Shuping Dang

Combined bulk and per-tone relay selection in super dense wireless networks

The combined bulk/per-tone transmit antenna selection strategy has been shown to achieve optimal diversity and coding gains for single-hop systems with multiple transmit and receive antennas. In this paper, we extend this strategy to the case in which a set of user pairs communicate via a cluster of intermediary amplify-and-forward relaying nodes. We obtain an upper bound on the outage probability of the network, and a closed-form expression for the multiuser contention probability (the probability that distinct user pairs select the same relay). Consequently, we are able to construct an upper bound on the failure probability of the network, i.e., the probability that either an outage or contention occurs. We show that there exists a critical average end-to-end SNR, above which the outage probability decays exponentially with the number of available relays. In this case, the network failure probability is dominated by the contention probability. Many of our results are of a fundamental (asymptotic) nature, but key results are verified with simulations and illustrated numerically for finite system sizes.

Resource Allocation for Full-Duplex Relay-Assisted Device-to-Device Multicarrier Systems

This letter analyzes the resource allocation problem for full-duplex relay-assisted device-to-device (D2D) multicarrier systems, where multiple D2D user groups (UGs) coexist in an underlaying manner. We formulate the optimization problem, which takes the maximization of the system throughput as an objective. Two resources, i.e., subcarrier and transmit power are considered to be appropriately allocated to UGs in order to meet the objective. The formulated problem can be independently divided into a quasi-concave problem and a mixed binary integer programming (MBIP) problem. The MBIP problem is NP-hard. Therefore, to solve this problem efficiently by standard optimization techniques, we propose an alternative algorithm, which is the linear relaxation of the MBIP problem. Then, we mathematically prove and numerically verify the equivalence of the MBIP problem and its linear relaxation. By this way, the resource allocation for UGs can be carried out by a small amount of computational overhead.

Outage Performance Analysis of Full-Duplex Relay-Assisted Device-to-Device Systems in Uplink Cellular Networks

This paper proposes a full-duplex cooperative device-to-device (D2D) communication system, where the relay employed can receive and transmit signals simultaneously. We adopt such a system to assist with D2D transmission. We first derive the conditional cumulative distribution function and the probability density function (pdf) of a series of channel parameters when the interference to the base station is taken into consideration and power control is applied at the D2D transmitter and the relay node. Then, we obtain an exact expression for the outage probability as an integral and as a closed-form expression for a special case, which can be used as a good approximation to the general case when residual self-interference is small. Additionally, we also investigate the power allocation problem between the source and the relay and formulate a suboptimal allocation problem, which we prove to be quasi-concave. Our analysis is verified by the Monte Carlo simulations, and a number of important features of full-duplex cooperative D2D communications can, thereby, be revealed.

An Equivalence Principle for OFDM-Based Combined Bulk/Per-Subcarrier Relay Selection Over Equally Spatially Correlated Channels

In this paper, we propose a novel relay selection scheme for orthogonal frequency-division multiplexing systems by combining conventional bulk and per-subcarrier selection schemes and analyze its outage performance over equally spatially correlated channels. Specifically, the combined selection scheme selects only two relays at the first attempt and performs per-subcarrier selection over these two relays. We analyze the asymptotic outage performance of the combined selection scheme in the high signal-to-noise ratio (SNR) region and prove a generalized theorem. This theorem states that the combined selection can achieve an optimal outage probability equivalent to the per-subcarrier selection at a high SNR without using the full set of available relays for selection. This unique property is termed the equivalence principle, and it holds for all correlation conditions. To explore this principle, we consider three examples: decode-and-forward, fixed-gain amplify-and-forward (AF), and variable-gain AF relay systems. Furthermore, two extended applications, i.e., antenna selection and branch selection, are also considered to reveal the feasibility and the expandability of the equivalence principle. Our analysis is verified by Monte Carlo simulations. The proposed combined selection and the proved theorem provide a general and feasible solution to the tradeoff between system complexity and outage performance when relay selection is applied.

Comparison of multicarrier relay selection schemes in super dense networks

In this paper, we critically compare the performances of bulk, per-subcarrier and combined selection schemes in super dense networks. Specifically, their outage and contention probabilities are critically appraised. To analyze the effects of outage and contention together, a performance parameter termed the bulk gain factor is defined and employed. Finally, we find that although the bulk selection scheme yields a worse outage performance, it would still be preferable in super dense networks as long as a sufficiently large transmit power is employed, since it only demands one relay and has a lower contention probability. Note, this conclusion is constructed based on the fact that when the bulk selection scheme is applied, the contention probability is still much higher than the outage probability in super dense networks. Our results serve as a design benchmark for physical layer applications/protocols used in super dense networks. Also, with these results, we provide a theoretical basis to further optimize super dense networks by reducing contention probability.

Combined Bulk/Per-Subcarrier Relay Selection in Two-Hop OFDM Systems

In this paper, we apply the concept of combined bulk/per-subcarrier selection to two-hop relay selection systems employing OFDM. The outage probability of the proposed strategy is analyzed in the high SNR regime when decode-and-forward, fixed-gain amplify-and-forward and variable-gain amplify-and-forward are employed at the relays. Meanwhile, a generalized situation without specifying the relaying protocol is also analyzed. We mathematically prove that the combined selection strategy is able to achieve an optimal outage probability equivalent to conventional per- subcarrier selection in the high SNR regime without using the full set of available relays for selection. Moreover, we demonstrate through numerical simulations that this performance advantage holds when channels are spatially correlated.

A SVD-Based Optimum Algorithm Research for Macro-Femto Cell Interference Coordination

The intra-tier interference in heterogeneous networks becomes more serious when the number of macro-femto cells dramatically increases. Based on the singular value decomposition (SVD) algorithm, this paper proposes an optimized interference alignment (IA) algorithm to improve the macro-femto cell downlink rate. To achieve the largest degrees of freedom (DOF), we adopt the precoding matrix as a powerful tool to mitigate the effect of inter-channel interference (ICI). In comparison with the conventional interference coordination methods, the SVD algorithm is capable of adjusting the coefficients of the precoding matrix with lower complexity. Furthermore, zero-forcing algorithm is also used to combat ICI in this proposed IA algorithm. The numerical results show that ICI can be suppressed effectively and the system performance in terms of throughput and signal-to-interference- plus-noise ratio (SINR) can be improved considerably.

Outage performance analysis of multicarrier relay selection for cooperative networks

In this paper, we analyze the outage performance of two multicarrier relay selection schemes, i.e. bulk and per-subcarrier selections, for two-hop orthogonal frequency-division multiplexing (OFDM) systems. To provide a comprehensive analysis, three forwarding protocols: decode-and-forward (DF), fixed-gain (FG) amplify-and-forward (AF) and variable-gain (VG) AF relay systems are considered. We obtain closed-form approximations for the outage probability and closed-form expressions for the asymptotic outage probability in the high signal-to-noise ratio (SNR) region for all cases. Our analysis is verified by Monte Carlo simulations, and provides an analytical framework for multicarrier systems with relay selection.