28 research outputs found

    Channel Estimation for Ambient Backscatter Communication Systems with Massive-Antenna Reader

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    Ambient backscatter, an emerging green communication technology, has aroused great interest from both academia and industry. One open problem for ambient backscatter communication (AmBC) systems is channel estimation for a massive-antenna reader. In this paper, we focus on channel estimation problem in AmBC systems with uniform linear array (ULA) at the reader which consists of large number of antennas. We first design a two-step method to jointly estimate channel gains and direction of arrivals (DoAs), and then refine the estimates through angular rotation. Additionally, Cramer-Rao lower bounds (CRLBs) are derived for both the modulus of the channel gain and the DoA estimates. Simulations are then provided to validate the analysis, and to show the efficiency of the proposed approach.Comment: 5 figures, submitted to IEEE Transactions on Vehicular Technology, 29 March, 201

    Virtual full-duplex multiple-input multiple-output relaying in the presence of inter-relay interference

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    Driven by the increasing demand for wireless broadband, low latency and power-efficient networks, multiple-input multiple-output (MIMO) full-duplex relaying (FDR) schemes have gained much attention in recent years. However, the performance of FDR schemes is impaired by sophisticated self-interference suppression techniques. As such, MIMO virtual FDR (VFDR) schemes have been considered as practical alternatives to recover spectral efficiency loss in half-duplex relays (HDR) without the need for sophisticated self-interference suppression algorithms. Successive relaying (SR) scheme is one of the VFDR techniques which uses a pair of HD relays that alternate between reception and retransmission of the source information to the destination. The performance of the SR based VFDR scheme is affected by inter-relay interference (IRI) due to the concurrent transmission of the source and relay nodes. The interference in VFDR schemes is conventionally treated as a degrading factor on the information decoding receivers resulting in the design of several interference avoidance and cancellation techniques. On the contrary, this thesis developed several VFDR schemes which exploit the interference to achieve performance improvement. In this study, interference management techniques, transmit/receive beamforming matrices, power allocation and joint optimisation algorithms were developed. First, a reliable MIMO VFDR scheme in the presence of IRI was designed, where the IRI was exploited for reliability improvements. The results showed significant reliability improvement over the existing schemes. Second, a joint power allocation for MIMO VFDR schemes under network power constraint was developed. The power allocation problem in the presence of IRI was formulated based on primal-dual algorithm. The results showed that the joint optimisation algorithm can efficiently utilise the network power when compared with the conventional approach. Third, simultaneous wireless information and power transfer (SWIPT) in MIMO VFDR system was proposed, where the transmit beamforming matrices which optimise the achievable rate and harvested energy at the relays were jointly designed. The results showed that the interference energy can be harnessed to improve the SWIPT system throughput. Finally, a joint optimisation of the power split and relay position in SWIPT MIMO VFDR network were investigated. Results showed that the joint optimisation of the power split and distance factors can greatly improve the system outage performance. The analytical and numerical results in the research showed that IRI can be exploited to improve the throughput, reliability and energy harvesting of a wireless communication system. The results also showed a minimum achievable rate improvement of 80% over the HDR schemes and a reliability of 100% over the FDR schemes

    Distributed space-time coding including the golden code with application in cooperative networks

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    This thesis presents new methodologies to improve performance of wireless cooperative networks using the Golden Code. As a form of space-time coding, the Golden Code can achieve diversity-multiplexing tradeoff and the data rate can be twice that of the Alamouti code. In practice, however, asynchronism between relay nodes may reduce performance and channel quality can be degraded from certain antennas. Firstly, a simple offset transmission scheme, which employs full interference cancellation (FIC) and orthogonal frequency division multiplexing (OFDM), is enhanced through the use of four relay nodes and receiver processing to mitigate asynchronism. Then, the potential reduction in diversity gain due to the dependent channel matrix elements in the distributed Golden Code transmission, and the rate penalty of multihop transmission, are mitigated by relay selection based on two-way transmission. The Golden Code is also implemented in an asynchronous one-way relay network over frequency flat and selective channels, and a simple approach to overcome asynchronism is proposed. In one-way communication with computationally efficient sphere decoding, the maximum of the channel parameter means is shown to achieve the best performance for the relay selection through bit error rate simulations. Secondly, to reduce the cost of hardware when multiple antennas are available in a cooperative network, multi-antenna selection is exploited. In this context, maximum-sum transmit antenna selection is proposed. End-to-end signal-to-noise ratio (SNR) is calculated and outage probability analysis is performed when the links are modelled as Rayleigh fading frequency flat channels. The numerical results support the analysis and for a MIMO system maximum-sum selection is shown to outperform maximum-minimum selection. Additionally, pairwise error probability (PEP) analysis is performed for maximum-sum transmit antenna selection with the Golden Code and the diversity order is obtained. Finally, with the assumption of fibre-connected multiple antennas with finite buffers, multiple-antenna selection is implemented on the basis of maximum-sum antenna selection. Frequency flat Rayleigh fading channels are assumed together with a decode and forward transmission scheme. Outage probability analysis is performed by exploiting the steady-state stationarity of a Markov Chain model

    Opportunistic relaying and random linear network coding for secure and reliable communication

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    Opportunistic relaying has the potential to achieve full diversity gain, while random linear network coding (RLNC) can reduce latency and energy consumption. In recent years, there has been a growing interest in the integration of both schemes into wireless networks in order to reap their benefits, while considering security concerns. This paper considers a multi-relay network, where relay nodes employ RLNC to encode confidential data and transmit coded packets to a destination in the presence of an eavesdropper. Four relay selection protocols are studied covering a range of network capabilities, such as the availability of the eavesdropper's channel state information or the possibility to pair the selected relay with a node that intentionally generates interference. For each case, expressions for the probability that a coded packet will not be recovered by a receiver, which can be either the destination or the eavesdropper, are derived. Based on those expressions, a framework is developed that characterizes the probability of the eavesdropper intercepting a sufficient number of coded packets and partially or fully recovering the confidential data. Simulation results confirm the validity and accuracy of the theoretical framework and unveil the security-reliability trade-offs attained by each RLNC-enabled relay selection protocol

    Hybrid satellite–terrestrial networks toward 6G : key technologies and open issues

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    Future wireless networks will be required to provide more wireless services at higher data rates and with global coverage. However, existing homogeneous wireless networks, such as cellular and satellite networks, may not be able to meet such requirements individually, especially in remote terrain, including seas and mountains. One possible solution is to use diversified wireless networks that can exploit the inter-connectivity between satellites, aerial base stations (BSs), and terrestrial BSs over inter-connected space, ground, and aerial networks. Hence, enabling wireless communication in one integrated network has attracted both the industry and the research fraternities. In this work, we provide a comprehensive survey of the most recent work on hybrid satellite–terrestrial networks (HSTNs), focusing on system architecture, performance analysis, design optimization, and secure communication schemes for different cooperative and cognitive HSTN network architectures. Different key technologies are compared. Based on this comparison, several open issues for future research are discussed
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