Minimum mean-squared error iterative successive parallel arbitrated decision feedback detectors for DS-CDMA systems

In this paper we propose minimum mean squared error (MMSE) iterative successive parallel arbitrated decision feedback (DF) receivers for direct sequence code division multiple access (DS-CDMA) systems. We describe the MMSE design criterion for DF multiuser detectors along with successive, parallel and iterative interference cancellation structures. A novel efficient DF structure that employs successive cancellation with parallel arbitrated branches and a near-optimal low complexity user ordering algorithm are presented. The proposed DF receiver structure and the ordering algorithm are then combined with iterative cascaded DF stages for mitigating the deleterious effects of error propagation for convolutionally encoded systems with both Viterbi and turbo decoding as well as for uncoded schemes. We mathematically study the relations between the MMSE achieved by the analyzed DF structures, including the novel scheme, with imperfect and perfect feedback. Simulation results for an uplink scenario assess the new iterative DF detectors against linear receivers and evaluate the effects of error propagation of the new cancellation methods against existing ones

Adaptive and Iterative Multi-Branch MMSE Decision Feedback Detection Algorithms for MIMO Systems

In this work, decision feedback (DF) detection algorithms based on multiple processing branches for multi-input multi-output (MIMO) spatial multiplexing systems are proposed. The proposed detector employs multiple cancellation branches with receive filters that are obtained from a common matrix inverse and achieves a performance close to the maximum likelihood detector (MLD). Constrained minimum mean-squared error (MMSE) receive filters designed with constraints on the shape and magnitude of the feedback filters for the multi-branch MMSE DF (MB-MMSE-DF) receivers are presented. An adaptive implementation of the proposed MB-MMSE-DF detector is developed along with a recursive least squares-type algorithm for estimating the parameters of the receive filters when the channel is time-varying. A soft-output version of the MB-MMSE-DF detector is also proposed as a component of an iterative detection and decoding receiver structure. A computational complexity analysis shows that the MB-MMSE-DF detector does not require a significant additional complexity over the conventional MMSE-DF detector, whereas a diversity analysis discusses the diversity order achieved by the MB-MMSE-DF detector. Simulation results show that the MB-MMSE-DF detector achieves a performance superior to existing suboptimal detectors and close to the MLD, while requiring significantly lower complexity.Comment: 10 figures, 3 tables; IEEE Transactions on Wireless Communications, 201

Performance Comparison Between Variable and Fixed Signature Codes in DS-CDMA Systems

In a CDMA or SCMA system, users can use a fixed signature for the whole transmission interval. But there is the possibility for two users to have highly correlated signatures. Hence, high interference exists in the system, and it will degrade the performance. On the other hand, if the users use variable signatures for spreading each modulation symbol, then the interference between the users will not be fixed for all the transmissions.In this way, we are avoiding clustering error symbols resulted from the high interference. As we show in this thesis, this prediction about better performance of variable spreading is not always true. We have discussed several scenarios and shown the performance for both the fixed and variable signature codes

Coherent receiver design and analysis for interleaved division multiple access (IDMA)

This thesis discusses a new multiuser detection technique for cellular wireless communications. Multiuser communications is critical in cellular systems as multiple terminals (users) transmit to base stations (or wireless infrastructure). Efficient receiver methods are needed to maximise the performance of these links and maximise overall throughput and coverage while minimising inter-cell interference. Recently a new technique, Interleave-Division Multiple Access (IDMA), was developed as a variant of direct-sequence code division multiple access (DS-CDMA). In this new scheme users are separated by user specific interleavers, and each user is allocated a low rate code. As a result, the bandwidth expansion is devoted to the low rate code and not weaker spreading codes. IDMA has shown to have significant performance gains over traditional DS-CDMA with a modest increase in complexity. The literature on IDMA primarily focuses on the design of low rate forward error correcting (FEC) codes, as well as channel estimation. However, the practical aspects of an IDMA receiver such as timing acquisition, tracking, block asynchronous detection, and cellular analysis are rarely studied. The objective of this thesis is to design and analyse practical synchronisation, detection and power optimisation techniques for IDMA systems. It also, for the first time, provides a novel analysis and design of a multi-cell system employing a general multiuser receiver. These tools can be used to optimise and evaluate the performance of an IDMA communication system. The techniques presented in this work can be easily employed for DS-CDMA or other multiuser receiver designs with slight modification. Acquisition and synchronisation are essential processes that a base-station is required to perform before user's data can be detected and decoded. For high capacity IDMA systems, which can be heavily loaded and operate close to the channel capacity, the performance of acquisition and tracking can be severely affected by multiple access interference as well as severe drift. This thesis develops acquisition and synchronisation algorithms which can cope with heavy multiple access interference as well as high levels of drift. Once the timing points have been estimated for an IDMA receiver the detection and decoding process can proceed. An important issue with uplink systems is the alignment of frame boundaries for efficient detection. This thesis demonstrates how a fully asynchronous system can be modelled for detection. This thesis presents a model for the frame asynchronous IDMA system, and then develops a maximum likelihood receiver for the proposed system. This thesis develops tools to analyse and optimise IDMA receivers. The tools developed are general enough to be applied to other multiuser receiver techniques. The conventional EXIT chart analysis of unequal power allocated multiuser systems use an averaged EXIT chart analysis for all users to reduce the complexity of the task. This thesis presents a multidimensional analysis for power allocated IDMA, and shows how it can be utilised in power optimisation. Finally, this work develops a novel power zoning technique for multicell multiuser receivers using the optimised power levels, and illustrates a particular example where there is a 50% capacity improvement using the proposed scheme. -- provided by Candidate

Journal of Telecommunications and Information Technology, 2004, nr 2

kwartalni

Cross-layer energy-efficient schemes for multimedia content delivery in heterogeneous wireless networks

The wireless communication technology has been developed focusing on fulfilling the demand in various parts of human life. In many real-life cases, this demand directs to most types of commonly-used rich-media applications which – with diverse traffic patterns - often require high quality levels on the devices of wireless network users. Deliveries of applications with different patterns are accomplished using heterogeneous wireless networks using multiple types of wireless network structure simultaneously. Meanwhile, content deliveries with assuring quality involve increased energy consumption on wireless network devices and highly challenge their limited power resources. As a result, many efforts have been invested aiming at high-quality and energy-efficient rich-media content deliveries in the past years. The research work presented in the thesis focuses on developing energy-aware content delivery schemes in heterogeneous wireless networks. This thesis has four major contributions outlined below: 1. An energy-aware mesh router duty cycle management scheme (AOC-MAC) for high-quality video deliveries over wireless mesh networks. AOC-MAC manages the sleep-periods of mesh devices based on link-state communication condition, reducing their energy consumption by extending their sleep-periods. 2. An energy efficient routing algorithm (E-Mesh) for high-quality video deliveries over wireless mesh networks. E-Mesh evolves an innovative energy-aware OLSR-based routing algorithm by taking energy consumption, router position and network load into consideration. 3. An energy-aware multi-flow-based traffic load balancing scheme (eMTCP) for multi-path content delivery over heterogeneous wireless networks. The scheme makes use of the MPTCP protocol at the upper transport layer of network, allowing data streams to be delivered across multiple consequent paths. Meanwhile, this benefit of MPTCP is also balanced with energy consumption awareness by partially off-loading traffic from the paths with higher energy cost to others. 4. A MPTCP-based traffic-characteristic-aware load balancing mechanism (eMTCP-BT) for heterogeneous wireless networks. In eMTCP-BT, mobile applications are categorized according to burstiness level. eMTCP-BT increases the energy efficiency of the application content deliveries by performing a MDP-based distribution of traffic delivery via the available wireless network interfaces and paths based on the traffic burstiness level