Cognitive radio is a low-cost communication system, which can choose the available frequencies and waveforms automatically on the premise of avoiding interfering the licensed users. The spectrum sensing is the key enabling technology in cognitive radio networks. It is able to fill voids in the wireless spectrum and can dramatically increase spectral efficiency.   In this thesis, the author use matlab to simulate the received signals from the cognitive radio networks and an energy detector to detect whether the spectrum is being used. The report also compares the theoretical value and the simulated result and then describes the relationship between the signal to noise ratio (SNR) and the detections. At last, the method, energy detection and simulation and result are discussed which is considered as the guidelines for the future work.

This thesis extensively analyses the performance of an energy detector which is widely employed to perform spectrum sensing in cognitive radio over different generalised channel models. In this analysis, both the average probability of detection and the average area under the receiver operating characteristic curve (AUC) are derived using the probability density function of the received instantaneous signal to noise ratio (SNR). The performance of energy detector over an ŋ --- µ fading, which is used to model the Non-line-of-sight (NLoS) communication scenarios is provided. Then, the behaviour of the energy detector over к --- µ shadowed fading channel, which is a composite of generalized multipath/shadowing fading channel to model the lineof- sight (LoS) communication medium is investigated. The analysis of the energy detector over both ŋ --- µ and к --- µ shadowed fading channels are then extended to include maximal ratio combining (MRC), square law combining (SLC) and square law selection (SLS) with independent and non-identically (i:n:d) diversity branches. To overcome the problem of mathematical intractability in analysing the energy detector over i:n:d composite fading channels with MRC and selection combining (SC), two different unified statistical properties models for the sum and the maximum of mixture gamma (MG) variates are derived. The first model is limited by the value of the shadowing severity index, which should be an integer number and has been employed to study the performance of energy detector over composite α --- µ /gamma fading channel. This channel is proposed to represent the non-linear prorogation environment. On the other side, the second model is general and has been utilised to analyse the behaviour of energy detector over composite ŋ --- µ /gamma fading channel. Finally, a special filter-bank transform which is called slantlet packet transform (SPT) is developed and used to estimate the uncertain noise power. Moreover, signal denoising based on hybrid slantlet transform (HST) is employed to reduce the noise impact on the performance of energy detector. The combined SPT-HST approach improves the detection capability of energy detector with 97% and reduces the total computational complexity by nearly 19% in comparison with previously implemented work using filter-bank transforms. The aforementioned percentages are measured at specific SNR, number of selected samples and levels of signal decomposition.

To achieve cooperative diversity in cognitive radio network, Decode and Forward (DF) protocol is implemented at Cognitive Radios (CRs) using Orthogonal Space Time Block Coding (OSTBC). The 2-hop communication between source and destination is completed with the help of Cognitive Relays (CRs) using Multiple Input Multiple Output (MIMO) technology within the network. To achieve spatial diversity and good code rate Alamouti 2×2 STBC is used for transmission. CR is using the decoding (Decode and Forward (DF)) strategy and without amplifying ability before forwarding data towards destination provide better performance. The main objective of this thesis is to detect Primary User (PU) spectrum availability or non-availability for the use of Secondary Users (SU). The Alamouti STBC encoded data is broadcasted to wireless Rayleigh faded channel through transmitter having two transmitting antennas. The CRs are preferred to place close with PU to detect transmitted signal and because of having decoding capability CRs decode the collected data using Maximum Likelihood (ML) decoding technique then re-encode the decoded data for further transmission towards receiver. The energy of PU signal received at relays is calculated using energy detector used at cognitive controller having authority to make final decision about presence or absence of PU signal within the spectrum by comparing calculated energy of PU received signal with a predefined value. If the calculated signal energy is less than threshold value it is pretended as the absence of PU and in the other case spectrum is assumed as occupied by PU. Decoding PU signal at relays before forwarding towards destination provide better performance in terms of detection probability and decreasing probability of false alarming as the Signal to Noise (SNR) increases. The proposed cooperative spectrum sensing using DF protocol at cognitive relays with Alamouti STBC is implemented and results are validated by MATLAB simulation. / +46 455 38 50 00

In this report, we introduce cooperative spectrum sensing using orthogonal space time block coding (OSTBC) in order to achieve cooperative diversity in the cognitive radios (CRs) network. Transmit diversity or gain is achieved by introducing more than one antenna on the transmitter and receiver side, but in small electronic mobile devices it looks impractical. The signals received from the primary users (PUs) are amplified by the cognitive relays and further forwarded to the cognitive controller where decisions are made on the basis of the information collected from each cognitive relay. The cooperative relaying protocol used here in cognitive relays is based on an amplifying-forward (AF) scheme. Alamouti scheme in OSTBC has been proposed to achieve better detection performance in CR network. The energy detector performance is analyzed over an independent Rayleigh fading channel. In CR network the secondary user (SU) shares PU's frequency band if it fi nds PU is not in its vicinity. The SU starts using the licensed band and leaves the band as soon as it finds the PU is present or going to use the same band. The detection of the spectrum holes by CRs has to be more agile and intelligent. The main objective of the CRs network is to use the free holes without causing any interference to the PUs. The energy detection technique is simple and outperforms other sensing techniques in cooperative cognitive radio networks. The energy detector collects information from different users, compares it with a certain prede fined threshold () value and then makes a fi nal decision. Detection and false alarm probabilities are derived and manipulated using OSTBC on PU and SU through AF protocol in cooperative communication. The performance of the system is analyzed with single and multiple relays and with and without direct path between the PUs and SUs. Maximum ratio (MRC) and selection combining (SC) schemes are used in energy detector and the results are compared with and without direct link between PU and SU. The analysis is performed by placing the relay close to the PUs. Our results are processed and validated by computer simulation.

Abstract This Thesis examines low complexity receiver structures for impulse-radio (IR) ultra-wideband (UWB) systems to be used in wireless sensor network applications. Such applications require radio communication solutions characterized by low cost, low complexity hardware and low power consumption to provide very long battery life. Analysis of several auto-correlation receiver (AcR) structures is performed in the presence of additive white Gaussian noise to identify receiver structures that offer a good compromise between implementation complexity and data communication performance. The classes of receiver that demonstrate the best complexity/performance trade-off are shown to be the AcR utilising transmitted-reference with binary pulse amplitude modulation signaling, and the energy detector (ED) utilising binary pulse position modulation. The analysis of these two schemes is extended to consider multipath fading channels. Numerically integrable bit error rate probability (BEP) expressions are derived in order to evaluate the receivers' performance in the presence of fading distributions characterized by closed form characteristic functions. Simulations utilising widely accepted UWB channel models are then used to evaluate the BEP in different indoor environments. Since UWB systems share frequency spectrum with many narrowband (NB) systems, and need to coexist with other UWB systems, the performance of low complexity receivers can be seriously affected by interference. In the presence of NB interference, two cases have been considered: 1) single NB interference, where the interfering node is located at a fixed distance from the receiver, and 2) multiple NB interference, where the interfering nodes are scattered according to a spatial Poisson process. When considering UWB interference, the case of multiple sources of interference has been considered. For both the multiple NB and the multiple UWB interference cases, the model derived considers several interference parameters, which can be integrated into BEP formulations for quick performance evaluations. The framework is sufficiently simple to allow tractable analysis and can serve as a guideline for the design of heterogeneous networks where coexistence between UWB systems and NB systems is of importance. The very large bandwidth of UWB signals offers an unprecedented possibility for accurate ranging operations. Signal leading-edge estimation algorithms based on average maximum likelihood estimators are derived considering different multipath channel fading distributions. Suboptimal solutions are proposed and investigated in order to support ranging capabilities in low complexity receiver structures. The ability to identify line-of-sight and non-line-of-sight conditions with the ED-based receiver is also addressed. An example of an IR-UWB low complexity transceiver based on ED for sensor network applications is proposed in this Thesis. Ad-hoc solutions for pulse transmission, synchronization and data detection are developed.

UWB has the huge potential to impact the present communication systems due to its enormous available bandwidth, range/data rate trade-off, and potential for very low cost operation. According to FCC, Ultra Wideband (UWB) radio signal defined as a signal that occupies a bandwidth of 500 MHz or fractional bandwidth larger than 20% with strict limits on its power spectral density to -41.3dBm/MHz in the range 3.1GHz to 10.6GHz. Decades of research in the area of wide-band systems have lead us to new possibilities in the design of low power, low complexity radios, comparing with existing narrowband radio systems. In particular, impulse radio based ultra wideband (IR-UWB) is a promising solution for short-range radio communications such as low power radio-frequency identification (RFID), wireless sensor network's and wireless personal area network (WPAN) etc. Since a simple circuit, architecture adopted in the IR-UWB system, the non-idealities of receiver front end may lead to degrade the overall performance. Therefore, it is important to study these effects in order to create robust and efficient UWB system. However, majorities of recent studies are formed on the channel analysis, rather than the receiver system. The main objectives of this thesis work are, (a) System level modeling of non-coherent IR-UWB receiver, (b) Performance analysis of IR-UWB receiver with the help of bit error rate (BER) estimation, (c) A study on the impact of receiver front end non-idealities over BER, (d) Analysis of charge leakage in integrator and its effect on overall performance of UWB receiver. In this work, IR-UWB non-coherent energy detector receiver operating in the frequency band of 3GHz-5GHz based on the on-off keying (OOK) modulation was simulated in Matlab/Simulink. The effect of receiver front end non idealities and integrator charge leakages were discussed in detail with respect to overall performance of the receiver. The results show that non idealities and leakage degrade the performance as expected. In order to achieve a specific BER of 10-2 with the integrator leakage of 25%, the SNR should be increased by 2.1 dB compared to the SNR with no leakage at a data rate of 200Mbps. Finally, integrator design and its specifications were discussed.

Recently, ultra-wideband (UWB) technology based on the transmission of short duration pulses has gained much interest for its application to wireless communications. This thesis covers a range of topics related to the analysis of indoor UWB channels for communications and to system level design issues for UWB receivers. Measurement based UWB small scale modeling and characterization efforts as well as UWB communications system analysis and simulation are presented. Relevant background material related to UWB communications and wireless channel modeling is presented. The details of the small scale channel modeling work, including statistical characterization and potential models, are discussed. A detailed analysis of the CLEAN algorithm, which was used to process all the measurement data, is also given, and some limitations of the algorithm are presented. The significance of the channel impulse response model chosen for the simulation of UWB communications systems is also evaluated. Three traditional models are found to be useful for modeling NLOS UWB channels, but not LOS channels. A new model for LOS UWB channels is presented and shown to represent LOS channels much more accurately than the traditional models. Receiver architectures for UWB systems are also discussed. The performance of correlation receivers and energy detector receivers are compared as well as Rake diversity forms of each of these types to show tradeoffs in system complexity with performance. Interference to and by UWB signals is considered. A narrowband rejection system for UWB receivers is shown to offer significant system improvement is the presence of strong interferers. / Master of Science

The objective of the research is to develop analog spectrum processing techniques for cognitive radio (CR) applications in CMOS technology. CR systems aim to use the unoccupied spectrum allocations without any license when the primary users are not present. Therefore, the successful deployment of CR systems relies on their ability to accurately sense the spectrum usage status over a wide frequency range serving various wireless communication standards. Meanwhile, to maximize the utilization of the available spectrum segments, the bandwidth of the signal has to be highly flexible, so that even a small fraction of spectrum resources can be fully utilized by CR users. One of the key enabling technologies of variable bandwidth communication is a tunable baseband filter. In this research, a reconfigurable CR testbed system is presented as groundwork for the researches related with CR systems. With the feasibility study on the multi-resolution spectrum sensing (MRSS) functionality, a method for determining sensing threshold for MRSS functionality is presented, and a fully integrated MRSS receiver in CMOS technology is demonstrated. On the other hand, a reconfigurable CMOS analog baseband filter which can change its bandwidth, type and order with high resolution for CR applications is presented. In sum, an analog spectrum sensing method as well as a highly flexible analog baseband filter architecture is established and implemented in CMOS technology. Both designs are targeting the utilization of the analog signal processing capability with the aid of the digital circuits.

Ultrawideband (UWB) is one of the promising technologies for future short-range high data rate communications (e.g. for wireless personal area networks) and longer range low data rate communications (e.g. wireless sensor networks).Despite its various advantages and potentials (e.g. low-cost circuitry, unlicensed reuse of licensed spectrum, precision ranging capability etc.), UWB also has its own challenges. The goal of this dissertation is to identify and address some of those challenges, and provide a framework for practical UWB transceiver design.In this dissertation, various modulation options for UWB systems are reviewed in terms of their bit error rate (BER) performances, spectral characteristics, modem and hardware complexities, and data rates. Time hopping (TH) code designs for both synchronous (introduced an adaptive code assignment technique) and asynchronous UWB impulse radio (IR) systems are studied. An adaptive assignment of two different multiple access parame ters (number of pulses per symbol and number of pulse positions per frame)is investigated again considering both synchronous and asynchronous scenarios, and a mathematical framework is developed using Gaussian approximations of interference statistics for different scenarios. Channel estimation algorithms for multiuser UWB communication systems using symbol-spaced (proposed a technique that decreases the training size), frame-spaced (proposed a pulse-discarding algorithm for enhanced estimationperformance), and chip-spaced (using least squares (LS) estimation) sampling are analyzed.A comprehensive review on multiple accessing andinterference avoidance/cancellation for IR-UWB systems is presented.BER performances of different UWB modulation schemes in the presence of timing jitter are evaluated and compared in static and multipath fading channels, and finger estimation error, effects of jitter distribution, and effects of pulse shape are investigated. A unified performance analysis app roach for different IR-UWB transceiver types (stored-reference, transmitted-reference, and energy detector) employing various modulation options and operating at sub-Nyquist sampling rates is presented. The time-of-arrival (TOA) estimation performance of different searchback schemesunder optimal and suboptimal threshold settings are analyzed both for additive white Gaussian noise (AWGN) and multipath channels.

The idea that the radio spectrum is growing ever more scarce has become commonplace, and is being reinforced by the recent bidding wars among telecom operators. New wireless applications tend to be deployed in the relatively narrow unlicensed frequency bands, worsening the problem of interference for all users.  However, not all frequency bands are in use in every location all the time, creating temporal and spatial gaps (also known as white spaces) that cognitive radio systems aim to take advantage of. In order to achieve that, such systems need to be able to constantly scan large chunks of the radio spectrum to keep track of which frequency bands are locally available any given moment, thus allowing users to switch to one of these unoccupied frequency bands once the current band becomes unusable (or less useful). This requirement of wideband sensing capabilities often translates into the need to install specialized radio components, raising the costs of such systems, and is often at odds with the focus on monitoring the current band as is done by traditional wireless devices. The goal of this master’s thesis project is to simplify cognitive radio systems by shifting the wideband sensing functionality to a specialized and inexpensive embedded platforms that will act as a white space sensor, thus freeing cognitive radio users from this task and making it easier to integrate dynamic spectrum management techniques into existing systems. To do that a wireless sensor gateway platform developed by a previous master’s thesis has been repurposed as a prototype white space detector and tested against several wireless transmitters.  The aim is to develop a standalone platform that can be deployed all around an area to collect data that can be used to create a geographical map of the use of the spectrum. Such a system should require as little maintenance as possible, thus auto-update and self-configuring features have been implemented in the detector, as well as a simple scanning protocol that allows for remote configuration of the wideband sensing parameters. Furthermore, a basic server has been developed to aggregate and display the data provided by the different sensors. / Tanken att radiospektrum blir allt knappare har blivit vardagsmat, och förstärks av de senaste budgivning krig mellan teleoperatörer. Nya trådlösa applikationer tenderar att sättas i de relativt smala olicensierade frekvensband, förvärrade problemet med störningar för alla användare. Men inte alla frekvensband som används i varje plats hela tiden, skapar tidsmässiga och rumsliga luckor (även känd som vita fläckar) som kognitiva radiosystem syftar till att dra nytta av.  För att uppnå detta, sådana system måste hela tiden kunna scanna stora delar av radiospektrum för att hålla reda på vilka frekvensband är lokalt tillgängliga varje givet ögonblick, vilket gör omkopplaren när den nuvarande bandet blir obrukbar.  Det här kravet på bredbands avkänning kapaciteter översätter ofta in behovet av att installera specialiserade radiokomponenter, höja kostnaderna för sådana system, och är ofta i strid med fokus på övervakning av strömmen band med traditionella trådlösa enheter. Målet med detta examensarbete är att förenkla kognitiva radiosystem med wideband avkänning funktionalitet till en specialiserad och billig inbäddad plattform som kommer att fungera som ett vitt utrymme sensor, vilket frigör kognitiva radio användare från denna uppgift och gör det enklare att integrera dynamiskt spektrum förvaltning tekniker i befintliga system. För att göra det en trådlös sensor gateway plattform som utvecklats av ett tidigare examensarbete har apterat som en prototyp blanktecken detektor och testas mot flera trådlösa sändare. Målet är att utveckla en fristående plattform som kan sättas runt för att skapa en geografisk karta av användningen av spektrum och kräva så lite underhåll som möjligt, har automatisk uppdatering och självkonfigurerande funktioner implementerats i detektorn, samt som en enkel scanning protokoll som möjliggör fjärrkonfiguration av den bredbandiga avkänningsparametrarna. Dessutom har en grundläggande server utvecklats för att aggregera och visa uppgifterna från de olika sensorerna.