Second and Third Generation HF Communications Dr A F R Gillespie and Mrs S E Trinder

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Second and Third Generation HF CommunicationsDr
A F R Gillespie and Mrs S E Trinder

• Presented by Dr A F R Gillespie
• KI Systems
• QinetiQ Portsdown West

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Presentation Structure

• Section 1 What are second and third generation HF
• Section 2 Key Features of 2nd Generation HF
• Section 3 Key Features of 3rd Generation HF
• Section 4 Performance Aspects
• Section 5 Factors influencing Choice of
  Technology
• Section 6 Conclusions

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Introduction

• The continued use of HF as an important military
  communications medium has become increasingly
  recognised over the last few years and most
  nations are now in the process of upgrading their
  HF communications capabilities
• Aim of presentation
• to provide a comparative analysis of the key
  features of modern 2nd and 3rd Generation HF
  communications to assist in the understanding of
  how best to use the new HF technologies to
  provide reliable and efficient communications

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2nd Generation HF - Definition

• The current NATO definition of 2nd Generation HF
  is embodied by the following key standards
• Modems - STANAG 4285/4539/MIL STD 188 110B
• ARQ - STANAG 5066
• ALE - MIL STD 188 141A
• Subnetwork - STANAG 5066
• HF Clients - STANAG 5066

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3rd Generation HF - Definition

• The current NATO definition of 3rd Generation HF
  is embodied in the following standards
• Waveforms - BW1-5 from STANAG 4538
• ARQ - HDL LDL from STANAG 4538
• ALE - STANAG 4538
• Subnetwork - STANAG 5066
• HF Clients - STANAG 5066

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2nd and 3rd Gen. HF Architectures
COTS SMTP Email Application
Specific 5066 Email Proxy agents CFTP and/ or HMTP
3rd GEN HF
STANAG 5066 Specific Software
5066 Subnet Interface
HOST COMPUTER (Windows NT)
Channel Access / Link Requests
HF Channel Management System Single
Frequency Listen before transmit (BFEM-66) or
Token Ring / TDMA (under investigation) Multiple
Frequency (future) ALE using MIL STD 188 141A/B
or STANAG 4538 ( when available)
STANAG 5066
Crypto
Data In/Out 4539/110B Modem Baseband In/Out
Data Rate Adaptation
ctrl
TX/RX CONTROL Change Channel Power Control
Baseband Out HF RADIO SYSTEM RF In/Out
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Key Features of 2nd Generation HF

• The key feature of 2nd generation HF technology
  is the ability to construct a complete automated
  HF system from loosely coupled multi vendor
  components
• Modems Harris, RC, RS,Marconi,GA,Thales.
• ARQ RC, RS, Thales, Marconi, Harris.
• ALE RS, Marconi, RC,Harris,Thales.
• HF Clients NC3A, 5066 vendors.
• Interfaces TCP Port to the STANAG 5066 stack.

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3rd Generation HF Technology

• 3rd generation HF technology is tightly coupled
  and the individual subsystems cannot easily be
  separated out into a multi-vendor system
• Modem/ARQ/ALE
• tightly coupled 3rd generation HF system
• HF Clients
• vendor specific gateway/proxy agent to COTS end
  user applications e.g SMTP email

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2nd Generation ARQ

• Selective ARQ with a max of 128 forward packets
• Asynchronous, event driven with time-outs
• does not require strict timing
• waveform independent
• can be configured to work with S4285, S4539, FSK
• Allows use of legacy cryptos e.g KG 84, BID 1650
  in current interoperable, operational
  architectures
• Connectionless protocol
• Software, firmware or embedded implementations

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3rd Generation ARQ

• Two ARQ protocols are defined - HDL and LDL,
  generically termed xDL
• xDL protocols are time, rather than event, driven
• Selective ARQ with a maximum of 24 forward
  packets
• Enables code combining to automatically and
  adaptively adjust coding rate to match channel
  conditions
• Impose strict timing constraints
• Require dual demodulation at the waveform level
• Connection oriented protocol

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3rd Generation Code Combining

• One of the key technological features of the HDL
  protocol is that it enables the use of a code
  combining approach to decode packets
• Successive repetitions of packets are encoded
  using a different convolutional encoder on each
  re-transmission thus adaptively reducing the
  coding rate and increasing the probability of
  decoding even when all individual packets are in
  error
• Does not require over the air co-ordination
• implementation details not in STANAG 4538

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Connection / Connectionless Protocols

• The xDL protocols are connection oriented
  protocols that require both physical and logical
  links to be set up using the LSU and TM processes
  respectively prior to use of xDL.
• no addressing information is contained in the xDL
  packets
• cannot reach multiple users over the same link
  simultaneously without using the roll call PTP
  link set-up
• connecting a new application over an existing
  physical link requires terminating/completing the
  current connection and establishing a new link

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Connection / Connectionless Protocols cont.

• STANAG 5066 is a connectionless bi-directional
  protocol (like IP) with every D_PDU containing
  both source and destination addresses
• allows multiple links to be maintained over one
  physical HF channel
• new applications can be connected over an
  existing physical/ logical link without
  additional link negotiation
• Provides efficient and easy to implement support
  for multi-user networks

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Performance Comparisons

• The baseline for performance comparisons
• no application overhead included in any figures
• modulation rate of 4800 bps and packet size 233
  bytes (as defined in HDL) for both 5066 and HDL
• LSU time and termination time included in the HDL
  throughputs since HDL cannot work without LSU/TM
• 5066 time to establish a physical link included
  in 5066 throughputs
• link termination time not included since 5066 can
  support additional applications and clients on an
  existing physical link

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Performance Comparisons Cont.

• The performance analysis of 2nd generation HF is
  based on using STANAG 5066 with the new STANAG
  4539 waveform
• STANAG 4539 provides significantly improved
  performance relative to the MIL STD 188
  110A/STANAG 4285 waveforms
• STANAG 4539 is a NATO standardised autobaud
  waveform
• Initial data rate of 300bps is not mandated for
  STANAG 5066 when autobaud is available
• Previous comparisons need to be re-appraised in
  the light of the factors above

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Optimisation of ARQ Throughput
Node 1
Delay
ACK
Delay
ACK
X
X
Node 2
time
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Impact of Message Size on Performance

• The efficiency of both the HDL and 5066 ARQ
  protocols are affected by the size of the message
  to be transmitted
• HDL protocol has a choice of transmitting 3, 6,
  12, or 24 forward packets
• sub multiples not allowed due to timing of
  protocol
• choice of number forward packets made during LSU
• 5066 has choice of 1 to 128 packets (each of
  variable size)
• less affected by message size

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Impact of Message Size on HDL and S5066
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HDL Throughputs (Poor Channels)
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HDL Throughput (Gaussian Channels)
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5066 versus HDL
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5066 versus HDL (linear scale)
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HDL and 5066 Throughput vs. SNR -CCIR Poor
Channel
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Performance Summary

• Analysis has clearly shown the advantages of 3rd
  Generation HF at at high frame error rates (lower
  SNRs) and advantages of 2nd generation ARQ at low
  frame error rates (high SNRs)
• highly variable channels will also benefit from
  code combining
• Where conditions are likely to be average/good
  use of 2nd Generation HF will provide comparable
  or better performance than 3rd Generation HF
• True even for fixed data rate 5066 operation at
  3200 bps
• Data rate change will further enhance 2nd
  generation performance

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Factors Influencing Choice of Technology
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Summary

• In many instances system design constraints will
  mandate the choice of HF technology so
  performance comparisons are irrelevant.
• Neither 2nd or 3rd Generation HF will meet the
  needs of all users and therefore both will be
  components of future military C4I systems
• Both technologies provide significant advances
  over traditional HF capabilities establishing HF
  as an important component of modern military
  communications.