Maximal Lifetime Scheduling for Cooperative Communications in Wireless Networks

Cooperative communication (CC) has been proposed to increase the wireless channel capacity and reliability by employing multiple single-antenna nodes to form a virtual antenna array. Many efforts focus on exploiting the benefits of CC among multiple source-destination pairs with an unrealistic assumption that each of them communicates over a dedicated channel without interference. In this paper, we investigate the transmission scheduling problem for multiple source-destination pairs under the assistance of a set of dedicated relay nodes on a single channel. By applying the protocol interference model, we propose a concept of cooperative link to characterize the interference regions of CC. Due to the NP-completeness of optimal scheduling, LP (linear programming) based heuristic algorithms are proposed to maximize the minimum transmission rate under a given relay assignment. Then, without specifying a relay node for each source-destination pair, we study the max-min rate problem by jointly considering transmission scheduling and relay assignment. Heuristic algorithms are proposed to solve this more challenging problem. Finally, extensive simulations are conducted to show that the proposed algorithm outperforms direct transmission substantially.

To exploit multiuser spatial cooperative diversity, relay nodes can assist the transmission of signal from multiple sources to their corresponding destinations in order to combat the noise, the channel fading and the cross-interferences. In this work, we consider a network consisting of N source-destination pairs and a set of M relay nodes. We assume that a fixed total budget of transmit energy is available for allotment among all transmitters, i.e., the source and relay nodes. For such network, we consider the time division Amplify-and-Forward (AF) scheme in 2N time slots, and propose an algorithm to optimize the beamformers and the powers allocated to all transmit nodes. The proposed method maximizes the network sum capacity assuming that the channels state information (CSI) is known. Numerical simulations illustrate the significant improvement obtained under power constraint. This betterment is more pronounced for low power regimes.

Cooperative diversity is an attractive way to combat fading in wireless networks,. Conventionally, the outage probability, which measures robustness of the transmission to fading in cooperative communication, is deduced on the condition that the signal-to-noise ratio (SNR) is very high. However, the result is only an approximation. In this paper, proposed a new way to deduce the accurate outage probability in the general case. Simulation results show that the proposed new scheme can obtain an accurate value in the case of both low SNR and high SNR.

Transmit diversity generally requires more than one antenna at the transmitter. However, many wireless devices are limited by size or hardware complexity to one antenna. Recently, a new class of methods called cooperative communication has been proposed that enables single-antenna mobiles in a multi-user environment to share their antennas and generate a virtual multiple-antenna transmitter that allows them to achieve transmit diversity. This article presents an overview of the developments in this burgeoning field.

The importance of cooperative communication in wireless networks cannot be stressed enough. It has drawn a lot of attention for its capability to successfully tackle the inherent problem of fading in wireless communication. As the world is moving towards precision in all aspects, it is only natural that people desire to watch high quality video for realistic experience. Cooperative communication can undoubtedly help in this regard if appropriate relay selection schemes are used.This paper focusses on two relay selection methods for video transmission. One of the methods is to select the best relay on the basis of channel strength and the other method is to select the best relay based on video awareness. Video is transmitted using QPSK, 16-QAM and 64-QAM modulation schemes. Results showed that the quality of video obtained was better for the relay selection method based on video awareness.

The fundamental idea of cooperative communications in wireless networks originates from the design of multiple-antenna systems. In multiple-antenna systems, communicating terminals are equipped with multiple antennas to mitigate the effects of multipath fading and optimise the communication rate in the network. Wireless communication nodes like cellular phones and sensor nodes have size restrictions, power supply limitations and are only able to accommodate a limited level of complexity. It is thus unfeasible to equip them with multiple antennas. The effects of multipath fading are critical in cellular, ad hoc and sensor networks because the physical deployment of communicating nodes makes them susceptible to interference. It is imperative to adopt a mechanism to combat fading in such networks. The broadcast nature of the wireless medium makes it easy for the communicating nodes to hear each other. They can share their physical resources specifically their single antennas, thereby creating a virtual multiple-antenna array. Cooperative communications is a concept where several single-antenna nodes cooperate and form a distributed multiple-antenna system which combats multipath fading. In recent years, cooperative communications have received extensive world-wide attention and significant advances in both research and applications have been achieved.

In this paper, we analyze and compare the outage probabilities of selection relaying protocols for cooperative communications in wireless networks. Depending on the quality of the source-relay channel, the relay may choose either decode-and-forward (DF), amplify-and-forward (AF), or direct-transmission (DT) to forward signals. It turns out that in terms of outage probability, two selection relaying protocols are better than others: either selection between DF and AF protocols (DF-AF) or selection between DF and DT protocols (DF-DT). We show that with an equal power allocation at the source and the relay, both the DF-AF and DF-DT selection protocols have the same asymptotic outage probability. However, with an optimum power allocation strategy, the DF-AF selection is in general better than the DF-DT selection. Simulations are also presented to validate the analytical results.

This paper is on the bit error probability (BEP) of opportunistic decode-and-forward (DF) relaying with coded cooperation, where cooperation diversity is achieved through both channel coding method and spatial diversity of relay selection. Codewords are partitioned into two parts which are source's data and parity, these are transmitted from source's antenna or selected relay's antenna. In this scheme, relay selection is performed in relay subset which consists of relay nodes that successfully decode source's data and parity is transmitted from selected relay node's antenna. If all the relay nodes are fail to decode source's data the source transmits its parity to the destination instead of the relay node. We derive the closed-form of bounds on BEP of this scheme based on Viterbi's upper bound. These results illustrate diversity gain with multiple relay nodes in coded cooperation and present the performance analysis of proposed scheme in numerical results.

In wireless sensor networks, several relay nodes can be used to support multiple transmission links between source and destination nodes simultaneously to achieve higher spectral efficiency. A channel state information sharing scheme among multiple relay nodes is presented in this letter, where only one angle per source-destination pair is sent from one relay node to another. Then, to enhance received signal powers, a distributed multiuser precoding scheme is presented to be used at each relay node with the angles sent by another relay node. Simulation results demonstrate that the proposed distributed precoding scheme enhances the capacity performance with slight overhead.

Recently, the cooperative communication has been explored more and more as an impressing technique to combat the effects of channel fading and to reduce the energy consumption in wireless networks. However, the impact of cooperative communications on transmission rate has not been well-addressed yet. In this paper, we provide an analytical framework for transmission rate enhancement issue in wireless communications. For a given transmit power and a desired probability of success, we investigate how much average transmission rate can be increased by cooperative communications. Three transmission models have been compared: the direct transmission, the cooperative transmission without maximal ratio combiner (MRC), and cooperative transmission with MRC. The analytical and numerical results show that around 1 - 3b/s/Hz transmission rate can be improved when the source-destination distance is 20m. We also reveal that the MRC scheme is not always beneficial, especially when the source-destination distance is short and the relay is close to the destination.

We propose a transmission model for bacteria networks inspired by ad hoc wireless mobile networks. Using bacteria as a message transmission medium has been proposed as a promising approach in molecular communication. The expected message delivery delay is derived for single source-destination pair and can be approximated by a convex function of the number of available carriers in the environment. In the scenario with multiple source-destination pairs, bacteria serving as the medium of message transmission are viewed as a limited resource, since each source-destination pair requires unoccupied carriers to transfer messages. We show that optimal resource allocation can be achieved while satisfying a priority requirement by controlling the release probability of messages at the source nodes. This suggests a guideline for communicating prioritized tasks in ad hoc bacteria networks

Based on the advantages of small size, lightweight, as well as flexible deployment and recycling, unmanned aerial vehicle (UAV) has been more and more widely used in military and civilian. As flying relays, UAVs can quickly set up relay communication links for different missions, to enhance the receiving signal power, increase the system capacity, and expand the communication coverage. In this article, we investigate full-duplex (FD) UAV relaying for multiple source–destination pairs. To fully exploit the flying flexibility of the UAV in serving multiple source–destination pairs, we propose a scheduling protocol that exploits time-division multiple access (TDMA) to serve different source–destination pairs in turns when flying along an optimized trajectory. Then, we further formulate a joint optimization problem of the TDMA-based user scheduling, the dynamic UAV trajectory, and the UAV transmit power to maximize the system throughput. The formulated problem is nonconvex that makes it difficult to solve directly, hence we propose an iterative algorithm to obtain an approximate optimal solution based on block coordinate descent and successive convex optimization techniques. Simulation results demonstrate that our proposed FD-based UAV relaying network achieves significant throughput gains compared with the half-duplex (HD) baseline, and the TDMA-based protocol outperforms the OFDMA-based ones with fixed UAV position/trajectory when the UAV helps relay information for multiple source–destination pairs.

Multiple-radio multiple-channel wireless mesh networks (MRMC WMNs) are fitting as the wireless backbone networks for ubiquitous Internet access. It is quite a challenge to satisfy the multiple traffic requests from multiple source-destination pairs with different data transmission requirements. The multiple pair traffic flows may cause heavy conflict via the nature of wireless media. To take almost full use of the limited resources, we design a routing algorithm based on ant colony optimization. The pheromone leads the finding of primary paths. The various simulations show the efficiency of the algorithm performance.KeywordsRoutingAnt colony optimizationWireless mesh networksLink interference

Since the information and communication technology industry is one of contributors to global warming, how to utilize self-organizing networks (SONs), which can simplify network management, to achieve energy saving over future cellular networks has been a significant issue. We propose an adaptive energy saving mechanism (AES) for LTE-A self-organizing heterogeneous networks (HetNets). The proposed AES is designed for multi-hop cellular networks, in which each cell has an enhanced Node B (eNB) and multiple relay nodes (RNs). The AES uses two-level multi-threshold load management for each RN under different eNBs (inter-cell level) and for each RN within the same eNB (intra-cell level) so as to reduce the congestion in hot spot eNBs and RNs. In addition, the AES can dynamically switch an RN between active and sleep modes to maximize the number of sleep RNs for adaptive energy saving. It can also dynamically change an RN's coverage area to reduce energy consumption and to increase radio resource utilization. Besides, the AES adopts a neural network predictor to forecast the loading of each RN to determine whether it is appropriate to switch an RN to sleep mode. Simulation results show that with slightly sacrificing average throughput (1.16% lower) and radio interface delay (1.4% higher), the proposed AES's percentage of sleep RNs is from 0.28 to 0.19 under the percentage of active UEs from 0.7 to 1. Comparing with a representative related work, reinforcement learning (RL), the proposed AES's average energy consumption is 26.44% lower than RL's.

Communication networks shared by selfish users are considered and modeled as noncooperative repeated games. Each user is interested only in optimizing its own performance by controlling the routing of its load. We investigate the existence of a NEP that achieves the system-wide optimal cost. The existence of a NEP that not only achieves the system-wide optimal cost but also yields a cost for each user no greater than its stage game NEP cost is shown for two-node multiple link networks. It is shown that more general networks where all users have the same source-destination pair have a NEP that achieves the minimum total system cost under a mild technical condition. It is shown general networks with users having multiple source-destination pairs do not necessarily have such an NEP.