Multi-Source Cooperative Communication with Opportunistic Interference Cancelling Relays

In this paper we present a multi-user cooperative protocol for wireless networks. Two sources transmit simultaneously their information blocks and relays employ opportunistically successive interference cancellation (SIC) in an effort to decode them. An adaptive decode/amplify-and-forward scheme is applied at the relays to the decoded blocks or their sufficient statistic if decoding fails. The main feature of the protocol is that SIC is exploited in a network since more opportunities arise for each block to be decoded as the number of used relays NRU is increased. This feature leads to benefits in terms of diversity and multiplexing gains that are proven with the help of an analytical outage model and a diversity-multiplexing tradeoff (DMT) analysis. The performance improvements are achieved without any network synchronization and coordination. In the final part of this work the closed-form outage probability model is used by a novel approach for offline pre-selection of the NRU relays, that have the best SIC performance, from a larger number of NR nodes. The analytical results are corroborated with extensive simulations, while the protocol is compared with orthogonal and multi-user protocols reported in the literature.Comment: in IEEE Transactions on Communications, 201

A Simple Cooperative Diversity Method Based on Network Path Selection

Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However most of the proposed solutions require distributed space-time coding algorithms, the careful design of which is left for future investigation if there is more than one cooperative relay. We propose a novel scheme, that alleviates these problems and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of M available relays and then uses this best relay for cooperation between the source and the destination. We develop and analyze a distributed method to select the best relay that requires no topology information and is based on local measurements of the instantaneous channel conditions. This method also requires no explicit communication among the relays. The success (or failure) to select the best available path depends on the statistics of the wireless channel, and a methodology to evaluate performance for any kind of wireless channel statistics, is provided. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing tradeoff as achieved by more complex protocols, where coordination and distributed space-time coding for M nodes is required, such as those proposed in [7]. The simplicity of the technique, allows for immediate implementation in existing radio hardware and its adoption could provide for improved flexibility, reliability and efficiency in future 4G wireless systems.Comment: To appear, IEEE JSAC, special issue on 4

Study on Generalized Buffer-State-Based Relay Selection in Cooperative Cognitive Radio Networks

学位の種別: 修士University of Tokyo(東京大学

Enhancing diversity and multiplexing gains in multi-user wireless relay systems

The demand for higher transmission rates and better quality of service in modern wireless communications is endless. The use of multiple transmit or /and receive antennas has been considered as one of the most powerful approaches to facilitate high -speed and high -quality communications. However, in practical cellular systems, mobile terminals may not be able to support a multiple- antenna setup. Thus an emerging technique called cooperative diversity is under consideration to utilize the multi -hop relay concept to realize the advantages of multiple - antenna systems in multi -user single- antenna networks. Cooperative diversity has attracted much interest in recent years as a very promising direction for future wireless communication evolution.Due to the fact that in practice terminals cannot transmit and receive simultaneously (i.e. the half -duplex limitation), the diversity improvement brought by the standard cooperative diversity transmission protocols is in general accompanied by a multiplexing loss (equivalent to a reduction in transmission data rate in high signal -to -nose ratio (SNR)). The purpose of this thesis is to use advanced transmission protocols to provide both good diversity and multiplexing performance when using the practical repetition -coded decode - and -forward (DF) relaying strategy in uplink mobile -to -base station transmission of cellular systems.The task is fulfilled by relaxing the orthogonal channel allocation requirement of the standard protocols and by using two relays to take turns forwarding source information to destination. We start our analysis from an M- source two -relay one -destination network. Through diversity -multiplexing tradeoff (DMT) analysis, we prove that for an isolated -relay scenario and a strong -interference scenario, the considered approach effectively recovers the multiplexing loss induced by the standard protocols while still obtaining diversity improvement over direct source -destination transmission without considering relaying.In addition, since the optimal multiplexing gain of the considered system can be achieved by the above approach, we study further improving diversity performance for a two -source network. We analyze taking full advantage of the multiple- source structure, multiple -relay structure, and the capability of affording complex signal processing at the destination (base station). For all three cases, we prove that the diversity performance of the above approach can be enhanced without a significant loss of multiplexing performance or using complex coding strategies at relays. Since the good DMT performance is not affected by source -relay channel conditions, the protocols discussed in this thesis make relaying more beneficial

Multi-points cooperative relay in NOMA system with N-1 DF relaying nodes in HD/FD mode for N user equipments with energy harvesting

Non-Orthogonal Multiple Access (NOMA) is the key technology promised to be applied in next-generation networks in the near future. In this study, we propose a multi-points cooperative relay (MPCR) NOMA model instead of just using a relay as in previous studies. Based on the channel state information (CSI), the base station (BS) selects a closest user equipment (UE) and sends a superposed signal to this UE as a first relay node. We have assumed that there are N UEs in the network and the N-th UE, which is farthest from BS, has the poorest quality signal transmitted from the BS compared the other UEs. The N-th UE received a forwarded signal from N - 1 relaying nodes that are the UEs with better signal quality. At the i-th relaying node, it detects its own symbol by using successive interference cancellation (SIC) and will forward the superimposed signal to the next closest user, namely the (i + 1)-th UE, and include an excess power which will use for energy harvesting (EH) intention at the next UE. By these, the farthest UE in network can be significantly improved. In addition, closed-form expressions of outage probability for users over both the Rayleigh and Nakagami-m fading channels are also presented. Analysis and simulation results performed by Matlab software, which are presented accurately and clearly, show that the effectiveness of our proposed model and this model will be consistent with the multi-access wireless network in the future.Web of Science82art. no. 16

Performance Analysis in Full-Duplex Relaying Systems withWireless Power Transfer

Energy harvesting (EH) technology has become increasingly attractive as an appealing solution to provide long-lasting power for energy-constrained wireless cooperative sensor networks. EH in such networks is particularly important as it can enable information relaying. Different from absorbing energy from intermittent and unpredictable nature, such as solar, wind, and vibration, harvesting from radio frequency (RF) radiated by ambient transmitters has received tremendous attention. The RF signal can convey both information and energy at the same time, which facilitates the development of simultaneous wireless information and power transfer. Besides, ambient RF is widely available from the base station, WIFI, and mobile phone in the current information era. However, some open issues associated with EH are existing in the state-of-art. One of the key challenges is rapid energy loss during the transferring process, especially for long-distance transmission. The other challenge is the design of protocols to optimally coordinate between information and power transmission. Meanwhile, in-band full-duplex (IBFD) communication have gained considerable attraction by researchers, which has the ability to improve system spectral efficiency. IBFD can receive information and forward information at the same time on the same frequency. Since the RF signal can be superimposed, the antenna of the IBFD system receives the RF signal from both desired transmitter and local transmitter. Due to the short distance of the local transmission signals, the received signal power is much larger than the desired transmission signals, which results in faulty receiving of the desired signals. Therefore, it is of great significance to study the local self-interference cancellation method of the IBFD system. In the recent state-of-art, three main types of self-interference cancellations are researched, which are passive cancellations, digital cancellations, and analog cancellations. In this thesis, we study polarization-enabled digital self-interference cancellation (PDC) scheme in IBFD EH systems which cancels self-interference by antenna polarization (propagation domain) and digital processing (digital domain). The theme of this thesis is to address the following two questions: how the selfinterference would be canceled in the IBFD EH system and how to optimize key performances of the system to optimal system performances. This thesis makes five research contributions in the important area of IBFD relaying systems with wireless power transfer. Their applications are primarily in the domains of the Internet of Things (IoT) and 5G-and-beyond wireless networks. The overarching objective of the thesis is to construct analytical system models and evaluate system performance (outage probability, throughput, error) in various scenarios. In all five contributions, system models and analytical expressions of the performance metrics are derived, followed by computer simulations for performance analysis