Performance Comparison of Routing Protocols for Cognitive Radio Networks

Cognitive radio networks (CRNs) have emerged as a promising solution to the ever-growing demand for additional spectrum resources and more efficient spectrum utilization. A large number of routing protocols for CRNs have been proposed recently, each based on different design goals, and evaluated in different scenarios, under different assumptions. However, little is known about the relative performance of all these protocols, let alone the tradeoffs among their different design goals. In this paper, we conduct the first detailed, empirical performance comparison of three representative routing protocols for CRNs, under the same realistic set of assumptions. Our extensive simulation study shows that the performance of routing protocols in CRNs is affected by a number of factors, in addition to PU activity, some of which have been largely ignored by the majority of previous works. We find that different protocols perform well under different scenarios, and investigate the causes of the observed performance. Furthermore, we present a generic software architecture for the experimental evaluation of CRN routing protocols on a testbed based on the USRP2 platform, and compare the performance of two protocols on a 6 node testbed. The testbed results confirm the findings of our simulation study.

Related papers:

title: Routing in cognitive radio networks: Challenges and solutions
abstract: Cognitive radio networks (CRNs) are composed of cognitive, spectrum-agile devices capable of changing their configurations on the fly based on the spectral environment. This capability opens up the possibility of designing flexible and dynamic spectrum access strategies with the purpose of opportunistically reusing portions of the spectrum temporarily vacated by licensed primary users. On the other hand, the flexibility in the spectrum access phase comes with an increased complexity in the design of communication protocols at different layers. This work focuses on the problem of designing effective routing solutions for multi-hop CRNs, which is a focal issue to fully unleash the potentials of the cognitive networking paradigm. We provide an extensive overview of the research in the field of routing for CRNs, clearly differentiating two main categories: approaches based on a full spectrum knowledge, and approaches that consider only local spectrum knowledge obtained via distributed procedures and protocols. In each category we describe and comment on proposed design methodologies, routing metrics and practical implementation issues. Finally, possible future research directions are also proposed.

title: Optimal spectrum sensing framework for cognitive radio networks
abstract: Spectrum sensing is the key enabling technology for cognitive radio networks. The main objective of spectrum sensing is to provide more spectrum access opportunities to cognitive radio users without interfering with the operations of the licensed network. Hence, recent research has been focused on the interference avoidance problem. Moreover, current radio frequency (RF) front-ends cannot perform sensing and transmission at the same time, which inevitably decreases their transmission opportunities, leading to the so-called sensing efficiency problem. In this paper, in order to solve both the interference avoidance and the spectrum efficiency problem, an optimal spectrum sensing framework is developed. More specifically, first a theoretical framework is developed to optimize the sensing parameters in such a way as to maximize the sensing efficiency subject to interference avoidance constraints. Second, in order to exploit multiple spectrum bands, spectrum selection and scheduling methods are proposed where the best spectrum bands for sensing are selected to maximize the sensing capacity. Finally, an adaptive and cooperative spectrum sensing method is proposed where the sensing parameters are optimized adaptively to the number of cooperating users. Simulation results show that the proposed sensing framework can achieve maximum sensing efficiency and opportunities in multi-user/multi-spectrum environments, satisfying interference constraints.

title: Robust Transmit Power Control for Cognitive Radio
abstract: A cognitive radio network is a multiuser system, in which different users compete for limited resources in an opportunistic manner, interacting with each other for access to the available resources. The fact that both users and spectrum holes (i.e., unused spectrum subbands) can come and go makes a cognitive radio network a highly dynamic and challenging wireless environment. Therefore, finding robust resource-allocation algorithms, which are capable of achieving reasonably good solutions fast enough in order to guarantee an acceptable level of performance under worst case interference conditions, is crucial in such environment. The focus of this paper is the transmit-power control in cognitive radio networks, considering a noncooperative framework. Moreover, tools from control theory are used to study both the equilibrium and transient behaviors of the network under dynamically varying conditions.

title: C-MAC: A Cognitive MAC Protocol for Multi-Channel Wireless Networks
abstract: A number of algorithmic and protocol assumptions taken for granted in the design of existing wireless communication technologies need to be revisited in extending their scope to the new cognitive radio (CR) paradigm. The fact that channel availability can rapidly change over time and the need for coordinated quiet periods in order to quickly and robustly detect the presence of incumbents, are just some of the examples of the unique challenges in protocol and algorithm design for CR networks and, in particular, in the medium access control (MAC) layer. With this in mind, in this paper we introduce a novel cognitive MAC (C-MAC) protocol for distributed multi-channel wireless networks. C-MAC operates over multiple channels, and hence is able to effectively deal with, among other things, the dynamics of resource availability due to primary users and mitigate the effects of distributed quiet periods utilized for primary user signal detection. In C-MAC, each channel is logically divided into recurring superframes which, in turn, include a slotted beaconing period (BP) where nodes exchange information and negotiate channel usage. Each node transmits a beacon in a designated beacon slot during the BP, which helps in dealing with hidden nodes, medium reservations, and mobility. For coordination amongst nodes in different channels, a rendezvous channel (RC) is employed that is decided dynamically and in a totally distributed fashion. Among other things, the RC is used to support network-wide multicast and broadcast which are often neglected in existing multi-channel MAC protocols. We present promising performance results of C- MAC. We also describe our efforts to implement features of C- MAC in a real CR prototype with Atheros chipset, which currently includes the spectrum sensing module and preliminary features of C-MAC.

title: HC-MAC: A Hardware-Constrained Cognitive MAC for Efficient Spectrum Management
abstract: Radio spectrum resource is of fundamental importance for wireless communication. Recent reports show that most available spectrum has been allocated. While some of the spectrum bands (e.g., unlicensed band, GSM band) have seen increasingly crowded usage, most of the other spectrum resources are underutilized. This drives the emergence of open spectrum and dynamic spectrum access concepts, which allow unlicensed users equipped with cognitive radios to opportunistically access the spectrum not used by primary users. Cognitive radio has many advanced features, such as agilely sensing the existence of primary users and utilizing multiple spectrum bands simultaneously. However, in practice such capabilities are constrained by hardware cost. In this paper, we discuss how to conduct efficient spectrum management in ad hoc cognitive radio networks while taking the hardware constraints (e.g., single radio, partial spectrum sensing and spectrum aggregation limit) into consideration. A hardware-constrained cognitive MAC, HC-MAC, is proposed to conduct efficient spectrum sensing and spectrum access decision. We identify the issue of optimal spectrum sensing decision for a single secondary transmission pair, and formulate it as an optimal stopping problem. A decentralized MAC protocol is then proposed for the ad hoc cognitive radio networks. Simulation results are presented to demonstrate the effectiveness of our proposed protocol.

title: Routing and QoS provisioning in cognitive radio networks
abstract: Cognitive radio (CR) is a new paradigm that enable nodes to exploit unoccupied frequency spectrum for communications. Cognitive radio based wireless mesh networks (CRNs) have been proposed to enable wireless mesh networks to communicate via dynamic channels. Many existing literature consider routing in static CRNs with relatively stable communication channel where the duration of the availability of the communication channel is much longer than the communication time. However, there is very limited work looking into routing related issues in dynamic CRNs where the average available duration of the communication channel can be much shorter than the communication time. To address this, we propose a cross-layer cognitive routing protocol, the Opportunistic Service Differentiation Routing Protocol (OSDRP) for the dynamic CRNs. OSDRP discovers the minimum delay - maximum stability route in dynamic CRNs by considering the availability of spectrum opportunity in addition to switching delay and queuing delay across primary user networks. In addition, service differentiation can be achieved through a combination of transmit power control and opportunistic routing. Simulation results demonstrate that the OSDRP achieves much better performance in terms of lower delay and higher throughput compared to other existing routing protocols across various scenarios.

title: White space networking with wi-fi like connectivity
abstract: Networking over UHF white spaces is fundamentally different from conventional Wi-Fi along three axes: spatial variation, temporal variation, and fragmentation of the UHF spectrum. Each of these differences gives rise to new challenges for implementing a wireless network in this band. We present the design and implementation of Net7, the first Wi-Fi like system constructed on top of UHF white spaces. Net7 incorporates a new adaptive spectrum assignment algorithm to handle spectrum variation and fragmentation, and proposes a low overhead protocol to handle temporal variation. builds on a simple technique, called SIFT, that reduces the time to detect transmissions in variable channel width systems by analyzing raw signals in the time domain. We provide an extensive evaluation of the system in terms of a prototype implementation and detailed experimental and simulation results.

title: Multihop cognitive radio networks: to route or not to route
abstract: Routing is a fundamental issue to consider when dealing with multihop cognitive radio networks. We investigate in this work, the potential routing approaches that can be employed in such adaptive wireless networks. We argue that in multihop cognitive radio environments no general routing solution can be proposed, but cognitive environments can be classified into three separate categories, each requiring specific routing solutions. Basically, this classification is imposed by the activity of the users on the licensed bands that cognitive radios try to access. First, over a relatively static primary band, where primary nodes idleness largely exceeds cognitive users communication durations, static mesh routing solutions can be reused, whereas second, over dynamically available spectrum bands new specific routing solutions have to be proposed, we give some guidelines and insights about designing such solutions. Third, if cognitive radios try to access over highly active and rarely available primary bands, opportunistic forwarding without preestablished routing is to be explored.

title: Routing Metrics of Cognitive Radio Networks: A Survey
abstract: The majority of work in cognitive radio networks have focused on single-hop networks with mainly challenges at the physical and MAC layers. Recently, multi-hop secondary networks have gained attention as a promising design to leverage the full potential of cognitive radio networks. One of the main features of routing protocols in multi-hop networks is the routing metric used to select the best route for forwarding packets. In this paper, we survey the state-of-the-art routing metrics for cognitive radio networks. We start by listing the challenges that have to be addressed in designing a good routing metric for cognitive radio networks. We then provide a taxonomy of the different metrics and a survey of the way they have been used in different routing protocols. Then we present a case study to compare different classes of metrics. After that, we discuss how to combine individual routing metrics to obtain a global one. We end the paper with a discussion of the open issues in the design of future metrics for cognitive radio networks.

title: SAMER: Spectrum Aware Mesh Routing in Cognitive Radio Networks
abstract: Cognitive radio technology holds great promises in enabling unlicensed operation in licensed bands, to meet the increasing demand for radio spectrum. The new open spectrum operation necessitates novel routing protocols to exploit the available spectrum opportunistically. In this paper we present SAMER, a routing solution for cognitive radio mesh networks. SAMER opportunistically routes traffic across paths with higher spectrum availability and quality via a new routing metric. It balances between long-term route stability and short-term opportunistic performance. SAMER builds a runtime forwarding mesh that is updated periodically and offers a set of candidate routes to the destination. The actual forwarding path opportunistically adapts to the dynamic spectrum conditions and exploits the link with the highest spectrum availability at the time. We evaluate SAMER through simulations, and show that it effectively exploits the available network spectrum and results in higher end-to-end performance.

title: Local Coordination Based Routing and Spectrum Assignment in Multi-hop Cognitive Radio Networks
abstract: Although Cognitive Radio technology brings efficient spectrum usage and effective interference avoidance, it also brings new challenges to routing in multi-hop Cognitive Radio Networks. Firstly, spectrum assignment is required for each hop in routing; secondly, new delay is introduced during multi-frequency scheduling and frequency switching in each node; thirdly, the intersecting nodes serving multi-frequency traffic is easy to be bottleneck in neighborhood region. In this paper, we analysis and model the per-node delay and the path delay in multi-hop Cognitive Radio Network. Then we propose a framework of local coordination based routing and spectrum assignment to solve above problems, which consists of one protocol for routing path and one scheme for neighborhood region. A on-demand Routing and Spectrum Assignment Protocol is proposed to exchange the local spectrum information and interact with multi-frequency scheduling in each node. A local coordination scheme is presented to support flow redirection at an intersecting node and distribute heavy multi-frequency workload to its neighborhood. We prove the correctness and effectiveness of the protocol by thorough simulations, and find that the proposed solution provides good adaptability to varying spectrum distribution. The end-to-end delay when adaptive relay is cooperating with routing protocol outperforms traditional bare-routing solutions.

title: Coolest Path: Spectrum Mobility Aware Routing Metrics in Cognitive Ad Hoc Networks
abstract: Cognitive Radio (CR) emerges as a promising solution to current unbalanced spectrum utilization. The cognitive ad hoc network can take advantage of dynamic spectrum access and spectrum diversity over wide spectrum. It could achieve higher network capacity compared to traditional ad hoc networks, thus supporting bandwidth-demanding applications. A cognitive radio operates over wide spectrum with unpredictable channel availability. Moreover, the transmission opportunity of a cognitive node is not guaranteed due to the presence of primary users (PUs). These two unique features define new routing problems in cognitive ad hoc networks. To better characterize the unique features of cognitive radio networks, we propose new routing metrics, including accumulated spectrum temperature, highest spectrum temperature, and mixed spectrum temperature to account for the time-varying spectrum availability. The proposed metrics favor the "coolest'' path, or the path with the most balanced and/or the lowest spectrum utilization by the primary users. We also study the computational complexity of the routing algorithm in cognitive ad hoc networks. Experiment results on our USRP-2 testbed show that the proposed metrics are capable of capturing the fluctuation of spectrum availability and suitable for cognitive ad hoc networks.

title: CRP: A Routing Protocol for Cognitive Radio Ad Hoc Networks
abstract: Cognitive radio (CR) technology enables the opportunistic use of the vacant licensed frequency bands, thereby improving the spectrum utilization. However, the CR operation must not interfere with the transmissions of the licensed or primary users (PUs), and this is generally achieved by incurring a trade-off in the CR network performance. In order to evaluate this trade-off, a distributed CR routing protocol for ad hoc networks (CRP) is proposed that makes the following contributions: (i) explicit protection for PU receivers that are generally not detected during spectrum sensing, (ii) allowing multiple classes of routes based on service differentiation in CR networks, and (iii) scalable, joint route-spectrum selection. A key novelty of CRP is the mapping of spectrum selection metrics, and local PU interference observations to a packet forwarding delay over the control channel. This allows the route formation undertaken over a control channel to capture the environmental and spectrum information for all the intermediate nodes, thereby reducing the computational overhead at the destination. Results reveal the importance of formulating the routing problem from the viewpoint of safeguarding the PU communication, which is a unique feature in CR networks.

title: A novel layered graph model for topology formation and routing in dynamic spectrum access networks
abstract: This paper studies a fundamental problem in dynamic spectrum access (DSA) networks: given a set of detected spectrum bands that can be temporarily used by each node in a DSA network, how to form a topology by selecting spectrum bands for each radio interface of each node, called topology formation in this paper. We propose a novel layered graph to model the temporarily available spectrum bands, called spectrum opportunities (SOPs) in this paper, and use this layered graph model to develop effective and efficient routing and interface assignment algorithms to form near-optimal topologies for DSA networks. We have evaluated the performance of our layered graph approach and compared it to a sequential interface assignment algorithm. The numerical results show that the layered graph approach significantly outperforms the sequential interface assignment

title: Route and spectrum selection in dynamic spectrum networks
abstract: Efficient spectrum allocation in dynamic spectrum systems is a challenging problem, particularly for multi-hops transmissions. The inter-dependence between route selection and spectrum management makes it important to examine interaction between the two and the corresponding performance and com- plexity tradeoffs. In this paper, we explore two design method- ologies: a decoupled design where these tasks are carried out independently by different protocol layers, and a collaborative design that integrates them into a single task. Experimental results show that the collaborative design, if well-provisioned, offers significant performance improvement compared to the decoupled design.

title: High Throughput Spectrum-aware Routing for Cognitive Radio Networks
abstract: Dynamic spectrum networks enable fast deployment of new wireless technologies by effectively utilizing allo cated yet unused wireless spectrum. By sensing and utilizing availab le wireless channels, cognitive radio devices can provide high thr oughput, low latency communication. Existing schemes for chann el assignment suffer drawbacks in throughput and reachability in the presence of location-dependent channel availability. We p ropose SPEctrum-Aware Routing Protocol (SPEAR), a robust and efficient distributed channel assignment and routing protocol for dynamic spectrum networks based on two principles: integrated spec trum and route discovery for robust multi-hop path formation, and distributed path reservations to minimize interand intra-flow interference. Through simulations and testbed measuremen ts, we show that SPEAR establishes robust paths in diverse spectru m conditions and provides near-optimal throughput and end-t o-end packet delivery latency. SPEAR performs extremely fast flow setup and teardowns, and can maintain interference-free flo ws in the presence of variance in channel availability.

title: Reactive routing for mobile cognitive radio ad hoc networks
abstract: Although more than a decade has passed from the proposal of the Cognitive Radio paradigm, in these years the research has mainly focused on physical and medium access issues, and few recent works focused on the problem of routing in cognitive networks. This paper addresses such a problem by evaluating the feasibility of reactive routing for mobile cognitive radio ad hoc networks. More specifically, we design a reactive routing protocol for the considered scenario able to achieve three goals: (i) to avoid interferences to primary users during both route formation and data forwarding; (ii) to perform a joint path and channel selection at each forwarder; (iii) to take advantage of the availability of multiple channels to improve the overall performance. Two different versions of the same protocol, referred to as Cognitive Ad-hoc On-demand Distance Vector (CAODV), are presented. The first version exploits inter-route spectrum diversity, while the second one exploits intra-route spectrum diversity. An exhaustive performance analysis of both the versions of the proposed protocol in different environments and network conditions has been carried out via numerical simulations. The results state the suitability of the proposed protocol for small mobile cognitive radio ad hoc networks.

title: ROSA: distributed joint routing and dynamic spectrum allocation in cognitive radio ad hoc networks
abstract: Throughput maximization is one of the main challenges in cognitive radio ad hoc networks, where local spectrum resources may change from time to time and hop-by-hop. For this reason, a cross-layer opportunistic spectrum access and dynamic routing algorithm for cognitive radio networks is proposed, called ROSA (ROuting and Spectrum Allocation algorithm). Through local control actions, ROSA aims at maximizing the network throughput by performing joint routing, dynamic spectrum allocation, scheduling, and transmit power control. Specifically, the algorithm dynamically allocates spectrum resources to maximize the capacity of links without generating harmful interference to other users while guaranteeing bounded BER for the receiver. In addition, the algorithm aims at maximizing the weighted sum of differential backlogs to stabilize the system by giving priority to higher-capacity links with high differential backlog. The proposed algorithm is distributed, computationally efficient, and with bounded BER guarantees. ROSA is shown through discrete-event packet-level simulations to outperform baseline solutions leading to a high throughput, low delay, and fair bandwidth allocation.

title: SEARCH: A routing protocol for mobile cognitive radio ad-Hoc networks
abstract: Recent research in the emerging field of cognitive radio (CR) has mainly focused on spectrum sensing and sharing, that allow an opportunistic use of the vacant portions of the licensed frequency bands by the CR users. Efficiently leveraging this node channel information in order to provide timely end-to-end delivery over the network is a key concern for CR based routing protocols. In addition, the primary users (PUs) of the licensed band affect the channels to varying extents, depending on the proportion of the transmission power that gets leaked into the adjacent channels. This also effects the geographical region, in which, the channel is rendered unusable for the CR users. In this paper, a geographic forwarding based SpEctrum Aware Routing protocol for Cognitive ad-Hoc networks (SEARCH), is proposed that jointly undertakes path and channel selection to avoid regions of PU activity during route formation. Specifically, the optimal paths found by geographic forwarding on each channel are combined at the destination with an aim to minimize the hop count. By binding the route to regions found free of PU activity, rather than particular CR users, the effect of the PU activity is mitigated. Our proposed approach is thoroughly evaluated through simulation study.

title: Collaborative Strategy for Route and Spectrum Selection in Cognitive Radio Networks
abstract: This paper studies collaborative strategy for route and spectrum selection in decentralized wireless cognitive radio network. We explore the problem from two aspects: the spectrum stability and the path stability, which we use stochastic processes and probability theory to analyze. Furthermore, we also design a method that measures the interference to licensed users. Under this measurement method, path selection criteria is explored. Theoretical analysis shows our criterion considering interference is better than random selection. The numerical results are in accord with the theoretical analysis.

title: STOD-RP: A Spectrum-Tree Based On-Demand Routing Protocol for Multi-Hop Cognitive Radio Networks
abstract: A unique challenge for routing in cognitive radio networks is the collaboration between the route selection and spectrum decision. To solve this problem, in this paper a Spectrum-Tree base On-Demand routing protocol (STOD-RP) is proposed where a spectrum-tree is built in each spectrum band. The formation of the spectrum-tree addresses the cooperation between spectrum decision and route selection in an efficient way. In addition, a new route metric is proposed as well as a fast and efficient spectrum-adaptive route recovery method. Simulation results show that our proposed STOD-RP reduces the control overhead and shortens the average end-to-end delay significantly.

title: Minimum maintenance cost routing in Cognitive Radio Networks
abstract: Cognitive Radio Networks (CRNs) are composed of frequency-agile radio devices that allow licensed (primary) and unlicensed (secondary) users to coexist, where secondary users opportunistically access channels without interfering with the operation of primary ones. From the perspective of secondary users, spectrum availability is a time varying network resource over which multi-hop end-to-end connections must be maintained. In this work, a theoretical outlook on the problem of routing secondary user flows in a CRN is provided. The investigation aims to characterize optimal sequences of routes over which a secondary flow is maintained. The optimality is defined according to a novel metric that considers the maintenance cost of a route as channels and/or links must be switched due to the primary user activity. Different from the traditional notion of route stability, the proposed approach considers subsequent path selections, as well. The problem is formulated as an integer programming optimization model and shown to be of polynomial time complexity in case of full knowledge of primary user activity. Properties of the problem are also formally introduced and leveraged to design a heuristic algorithm to solve the minimum maintenance cost routing problem when information on primary user activity is not complete. Numerical results are presented to assess the optimality gap of the heuristic routing algorithm.

title: Performance comparison of two on-demand routing protocols for ad hoc networks
abstract: Ad hoc networks are characterized by multi-hop wireless connectivity, frequently changing network topology and the need for efficient dynamic routing protocols. We compare the performance of two prominent on-demand routing protocols for mobile ad hoc networks - dynamic source routing (DSR) and ad hoc on-demand distance vector routing (AODV). A detailed simulation model with MAC and physical layer models is used to study inter-layer interactions and their performance implications. We demonstrate that even though DSR and AODV share a similar on-demand behavior the differences in the protocol mechanics can lead to significant performance differentials. The performance differentials are analyzed using varying network load, mobility and network size. Based on the observations, we make recommendations about how the performance of either protocol can be improved.

title: Comparison of routing metrics for static multi-hop wireless networks
abstract: Routing protocols for wireless ad hoc networks have traditionally focused on finding paths with minimum hop count. However, such paths can include slow or lossy links, leading to poor throughput. A routing algorithm can select better paths by explicitly taking the quality of the wireless links into account. In this paper, we conduct a detailed, empirical evaluation of the performance of three link-quality metrics---ETX, per-hop RTT, and per-hop packet pair---and compare them against minimum hop count. We study these metrics using a DSR-based routing protocol running in a wireless testbed. We find that the ETX metric has the best performance when all nodes are stationary. We also find that the per-hop RTT and per-hop packet-pair metrics perform poorly due to self-interference. Interestingly, the hop-count metric outperforms all of the link-quality metrics in a scenario where the sender is mobile.

title: Platforms and testbeds for experimental evaluation of cognitive ad hoc networks
abstract: This article reviews, discusses, and classifies the existing experimental platforms and testbeds for experimental evaluation of CR ad hoc networks. The article first describes the internal organization of typical existing software defined radio platforms. Then the existing software frameworks are discussed and classified. Consequently, the challenges involved in integration of these platforms to form multihop networks are discussed, and the major efforts for large-scale testbed implementations described. Finally, limitations of existing platforms and future research challenges toward the design of accurate open testbeds that will enable sound experimental evaluation of CR networks are discussed.

title: Software-defined joint routing and waveform selection for cognitive Ad Hoc networks
abstract: The problem of throughput maximization in a cognitive radio network with decentralized control (i.e., a cognitive radio ad hoc network) is considered in this paper. First, decentralized and localized algorithms for throughput maximization through joint cognitive routing and interference-avoiding waveform selection are proposed, based on a nonlinear optimization framework. The proposed algorithms adapt to time-varying traffic demands, interference profile, and network topology to locally maximize the achievable data rate while avoiding harmful interference to co-located primary or secondary users. Second, a prototype implementation of the proposed decentralized control algorithms is presented. The prototype is based on a software-defined-radio USRP2 platform that distributively senses and adapts its transmission based on results from real-time nonlinear optimization. Experiments on the software-defined-radio platform demonstrate the superior adaptivity of the proposed algorithm with respect to state-of-the-art non-cognitive approaches.

title: Implementation of a Distributed Joint Routing and Dynamic Spectrum Allocation Algorithm on USRP2 Radios
abstract: A cognitive radio network with decentralized control (i.e., a cognitive ad hoc network) is considered in this demonstration. The demo implements a decentralized and localized algorithm for throughputmaximization through joint routing and interference-avoiding waveform selection. The algorithm adapts to time-varying traffic demands, interference profile, and network topology to locally maximize the achievable data rate while avoiding harmful interference to co-located primary or secondary users. The prototype is based on a cross-layer protocol stack implemented in Python, which leverages GNU Radio for adaptive signal generation on a USRP2 software-defined-radio platform.

title: Ad-hoc on-demand distance vector routing
abstract: An ad-hoc network is the cooperative engagement of a collection of mobile nodes without the required intervention of any centralized access point or existing infrastructure. We present Ad-hoc On Demand Distance Vector Routing (AODV), a novel algorithm for the operation of such ad-hoc networks. Each mobile host operates as a specialized router, and routes are obtained as needed (i.e., on-demand) with little or no reliance on periodic advertisements. Our new routing algorithm is quite suitable for a dynamic self starting network, as required by users wishing to utilize ad-hoc networks. AODV provides loop-free routes even while repairing broken links. Because the protocol does not require global periodic routing advertisements, the demand on the overall bandwidth available to the mobile nodes is substantially less than in those protocols that do necessitate such advertisements. Nevertheless we can still maintain most of the advantages of basic distance vector routing mechanisms. We show that our algorithm scales to large populations of mobile nodes wishing to form ad-hoc networks. We also include an evaluation methodology and simulation results to verify the operation of our algorithm.

title: CRAHNs: Cognitive radio ad hoc networks
abstract: Cognitive radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum-aware communication paradigm in wireless communications. CR networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse quality-of-service (QoS) requirements. Specifically, in cognitive radio ad hoc networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, intrinsic properties and current research challenges of the CRAHNs are presented. First, novel spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. A particular emphasis is given to distributed coordination between CR users through the establishment of a common control channel. Moreover, the influence of these functions on the performance of the upper layer protocols, such as the network layer, and transport layer protocols are investigated and open research issues in these areas are also outlined. Finally, a new direction called the commons model is explained, where CRAHN users may independently regulate their own operation based on pre-decided spectrum etiquette.

title: A Quantitative Measure Of Fairness And Discrimination For Resource Allocation In Shared Computer Systems
abstract: Fairness is an important performance criterion in all resource allocation schemes, including those in distributed computer systems. However, it is often specified only qualitatively. The quantitative measures proposed in the literature are either too specific to a particular application, or suffer from some undesirable characteristics. In this paper, we have introduced a quantitative measure called Indiex of FRairness. The index is applicable to any resource sharing or allocation problem. It is independent of the amount of the resource. The fairness index always lies between 0 and 1. This boundedness aids intuitive understanding of the fairness index. For example, a distribution algorithm with a fairness of 0.10 means that it is unfair to 90% of the users. Also, the discrimination index can be defined as 1 - fairness index.