Extracting More Capacity from Multi-channel Multi-radio Wireless Networks by Exploiting Power

As wireless networks are gaining increasing popularity, the network energy efficiency has become a critical issue. In this paper, we focus on energy-efficient networking in a generic multi-radio multi-channel (MR-MC) wireless network where transmission scheduling, transmit power control, radio and channel assignment are coupled together in a multi-dimensional resource space, thus requiring joint optimization and low complexity algorithms. We propose a novel Decomposed Approach For energy-efficient (DAFEE) networking in MR-MC networks, with the objective to minimize network energy consumption while guaranteeing a certain level of performance. In particular, we leverage a multi-dimensional tuple-link based model and a concept of resource allocation pattern to transform the complex optimization problem into a linear programming (LP) problem. The LP problem however has a very large solution space due to the exponentially many possible resource allocation patterns. We then exploit delay column generation and distributed learning techniques to decompose the problem and solve it with an iterative process. Furthermore, we propose a sub-optimal algorithm to speed up the iteration with constant-bounded performance. Simulation results are presented to demonstrate the effectiveness of the proposed algorithm.

In this paper we present a method to assess measurements for link quality estimation in wireless networks. Quality of service (QoS) is increasingly important in 3G wireless networks. Commonly, the end to end QoS is defined by delay and error rate. To meet the end-to-end QoS requirements it is very important to control the error rates on the air interface. The error rates can be controlled by change the energy per bit on the air interface. A mismatching energy assignment will either result in a waste of capacity or in a violation of the error rate requirements for the air interface. Thus, the link quality estimation is critical for performance and capacity of wireless networks. In this paper we present a method to evaluate the value of possible measurements for link quality estimation. This method supports the selection process of appropriate measurements and allows the comparison of their performance. As an example, we apply the presented method to an UMTS 12.2 kbps connection.

The increasing use of multi-hop wireless networks and the growing demand of bandwidth-intensive multimedia applications are the driving force to explore innovative techniques that can enhance the capacity of multi-hop wireless networks. The commonly used omni-directional antennas limit the spatial reusability of the wireless channel and hence reduce the available capacity of wireless networks. On the contrary, bandforming antennas, that enable directional transmissions and receptions, can overcome the aforementioned limitation. With the recent advances in signed processing and antenna technologies, smart beamforming antennas have become feasible in compact sizes and suitable prices and hence pertinent to multi-hop wireless networks. However, lack of appropriate control over the antenna beamforming may deteriorate the overall performance even below the level achieved by omni-directional antennas. Moreover, beamforming antennas introduce unprecedented challenges including deafness and directional hidden terminal problems. Hence, it is important to design efficient mechanisms for both Medium Access Control (MAC) and routing to deal with these challenges that hinder the full exploitation of spatial reusability offered by smart beamforming antennas. In this dissertation, we develop an analytical framework for modeling directional contention-based MAC protocols, which is, up to our knowledge, the first model to include deafness in the analysis. We show that deafness can severely limit the network capacity. Based on the insights gained from our analysis of the limitations of the existing solutions, we propose a novel opportunistic directional MAC protocol for multi-hop wireless networks with beamforming antennas. The proposed MAC protocol employs a new backoff mechanism that aims at minimizing the unnecessary idle waiting time, which is a key factor in leveraging the spatial reuse. Through extensive simulations, we demonstrate that the proposed MAC protocol enhances the performance in terms of throughput, delay, packet delivery ratio and fairness. We have also addressed the question about the theoretical capacity gain achieved by beamforming antennas. We derive a generic interference model that can accommodate any antenna radiation pattern and show that the capacity gain is significant even when realistic antenna radiation patterns are used. Since smart beamforming antennas can significantly spare the network resources, they can be utilized to provide Quality of Service (QoS) guarantees. We study the bandwidth-guaranteed routing problem in contention-based multi-hop wireless networks with beamforming antennas. We first present an analysis for the wireless links interdependencies in a contention-based environment in the presence of beamforming, which helps in our formulation of the QoS routing problem as a mixed-integer non-linear optimization problem. We then propose a routing and admission control algorithm for its solution. Our simulation results demonstrate the accuracy of our analysis and the ability of our proposed algorithm to find bandwidth-guaranteed routes. In summary, the analysis and design approaches, adopted in this dissertation, enhance the throughput of multi-hop wireless networks by grasping the transmission opportunities offered by smart beamforming antennas while dealing with the beamforming-related challenges at the MAC and network layers, which otherwise limit the spatial reusability of the wireless channel.

The throughput capacity of arbitrary wireless networks under the physical Signal to Interference Plus Noise Ratio (SINR) model has received much attention in recent years. In this paper, we investigate the question of how much the worst-case performance of uniform and non-uniform power assignments differ under constraints such as a bound on the area where nodes are distributed or restrictions on the maximum power available. We determine the maximum factor by which a non-uniform power assignment can outperform the uniform case in the SINR model. More precisely, we prove that in one-dimensional settings the capacity of a non-uniform assignment exceeds a uniform assignment by at most a factor of O(logL max ) when the length of the network is L max . In two-dimensional settings, the uniform assignment is at most a factor of O(logP max ) worse than the non-uniform assignment if the maximum power is P max . We provide algorithms that reach this capacity in both cases. Due to lower bound examples in previous work, these results are tight in the sense that there are networks where the lack of power control causes a performance loss in the order of these factors. As a consequence, engineers and researchers may prefer the uniform model due to its simplicity if this degree of performance deterioration is acceptable.

The capacity of wireless networks can be increased via dynamic load balancing/sharing by employing overlay networks on top of the existing cellular networks. One such recently proposed system is the integrated cellular and ad hoc relay (iCAR) system, where an overlay ad hoc network is employed to use the resources efficiently by dynamically balancing the load of the hot spots in the cellular network, and to provide quality-of-service to subscribers, no matter where they are located and when the request is made. It is assumed that this overlay network operates in the 2.4-GHz Industrial, Scientific, and Medical (ISM) band and, hence, the number of available ISM-band relay channels used for load balancing will be limited due to other users' interference at a given point in time. In this paper, the impact of ISM-band interference on the performance of iCAR systems, which is a representative hybrid wireless network, is studied, and it is shown that dynamic load balancing and sharing capabilities of iCAR systems are strictly dependent on the availability of the ISM-band relay channels. In addition to quantifying the impact of the number of available relay channels on the performance of iCAR systems, a simple channel assignment scheme to reduce the performance degradation due to other users' interference is also provided. Results show that this interference avoidance technique can improve the realistic performance of iCAR-like hybrid wireless networks by 12%-23% when the interferers are uniformly distributed in the ISM-band.

Recent works show conflicting results: network capacity may increase or decrease with higher transmission power under different scenarios. In this work, we want to understand this paradox. Specifically, we address the following questions: (1)Theoretically, should we increase or decrease transmission power to maximize network capacity? (2) Theoretically, how much network capacity gain can we achieve by power control? (3) Under realistic situations, how do power control, link scheduling and routing interact with each other? Under which scenarios can we expect a large capacity gain by using higher transmission power? To answer these questions, firstly, we prove that the optimal network capacity is a non-decreasing function of transmission power. Secondly, we prove that the optimal network capacity can be increased unlimitedly by higher transmission power in some network configurations. However, when nodes are distributed uniformly, the gain of optimal network capacity by higher transmission power is upper-bounded by a positive constant. Thirdly, we discuss why network capacity in practice may increase or decrease with higher transmission power under different scenarios using carrier sensing and the minimum hop-count routing. Extensive simulations are carried out to verify our analysis.

Reconfigurable antennas have been proposed for mitigating multipath interference and increasing channel capacity in wireless networks. The majority of studies which have investigated these claims do so either in simulation or through the use of software defined radios in lab or office environments. There has been little work in quantifying experimentally the performance gains of a reconfigurable antenna in highly metallic environments representative of military and industrial applications. This letter quantifies the performance gains provided by the use of electrically reconfigurable antennas in the place of omnidirectional antennas given varying environmental and system configurations. Wireless measurements for various 802.11-like physical layers were performed in a set of multideck, coupled compartments aboard Thomas S. Gates (CG 51), a decommissioned Ticonderoga-class U.S. Navy cruiser. The reconfigurable antennas were observed to provide higher channel capacities than omnidirectional antennas. When the bulkhead doors connecting the coupled compartments were left open, the postprocessing signal to noise ratio (PP-SNRs) of signals received from reconfigurable antennas were up to 4 dB higher than what was observed when using omnidirectional antennas. As the compartments became less electrically coupled (i.e., bulkhead doors were closed), the benefit provided via the antenna pattern diversity of the reconfigurable antennas diminished.

Wireless networking is a crucial component of communication in this era of digitization. The key characteristics that determine a wireless network's performance are smooth connectivity, quicker communication, and increased customer satisfaction. Scalability deals with the erratic workload and new resources that are added to the network. Scalability is crucial for both Quality of Experience (QoE) and Quality of Service (QoS) in such a power-constrained environment because wireless devices are battery-operated. Managing power consumption and network performance simultaneously in scalable networking scenario is quite challenging, especially during handover. This research proposed a methodology to assess the impact of scalability on wireless node power consumption and network performance in order to develop energy-efficient handoff mechanisms. The Type-I and Type-II wireless node sets were used between the WiFI and WiMAX networks in a vertical handover scenario. In the study, two distinct scalability scenarios were taken into account. Three distinct voltage levels—cutoff voltage, nominal voltage, and charge voltage —had been used to examine the consumption of power. Throughput, residual energy, and Packet Delivery Ratio (PDR) were computed to examine the network's performance in a scalable, power-constrained context. Two different scalability scenarios were considered in the study. The power consumption was investigated using three different voltage levels: charge voltage, nominal voltage, and cutoff voltage. The network's performance under scalable, power-constrained conditions was investigated by computing throughput, packet delivery ratio (PDR), and residual energy. The result obtained in the study showed the variation in battery drainage of wireless nodes under the effect of various scalability factors. This study will provide a blueprint for developing novel algorithms which eventually will improvise network performance and strengthen the base of Green Networking.

We present the first unified modeling framework for the computation of the throughput capacity of random wireless ad hoc networks in which information is disseminated by means of unicast routing, multicast routing, broadcasting, or different forms of anycasting. We introduce (n,m, k)-casting as a generalization of all forms of one-to-one, one-to-many and many-to-many information dissemination in wireless networks. In this context, n, m, and k denote the total number of nodes in the network, the number of destinations for each communication group, and the actual number of communication-group members that receive information (i.e., k lesm), respectively. We compute upper and lower bounds for the (n, m, k)- cast throughput capacity in random wireless networks. When m = k = ominus(1), the resulting capacity equals the well-known capacity result for multi-pair unicasting by Gupta and Kumar. We demonstrate that ominus(1/radic(mnlogn)) bits per second constitutes a tight bound for the capacity of multicasting (i.e., m = k < n) when m les ominus (n/(log n)). We show that the multicast capacity of a wireless network equals its capacity for multi-pair unicasting when the number of destinations per multicast source is not a function of n. We also show that the multicast capacity of a random wireless ad hoc network is ominus (1/n), which is the broadcast capacity of the network, when m ges ominus(n/ log n). Furthermore, we show that ominus (radicm/(kradic(n log n))),ominus(1/(k log n)) and ominus(1/n) bits per second constitutes a tight bound for the throughput capacity of multicasting (i.e., k < m < n) when ominus(1) les m les ominus (n/ log n), k les ominus(n / log n) les m les n and ominus (n/ log n) les k les m les n respectively.

Abstract—We study the capacity of a large-scale random wireless network for multicast. Assume that n wireless nodes are uniformly randomly deployed in a square region with sidelength a and all nodes have the uniform transmission range r and uniform interference range R&amp;gt; r. We further assume that each wireless node can transmit (or receive) at W bits/second over a common wireless channel. For each node vi, we randomly and independently pick k − 1 points pi,j (1 ≤ j ≤ k − 1) from the square, and then multicast data to the nearest node for each pi,j. The aggregated multicast capacity is defined as the total data rate of all multicast sessions in the network. We derive matching asymptotic upper bounds and lower bounds on multicast capacity of random wireless networks. Under protocol interference model, when a 2 /r 2 = �O(n / log(n)), we show that the total multicast n capacity is Θ ( log n · W √ ) when k = O( k n); the total multicast log n capacity is Θ(W) when k = Ω ( n log n Xiang-Yang Li, Associate Member, IEEE,). Our bounds unify the previous capacity bounds on unicast (when k = 2) by Gupta and Kumar [6] and broadcast (when k = n) in [9], [20]. We also study the capacity of group-multicast for wireless networks where for each source node, we randomly select k − 1 groups of nodes as receivers and the nodes in each group are within a constant hops from the group leader. The same asymptotic upper bounds and lower bounds still hold. We also extend our capacity bounds to d-dimensional networks. Index Terms—Wireless ad hoc networks, capacity, multicast, broadcast, unicast, scheduling, optimization, VC dimension. I.

The problem of communication among nodes in an extended network is considered, where radio power decay and interference are limiting factors. It has been shown previously that, with simple multi-hopping, the achievable total communication rate in such a network is at most Theta(radic(N)). In this work, we study the benefit of node cooperation in conjunction with multi-hopping on the network capacity. We propose a multi-phase communication scheme, combining distributed MIMO transmission with multi-hop forwarding among clusters of nodes. We derive the network throughput of this communication scheme and determine the optimal cluster size. This provides a constructive lower bound on the network capacity. We first show that in regular networks a rate of omega(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> ) can be achieved with transmission power scaling of Theta(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">alpha/6-1/3</sup> ), where alpha > 2 is the signal path-loss exponent. We further extend this result to random networks, where we show a rate of omega(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> (logN) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-alpha/6</sup> ) can be achieved with transmission power scaling of Theta(N <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">alpha/6-1/3</sup> (logN) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(alpha-2)</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">/6</sup> . In particular, as alpha approaches 2, only constant transmission power is required.

In this paper, we investigate the throughput capacity of large-scale wireless networks, in which three network-assisted coding schemes are considered: (1) multi-point-to-point coding (MPPC); (2) MPPC based network coding (NC); and (3) MPPC based physical-layer network coding (PLNC). This study is based on the generalized physical model, in which the transmission rate depends on the signal to noise and interference ratio (SINR). Such a model has not been used to analyze the behaviors of large-scale wireless networks with the aforementioned coding schemes. To understand the capacity gains of these schemes, we develop constructive lower bounds for one-dimensional (1D) and two-dimensional (2D) networks with size factor w, in which we construct novel wireless highway systems. This study shows that, compared to point-to-point coding (PPC), MPPC can improve the scaling law of network capacity when w exceeds a certain scale. In addition, this study reveals that MPPC based NC and PLNC can improve the capacity by constant factors. Specifically, NC can always obtain a gain of 2 in both 1D and 2D networks. On the other hand, the gain of PLNC can be larger than 2 in 1D networks, and can be up to 2 in 2D networks, depending on w, transmission power, noise, and path-loss of propagation.

This paper addresses the issue of multicast scaling performance in multichannel multiradio (MC-MR) networks. Under the assumption of both limited bandwidth and node tunability, a total fixed bandwidth $(W)$ is equally split into $(c)$ channels with $(0<m\le c)$ interfaces equipped on each node for channel switching. The network contains totally $(n)$ nodes, each serving as a source with $(k)$ randomly and uniformly selected destinations. We try to give a comprehensive picture of multicast scalings by investigating both the static and mobile networks, with the metrics being capacity and delay. Previous literature has indicated that unicast capacity is solely determined by the ratio of channels to interfaces $(c/m)$ in MC-MR networks. However, in multicast our problem is made more complicated by the interplay among $(k)$, $(c/m)$ and node mobility (if considered in mobile scenario). We characterize their impact on multicast scaling and obtain three remarkable findings from our results. First, we find capacity loss exists in static networks even if the ratio $(c/m=O(\log n))$ (We use the following notation throughout our paper: $(f(n)=O(g(n))\Leftrightarrow \limsup _{n\rightarrow \infty }{f(n)\over g(n)} <\infty)$, $(f(n)=\Omega (g(n))\Leftrightarrow \liminf _{n\rightarrow \infty }{f(n)\over g(n)} <\infty)$, $(f(n)=\Theta (g(n))\Leftrightarrow f(n)=O(g(n)))$ and $(g(n)=O(f(n)))$, $(f(n)=\widetilde{\Theta }(\cdot ))$: The corresponding order $(\Theta (\cdot ))$ which contains a logarithmic order.) when $(k)$ is close to $(\Theta (n))$. This differs from unicast that is free of capacity loss as long as $(c/m=O(\log n))$. Second, mobility is manifested to improve multicast capacity in MC-MR networks, where two major capacity bottlenecks, i.e., connectivity and interference constraints, in static networks can be effectively broken. Third, a largely reduced delay is possible by simply seeking for multichannel reuse in 2-hop algorithm without redundancy. This even outperforms the delay scaling in single channel framework , where a delay smaller than $(\Theta (\sqrt{n\log k}))$ is not achievable even with more than $(\Theta (\sqrt{n\log k}))$ relay nodes involved in 2-hop mode. As a high-level summary of our results, our work discloses analytically where the performance improvement and degradation exhibit in MC-MR networks, meanwhile unifying the previous bounds on unicast (setting $(k=1)$) in .

Wireless use is growing in the health-care industry. A good wireless solution has the potential to reduce deployment cost, facilitate ubiquitous information access, and improve patient care by eliminating wires, which are a source of infection and physical impediment to clinical care. However, the general perception of wireless communication as being unreliable, unpredictable and unsuitable for safe-critical applications hampers wider adoption of wireless solutions beyond best effort services. In this paper, we argue and demonstrate that wireless networks can in fact be made more reliable by robust resource management. In particular, predictable services can be achieved using joint power control, channel assignment and radio interface selection in multi-radio multi-channel(MR-MC) wireless networks in presence of unpredictable channel dynamics and interferences. Trace-driven simulation study using data collected from our wireless mesh testbed show that the proposed algorithm is indeed superior to existing schemes in reducing outage and packet loss probabilities.

Capacity is one fundamental problem in wireless Ad hoc networks. Deploying directional antennas to wireless networks can reduce interference among concurrent transmissions and increase spatial reuse, while the technology of multi-channel can separate concurrent transmissions. Therefore, combining these two technologies into one wireless network is capable of great improvement on the network capacity. Recent studies proposed a multi-channel network architecture that equips each wireless node with multiple directional antennas, which is called MC-MDA network. The capacity in MC-MDA network is derived under arbitrary and random placements. However, they only used a simplified directional antenna model. For approaching the more accurate capacity in real scenario, we consider a hybrid antenna model, which takes the effect of side lobe into account. We derive the capacity upper-bounds of MC-MDA networks in arbitrary and random network with the hybrid model to find the effect of side lobe. We show that the network capacity is closely related to the ratio of the radiuses of side lobe to main lobe. The capacity decreases when the ratio increases. Moreover, we compare the network capacity of MC-MDA using the simplified antenna model with our results.