The Software Defined Radio (SDR) is a term for describing the reconfigurable digital signal processing based communication systems. In SDR based systems most of the baseband processing is done in a reconfigurable digital processor. This feature leads to greater flexibility in these systems and permit them to reconfigure their baseband processing behavior just with a click!
The SDR based communication systems are growing in past years very quickly. SDR Brings many new motivations and features that can’t be achieved in legacy communication systems. The features like high stability over the mass production and generalized use of hardware’s makes them a good choice for new designs and low cost production.
Recently I have completed my B.S project at the University of Isfahan, named “Design & Implementation a Software Radio Receiver for Operating in VHF/UHF/L Bands” which I would like to share the achievement’s and design procedure with other interested peoples. I used the project name of ESDR which stands for Ebrahim Software Defined radio Receiver.
The receiver I have implemented is capable of receiving signals in VHF/UHF and L Bands with the aim of CMOS integrated Tuner Chip. The tuner I have used is Elonics E4000 Chip which is used in many low cost DVB-T Dongles (ex. RTL-SDR). E4000 is a complete solution with onchip wide band RF PLL, quadrature I-Q mixers, configurable input low noise amplifier and staged amplifiers, DC correction unit, digital RSSI measuring unit, RF-IF filters with reconfigurable bandwidths and center frequencies.
On the digital hardware side, I have used FPGA’s for implementing Digital Down Converters, baseband filters & network streaming interface. Two FPGA’s are used from Xilinx Spartan-3 and Spartan-6 Families. These FPGA’s are exist in two FPGA development boards. One of the boards has Spartan-3 XC3S400 FPGA with high speed A2D & D2A Chips but no network interface, and another has Sparntan-6 XC6SLX9 with on-board 100BASE-TX ethernet interface and some other IC chips.
The Spartan-3 development board has one dual channel pipelined 40MSPS 10bit ADC with good SFDR & SNR responses. This board is used for data acquisition subsystem. On the other side the Spartan-6 development board is used for digital signal preprocessing and streaming baseband signals over the network.
The network interface streams the digital baseband signals to a PC running software processor. The Spartan-6 development board has a Wiznet W5300 which is an integrated Ethernet TCP/MAC/PHY Chip. The W5300 is a complete solution for simple & low cost 100Mbps network connectivity. it has internal physical layer, MAC layer and TCP/UDP/PPoE processor. Also, it has 128KB of SRAM FIFO Memory which is used for buffering transmitting & receiving packets.
Final processing staged is done via GNU Radio baseband software processor. GNU Radio is a free software development toolkit that provides signal processing blocks to implement software-defined radios and signal processing systems. It can be used with external RF hardware to create software-defined radios, or without hardware in a simulation-like environment. It is widely used in hobbyist, academic, and commercial environments to support both wireless communications research and real-world radio systems.
GNU Radio has a modular architecture which allows the developers to create new modules with their desired behavior.
In the last stage, a source block developed for GNU Radio which act as an interface between GNU Radio & ESDR hardware. The source block, receiving initial parameters and commands from GNU Radio and setup the ESDR hardware. Then it grabs the baseband data coming from the network and convert them appropriate form needed by GNU Radio and then pass them in packets to the GNU Radio scheduler.
The ESDR Source will act as a signal source with actual hardware and RF baseband signals, and the GNU Radio act as a big processing organizer. Received data can be demodulated or recorded for real world communication systems or research proposes.
The thesis report (In Persian) can be downloaded freely from my website. This document is copyright protected and any abuse or usage without my permission is prohibited.
Design & Implementation a Software Radio Receiver for Operating in VHF/UHF/L Bands