Joint Routing and Scheduling in WMNs with Variable-Width Spectrum Allocation

Throughput is an important performance consideration for multihop wireless networks. In this paper, we study the joint link scheduling and power control problem, focusing on maximizing the network throughput. We formulate the maximum throughput link scheduling with power control (MATH-SPC) problem, and present a mixed integer linear programming (MILP) formulation to provide optimal solutions. However, simply maximizing the throughput leads to a severe bias on bandwidth allocation among all links. In order to enhance both throughput and fairness, we define a new parameter, the demand satisfaction factor (DSF), to characterize the fairness of bandwidth allocation. We formulate the maximum throughput fair link scheduling with power control (MATA-SPC) problem and present an MILP formulation for this problem. We also present an effective polynomial time heuristic algorithm, namely, the serial LP rounding (SLPR) heuristic. Our numerical results show that bandwidth can be fairly allocated among all links/flows by solving our MATA-SPC formulation or using our heuristic algorithm at the cost of a minor reduction of network throughput

Since the unlicensed 60 GHz band has the extensively wide continuous spectrum and its corresponding millimeter-wave signal has high directivity gain, the 60 GHz band is a good option for the broadband wireless mesh networks. This paper focuses on link scheduling and routing over the 60 GHz multi-channel wireless mesh networks, where each mesh router has multiple radios and multiple directional antennas. We formulate a linear programming based framework, which incorporates multi-channel and multi-radio, directional antenna, and 60 GHz millimeter-wave communications, to model the network throughput of the directional antenna based 60 GHz mesh networks. Under this framework, we derive the solution to the problem of maximizing the network throughput subject to the fairness constraint and the directional-antenna based wireless channel interference constraint. Then, we design a heuristic joint link scheduling and routing scheme which aims at approximately attaining the optimal solution to the joint optimization problem under our proposed framework. We conduct extensive simulations to validate and evaluate our proposed scheme.

The performance of Multi-Channel Multi-Radio (MC-MR) Wireless Mesh Networks (WMNs) can be improved significantly with the increase in number of channels and radios. Despite the availability of multiple channels in several of the current wireless standards, only a few of them are non-overlapping and many channels are partially overlapped. In this paper, we formulate the joint channel assignment and flow allocation problem for MC-MR WMNs as a Mixed Integer Linear Program (MILP). Unlike most of the previous studies, we consider the case of using both non-overlapped and partially overlapped channels. We consider an objective of maximizing aggregate end-to-end throughput and minimizing queueing delay in the network, instead of the sum of link capacities, since the traffic characteristics of a multihop WMN are quite different from a single hop wireless network. Our formulation takes into consideration several important network parameters such as the transmission power of each node, path loss information, signal to interference plus noise ratio at a node, and frequency response of the filters used in the transmitter and receiver. We show by simulations that our MILP formulation makes efficient use of the spectrum, by providing superior channel assignments and flow allocations with the addition of partially overlapped channels, without the use of any additional spectrum.

Joint scheduling and power control schemes have previously been proposed to reduce power dissipation in wireless ad hoc networks. However, instead of power consumption, throughput is a more important performance concern for some emerging multihop wireless networks, such as wireless mesh networks. This paper examines joint link scheduling and power control with the objective of throughput improvement. The MAximum THroughput link Scheduling with Power Control (MATH-SPC) problem is first formulated and then a mixed integer linear programming (MILP) formulation is presented to provide optimal solutions. However, simply maximizing the throughput may lead to a severe bias on bandwidth allocation among links. To achieve a good tradeoff between throughput and fairness, a new parameter called the demand satisfaction factor (DSF) to characterize the fairness of bandwidth allocation and formulate the MAximum Throughput fAir link Scheduling with Power Control (MATA-SPC) problem is defined. An MILP formulation and an effective polynomial-time heuristic algorithm, namely, the serial linear programming rounding (SLPR) heuristic, to solve the MATA-SPC problem are also presented. Numerical results show that bandwidth can be fairly allocated among all links/flows by solving the MILP formulation or by using the heuristic algorithm at the cost of a minor reduction of network throughput. In addition, extensions to end-to-end throughput and fairness and multiradio wireless multihop networks are discussed.

The problem of scheduling and routing tree construction in WiMAX/802.16 based mesh networks is not defined in the standard and has thus been the subject to extensive research. We consider the problem of joint routing and scheduling in WiMAX-based mesh networks, with the objective of determining a minimum schedule period that satisfies a given (uplink/downlink) traffic demand. Minimizing the length of a schedule amounts to maximizing the spectrum spatial reuse by activating concurrently as many links. This group of transmission links active concurrently is referred to as the transmission group and refers to the set of wireless links that can simultaneously transmit without violating the signal-to-interference-plus-noise ratio (SINR) requirement. Our model is referred to as maximum spatial reuse (MSR). We assume centralized scheduling at the base station and attempt to maximize the system throughput through appropriate routing tree selection and achieving efficient spectrum reuse through opportunistic link scheduling. We present an ILP optimization model for the joint problem, which relies on the enumeration of all possible link schedules. Given its complexity, we decompose the problem using a column generation (CG) approach. We present two formulations for modeling MSR, namely the link-based (CGLink) and the path-based (CGPath) formulation. These two formulations differ mainly in the number of routing decision variables. Our experimental results indicate that the path-based formulation needs much less computational (CPU) time than the link-based in order to determine the (same) optimal solution with the same spatial reuse gain.

We consider the problem of joint routing, scheduling and power control in multi-hop wireless networks. We use a linear relation between link capacity and signal to interference noise ratio in our formulation. In a previous work, using a duality approach, the optimal link scheduling and power control that minimizes the total average transmission power is found. We formulate this problem as a linear programming problem with exponential number of constraints. To cope with the exponential number of constraints, we propose an iterative algorithm based on the cutting plane method. The separation oracle for the cutting plane algorithm turns out to be an element-wise concave optimization problem that can be effectively solved using branch and bound algorithm. We extend the same method to find the optimal routing scheduling and power control. Simulation results show that this methodology is more efficient and scalable compare to the previously proposed algorithm.

Joint routing and scheduling in multi-Tx/Rx wireless mesh networks with random demands

Operating on a frequency band occupying several nonoverlapping channels, IEEE 802.11 is now widely used in wireless mesh networks (WMNs). Many multichannel MAC protocols are proposed to improve the spatial reuse in the network under the assumption that the transmissions on nonoverlapping channels do not interfere with each other. Some joint routing and channel assignment algorithms are also designed to increase the network throughput based on the premise that we can switch between different channels freely. Although simulations show that great improvements on network throughput can be observed in both cases, two fundamental questions remain: 1) Can we really use multiple nonoverlapping channels freely in WMNs? 2) If we can, what will be the cost when we switch channels dynamically and frequently? In this paper, by conducting extensive experiments on our testbed, we attempt to answer these questions. We find that in spite of interference between both overlapping and nonoverlapping channels, we can still use multiple channels in mesh networks under certain conditions but with care. We also show that the channel switching cost is actually very significant in WMNs. We recommend not to switch the channels too frequently when designing the channel assignment algorithms, and those channel assignment algorithms selecting one channel for each packet are not really beneficial.

Current works on the joint routing and channel assignment (JRC) problem in wireless mesh networks (WMNs) assume that all links operate at the base rate. In other words, they do not consider the presence of multiple bit-rates. However, in multi-rate WMNs, the achievable throughput of a link operating at higher rates could be much less than its bit-rate when it has to contend with low-rate links. This is also known as the multirate sharing problem. To address the problem, we first present a numerical formulation for estimating the dynamic link capacity, which can indicate the degree of the multi-rate sharing problem. Next, we propose an optimization model called MR <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C, which solves the JRC problem by considering the dynamic link capacity in order to maximize the throughput in multi-rate, multi-radio, multi-channel WMNs. We then reformulate the primal problem as a Lagrangian dual problem, and apply the subgradient method to approach the dual. Finally, since each subproblem in the dual problem is also a non-linear problem, we design a polynomialtime algorithm to solve it. Our experiment results demonstrate that the proposed capacity formulation can approximate the actual link throughput. We compare MR <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C with the base-rate JRC model via simulations. The results show that MR <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> C achieves throughput gains of 3-4 times and recover from network failure efficiently.

The authors address the problem of link activation or scheduling in multihop packet radio networks, a contention-free form of channel access that is appropriate for many military communication applications. This problem, in almost all of its forms, is a combinatorial-optimization problem of high complexity. They approach this problem by the use of a Hopfield neural network model in which the method of Lagrange multipliers is used to dynamically vary the values of the coefficients used in the connection weights. Extensive software simulation results demonstrate the effectiveness of this approach in producing schedules of optimal length. Issues associated with the extension of this approach to the joint routing/scheduling problem are discussed. >

In this paper, we study the link scheduling problem in wireless cooperative communication networks, in which receivers are allowed to combine copies of a message from different senders to combat fading. We formulate a problem called cooperative link scheduling problem (CLS), which aims to find a schedule of links that uses the minimum number of time slots to inform all the receivers. As a solution, we propose an algorithm for CLS with g(K) approximation ratio, where g(K) is so called diversity of key links. Simulation results indicate that our cooperative link scheduling approaches outperform noncooperative ones.

Ad hoc network is an extensive research area in wireless communications nowadays, and is particularly studied under energy constraints, since energy consumption of the network should be minimized. The physical layer (power control), link layer (scheduling), and network layer (routing) are known to have great impact on network performance as well as on power consumption. In this paper, we present an optimization problem that there may exist a power vector that minimizes the overall transmission power of the network which at the same time supports a particular data rate on each link and satisfies the SINR and maximum transmission power constraints at each node. We also formulate an optimization problem where we use both the energy consumed of each node in the routing path and the delay associated on each link as link costs. We provide numerical examples for our schemes and relationships between the parameters. An overview of our intended routing algorithm for ad hoc networks is also given as a preliminary step towards our distributed joint scheduling, power control and routing algorithm for ad hoc networks using cross layer approach.

An interesting feature of IEEE 802.11 wireless LAN cards is that they support multiple transmission modes. For example, the 802.11b cards support four transmission modes of I, 2, 5.5 and 11 Mbps, whereas, the 802.11a cards support eight transmission modes, up to a maximum of 54 Mbps. In this paper, we study layer four protocols over multi-rate multi-hop wireless networks and attempt to answer the question whether higher bandwidth links necessarily outperform lower bandwidth links in these networks. We examine this question by taking into account the transport layer protocols such as the TCP and UDP. While network capacity is a topic of active interest in the research community, a comparative study of the ad hoc network throughput at the different link bandwidths has not been made. We then propose a bandwidth-based ad hoc routing protocol and look at how to integrate QoS with routing.

In 60 GHz wireless networks, relay-based dual-hop transmission is an effective solution to prolong the communication range and bypass the obstacles. However, it is very challenging to determine link scheduling in the dual-hop network architecture while considering several factors, such as reducing network power consumption and avoiding overloaded APs/relays. Here, we investigate the problem of energy-efficient link scheduling with load constraints (ELL). Firstly, we present a fine-grained energy model for dual-hop 60 GHz wireless networks, and formulate the ELL problem as an integer linear programming (ILP) model that aims to minimize the network power consumption with AP/relay load constraints. Then, we propose a polynomial time algorithm that obtains a near-optimal link scheduling solution via iterative relaxation, and the load constraint of each AP/relay can only be violated by at most an additive constant of two. Finally, we conduct simulation experiments that validate our algorithm's effectiveness and efficiency.

Empowered by the cognitive radio technology and motivated by the sporadic channel utilization, both spatially and temporally, dynamic spectrum access networks, also referred to as cognitive radio networks, have emerged as a solution to improve spectrum utilization and provide more flexibility to wireless communication. In this paper, we study the channel allocation problem in wireless cognitive mesh networks. For the allocation to be feasible, served mesh clients must establish connectivity with a backbone network in both the upstream and the downstream directions, and must have the SINR (signal-to-interference and noise-ratio) of the uplink and the downlink with their parent mesh routers within a predetermined threshold. We propose a receiver-based channel allocation strategy and show that this strategy outperforms other strategies in terms of the number of mesh clients served, and the fact that no common control channel is needed for coordinating the communication process. Furthermore, we formulate the receiver-based channel allocation problem in wireless cognitive mesh network as a mixed integer linear program (MILP) and propose a heuristic solution.