Transcript
NatureDSP 4FSK Multistandard 4FSK/C4FM digital modem
Overview NatureDSP 4FSK is software data pump for 4FSK/C4FM data transmission over UHF channels. It supports 4800/9600 bps data modulation formats for PMR/LMR and APCO P25 standards both for 12.5 kHz and 25 kHz channels. Flexible interfaces allow to integrate it into base-stations, repeaters and inexpensive handheld radios.
Features • • • • • • • • • • • •
support both 4800/9600 bps PMR/LMR modes and 9600 bps APCO P25 mode flexible test pattern generator and BER tester fast synchronization on two user-selectable bit patterns or by soft decision threshold repeater mode with automatic TX clock rate adjustment TX jitter buffer enables clock rate alignment log-likelihood soft decision output compatible with DVSI AMBE vocoder data format I/Q and voiceband inputs Adaptive adjustment of RX deviation economy DARAM/cache usage true fixed point implementation with saturation, no floating point fully portable ANSI C code library for MS Visual Studio for free – enables development under PC environment
Applications • • • •
digital UHF two-way radios base-stations and repeaters APCO P25/PMR/LMR equipment software defined radio
Specifications Modulator includes test pattern generator, 4FSK/C4FM modulator with needed shaping filters and jitter buffer combined with output interpolation stage. Modulator forms voiceband signal that could be applied to standard FM modulation circuitry or directly to the PLL. Demodulator could be fed twofold: via I/Q input or from analogue FM discriminator. Using I/Q input is recommended for base-stations and repeater configurations. This way provides wider dynamic range and allows using RSSI and C/N information to acquire signal faster. However, inexpensive radios can use existing analog discriminators. Coarse RX deviation adjustment function is intended to compensate gain distortions introduced by discriminator. Adaptive deviation adjustment block compensates possible variations of nominal deviation introduced by transmitting stations. DC offset removal module subtracts the DC arising in the RX path due to the carrier offset between receiver and transmitter. Combined blind and data-driven tracking allow to lock signal with very big carrier offset (up to ±8 kHz) and avoids data distortion on continuously repeating bit sequences. RX matched filter combines RRC and Integrate-Dump filters for PMR/LMR or APCO P25. Timing recovery circuit can control output stage of modulator thus enabling repeater mode operation. Soft decision module forms log-likelihood output and SNR estimation. SNR, RSSI and C/N information create integral link quality indicator. Synchronization logic allows to make initial synchronization of data either by continuous search of 2 predefined bit sequences or by link quality indicator. BER tester synchronizes automatically on 511 PRS pattern. It makes easier checking and testing the system. Figure below shows simplified block diagram of modem.
Contacts
[email protected] Tel: +7 962 991 04 22
www.integrit.ru
NatureDSP 4FSK Multistandard 4FSK/C4FM digital modem
NatureDSP 4FSK modem TX bits FM modulator
Interpolator/ jitter buffer
Modulator
TX deviation ajustment RF
Analogue discriminator
Matched filtering
DC offset removal
Timing recovery
Coarse RX deviation ajustment
I/Q
BER tester
Test pattern generator
Adaptive deviation adjustment
Soft decision formation RX bits SNR
Digital FM discriminator
RSSI, C/N
Syncronization logic
Simplified block diagram Parameter Min
Value Max
Units
Notes
Typ
General Supported standards
4800/9600 bps PMR/LMR modes, 9600 bps mode for APCO P25
Data rate Symbol rate Sample rate I/Q data rate Modulator Symbol rate accuracy Test patterns
4800 2400
9600 4800
TX deviation adjustment Demodulator Coarse RX deviation adjustment Symbol rate accuracy Carrier offset Adaptive deviation adjustment
-50
+50
%
low deviation, high deviation, fidelity pattern, ITU-T O.153 511 PRS, zero bits, mark bits in percents from nominal value
-50
+50
%
in percents from nominal value
-8 -20
100 +8 20
ppm kHz %
in percents from nominal value
8 32 100
bps sym/sec kHz kHz
voiceband input and output I/Q input
ppm
Availability This software package is available in binaries and in source code written on fully portable C-language for: • Texas Instruments TMS320C54xx, TMS320C55xx, TMS320C64xx, OMAP, DaVinci • ARM7, ARM9, ARM9E • MS Windows XDAIS compliant library is available upon request
Contacts
[email protected] Tel: +7 962 991 04 22
www.integrit.ru
