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Performance Analysis and Improvements for the Future Aeronautical Mobile Airport Communications System (AeroMACS)(AeroMACS)
Candidate: Paola PuliniCandidate: Paola PuliniAdvisor: Marco Chiani
Outline
Introduction and Motivations
Thesis SummaryMain Contributions
Unequal Diversity CodingFundamentalsFundamentalsSystem DescriptionPerformance Results
Conclusions
Introduction and Motivations (1/3)
Current aeronautical communications system - air traffic control (ATC) and air traffic management (ATM)
Voice based - Double-sideband amplitude modulation (DSB-AM)Data link based - VDL (VHF digital link) mode 2Capacity of the system is already saturatedCapacity of the system is already saturated
Necessity of a new aeronautical communications infrastructureRobust, efficient, secure, flexibleAble to cope with the future long-term increasing demands
Introduction and Motivations (2/3)New global aeronautical communications system
Air to air communications
Satellite-based communications
Air-to-air communications
Ground-based communications
communications
Airport communications (AeroMACS)
Introduction and Motivations (3/3)Airport Surface Communications
High demand of capacityNew frequencies assignments (ITU world radio conference 2007)
C band (5091 – 5150 MHz)
IEEE 802.16 standard (mobile WiMAX) has been chosen as the base technology for the future system (AeroMACS)
Thesis Summary
Analysis and investigation of the performance of AeroMACS
Evaluation of potential solutions for enhancing the performance of the system
Improvement through the introduction of diversity techniquesMIMO schemes with multiple antennas only on the control O sc e es t u t p e a te as o y o t e co t otower (space diversity)Cooperative Communications with single relay (cooperative di ersit )diversity)Packet level coding (time diversity)
Main Achievements (1/3)Preliminary Studies
Development of a novel stochastic airport channel modelParameters based on measurement campaign at MUCp g
Analysis of the performance of two WiMAX profiles in a realistic i t i tairport environment
OFDM based waveformOFDMA based waveformOFDMA based waveform
Selection of the most suitable profile for AeroMACSp
Main Achievements (2/3)
Analysis of MIMO schemes and relative performance evaluationSIMO 1x2 with MRC (reverse link)( )MISO 2x1 STC (forward link)Introduction of a novel implementation of 2x1 STC for A MACSAeroMACS
Investigation of the use of cooperative communications strategiesInvestigation of the use of cooperative communications strategies in the airport contextStudy and performance analysis of single relay schemes
Amplify and forwardDecode and forward
Main Achievements (3/3)
Introduction of the novel concept of unequal diversity (UD) coding for the relay channel (high efficiency)
Development of a novel class of LDPC codesAnalytical study of the codesA li ti f th d th d t A MACSApplication of the proposed method to AeroMACS
Packet level codingPacket level codingDevelopment of two algorithms for the online design of LDPC codesAnalytical study of the proposed methodApplication of the proposed scheme to AeroMACS
FundamentalsCooperative Communications
New paradigm based on the utilization of heterogeneous resources to improve the overall performance of the systemoverall performance of the system
Virtual antenna array by the combination of antennas of different users (also singleantennas of different users (also single antenna)
Distributed MIMO networkSpatial diversity (cooperativeSpatial diversity (cooperative diversity)
In a multi-user systemIn a multi user systemEach user represents a potential cooperative-partnerNo requirement of a dedicated
Potential cooperative-tNo requirement of a dedicated
infrastructure partners
Cooperative Communications
Example: Single relay (cooperation between partner A and B)
t1Source
t2
Partner
t2
Cooperative CommunicationsBasic Methods
Amplify and Forward
Decode and Forward
Coded Cooperation
Diversity gain of order 2Reduction of the efficiency overall coding rate ≤1/2 forReduction of the efficiency, overall coding rate ≤1/2 for achieving diversity-2
Cooperative CommunicationsHigh-Rate Coded Cooperation
We introduce a coded cooperation scheme which allows high code rates
Diversity-2 is guaranteed for a part of the source message
U l Di it (UD) E t i f l t tiUnequal Diversity (UD) Extension of unequal error protection Relevant for messages composed by parts having differentpriority/QoS requirementsp o ty/QoS equ e e ts
Video streamingAircraft communications (messages with different level of criticality) within the airport domain
Cooperative CommunicationsHigh-Rate Coded Cooperation
We propose a novel construction based on Low-Density Parity-Check codes which achieves the promised performance
We provide an analysis on block-fading channels complemented by simulationsby simulations
Low-Density Parity-Check CodesBasics
Low-Density Parity-Check Codes (Gallager,1960)Near-Shannon limit error correcting codes with iterative (message-passing) decoding
Parity-check matrix:Check nodes
100111001011010011011
H Tanner graph:
Check nodes
1001110
05421 cccc
Parity-check equations:
000
7432
6431
5421
cccccccccccc
Variable nodes
Low-Density Parity-Check CodesProtograph Construction of the Tanner Graph
Protograph: small bipartite graph describing the macroscopic structure of an LDPC code
Tanner Graph: obtained by Q-fold replication of the protograph and by edge permutation among the protograph replicasedge permutation among the protograph replicas
Low-Density Parity-Check CodesProtograph Construction of the Tanner Graph
For the LDPC code associated with the Tanner graph,Minimum distance propertiesIterative decoding threshold
depend on the starting protograph only
Code design reduces to protographdesign!
Additionally, protograph LDPC codes have structured parity-checkAdditionally, protograph LDPC codes have structured parity check matrices which facilitate the decoder implementation
Low-Density Parity-Check CodesProtograph Extrinsic Information Transfer (EXIT)
Protograph EXIT analysis: track the evolution of the message probability densities over theprobability densities over the protograph edges
Allows to accurately predict the iterative decoding threshold, i.e. the signal-to-noise ratio (SNR) at which iterative decoding starts to converge
EXIT analysis can be adapted toEXIT analysis can be adapted to block-fading channels
Low-Density Parity-Check CodesProtograph Analysis over Block Fading Channels (1/2)
Block fading channel (BFC): The codeword is split into
N blocksN blocksEach block is transmitted over a different flat fading channelEach block experiences aEach block experiences a different SNRIn each channel, the SNR follows an exponentialfollows an exponential distribution
Accurate model forFrequency-hoppingFrequency hoppingRelay communications
Low-Density Parity-Check CodesProtograph Analysis over Block Fading Channels (2/2)
We introduced a modification of the protographEXIT analysis in order to account for different SNRsfor each variable nodefor each variable node
Protograph variable nodes = codeword blocksFeed each protograph variable node with a
different SNR levelGiven a SNR profile, we determine whether
iterative decoding converges or not (outage)g g ( g )Outage region of a protograph G,The definition of outage region can be
extended to each single variable node (= block)extended to each single variable node (= block)
We can characterize the UEP of the protographnodes!
Protograph Analysis over the Relay ChannelBlock Fading Channel Approximation
Conventional assumption: the Source-Relay (S-R) link is reliableValid if the SNR over the S-R link is larger than the decoding threshold of the code employed at the Sourcethe code employed at the SourceRealistic assumption (relay selection protocol)
Approximation with block fading channel withtwo independent channels (=two fading levels / SNRs), and
Conventional Approach for the Relay ChannelCoded Cooperation
The Source encodes the packet with a (nS,k) code CS and broadcasts (Time Frame 1)The Relay decodes and re-encodes nR additional parity bits with a code CR, whichThe Relay decodes and re encodes nR additional parity bits with a code CR, which are sent to the Destination (Time Frame 2)
S D
R
S DTime frame 1
Time frame 2
The overall code has block length nS+nR the overall code rate is R=k/(nS+nR)Diversity-2 can be achieved only if R≤1/2New solution:
By re-encoding just a fraction of the information bits at the Relay, we can provide diversity-2 for certain codeword bits even if R>1/2…
Unequal Diversity CodingA New Scheme for the Relay Channel
The Source encodes the packet with an (nS,k) code CS and broadcasts (Time Frame 1)(Time Frame 1)The Relay decodes and re-encodes nR additional parity bits with a code CR, out of kh<k information bits R h(Time Frame 2)
u = informationword (k bits)
Unequal Diversity CodingA New Scheme for the Relay Channel
The Source encodes the packet with an (nS,k) code CS and broadcasts (Time Frame 1)(Time Frame 1)The Relay decodes and re-encodes nR additional parity bits with a code CR, out of kh<k information bits R h(Time Frame 2)
uh = high-priorityfragment (kh bits)
Unequal Diversity CodingA New Scheme for the Relay Channel
The Source encodes the packet with an (nS,k) code CS and broadcasts (Time Frame 1)(Time Frame 1)The Relay decodes and re-encodes nR additional parity bits with a code CR, out of kh<k information bits R h(Time Frame 2)
ul = low-priorityfragment (kl bits)
Unequal Diversity CodingA New Scheme for the Relay Channel
The Source encodes the packet with an (nS,k) code CS and broadcasts (Time Frame 1)(Time Frame 1)The Relay decodes and re-encodes nR additional parity bits with a code CR, out of kh<k information bits R h(Time Frame 2)
Ti F 1Time Frame 1:S encodes u (low+high priority fragments)f g )
Unequal Diversity CodingA New Scheme for the Relay Channel
The Source encodes the packet with an (nS,k) code CS and broadcasts (Time Frame 1)(Time Frame 1)The Relay decodes and re-encodes nR additional parity bits with a code CR, out of kh<k information bits R h(Time Frame 2)
Ti F 2Time Frame 2:R encodes uh(high priority fragment ONLY)f g )
Unequal Diversity CodingProtograph Design
Encoding at the Source with a high-rate LDPC codeEncoding at the Relay with a short LDPC codeSi l ll l t ti f t LDPC dSimple parallel concatenation of two LDPC codes
S DTime frame 1
R Time frame 2
Unequal Diversity CodingProtograph Design
Encoding at the Source with a high-rate LDPC codeEncoding at the Relay with a short LDPC codeSi l ll l t ti f t LDPC dSimple parallel concatenation of two LDPC codes
At the Destination, joint decoding th ll hover the overall graph
EXIT analysis: only two SNRsThe channel profile is a 2-D
tvector
Unequal Diversity CodingPerformance
Overall code rate: 7/10Block length k=1792 bits
Probability Distribution of the channel profile
Outage regionOutage region for high-priority fragments
Outage regions Outage / Block Error ProbabilityOutage regions Outage / Block Error Probability
Unequal Diversity CodingPerformance
Overall code rate: 7/10Block length k=1792 bits
Outage region f l i i ffor low-priority fragments
Outage regions Outage / Block Error ProbabilityOutage regions Outage / Block Error Probability
Unequal Diversity CodingPerformance
Overall code rate: 7/10Excellent match between EXIT analysisand simulations
Outage regions Outage / Block Error ProbabilityOutage regions Outage / Block Error Probability
Unequal Diversity CodingPerformance of AeroMACS
Bandwidth 5 MHz, 512 subcarriers, ∆f = 10.94 KHz, OFDMA b lOFDMA symbolsParking scenarioLack of diversity, low Rice y,factor (K = 0 dB, no/limited mobility, low Doppler)
The design may be tailored to the different PER requirements of the COCR messagesof the COCR messages
Unequal diversity is achieved also over the aeronautical channel modelmodel
SummaryUnequal Diversity Coding
A coded cooperation scheme targeting high code rates (R>1/2)Diversity / coding rate trade-off by introducing an Unequal Diversity distributed coding scheme
High priority fragments enjoy diversity, low priority fragments do notAccurate EXIT analysis for protograph LDPC codes over block fadingAccurate EXIT analysis for protograph LDPC codes over block fading channelsDesign of distributed protograph codes for Unequal Diversity achieving the target performancethe target performancePotentially suitable for in-airport communications to protect messages with different priority levels
Conclusions
We investigated the performance of the future system for the airport surface communications and we analyzed and proposed methods for improving its performanceimproving its performance.
We focused on techniques that increase the diversity of the system, and in particular space diversity (MIMO and cooperative communications) and time diversity (packet level coding)
Generally, all the methods investigated may be suitable for AeroMACS
PublicationsConference Proceedings
P. Pulini, G. Liva, and M. Chiani “Protograph EXIT Analysis over Block Fading Channels with Application to Relays,” ICC’12, June 2012, Ottawa, CAP Pulini and M Chiani “Improving the performance of AeroMACS by cooperativeP. Pulini, and M. Chiani, Improving the performance of AeroMACS by cooperative communications,” DASC’30th, October 2011, Seattle, USG. Liva, P. Pulini, and M. Chiani, “Flexible on-line construction of IRA codes for packet erasure correction with application to aeronautical communications,” ICC’11,packet erasure correction with application to aeronautical communications, ICC 11, June 2011, Kyoto, JapanP. Pulini, “Forward Link Performance Analysis for the Future IEEE 802.16-based Airport Data Link,” ICC’2010, May 2010, Cape Town, South AfricaP. Pulini, and M. Chiani, “Improving the forward link of the future airport data link by space-time coding,” InOWo’10, September 2010, Hamburg, GermanyS. Gligorevic, and P. Pulini, “Simplified airport surface channel model based on the WSSUS assumption,” ICNS’10, May 2010, Washington, USP. Pulini, and S. Gligorevic, “WiMAX performance in the airport environment,” MCSS’09, May 2009, Hersching, Germany
PublicationsSubmitted
Journals:G. Liva, P. Pulini and M. Chiani, “On-Line Construction of Irregular Repeat Accumulate Codes for Packet Erasure Channels” submitted to IEEEAccumulate Codes for Packet Erasure Channels , submitted to IEEE Transaction on wireless communicationsP. Pulini, G. Liva, and M. Chiani, “Unequal Diversity LDPC Codes for Relay Channels”, submitted to IEEE Transaction on communicationsChannels , submitted to IEEE Transaction on communications
Patents:G Liva P Pulini “Method for flexible transmission with LDPC codes”G. Liva, P. Pulini, Method for flexible transmission with LDPC codes . (Sub. January 2011)P. Pulini, G. Liva, “Method for relay transmission with UEP”. (Sub. May 2011)2011)P. Pulini, G. Liva, “Coded cooperation with information appending” (Sub. May 2011)
Seminars
“Future Airport Data Link Based on WiMAX – Forward Link Performance”, 22 October 2009, Oberpfaffenhoffen, Germany
“Improving the Performance of AeroMACS by Cooperative Communications”, 11 November 2011, Oberpfaffenhoffen, Germany
“Unequal Diversity Coding for the Relay Channel”, 14 December 2011, Oberpfaffenhoffen, Germany
Thanks for your attention!
Introduction and Motivations (4/4)Airport Surface Communications
WiMAX foresees a large number of profiles with different efficiency/robustness trade-offs
The most suitable profiles should be selected, taking into account the airport environment peculiarities
Analysis of the strengths/weaknesses of the selected profile may reveal the need for enhancements
Low-Density Parity-Check CodesProtograph Analysis over Block Fading Channels (3/4)
Given an SNR profile,
determine whether iterative decoding converges or not (outage)
Outage region of a protograph G,
SNR ° (0) SNR ° (1) SNR ° (2)= set of channel profiles for which
iterative decoding does not converge
SNR ° (0) SNR ° (1) SNR ° (2)
Low-Density Parity-Check CodesProtograph Analysis over Block Fading Channels (4/4)
Block error probability (outage probability) = probability of having a channel profile inchannel profile in
Probability Distribution of the channel profile
Th d fi iti f t i b SNR ° (0) SNR ° (1) SNR ° (2)The definition of outage region can be extended to each single variable node (= block)
SNR ° (0) SNR ° (1) SNR ° (2)
We can characterize the UEP of the protograph nodes!