First-generation, line-of-sight (LOS) fixed broadband wireless access techniques have been around for several years. However, services based on this technology have been limited in scope to service areas where transceivers can communicate with their base stations, unimpeded by trees, buildings and other obstructions. This limitation has serious consequences in that the system can deliver only 50% to 70% coverage within a given cell radius, thus affecting earned revenue. Next generation broadband fixed wireless access techniques are aimed at achieving a coverage area greater than 90%. To achieve this target, these techniques must be based on a point-to-multipoint (PMP) cellular architecture with low base station antennas, thus possessing the ability to operate in true non-line-of-sight (NLOS) conditions. A possible limiting factor for these systems is link degradation due to interference. This thesis presents a new model to estimate the levels of co-channel interference for such systems operating within the 3.5 GHz multichannel multipoint distribution service (MMDS) band. The model is site-specific in that it uses statistical building/roof height distribution parameters obtained from practically modeling several metropolitan cities in the U.S. using geographic information system (GIS) tools. This helps to obtain a realistic estimate and helps analyze the tradeoff between cell radius and modulation complexity. Together, these allow the system designer to decide on an optimal location for placement of customer premises equipment (CPE) within a given cell area. / Master of Science

寬頻擴散可促進國家之生產力、就業、經濟成長及國家競爭力等，若能精準找出促進寬頻擴散之關鍵影響因素，將有利於政府集中資源有效率地推動寬頻發展。本研究提出研究問題與假說，以Rogers (2003)及Hall (2006)所提出影響創新擴散速率之社經因素、採用成本、採用效益、網路效應、資訊及不確定性及產業環境等6大因素面向為基礎，蒐集OECD國家及台灣等31國家相關資料，挑選Gompertz模型進行固定寬頻擴散Panel資料迴歸分析，發現各因素在全期及不同擴散階段有不同之顯著性與影響程度，表示分階段分析有其必要性。擴散初期之關鍵影響因素為收入、教育水準、平台競爭程度、人口密度及實施LLU累積年度等5項，而擴散後期之關鍵影響因素為寬頻價格、網際網路內容、決定採用時固定寬頻用戶比例、撥接用戶比例及擁有PC家庭比例等5項，可作為政府及業者於不同擴散階段精準投入資源以有效推動寬頻擴散之參考。 本研究續以前述分析結果選取日本、南韓、美國、丹麥、瑞士及台灣進行實際擴散比較，確認前述關鍵影響因素挑選之有效性。擴散初期，台灣有高人口密度優勢，若能提早推動寬頻並推動促進競爭措施，可促進初期之快速擴散。擴散後期，台灣國際排名退步，原因為寬頻價格過高，故此階段政府及業者應特別確保寬頻價格能夠使潛在採用者有能力並願意付費採用，才能促使寬頻持續有效擴散。 最後，本研究採用與固定寬頻相同迴歸分析模型對FTTX及行動寬頻分別進行分析後，有關行動寬頻，教育水準、寬頻價格、決定採用時行動寬頻用戶比例、人口密度、網際網路內容、使用固定寬頻語音服務比例、決定採用時FTTX用戶比例及使用網際網路家庭比例等8項變數有顯著效應；有關行動寬頻，收入、寬頻價格、網際網路內容、決定採用時行動寬頻用戶比例、使用網際網路家庭比例及人口密度等6項變數有顯著效應。因此，政府及業者若擬促進特定寬頻服務發展，仍須針對其服務特性推動特定之政策或策略。其中，寬頻價格、網際網路內容、網路效應及使用網際網路家庭比例等4項因素對FTTX及行動寬頻服務之影響類似，而此4個因素與固定寬頻後期擴散之關鍵影響因素較相近，因此，對於已存在市場的服務，即使是後來以較佳品質或功能之新服務型式提供，新服務之關鍵影響因素仍較接近已存在市場服務關鍵因素。 總之，本研究不同於過去文獻，以創新擴散理論為基礎，以國家層級資料量化分析與探討寬頻擴散之關鍵影響因素，除分別提供政策及管理建議供政府及業者參考外，亦補強Rogers (2003)及Hall (2006)所提出創新擴散理論未釐清與比較創新擴散影響因素在不同擴散階段影響之不足。 / Broadband diffusion may enhance innovation, productivity, employment, economic growth, and, ultimately, national competitiveness. If key determinants for broadband diffusion are identified, governments can align its resources with them to effectively promote the diffusion. Based on the determinants of the diffusion rate identified by Rogers (2003) and Hall (2006), this research compiled data available about OECD countries as well as Taiwan to implement overall and staged panel regressions on fixed broadband diffusion by adopting Gompertz model. The findings indicate that the significance of the determinants varies between overall and staged analysis, which consequently justifies the necessity of a staged analysis. The key determinants in the early stage are income, education level, platform competition, population density, and the accumulated years of implementing LLU policy; however, in the late stage they are broadband price, Internet content, network effect, the penetration of dial-up users, and percentage of household with computer. Governments may more accurately promote broadband diffusion according to different key determinants in different stages. This research further compared the real fixed broadband diffusion of Japan, South Korea, USA, Denmark, Switzerland, and Taiwan based on the previous analysis results. The findings generally justify the choice of key determinants in the previous analysis. In the early stage, Taiwan had the advantage of high population density. If the government could have promoted fixed broad banded services and market competition earlier, the penetration would have grown much faster. In the late stage, since the broadband price was too high in Taiwan, its international ranking of fixed broadband penetration declined. Therefore, in order to further promote the diffusion of fixed broadband, the government should have ensured that the price was low enough to convince the potential adoptors to purchase broadband services. Finally, this research adopted the same approach as that of previous fixed broadband to analyze the diffusion of FTTX and mobile broadband, respectively. Education level, broadband price, network effect of FTTX, network effect of mobile broadband, Internet content, population density, percentage of household with computer, and the penetration of fixed VOIP users have significant effect on FTTX diffusion. However, income, broadband price, network effect of mobile broadband, Internet content, population density, and percentage of household with computer have significant effect on mobile broadband diffusion. Therefore, governments or operators should tailor their policies or strategies for specific services. The effects of broadband price, Internet content, network effect, and percentage of household with computer are similar in both FTTX and mobile broadband, and they are also similar to the key determinants of fixed broadband diffusion in the late stage. Therefore, even though a new service with better quality or function is introduced in an existing market, its key determinants are more similar to those of the existing service depending on its diffusion stage. In conclusion, different from previous research, this one applied national-level data to quantatively analyzed and explore the key determinants of broadband diffusion based on innovation diffusion theory. The research findings not only propose policy and management suggestions to governments and service providers, but also supplement the the theory proposed by Rogers (2003) and Hall (2006), which did not identify and compare the determinants of innovation in different diffusion stages.

Fixed Broadband Wireless Access (FBWA) is a technology aimed at providing high-speed wireless Internet access, over a wide area, from devices such as personal computers and laptops. FBWA channels are defined in the range of 1-20 MHz which makes the RF front end (RFE) design extremely challenging. In its pursuit to standardize the Broadband Wireless Access (BWA) technologies, IEEE working group 802.16 for Broadband Wireless Access has released the fixed BWA standard IEEE 802.16 – 2004 in 2004. This standard is further backed by a consortium, of leading wireless vendors, chip manufacturers and service providers, officially known as Wireless Interoperability for Microwave Access (WiMAX). In general, any wireless base station (BS), supporting a number of contiguous Frequency Division Multiplexed (FDM) channels has to incorporate an RF front end (RFE) for each RF channel. The precise job of the RFE is to filter the desired channel from a group of RF channels, digitize it and present it to the subsequent baseband system at the proper sampling rate. The system essentially has a bandpass filter (BPF) tuned to the channel of interest followed by a multiplier which brings the channel to a suitable intermediate frequency (IF). The IF output is digitized by an ADC and then brought to the baseband by an appropriate digital multiplier. The baseband samples, thus generated, are at the ADC sampling rate which is significantly higher than the target sampling rate, which is defined by the wireless protocol in use. As a result a sampling rate conversion (SRC) is performed on these baseband samples to bring the channel back to the target sampling rate. Since the input sampling rate need not be an integer multiple of the target sampling rate, Fractional SRC (FSRC) is required in most of the cases. Instead of using a separate ADC and IF section for each individual channels, most systems use a common IF section, followed by a wideband ADC, which operates over a wide frequency band containing a group of contiguous FDM channels. In this case a channelizer is employed to digitally extract the individual channels from the digital IF samples. We formally call this system a receiver channelizer. Such an implementation presents considerable challenge in terms of the computational requirement and of course the cost of the BS. The computational complexity further goes up for FBWA system where channel bandwidth is in the order of several MHz. Though such a system has been analyzed for narrow band wireless systems like GSM, to the best of our knowledge no analysis seems to have been carried out for a wideband system such as WiMAX. In this work, we focus on design of a receiver channelizer for WiMAX BS, which can simultaneously extract a group of contiguous FDM RF channels supported by the BS. The main goal is to obtain a simple, low cost channelizer architecture, which can be implemented in an FPGA. There are a number of techniques available in the literature, from Direct Digital Conversion to Polyphase FFT Filter Banks (PFFB), which can do the job of channelization. But each of them operates with certain constraints and, as a result, suits best to a particular application. Further all of these techniques are generic in nature, in the sense that their structure is independent of any particular standard. With regard to computational requirement of these techniques, PFFB is the best, with respect to the number of complex multiplications required for its implementation. But it needs two very stringent conditions to be satisfied, viz. the number of channels to be extracted is equal to the decimation factor and the sampling rate is a power of 2 times baseband bandwidth. Clearly these conditions may not be satisfied by different wireless communication standards, and in fact, this is not satisfied by the WiMAX standard. This gives us the motivation to analyze the receiver channelizer for WiMAX BS and to find an efficient and low cost architecture of the same. We demonstrate that even though the conditions required by PFFB are not satisfied by the WiMAX standard, we can modify the overall architecture to include the PFFB structure. This is achieved by dividing the receiver channelizer into two blocks. The first block uses the PFFB structure to separate the desired number of channels from the input samples. This process also achieves an integer SRC by a factor that is equal to the number of channels being extracted. This block generates baseband outputs whose sampling rates are related to their target sampling rate by a fractional multiplication factor. In order to bring the channels to their target sampling rate, each output from the PFFB block is fed to a FSRC block, whose job is to use an efficient FSRC algorithm to generate the samples at the target sampling rate. We show that the computational complexity, as compared to the direct implementation, is reduced by a factor, which is approximately equal to the square of the number of channels. After mathematically formulating the receiver channelizer for WiMAX BS, we perform the simulation of the system using a software tool. There are two basic motives behind the simulation of the system which has a mathematical model. Firstly, the software simulation will give an idea whether the designed system is physically realizable. Secondly, this will help in designing the logic for different blocks of the system. Once these individual blocks are simulated and tested, they can be smoothly ported onto an FPGA. For simulation purpose, we parameterize the receiver channelizer in such a way that it can be reconfigured for different ADC sampling rates and IF frequencies, by changing the input clock rate. The system is also reconfigurable in terms of the supported channel bandwidth. This is achieved by storing all the filter coefficients pertaining to each channel type, and loading the required coefficients into the computational engine. Using this methodology we simulate the system for three different IF frequencies (and the corresponding ADC sampling rates) and three different channel types, thus leading to nine different system configurations. The simulation results are in agreement with the mathematical model of the system. Further, we also discuss some important implementation issues for the reconfigurable receiver channelizer. We estimate the memory requirement for implementing the system in an FPGA. The implementation delay is estimated in terms of number of samples. The thesis is organized in five chapters. Chapter 1 gives a brief introduction about the WiMAX system and different existing channelization architecture followed by the outline of the proposed receiver channelizer. In chapter 2, we analyze the proposed receiver channelizer for WiMAX BS and evaluate its computational requirements. Chapter 3 outlines the procedure to generate the WiMAX test signal and specification of the all the filters used in the system. It also lists the simulation parameters and records the results of the simulation. Chapter 4 presents the details of a possible FPGA implementation. We present the concluding remarks and future research directions in the final chapter.