The rapid development of portable devices, and the increasing trend toward a single device integrating several features, encourage the companies and research centers to develop the multi-standard front-ends. This research is an effort to develop a multi-standard multi-mode receiver by employing RF sub-sampling receiver architecture. This PhD project is part of danish ministry of science, technology and innovation (VTU) supported project WANDA (Wireless Access Network Devices & Applications).

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... WANDA project is a joint research activity in a consortium consisting of Texas Instruments, Motorola (former Siemens and BenQ), RF Micro devices, BLIP Systems, Technological Institute, and Aalborg University. The overall goal of the project was to develop techniques to efficient, robust, and flexible multi-band receiver architecture. The application area was the battery-powered mobile devices. The trend in modern wireless communication systems is to have several communication links integrated in a single user equipment [1] . For the portable battery-powered receivers, high level of integration, high flexibility, and low power dissipation are precedence objectives. Thus it is required to avoid expensive and power hungry parallel transceivers by employing more integrated and flexible devices in multi-band applications. To accomplish this, the system level investigation of the promising wireless RF receiver for multi-band application has been done. It is concluded that for the receiver part, the sampling receiver [2], [3] is a viable solution. This is one step toward the software defined radio vision with the majority of processing being done in the digital domain [4] . It provides the ability of processing several different signals in a single receiving chain. The verification of the theoretic studies is done through an experimental test set up. The key parts of the receiver such as sampler block and RF filters and amplifiers are implemented using off the shelf components. The soundness of the proposed ideas is acquired through experimental proof by considering the limitations of commercially developed components. This part of the work was done in a close cooperation with Motorola A/S, one of the project partners. At the company, the work was carried out in RF department especially in the RF labs. Including this preface and the publications at the end, the dissertation form a 180 pages extended summary of the work done in the period of this Ph.D. research. The organizaiii iv Preface tion of the thesis, the list of the publications resulted from this work and a short description of each are presented in the following parts of the preface. Organization of the Thesis This dissertation is divided into 5 main Chapters. Each chapter contains an abstract, an extended summary and a brief discussion and conclusion at the end. Chapter 1 provides an introduction to the whole work. The required background knowledge to create a common understanding ground for the dissertation is presented in this chapter. The scopes of the thesis are set by providing an overview to the wireless multi-band systems for mobile communications and the challenges in the field. The state of the art RF receivers for multi-band applications is presented in this chapter to fundament the selected RF subsampling architecture for the further investigation. A comparison of the architectures are made with respect to their multi-band capabilities. A description of the signals used for the current research, the methodology and the simulation environment is explained. Chapter 2 describes in detail the proposed receiver architecture of the thesis -RF subsampling receiver. The basic principles of the architecture are presented. Thermal noise and jitter are considered as the important noise sources of the proposed architecture. Thus, to model the receiver precisely, they are involved. Moreover, an overview of the RF requirements for this receiver architecture is presented. The receiver must be able to maintain the adequate performance by preserving the bit error rate (BER) below a certain value even in the existence of noise and undesired signals from different sources. Chapter 3 includes the frequency planning of the receiver and the required knowledge to select the best possible sampling frequency. First an exposition of the sampling frequency and its important role in RF sub-sampling receiver is given. It follows by the different methodologies for calculation of sampling frequency in terms of the Nyquist criteria, image noise and improving the signal to noise ratio based on pursuing the environment. Summing up all the techniques, a complete flow is achieved to calculate the most optimum sampling frequency for the receiver. The proposed concepts are supported by simulations and measurements on the specific subsampling receiver defined in the thesis. Chapter 4 concerns RF requirements of the receiver to ensure the proper functionality of the RF Sub-sampling architecture in the multi-band applications. The RF requirements of a multi-standard receiver in the presence of the noise and nonlinear distortions are investigated in this chapter. The necessary design constrains are also derived. The sensitivity, linearity and selectivity issues are investigated for the multi-band applications. The derived constrains for selectivity and linearity are not dependent on any specific receiver architecture and are applicable for all types of receivers. The special selectivity requirements in accordance with the RF sub-sampling receivers are derived consequently. That is due to the indispensable role of filtering in sampling techniques to prevent the folding of noise along with desired signal to the band of interest. A technique on how to calculate the needed front-end selectivity to obtain a specified SNR at the output of the sampler is presented. This procedure combines v blocking tests of the relevant communication standard with the special image properties of the sub-sampling receiver. Moreover, the filter specifications based on out-of-band blocking requirements is discussed. The correct filtering in sampling based architecture improves the final performance of the receiver significantly. The derived specifications are verified by simulations and measurements on the specific sub-sampling receiver. Chapter 5 is dedicated to the design issues of an RF sub-sampling architecture for target signals. The novel idea of selecting this architecture for multi-band application provides more flexibility and integration level by realizing most of the receiver functionality in digital domain. In the defined scenario of this study, the RF front-end is operating for the WLAN and UMTS signals at the same time with a single user equipment (UE) by employing RF sub-sampling architecture. The example for using these standards are when the user is downloading or transferring the information from the net while talking with the UMTS mobile phone simultaneously. The best sampling frequency is found by employing the method introduced in chapter 3. Moreover, the technique of chapter 4 is employed to define the RF requirements of the receiver. The simulation environment and methodology of receiver modeling are explained. The proposed concepts are supported by simulations of the target sub-sampling receiver.