Resource-efficient wireless relaying protocols

Relay-aided communication is considered one of the key techniques to achieve high throughput at low cost in future wireless systems. However, when transmitting signals via a relay, additional time slots, antennas, or frequency slots are required, which may erode the potential gain of relay-aided systems. In this article various approaches to creating relay-aided systems are reviewed. The advantages and disadvantages of various relaying schemes are compared in terms of their slot efficiency, error rate performance, and feasibility. Our detailed comparisons and the numerical results indicate that the specific family of network coding aided relaying protocols constitutes one of the most promising solutions. We conclude this article by listing a number of open problems

Cooperative Compute-and-Forward

We examine the benefits of user cooperation under compute-and-forward. Much like in network coding, receivers in a compute-and-forward network recover finite-field linear combinations of transmitters' messages. Recovery is enabled by linear codes: transmitters map messages to a linear codebook, and receivers attempt to decode the incoming superposition of signals to an integer combination of codewords. However, the achievable computation rates are low if channel gains do not correspond to a suitable linear combination. In response to this challenge, we propose a cooperative approach to compute-and-forward. We devise a lattice-coding approach to block Markov encoding with which we construct a decode-and-forward style computation strategy. Transmitters broadcast lattice codewords, decode each other's messages, and then cooperatively transmit resolution information to aid receivers in decoding the integer combinations. Using our strategy, we show that cooperation offers a significant improvement both in the achievable computation rate and in the diversity-multiplexing tradeoff.Comment: submitted to IEEE Transactions on Information Theor

An Opportunistic-Non Orthogonal Multiple Access based Cooperative Relaying system over Rician Fading Channels

Non-orthogonal Multiple Access (NOMA) has become a salient technology for improving the spectral efficiency of the next generation 5G wireless communication networks. In this paper, the achievable average rate of an Opportunistic Non-Orthogonal Multiple Access (O-NOMA) based Cooperative Relaying System (CRS) is studied under Rician fading channels with Channel State Information (CSI) available at the source terminal. Based on CSI, for opportunistic transmission, the source immediately chooses either the direct transmission or the cooperative NOMA transmission using the relay, which can provide better achievable average rate performance than the existing Conventional-NOMA (C-NOMA) based CRS with no CSI at the source node. Furthermore, a mathematical expression is also derived for the achievable average rate and the results are compared with C-NOMA based CRS with no CSI at the transmitter end, over a range of increasing power allocation coefficients, transmit Signal-to-Noise Ratios (SNRs) and average channel powers. Numerical results show that the CRS using O-NOMA with CSI achieves better spectral efficiency in terms of the achievable average rate than the Conventional-NOMA based CRS without CSI. To check the consistency of the derived analytical results, Monte Carlo simulations are performed which verify that the results are consistent and matched well with the simulation results.Comment: arXiv admin note: substantial text overlap with arXiv:1709.0822

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