Quality of Service Provisioning in Cognitive Radio Network

Cognitive radio is a future technology coined for increasing the utilization of otherwise under-utilized spectrum channels. Providing quality of service (QoS) to diverse flows as per their requirements is a very difficult job as there is no dedicated allocation of wireless channels in cognitive radio (CR) network. The paper selects few critical QoS parameters such as signalstrength, bandwidth and user-mobility that assess the influence on quality of communication between users using rule-based fuzzy inference system. The analytical results show the influence of those QoS parameters on the quality of communicating channels and open new issues in designing protocol structure for CR. Oriental Journal of Computer Science and Technology Journal Website: www.computerscijournal.org ISSN: 0974-6471, Vol. 10, No. (4) 2017, Pg. 780-787


Introduction
The utilization repor t provided by Federal Communications Commission (FCC) 1 spectrum task force indicates that utilization of the allocated spectrum varies between 15% to 85%.Mitola 2,3 is considered to be the pioneer of the idea of cognitive radio (CR).CR 4 is a smart device having the capability to sense the entire spectrum in order to find the idle channels and utilizing these idle channels opportunistically for communication as and when required.
The important issues of CR are as under:

Spectrum Sensing
This function finds the idle spectrum to be used for its communication and the arrival of PU on the spectrum channels presently occupied by CR.

Spectrum Management
Large chunks of idle spectrum are identified through spectrum sensing that needs to be categorized so that the best spectrum channel is selected for CR's communication.

Spectrum Mobility
Primary user has the priority to access the spectrum.Once PU appears on the channels occupied by CR, it needs to change the operating frequency instantly to minimize the interference.

Spectrum Sharing
Once transmitting channels are selected, handshaking process is initiated between communicating users first, before actual communication starts.
Providing QoS guarantees to different flows as per their requirement in CR is a very difficult job.QoS 5 is the ability of the system to provide minimum requisite service needed for satisfactory communication between users and has direct impact over CR performance.It is also defined by the degree of satisfaction of the CR users and their skill to treat different flows differently 6,7 .The definition of QoS changes with types of traffic and network.The QoS is a function of multiple contradictory parameters and those are not certain and exact.Application of fuzzy logic gives more effective solution when the available information is vague and imprecise.This paper proposes to use rule based fuzzy logic for assessing the influence of three critical parameters on QoS in a cognitive radio network.At the onset, fuzzy logic found applications in control system 8,9 and then in telecommunication networks [10][11][12] .Fuzzy logic found more applications in cellular networks for admission control 13 and for routing 14 .It was extended to CR network for transmitting power control 15 and for optimization 16 .It found more applications for controlling the spectrum access 17,18 and spectrum handoff [19][20][21] in cognitive radio.The authors of 22,23 have analysed impact of some QoS parameters.

Materials and Methods
An algorithm, using rule-based fuzzy inference system, is proposed in this paper to analyse the impact of three critical parameters namely signalstrength, bandwidth and user-mobility on the QoS in cognitive radio.We have used Hong and Rappaport traffic model 24,25 for user-mobility.The assumptions of the model are: • That all the users are uniformly distributed in that cell when a call is started.

•
The users, starting the call, have equal probabilities of moving in any direction but afterwards move in the same direction during the call.
The handoff requests 24,25 arrive into the system as P h is the probability that the communication at least need one more handoff without blocking the service request.
P hh is the probability that the on-going communication need one more handoff.
B o is the probability of blocking of new service requests.
P f ' is the probability that handoff is not successful.
l o is the arrival rate of service requests in a cell.
Three inputs to fuzzy inference system are given as: and the output of the fuzzy inference system is the quality of the communication channel in CR.Each input is characterized by three fuzzy sub-sets, such as low, medium and high, as shown in (2) defined by universe of discourse in the range[0,1] S(signal-strength) = S(bandwidth) = S(usermobility) = {low, medium, high} ... (2)   and QoS is characterized by five fuzzy sub-sets, such as poor, average, good, very-good and excellent, as shown in (3), defined by universe of discourse in the range[0,1] S(QoS)={poor, average, good, very-good, excellent} ..

.(3)
The analysis of the proposed algorithm is being done using trapezoidal membership functions for inputs and the QoS, depicted in Figs.1(a Table .adepicts the rules of the fuzzy inference system.The rules are designed to have the suitable values of the three contradictory inputs so as to satisfy the QoS requirement of the communicating users.For instance, rule 2 demonstrates that if the signal-strength is low, unused bandwidth is low and user-mobility is medium, then the quality of the communicating channel is poor.
user is moving with speeds that fall under middle category.As a result, the quality of the channel is just sufficient to satisfy QoS requirements of the communicating users.Also rule 26 demonstrates that if the signal-strength is high, bandwidth is high and user-mobility is medium, then the quality of the communicating channel is excellent.The rule is translated into actual channel condition in which transmission loss of the communication channel is negligible, availability of unused bandwidth is very large and the user is moving with speeds that fall under middle category.As a result, the quality of the channel is more than sufficient so that the QoS requirement of the communicating users is easily satisfied.
The rule is translated into actual channel condition in which transmission loss of the communicating channel is very large, availability of unused bandwidth is limited and the user is moving with speeds that falls under middle category.As a result, the quality of the channel is not sufficient to satisfy QoS requirements of the communicating users.Rule 14 demonstrates that if the signal-strength is medium, bandwidth is medium and user-mobility is medium, then the quality of the communicating channel is average.The rule is translated into actual channel condition in which transmission loss of the communication channel is in middle range, availability of unused bandwidth is sufficient and the

Results and Discussions
The proposed algorithm is analysed for static data transfers in Matlab's fuzzy toolbox.Figs.3(a), 3(b) and 3(c) demonstrate the effect of signal-strength, bandwidth and user-mobility on the quality of the communication between users while keeping the other two parameters constant at middle values (=0.5).The results indicate that with increase in the signal-strength there is increase in the quality of the communication of the users, while keeping bandwidth and user-mobility constant at middle values, as shown in Fig. 3(a).The further results indicate that with the increase in available unused bandwidth of a communication channel, there is also an increase in the quality of the communication of the users, while keeping signal-strength and usermobility constant at middle values, as shown in Fig. 3(b).Fig. 3(c) indicates that with the increase in usermobility i.e. when the speed of the user increases, there is decrease in the quality of the communication of the users, while keeping bandwidth and signalstrength constant at middle values.

Conclusion
The paper proposed an algorithm using fuzzy inference system that assesses the impact of signal-strength, bandwidth and user-mobility on QoS in cognitive radio.The analysis of the proposed algorithm is being performed in Matlab's fuzzy toolbox.The results indicate that with increase in the signal-strength and unused bandwidth, and decrease in user-mobility, there is increase in QoS of the communication between CR's.

Fig. 3 :Fig. 4 :
Fig. 3: Analytical results show effect of a) signal-strength on QoS b) bandwidth on QoS c) usermobility on QoS while keeping other two parameters constant at middle values (= 0.5)

Table a : Rules in fuzzy inference system Rule signal-bandwidth user-
I would like to acknowledge and express my heartiest gratitude to my Ph.D supervisor Professor Moin-Uddin who introduced me to the very interesting subject "Cognitive Radio Technology".I have benefitted tremendously from his vision, technical insight and valuable suggestions.Prof. Moin Uddin is a senior member, IEEE.He has more than 35 years of experience in academics and research and has served at key Positions as Director, NIT Jallandhar, Pro-ViceChancellor, Delhi Technological University .