Modulation mapperV15.8.0

The modulation mapper takes binary digits, 0 or 1, as input and produces complex-valued modulation symbols as output. Table below describes the modulation schemes used in NR.

Note: Qm is the modulation order, which quantifies the capacity of a single modulation symbol. Qm equals the number of source bits per modulated symbol.

Note: b denotes the input binary digits, and d denotes the complex-valued modulation symbols.

Note:

• PUSCH and PDSCH are responsible for transferring data. These channels require the greatest range of modulation schemes. High modulation orders are required to tranfer high throughputs in good coverage, whjile low modulation orders are required to maximize coverage. These two channels both support QPSK, 16QAM, 64QAM and 256QAM.
• PUSCH also supports PI/2 BPSK, which is used to help boost uplink coverage performance. PI/2 BPSK is only permitted when the PUSCH is using the DFT-S-OFDM waveform, which is also designed to boost uplink coverage. PI/2 BPSK offers lower a lower Peak to Average Power Ratio (PAPR) than BPSK. BPSK suffers from zero crossings every time the bit stream changes from 0 to 1, or from 1 to 0. These zero crossings are caused by the 180-deg phase change when moving from one modulation constellation points to the other. Zero crossings cause the signal envelope to pass through zero and consequently results in a high PAPR.
• PUCCH uses different modulation schemes depending on the PUCCH format. In general, lower order modulation schemes are used by PUCCH to help ensure reliable reception across the whole coverage area:
  • PUCCH format 0 does not use a modulation scheme.
  • PUCCH format 1 can use either BPSK or QPSK depending on the quantity of information to be transferred. BPSK is used when PUCCH format 1 transfers a sigle bit of information, whereas QPSK is used when PUCCH format 1 transfers two bits of information.
  • PUCCH format 2 always uses QPSK.
  • PUCCH format 3 and 4 can use either PI/2 BPSK or QPSK depending on the configuration from the base station.
• PRACH does not use a modulation scheme.
• PBCH and PDCCH both use QPSK to help ensure reliable reception across the whole coverage area. PBCH also uses a low coding rate to further help reliable reception.
• Physical signals do not use modulation schemes. They are sequences of complex numbers and those sequences are mapped directly onto their allocated Resource Elements before generating the waveform for transmission across the air-interface.