09-11-2012 Ebro Observatory, October 1st, 2013 Internet Failure and Physical Layer Architecture Short Wave critical Infrastructure Network based on new Generation of high survival radio communication system With the support of the Prevention, Preparedness and Consequence Management of Terrorism and other Security-related Risks Programme European Commission - Directorate-General Home Affairs
Internet Failure and Physical Layer Architecture. Ebro Observatory, October 1st, 2013. With the support of the Prevention, Preparedness and Consequence Management of Terrorism and other Security-related Risks Programme European Commission - Directorate-General Home Affairs. - PowerPoint PPT Presentation
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09-11-2012
Ebro Observatory, October 1st, 2013
Internet Failure and Physical LayerArchitecture
Short Wave critical Infrastructure Network based on new Generation of high survival radio communication system
With the support of the Prevention, Preparedness and Consequence Management of Terrorism and other Security-related Risks ProgrammeEuropean Commission - Directorate-General Home Affairs
Internet Failure
1) Description of the early warning alert scenario
2) Supervision of the internet links
3) Reactivation of the internet links
Early warning alert
Description of the scenario.
Most Reasonable Scenario Worst Case Analysis
Supervision of the Internet links
End-User
Router
Ethernet LAN
Internet
ECI/CGA Site
WebServer
GatewayHF
HFNetwork
NMS
the reference scenario for each ECI/CGA site
NMS= NETWORK MANAGEMENT SYSTEM
Agents (managed devices)
Management application (central station)
- NMSs hierarchically structured in two levels: Level 0: CGA NMSsLevel 1: ECI NMSs
Nagios (a powerful monitoring system that enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes) deployment could be quite straightforward in the SWING scenario thanks to its adaptability to distributed system case
Supervision of the Internet links
NAGIOS Architecture
NCSA= Nagios Service Check
Acceptor
OCSP= obsessive compulsive service processor
Supervision of the Internet links
Reactivation of the Internet links.
The reactivation of the traditional Internet links and the consequent interruption of the HF links cannot be directly operated by any ECI, but they should be controlled by the interested CGA
A CGA that experiences a resurgence of its Internet connection just needs to transmits a message to the other CGAs, notifying that its normal operational status has been restored and to switch from the HF link to the restored broadband Internet connection.
PHY layer architecture
of the SWING system
1) Selection of the modulation technology
2) System design for voice transmission
3) System design for data transmission
Selection of the modulation technology
Most military HF standards employ a serial-tone waveform with a powerful FEC code and temporal interleaving to exploit the time-diversity of the HF channel
The use of a temporal interleaver with an interleaving depth greater than the HF channel coherence time poses a serious problem in terms of overall link latency
The alternative approach to increase the system reliability is to exploit the frequency diversity offered by the multipath phenomenon
Advantages of the OFDM technology
The channel distortion appears as a multiplicative factor which can be compensated for through a bank of complex multipliers
Increased spectral efficiency due to partially overlapping subbands in the frequency domain
Simple digital implementation by means of DFT/IDFT operations
Increased resilience against narrowband interference, which only hits a small portion of the signal spectrum
Possibility of adaptively selecting the constellation size on each subband (autobaud capability)
Requirements of the digital voice link
1) It will support interactive voice communications. Interactivity is a basic design constraint
2) The maximum accepted delay is around 120 ms so as to guarantee a whole delay observed by the user below the subjective limit of 250 ms
3) Temporal interleaving cannot be used due to the strict requirement in terms of overall delay
4) In order for the system to be applicable to commercial vocoders, the bit rate should be 2400 bps with a BER lower than 10-2
5) A fixed 4-QAM constellation is used (no autobaud capability)
Guidelines for the design of the digital voice link
The signal bandwidth B must exceed the channel coherence bandwidth so as to capture most of the frequency diversity offered by the HF channel
B Bcoh
The subcarrier spacing f must be much smaller than the channel coherence bandwidth Bcoh so as to make the channel response nearly flat over each subcarrier and much larger than the Doppler spread in order to avoid significant channel variations over one OFDM block
5 Hz : BDoppler f Bcoh : 500 Hz
Design of the main system parameters
The sampling frequency fs is fixed to 14.4 kHz, which seems reasonable for implementation on commercial HW platforms
The IDFT/DFT size is fixed to N=256. This value results into a subcarrier distance f =56.25 Hz
The number of modulated subcarriers is Nu=171, while the number of null subcarriers placed at the spectrum edges is Nv=N-Nu=85
The signal bandwidth is B=Nu f = 9600 Hz
Transmitter structure for the voice link
informationbits FEC Mapper OFDM
modulatorInterleaverSubcarrierallocation
FEC is accomplished by means of the industry-standard convolutional encoder with rate 1/2 and constraint length 7
Bit interleaving is accomplished by means of a block interleaver matrix
Interleaved bits are mapped onto 4-QAM symbols without any autobaud capability
Requirements of the data link
1) The data link provides non-delay sensitive services, meaning that we can relax the interactivity constraint
2) Channel coding is necessary to provide sufficiently low packet error rate
3) The signal bandwidth is chosen large enough so as to provide the system with the desired frequency diversity
4) CRC and ARQ are requested for error-free packet delivery
5) An autobaud capability is employed to adaptively select the most appropriate constellation
PARA METER VAL UE
IDFT/DFT size 2048
Subcarrier spacing 56.25 Hz
Length of the useful part of the OFDM block 17.78 ms
CP length 5 ms
Length of the extended OFDM block 22.78 ms
Number of virtual carriers 320
Number of cyclic prefix samples 576
Number of mod ulated subcarriers 1728
Row bandwidth 115.2 kHz
Channel bandwidth 97.2 kHz
Main system parameters
Transmitter structure for the data link
A 16-bit CRC is appended to each data packet
FEC and bit interleaving as in the voice link
The overall bandwidth is divided into 8 subbands. A different constellation size can be used on different subbands (autobaud)
The interleaved bits are mapped onto 4QAM, 16QAM or 64QAM constellation symbols, which are transmitted within one single subband.
CRC16-bit
datapacket FEC Interleaver Mapper
Subcarrierallocation
OFDMmodualtor...from other
subbands
Data link waveformsTab 1 Ğ Parameters for the six transmission modes of the SWING data link
PARA METERS MODE I MODE II MODE III MODE IV MODE V MODE VI