PDSCH channel quality indication calculation
An empty resource grid for RMC R.13 is populated with cellspecific reference signals symbols. The signal is filtered through the channel, demodulated and the corresponding channel is estimated along with an estimate of noise power spectral density on the reference signal subcarriers. The estimates are used for CQI calculation.
Populate an empty resource grid for RMC R.13 with cellspecific reference signal symbols and modulate the waveform. Add noise to txWaveform
. Configure an EPA fading channel and filter the signal through this channel.
enb = lteRMCDL('R.13'); reGrid = lteResourceGrid(enb); reGrid(lteCellRSIndices(enb)) = lteCellRS(enb); [txWaveform,info] = lteOFDMModulate(enb,reGrid); noise = 0.5*complex(randn(size(txWaveform)),randn(size(txWaveform))); txWaveform_nz = txWaveform + noise; chcfg.SamplingRate = info.SamplingRate; chcfg.DelayProfile = 'EPA'; chcfg.NRxAnts = 4; chcfg.DopplerFreq = 5; chcfg.MIMOCorrelation = 'Low'; chcfg.InitTime = 0; chcfg.Seed = 1; rxWaveform = lteFadingChannel(chcfg,txWaveform_nz);
Demodulate the received signal. Perform downlink channel estimate and noise power spectral density estimation on the demodulated signal. Use estimates of channel and noise power spectral density for CQI calculation.
rxSubframe = lteOFDMDemodulate(enb,rxWaveform); cec.FreqWindow = 1; cec.TimeWindow = 15; cec.InterpType = 'cubic'; cec.PilotAverage = 'UserDefined'; cec.InterpWinSize = 1; cec.InterpWindow = 'Centered'; [hest, noiseEst] = lteDLChannelEstimate(enb,cec,rxSubframe); cqi = lteCQISelect(enb,enb.PDSCH,hest,noiseEst)
cqi = 5
enb
— eNodeB cellwide settingseNodeB cellwide settings, specified as a structure. The structure contains the following parameter fields.
Parameter Field  Required or Optional  Values  Description 

NDLRB  Required  Scalar integer from 6 to 110  Number of downlink resource blocks. ($${N}_{\text{RB}}^{\text{DL}}$$) 
NCellID  Required  Integer from 0 to 503  Physical layer cell identity 
CellRefP  Required  1, 2, 4  Number of cellspecific reference signal (CRS) antenna ports 
CyclicPrefix  Optional 
 Cyclic prefix length 
DuplexMode  Optional 
 Duplexing mode, specified as:

The following parameters
apply when  
TDDConfig  Optional  0, 1 (default), 2, 3, 4, 5, 6  Uplink–downlink configuration 
SSC  Optional  0 (default), 1, 2, 3, 4, 5, 6, 7, 8, 9  Special subframe configuration (SSC) 
The following
parameters apply when  
NSubframe  Required  0 (default), nonnegative scalar integer  Subframe number 
The following parameters apply when
 
CSIRefP  Required  1, 2, 4, 8  Array of number of CSIRS antenna ports 
CSIRSConfig  Required  Scalar integer  Array CSIRS configuration indices. See TS 36.211, Table 6.10.5.21. 
CSIRSperiod  Optional 
 CSIRS subframe configurations for one or more CSIRS resources. Multiple CSIRS resources can be configured from a single common subframe configuration or from a cell array of configurations for each resource. 
NFrame  Optional  0 (default), nonnegative scalar integer  Frame number 
chs
— Channelspecific transmission configurationChannelspecific transmission configuration, specified as a structure or structure array. The structure contains the following parameter fields:
Parameter Field  Required or Optional  Values  Description  

NLayers  Required  Integer from 1 to 8  Number of transmission layers.  
CSIMode  Required 
 CSI reporting mode  
TxScheme  Required  'Port0' , 'TxDiversity' , 'CDD' ,
'SpatialMux' ,
'MultiUser' ,
'Port5' ,
'Port78' , 'Port8' ,
'Port714' .  PDSCH transmission scheme, specified as one of the following options.
 
SINRs90pc  Optional  15 element vector, or function handle  A vector of 15 SINR values or a function handle to a function of the form f(enb, chs) which returns a vector of 15 SINR values, one for each CQI index 1, ..., 15. These correspond to the lowest SINR for which the throughput of the PDSCH in the CQI/CSI reference resource, for the given configuration and CQI index, is at least 90%. Default is to internally select SINRs based on configuration given in enb and chs, assuming perfect channel estimation and either MMSE equalization or transmit diversity decoding (as appropriate for the transmission scheme) at the receiver.  
The following parameter applies for
 
PMISet  Required  Integer vector with element values from 0 to 15.  A vector of Precoder Matrix Indications. The vector may contain
either a single value (corresponding to single PMI mode) or multiple values (corresponding to
multiple or subband PMI mode). For the  
The following parameter applies for
 
AltCodebook4Tx  Required 
 If set to  
Additionally, one of the following fields must be included. ^{see note 1}  
NCodewords  Required  1, 2  Number of codewords  
Modulation  Required  'QPSK' , '16QAM' , '64QAM' ,
'256QAM' ,
'1024QAM'  Modulation type, specified as a character vector, cell array of character vectors, or string array. If blocks, each cell is associated with a transport block.  
^{note 1} –
Specify the number of codewords directly in the 
hest
— Channel estimateChannel estimate, specified as a KbyLbyNRxAntsbyP array, where:
K is the number of subcarriers.
L is the number of OFDM symbols.
NRxAnts is the number of receive antennas.
P is the number of transmit antennas.
Data Types: double
Complex Number Support: Yes
noiseest
— Receiver noise varianceReceiver noise variance, specified as a numeric scalar. noiseest
is
an estimate of the received noise power spectral density.
Data Types: double
cqi
— Channel quality informationChannel quality information, returned as a column vector containing a channel quality information report. Report contents depend on the CSI reporting mode.
Report Mode  Reporting Contents 

Single codeword:  
'PUCCH 10'  A single wideband CQI index 
'PUSCH 30'  A single wideband CQI index, followed by a subband differential CQI offset level for each subband. 
Two codewords:  
'PUCCH 11'  A single wideband CQI index for codeword 0, followed by a spatial differential CQI offset level for codeword 1. 
'PUSCH 12'  A single wideband CQI index for codeword 0, followed by a single wideband CQI index for codeword 1. 
'PUSCH 31'  A single wideband CQI index for codeword 0, followed by a subband differential CQI offset level for each subband for codeword 0, followed by a single wideband CQI index for codeword 1, followed by a subband differential CQI offset level for each subband for codeword 1. 
Note
CSI reporting modes, are separated into the modes that support
one or two codewords, as described by the standard. The CQI select
function derives these code words from chs
.
NCodewords
or chs
.
Modulation
.
sinrs
— signaltointerference plus noise ratiosSignaltointerference plus noise ratios, in dB, returned as
a matrix. Each column of the matrix represents a single codeword.
If subband CQI reporting is configured, the SINR for the wideband
CQI is in the first row, followed by the sinrs
for
the subband CQIs in subsequent rows. sinrs
is
an optional output.
The function performs the CQI selection by
first obtaining SINR (Signal to Interference and Noise Ratio) estimates
for a given configuration from ltePMISelect
.
Then the function performs a lookup between those SINR estimates and
the CQI index. The lookup tables are precomputed and stored in this
function. CQI selection is conditioned on the rank indicated by chs
.
NLayers
,
except for the 'TxDiversity'
transmission scheme
which has a rank of 1. On PUCCH, CQI selection corresponds to Report
Type 2 (for reporting Mode11) or Report Type 4 (for reporting Mode
10). On PUSCH, the reporting is Mode 12, Mode 30, or Mode 31.
A CQI Index is a scalar (0,...,15), indicating the selected value of the CQI index. The CQI index is defined as per TS 36.213. The highest CQI index is selected when a single PDSCH transport block with a modulation scheme and transport block size of CQI index, and occupying a group of downlink physical resource blocks termed the CSI reference resource, can be received with a transport block error probability not exceeding 0.1. If a CQI index of 1 does not satisfy this condition, then the returned CQI index is 0. The CQI reference resource is defined in TS 36.213, Section 7.2.3. The relationship between CQI indices, modulation scheme, and code rate (from which transport block size is derived) is described in TS 36.213, Tables 7.2.31 and 7.2.32.
A subband differential CQI offset level is the difference between a subband CQI index and the corresponding wideband CQI index.
A spatial differential CQI offset level is the difference between the wideband CQI index for codeword 0 and the wideband CQI index for codeword 1.
Within the 3GPP standard, CQI offsets are reported as CQI values. These values are nonnegative integers corresponding to single CQI offset levels or ranges of CQI offset levels (see TS 36.213, Tables 7.22 and 7.2.12). The CQI offset levels reported here are either the single CQI offset level corresponding to the CQI value reported or the boundary value of the CQI offset level range corresponding to the CQI value reported. For example, a calculated spatial differential CQI offset level of –6 would be reported per the standard as a spatial differential CQI value of 4. This function will return a spatial differential offset level of –4 because the calculated differential CQI offset level exceeds this boundary value, meaning –6 < –4 (see TS 36.213, Table 7.22).
For transmission schemes using UEspecific beamforming ('Port 5'
,
'Port 78'
, 'Port 8'
,
'Port714'
), the performance depends on the beamforming used. For
UEspecific beamforming, the appropriate value of
chs
.
SINRs90pc
field is
provided. If this field is not provided, for single antenna ports, the function uses default
SINRs90pc
values.
[1] 3GPP TS 36.213. “Evolved Universal Terrestrial Radio Access (EUTRA); Physical layer procedures.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.
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