Distributed Space-Time Message Relaying for Uncoded/Coded Wireless Cooperative Communications

During wireless communications, nodes can overhear other transmissions through the wireless medium, suggested by the broadcast nature of plane wave propagation, and may help to provide extra observations of the source signals to the destination. Modern research in wireless communications pays more attention to these extra observations which were formerly neglected within networks. Cooperative communication processes this abundant information existing at the surrounding nodes and retransmits towards the destination in various forms to create spatial and/or coding diversity, thereby to obtain higher throughput and reliability. The aim of this work is to design cooperative communication systems with distributed space-time block codes (DSTBC) in different relaying protocols and theoretically derive the BER performance for each scenario. The amplify-and-forward (AF) protocol is one of the most commonly used protocols at the relays. It has a low implementation complexity but with a drawback of amplifying the noise as well. We establish the derivation of the exact one-integral expression of the average BER performance of this system, folloby a novel approximation method based on the series expansion. An emerging technology, soft decode-and-forward (SDF), has been presented to combine the desired features of AF and DF: soft signal representation in AF and channel coding gain in DF. In the SDF protocol, after decoding, relays transmit the soft-information, which represents the reliability of symbols passed by the decoder, to the destination. Instead of keeping the source node idling when the relays transmit as in the traditional SDF system, we let the source transmit hard information and cooperate with the relays using DSTBC. By theoretically deriving the detection performance at the destination by either using or not using the DSTBC, we make comparisons among three SDF systems. Interesting results have been shown, together with Monte-Carlo simulations, to illustrate that our proposed one-relay and two-relay SDF & DSTBC systems outperform traditional soft relaying for most of the cases. Finally, these analytic results also provide a way to implement the optimal power allocation between the source and the relay or between relays, which is illustrated in the line model

Performance Enhancement in SU and MU MIMO-OFDM Technique for Wireless Communication: A Review

The consistent demand for higher data rates and need to send giant volumes of data while not compromising the quality of communication has led the development of a new generations of wireless systems. But range and data rate limitations are there in wireless devices. In an attempt to beat these limitations, Multi Input Multi Output (MIMO) systems will be used which also increase diversity and improve the bit error rate (BER) performance of wireless systems. They additionally increase the channel capacity, increase the transmitted data rate through spatial multiplexing, and/or reduce interference from other users. MIMO systems therefore create a promising communication system because of their high transmission rates without additional bandwidth or transmit power and robustness against multipath fading. This paper provides the overview of Multiuser MIMO system. A detailed review on how to increase performance of system and reduce the bit error rate (BER) in different fading environment e.g. Rayleigh fading, Rician fading, Nakagami fading, composite fading

Adaptive relaying protocol multiple-input multiple-output orthogonal frequency division multiplexing systems

In wireless broadband communications, orthogonal frequency division multiplexing (OFDM) has been adopted as a promising technique to mitigate multi-path fading and provide high spectral efficiency. In addition, cooperative communication can explore spatial diversity where several users or nodes share their resources and cooperate through distributed transmission. The concatenation of the OFDM technique with relaying systems can enhance the overall performance in terms of spectral efficiency and improve robustness against the detrimental effects of fading. Hybrid relay selection is proposed to overcome the drawbacks of conventional forwarding schemes. However, exciting hybrid relay protocols may suffer some limitations when used for transmission over frequency-selective channels. The combination of cooperative protocols with OFDM systems has been extensively utilized in current wireless networks, and have become a promising solution for future high data rate broadband communication systems including 3D video transmission. This thesis covers two areas of high data rate networks. In the first part, several techniques using cooperative OFDM systems are presented including relay selection, space time block codes, resource allocation and adaptive bit and power allocation to introduce diversity. Four (4) selective OFDM relaying schemes are studied over wireless networks; selective OFDM; selective OFDMA; selective block OFDM and selective unequal block OFDM. The closed-form expression of these schemes is derived. By exploiting the broadcast nature, it is demonstrated that spatial diversity can be improved. The upper bound of outage probability for the protocols is derived. A new strategy for hybrid relay selection is proposed to improve the system performance by removing the sub-carriers that experience deep fading. The per subcarrier basis selection is considered with respect to the predefined threshold signal-to-noise ratio. The closed-form expressions of the proposed protocol in terms of bit error probability and outage probability are derived and compared with conventional hybrid relay selection. Adaptive bit and power allocation is also discussed to improve the system performance. Distributed space frequency coding applied to hybrid relay selection to obtain full spatial and full data rate transmission is explored. Two strategies, single cluster and multiple clusters, are considered for the Alamouti code at the destination by using a hybrid relay protocol. The power allocation with and without sub-carrier pairing is also investigated to mitigate the effect of multipath error propagation in frequency-selective channels. The second part of this thesis investigates the application of cooperative OFDM systems to high data rate transmission. Recently, there has been growing attention paid to 3D video transmission over broadband wireless channels. Two strategies for relay selection hybrid relay selection and first best second best are proposed to implement unequal error protection in the physical layer over error prone channels. The closed-form expressions of bit error probability and outage probability for both strategies are examined. The peak signal-to-noise ratio is presented to show the quality of reconstruction of the left and right views

Técnicas com múltiplas antenas distribuídas para sistemas sem fios

Mestrado em Engenharia Electrónica e TelecomunicaçõesTransmissão cooperativa, em que uma fonte e um relay cooperam para enviar uma mensagem para o destino, pode proporcionar diversidade espacial contra o desvanecimento nas comunicações sem fios. O objectivo deste projecto é estudar a performance de um sistema de transmissão cooperativo com dois relays equipados com duas antenas, entre o transmissor e o utilizador. Considera-se que a estação base está equipada com duas antenas e o terminal móvel apenas com uma. O sistema cooperativo foi implementado de acordo com as especificações do LTE e avaliado em diversos cenários de propagação, considerando canais com diferentes Relação Sinal Ruído (SNR). Verificou-se que o desempenho do sistema proposto é melhor, quando comparado com o sistema não cooperativo, na maior parte dos cenários estudados.Cooperative transmission, in which a source and relay cooperate to sent a mensage to destination, can provide spatial diversity against fading in wirless telecomunications. The goal of this project is to study the perfomance of a cooperative tranmition systems with two relays equiped with two antennas, between transmitter and user. It is considered that the base station is equipped with two antennas and the mobile terminal with only one. The cooperative system was implemented according to the specifications of the LTE and evaluated at several propagation scenarios, considering channels with diferents Signal to Noise Ratio (SNR). It was found that the perfomance of the proposed system is better when compared with the non-cooperative ones, in most scenarios considered.CODIV/FP7-ICT-200

Novel transmission schemes for application in two-way cooperative relay wireless communication networks

Recently, cooperative relay networks have emerged as an attractive communications technique that can generate a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. To achieve cooperative diversity single-antenna terminals in a wireless relay network typically share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. However, there remain technical challenges to maximize the benefit of cooperative communications, e.g. data rate, asynchronous transmission, interference and outage. Therefore, the focus of this thesis is to exploit cooperative relay networks within two-way transmission schemes. Such schemes have the potential to double the data rate as compared to one-way transmission schemes. Firstly, a new approach to two-way cooperative communications via extended distributed orthogonal space-time block coding (E-DOSTBC) based on phase rotation feedback is proposed with four relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain. Then, distributed orthogonal space-time block coding (DOSTBC) is applied within an asynchronous two-way cooperative wireless relay network using two relay nodes. A parallel interference cancelation (PIC) detection scheme with low structural and computational complexity is applied at the terminal nodes in order to overcome the effect of imperfect synchronization among the cooperative relay nodes. Next, a DOSTBC scheme based on cooperative orthogonal frequency division multiplexing (OFDM) type transmission is proposed for flat fading channels which can overcome imperfect synchronization in the network. As such, this technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, a closed-loop EDOSTBC approach using through a three-time slot framework is proposed. A full interference cancelation scheme with OFDM and cyclic prefix type transmission is used in a two-hop cooperative four relay network with asynchronism in the both hops to achieve full data rate and completely cancel the timing error. The topic of outage probability analysis in the context of multi-relay selection for one-way cooperative amplify and forward networks is then considered. Local measurements of the instantaneous channel conditions are used to select the best single and best two relays from a number of available relays. Asymptotical conventional polices are provided to select the best single and two relays from a number of available relays. Finally, the outage probability of a two-way amplify and forward relay network with best and Mth relay selection is analyzed. The relay selection is performed either on the basis of a max-min strategy or one based on maximizing exact end-to-end signal-to-noise ratio. MATLAB and Maple software based simulations are employed throughout the thesis to support the analytical results and assess the performance of new algorithms and methods

Performance Evaluation and Improvement of Wireless Amplify-and-Forward Cooperative-Based Systems under Nodes Mobility and Imperfect CSI Estimation Impacts

Cooperative communication techniques have been introduced in wireless networks to achieve spacial diversity-gain via the readiness of multiple users (via relays) to assist a source forwarding its data to a final destination. Cooperative communication techniques have shown their capability in improving system reliability and extending coverage area, and hence, it is believable that they will act as a promising technology for the coming fifth-generation (5G). Nevertheless, most existing work reported in literature on performance studies of wireless cooperative-based systems are based on the assumptions that the multipath fading channels among systems cooperating nodes are quasi-static (i.e., fading channels coefficients are constant over a number of consecutive signaling periods) and channel-state-information (CSI) estimation processes at systems receivers are perfect. Nowadays, however, there is an increased number of users riding high-speed public transportation vehicles and demanding wireless data services through their own terminals. As a result of such high mobility wireless terminals, the assumption of time-selective (i.e., non quasi-static) fading is more realistic. This time-selective fading environment would severely deteriorate the performance of existing wireless cooperative systems that have been already designed based on the assumption of quasi-static fading (low users speeds). Further, due to impairments associated with practical receiver tracking-loops implementation issues, it is more general to assume that CSI estimations at systems receiving sides are imperfect. The scope of this dissertation is to provide comprehensive performance evaluation study for several emerging models of wireless amplify-and-forward (AF) cooperative-based communication systems that operate under the effects of the more general scenarios of high nodes mobility (time-selective fading) and imperfect channel estimations. This performance evaluation study is conducted by deriving closed-form expressions for different performance metrics; including error probability, outage probability and channel capacity. Monte Carlo simulations are also provided to complement and validate the analytical analyses. All of the obtained results in this dissertation are novel and general for mobile as well as non-moving nodes and for imperfect as well as perfect CSI estimations. Moreover, in this dissertation we develop innovative and applicable solutions and receiver designs that are capable of mitigating the detrimental impacts of the high nodes mobility on the performance of the cooperative system models under study

Space-time coded cooperation in Wireless Networks

Nowadays, the concept of spatial diversity and cooperative networks attract a lot of interest because they improve the reliability of transmission in wireless networks. Spatial diversity is achieved when multiple antennas are at the transmitter. With great growth and demand for high speed high data rate wireless communication, more and more antennas are required. In order to achieve maximum diversity, these antennas should be well separated so that the fading on each link is uncorrelated. This condition makes it difficult to have more than two antennas on a mobile terminal. The relay's cooperation helps increase the diversity order without extra hardware cost. However, its main inconvenience is the use of multiple time slots compared to the direct link transmission. In this thesis, we develop a cooperation model which is composed of three terminals: source, relay and destination. The transmitters (source and relay) are composed of 2 antennas at the transmitter and the receivers (relay and destination) have 4 antennas. In the first proposed model, transmitters and decoders are composed of an Alamouti encoder and decoder respectively. In the second model, we also add a turbo encoder at transmitters and iterative decoding takes place at receivers. In both cases, the transmission cycle is composed of two time slots and the decode and forward (DF) protocol is applied. Multiple scenarios are considered by changing the environment of the transmission, such as line of sight (LOS) or non line of sight (NLOS) or by modifying the location of the relay between the source and destination. We also simulate an uplink and a downlink communication. All the scenarios show a coding gain with the turbo coded space-time cooperation

Distributed Quasi-Orthogonal Space-Time coding in wireless cooperative relay networks

Cooperative diversity provides a new paradigm in robust wireless re- lay networks that leverages Space-Time (ST) processing techniques to combat the effects of fading. Distributing the encoding over multiple relays that potentially observe uncorrelated channels to a destination terminal has demonstrated promising results in extending range, data- rates and transmit power utilization. Specifically, Space Time Block Codes (STBCs) based on orthogonal designs have proven extremely popular at exploiting spatial diversity through simple distributed pro- cessing without channel knowledge at the relaying terminals. This thesis aims at extending further the extensive design and analysis in relay networks based on orthogonal designs in the context of Quasi- Orthogonal Space Time Block Codes (QOSTBCs). The characterization of Quasi-Orthogonal MIMO channels for cooper- ative networks is performed under Ergodic and Non-Ergodic channel conditions. Specific to cooperative diversity, the sub-channels are as- sumed to observe different shadowing conditions as opposed to the traditional co-located communication system. Under Ergodic chan- nel assumptions novel closed-form solutions for cooperative channel capacity under the constraint of distributed-QOSTBC processing are presented. This analysis is extended to yield closed-form approx- imate expressions and their utility is verified through simulations. The effective use of partial feedback to orthogonalize the QOSTBC is examined and significant gains under specific channel conditions are demonstrated. Distributed systems cooperating over the network introduce chal- lenges in synchronization. Without extensive network management it is difficult to synchronize all the nodes participating in the relaying between source and destination terminals. Based on QOSTBC tech- niques simple encoding strategies are introduced that provide compa- rable throughput to schemes under synchronous conditions with neg- ligible overhead in processing throughout the protocol. Both mutli- carrier and single-carrier schemes are developed to enable the flexi- bility to limit Peak-to-Average-Power-Ratio (PAPR) and reduce the Radio Frequency (RF) requirements of the relaying terminals. The insights gained in asynchronous design in flat-fading cooperative channels are then extended to broadband networks over frequency- selective channels where the novel application of QOSTBCs are used in distributed-Space-Time-Frequency (STF) coding. Specifically, cod- ing schemes are presented that extract both spatial and mutli-path diversity offered by the cooperative Multiple-Input Multiple-Output (MIMO) channel. To provide maximum flexibility the proposed schemes are adapted to facilitate both Decode-and-Forward (DF) and Amplify- and-Forward (AF) relaying. In-depth Pairwise-Error-Probability (PEP) analysis provides distinct design specifications which tailor the distributed- STF code to maximize the diversity and coding gain offered under the DF and AF protocols. Numerical simulation are used extensively to confirm the validity of the proposed cooperative schemes. The analytical and numerical re- sults demonstrate the effective use of QOSTBC over orthogonal tech- niques in a wide range of channel conditions