Distributed transmission schemes for wireless communication networks

In this thesis new techniques are presented to achieve performance enhancement in wireless cooperative networks. In particular, techniques to improve transmission rate and maximise end-to-end signal-to-noise ratio are described. An offset transmission scheme with full interference cancellation for a wireless cooperative network with frequency flat links and four relays is introduced. This method can asymptotically, as the size of the symbol block increases, achieve maximum transmission rate together with full cooperative diversity provided the destination node has multiple antennas. A novel full inter-relay interference cancellation method that also achieves asymptotically maximum rate and full cooperative diversity is then designed for which the destination node only requires a single antenna. Two- and four-relay selection schemes for wireless cooperative amplify and forward type networks are then studied in order to overcome the degradation of end-to-end bit error rate performance in single-relay selection networks when there are feedback errors in the relay to destination node links. Outage probability analysis for a four-relay selection scheme without interference is undertaken. Outage probability analysis of a full rate distributed transmission scheme with inter-relay interference is also studied for best single- and two-relay selection networks. The advantage of multi-relay selection when no interference occurs and when adjacent cell interference is present at the relay nodes is then shown theoretically. Simulation results for outage probability analysis are included which support the theoretical expressions. Finally, outage probability analysis of a cognitive amplify and forward type relay network with cooperation between certain secondary users, chosen by best single-, two- and four-relay selection is presented. The cognitive amplify and forward relays are assumed to exploit an underlay approach, which requires adherence to an interference constraint on the primary user. The relay selection scheme is performed either with a max−min strategy or one based on maximising exact end-to-end signal-to-noise ratio. The outage probability analyses are again confirmed by numerical evaluations

Modified quasi-orthogonal space-time block coding in distributed wireless networks

Cooperative networks have developed as a useful technique that can achieve the same advantage as multi-input and multi-output (MIMO) wireless systems such as spatial diversity, whilst resolving the difficulties of co-located multiple antennas at individual nodes and avoiding the effect of path-loss and shadowing. Spatial diversity in cooperative networks is known as cooperative diversity, and can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. However, there remain technical challenges to maximize the benefit of cooperative communications, e.g. data rate, asynchronous transmission and outage. In this thesis, therefore, firstly, a modified distributed quasi-orthogonal space-time block coding (M-D-QO-STBC) scheme with increased code gain distance (CGD) for one-way and two-way amplify-and-forward wireless relay networks is proposed. This modified code is designed from set partitioning a larger codebook formed from two quasi-orthogonal space time block codes with different signal rotations then the subcodes are combined and pruned to arrive at the modified codebook with the desired rate in order to increase the CGD. Moreover, for higher rate codes the code distance is maximized by using a genetic algorithm to search for the optimum rotation matrix. This scheme has very good performance and significant coding gain over existing codes such as the open-loop and closed-loop QO-STBC schemes. In addition, the topic of outage probability analysis in the context of multi-relay selection from $N$ available relay nodes for one-way amplify-and-forward cooperative relay networks is considered together with the best relay selection, the $N^{th}$ relay selection and best four relay selection in two-way amplify-and-forward cooperative relay networks. 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. Furthermore, in this thesis, robust schemes for cooperative relays based on the M-D-QO-STBC scheme for both one-way and two-way asynchronous cooperative relay networks are considered to overcome the issue of a synchronism in wireless cooperative relay networks. In particular, an orthogonal frequency division multiplexing (OFDM) data structure is employed with cyclic prefix (CP) insertion at the source in the one-way cooperative relay network and at the two terminal nodes in the two-way cooperative network to combat the effects of time asynchronism. As such, this technique can effectively cope with the effects of timing errors. Finally, outage probability performance of a proposed amplify-and-forward cooperative cognitive relay network is evaluated and the cognitive relays are assumed to exploit an overlay approach. A closed form expression for the outage probability for multi-relay selection cooperation over Rayleigh frequency flat fading channels is derived for perfect and imperfect spectrum acquisitions. Furthermore, the M-QO-STBC scheme is also proposed for use in wireless cognitive relay networks. 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

Rate enhancement and multi-relay selection schemes for application in wireless cooperative networks

In this thesis new methods are presented to achieve performance enhancement in wireless cooperative networks. In particular, techniques to improve transmission rate, mitigate asynchronous transmission and maximise end-to-end signal-to-noise ratio are described. An offset transmission scheme with full interference cancellation for a two-hop synchronous network with frequency flat links and four relays is introduced. This approach can asymptotically, as the symbol block size increases, achieve maximum transmission rate together with full cooperative diversity provided the destination node has multiple antennas. A novel full inter-relay interference cancellation method that also achieves asymptotically maximum rate and full cooperative diversity is then designed which only requires a single antenna at the destination node. Extension to asynchronous networks is then considered through the use of orthogonal frequency division multiplexing (OFDM) type transmission with a cyclic prefix, and interference cancellation techniques are designed for situations when synchronization errors are present in only the second hop or both the first and second hop. End-to-end bit error rate evaluations, with and without outer coding, are used to assess the performance of the various offset transmission schemes. Multi-relay selection methods for cooperative amplify and forward type networks are then studied in order to overcome the degradation of end-to-end bit error rate performance in single-relay selection networks when there are feedback errors in the destination to relay node links. Outage probability analysis for two and four relay selection is performed to show the advantage of multi-relay selection when no interference occurs and when adjacent cell interference is present both at the relay nodes and the destination node. Simulation studies are included which support the theoretical expressions. Finally, outage probability analysis of a cognitive amplify and forward type relay network with cooperation between certain secondary users, chosen by single and multi-relay (two and four) selection is presented. The cognitive relays are assumed to exploit an underlay approach, which requires adherence to an interference constraint on the primary user. The relay selection is performed either with a max-min strategy or one based on maximising exact end-to-end signal-to-noise ratio. The analyses are again confirmed by numerical evaluations

Performance enhancement solutions in wireless communication networks

In this dissertation thesis, we study the new relaying protocols for different wireless network systems. We analyze and evaluate an efficiency of the transmission in terms of the outage probability over Rayleigh fading channels by mathematical analyses. The theoretical analyses are verified by performing Monte Carlo simulations. First, we study the cooperative relaying in the Two-Way Decode-and-Forward (DF) and multi-relay DF scheme for a secondary system to obtain spectrum access along with a primary system. In particular, we proposed the Two-Way DF scheme with Energy Harvesting, and the Two-Way DF Non-orthogonal Multiple Access (NOMA) scheme with digital network coding. Besides, we also investigate the wireless systems with multi-relay; the best relay selection is presented to optimize the effect of the proposed scheme. The transmission protocols of the proposed schemes EHAF (Energy Harvesting Amplify and Forward) and EHDF (Energy Harvesting Decode and Forward) are compared together in the same environment and in term of outage probability. Hence, with the obtained results, we conclude that the proposed schemes improve the performance of the wireless cooperative relaying systems, particularly their throughput. Second, we focus on investigating the NOMA technology and proposing the optimal solutions (protocols) to advance the data rate and to ensure the Quality of Service (QoS) for the users in the next generation of wireless communications. In this thesis, we propose a Two-Way DF NOMA scheme (called a TWNOMA protocol) in which an intermediate relay helps two source nodes to communicate with each other. Simulation and analysis results show that the proposed protocol TWNOMA is improving the data rate when comparing with a conventional Two-Way scheme using digital network coding (DNC) (called a TWDNC protocol), Two-Way scheme without using DNC (called a TWNDNC protocol) and Two-Way scheme in amplify-and-forward(AF) relay systems (called a TWANC protocol). Finally, we considered the combination of the NOMA and physical layer security (PLS) in the Underlay Cooperative Cognitive Network (UCCN). The best relay selection strategy is investigated, which uses the NOMA and considers the PLS to enhance the transmission efficiency and secrecy of the new generation wireless networks.V této dizertační práci je provedena studie nových přenosových protokolů pro různé bezdrátové síťové systémy. S využitím matematické analýzy jsme analyzovali a vyhodnotili efektivitu přenosu z hlediska pravděpodobnosti výpadku přes Rayleighův kanál. Teoretické analýzy jsou ověřeny provedenými simulacemi metodou Monte Carlo. Nejprve došlo ke studii kooperativního přenosu ve dvoucestném dekóduj-a-předej (Two-Way Decode-and-Forward–TWDF) a vícecestném DF schématu s větším počtem přenosových uzlů pro sekundární systém, kdy takto byl získán přístup ke spektru spolu s primárním systémem. Konkrétně jsme navrhli dvoucestné DF schéma se získáváním energie a dvoucestné DF neortogonální schéma s mnohonásobným přístupem (Non-orthogonal Multiple Access–NOMA) s digitálním síťovým kódováním. Kromě toho rovněž zkoumáme bezdrátové systémy s větším počtem přenosových uzlů, kde je přítomen výběr nejlepšího přenosového uzlu pro optimalizaci efektivnosti navrženého schématu. Přenosové protokoly navržených schémat EHAF (Energy Harvesting Amplify and Forward) a EHDF(Energy Harvesting Decode and Forward) jsou společně porovnány v identickém prostředí z pohledu pravděpodobnosti výpadku. Následně, na základě získaných výsledků, jsme dospěli k závěru, že navržená schémata vylepšují výkonnost bezdrátových kooperativních systémů, konkrétně jejich propustnost. Dále jsme se zaměřili na zkoumání NOMA technologie a navrhli optimální řešení (protokoly) pro urychlení datového přenosu a zajištění QoS v další generaci bezdrátových komunikací. V této práci jsme navrhli dvoucestné DF NOMA schéma (nazýváno jako TWNOMA protokol), ve kterém mezilehlý přenosový uzel napomáhá dvěma zdrojovým uzlům komunikovat mezi sebou. Výsledky simulace a analýzy ukazují, že navržený protokol TWNOMA vylepšuje dosaženou přenosovou rychlost v porovnání s konvenčním dvoucestným schématem používajícím DNC (TWDNC protokol), dvoucestným schématem bez použití DNC (TWNDNC protokol) a dvoucestným schématem v zesil-a-předej (amplify-and-forward) přenosových systémech (TWANC protokol). Nakonec jsme zvážili využití kombinace NOMA a zabezpečení fyzické vrstvy (Physical Layer Security–PLS) v podpůrné kooperativní kognitivní síti (Underlay Cooperative Cognitive Network–UCCN). Zde je zde zkoumán výběr nejlepšího přenosového uzlu, který užívá NOMA a bere v úvahu PLS pro efektivnější přenos a zabezpečení nové generace bezdrátových sítí.440 - Katedra telekomunikační technikyvyhově

Exact Outage Performance Analysis of Multiuser Multi-relay Spectrum Sharing Cognitive Networks

In this paper, we investigate the outage performance of dual-hop multiuser multi-relay cognitive radio networks under spectrum sharing constraints. Using an efficient relay-destination selection scheme, the exact and asymptotic closed-form expressions for the outage probability are derived. From these expressions it is indicated that the achieved diversity order is only determined by the number of secondary user (SU) relays and destinations, and equals to M+N (where M and N are the number of destination nodes and relay nodes, respectively). Further, we find that the coding gain of the SU network will be affected by the interference threshold $bar I$ at the primary user (PU) receiver. Specifically, as the increases of the interference threshold, the coding gain of the considered network approaches to that of the multiuser multi-relay system in the non-cognitive network. Finally, our study is corroborated by representative numerical examples

Performance Analysis of Best Relaying Protocol Selection with Interferences at Relays

In this paper, we investigate the performance of selecting the best protocol between amplify and forward (AF) and decode and forward (DF) in multiple relay networks with multiple interferences at relays. In the selection scheme, the best protocol between AF and DF is selected depending on the comparisons of signal-to-interference and noise ratio (SINR) for all source-relay links. All relays measure the received SINR to decide forwarding signal or not. When SINR is above a certain threshold then DF is used otherwise AF is used. Particularly, we develop an accurate mathematical model for best relaying protocol by considering the effect of interferences to our scheme. Firstly, we derive the asymptotic closed form expression for the symbol error rate (SER) for the system under study. Also we derive an upper and lower bound of symbol error rate and show how they were tight with exact SER. Furthermore an approximate expression for the outage probability is derived. Numerical results are finally presented to validate the theoretical analysis with a different number of relays

Cognitive Multihop Wireless Sensor Networks over Nakagami-m Fading Channels

This work is supported by the National Science Foundation of China (NSFC) under Grant 61372114, by the National 973 Program of China under Grant 2012CB316005, by the Joint Funds of NSFC-Guangdong under Grant U1035001, and by Beijing Higher Education Young Elite Teacher Project (no. YETP0434)

Outage Performance Analysis of Multicarrier Relay Selection for Cooperative Networks

In this paper, we analyze the outage performance of two multicarrier relay selection schemes, i.e. bulk and per-subcarrier selections, for two-hop orthogonal frequency-division multiplexing (OFDM) systems. To provide a comprehensive analysis, three forwarding protocols: decode-and-forward (DF), fixed-gain (FG) amplify-and-forward (AF) and variable-gain (VG) AF relay systems are considered. We obtain closed-form approximations for the outage probability and closed-form expressions for the asymptotic outage probability in the high signal-to-noise ratio (SNR) region for all cases. Our analysis is verified by Monte Carlo simulations, and provides an analytical framework for multicarrier systems with relay selection