Soft Radio
VOCAL's extensive library of Soft Radio modules includes support for a wide range of industrial
and RF signalling standards, including error correction, signal detectors, encryption, and various
modulations. Computationally intensive routines have been optimized to meet MIPS and memory
constraints on a variety of different platforms. VOCAL has the expertise and experience to
develop and integrate custom signalling solutions to meet specific user requirements and
environmental constraints.
NBFM Soft Radio
The VOCAL NBFM soft radio module is intended for transmission of voice band
audio in the range of 300 hz to 3 khz across a narrow-band FM channel approximately
15 khz wide. The frequency spread of the transmit path is adjustable, and the
receiver utilizes an optimal carrier tracking PLL with a matched prefilter.
Pre- and de-emphasis are available of the final signal are optional. Quadrature input samples
are preferred for the receiver, with a sample rate in the range of 20 to 50 khz. Other
types of input signals can also be handled.
12 Kbps Soft Radio FSK
The VOCAL Soft Radio FSK module implements a standard FSK modulation with a +-6 khz
frequency variation and 12 khz baud rate. This type of data modulation is used in
several governmental and civilian standards. Quadrature input samples
are preferred, with a sample rate in the range of 20 to 50 khz. Other
types of input data stream can also be handled. Soft or hard decision outputs are
available.
Custom modulations, including QPSK and QAM, are available on request.
CTCSS Signalling
CTCSS is a set of sub-audible low frequency tones normally used for channel
separation or identification when multiple devices are using the same physical
channel. A typical usage would be to assign a different CTCSS tone to a number
of hand-held radios, allowing each radio to be identified by the tone it transmits.
Other uses include using different CTCSS tones for different channels, allowing
receivers to ignore channels that are meaningless to it.
VOCAL's CTCSS detection module has a typical 300 ms detect time, with noise floor
performance that exceeds most FM carrier detect thresholds. Tone precision may be
specified in tenths of a hz. Detect time and bandwidth may be adjusted based on
application.
A CTCSS generation module is also available.
Selcall Signalling
Selcall is a single-tone signalling method used to communicate equipment or other
machine information over a channel. The tone set typically consists of 18 tones,
including 16 data tones, a tone for repetition, and a control signal tone. Tones
are generally 20 ms long, though different international standards may mandate
different tone periods.
The VOCAL Selcall detector module can be configured with arbitrary tone periods and
frequencies. Multiple detect patterns may be specified, such as patterns for
initial Selcall identification and Extended Selcall data. The detector performance
is near the noise floor and nyquist limit for detection, and uses the inter-tone
restrictions to disqualify illegal patterns and improve detection quality.
A Selcall generation module is also available.
Convolutional Coding
The VOCAL Soft Radio FSK module is often used in tandem with a seven state, rate 1/2
convolutional coder to reduce bit errors. A number of different types of convolutional
coders and interleavers are available, with both hard and soft decision decoding.
Standard turbo coding modules as well as custom modules, may be available depending on
application.
Reed-Solomon Coding
Reed-Solomon error correction modules are available to further improve the quality
of data modulation links. Typically, RS coding is used as an outer code with an
interleaver to clean up errors produced by an inner convolutional code. A number of
standard RS types are available, including those for Red Book and CCSDS. Custom
Reed-Solomon decoders can easily be created for specific applications.
Soft Radio Voice and Data Reference Designs
VOCAL's Soft Radio Voice and Data Reference Designs use our extensive software suite, with computational intensive routines optimized to meet MIPS and
memory constraints. The hardware design supports various DSP options, such as the TI TMS320C55x or ADI BF-532. Development hardware is available
on a demonstration board. The firmware also provides optional software interfaces for memory, LCD display, GPIO, Codec and RS232.
Additional configurable possibilities include the use of a low bandwidth vocoder, such as MELP/MELPe. As well,
to secure transmission between units is also available, using VOCAL's security stack and encryption libraries. AES encryption is available
in hardware or in software modules.
Figure 1. Soft Radio Voice Hardware Design
Features
- LCD display
- Keypad input
- RF Signal Strength
- Push-to-Talk (PTT)
- Battery strength indication
- Headset, speaker and microphone
- Flash
- SDRAM
Configuration
- customizable LCD display
- vocoders (i.e. MELP, MELPe)
- secure communication
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