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Project IEEE 802.20 Working Group on Mobile Broadband Wireless Access <http://grouper.ieee.org/groups/802/20/>
Title Link-system interface simulation methodologies
Date Submitted
2004-07-12
Source(s) Anna Tee 1301 E Lookout Dr.,Richardson, TX 75082
Voice: (972) 761-7437Fax: (972) 761-7909Email: [email protected]
Seokhyun Yoon416 Maetan 3-DongSuwon, Korea 442-742
Voice: +82-31-279-5841Fax: +82-31-279-5130Email: [email protected]
Joseph Cleveland 1301 E Lookout Dr.,Richardson, TX 75082
Voice: (972) 761-7981Fax: (972) 761-7909Email: [email protected]
Re: MBWA Call for Contributions, Session #9, July 2004
Abstract This contribution discusses the possible methodologies for link-system simulation interface. The various methodologies are compared and recommendation is made to adopt the most appropriate method for the simulation and evaluation of IEEE 802.20 proposals.
Purpose For discussion and adoption into IEEE 802.20 Evaluation Criteria Document.
Notice This document has been prepared to assist the IEEE 802.20 Working Group. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
Release The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.20.
Patent Policy The contributor is familiar with IEEE patent policy, as outlined in Section 6.3 of the IEEE-SA Standards Board Operations Manual <http://standards.ieee.org/guides/opman/sect6.html#6.3> and in Understanding Patent Issues During IEEE Standards Development <http://standards.ieee.org/board/pat/guide.html>.
Link-System Interface Simulation Link-System Interface Simulation MethodologiesMethodologies
Anna TeeAnna TeeSeokhyun YoonSeokhyun Yoon
Joseph ClevelandJoseph ClevelandJune 29, 2004June 29, 2004
TopicsTopics
Problem statementsProblem statements
Advantages & Requirements of a Link-System Simulation Interface Advantages & Requirements of a Link-System Simulation Interface (aka: PHY Abstraction) Methodology(aka: PHY Abstraction) Methodology
General Overview of Methods used in other Communication General Overview of Methods used in other Communication Standards OrganizationsStandards Organizations
Methods based on Shannon’s Theorem on Channel CapacityMethods based on Shannon’s Theorem on Channel Capacity Estimates on effective EEstimates on effective Ebb/N/Noo for convolutional codes in fading channels for convolutional codes in fading channels Methods for OFDM based SystemsMethods for OFDM based Systems Exponential Effective SIR MappingExponential Effective SIR Mapping
Simulation Results for EESMSimulation Results for EESM
ReferencesReferences
Problem StatementProblem Statement
Modeling Performance of Wireless Link in a System Level Modeling Performance of Wireless Link in a System Level SimulationSimulation
In the System Simulation, the profile of Received Signal to In the System Simulation, the profile of Received Signal to Interference Ratio (SIR) is computed and sampled at regular time Interference Ratio (SIR) is computed and sampled at regular time intervals for each user in the cell layout model.intervals for each user in the cell layout model.
The same SIR value in different channels environment typically The same SIR value in different channels environment typically results in different performance in BER and PERresults in different performance in BER and PER
For example, in a frequency selective fading channel, the SIR value For example, in a frequency selective fading channel, the SIR value fluctuates from one subcarrier to another in an OFDM system. Thus the fluctuates from one subcarrier to another in an OFDM system. Thus the PER performance cannot be predicted correctly using the average PER performance cannot be predicted correctly using the average packet SIR.packet SIR.
Infeasible and Impractical to Simulate the Instantaneous Infeasible and Impractical to Simulate the Instantaneous Performance of a Wireless Link in Real-time Performance of a Wireless Link in Real-time
A mapping is required between each sampled SIR value in the A mapping is required between each sampled SIR value in the system level and the implied BER or FER performancesystem level and the implied BER or FER performance
Advantages & Requirements of a Link-System Advantages & Requirements of a Link-System Simulation Interface MethodologySimulation Interface Methodology
Reduce computation load for off-line link level simulationReduce computation load for off-line link level simulation
An ideal method should have a computation load that is independent of An ideal method should have a computation load that is independent of the channel modelsthe channel models
The link performance should be estimated accurately, based on The link performance should be estimated accurately, based on performance of modulation and coding schemeperformance of modulation and coding scheme
A method that computes the equivalent SIR which corresponds to the A method that computes the equivalent SIR which corresponds to the same BER/FER performance in an AWGN channel same BER/FER performance in an AWGN channel
General Overview of Methods used in other General Overview of Methods used in other Communication Standards OrganizationsCommunication Standards Organizations
3GPP2: 1xEV-DV/DO [1,2]3GPP2: 1xEV-DV/DO [1,2] Method 1: Quasi-Static MethodMethod 1: Quasi-Static Method
bE
n
j jt
sj
effo
b
N
EN
NN
E
110
1log10
jslotforsymbolulationperSNRN
E
jslotindtransmittesymbolsulationofNoN
dtransmitteredtransmitteispacketencodedanwhichoverslotsofnumberTotaln
bitsormationofNoNwhere
jt
s
j
mod
mod.
)(&
inf.
Further account for:-
Coding Gain
Doppler Penalty
De-mapping Penalty
Methods based on Shannon’s Theorem on Methods based on Shannon’s Theorem on Channel CapacityChannel Capacity
1xEV-DV/DO Method 2 - Convex Method:1xEV-DV/DO Method 2 - Convex Method: Use Shannon’s Theorem to compute the instantaneous channel capacity Use Shannon’s Theorem to compute the instantaneous channel capacity
based on the SIR sample at the system levelbased on the SIR sample at the system level Compute the equivalent SNR in an AWGN channel that results in the same Compute the equivalent SNR in an AWGN channel that results in the same
average channel capacityaverage channel capacity A correction factor (Q) is included to account for practical performance A correction factor (Q) is included to account for practical performance
degradation from Shannon’s capacity limitdegradation from Shannon’s capacity limit
bE
N
jjeff Q
Nf
12 )1(log
1
where eff = Effective SNR
j = SIR of j-th segment in which channel response remains ~constant
N = Total number of segments that have ~constant channel response
QCfwhere
C 12)(
Methods for OFDM based systemMethods for OFDM based system
A similar method that is based on the application of Shannon’s Theorem on A similar method that is based on the application of Shannon’s Theorem on Channel Capacity is proposed by the European IST project: FITNESS [3]Channel Capacity is proposed by the European IST project: FITNESS [3]
A mapping between Channel Capacity and Block Error Rate (BLER) is required A mapping between Channel Capacity and Block Error Rate (BLER) is required and is modeled by a 2and is modeled by a 2ndnd order polynomial order polynomial
Coefficients of the polynomial (Coefficients of the polynomial () can be found by the least squares fitting to ) can be found by the least squares fitting to simulation datasimulation data
The above method has also been proposed in IEEE 802.11n PHY The above method has also been proposed in IEEE 802.11n PHY abstraction ad hoc group [4]abstraction ad hoc group [4]
A packet is declared in error when the instantaneous data rate exceeds the A packet is declared in error when the instantaneous data rate exceeds the channel capacity channel capacity
min
min
)(
,1
,10)(
2101
CC
CCCPERCC
Methods to Predict Performance of Convolutional CodesMethods to Predict Performance of Convolutional Codes Other methods that have been discussed in the literature and proposed in Other methods that have been discussed in the literature and proposed in
802.11n include methods to predict error rate performance for convolutional 802.11n include methods to predict error rate performance for convolutional codes based on the probability of error event sequence [5, 6] codes based on the probability of error event sequence [5, 6]
Two possible estimates have been derived based on the Two possible estimates have been derived based on the Bhattacharya bound Bhattacharya bound for error rate performance of convolutional codes infor error rate performance of convolutional codes in [6]. [6].
For a minimum distance error event of length D, For a minimum distance error event of length D,
/D])N
E[( )
N
E(
1-D
0ll)J(k
o
beff
o
b
where J(k) is the index of the Ewhere J(k) is the index of the Ebb/N/Noo level corresponding to the bit in position k. level corresponding to the bit in position k.
1)1) Choose the minimum (EChoose the minimum (Ebb/N/Noo))effeff , for k = 1, 2, … (N-D+1), N = length of frame , for k = 1, 2, … (N-D+1), N = length of frame ZZworstworst = Max {Geometric mean of Z = Max {Geometric mean of Zkk} where Z} where Zk k are the error probabilities at each Eare the error probabilities at each Ebb/N/Noo
level (bit group k) corresponding to the bit sequence of length Dlevel (bit group k) corresponding to the bit sequence of length D
2)2) Compute (ECompute (Ebb/N/Noo))effeff corresponding to the same AWGN error rate performance as corresponding to the same AWGN error rate performance as
the Arithmetic Mean of the AWGN error probabilities for all (Ethe Arithmetic Mean of the AWGN error probabilities for all (Ebb/N/Noo))effeff computed computed
using the above equation for kusing the above equation for k = 1, 2, …, (N-D+1).(N-D+1).
Exponential Effective SIR Mapping (EESM)Exponential Effective SIR Mapping (EESM)
EESM has been discussed and adopted in 3GPP feasibility study on OFDM [7,8,9,10]EESM has been discussed and adopted in 3GPP feasibility study on OFDM [7,8,9,10]
Derivation of EESM is based on the Union-Chernoff bound for error probabilitiesDerivation of EESM is based on the Union-Chernoff bound for error probabilities
Basic idea is to find an equivalent SIR in the AWGN channel that results in the same Basic idea is to find an equivalent SIR in the AWGN channel that results in the same BLER, using the Union-Chernoff bound to relate the error probability to the BLER, using the Union-Chernoff bound to relate the error probability to the corresponding SIR in a channel/subchannel with an approximately constant channel corresponding SIR in a channel/subchannel with an approximately constant channel responseresponse
An adjustment factor (An adjustment factor () is necessary for QPSK and higher-order modulation schemes) is necessary for QPSK and higher-order modulation schemes
N
ieff
i
eN 1
1ln
where eff = Effective SIR
j = SIR of j-th subcarrier, or segment in which channel response remains ~constant
N = Total number of subcarriers, or segments that have ~constant channel response
Simulation results for EESMSimulation results for EESM Simulation data shown in [9] has indicated good match of results, independent of Simulation data shown in [9] has indicated good match of results, independent of
channel models, channel models, i.e., the same factor i.e., the same factor has been used for different channel has been used for different channel models with the same modulation and coding scheme (MCS)models with the same modulation and coding scheme (MCS)
Less accurate in case of M-QAM, for M > 4Less accurate in case of M-QAM, for M > 4
Simulation Assumptions: Simulation Assumptions: Channel model unchanged during the simulation duration, i.e., either 10000 TTIs Channel model unchanged during the simulation duration, i.e., either 10000 TTIs
(2ms/TTI) or until 200 block errors were observed.(2ms/TTI) or until 200 block errors were observed. Random interleaving applied to each OFDM symbol Random interleaving applied to each OFDM symbol
For each MCS, For each MCS, is estimated using the Minimum Mean Square Error (MMSE) is estimated using the Minimum Mean Square Error (MMSE) criterion:criterion:
where eff () = Mean square error of the Effective SIR computed based on
SIReff,m() = Effective SIR computed for the mth BLER point, as a function of
SIRAWGN,m = SIR in AWGN channel which corresponds to mth BLER point
NB = Total number of BLER points
2
1,, )(
1)(
BN
mmAWGNmeff
Beff SIRSIR
N
Comments & RecommendationComments & Recommendation
EESM has been shown to be effective in predicting link-level performance in a EESM has been shown to be effective in predicting link-level performance in a system level simulationsystem level simulation
Through a smaller number of link-level simulation runs, the parameter Through a smaller number of link-level simulation runs, the parameter can can be estimated for each modulation and coding combination, using the least- be estimated for each modulation and coding combination, using the least- squares criteriasquares criteria
For each SIR sample from the system simulation based on any multipath For each SIR sample from the system simulation based on any multipath fading channel profile, the effective SIR in the AWGN channel can be fading channel profile, the effective SIR in the AWGN channel can be computed using EESM. The corresponding BLER performance can be found computed using EESM. The corresponding BLER performance can be found through table look-up from the pre-computed AWGN BLER performance for through table look-up from the pre-computed AWGN BLER performance for each modulation and coding combination. each modulation and coding combination.
Recommendation:Recommendation: Adopt EESM in IEEE 802.20 evaluation methodologyAdopt EESM in IEEE 802.20 evaluation methodology
ReferencesReferences
1.1. ““1xEV-DV Evaluation Methodology (V13), 3GPP2 / TSG-C.R10021xEV-DV Evaluation Methodology (V13), 3GPP2 / TSG-C.R1002
2.2. 3GPP2 TSG-C, “1xEV-DO Evaluation Methodology (V1.3), C30-DOAH-20030807-0043GPP2 TSG-C, “1xEV-DO Evaluation Methodology (V1.3), C30-DOAH-20030807-004
3.3. ““MTMR Baseband Transceivers Needs for Intra- & Inter-system transparent MTMR Baseband Transceivers Needs for Intra- & Inter-system transparent UMTS/WLAN Operation”, IST-2000-30116 FITNESS, D3.3.1/v1.0UMTS/WLAN Operation”, IST-2000-30116 FITNESS, D3.3.1/v1.0
4.4. S. Valle, A. Poloni, G. Villa, “802.11 TGn Proposal for PHY abstraction in MAC S. Valle, A. Poloni, G. Villa, “802.11 TGn Proposal for PHY abstraction in MAC simulators”, IEEE 802.11-04/0184, February 16, 2004.simulators”, IEEE 802.11-04/0184, February 16, 2004.
5.5. J. Ketchum, B. Bjerke, S. Nanda, R. Waldon, “PHY Abstraction for System Simulation”, J. Ketchum, B. Bjerke, S. Nanda, R. Waldon, “PHY Abstraction for System Simulation”, IEEE 802.11-04/0174r1, February 2004.IEEE 802.11-04/0174r1, February 2004.
6.6. S. Nanda, K. Rege, “Frame Error Rates for Convolutional Codes on Fading Channels S. Nanda, K. Rege, “Frame Error Rates for Convolutional Codes on Fading Channels and the Concept of Effective Eand the Concept of Effective Ebb/N/Noo”, IEEE Trans. Vehicular Technology, Vol. 47, No. 4, ”, IEEE Trans. Vehicular Technology, Vol. 47, No. 4,
Nov. 1998.Nov. 1998.
7.7. ““Considerations on the System-Performance evaluation of HSDPA using OFDM Considerations on the System-Performance evaluation of HSDPA using OFDM modulation”, Ericsson, 3GPP TSG_RAN WG1 #34, R1-030999, October, 2003.modulation”, Ericsson, 3GPP TSG_RAN WG1 #34, R1-030999, October, 2003.
8.8. ““System-Level evaluation of OFDM - further Considerations”, Ericsson, 3GPP TSG-System-Level evaluation of OFDM - further Considerations”, Ericsson, 3GPP TSG-RAN WG1 #35, R1-031303, November 17-21, 2003.RAN WG1 #35, R1-031303, November 17-21, 2003.
9.9. ““OFDM EESM simulation Results for System-Level Performance Evaluations, and Text OFDM EESM simulation Results for System-Level Performance Evaluations, and Text Proposal for Section A. 4.5 of TR 25.892”, Nortel Networks, R1-04-0089, January, 2004Proposal for Section A. 4.5 of TR 25.892”, Nortel Networks, R1-04-0089, January, 2004
10.10. ““Feasibility Study for OFDM for UTRAN enhancement, Release 6”, 3GPP TSG RAN, Feasibility Study for OFDM for UTRAN enhancement, Release 6”, 3GPP TSG RAN, TR 25.892 v1.1.0, March 2004.TR 25.892 v1.1.0, March 2004.
