The presented work considers a CDMA-based Wireless Body Area Network (WBAN) where multiple biosensors communicate simultaneously to a central node in an asynchronous fashion. The asynchronous nature of the WBAN introduces Multiple Access Interference (MAI). To combat this problem, presented is a methodology that uses a set of cyclically orthogonal spreading codes extracted from the Walsh-Hadamard matrix. When using the Cyclic Orthogonal Walsh-Hadamard Codes (COWHC) as spreading codes in the CDMA-based WBAN, the cyclic orthogonality property helps mitigate MAI amongst the on-body sensors. Presented is an ideal communication system that is most effective at mitigating MAI in proactive WBANs. The work illustrates the system optimality and effectiveness at mitigating MAI by studying the sensitivity to packet-loss through simulating the link Bit Error Rate (BER) performance. It is shown that the proposed design with COWHC, a Rayleigh flat-fading channel, BPSK modulation and a conventional receiver produce optimum MAI mitigation.

The presented work considers a CDMA-based Wireless Body Area Network (WBAN) where multiple biosensors communicate simultaneously to a central node in an asynchronous fashion. The asynchronous nature of the WBAN introduces Multiple Access Interference (MAI). To combat this problem, presented is a methodology that uses a set of cyclically orthogonal spreading codes extracted from the Walsh-Hadamard matrix. When using the Cyclic Orthogonal Walsh-Hadamard Codes (COWHC) as spreading codes in the CDMA-based WBAN, the cyclic orthogonality property helps mitigate MAI amongst the on-body sensors. Presented is an ideal communication system that is most effective at mitigating MAI in proactive WBANs. The work illustrates the system optimality and effectiveness at mitigating MAI by studying the sensitivity to packet-loss through simulating the link Bit Error Rate (BER) performance. It is shown that the proposed design with COWHC, a Rayleigh flat-fading channel, BPSK modulation and a conventional receiver produce optimum MAI mitigation.

¡@¡@Pseudo-noise (PN) code synchronizer is an essential element of direct-sequence code division multiple access (DS-CDMA) system because data transmission is possible only after the receiver accurately synchronizes the locally generated PN code with the incoming PN code. The code synchronization is processed in two steps, acquisition and tracking, to estimate the delay offset between the two codes. Recently, the adaptive LMS filtering scheme has been proposed for performing both code acquisition and tracking with the identical structure, where the LMS algorithm is used to adjust the FIR filter taps to search for the value of delay-offset adaptively. A decision device is employed in the adaptive LMS filtering scheme as a decision variable to indicate code synchronization, hence it plays an important role for the performance of mean acquisition time (MAT). In this thesis, only code acquisition is considered. ¡@¡@In this thesis, a new decision device, referred to as the weight vector square norm (WVSN) test method, is devised associated with the adaptive LMS filtering scheme for code acquisition in DS-CDMA system. The system probabilities of the proposed scheme are derived for evaluating MAT. Numerical analyses and simulation results verify that the performance of the proposed scheme, in terms of detection probability and MAT, is superior to the conventional scheme with mean-squared error (MSE) test method, especially when the signal-to-interference-plus-noise ratio (SINR) is relatively low. ¡@¡@Furthermore, an efficient and joint-adaptation code acquisition scheme, i.e., a smart antenna coupled with the proposed adaptive LMS filtering scheme with the WVSN test method, is devised for applying to a base station, where all antenna elements are employed during PN code acquisition. This new scheme is a process of PN code acquisition and the weight coefficients of smart antenna jointly and adaptively. Numerical analyses and simulation results demonstrate that the performance of the proposed scheme with five antenna elements, in terms of the output SINR, the detection probability and the MAT, can be improved by around 7 dB, compared to the one with single antenna case.

The system capacity of the direct-sequence code division multiple access (DS-CDMA) system is limited mainly due to the multiple access interference (MAI), this is basically due to the incomplete orthogonality of spreading codes between different users. In wireless communication environments, the use of DS-CDMA system over multipath channels will introduce the effect of inter-symbol interference (ISI), thus the system performance might degrade, dramatically. To circumvent the above-mentioned problems many adaptive multiuser detectors are proposed, such as the minimum mean square error (MMSE) criteria subject to certain constraints. Unfortunately, with the MMSE receiver it requires an extra training sequence, which decreases the spectral efficiency. To increase the spectral efficiency, the blind adaptive receivers are adopted. In the conventional approach the blind adaptive receiver is developed based on the linear constrained minimum variance (LCMV) criteria, which can be viewed as the constrained version of the minimum output energy (MOE) criteria. Other alternative of designing the blind adaptive receiver is to use the linear constrained constant modulus (LCCM) criteria. In general, the LCCM receiver could achieve better robustness due to the changing environment of channel. With the above-mentioned adaptive linearly constrained multi-user receivers, we are able to reduce the effects of ISI and MAI and achieve desired system performance. However, for worse communication link, the conventional adaptive multi-user detector might not achieve desired performance and suppress interference effectively. In this thesis, we consider a new approach, in which the pre-coder similar to the Orthogonal Frequency Division Multiplexing (OFDM) systems is introduced in the transmitter of the DS-CDMA system. In the receiver, by using the characteristics of pre-coder we could remove the effect of ISI, effectively, and follows by the adaptive multi-user detector to suppress the MAI. Two most common use pre-coders of the OFDM systems are the Cyclic Prefix (CP) or Zero Padding (ZP). Thus the pre-coded DS-CDMA systems associated with the adaptive blind linearly constrained receiver could be employed to further improve the system performance with the cost of decreasing the spectral efficiency.

A wireless local area network (WLAN) provides high bandwidth to users in a limited geographical area. This network faces certain challenges and constraints that are not imposed on their wired counterparts. They are: frequency allocation, interference and reliability, security, power consumption, human safety, mobility, connection to wired LAN,service area, handoff and roaming, dynamic configuration and the throughput. But the wireless medium relies heavily on the features of MAC protocol and the MAC protocol is the core of medium access control for WLANs. The available MAC protocols all have their own merits and demerits. In our research works, we propose a hybrid MAC protocol forWLAN. In the design, we have combined the merits of the TDMA and CDMA systems to improve the throughput of the WLAN in a picocellular environment. We have used the reservation and polling methods of MAC protocols to handle both the low and high data traffics of the mobile users. We have strictly followed the standards specified by IEEE 802.11 for WLANs to implement the designed MAC protocol. We have simulated the hybrid TDMA/CDMA based MAC protocols combined with RAP (Randomly Addressed Polling) for Wireless Local Area Networks. We have developed a closed form mathematical expressions analytically for this protocol. We have also studied the power control aspects in this environment and we derived a closed form mathematical expressions analytically for this power control technique. This hybrid protocol is capable of integrating different types of traffic (like CBR,VBR and ABR services) and compiles with the requirements of next-generation systems.The lower traffic arrival is dealt with the Random Access and the higher traffic arrival is with the Polling methods. This enables us to obtain higher throughput and lowmean delay performance compared to the contention-reservation-based MAC schemes. The protocol offers the ability to integrate different types of services in a flexible way by the use of multiple slots per frame, while CDMA allows multiple users to transmit simultaneously using their own codes. The RAP uses an efficient "back-off" algorithm to improve throughput at higher arrival rates of user's data. The performance is evaluated in terms of throughput, delay, and rejection rate using computer simulation. A detailed simulation is carried out regarding the maximum number of users that each base station can support on a lossy channel. This work has analyzed the desired user's signal quality in a single cell CDMA (Code Division Multiple Access) system in the presence of MAI (Multiple Access Interference). Earlier power control techniques were designed to assure that all signals are received with equal power levels. Since these algorithms are designed for a imperfect control of power, the capacity of the system is reduced for a given BER (Bit-Error Rate). We proposed an EPCM (Efficient Power Control Mechanism) based system capacity which is designed for the reverse link (mobile to base station) considering the path loss, log-normal shadowing and Rayleigh fading. We have simulated the following applications for the further improvement of the performance of the designed MAC protocol:Designed protocol is tested under different traffic conditions. The protocol is tested for multimedia traffic under application oriented QoS requirements. Buffer Management and resource allocation. Call Admission Control (hand-offs, arrival of new users). The adaptability to the variable nature of traffic.The propagation aspects in the wireless medium. The proposed MAC protocol has been simulated and analysed by using C++/MATLAB Programming in IBM/SUN-SOLARIS UNIX environment. The results were plotted using MATLAB software. All the functions of the protocol have been tested by an analysis and also by simulation. Call admission control function of the protocol has been tested by simulation and analysis in a multimedia wireless network topology and from analysis we found that at low traffic the throughput is high and at high traffic the throughput is kept constant at a reasonable high value. The simulation results also justify/ coordinate the analysis results. Dynamic channel allocation function of the protocol was tested and analysed and the coordinated results show that at low traffic, high throughput and at high traffic the throughput is constant. Buffer management function of the protocol simulation shows the results that the packet loss can be controlled to a minimum by adjusting the buffer threshold level at any traffic conditions. Maintenance of data transfer during the hand-offs function was simulated and the results show that the blocked calls are less during low traffic and at high traffic the blocked calls can be kept constant at low value. Thus, the proposed model aimed at having high throughput, high spectral efficiency, low delay, moderate BER and moderate blocking probability. We have considered a pico cell with a maximum of several users and studied the power efficiency of combined channel coding and modulation with perfect power controlled CDMA system. Thus our simulation of the "software radio" has flexibility in choosing the proper channel coders dynamically depending upon the variations of AWGN channel.

In this doctoral dissertation, the author presents the theoretical foundation, the analysis and design of analog and RF circuits, the chip level implementation, and the experimental validation pertaining to a new radio frequency integrated circuit (RFIC) power amplifier (PA) architecture that is intended for wireless portable transceivers. / A method called Gated Envelope Feedback is proposed to allow the automatic hardware reconfiguration of a stand-alone RFIC PA in multiple states for power efficiency improvement purposes. The method uses self-operating and fully integrated circuitry comprising RF power detection, switching and sequential logic, and RF envelope feedback in conjunction with a hardware gating function for triggering and activating current reduction mechanisms as a function of the transmitted RF power level. Because of the critical role that RFIC PA components occupy in modern wireless transceivers, and given the major impact that these components have on the overall RF performances and energy consumption in wireless transceivers, very significant benefits stem from the underlying innovations. / The method has been validated through the successful design of a 1.88GHz COMA RFIC PA with automatic hardware reconfiguration capability, using an industry renowned state-of-the-art GaAs HBT semiconductor process developed and owned by Skyworks Solutions, Inc., USA. The circuit techniques that have enabled the successful and full on-chip embodiment of the technique are analyzed in details. The IC implementation is discussed, and experimental results showing significant current reduction upon automatic hardware reconfiguration, gain regulation performances, and compliance with the stringent linearity requirements for COMA transmission demonstrate that the gated envelope feedback method is a viable and promising approach to automatic hardware reconfiguration of RFIC PA's for current reduction purposes. Moreover, in regard to on-chip integration of advanced PA control functions, it is demonstrated that the method is better positioning GaAs HBT technologies, which are known to offer very competitive RF performances but inherently have limited integration capabilities. / Finally, an analytical approach for the evaluation of inter-modulation distortion (IMD) in envelope feedback architectures is introduced, and the proposed design equations and methodology for IMD analysis may prove very helpful for theoretical analyses, for simulation tasks, and for experimental work.

Mobile communications are becoming integrated into society at an explosive rate. While 2nd generation (2G) systems limit the user to basic services such as voice and low-bit rate data, 3G networks are characterized by their ability to accommodate wideband multi-media traffic with Quality of Service (QoS) guarantees. In the design of a system the Medium Access Control (MAC) layer is responsible for multiplexing heterogeneous traffic onto a common transmission link and its design is critical to the overall performance of a system. A number of MAC protocols for wireless networks have been proposed in the literature - the majority having time division multiple access (TDMA) at the MAC layer. However in 3G systems there is a trend towards the use of code division multiple access (CDMA) due to its proven advantages in a wireless environment. Although several papers on CDMA based MAC protocols have been published, virtually none of them tackle the analysis aspect of the protocols. Those papers that do perform analyses of CDMA protocols don't often consider heterogeneous traffic, and even fewer support QoS. The thesis addresses these shortcomings by proposing a MAC protocol that supports QoS in the form of Bit Error Rate (BER) and packet delay guarantees. The thesis begins by giving an overview of proposed wireless ATM and 3G CDMA protocols and then details how power control may be used to support BER guarantees. Various Markov based analyses are presented along with Monte-Carlo Simulations. An Equilibrium Point Analysis is then performed and the work discusses how such analyses are generally infeasible for systems supporting heterogeneous traffic. After an overview of conventional scheduling algorithms the thesis proceeds to outline a novel approach by which delay guarantees may be offered using packet dropping rates as the QoS metric. Using a stochastic source model as opposed to the conventional leaky bucket traffic regulator the thesis diverges significantly from conventional literature. The thesis also details how to calculate the probability of QoS violation and concludes with suggestions on further research avenues. As a whole the work is unique in its approach to analyse heterogeneous traffic and the methods it uses to construct session admission zones for QoS guarantees. / Thesis (Ph.D.)-University of Natal,Durban, 2002.

The problems of optimal as well as suboptimal detection for CDMA transmissions over an additive white Gaussian noise (AWGN) channel, have been the focus of study in the recent past. However, CDMA transmissions are frequently made over channels which exhibit fading and/or dispersion; hence receivers need to be designed which take into account this behaviour. In spite of the major research effort invested in multiuser demodulation techniques, several practical as well as theoretical open problems still exist. Some of them are considered in more detail in this thesis. The aim of the thesis is to develop multiuser demodulation algorithms for mobile communication systems in frequency-selective fading channels, and to analyze their implementation complexity. The emphasis is restricted to the uplink of an asynchronous DS-CDMA system where the users transmit in an uncoordinated manner and are received by one centralized receiver. The original work that is undertaken for the MScEng study is the evaluation of a multiuser receiver structure for a frequency-selective fading channel, where there exists a steady specular path and two fading paths. Furthermore, the effect of using selection diversity is investigated by examining the bit error rate, asymptotic multi user efficiency and near-far resistance of the proposed detector structure. These results are confirmed both analytically and by simulation in the thesis. An investigation is also conducted into the application of neural networks to the problem of multiuser detection in code division multiple access systems. The neural network will be used as a classifier in an adaptive receiver which incorporates an extended Kalman filter for joint amplitude and delay estimation. Finally, some open problems for future research will be pointed out in the thesis. Keywords: AWGN channel , DS-CDMA system, frequency-selective, multi user demodulation, asymptotic multiuser efficiency, near-far resistance, neural network, Kalman filter. / Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.

In order to meet the ever-growing demand for mobile data, a number of different technologies have been adopted by the fourth generation standardization bodies. These include multiple access schemes such as spatial division multiple access (SDMA), and efficient modulation techniques such as orthogonal frequency division multiplexing (OFDM)-based modulation. The specific objectives of this theses are to develop an effective feedback method for interference management in smart antenna SDMA systems and to design an efficient OFDM-based modulation technique, where an additional dimension is added to the conventional two-dimensional modulation techniques such as quadrature amplitude modulation (QAM). In SDMA time division duplex (TDD) systems, where channel reciprocity is maintained, uplink (UL) channel sounding method is considered as one of the most promising feedback methods due to its bandwidth and delay efficiency. Conventional channel sounding (CCS) only conveys the channel state information (CSI) of each active user to the base station (BS). Due to the limitation in system performance because of co-channel interference (CCI) from adjacent cells in interference-limited scenarios, CSI is only a suboptimal metric for multiuser spatial multiplexing optimization. The first major contribution of this theses is a novel interference feedback method proposed to provide the BS with implicit knowledge about the interference level received by each mobile station (MS). More specifically, it is proposed to weight the conventional channel sounding pilots by the level of the experienced interference at the user’s side. Interference-weighted channel sounding (IWCS) acts as a spectrally efficient feedback technique that provides the BS with implicit knowledge about CCI experienced by each MS, and significantly improves the downlink (DL) sum capacity for both greedy and fair scheduling policies. For the sake of completeness, a novel procedure is developed to make the IWCS pilots usable for UL optimization. It is proposed to divide the optimization metric obtained from the IWCS pilots by the interference experienced at the BS’s antennas. The resultant new metric, the channel gain divided by the multiplication of DL and UL interference, provides link-protection awareness and is used to optimize both UL and DL. Using maximum capacity scheduling criterion, the link-protection aware metric results in a gain in the median system sum capacity of 26.7% and 12.5% in DL and UL respectively compared to the case when conventional channel sounding techniques are used. Moreover, heuristic algorithm has been proposed in order to facilitate a practical optimization and to reduce the computational complexity. The second major contribution of this theses is an innovative transmission approach, referred to as subcarrier-index modulation (SIM), which is proposed to be integrated with OFDM. The key idea of SIM is to employ the subcarrier-index to convey information to the receiver. Furthermore, a closed-form analytical bit error ratio (BER) of SIM OFDM in Rayleigh channel is derived. Simulation results show BER performance gain of 4 dB over 4-QAM OFDM for both coded and uncoded data without power saving policy. Alternatively, power saving policy maintains an average gain of 1 dB while only using half OFDM symbol transmit power.

The work reported in this thesis is divided in to two parts. In the first part, we report a closed-form bit error rate (BER) performance analysis of orthogonal frequency division multiple access (OFDMA) on the uplink in the presence of carrier frequency offsets (CFOs) and/or timing offsets (TOs) of other users with respect to a desired user. We derive BER expressions using probability density function (pdf) and characteristic function approaches, for a Rician faded multi-cluster multi-path channel model that is typical of indoor ultrawideband channels and underwater acoustic channels. Numerical and simulation results show that the BER expressions derived accurately quantify the performance degradation due to non-zero CFOs and TOs. Ultrawideband channels in indoor/industrial environment and underwater acoustic channels are severely delay-spread channels, where the number of multipath components can be of the order of tens to hundreds. In the second part of the thesis, we report low complexity equalization algorithms for cyclic-prefixed single carrier (CPSC)systems that operate on such inter-symbol interference(ISI) channels characterized by large delay spreads. Both single-input single-output and multiple-input multiple-output(MIMO) systems are considered. For these systems, we propose a low complexity graph based equalization carried out in frequency domain. Because of the noise whitening effect that happens for large frame sizes and delay spreads in the frequency domain processing, improved performance compared to time domain processing is shown to be achieved. Since the graph based equalizer is a soft-input soft-output equalizer, iterative techniques(turbo-equalization) between detection and decoding are shown to yield good coded BER performance at low complexities in convolutional and LDPC coded systems. We also study joint decoding of LDPC code and equalization of MIMO-ISI channels using a joint factor graph.