M.Phil Research ProposalBy Mohammad Muntasir RahmanLecturer Dept. of Computer Science & EngineeringIslamic University, Kushtia-7003, Bangladesh

Title: Packet transmission strategies to reduce interference of Cognitive Radio

I. INTRODUCTION AND BACKGROUND

Cognitive radio is a paradigm for wireless communication in which either a network or a wireless node changes its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users. This alteration of parameters is based on the active monitoring of several factors in the external and internal radio environment, such as radio frequency spectrum, user behavior and network state.

The idea of cognitive radio was first presented officially by Joseph Mitola [1] in a seminar at KTH, The Royal Institute of Technology, in 1998, published later in an article by Mitola and Gerald Q. Maguire, Jr in 1999. Cognitive radio is a revolutionary technology that aims for remarkable improvements in efficiency of spectrum usage. It will change the way the radio spectrum is regulated, but also requires new enabling techniques such as improved spectrum sensing and dynamic spectrum assignment.

II. IMPORTANCE OF COGNITIVE RADIO

Modern wireless systems aim at offering a wide variety of high data rate applications to numerous users at the same time. In order to realize this objective, they have to overcome the practical constraints imposed by the resources they need such as power and spectrum, which are limited in nature. Since the number of wireless systems is increasing very rapidly, the scarcity of these resources, especially of the frequency spectrum, becomes a more vital problem day by day.

Cognitive radio is a concept that targets at a future solution for the spectrum scarcity problem by proposing an opportunistic spectrum usage [2] approach, in which frequency bands that are not being used by their licensed users are utilized by cognitive radios. Since Cognitive radios do not need to have a license and since they do not affect the operation of licensed systems, this approach leads to a highly economic and efficient usage of the frequency spectrum.

III.RESEARCH ISSUES IN COGNITIVE RADIO

Cognitive radio techniques provide the capability to use or share the spectrum in an opportunistic manner. Dynamic spectrum access techniques allow the cognitive radio to operate in the best available channel. More specifically, the cognitive radio technology will enable the users to (1) determine which portions of the spectrum is available and detect the presence of licensed users when a user operates in a licensed band (spectrum sensing), (2) select the best available channel (spectrum management), (3) coordinate access to this

channel with other users (spectrum sharing), and (4) vacate the channel when a licensed user is detected (spectrum mobility) [3].

Although cognitive radio was initially thought of as a software-defined radio (SDR) extension, most of the research work is currently focusing on Spectrum Sensing Cognitive Radio. The essential problem of Spectrum Sensing Cognitive Radio is in designing high quality spectrum sensing devices and algorithms for exchanging spectrum sensing data between nodes. A cognitive radio should monitor the available spectrum bands, capture their information, and then detect the spectrum holes. Hence, spectrum sensing is a key enabling technology in cognitive radio networks. In spectrum sensing, the detection accuracy has been considered as the most important factor to determine the performance of cognitive radio networks. However, in reality, RF front-end of CR users cannot differentiate the primary user signals and CR user signals. In case of the energy detection, widely used in spectrum sensing, transmission and sensing cannot be performed at the same time. Thus, during the sensing (observation time), all CR users should stop their transmissions and keep quiet. However, the periodic spectrum sensing should consider following design issues:

Interference Avoidance: In the periodic sensing, interference is related to not only sensing accuracy depending on observation time but also the CR transmission time and traffic statistics.

Spectrum Efficiency: The main objective of cognitive radio is the efficient use of spectrum resources. However, since CR users cannot transmit during the sensing, spectrum efficiency will be degraded inevitably.

The cognitive radio should adapt its transmission parameters so that it can avoid the interference from primary system in order to guarantee its own QoS while it minimizes the interference to the primary system.

IV. AIMS AND OBJECTIVES

Minimizing the interference to the primary system in cognitive radio is a challenging task since exact traffic pattern and receiver position of the primary system are generally unknown to the cognitive radio transmitter. Such an interference minimization, i.e., keeping high etiquette towards the primary system, is a crucial requirement for cognitive radio to be allowed to operate in the same frequency band as the primary system.

To investigate mechanisms for control the interference level to the primary receiver with some packet transmission strategies in MAC level. For example, one possible method to keep high etiquette of the cognitive radio is to always use short packet and after every short-packet transmission, make carrier-sense. Only if the carrier is free, it continues to transmit short packet. If it detects the transmission of primary user, it stops the transmission. With this method, the cognitive radio can control the interference to the primary users, and keep high etiquette. However, such a strategy can result in the degradation of system performance for cognitive radio due to large overhead and frequent carrier sensing. Furthermore, this strategy cannot completely eliminate the interference to the primary system, and could result in an unacceptable interference to the primary system.

The goal of this investigation is to analyze such a relationship between different packet transmission strategies and interference level, and to propose methods to solve the problem arisen in such strategies. The final outcome from the mission should be the quantized results for the interference level between primary system and cognitive radio, and several strategies which can reduce such interference. The main focus and objective will be:

To investigate the transmission strategies for cognitive radio to minimize the interference to the primary system (e.g. short packet transmission).

To analyze the interference between cognitive radio and primary system with different transmission strategies and investigate the impact of different system parameters/strategies on the amount of interference caused from/to the cognitive radio to/from the primary system.

To propose the packet transmission strategies which can minimize the interference caused from/to cognitive radio to/from the primary system.

To identify the cost implied for the performance of the cognitive radio system due to the usage of shorter packets.

To analyze the proposed strategies with computer simulation and /or theoretical analysis.

V. RESEARCH METHOD

I wish to accomplish my targeted research goal in the following steps:

At the very first stage of my study period I want to acquire a vast idea about the concurrent researches going on in my area of interest i.e. minimizing the interference to the primary system in cognitive radio.

My main objective is to develop a communication protocol to minimize the interference level between primary system and cognitive radio.

In order to prove the competence of our proposed work I need to compare the protocol with other existing protocols by simulating it in a realistic simulator environment. MATLAB is a high-level technical computing language and interactive environment for algorithm development, data visualization, data analysis, and numeric computation. On the other hand, OMNeT is a component-based, modular and open-architecture discrete event network simulator. The most common use of OMNeT is the simulation of computer networks. Therefore, in this stage I need to find out suitable simulator among all available ones in order to fit with our specific requirements and extend that according to our need.

Next step is to validate our assumption with the other contemporary protocols and find all the pros and cons of our developed solution using simulation. After finding the effectiveness of our solution in comparison with others, probably we need to carry on the experiment a little bit further to achieve the desired mark. In order to do this, I need to finalize it with my supervisor once I have been admitted in the M.Phil course.

In the final stage of my research I need to write down dissertation paper describing all our findings.

VI. RESOURCE REQUIRED

To implement this proposal and measure it usefulness, I need to use simulators and for that, essentials like laboratory facility with computers and associated software e.g. Matlab, OMNeT, C compiler etc. are required. Obviously I need Internet facility to download research material, open source software as well as to communicate with the research community via mail services.

VII. TIME SCHEDULE

The first six months are needed for going through required literature and analysis of the proposal. Next six months are needed to figure out an apt solution for the addressed problem and to set up a simulation environment. In the next six months I plan to carry out the experiments and compare the result with the other state of the art solutions. Finally last six months are required for the thesis write up and necessary corrections (if required).

VIII. RISK ASSESSMENT AND CONTINGENCY PLAN

I am not aware of any risk associated with my research proposal.

IX. ETHICAL CONSIDERATIONS (IF REQUIRED)

So far, best of my knowledge, no ethical conflict is associated with this research proposal.

REFERENCES:

[1] J. Mitolla, “Cognitive Radio – An Integrated Agent Architecture for Software Defined Radio, “Royal Institute of Technology (KTH), 2000

[2] S. Mangold, Z. Zhong, K. Challapali, and C. –T. Chou, “Spectrum agile radio: radio resource measurements for opportunistic spectrum usage,” in Proc. IEEE global Telecomm. Conf. (Globecom), vol. 6, Dallas, TX, Dec. 2004, pp. 3467 – 3471.

[3] I. F. Akyildiz, et al., "NeXt Generation/Dynamic Spectrum Access/Cognitive Radio Wireless Networks: A Survey,'' Elsevier Computer Networks Journal, vol. 50, issue 13, pp. 2127-2159, Sept. 2006.