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.Theinformation rate of a physical channel varies with the symbol rate derivedfrom the chip rate of 3.84 Mcps and the spreading factor (SF).SF varies from 256 to 4 in FDD on the UL and from 512 to 4 on the FDD DL, while inTDD it varies from 16 to 1.These give respective symbol rates from 15k to960k symbols/s on FDD UL and 7.5k to 960k for FDD DL, with 3.84Msymbols/s to 240 k/s in TDD in either direction.Spreading codes (as outlined in the previous chapter) are used to distin-guish between the following:• Different channels from the same source via channelization codes;• Different cells via scrambling codes;• Different UE via another set of scrambling codes.One of the main factors influencing QoS is the mapping of transport chan-nels to physical channels.3.4.2 Physical ChannelsLayer 1 maps the various transport channels to/from the MAC layer to spe-cific physical channels that are transmitted at level 1 on the UL and DL.The way in which these channels are mapped is shown in Figure 3.4 for FDD.Physical channels without any transport association are purely for layer 1functionality between the UE and Node B.WCDMA51Transport channelsPhysical channelsDCHDedicated physical data channel (DPDCH)Dedicated physical control channel (DPCCH)RACHPhysical random access channel (PRACH)CPCHPhysical common packet channel (PCPCH)Common pilot channel (CPICH)BCHPrimary common control physical channel (P-CCPCH)FACHSecondary common control physical channel (S-CCPCH)PCHSynchronization channel (SCH)DSCHPhysical downlink shared channel (PDSCH)Acquisition indicator channel (AICH)Access preamble acquisition indicator channel (AP-AICH)Paging indicator channel (PICH)CPCH status indicator channel (CSICH)Collision-detection/channel assignment indicatorchannel (CD/CA-ICH)Figure 3.4 Transport and physical channels.(Source: [12] © ETSI 2001.)The role of many physical channels is outside the scope of this book,and only a subset with above average significance for quality is describedbelow.Physical channels are characterized by means of a specific carrier frequency, scrambling code, channelization code (optional, but used on many),stop and start times in relation to chips, and for the UL only a relative phase.Radio frames correspond to a duration of 15 slots of 2,560 chips each or38,400 chips in all, hence a duration of 10 ms at 3.84 Mcps.3.4.2.1 Dedicated Physical ChannelsThe channels most directly relevant to the transmission of user data are thededicated physical channels, DPDCH and dedicated physical control channel(DPCCH).CS and most real-time traffic use dedicated channels, while inter-mittent data traffic can use common or shared channels.The UL DPDCHcarries the DCH transport channel from the MAC, while the control channel(DPCCH) is used purely for control information generated in layer 1.Ineither case each 10-ms radio frame is split into 15 slots of 2,560 chips corresponding to single power cycles, that for DPDCH containing data, while theDPCCH slots carry control information, as shown in Figure 3.5.The pilot field bits conform to one of a specified set of preset patternsand are used in frame synchronization.TFCI is used for variable rate chan-nels or for channels carrying multiple services, but not for single fixed rate52QoS in Integrated 3G NetworksDPDCHData2,560 chips, 10*2k (k = 0 − 6) data bitsDPCCHPilot bitsTFCI bitsFBITPC2,560 chips, 10 control bits10 msecFigure 3.5 UL DPCH slot.(Source: [12] © ETSI 2001.)channelsthe decision on TFCI usage is determined by the UTRAN, notthe UE.The feedback information (FBI) field is used in relation to diversity[13] and power control during soft handovers.Transmit power control (TPC)indicates whether to change transmitter power level (see Section 3.4.6).On the DL there is only one type of dedicated physical channel, theDPCH, and it carries multiplexed DPDCH and DPCCH traffic.A singleslot contains two data segments and two control segments, as in Figure 3.6.The two DPDCH segments have unequal sizes that are specified intables and are dependent on the spreading factor and control TFCI [12],while the parameter k is related to the spreading factor bySF = 512/2kThe DPCCH information consists of TFCI, where applicable, TPC as onUL, and another set of pilot bits with numbers as per the tables.It is possible DPDCHDPCCHDPDCHDPCCHData 1TCPTFIData 2PilotN1 bitsNTCP bits NTFI bitsN2 bitsNp bits2,560 chips, 10*2k bits (k = 0.7)Slot #0Slot #1Slot #iSlot #14T =f10 msFigure 3.6 DL DPCH slot structure.(Source: [12] © ETSI 2001.)WCDMA53to have more than one DPDCH if the required rate is too high for a singlechannel.If so, then the spreading factor is 4 for each such channel.Other physical channels have different structures for their slots [12].3.4.2.2 Common Physical ChannelsThe UL random access channel carries 4,096 chip preambles and a 10-msmessage radio frame slit into 15 slots, each of which has both data and con-trol parts [ Pobierz całość w formacie PDF ] |
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