Shen Qian

Outage based power allocation for a lossy-forwarding relaying system

In this paper, an optimal power allocation scheme for a simple lossy-forwarding relaying system is provided. Here, we extend our previous work of optimal power allocation of Slepian-Wolf relay system with constant source-relay error probability, to such that block Rayleigh fading is assumed for all transmission channel and lossy transmission is assumed in source-relay channel. Since data sequences transmitted from source and relay nodes are sent from one original source, they are correlated. At destination node, by exploiting the correlation knowledge between the two data sequences in joint decoding, the performance of the whole system can be significantly enhanced. This is because the network can be seen as a distributed Turbo code. A closed-form expression of the outage probability is derived at high signal-to-noisy ratios regime. It is shown that the outage curves calculated from the closed-form expression are sufficiently close to that obtained by the numerical calculation. Then, the optimum power allocation to the nodes for the system can be formulated as a convex optimization problem. Specifically, we minimize the outage probability while assuming the total transmit power is fixed, and also to minimize the total power under an given outage requirement. It is found that the system performance with the proposed optimum power allocation scheme outperform that with equal power allocation.

Performance Analysis of OSTBC Transmission in Lossy Forward MIMO Relay Networks

We analyze the outage probability for the orthogonal space-time block code based multiple-input multiple-output (MIMO) relay networks, composed of one source, one relay, and a single destination. The relay forwards the decoded and interleaved information sequence even though the information part may contain error(s), according to the lossy forward strategy. In spatially independent MIMO channels, we find that the diversity order of the relay network can be interpreted and formulated by the well-known max-flow min-cut theorem. Moreover, we extend the analysis to the case of spatially correlated MIMO channels. Approximated explicit expressions for the outage probabilities are obtained in high signal-to-noise ratio regime.

Outage probability analysis for correlated sources transmission over Rician fading channels

In this paper, the outage probability of a Slepian-Wolf transmission system is analysed theoretically. We consider two correlated binary information sequences where bit-flipping model is adopted, where the the information bits of the second source are the flipped version of the information bits of the first one, with a probability Pf. Here, we extend our previous work of the correlated sources transmission over block Rayleigh fading channels to such that the channel between one source and the destination is assumed to suffer from block Rayleigh fading, whereas the channel between the other source and the destination is assumed to suffer from block Rician fading. The outage probability is analysed theoretically. The results show that when Pf = 0, the outage curves versus signal-to-noise power ratio (SNR) exhibits sharper decay than that with the 2nd order diversity, as the line-of-sight (LOS) component power of Rician channel increases. It is also found that the outage curves asymptotically converge in to that with the 1st order diversity when Pf ≠ 0. Furthermore, this paper also determines the optimal power allocation under the condition that total transmit power of the system is kept constant. It can be concluded that increasing the ratio of LOS component power of Rician channels can not always improve the outage performance, so far as Pf ≠ 0.

Joint optimization of power allocation and relay position for lossy-forwarding relaying

Joint optimization of power allocation (PA) and relay position (RP) is investigated for a lossy-forwarding relaying in order to minimize the outage probability. We investigate adaptive PA with fixed relay position, adaptive RP with fixed PA ratio, and joint optimization of the PA and RP under total transmit power constraint. A closed-form expression of the outage probability is derived at the high signal-to-noise ratio regime. It is shown that the closed-form expression is sufficiently accurate compared to numerical calculation results. Then, the optimum PA and the optimum RP can be formulated as a convex optimization problem. It is found that the system performance with the adaptive optimum PA outperforms that with equal power allocation. The outage performance with the adaptive optimum RP outperforms that with midpoint RP. However, the joint optimization of the PA and RP is superior to the semi-adaptive optimization algorithms.

Performance Improvement of Joint Source-Channel Coding With Unequal Power Allocation

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.

Fading Correlations for Wireless Cooperative Communications: Diversity and Coding Gains

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 revealed 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 with the case in independent fading.

Performance analysis for multi-source multi-relay transmission over κ-μ fading channels

We derive the outage probability of a multi-source multi-relay transmission system, where all the links experience κ-μ fading variations. The source-relay links are assumed to be non-orthogonal multiple access channels (MACs). Two transmission schemes are considered for relay-destination transmission, i.e., non-orthogonal maximum ratio transmission (MRT) and orthogonal transmission with joint-decoding (JD) at the destination. The outage probability is formulated by taking into consideration the different decoding results at the relays. It is found that, with or without the impact of line-of-sight (LOS) component or the number of multipath clusters in channels, the outage performance of the system with JD is superior to that with MRT. Furthermore, we investigate the impact of the geometric gain based relay location and power allocation for relays on the performance.

Finite-SNR diversity-multiplexing tradeoff for decode-and-forward relaying system allowing intra-link errors

We analyse finite-SNR diversity-multiplexing tradeoff (f-DMT) for a recently emerging decode-and-forward relaying system allowing intra-link errors (DF-IE). In this framework, an adaptive system spectrum efficiency which is assumed to be used in the system, is proportional to the capacity of an additive white Gaussian noise (AWGN) channel. The proportionality is referred as multiplexing gain to the aggressiveness of scaling the data rate by the system. The diversity gain is given by the negative log-log slope of outage probability to depict the reliability enhanced with increasing signal-to-noise ratio (SNR). The f-DMT for DF-IE is derived according to the Slepian-Wolf theorem-based outage analysis. The main results are: (i) the DF-IE system outperforms the conventional decode-and-forward (DF) system in whole SNR region, (ii) additional 0.25 multiplexing gain can be achieved by the DF-IE system. Finally, the analytical results are verified by Monte Carlo simulations.

A comparative study on outage probabilities of decode-and-forward and lossy-forward relay techniques

The primary objective of this paper is to make a performance comparison in terms of outage probability between decode-and-forward with joint decoding (DF-JD) and lossy-forward (LF) techniques. With DF-JD, only if the relays received information sequence can be decoded with an arbitrarily low error probability, it is forwarded to the destination. On the contrary, with LF, the relay node always forwards decoded information sequence to the destination even if a decoding error is detected. Interleaving is used at relay and joint decoding is utilized at the destination to exploit the source-relay correlation for both techniques. The outage probability of conventional DF system with maximum ratio combining (DF-MRC) performed at the destination is also presented. Asymmetric statistical properties of the fading variations for each link are taken into account. It is shown that regardless of the presence of line-of-sight component, the outage probability with LF relay system is significantly smaller than that with DF-JD and DF-MRC relay systems. The impact of the per-link spectrum efficiency, representing the modulation multiplicity and channel coding rate, on outage probability is also investigated. It is found that, given that the specified per-link spectrum efficiency is satisfied, LF relay system always achieves lower outage performance than that with DF-JD and DF-MRC systems. The accuracy of the analytical results are verified by a series of Monte Carlo simulations.