NG-RAN and 5G-NR

45G-NR Radio Interface – The Physical Layer

4.1. 5G-NR radio interface

4.1.1. OFDM waveform

OFDM modulation consists of modulating orthogonal subcarriers (Figure 4.1).

Figure 4.1. OFDM modulation on three subcarriers

The two subcarriers c₁(t) and c₂(t) are orthogonal if and only if their scalar product is null: .

Orthogonality conditions impose that , where Δf is the subcarrier spacing and T represents the duration of a symbol.

Thanks to orthogonality, OFDM modulation offers good spectral efficiency and provides resilience to the frequency selective fading of the propagation channel.

The OFDM signal is used on the downlink as it allows multiple access capacities according to the OFDMA (Orthogonal Frequency Division Multiple Access) technique. The zero-padding technique makes it possible to reduce the PAPR (Power Average Power Ratio) and the power rejection on the neighboring bands. The PAPR represents the ratio of the maximum power of the OFDM signal to the average power in a bandwidth.

The uplink transmission uses either the OFDM signal or the DFT-S-OFDM (Discrete Fourier Transform Spread OFDM) signal. The DFT-S-OFDM signal is derived from OFDM modulation using transform precoding ...