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Fixed-Point Signal Processing Development

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Fixed-Point Features Benefits of Fixed-Point Hardware Benefits of Fixed-Point Design with Signal Processing Blockset Software Fixed-Point Signal Processing Applications

Note   To take full advantage of fixed-point support in Signal Processing Blockset software, you must install Simulink® Fixed Point™ software.

Fixed-Point Features

Many of the blocks in Signal Processing Blockset software have fixed-point support, so you can design signal processing systems that use fixed-point arithmetic. Fixed-point support in Signal Processing Blockset software includes

• Signed two's complement and unsigned fixed-point data types

• Word lengths from 2 to 128 bits in simulation

• Word lengths from 2 to the size of a long on the Real-Time Workshop C code-generation target

• Overflow handling and rounding methods

• C code generation for deployment on a fixed-point embedded processor, with Real-Time Workshop code generation software. The generated code uses all allowed data types supported by the embedded target, and automatically includes all necessary shift and scaling operations

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Benefits of Fixed-Point Hardware

There are both benefits and trade-offs to using fixed-point hardware rather than floating-point hardware for signal processing development. Many signal processing applications require low-power and cost-effective circuitry, which makes fixed-point hardware a natural choice. Fixed-point hardware tends to be simpler and smaller. As a result, these units require less power and cost less to produce than floating-point circuitry.

Floating-point hardware is usually larger because it demands functionality and ease of development. Floating-point hardware can accurately represent real-world numbers, and its large dynamic range reduces the risk of overflow, quantization errors, and the need for scaling. In contrast, the smaller dynamic range of fixed-point hardware that allows for low-power, inexpensive units brings the possibility of these problems. Therefore, fixed-point development must minimize the negative effects of these factors, while exploiting the benefits of fixed-point hardware; cost- and size-effective units, less power and memory usage, and fast real-time processing.

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Benefits of Fixed-Point Design with Signal Processing Blockset Software

Simulating your fixed-point development choices before implementing them in hardware saves time and money. The built-in fixed-point operations provided by Signal Processing Blockset software save time in simulation and allow you to generate code automatically.

Signal Processing Blockset software allows you to easily run multiple simulations with different word length, scaling, overflow handling, and rounding method choices to see the consequences of various fixed-point designs before committing to hardware. The traditional risks of fixed-point development, such as quantization errors and overflow, can be simulated and mitigated in software before going to hardware.

Fixed-point C code generation with Signal Processing Blockset software and Real-Time Workshop code generation software produces code ready for execution on a fixed-point processor. All the choices you make in simulation with Signal Processing Blockset software in terms of scaling, overflow handling, and rounding methods are automatically optimized in the generated code, without necessitating time-consuming and costly hand-optimized code. For more information on generating fixed-point code, see Code Generation in the Simulink Fixed Point User's Guide.

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Fixed-Point Signal Processing Applications

Fixed-point support in Signal Processing Blockset software facilitates development of a wide variety of signal processing applications:

• Wireless and broadband communications

  • Cellular phones

  • Radio

  • Satellite communications

• Speech and audio processing

  • Speech processing

  • High-end audio processing

• Telephony

  • Speech coding

  • Dual tone multifrequency (DTMF)

  • Echo cancellation

• Hand-held and battery-operated consumer electronics

  • Digital recording devices

  • Personal digital assistants (PDAs)

• Computer peripherals

• Radar and sonar

• Medical electronics

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Working with Fixed-Point Data

Concepts and Terminology

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