Channel assembling and resource allocation in multichannel spectrum sharing wireless networks

Submitted in fulfilment of the academic requirements for the degree of Doctor of Philosophy (Ph.D.) in Engineering, in the School of Electrical and Information Engineering, Faculty of Engineering and the Built Environment, at the University of the Witwatersrand, Johannesburg, South Africa, 2017The continuous evolution of wireless communications technologies has increasingly imposed a burden on the use of radio spectrum. Due to the proliferation of new wireless networks applications and services, the radio spectrum is getting saturated and becoming a limited resource. To a large extent, spectrum scarcity may be a result of deficient spectrum allocation and management policies, rather than of the physical shortage of radio frequencies. The conventional static spectrum allocation has been found to be ineffective, leading to overcrowding and inefficient use. Cognitive radio (CR) has therefore emerged as an enabling technology that facilitates dynamic spectrum access (DSA), with a great potential to address the issue of spectrum scarcity and inefficient use. However, provisioning of reliable and robust communication with seamless operation in cognitive radio networks (CRNs) is a challenging task. The underlying challenges include development of non-intrusive dynamic resource allocation (DRA) and optimization techniques. The main focus of this thesis is development of adaptive channel assembling (ChA) and DRA schemes, with the aim to maximize performance of secondary user (SU) nodes in CRNs, without degrading performance of primary user (PU) nodes in a primary network (PN). The key objectives are therefore four-fold. Firstly, to optimize ChA and DRA schemes in overlay CRNs. Secondly, to develop analytical models for quantifying performance of ChA schemes over fading channels in overlay CRNs. Thirdly, to extend the overlay ChA schemes into hybrid overlay and underlay architectures, subject to power control and interference mitigation; and finally, to extend the adaptive ChA and DRA schemes for multiuser multichannel access CRNs. Performance analysis and evaluation of the developed ChA and DRA is presented, mainly through extensive simulations and analytical models. Further, the cross validation has been performed between simulations and analytical results to confirm the accuracy and preciseness of the novel analytical models developed in this thesis. In general, the presented results demonstrate improved performance of SU nodes in terms of capacity, collision probability, outage probability and forced termination probability when employing the adaptive ChA and DRA in CRNs.CK201

Integrating Two Feedback Queuing Discipline into Cognitive Radio Channel Aggregation

Queuing regime is one outstanding approach inimproving channel aggregation. If well designed and incorporatedwith carefully selected parameters, it enhances the smoothrollout of fifth/next generation wireless networks. While channelaggregation is the merging of scattered TV white space (spectrumholes) into one usable chunk for secondary users (SU). Thequeuing regime ensures that these unlicensed users (SUs) traffic/services are not interrupted permanently (blocked/dropped orforced to terminate) in the event of the licensed users (primaryuser) arrival. However, SUs are not identical in terms of trafficclass and bandwidth consumption hence, they are classified asreal time and non-real time SU respectively. Several of thesestrategies have been studied considering queuing regime with asingle feedback queuing discipline. In furtherance to previousproposed work with single feedback queuing regime, this paperproposes, develops and compares channel aggregation policieswith two feedback queuing regimes for the different classes ofSUs. The investigation aims at identifying the impacts of the twofeedbackqueuing regime on the performance of the secondarynetwork such that any SU that has not completed its ongoingservice are queued in their respective buffers. The performance isevaluated through a simulation framework. The results validatethat with a well-designed queuing regime, capacity, access andother indices are improved with significant decrease in blockingand forced termination probabilities respectively

Dynamic Flow-Adaptive Spectrum Leasing with Channel Aggregation in Cognitive Radio Networks

Cognitive radio networks (CRNs), which allow secondary users (SUs) to dynamically access a network without affecting the primary users (PUs), have been widely regarded as an effective approach to mitigate the shortage of spectrum resources and the inefficiency of spectrum utilization. However, the SUs suffer from frequent spectrum handoffs and transmission limitations. In this paper, considering the quality of service (QoS) requirements of PUs and SUs, we propose a novel dynamic flow-adaptive spectrum leasing with channel aggregation. Specifically, we design an adaptive leasing algorithm, which adaptively adjusts the portion of leased channels based on the number of ongoing and buffered PU flows. Furthermore, in the leased spectrum band, the SU flows with access priority employ dynamic spectrum access of channel aggregation, which enables one flow to occupy multiple channels for transmission in a dynamically changing environment. For performance evaluation, the continuous time Markov chain (CTMC) is developed to model our proposed strategy and conduct theoretical analyses. Numerical results demonstrate that the proposed strategy effectively improves the spectrum utilization and network capacity, while significantly reducing the forced termination probability and blocking probability of SU flows.publishedVersio

Channel assembling policies for heterogeneous fifth generation (5G) cognitive radio networks.

Doctor of Philosophy in Electronic Engineering. University of KwaZulu-Natal, Durban 2016.Abstract available in PDF file

Parallelising reception and transmission in queues of secondary users

In a cognitive radio network, the secondary users place the packets to be transmitted on a queue to control the order of arrival and to adapt to the network state. Previous conceptionsassigned to each secondary user a single queue that contains both received and forwarded packets. Our present article divides the main queue into two sub queues: one to receive the arrived packets and the other to transmit the available packets. This approach reduces the transmission delay due on the one hand; to the shifting of data placed on the single queue, and on the other hand; to the sequential processing of reception and transmission, in theprevious designs. All without increasing the memory capacity of the queue, in the new approach

Enhancing the Performance of Low Priority SUs Using Reserved Channels in CRN

Cognitive radio networks (CRNs) are considered a promising solution for spectrum resources scarcity and efficient channel utilization. In this letter, multi-dimensional analytical Markov model based on reservation channel access scheme and channel aggregation method is proposed to enhance spectrum utilization, capacity of low priority secondary users (SUs) and reducing handoff probability of SUs. Moreover, the proposed method improves the performance of high priority SUs by providing the capability to resume the connection after dropping. The numerical results indicate that the modified reservation access model can enhance the performance of SUs compared to the traditional basic random access model

Performance optimization of the mini-slotted spectrum allocation strategy with imperfect sensing

In this paper, in order to improve the normal throughput of secondary user packets and reduce the spectrum switching frequency in cognitive radio networks, a novel mini-slotted spectrum allocation strategy is proposed. Due to the mistake detection in practice, the secondary user packet and the primary user packet will occupy the spectrum simultaneously, i.e., a collision will occur on the spectrum. A heterogeneous discrete-time queueing model with possible collisions is established to model the system operation. Taking into account imperfect sensing results, the transition probability matrix is constructed. Applying the method of matrix geometric solution, performance measures in terms of the disruption rate of primary user packets, the normal throughput of secondary user packets, the spectrum switching rate and the average latency of secondary user packets are given. Numerical results are provided to verify the effectiveness of the proposed mini-slotted spectrum strategy. Finally, by trading off different system performance measures, a net benefit function is constructed, then the slot size is optimized