Modulation Recognition for Software Defined Radio Signal

Modulation Recognition for Software Defined Radio Signal

Sudhar Sophia (Sri Krishna College of Engineering & Technology, India), M. Madheswaran (Muthayammal College of Engineering, India) and S. Sasikumar (Hindustan College of Engineering & Technology, India)
DOI: 10.4018/978-1-61520-655-1.ch023
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Software Defined Radio (SDR) is the foundation for universal wireless devices. To realize SDR system, the parameters like carrier frequency, symbol rate, and modulation scheme should be reconfigured by the adaptive receiver. Automatic modulation recognition (AMR) algorithm has to identify the modulation scheme of a transmitted signal with a high probability of success within a short observation time. Blind recognition algorithms are useful in identifying the modulation type without any prior knowledge of the transmitted signal parameters. The blind modulation detection determines the type of modulation within the information conveyed by the least possible number of received samples. Therefore, the objective is to make use of the distribution of data or errors to make a statistical inference about type of modulation used.
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The existence of incompatible wireless standards in different countries often inhibit deployment of global roaming facilities and problems in rolling out new service features due to widespread presence of legacy subscriber handset. The need for ability of radio to operate with all standards in different geographical regions of the world has fostered the growth of SDR concept. Traditional radios use hardware circuits, fixed at time of manufacture to perform the high speed signal processing to convert back and forth between user data and radio waveform. Since frequent redesign is expensive, time consuming and inconvenient to end users, interest is increasing towards future proof radios. Integrated services can be obtained with a single device capable of delivering various services and providing complementary services. This single platform can be shared dynamically among multiple users operating with different communication standards. This significantly reduces the cost of infrastructure to support the newly deployed standards. SDR technology promises to solve these problems by implementing the radio functions as software modules running on generic platform. It allows ease of design, multimode operation, flexibility to incorporate additional functions and use of advanced signal processing techniques.

SDR represents an emerging concept that may offer a pragmatic approach to address the multiple-standard problems. It also enables radio processing to reach a new level by permitting the systems to switch from analog to digital. The advent of realizable SDR allows implementation of creative transceiver design, which can dynamically adapt to communication channel and user application. Instead of dedicated hardware designed to carry out a rigid set of objectives, software implementation of hardware devices are entirely flexible regarding their functionality. Supplementary information transmitted is used to reconfigure SDR systems. Some of the major advantage in deploying SDR terminal is that as network topology changes the terminal can adapt to user requirement, change the mode of operation, channels and access methods and request new software upgrades if required without user intervention.

SDR evolving as a 4G technology offers flexibility, global mobility, service portability, wider bandwidth and higher bit rates. The general idea behind the SDR architecture is to perform signal processing in software instead of being defined in hardware. This enables the radio to get adapted to change in environment and user requirements by simply updating the software or by using adaptable software systems. In such scenarios, a broadcaster could change the appropriate modulation scheme according to the capacity of the channel. Since a single SDR system robustly handles multiple modulations, AMR is an important issue for such system. Meaning thereby, an intelligent algorithm identifying the modulation must be running at the receiver side.

Key Terms in this Chapter

Matlab: Is the acronym for MATrix LABoratory. It is the programming language for technical computing, used for a wide variety of scientific and engineering calculations, especially for automatic control and signal processing. It has extensive graphics capabilities .

Gaussian Noise: Is the additive noise that arises from electronic components and amplifiers in a receiver. This noise can be modeled as a Gaussian noise process (Gaussian process has the flat or constant PSD over the entire frequency range).It applies for a broad class of physical communication channels as the mathematical tractability is good. The resulting mathematical model is called AWGN.

Automatic Modulation Recognition: Is a method of recognizing the type of modulation without any Prior information bits among the multiple transmitted signals.

Signal to Noise Ratio: is the ratio of the wanted signal strength to the unwanted background noise at a given point in a given system. It is expressed in decibels (dB). It measures the clarity of the signal in a transmission channel.

Quadrature Shift Keying: Quadrature Phase Shift Keying (QPSK) is a form of Phase Shift Keying in which dibits are modulated at once, selecting one of four possible carrier phase shifts (0, 90, 180, or 270 degrees). As a symbol is transmitted by two bits it carries twice as much information as ordinary PSK using the same bandwidth. QPSK is used for satellite transmission of MPEG2 video, cable modems, videoconferencing, cellular phone systems, and other forms of digital communication over an RF carrier.

Constellation Diagram: Is a graphical representation of a signal components modulated by a digital modulation scheme. It displays the signal as a two-dimensional scatter diagram in the complex plane at symbol sampling instants. It represents the possible symbols that may be selected by a given modulation scheme as points in the complex plane.

Software Defined Radio: Is a radio that can reconfigure its functions, standards by software downloading. SDR equipment and network devices can be reconfigured and updated using dynamic programming of its software in order to improve its features, security protocols, performance and services.

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