Communication Engineering

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    Simulation of Flight Following System
    (Addis Ababa University, 1989-06) Mathewos, Essatu; Klous, Kissig (PhD)
    The simulation of the flight following system i6 primarily chosen in the interest of Ethiopian Airlines need to implement the system to replace the currently used flight following system which is based on verbal communication between aircraft and ground control people. The first section of this paper discusses the components of data communication system, aspects and objective of data communication system. The second section laid the emphasis on the fundamental communication concepts parallel transmission, serial transmission and the different types of serial transmission. The theory behind the simulation is basically based on the different types of transmission modes. The third section build the foundation for the characteristics of data transmission, direction of information flow: simplex, half-duplex and full duplex and finally rate of transmiesion effect on data transmission. In section 4 the different coding technology and structures are presented. A unique feature of the paper is section 5 protocol. There are sections on identifying and defining a problem in data communication specially for good understanding between a sender and a receiver.
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    Design and Realization of an Audio Frequency Filter Unit for Shortwave Communication System Using TMS320CSO DSP Kit
    (Addis Ababa University, 1998-12) Mengesha, Seble; Haferkorn, Habil P(PhD)
    Causes that may affect the quality of shortwave data communication over radio are presented. Designing an audio-frequency filter unit, other than the filters exist in the transceiver, is considered as one solution to improve the quality of this shortwave data communication. Among the different data communication modes exist in the communication system, the CW (continuous wave), RTTY (Radio teletype) and AMTOR (amateur teleprinting over radio) types are selected to test the performance of the designed filter unit. The filter unit is of FIR digital filter type which the impulse response coefficients are obtained using the Kaiser Window design technique. The DSK (digital signal processor starter kit) assembler and debugger are used to develop the assembly code so as to realize and implement the filter on TMS320C50 digital signal processor. The magnitude response of the resulting filter unit is estimated by a spectrum analyzer. Finally, the designed filter unit is tested in an Amateur Radio Communication System.
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    Design and Realization of Adaptive Channel Equalizer for Shortwave Communication using TMS320C50 DSP Kit
    (Addis Ababa University, 2003-12) Ayalew, Mesfin; Haferkorn, Habil P(PhD)
    The high frequency (HF) band is a cost effective medium for a long distance transmission beyond the horizon, for limited bandwidth of up to 3 kHz. However, the HF channel is simultaneously a time and frequency dispersive environment. Time spread is two fold and results from multiple reflections between earth surface and ionosphere, where the latter is known to have various reflection layers. This multipath behavior results in various received modes at the receiver site corresponding to a time spread of a few milliseconds. Frequency spread is due to motion of electron density distributions in the ionospheric media, and can be as high as 10 Hz. In addition to time and frequency spread the relative movements of ionospheric layers impose a Doppler shift on transmitted signals. The received signal in fading often modeled by a Rayleigh distributed envelope and a uniformly distributed phase. Frequency selective fading channels produce intersymbol interference (ISI) in the received signal. In these channels an increase in the power does not improve performance, since additional power amplifies the ISI in step with the desired signal. The maximum likelihood sequence estimator (MLSE) is the optimal method of canceling the ISI; however, it is prohibitively complex. Suboptimal but efficient method of compensating for the ISI is to equalize the channel impairments by applying a filter at the receiver. In general radio channel characteristics are subject to variation in time, and this leads to the need for adaptive equalizers. In this development, a linear frequency selective slowly fading model is used for the channel. A linear adaptive channel equalizer is considered as a solution to improve the performance of digital communication over this short wave channel. The performance of the equalizer is studied under a software simulated environment using MATLAB programming for a linearly modulated, binary phase shift keyed (BPSK), signals. The TMS320C50 DSK (digital signal processor starter kit) assembler and debugger are used to develop the assembly code so as to realize and implement the filter on TMS320C50 digital signal processor. Finally, the designed equalizer is tested for its performance.
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    Long Distance Point-to-Point Wi-Fi Link for Connectivity in Rural Areas of Ethiopia
    (Addis Ababa University, 2005-06) Miresa, Talile; Hailemariam, Dereje (PhD)
    Internet coverage in rural areas of Ethiopia is extremely limited which, in turn, limits access to knowledge, education, health, commerce and other important services. As rural areas are characterized by low-income, highly scattered and low population density, traditional approaches for backhauling based on telephone, cellular, satellite or fiber is in general expensive, especially, in low population density and low-income regions like Ethiopia. To address this rural area network access problem, this thesis proposes Institute of Electrical and Electronics Engineers (IEEE) 802.11n-based point-point technology as a backhauling solution. The thesis shows that, with careful planning, using high gain antennas and tuning relevant medium access control (MAC) layer parameters, inexpensive, off-the-shelf Wi-Fi radios can be viable solution to rural connectivity problem. The work started by assessing limitations of IEEE 802.11-based access point in a long-distance point-to-point setup. Due to the long distance, high gain antennas are required. A pair of parabolic reflectors, originally designed for satellite TV reception with their feeders replace with that of Wi- Fi, are used. The standard IEEE802.11 MAC layer performs poorly in a long-distance step; hence, the necessary MAC layer parameters were changed to fit the long distance requirements. Before deploying the system a link budget analysis had to be conducted for selected sites to predict the performance of the system. To demonstrate the appropriateness of this solution a testbed was built and deployed in the premises of Addis Ababa Institute of Technology (AAiT) over 128 meters. The testbed is built from a pair of Dragino MS14 access points connected to parabolic reflectors of 175 centimeters diameter. Several experiments were conducted on this testbed to evaluate its performance. The measured results indicate that at 128 meters distance a maximum throughput of 32.8 Mega bits per second and received signal power of -72dB was achieved by adjusting antenna height and orientation. Another experiment was conducted using Radiomobile link simulation tool to evaluate the performance of this same system when implemented in a real rural area. The simulation result showed that with extensive link planning, the same antenna can give coverage to rural area about 30 kilometers away a city. The simulation was conducted between Bishoftu city and a rural location called Chaffee Donsa.
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    New Bandwidth Allocation Scheme for Handover Voice Calls in Mobile Cellular Networks
    (Addis Ababa University, 2006-08) Wakijira, Fikadu; Ayele, Hailu (PhD)
    The demand of mobile communication has grown remarkably in past years. Mobile communication network (system) should use limited resources in efficient and convenient manner. One way of achieving this is to use smaller cells in the expense of the corresponding handover management and system administration overhead. The limited radio frequency spectrum available cannot be longer support the increasing number of mobile user, and user demand, and the required quality of service (QoS) no longer are attainable if a best solution is not found. The other simplest solution proposed to overcome this problem is to increase the network capacity, which is not economical and not really practical. The work in this thesis demonstrates the different types of channel allocation schemes and call admission control with handover management for voice call. This paper goes through the cellular capacity improvement: cell reuse, cell splitting cell tiering and cellular structure. Most of the proposed schemes in the literature give priority to ongoing (handover) calls on the expense of blocking the originating calls. We deem to introduce a new bandwidth reservation scheme based on guard channel policy. Accordingly, new calls are blocked if the amount of occupied bandwidth is greater or equal to a bandwidth threshold; Bt. The novelty of the proposed Time Threshold Based Scheme (TTBS) is based on the elapsed real time of voice handover call and according to a time threshold, Tr parameter, handover calls could be either prioritized or treated as new calls. The major contribution of this work is to exploit time threshold scheme to perform autonomous and intelligent negotiation to improve wireless resource allocation. We use simulation study to evaluate the performance of the proposed scheme. The TTBS scheme is simulated under different scenarios and the result show that, the proposed schemes provide good performance in terms of handover call dropping probability, new call blocking probability, and bandwidth utilization
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    Performance Study of Space-Time Coding over Spatially Correlated Rayleigh Fading Channel
    (Addis Ababa University, 2007) Kiros, Mulugeta; Ayele, Hailu (PhD)
    In this thesis we discuss the space-time block coding, a new paradigm for communication over Rayleigh fading channels using multiple transmit antennas with out information of the channel at the transmitter. Data is encoded using a space-time block code and the encoded data is split into nT transmit antennas. The received signal is linear superposition of the nT transmitted signals perturbed by noise. Previous work on space-time coding has been restricted on the idealistic case of uncorrelated spatial fading. In practice, however, insufficient antenna spacing or lack of scattering cause the individual antennas to be correlated. In the second part of this work, we study the impact of spatial fading correlation on the diversity and coding gains. We derive the exact pairwise error probability (PEP) for space-time coding over qusistatic Rayleigh fading channels. We furthermore show that if a space-time code achieves full diversity in the uncorrelated case, the diversity order achieved in the correlated case is given by the product of rank of the transmit correlation matrix and the rank of receive correlation matrix. Finally, we provide simulation results demonstrating the impact of transmit spatial fading correlation on the performance of space-time block coding for different correlation values.
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    Handoff Initiation and Performance Analysis in Cdma Cellular Systems
    (Addis Ababa University, 2007-02) Sori, Negassa; Adugna, Eneyew(PhD)
    Mobile terminals allow users to access services while on the move. This unique feature has driven the rapid growth in the mobile network industry, changing it from a new technology into a massive industry within less than two decades. Handoff is the essential functionality for dealing with the mobility of the mobile users. Compared with the conventional hard handoff employed in the GSM mobile networks, the soft handoff used in IS-95 CDMA and being proposed for 3G has better performance on both link and system level. In this thesis, an in-depth study of the soft handoff effects on the uplink direction of IS-95 CDMA networks is carried out, leading to optimize soft handoff for capacity under perfect power control approach. We analyze the performance of different handoff algorithms on the forward link or downlink of a CDMA cellular system. Unlike the reverse link, soft handoffs on the forward link requires additional resources such as CDMA codes and transmit power and also causes additional interference. If handoff requests can be processed and completed instantaneously, transmission from the base station with the best link to the user would achieve a significant fraction of the macro diversity gain without utilizing additional resources. However, in practical systems, there is a nonzero handoff completion delay and soft handoff provides the required robustness to delays, although it comes at the expense of additional network resources. Thus, there is a tradeoff between the extent of soft handoff required and the handoff execution delay. We present an analytical framework to study this tradeoff and also discuss simulation results simulated with the help of Matlab. For this, handoff dropping probability is minimized up to 0.1%. Markov concept is applied to describe the system’s statistic behavior in steady state. System performances such as blocking and dropping probabilities and channel efficiency are also determined
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    Performance Evaluation of Interference Cancellation using SIC and PIC for WCDMA Systems
    (Addis Ababa University, 2007-09) Kebede, Gebru; Ayele, Hailu (PhD)
    Third generation wireless communications in conjunction with multimedia services has produced an increased demand for bandwidth efficient multiple access schemes. The need for increased capacity and improved performance motivate the search for better receiver structures, of which multiuser detection is a key technology that can substantially increase the system capacity and data rate. Due to the limitations of the conventional matched filter, the capacity of a single cell using CDMA is limited by self-interference and is subject to the near–far problem, and treats multiple access interference (MAI) as if it were AWGN. This thesis presents under a category of multiuser detection the most promising sub-optimal receiver structures, successive interference cancellation (SIC) and parallel interference cancellation (PIC) which are used to combat MAI in order to increase the data rate and capacity of the system which is applicable for WCDMA system and beyond. These subtractive interference cancellation receivers treat MAI as additional information to aid in detection in order to overcome the drawbacks seen by conventional matched filter. In this work we present a performance evaluation of these interference cancellers using SIC and PIC, and their performance is compared based on theoretical analysis and simulation results in AWGN and multipath fading channels. Simulation results using bit error rate (BER) versus signal to noise ratio (SNR) in multipath fading channel for different value of data size and number of users under perfect power control condition reveals that PIC achieves significant performance over conventional matched filter and SIC. And, as the data size (in bits) from the transmitting end increases the computational complexity of the multiuser detector become higher, however in PIC as the stage of multiple access interference cancellation increases the performance is reached remarkable level. In AWGN channel, simulation results confirmed that matched filter has shown optimum performance over SIC and PIC multiuser detectors when orthogonal spreading codes are assigned for each user in the network. Additionally, in this work receiver structures are evaluated on the basis of computational complexity.
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    Performance of Beamforming Techniques Using Uplink Channel Characteristics in Cellular CDMA Communication Systems
    (Addis Ababa University, 2007-09) Dida, Degebassa; Ayele, Hailu (PhD)
    The demand of code division multiple access (CDMA) cellular communication has grown remarkably in the past few years. Due to this reason mobile communication networks should use the limited resources of the system in efficient and convenient manner. One of the techniques is digital beamforming, in which energy is dynamically adjusted to the desired direction. In beamforming, we multiply a complex-valued weighting vector by the outputs of antenna array and sum these outputs to generate a signal for each user. As each user will have a unique weight, we can select the weights to greatly decrease interference from other users, and therefore increase system capacity. In this thesis, the uplink CDMA cellular systems is modeled and investigated to show how different beamforming algorithms are effective in improving system performance and capacity using adaptive antenna arrays at base station. It was initially thought that only the uplink would be the capacity limiting link in CDMA cellular systems but this assumption turned out to be incorrect and the capacity in actual fact is limited by the both links. To determining uplink CDMA system capacity and the effect of inter-element antenna array spacing, step size and number of antenna elements on the overall system capacity using adaptive antenna array elements. Adaptive beamforming is more complex, but highly efficient where the radiation pattern is constructed dynamically in which interferers are blocked and beam is formed in the direction of users. The adaptive algorithms such as, LMS and CMA are investigated to estimate error and to compute array factor for CDMA system, because the spreading codes can be used as a reference for beamforming. Results of comparison show that the LMS algorithm performs better than the CMA algorithm under the same condition. The performance obtained from using beamforming techniques using six (6) adaptive antenna array element results in an improvement by about 30% on average over the non beamforming techniques from the simulation result obtained.
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    Performance Analysis of CDMA Based Wireless Local Loop (WLL) Communication, Case of ETC’s Implementation in Addis Ababa
    (Addis Ababa University, 2007-10) Zeleke, Getu; Ayele, Hailu (PhD)
    The demand for CDMA –WLL, Wireless Local Loop, Communication system is higher than wired network. The CDMA–WLL system in Addis Ababa is providing voice and data communication services. Because of its fast and reliable service, many customers are looking forward to be connected to the system. As CDMA’s nature, each CDMA –WLL user generates interference on the other users (Self jamming). The increasing number of users is going to cause system capacity limitation, unsatisfactory and degraded service quality , QoS. Addis Ababa CDMA-WLL system has started service provision with about 31,000 voice and 960 data communication users. As indicated above when the number of users increases, the service quality started degradation by dropping and blocking calls from the system with limited capacity allocation. These problems are results of improper planning and implementation work so that the system needs more technical solutions to provide better service quality, QoS and higher system capacity. To reduce the effect of the mentioned system problems, this thesis explores different techniques and methodologies. Cell sectoring and power controlling techniques pointed as the main performance enhancement methods3. . Using Power control as the main solution, WLL system’s major problems would be enhanced both in service quality and capacity. This thesis proposes efficient power control technique based on centralized SIR balancing algorithm. Performance characteristics, enhanced service quality and system capacity of the proposed technique are presented. The study also explains related advantages of signal to interference, SIR, based power control algorithm which are used to increase network capacity, extend battery life and improve quality of service
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    Analysis of Electronic Attack Under Uav Platform Jamming
    (Addis Ababa University, 2008) Getnet, Ashagrie; Roy, DP (Professor)
    Ground base jammer cannot provide air space dominance for Ethiopia due to the massive highland complex of the country characterized by high rising mountains and dissected plateaus. In addition to this if high-flying systems and unsecured air space are piloted; it may be too dangerous in some situation to over fly certain areas. To overcome the above problem this thesis provides a good solution which is implementing a jammer on a UAV-platform. In this thesis, the Electronic Attack systems and the performance degradation of Surveillance Radar (P-15) due to UAV-platform jammer are described and analyzed. The jammer parameters were collected from simulation result as well as standards data. Using these parameters the effect of jamming on detection of targets is evaluated. The evaluation is performed by finding the change in radar SNR due to jamming and range reduction. The Predator-UAV type is the base system for this study much like the stand-off jammer. However, since the distance is closer to the radar, the EIRP jamming requirements are reduced. Stand-in jammer requires 6.3 watt at 50Km and stand- off jammer need 50 watt at 130Km from victim radar i.e. sufficient to jam P-15 Radar. For economical aspect stand-in jammer is much preferable for our country, since it provides 93% range reduction with a minimum amount of power.
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    Comparative Study on Bandwidth Enhancement Techniques of Microstrip Patch Antenna
    (Addis Ababa University, 2008-01) Hailu, Zewdu; Abdo, Mohammed (PhD)
    Conventional microstrip antennas in general have the attractive features such as low profile, light weight, easy fabrication, and conformability to mounting hosts. However, microstrip antennas inherently have a narrow bandwidth, low gain, and bandwidth enhancement is usually demanded for practical applications. In addition, applications in present-day mobile communication systems usually require smaller antenna size in order to meet the miniaturization requirements of mobile units. Thus, size reduction and bandwidth enhancement are becoming major design considerations for practical applications of microstrip antennas. For this reason, conducting studies to achieve compact and broadband operations of microstrip antennas is thought to be very important. The purpose of this thesis is to make a comparative study on the techniques that help to overcome the bandwidth constraint of microstrip patch antennas and to propose the better technique by taking different consideration such as the antenna gain, bandwidth and related issues. In this thesis work broad banding techniques like using feeding techniques (proximity coupled), stacked patches, parasitic arrangement of patches and the use of different shapes (i.e. E-shaped) are studied. The bandwidth obtained for each type of the antenna are 10.8%, 11.5%, 15.6% and 25.6% respectively with respect to the operating frequency of each of the antennas. The result shows that the E-shaped patch antenna has better performance. Key Words: patch antenna, return loss, bandwidth, gain
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    Bandwidth Improvement of Microstrip Antenna Using Log Periodic Technique
    (Addis Ababa University, 2008-03) Maare, Mekonen; Mohammod, Abdo (PhD)
    The thesis covers two aspects of microstrip antenna designs. The first is the analysis and design of single element narrowband rectangular microstrip antenna which operates at the central frequency of 2.4 GHz and the second aspect is the design of five element broadband Log Periodic microstrip antenna. Both antennas have been modeled, designed and simulated. Basically, transmission line and cavity modeling are going to use to model both antennas. First, the design parameters for single element of rectangular patch antenna have been calculated from the transmission line model equation and extend the antenna design to five element log periodic microstrip antenna using log periodic analytical technique. The simulation process has been done through momentum simulation using Empire software. Each data from the Finite Difference Time Domain Method (FDTD) simulation extract and combine with the microstrip transmission line. The rectangular microstrip antenna design uses Flame Retardant 4, FR4, microstrip board with dielectric constant 4.7, scaling factor 0.95 and loss tangent is 0.019. The properties of antenna such as bandwidth, S parameter has been investigated and compared between a single element rectangular and a five element log periodic rectangular microstrip antenna. .
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    Synthetic Speech Trained - Large Vocabulary Amharic Speech Recognition System (SST-LVASR)
    (Addis Ababa University, 2008-07) Birile, Mesfin; Mamo, Mengesha(PhD)
    Amharic is the official language of Ethiopia, which is characterized by very large morphological forms of words. This thesis is an investigation of the possibility of developing an Automatic speech recognition system (ASR) for Amharic using synthesized Amharic speech generated through concatenation of prerecorded morphemes, can be used to train a hidden markov model (HMM) based ASR system. The development of HMM based ASR system requires identification of all possible words and a construction of text and speech corpora containing multiple samples of the words to be recognized by the system. These data are then used as training sets in the development of the models, the final objective being the construction of HMM models for each recognition unit. Since there are a large number of morphological forms for the words in Amharic, the effort of collecting the Amharic words for constructing the text corpus and the recording and labeling of the same words for the speech corpus is extremely difficult. This thesis demonstrates that by developing an automatic morphological expander, the effort of developing the text corpus is reduced to a manageable level. Additionally, a significant reduction in the speech corpus development is achieved by using machine generated speech for training the HMM models of the ASR system. These reductions in the development efforts of the text and speech corpora greatly reduce the most prominent of the obstacles in developing a general purpose Amharic speech recognizer. The 62.37% word accuracy for naturally recorded speech indicates that using synthetic speech for training at least 62% of the words are correctly identified and suggests that with synthetic speech some level of recognition is possible, giving the imputes for more research in finding ways to increase this accuracy.
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    Usb Interface for Communication Between Fpga and Personal Computer
    (Addis Ababa University, 2009-03) Tadesse, Abiy; Higelin, Gerald (Professer)
    The USB Interface provides capability of utilizing the new bus standard to interface programmable device designs to personal computers. This is useful for real time applications such DAS. The USB Interface is described in VHDL which is synthesizable, implement-able and programmable on FPGA. The Xilinx ISE 8.2i is the design software suite which allowed taking the design from design entry through Xilinx device programming. The design is implemented on the Xilinx Spartan 3 (XC3S200) FPGA. The Xilinx Spartan-3 Starter Kit is used for testing the FPGA with PC using USB cable. The outshined performance of USB as compared to the previous interfaces and the reprogrammable feature and the wide use of FPGAs are the motivations for this thesis
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    Investigation of Mobile Station Position Location Technique for Cellular System
    (Addis Ababa University, 2009-08) Kefyalew, Dawit; Abdo, Mohammed (PhD)
    Wireless position location (PL) is a relatively recent technology in the field of wireless communication. The US federal communication commission FCC recommendation is the driving force for PL research since it requires that the wireless service provider include PL service for emergency calls. It is believed the majority of emergency calls come from mobile subscribers. In order to locate these subscribers by public safety answering point (PSAP) a lot of research is going on. Wireless PL is also an attractive business for service provider in the field of advertising, navigation, effective workforce management, information broadcast and other value added services for users. In this thesis an investigation of different PL technique is made. The advantages and disadvantages of the PL techniques are surveyed. Based on the investigation an optimum PL technique proposed. On investigation it is found that most PL techniques need three or more base stations (BS). There should be synchronization among them; which increases the signaling load of the network. Moreover these techniques assume a line of sight signal which is not valid specifically for urban environment. In order to solve this problem, this work focuses on PL technique using single BS using smart antenna. i In an urban environment where line of sight assumption is not valid Fingerprint Matching Technique is an optimum solution. Implementation of this technique across a test route near Tikur Anbessa Hospital shows 67% of location error is less than 72m. For suburban and rural environment with the assumption that at least one line of sight signal is available, a hybrid TOA/AOA technique using smart antenna is found to be an optimum solution for this environment. The simulation result shows that location error below 66m for 67% cab be attained
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    Analysis and Design of A Compact Microstrip Patch Antenna With Enhanced Bandwidth and Gain for Wireless Local Area Network (Wlan) Communications
    (Addis Ababa University, 2010-07) Debo, Feyisa; Abdo, Mohammed (PhD)
    In this thesis, the compact microstrip patch antennas in stacked configuration have been proposed. The microstrip patch antenna structure consists of a square patch with four equal u-shape on four sides of each patches. These structures provide an optimized patch area resulting in a substantial reduction in size compared to a typical microstrip square patch designed at the same frequency of operation. The characteristics of the antenna are obtained in terms of return loss, gain, radiation pattern and bandwidth and are compared with the conventional microstrip patch. The stacked configuration enhances both gain and bandwidth of the microstrip patch antenna at 2.45GHZ operating frequency. A size reduction of 70% is obtained along width 24.4dB gain and 6.6519GHZ bandwidth. The empire software is used to obtain the optimized performance of the proposed antenna. This antenna is found to be suitable for WLAN communications. Key Words: size reduction, stacked microstrip patch antenna, gain, bandwidth.
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    Bandwidth and Gain Performance Comparison Of Rectangular-Patch Microstrip Antenna (RMSA) And Coplanar Waveguide (CPW) Rectangular-Patch Antenna
    (Addis Ababa University, 2011-01) Abiy, Bekele; Mohammed, Abdo (PhD)
    In today’s world, microstrip antenna and coplanar waveguide patch antenna are used in all wireless communication such as cellular telephony, satellite, portable personal communication, aircraft, spacecraft, and missile applications. The growth and popularity of wireless application is quite dominant because of its mobility, the demand for high speed transmission of large data, customer request for multi-media service, and the need for new technologies, as well. This shows that there is a large investment that has been put in to wireless communication by major companies in the telecommunication industry. WLAN is one part of the investment that gains an increase in its usage because it provides high quality of services with low cost to more users. The IEEE 802.11 workgroup currently use three frequency ranges 2.4 GHz, 3.6 GHz and 5 GHz for WLAN technologies. Each range is divided into a multitude of channels. Countries apply their own regulations to both the allowable channels, allowed users and maximum power levels within these frequency ranges [1].
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    Performance Evaluation of Receivers for Ultra-Wideband Wireless Communication Systems
    (Addis Ababa University, 2011-07) Yenieneh, Welelaw; Adugna, Eneyew(PhD)
    Ultra Wide Band (UWB) is a promising technology for short range broadband wireless data communication, sensor networks, radar imaging and target identification, location finding and positioning applications. This technology is the best choice for short range wireless communication systems since it is cost-effective, power-efficient and has extremely higher data rates. Any wireless system that has a fractional bandwidth greater than or equal to 20% or a total bandwidth larger than or equal to 500MHz enters in the UWB definition. The Federal Communications Commission (FCC) has allocated 7.5GHz of spectrum for unlicensed use of ultra-wideband (UWB) devices in the 3.1 to 10.6 GHz frequency band and limits the maximum power spectral density (PSD) of the transmitted signal to -41.3dBm/MHz. The main subject of this thesis is to evaluate bit error rate (BER) performance of RAKE and adaptive MMSE receivers for UWB wireless communication systems. First, bit error rate (BER) performance of RAKE receiver on standard IEEE 802.15.3a channel model has been simulated. Here, the BER performance of RAKE receiver for different RAKE types, number of RAKE fingers, combining techniques, length of bit repetition codes, transmitted signal formats and channel types has been evaluated and compared for single user scenario. The simulation results show that an ideal ARAKE receiver using TH-BPSK-UWB transmitted signal format, MRC technique and applying bit repetition coder has the best performance. Then, bit error rate (BER) performance of adaptive MMSE receiver using LMS, NLMS and RLS adaptive algorithms has been evaluated and analyzed on standard IEEE 802.15.3a channel model for different number of users and the simulation results illustrate that adaptive MMSE receiver using RLS algorithm has the best BER performance. Finally, BER performance SRAKE receiver with 5 and 10 fingers has been compared with BER performance adaptive MMSE receiver using the above three adaptive algorithms for single user scenario. The simulation result describes that adaptive MMSE receiver using all the above three algorithms has by far the best BER performance compared to SRAKE receiver with 5 and 10 fingers. All the above simulations have been conducted using MATLAB software. Key Words: UWB, RAKE Receiver, Adaptive MMSE Receiver, LMS, NLMS, RLS, Modulation, Multiple Access, Spread Spectrum, WPAN
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    Performance evaluation of a layered space-time structure for MIMO systems
    (Addis Ababa University, 2011-07) Getaneh, Birlew; Hailu, Ayele (PhD)
    MIMO systems are an appealing candidate for emerging fourth-generation wireless networks due to their potential to exploit space diversity for increasing conveyed throughput without wasting bandwidth and power resources. Particularly, layered space-time architecture (LST) proposed by Foschini, is a technique to achieve a significant fraction of the theoretical capacity with a reasonable implementation complexity. It is based on signal processing and conventional one dimensional coding, which includes vertical BLAST (Bell Laboratories Layered Space Time) and diagonal BLAST. BLAST accomplishes this by splitting a single user’s data stream into multiple sub-streams and using an array of transmitter antennas to simultaneously launch the parallel sub-streams. All sub-streams are transmitted in the same frequency band, so spectrum is used very efficiently. Since the user’s data is being sent in parallel over multiple antennas, the effective transmission rate is increased roughly in proportion to the number of antenna elements used. In this thesis, we focus on the performance evaluation of a layered space-time structure for MIMO systems under Rayleigh fading condition. Firstly, we throughly understand the different layered space-time architectures and investigate the performance of general V-BLAST architecture with Maximum Likelihood (ML), Zero-Forcing (ZF), Minimum Mean-Square Error (MMSE), the Successive Interference Cancellation (SIC) and the Ordered Successive Interference Cancellation (OSIC) detectors for 2 × antenna arrangement. Here, in addition to performance (BER), the different detection algorithms are evaluated in terms of computational complexity. From the results, we have seen that the maximum-likelihood (ML) detector is optimum in the sense of achieving the minimum error probability. Unfortunately, the complexity of the ML detector is exponential in the constellation size and the dimensions of the system. But, by using the SIC & OSIC detectors, we approach the performance of the ML detector with lower computational complexity. It is also shown that the average performance is improved when the number of receive antenna increases. Finallly we understand and evaluate performance bound trends of Rate Compatible Punctured Convolutional (RCPC) codes and investigate the unequal error protection capabilities of rate compatible punctured convolutional codes (RCPC codes) when used together with V-BLAST MIMO systems for a mother code rate of 1/4. The