Spectrum Handoff Research Articles

A Novel Approach to Real Time Spectrum Handoff

A Novel Approach to Real Time Spectrum Handoff

Handoff Mechanism using Spectrum Pool

In this paper, spectrum pool is one of the efficient techniques for spectrum sensing selection. Cognitive radio always preferred for accessing free channels efficiently with minimum handoff delay .The performance of spectrum pool has been implemented and compared with conventional handoff mechanism. Spectrum handoff occurs when primary user appears and the secondary users using this particular licensed channel. This particular spectrum handoff would use channels for the handoff process from the spectrum pool formed by proposed method. Spectrum sensing plays important role in case of cognitive radio. For accessing the spectrum reuse functionality, secondary users used to sense the radio frequency environment. For this propose we proposed two different modules one is spectrum pool and other will be secondary user with multiple antennas.

Analysis of Reactive Spectrum Handoff in Cognitive Radio Networks

In this paper, we present an analytical framework to evaluate the effects of multiple spectrum handoffs on channel utilization and latency performances in cognitive radio (CR) networks. During the transmission period of a secondary connection, multiple interruptions from the primary users result in multiple spectrum handoffs. In order to decide the target channel for each spectrum handoff and resume the unfinished transmission, wideband sensing is performed in an on-demand reactive manner. Although spectrum handoff procedure can enhance channel utilization, transmission latency of the secondary users is prolonged due to multiple handoffs. Thus, two fundamental issues in CR networks with multiple spectrum handoffs arise: (1) to what extent the channel utilization can be improved; and (2) how long the transmission latency will be extended for the secondary users. To solve the first problem, we introduce the preemptive resume priority (PRP) M/G/1 queueing network to characterize the channel usage behaviors of CR networks. Based on this queueing network, channel utilization under various traffic arrival rates and service time distributions can be evaluated. Furthermore, on top of the proposed queueing network, a state diagram is developed to characterize the effects of multiple handoff delay on the transmission latency of the secondary users. The analytical results can provide a helpful insight to study the effects of traffic arrival rates and service time on channel utilization and transmission latency and then facilitate the designs of admission control rules for the secondary users subject to their performance requirements.

A Novel Spectrum Handoff Scheme in Cognitive Radio Networks: An Improved Fuzzy Inference Approach

A Novel Spectrum Handoff Scheme in Cognitive Radio Networks: An Improved Fuzzy Inference Approach

무선 인지 셀룰러 망에서 자원예측에 의한 가드채널 할당기법의 성능개선

본 논문에서는 셀룰러 기반 무선 인지망에서 핸드오프 호를 위한 가드채널할당기법(guard channel scheme)의 자원이용률의 저하를 개선하기 위해 무선인지 기술을 사용하여 자원 이용률을 향상시키면서, 무선 인지망의 부 사용자(cognitive radio user) 손실률을 줄이는 방법을 제안한다. 제안한 방법에서는 핸드오프 호의 전용채널(guard channel)을 부 사용자가 이용하도록 하고, MMOSPRED(Multi-Media One Step Prediction)기법으로 핸드오프 호의 발생을 예측한 다음, 핸드오프 호가 발생하면 핸드오프 호의 전용채널을 넘겨주고, 부 사용자는 예약된 자원으로 스펙트럼 핸드오프를 하여 서비스를 완료 하도록 한다. 시뮬레이션을 통하여, 제안한 기법의 자원 이용률과 부 사용자의 손실률에 대한 성능이 기존의 가드채널 할당기법과 모바일의 이동성을 예측하지 않은 채널할당기법 보다 우수함을 보인다. In this paper, we propose a scheme for improving not only the utilization of frequency bands in the guard channel scheme but also the dropping rate of cognitive radio user in the wireless cognitive radio-based cellular network. The proposed scheme enables cognitive radio users to utilize the guard channel for servicing only handoff calls in normal times, but cognitive radio users must vacate the frequency channel when handoff call appearing. At this time our scheme ensures their seamless services for cognitive radio users, by predicting handoff call's appearance by MMOSPRED (Multi-Media One Step Prediction) method and then reserving the demanded channels for spectrum handoff calls. Our simulations show that our scheme performs better than other schemes; GCS(Guard Channel Scheme) and a scheme without prediction in terms of cognitive users call's dropping rate and resource utilization efficiency.

Modeling and Analysis for Spectrum Handoffs in Cognitive Radio Networks

In this paper, we present an analytical framework to evaluate the latency performance of connection-based spectrum handoffs in cognitive radio (CR) networks. During the transmission period of a secondary connection, multiple interruptions from the primary users result in multiple spectrum handoffs and the need of predetermining a set of target channels for spectrum handoffs. To quantify the effects of channel obsolete issue on the target channel predetermination, we should consider the three key design features: 1) general service time distribution of the primary and secondary connections; 2) different operating channels in multiple handoffs; and 3) queuing delay due to channel contention from multiple secondary connections. To this end, we propose the preemptive resume priority (PRP) M/G/1 queuing network model to characterize the spectrum usage behaviors with all the three design features. This model aims to analyze the extended data delivery time of the secondary connections with proactively designed target channel sequences under various traffic arrival rates and service time distributions. These analytical results are applied to evaluate the latency performance of the connection-based spectrum handoff based on the target channel sequences mentioned in the IEEE 802.22 wireless regional area networks standard. Then, to reduce the extended data delivery time, a traffic-adaptive spectrum handoff is proposed, which changes the target channel sequence of spectrum handoffs based on traffic conditions. Compared to the existing target channel selection methods, this traffic-adaptive target channel selection approach can reduce the extended data transmission time by 35 percent, especially for the heavy traffic loads of the primary users.

Optimal Target Channel Sequence Design for Multiple Spectrum Handoffs in Cognitive Radio Networks

In this paper, we investigate how to determine an optimal target channel sequence with the minimum cumulative handoff delay in cognitive radio networks. When the secondary user encounters multiple spectrum handoffs during its transmission period, the effects of multiple interruptions from the high-priority primary users and the traffic statistics of both the primary and the secondary users should be incorporated in the design of the optimal target sequence. The optimal target channel sequence can guild the secondary user to change its operating channel when the primary user's interruptions occur. With M candidate channels and L elements in the target channel sequence for spectrum handoffs, the exhaustive search (ES) requires time complexity of O(ML). In this paper, we propose a dynamic programming (DP) algorithm with time complexity of O(LM2) to determine an optimal target channel sequence. Furthermore, we propose a greedy algorithm with time complexity of O(M) and prove that the greedy algorithm only requires comparing six target channel sequences. Numerical results show that the low-complexity greedy algorithm can yield similar cumulative handoff delay performance as the optimal DP-based or ES-based algorithms in most cases except when the primary users' service time distributions at their operating channels are different.

Analysis of Channel Selection and Heterogeneous Spectrum Handoff in Cognitive Radio Ad Hoc Networks

This paper addresses the priority of channel selection and switch over heterogeneous spectrum in cognitive radio ad hoc networks, which is not addressed carefully in the literature, with the aid of a novel 3-D structured Markov-chain model analysis. Our analysis indicates that the performance of the capacity, the probability of collision or switch of the Secondary Users (SUs) will be improved if the new SUs select available channels to initialize a session with a proper priority of Secondary Channels (SCs). Moreover, our work indicates that the same performance improvement would be gained if the active SUs interrupted by the PUs switch their working spectrum to available secondary channels with a proper priority. Extensive numerical analysis results verify the effectiveness of the proposed models and analysis methods.

Performance analysis of dynamic spectrum handoff scheme with variable bandwidth demand of secondary users for cognitive radio networks

Cognitive radio (CR) has attracted considerable attention as a promising technology for solving the current inefficient use of spectrum. In CR networks, available sub-channels are dynamically assigned to secondary users (SUs). However, when a primary user accesses a primary channel consisting of multiple sub-channels, data transmissions of the SUs already using the sub-channels may be terminated. In this paper, we analyze the performance of dynamic spectrum handoff scheme with channel bonding, in which the number of sub-channels used by an SU are variable. We model the multichannel CR network as a multiserver priority queueing system without waiting facility, deriving the blocking probability, the forced termination probability and the throughput for SUs. In terms of the way of forced termination, we consider two policies; one is that SUs using the largest number of sub-channels are forced to terminate their transmissions, and the other is that SUs using the smallest number of sub-channels are chosen for termination. The analysis is also validated by simulation. Numerical examples show that in both forced-termination policies, the throughput of SUs that are forced to terminate their transmissions degrades as the offered load to the system increases.

ProSpect: A Proactive Spectrum Handoff Framework for Cognitive Radio Ad Hoc Networks without Common Control Channel

Cognitive Radio (CR) technology is a promising solution to enhance the spectrum utilization by enabling unlicensed users to exploit the spectrum in an opportunistic manner. Since unlicensed users are temporary visitors to the licensed spectrum, they are required to vacate the spectrum when a licensed user reclaims it. Due to the randomness of the appearance of licensed users, disruptions to both licensed and unlicensed communications are often difficult to prevent, which may lead to low throughput of both licensed and unlicensed communications. In this paper, a proactive spectrum handoff framework for CR ad hoc networks, ProSpect, is proposed to address these concerns. In the proposed framework, Channel-Switching (CW) policies and a proactive spectrum handoff protocol are proposed to let unlicensed users vacate a channel before a licensed user utilizes it to avoid unwanted interference. Network coordination schemes for unlicensed users are also incorporated into the spectrum handoff protocol design. Moreover, a distributed channel selection scheme to eliminate collisions among unlicensed users in a multiuser spectrum handoff scenario is proposed. In our proposed framework, unlicensed users coordinate with each other without using a Common Control Channel (CCC), which is highly adaptable in a spectrum-varying environment. We compare our proposed proactive spectrum handoff protocol with a reactive spectrum handoff protocol, under which unlicensed users switch channels after collisions with licensed transmissions occur. Simulation results show that our proactive spectrum handoff outperforms the reactive spectrum handoff approach in terms of higher throughput and fewer collisions to licensed users. Furthermore, our distributed channel selection can achieve higher packet delivery rate in a multiuser spectrum handoff scenario, compared with existing channel selection schemes.

Spectrum mobility in cognitive radio networks

Cognitive radio networks (CRNs) offer a promising solution for spectrum scarcity problem by means of dynamic spectrum access. So long as in highly dynamic environments, the secondary user (SU) communication is often interrupted, spectrum mobility is a key feature enabling continuous SU data transmission. Namely, SU performs spectrum handoff by transferring ongoing communication to a vacant channel. This article discusses some important features of spectrum mobility in CRNs. Qualitative comparison of various handoff strategies is considered with regard to handoff latency. Furthermore, essential design issues and associated research challenges are also addressed.

A Fuzzy Logic Based Handoff Technique in Cognitive Radio Network

To address the problem of the under-utilization of the licensed spectrum in cognitive radio networks(CRN), secondary (unlicensed) users(SUs) are allowed to sense and access available spectrum opportunistically without causing harmful interference to primary users(PU)s. Fuzzy logic theory is suitable to deal with the uncertain and heterogeneous information in CRN , there has been some work in this area, however, validate the Fuzzy Logic Control System for a more general context has not been carefully investigated so far. In this paper , a whole process to perform spectrum handoff in a general framework in CRN is described and a concrete spectrum handoff paradigm based on Fuzzy Logic Control System is proposed . The proposed approach is able to make effective spectrum handoff decision on the condition that SUs causing harmful interference to PUs. Simulated results demonstrate that fuzzy logic based power control scheme can increase the transmit efficiency and achieve lower spectrum handoff rates .

Performance Analysis of Cognitive Radio Spectrum Access With Prioritized Traffic

Dynamic spectrum access (DSA) is an important design aspect for cognitive radio networks. Most of existing DSA schemes are to govern unlicensed user (i.e., secondary user, SU) traffic in a licensed spectrum without compromising the transmissions of the licensed users, in which all the unlicensed users are typically treated equally. In this paper, prioritized unlicensed user traffic is considered. Specifically, the unlicensed user traffic is divided into two priority classes (i.e., high and low priority). We consider a general setting in which the licensed users' transmissions can happen at any time instant. Therefore, the DSA scheme should perform spectrum handoff to protect the licensed user's transmission. Different DSA schemes (i.e., centralized and distributed) are considered to manage the prioritized unlicensed user traffic. These DSA schemes use different handoff mechanisms for the two classes of unlicensed users. We also study the impact of subchannel reservation for high-priority SUs in both DSA schemes. Each of the proposed DSA schemes is analyzed using a continuous-time Markov chain. For performance measures, we derive blocking probability, the probability of forced termination, call completion rate, and mean handoff delay for both high- and low-priority unlicensed users. The numerical results are verified using simulations.

A survey on dynamic spectrum access protocols for distributed cognitive wireless networks

With the rapid development of wireless communications technologies, radio spectrum has become a type of extremely scarce resources in meeting the increasing demands for broadband wireless services. However, the traditional static spectrum allocation policy leads to severe spectrum underutilization and spectrum shortage problems. The cognitive radio (CR) technology can detect the occupancy of the spectrum and enable the dynamic spectrum access (DSA) to fill the spectrum hole caused by the static allocation policy, and thus has been widely recognized as an efficient approach to solve the above problems. The distributed cognitive wireless network (CWN), which does not have central entities, is one of the major networking architectures applying the CR technology. Correspondingly, the design of DSA in distributed CWNs is crucial, yet challenging, to increasing the utilization efficiency of the wireless spectrum with dynamically-varying occupancy statuses. In this article, we present a survey on DSA protocols for distributed CWNs. In particular, we first address the challenges in the design and implementation of distributed DSA protocols. Then, we categorize the existing distributed DSA protocols based on different criteria, such as spectrum sharing modes, spectrum allocation behaviors, spectrum access modes, the usage of common control channel, spectrum usage strategies, the number of radios, and spectrum sensing techniques. We also discuss the advantages and disadvantages of each category under diverse classification criterion. Moreover, we make a comprehensive survey of the state-of-the-art distributed DSA protocols using different spectrum access modes, which can be categorized into contention-based, time-slotted, and hybrid protocols. Through the study, we find out that most of distributed DSA protocols fall into the contention-based and hybrid protocols. In addition, the ongoing standardization efforts are also reviewed. Finally, several open research issues for the distributed DSA protocols are presented, such as spectrum handoff based protocols, spectrum prediction based protocols, adaptation of the spectrum-sharing modes, protocols with cooperative spectrum sensing, as well as distributed collision avoidance mechanisms.

Energy-Efficient Spectrum Sensing and Access for Cognitive Radio Networks

We consider a cognitive radio system with one secondary user (SU) accessing multiple channels via periodic sensing and spectrum handoff. We propose an optimal spectrum sensing and access mechanism such that the average energy cost of the SU, which includes the energy consumed by spectrum sensing, channel switching, and data transmission, is minimized, whereas multiple constraints on the reliability of sensing, the throughput, and the delay of the secondary transmission are satisfied. Optimality is achieved by jointly considering two fundamental tradeoffs involved in energy minimization, i.e., the sensing/transmission tradeoff and the wait/switch tradeoff. An efficient convex optimization procedure is developed to solve for the optimal values of the sensing slot duration and the channel switching probability. The advantages of the proposed spectrum sensing and access mechanism are shown through simulations.

Neuro-fuzzy-based hand-off and opportunistic spectrum access for cognitive cooperative network

This paper investigates neuro-fuzzy (NF)-based opportunistic spectrum access and spectrum hand-off (HO) for a cognitive cooperative network (CCN). The main aim is to increase the average throughput of the CCN. Secondary users (SUs) in the CCN are scheduled using α-proportional scheduling. The NF α-based algorithm enables each SU to determine the most appropriate channel for its data transmission. SUs keep their transmission power below the interference temperature through power control and do not interfere with the normal operation of primary radio network (PRN). If the quality of service (QoS) of the SU is not obtained, a HO occurs. Mamdani-adaptive neuro-fuzzy inference system (M-ANFIS) is used to construct spectrum access and HO controllers. The proposed algorithm is compared with the existing algorithms. Performance evaluations clearly reveal that the outage probability is reduced and average throughput of the CCN is increased.

Cognitive Learning-Based Spectrum Handoff for Cognitive Radio Network

In cognitive radio network, spectrum handoff occurs when primary user appears in the licensed band which is occupied by the cognitive user. Spectrum handoff aims to help cognitive user find suitable channel to resume the unfinished transmission as quickly as possible. In this paper, we propose a cognitive learning algorithm which can be used to decide the order of channel-sensing when the cognitive user needs to carry on spectrum handoff. Both theoretical analysis and simulation results show that using the cognitive learning algorithm to predict the channel status can reduce the average spectrum handoff time compared with the random access algorithm. Index Terms—Spectrum-handoff, average handoff time, cognitive learning algorithm.

Coordination of multi-link spectrum handoff in multi-radio multi-hop cognitive networks

In cognitive networks, spectrum handoff occurs when primary users reclaim their rights to access their licensed spectrum. When links perform spectrum handoff, their communication may be interrupted for a certain period and incurs spectrum handoff delay. Existing work only considered the problem of minimizing spectrum handoff delay of a single link in single-hop cognitive networks, referred to as the SH-SLSH problem. This paper studies a more challenging problem (referred to as the SH-MLMH problem) in which multiple links perform spectrum handoff in multi-hop cognitive networks. Assuming each node is equipped with multiple radios and multi-path routing is adopted, the SH-MLMH problem targets at maintaining the network connectivity and minimizing the Total Handoff Completion Time (THCT) by coordinating multiple links to perform spectrum handoff. THCT is defined as the time for all links to finish spectrum handoff. We can keep the communication of switching links uninterrupted by maintaining network connectivity and adopting multi-path routing. To the best of our knowledge, we are the first to study the SH-MLMH problem. We make following contributions in this paper. We prove that the SH-MLMH problem is NP-hard. We propose both centralized and distributed algorithm to solve the SH-MLMH problem. We prove that the centralized algorithm can achieve a logarithmic approximation ratio. The simulation results show that our proposed algorithms not only improve the network throughput but also reduce THCT compared with spectrum handoff without coordination.

Target Channel Sequence Selection Scheme for Proactive-Decision Spectrum Handoff

The problem of target channel sequence selection for proactive-decision spectrum handoff in cognitive radio networks with Poisson arriving primary users is formulated and a target channel sequence selection scheme is proposed. Theoretical analysis shows the proposed scheme can realize the minimum probability of spectrum handoff failure. Simulations show that the proposed scheme outperforms random target channel sequence selection and it performs comparable to the optimal solution in terms of the expected number of handshake trials till success.

A queueing-theoretical framework for QoS-enhanced spectrum management in cognitive radio networks

This article outlines the fundamental modeling issues of opportunistic spectrum access in cognitive radio networks. In particular, we identify the effects of connection-based channel usage on the QoS performance of spectrum management techniques. During the transmission period of a secondary user's connection, the phenomenon of multiple spectrum handoffs due to interruptions of primary users arises quite often. In addition to multiple interruptions, the connection-based channel usage behaviors are also affected by spectrum sensing time, switching between different channels, generally distributed service time, and channel contention between multiple secondary users. An analytical framework based on the preemptive resumption priority M/G/1 queueing theory is introduced to characterize the effects of the above factors simultaneously. The proposed generalized analytical framework can incorporate various system parameters into the design of very broad spectrum management techniques, including spectrum sensing, spectrum decision, spectrum sharing, and spectrum mobility. The applications of this analytical framework on spectrum decision as well as spectrum mobility are discussed, and some open issues using this framework are suggested in this article.