Static Wireless Networks Research Articles

The capacity of random wireless networks

We analyze how the capacity of the random wireless network scales with node density for stationary nodes, taking jointly into account link adaptation, media access control (MAC), routing and retransmission for error recovery (ARQ). For the purpose, we propose a generic per-hop-based routing scheme, in which relay probability is a key parameter, and use the routing scheme as a basis for our analysis. By jointly optimizing the above factors, we derive the capacity of the random network. Our analysis shows that the per-node throughput of a static random wireless network composed of n source-destination pairs is O(1/radic(n log n)). This capacity estimation is similar to that of Gupta and Kumar, even if the assumptions are quite different.We also use simulations to investigate how node mobility affects the capacity of a random network. We have found that mobility can increase network capacity, by giving the nodes more chances to be close to each other. Our simulation results empirically show that the capacity of the random network under a mobility condition declines in the order of O(1/radicn).

Interference-Aware Joint Routing and TDMA Link Scheduling for Static Wireless Networks

We study efficient interference-aware joint routing and TDMA link scheduling for a multihop wireless network to maximize its throughput. Efficient link scheduling can greatly reduce the interference effect of close-by transmissions. Unlike the previous studies that often assume a unit disk graph model, we assume that different terminals could have different transmission ranges and interference ranges. In our model, a communication link may not exist due to barriers or is not used by a predetermined routing protocol. Using a mathematical formulation, we develop interference aware joint routing and TDMA link schedulings that optimize the networking throughput subject to various constraints. Our linear programming formulation will find a flow routing whose achieved throughput (or fairness) is at least a constant fraction of the optimum. Then, by assuming known link capacities and link traffic loads, we study link scheduling under the RTS/CTS interference model and the protocol interference model with fixed transmission power. For both models, we present both efficient centralized and distributed algorithms that use time slots within a constant factor of the optimum. We also present efficient distributed algorithms whose performances are still comparable with optimum, but with much less communications. Our theoretical results are corroborated by extensive simulation studies.

Three Dimensional Scalable Video Adaptation via User-End Perceptual Quality Assessment

For wireless video streaming, the three dimensional scalabilities (spatial, temporal and SNR) provided by the advanced scalable video coding (SVC) technique can be directly utilized to adapt video streams to dynamic wireless network conditions and heterogeneous wireless devices. However, the question is how to optimally trade off among the three dimensional scalabilities so as to maximize the perceived video quality, given the available resource. In this paper, we propose a low-complexity algorithm that executes at resource-limited user end to quantitatively and perceptually assess video quality under different spatial, temporal and SNR combinations. Based on the video quality measures, we further propose an efficient adaptation algorithm, which dynamically adapts scalable video to a suitable three dimension combination. Experimental results demonstrate the effectiveness of our proposed perceptual video adaptation framework.

Fault-Tolerant Topology Control for All-to-One and One-to-All Communication in Wireles Networks

This paper introduces the problem of fault-tolerant topology control for all-to-one and one-to-all communication in static wireless networks with asymmetric wireless links. This problem is important in both theoretical and practical aspects. We investigate two approaches, namely, the minimum-weight-based approach and the augmentation-based approach, to address this problem. Furthermore, we prove that the minimum-weight-based approach has a k-approximation algorithm for all-to-one fault-tolerant topology control, where k is the number of node-disjoint paths. When k = 1, this approach solves the minimum power sink tree problem. To the best of our knowledge, this paper is the first to study the fault-tolerant topology control for all-to-one and one-to-all communication in asymmetric static wireless networks and is also the first to demonstrate that the minimum power sink tree problem has a polynomial time optimal solution.

A link layer adaptive pacing scheme for improving throughput of transport protocols in wireless mesh networks

In this paper, we study the performance of a static multihop wireless network, specifically that of the backhaul network of a two-tier Wireless Mesh Network (WMN) operating on IEEE 802.11 Medium Access Control (MAC) protocol. The performance of an IEEE 802.11 based backhaul network is greatly affected by the MAC contention and congestion in the network. If the sources pump data into the network than can be supported, loss rate increases due to MAC contention and congestion in the network. This also leads to the problem of unfairness among flows. In this paper, we propose a Link Layer Adaptive Pacing (LLAP) scheme that adaptively controls the offered load into the network. This improves the performance of higher layer protocols without any modifications to them. Our LLAP scheme estimates the four hop transmission delay in the network path without incurring any additional overhead (Control packets) and accordingly paces the packet transmissions to reduce MAC contentions in the network. We implement the LLAP scheme in ns-2.29 network simulator and extensively study its performance for both User Datagram Protocol (UDP) and Transmission Control Protocol (TCP) traffic in different network scenarios. In all the cases, our scheme shows a significant improvement in the performance of both UDP and TCP traffic.

Measurement-driven admission control on wireless backhaul networks

IEEE 802.11 wireless networks perform poorly in the presence of large traffic volumes. Measurements have shown that packet collisions and interference can lead to degraded performance to the extent that users experience unacceptably low throughput, which can ultimately lead to complete network breakdown [12]. An admission control framework that limits network flows can prevent network breakdown and improve the performance of throughput and delay-sensitive multimedia applications. In this paper, we present a measurement-driven admission control scheme that leverages wireless characteristics for intelligent flow control in a static wireless network. Experiments on the 25 node UCSB MeshNet show that the proposed admission control scheme can enhance network performance such that the QoS requirements of real time applications, such as VoIP, can be met.

Power Optimization in Fault-Tolerant Topology Control Algorithms for Wireless Multi-hop Networks

In ad hoc wireless networks, it is crucial to minimize power consumption while maintaining key network properties. This work studies power assignments of wireless devices that minimize power while maintaining k-fault tolerance. Specifically, we require all links established by this power setting be symmetric and form a k-vertex connected subgraph of the network graph. This problem is known to be NP-hard. We show current heuristic approaches can use arbitrarily more power than the optimal solution. Hence, we seek approximation algorithms for this problem. We present three approximation algorithms. The first algorithm gives an O(kalpha)-approximation where is the best approximation factor for the related problem in wired networks (the best alpha so far is O(log k)). With a more careful analysis, we show our second (slightly more complicated) algorithm is an O(k)-approximation. Our third algorithm assumes that the edge lengths of the network graph form a metric. In this case, we present simple and practical distributed algorithms for the cases of 2- and 3-connectivity with constant approximation factors. We generalize this algorithm to obtain an O(k <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2c+2</sup> )-approximation for general k-connectivity (2 les c les 4 is the power attenuation exponent). Finally, we show that these approximation algorithms compare favorably with existing heuristics. We note that all algorithms presented in this paper can be used to minimize power while maintaining -edge connectivity with guaranteed approximation factors. Recently, different set of authors used the notion of k-connectivity and the results of this paper to deal with the fault-tolerance issues for static wireless network settings.

Cooperative Routing in Static Wireless Networks

We study the problem of transmission-side diversity and routing in a static wireless network. It is assumed that each node in the network is equipped with a single omnidirectional antenna and that multiple nodes are allowed to coordinate their transmissions in order to obtain energy savings. We derive analytical results for achievable energy savings for both line and grid network topologies. It is shown that the energy savings of and are achievable in line and grid networks with a large number of nodes, respectively. We then develop a dynamic-programming-based algorithm for finding the optimal route in an arbitrary network, as well as suboptimal algorithms with polynomial complexity. We show through simulations that these algorithms can achieve average energy savings of about in random networks, as compared to the noncooperative schemes.

Bits-per-Joule Capacity of Energy-Limited Wireless Networks

For a wireless network in which every node is bounded in its energy supply, we define a new concept of network capacity called "bits-per-Joule capacity", which is the maximum total number of bits that the network can deliver per Joule of energy deployed into the network. For a fixed network size, a finite number of information bits is delivered for each source-destination pair, under a fixed end-to-end probability of error constraint. We prove that under the one-to-one traffic model in which every node wants to send traffic to a randomly chosen destination node, the bits-per-Joule capacity of a stationary wireless network grows asymptotically as Omega((N/logN) <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(q-1)/2 </sup> ), where N is the number of nodes randomly deployed onto the surface of a sphere and q is the path loss exponent. Further, the length of the block codes used grows only logarithmically in N, which indicates manageable decoder complexity as the network scales. The fact that the bits-per-Joule capacity grows with the number of nodes contrasts sharply with the scaling laws that have been derived for throughput capacity and implies that large-scale deployments for energy-limited sensor and ad hoc networks may be suitable for delay-tolerant data applications

Power-efficient topology control for static wireless networks with switched beam directional antennas

Topology control problems are associated with assignment of power levels to nodes of a wireless network so that the resulting graph topology satisfies certain properties. In this paper we consider the problem of power-efficient topology control with switched beam directional antennas taking into account their non-uniform radiation pattern within the beamwidth. Previous work in the area have all assumed a uniform gain model with these antennas which renders antenna orientation insignificant as a parameter in topology control algorithms. We present algorithms that take into account a model of non-uniform gain with the objectives of minimizing the total power and maximum power to keep the network connected. We consider two cases: one where the antenna orientation is assumed given and another where the antenna orientation needs to be derived as well. For the first case, we present optimal and approximation algorithms for constructing power-efficient topologies. For the second case, we prove the problem to be NP-complete and present heuristic solutions along with approximation bounds. Through comparison of the two cases by simulation, significant reductions are shown in the maximum as well as total power required to keep the network connected for the second case, thus demonstrating the benefits of using antenna orientation as parameter in topology construction.

Optimal Throughput–Delay Scaling in Wireless Networks—Part II: Constant-Size Packets

In Part I of this paper, the optimal throughput-delay tradeoff for static wireless networks was shown to be D(n)=Theta(nT(n)), where D(n) and T(n) are the average packet delay and throughput in a network of n nodes, respectively. While this tradeoff captures the essential network dynamics, packets need to scale down with the network size. In this "fluid model, " no buffers are required. Due to this packet scaling, D(n) does not correspond to the average delay per bit. This leads to the question whether the tradeoff remains the same when the packet size is kept constant, which necessitates packet scheduling in the network. In this correspondence, this question is answered in the affirmative by showing that the optimal throughput-delay tradeoff is still D(n)=Theta(nT(n)), where now D(n) is the average delay per bit. Packets of constant size necessitate the use of buffers in the network, which in turn requires scheduling packet transmissions in a discrete-time queuing network and analyzing the corresponding delay. Our method consists of deriving packet schedules in the discrete-time network by devising a corresponding continuous-time network and then analyzing the delay induced in the actual discrete network using results from queuing theory for continuous-time networks.

Applying Coordination for Service Adaptation in Mobile Computing

Mobile computing devices vary in terms of display, memory, and battery life, and current network protocols aren't necessarily suited to the mobile computing environment. As computer networks' complexity increases, communication-related software must be able to adapt to mobile computing's constraints. This study aims to develop a software system that adapts data flows over dynamic wireless network conditions and various mobile devices. With their MobiGATE system, the authors adopt the principle of separation of concerns to support the system's service composition and reconfiguration. This approach can support ease of dynamic reconfiguration and the reusability of adaptation services across applications

Measurement-based models of delivery and interference in static wireless networks

We present practical models for the physical layer behaviors of packet reception and carrier sense with interference in static wireless networks. These models use measurements of a real network rather than abstract RF propagation models as the basis for accuracy in complex environments. Seeding our models requires N trials in an N node network, in which each sender transmits in turn and receivers measure RSSI values and packet counts, both of which are easily obtainable. The models then predict packet delivery and throughput in the same network for different sets of transmitters with the same node placements. We evaluate our models for the base case of two senders that broadcast packets simultaneously. We find that they are effective at predicting when there will be significant interference effects. Across many predictions, we obtain an RMS error for 802.11a and 802.11b of a half and a third, respectively, of a measurement-based model that ignores interference.

Closed-loop architecture and protocols for rapid dynamic spreading gain adaptation in CDMA networks

We present a closed-loop architecture and protocols for rapid dynamic spreading gain adaptation and fast feedback between a transmitter and a receiver communicating with each other in CDMA networks. These protocols and architecture do not require the transfer of an explicit control message indicating the change of CDMA spreading gain from transmitter to receiver. Also, with these protocols, the transmitter can change the spreading gain symbol-by-symbol as opposed to frame-by-frame, and feedback information (e.g., the fast-varying channel condition) can be exchanged almost as frequently as the symbol rate. Thus, adaptation to the time-varying channel conditions of wireless networks and/or to the rate variation of traffic can be much faster than is possible with the existing frame-by-frame approach.

A middleware architecture for mobile 3D graphics

Mobile graphics, which involves running networked computer graphics applications on mobile devices across wireless networks, is a fast growing segment of the networks and graphics industries. Running networked graphics applications in mobile environments faces a fundamental conflict; graphics applications require large amounts of memory, CPU cycles, battery power and disk space, while mobile devices and wireless channels tend to be limited in these resources. In order to mitigate mobile environment issues, some form of adaptation based on a client device's capabilities, prevailing wireless network conditions, characteristics of the graphics application and user preference, is necessary. In this paper, we describe the mobile adaptive distributed graphics framework (MADGRAF), a graphics-aware middleware architecture that makes it feasible to run complex 3D graphics applications on low-end mobile devices over wireless networks. In MADGRAF, a server can perform mobile device-optimized pre-processing of complex graphics scenes in order to speed up run time rendering, scale high-resolution meshes using polygon or image-based simplification, progressively transmit compressed graphics files, conceal transmission errors by including redundant bits or perform remote execution, all tailored to the client's capabilities. MADGRAF exposes our mobile adaptive distributed graphics language (MADGL), an API that facilitates the programming and management of networked 3D graphics in mobile environments.

Performance Evaluation and Comparison of TCP Algorithms in Static Multihop Wireless Networks

Wireless ad hoc networks are characterized by multihop wireless connectivity and limited bandwidth shared among neighbouring nodes. In this paper, we investigate and evaluate the performance of TCP NewReno, TCP SACK and TCP Vegas in this kind of network over AODV routing protocol and the wireless LAN standard IEEE 802.11 MAC layer. The performance of these TCP variants is compared on the basis of several performance measures that include throughput, retransmission ratio, average congestion window size and routing overhead. Simulation results using ns-2.28 show that TCP Vegas achieves between 15% and 130% more throughput, around 99% less packet retransmissions and around 93% less routing overhead than TCP NewReno and TCP SACK. The paper gives insight on the particular reasons for such performance advantages of TCP Vegas in comparison to TCP NewReno and TCP SACK. Furthermore, we investigate the performance of these TCP algorithms when they are run with the Delayed Acknowledgment (DA) option defined in IETF RFC 1122, which allows the TCP receiver to transmit an ACK for every two incoming packets. Simulation results show that use of DA option substantially improves the performance for TCP NewReno and TCP SACK. It also results in performance improvement for TCP Vegas but as not as much as that of TCP NewReno and for longer hop connections, it can even cause throughput degradation of Vegas. We also observed the effect of TCP packet size on the throughput and packet delivery ratio of TCP NewReno and Vegas. Simulation results show that an increase in packet size reduces the fraction of packets delivered successfully. Increasing the packet size increases the throughput till a certain threshold and there is a decrease in throughput after the threshold.

A Fair Scheduling Algorithm for Wireless Internet Differentiated Service Networks

The recent Internet needs a network structure and traffic engineering that can support various applications requiring differentiated traffic processing and a high quality of service. The extension of the Internet from wired to wireless systems that generate location-dependent and burst errors has made the support of good services more difficult with existing packet scheduling algorithms. Accordingly, this paper troposes a wireless differentiated service packet scheduling (WDSPS) algorithm that can provide reliable and fair services in differentiated wireless internet service networks. As such, the proposed scheduling algorithm solves the HOL blocking problem within a class packet queue that occurs in a wireless network, supports differentiated services for each class defined in a differentiated service network, and facilitates gradual and efficient service compensation not only among classes but also among flows within a class, thereby preventing a monopoly by one class or one flow. Simulations confirmed that the proposed WDSPS scheduling algorithm could provide the required QoS differentiation between classes and enhanced the service throughput under various wireless network conditions.

Erratum: Minimum-Energy Broadcast in Static Ad Hoc Wireless Networks

(S(α + β − θ) + S(θ)) − (S(α) + S(β)) = (S(α + β) − S(α) − S(β)) − (S(α + β) − S(α + β − θ) − S(θ ))

Capacity bounds for ad hoc and hybrid wireless networks

We study the capacity of static wireless networks, both ad hoc and hybrid, under the Protocol and Physical Models of communication, proposed in [1]. For ad hoc networks with &lt;i&gt;n&lt;/i&gt; nodes, we show that under the Physical Model, where signal power is assumed to attenuate as 1/r&lt;sup&gt;α&lt;/sup&gt;, α &gt; 2, the transport capacity scales as Θ(√&lt;i&gt;n&lt;/i&gt;) bit-meters/sec. The same bound holds even when the nodes are allowed to approach arbitrarily close to each other and even under a more generalized notion of the Physical Model wherein the data rate is Shannon's logarithmic function of the SINR at the receiver. This result is sharp since it closes the gap that existed between the previous best known upper bound of O(&lt;i&gt;n&lt;/i&gt;&lt;sup&gt;α-1/α&lt;/sup&gt;) and lower bound of Ω(√n). We also show that any spatio-temporal scheduling of transmissions and their ranges that is feasible under the Protocol Model can also be realized under the Physical Model by an appropriate choice of power levels for appropriate thresholds. This allows the generalization of various lower bound constructions from the Protocol Model to the Physical Model. In particular, this provides a better lower bound on the best case transport capacity than in [1]. For hybrid networks, we consider an overlay of μ&lt;i&gt;n&lt;/i&gt; randomly placed wired base stations. It has previously been shown in [6] that if all nodes adopt a common power level, then each node can be provided a throughput of at most Θ(1/log &lt;i&gt;n&lt;/i&gt;) to randomly chosen destinations. Here we show that by allowing nodes to perform power control and properly choosing ν(1/log &lt;i&gt;n&lt;/i&gt;), it is further possible to provide a throughput of Θ(1) to any fraction &lt;i&gt;f&lt;/i&gt;, 0 &lt; &lt;i&gt;f&lt;/i&gt; &lt; 1, of nodes. This result holds under both the Protocol and Physical models of communication. On the one hand, it shows that that the aggregate throughput capacity, measured as the sum of individual throughputs, can scale linearly in the number of nodes. On the other hand, the result underscores the importance of choosing minimum power levels for communication and suggests that simply communicating with the closest node or base station could yield good capacity even for multihop hybrid wireless networks.

Trace-based mobile network emulation

Subjecting a mobile computing system to wireless network conditions that are realistic yet reproducible is a challenging problem. In this paper, we describe a technique called trace modulation that re-creates the observed end-to-end characteristics of a real wireless network in a controlled and repeatable manner. Trace modulation is transparent to applications and accounts for all network traffic sent or received by the system under test. We present results that show that it is indeed capable of reproducing wireless network performance faithfully.