For improved spectrum utilization, the key technique for acquiring spectrum situational awareness (SSA) -- spectrum sensing -- is greatly improved by cooperation among the active spectrum users, as network size increases. However, the many cooperative spectrum sensing (CSS) schemes that have been proposed are based on the assumptions of accurate noise power estimates, characterizable variation in noise level and absence of false or malicious users. As part of a series of SSA research projects, in this research work, we propose a novel scheme for minimizing the effects of noise power estimation error (NPEE) and received signal power falsification (RSPF) by energy-based reliability evaluation. The scheme adopts the Voting rule for fusing multiple spectrum sensing data. Based on simulation results, the proposed scheme yields significant improvement, 68.2 - 88.8%, over the conventional CSS schemes, when compared on the basis of the schemes' stability to uncertainties in noise and signal power.

We consider the problem of secure detection in wireless sensor networks operating over insecure links. It is assumed that an eavesdropping fusion center (EFC) attempts to intercept the transmissions of the sensors and to detect the state of nature. The sensor nodes quantize their observations using a multilevel quantizer. Before transmission to the ally fusion center (AFC), the senor nodes encrypt their data using a probabilistic encryption scheme, which randomly maps the sensor's data to another quantizer output level using a stochastic cipher matrix (key). The communication between the sensors and each fusion center is assumed to be over a parallel access channel with identical and independent branches, and with each branch being a discrete memoryless channel. We employ J-divergence as the performance criterion for both the AFC and EFC. The optimal solution for the cipher matrices is obtained in order to maximize J-divergence for AFC, whereas ensuring that it is zero for the EFC. With the proposed method, as long as the EFC is not aware of the specific cipher matrix employed by each sensor, its detection performance will be very poor. The cost of this method is a small degradation in the detection performance of the AFC. The proposed scheme has no communication overhead and minimal processing requirements making it suitable for sensors with limited resources. Numerical results showing the detection performance of the AFC and EFC verify the efficacy of the proposed method.

Homogeneous wireless sensor networks (HWSNs) are a class of WSNs in which nodes have identical hardware configurations. A HWSN inherits the same constraints from WSNs such as limited processing capacity and resources. However, the unique characteristic of HWSNs gets more attention for recent security applications. The environment of these applications mandates lightweight security provisions, especially a key management protocol that endures security threats such as node capture attack. On the other hand, the limited computation and communication capabilities of sensor nodes make it hard to deal with such security threats. Thus, in this paper, we introduce a novel clustering paradigm to be used in a key pre-distribution key management scheme designed for HWSNs. Then, we develop a cluster-based key pre-distribution based on this paradigm. Our developed scheme improves the security dramatically by partitioning sensor nodes to the disjointed clusters and letting clusters to be inter-connected via randomly selected nodes as consular nodes from all the clusters to form a universal cluster. As opposed to the adopted schemes, we provide a comprehensive analysis for both sensor node connectivity, and resiliency against node capture attack, and also computational results are presented.

The Optimized Link State Routing (OLSR) protocol has received considerable attention as a viable routing solution for mobile ad hoc networks. However, OLSR suffers from high routing and computational overhead, resulting in significant energy consumption and is quite detrimental to the lifetime and service duration of mobile ad hoc networks. In this work, we provide a detailed analysis of the OLSR protocol and show that its route calculation (RC) algorithm is responsible for the majority of the overhead as it redundantly re-computes the entire routing table after each routing change. We further evaluate the performance of the classic RC algorithm as a function of network size, node mobility, and network density and determine that the RC algorithm is overwhelmingly triggered by very localized topology changes. Interestingly, our analysis shows that after a local topology change, the majority of the recomputed routing tables remain unchanged from their original state. Based on this analysis we identify two distinct types of routing table re-calculations that are not necessary: local changes and vain changes. Hence, we proposed novel algorithms to optimize route table calculation in the case of these two changes. The proposed ARC algorithms work cooperatively to reduce overall runtime (and therefore energy consumption) by utilizing spatial locality to provide incremental updates to the routing tables (as opposed to re-computing the entire table upon each route change). Extensive experiments verify that the proposed method is scalable with respect to both network size and node density and reduces overall RC runtime by 80% - 90% for practical scenarios. Moreover, the proposed RC algorithms are fully-compatible with existing OLSR implementations.

Opportunistic Spectrum Access (OSA) in distributed cognitive radio networks (CRNs) has been well studied in the literature from a theoretical perspective. However, such theoretically-optimized distributed OSA approaches are challenged by several practical implementation issues. In this paper, we design a custom cross-layer framework that enables the: (i) clean-slate implementation of a wide variety of OSA mechanisms; (ii) experimental evaluation of the individual practical OSA components of the Rate-Adaptive Probabilistic (RAP) framework; and (iii) detailed comparison of the performance of such a practical OSA approach against theoretical OSA approaches developed for fully-capable CRNs. Our evaluation reveals the multi-fold goodput improvement and remarkable fairness characteristics of the practical RAP OSA approach compared to the OSA approaches that overlook the OSA and CR practical limitations. However, the superior performance of practical OSA comes at the expense of more outages to the primary licensed networks but within the permissible bounds. Another key finding is that the wide family of existing theoretically-optimized OSA protocols can benefit from the gains available to the individual components of the practical RAP approach, namely, the random spectrum sensing and the probabilistic non-greedy access.

Opportunistic Spectrum Access (OSA) is foreseen as the future of wireless communications. However, today's cognitive radio technologies lag far behind the OSA goals and do not allow for the applicability of exiting theoretical distributed OSA techniques. In this paper, we experimentally demonstrate the ability of realizing OSA despite the practical limitations of existing transceiver technologies. We use the general purpose Wireless open-Access Research Platform (WARP) to instrument the implementation of fundamental OSA functionalities. Then we implement a suite of OSA schemes using this implementation framework. Our experiments show that suboptimal but practical OSA approaches such as random spectrum sensing and non-greedy access achieve superior performance given cognitive radios with limited capabilities compared to OSA approaches that are optimized for fully-capable cognitive radio networks (e.g., with wide-band sensing capability and adopt winner-takes-all access relying on network-wide coordination mechanisms).

Existing distributed opportunistic spectrum management schemes do not consider the inability of today's cognitive transceivers to measure interference at primary receivers. Consequently, optimizing the constrained cognitive radio network performance based only on local interference measurements at cognitive senders does not lead to truly optimal performance due to hidden and exposed primary senders. In this paper, we present the rate-adaptive probabilistic medium access protocol (RAP-MAC) for opportunistic spectrum management. In contrast to existing techniques, our approach addresses the unavoidable inaccuracy in spectrum sensing via a probabilistic spectrum access strategy. Furthermore, RAP-MAC allows multiple cognitive flows to fairly share the available bandwidth without explicit coordination by adopting a non-greedy transmission approach that prevents a single cognitive transmitter from monopolizing an available spectral opportunity. We analytically formulate the cognitive user performance optimization problem as a mixed integer non-linear programming to derive the optimal parameter values. Packet-level simulations show that RAP-MAC achieves between 65% to 119.5% higher goodput with significantly better fairness characteristics compared to existing greedy approaches that overlook the spectrum sensing limitations.

This paper describes the deployment and evaluation of a 700MHz WiFi-based Wireless Mesh Network (WMN) testbed. To our knowledge, this is the world's first WiFi-based testbed using the recently-released 700MHz frequency band and deployed under both indoor and outdoor environments, including open space and a Louisiana swamp with dense cypress trees. Initial experimental results show that the 700MHz WMN has a significantly larger transmission range and better penetration ability compared to a traditional 2.4GHz WMN, which indicates that utilizing the 700MHz frequency band will considerably enhance the performance of WMNs, including the ability to support real-time applications.

Multi-radio multi-channel Wireless Mesh Networks (WMNs) are being increasingly deployed for broadband provision in enterprise, community, metropolitan and rural areas, due to their lower cost and faster deployment compared to the traditional wired broadband networks. In comparison with the former single-radio WMNs, multi-radio multi-channel WMNs can provide higher capacity and more fine-grained interference management. In this paper, we compare the performance of Wireless Mesh Networks with four different backhaul configurations (with different number of radios, different antenna types and different number of parallel backhauls, etc.) for the deployments in the residential areas. Simulation results show that the interference among client access cells makes the access channel the bottleneck of the end-to-end performance no matter what backhaul configuration is used, and tuning the transmission power of the access channel radio can improve the end-to-end performance substantially. We also find that the multi-radio backhaul WMNs do not have the serious performance unfairness among clients with different hop counts from the gateways as the single-radio backhaul WMNs have.

The standard way to handle frequent transmission errors over wireless links is to use a link-layer automatic retransmission mechanisms. However, multiple retransmissions per link along an n-hop path leads to significant channel usage inefficiency and poor end-to-end performance. We propose a novel cooperative diversity based multi-copy relaying (CDMR) scheme for wireless mesh networks. CDMR improves system performance by effectively utilizing available network resources, allowing neighboring (helper) nodes along a selected route to cooperatively deliver (as opposed to using retranmissions) packets to the final destination. CDMR operates in two phases: helper establishment and cooperatively delivery. The fundamental challenges are to identify effective helpers and to synchronize helper transmissions in order to avoid collisions. CDMR provides a simple and effective solution with low overhead. Simulation results show that (even with just one helper node), CDMR is able to reduce retransmissions and improve end-to-end delay by 39% to 86% depending on the path length.

Host resources (e.g., CPU time and buffer space) in mobile ad hoc networks must be shared between the devices own applications and networking functions, such as routing and packet forwarding on behalf of remote nodes. Previous work has ignored the performance conflicts that arise due to the need to share host resources. In this work, using both analytical and statistical-based empirical analysis, we investigate the conflicting roles that the host must serve and provide the first detailed study on the impact that host capacity has on the performance of ad hoc networks. The results of this study demonstrate that host capacity has a significant impact on network performance (e.g., throughput drops by up to 74.5% depending upon available host capacities, as shown in our case study) and thus should be considered in the protocol and system design process.

The scalability of routing protocols for ad hoc networks is a key design issue for achieving large-scale deployments of MANETs. In this work, we propose S-Box, a ldquoblack-boxrdquo type scalability analysis framework. S-Box combines statistical design of experiments (DOE) methods, empirical modeling techniques, and a newly proposed performance measure, called the scalability index. The proposed scalability index is able to quantify the overall scalability performance of ad hoc routing protocols by aggregating the values of multiple individual metrics into a single scalar value. Given a specific deployment scenario, S-Box can be used to (1) determine the routing protocol that achieves the best overall scalability among a set of candidate protocols and (2) determine how to adjust parameter values (e.g., number of RREQ retries) of a routing protocol to achieve optimal scalability performance. To demonstrate its systematic operation and effectiveness, we use S-Box to study the scalability of DSR and AODV (with and without local repair), which shows S-Box can provide a convenient and systematic way to address practical scalability problems.

The poor performance of TCP in wireless networks is further diminished in IEEE 802.11-based ad hoc networks networks due to the unnecessary actions of on-demand routing protocols when interference-induced packet drops happen at the medium access control (MAC) layer. In this paper, we present a cross-layer hop-by-hop congestion control scheme designed to improve TCP performance in multihop wireless networks. The proposed scheme, which we will refer to as CHCC, attempts to determine the actual cause of a MAC-layer packet loss and then coordinates the congestion-control response among the MAC, network, and transport protocols. The congestion control efforts are invoked at all intermediate and source nodes along the upstream paths directed from the wireless link experiencing the congestion-induced packet drop. Simulation results show that the proposed scheme achieves up to 70% higher throughput than TCP-Reno. The CHCC approach is interoperable with standard TCP and can be used transparently when using transport protocols (e.g., UDP) that do not implement congestion control.

Wireless Mesh Networks (WMNs) are comprised of mesh routers whose relatively small transmission range may result infrequent handoffs, leading to high packet delays and loss rates and limiting the performance of real-time applications over WMNs. In this work, we propose BASH - a backhaul-aided seamless handoff scheme. Our scheme takes advantage of the wireless backhaul feature of WMNs and allows a mobile station to probe the neighboring mesh routers by accessing the backhaul channel. After the probe request, the mobile station is able to switch back to its primary communication channel and resume its ongoing communication without waiting for the probe responses. The currently associated mesh router of the mobile station collects the probe responses and selects the new mesh route on behalf of the mobile station. Our works show 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 8.7ms, which supports the real-time applications during the handoff.

This work is concerned with defining aperformanceindexthat can be used as an objective measure in the evaluation and comparison of ad hoc networking protocols. Specifically, we introduce a performance index that aggregates performance results from multiple response metrics into a single scalar value that quantifies overall system performance, leading to more objective evaluations and comparisons. Using a statistical-based experimental design and analysis strategy, we illustrate the advantages of the proposed performance index by comparing two ad hoc networking systems over a wide range of networking scenarios. Based on the results of this analysis, we develop an empirical model that characterizes the relationship between the proposed performance index, four response metrics (packet delivery ratio, end-to-end delay, routing overhead, and jitter) and four influential factors (node mobility, offered load, network size, and routing protocol).

In this paper, we propose a novel medium access control protocol with a separate control channel (MAC-SCC) to increase the channel efficiency and address the unfairness and instability problems of IEEE 802.11 MAC protocol. In MAC-SCC, the available bandwidth is partitioned into two channels: a data channel and a control channel, each associated with a network allocation vector (NAV). To reduce hardware complexity, the station transmits or receives on one channel only at any given time. In the network employing MAC-SCC, the next data frame can be pre-scheduled during the current data transmission via the separate control channel, and thus reducing the frame collision probability and the bandwidth wasted during backoff. Moreover the use of the separate control channel helps to achieve fair medium access and solve the instability problem resulted from frequent link failures. The optimal bandwidth partitioning between the two channels is analyzed via a statistical model, which shows 10% bandwidth for the control channel and 90% bandwidth for the data channel. The performance of MAC-SCC is quantified via extensive simulations in both a stand-alone simulator developed by using PARSEC and a comprehensive network simulator called QualNet with whole protocol stack. Our results show that MAC-SCC can effectively reduce the link failure probability, achieve fair medium access when running multiple TCP sessions, and yield a throughput gain up to 60% under high traffic load

The performance of mobile ad hoc networks can be influenced by numerous factors, including protocol design at every layer; parameter settings such as retransmission limits and timers; system factors such as network size and traffic load; as well as environmental factors such as channel fading. In this work, we are concerned with understanding the functional relationship between these influential factors and performance of mobile ad hoc networking systems. We show how a systematic statistical design of experiments (DOE) strategy can be used to analyze network system and protocol performance, leading to more objective conclusions valid over a wide range of network conditions and environments. Using a DOE strategy and a 2 k factorial design, we quantify the main and interactive effects of five factors (i.e., network density, node mobility, traffic load, network size, and medium access control scheme) on two response metrics (i.e., packet delivery ratio and end-to-end delay). Using these effects measures, we then develop two first-order linear regression models that define the functional relationship between the influential factors and two performance metrics. Categories and Subject Descriptors C.4 [Performance of Systems]: modeling techniques, performance attributes; G.3 [Probability and Statistics]: Experimental design, Correlation and regression analysis; I.6.6 [Simulation and Modeling]: Simulation output analysis

In this paper, we introduce QMR/PR, a flexible QoS-sensitive routing framework for mobile ad hoc networks, which addresses the problems caused by mobility-induced route failures. QMR/PR combines packet-interleaving using multipath routing and packet-level forward error correction. A particularly promising feature is its ability to significantly reduce both random and correlated packet losses, a critical issue for real-time applications. To provide accurate and reliable performance evaluation results, we have integrated QMR/PR into the QualNet simulation software, allowing us to conduct an extensive performance evaluation in a realistic networking architecture including all layers of the protocol stack. Simulation results demonstrate the effectiveness of the proposed framework and show that, compared to single-path routing, QMR/PR can reduce packet loss by 42-84 percent depending on the networking environment (e.g, node mobility, frequency of path failures), while simultaneously reducing routing overhead.

In this paper, we present a localization system comprising two simple and efficient localization algorithms for sensor networks. We refer to the proposed localization system as the differential ad-hoc positioning system (DAPS). Differential GPS motivated the underlying idea on which the proposed localization system is based. Specifically, the algorithms use a differential error correction scheme that is designed to reduce the cumulative distance and positioning error accumulated over the multiple hops. Using simulation, we investigate DAPS and compare the proposed algorithms with non-differential based schemes. The key contribution of this work is the illustration of how differential error corrections can be calculated and incorporated into the localization process to effectively reduce the range measurement errors and, as such, significantly improve positioning accuracy.

Mobile ad hoc networks (MANETs) are an emerging class of network architectures that are characterized by their highly dynamic topology, limited resources (i.e., bandwidth and power), and lack of fixed infrastructure. The primary motivation for such networks is increased flexibility and mobility. Random node mobility along with various other factors such as network size and traffic intensity may be very dynamic, resulting in unpredictable variations in the overall network performance. This study centers on investigating and quantifying the effects of various factors and their two-way interactions on the overall performance of ad hoc networks. This study contributes to the modeling and development of adaptive ad hoc protocols (routing, medium access control, scheduling and buffer management). Using 2/sup k/r factorial experimental design, we isolate and quantify the effects of five factors: node speed, pause-time, network size, number of traffic sources, and type of routing (source versus distributed), that affect the performance of ad hoc networks. Specifically, this paper evaluates the impact of these factors on the following performance metrics: throughput, average routing overhead, and power consumption. Our study was conducted using a library-based simulator for sequential and parallel simulation of wireless networks.

Abstract The general field of mobile ad hoc networking is still in its infancy. Particularly, the challenge of providing Quality‐of‐Service (QoS) support for ad hoc networks is an open problem and remains relatively uncharted territory. Providing a complete QoS solution for the ad hoc networking environment requires the interaction and cooperation of several components. These components include: (1) a QoS routing protocol, (2) a resource reservation scheme and (3) a QoS capable medium access control (MAC) layer. In this paper, we present a survey of the current research that has addressed each of these components in the context of ad hoc networks. This work is intended to provide a broad and comprehensive view of the various components and protocols required to provide QoS support in computer networks, focusing primarily on ad hoc networks. First, we introduce the unique characteristics of mobile ad hoc networks, which distinguishing this new network architecture from traditional infrastructured wired and wireless networks (i.e. cellular‐based networks). We also discuss the impact of these characteristics on QoS provisioning. Next, we describe the first QoS model proposed for mobile ad hoc networks and its relationship to QoS models proposed for the Internet. We then present a review of the proposed algorithms for each QoS component (e.g. QoS routing, resource reservation and the MAC layer). Copyright © 2002 John Wiley & Sons, Ltd.