Yindong Zhang

Bandwidth-Power Aware Cooperative Multipath Routing for Wireless Multimedia Sensor Networks

Cooperative communication is becoming an attractive technology as it can greatly improve the spatial diversity without additional antennas. This novel communication paradigm can effectively reduce power consumption via multi-node cooperation and resource allocation. This paper studies the energy-efficient node-disjoint multi-path routing for a given source-destination pair by joint route construction, relay assignment and power allocation methods. We first define a new bandwidth-power aware cooperative multi-path routing (BP-CMPR) problem, and formally prove its NP-hardness. The paper then presents a polynomial-time heuristic algorithm CMPR to solve the above problem. The algorithm adopts the Suurballes method to find k minimal-weight node-disjoint paths from source to destination on a weighted graph. Then, dynamic programming is used to implement relay assignment and power allocation. The theoretical analysis shows that CMPR can reach approximation factors of 2 and \frac{4}{3} for BP-CMPR under the amplify-and-forward and decode-and-forward schemes respectively. The distributed version of the algorithm DCMPR is also presented for this problem. We also prove that both CMPR and DCMPR construct the same cooperative multi-path routing, and show via simulations that the performance of the proposed scheme is more than 15% better than that of a traditional multi-path routing scheme, and close to the optimal result for BP-CMPR in variety of situations.

Energy-efficient cooperative data aggregation for wireless sensor networks

Recently, cooperative communication mechanism is shown to be a promising technology to improve the transmit diversity only by a single transceiver antenna. Using this communication paradigm, multiple source nodes are able to coordinate their transmissions so as to obtain energy savings. As data aggregation is one of the most important operations in wireless sensor networks, this paper studies the energy-efficient data aggregation problem through cooperative communication. We first define the cooperative data aggregation (CDA) problem, and formally prove that this problem is NP-Hard. Due to the difficult nature of this problem, we propose a heuristic algorithm MCT for cooperative data aggregation. The theoretical analysis shows that this algorithm can reach the approximate performance ratio of 2. Moreover, the distributed implementation DMCT of the algorithm is also described. We prove that both centralized and distributed algorithms can construct the same topology for cooperative data aggregation. The experimental simulations show that the proposed algorithms will decrease the power consumption by about 12.5% and 66.3% compared with PEDAP and PEGASIS algorithms respectively.

Optimal relay assignment for fairness in wireless cooperative networks

Under this cooperative communication, the selection of relay node significantly affects the performance of wireless networks. The previous researches optimised the Max-Min Fairness (MF), which may drastically decrease the network throughput. Thus, this paper studies the fairness-aware relay assignment to improve the network throughput. First, we develop the PFRA algorithm, which assigns the relays by saturated bipartite matching, to reach the proportional fairness. Next, a distributed version of Proportional Fairness Relay Assignment (PFRA) algorithm is also proposed. Moreover, lexicographical Max-Min fairness is achieved by Lexicographical Fairness Relay Assignment (LFRA) algorithm. We formally prove the optimality of above three algorithms. The experimental results show the efficiency of the proposed algorithms.

Cooperative relay assignment for static energy-constrained networks

Cooperative communication has become an efficient technology to improve the spatial diversity. Among this, relay assignment significantly affects power consumption of the entire network. This paper first analyses the relationship between power consumption and the number of relay nodes. Then, we define the relay assignment k-RA problem where k is the maximum number of relay nodes participating into each cooperative transmission pair, and k = 1 or 2. We design an optimal algorithm ESRA to solve the 1-RA problem. The proposed algorithm transforms this problem into bipartite matching, and assigns relay nodes to transmission pairs based on the matching result. Next, a heuristic algorithm ETRA is presented for the 2-RA problem. The theoretical analyses show that ETRA can provide a good approximation of the optimal one. The simulation results show that ESRA and ETRA will decrease the power consumptions about 45.8% and 51.7% compared with direct transmission scheme under many situations.

An incentive energy-efficient routing for data gathering in wireless cooperative networks

Because of energy-constraint, it is an attractive problem to select energy-efficient paths from source nodes to sink for data gathering in wireless ad hoc networks. Cooperative communication is a promising mechanism to reduce transmit energy in such kind of case. One of the fundamental assumptions for cooperative communication is that each node should be unselfish, responsible, and willing to forwarding data he has received. However, in energy-constrained environment, because of limited energy, each node hates participating in data transmission without any incentive and tries to avoid forwarding data (this behavior is selfish). In this paper, a utility function is proposed to stimulate nodes to behave unselfishly. We prove that it is a Nash Equilibrium when nodes work in an unselfish manner. Also, we show that the selection of forwarding nodes and relay nodes for data transmission is a NP-hard problem even when nodes behave unselfishly. A heuristic algorithm (Algorithm for Node Selection Problem, ANSP) is provided to solve this selection problem. We also prove the convergence of this algorithm. The analysis shows that this algorithm can reach the approximate performance ratio of 2⋅(1+α), where α is the maximal ratio of two power consumptions on two adjacent links in the network. The numerical results show that in a 100 node network, if nodes behave unselfishly, they will obtain a better utility, and more energy will be saved. The average saved energy when each node takes a selfish behavior, is 52.5% less than the average when nodes behave in an unselfish manner.

Spanner-Aware Relay Node Placement in Wireless Ad Hoc Sensor Networks

Relay node placement is an important issue because it greatly affects the performance of wireless ad hoc sensor networks. The pervious works mainly pay attentions on placing the minimum number of relay nodes to connect all the sensor nodes. But we find that this placement scheme may result in QoS reduction of the network, such as transmission delay, energy cost, etc. Therefore, this work studies the minimum relay node placement problem to guarantee both the connectivity and geometric spanner properties. We first show that there is no algorithm with the performance O(opt) for this problem, where opt is the minimum number of relay nodes to connect the sensor nodes. Thus, this paper presents an efficient placement algorithm MSGP with O(max{n, opt}) relay nodes, where n is the number of sensor nodes. Specially, if any two sensor nodes cannot communicate directly, the algorithm obtains O(1)-approximation bound. Then, as data gathering is one of the most important operations in sensor networks, we also study the spanner-aware placement problem for this communication scheme. The simulation results show the efficiency of the proposed algorithm. For example, MSGP algorithm can reach the spanner factor 3 with the additional 30% relay nodes compared with MST-based placement algorithm.

Degree-bounded minimum spanning tree for unit disk graph

Degree-bounded minimum spanning tree (DBMST) has been widely used in many applications of wireless sensor networks, such as data aggregation, topology control, etc. However, before construction of DBMST, it is NP-hard to determine whether or not there is a degree-k spanning tree for an arbitrary graph, where k is 3 or 4. The wireless sensor network is usually modeled by a unit disk graph (UDG), where two vertices are connected in UDG G(R) if their Euclidean distance is not more than a given constant R in the field. The previous works have predicated the necessary conditions for the existence of DBMST on UDG. Given that sub-graphs G(R/2) and G(R/3) can keep connected, there exist degree-3 or degree-4 spanning trees for UDG G(R). In this paper, we design two algorithms to construct the degree-3 and degree-4 spanning trees for UDG respectively. The more relaxed conditions are explored for the existence of DBMST for unit disk graphs according to the proposed algorithms. That is, given that sub-graphs G(R/1.81) and G(R/2) keep connected, the existence of degree-3 and degree-4 spanning trees is guaranteed for UDG G(R). The theoretical analyses show that the performances of constructed degree-3 and degree-4 spanning trees are at most (4+6^@a)/4 and (1+2^@a)/2 times as that of minimum spanning tree (MST) respectively, where @a>=2 is a constant. The simulation results show the high efficiency of two proposed algorithms. For example, total link weights of degree-3 and degree 4 spanning trees are about 1.05 and 1.01 times as that of MST where @a is 2.

An energy-efficient opportunistic relay assignment in wireless cooperative networks

It is very important to assign proper relays to transmission pairs so as to explore the efficiency of cooperative communication CC. Most of the previous protocols were designed for ideal circumstances, where the Packet Drop Loss Ratio PDLR on each communication link is 0. Moreover, in hazardous surroundings, channel state is unstable, which is ignored by many algorithms. In this paper, we investigate an Opportunistic Relay Assignment Problem ORAP in a wireless cooperative network where channel state is unstable. We take into consideration the PFLR, while still guaranteeing energy-efficiency. We prove that this problem ORAP is NP-hard. A distributed algorithm, called DORAA, is proposed to solve this problem. We analyse the approximate performance ratio of DORAA. Our numerical results show that DORAA can reduce expected transmission time by 15.44% and save energy by 19.45% on average.

Interference-Aware Relay Assignment for Cooperative Networks

Recently, cooperative communication is shown to be a promising approach to improve the transmission’s bandwidth without additional antennas on each node. Under this communication paradigm, the selection of relay nodes significantly affects the network throughput. As interfer-ence will greatly decrease the link’s rate, this paper stud-ies the interference-aware relay node assignment problem for multiple transmission pairs which compete for a set of relay nodes to achieve the Max-Min fairness. The main contribution of this paper is formulation of interference- aware relay node assignment problem and development of a heuristic algorithm, called as IRA. This algorithm first assigns an appropriate weight for each transmission pair and enhances the minimum bandwidth of all transmission pairs by an iterative process. The simulation results show that the proposed algorithm can improve the bandwidth provision at least 21.6% and 42.5% compared with ORA algorithm and the direct transmission scheme respectively.

A Transmit Antenna Selection for MIMO Wireless Ad-Hoc Networks in Lossy Environment

Because of rapid channel attenuation in lossy environment, there is a severe packet drop loss problem in wireless ad hoc networks. Though MIMO (Multi-Input Multi-Output) technology can alleviate this effect greatly, it will result in higher transmission energy depletion as using more transmit antennas. Lots of schemes have been proposed to reduce such energy cost by transmit antenna selection. However, most of those only consider QoS requirements between neighbor nodes while ignoring QoS requirements for entire network. In this paper, we investigate an energy-efficient transmit antenna selection problem for many-to-one communications, while guaranteeing a certain packet drop loss ratio from any node to the sink. We prove that this problem (Transmit Antenna Selection Problem, TASP) is NP-hard. Thus, a greedy algorithm TASA (Transmit Antenna Selection Algorithm) is proposed to solve this problem. This paper also prove the correctness of the proposed algorithm and the time complexity of TASA algorithm is O(|E|+|V|×M_T), where |V| represents the number of nodes, |E| indicates the number of links and M_T is the number of transmit antennas on each node, respectively. Our numerical results show that in a 100 node network, TASA can reduce transmission energy cost by 44.3% on average.