Download - Performance improving of HF modem using TCM
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Performance improving of HF modem using TCMPerformance improving of HF modem using TCM
Saša Đorđević, Aleksandar Đorđević
Mihailo Pupin Institute, Belgrade, Serbia and Montenegro
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
HF channel HF channel pro’spro’s
• Long range transmission• Immune to large obstacles• Large number of 3kHz voice channels• HF equipment is relatively inexpensive
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
HF channel con’sHF channel con’s
• Impulse noise made by both man and nature • Slow multipath fading• Random (solar induced) ionospheric disturbances• Long distance HF communication can not be
available for 100% of a time
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Typical HF propagation exampleTypical HF propagation example
The Earth
Ionospheric layers
Propagation paths
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
HF modem design approachesHF modem design approaches
• Single tone modem
• Parallel tone modem
• “CHIRP” tone modem
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Single tone modemSingle tone modem
• Single carrier frequency• Simpler design• Relatively high bit rate (2400bps)• Very low robustness
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
““CHIRP” tone modemsCHIRP” tone modems
• Continuous frequency sweep in voice band• Relatively complex design • Very low bit rate (up to 75 bps)• Extremely robust
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Parallel tone modemParallel tone modem
• Multiple carrier frequencies (16 to 20)• Complex design• Relatively high bit rate• Rather robust
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
20 tone parallel modem HF361820 tone parallel modem HF3618
• 20 carrier frequencies with DQPSK modulation• Symbol rate is 75 baud per carrier• Total bit rate 20 75 2 = 3000 bps• 3 Doppler shift correction tones are sent prior data
transmission
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Transmitted composite OFDM signalTransmitted composite OFDM signal
n
N
kstkkn
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2
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
16 tone parallel modem16 tone parallel modem
605 935 2585Frequency
110
16 DQPSK data carriers
Doppler-shift correction tone
7dB
[Hz]
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
HF3618 signal structureHF3618 signal structure
605495 2585 Frequency
110
20 DQPSK data carriers
Doppler-shift correction tone
7dB
[Hz]1595
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
““Guard time”Guard time”
13.5ms 13.5ms4.5ms
Active symbol periode“Guard time”
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
HF channel characteristicsHF channel characteristics
• In most cases there is no direct radio wave.• Usable information consists of at least two waves
reflected from ionosphere layers,• Because of different paths of this components a
slow Rayleigh fading occurs
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
HF channel characteristics, cont’dHF channel characteristics, cont’d
• Time varying impulse noise – Industrial
– Solar induced
– From lightning
• Deliberate interference (ECM)
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
CCIR definitions of HF radio channelCCIR definitions of HF radio channel
Good channel Poor channel
Fade rate fd [Hz] 0.1 1
Interpath delay td [ms] 0.5 2
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Elimination of time/space variationsElimination of time/space variations
• Time diversity (interleaving)– Can’t be used in voice transmission due to time gaps
– Can’t be used in ARQ systems
– Creates periodic error bursts
• Space diversity (multiple receiving points/ antennae).– More expensive infrastructure
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Use of trellis-coded modulation (TCM)Use of trellis-coded modulation (TCM)
• TCM implies use of redundant data bits, thus decreasing effective data rate.
• To maintain constant bit rate a different modulation than DQPSK must be used.
• Since every carrier carries two information bits it is logical to use 2/3 convolutional encoder.
• This implies use of 8PSK modulation
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Additional simulation parametersAdditional simulation parameters
• Simulation was done with 2 sec. interleaving on assumption that a space diversity is used
• No Doppler shift correction tones ( use of FFT gives 20 phasors regardless of Doppler shift)
• Eliminating pilot tone “empties” lower portion of voice band with possibility of raising data rate up to 3600 bps with a loss of only 1.8dB in SNR
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Comparison of simulation resultsComparison of simulation results
• Simulated 3000 bps modem with 8PSK TCM • Single tone 2400 bps HF modem (MIL-ST-188-
110A) • 16-tone 2400 bps modem with 8PSK TCM • 16-tone 3600 bps modem with 16PSK TCM
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Performance over CCIR Performance over CCIR GGoooodd channel channel 0 5 10 15 20 25 30 35 40
SNR[dB]
1E-05
1E-04
1E-03
1E-02
1E-01
1E+00
Bit
Err
or
Rate
Single tone 2400 2400 TCM 3000 TCM 3600 TCM
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Performance over CCIR Performance over CCIR PoorPoor channel channel 0 5 10 15 20 25 30 35 40
SNR[dB]
1E-05
1E-04
1E-03
1E-02
1E-01
1E+00
Bit
Err
or
Rate
Single tone 2400 2400 TCM 3000 TCM 3600 TCM
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Benefit of parallel tone modemBenefit of parallel tone modem
• Possibility to improve current modems with small, if any, modification of hardware, enabling simple upgrade by "flashing" new DSP code into processor.
• Multirate" modems, with selection of modulation type during initial handshaking of modems according to channel characteristics.
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
ConclusionConclusion
There are many possibilities that should be accounted for, whether the goal is improving performance or data rate. It is sure that, by applying newly acquired knowledge in DSP and information theory, data rate will increase, as it is sure that a HF band would remain interesting for both military and civil services.
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Performance Improving of HF Modem using TCM ICEST 2004, BitolaPerformance Improving of HF Modem using TCM ICEST 2004, Bitola
institut MIHAJLO PUPIN
IMP-TELEKOMUNIKACIJE, d.o.o.
B
S N
Institute Mihailo Pupin
IMP – Telecommunications
Volgina 15
11060 Belgrade
Serbia and Montenegro
+381 11 27 72 953
www.telecom.imp.bg.ac.yu
Sasha Djordjevic email: [email protected]
Aleksandar Djordjevic email: djole @kondor.imp.bg.ac.yu