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LTE Harq simulation based on Link Abstraction Author : Tomasi Giovanni Advisors : Marco Miozzo (CTTC), Marco Mezzavilla (DEI). LTE Mac Layer. Link Abstraction. Compression. Effective SINR. Tuning. Metrics Performances. MIESM mutual information effectiveSINR.
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LTE Harqsimulationbased on Link AbstractionAuthor: Tomasi GiovanniAdvisors: Marco Miozzo (CTTC), Marco Mezzavilla (DEI)
MIESMmutual information effectiveSINR The computation of the mutual information per coded bit can be derived from the received symbol-level mutual information; this approach is termed received bit mutual information rate (RBIR). An alternative is a method that directly arrives at the bit-level mutual information; this method called mean mutual information per bit (MMIB).
MMIB Forothersmodulations
MI-Blermapping approximation BCR blockdimension and code rate
MultipathChannel (alreadyimplemented in ns3) • Based on randomselectionof a 250 ms window on 3 s Jakessequences dB [ms] dB [ms] dB [ms] dB [ms]
Shadowing • Modelwith a log-normalrandomvariable
Simulation: error vs multipath dB [ms]
LTE Simulator • Simulationsparameter
Allocation • Symb per Frame = nSubCarr*nSubCh*nSymbOfdm = 42000 • Data Symb per Frame = (Symb per Frame) – ( ContolSymb) = 28248 • Mean Data Symb per SubFrame≈ 2825 • Packets per SubFrame = 5 • Mean Data Symb per Packet≈ 565
Harq in LTE Only 4 processes are used in a idealack/nakchannel
HarqCombining • CC • Sistematicsymbols: 565 • New symbols per rtx: 0 • Retransimittedsymbols: 565 • IR v1 • Sistematicsymbols: 565 • New symbols per rtx: 377 • Retransimittedsymbols: 280 • IR v2 • Sistematicsymbols: 565 • New symbols per rtx: 377 • Retransimittedsymbols: 0
HarqCombining • CC - case combining • IR - incrementalredundancy
Throughput • throughput = (n_pak_to_tx - n_drop_pak) * simb_per_pak * modulation_order * code_rate / simulation_time Capacity (Shannon formula) • Capacity = F * B * log2 (1 + SNR) • System bandwidth • B = NsubCh * NsubCarr * NofdmSymb / TsubFrame • Correctionfactor • F = (Tframe – TcyclicPref)/Tframe * (NsubCarr*NofdmSymb/2-4) • NsubCarr*NofdmSymb/2 CP loss ReferenceSymbol loss
Conclusions • Understand and implement the link abstraction • Create Harq system and the part of the Schedulerthatmanages the harqprocesses • Performance in octave • Import the system in ns3