UMTS/HSPA

ECE 5221 Personal Communication Systems Prepared by:Dr. Ivica KostanicLecture 24 Basics of 3G UMTS (3)

Spring 20111OSI Communication modelEach layer communicates only with two adjacent layers and its peer on the other sideEach layer receives services from the layer below and provides services to the layer above

Page 2Intermediate communication nodes require layers 1 through 3Internal operation within each layer is independent of the internal operation in any other layer

WCDMA interfaces described using OSI modelOSI = Open System InterconnectDeveloped by ISO as a general model for computer communicationUsed as a framework for development and presentation of most contemporary communication standardsNote: WCDMA covers Layers 1-3 of OSI Model2Page 3UMTS Protocol stackUMTS offers new Access stratum protocol stackNon-Access Stratum is largely inherited from GSMFirst three layers of the protocol stack are part of UTRAN

Note: SMS exists on both circuit switched and packet switched side3UMTS CS protocols control planeControl plane carries signalingRNC terminates the Access Stratum (AS)RRC, RLC and MAC terminate at RNCPHY terminates at Node B except for outer loop power controlRAN (access stratum) acts as transport for NAS4Note: UTRAN protocols are layered in an architecture that follows OSI model

UMTS CS protocols user planeUser plane caries user dataApplication end to end protocolAccess stratum the same for both control plane and user plane5

UMTS PS protocols control planeControl plane for packet dataVery similar to control plane for PSIdentical access stratum6

UMTS PS protocols user planeAdditional protocol PDCPPDCP compression of IP headersPDCP may or may not be used

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Layout of the Access Stratum Two planesUser plane - user dataControl plane signalingUser data enters access through radio bearers (RABs)Signaling is handled by RRCUpper layer signaling encapsulated through RRC messages (direct transfer)RRC has a capability of reconfiguring all lower layers

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Elements of PHY Layer processingPart 69UMTS-FDD PHY frame structureUMTS-FDD PHY frame structure is based on 10ms framesFrames are broken in 15 time slotsThe number of bits/slot is variableChip rate is always the same (3.84 Mchips/sec)

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10UMTS-FDD DL processingThere are 6 steps in DL PHY processingI/Q separationVariable spreadingScramblingGain adjustmentSync additionModulation Page 11

Note: Number of channels depends on number of active users. P-SCH and S-SCH are always transmitted 11W-CDMA DL Modulation UMTS-FDD uses simple QPSK modulation schemeComplex code sequence is split into real and imaginary part and modulated using carriers in quadrature Page 12

12W-CDMA Modulation UMTS-FDD uses root-raised cosine for the shaping filterThe roll-off is a = 0.22Page 13

Impulse response of the shaping filterFrequency response of the shaping filterAnalytical expression of the shaping filter impulse response Note: only 30dBc on the sidebands may cause interference to GSM in non 1-1 overlay scenarios13W-CDMA DL variable spreading Different data channels have different ratesThe chip rate is always the sameW-CDMA supports variable spreading on the DLVariable spreading is accomplished through use of orthogonal codes of different length Page 14

UMTS-FDD available DL data ratesUMTS-FDD provides high data rates through variable spreading code aggregation User data rates assume 1/2 convolutional encoding14W-CDMA scrambling codesOVSF codes provide orthogonality between signals coming from the same BTS form of channelizationScrambling codes allow mobile to distinguish signals coming from different base stationsScrambling codes do not change signal bandwidthDecoding a signal from a user is in 2 stepsDescrambling the signal from the Node BDe-spreading the signal from individual userPage 15

15W-CDMA scrambling codesUMTS-FDD uses 8192 complex scrambling codesThe codes are selected as parts of a 218 -1 long gold sequence (good correlation prperties)Each of the codes are associated with left and right alternative scrambling code

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Scrambling codes are 38400 chips long (10ms)Scrambling code repeats every frameOrganized in 512 groups of 16 codesThe first code in each group is declared as the primary scrambling code (PrSC)PrSC are used for cell identification

Scrambling code tree16W-CDMA synchronization codesSynchronization codes are used for system detection They are 256 chips long complex codesOne primary and 64 secondary codesSecondary codes consist of 15 code words Secondary codes remain unique under cyclic shifts smaller than 15Page 17A cell is allocated one primary synchronization code The primary code is the same for all cells in the system Secondary code points to a group of primary scrambling codes

Note: PSC allows mobile to synchronize to the time slots. SSC allows mobile to synchronize with the beginning of frame.17W-CDMA primary scrambling codesThere are 512 primary scrambling codesThey are divided in 64 groups of 8 codesEach cell is assigned one primary code Primary scrambling code is used to provide orthogonality between different BSPrimary scrambling code is broadcast on the Common Pilot Channel (CPICH)Page 18

Note: after decoding SSC, the mobile needs to consider only 8 out of 512 PrSC 18W-CDMA code assignment examplePrimary sync code is the same for all cellsSecondary sync code number is the same as the group of the primary pSCPage 19

Task: use previous two slides to verify code assignments for the above cellsNote: in practice network operator assigns only PrSC. SSC is assigned automatically on the basis of PrSC assignment 19W-CDMA UL processing - dedicated channelsThere are 5 steps in the UL DCHs processingSpreadingGain adjustmentComplex additionScrambling Modulation Page 20

DPDCH - Dedicated Physical Data ChannelDPCCH - Dedicated Physical Control ChannelNote: transmission from a single mobile can aggregate multiple codes to achieve higher data rate 20W-CDMA UL variable spreading Variable data rates are allowed on U DPDCHVariable data rate achieved throughvariable spreading 4 to 256code aggregation - up to 6 parallel codesif code aggregation is used, spreading for all DPDCH is 4UL DPCCH is a constant rate channel ~ 15kb/sec (assigned code C256,0)Page 21

User data rates assume 1/2 convolutional encoding21

Spreading FactorUser data rate

After coding

[Kb/sec]Approximate rate before coding

[Kb/sec]

512151-3

256306-12

1286042-52

64120~ 45

32240~ 105

16480~ 215

8960~ 450

41920~ 930

4, with 3 parallel codes5760~ 2300

Spreading FactorUser data rate

[Kb/sec]Approximate rate before coding

[Kb/sec]

256151-3

128306-12

646042-52

32120~ 45

16240~ 105

8480~ 215

4960~ 450

4, with 6 parallel codes5740~ 2300