What is a Software Defined Radio, SDR?
Large amount of data is transmitted through the entire earth every day. There are different types of communications such as data communications, video communications, voice communications, broadcast messaging, etc. To modify the radio devices cost effectively is really critical. The Software Defined Radio (SDR) technology is a flexible, cost efficient technology having lot of advantages. It is also called software radio. It is a radio communication system based on software defined wireless communication protocol. Instead of using components in hardware such as mixers, amplifiers etc.the software defined radio uses a software on embedded or computer system.
Software Defined Radio consists of a personal computer which includes sound card, analog to digital converter, a general purpose processor for signal processing. In this radio,the transmission and reception is based on the software used. For selecting a particular modulation, a proper program must run in the microcontroller which controls the transmitter and receiver. In this,some or all physical layer is software defined. This software is used to determine all the specifications of radio. It also determines what it does. If any changes occur in the software, the performance of radio also gets changed. The software provides functions such as modulation, demodulation, filtering, frequency selections etc. Wireless system protocols are different in each country. The single Software Defined Radio set can be used anywhere in the world. By simply selecting and changing the computer program, the service type, modulation protocol etc. can be changed. Before portable operation has done, make sure that the battery is fully charged.
The SDR technologies used in adaptive radio system increases the degree of freedom for adaptation. It provides high performance and better quality of service. The adaptive radio is a radio which can monitor their performance and can change the operating parameters improving its performance. Cognitive radio uses Software Defined Radio technologies for adjusting the operations automatically to achieve desired requirements and objectives. Cognitive radio is a radio which can take decisions about radio operating behavior. The main aim of Software Defined Radio engineers is that providing single radio transceiver for cordless telephone, wireless email and fax system, cell phone, wireless web browser, wireless video conferencing unit, etc. operable at any location in the earth and perhaps in space too.
Working Principle of Software Defined Radio
An ideal receiver would be attaching an ADC to an antenna. A Digital Signal Processor (DSP) is used for signal processing. The digital signal processor generates a stream of output which is given to digital to analog converter. An ideal transmitter is also attached. Th output is connected to the radio antenna. The ideal transmitter and receiver cannot be achieved due to its practical limitations of technology. The main problem is the analog to digital conversion and digital to analog conversion. It is difficult to maintain high accuracy and rate simultaneously. Other reasons are interference and electromagnetic resonance.
The receivers use oscillators, filters, and mixers etc. for tuning the desired baseband signal. Then it is sampled using analog to digital converter. But in some cases, there is no need for tuning the signal into intermediate or baseband signal. At that case the radio is directly sampled using analog to digital converter.
A low noise amplifier is used before analog to digital conversion. But this introduces some problems. For example, if noise signals are present, it will introduce distortion in the desired signal. To overcome this problem, a band pass filter is used between amplifier and antenna. It reduces its flexibility. The real software radios have two or three analog channel filters and the different bandwidths are switched in and out.
The typical Software Defined Radio mainly consists of a microphone, audio amplifier, ADC (Analog to Digital Converter) , modulator, amplifiers, transmitting and receiving antenna, super heterodyne system, demodulator, DAC (Digital to Analog Converter) , audio amplifier, speaker or headset.
Block diagram of Software Defined Radio
- RF amplification: - In the transmission side of amplifier, the level of RF signal in a level equal to the transmitted power. At the receiver, the signals from antenna are amplified before passing into receiver.
- Frequency conversion: - In some, analog processing is required. The radio frequency is convert.
- Digital conversion: - In this stage the analog signal and digital signal is converted.
- Baseband processor: - It digitally converts the incoming or outgoing signals. The main issue of the baseband processor is the amount of processing power required. The level of processing increases will increase the current consumption and it requires cooling.
A Simple blockdiagram of Software Defined Radio
It is not practically possible that all features in a radio is fully based on software. Only some features of Software Defined Radio are supported by some radios and others are fully based on software. SDR forum defined number of tiers which is given below.
Tier 0:- It is non configurable hardware radio. In this the software cannot be changed.
Tier 1:- Some functions are controllable such as power level, interconnections etc.
Tier 2:- In this some portion of radio is software configurable. It is called software controlled radio (SCR). It controls the parameters such as frequency, modulation, detection, security etc.
Tier 3:- It is in between configurable and non-configurable elements.
Benefits of Software Defined Radio
- New radio products are quickly introduced in the market by using the common platform architecture implemented in products.
- It reduces the development cost because the software can be reused.
- The time and cost for operation and maintenance can be reduced due to the bug fixing during radio is in service.
- It uses wireless communication. It uses for communicating with anyone at any time in any manner.
- Software upgrade automatically done and new features inserted. The capacity is improved by remote software downloads.
Applications of Software Defined Radio
- Military: - Software Defined Radio used in a military venture called Joint Tactical Radio System (JRTS). By using this single hardware platform, it could communicate using one if different waveforms by configuring the software for required application. JTRS is the program of US military. It provides flexible and interoperable communications.
- Amateur and home use:- The amateur radio uses a direct conversion receiver. The SDR software performs all functions such as filtering, demodulation etc.
- Satellite modems used in defense markets and commercial uses programmable processing devices for signal processing of baseband signals or intermediate signals.
- Cellular handsets uses System on Chip (SoC) devices which incorporate programmable DSP for processing baseband signals.
- Cellular infrastructure utilizes programmable processing devices for creating common platform or multiband multiple protocol base station which supports multiple cellular infrastructure standards.