Joint optimization of transmission scheduling and relay assignment for cooperative communications

Cooperative communication (CC) has been proposed to achieve spatial diversity without requiring multiple antennas on a single device. Many efforts in exploiting the benefits of CC focus on improving the performance in terms of outage probability and channel capacity. However, the energy efficiency of CC, which is critical for the applications with energy constraints, has been little studied. In this paper, we study the problem of energy-efficient CC in cognitive radio networks by taking power control, relay assignment and channel allocation into consideration. We obtain the optimal power control for a single source-destination pair. After that, a heuristic algorithm is proposed to solve the the relay assignment and channel allocation problem for multiple source-destination pairs. Extensive simulations are conducted to show that the proposed algorithm can significantly improve the performance of energy efficiency over the direct transmission approach.

Recently, cooperative communication is shown to be a promising technology to achieve spatial diversity by keeping each node with only one antenna and having a node exploit a relay node's antenna. Most previous works assume that there are multiple source-destination pairs and multiple relay nodes in a network where each node only serves as one role: either transmission node or relay node. However, this assumption will not always hold in practice where each node has its own information to transmit. This paper studies the maximal lifetime scheduling problem for cooperative communication with guaranteed throughput service in a network environment where there are multiple source-destination pairs and each node can serve as both two roles: transmission node and "relay" node. We first analyze the power allocation of optimal lifetime for a single source-destination pair with a bounded throughput in different communication modes, and then design an optimal polynomial-time algorithm to maximize the network lifetime. This algorithm is based on iteration and tries to find a better solution than that before in each iteration. After that, the optimality of this algorithm has been proved formally. The simulation results show that the algorithm can prolong about 199% lifetime than that of direct transmission.

Recently, cooperative communication is shown to be a promising approach to achieve spatial diversity. The performance improvement by cooperative communication heavily depends on selecting suitable relay node. Therefore, designing effective relay assignment algorithm becomes critical in wireless cooperative networks. Although many studies focus on relay assignment problem, none of them concerns the interference problem, produced by relay nodes. In this paper, we investigate how the interference impacts the relay assignment problem. In addition, we give a relay assignment algorithm with interference mitigation for cooperative communication.

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.

In order to cope with the degradation of communication quality due to fading of wireless signals when transmitted over long distances, cooperative communication techniques are often applied to long-distance wireless communications due to their relay cooperative forwarding characteristics. A reasonable relay assignment scheme can significantly improve the network throughput. In order to solve the problem of irrational relay resource assignment in the existing relay assignment under the multi-node cooperative communication network, this paper proposes a relay assignment method that balances the communication quality (BQRA). Firstly, a multi-node cooperative communication system model is established, and a node pre-assignment set is established based on node distance. Then, with the goal of maximizing the overall network capacity, the proposed relay assignment method is used to allocate relay nodes for each source node. The effective performance of the proposed method is evaluated through simulation experiments. Simulation results show that the system channel capacity index is slightly better than several other methods. 15% increase in system channel capacity compared to the classical relay assignment method, LIRA.

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

Motivated by the urgent need of green communications, this paper investigates energy-efficient cooperative relaying methods for multi-source multi-relay wireless networks. Existing cooperative relaying schemes primarily focus on single-source cooperative networks and aim to maximize diversity gain exploitation, yet ignore the extra energy consumption used by relay nodes and fairness between source nodes. Instead, our object is to minimize relay power consumption and maintain network-wide fairness without throughput penalty. The considered problem includes two parts, namely source scheduling and relay assignment that are addressed separately. We derive the feasible condition for the green source-relay assignment problem and show that it is NP-hard. We propose a heuristic algorithm that deliver good performance with low complexity. Simulation results are presented to evaluate the efficacy of the proposed scheme in terms of average throughput, throughput fairness, average relay power consumption, and average outage probability, as compared to two related schemes, under both independent and identically distributed (i.i.d.) and independent and non-identically distributed (i.n.d.) channel configurations.

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.

The wireless relay mesh network (WRMN) is designed to provide robust and fault tolerant communications between relay and user nodes in broadband wireless networks. In this paper, we investigate the benefits of decoupled optimization of routing and scheduling in WRMNs using the physical interference model and spatial reuse to maximize overall throughput. We model the routing optimization as a linear program using multicommodity flows (MCF). We refer to this problem as multicommodity flow routing optimization (MCF-ROPT). Using the flow per link determined from MCF-ROPT, we develop an optimization formulation to schedule the link traffic such that interference is minimized and time slots are reused appropriately based on spatial TDMA (STDMA). Furthermore, our scheduling approach incorporates the effect of reuse of multiple carriers on the transmission schedule. We refer to this problem as SM-TSS (STDMA multicarrier traffic sensitive scheduling). The SM-TSS is NP-hard and thus is solved using column generation. We compare our formulations with decoupled optimizations that use the protocol interference model and/or single carrier systems and show that our approach guarantees higher throughput by mitigating interference effectively.

Relay assignment means assigning the proper relay nodes (RN) to cell-edge users (UE) in order to exploit the spatial diversity through relay nodes and improve cell-edge performance. An optimal algorithm, called ORA, is to maximize the minimum data rate among all users. ORA is shown to find the optimal objective regardless the initial relay node. Although the algorithm is shown to converge (the minimum data rate is maximized), there exist several different RN-to-UE assignment pairs for the remaining UEs assigned to RNs. This paper is motivated to enhance the performance of the relay assignment for the remaining UEs, provided that the minimum data rate is maximized. In this paper, we propose a new strategy whose main objective is to maximize the relative performance improvement, which is a ratio of the performance improvement to original direct transmission, under the max-min constraint. Under the new assignment algorithm, not only the original optimal property of ORA is preserved, but also the performance of remaining UEs assigned to RNs is maximized. Simulation results demonstrate the effectiveness of the proposed approach.

Cooperative communication has great potential to improve the wireless channel capacity by exploiting the antennas on wireless devices for spatial diversity. The performance in cooperative communication depends on careful resource allocation such as relay selection and power control. In this paper, the network is expanded and more than one source is used. What is proposed is a distributed buyer/seller game theoretic framework over multiuser cooperative communication networks in order to stimulate cooperation and improve the system performance. A two-level Stackelberg game is employed to jointly consider the benefits of the source node and the relay nodes in which the source node is modeled as a buyer and the relay nodes are modeled as sellers, respectively. In this work we proposed coded method in which relays amplify and code Source data and send it to destination at the same time and then signal detection occur in destination, but in the codeless network relays send source data separately to destination. So, here coded and codeless networks are compared and contrasted. The stimulation results revealed that the proposed coded method performed better than the codeless ones; furthermore, the research shows that relays near the sources can play a significant role in increasing source node's utility, so every source would like to buy more power from these preferred relays. Also, the proposed algorithm enforces truthful power demands.

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.

Routing in delay tolerant network (DTN) closely depends on the cooperation of nodes. At present, there are many works exploring the impact of the selfish behavior. However, most of these works assume that there is only one source-destination pair, and the source just generates one message. For this reason, this paper studies the impact of selfish behavior when many messages are transmitted at the same time. In particular, there are multiple source-destination pairs, and each source generates the messages according to the Poisson process. Due to the selfish behavior, the nodes may be more willing to forward their own messages. In addition, the nodes may have closer relation with certain nodes (friends). Due to selfishness, the nodes may be more willing to help their friends other than the strangers. In such complex scenario, this paper proposes the theoretical models to evaluate the performance of the two-hop routing algorithm with single-copy and redundancy, respectively. Simulations show the accuracy of the models. Numerical results show that the selfish behavior may significantly increase the average delivery delay. In addition, the selfishness may also decrease the maximal flow.

Recent research has shown that the cooperative diversity can efficiently combat the fading effects caused by the hostile wireless channels just as the multiple-input multiple-output (MIMO) antenna systems do. Besides, due to the inherent cost and size constraints by many small area wireless networks, e.g. wireless ad hoc networks and wireless sensor networks, in such environments, it would be almost impossible to deploy the antenna array in a mobile node. However, cooperative diversity can provide an economical and viable solution by sharing each mobile node’s single-antenna with others to form a virtual antenna array, while it still can maintain significant performance gains similar to MIMO systems. Meanwhile, the adaptive modulation is a proven technique which can significantly increase the spectral efficiency when perfect channel estimation can be achieved, and many wireless standards have adopted it as an implementation option. It also has been shown that combining these two techniques can greatly raise the system efficiency. Nevertheless, in the multiple nodes cooperative communication networks, the randomness of demodulation process at each relay node makes the task of correctly selecting the forwarding relay nodes very complicated. In view of this problem, a novel adaptive node selection algorithm is proposed for the destination node to effectively select the forwarding relay nodes to help the source node transfer the signals. In this paper, the decode-and-forward (DF) protocol is employed as the cooperative diversity signaling, and the constant-power variable-rate M-ary phase shift keying (M-PSK) is adopted as the adaptive modulation scheme. At the destination node, the maximal-ratio-combining (MRC) method is used to combine all of the signals from diversity branches with the main path transmitted directly from the source node. Because of the random phenomenon of the demodulation process, the outage requirement is used as the baseline in the first stage of the proposed node selection algorithm to choose the maximal transmission rate. Hence the maximal overall system throughput in terms of rate can be achieved. In the meantime, the first candidate forwarding sets of the relay nodes which collectively meet the required outage probability are also been chosen. Then in the second stage, we can further refine the number of the relay nodes among the first candidate forwarding sets by using the following criterion — maximum average rate per node. It will screen out the first candidate sets with the minimum number of the relay nodes. If only one candidate set is left at the end of the second stage, it will be the end of the proposed algorithm. However, if the result of the screening still has more than one set, then the final election among the second candidate sets would be the one which can give the minimum outage probability. In the simulation results, our proposed node selection algorithm can even further improve the spectral efficiency while the deleteriously fading effect induced by the wireless channels can also be effectively removed.

On one hand, cooperative communication has been gaining more and more popularity since it has great potential to increase the capacity of wireless networks. On the other hand, the applications of cooperative communication technology are rarely seen in reality, even in some scenarios where the demands for bandwidth-hungry applications have pushed the system designers to develop innovative network solutions. A main obstacle lying between the potential capability of channel capacity improvement and the wide adoption of cooperative communication is the lack of incentives for the participating wireless nodes to serve as relay nodes. Hence, in this paper, we design TASC, an auction scheme for the cooperative communications, where wireless node can trade relay services. TASC makes an important contribution of maintaining truthfulness while fulfilling other design objectives. We show analytically that TASC is truthful and has polynomial time complexity. Extensive experiments show that TASC can achieve multiple economic properties without significant performance degradation compared with pure relay assignment algorithms.