Modem vhf

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TC4:

V/UHF Modem Module
Waveforms

[Prelim.]

High Data Rate Modem
The TC4 is a very compact high-performance V/UHF high data rate (HDR) modem module. The module is intended for integration into V/UHF radios and systems with an audio bandwidth exceeding 21 kHz (-30 db). Data is transferred at rates of up to 96,000 bps over a standard 25 kHz (-50 dB) V/UHF radio channel.

The TC4 offersa choice of two waveforms: • • RM-VH1: Optimized for naval channels RM-VH2: Optimized for land mobile channels

TC4-HDR supports following modem data rates:
DATA R ATE 96000 76800 64000 48000 32000 16000 MODULATION 128-QAM* 64-QAM 32-QAM 16-QAM 3π/8 8-PSK π/4 QPSK
CODE RATE

SNR FOR BER< 10-5 27 23 18 14 10 4

0.86 0.80 0.80 0.75 0.67 0.50

* This data rate requires an end-usercertificate. The interleaver settings are shown in the table below.
# 1 2 DATA RATE 96000 76800 64000 48000 32000 16000 USER DATA PAYLOAD [BYTES] US 20 MS 240 192 160 120 80 40 S 160 MS 1920 1536 1280 960 640 320 L 2560 MS 30720 24576 20480 15360 10240 5120

Key Features & Benefits
• • • • • • • • • • High Data Rate Modem 96000 bps (coded) in a 25 kHz VHF or UHF channel Embedded ARQ Interface forexternal ARQ (e.g. S 5066) Collision Avoidance Capability Analog or digital audio interface Low power consumption (< 1.3 W) Compact size: 33 x 55 x 8 mm RAP1/RIPC Control Protocol Easy system integration

3 4 5 6

Embedded ARQ
The TC4 offers the optional use of an internal ARQ protocol which ensures error-free delivery of data. This has advantages including following: • Wide SNR range and V/UHFchannel conditions • No error-amplification due to crypto
MOD. 64-QAM 8-PSK PACKET [BYTES] 377 313 THROUGHPUT* [BPS] 63,495 26,358 EFFICIENCY

ARQ MODE V-25-Q64-H4 V-25-Q8-H2

82.68% 82.37%

* Max data rate excluding link setup (LSU).

Low data rates (up to 32 kbps) use Offset QPSK and 8-PSK waveforms. The low data rates are suitable for radios with a non-linear power amplifier (PA). Thevery high rates use QAM and require a linear PA or can work with wideband FM or AM radios. Adaptive equalization mitigates the effects of channel multi-path. Convolutional encoding and soft-decision Viterbi decoding provides forward error correction.

Collision avoidance, ACS
The collision avoidance mechanism uses an ALLCALL (no address information transmitted). The transmitter first listens onthe channel. If the channel is occupied, the operation depends on the mode, namely: • Fixed Frequency No ACS: Keep listening on the channel until NO ACTIVITY, then start 2-way ALLCALL after a Random Back-off period ACS & Radio Control: Change channel and keep listening until a channel is found with NO ACTIVITY, then start ALLCALL

Control Protocol
The TC4 uses a sub-set of the RAP1/RIPC ControlProtocol. Alternatively a simple ASCII protocol is supported. The TC4 Control Protocol also enables the user to log key communication parameters: • • Signal to noise ratio Frequency offset, Doppler Frequency etc.



Transmission of data is only possible once the system is in the LINKED state. Linking Protection (LP) is used to isolate the network from denial of service attacks. This requiresan accurate time base, (±7 minutes).

Copyright © 2009 RapidM

Performance
The performance of the RM-VHF1 and RM-VHF2 waveforms are shown in the figures below.

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0

VHF Gaussian performance RM-VHF1: RM-VHF1: RM-VHF1: RM-VHF1: RM-VHF1: RM-VHF1: RM-VHF1: 4800S 9600S 16000S 32000S 48000S 64000S 76800S

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0

VHF RA125-400 SHORT IB performance

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-1

10

-1

10Average BER

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10 Average BER

-2

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-3

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-3

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-4

10

-5

10

-5

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-6

10 -5 0 5 10 15 20 SNR in 25 kHz [dB] 25 30 35

-6

RM-VHF2: RM-VHF2: RM-VHF2: RM-VHF2: RM-VHF2: RM-VHF2: 0 5 10 15 20 SNR in 25 kHz [dB] 25

4800S 9600S 16000S 32000S 48000S 64000S 35

30

RM-VHF1: Bit Error Rate Results for Gauss Channel

RM-VHF2: Bit Error...
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