A radio is any kind of device that wirelessly transmits or receives signals in the radio frequency (RF) part of the electromagnetic spectrum to facilitate the transfer of information. In today's world, radios exist in a multitude of items such as cell phones, computers, car door openers, vehicles, and televisions.
Traditional hardware based radio devices limit cross-functionality and can only be modified through physical intervention. This results in higher production costs and minimal flexibility in supporting multiple waveform standards. By contrast, software defined radio technology provides an efficient and comparatively inexpensive solution to this problem, allowing multimode, multi-band and/or multi-functional wireless devices that can be enhanced using software upgrades.
Joseph Mitola coined the term ‘Software Radio’. In an introduction of reconfigurable logic and the coining of the term SDR, the dominant implementation architecture used for RF Front-Ends (FEs) was the super-heterodyne architecture. The SDR is a radio communication system, which provides software control for a variety of modulation method, filtering, wideband or narrowband operations, spread spectrum techniques and waveform requirements etc. The frequency bands are still constrained at the RF Front-Ends.
Fig 1 Block Diagram of SDR
The development of an SDR system implies to achieve two main goals:
1. To move the border between the analog and digital world (in Tx and Rx Paths) as much as possible toward radio frequency (RF) by adopting analog-digital (A/D) and digital-analog (D/A) conversion as near ar possible to the antenna.
2. To replace the application specific integrated circuits (ASICS) dedicated hardware, with the re-configurable computing (FPGA) for baseband signal processing.
The FPGAs are mainly used in SDR RF Front-Ends (FEs) to improve the performance of DSP-chip-based systems. There is currently a wide range of FPGA products bring offered by many semiconductor vendors; Xilinx, Altera, Atmel and AT&T etc. The architecture approaches used in these FPGAs are as diverse as their manufacturers. The obvious benefits of wireless transmission have led to a number of radio systems.
SDR Hardware Platforms:
The hardware aspects of a SDR platform consist of the radio-frequency (RF) parts, communications links to the software-based signal processing elements (mostly a Host-PC). The rest may consist one or more of the following:
• ASICs (application-specific integrated circuits)
• FPGAs (field-programmable gate arrays)
• DSPs (digital signal processors)
• GPPs (general-purpose processors)
Table 1 shows details survey of existing SDR hardware platforms and their performance.
Universal Software Radio Peripheral 2 (USRP2) is a brainchild of Matt Ettus. The USRP family of products has been nominated “Technology of the Year” award from the Wireless Innovation Forum, 2010. The KUAR hardware employs a Xilinx Virtex II Pro P30 FPGA along with 1.4 GHz Pentium M processor. It has been promoted through the defense advanced research projects agency (DARPA) next generation (XG) program. The complete system was developed in Simulink, implemented in Xilinx VHDL, by generating the VHDL code from Simulink model(s) using a Modelsim of Mentor Graphics.
SDR Software Platforms:
GNU Radio: is an open source software development toolkit that provides the signal processing runtime and processing blocks to implement software radios. The radio applications are written in Python, while the performance-critical signal processing components, implemented in C++ using processor floating point extensions where available. In GNU Radio Python (gr.flow_graph) library of signal processing blocks is used to tie together the signal processing blocks of the waveforms. GNU Radio Companion (GRC) is a graphical tool for creating signal flow graphs and generating flow-graph source code.
Open-Source SCA Implementation-Embedded (OSSIE): The OSSIE is an object-oriented SCA operating environment, where signal processing components are written in C++. The operating environment, often referred to as the core framework, implements the management, configuration, and control of the radio system.
Wireless Open-Access Research Platform for Network (WARPnet): is an SDR framework that is built around client-server architecture in Python. With WARPLab, one can interact with WARP nodes directly from the MATLAB workspace and signals generated in MATLAB can be transmitted in real-time over-the-air using WARP nodes.