DSP Data Vocoder

Sub-Systems
S
for HF
Application
Rafi Hana M.Sc.E.E
General Manager
MOBAT
A Tadiran Communications Division

The New HF Systems
Advantages
Stable and Accurate Frequencies
- Improves the Quality
ALE STD (141B)
- Simplifies the Operation
New MODEM Technology
- Expanded dthe Use of fData App.
New Digitized Voice Technique - Improves the Voice Quality &
Reduces the HF Noise.

Voice & Data Applications
based on
VOCODER & HF Data Modem
• VOCODER 1200, 2400 bps
• MODEM MIL-STD-188-110B
Side Effect :
• Encryption AES Standard

Basic Block Diagram
PC
RS232
USB
HOST
CPU
Interface
AES 188-110B
Encryptor MODEM
Audio
Handset
Fixed Lvel
1200,2400
VOCODER

Basic System
Configuration
Secure
Voice & Data
Plain Voice

Special Features
• V-AMD Allows Voice- Messages that
penetrate t negative-SNR channels
for emergency application
• Operational features:
REC. Recording messages.
SEL. Selecting one / five.

Encryptor
• AES Advanced Encryption Standard.
The New Federal Information
Processing Standard d (FIPS)
• #Keys 7 + technician-key (option 31k)
• HMI PC-menu or MICOM front panel.
• OTAR Select Keys (Option: Key Loading)

• Two approaches for Voice coding :
Waveform Coders
Among popular methods : CVSD , ADPCM , PCM …
(16K,32K,64K 64K bps)
Parametric representation (Vocoders)
Speech model derived from speech characteristics
Low bandwidth (600,1200,2400 bps)

PI TCH
PERI ODI C
EXCI TATI ON
VOI CED/ UNVOI CED
SWI TCH
SPECTRAL
PARAMETERS
GAI N
SPECTRAL
ENVELOPE
MODEL
SPEECH
RANDOM
NOI SE
Speech model

• Two principal families of Voice Coders:
Source Codecs - operate based on the
speech model ( LPC)
Hybrid Codecs - attempt to bridge between
Source Codecs and Waveform Codecs
(MPE, RPE, CELP, MBE, MELP).

Algorithm
Bit Rate
MOS(1-5)
PCM(G.711)
LPC-10e(FS1015)
RPE-LTP(GSM)
CELP(FS1016)
AMBE (DVSI)
MELP
TADIRAN-Mobat
TADIRAN - Mobat
TADIRAN - Mobat
64K
2.4K
13K
4.8K
2.4K
2.4K
1.2K
2.4K
4.8K
4.3
2.3
3.47
3.2
3.6
3.3
3.1
3.5
3.8
MOS - Mean Opinion Score : Voice Quality measure

Link Quality CVSD Vocoder 2400
5% BER Speech with Noise Good
8% BER Speech with Noise Good
5% BER + 30%
JAM
Noisy Speech
(intelligibility
limited)
50% JAM Very Noisy
(no intelligibility)
Good
Good with few
disturbances
Digital voice is the New Generation Requirement

MODEM
• MIL-STD-188-110B 75-4800 bps
with better & Adopt performance.
• DSP Implementation
Ready for Future
Growth

Basic MODEM BLOCK DIAGRAM
TRANSMITER
FEC INTERLEAVER MAPPER SCRAMBLER
MOD
DATA
RECEIVER
DEMOD EQUALIZER DECODER DATA
SYNC
LOOPS

CONSTELLATION FOR
MIL-STD-188-110B sec. 5.3.2

Modem Performance
• Performance is NOT essentially dictated by
SNR.
• ISI-length & Doppler-Spread
can cause modem collapse in spite of very
high SNR.

“Surface” Performance
a 300 bit/sec
8PSK Serial Tone
MODEM

MOBAT-MODEM MODEM PERFORMANCE
VERSUS
STANDARD PERFORMANCE:
MIL-STD-188-110B sec. 5.3.2
User
Channel
Multipath
th Fading
SNR
BER
MOBAT
Data Rate
[bps]
Multi-Paths [ms] BW
[Hz]
[dB] As Required
by 110A &
110B STDs
MODEM
BER
4800 1 Fixed - - 17 1.0 E-3 9.0 E-6
4800 2 Fading 2 0.5 27 1.0 E-3 3.3 E-4
2400 1 Fixed - - 10 1.0 E-5 0
2400 2 Fading 2 1 18 1.0 E-5 1.0 E-6
2400 2 Fading 2 5 30 1.0 E-3 0
2400 2 Fading 5 1 30 1.0 E-5 0
1200 2 Fading 2 1 11 1.0 E-5 0
600 2 Fading 2 1 7 1.0 E-5 1.8 E-6
300 2 Fading 5 5 7 1.0 E-5 0
150 2 Fading 5 5 5 1.0 E-5 0
75 2 Fading 5 5 2 1.0 E-5 0

HF CHANNEL Multi-Path (RAYS)
IN STANDARDS & LITERATURE
Watterson [1970] Measurements:
• Found up to 4-Rays (Multi Path).
• Two Magneto-ionic components.
ETSI DRM STANDARD (Digital Radio Mondiale)
• Up to 4-Rays should be tested.
• Field-test found 5-Rays.
MIL-STD-188-110A, 110B, STANAG-4539, …
• Only Two-Rays should be tested.
•In Real HF Conditions There are More than 2 Rays.

MODEM Visualization Tools
Scatter-Diagram & Impulse-Response

MOBAT HF-MODEM
MULTI-RAY
OVER-STANDARD TESTING
• Up to 5-Rays5 were tested.
User
Data-Rate
[bps]
Channel
Multi-Paths
Multipath
[msec]
Fading BW
[Hz]
SNR
[dB]
MOBAT
MODEM
BER
4800 5 Fading 2 0.5 32 4.5 E-3
2400 5 Fading 2 1 23 1.3 E-5
2400 5 Fading 2 5 35 7.0 E-4
2400 5 Fading 5 1 35 2.6 E-6
1200 5 Fading 2 1 16 5.0 E-5
600 5 Fading 2 1 12 0
300 5 Fading 5 5 12 0
150 5 Fading 5 5 10 0
75 5 Fading 5 5 7 0

FIELD-TESTS
RESULTS
Conducted Nov 28 – Dec 10 2002
Link-Range = 200 KM
Rate
[bps]
Intrlvr
RF
Freq
[MHz]
Freq
Quality
By ALE
% -> %
Trans
Duration
[min]
Start
Time
Det
Fading
BW
[Hz]
Det
Num
of
Rays
Det
Channel
Impulse R.
Length
[msec]
2400 long 9.387 90->89 2x6 10:00 0.1-0.7 2 3-5
150 long 9.387 76->77 1x26+4 13:32 0.1-1.3 1-3 1.25-5.4
2400 long 5.395 47->59 2x6 14:55 0-1 2-4 1.25-4.15
Summary of field test results from 9/12/2002

Received Signal for the 3 cases above
From field test results of 9/12/2002
6
dB/Div
Despite the severe conditions, reception was achieved with BER=0.
Spectrum for 2400, long, 9.387MHz,
time 10:01:00

6
dB/Div
Spectrum for 150, long, 9.387MHz,
time 13:38:00

Signal for 2400, long, 5.395MHz, time
14:58:50, length 40 sec

6
dB/Div
Spectrum for 2400 long 5 395MHz
Spectrum for 2400, long, 5.395MHz,
time 14:59:30

Summary & Recommendations
• We presented the MICOM MD-4800:
As a new Technology application for Digital Secure
Data and Voice
• Our recommendations:
To add one more ray to the 110B STD.
To specify a voice coder for HF application.
To add a Voice-AMD to the STD.

MICOM MD-4800
Technology for the
New Generation