Mobile Secondary Users Research Articles

Rendezvous in Cognitive Radio Ad hoc Networks: A Survey

Cognitive radio networks (CRNs) cope with spectrum scarcity and underutilisation problem through opportunistic sharing of spectrum and provide dynamic access to the free portions of spectrum allotted to licensed users. Fundamental step during the formation of CRN is the rendezvous process where secondary users (SUs) meet on commonly available channels and establish communication links for information exchange, spectrum management, and data communication. Non-availability of any prior network-related information and non-awareness of the presence of other SUs before the rendezvous process makes rendezvous a non-trivial task. Further, owing to the dynamics in licensed users' activity, diversities in the temporal and geographical location of SUs, absence of central authority, multi-hop architecture and mobility of SUs complicate the rendezvous process. This paper focuses on the taxonomy and challenges relevant to rendezvous phenomena of SUs and provides a brief overview and comparative qualitative analysis of the state-of-the-art rendezvous algorithms designed for CRNs.

Throughput and Delay in Heterogeneous Cognitive Radio Networks with Cooperative Secondary Users

In this paper,1 we investigate the throughput and delay in heterogeneous cognitive radio networks (HCRN), where the data source and the destination (S-D) is heterogeneously distributed following a rank based model and secondary users (SUs) provide relay service for primary users (PUs). We consider two scenarios: 1) PUs and SUs are both static; and 2) PUs are static and SUs are mobile. For scenario 1, we show that the primary network throughput is the same for different heterogeneous extents of S-D distribution owing to the flexible assistance of SUs, while the throughput of secondary networks is proven to be changing with the S-D heterogeneity exponent $\alpha$ , which depicts the variation of different heterogeneous extents of S-D distribution. In addition, the delay of both primary and secondary networks are shown to be altering with $\alpha$ . Further, we reveal that the number of SUs required to assist PUs can be dramatically reduced when considering the S-D heterogeneity, while achieving the same primary network throughput. For scenario 2, we utilize a modified uniform mobility (MUM) model to depict the motion of SUs and mainly focus on the analysis of throughput and delay for primary networks. It shows that the primary network throughput is also free of the heterogeneous extent of S-D distribution, while the delay changes with $\alpha$ . Due to the mobility of SUs, a better delay-throughput tradeoff of primary networks is achieved compared with that in scenario 1.

Performance Evaluation of Joint Path and Spectrum Diversity Based Routing Protocol in Cognitive Radio Ad Hoc Networks under Critical Conditions

Cognitive Radio (CR) technology has been introduced to solve the problems of spectrum underutilization and spectrum scarcity caused by improper spectrum management policies. The main concept of Cognitive Radio Ad Hoc Network (CRAHN) is that, in a wireless ad hoc network, the unlicensed users (or Secondary Users (SUs)) are allowed to access the temporally unused licensed spectrum bands for data communications without harmful interference to the licensed users (or Primary Users (PUs)). In CRAHNs, the mobile SUs communicate with each other without the use of any centralized network infrastructure. Routing in CRAHNs is an important task and faces various challenges including PU interference, frequent network topology changes, energy constraint, volatile bandwidth and fragile connectivity. In this study, an attempt is made to evaluate the performance of the Dual Diversity Cognitive Ad-hoc Routing Protocol (D2CARP) in CRAHNs under critical conditions, i.e., high node mobility rate and number of PUs. The D2CARP protocol is a joint path and spectrum diversity based routing protocol for CRAHNs. The performance evaluation is conducted through simulation using NS-2 simulator. The performance metrics to be considered include average throughput, percentage of packet loss, average end-to-end delay and average jitter. The simulation results prove that the protocol performance is significantly affected in the networks with high number of PUs and mobility rate, leading to high path failure rate and severe service outages.

Cross-Layer Design for Primary User Emulation Attacks Detection in Mobile Cognitive Radio Networks

In this letter, the channel-tap power is utilized as a radio-frequency fingerprint (RF) to completely identify primary user emulation attacks (PUEAs) over multipath Rayleigh fading channels. To accurately know identities of primary users (PUs) and PUEAs, the cross-layer intelligent learning ability of a mobile secondary user (SU) is exploited to establish detection databases by seamlessly combining the quick detection of physical (PHY) layer with the accuracy of higher layer authentication. The proposed method helps PHY layer completely detect the identities of PUs and PUEAs. For SNR = -2 dB and the false alarm probability of 0.1, the SU can detect a PUEA with the detection probability of 0.9673 under the mobile speed of 70 km/h.

Near-Optimal Scheme for Cognitive Radio Networks With Heterogeneous Mobile Secondary Users

In this paper, we study the throughput and delay scaling laws for cognitive radio network with static primary users and heterogeneous mobile secondary users coexist in the unit planar region for both without base-station case and with base-station case. The primary network consists of $n$ randomly and uniformly distributed static primary users with higher priority to access the spectrum. The secondary network consists of $m=(h+1)n^{1+\epsilon}$ heterogeneous mobile secondary users with $h=O(\log n)$ We use standard asymptotic notations in our paper. Consider two nonnegative function $f(\cdot)$ and $g(\cdot)$ : (1) $f(n)=o(g(n))$ means $\lim_{n\rightarrow\infty}f(n)/\break g(n)= 0$ . (2) $f(n)=O(g(n))$ means $\lim_{n\rightarrow\infty}f(n)/g(n) . (3) $f(n)=\omega(g(n))$ means $\lim_{n\rightarrow\infty}f(n)/g(n)=\infty$ . (4) $f(n)=\Omega(g(n))$ means $\lim_{n\rightarrow\infty}f(n)/g(n) > 0$ . (5) $f(n)=\Theta(g(n))$ means $f(n)=O(g(n))$ and $g(n)=O(f(n))$ . (6) $f(n)=\mathtilde{\Theta}(g(n))$ means that $f(n)=\Theta(g(n))$ when poly-logarithmic factors are ignored.

Evolution handoff strategy for real-time video transmission over practical cognitive radio networks

The transmission delay of real-time video packet mainly depends on the sensing time delay (short-term factor) and the entire frame transmission delay (long-term factor). Therefore, the optimization problem in the spectrum handoff process should be formulated as the combination of microscopic optimization and macroscopic optimization. In this paper, we focus on the issue of combining these two optimization models, and propose a novel Evolution Spectrum Handoff (ESH) strategy to minimize the expected transmission delay of real-time video packet. In the micro-optimized model, considering the tradeoff between Primary User's (PU's) allowable collision percentage of each channel and transmission delay of video packet, we propose a mixed integer non-linear programming scheme. The scheme is able to achieve the minimum sensing time which is termed as an optimal stopping time. In the macro-optimized model, using the optimal stopping time as reward function within the partially observable Markov decision process framework, the EHS strategy is designed to search an optimal target channel set and minimize the expected delay of packet in the long-term real-time video transmission. Meanwhile, the minimum expected transmission delay is obtained under practical cognitive radio networks' conditions, i.e., secondary user's mobility, PU's random access, imperfect sensing information, etc‥ Theoretical analysis and simulation results show that the ESH strategy can effectively reduce the transmission delay of video packet in spectrum handoff process.

SoRoute: a reliable and effective social-based routing in cognitive radio ad hoc networks

A cognitive radio ad hoc network (CRAHN) can be considered as a special delay tolerant network (DTN) that is composed of mobile secondary users (SUs) with social characteristics. Given intermittent connectivity and spectrum availability, it is a challenging issue regarding how to transmit messages between SUs in a reliable and effective way in CRAHNs. To tackle this challenge, we propose a social-aware opportunistic routing and relay selection scheme, called SoRoute, which first predicts the link reliability based on a new social-relationship-aware mobility model and then fuses the relationships of SUs to make a routing and relay decision. In our design, different prediction schemes are employed for the nodes with different relationships. A message is forwarded to the relay node with the largest encounter probability with the destination. The evaluation results demonstrate that our social-based opportunistic routing scheme significantly improves the performance compared to the existing routing schemes such as Direct Delivery, First Contact, MaxProp, and Prophet.

Fuzzy Based PC-PUSH in CR-MANETs

In cognitive radio (CR), the secondary user (SU) needs to hand off its ongoing communication to an idle channel in order to avoid interference to the primary user (PU). Spectrum hand off issue becomes challenging in CR mobile ad hoc networks (CR-MANETs) because of the uncertainty in spectrum availability, broad range of spectrum bands and lack of central entity. The purpose of this study is to design a unified spectrum handoff (USH) scheme for CR-MANETs that considers the spectrum heterogeneity and its availability over time and space. A local flow hand off is performed when spectrum hand off cannot be carried out due to the SUs mobility. To improve further USH, preemptive unified spectrum handoff (PUSH) algorithm is proposed in which two different preemptive hand off threshold regions are defined. The PUSH algorithm also predicts the cognitive link availability considering the PU interference boundary. Although the PUSH scheme improves the hand off performance, the number of spectrum hand offs due to the PU activity should be reduced in this scheme. Therefore, the PC-PUSH (Power Controller-PUSH) scheme is proposed in which the fuzzy logic is used to improve the PUSH in terms of the number of spectrum handoffs because of the PU activity. The PC-PUSH decreases the interference to the PUs, while reducing the number of spectrum handoffs. The results show that the proposed scheme improves the link maintenance probability, decreases the hand off delay, and reduces the number of spectrum handoffs.

An energy‐preserving spectrum access strategy in mobile cognitive radio networks

ABSTRACTCognitive radio techniques provide potential solutions to the spectrum crisis problem. In cognitive radio networks, a secondary user (SU) opportunistically accesses the authorised spectrum of a primary user (PU) to transmit its data. In order to avoid collisions with the PU, the SU needs to frequently detect the status of the channel before accessing the spectrum. However, frequent detection of channel status consumes a lot of energy, which is unaffordable for mobile SUs. In this paper, we investigate how to preserve the limited energy of SUs in mobile cognitive networks. Besides the sensing and transmitting actions used in traditional spectrum access policies, we introduce a new sleeping action with which mobile SUs can better exploit the trade‐off between their consumption and data transmission throughput. We define a utility function to characterise the effect of sleeping actions, in which correct sleeping actions are rewarded for preserving energy, and incorrect sleeping actions are penalised for wasting data transmission opportunities. We prove that, in the meaning of maximising the mean benefit, the utility function exhibits a threshold‐based structure. Based on this structure, we design a new spectrum access strategy with which mobile SUs can chose their optimal actions to achieve the best trade‐off between energy consumption and throughput. Simulation results show that our spectrum access strategy greatly reduces energy consumption of mobile SUs by up to 85% and, meanwhile, incurs nearly the same PU collision rate and throughput as in state‐of‐the‐art solutions. Copyright © 2013 John Wiley & Sons, Ltd.

Proactive integrated handoff management in cognitive radio mobile ad hoc networks

In cognitive radio networks, the secondary users (SUs) switch the data transmission to another empty spectrum band to give priority to primary users (PUs). In this paper, channel switching in cognitive radio mobile ad hoc networks (CR-MANETs) through an established route is modeled. The probability of channel availability in this route is calculated based on the PU's activity, SU's mobility, and channel heterogeneity. Based on the proposed model, the channel and link availability time are predicted. These predictions are used for channel assignment in the proposed channel allocation scheme. A handoff threshold as well as a life time threshold is used in order to reduce the handoff delay and the number of channel handoffs originating from the short channel usage time. When the channel handoff cannot be done due to the SU's mobility, the local flow handoff is performed to find an appropriate node in the vicinity of a potential link breakage and transfer the current data flow to it. The local flow handoff is performed to avoid possible flow disruption and also to reduce the delay caused by the link breakage. The study reveals that the channel heterogeneity and SU's mobility must be considered as important factors, which affect the performance of the handoff management in the CR-MANETs. The results emphasize on the improvement of the route maintenance probability after using the local flow handoff. It is also stated that the amounts of handoff requirement and handoff delay are decreased after using the predicted channel usage life time and handoff threshold time.

Dynamic spectrum sharing in cognitive radio networks using truthful mechanisms and virtual currency

In cognitive radio networks, there are scenarios where secondary users (SUs) utilize opportunistically the spectrum originally allocated to primary users (PUs). The spectrum resources available to SUs fluctuates over time due to PUs activity, SUs mobility and competition between SUs. In order to utilize these resources efficiently spectrum sharing techniques need to be implemented. In this paper we present an approach based on game-theoretical mechanism design for dynamic spectrum sharing. Each time a channel is not been used by any PU, it is allocated to SUs by a central spectrum manager based on the valuations of the channel reported by all SUs willing to use it. When an SU detects a free channel, it estimates its capacity according to local information and sends the valuation of it to the spectrum manager. The manager calculates a conflict-free allocation by implementing a truthful mechanism. The SUs have to pay for the allocation an amount which depends on the set of valuations. The objective is not to trade with the spectrum, but to share it according to certain criteria. For this, a virtual currency is defined and therefore monetary payments are not necessary. The spectrum manager records the credit of each SU and redistributes the payments to them after each spectrum allocation. The mechanism restricts the chances of each SU to be granted the channel depending on its credit availability. This credit restriction provides an incentive to SUs to behave as benefit maximizers. If the mechanism is truthful, their best strategy is to communicate the true valuation of the channel to the manager, what makes possible to implement the desired spectrum sharing criteria. We propose and evaluate an implementation of this idea by using two simple mechanisms which are proved to be truthful, and that are tractable and approximately efficient. We show the flexibility of these approach by illustrating how these mechanisms can be modified to achieve different sharing objectives which are trade-offs between efficiency and fairness. We also investigate how the credit restriction and redistribution affects the truthfulness of these mechanisms.

Designing Two-Dimensional Spectrum Auctions for Mobile Secondary Users

Dynamic spectrum access by non-licensed users has emerged as a promising solution to address the bandwidth scarcity challenge. In a secondary spectrum market, primary users lease chunks of unused spectrum to secondary users. Auctions perform as one of the natural mechanisms for allocating the spectrum, generating an economic incentive for the licensed user to relinquish channels. Existing spectrum auction designs, while taking externality introduced by interference into account, fail to consider the potential mobility of secondary users, which leads to another dimension of externality: mobile communication motivates a secondary user to exclusively occupy a channel, i.e., forbidding channel reuse in its mobility region. In this work, we design two expressive auctions for mobility support, by introducing two-dimensional bids that reject a secondary user's willingness to pay for exclusive and non-exclusive channel usage, for the single-channel and multiple-channel scenarios, respectively. In the outcome of our 2D auctions, a channel is either monopolized or simultaneously reused without interference, whereas a secondary user can be mobile or is regulated to be static. We prove the existence of desirable equilibria in both auctions, where 1/10 and c/7(1+c) of optimal social welfare are guaranteed to be recoverable, respectively (c is the number of channels).

Power Allocation for a Mobile Secondary User in OFDM based Cognitive Radio

Power Allocation for a Mobile Secondary User in OFDM based Cognitive Radio

Opportunistic Scheduling with Reliability Guarantees in Cognitive Radio Networks

We develop opportunistic scheduling policies for cognitive radio networks that maximize the throughput utility of the secondary (unlicensed) users subject to maximum collision constraints with the primary (licensed) users. We consider a cognitive network with static primary users and potentially mobile secondary users. We use the technique of Lyapunov optimization to design an online flow control, scheduling, and resource allocation algorithm that meets the desired objectives and provides explicit performance guarantees.