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

Constellation 4-QAM 4-QAM 4-QAM 4-QAM 16-QAM 64-QAM

Repetition factor 8 4 2 1 1 1

Data packets over the 8 subbands

1 2 4 8 16 24

Information bits over the 8 subbands

432 864 1728 3456 6912 10368

Flush bits over the 8 subbands

8 16 32 64 128 192

CRC bits over the 8 subbands

16 32 64 128 256 384

Coded bits over the 8 subbands

912 1824 3648 7296 14592 21888

Channel symbols over the 8 subbands

456 912 1824 3648 3648 3648

Interleaver matrix dimension

48x19 48x19 48x19 48x19 48x38 48x57

Bit rate (kbit/s) 6.322 12.644 25.288 50.576 101.152 151.728

HF Channel Model

Channel type Mid-latitude disturbed

Mid-latitude moderate

Mid-latitude good

Delay spread(ms)

2.0 1.0 0.5

Doppler spread (Hz) 1.0 0.5 0.1

Coherence bandwidth can range from 500 Hz to some kHz

Coherence time can range from 1 second to more than 10 seconds

Data link with moderate channel condition