Minimum energy scheduling in multi-hop wireless networks with retransmissions

MaxWeight algorithm, a.k.a., back-pressure algorithm, has received much attention as a viable solution for dynamic link scheduling in multi-hop wireless networks. The basic principle of the MaxWeight algorithm is to select a set of interference-free links with the maximum overall link weights in the network, where the link weight is determined by the queue difference between the transmitter and the receiver. While the throughput-optimality of the MaxWeight algorithm is well understood in the literature, the energy consumption induced by the MaxWeight algorithm is less studied, which is of great interest in energy-constrained wireless networks such as wireless sensor networks. In this paper, we propose an energy-conserving scheduling scheme, a.k.a., minimum energy scheduling (MES) algorithm for multi-hop wireless networks with stochastic traffic arrivals and time-varying channel conditions. We show that our algorithm is energy optimal in the sense that the proposed MES algorithm can achieve an energy consumption which is arbitrarily close to the global minimum solution. Moreover, the energy efficiency of the MES algorithm is achieved without losing the throughput- optimality. In other words, the proposed MES algorithm is still throughput optimal whereas the average consumed energy in the network is significantly reduced, as compared to the traditional MaxWeight algorithm. The theoretical results are substantiated via simulations.

Information-theoretic broadcast channels (BCs) and multiple-access channels (MACs) enable a single node to transmit data simultaneously to multiple nodes, and multiple nodes to transmit data simultaneously to a single node, respectively. In this paper, we address the problem of link scheduling in multihop wireless networks containing nodes with BC and MAC capabilities. We first propose an interference model that extends protocol interference models, originally designed for point-to-point channels, to include the possibility of BCs and MACs. Due to the high complexity of optimal link schedulers, we introduce the Multiuser Greedy Maximum Weight algorithm for link scheduling in multihop wireless networks containing BCs and MACs. Given a network graph, we develop new local pooling conditions and show that the performance of our algorithm can be fully characterized using the associated parameter, the multiuser local pooling factor. We provide examples of some network graphs, on which we apply local pooling conditions and derive the multiuser local pooling factor. We prove optimality of our algorithm in tree networks and show that the exploitation of BCs and MACs improve the throughput performance considerably in multihop wireless networks.

We study the performance of greedy scheduling in multihop wireless networks where the objective is aggregate utility maximization. Following standard approaches, we consider the dual of the original optimization problem. Optimal scheduling requires selecting independent sets of maximum aggregate price, but this problem is known to be NP-hard. We propose and evaluate a simple greedy heuristic. Analytical bounds on performance are provided and simulations indicate that the greedy heuristic performs well in practice.

In recent years, there has been a significant amount of work done in developing low-complexity scheduling schemes to achieve high performance in multihop wireless networks. A centralized suboptimal scheduling policy, called Greedy Maximal Scheduling (GMS) is a good candidate because its empirically observed performance is close to optimal in a variety of network settings. However, its distributed realization requires high complexity, which becomes a major obstacle for practical implementation. In this paper, we develop simple distributed greedy algorithms for scheduling in multihop wireless networks. We reduce the complexity by relaxing the global ordering requirement of GMS, up to near zero. Simulation results show that the new algorithms approximate the performance of GMS, and outperform the state-of-the-art distributed scheduling policies.

Cooperative communication has emerged as a promising technique to improve transmission reliability and spectral efficiency by utilizing virtual antenna arrays formed by multiple nodes in wireless networks. In this paper, we study distributed interference-aware random access strategies based on cooperative link selection scheduling for multi-hop wireless networks. In order to fully exploit the broadcast feature of wireless channels, improve spatial reuse, and achieve diversity gains, the cooperative random access is formulated as a network utility optimization problem with probabilistic model and interference avoidance. In the multi-hop wireless networks, the nodes near the destination node in the current hop that can decode the data packets from the source node are able to serve as candidate relays to take part in the cooperative transmission in the next hop. Simulation results show that our proposed spectrum access strategy significantly improves the system average throughput and spectrum efficiency compared with the existing solutions.

In a multi-hop wireless network, routing is closely interdependent with scheduling as the chosen routes affect the possible schedules and vice versa. Thus it is necessary to consider routing and scheduling jointly to optimize the overall performance. In this paper, we look at the above challenge from a new perspective and present a novel ILP(Integer Linear Programming)-based optimization design for resolving the joint multicast routing and scheduling problem. Numerical results show that the proposed optimization design constructs both routing trees balancing the workload among nodes and schedules for conflict-free transmission.

Long-distance multi-hop wireless networks have been used in recent years to provide connectivity to rural areas. The salient features of such networks include TDMA channel access, nodes with multiple radios, and point-to-point long-distance wireless links established using high-gain directional antennas mounted on high towers. It has been demonstrated previously that in such network architectures, nodes can transmit concurrently on multiple radios, as well as receive concurrently on multiple radios. However, concurrent transmission on one radio, and reception on another radio causes interference. Under this scheduling constraint, given a set of source-destination demand rates, we consider the problem of satisfying the maximum fraction of each demand (also called the maximum concurrent flow problem). We give a novel joint routing and scheduling scheme for this problem, based on linear programming and graph coloring. We analyze our algorithm theoretically and prove that at least 50% of a satisfiable set of demands is satisfied by our algorithm for most practical networks (with maximum node degree at most 5).

A major design issue in Multi-hop Wireless Networks is the Medium Access Control (MAC) protocols that determine how nodes share the channel to transmit their packets. One type of MAC protocol with efficient spatial reuse characteristics are the Spatial TDMA (STDMA) protocols. STDMA protocols are a class of conflict-free MAC protocols that enable high spectral utilization by scheduling transmissions on the channel. Its main features are high throughput and the possibility of providing delay guarantees. We studied the sensibility of STDMA networks to disruption caused by slow mobility of one critical node (single-user perturbation), that causes problems to the schedule maintenance. We assessed a framework that produces robust STDMA scheduling against these topological changes. To do that, we introduced and analyzed heuristic algorithms that mainly exploit capabilities of the physical layer such as power and rate control, and rerouting. We considered the limited-mobility management in STDMA networks to find the ranges where our heuristics will avoid re-scheduling of the whole STDMA frame. We found that a substantial throughput degradation due to slow mobility in STDMA networks can be compensated by means of power or rate control, and rerouting. Our results showed that rate-controlled (RC) STDMA is the most promising scheme to maintain communication under slow mobility.

This paper addresses the Quality of Service (QoS) degradation problem of wireless relay node failures in multihop Worldwide interoperable Microwave Access (WiMAX) and Long Term Evolution (LTE) networks. In general, node protection in a communication network increases the reliability of the traffic flow from source to destination. For wireless networks, implementing the traditional 1+1 protection scheme increases the capital cost, as resources cannot be fully utilized. On the other hand, the design and implementation of the 1:N protection scheme in wireless networks for greater value of N (> 2) is very difficult, due to wireless network coverage and the physical layer design. To overcome the above drawbacks, a technique based on network coding is proposed for node protection in multihop wireless networks. In multihop wireless networks, few research efforts are concentrated on node protection schemes using network coding. Moreover, to best of our knowledge, no reports have been published on measuring the QoS performance for node protection in 4G wireless networks using network coding. In this paper, we first describe the node protection scheme using XOR network coding for multihop 4G wireless networks. Then, we measure the QoS performance, such as packet delivery ratio (PDR), latency and jitter, for different scenarios. The scenarios include a failure of a single relay node and failures of two relay nodes with and without our protection scheme and user's mobility. The simulation results show that the QoS performance with protection against a single relay node failure and failures of two relay nodes are very close to that of no failure scenario, while the network reliability increases due to the protection mechanism. Also, we report a decoding problem in multihop wireless networks using XOR network coding.

For complicated traffic-oriented transmissions (e.g., multiple multicasting) in Spatial Time Division Multiple Access (STDMA) network, scheduling algorithms are employed to determine an efficient assignment for the transmissions. In this paper, a scheduling algorithm, designated as traffic-oriented scheduling assignment (TOSA), is proposed to effectively allocate available network resource in the link-based and node-based STDMA networks. The objective of TOSA is to reduce schedule frame length by enhancing the spatial utilization within each time slot. Simulation results demonstrate that the proposed algorithms achieve a lower schedule frame length than existing STDMA scheduling algorithms.

In this paper, we consider the problem of link scheduling in multihop wireless networks under general interference constraints. Our goal is to design scheduling schemes that do not use per-flow or per-destination information, maintain a single data queue for each link, and exploit only local information, while guaranteeing throughput optimality. Although the celebrated back-pressure algorithm maximizes throughput, it requires per-flow or per-destination information. It is usually difficult to obtain and maintain this type of information, especially in large networks, where there are numerous flows. Also, the back-pressure algorithm maintains a complex data structure at each node, keeps exchanging queue-length information among neighboring nodes, and commonly results in poor delay performance. In this paper, we propose scheduling schemes that can circumvent these drawbacks and guarantee throughput optimality. These schemes use either the readily available hop-count information or only the local information for each link. We rigorously analyze the performance of the proposed schemes using fluid limit techniques via an inductive argument and show that they are throughput-optimal. We also conduct simulations to validate our theoretical results in various settings and show that the proposed schemes can substantially improve the delay performance in most scenarios.

Most distributed wireless scheduling schemes that are provably efficient have been developed under the protocol model, which describes interference constraints in a binary form. However, the oversimplified interference model imposes fundamental limitations on the performance in practice. The signal-to-interference-plus-noise-ratio (SINR) based interference model is more accurate and realistic accounting for the cumulative nature of the interference signals, but its complex structure makes the design of scheduling schemes much more challenging. In this paper, we focus on the scheduling performance under the SINR model and develop random access scheduling schemes that are amenable to implement in a distributed fashion with only local information. We analytically show that they are provably efficient under the SINR model, and through simulations demonstrate that they empirically perform better than the theoretical performance bound.

HITLinQ: Improving path capacity through hybrid information-theoretic link scheduling in multi-hop wireless networks

Wireless networks are defined as that the network nodes which are connected by wireless data connections. The devices are connected via wireless link to communicate with each other. Measuring the delay performance of end-to-end nodes is the one of the most convoluted issues in wireless networks. In wireless networks, it is very difficult to maintain the substitution between throughput and delay. This paper proposes a new joint scheduling and congestion control algorithm for multihop wireless networks with dynamic route flows. The proposed algorithm achieves a provable throughput guarantee and provable end-to-end delay of every flow. The new joint scheduling and congestion control algorithm improves throughput and delay for dynamic wireless network by shifting scheduling scheme with virtual adaptation model. The proposed algorithm combines window-based flow control with a new rate based distributed scheduling algorithm to survive the quality of the system. This approach adaptively selects a set of routes according to the traffic load. Furthermore this dynamic adaptation mechanism achieves better concert in terms of throughput, end-to-end delay and packet delivery ratio.

The key factor of influencing the network capacity performance is the effect of interference power of receiving nodes, which is obtained from the other transmitting nodes in multihop wireless networks (MWNs) that are simultaneously using the same channel. Minimizing total interference power can improve overall network capacity and reduce total energy consumption. In this paper, we propose a consensus transmit power control (CTPC) algorithm to maximize end-to-end throughput in MWNs. The CTPC algorithm tunes the nodes' transmit powers to maximize the average end-to-end throughput with a consensus coefficient. Simulation results reveal that the CTPC algorithm enables all the traffic flows to accomplish the maximum average end-to-end throughput. At the same time, the total interference power and the total power consumption are decreasing. Only in the dense MWNs, under usual threshold of received signal strength indicator (RSSI) setting, the CTPC algorithm cannot achieve good performance. In addition, an advanced wmediumd emulator over the StarBED testbed is used to further verify the performance evaluation of CTPC algorithm.