TITLE (tentative) A Quality-of-Service (QoS) based broadcast protocol in a multi- hop Cognitive Radio ad hoc network under blind information D.Veeraswamy M.Tech-A.C.S Under the guidance of Sri M.V.Raghunadh Associate Professor

Introduction What is Cognitive Radio? Cognitive is derived from word cognition which means “the process of acquiring knowledge through thought, experience and the senses”. The cognitive radio, built on a software-defined radio, is defined as an intelligent wireless communication system that is aware of its environment and adapt to statistical variations in the input stimuli, by making corresponding changes in certain operating parameters (e.g., transmit-power, carrier-frequency, and modulation strategy) in real-time, with two primary objectives in mind: highly reliable communication whenever and wherever needed; efficient utilization of the radio spectrum.

Why Cognitive Radio? In many bands, spectrum access is a more significant problem than physical scarcity of spectrum, in large part due to legacy command- and-control regulation that limits the ability of potential spectrum users to obtain such access. Indeed, if we were to scan portions of the radio spectrum including the revenue-rich urban areas, we would find that 1) some frequency bands in the spectrum are largely unoccupied. most of the time; 2) some other frequency bands are only partially occupied; 3) the remaining frequency bands are heavily used. The underutilized bands of electromagnetic spectrum are called spectrum holes, which are defined as follows: A spectrum hole is a band of frequencies assigned to a primary user, but, at a particular time and specific geographic location, the band is not being utilized by that user.

Cognitive radio networks consist of primary and secondary users/networks. Primary users (PU) are usually licensed to access a spectrum band. The secondary users (SU) sense available opportunity to access in licensed band in absence of primary users. The main functions of Cognitive Radios are: Spectrum Sensing-detecting the unused spectrum Spectrum Management -decide on the best spectrum band to meet the quality of service requirements over all available spectrum bands Spectrum Sharing -providing the fair spectrum scheduling method. Equivalent to MAC in traditional wireless networks.

Significance of common control channel (CCC) Two neighbouring nodes can exchange available channel information or negotiate channel assignments of a link via the control channel. CCC can be classified as an in-band CCC or out-of-band CCC, depending on whether the control channel shares the data channel or uses a dedicated channel, respectively. In ad hoc cognitive radio networks, a control channel is usually used for supporting transmission coordination and spectrum- related information exchange. But in ad hoc cognitive radio networks control channel cannot be common in a practical scenario.

Problem identification Broadcast is an important operation in wireless networks where control information is usually propagated as broadcasts for the realization of most networking protocols. In traditional ad hoc networks, broadcasts are conducted on a common channel which is shared by all nodes in the network. However, in cognitive radio (CR) networks, unlicensed users may observe heterogeneous spectrum availability which is unknown to other users before broadcasts are executed. Thus, it is extremely challenging that broadcasts can be successfully conducted without the spectrum availability information.

Related work: Solution-1: To broadcast the control information on every channel in the band / Sender randomly select a channel to broadcast, while the receiver also randomly selects a channel to listen. Disadvantage: Long broadcast delays and probability that the sender and the receiver select the same channel is low. Solution-2: A selective broadcasting scheme is proposed to reduce the broadcast delay.(ref-3) Disadvantage: Network topology and the available channel information of all nodes is assumed to be known

Solution-3: A channel hopping algorithm is proposed for guaranteed rendezvous(ref-4) Disadvantage: Expected rendezvous time for the asymmetric model (i.e., different users have different available channels) increases exponentially where the total number of channels increases. Therefore, to design a broadcast protocol which has high success rate and short broadcast delay is a very challenging issue for multi-hop CR ad hoc networks.

Proposed Scheme A Quality-of-Service (QoS)- based broadcast protocol in a multi-hop Cognitive Radio ad hoc network under blind information is proposed (ref-1). In this design, a practical scenario is considered: 1) the network topology is not known; 2) the available channel sets of different SUs are not assumed to be the same; and 3) tight time synchronization is not required. The QoS requirements of the proposed protocol are the success rate and the average broadcast delay. Success rate of broadcast is the probability that all nodes in a network successfully receive a broadcast message. Broadcast delay is the duration from the moment a source node starts a broadcast until the moment the last node in the network receives the broadcast message.

Work details and Problems in implementation Secondary user Primary user Red-1 Yellow-2 Brown-3 D S PUs are licensed to use any of chaneels-1,2,3,4,5 SUs are permitted to use licensed channels when free Every node has a node ID Source-S can use channels 1,2,3,4,5 Destination-D can use 4,5

BROADCAST SCHEME: The main idea of the proposed protocol is to let the sender broadcast on a subset of its available channels in order to reduce the broadcast delay. In addition, the channel hopping sequences of both the sender and the receiver are designed for guaranteed rendezvous, given that the sender and the receiver have at least one channel in common.

Example Let the available channel set of the sender is {1, 2, 3, 6}, it randomly selects two channels (i.e., {3, 6}) to broadcast for S slots (i.e., n = 2). Each receiver listens for two time slots on each available channel of its available channel set (e.g., {1, 2, 6}) periodically. The shaded part in Fig. 1 represents a successful broadcast. Based on the above rules, if the sender and each receiver have at least one channel in common and the length of the broadcast sequence S is equal to n × M, the broadcast is ensured to be successful.

Simulator used: NS3, open source discrete event network Simulator, programming language used: c++ PROBLEMS: Though chosen reference paper simplifies broadcasting; complete implementation details were not given clearly. Using multiple channels for message transfer simultaneously. No built-in functions supporting Cognitive Radio network.

References: 1.Yi Song and Jiang Xie: A QoS-based Broadcast Protocol for Multi-hop Cognitive Radio Ad Hoc Networks under Blind Information, IEEE Globecom J. Mitola, “Cognitive radio: an integrated agent architecture for software defined radio,” Ph.D. dissertation, KTH Royal Institute of Technology, Y.Kondareddy and P.Agrawal, “Selective broadcasting in multi-hop cognitive radio networks,” in Proc. IEEE Sarnoff Symposium, April 2008, pp. 1–5. 4.Z. Lin, H. Liu, X. Chu, and Y.-W. Leung, “Jump-stay based channel hopping algorithm with guaranteed rendezvous for cognitive radio networks,” in Proc. IEEE INFOCOM, J. Mo, H.-S. W. So, and J. Walrand, “Comparison of multichannel MAC protocols,” IEEE Trans. Mobile Computing, vol. 7, no. 1, pp. 50–65, Distributed Coordination Protocol for Ad Hoc Cognitive Radio Networks, Journal of Communication and Networks, Vol. 14, NO. 1, February 2012

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