Muhammed Enes Bayrakdar

Fuzzy logic based spectrum handoff decision for prioritized secondary users in cognitive radio networks

Recent studies have revealed that due to the increasing number of wireless users, spectrum scarcity problem has arisen. In order to alleviate this problem, cognitive radio technology has emerged with the aim of using available spectrum in an opportunistic manner by secondary users. While utilizing licensed spectrum, it is inevitable for secondary users not to cause any interference to the primary users. Once the primary user activity is detected on the licensed channel at the time of on-going transmission of secondary user, secondary user must either change the licensed spectrum or stop its transmission. This case of changing spectrum by secondary user is known as spectrum handoff. In this paper, fuzzy logic based spectrum handoff decision is carried out by using data rate, channel usage, and priority. Different data traffics such as audio, and video are considered for secondary users. In order to simulate data traffics, two different simulation scenarios are realized. Besides, several priority classes are taken into account for urgent and real-time communications. In the proposed system, it is seen that accurate spectrum handoff decisions are made for different traffic types.

Simulation model of spectrum handoff process for medium access control protocols in cognitive radio networks

Cognitive radio is a new technology that improves spectrum utilization by allowing secondary users to use licensed channels in an opportunistic manner. Because primary users have a right to use their licensed channels at any time, it is necessary for secondary users to stop their transmissions or to continue their transmissions in other channels in case of action of primary users. The event of changing channel for secondary users is known as spectrum handoff. Spectrum handoff for medium access protocols is an emerging topic because of the increasing spectrum scarcity. In this paper, simulation model of a cognitive radio network that consists of primary users and secondary users is considered. Riverbed Modeler Simulation Software is used for simulation scenarios. Secondary users are designed to make spectrum handoff between time slots of primary users with reactive decision spectrum handoff. It is clearly seen that number of handoff is significantly decreased by means of instant sensing based reactive spectrum handoff.

Spectrum handoff process with aging solution for secondary users in priority based cognitive networks

Spectrum handoff is a process performed by secondary users in cognitive radio networks. To accomplish this, the base station that coordinates the secondary users decides which user will make the spectrum handoff process according to certain criteria. The priority classes of the secondary users are at the top of these criteria. In traditional priority based queues, packets with higher priority are transmitted first, and lower priority packets waits for the other higher-priority packet transmissions to finish. In this study, priority data traffic is used in queue structure in order to meet the different requirements of secondary users. In addition, we have added the aging solution to the spectrum handoff mechanism in order to shorten the long wait times of low priority packets. The aging solution is defined as the increase of the priority of lower priority packets waiting for too long in the queue over certain waiting periods. Analytical and simulation models of the aging solution have been designed in order to prove validation. It has been shown that the total number of spectrum handoff on the network for different priority packets and different loads is reduced significantly.

Performance analysis of sensing based spectrum handoff process for channel bonding mechanism in wireless cognitive networks

Recently, wireless cognitive networks have taken great attention due to the increasing spectrum scarcity. For example, the usage of a cognitive radio network infrastructure is inevitable for emergency communication needs in cases of natural disaster and extraordinary situations. Apart from this, cognitive networks may also be utilized in daily life by providing necessary permissions. Channel bonding approach is also widely used to increase the bandwidth demand in network systems using wireless infrastructure. Channel bonding is defined as the usage of consecutive time slots in combination when multiple time slots are required for packet transmission. The spectrum handoff process performed by the secondary users in the cognitive radio networks is expressed as the transfer of the secondary user to another channel or time slot. The idle time slots for channel bonding process may be determined with sensing based approach as well as predefined approach. In our study, sensing based spectrum handoff process with channel bonding mechanism is utilized. Both the analytical and the simulation model results of the channel bonding based spectrum handoff process are obtained in order to prove validation of the work.

Optimization of spectrum handoff with artificial bee colony algorithm

Cognitive radio has been regarded as a technology that guarantees a significant increase in spectrum utilization efficiency. Depending on this technology; spectrum management, spectrum sensing and spectrum handoff have emerged. In cognitive radio networks, how the frequency channels are to be assigned between users is at the top of the newsworthy topics. In addition, it is also the current topic to reduce the delay to the minimum in the spectrum handoff process. In the case of minimizing a value, optimization algorithms should be utilized. In recent times, the widely used artificial bee colony algorithm has an important place among all the optimization algorithms. In this study, firstly designed spectrum handoff model is presented and then artificial bee colony based spectrum handoff algorithm is developed. In the developed algorithm, the channel availability characteristic is examined based on the position of the bees in the artificial bee colony algorithm in order to optimize the spectrum handoff delay. With the help of the algorithm developed using the artificial bee colony, the spectrum handoff delay of the secondary users is significantly reduced and total service time is increased.

Medium access control protocols for secondary users in wireless cognitive radio networks

Kablosuz bilişsel radyo ağ çalışmaları yeni uygulamalar için gün geçtikçe önem kazanmaktadır. Kablosuz ağlarda, düğümler arası haberleşmeyi MAC (Ortam Erişim Kontrol) protokolleri sağlamaktadır. MAC protokolleri kablosuz haberleşme kanallarında oluşan gizli terminal ve sinyal kaybolma etkileri gibi hata ve problemlerden dolayı daha da önemli bir hale gelmektedir. MAC protokolleri ile ilgili birçok çalışma yapılmasına rağmen, yapılan çalışmaların büyük çoğunluğu izole şekilde kullanılmıştır. Bu çalışmada, birbirinden habersiz yapılan literatürdeki bütün çalışmaların derlemesi yapılmıştır. Ayrıca, MAC protokollerinin tanımı ve kısa açıklamaları da bu çalışmada yer almaktadır. Sonuç kısmında, gelecek çalışmalar için önerilerde bulunulmuş ve MAC alanı ile ilgili genel ifadeler vurgulanmıştır. Wireless cognitive radio network studies are gaining importance day by day for new applications. In wireless networks, communication between nodes is provided by MAC (Medium Access Control) protocols. MAC protocols are becoming more important due to hidden wireless communication terminal problem, signal errors and problems that occur in channels such as loss effects. Although there are many studies on the MAC protocols, majority of these studies are isolated from each other. In this study, the compilation of all work that is unaware of each other in the literature has been made. In addition, the definition of MAC protocols and brief descriptions are also included in this study. In the concluding part, some suggestions for future work are presented and general terms about MAC are emphasized.

Delay characteristics of TDMA medium access control protocol for cognitive radio networks

In this work, we have evaluated the delay characteristics of Time Division Multiple Access (TDMA) protocol. In our simulation scenarios, primary users and secondary users exploit TDMA as a medium access control protocol. We have designed a network environment in Riverbed (OPNET) simulation software that consists of primary users, secondary users, and base stations. In our network model, secondary users sense the spectrum and inform the base station about empty channels. Then, the base station decides accordingly which secondary user may exploit the empty channel. Energy detection technique is employed as a spectrum sensing technique because it is the best when information about signal of primary user is obtained. Besides, different number of users is selected in simulation scenarios in order to achieve accurate delay results. Comparing analytical model with simulation results, we have shown that delay analysis of our system model is reliable and correct.

Fuzzy logic based channel selection for mobile secondary users in cognitive radio networks

Cognitive radio is a new technology that aims to solve the spectrum scarcity problem. In cognitive radio networks; because secondary users utilize the spectrum in an opportunistic manner, it is crucial not to cause any interference to the primary users. In this work, a new approach for channel assignment to mobile secondary users by means of fuzzy logic is proposed. In the proposed fuzzy logic system; by using input parameters of density, mobility, and noise, channel selection probability is obtained. Density parameter expresses how intense the spectrum is used by primary users. Mobility parameter is a distance among secondary users, primary users, and base station. Noise parameter represents the noise, and other disruptive effects in the spectrum. Channel selection probability shows which frequency band of primary users to use according to the parameters of mobile secondary user. In the proposed system, the most suitable channel selection is provided for mobile secondary users.