Lossy decode-and-forward (DF) relaying, also referred to as lossy forwarding (LF), can significantly enhance the transmission reliability and expand the communication coverage at the cost of a small increase in computational effort compared to its DF counterpart. Furthermore, it can further simplify the operations at the relay nodes by removing the error-detecting operation, e.g., cyclic redundancy check, which is used in the conventional DF systems. Due to these advantages, LF has been intensively investigated with the aim of its applications to various cooperative communication networks with different topologies. This paper offers a comprehensive literature review on the LF relaying strategy and makes comparisons between LF and DF. Five basic exemplifying scenarios are taken into consideration. These are the three-node network, the single-source multi-relay network with direct source-to-destination link, the multiple access relay channel, the two-way relay network, and the general multi-source multi-relay network. The paper includes not only theoretical performance limit analyses, but also performance evaluation by employing low-complexity accumulator aided turbo codes at the sources and relays as well as joint decoding at the destination. As expected, the performance enhancement in terms of outage probability, frame error rate, and -outage achievable rate by LF over DF is significant, which is demonstrated in all the exemplifying scenarios in the literatures. Hence LF has a great potential to be applied to future 5G wireless communication networks, e.g., device-to-device, vehicle-to-vehicle, and machine-type communications, which are composed of the aforementioned exemplifying scenarios.

We develop a joint source-channel coding (JSCC) scheme based on an unequal power allocation strategy, in which different levels of power are allocated according to a priori probability distribution of the information bits. Two protograph low-density parity-check codes are used as the source code and the channel code, respectively, in the proposed JSCC scheme. With fixed row weight and row element alphabet, optimization on the source code is conducted via random search to obtain a best-found base matrix with the lowest decoding threshold among all the searched base matrices. Simulation results show that the new JSCC scheme outperforms the traditional equal power allocation-based JSCC by exploiting the source statistics at the decoder. Moreover, theoretical threshold analysis is in agreement with the practical simulation results.

This paper investigates short-packet communications over a diamond relay network with two untrusted relays (potential eavesdroppers) with the purpose of guaranteeing reliability and security simultaneously. As the performance metric, reliable-and-secure probability (RSP), considering both reliability and secrecy, is defined from the perspective of physical layer security. An analytical approach is proposed to investigate reliability and security by taking into account the characteristics of the short-packet transmission. RSPs are numerically obtained via the analytical framework by utilizing the source-channel separation theorem for the source-to-relay transmission and chief executive officer (CEO) problem analyses for the relay-to-destination transmission. It is found that the optimal RSP is achieved when the contributions from the source-relay transmission and the relay-destination transmission are balanced, even without support from a friendly jamming signal or artificial noise.

Non-orthogonal transmission is considered to be one of the promising techniques for improving the throughput of the existing and future wireless communication networks. We concentrate on the transmission of both independent and correlated binary sources over a non-orthogonal multiple access relay channel (MARC), which consists of two sources, one relay, and one destination. The lossy decode-and-forward (DF), developed from the conventional DF, is adopted at the relay. Two time slots are required with non-orthogonal transmission over such network setup, while three time slots are required with the conventional orthogonal transmission. We analyze the outage probability of transmission of independent binary sources over the non-orthogonal MARC based on the theorem of multiple access channel (MAC) with a helper, which combines the Slepian-Wolf rate region and the MAC capacity region. For the performance verification, we implement a practical coding-decoding chain, which is applicable to the transmission of both independent and correlated binary sources. Exclusive-OR based multi-user complete decoding is introduced at the relay node, and iterative joint decoding is utilized at the destination by taking into consideration the estimated intra-link error probability and correlation information between the sources. The practical simulation results are well matched with the theoretical analyses.

This paper presents an in-depth performance analysis of lossy communications in a single-relay system, where the recovered information is not necessarily lossless in both the relay and the destination. In this system, the relay continues transmitting the sequence with source-relay link errors to the destination even if errors are detected after decoding, i.e., so-called Lossy-Forward (LF) strategy. The problem can be decomposed into two parts as follows: a point-to-point coding problem in the source-relay (S-R) link, and a lossy source coding problem with a LF relay in the source-destination (S-D) and relay-destination (R-D) links. To begin with, we derive the admissible rate region of the lossy source coding problem with a LF relay for a specified distortion requirement. Then, we focus on the analysis of outage probability over block Rayleigh fading channels. Finally, a practical encoding/decoding scheme is proposed for the evaluation of system performance by computer simulations. Due to the suboptimal channel coding and incomplete utilization of joint typicality, the theoretical performance cannot be achieved in the simulation; however, the tendency of curves in simulations matches that in theoretical calculation.

We theoretically analyze outage probabilities of the lossy-forward (LF), decode-and-forward (DF) and adaptive decode-and-forward (ADF) relaying techniques, with the aim of characterizing the impact of the spatial and temporal correlations of the fading variations. First, the exact outage probability expressions are analytically obtained for LF, DF, and ADF relaying assuming each link suffers from statistically independent Rayleigh fading. Then, approximated, yet accurate closed-form expressions of the outage probabilities for the relaying schemes are derived. Based on the expressions, diversity and coding gains are found. The mathematical methodology for the derivation of the explicit outage probability is further extended to the case where the account is taken of the spatial and temporal correlations of the fading variations. The diversity gains with LF, DF, and ADF are then derived in the presence of the correlations. It is found out that the three techniques can achieve full diversity, as long as the fading variations are not fully correlated. We then investigate the optimal relay location and the optimal power allocation for the three relaying techniques. It is shown that the optimal solutions can be obtained under the framework of convex optimization. It is reveal that in correlated fading, the relay should move close to the destination or allocate more transmit power to the relay for achieving lower outage probabilities, compared to the case in independent fading.