12-05-2011, 02:35 PM
Abstract
In order to evaluate the performance of new mobilenetwork technologies, system level simulations are crucial. Theyaim at determining whether, and at which level predicted linklevel gains impact network performance. In this paper we presenta MATLAB computationally efficient LTE system level simulator.The simulator is offered for free under an academic, noncommercialuse license, a first to the authors’ knowledge. Thesimulator is capable of evaluating the performance of the DownlinkShared Channel of LTE SISO and MIMO networks usingOpen Loop Spatial Multiplexing and Transmission Diversitytransmit modes. The physical layer model is based on the postequalizationSINR and provides the simulation pre-calculated”fading parameters” representing each of the individual interferenceterms. This structure allows the fading parameters to bepregenerated offline, vastly reducing computational complexityat run-time
.I. INTRODUCTION
The Long Term Evolution (LTE) standard, specified bythe 3rd Generation Partnership Project (3GPP) in Release 8,defines the next evolutionary step in 3G technology. LTE offerssignificant improvements over previous technologies such asUniversal Mobile Telecommunications System (UMTS) andHigh-Speed Packet Access (HSPA) by introducing a novelphysical layer and reforming the core network. The mainreasons for these changes in the Radio Access Network(RAN) system design are the need to provide higher spectralefficiency, lower delay, and more multi-user flexibility than thecurrently deployed networks [2].In the development and standardization of LTE, as wellas the implementation process of equipment manufacturers,simulations are necessary to test and optimize algorithms andprocedures. This has to be performed on both, the physicallayer (link-level) and in the network (system-level) context.While link-level simulations allow for the investigationof issues such as Multiple-Input Multiple-Output (MIMO)gains, Adaptive Modulation and Coding (AMC) feedback,modeling of channel encoding and decoding [3] or physicallayer modeling for system-level [4], system-level simulationsfocus more on network-related issues such as scheduling [5],mobility handling or interference management [6].Along with the standardization process, commercially availableLTE simulators have been developed. Equipment vendors,to this effect, have also implemented their own, proprietarysolutions. Some universities and research centers have alsodeveloped such simulators, but to the authors’ knowledge nonewith publicly available source code.The LTE system-level simulator [1] supplements an alreadyfreely-available LTE link-level simulator [7]. This combinationallows for detailed simulation of both the physical layerprocedures to analyze link-level related issues and system-levelsimulations where the physical layer is abstracted from linklevel results and network performance is investigated.The license under which the simulators are published allowsfor academic research and a closer cooperation betweendifferent universities and research facilities. In addition, developedalgorithms can be shared under the same license again,facilitating the comparison and cross validation of algorithmsand results and making them more credible.The LTE system-level simulator implementation offers ahigh degree of flexibility. For the implementation, extensiveuse of the Object-oriented programming (OOP) capabilities ofMATLAB, introduced with the 2008a Release have been made.Having a modular code with a clear structure based inobjects results in a much more organized, understandable andmaintainable simulator structure in which new functionalitiesand algorithms can be easily added and tested.This paper is organized as follows: in Section II we describethe overall structure of the LTE system-level simulator. InSection III we show how the physical layer has been abstractedin the page link measurement model. Afterwards, we present thelink performance model in Section IV, and Section V presentsthe main uses of the simulator as well as some conclusions.
II. SIMULATOR OVERVIEW
While link-level simulations are suitable for developingreceiver structures [8], coding schemes or feedback strategies[9], it is not possible to reflect the effects of issuessuch as cell planning, scheduling, or interference using thistype of simulations. Simulating the totality of the radio linksbetween the User Equipments (UEs) and eNodeBs is animpractical way of performing system level simulations dueto the vast amount of computational power that would berequired [10]. Thus, in system-level simulations the physicallayer is abstracted by simplified models that capture its essentialcharacteristics with high accuracy and simultaneously lowcomplexity.Figure 1 depicts a schematic block diagram of the LTEsystem-level simulator. Similarly to other system-level simulators,the core part consists of: (i) a page link measurementmodel [11] and (ii) a page link performance model
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