Downlink Resource Allocation In Long Term Evolution (LTE)
IJCSI International Journal of Computer Science Issues, Vol. 9, Issue 3, No 2, May 2012ISSN (Online): 1694-0814www.IJCSI.org185Downlink Resource Allocation in Long Term Evolution (LTE)Normaliza Omar 1, Abid Yahya 2, RB Ahmad3 and ‘Aini Syuhada Md Zain41School of Computer & Communication Engineering, Universiti Malaysia PerlisKuala Perlis, 02000, Malaysia2School of Computer & Communication Engineering, Universiti Malaysia PerlisKuala Perlis, 02000, Malaysia3School of Computer & Communication Engineering, Universiti Malaysia PerlisKuala Perlis, 02000, Malaysia4School of Computer & Communication Engineering, Universiti Malaysia PerlisKuala Perlis, 02000, MalaysiaAbstractA scheduler is very imperative constituent in base station (BS)because it allocates the resource block (RB) to differentconsumers. The preeminent scheduler is a scheduler which canproduce optimize throughput, low latency system and canproduce best coverage gains. In order to improve a bestscheduling, the scheduler must be conscious of the channelquality and also the scheduler should have acquaintance of thechannel quality for each sub carrier and each user. This paper ismore discussing on a model for downlink scheduling in longterm evolution (LTE) system, which focus on both consumersituations and retransmissions with packet blending hybridautomatic repeat request (HARQ).Keywords: Downlink, HARQ, LTE, MCS, OFDMA, ResourceAllocation, Scheduling.1. IntroductionScheduling is one of important thing in wireless scheme.To produce high speed data services to mobile consumers,scheduling in wireless networks has hidden substantialcontemplation [1]. An important representative in wirelessconfigurations is that the channel quality fluctuates acrossthe consumer citizens due to variances in path loss, as wellas fading property. While scheduling choices are adopts,concern of every consumer’s channel quality can beoppressed. One limit in LTE downlink scheduling is thatall RBs fitting to a single consumer can be allocated toonly one modulation and coding scheme (MCS) in eachtransmission time interval (TTI) or scheduling period.One of important characteristic of mobile radiocommunication is the characteristically hasty andsubstantial differences in the immediate channelcircumstances. There are numerous causes for thesedifferences. Frequency selective fading will effect in hastyand random differences in the channel attenuation. Theaverage received signal strength will be affect by shadowfading and distance-dependent path loss.To attain as effective resource consumption as possible,channel-dependent scheduling in a mobile communicationsystem contracts with how to portion between differentterminals and the radio resource(s) existing in the system.Normally, this suggests reducing the quantity of resourcesdesirable per consumer and hence permitting for as manyconsumers as possible in the system, while still substantialwhatever quality-of-service requirements that may occur.Closely related to scheduling is link adaptation, whichcontracts with how to set the broadcast limits of a radiolink to handle differences of the radio-link quality.2. Related worksScheduling in wireless networks has encounteredextensive aid as a mean for allowing high speed dataservices to mobile users. An aim of any wirelessscheduling scheme balances the users’ QoS requirements.Jianwei et.al; proposed a model for downlink wirelessscheduling, which takes into account both consumerchannel situations and retransmissions with packetblending HARQ [2]. The goal of this project is to control ascheduling rule that reduces the average cost over time.Copyright (c) 2012 International Journal of Computer Science Issues. All Rights Reserved.
IJCSI International Journal of Computer Science Issues, Vol. 9, Issue 3, No 2, May 2012ISSN (Online): 1694-0814www.IJCSI.orgFor the draining difficult, their exertion has recognizedthat the optimum strategy by no means interrupts theretransmission of a packet.The technique of orthogonal frequency divisionmultiplexing (OFDM) is the main physical layer designelement for 3G-LTE downlink transmission schemecollective through either FDM or TDM as a multipleaccess method for the downlink shared data trafficchannels. Youngnam et.al; proposed multiplexingtechnique collective through transmit antenna multiplicityfor the downlink control channels in 3G-LTE [3]. Throughcomputer simulation, the receiver performance of severalcandidate schemes are analysed under multi-path fadingchannel environments.Adaptive modulation and coding (AMC) characteristicshave been validated as an efficient and authentictransmission technique to maximize the spectral efficiencywhile fulfilling the bit error rate (BER) requirements. Juanet.al; proposed performance evaluation of LTE downlinkphysical layer according to the latest 3GPP specification[4]. The main characteristics at the LTE physical layer(like spatial multiplexing or AMC) are identified andstudied.Hybrid ARQ is ultimately a compounding of ForwardError Correction (FEC) with ARQ, in an optimal way.Hybrid ARQ schemes are ordinarily used to provide areliable communication over noisy wireless channels. Kianet.al; proposed the evaluation of the performance ofrespective HARQ technique over the OFDMA downlinkof the presently offered 3GPP LTE specification [5]. Theschemes are associated in terms of Packet Error Rate (PER)and throughput in the setting their differing memorydesires for implementation. Simulation results display thatType II Incremental Redundancy proposals the greatestthroughput performance but at the cost of higher memoryrequirement.A well-defined radio planning model including thecoverage and capacity evaluations as well as frequencyallocations attract great attention as it allows amacroscopic and valuable estimation for the entirenetwork and can ease the decision making and networkpreparation for the operators. Liang proposed LTE systemcapacity and coverage had been investigated and themodel has been suggested on the base of 3GPP LTEprinciples Release 8 [6]. This project also had studiedabout the frequency planning of LTE. The results of thisproject cover the intervention partial calculation ofcoverage, frequency of radio and the calculation of trafficcapacity task. The application for the LTE Radio planningof this project was accomplished on the WRAP software186platform.HARQ schemes are basically used to provide a reliablecommunication over wireless multi-path fading channels.HARQ is able to compensate for errors and allows a betterthroughput performance. Zhongqui and Fei offered thedownlink of LTE must be OFDMA established and mightbe employed AMC at the physical layer with combinationof Hybrid ARQ at the data link layer [7]. ConstellationRearrangement (CR) method is applied in HARQ to raiseM-QAM performance. Enhancement of systemperformance is perform by a developed mappingtechnique is used in full Incremental Redundancy (IR). Animproved SNR approximation algorithm which condensescomputational period is applied to get Channel QualityIndicator (CQI) and consistent MCS is selected to exploitthroughput performance. Considerable spectral efficiencygain can be achieved from the joint design of AMC andHARQ.3. Scheduling3.1 Downlink SchedulingIn downlink, the process transmission of packet will befrom BS to UE. In fact of dissimilar of requirementsbetween the two directions and the tools at either end, theauthentic application of the technology will be dissimilaramong the downlink (from BS to UE) and the uplink (UEto the BS).Nevertheless, OFDM was preferred as the signal carrierformat since it is very irrepressible to interfering. Inpresent years a considerable level of experience has beenextended in its apply since the several methods ofpropagation that practise it along through WiMAX andWi-Fi. OFDM is likewise a modulation format that is veryappropriate for transmitting high data rates - one of themain requirements for LTE.Orthogonal Frequency Division Multiple Access(OFDMA) is a multi-consumer version of OFDM. In acertain time, each consumer in an OFDMA system iscommonly given convinced subcarriers to communicate.Synchronization of the uplink transmission is the one ofthe main difficulties with an OFDMA system. This isbecause each consumer has to transfer its frame so thatthey avoid to interfering the other consumers.OFDM is a broadcast method that is developed by manyindependent carriers that communicates instantaneously.The key idea behind OFDM is that a signal with aCopyright (c) 2012 International Journal of Computer Science Issues. All Rights Reserved.
IJCSI International Journal of Computer Science Issues, Vol. 9, Issue 3, No 2, May 2012ISSN (Online): 1694-0814www.IJCSI.orgstretched symbol period time is fewer sensitive tomultipath fading, than a signal with a small symbol time.Therefore, an improvement in performance can be attainedthrough conveyance some parallel symbols with astretched symbol time than conveyance them in a serieswith a smaller symbol time.For the LTE uplink, another scheme is used for theadmittance is known as Single Carrier Frequency DivisionMultiple Access (SC-FDMA) which is a hybrid format [8].This combines pliable subcarrier frequency allocation thatOFDM offer and the low peak to average ratio accessibleby single carrier systems through the multipath interferingflexibility.4. System Structure4.1 Scheduling Method1. Scheduling ensures the apportionment ofapportioned time frequency resource betweenconsumers at every time instant2. Scheduler is placed in the BS and conveyinguplink and downlink resources3. Scheduler controls which consumer the apportionresources (time and frequency) for every TTIwould be apportioned for treatment of DL-SCHinfection.4.2 Proposed System Model1.2.Classificationa. Elementary unit of time, 0.5 millisecond: slotb. Resources are allocated at sub frame coarseness,unit of time, 1 millisecond: sub framec. The BS, states to evolved Node B: eNBd. The mobile, states to user equipment: UEe. Physical resources in frequency and timeapplied to convey control information fromeNB to UE, physical downlink control channel:PDCCH:f.Physical resources in frequency and timeapplied to convey data from eNB to UE,physical downlink shared channel: PDSCH:g. Extent of the signal to noise ratio (SINR) at theUE when eNB conveys at a reference power,fed back repetitively from the UE to the eNB,channel quality indicator: CQI:LTE Downlink Scheduling187LTE is an OFDM system where apparitionalresources are shared in both frequency and time. ARB entails of 180 kHz of bandwidth for a timeperiod of 1 millisecond. Consequently, apparitionalresource allocation to diverse consumers on thedownlink can be reformed every 1 millisecond (subframe) at a coarseness of 180 kHz. LTE structures aHybrid-ARQ apparatus founded on incrementalredundancy. A transport block is encoded by a rate1/3 Turbo encoder and, reliant on the CQI feedback,allocated RBs, and modulation, the encodedtransport block is rate-matched applicably tocompetition the code rate reinforced by theindicated CQI. Retransmission in LTE is permits atan altered modulation pattern related to the firstconduction.Downlink scheduling choices can be prepared on thebeginning of the ensuing figures for each consumer.i. In the LTE construction downlink data movementsfrom a Packet Gateway to eNB and then to the UE.An IP link and the eNB to UE is across the wirelesslink is PDN GW to eNB. Once the logical linkfrom the carrier to the UE is group, a QoS ClassIdentifier (QCI) is specified: QoS Class Identifier(QCI).ii. CQI rumours are formed by the UE and fed back tothe eNB in quantised form sporadically, but with anassured delay. These reports comprise the rate ofthe signal-to-noise and -interference ratio (SINR)evaluated by the consumer. The LTE systempermits some reporting choices for both wideband(over the system bandwidth) and sub band(slimmer than the system bandwidth) CQI, with thesecond permitting manipulation of frequencyselective fading: CQI.iii. The buffer state concerns to the state of theconsumers’ buffers, demonstrating the datapresented for scheduling: Buffer State.iv. At time t, ACK/NACK for all broadcasts arrangedin sub frame (t 8) are acknowledged to thescheduler: Phy ACK/NACK.v. Scheduling choices can also be created onscheduling choices in the past. Let's say, if aconsumer was assigned various RBs over theprevious limited sub frames, then its urgency at thepresent sub frame may be abridged. A generallyapplied method is to sustain the average rate, xi(t)at which a consumer is obliged: ResourceAllocation History.Intended for every sub frame t, the scheduler first allocatesRBs and power to retransmissions for packets which werenot decrypted effectively at time (t 8); the modulationCopyright (c) 2012 International Journal of Computer Science Issues. All Rights Reserved.
IJCSI International Journal of Computer Science Issues, Vol. 9, Issue 3, No 2, May 2012ISSN (Online): 1694-0814www.IJCSI.organd coding scheme for a retransmission is reserved thematching as for the prior broadcast. The outstandingapparitional resources and power are scattered between theoutstanding consumers for broadcasts of novel packets.Precisely, every obligation involves of the following:i. character of the consumer for which the obligationis prepared,ii. quantity of RBs allocated,iii. broadcast power for every RB,iv. MCS for packet broadcast.4.3 Generic LTE Frame StructureOFDM has various benefits containing its hardiness tointerference and multipath fading. Although, it mightperform to be a principally complex method ofmodulation, it offers this one to digital signal processingmethods. In opinion of its benefits, the application ofODFM and the related admission technologies, OFDMAand SC-FDMA are best varieties for the different LTEmobile standard.The benefit with OFDM systems is the ability tocompletely remove ISI (Inter Symbol Interference)between OFDM symbols [9]. The ISI is usually removedby adding a cyclic prefix to the OFDM symbol beforetransmitting it. A disadvantage with an OFDM system isthat usually the subcarriers will not be orthogonal whenreceived at the receiver due to Doppler shift and differentfrequencies in the local oscillators at the transmitter thereceiver. Hence, this frequency offset has to be estimated.Since the ISI can be removed; each subcarrier willexperience only a flat fading channel. This statementwould also hold for a Frequency division multiplexing(FDM) system, but in FDM there are guard bands betweeneach bearer.Nevertheless, even though it’s various benefits, OFDMAhas some weaknesses such as high peak to average powerratio (PAPR) and high sensitivity to frequency offset.PAPR occurs justify to casual dynamic adding ofsubcarriers and effects in spectral spreading of the signalsignificant to attached channel interfering. It is a difficultthat can be swamped through high density amplifierlinearization and point power amplifiers techniques. UEbecomes costly while these approaches can be applied onthe BS. Therefore, LTE uses SC-FDMA with cyclic prefixon the uplink which decreases PAPR by way of there isonly a single carrier as disparate to N bearers.188Every frame is separated into ten as a sized sub frame of1ms in distance with the radio frame has a distance of10ms. Scheduling is complete on a sub frame foundationfor both the downlink and uplink. Each sub frame containsof two correspondingly slots sized which is 0.5ms inlength. Every slot in routine contains of an amount ofOFDM symbols which can be either seven for normalcyclic prefix or six for extended cyclic prefix [10]. Figure1 presentments the frame structure in FDD mode (FrameStructure Type 1).The useful symbol time is 66.7μs. The first symbol has CPlength is 5.2μs for the normal mode. The outstanding ofsix symbols have a CP of length 4.7μs. The purpose forvaried CP size of the first symbol is to attain the overallslot size in associations of period units dividable by15360. The CP is
2. LTE Downlink Scheduling LTE is an OFDM system where apparitional resources are shared in both frequency and time. A RB entails of 180 kHz of bandwidth for a time period of 1 millisecond. Consequently, apparitional resource allocation to diverse consumers on the downlink can be reformed every 1 millisecond (sub frame) at a coarseness of 180 kHz.
allocation matrices to allocate the resources to the users and to ensure contiguous resource allocation. The downlink algorithm is an extension of the proposed uplink algorithm avoiding uplink constraints. The downlink algorithm employs the two resource distribution matrices to provide an efficient resource allocation by expanding the .
In this paper, we propose a novel resource allocation algorithm for downlink OFDMA systems supporting both RT and NRT multimedia traffic. Unlike the conventional approaches, which decompose the resource allocation into two steps: packet scheduling and subcarrier-and-power allocation [4,11], the proposed algorithm tightly
next-generation cellular systems such as the 3GPP Long-Term Evolution (LTE) [1] and IEEE 802.16m [2] due to its effectiveness and flexibility in radio resource allocation, . CHANG et al.: MULTICELL OFDMA DOWNLINK RESOURCE ALLOCATION USING A GRAPHIC FRAMEWORK 3495 Fig. 1. Hexagonal multicell OFDMA cellular network and the associated resource .
R&S FSV-K100 EUTRA / LTE FDD Downlink Measurement Application (1308.9006.02) R&S FSV-K102 EUTRA / LTE MIMO Downlink Measurement Application (1309.9000.02) R&S FSV-K104 EUTRA / LTE TDD Downlink Measurement Application (1309.9422.02) This manual describes the following R&S FSVA/FSV models with firmware version 3.30 and higher:
Overload-State Downlink Resource Allocation [72-74] Assign resources based on the queue state information Greedy Resource Block (RB) Allocation [13] Assign resources based on the queue and channel state information 3. Problem Formulation Figure2shows the downlink time-slotted architecture inspired by [13]. It consists of mainly
Queue-Aware Resource Allocation for Downlink OFDMA Cognitive Radio Networks Patrick Mitran, Member, IEEE, Long Bao Le, Member, IEEE, Catherine Rosenberg, Senior Member, IEEE Abstract—In this paper we consider resource allocation for an OFDMA-based cognitive radio point-to-multipoint network with fixed users.
resource-allocation optimization for the downlink multiuser OFDM DAS with proportional fairness. In Section III, a suboptimal energy-efficient resource-allocation scheme is developed. Numerical results are presented to demonstrate the effectiveness of the proposed energy-efficient resource-allocation scheme in Section IV.
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