Showing papers by "Mai Vu published in 2014"

Impact of Propagation Environment on Energy-Efficient Relay Placement: Model and Performance Analysis

Abstract: The performance of a relay-based cellular network is greatly affected by the relay location within a cell. Existing results for optimal relay placement do not reflect how the radio propagation environment and choice of the coding scheme can impact system performance. In this paper, we analyze the impact on relaying performance of node distances, relay height and line-of-sight conditions for both uplink and downlink transmissions, using several relay coding schemes. Our first objective is to propose a geometrical model for energy-efficient relay placement that requires only a small number of characteristic distances. Our second objective is to estimate the maximum cell coverage of a relay-aided cell given power constraints, and conversely, the averaged energy consumption given a cell radius. We show that the practical full decode-forward scheme performs close to the energy-optimized partial decode-forward scheme when the relay is ideally located. However, away from this optimum relay location, performance rapidly degrades and more advanced coding scheme, such as partial decode-forward, is needed to maintain good performance and allow more freedom in the relay placement. Finally, we define a trade-off between cell coverage and energy efficiency, and show that there exists a relay location for which increasing the cell coverage has a minimal impact on the average energy consumed per unit area.

Link-State Based Decode-Forward Schemes for Two-way Relaying

Abstract: In this paper, we analyze a composite decode-and-forward scheme for the two-way relay channel with a direct link. During transmission, our scheme combines both block Markov coding and an independent coding scheme similar to network coding at the relay. The main contribution of this work is to examine how link state impacts the allocation of power between these two distinct techniques, which in turn governs the necessity of each technique in achieving the largest transmission rate region. We analytically determine the link-state regimes and associated relaying techniques. Our results illustrate an interesting trend: when the user-to-relay link is marginally stronger than the direct link, it is optimal to use only independent coding. In this case, the relay need not use full power. However, for larger user-to-relay link gains, the relay must supplement independent coding with block Markov coding to achieve the largest rate region. These link-state regimes are important for the application of two-way relaying in 5G networks, such as in D2D mode or relay-aided transmission.

Link-state based decode-forward schemes for two-way relaying

Abstract: In this paper, we analyze a composite decode-and-forward scheme for the two-way relay channel with a direct link. During transmission, our scheme combines both block Markov coding and an independent coding scheme similar to network coding at the relay. The main contribution of this work is to examine how link state impacts the allocation of power between these two distinct techniques, which in turn governs the necessity of each technique in achieving the largest transmission rate region. We analytically determine the link-state regimes and associated relaying techniques. Our results illustrate an interesting trend: when the user-to-relay link is marginally stronger than the direct link, it is optimal to use only independent coding. In this case, the relay need not use full power. However, for larger user-to-relay link gains, the relay must supplement independent coding with block Markov coding to achieve the largest rate region. These link-state regimes are important for the application of two-way relaying in 5G networks, such as in D2D mode or relay-aided transmission.

Outage Performance of Uplink User-Assisted Relaying in 5G Cellular Networks

Abstract: We use stochastic geometry to analyze the performance of a user-assisted decode-and-forward (DF) relaying scheme where an active user relays data through another idle user in uplink cellular communication. We propose a new geometric policy based on the random selection of an idle user within a certain area mid-way between the active user and base station, and compare this policy to the common nearest neighbor geometric policy. These probabilities are further used in the analytical derivation of the moments of inter-cell interference power caused by system-wide deployment of this user-assisted DF relaying. We then numerically evaluate the outage probability performance and show that user-assisted relaying can significantly improve reliability for active users near the cell edge. We also show that the proposed mid-way policy significantly improves outage performance over the nearest neighbor policy even when the nearest neighbor cooperation probability is higher. This result suggests that mid-way relay selection is a highly effective cooperation policy.

Interference and throughput analysis of uplink user-assisted relaying in cellular networks

Abstract: Relay-aided cooperative communication is a critical component of next generation cellular networks as it improves coverage and boosts system capacity. In this paper, we use stochastic geometry to study the performance of partial decode-and-forward (PDF) relaying through another idle user in uplink cellular communication. We analytically derive the average inter-cell interference power caused by system-wide deployment of this PDF relaying. This interference analysis provides the basis for quantitatively evaluating performance impacts of user-assisted relaying in cellular networks. We show that user-assisted relaying can significantly improve per-user transmission rate despite of increased inter-cell interference. This throughput gain further increases with higher idle-user density.

Outage Analysis and Power Savings for Independent and Coherent Decode-Forward Relaying

Abstract: In this paper, we consider a composite independent and coherent decode-forward (DF) relaying scheme and analytically evaluate its outage performance over Rayleigh fading channels. We examine the link-state regimes in which the optimal strategy is either direct transmission, independent DF (IDF), or coherent DF (CDF), depending on the relation among the links. Outage probabilities at both the relay and destination are determined in order to analytically derive the overall outage performance. With full channel state information (CSI), the relay can save power without affecting the overall outage performance. Specifically, by using only a portion of its maximum power for transmission, the relay conserves power in the IDF regime while still achieving the maximum transmission rate. Even with just statistical CSI, the relay can employ these link regime results to reduce transmit power significantly while maintaining the same outage performance as that of using full power.

Outage analysis for half-duplex partial decode-forward relaying over fading channels

Abstract: We analytically evaluate the outage performance of the half-duplex partial decode-forward (PDF) relaying over Rayleigh fading channels. In PDF relaying, the source splits its information into cooperative and private parts, and the relay decodes only the cooperative information then forwards it to the destination coherently with the source. Assuming full CSI at the receivers and limited CSI at the transmitters, we analyze the outage performance by jointly considering outages of the cooperative and private parts at both the relay and the destination. In spite of additional outage at the relay and limited CSI at the transmitters, we show that PDF relaying achieves the full diversity order of 2 at high SNR. Numerical results confirm the analysis and show the advantage of the considered PDF scheme, with coherent transmission and joint decoding at the destination, over the existing DF and PDF schemes.

Uplink User-Assisted Relaying Deployment in Cellular Networks.

Abstract: We use stochastic geometry to analyze the performance of a partial decode-and-forward (PDF) relaying scheme applied in a user-assisted relaying setting where an active user relays data through another idle user in uplink cellular communication. We present the geometric model of a network deploying user-assisted relaying and propose two geometric cooperation policies for fast and slow fading channels. We analytically derive the cooperation probability for both policies which is further used in the analytical derivation of the moments of inter-cell interference power caused by system-wide deployment of this user-assisted PDF relaying. We then model the inter-cell interference power statistics using the Gamma distribution by matching the first two moments analytically derived. This cooperation and interference analysis provides the theoretical basis for quantitatively evaluating performance impacts of user-assisted relaying in cellular networks. We then numerically evaluate the average transmission rate performance and show that user-assisted relaying can significantly improve per-user transmission rate despite of increased inter-cell interference. This throughput gain is significant for active users near the cell edge and further increases with higher idle user density, supporting user-assisted relaying as a viable solution to crowded population areas.

Trade-offs on energy-efficient relay deployment in cellular networks

Abstract: Relay-based cellular networks are likely to play an important role in the race for energy efficiency. However, potential gains greatly depend on how relay stations are deployed within the cell. Using a geometrical model for energy-efficient analysis, we investigate the impact of the number and location of relays on energy consumption, and its dependence on the relay coding scheme and the propagation environment, i.e. the pathloss and the line-of-sight conditions. In addition to the transmit energy, we account for the economic cost of relay deployment, as well as the overhead energy dissipated at each relay stations due to data processing and network maintenance. We then bring out four key trade-offs which balance the cost and flexibility of relay deployment, the energy efficiency and the coverage extension.

Relay Power Savings through Independent Coding

Abstract: We present a link-state based composite decode-forward (DF) scheme for the relay channel comprised of independent coding and coherent block Markov coding. Although it is believed that block Markov coding is the optimal DF technique whenever the source- to-relay link is stronger than the direct link, we show that under some link-state conditions, independent coding achieves the same rate but also results in power savings at the relay. We then apply this composite scheme in fading under a practical channel state information (CSI) assumption in which nodes have perfect receive CSI and long-term transmit CSI. Through simulation, we demonstrate that the throughput with practical CSI achieves a rate comparable to that of block Markov coding, but with less required relay power. Further, we expose a novel trade-off between consumed relay power and rate gain for relay placement. Specifically, the relay conserves the most power when closer to the destination but achieves the most rate gain when closer to the source.

Exhaustive message splitting for partial decode-forward in single-source single-destination relay networks

Abstract: We introduce exhaustive message splitting for partial decode-forward in a single-source single-destination relay network with N relays, in which every relay subset has a private message to decode. We apply this idea to a three-relay network and propose a partial decode-forward scheme based on block Markov encoding with exhaustive message splitting and derive its achievable rate. A directed graph of the superposition codebook structure is provided to assist the understanding of the code hierarchy. We also apply the scheme to a Gaussian network and show that our scheme generalizes network decode-forward in [1] and the private message scheme in [2].

Uplink User-Assisted Relaying in Cellular Networks

Abstract: We use stochastic geometry to analyze the performance of a partial decode-and-forward (PDF) relaying scheme applied in a user-assisted relaying setting, where an active user relays data through another idle user in uplink cellular communication. We present the geometric model of a network deploying user-assisted relaying and propose two geometric cooperation policies for fast and slow fading channels. We analytically derive the cooperation probability for both policies. This cooperation probability is further used in the analytical derivation of the moments of inter-cell interference power caused by system-wide deployment of this user-assisted PDF relaying. We then model the inter-cell interference power statistics using the Gamma distribution by matching the first two moments analytically derived. This cooperation and interference analysis provides the theoretical basis for quantitatively evaluating the performance impact of user-assisted relaying in cellular networks. We then numerically evaluate the average transmission rate performance and show that user-assisted relaying can significantly improve per-user transmission rate despite of increased inter-cell interference. This transmission rate gain is significant for active users near the cell edge and further increases with higher idle user density, supporting user-assisted relaying as a viable solution to crowded population areas.