CHANNEL AWARE MEDIUM ACCESS CONTROL IN COGNITIVE RADIO NETWORKS PALASH KATIYAR(10475) ELECTRICAL ENGINEERING INDIAN INSTITUTE OF TECHNOLOGY KANPUR

Cognitive Radios Radio spectrum is a limited resource Has gone starved and is more scarce to get Need to come up with solutions that would not only solve the problem of under usage of spectrum but also improve the current usage. Cognitive radio is a novel method that might propose new solutions Spectral usage in a urban area [1]

Cognitive Radios Some of the challenges to mention in this field are : Identify frequency bands incumbent by licensed users and those that are vacant. Unlicensed users exploit vacant bands also know as “spectrum holes”[2] Medium access for unlicensed users is highly dynamic and opportunistic

Medium Access Control in CR Attracts attention of a larger research community Focus on design of robust and effective spectrum access techniques for cognitive radio networks Closely related to MAC development in multichannel wireless networks, but different Development of CR-MAC protocols has often borrowed design ideas from existing protocols in multichannel wireless networks

CR – MAC protocols A Cognitive radio medium access scheme should perform Channel Sensing Detection of primary users Dynamic channel selection Robust channel switching mechanism Improve overall usage in both licensed and unlicensed bands

IEEE 802.22[3] IEEE 802.22 WRAN standard Aimed at using CR techniques to allow sharing of unused spectrum allocated to television broadcast services [4] What is WRAN - A WRAN network uses the white spaces in television broadcasts to facilitate broadband access. The point of a WRAN is to provide Internet access to areas that are difficult to reach by other means. The standard is centralized and does not serve distributed architecture No such standard exists for medium access in a distributed network cases

Cognitive Radio MAC Control information exchange in design of distributed MAC Overhead considerably higher than that in simple wireless networks Most of the schemes exploit out of band signaling Use of a dedicated control channel is quite popular – a widely accepted idea Use of IEEE 802.11 DCF [5] like architecture is also very common Use of CCC

Various CR – MAC protocols [6]

Channel aware MAC schemes Channel Aware Schemes focus to exploit the Channel state information around a user Can be used to better model the competitive scenario a user faces Makes a user self aware of the surroundings it is operating in and enables it to make independent decisions Makes competition fair and ensure good throughput values, many of channel aware schemes have achieved throughput values comparable to centralized scheduling schemes Some example of prior works done in this fields are - CAD-MAC [7] and CAAC [8] Channel awareness and CCC can be a handy tool in designing such protocols

Channel Aware Distributed MAC(CAD-MAC[7]) Designed for competitive and distributed network case, where users negotiate communication over a single channel Primarily a channel aware aloha scheme Each user opportunistically contends for its success, directed by its own CSI and competition it faces in surroundings Protocol selects the best links in terms of channel states and therefore achieves performance close to that of centralized schedulers Onr such protocol is CAD -MAc

CAD-MAC[7] Outline Three step signaling before confirmation of the success of a link(RTS-CTS- ACK) Each user maintains and modifies its own threshold values (derived from CSI) Channels are modelled as Rayleigh fading About 10% time of a Frame time is spent in resolution of contentions Optimizes network throughput and minimizes interference between selected links 3 step signaling and threshold control

Time frame organization in CAD-MAC[7]

Optimization of Thresholds Optimize for the opening Contention resolution slot – set the initial values The values of optimal thresholds 𝐻 𝑖𝑗 [1] are: 𝐻 𝑖𝑗 1 = 𝐹 𝑖𝑗 −1 𝑌 𝑖𝑗 1 Where 𝑌 𝑖𝑗 1 = 1− 𝑇 𝑖 𝑆 𝑖 + 𝑚 ∈ 𝑁 𝑖 𝑆 𝑚 1 𝑇 𝑖 𝐹 𝑖𝑗 is the distribution function for Rayleigh fading channels. |𝑇 𝑖 | 𝑖𝑠 𝑡ℎ𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑢𝑠𝑒𝑟𝑠 𝑟𝑒𝑐𝑒𝑖𝑣𝑖𝑛𝑔 𝑝𝑎𝑐𝑘𝑒𝑡𝑠 𝑓𝑟𝑜𝑚 𝑢𝑠𝑒𝑟 𝑖 |𝑆 𝑖 | 𝑖𝑠 𝑡ℎ𝑒 𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑢𝑠𝑒𝑟𝑠 𝑠𝑒𝑛𝑑𝑖𝑛𝑔 𝑝𝑎𝑐𝑘𝑒𝑡𝑠 𝑡𝑜 𝑢𝑠𝑒𝑟 𝑖 |𝑁 𝑖 | 𝑖𝑠 𝑡ℎ𝑒 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑢𝑠𝑒𝑟𝑠 𝑖𝑛 𝑟𝑎𝑛𝑔𝑒 𝑡𝑜 𝑢𝑠𝑒𝑟 𝑖

Optimization of Thresholds Update thereafter for every next threshold- whether to increase, decrease and keep the thresholds same Increase if a collision of requests has happened Decrease if no request was transmitted in the previous resolution slot, and receiver has invited requests In other cases, keep the values same

Our Proposal We try to extend this scheme in first, multichannel distributed network case Also try to embed the following concepts to make it applicable for cognitive radio networks - Spectrum mobility - Dynamic spectrum access - Channel Switching mechanism Our proposal also uses a separate control channel and time synchronization of secondary users Simulated the design over several test topologies that include the presence of both primary and secondary users

Our Proposal Introduce some changes in control signaling mechanism Different from Single band CAD-MAC, we have following changes Selection of best possible links for contentions, where we have to consider all the opportunities that are available to users across the spectrum Switching mechanism – failing to get success for data transmission on one channel makes a user contend for another channel Threshold modification - need to consider the dynamic spectral environment in calculation and optimization of these values

Example test case with presence of both primary and secondary users

Revised control signaling exchange

Results And Conclusions We are able to see that the application of a slotted aloha protocol for contention among users with varying spectral opportunities can produce good values of network throughput for secondary users. Not only our design is able to fairly choose interference free links among the contending users making it highly probable the selection of those links with comparably better channel states in a neighborhood We were able to implement the protocol for network cases with both primary and secondary users present.

References [1]. By Raghvendra Rao, Qi Cheng, Aditya Kelkar and Dhavel Chaudhary, in ICAST global community magazine [2]. Ekram Hossain, Vijay K. Bhargava (2007) Cognitive Wireless Communication Networks, 1st edition, Springer, New York. [3]. C. M. Cordeiro, K. Challapali, and D. Birru, \IEEE 802.22: An Introduction to the First Wireless Standard based on Cognitive Radios, J. Commun., Special Issue from selected papers from DySPAN 2005, vol. 1, no. 1, pp. 328337, April 2006 (Invited Paper). [4]. http ://en:wikipedia:org/wiki/CognitiveRadio [5]. IEEE 802.11 WG,\Part 11:Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specication, in IEEE Std 802.11-1999, August 1999.

References [6]. Antonio De Domenico, Emilio Calvanese Strinati, and Maria-Gabriella Di Benedetto,\A Survey on MAC Strategies for Cognitive Radio Networks,“ IEEE communications surveys and tutorials, Vol. 14, NO. 1, first quarter 2012 [7]. Guowang Miao, Ye(Georey)Li and Ananthram Swami,\Channel aware distributed Medium Access control", in IEEE/ACM transactions on networking, Vol. 20, No. 4,August 2012. [8]. Bo Yang, Gang Feng, Yanyan Shen, Chengnian Long, Xinping Guan,\Channel-Aware Access for Cognitive Radio Networks", IEEE transactions on vehicular technology, VOL. 58, NO. 7, September 2009.