What is SDR technology ?
SDR technology is a radio communication system where components that have been traditionally implemented in hardware (for example mixers, filters, amplifiers, modulators/demodulators, detectors, etc.) are instead implemented by means of software on a personal computer or embedded system.while the concept of SDR is not new, the rapidly evolving capabilities of digital electronics render practical many processes which were once only theoretically possible.
A basic SDR system may consist of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware (electronic circuits). Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.
Software radios have significant utility for the military and cell phone services, both of which must serve a wide variety of changing radio protocols in real time.
In the long term, software-defined radios are expected by proponents like the SDRForum (now The Wireless Innovation Forum) to become the dominant technology in radio communications. SDRs, along with software defined antennas are the enablers of the cognitive radio.
A software-defined radio can be flexible enough to avoid the "limited spectrum" assumptions of designers of previous kinds of radios, in one or more ways including.
Spread spectrum and ultrawideband techniques allow several transmitters to transmit in the same place on the same frequency with very little interference, typically combined with one or more error detection and correction techniques to fix all the errors caused by that interference.
Software defined antennas adaptively "lock onto" a directional signal, so that receivers can better reject interference from other directions, allowing it to detect fainter transmissions.
Cognitive radio techniques: each radio measures the spectrum in use and communicates that information to other cooperating radios, so that transmitters can avoid mutual interference by selecting unused frequencies. Alternatively, each radio connects to a geolocation database to obtain information about the spectrum occupancy in its location and, flexibly, adjusts its operating frequency and/or transmit power not to cause interference to other wireless services.
Dynamic transmitter power adjustment, based on information communicated from the receivers, lowering transmit power to the minimum necessary, reducing the near-far problem and reducing interference to others, and extending battery life in portable equipment.
Wireless mesh network where every added radio increases total capacity and reduces the power required at any one node.Each node transmits using only enough power needed for the message to hop to the nearest node in that direction, reducing the near-far problem and reducing interference to others.
What type of hardware in SDR technology?
Hardware
Basic Specifications
A software-defined radio receiver is defined by three basic specifications: bandwidth, resolution, and tuning range. The receiver is further characterized by many important figures of merit that reflect performance in noise, selectivity, and frequency stability, but these specifications are deferred to more advanced discussions.
Bandwidth is the instantaneous width of frequency content that the SDR receiver can receive. It can be thought of as the width of the SDR’s window into the RF spectrum. This is usually in the range of 1 to 10 MHz for entry-level SDR receivers, and in the 20 to 60 MHz range for the more advanced SDR transceivers. Bandwidth is different from tuning frequency; rather, more bandwidth means that the SDR receiver can capture a wider window of signals simultaneously when tuned to a particular frequency. In some cases, more bandwidth is required to capture a very wide signal, like a 6 MHz wide DVB-T channel.
The sample rate of an SDR receiver is the rate the radio signal is sampled by the receiver and streamed to the host. Sample rate is directly related to the bandwidth, and while bandwidth is ultimately the specification of interest, SDRs are typically described by their sample rate, as it is the underlying design parameter. An SDR’s effective bandwidth is usually slightly less than its sample rate. Sample rate also dictates the computational burden on the host: the wider the receive bandwidth, the more samples per second are required to represent it, and consequently, the more bus throughput is required to stream it to the host, and the more host computational power is required to process it.
Resolution is the bit resolution of the analog to digital converter that samples the radio signal. This represents the quantization range of each sample. For example, an 8-bit ADC will have 256 levels of quantization, whereas as 12-bit ADC will have 4096 levels. All things equal, more bit resolution means less quantization noise — the “noise” resulting from the error in mapping an analog level onto a discrete level, and more dynamic range — the ability to capture both strong and weak signals simultaneously. In practice, the usable resolution is highly dependent on the signal conditioning by the frontend RF circuitry.
Tuning range is the frequency range that the SDR receiver can tune to. This range typically starts in the tens of megahertz and goes up to a few gigahertz. However, SDR receivers can receive signals outside of this range with the help of an RF upconverter or downconverter, an inline device that translates signals by a fixed frequency offset, so that they fall into the tuning range of the SDR. For example, an SDR receiver with a tuning range of 24 MHz to 1766 MHz can be paired with a 125 MHz RF upconverter, so that it can pick up 0 to 30 MHz at the offset frequencies of 125 to 155 MHz.
A basic SDR system may consist of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware (electronic circuits). Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.
Software radios have significant utility for the military and cell phone services, both of which must serve a wide variety of changing radio protocols in real time.
In the long term, software-defined radios are expected by proponents like the SDRForum (now The Wireless Innovation Forum) to become the dominant technology in radio communications. SDRs, along with software defined antennas are the enablers of the cognitive radio.
A software-defined radio can be flexible enough to avoid the "limited spectrum" assumptions of designers of previous kinds of radios, in one or more ways including.
Spread spectrum and ultrawideband techniques allow several transmitters to transmit in the same place on the same frequency with very little interference, typically combined with one or more error detection and correction techniques to fix all the errors caused by that interference.
Software defined antennas adaptively "lock onto" a directional signal, so that receivers can better reject interference from other directions, allowing it to detect fainter transmissions.
Cognitive radio techniques: each radio measures the spectrum in use and communicates that information to other cooperating radios, so that transmitters can avoid mutual interference by selecting unused frequencies. Alternatively, each radio connects to a geolocation database to obtain information about the spectrum occupancy in its location and, flexibly, adjusts its operating frequency and/or transmit power not to cause interference to other wireless services.
Dynamic transmitter power adjustment, based on information communicated from the receivers, lowering transmit power to the minimum necessary, reducing the near-far problem and reducing interference to others, and extending battery life in portable equipment.
Wireless mesh network where every added radio increases total capacity and reduces the power required at any one node.Each node transmits using only enough power needed for the message to hop to the nearest node in that direction, reducing the near-far problem and reducing interference to others.
What type of hardware in SDR technology?
Hardware
Basic Specifications
A software-defined radio receiver is defined by three basic specifications: bandwidth, resolution, and tuning range. The receiver is further characterized by many important figures of merit that reflect performance in noise, selectivity, and frequency stability, but these specifications are deferred to more advanced discussions.
Bandwidth is the instantaneous width of frequency content that the SDR receiver can receive. It can be thought of as the width of the SDR’s window into the RF spectrum. This is usually in the range of 1 to 10 MHz for entry-level SDR receivers, and in the 20 to 60 MHz range for the more advanced SDR transceivers. Bandwidth is different from tuning frequency; rather, more bandwidth means that the SDR receiver can capture a wider window of signals simultaneously when tuned to a particular frequency. In some cases, more bandwidth is required to capture a very wide signal, like a 6 MHz wide DVB-T channel.
The sample rate of an SDR receiver is the rate the radio signal is sampled by the receiver and streamed to the host. Sample rate is directly related to the bandwidth, and while bandwidth is ultimately the specification of interest, SDRs are typically described by their sample rate, as it is the underlying design parameter. An SDR’s effective bandwidth is usually slightly less than its sample rate. Sample rate also dictates the computational burden on the host: the wider the receive bandwidth, the more samples per second are required to represent it, and consequently, the more bus throughput is required to stream it to the host, and the more host computational power is required to process it.
Resolution is the bit resolution of the analog to digital converter that samples the radio signal. This represents the quantization range of each sample. For example, an 8-bit ADC will have 256 levels of quantization, whereas as 12-bit ADC will have 4096 levels. All things equal, more bit resolution means less quantization noise — the “noise” resulting from the error in mapping an analog level onto a discrete level, and more dynamic range — the ability to capture both strong and weak signals simultaneously. In practice, the usable resolution is highly dependent on the signal conditioning by the frontend RF circuitry.
Tuning range is the frequency range that the SDR receiver can tune to. This range typically starts in the tens of megahertz and goes up to a few gigahertz. However, SDR receivers can receive signals outside of this range with the help of an RF upconverter or downconverter, an inline device that translates signals by a fixed frequency offset, so that they fall into the tuning range of the SDR. For example, an SDR receiver with a tuning range of 24 MHz to 1766 MHz can be paired with a 125 MHz RF upconverter, so that it can pick up 0 to 30 MHz at the offset frequencies of 125 to 155 MHz.