Software defined radio receiver platform based on six-port technology
Authors: Xin Yu Xu
Venue:  (2006)

Software Defined Radio (SDR) has been considered as one of the most vital techniques for practical implementation of future wireless communication systems. In the past, limited operation speed of analog digital converter (ADC) and processing ability of reconfigurable chips for digital signal processing slowed down the development of SDR for useful commercial application. With recent advance in semi-conductor processing technology and the development of re-configurable devices such as digital signal processors (DSP) and field programmable gate arrays (FPGA), SDR has now become practical solutions for many commercial communication systems. Presently, most SDR system digitalized signal at intermediate frequency (IF). Although DSP and semiconductor technologies have been developed rapidly in the past ten years, it is still difficult for the operating speed level of current DSP chip to completely support a high-speed multi-channel and multi-mode SDR at IF level. In the interim, SDR implementations will require a mix of hardware-intensive techniques such as application-specific integrated circuits (ASICs). Certain software radio systems adopt multi-chips architecture and parallel algorithms, thereby increasing the design complexity and potential cost. Instead of digitalizing signals at IF, microwave/millimeter wave signals can be digitalized at baseband with six-port technology, hence reducing the processing requirement for DSP chips. This new solution to SDR design is based on direct demodulation with "six-port technology", down-converting radio frequency (RF) signal to base-band directly by a six-port circuit. This dissertation describes the works and results in designing a new software defined radio digital receiver based on six-port technology. The objective of the project is to realize an application of SDR based on six-port technology to provide a multi-channel, multi-mode direct wireless digital receiver for microwave/millimeter wave wireless mass-market communications. Six-port circuit is used as a mixer instead of conventional RF circuit, which offers some important advantages, such as simplicity, small size, low-cost and excellent electrical performances. The combination of SDR and six-port technology provides great flexibility in system configuration, significant reduction in system development cost and very high potential for software reuse. As principal components of receiver RF front end, two different types of six-port circuit have been designed with the center frequency of 24 GHz and operating frequency bandwidth from 22GHz to 26GHz. One is based on traditional miniaturized hybrid microwave integrated circuit (MHMIC) technology and the other based on a novel substrate integrated waveguide (SIW) technology. The scattering parameters of these two six-port circuits are analyzed and presented. Three modulation schemes QPSK, QAM16 and OFDM are selected to test performance of the receiver. The basic concept and architecture of the SDR six-port receiver were tested by performing circuit and system simulations using a series of software such as the Agilent Advanced Design System (ADS), Ansoft High-Frequency Structure Simulator (HFSS), Mathworks Matlab and Simulink. The simulation performance of the SDR receiver is presented, along with different modulation schemes demodulation, noise performance analysis and calibration algorithms which are normally associated with this class of receiver. Based on the simulated results, a physical six-port SDR receiver platform is fabricated and system measurements are performed to validate the receiver design. The proposed six-port SDR receiver has been proved adaptive for amplitude, phase and frequency modulation schemes. Compared with traditional SDR receiver, the six-port SDR receiver has wider bandwidth, lower cost for RF front-end circuits and lower DSP capability requirement. The simulated and measured results show that the receiver has bit error rates (BER) of as low as 1 E-6for Eb/NO of I 1 dB (for QPSK) and 15dB (for QAM16). The proposed six-port SDR receiver has been proved adaptive for different modulation schemes, showing a possible application of direct demodulator for future SDR terminals in various low cost communication systems.