Downlink Throughput Maximization in CDMA Wireless Networks

We investigate optimum rate assignment scheme maximizing network throughput on the downlink of a multirate CDMA wireless network. Systems employing orthogonal variable spreading factor (OVSF) codes as well as systems employing multiple codes have been studied. Our objective is to maximize the network throughput under constraints on total transmit power, total bandwidth and individual QoS requirements specified in terms of minimum rates. First, users are ordered based on their transmit energy per bit requirements to achieve the target received energy per bit to interference power spectral density ratio at the receivers. Based on the initial ordering, we prove that for systems employing multiple codes, greedy rate assignment yields maximum network throughput. For systems employing variable spreading codes, we show that greedy rate assignment is optimal if the minimum rate requirement of a user is larger than or equal to the minimum rate requirement of any other user with a larger transmit energy per bit requirement. Simulation results verify the superiority of the greedy algorithm under various system and channel assumptions     

Joint Throughput Optimization for Wireless Mesh Networks

In this paper, we address the problem of joint channel assignment, link scheduling, and routing for throughput optimization in wireless networks with multiradios and multichannels. We mathematically formulate this problem by taking into account the interference, the number of available radios the set of usable channels, and other resource constraints at nodes. We also consider the possible combining of several consecutive channels into one so that a network interface card (NIC) can use the channel with larger range of frequencies and thus improve the channel capacity. Furthermore, we consider several interference models and assume a general yet practical network model in which two nodes may still not communicate directly even if one is within the transmission range of the other. We designed efficient algorithm for throughput (or fairness) optimization by finding flow routing, scheduling of transmissions, and dynamic channel assignment and combining. We show that the performance, fairness and throughput, achieved by our method is within a constant factor of the optimum. Our model also can deal with the situation when each node will charge a certain amount for relaying data to a neighboring node and each flow has a budget constraint. Our extensive evaluation shows that our algorithm can effectively exploit the number of channels and radios. In addition, it shows that combining multiple channels and assigning them to a single user at some time slots indeed increases the maximum throughput of the system compared to assigning a single channel.     

TCP Throughput Enhancement over Wireless Mesh Networks

TCP is the predominant technology used on the Internet to support upper layer applications with reliable data transfer and congestion control services. Furthermore, it is expected that traditional TCP applications (e.g., Internet access) will continue to constitute the major traffic component during the initial deployment of wireless mesh networks. However, TCP is known for its poor throughput performance in wireless multihop transmission environments. For this article, we conducted simulations to examine the impact of two channel interference problems, the hidden terminal and exposed terminal, on TCP transmissions over wireless mesh networks. We also propose a multichannel assignment algorithm for constructing a wireless mesh network that satisfies the spatial channel reuse property and eliminates the hidden terminal problem. The simulation results demonstrate the effectiveness of the proposed approach in improving the performance of TCP in wireless multihop networks.     

Gateway Placement for Throughput Optimization in Wireless Mesh Networks

In this paper, we address the problem of gateway placement for throughput optimization in multi-hop wireless mesh networks. Assume that each mesh node in the mesh network has a traffic demand. Given the number of gateways to be deployed (denoted by k) and the interference model in the network, we study where to place exactly k gateways in the mesh network such that the total throughput is maximized while it also ensures a certain fairness among all mesh nodes. We propose a novel grid-based gateway deployment method using a cross-layer throughput optimization, and prove that the achieved throughput by our method is a constant times of the optimal. Simulation results demonstrate that our method can effectively exploit the available resources and perform much better than random and fixed deployment methods. In addition, the proposed method can also be extended to work with multi-channel and multi-radio mesh networks under different interference models.     

基于网络利用率最大化来提高无线Mesh网络中TCP协议的传输性能

In Wireless Mesh Networks (WMNs), the performance of conventional TCP significantly deteriorates due to the unreliable wireless channel. To enhance TCP performance in WMNs, TCP/LT is proposed in this paper. It introduces fountain codes into packet reorganization in the protocol stack of mesh gateways and mesh clients. Furthermore, it is compatible with conventional TCP. Regarded as a Performance Enhancement Proxies (PEP), a mesh gateway buffers TCP packets into several blocks. It simultaneously processes them by using fountain encoders and then sends them to mesh clients. Apart from the improvement of the throughput of a unitary TCP flow, the entire network utility maximization can also be ensured by adjusting the scale of coding blocks for each TCP flow adaptively. Simulations show that TCP/LT presents high throughput gains over single TCP in lossy links of WMNs while preserving the fairness for multiple TCPs. As losses increase, the transmission delay of TCP/LT experiences a slow linear growth in contrast to the exponential growth of TCP.     

Adaptive Distributed Channel Assignment in Wireless Mesh Networks

From the channel assignment schemes in time division multiple access (TDMA) slot assignment protocols developed in previous studies, we have found that these protocols do not have a convenient frame length reduction scheme after the expansion of the frame length. As the network size grows, the frame length expands rapidly, particularly when we set it as a power of two. A very long frame may result in poor channel utilization when it contains many unused slots. In this paper, we consider a wireless mesh network with a TDMA structure. We divide each code into time slots to form the channels. We propose a dynamic frame length expansion and recovery method termed adaptive distributed channel assignment (ADCA). This strategy is designed to enhance the utilization of the available channels by taking advantage of the spatial reuse concept. In ADCA, an increase in spatial reuse is achieved by adding a certain amount of control overhead. We show that the bandwidth saved due to the channel spatial reuse is larger than the additional bandwidth spent on the control overhead.

Asymptotic Throughput Capacity Analysis of Multi-Channel, Multi-Interface Wireless Mesh Networks

Research into the analytical solutions for the capacity of the infrastructure wireless mesh networks (InfWMN) is highly interesting. An InfWMN is a hierarchical network consisting of mesh clients, mesh routers and gateways. The mesh routers form a wireless mesh infrastructure to which the mesh clients are connected through the use of star topology. The previous analytical solutions have only investigated the asymptotic per-client throughput capacity of either single-channel InfWMNs or multi-channel InfWMNs under conditions in which each infrastructure node (i.e. wireless routers and gateways), has a dedicated interface per-channel. The results of previous analytical studies show that there are quite few studies that have addressed the more practical cases where the number of interfaces per-node is less than the number of channels. In this paper, we derive an original analysis of the asymptotic per-client throughput capacity of multi-channel InfWMNs in which the number of interfaces per-infrastructure node, denoted by m, is less than or equal to the number of channels, denoted by c. Our analysis reveals that the asymptotic per-client throughput capacity of multi-channel InfWMNs has different bounds, which depend on the ratio between c and m. In addition, in the case that m < c, there is a reduction in the capacity of the InfWMN compared to the case in which c = m. Our analytical solutions also prove that when ${\frac{\text{c}}{\text{m}}=\Omega\left({\frac{{\rm N}_g^2}{{\rm N}_{\rm r}}}\right)}$ , where N_g and N_r denote the number of gateways and mesh routers respectively, gateways cannot effectively increase the throughput capacity of the multi-channel InfWMNs.     

Energy Balanced Model for Lifetime Maximization in Randomly Distributed Wireless Sensor Networks

In this paper, an energy balanced model (EBM) for lifetime maximization for a randomly distributed sensor network is proposed. The lifetime of a sensor network depends on the rate of energy depletion caused by multiple factors, such as load imbalance, sensor deployment distribution, scheduling, transmission power control, and routing. Therefore, in this work, we have developed a mathematical model for analysis of load imbalance under uniform and accumulated data flow. Based on this analysis, we developed a model to rationalize energy distribution among the sensors for enhancing the lifetime of the network. To realize the proposed EBM, three algorithms—annulus formation, connectivity ensured routing and coverage preserved scheduling have been proposed. The proposed model has been simulated in ns-2 and results are compared with Energy-Balanced Transmission Policy and Energy Balancing and unequal Clustering Algorithm. Lifetime has been measured in terms of the time duration for which the network provides satisfactory level of coverage and data delivery ratio. EBM outperform both the existing models. In our model the variance of residual energy distribution among the sensors is lower than other two models. This validated the essence of energy rationalization hypothesized by our model.     

Energy Efficient QoS Aware SOCCOR Protocol for Improving Throughput in Wireless Mesh Networks

Wireless Personal Communications - In this paper a new propagation model is proposed for use in complex indoor environments. The model was tested in the frequency range of 2.4&nbsp;GHz in the...     

Cross-Layer Design for End-to-End Throughput and Fairness Enhancement in Multi-Channel Wireless Mesh Networks

In this paper, we study joint rate control, routing and scheduling in multi-channel wireless mesh networks (WMNs), which are traditionally known as transport layer, network layer and MAC layer issues respectively. Our objective is to find a rate allocation along with a flow allocation and a transmission schedule for a set of end-to-end communication sessions such that the network throughput is maximized, which is formally defined as the maximum throughput rate allocation (MRA) problem. As simple throughput maximization may result in a severe bias on rate allocation, we take account of fairness based on a simplified max-min fairness model and the proportional fairness models. We define the max-min guaranteed maximum throughput rate allocation (MMRA) problem and proportional fair rate allocation (PRA) problem. We present efficient linear programming (LP) and convex programming (CP) based schemes to solve these problems. Numerical results show that proportional fair rate allocation schemes achieves a good tradeoff between throughput and fairness.     

A Novel Gateway Selection Technique for Throughput Optimization in Configurable Wireless Mesh Networks

Wireless mesh networks (WMNs) have attracted much attention due to their low up-front cost, easy network deployment, stable topology, robustness, reliable coverage, and so forth. These advantages are suitable for the disaster recovery applications in disaster areas, where WMNs can be advantageously utilized to restore network collapse after the disaster. In this paper, based on a new network infrastructure for WMNs, to guarantee high network performance, we focus on the issue of throughput optimization to improve the performance for WMNs. Owing to selecting different mesh router (MR) as the gateway will lead to different network throughput capacity, we propose a novel gateway selection technique to rapidly select the optimal MR as the gateway, in order to maximize the network throughput. In addition, we take into account the traffic distribution for the MR to eliminate traffic congestion in our method. The performance of our proposed method is evaluated by both numerical and simulated analysis. The simulation results demonstrate that the gateway selection method is effective and efficient to optimize the throughput for WMNs.     

Joint Channel Assignment and Routing for Throughput Optimization in Multiradio Wireless Mesh Networks

Multihop infrastructure wireless mesh networks offer increased reliability, coverage, and reduced equipment costs over their single-hop counterpart, wireless local area networks. Equipping wireless routers with multiple radios further improves the capacity by transmitting over multiple radios simultaneously using orthogonal channels. Efficient channel assignment and routing is essential for throughput optimization of mesh clients. Efficient channel assignment schemes can greatly relieve the interference effect of close-by transmissions; effective routing schemes can alleviate potential congestion on any gateways to the Internet, thereby improving per-client throughput. Unlike previous heuristic approaches, we mathematically formulate the joint channel assignment and routing problem, taking into account the interference constraints, the number of channels in the network, and the number of radios available at each mesh router. We then use this formulation to develop a solution for our problem that optimizes the overall network throughput subject to fairness constraints on allocation of scarce wireless capacity among mobile clients. We show that the performance of our algorithms is within a constant factor of that of any optimal algorithm for the joint channel assignment and routing problem. Our evaluation demonstrates that our algorithm can effectively exploit the increased number of channels and radios, and it performs much better than the theoretical worst case bounds     

Distributed Synchronization for OFDMA‐Based Wireless Mesh Networks

In this paper, we propose a distributed synchronization algorithm for wireless mesh networks based on orthogonal frequency division multiple access. For time and frequency synchronization, a node requests its neighbor nodes for a change of fast Fourier transform starting points, transmission times, and carrier frequencies needed for synchronization. The node also updates its own time and frequency elements through simple formulas based on request messages received from neighbor nodes using a guard interval and a cyclic prefix. This process with the cooperation of neighbor nodes leads to a gradual synchronization of all nodes in the network. Through a performance comparison with a conventional scheme, we obtain simulation results indicating that the proposed scheme outperforms the conventional scheme in random topologies and a grid topology.     

Distributed Transmit Power Control for Maximizing End-to-End Throughput in Wireless Multi-hop Networks

Wireless multi-hop networks have a solidarity property, in which each multi-hop link interferes mutually and so an increase in one link’s rate results in a decrease of the other links’ rate. In a multi-hop link, the end-to-end throughput between a source and destination is restricted by the lowest link rate, so the max-min fair allocation on the link rates is an optimal strategy to maximize the end-to-end throughput. In this paper, we verify that if the wireless links have a solidarity property, the max-min fair allocation has all link rates equal, so we propose a transmit power control (TPC) algorithm that decides the transmit power of multi-hop nodes to equalize all link rates. The proposed algorithm operates in a distributed manner, where each node averages the recognized link rates around itself, allocates its transmit power to achieve this average rate, and iterates this operation until all link rates become equal. Intensive simulation shows that the proposed TPC algorithm enables all link rates to converge on the same value, and thus maximizes the multi-hop end-to-end throughput while decreasing the power consumption of multi-hop nodes.     

Achieving seamless handoffs via backhaul support in Wireless Mesh Networks

In Wireless Mesh Networks (WMNs), mobile clients may experience frequent handoffs due to the relatively small transmission range of the mesh routers. Each handoff may lead to packet delays and/or packet losses, which limits the performance of real-time applications over WMNs. In this work, we propose BASH—a Backhaul-Aided Seamless Handoff scheme. BASH takes advantage of the wireless backhaul feature of WMNs, and allows a mobile station to directly access the backhaul channel to probe the neighboring mesh routers. Our work shows that by utilizing the wireless backhaul, BASH (1) reduces the probing latency and, thus, the Layer-2 handoff latency; (2) allows partial overlap of the Layer-2 and Layer-3 handoffs, reducing the overall handoff latency; and (3) shortens the authentication latency by utilizing the transitivity of trust relationship. The experimental results show that BASH achieves an average Layer-2 handoff of 8.9 ms, which supports real-time applications during the handoff.     

A Distributed and Collaborative Intrusion Detection Architecture for Wireless Mesh Networks

Wireless Mesh Network (WMN) is an emerging heterogeneous network architecture that is growing in importance among traditional wireless communication systems as a cost-effective way of providing Internet services. However, WMNs are particularly vulnerable to malicious nodes given their inherent attributes such as decentralized infrastructure and high dependence of node cooperation. We then propose a distributed and Collaborative Intrusion Detection System (CIDS) architecture for detecting insider attacks at real-time, which comprises: i) a Routing Protocol Analyzer (RPA) to analyze the collected routing traffic and generate respective Routing Events; ii) a Distributed Intrusion Detection Engine (DIDE) that treats the Routing Events by applying Routing Constraints and calculate related Misbehaving Metrics; iii) a Cooperative Consensus Mechanism (CCM) to check the Misbehaving Metrics using a proposed threshold scheme and to track down the source of intrusion. The entire CIDS solution is implemented in a virtualized mesh network platform. The experimental results show the proposed CIDS architecture efficiently detects message fabrication attacks with good precision and low resource consumption.     

A Distributed Sequential Link Schedule Combined with Routing in Wireless Mesh Networks

This letter proposes a new distributed scheduling scheme combined with routing to support the quality of service of real‐time applications in wireless mesh networks. Next, this letter drives average end‐to‐end delay of the proposed scheduling scheme that sequentially schedules the slots on a path. Finally, this letter simulates the time division multiple access network for performance comparison. From the simulation results, when the average number of hops is 2.02, 2.66, 4.1, 4.75, and 6.3, the proposed sequential scheduling scheme reduces the average end‐to‐end delay by about 28%, 10%, 17%, 27%, and 30%, respectively, compared to the conventional random scheduling scheme.     

在多天线多信道无线Mesh网络中基于利用率最大化来融合网络编码和TCP协议

A new approach, named TCP-I2 NC, is proposed to improve the interaction between network coding and TCP and to maximize the network utility in interference-free multi-radio multi-channel wireless mesh networks. It is grounded on a Network Utility Maxmization ( NUM ) formulation which can be decomposed into a rate control problem and a packet scheduling problem. The solutions to these two problems perform resource allocation among different flows. Simulations demonstrate that TCP-I2NC results in a significant throughput gain and a small delay jitter. Network resource is fairly allocated via the solution to the NUM problem and the whole system also runs stably. Moreover, TCP-I2NC is compatible with traditional TCP variants.