Zhengchuan Chen

Optimum Transmission Policies for Energy Harvesting Sensor Networks Powered by a Mobile Control Center

Wireless energy transfer, namely, radio frequency (RF)-based energy harvesting, is a potential way to prolong the lifetime of energy-constrained devices, especially in wireless sensor networks. However, due to huge propagation attenuation, its energy efficiency is regarded as the biggest bottleneck to wide applications. It is critical to find appropriate transmission policies to improve the global energy efficiency in this kind of system. To this end, this paper focuses on the sensor networks scenario, where a mobile control center powers the sensors by RF signal and also collects information from them. Two related schemes, called harvest-and-use scheme and harvest-store-use scheme, are investigated. In the harvest-and-use scheme, as a benchmark, both constant and adaptive transmission modes from sensors are discussed. In the harvest-store-use scheme, we propose a new concept, the best opportunity for wireless energy transfer, and use it to derive an explicit closed-form expression of optimal transmission policy. It is shown by simulation that a considerable improvement in terms of energy efficiency can be obtained with the help of the transmission policies developed in this paper. Furthermore, the transmission policies are also discussed under the constraint of fixed information rate. The minimal required power, the performance loss from the new constraint, and the effect of fading are then presented.

How channel fadings affect the system service of high speed railway communications

As the rapid development of high speed railway (HSR) all over the world, the very high data rate wideband communication on HSR attracts huge attention. Since there exists a dominant line of sight component in the communication channel in most cases, most of works in the literature employed the assumption that the transmission channel is with additive white Gaussian noise (AWGN), referred to the quasi-AWGN model. However, a small scale channel fading is always existing, which can be characterized by using the Nakagami model due to its flexibility with adaptive parameter m. In this paper, we shall investigate how the channel fading affect the mobile service of system in very high speed railway communication systems and try to answer when the quasi-AWGN approach model is valid. Some theoretical analysis and numeral results are presented. It will show that there exists a threshold. When fading parameter is larger than the value of threshold, the effect of fading can be neglected. Otherwise, the channel fading need to be taken into account when discussing the system design or making the railway communication system planning.

Cooperation in 5G Heterogeneous Networking: Relay Scheme Combination and Resource Allocation

In 5G heterogeneous networking, it is promising to integrate different wireless networks to provide higher data rate. This paper models the integrated system as a receiver frequency division relay channel (RFDRC) and studies how to improve the transmission rate by combining decode-forward (DF), compress-forward (CF), and amplify-forward (AF) schemes. First, we establish clear criterions on how to select a relay scheme among DF, CF, and AF schemes and prove that the CF outperforms AF for all possible configurations. Based on the scheme selection criterions, we propose a hybrid DF-CF scheme which takes advantage of both DF and CF schemes in RFDRC. A near-optimal resource allocation is presented for the DF-CF-based system, leading to a new achievable rate for RFDRC. For ease of implementation, we further put forward a hybrid DF-AF scheme and reconsider the joint bandwidth and power allocation. Two suboptimal resource allocation solutions are established. In particular, when source frequency band and relay frequency band have equivalent bandwidth, we show that the proposed hybrid DF-AF scheme can achieve the concave envelope of the maximum between DF rate and AF rate. Numerical results show that the proposed schemes bring significant gains for RFDRC.

SNR Decomposition for Full-Duplex Gaussian Relay Channel

A relay channel (RC), consisting of a source, a relay, and a destination, is a basic transmission unit of cooperative communication networks. The capacity of an RC is not known in general. In this paper, an SNR decomposition (SD) strategy is presented to implement time sharing, which provides a new tractable and achievable rate for a full-duplex Gaussian RC. More specifically, we first expand the SNR of a relay destination channel (SNR-RD) into two terms under the relay power constraint and divide the system into two subbands. Then, we assign the obtained SNR-RD for each subband and employ decode-forward (DF) or compress-forward (CF) according to the assigned SNR-RD. It is shown that the achievable rate of the SD strategy is competitive with that of superposing CF on DF. As the superposition structure requires a sophisticated codeword design, the SD strategy provides another practical combination structure of DF and CF strategies. Approximations for the SNR-RD and bandwidth allocation for subbands are also given. Based on the obtained results, two application scenarios, i.e., mobile relay and quasi-static fading RCs, are also considered. Finally, various numerical results are shown to support our developed theoretical results.

Subband division for Gaussian relay channel

This work considers the achievable rate region of full-duplex Gaussian relay channel. Under Gaussian signaling, it was found that neither Decode-Forward (DF) nor Compress-Forward (CF) can achieve better performance than the other for all channel gains. Recently, it was verified that superposing CF on DF in one band has a better performance than both DF and CF for Gaussian signaling. In this work, we consider another combining structure of CF and DF by making use of Subband Division (SD). It will show that our new developed strategy will achieve a larger rate for Gaussian signaling by comparing with DF lower bound, CF lower bound and the result of superposing CF on DF. In addition, a closed form solution of the achievable rate is found, in which the subband division factors are also given. Numerical results confirm our developed theoretical results.

Position-Based Power Allocation for Uplink HSRs Wireless Communication When Two Trains Encounter

Highly mobile wireless communication attracts much more attention currently due to the rapid development of high speed railways (HSRs) all over the world. Although the single train scenario has been well studied by now, two trains encountering scenario over the general two-way railways is also an important problem deserving to investigate. To this end, this paper concentrates on the uplink information transmission of HSRs in the two trains encountering scenario, which is modeled as a time- varying partial multiple access channel. In order to evaluate the transmission performance, the achievable rate region is utilized as a metric to characterize the tradeoff between the rates that each train can obtain under limited channel source constraint. With the help of superposition modulation and sequential interference cancelling, an optimal adaptive power allocation scheme aided by real-time position information is proposed to achieve the maximal boundary of the achievable rate region, namely alleviating the effect of encountering on information transmission to the largest extent. According to the numerical results, great improvement can be obtained by new proposed adaptive power allocation along time.

Multiple multicast for a half-duplex butterfly network: a deterministic approach

We investigate the multicast throughput of a butterfly network, which may be a promising topology for network coding application in next-generation wireless communication systems. The butterfly network consists of two sources, two destinations and a relay, where each destination requires decoding of data from two independent sources. It is assumed that all the nodes are operated in half-duplex mode. Each end-to-end packet transmission should be completed in a two-phase period. In order to reduce processing complexity and multiple interference, other nodes should keep silent when the relay transmits a signal. By using Avestimehr, Diggavi and Tses deterministic model, we first introduce a deterministic butterfly network and demonstrate that its maximal multicast rate region can be achieved by employing a network coding policy. According to the results obtained in deterministic case, we then put forward a near-optimal design on the transmitted signal and decoding scheme for Gaussian scenarios based on a nested lattice code. It is proved that the gap between the achievable rate region and an outer bound is less than 3bits/s/Hz, which is not related to the signal-to-noise ratio. That is, the proposed scheme can approach the maximal multicast throughput. Finally, numerical results demonstrate that the gap is robust to both channel gains and time division of the two phases. Copyright

Spectral Efficiency and Relay Energy Efficiency of Full-Duplex Relay Channel

Full-duplex relaying has the potential to improve the spectral efficiency (SE) of cooperative communication systems. Due to residual self-interference (RSI), increase of the relay power does not always contribute to SE improvement. To fully utilize full-duplex relaying in cooperative communications, the effect of RSI on the SE achieved by different relay schemes need to be investigated. In this paper, we study bounds on the SE of full-duplex relay channel with decode-forward (DF) relaying, compress-forward (CF) relaying, and amplify-forward (AF) relaying in the presence of RSI. For respective schemes, optimal relay power and the corresponding maximal SE are derived in closed-form. Bounds on the relay energy-efficiency (REE) are presented for different schemes, which are useful for system design under per-node energy efficiency constraint. Based on the SE performance, the conditions of employing full-duplex relay, criteria for selecting relay scheme among DF, CF, and AF schemes, and the conditions of adopting hybrid full-duplex or half-duplex mode are elaborated regarding to RSI strength. In summary, this paper investigates the relationship among SE, REE, and system design by taking into account the effect of RSI for a general class of cooperation schemes.

Coherent Signaling for Full-Duplex Relay Channel With Self-Interference

To improve the spectral efficiency (SE), coherent signaling is investigated for full-duplex relay channel (FDRC) in the presence of residual self-interference. First, we propose a novel coherent amplify-forward scheme and derive the SE achieved by both forward decoding and backward decoding. Condition on selecting forward/backward decoding is clearly given. Then, we elaborate the signal design for coherent decode-forward scheme and derive the optimal correlation coefficient for signaling. The optimal relay power that maximizes the SE is obtained in the closed form. Representative numerical results show that coherent signaling brings significant SE gain for FDRC.

A hybrid DF and CF scheme with adaptive power allocation for half-duplex relay channel

The relay scheme and the corresponding rate performance are considered for a half-duplex relay channel in which the source can only transmit information with fixed power. As different relay strategies result in different rate performance, we first present a decision criterion for selecting between Decode-and-Forward (DF) and Compress-and-Forward (CF) strategies by thoroughly analyzing their achievable rate. Based on the analysis result, the maximum of the DF rate and CF rate can be achieved by strategy selection procedure. To further obtain a larger rate, we put forward a hybrid DF-CF scheme in which the strategy selection between DF and CF is combined with active relay power allocation efficiently. It is shown that the concave envelope of the maximum of DF rate and CF rate is achievable via our new developed hybrid scheme. For the convenience of implementation, we also present a suboptimal setting for the hybrid DF-CF scheme. Numerical results show that the suboptimal setting can achieve a rate approaching the maximal rate.