Browsing by Author "Hailemariam, Dereje (PhD)"
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Item Analysis of Blind Adaptive Equalization Techniques for Audio Broadcast System(Addis Ababa University, 2017-05) Amsalu, Tewodros; Hailemariam, Dereje (PhD)The wireless channel, in general, and the audio broadcasting range in particular is prone to time dispersion, which causes inter symbol interference (ISI). This dispersive channel must be compensated (equalized) by making a communication system adaptive to the time varying properties of the channel. Practically, in digital audio broadcasting training sequences may not be available to implement the adaptation, which makes blind adaptive equalization methods more appropriate for such application. In this thesis the performance of three blind adaptive equalization techniques; namely, constant modulus algorithm (CMA), multi modulus algorithm (MMA) and fractionally spaced constant modulus algorithm (FS CMA) are investigated for application in audio broadcasting. This investigation is part of a joint project between Information Networks Security Agency (INSA) of Ethiopia and the Addis Ababa University (AAU) that intends to implement advanced digital receiver for a certain application. To capture the broadcasting environment three channel models are used. Moreover, 16-quadrature amplitude modulation (QAM) is considered for the simulation. Symbol error rate (SER), rate of convergence, stability, complexity and audibility are used as performance metrics. The simulation result shows that FSCMA has much better SER performance than CMA & MMA which provide 1 to 1.5 SNR advantages over the other two methods. The three equalizers are able to recover the transmitted audio bit streams when the channel do not introduce phase shift; MMA being the only method capable of recovering phase shift. On convergence, once the algorithms converged they stay stable until the channel condition start to change. Finally, it was noted that the three equalizers are able to equalize the received input data faster than the sampling rate of the audio signal. From all the simulation results, FS CMA has better or comparable performance than the CMA and MMA. Therefore, the thesis recommends FS CMA for implementation by INSA with the assumption that a separate unit will handle the phase recovery implementation. AnalysisItem Channel Equalization Techniques for Amplify-and-Forward Cooperative Diversity Relaying Scheme(Addis Ababa University, 2012-03) Demissie, Mihret; Hailemariam, Dereje (PhD)Spatial diversity is a technique used in wireless communication to combat the effect of fading. This diversity scheme generally requires more than one antenna at transmitting and/or receiving node(s). However, many wireless devices are limited to one antenna because of size or hardware complexity. Recently, a new class of method called cooperative communication has been proposed. This method enables single antenna mobiles in a multi-user environment to share their antennas and generate a virtual multiple-antenna transmitter that allows them to achieve transmit diversity. Broadband wireless systems are emerging in order to provide high data rate services. However, the overall system performance will be degraded because of the frequency selectivity nature of the wireless channel. Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation technique which can mitigate inter-symbol interference (ISI) caused by the frequency selective fading. OFDM possesses the advantages of frequency parallel transmission, high speed communication and efficient spectrum usage. By introducing OFDM transmission into the cooperative communication technique, the gains from both sides are combined. However, one prominent problem of OFDM is its sensitivity against carrier frequency offset which results from either Doppler shift or synchronization loss at the transmitter and receiver oscillators. This carrier offset causes inter-carrier interference (ICI). Hence, efficient ICI reduction techniques are necessary to improve system performance. In this thesis, we focus on two methods of ICI reduction techniques; namely, time- and frequency-domain equalizations. In the frequency-domain equalization a correlative polynomial is used in the frequency domain to suppress the ICI. In time-domain equalization technique a window function is employed. MATLAB simulation of the two techniques shows that, the time-domain equalization scheme achieves better performance in ICI suppression compared to the correlative coding technique. In other words, time domain equalization technique offers better carrier-to-interference ratio (CIR) as compared to the correlative coding method. Key words: Cooperative diversity, OFDM, ISI, ICI, CIR.Item Cooperative Diversity for Broadband Vehicular Communication under Doubly-Selective Channel(Addis Ababa University, 2014-09) Mekonnen, Elleni; Hailemariam, Dereje (PhD)Previous works on vehicular communication assume the channel to be frequency-flat and quasi-static. But this assumption is unrealistic in now days where communication takes place at a high data rate and also when large number of reflectors are present between transmitter and receiver. These factors introduce frequency-selective behavior to the channel and also the movement of reflectors and/or communicating terminals makes the channel to be time-selective. Therefore it is better to assume our channel to be doubly-selective. Mitigation techniques are required to have a reliable communication in this type of channel. Precoding, equalizer and cooperative communication are considered as mitigation techniques in this thesis work. Selection Combining (SC) and Equal Gain Combining (EGC) are used as diversity combining scheme. It is assumed that the relay just amplifies and forwards (AF) the information it has received from the source. Simulation results show that cooperative diversity along with precoding and equalizer improves the performance of fading channel and hence provide a better service even in the worst type of fading channel i.e., doubly-selective channel. Taking a fixed bit error rate (BER) of 10-4, performance was improved by 2.5dB for EGC scheme and by 0.5dB for SC. Key Words: Doubly-selective channels, Equalizer, Precoding, Cooperative communication, Diversity combining.Item Cooperative MIMO System for WiMAX Technology(Addis Ababa University, 2012-09) Medhn, Samuel; Hailemariam, Dereje (PhD)Multipath fading is one of the primary factors that degrade the performance of wireless networks. One of the most powerful techniques to combat the effect of fading is by using multiple antennas that provides space diversity and spatial multiplexing; this technique is called Multiple-Input Multiple-Output (MIMO). Cooperative diversity, an alternative form of realizing MIMO, has been recently proposed to realize the diversity advantage in a distributed manner. Cooperative diversity exploits the broadcast nature of wireless transmission and creates a virtual antenna array through cooperating nodes. Although, prior research in cooperative diversity considers users equipped with single antenna, in practical scenarios users may be able to accommodate multiple antennas due to the recent advances in semiconductor industry. Hence, the primary purpose of this thesis is to model, and by using simulation, investigates the end-to-end performance of a cooperative diversity system employing multi-antenna at cooperating nodes; the intention is to simultaneously exploit the diversity gain offered by the cooperative diversity and multiple antennas. One contribution of this work is, we propose a cooperative MIMO system where the cooperation uses amplify-and-forward (AF) relaying strategy and the MIMO is based on Vertical Bell-Labs Layered Space Time architecture (VBLAST). The proposed system is to be used for WiMAX technology. Complexity of the cooperative MIMO system is also analyzed considering Maximum Ratio Combining (MRC) and Equal Gain Combining (EGC) schemes for Zero Forcing (ZF), Minimum Mean Square Error (MMSE) and Maximum Likelihood (ML) detection techniques. Simulation results show that cooperative MIMO system achieves significantly better symbol error rate (SER) performance than conventional cooperative diversity and MIMO systems with comparable complexity. As an example, for SER of 10-3, cooperative MIMO system using MMSE detection has 10 dB SNR gain over systems that employ cooperative diversity or MIMO only. Key words: Cooperative Diversity, MIMO, AF, VBLAST, WiMAX, SER, ComplexityItem Design and Development of WCDMA-based Distribution Transformer Monitoring System(Addis Ababa University, 2014-12) Eyasu, Biruk; Hailemariam, Dereje (PhD)In electrical power systems, distribution transformer is an equipment which distributes power to the low-voltage users. For proper operation (i.e., under rated conditions) of the transformers, their operational conditions should be monitored and maintained. Overloading and overheating are two sources of transformers failure that cause power disruption for the customers and reduce the life time of the equipments on the power distribution system. Since it is very costly to repair or replace a single transformer, it also has its impact on the economy of the country. Hence, a system that properly monitors the power system and take corrective action should be in place. This thesis presents the design and implementation of a Wideband Code Division Multiple Access (WCDMA) based distribution transformer monitoring system. This system monitors and records key parameters of a distribution transformer like load currents, load voltage, and transformer oil temperatures. These parameters provide useful information about the status of a transformer. The acquired parameters are processed and the data is sent to a central monitoring station through the WCDMA air interface. The data will then be further processed and analyzed each moment by the system operator. WCDMA has a very low latency which is best for real time systems. Besides that it provides a balance of trade-offs between cost, capacity, performance, and density. The system is designed and implemented in a laboratory using Wi-Fi network and key parameters were recorded. The variations of the recorded values help us in identifying the possible failure that could occur, if the values are over the rated values. Monitoring of the transformer has been achieved in the laboratory through our system. Then, possibly corrective actions, like balancing the loads on each phase or even switching the transformer off, can be taken before the failures happen and we can identify the parts of the electric power distribution system which need stabilizing from the history we get. The latency of the WCDMA was also calculated. The maximum time of arrival of the data at the central station was found to be less than 100ms. Thus, this implemented system will help the utility to improve fault restoration time and optimally utilize distribution transformers for a longer period of time. Key words: WCDMA, distribution transformer, monitoring Design and Development of WCDMA based DTMS ii AcknowledgmentItem Digital Dividend and its Opportunities for Emerging Wireless Services: the case of Ethiopia(Addis Ababa University, 2016-03) Matewos, Zemene; Hailemariam, Dereje (PhD)Digital television and mobile broadband services are significantly progressing for the past three decades; this progress, in turn, is putting a burden in the available spectrum. Two of the factors that contribute to the burden are: underutilization of the spectrum occupied by the previous analogue television transmission and congestion of the spectrum due to several wireless services supported by the spectrum. In Ethiopia, there are a limited number of terrestrial television channels and a single mobile service provider. Hence, there is no imminent challenge from spectrum scarcity at the present. However, as more television services commence in the future and the telecom infrastructure expands further, where both are in the immediate plans of the Government of Ethiopia, spectrum scarcity will likely be encountered. Digital dividend, which creates an opportunity in making use of the underutilized spectrum, is a promising solution for the problem facing the spectrum. Digital Dividend is a free spectrum band that will be created as a result of the transition from analogue to digital terrestrial television transmission. This spectrum can be used to support emerging services from the broadcast and telecom sectors. Therefore, a proper frequency resource planning that accommodates the two wireless systems is needed sooner or later. In light of this, this thesis shows how the resource can efficiently be used without a considerable interference impact between the two systems. As the world has sought the digital dividend as a hopeful solution in dealing with spectrum issues, this paper discusses the context of Ethiopia's spectrum issues Digital Dividend and its Opportunities for Emerging Wireless Services: the Case of Ethiopia Page IV in proposing the analogue switchover and showing coexistence among other wireless services. The coexistence and compatibility studies help radio planners and national frequency regulator bodies to come up with new management of the frequency resource. This facilitates a way forward for designing a standard spectrum plan before many wireless services begin to operate. In this study, the wireless environment of the City of Addis Ababa is analyzed with the possibility of applying the study for the rest of the country as well. The results obtained identify the region 700-1429 MHz band as a digital dividend out of which 795-1429 MHz band can be used for non television wireless services, particularly for broadband mobile services such as the Long Term Evaluation (LTE).Item Dimensioning and Radio Network Planning of Mobile WiMAX The Case of Addis Ababa(Addis Ababa University, 2013-02) Getenet, Benyam; Hailemariam, Dereje (PhD)Mobile Worldwide Interoperability for Microwave Access (WiMAX) is a broadband wireless technology based on the IEEE 802.16e standard. It is designed to provide voice, data and video services that require high data rates for fixed, nomadic and mobile users moving at vehicular speeds greater than 120 km/hr. Growth trends of voice and data traffic in various African countries reflect a huge increment in recent years. Currently deployed second and third generation telecommunication technologies will eventually struggle to swallow this perpetual traffic growth. This signals an eminent need to ultimately resort to deploying fourth generation (4G) technologies such as WiMAX that offer better throughput and coverage. This presents an opportunity/market potential for WiMAX or other 4G technologies. In order to deploy WiMAX in any given metropolitan area, it is imperative to perform dimensioning and radio network planning steps. The IEEE 802.16e standard offers several options/choices in its physical and medium access control layers. Within these choices, this thesis work focuses on carving out a mobile WiMAX package that fits a pre-defined coverage and capacity requirement of Addis Ababa city. The basic dimensioning steps for the access and core network are outlined and conducted using the geographic and demographic data of the aforementioned city. Radio network planning tools such as EDX-PRO and ATTOL cost in the order of thousands of US dollars. Therefore, in this research, a Radio Network Planning (RNP) tool/MATLAB program that operates on a selected propagation model and a digital terrain model database is developed and used. This thesis work, to the best of my knowledge, is the first research/case study to be conducted taking capacity and coverage requirements of developing nations. It is also the first research that is not constrained to capacity and coverage planning via theoretical analysis. Theoretical coverage estimations make use of empirical propagation models without any special consideration to the specific terrain type. The development of the RNP tool allows us to perform a more accurate coverage analysis based on actual terrain parameters that are extracted from a digital map. The RNP tool is used on five distinct metropolitan areas with different terrain type, namely, Bole Medhanialem, Gerji, Meskel Square, Piassa and Sidist Kilo. The average coverage per base station is computed from the results of these five areas. This process is useful in forecasting the total number of base stations required to offer the service on every corners of Addis Ababa or a selected portion of the city.Item Downlink Performance Evaluation of Coordinated Multi-Point: The Case of Addis Ababa LTE Network(Addis Ababa University, 2017-02) Beyene, Sisay; Hailemariam, Dereje (PhD)The current Addis Ababa Long Term Evolution (AA LTE) is deployed to provide better data service for users. But mobile data network performance is negatively affected - especially for cell edge users - by inter-cell interference (ICI) resulting from short inter-site distance and the use of frequency reuse factor 1. One method to overcome the ICI is the use of coordinated multi-point (CoMP). In this thesis the effect of CoMP joint transmission was studied for mitigating the ICI in the AA LTE. To check the feasibility of the proposed solution, the performance of the current AA LTE is evaluated using simulation and considering CoMP joint transmission. Evaluation of the network performance is done for a selected test case area in Addis Ababa city and considering actual base station locations and the terrain data of the city. The simulation is done for a 20 MHz bandwidth and the round ribbon scheduling algorithm is used for radio resource allocation for both CoMP and non-CoMP system. The results from the simulation show that by using CoMP the signal to interference noise ratio (SINR), and throughput for the average and cell-edge user show considerably significant improvement. The results show that the SINR increased by 1.5dB for the cell edge user and by 1.9dB for the average user in intra-site CoMP. For the inter-site CoMP system, an increase in SINR of 5.6dB and 4.3dB for the cell edge user and cell average user respectively is observed. In addition, the throughput for the cell edge user and average user improved by 14% and 6% respectively for intra-site CoMP and by 18 % and 10% for inter-site CoMP. These results show that CoMP joint transmission is worthy for deployment in the current AA LTE and can improve the coverage for cell edge usersItem Estimation and Analysis of Network Capacity Under the Introduction of Mobile Banking: Case of Ethiopia(Addis Ababa University, 2014-03) Asmelash, Hilfti; Hailemariam, Dereje (PhD)This thesis work is based on a value added cellular technology service called mobile banking (m-banking). Mobile banking is a term used for performing balance checks, account transactions, payments, credit applications via a mobile device such as a mobile phone. Since mobile banking is a new avenue in Ethiopia for bringing financial service to the unbanked, how the additional traffic generated by mobile banking will impact the existing telecom network by forecasting its traffic demand is done in this particular paper. Therefore by clearly understanding the mobile banking system and platform implementation, network capacity audit is performed for the existing telecom system against the additional capacity this service requires for the case of Ethiopia. So this way one can recommend the best business model or technology option that suits the country the most. Network performance analysis and evaluation is normally done to keep subscribers satisfied with the delivered quality of service. In this thesis, the existing network is studied and evaluated whether or not it can handle the additional traffic introduced by mobile banking. Network performance audit for the radio access network is done using a comparative process with an initial baseline of Key Performance Indicator (KPI). The performance indicators used to evaluate the radio access network are: Traffic Channel (TCH) and Standalone Dedicated Control Channel (SDCCH). The experience of several African countries was taken into account to create the scenarios used in this research due to the fact that previous work to bridge the two areas, i.e. mobile banking and network capacity hasn’t been made in the country. For this study two sites in Addis Ababa are selected. One of the sites is considered to have a very high traffic volume or congestion rate and the other is with a moderate trafficThis thesis work is based on a value added cellular technology service called mobile banking (m-banking). Mobile banking is a term used for performing balance checks, account transactions, payments, credit applications via a mobile device such as a mobile phone. Since mobile banking is a new avenue in Ethiopia for bringing financial service to the unbanked, how the additional traffic generated by mobile banking will impact the existing telecom network by forecasting its traffic demand is done in this particular paper. Therefore by clearly understanding the mobile banking system and platform implementation, network capacity audit is performed for the existing telecom system against the additional capacity this service requires for the case of Ethiopia. So this way one can recommend the best business model or technology option that suits the country the most. Network performance analysis and evaluation is normally done to keep subscribers satisfied with the delivered quality of service. In this thesis, the existing network is studied and evaluated whether or not it can handle the additional traffic introduced by mobile banking. Network performance audit for the radio access network is done using a comparative process with an initial baseline of Key Performance Indicator (KPI). The performance indicators used to evaluate the radio access network are: Traffic Channel (TCH) and Standalone Dedicated Control Channel (SDCCH). The experience of several African countries was taken into account to create the scenarios used in this research due to the fact that previous work to bridge the two areas, i.e. mobile banking and network capacity hasn’t been made in the country. For this study two sites in Addis Ababa are selected. One of the sites is considered to have a very high traffic volume or congestion rate and the other is with a moderate trafficUSSD ;STKItem Feasibility Study of TV White Space for Broadband Internet Services The Case of Rural Ethiopia(Addis Ababa University, 2017-01) Mekonnen, Mesele; Hailemariam, Dereje (PhD)Now a day’s internet is one of the most important things in our daily activities. Providing broadband internet by currently prevailing technologies for all people is challenging task especially for communities who live in rural and remote areas. One possible solution to provide broadband internet for rural areas is by using wireless technologies which work at unused spectrum. One of the candidate technologies which can minimize the problem of the rural broadband connectivity is a band which is allotted for terrestrial TV broadcasting but not used; referred as TV white space. The work of using TV white space for rural broadband internet service has been started in different parts of the world. In order to deploy TV white space network for rural Ethiopia, the government’s policy toward the use of communication media and the pattern of community settlement will affect the network architecture. In Ethiopian scenario, it is assumed that available telecom infrastructure will be used for backbone network; since Ethiopian government takes monopoly of all communication media and there will be no private service provider. From the simple mathematical computation, it is assumed that Okumura-Hata path loss model can be used for rural Ethiopia. Even though ample amount of spectrum is allocated for terrestrial TV broadcasting in Ethiopia, only fraction of it is being used and it will be available for other secondary applications. Finally, this thesis showed that TV white space is financial feasible for rural Ethiopia compared with currently prevailing technologies even though handset cost is unaffordable. Key Words: TV White Space; Rural broadband; Financial Feasibility; Quantitative Amount of TVWSItem Genetic Algorithm-Based Joint Channel Estimation and Data Detection For Multi-User Mimo(Addis Ababa University, 2014-04) Getu, Asmamaw; Hailemariam, Dereje (PhD)To increase the number of users supported by a basestation, current technologies use space division multiple access (SDMA) as one of spectral efficient multiplexing method. Multi-user multiple-input multiple-output (MU-MIMO) is one of the special cases of SDMA which uses different channel estimation (CE) and data detection (DD) methods at the receiver. In this thesis uplink cellular communication system with four simultaneous users, each occupied with a single transmitter antenna and two receiver antennas at the basestation is designed. Transmitted signals from different users are detected at the basestation receiver using their unique user specific spatial signature constituted by their frequency domain channel transfer functions (FD-CHTFs). Accurate channel state information (CSI) is required at the receiver for coherent demodulation and interference cancelation. Due to large number of independent transmitter to receiver links CE is more challenging for MU-MIMO. Genetic algorithm (GA) is used as an effective solution to the MU-MIMO joint CE and DD problem in the above mentioned overloaded scenario. GA-based channel estimator and GA-based data detector are designed independently using selection, crossover, mutation, and replacement operators. Optimum parameter values are selected using observation of change in fitness values with change in parameter values. Performance comparisons between different CE and DD methods are made by using bit error rate (BER) and mean square error (MSE) values at specific signal-to-noise ratio (SNR) points. GA-based joint channel estimation and data detection (JCEDD) is designed by combining GA-based CE and GA-based DD and performance of the receiver is compared with other JCEDD methods. Reliability of the overloaded receiver is further increased by the use of low-density parity-check (LDPC) channel encoder. Key words: MU-MIMO, Channel estimation, Multi-user detection, Genetic algorithm.Item Green GSM Network Operation for Energy-Efficiency via Basestations Switching Technique The Case of Addis Ababa, Ethiopia(Addis Ababa University, 2017-02) Mesfin, Mikias; Hailemariam, Dereje (PhD)Green communication is an innovative research area to find information and communication technology (ICT) solutions that can greatly improve efficient utilization of resources such as energy and network equipments with minimum compromise in the users quality of service (QoS). Nowadays, the globe is facing a number of serious global warming problems; these problems have a significant negative impact in terms of the environment, global health, social and economic well being. The main causes of global climate change are growing need of energy, wastage, cutting trees, global industries, etc. From the global growing need of energy, 2 up to 10% are consumed by the global ICT industry in manufacturing, using, and disposal of ICT equipments. One third (1/3) of the total ICT's energy is consumed by the telecommunication equipments; cellular networks consume 90% of it. Basestations, in turn, consume 60 to 80% of the cellular network consumption. So, green communication researches are getting high interest recently years to minimize greenhouse gas emission and also operator energy bill. Considering the densely deployed basestations in the city of Addis Ababa, Ethiopia, this thesis focuses on applying switching-off basestations during off-peak (low traffic) hours as one strategy to realize green cellular network while fulfilling the requirements of voice and data traffic. The study considers 26 Global System for Mobile communications (GSM) basestations in Addis Ababa around Leghare area. Based on the hourly traffic statistics obtained from the ethio telecom, which is the sole telecommunication network service provider in Ethiopia, the area has high traffic from 5:00 am to 11:00 pm and low traffic during night time which is from 11:00 pm to 5:00 am. The latter is considered as the off-peak hours in this thesis. The basestations switching off technique is done by turning off basestations remote radio unit (RRU) and applying antenna electrical downtilt and azimuth angles chang [Green GSM Network Operation for Energy-Efficiency via Basestations Switching Technique.. on active basestations by considering ethio telecom basestations operation and maintenance (OAM) system capabilities of both turning off and angles changes. The switching-off strategy requires first sub-clustering basestations from the selected 26 basestations which are called in this thesis as cluster that are needed to cover the area of Leghar. This is done by comparing the existing coverage radius of basestations which are expected to cover at peak hours with that of the maximum coverage radius of basestations which basestations can cover theoretically. Each sub-cluster members are grouped as one sub-cluster if they can able to cover each other during switching off. Secondly, the traffic capacity of the sub-cluster is compared with the traffic prediction of the off-peak hours to ensure that the sub-clusters (and hence, the total active basestations) can handle the generated traffic. Then, optimize the coverage area of the sub-clusters by modifying the basestations antenna electrical downtilt and azimuth angles. The area of Leghar can be covered by 11 basestations out of 26 basestations during off-peak hours by applying the tilt and azimuth angles change. With acceptable coverage and service quality, the proposed solution of switched off basestations during off-peak hours yields above 10% energy saving for the all 26 basestations. Key words: GSM, Green communication, power consumption, energy consumption, prediction, sub-clusterItem Inter-Cell Interference Mitigation in LTE Downlink Using Static Interference Coordination: Case of Addis Ababa(Addis Ababa University, 2016-01) Moges, Michael; Hailemariam, Dereje (PhD)Recently, Long Term Evolution (LTE) has been deployed by many operators to address the growing data needs. Ethio telecom is among those operators that have deployed LTE in Addis Ababa. As other new emerging technologies, LTE uses orthogonal frequency division multiple access (OFDMA) technology to improve the system performance. However, the currently deployed LTE network has low average downlink throughput due to the deployment uses reuse factor of 1 in which every cell can provide services over the entire system band. Associated with reuse factor of 1, therefore, there will be inter-cell interference between neighbor eNodeBs when they try to use the same resource blocks to their user equipment. For cell-edge users (CEUs), the effect of inter-cell interference is especially severe. Therefore, to improve the throughput, inter-cell interference must be mitigated. Different methods have been proposed to mitigate this interference and interference coordination using static inter-cell interference coordination (ICIC) algorithm is the main one. Hence, this thesis focuses on the evaluation of static ICIC algorithms: hard fractional frequency reuse (Hard FFR), soft frequency reuse (SFR), partial frequency reuse (PFR) and soft fractional frequency reuse (SFFR) in already existed LTE network of Addis Ababa using simulation software. For this case study, sample sites around Gotera area of Addis Ababa are randomly selected. All these static ICIC algorithms are compared using the performance metrics such as peak throughput, the carrier to interference plus noise ratio (CINR) of the data channel and coverage probability. Simulation results shows that static ICIC schemes have better performance than reuse 1 scheme and from static ICIC algorithms, PFR algorithm has better average throughput and coverage probability of throughput. Key words: Cell-edge user (CEU); Inter-cell Interference coordination (ICIC); Hard fractional frequency reuse; Partial frequency reuse (PFR); Soft frequency reuse (SFR); Soft fractional frequency reuse (SFFR).Item 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.Item LTE Radio Network Planning: Modeling Approaches for The Case of Addis Ababa.(Addis Ababa University, 2012-07) Seifu, Bethelhem; Hailemariam, Dereje (PhD)This particular thesis paper is based on the newly advanced cellular technology called Long Term Evolution (LTE). It is intended to give a good understanding of Radio Network planning of LTE and perform a case study in Addis Ababa as to improve the existing network deployment. The LTE Radio network planning involves coverage estimation, capacity evaluation and frequency planning. In this thesis the coverage estimation is done with consideration of the real environment information at its nominal stage to obtain better estimations. The propagation modeling is done using COST 231 W/I model with inclusion of additional parameters obtained from the real environment/terrain model which improves the coverage estimation. The LTE planning was performed as case study in selected area of Addis Ababa with 53 km2 area around the National Hotel. The existing GSM network in the area entertains more than 40 GSM basestations with 1800 MHz bandwidth where one GSM basestation is planned to cover only 0.86 Km2. With proper network planning or optimization of the existing GSM network or even implementing of newly developed cellular technologies such as LTE surely improve the coverage area. Thus, this thesis commence LTE implementation in the area with initial radio planning to properly reduce the number of basestations to less than 10 eNodeBs (eNBs) and at the same time improve the capacity. Key Words: LTE Radio Network Planning; Coverage Planning; Capacity PlanningItem Multichannel Multipoint Distribution Service Coverage Planning for Addis Ababa City(Addis Ababa University, 2012-10) Azmeraw, Bereket; Hailemariam, Dereje (PhD)Multichannel Multipoint Distribution Service (MMDS) is one of the currently used Fixed Wireless Broadband (FWB) systems that provide multichannel broadcasting, broadband internet and other interactive services. It works mostly at 2.5-2.7 GHz frequency band through terrestrial propagation. As its name implies, it provides multiple television channels because of its high frequency band. It is more cost efficient than cable and satellite broadcastings for relatively small coverage areas like cities and towns. Addis Ababa is a city with a population size of more than 4 million that have complex linguistic, cultural, religious and ideological varieties. The city is the site for many diplomatic community and hosts many international organizations. Moreover, it accommodates many international conferences. Addis Ababa, which has now only few television channels, needs to benefit from broadcast communication systems like MMDS that can provide far more number of channels with relatively lower cost to foster its national and international values for maximum benefit. In this thesis, coverage planning of MMDS, which is an integral part of the entire planning, is carried out for Addis Ababa. In coverage planning, propagation models are used to predict the path loss at a certain distance from the transmitter site considering terrain and other environmental effects. The planning involves two steps; firstly, system dimensioning is done using the Institute of Electrical and Electronic Engineering, IEEE 802.16 (Stanford University Interim) model. Secondly, detail planning is accomplished using the International Telecommunications Union Recommendation, ITU-R P.1546-5 model. In coverage planning, the important parameters are the transmitter output power, number of transmitters needed, locations of transmitters for maximum coverage, and the positions and output powers of repeaters to cover small shadowed areas. Most of these parameters are determined based on the propagation models used. This work took 10 high altitude locations in the city as candidate sites for maximum coverage. The result shows that one 70 meter transmitter with 57dBm output power located at a mountain around Lebu area (South-Western part of Adds Ababa) and a 25 meter repeater with 32 dBm MMDS Coverage Planning for the City of Addis Ababa Page V output power located around Country Club Developers Homes (North-Eastern tip of Addis Ababa) can cover 96.14% of the area of the city, which is satisfactory coverage. Keywords Multichannel Multipoint Distribution Service, Propagation models, Broadcasting, Coverage planning, System dimensioning, detailed planning, ITU-R P.1546-5 model.Item Nominal and Detailed LTE Radio NetworkPlanning: Case of Kirkos Sub Sub-City in Addis Ababa(Addis Ababa University, 2016-05) Mamo, Tewodros; Hailemariam, Dereje (PhD)The requirements of higher data rate, l network architecture evolves the third generation mobile Generation (4G). Being part of 4G, Long Term Evolution (LTE) is the evolution of 3G counterparts, Universal Mobile Telecommunications System (UMTS) and Code division multiple access (CDMA), to provide a seamless connectivi (UE). The advancement of wireless communication technologies and the increasing size of radio network make the tasks of radio network planning more challenging and attention has to be given for nominal and the desired requirements after deployment. The nominal and detailed LTE radio network planning involves consideration of basic network requirements in terms of coverage, capacity and Quality of Service (QoS). In this study, the importance of such basic requirements has been illustrated using mathematical analysis as well as computer radio network planning strategies to the operator and local practicing planning area. The study considers Kirkos sub city in Addis Ababa, deployment scenario for the sub city. using the nominal parameters in the detailed plannin coverage prediction and capacity evaluation in terms of a given subscriber future growth. result shows a better network coverage with an optimum network capacity can be achieved in due consideration of network parameters starting from the nominal planning stage till the detailed planning phases in combination of pre optimization requirements at the initial stage. As there will be a similar need in the other part of the country, these findings can be used as reference for new build as well as expansion of the existing LTE network in the future. Keywords: Long Term Evolution, LTE Planning, Nominal Plan Link Budget, Cellular Network Planning, and 4G. Planning: Case of Kirkos Sub-City in Addis Ababa Abstract low latency system, and all-IP (Internet Protocol) communication towards the Fourth connectivity between two end User Equipments s and, hence detailed LTE radio network planning so as to achieve eration computer-aided simulations in order to disclose the LTE engineering in the Ethiopia, in view of new After analysis of the data taken from the sub city and planning, the study resulted in target area erence Planning, Detailed Planning, LTE RadioLink Budget, Cellular Network Planning, and 4G.Item Performance Analysis and Investigation of Non-blind Adaptive Equalizers for Broadcasting Channels(Addis Ababa University, 2016-10) Tesfaw, Amare; Hailemariam, Dereje (PhD)Adaptive equalization is a process of compensating the disruptive effects caused by inter symbol interference (ISI) in a band limited channel and plays a vital role for enabling higher data rate transmissions in digital communication systems. In this thesis, different linear and non-linear non-blind equalization techniques were studied to select the appropriate technique to be applied in frequency selective broadcasting channels. The study is part of a joint project between Information Networks Security Agency (INSA) of Ethiopia and Addis Ababa University (AAU) that intends to implement advanced digital receiver with adaptive equalizer for a certain application in broadcasting systems. For simulation test, Recursive Least Square (RLS) algorithm based linear equalizer was implemented in MATLAB software. Using this equalizer, it was possible to recover a corrupted image signal successfully after passing through a frequency selective fading channel modeled as typically urban (TU) model with 6 signal paths. Performance of the RLS equalizer in training only and decision directed training modes were also compared and simulation results show that the RLS equalizer in decision directed training mode performs better than the same equalizer in training only mode. Therefore, based on the results obtained, the RLS equalizer in decision directed training mode is recommend for implementation by the industry. Keywords: Adaptive Equalizer, Frequency Selective Channel, Adaptive Algorithms, LMS Algorithm, RLS Algorithm, Broadcast Channels, TU6 Channel Model.Item Performance Analysis of Space Time Coding on Mimo and Cooperative Diversity System(Addis Ababa University, 2011-07) Girma, Dereje; Hailemariam, Dereje (PhD)In a wireless network, users can relay information to exploit cooperative diversity, thereby increasing reliability. The uses of multiple transmit and receive antennas (MIMO) can help to exploit transmit and receive diversity respectively. This thesis discusses the application of a technique called space time block coding (STBC) on a system based on the joint use of cooperative diversity and MIMO schemes, which we hope intuitively that the system performance can be increased further. A source node, equipped with two transmits antennas, first encodes incoming data using STBC and then broadcasts the resulting code to relay and destination nodes. Then, the two relay nodes, each equipped with single antenna, either amplify-and-forward (AF) or decode-and-forward (DF) the received codes to the destination. The destination node combines (e.g., using maximum ratio combining (MRC)) signals received from the source’s and relay’s antennas and decodes the combined signal in order to recover the original data. As the signals from the source and relay are received through different paths, which are assumed to be spatially independent, spatial diversity can be exploited. Compared with point-to-point transmission system and simple Alamouti STBC system with no relays, AF based STBC system obtains one additional benefit, achieving spatial diversity offered by the relays. Moreover, the STBC-based DF cooperative system has two additional benefits. First, it achieves the spatial diversity offered by the relay channel and secondly, it has the ability to introduce the characteristics of STBC into the relay system. In addition, the system model and performance evaluation of these systems in various channel conditions and modulations (using simulation) will be addressed.Item Performance Evaluation of Pilot-based Channel Estimation Techniques at Higher Modulation Order for LTE MIMO Downlink System(Addis Ababa University, 2016-02) Berhan, Daniel; Hailemariam, Dereje (PhD)The number of smartphone users is increasing with increase in demand for high data rate. To fulfill this growing data rate demand, Long Term Evolution (LTE) is one technology option that is being widely deployed nowadays. LTE uses Orthogonal Frequency Division Multiplexing (OFDM) in the downlink system as its modulation scheme and multiple-input multiple-output (MIMO) antenna to achieve the high data rate. OFDM has the advantage over the conventional single-carrier modulation schemes when the channel is frequency-selective fading and is widely used in current wireless networks. There are different types of data detection methods used in the current wireless technology. However, detection without the knowledge of the channel state information (CSI) is challenging and if not impossible. This is because of the fact that the transmission channel between a transmitter and a receiver can vary be from a simple line-of-sight to a severely faded one by multipath fading; moreover, the channel is random and time varying in nature. Hence, channel estimation methods are required to acquire the CSI. LTE uses cell-specific reference signals (CRS) or known pilots to estimate the channel properties. Different pilot-based channel estimation techniques are developed over the last few decades. These include Least Square (LS) and Linear Minimum Mean Square Error (LMMSE) algorithms. Previous work on channel estimation is limited to single-input single-output (SISO)-OFDM and MIMO-OFDM systems in combination with lower modulation schemes like binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK). Further study is required to understand the performance of MIMO-OFDM technology in LTE and at higher order modulation schemes that include 16 quadrature amplitude modulation (QAM) and 64 QAM. This thesis investigates the performance of higher-order modulation schemes for the downlink of LTE based on MIMO-OFDM. LS and LMMSE channel estimation algorithms are considered at the receiver. Moreover, international telecommunication union (ITU) channel models such as extended pedestrian A model (EPA), extended vehicular A model (EVA) and extended typical urban (ETU) are used to characterize the propagation environment. Simulation results show that, ii LMMSE has a higher gain than LS; however, the relative gain diminishes at higher SNR regions, specifically for SNR >30 dB. Similar results were reported in previous researches for the same system and channel model types but for lower order modulations. Key words: - LTE, pilot-based channel estimation, MIMO, EPA, EVA, ETU