ltePSCCHDecode

PSCCH decoding

Syntax

softbits = ltePSCCHDecode(sym)

[softbits,symbols] = ltePSCCHDecode(sym)

Description

softbits = ltePSCCHDecode(sym) returns a vector of log-likelihood ratio (LLR) soft bits for the input modulated PSCCH symbols.

The PSCCH decoder performs SC-FDMA transform deprecoding, QPSK demodulation, and PSCCH-specific descrambling. These operations are the inverse of the ltePSCCH function processing, as defined in TS 36.211 [1], Section 9.4. For more information, see Physical Sidelink Control Channel Processing.

[softbits,symbols] = ltePSCCHDecode(sym) also returns the intermediate QPSK modulation symbols.

Examples

Decode PSCCH Symbols

Decode PSCCH symbols that contain a fully encoded SCI format 0 message with noise added. After PSCCH demodulation, decode and recover the SCI message structure.

Create UE settings and SCI message configuration structures. Generate a PSCCH transmission. Add noise to the symbols.

ue = struct('NSLRB',50,'CyclicPrefixSL','Normal');
sci0 = struct('FreqHopping',1,'ModCoding',3);

[sci0,scibits] = lteSCI(ue,sci0);
cw = lteSCIEncode(ue,scibits);
sym = ltePSCCH(cw);

rxsym = sym + 0.1*randn(size(sym));

Decode the PSCCH symbols and SCI message. View the SCI message structure settings. Confirm that the transmitted and recovered SCI messages match.

[rxsoftbits,sym] = ltePSCCHDecode(rxsym);
[rxinfo,rxerr] = lteSCIDecode(ue,rxsoftbits);

[recsci0,recscibits] = lteSCI(ue,rxinfo);
recsci0

recsci0 = struct with fields:
              SCIFormat: 'Format0'
            FreqHopping: 1
             Allocation: [1x1 struct]
    TimeResourcePattern: 0
              ModCoding: 3
            TimeAdvance: 0
                  NSAID: 0

isequal(scibits,recscibits)

ans = logical
   1

Plot Decoded PSCCH Symbols

Decode PSCCH symbols that contain a fully encoded SCI format 0 message with noise added. After PSCCH demodulation, plot the intermediate QPSK modulated symbols.

Create UE settings and SCI message configuration structures. Generate a PSCCH transmission. Add noise to the symbols.

ue = struct('NSLRB',50,'CyclicPrefixSL','Normal');
sci0 = struct('FreqHopping',1,'ModCoding',3);

[sci0,scibits] = lteSCI(ue,sci0);
cw = lteSCIEncode(ue,scibits);
sym = ltePSCCH(cw);

rxsym = sym + 0.1*randn(size(sym));

Decode the PSCCH symbols and plot the output intermediate QPSK modulated symbols.

[rxsoftbits,symbols] = ltePSCCHDecode(rxsym);
plot(symbols,'o')

Input Arguments

sym — Modulated PSCCH symbols

column vector

Modulated PSCCH symbols, specified as an N_RE-by-1 column vector. N_RE is the number of resource elements in a PSCCH subframe, including the SC-FDMA guard symbol. For D2D sidelink, nominally N_RE is 144 or 120 for normal and extended cyclic prefix respectively. For V2X sidelink, nominally N_RE is 240 bits, defined for normal cyclic prefix only. For more information, see Physical Sidelink Control Channel Processing.

Data Types: double
Complex Number Support: Yes

Output Arguments

softbits — Log-likelihood ratio soft bits

vector

Log-likelihood ratio (LLR) soft bits, returned as a (2 × N_RE)-by-1 vector. N_RE is the number of resource elements in a PSCCH subframe, including the SC-FDMA guard symbol. The LLR of the punctured soft bits associated with the last SC-FDMA symbol in the subframe are set to 0. For more information, see Physical Sidelink Control Channel Processing.

symbols — Modulated PSCCH symbols

column vector of complex numbers

Modulated PSCCH symbols, returned as an N_RE-by-1 column vector. N_RE is the number of resource elements in a PSCCH subframe, including the SC-FDMA guard symbol. For more information, see Physical Sidelink Control Channel Processing.

More About

Physical Sidelink Control Channel Processing

Physical sidelink control channel (PSCCH) processing includes PSCCH-specific scrambling, QPSK modulation, and SC-FDMA transform precoding. PSCCH processing follows the processing steps used for PUSCH, with variations defined in TS 36.211, Section 9.4.

For PSCCH, the input codeword length is M_bits = N_RE × N_bps, where N_RE is the number of PSCCH resource elements in a subframe and N_bps is the number of bits per symbol. Because the PSCCH is QPSK modulated, there are 2 bits per symbol. Nominally, the codeword length for PSCCH is 288 bits for D2D normal cyclic prefix, 240 bits for D2D extended cyclic prefix and 480 for V2X. Nominally, N_RE is 144 for D2D normal cyclic prefix or 120 for D2D extended cyclic prefix. For V2X, it is 240 defined for normal cyclic prefix only. Specifically, N_RE = N_PRB × N_REperPRB × N_SYM and includes symbols associated with the sidelink SC-FDMA guard symbol.

• N_PRB is the number of physical resource blocks (PRB) used for transmission. PSCCH is transmitted on a single PRB.

• N_REperPRB is the number of resource elements in a PRB. Each PRB has 12 resource elements.

• N_SYM is the number of SC-FDMA symbols in a PSCCH subframe, including symbols associated with the sidelink SC-FDMA guard symbol. The number of SC-FDMA symbols is a PSCCH subframe is 12 for D2D normal cyclic prefix or 10 for D2D extended cyclic prefix and V2X.

For D2D sidelink, when an SCI message is sent as a sidelink shared grant, it is transmitted twice on two separate PSCCH instances within the associated PSCCH resource pool. For V2X, only a single instance of PSCCH is transmitted for each scheduling grant.

References

[1] 3GPP TS 36.211. “Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels and Modulation.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.

Version History

Introduced in R2016b