System Level Modeling and Optimization of the LTE Downlink

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4. Extensions to the L2S Modeleach of the TB rv idx are extracted.Given D original data bits, the rate matching process outputs a TB of size G bits,where G > D. After the rate 1/3 turbo code, the bits are placed on a circular buffer,with the systematic bits being placed consecutively and the parity bits interleavedone-to-one, as depicted in Figure 4.1.... ......: starting pointsystematic bits (v (0) )...1st parity bits (v (1) )2nd parity bits (v (2) )Figure 4.1: Positioning of the turbo-encoded bits (both systematic and parity) in the ratematching circular buffer. The output bits are obtained by setting a startingpoint k 0 and extracting G bits. The systematic bits are placed consecutively inthe buffer, while the parity bits are interleaved.In order to generate different TB versions for different values of rv idx , a differentstarting point k 0 , based on the value of rv idx , is calculated for each retransmission.Two modes of HARQ exist, which are depicted in Figure 4.2: in Chase Combining(CC) [108] (named after David Chase, its inventor), each retransmission is identicalto the original transmission, while in Incremental Redundancy (IR) each retransmissionconsists of new redundancy bits from the channel encoder. With theaforementioned circular buffer setup, and assuming k 0 advances exactly D/3 positionsfor each retransmission, full IR is only possible if G < rv max+1 · D.In both cases, the received retransmissions are combined and the resulting packet isjointly decoded. LTE HARQ applies a hybrid CC/IR approach, in which a mixtureof repeated and new bits are sent during the retransmissions, corresponding to theright figure in Figure 4.2.original code blockequalretransmissionscombined bits punctured bitsreconstructed code block (chase combining)original code blockdifferentversionscombined bitsreconstructed code block (LTE incremental redundancy)Figure 4.2: Chase combining (left) and the partial incremental redundancy (combining CCbits and IR bits) employed in LTE HARQ (right).52
4. Extensions to the L2S Model4.1.2. HARQ ModelingIn this section, the concepts presented in Section 3.1.2 for the calculation of theeffective post-equalization SINR (γ eff ) are extended to the modeling of the combininggain due to the use of HARQ in constant channels. The model is based on a MIbasedinterpretation of HARQ combining and adapts the MIESM SINR averagingprocedure to take into account the total MI of the combined TB [109].As detailed in Section 4.1, the combined HARQ TB combines both repeated andnewly-transmitted bits. This combining of new and repeated information can beexpressed in terms of Accumulated Mutual Information (ACMI) [110, 111], whichwe denote as I ∗ .In the CC case, as the same bits are retransmitted M times, it can be interpretedas an increase in the receive SNR. With every retransmission, energy is added, butno new information is sent. Thus, the CC ACMI of a set of M retransmissions sentover SNR γ, can be expressed as( M)∑I∗CC (γ) = I n γ , (4.1)m=0where m denotes the m-th retransmission (m = {0, 1, . . . , M}, with m = 0 correspondingto the initial transmission) and I n denotes the BICM capacity for theemployed MCS which n bits per symbol [72], shown in Equation (3.22).For IR, if only new parity bits are sent in subsequent retransmissions, the result isan increase in the amount of information, thus increasing the ACMI such thatI IR∗ (γ) =M∑I n (γ) . (4.2)m=0For the combined CC-IR HARQ scheme employed in LTE, we define G HARQ =(M + 1) G as the total number of received bits after M retransmissions and separateinto G CC and G IR , which represent the set of repeated and non-repeated bits,respectively, where G HARQ = G CC + G IR . In this case, I ∗ results in a combinationof Equations (4.1) and (4.2), which we denote as I∗LTE (γ):I∗LTE (γ) = G ((IRn · I n 1 + G ) )CC· γ , (4.3)G HARQas G IR unique bits are sent, repeated on average(1 + G )CCtimes.G HARQ53
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DissertationSystem Level Modeling a
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I hereby certify that the work repo
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KurzfassungDie vorliegende Arbeit p
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ContentsContents1 Motivation and Sc
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Contentsix
Page 17 and 18: 1. Motivation and Scope of Work1. M
Page 19 and 20: 1. Motivation and Scope of Worklaye
Page 21 and 22: 1. Motivation and Scope of Workperf
Page 23 and 24: BibliographyThe combined throughput
Page 25 and 26: 2. 3GPP Long Term Evolution2. 3GPP
Page 27 and 28: 2. 3GPP Long Term Evolutionup to 30
Page 29 and 30: 2. 3GPP Long Term EvolutionNAS proc
Page 31 and 32: 2. 3GPP Long Term Evolutionchannel
Page 33 and 34: 2. 3GPP Long Term EvolutionSince th
Page 35 and 36: 2. 3GPP Long Term EvolutionThe chan
Page 37 and 38: 2. 3GPP Long Term EvolutionTable 2.
Page 39 and 40: 3. Physical Layer Modeling and LTE
Page 67: 4. Extensions to the L2S Model4. Ex
Page 71 and 72: 4. Extensions to the L2S ModelTo ac
Page 73 and 74: 4. Extensions to the L2S ModelBLER1
Page 75 and 76: 4. Extensions to the L2S ModelThe M
Page 77 and 78: 4. Extensions to the L2S Modelthe a
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Page 81 and 82: 5. Performance Evaluation of Fracti
Page 97 and 98: 6. Summary and Outlook6. Summary an
Page 99 and 100: 6. Summary and Outlook6.2. OutlookW
Page 101 and 102: A. SNR-independence of the CLSM Pre
Page 107 and 108: B. Correlation Matrices for Shadow
Page 109 and 110: C. Taylor Expansion of the ZF MSEC.
Page 111 and 112: C. Taylor Expansion of the ZF MSEAp
Page 113 and 114: D. Evaluation of Multi-User GainD.
Page 115 and 116: D. Evaluation of Multi-User GainAvg
Page 117 and 118: Abbreviations and AcronymsAbbreviat
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Abbreviations and AcronymsKPILLRL2S
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Abbreviations and AcronymsU-PlaneUT
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Abbreviations and AcronymsBibliogra
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Abbreviations and Acronymsdescripti
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Abbreviations and Acronyms[69] Tech
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Abbreviations and Acronymsfemto cel
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Abbreviations and Acronyms[134] Z.
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System Level Modeling and Optimization of the LTE Downlink

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