A Cognitive Radio Network (CRN) is a technology that allows unlicensed users to utilise licensed spectrum by detecting an idle band through sensing. How- ever, most research studies on CRNs have been carried out without considering the impact of sensing on the performance and security of CRNs. Sensing is essential for secondary users (SUs) to get hold of free band without interfering with the signal generated by primary users (PUs). However, excessive sensing time for the detection of free spectrum for SUs as well as extended periods of CRNs in an insecure state have adverse effects on network performance. Moreover, a CRN is very vulnerable to attacks as a result of its wireless nature and other unique characteristics such as spectrum sensing and sharing. These attacks may attempt to eavesdrop or modify the contents of packets being transmitted and they could also deny legitimate users the opportunity to use the band, leading to underutilization of the spectrum space. In this context, it is often challenging to differentiate between networks under Denial of Service (DoS) attacks from those networks experiencing congestion. This thesis employs a novel Stochastic Activity Network (SAN) model as an effective analytic tool to represent and study sensing vs performance vs security trade-offs in CRNs. Specifically, an investigation is carried out focusing on sensing vs security vs performance trade-offs, leading to the optimization of the spectrum band’s usage. Moreover, consideration is given either when a CRN experiencing congestion and or it is under attack. Consequently, the data delivery ratio (PDR) is employed to determine if the network is under DoS attack or experiencing congestion. In this context, packet loss probability, queue length and throughput of the transmitter are often used to measure the PDR with reference to interarrival times of PUs. Furthermore, this thesis takes into consideration the impact of scalability on the performance of the CRN. Due to the unpredictable nature of PUsactivities on the spectrum, it is imperative for SUs to swiftly utilize the band as soon as it becomes available. Unfortunately, the CRN models proposed in literature are static and unable to respond effectively to changes in service demands. To this end, a numerical simulation experiment is carried out to determine the impact of scalability towards the enhancement of nodal CRN sensing, security and performance. Atthe instant the band becomes idle and there are requests by SUs waiting for encryption and transmission, additional resources are dynamically released in order to largely utilize the spectrum space before the reappearance of PUs. These additional resources make the same service provision, such as encryption and intrusion detection, as the initial resources. To this end,SAN model is proposed in order to investigate the impact of scalability on the performance of CRN. Typical numerical simulation experiments are carried out, based on the application of the Mobius Petri Net Package to determine the performance of scalable CRNs (SCRNs) in comparison with unscalable CRNs (UCRNs) and associated interpretations are made.

<p>In this thesis we study radio resource management (RRM) in two types of CDMA-based wireless networks, cognitive radio networks (CRNs) and cooperative communication networks. In the networks, all simultaneous transmissions share the same spectrum and interfere with one another. Therefore, managing the transmission power is very important as it determines other aspects of the network resource allocations, such as transmission time and rate allocations. The main objective of the RRM is to efficiently utilize the available network resources for providing the mobile users with satisfactory quality of service (QoS).</p> / Doctor of Philosophy (PhD)

GSM has been developed during more than a decade and has grown to a very complex system. Due to the wide range of functionality, the high capacity and the complexity of the BSC the testing of stability and performance is time consuming. A simulator is needed for these tests as live networks are not available at this stage in the development process. The performance and stability need to be verified for each new release of functionality. This thesis describes a conceptual model of a GSM network. The conceptual model can be used to configure a simulated radio network and to communicate what is simulated on a conceptual level rather than a detailed level. The model presented consists of several sub models. The subscriber model describes the actions and movement of subscribers; the cell model describes the radio conditions experienced by a subscriber moving within one cell; and the cell network model describes the geographical and structural properties of the network. Together the models are used to compose scenarios with the aim to describe varying radio conditions, varying subscriber behavior and varying cell structures. The aim is that different features of the Ericsson base station controller shall be used in the different scenarios. The scenarios represent different parts of a radio network connected to the same base station controller.

Thesis ( M.Sc. (Computer Science)) -- University of Limpopo, 2019 / Cognitive radio network, which enables dynamic spectrum access, addresses the shortage of radio spectrum caused by ever-increasing wireless technology. This allows efficient utilisation of underutilised licenced spectrum by allowing cognitive radios to opportunistically make use of available licenced spectrum. Cognitive radios (CR), also known as secondary users, must constantly sense the spectrum band to avoid interfering with the transmission of the licenced users, known as primary users. Cognitive radios must cooperate in sensing the spectrum environment to avoid environmental issues that can affect the spectrum sensing. However, cooperative spectrum sensing is vulnerable to Byzantine attacks where selfish CR falsify the spectrum reports. Hence, there is a need to design and implement a defence mechanism that will thwart the Byzantine attacks and guarantee correct available spectrum access decisions. The use of extreme studentized deviate (ESD) test together with consensus algorithms are proposed in this study to combat the results of the availability of Byzantine attack in a cognitive radio network. The ESD test was used to detect and isolate falsified reports from selfish cognitive radios during the information sharing phase. The consensus algorithm was used to combine sensing reports at each time k to arrive at a consensus value which will be used to decide the spectrum availability. The proposed scheme, known extreme studentized cooperative consensus spectrum sensing (ESCCSS), was implemented in an ad hoc cognitive radio networks environment where the use of a data fusion centre (DFC) is not required. Cognitive radios make their own data fusion and make the final decision about the availability of the spectrum on their sensed reports and reports from their neighbouring nodes without any assistance from the fusion centre. MATLAB was used to implement and simulate the proposed scheme. We compared our scheme with Attack-Proof Cooperative Spectrum Sensing to check its effectiveness in combating the effect of byzantine attack.

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The 3G and 4G networks have drastically improved availability and quality in data transmission for bandwidth hungry services such as video streaming and location-based services. As 3G networks are very widely deployed, there exists increased capacity requirement and transport channel allocation to simultaneous users under a particular cell. Due to this reason, adequate resources are not available, which in turn degrades both service quality and user experienced quality. This research aims at understanding the characteristics of buffer filling during dedicated channel (DCH) transmission under fixed bit-rate assumptions on a per-user level taking different services into consideration. Furthermore, the resource utilisation in terms of empty buffer durations and user throughput achieved during dedicated channel transmission are also analysed for different data services existing in the mobile networks. The traces are collected from a real network and characteristics of the traffic are analysed prior to understanding its buffer filling in Radio Network Controller (RNC) during downlink data transmission. Furthermore, the buffer is modelled with some series of assumptions on channel bit-rates and simulations are performed taking single user scenario into consideration, for different services with the help of obtained traces as input to the buffer. This research is helpful in understanding the RNC buffer filling for different services, in turn yielding possible understanding on the existing transport channel switching scenario. With the help of analysing the buffer filling for different services and transport channel utilisation, we learn that most of the data services show low DCH utilisation of approximately around 20% and also found to have 80% of the total DCH session duration with empty buffer, causing sub-optimal radio resource utilization.

Radio access technologies for cellular mobile networks are continuously being evolved to meet the future demands for higher data rates, and lower end‐to‐end delays. In the research and development of LTE, radio network simulations play an essential role. The evolution of parallel processing hardware makes it desirable to exploit the potential gains of parallelizing LTE radio network simulations using multithreading techniques in contrast to distributing experiments over processors as independent simulation job processes. There is a hypothesis that parallel speedup gain diminishes when running many parallel simulation jobs concurrently on the same machine due to the increased memory requirements. A proposed multithreaded prototype of the Ericsson LTE simulator has been constructed, encapsulating scheduling, execution and synchronization of asynchronous physical layer computations. In order to provide implementation transparency, an algorithm has been proposed to sort and synchronize log events enabling a sequential logging model on top of non‐deterministic execution. In order to evaluate and compare multithreading techniques to parallel simulation job distribution, a large number of experiments have been carried out for four very diverse simulation scenarios. The evaluation of the results from these experiments involved analysis of average measured execution times and comparison with ideal estimates derived from Amdahl’s law in order to analyze overhead. It has been shown that the proposed multithreaded task‐oriented framework provides a convenient way to execute LTE physical layer models asynchronously on multi‐core processors, still providing deterministic results that are equivalent to the results of a sequential simulator. However, it has been indicated that distributing parallel independent jobs over processors is currently more efficient than multithreading techniques, even though the achieved speedup is far from ideal. This conclusion is based on the observation that the overhead caused by increased memory requirements, memory access and system bus congestion is currently smaller than the thread management and synchronization overhead of the proposed multithreaded Java prototype.

This thesis deals with radio network design for a chosen part of a map. Here map is represented by digital map file, which was created within the project DEM. First step is to calculate distances between points in chosen map. With help of optimization algorithms, appropriate position of transceiver in the map and parameters of radio systems are determined, also final coverage by radio signal, represented by intensity of electric field or received power in whole map. The optimization algorithm is used to find the best solution in terms of input parameters (e.g. power of transmitter, height of mast) and resulting coverage of land by radio signal.

Thesis( M. A. (Computer Science)) -- University of Limpopo , 2021 / In Software Defined Cognitive Radio Network (SDCRN), network security is a significant issue. This issue arises when Software Defined Network (SDN) architecture integrates with the Cognitive Radio Network (CRN) technology. SDN is designed to improve network resource management, while CRN technology is meant at improving spectrum management. These technologies are vulnerable to several malicious attacks. These attacks include Distributed Denial of Service (DDoS) and Primary User Emulation (PUE). Both the DDoS and PUE can be disrupt services in the SDCRN. To curb these attacks, schemes which hardens the security of SDCRN need to be designed. Thus, in this study we propose a security mechanism called Extreme_Controller_Mechanism (XCM) that reduce the effects of DDoS and PUE. The proposed XCM scheme was designed and evaluated in three simulation environment, the OMNeT++, Octave, and MATLAB simulators. The SDCRN data set was generated using the Neural Network back propagation algorithms. The data set was then used in Matlab to evaluate the effectiveness of the prosed XCM scheme. XCM proved to be effective and efficient at detection and prevention of DDoS and PUE attacks in SDCRN. In terms of memory and processor utilisation, XCM proved to the best when compared to other schemes such as the Advanced Support Vector Machine (ASVM) and deep learning convolution network (CDLN). But in terms of detection time, the ASVM was found to be the best performing scheme. Regarding our test for detection rate, false positive and false negative, the XCM, ASVM and CDLM performed the same. The results of the XCM were therefore the best and superior to the ASVM and CDLM. This can be attributed to the fact that the XCM scheme is optimised for DDoS and PUE attacks. We can therefore conclude that our XCM scheme is the best performing scheme compared to the ASVM and CDLN schemes.

No / Cognitive Radio (CR) is an emerging technology used to significantly improve the efficiency of spectrum utilization. Although some spectrum bands in the primary user's licensed spectrum are intensively used, most of the spectrum bands remain underutilized. The introduction of open spectrum and dynamic spectrum access lets the secondary (unlicensed) users, supported by cognitive radios; opportunistically utilize the unused spectrum bands. However, if a primary user returns to a band occupied by a secondary user, the occupied spectrum band is vacated immediately by handing off the secondary user's call to another idle spectrum band. Multiple spectrum handoffs can severely degrade quality of service (QoS) for the interrupted users. To avoid multiple handoffs, when a licensed primary user appears at the engaged licensed band utilized by a secondary user, an effective spectrum handoff procedure should be initiated to maintain a required level of QoS for secondary users. In other words, it enables the channel clearing while searching for target vacant channel(s) for completing unfinished transmission. This paper proposes prioritized proactive spectrum handoff decision schemes to reduce the handoff delay and the total service time. The proposed schemes have been modeled using a preemptive resume priority (PRP) M/G/1 queue to give a high priority to interrupted users to resume their transmission ahead of any other uninterrupted secondary user. The performance of proposed handoff schemes has been evaluated and compared against the existing spectrum handoff schemes. Experimental results show that the schemes developed here outperform the existing schemes in terms of average handoff delay and total service time under various traffic arrival rates as well as service rates.