System Level Modeling and Optimization of the LTE Downlink

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2. 3GPP Long Term EvolutionTable 2.1.: 3GPP requirements for E-UTRAN [15].Requirementspeak data rate 100 Mbit/sDL UE throughput 5% point of cdf 3x-4x Rel’6 HSDPAavg. throughput 3x-4x Rel’6 HSDPAspectral efficiency3x-4x Rel’6 HSDPApeak data rate 50 Mbit/sUL UE throughput 5% point of cdf 2x-3x Rel’6 HSDPAavg. throughput 2x-3x Rel’6 HSDPAspectral efficiencyspectrum allocation2x-3x Rel’6 HSDPAConfigurations2 TX×2 RXantennas,20 MHz DL1 TX×2 RXantennas,20 MHz UL1.4, 3, 5, 10, 15, 20 MHz possible(OPEX) and support for high user mobility.Table 2.1 lists the 3GPP requirements for the LTE Radio Access Network (RAN),termed Evolved UMTS Terrestrial Radio Access Network (E-UTRAN). The finalcapabilities of LTE, however go beyond those of the defined target requirements. Forinstance, although, the targets for DL and UL peak data rate were set to 100 Mbit/sand 50 Mbit/s respectively [18], LTE users, termed User Equipments (UEs), supportup to 300 Mbit/s DL and 75 Mbit/s UL peak data rates.Diverging from the previous UMTS standard, which is based on Wideband CodeDivision Multiple Access (W-CDMA), the LTE PHY is based on OrthogonalFrequency-Division Multiple Access (OFDMA) [19] in the DL, and Single-carrierFDMA (SC-FDMA) [20] in the UL [21–24], which both convert the wide-band frequencyselective channel into a set of flat fading subchannels by means of a CyclicPrefix (CP) [25]. The flat fading subchannels have the advantage that even in thecase of MIMO transmission, optimum receivers can be implemented with reasonablecomplexity, as opposed to W-CDMA systems, where time-domain equalization isneeded [26]. OFDMA additionally allows for frequency domain scheduling, makingit possible to assign PHY resources to users with optimum channel conditions. Thisoffers large potential throughput gains in the DL due to multi-user diversity [27, 28].LTE also includes an interface for communication between base stations (eNodeBsin LTE nomenclature), named X2-interface, which can be used for interference managementand eNodeB coordination, aiming at decreasing inter-cell interference.Regardless of the network capabilities, the system is nevertheless constrained by theactual capabilities of the receiver mobile equipment. That is, the UE capabilities.LTE defines five UE radio capability categories, to which a given UE has to conformto [29]. These range from a UE not capable of MIMO transmission with a maximumthroughput of 10 Mbit/s DL and 5 Mbit/s UL to a 4×4-capable MIMO terminal with10
2. 3GPP Long Term Evolutionup to 300 Mbit/s DL and 70 Mbit/s UL. Table 2.2 details the maximum throughputfor both DL and UL, as well as their MIMO Spatial Multiplexing (SM) capabilities.Table 2.2.: LTE UE categories [29]. Each UE category constrains the maximum throughputand SM capabilities supported in DL and UL.UE CategoryDLUL1 2 3 4 5peak throughput [Mbit/s] 10.3 51 102 150.8 302.8max. number of supported layers for SM 1 2 2 2 4max. number of supported streams for SM 1 2 2 2 2peak throughput [Mbit/s] 5.2 25.5 51 51 75.4support for 64-QAM No No No No Yes2.1. Network ArchitectureThe basic network architecture of LTE remains comprised of three parts: (i) themobile terminal, termed UE, which is connected, the (ii) E-UTRAN radio accessnetwork, and (iii) the core network, termed System Architecture Evolution (SAE),the main component of which is the Evolved Packet Core (EPC). Figure 2.1 depictsboth the elements comprising each of the parts from the network and its interconnectionto 2G/3G network elements.In the now-all-IP SAE architecture the core network provides access to externalpacket networks based on IP and performs a number of functions for idle and activeterminals. Connected to the core network, the RAN performs all radio interfacerelatedfunctions for terminals in active mode [30].In contrast to prior architectures, the LTE RAN is a meshed network where the functionspreviously fulfilled by the Radio Network Controller (RNC) in UMTS and/orthe Base Station Controller (BSC) in GSM are integrated into the eNodeB. In orderto enable a meshed RAN topology, the eNodeBs are now not only hierarchically connectedto the core network but are also able to communicate with each other, whichmakes it potentially possible to employ eNodeB cooperation schemes to increase networkperformance. eNodeBs implements the following RAN functionalities, whichare shown in Figure 2.2:ˆ All PHY and MAC layer procedures, including link adaptation, Hybrid AutomaticRepeat reQuest (HARQ), and cell search.ˆ Radio Link Control (RLC): Segmentation and Automatic Repeat reQuest (ARQ)control of the radio bearers.11
Page 1: DissertationSystem Level Modeling a
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6. Summary and Outlook6. Summary an
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6. Summary and Outlook6.2. OutlookW
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A. SNR-independence of the CLSM Pre
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B. Correlation Matrices for Shadow
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C. Taylor Expansion of the ZF MSEC.
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C. Taylor Expansion of the ZF MSEAp
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D. Evaluation of Multi-User GainD.
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D. Evaluation of Multi-User GainAvg
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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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System Level Modeling and Optimization of the LTE Downlink

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