figures List of Tables Preface Acknowledgments 1: Multiuser Detection For Wireless Networks 1. Future Generation Wireless Networks 1.1 Third Generation (3G) Cellular Networks 1.2 Wireless Application Protocol (WAP) 1.3 Network Costs for Data Transmission 1.4 Wireless Networks for Unlicensed Bands: WiFi, WiMax, HomeRF, Bluetooth and Infostations 1.5 Ad Hoc Networks 1.6 Cross-Layer Design 2. Introduction to Multiuser Receivers: Pros and Cons 2.1 Performance of Matched Filter Receivers 2.2 Multiuser Detectors 2.3 Performance of Blind Receivers 3. Multiuser Detection for Next Generation Wireless Networks 4. Multi-Rate Multiuser Detection 5. Information Theoretic Aspects: Spectral Efficiency 6. Multiuser Detection in Cross-Layer Design: Introductory Remarks and Book Outline 2: Integrated Radio Resource Allocation 1. Introduction to Radio Resource Allocation 2. Power Control 3. Integrated Power Control and Multiuser Detection 4. Access Control, Power Control and Multiuser Detection 5. Traffic-Aided Multiuser Detection 6. Medium Access Control for Multipacket Reception Networks 7. Routing and Multiuser Detection in Ad Hoc Networks 8. Admission Control: General Framework 3: Asymptotic Capacity For Wireless Networks With Multiuser Receivers 1. Effective Bandwidths and Capacity for Linear Receivers in Cellular Networks 1.1 General Formulation for Synchronous Networks 1.2 Partial Hybrid Networks 1.3 Optimal Signature Sequences 1.4 Multipath Fading Channels 1.5 Multi-Rate Networks 1.6 Asynchronous Networks 1.7 Imperfect Power Control 1.8 Blind and Group-Blind Multiuser Receivers 2. Ad Hoc Networks 2.1 Asymptotic Capacity 2.2 Capacity for Finite Networks: Simulations 2.3 Implications for Admission Control 4: Integrated Admission Control 1. Cellular Wireless Networks 2. Ad Hoc Networks 5: Multiuser Detection In Cross-Layer Design: Perspectives List of Acronyms References About the authors Index

Wireless Networks: Multiuser Detection in Cross-Layer Design

We provide a rigorous mathematical analysis of two communication strategies: soft decode-and-forward (soft-DF) for relay channels and soft partial interference-cancelation (soft-IC) for interference channels. Both strategies involve soft estimation, which assists the decoding process. We consider LDPC codes, not because of their practical benefits, but because of their analytic tractability, which enables an asymptotic analysis similar to random coding methods of information theory. Unlike some works on the closely-related demodulate-and-forward, we assume non-memoryless, code-structure-aware estimation. With soft-DF, we develop simultaneous density evolution to bound the decoding error probability at the destination. This result applies to erasure relay channels. In one variant of soft-DF, the relay applies Wyner-Ziv coding to enhance its communication with the destination, borrowing from compress-and-forward. To analyze soft-IC, we adapt existing techniques for iterative multiuser detection, and focus on binary-input additive white Gaussian noise interference channels. We prove that optimal point-to-point codes are unsuitable for soft-IC, as well as for all strategies that apply partial decoding to improve upon single-user detection and multiuser detection, including Han-Kobayashi.

Soft-Decoding-Based Strategies for Relay and Interference Channels: Analysis and Achievable Rates Using LDPC Codes

This paper considers robust code division multiple access (CDMA) system design and capacity analysis under disguised jamming, where the jammer generates a fake signal using the same spreading code, constellation, and pulse shaping filter as that of the authorized signal. Unlike Gaussian jamming, which is destructive only when jamming is dominant, disguised jamming can be devastating even if the jamming power is comparable to the signal power. In this paper, first, we analyze the performance of the conventional CDMA under disguised jamming, and show that due to the symmetricity between the authorized signal and the jamming interference, the receiver cannot really distinguish the authorized signal from jamming, leading to complete communication failure. Second, we propose to combat disguised jamming using secure scrambling. Instead of using conventional scrambling codes, we apply advanced encryption standard to generate the security-enhanced scrambling codes. Theoretical analysis based on the arbitrarily varying channel model shows that the capacity of conventional CDMA without secure scrambling under disguised jamming is actually zero; however, secure scrambling can break the symmetricity between the authorized signal and the jamming interference, and hence ensures positive channel capacity under disguised jamming. Numerical examples are provided to demonstrate the effectiveness of secure scrambling in combating disguised jamming.

CDMA System Design and Capacity Analysis Under Disguised Jamming

When overlaying spread spectrum (SS) transmission over a narrowband system, the performance of the spread spectrum system will be significantly degraded due to the interference from the narrowband signal. This paper proposes two computationally attractive and efficient adaptive techniques for narrowband interference (NBI) suppression in DS-CDMA system: adaptive linear predictor algorithm and adaptive NBI re-estimation algorithm. Unlike existing techniques in literature which use either estimator/subtracter approach or code-aided approach, the proposed methods combine these two approaches together and show that a much better performance can be achieved. In addition, the proposed algorithms are blind and do not require any training symbols and interference characteristics. The proposed methods not only provide faster convergence speed than the pure code-aided approach (without using a predictor and subtractor), but also give better BER performance

Adaptive Blind Narrowband Interference Cancellation for Multi-User Detection

The generalized receiver (GR) based on a generalized approach to signal processing (GASP) in noise is investigated in a direct-sequence code-division multiple access (DS-CDMA) wireless communication system with frequency-selective channels. We consider four avenues: linear equalization with finite impulse response (FIR) beamforming filters; channel estimation and spatially correlation; optimal combining; and partial cancellation. We investigate the GR with simple linear equalization and FIR beamforming filters. Numerical results and simulation show that the GR with FIR beamforming filters surpasses in performance the optimum infinite impulse response beamforming filters with conventional receivers, and can closely approach the performance of GR with infinite impulse response beamforming filters. Channel estimation errors are taken into consideration so that DS-CDMA wireless communication system performance will not be degraded under practical channel estimation. GR takes an estimation error of a maximum likelihood (ML) multiple-input multiple-output (MIMO) channel estimation and GR spatially correlation into account in computation of minimum mean square error (MMSE) and log-likelihood ratio (LLR) of each coded bit. The symbol error rate (SER) performance of DS-CDMA employing GR with a quadrature sub-branch hybrid selection/maximal-ratio combining (HS/MRC) scheme for 1-D modulations in Rayleigh fading is obtained and compared with that of conventional HS/MRC receivers. Procedure of selecting a partial cancelation factor (PCF) for the first stage of a hard-decision partial parallel interference cancellation (PPIC) of the GR employed in DS-CDMA wireless communication system is proposed. A range of optimal PCFs is derived based on the Price’s theorem. Computer simulation results show superiority in bit error rate (BER) performance that is very close to that potentially achieved and surpasses the BER performance of the real PCF for DS-CDMA systems discussed in literature.

Signal Processing by Generalized Receiver in DS-CDMA Wireless Communication Systems with Frequency-Selective Channels

A low-complexity multiuser receiver for turbo-coded DS-CDMA systems is presented to perform jointly iterative multiuser detection and turbo decoding. The proposed approach consists of a new multistage partial parallel interference cancellation (NPPIC) detector and K single-user turbo decoders, where K is the number of active CDMA users. The NPPIC detector is derived based on the single-user maximum a posteriori criterion and has a similar simple structure to the conventional partial parallel interference cancellation scheme presented by Divsalar et al. (see IEEE Trans. Commun., vol.46, p.258-268, Feb. 1998). A prominent feature of this detector is that it delivers interference-cancelled soft outputs to the turbo decoders and utilizes the soft information from the turbo decoders' output. Extensive computer simulations demonstrate that the cooperation between NPPIC and turbo decoding offers significant performance gain over the traditional non-iterative receivers and performs comparably to some existing iterative schemes of much higher complexity.

An iterative multiuser receiver using partial parallel interference cancellation for turbo-coded DS-CDMA systems

This paper presents a new nonlinear approach for narrowband interference (NBI) suppression in code-division multiple-access (CDMA) systems. The proposed scheme is an adaptive nonlinear predictor that consists of an (N+1)-level quantizer, four adders, and two adaptive linear filters, where N is the number of users in the CDMA system. Both adaptive filters have the same coefficients at each iteration: one for feedforward estimation of NBI and the other for feedback compensation for the estimated result. It could be regarded as an improved version of the nonlinear predictor with offset outputs presented recently by Wang et al. (1996). Computer simulation results support that the improved offset predictor performs much better than the original one under the same complexity. As compared with the nearly optimal approximate conditional mean filter, it achieves almost the same performance even at very low signal-to-noise ratio but involves much less complexity.

A new narrowband interference suppression scheme for spread-spectrum CDMA communications

This paper presents a new soft-input soft-output multistage partial parallel interference cancellation (PPIC) detector for direct-sequence code-division multiple-access (DS-CDMA) systems. The proposed detector has a similar simple structure to the conventional PPIC scheme presented by Divsalar et al. (1998). A new way of reliability iterating is derived based on the single-user maximum a posteriori (MAP) criterion. At each stage, extrinsic information is extracted and then used as the a priori information for the next stage. Extensive computer simulations have shown that the proposed approach is capable of offering a good performance gain over the conventional PPIC scheme and some other well-known multiuser detectors, especially when the system load is heavy.

Soft-input soft-output partial parallel interference cancellation for DS-CDMA systems

In this paper, we propose a reduced-complexity interference suppression strategy to achieve well-conditioned power control for direct-sequence code-division multiple access systems. The proposed method can be regarded as a simplified version of the power control scheme presented by Ulukus and Yates, which employs a complicated instantaneous minimum mean-squared error (MMSE) filter for interference suppression. In the proposed structure, a new method is developed for estimation of the required parameters for power control and interference suppression is attained through adaptive filtering. As compared to the instantaneous MMSE scheme, the proposed adaptive method achieves similar convergence performance with much lower complexity.

Adaptive interference suppression with power control for CDMA systems

A low-complexity power control scheme for direct-sequence code-division multiple access systems is presented. In the proposed structure, we exploit the interference cancellation capability of the turbo partial parallel interference cancellation (TPPIC) algorithm presented by Wu and Wang (see Proc. 2001 IEEE Global Telecommun. Conf (Globecom 2001), San Antonio, TX, Nov. 2001, p.244-248). A new method for parameter estimation is also presented and is integrated with the powerful TPPIC in power control algorithm design. Computer simulation results show that this new approach significantly outperforms the previous scheme using conventional parallel interference cancellation, where both involve the same order of complexity. As compared to the more complicated power control methods using minimum mean-squared error (MMSE) filtering, the proposed approach still provides better performance but involves much less complexity.

Kuo-Ming Wu

Papers

An iterative multiuser receiver using partial parallel interference cancellation for turbo-coded DS-CDMA systems

A new narrowband interference suppression scheme for spread-spectrum CDMA communications

Soft-input soft-output partial parallel interference cancellation for DS-CDMA systems

Adaptive interference suppression with power control for CDMA systems

A power control scheme using turbo partial parallel interference cancellation for DS-CDMA wireless communications