Cross-Layer Design for QoS Routing in Multi-Hop Wireless Networks

Mobile Ad Hoc Networks (MANETs) are gaining increasing popularity in recent years because of their ease of deployment. They are distributed, dynamic, and self-configurable without infrastructure support. Routing in ad hoc networks is a challenging task because of the MANET dynamic nature. Hence, researchers were focused in designing best-effort distributed and dynamic routing protocols to ensure optimum network operations in an unpredictable wireless environment. Nowadays, there is an increased demand on multimedia applications (stringent delay and reliability requirements), which makes a shift from best-effort services to Quality of Services. Actually, the challenge in wireless ad hoc networks is that neighbor nodes share the same channel and they take part in forwarding packets. Therefore, the total effective channel capacity is not only limited by the raw channel capacity but is also limited by the interactions and interferences among neighboring nodes. Thus, such factors should be taken in consideration in order to offer QoS routing. While, some of the distributed QoS route selection algorithms assume the availability of such information, others propose mechanisms to estimate them. The goals of this thesis are: (i) to analyze the performance of IEEE 802.11 MAC mechanism in non-saturation conditions, (ii) to use the analysis in the context of multi-hop ad hoc networks, (iii) to derive theoretical limits for nodes performance in multi-hop ad hoc networks, (iv) to use the multi-hop analysis in QoS route selection. We start the thesis by proposing a discrete-time 3D Markov chain model to analyze the saturation performance of the RTS/CTS access mode. This model integrates the backoff countdown process, retransmission retry limits, and transmission errors into one model. The impact of system parameters (e.g., number of nodes, packet size, retry limits, and BERs) are analyzed. Next, we extend the 3D model to analyze the performance under non-saturation conditions and finite buffer capacity using two different approaches. First, we extend the 3D model into a 4D model to integrate the transmission buffer behavior. Second, we replace the 4D model by an M/G/1/K queueing system model with independent samples from the saturation analysis. The latter model gives similar results as the former but with a reduction in the analysis complexity. Next and by means of the non-saturation analysis, we proposed an approximate mathematical model for multi-hop ad hoc networks. Furthermore, we proposed an iterative mechanism to estimate the throughput in the presence of multiple flows. Finally, we used the multi-hop analysis to propose a QoS route selection algorithm. In this algorithm, we concentrate on the throughput as a QoS parameter. However, the proposed algorithm is valid to be used with other QoS parameters, such as packet delay, packet loss probability, and fairness. Analytical and simulation results show the deficiency of the current route selection algorithm in AODV and at the same time verifies the need for QoS route selection algorithms

Distributed Power Control and Medium Access Control Protocol Design for Multi-Channel Ad Hoc Wireless Networks

In the past decade, the development of wireless communication technologies has made the use of the Internet ubiquitous. With the increasing number of new inventions and applications using wireless communication, more interference is introduced among wireless devices that results in limiting the capacity of wireless networks. Many approaches have been proposed to improve the capacity. One approach is to exploit multiple channels by allowing concurrent transmissions, and therefore it can provide high capacity. Many available, license-exempt, and non-overlapping channels are the main advantages of using this approach. Another approach that increases the network capacity is to adjust the transmission power; hence, it reduces interference among devices and increases the spatial reuse. Integrating both approaches provides further capacity. However, without careful transmission power control (TPC) design, the network performance is limited. The first part of this thesis tackles the integration to efficiently use multiple channels with an effective TPC design in a distributed manner. We examine the deficiency of uncontrolled asymmetrical transmission power in multi-channel ad hoc wireless networks. To overcome this deficiency, we propose a novel distributed transmission power control protocol called the distributed power level (DPL) protocol for multi-channel ad hoc wireless networks. DPL allocates different maximum allowable power values to different channels so that the nodes that require higher transmission power are separated from interfering with the nodes that require lower transmission power. As a result, nodes select their channels based on their minimum required transmission power to reduce interference over the channels. We also introduce two TPC modes for the DPL protocol: symmetrical and asymmetrical. For the symmetrical mode, nodes transmit at the power that has been assigned to the selected channel, thereby creating symmetrical links over any channel. The asymmetrical mode, on the other hand, allows nodes to transmit at a power that can be lower than or equal to the power assigned to the selected channel. In the second part of this thesis, we propose the multi-channel MAC protocol with hopping reservation (MMAC-HR) for multi-hop ad hoc networks to overcome the multi-channel exposed terminal problem, which leads to poor channel utilization over multiple channels. The proposed protocol is distributed, does not require clock synchronization, and fully supports broadcasting information. In addition, MMAC-HR does not require nodes to monitor the control channel in order to determine whether or not data channels are idle; instead, MMAC-HR employs carrier sensing and independent slow channel hopping without exchanging information to reduce the overhead. In the last part of this thesis, a novel multi-channel MAC protocol is developed without requiring any change to the IEEE 802.11 standard known as the dynamic switching protocol (DSP) based on the parallel rendezvous approach. DSP utilizes the available channels by allowing multiple transmissions at the same time and avoids congestion because it does not need a dedicated control channel and enables nodes dynamically switch among channels. Specifically, DSP employs two half-duplex interfaces: One interface follows fast hopping and the other one follows slow hopping. The fast hopping interface is used primarily for transmission and the slow hopping interface is used generally for reception. Moreover, the slow hopping interface never deviates from its default hopping sequence to avoid the busy receiver problem. Under single-hop ad hoc environments, an analytical model is developed and validated. The maximum saturation throughput and theoretical throughput upper limit of the proposed protocol are also obtained

On Capacity and Delay of Multi-channel Wireless Networks with Infrastructure Support

In this paper, we propose a novel multi-channel network with infrastructure support, called an MC-IS network, which has not been studied in the literature. To the best of our knowledge, we are the first to study such an MC-IS network. Our proposed MC-IS network has a number of advantages over three existing conventional networks, namely a single-channel wireless ad hoc network (called an SC-AH network), a multi-channel wireless ad hoc network (called an MC-AH network) and a single-channel network with infrastructure support (called an SC-IS network). In particular, the network capacity of our proposed MC-IS network is $\sqrt{n \log n}$ times higher than that of an SC-AH network and an MC-AH network and the same as that of an SC-IS network, where $n$ is the number of nodes in the network. The average delay of our MC-IS network is $\sqrt{\log n/n}$ times lower than that of an SC-AH network and an MC-AH network, and $\min\{C_I,m\}$ times lower than the average delay of an SC-IS network, where $C_I$ and $m$ denote the number of channels dedicated for infrastructure communications and the number of interfaces mounted at each infrastructure node, respectively. Our analysis on an MC-IS network equipped with omni-directional antennas only has been extended to an MC-IS network equipped with directional antennas only, which are named as an MC-IS-DA network. We show that an MC-IS-DA network has an even lower delay of $\frac{c}{\lfloor \frac{2\pi}{\theta}\rfloor \cdot C_I}$ compared with an SC-IS network and our MC-IS network. For example, when $C_I=12$ and $\theta=\frac{\pi}{12}$, an MC-IS-DA network can further reduce the delay by 24 times lower that of an MC-IS network and reduce the delay by 288 times lower than that of an SC-IS network.Comment: accepted, IEEE Transactions on Vehicular Technology, 201

Multi-channel Wireless Networks with Infrastructure Support: Capacity and Delay

In this paper, we propose a novel multi-channel network with infrastructure support, called an \textit{MC-IS} network, which has not been studied in the literature. To the best of our knowledge, we are the first to study such an \textit{MC-IS} network. Our \textit{MC-IS} network is equipped with a number of infrastructure nodes which can communicate with common nodes using a number of channels where a communication between a common node and an infrastructure node is called an infrastructure communication and a communication between two common nodes is called an ad-hoc communication. Our proposed \textit{MC-IS} network has a number of advantages over three existing conventional networks, namely a single-channel wireless ad hoc network (called an \textit{SC-AH} network), a multi-channel wireless ad hoc network (called an \textit{MC-AH} network) and a single-channel network with infrastructure support (called an \textit{SC-IS} network). In particular, the \textit{network capacity} of our proposed \textit{MC-IS} network is $\sqrt{n \log n}$ times higher than that of an \textit{SC-AH} network and an \textit{MC-AH} network and the same as that of an \textit{SC-IS} network, where $n$ is the number of nodes in the network. The \textit{average delay} of our \textit{MC-IS} network is $\sqrt{\log n/n}$ times lower than that of an \textit{SC-AH} network and an \textit{MC-AH} network, and $\min(C_I,m)$ times lower than the average delay of an \textit{SC-IS} network, where $C_I$ and $m$ denote the number of channels dedicated for infrastructure communications and the number of interfaces mounted at each infrastructure node, respectively.Comment: 12 pages, 6 figures, 3 table

Adaptive Resource Control in 2-hop Ad-Hoc Networks

This paper presents a simple resource control\ud mechanism with traffic scheduling for 2-hop ad-hoc networks, in\ud which the Request-To-Send (RTS) packet is utilized to deliver\ud feedback information. With this feedback information, the\ud Transmission Opportunity (TXOP) limit of the sources can be\ud controlled to balance the traffic. Furthermore, a bottleneck\ud transmission scheduling scheme is introduced to provide fairness\ud between local and forwarding flows. The proposed mechanism is\ud modeled and evaluated using the well-known 20-sim dynamic\ud system simulator. Experimental results show that a fairer and\ud more efficient bandwidth utilization can be achieved than\ud without the feedback mechanism. The use of the structured and\ud formalized control-theoretical modeling framework has as\ud advantage that results can be obtained in a fast and efficient way

Cooperative power control approaches towards fair radio resource allocation for wireless network

Performance optimization in wireless networks is a complex problem due to variability and dynamics in network topology and density, traffic patterns, mutual interference, channel uncertainties, etc. Opportunistic or selfish approaches may result in unbalanced allocation of channel capacity where particular links are overshadowed. This degrades overall network fairness and hinders a multi-hop communication by creating bottlenecks. A desired approach should allocate channel capacity proportionally to traffic priority in a cooperative manner. This work consists of two chapters that address the fairness share problem in wireless ad hoc, peer-to-peer networks and resource allocation within Cognitive Radio network. In the first paper, two fair power control schemes are proposed and mathematically analyzed. The schemes dynamically determine the viable resource allocation for a particular peer-to-peer network. In contrast, the traditional approaches often derive such viable capacity for a class of topologies. Moreover, the previous power control schemes assume that the target capacity allocation, or signal-to-interference ratio (SIR), is known and feasible. This leads to unfairness if the target SIR is not viable. The theoretical and simulation results show that the capacity is equally allocated for each link in the presence of radio channel uncertainties. In the second paper, based on the fair power control schemes, two novel power control schemes and an integrated power control scheme are proposed regarding the resource allocation for Cognitive Radio network to increase the efficiency of the resource while satisfying the Primary Users\u27 Quality of Service. Simulation result and tradeoff discussion are given --Abstract, page iv

An Upper Bound on Multi-hop Transmission Capacity with Dynamic Routing Selection

This paper develops upper bounds on the end-to-end transmission capacity of multi-hop wireless networks. Potential source-destination paths are dynamically selected from a pool of randomly located relays, from which a closed-form lower bound on the outage probability is derived in terms of the expected number of potential paths. This is in turn used to provide an upper bound on the number of successful transmissions that can occur per unit area, which is known as the transmission capacity. The upper bound results from assuming independence among the potential paths, and can be viewed as the maximum diversity case. A useful aspect of the upper bound is its simple form for an arbitrary-sized network, which allows insights into how the number of hops and other network parameters affect spatial throughput in the non-asymptotic regime. The outage probability analysis is then extended to account for retransmissions with a maximum number of allowed attempts. In contrast to prevailing wisdom, we show that predetermined routing (such as nearest-neighbor) is suboptimal, since more hops are not useful once the network is interference-limited. Our results also make clear that randomness in the location of relay sets and dynamically varying channel states is helpful in obtaining higher aggregate throughput, and that dynamic route selection should be used to exploit path diversity.Comment: 14 pages, 5 figures, accepted to IEEE Transactions on Information Theory, 201

Research on Wireless Multi-hop Networks: Current State and Challenges

Wireless multi-hop networks, in various forms and under various names, are being increasingly used in military and civilian applications. Studying connectivity and capacity of these networks is an important problem. The scaling behavior of connectivity and capacity when the network becomes sufficiently large is of particular interest. In this position paper, we briefly overview recent development and discuss research challenges and opportunities in the area, with a focus on the network connectivity.Comment: invited position paper to International Conference on Computing, Networking and Communications, Hawaii, USA, 201