Efficient space-time block codes for cooperative MIMO communications

Cooperative virtual MIMO for wireless sleep apnoea monitoring system

In this thesis, major attention is paid to cooperative diversity as an alternative way to achieve spatial diversity when the multiple antenna structure is not an option. By adopting the cooperative relay nodes to forward information, we can mitigate the fading effects, increase the capacity, lower the bit-error rate, increase the achievable transmission range, and without sacrificing time and bandwidth efficiency. Orthogonal Frequency Division Multiplexing (OFDM) is a popular multicarrier modulation technique in the modern wireless communications, since it possesses the advantages of frequency parallel transmission, high speed communications and efficient spectrum usage. In this Ph.D. thesis OFDM transmission into the cooperative communication domain is investigated. The diversity gains from both spatial domain and frequency domain are combined and so cooperative communication can further enhance the reliable, high speed transmission, and enable the spectrum efficiency. We propose a cooperative OFDM tall Toeplitz scheme, which guarantees full cooperative diversity, taking outage diversity and multipath diversity into account; in addition it easily combats Carrier Frequency Offsets (CFOs), using Linear Equalizers (LEs) only. Compared to the conventionally used Maximum-Likelihood Equalizers (MLEs), the system complexity is reduced significantly. There are mainly two relaying protocols in cooperative relay networks: Amplify-and-Forward (AF) and Decode-and-Forward (DF). In the research on relay selection and resource allocation issues in cooperative communications, we propose a dynamic optimal combination strategy for the hybrid DF-AF cooperative OFDM communications and removing unsuitable AF relays. Subsequently, we propose relay selection and resource allocation and optimization schemes for cooperative wireless communication networks with interference based on the so called Stackelberg game approach. This approach is a proper game model for solving the relay selection and power allocation problem in a distributed manner, when pricing and power allocation of the relay both are taken into account. As an extension of our research on cooperative wideband communication, we study wideband scale-lag channels as well, present in many ultra-wideband communication applications. In our research, cooperative relaying communication network is set for multi-scale and multi-lag wideband channels. We also provide a dynamic optimal selection strategy for relay selection to take advantage of the multi-relay, multi-scale and multi-lag diversity and maximize the system Bit-Error Rate (BER) performance. Cooperative localization research is growing when larger wireless networks are deployed and more applications are developed which require accurate position information. Therefore, cooperative locationing research becomes an important part of this Ph.D. research on cooperative wideband OFDM communications. In this research, we propose a trigger relay based cooperative localization technique. Because the trigger relay only needs to be switched on by the incoming signal, and to be sent as a simple pilot to the receiver, our technique gains from the easy processing together with noise and interference immunity of the base station to relay link. Compared to AF relay and DF relay Time Difference of Arrival (TDOA) estimation cases, the trigger relay reduces the system complexity. Meanwhile, trigger relay enables the bandwidth efficient TDOA, since it significantly reduces the amount of data for transmission. Furthermore, by exploiting cooperative-multipath diversity, the improved signal detection further contributes to a better TDOA estimation.

The demand for higher data rates in wireless communication systems has become inevitable with the availability of diverse range of multimedia applications in mobile communications today. Multiple Input Multiple Output (MIMO) antennas is one of the technologies utilized to support the required higher data rates in wireless communications. However, energy efficiency in cellular communications has generated lots of interest recently. Energy efficiency metrics will provide a yardstick for comparison and a pathway towards achieving the objectives of green communications in cellular networks. This paper investigates the energy efficiency of different MIMO transmission schemes applicable in 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) and compares them with each other and SISO transmission. The Energy Consumption Rating (ECR) of the various MIMO schemes are derived and discussed.

In a real cellular system, existence of a number of multi-antenna schemes in neighboring cells means that different multi-antenna schemes will experience co-channel interference (CCI) from the same or other multi-antenna schemes. In this work, we have summarized our analysis and simulations related to cellular interference of some specific multiple input multiple output (MIMO) schemes on the same and other MIMO schemes. The goal is to study the impact of interference from MIMO schemes at a user located in the cell edge. Semi-Analytical evaluations of signal to interference and noise ratio (SINR) is done to find out the SINR statistics of different combinations of desired and interfering links. We have studied linear combining receivers for all the link combinations. Based on the current analysis, it is found that space-time block code (STBC) is a severe interferer compared to others, and specific attention is needed to counter the interference introduced by STBC interfering link.

Multiple-input multiple-output (MIMO) and cooperative communications have been attracted great attention for the improvements of communication capacity, power consumption, and transmission coverage. The conventional fixed relaying protocols, amplify-and-forward (AF) and decode-and-forward (DF), have their own advantages and disadvantages, i.e. AF performs better than DF for low signal-to-noise ratio (SNR) region, while the reverse is true for high SNR region. Therefore, this paper proposes an SNR-adaptive forward (SAF) relaying scheme obtaining the advantages of both AF and DF. Furthermore, the proposed SAF does not need to switch between AF and DF when SNR changes. The main idea is to adaptively derive the soft information at the cooperative relay nodes based on the information of the received signal and the SNR. Besides, based on the theoretical analysis and the simulation results, it is affirmed that the proposed SAF achieves superior performance than both AF and DF for all SNRs. Moreover, the performance gain would be improved with the increasing number of parallel cooperative relay nodes.

Realizing high-accuracy transmission in high-rate data broadcasting networks with heterogeneous users via cooperative communication

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. This paper addresses a number of multiple input multiple output (MIMO) precoding and scheduling techniques across the PHY and MAC layers that can operate under a reduced link budget and collectively improve the transmit power efficiency of a base station, while maintaining the same levels of service. Different MIMO transmission and precoding schemes proposed for LTE, achieving varying degrees of multiuser diversity in both the time, frequency as well as the space domain, are examined. Several fairness-aware resource allocation algorithms are applied to the considered MIMO schemes and a detailed analysis of the tradeoffs between power efficiency and quality of service is presented. This paper explicitly examines the performance of a system serving real-time, VoIP traffic under different traffic loading conditions and transmit power levels. It is demonstrated that by use of efficient scheduling and resource allocation techniques significant savings in terms of consumed energy can be achieved, without compromising QoS.

In this paper, a new hybrid multiple-input multiple-output (MIMO) cooperative scheme is proposed in wireless orthogonal frequency division multiplexing (OFDM) systems. MIMO---OFDM systems have allowed the improvement of the system performance as reliability and data rate. However, MIMO---OFDM systems have limitations of supporting reliable transmission and high data rate due to size, cost and complexity limitation of device. So, the hybrid MIMO cooperative communication has been studied to compensate the defects. The hybrid MIMO cooperative scheme has advantages of MIMO and cooperative communication. But the conventional hybrid MIMO cooperative scheme has a few defects under particular environments. So, the proposed hybrid MIMO cooperative scheme supplements the defects of the conventional schemes.

This paper addresses advanced radio resource management (RRM) algorithms for multiple-input multiple-output (MIMO) transmission schemes in downlink OFDMA systems. The analysis covers the main RRM mechanisms including MIMO rank adaptation and time-frequency packet scheduling. The UTRAN Long Term Evolution (LTE) system is used as case study. System-level performance analysis is presented for 2 times 2 and 4 times 4 spatial-multiplexing, single-user MIMO transmission schemes in typical macro- and micro-cell scenarios including the effects of limited and imperfect CQI feedback from the terminals. We show that time-frequency domain RRM schemes can be successfully adapted and optimized for operations with high-rate adaptive MIMO transmission schemes.

We develop a general framework for the analysis of a broad class of point-to-point linear multiple-input multiple-output (MIMO) transmission schemes in decentralized wireless ad hoc networks. New general closed-form expressions are derived for the outage probability, throughput and transmission capacity. For the throughput, we investigate the optimal number of data streams in various asymptotic regimes, which is shown to be dependent on different network parameters. For the transmission capacity, we prove that it scales linearly with the number of antennas, provided that the number of data streams also scales linearly with the number of antennas, in addition to meeting some mild technical conditions. We also characterize the optimal number of data streams for maximizing the transmission capacity. To make our discussion concrete, we apply our general framework to investigate three popular MIMO schemes, each requiring different levels of feedback. In particular, we consider eigenmode selection with MIMO singular value decomposition, multiple transmit antenna selection, and open-loop spatial multiplexing. Our analysis of these schemes reveals that significant performance gains are achieved by utilizing feedback under a range of network conditions.

In this paper, we propose and analyze an adaptive modulation system with optimal turbo coded V- BLAST (vertical-bell-lab layered space-time) technique that adopts the extrinsic information from MAP (maximum a posteriori) decoder with iterative decoding as a priori probability in two decoding procedures of V-BLAST scheme; the ordering and the slicing. Also, we consider and compare The adaptive modulation system using conventional turbo coded V-BLAST technique that is simply combined V-BLAST scheme with turbo coding scheme and that is decoded by the ML(maximum likelihood) decoding algorithm. In addition, we apply MIMO (multiple input multiple output) schemes to the systems for more performance improvement. The result indicates that the proposed systems achieve a better throughput performance than the conventional systems in the whole SNR range. And in terms of the throughput performance, the suggested system is close proximity to the conventional system using the ML decoding algorithm. In addition, the simulation result shows that the maximum throughput improvement in each MIMO scheme is respectively about 350 kbps, 460 kbps, and 740 kbps. It is suggested that the effect of the proposed decoding algorithm accordingly gets higher as the number of system antenna increases.

Cooperative Multiple-Input Multiple-Output (MIMO) has been proposed as a transmission strategy to combat the fading problem in Wireless Sensor Networks (WSNs) to reduce the retransmission probability and lower the transmission energy. Among the earliest work on cooperative MIMO in WSNs is the analysis of the Space-Time Block Coding (STBC) scheme to achieve lower Bit Error Rate (BER) and significant energy savings. The work is continued with the implementation of the Low-Energy Adaptive Clustering Hierarchy (LEACH) Medium Access Control (MAC) protocol for clustered-based architectures. The combination of STBC and the LEACH scheme resulted in a significant improvement in transmission energy efficiency compared to the Single-Input Single Output (SISO) scheme. Further study is conducted to compare the performance of STBC and various Spatial Multiplexing (SM) schemes such as Vertical Bell Labs Layered Space-Time (V-BLAST) and Diagonal BLAST. In this study, LEACH MAC was also utilized and lower transmission energy and latency were achieved against the SISO scheme. However, the centralized architecture leads to energy wastage and higher latency compared to a distributed architecture. On the other hand, the implementation of a distributed architecture needs to consider synchronisation issues. Thus a practical cooperative MIMO scheme for distributed asynchronous WSNs is needed. Moreover, a practical MAC that can suit cooperative transmission is required. A combination of a practical MAC protocol and an efficient MIMO scheme for asynchronous cooperative transmission leads to a more energy efficient and lower latency cooperative MIMO system. A combination of a MAC protocol and a cooperative SM scheme for cooperative MIMO transmission has been proposed in previous study where the combined scheme achieves significant energy efficiency and lower latency. Furthermore, a transmit Maximum Ratio Combiner (MRC) scheme is suggested to be more tolerant to the jitter difference than the Alamouti STC scheme in network with imperfect transmitting nodes synchronisation. In this chapter, we expand these studies to two other cooperative MIMO schemes, namely Beamforming (BF) and STBC for both network scenarios: perfect and imperfect transmitting nodes synchronisation. The optimal cooperative MIMO scheme combined with an appropriate MAC protocol should lead to the lowest energy consumption and lowest packet latency.

Wireless cellular networks have to be designed and deployed with unavoidable constraints on the limited radio resources such as bandwidth and transmit power. With the boom in the number of new users and the introduction of new wireless cellular services that require a large bandwidth or data rate, the demand for these resources, however, is rising exponentially. Finding a solution to meet this increasing demand with the available resources is a challenging research problem. The primary objective of such research is to find solutions that can improve the capacity and utilization of the radio resources that are available to the service providers. Based on the concept of relay channels, cooperative communication has been found to greatly enhance the performance of a resource-constrained wireless network. It can achieve benefits similar to those of the multipleinput multiple-output (MIMO) system without the need for multiple antennas at each node. By allowing users to cooperate and relay each other's messages to the destination, cooperative communication also improves the transmission quality. Because of the limited power and bandwidth resources of the cellular networks and the multipath fading nature of the wireless channels, the idea of cooperation is particularly attractive for wireless cellular networks.

Currently, the increasing energy consumption is a global issue. Information technology and telecommunication industry is one of the areas with the largest energy consumption. The growth of mobile data users is an issue and the biggest challenge for the future. The cooperative wireless communication system has been the focus of research as one of the information delivery strategy with more efficient energy consumption. Energy efficiency in the cooperative wireless communication system can be improved by using a relay between base station and user device, where the distance between base station and user can be shortened, thus, the energy transmission can be minimized. Relay mechanism can be built by utilizing the protocol in the cooperative communication system, such as amplify and forward (AF), decode and forward (DF), and quantize and forward (QF). Relay-selection is an important issue in a cooperative wireless communication system that can reduce energy consumption at the system level. This study analyzes energy efficiency of multi-relay QF cooperative communication for line-of-sight (LOS) and non-line-of-sight (NLOS) environment based on relay selection strategies: reactive and proactive relay selection. A computer simulation is conducted based on a system model and mathematical analysis. Energy efficiency is calculated based on power consumption of signal transmission and observed in the distance between the source, relay, and destination. Simulation result shows that multi-relay QF networks with relay selection consume lower energy than without relay selection, hence, the energy usage in the relay selection networks is more efficient. Moreover, the strategy of proactive relay selection provides low energy consumption and high energy efficiency compared to the reactive relay selection strategy.

In this paper, we investigate power allocation problem with the use of transmit beamforming in a dual hop MISO (multiple input single output) relay channel. We consider either amplify and forward (AF) or decode and forward (DF) cooperative protocols at the relay and optimize the power allocated to the relay and the source, under total transmit power constraint, to minimize the bit error rate (BER) of relaying system. Cooperative communication is viewed as a method for increasing diversity gain and reducing end to end path loss. The use of relay can create a virtual antenna array so that it allows users to exploit the advantages of multiple input multiple output (MIMO) techniques. In this work, we solve cooperative ratio, which is defined as the ratio power used for cooperative transmission over the total power. This approach is then compared to an equal power assignment method and its performance enhancement is verified by simulation results.