1,720,973 research outputs found
Ripples in Communication: Reconfigurable and Adaptive Wireless Communication Systems based on Wavelet Packet Modulators
No full textWavelet Packet Modulation (WPM) is a multi-carrier transmission technique that uses orthogonal wavelet packet bases to combine a collection of information bits into a single composite signal. This system can be considered as a viable alternative, for wide-band communication, to the popular Orthogonal Frequency DivisionMultiplexing (OFDM) system. The main advantage of WPM is that the transmission characteristics of the system can be adapted according to the radio environment to maximize resource utilization. The WPM is a system under development and has not been studied extensively. In this research work the operation of aWPMradio is successfully evaluated. The thesis primarily focuses on the question of how efficient and robust wireless radios can be designed with the aid of wavelet theory. To do so the challenges involved in the practical implementation of the system are evaluated and understood. Suitable mechanisms that address communication theory figure-of-merits such as Peak-to-average power ratio (PAPR), loss of time/phase/frequency synchronization, channel equalization are devised and tested. Furthermore, the advantages of the WPM system for wireless transmission are demonstrated in three scenarios,namely, 1. Wavelet packets for spectrum estimation. 2. Wavelet packets for dynamic spectrum access. 3. Design of new wavelets based on system requirements. The efficacy of the proposed algorithms is validated using computer simulations and numerical analysis. The results of the research show that the WPM is an effective addition to existing wireless transmission modes.EEMCSElectrical Engineering, Mathematics and Computer Scienc
Peak-to-Average Power Ratio Reduction Techniques for Wavelet Packet Modulation
No full textWavelet Packet Modulation (WPM) is a novel multicarrier modulation technique and a promising alternative to the well established Orthogonal Frequency Division Multiplexing (OFDM). WPM has been shown to be an efficient technique with interesting features like adaptation and flexibility and improved characteristics in comparison to OFDM. A major drawback of multicarrier systems is their high peak-to-average power ratio (PAPR). The average signal power must be kept low in order to ensure that the transmitter amplifier operates in the linear region. This however will have a detrimental effect on the efficiency of power utilization particularly in mobile systems where battery lifetime is a premium resource. Minimizing the PAPR allows a higher average power to be transmitted for a fixed peak power, improving the overall signal to noise ratio at the receiver. In the literature several methods are reported to reduce the PAPR problem of OFDM. The PAPR for WPM is extremely novel. This thesis work presents several original contributions to the field of PAPR reduction for the multi-carrier WPM system. We focus on the selected mapping techniques since they are distortionless and their complexity is lower compared to other techniques. After studying the selected mapping with scrambling technique to reduce PAPR, we present a novel WPM architecture that employs our proposed secure PAPR reduction technique. Besides scrambling techniques, phase modification is another PAPR reduction technique and in this thesis we present how selected mapping with phase modification can be applied to reduce PAPR. In all instances the proposed technique reduces the PAPR between 1.5 and 2.5 dB. A smarter approach can be developed to optimize the selected mapping techniques. Consequently, we introduce an optimized WPM architecture that employs optimized selected mapping with phase modification technique. The designed optimization algorithm improves the PAPR reduction performance further than the selected mapping with phase modification. For a complementary cumulative distribution function (CCDF) value of , the PAPR of the original frame is around 10 dB; whereas, optimized phase-shifted frame produces a PAPR value around 8.2 dB. While, a PAPR value below 8.7 dB cannot be reached with the selected mapping techniques, which depends on randomization such as randomly phase-shifting or random scrambling.IRCTRTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
On Wavelet Based Spectrum Estimation for Dynamic Spectrum Access
No full textOne of the important functionalities of Dynamic Spectrum Access is spectrum estimation. Accuracy and speed of estimation are the key indicators to select the appropriate spectrum estimation technique. In this thesis work, the possibility of employing wavelet packet decomposition as a basis for a new spectrum estimation approach is investigated. Once the new approach is developed, four types of sources, namely partial band, single tone, multi-tones, and swept tone, are used to investigate the performance of the proposed wavelet based approach. Preliminary comparative analysis between the performance of wavelet based approach with conventional techniques, such as Periodogram and Welch technique has also been conducted. The studies show that the wavelet based approach offers great flexibility, reconfigurability and adaptability. Key to the successful operation of the wavelet based spectrum estimation is the choice of the wavelet used. Commonly known wavelets are not suitable for spectrum estimation because they result in estimates with poor frequency resolution. To alleviate this problem, we design and develop a family of wavelets that are maximally frequency selective in nature as our second contribution in this thesis work. To this end, the design constraints are first enlisted. Then the problem, originally non-convex, is reformulated into a convex optimization problem and solved using Semi Definite Programming (SDP) tools. Through simulation studies the benefits of the newly designed wavelets are demonstrated. The next contribution of this thesis work is to combine the existing wavelet packet multi-carrier modulation (WPMCM) technique with our wavelet based spectrum estimator in order to form a wavelet packet transceiver for a dynamic spectrum access environment. To enable the wavelet packet transceiver cognitive radio (CR) system to co-exist with other Licensed Users (LU), a common spectrum pool is maintained and the WPMCM transmission waveform characteristics are shaped to communicate in the idle time-frequency gaps of the licensed user. This is achieved by dynamically vacating wavelet packet carriers in and near the region of the licensed user spectrum. The spectrum estimation unit is tagged to the WPMCM transceiver structure by exploiting the filter bank infrastructure used for Discrete Wavelet Packet Transform implementation. Thus spectrum analysis is done at no additional cost. In the studies, four types of LUs are employed, namely, partial band, single tone, swept and multiple tone. The simulation results show that in the presence of an LU, the proposed spectrum adaptation method offers significant BER improvements allowing the CR to operate invisibly to the LU.TelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Relay Selection and Resource Allocation in Cooperative Wireless Communication Networks
No full textCooperative communication is a technique to use nodes in the wireless network as relays to forward information to the destination. Cooperative communication technique relies on the relay selection and power allocation process to optimize its performance since not all available nodes are beneficial to use for forwarding. Game theory is a branch of mathematics theory which tries to model the behavior of a player in strategic situation, or games, when dealing with other players’ choices. In the cooperative communication networks, the game theoretical approach has been shown to be a good means to solve the relay selection and resource allocation problems which have multiple objectives. In this thesis we analyze the relay selection and resource allocation using pricing game in a cooperative wireless communication network with interference. Using simulation results we show that interference affects the relay selection and resource allocation process. From the relay selection result we also find that the number of selected relay nodes influences the optimization process and when the number of selected nodes is large, the source node significantly suffers from payment to relay nodes. We propose an algorithm to limit the number of selected relay nodes and to keep the benefit of the source node. We also propose an evolutionary game approach for resource allocation in cooperative wireless networks. The method has flexibility in optimizing the system based on preferred objectives. The evolutionary game approach is based on evolutionary programming, where the behavior of each node is modeled to mimic the biological evolution process. Results of this study can be used in a wide range of wireless sensor networks where power, bandwidth, and other resource constraints are present. The proposed scheme provides a flexible relay node selection given the resource constraints of the wireless network.TelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Wireless Channel Modeling and Code Division Multiple Access for Indoor Communications
No full textElectrical Engineering, Mathematics and Computer Scienc
Effect of Pulse Shaping on the Performance of DS-CDMA in a Multipath Fading Channel
No full textThis report gives first an overview of the main modulation methods and of the multipath propagation effects. A model is described to simulate BPSK, QPSK and OK-QPSK in some measured indoor channels. Several pulse shapes are analysed and their effects discussed on single-user systems and on DS-CDMA. The main performance parameter is the bit error rate for different noise levels. Finally, some conclusions on the possible increase of a DS-CDMA system capacity are exposed, based on the different interference reductions achieved by pulse shaping.Electrical Engineering, Mathematics and Computer ScienceTelecommunicatie- en Verkeersbegeleidingssysteme
Interference cancellation techniques for low power wireless sensors
No full textNon-coherent on-off keying (OOK) receivers are preferred in ultra low power (ULP) wireless devices as they consume less power when compared to receivers based on other modulation schemes. However, these devices are highly susceptible to co-channel interference (CCI). Therefore, interference cancellation (IC) techniques for ULP non-coherent OOK receivers are investigated in this thesis. Various IC techniques are discussed in literature. However, the non-coherent OOK receiver architecture calls for the design of new low complexity IC techniques. The main constraint of the system is imposed by the analog front end that uses a simple square law detector to down-convert the RF signals to baseband and there is also only single radio frequency (RF) chain. The challenge is to mitigate CCI under these constraints and improve the detection performance. The non-coherent detection of OOK signals requires the knowledge of the signal to noise ratio (SNR) of the incoming signal. Therefore, SNR estimation plays an important role in non-coherent OOK receivers. Thus the scope of this thesis is twofold. Firstly, the SNR estimation and non-coherent detection techniques are proposed for OOK signals. Secondly, the interference mitigation techniques are proposed for the case of continuous wave (CW) CCI and OOK modulated interferers. The problems of the proposed techniques for the case of M-ary phase shift keying (MPSK) modulated interferers are also investigated. Finally, the implementation of the SNR estimation techniques on real time hardware platform is discussed.TelecommunicationsTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Performance evaluation of multi-user detectors for DS-CDMA systems over multi-path Rayleigh fading channels with AWGN
No full textThe third generation of the mobile communications network is the Universal Mobile Telecommunications System (UMTS). One of the multiple access techniques will be Direct Sequence Code Division Multiple Access (DS-CDMA). This report evaluates the performance of different detectors for DS-CDMA systems for the specifications of the UMTS environment...Applied SciencesElectrical EngineeringInformation Technology and SystemsLaboratory of Telecommunications and Traffic-Control System
A Study On Wavelet Packet Based Algorithm For Representation of Wireless Channel
No full textWireless telecommunication services are growing rapidly both in terms of the underlying technology as well as in the nature of the applications. The trends point to further growth in the foreseeable future. However, the dynamic nature of the wireless channel places fundamental limitations on the performance of wireless communication system. Unlike wired channels, which are by-and-large stationary and predictable, wireless channels are extremely random and do not offer easy analysis. Therefore, in order to gain better system performance it is of great importance to accurately and efficiently map the wireless channels. Existing wireless channel models are based on statistical impulse response methods derived from empirical analysis. Such models employ a lot of channel coefficients which affect the complexity of computation. In this context the theory of wavelets and wavelet packets, which have recently found applicability for signal processing applications, hold the promise for wireless channel modeling. Wavelet packets offer the important feature of localization in both frequency and time domains. This property can be exploited to model channels with reduced complexity. In this thesis report, the applicability of wireless channel representation based on wavelet packet algorithm is addressed. The possibility of one-dimensional and two-dimensional wavelet packet algorithm for time-invariant and time-varying representation, respectively, is investigated. The results illustrating the efficiency of one-dimensional and two-dimensional approach are presented. To improve the performance of the proposed system, two optimization methods, namely coefficient reduction and tree pruning are implemented. Furthermore, the impact of the number of decomposition levels and the type of mother wavelet employed are also investigated. To measure the system performance, first and second order stochastic metrics such as Mean-square Error (MSE), Level-Crossing Rate (LCR) and correlation were employed.TelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Synchronization Methods for Wavelet Packet Multicarrier Modulation
No full textWavelet Packet based Multi-Carrier Modulation (WPM) offers an alternative to the well-established Orthogonal Frequency Division Multiplexing (OFDM) as an efficient multicarrier modulation technique. It has strong advantage of being generic transmission scheme whose actual characteristics can be widely customized to fulfill several requirements and constraints of advanced communication systems. In the last decades wavelets have been favorably applied in signal and image processing fields but they just recently attracted attention of the telecommunication community. Therefore, some research questions remain to be addressed before novel WPM can be used in practice. One of the major concerns involves the performance of WPM transceivers under various synchronization errors. In this thesis we analyze the interference in WPM transmission caused by the carrier frequency offset and time synchronization errors. Using standard wavelets, the sensitivity of WPM transceivers to these errors is evaluated through simulation studies and their performances are compared and contrasted to OFDM. To alleviate the WPM‘s vulnerability to time synchronization errors, a method of synchronization is proposed. The proposed time synchronization method in WPM is based on already published feed-forward decision-directed approach which uses correlation method in the wavelet domain (after processed by the analysis filter bank in the receiver side), with lower implementation complexity and improved stability. The proposed method can be considered as “coarse” time synchronization, suitable for estimating large time offset but with less precision. Through computer simulations the performance of the proposed method is proven and further its performance is compared for different parameters of wavelet filters.TelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
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