Matlab Toolbox - 4G/LTE

Detecting Downlink Frame Offset

This page will show you the process of detecting the Frame Offset for one radio frame (10 ms) from the received time domain data.

i) Create a physical layer symbols for all the channels (RS, PSS, SSS, PDCCH, PDSCH) for one subframe

ii) Put all the channel data into a resource grid of one subframe (1 ms)

iii) Repeat the step i)~ii) 10 times to produce the grid of one radio frame (10 ms)

iv) Perform OFDM Modulation to convert the resrouce grid to 10 ms of time domain data.

v) Apply Fading to the time domain data (This is optional)

vi) Calculate Frame Offset from the data from step iv) (or step v))

< Detecting Frame Offset for Ideal Signal >

% First you have to define properites of a eNodeB.  

% NDLRB indicate System Bandwith in the unit of RBs.

% NDLRB 6 = 1.4 Mhz, NDLRB 15 = 3.0 Mhz, NDLRB 25 = 5.0 Mhz,

% NDLRB 50 = 10 Mhz, NDLRB 75 = 15 Mhz, NDLRB 100 = 20 Mhz

% CellRefP indicate number of downlink Antenna. CellRefP = 1 means 1 transmission antenna (SISO)

% NCellID indicate PCI (Physical Channel Identity) of the Cell

% NSubframe indicate the subframe number.

enb.CyclicPrefix = 'Normal';

enb.PHICHDuration = 'Normal';

enb.Ng = 'Sixth';

enb.NDLRB = 6;

enb.CellRefP = 1;

enb.DuplexMode = 'FDD';

enb.NFrame = 0;

enb.NCellID = 0;

 

txFrameGrid = [];

 

for subframeNo = 0:9

    

enb.NSubframe = subframeNo;

enb.CFI = 1;

 

PHICH_Group_Index = 0;

PHICH_Sequence_Index = 1;

HARQ_Indicator_Value = 0; % 0 = NACK, 1 = ACK

 

dci.NDLRB = enb.NDLRB;

dci.DCIFormat = 'Format1A';

dci.AllocationType = 0;

dci.Allocation.RIV = 18;

dci.ModCoding = 10;

dci.HARQNo = 0;

dci.NewData = 0;

dci.TPCPUCCH = 0;

dci.DuplexMode = 'FDD';

dci.NTxAnts = 1;

 

[dciMessage,dciMessageBits] = lteDCI(enb,dci);

 

C_RNTI = 100;                         

pdcchConfig.RNTI = C_RNTI;            

pdcchConfig.PDCCHFormat = 0;          

 

codedDciBits = lteDCIEncode(pdcchConfig, dciMessageBits);

pdcchDims = ltePDCCHInfo(enb);

pdcchBits = -1*ones(pdcchDims.MTot, 1);

candidates = ltePDCCHSpace(enb, pdcchConfig, {'bits', '1based'});

pdcchBits ( candidates(1, 1) : candidates(1, 2) ) = codedDciBits;

 

pdcch_sym = ltePDCCH(enb, pdcchBits);

pdcch_sym_ind = ltePDCCHIndices(enb,{'1based','re'});

pdcch_sym_arrayIndex = 0:length(pdcch_sym)-1;

 

 

% Generating PDSCH Symbols

 

pdsch.NTxAnts = 1;

pdsch.NLayers = 1;

pdsch.TxScheme = 'Port0';

pdsch.Modulation = {'16QAM'};

pdsch.RV = 0;

pdsch.RNTI = C_RNTI;

 

START_RB = 0;

N_RB = 4; %enb.NDLRB;

 

pdsch_prbs = (START_RB:(START_RB+N_RB-1)).';

[pdsch_sym_ind,pdschIndInfo] = ltePDSCHIndices(enb,pdsch,pdsch_prbs,{'1based','re'});

codedTrBlkSize = pdschIndInfo.G;

dlschTransportBlk = round(rand(1,codedTrBlkSize));

codeword = lteDLSCH(enb,pdsch,codedTrBlkSize,dlschTransportBlk);

 

pdsch_sym = ltePDSCH(enb,pdsch,codeword);

pdsch_sym_arrayIndex = 0:length(pdsch_sym)-1;

 

%fill in the resource grid

 

resourceGrid = lteDLResourceGrid(enb);

rsAnt0 = lteCellRS(enb,0);

indAnt0 = lteCellRSIndices(enb,0);

resourceGrid(indAnt0) = rsAnt0;

 

mib_bits = lteMIB(enb);

bch_cw = lteBCH(enb,mib_bits);

 

pss = ltePSS(enb);

pss_arrayIndex = 0:length(pss)-1;

pss_sym_ind = ltePSSIndices(enb,0,{'1based','re'});

 

sss = lteSSS(enb);

sss_arrayIndex = 0:length(sss)-1;

sss_sym_ind = lteSSSIndices(enb,0,{'1based','re'});

 

cfi_cw = lteCFI(enb);

pcfich_sym = ltePCFICH(enb,cfi_cw);

pcfich_sym_arrayIndex = 0:length(pcfich_sym)-1;

pcfich_sym_ind = ltePCFICHIndices(enb,{'1based','re'});

 

phich_sym = ltePHICH(enb,[PHICH_Group_Index,PHICH_Sequence_Index,HARQ_Indicator_Value]);

phich_sym_arrayIndex = 0:length(phich_sym)-1;

phich_sym_ind = ltePHICHIndices(enb,{'1based','re'});

 

pbch_sym = ltePBCH(enb,bch_cw);

pbch_sym_arrayIndex = 0:length(pbch_sym)-1;

pbch_sym_ind = ltePBCHIndices(enb,{'1based','re'});

 

pss_scale = 1.0;

sss_scale = 1.0;

phich_scale = 1.0;

pcfich_scale = 1.0;

pbch_scale = 1.0;

pdcch_scale = 1.0;

pdsch_scale = 1.0;

 

resourceGrid(pss_sym_ind) = pss_scale .* pss;

resourceGrid(sss_sym_ind) = sss_scale .* sss;

resourceGrid(pcfich_sym_ind) = pcfich_scale .* pcfich_sym;

resourceGrid(phich_sym_ind) = phich_scale .* phich_sym;

resourceGrid(pbch_sym_ind) = pbch_scale .* pbch_sym(1:length(pbch_sym_ind));

resourceGrid(pdcch_sym_ind) = pdcch_scale .* pdcch_sym;

resourceGrid(pdsch_sym_ind) = pdsch_scale .* pdsch_sym;

 

txFrameGrid = [txFrameGrid resourceGrid];

 

end;

 

[tx_waveform,tx_waveform_info] = lteOFDMModulate(enb,txFrameGrid);

 

[frame_offset,offset_corr]=lteDLFrameOffset(enb,tx_waveform);

 

Result =

0

< Detecting Frame Offset for Faded Signal >

% First you have to define properites of a eNodeB.  

% NDLRB indicate System Bandwith in the unit of RBs.

% NDLRB 6 = 1.4 Mhz, NDLRB 15 = 3.0 Mhz, NDLRB 25 = 5.0 Mhz,

% NDLRB 50 = 10 Mhz, NDLRB 75 = 15 Mhz, NDLRB 100 = 20 Mhz

% CellRefP indicate number of downlink Antenna. CellRefP = 1 means 1 transmission antenna (SISO)

% NCellID indicate PCI (Physical Channel Identity) of the Cell

% NSubframe indicate the subframe number.

enb.CyclicPrefix = 'Normal';

enb.PHICHDuration = 'Normal';

enb.Ng = 'Sixth';

enb.NDLRB = 6;

enb.CellRefP = 1;

enb.DuplexMode = 'FDD';

enb.NFrame = 0;

enb.NCellID = 0;

 

txFrameGrid = [];

 

for subframeNo = 0:9

    

enb.NSubframe = subframeNo;

enb.CFI = 1;

 

PHICH_Group_Index = 0;

PHICH_Sequence_Index = 1;

HARQ_Indicator_Value = 0; % 0 = NACK, 1 = ACK

 

dci.NDLRB = enb.NDLRB;

dci.DCIFormat = 'Format1A';

dci.AllocationType = 0;

dci.Allocation.RIV = 18;

dci.ModCoding = 10;

dci.HARQNo = 0;

dci.NewData = 0;

dci.TPCPUCCH = 0;

dci.DuplexMode = 'FDD';

dci.NTxAnts = 1;

 

[dciMessage,dciMessageBits] = lteDCI(enb,dci);

 

C_RNTI = 100;                         

pdcchConfig.RNTI = C_RNTI;            

pdcchConfig.PDCCHFormat = 0;          

 

codedDciBits = lteDCIEncode(pdcchConfig, dciMessageBits);

pdcchDims = ltePDCCHInfo(enb);

pdcchBits = -1*ones(pdcchDims.MTot, 1);

candidates = ltePDCCHSpace(enb, pdcchConfig, {'bits', '1based'});

pdcchBits ( candidates(1, 1) : candidates(1, 2) ) = codedDciBits;

 

pdcch_sym = ltePDCCH(enb, pdcchBits);

pdcch_sym_ind = ltePDCCHIndices(enb,{'1based','re'});

pdcch_sym_arrayIndex = 0:length(pdcch_sym)-1;

 

 

% Generating PDSCH Symbols

 

pdsch.NTxAnts = 1;

pdsch.NLayers = 1;

pdsch.TxScheme = 'Port0';

pdsch.Modulation = {'16QAM'};

pdsch.RV = 0;

pdsch.RNTI = C_RNTI;

 

START_RB = 0;

N_RB = 4; %enb.NDLRB;

 

pdsch_prbs = (START_RB:(START_RB+N_RB-1)).';

[pdsch_sym_ind,pdschIndInfo] = ltePDSCHIndices(enb,pdsch,pdsch_prbs,{'1based','re'});

codedTrBlkSize = pdschIndInfo.G;

dlschTransportBlk = round(rand(1,codedTrBlkSize));

codeword = lteDLSCH(enb,pdsch,codedTrBlkSize,dlschTransportBlk);

 

pdsch_sym = ltePDSCH(enb,pdsch,codeword);

pdsch_sym_arrayIndex = 0:length(pdsch_sym)-1;

 

%fill in the resource grid

 

resourceGrid = lteDLResourceGrid(enb);

rsAnt0 = lteCellRS(enb,0);

indAnt0 = lteCellRSIndices(enb,0);

resourceGrid(indAnt0) = rsAnt0;

 

mib_bits = lteMIB(enb);

bch_cw = lteBCH(enb,mib_bits);

 

pss = ltePSS(enb);

pss_arrayIndex = 0:length(pss)-1;

pss_sym_ind = ltePSSIndices(enb,0,{'1based','re'});

 

sss = lteSSS(enb);

sss_arrayIndex = 0:length(sss)-1;

sss_sym_ind = lteSSSIndices(enb,0,{'1based','re'});

 

cfi_cw = lteCFI(enb);

pcfich_sym = ltePCFICH(enb,cfi_cw);

pcfich_sym_arrayIndex = 0:length(pcfich_sym)-1;

pcfich_sym_ind = ltePCFICHIndices(enb,{'1based','re'});

 

phich_sym = ltePHICH(enb,[PHICH_Group_Index,PHICH_Sequence_Index,HARQ_Indicator_Value]);

phich_sym_arrayIndex = 0:length(phich_sym)-1;

phich_sym_ind = ltePHICHIndices(enb,{'1based','re'});

 

pbch_sym = ltePBCH(enb,bch_cw);

pbch_sym_arrayIndex = 0:length(pbch_sym)-1;

pbch_sym_ind = ltePBCHIndices(enb,{'1based','re'});

 

pss_scale = 1.0;

sss_scale = 1.0;

phich_scale = 1.0;

pcfich_scale = 1.0;

pbch_scale = 1.0;

pdcch_scale = 1.0;

pdsch_scale = 1.0;

 

resourceGrid(pss_sym_ind) = pss_scale .* pss;

resourceGrid(sss_sym_ind) = sss_scale .* sss;

resourceGrid(pcfich_sym_ind) = pcfich_scale .* pcfich_sym;

resourceGrid(phich_sym_ind) = phich_scale .* phich_sym;

resourceGrid(pbch_sym_ind) = pbch_scale .* pbch_sym(1:length(pbch_sym_ind));

resourceGrid(pdcch_sym_ind) = pdcch_scale .* pdcch_sym;

resourceGrid(pdsch_sym_ind) = pdsch_scale .* pdsch_sym;

 

txFrameGrid = [txFrameGrid resourceGrid];

 

end;

 

[tx_waveform,tx_waveform_info] = lteOFDMModulate(enb,txFrameGrid);

 

chcfg.Seed = 1;

chcfg.DelayProfile = 'EVA';

chcfg.NRxAnts = 1;

chcfg.InitPhase = 0;

chcfg.ModelType = 'GMEDS';

chcfg.NTerms = 16;

chcfg.NormalizeTxAnts = 'On';

chcfg.NormalizePathGains = 'On';

chcfg.DopplerFreq = 10;

chcfg.MIMOCorrelation = 'Low';

chcfg.SamplingRate = tx_waveform_info.SamplingRate;

chcfg.InitTime = 0;

 

rx_waveform = lteFadingChannel(chcfg,tx_waveform);

 

[frame_offset,offset_corr]=lteDLFrameOffset(enb,rx_waveform);

 

Result =

7

Disclaimer ! :

This page is only to show you the overall logics and visualization for various LTE physical layer channels. I haven't investigated much about verifying about the accuracy.

If you think the code is not so efficient, it is 100% my fault. I haven't made any effort for effiecient code. I just tried to create code as simple as possible for the readers. As you know, easy-to-read code is not always efficient for a specific chipset.

If you find any mistake in terms of accuracy, it is also very highly likely be my fault. Not the problem of Matlab tool box itself.

Any comment and corrections if you find any mistake will be welcome and appreciated.