Optimizing dynamic spectrum allocation for cognitive radio networks using hybrid access scheme

Cognitive radio technology is considered to be an effective solution to improve the spectrum utilization efficiency. The dynamic spectrum allocation algorithm assigns the available spectrum to the secondary users. In this paper, we propose a spectrum allocation algorithm based on the graph-coloring theory. Unlike some already existed allocation algorithm, our algorithm considers the bandwidth matching between secondary users' bandwidth requirements and the available channels. The interference avoidance to the primary users is also taken into account. Our objective is to optimize the total spectrum reward under the premise of fully protecting the primary users. Simulation results prove that this algorithm can improve the total spectrum reward, the satisfaction rate of secondary users, the protection rate of primary users, and the spectrum allocation efficiency.

QoS-aware distributed spectrum sharing for heterogeneous wireless cognitive networks

For wideband Cognitive Radio (CR) devices, the availability of primary user (PU) activity prediction model can save sensing energy and time, track spectrum variations, reduce switching overhead, improve spectrum usage and lower interference to PU. Using Universal Software Radio Peripheral (USRP) generated data, this paper has verified the superiority of Hidden Semi-Markov model (HSMM) over the conventional HMM in learning and predicting temporal correlations in PU spectral activity under non-geometric distribution of state durations. Numerical simulations further show that in a coordinated multi-SU/PU scenario, compared to the traditional random Carrier Sense Multiple Access (CSMA), the proposed HSMM-dynamic spectrum allocation (DSA) protocol significantly reduces aggregate interference to PU. Depending on the number of SU, there exists a trade-off between “interference-free coexistence with PU” and “self-existence of a large number of SU”. This problem is addressed further by statistically modeling probability of free channels and using it to optimize the number of SU that can be allocated. The proposed scheme outperforms the conventional sensing based dynamic spectrum allocation (DSA) in terms of reduced PU interference, lower spectrum handoff requirements and higher spectrum utilization efficiency. The predictive optimized HSMM-DSA can be used as an additional layer of intelligence for any CR device for efficient spectrum sharing.

The emerging feature-rich and high-data-rate wireless applications have put increasing demand on radio spectrum. The scarcity of spectrum and the inefficiency in its usage, as caused by the current radio spectrum regulations, necessitate the development of new dynamic spectrum allocation policies to better exploit the existing spectrum. The current spectrum allocation regulations assign specific bands to particular services, and grant licensed band access to licensed users only. Cognitive Radio (CR) will revolutionize the way spectrum is allocated. In a CR network, the intelligent radio part allows unlicensed users (secondary users) to access spectrum bands licensed to primary users, while avoiding interference with them. In this scheme, a secondary user can use spectrum sensing hardware/software to locate spectrum portions with reduced primary user activity or idle spectrum slots, select the best available channel, coordinate access to this channel with other secondary users, and vacate the channel when a primary user needs it. To achieve this, the transceiver in a CR system should have awareness of the radio environment in terms of spectrum usage, power spectral density of transmitted/received signals, and wireless protocol signaling, should be able to adaptively tune system parameters such as transmit power, carrier frequency, and modulation strategy. The transceiver should also be ended with an antenna system that can simultaneously operate over a wide frequency band (sensing) and a chosen narrow band (communication), or operate over an ultra-wide frequency band while possibly blocking signals in a narrow frequency range. Ultra-wideband (UWB) is a transmission technique that uses pulses with a very short time duration across a very large frequency portion of the spectrum. UWB is different from other radio frequency communication techniques in that it does not use RF carriers, but instead employs modulated high frequency pulses of low power with a duration of less than 1 nanosecond. From the perspective of other communication systems, the UWB transmissions are part of the low power background noise. Therefore UWB promises to enable the usage of licensed spectrum without harmful interference to primary communication systems, and can be used as an enabling technology for implementing CR. In this chapter, we offer a general overview of Cognitive Radio and dynamic spectrum access, discuss the advantages of using UWB as an enabling technology for CR, and give

We focus on dynamic crosstalk-aware lightpath provisioning in translucent space-division multiplexing (SDM) elastic optical networks, in which spectral super-channels are carried over multi-core fibers (MCFs), distance-adaptive transmission is considered, and back-to-back (B2B) signal regeneration is applied. We aim at establishing lightpaths for connection requests in such a way that the inter-core crosstalk (XT) impairment affecting the quality of lightpaths in the network does not exceed allowable threshold levels. To this end, we propose and analyze a method that is based on per-core static/worst-case XT estimation. This method is implemented in a dynamic XT-aware routing, spatial mode, and spectrum allocation (RSSA) algorithm, which is used to solve the lightpath provisioning problem in an efficient way, such that the bandwidth blocking probability is minimized. The performed extensive simulation experiments in realistic network scenarios show a significant impact of this method on network performance and motivate for its application instead of commonly used per-fiber worst-case XT estimation.

Empowered by the cognitive radio technology, and motivated by the sporadic channel utilization, both spatially and temporally, dynamic spectrum access networks (also referred to as cognitive radio networks and next generation wireless networks) have emerged as a solution to improve spectrum utilization and provide more flexibility to wireless communication. A cognitive radio network is composed of wireless users, referred to as secondary users, which are allowed to use a given licensed spectrum band as long as there are no primary, licensed, users occupying this band in their vicinity. This restricted spectrum access strategy leads to heterogeneity in channel availability among secondary users. Heterogeneity in channel availability forms a significant source of performance degradation for cognitive radio networks, and poses a great challenge on protocol design. In this dissertation, we propose spectrum allocation algorithms that take this heterogeneity property and its effect on the network performance into consideration. The spectrum allocation solutions proposed in this dissertation address three major objectives in cognitive radio mesh networks. The first objective is maximizing the network coverage, in terms of the total number of served clients, and at the same time simplifying the communication coordination function. To address this objective, we proposed a received based channel allocation strategy that alleviates the need for a common control channel, thus simplifying the coordination function, and at the same time maximizes the number of clients served with link reliability guarantees. We show the superiority of the proposed allocation strategy over other existing strategies. The second objective is improving the multicast throughput to compensate for the performance degradation caused by the heterogeneity in channel availability. We proposed a

Development of dynamic spectrum access and allocation techniques recently have made feasible the vision of cognitive radio systems. However, a fundamental question arises: Why would licensed primary users of a spectrum band allow secondary users to share the band and degrade performance for them? And how can we design incentive schemes to enable spectrum sharing using cooperative communication schemes? We consider a principal-agent framework, and propose a contracts-based approach. First, a single primary and a single secondary transmitter-receiver pair with a Gaussian interference channel between them are considered. The two users may contract to cooperate in doing successive-interference cancellation. Under full information, we give equilibrium contracts for various channel conditions. These equilibrium contracts yield Pareto-optimal rate allocations when physically possible. We then allow for time-sharing and observe that in equilibrium contracts there is no actual time-sharing. We show that the designed contracts can be made robust to deviation by either user post-contract. We also show how these can be extended to multiple secondary users. We show that under hidden information, when the primary user has a dominant role, neither user has an incentive to lie about their direct channel coefficients, or manipulate the cross channel measurements, and Pareto-optimal outcomes are achieved at equilibrium.

In cognitive radio (CR) networks, proper power controlling is of importance to ensure efficient operation of both primary and secondary networks. The previous work on power control in cognitive radios has mainly focused on the interactions among a set of secondary users while ignoring the influence of primary users. In [1], we introduced a new game model for power control in cognitive radios by incorporating the primary users into the player set of the game. In this new framework, the primary users are rewarded (for example, monetarily) for sharing their licensed spectrum with secondary users. In our proposed game formulation, they achieve this by setting a reasonable interference cap (IC) for the secondary users. However, the primary users are to be severely penalized if they do not meet their transmission quality. To ensure this, an exponential pricing term is incorporated into their utility function. Simultaneously, the secondary users aim to achieve energy efficient transmissions while not introducing too much interference to the primary as well as other secondary users. In this paper, we investigate the CR system design aspects based on our proposed new game theoretic spectrum sharing framework. In particular, the performance of the system is compared under different linear detector schemes at the secondary receiver, namely, the matched filter (MF) and the linear MMSE (LMMSE) receivers.

A RMSCA algorithm for space division multiplexing elastic optical networks with core switching

Cognitive radio has developed as a novelapproach that enables efficient use of unexploited or underutilized parts of frequency bands. Wireless cognitive radio networks aim to speculativelyfeat the empty or underutilized parts of the spectrum by listening to the frequency bands of their secondary users with various sensing techniques. For this purpose, the process of switching from a frequency channel used by secondary users for various reasons to another free channel is defined as spectrum allocation. At the beginning of the cases where the spectrum allocation takes place, the frequency channels allocated to secondary users are put back into the service of primary users. Severaltechniques are utilized for the spectrum allocation process decided by the access points. Artificial intelligence techniques are used to make the decision to realize the spectrum allocation transaction. In this paper, we present a fuzzy logic based spectrum allocation technique and thus ensure better management. The simulation results shows the performance in terms of received signal strength and signal to noise power.

Dynamic Routing and Spectrum Allocation Algorithms in Elastic Optical Networks for Satellite Internet (Invited)

We focus on the problem of crosstalk-aware lightpath provisioning in a dynamic, spectrally and spatially flexible optical network, in which spectral super-channels are carried over multi-core fibers with distance-adaptive transmission. The problem involves establishing a lightpath for a connection such that the inter-core crosstalk (XT) between the new lightpath and any exiting lightpaths does not cause the quality of transmission of any of these light-paths to be below an acceptable level. To this end, we analyze and compare two broad classes of schemes that aim to ensure acceptable XT levels in the network. The first is based on static/worst-case XT, whereas the second uses dynamic/ precise XT estimation. These methods are implemented in a dynamic XT-aware routing, spatial mode, and spectrum allocation algorithm that solves the lightpath-provisioning problem efficiently with the goal of minimizing bandwidth blocking. Extensive simulation experiments performed in realistic network scenarios indicate that the utilized XT estimation methodology has a significant impact on network performance, with the precise XT approach favored over the worst-case XT strategy.

In cognitive radio networks, secondary users need to access the licensed spectrum while neither disturbing the transmissions of the primary users nor introducing much interference to other secondary users. Hence, proper power controlling is of paramount importance to ensure efficient system operation. The previous work on power control in cognitive networks mainly focuses on the interactions among a set of secondary users. The primary users' influence is rarely considered. In this paper, a new power control game model is formulated, by including the primary users into the player set of the game. The primary users are rewarded for sharing their licensed spectrum with secondary users by setting a reasonable interference cap for the secondary transmissions. However, we ensure a minimum required Quality of Service (QoS) for primary users by severely penalizing their utility if their required transmission quality is not met. Simultaneously, the secondary users achieve energy efficient transmissions while not introducing much interference to both the primary and other secondary users. We prove that the proposed cognitive power control game has a unique Nash equilibrium (NE). The numerical examples show that the proposed game theoretical power control algorithm can provide the secondary users with energy efficient transmissions and the primary users with reasonable monetary rewards, while not compromising their required QoS.

Recent developments in wireless communications and the emergence of high data rate services have consumed almost all the accessible spectrum making it a very scarce radio resource. Spectrum from very low frequencies to several GHz range has been either dedicated to a particular service or licensed to its providers. It is very difficult to find sufficient bandwidth for new technologies and services within accessible spectrum range. Contrarily, studies in different parts of the world reveal that the licensed and/or dedicated spectrum is underutilized leaving unused bands at different frequencies. These idle bands; however, cannot be used by non-licensed users due to current spectrum management practices throughout the world. This fact forced the regulatory authorities and academia to rethink the spectrum allocation policies. This resulted in the idea of spectrum sharing systems, generally known as cognitive radio, in which non-licensed or secondary users can access the spectrum licensed to the primary users. Many techniques and procedures have been suggested in the recent years for smooth and transparent spectrum sharing among the primary and secondary users. The most common approach suggests that the secondary users should perform spectrum sensing to identify the unused bands and exploit them for their own transmission. However, as soon as the primary user becomes active in that band, secondary transmission should be switched off or moved to some other idle band. A major problem faced by the secondary users is that the average width of the idle bands available at different frequencies is not large enough to support high data rate wireless applications and services. A possible solution is to integrate few idle bands together to generate a larger bandwidth. This technique is also known as spectrum aggregation. Generally, it is proposed to build the transmitter with multiple radio frequency chains which are activated according to the availability of idle bands. A combiner or aggregator is then used to transmit the signal through the antenna. Similarly, a receive antenna can be realized through multiple receive RF chains through a separator or splitter. Another option is to use orthogonal frequency division multiplexing in which sub-carriers can be switched on and off based on unused and active primary bands, respectively. These solutions are developed and analyzed for direct point to point links between the nodes. In this work, we analyze spectrum aggregation for indirect links through multiple relays. We propose a simple mechanism for idle band integration in a secondary cooperative network. Few relays in the system partly facilitate the source to aggregate available idle bands and collectively all the involved relays provide an aggregated larger bandwidth for the source to destination link. We analyze two commonly used forwarding schemes at the relays; namely, amplify-and-forward and decode-and-forward. We focus on outage probability of the scheme and derive a generalized closed form expression applicable to both scenarios. We analyze the system performance under different influential factors and reveal some important trade-offs.

In a cognitive radio (CR) system, an achievable throughput of secondary users (SU) primarily depends on the activity level of primary users (PU) in the channels. More the PU are active in the channels, lesser the opportunity of SU transmission. Protecting the PU from a harmful interference introduced by SU is also a challenging task specifically when multiple PU and SU exist in the system. The trade-off between SU sum throughput and PU occupancy level has been thoroughly analysed considering a zero interference tolerance of an interweave CR system. PU activity level in the channel is measured in terms of duty cycle (DC). The interplay between DC of PU and throughput of SU is presented here for Poisson and binomial distribution based SU arrival processes. The results identify the opportunistic channels when SU aims a particular sum throughput and find the optimal numbers of SU in the channels for various DC.