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| 26 subcarriers that make up the composite radio signal. OFDM access is the multiple-access scheme that NR has adopted. For downlink and uplink transmissions, without multiuser multiple input, multiple output (MIMO), different users are allocated to different subcarriers. The waveform of the transmitted signal in NR uses cyclic prefix (CP)-OFDM for downlink and uplink transmissions. In addition, a discrete Fourier transform-spread OFDM (DFT-S-OFDM) waveform is used in the uplink because of the DFT-S-OFDM waveform's low peak-to-average power ratio (PAPR) for user equipment (UE) in power-limited regions. DFT-S-OFDM is used only with single-layer uplink transmissions. In the case of DFT-S-OFDM, a signal goes through a DFT precoder before reaching the subcarriers allocated for the transmission. After conversion back to the time domain, a CP appends to the OFDM symbol. Subcarrier Spacing 5G NR is a unified air interface that supports many frequencies, ranging from less than 1GHz to tens of gigahertz—about two orders of magnitude of change in the carrier frequency. Typically, the bandwidth scales with the carrier frequency to maintain a bandwidth-to-carrier frequency ratio within a certain range. Relying only on the number of subcarriers that support different channel bandwidths leads to a small number of subcarriers for small channel bandwidths, which has less multiplexing granularity. Such is the case when relying on a large number of subcarriers for large channel bandwidths, which increases hardware complexity, because it requires FFT/ inverse FFT (IFFT) blocks with larger sizes. However, by allowing the subcarrier spacing to scale, it is possible to maintain a reasonable range for the subcarriers while still supporting a range of channel bandwidths. The subcarrier spacing is designed to scale in powers of two, where the supported subcarrier spacing is 15, 30, 60, 120, or 240kHz, with 240kHz in use only for synchronization signals and the broadcast channel. Low-Latency Transmissions 5G NR introduces several technology improvements designed to support low-latency operations: • Higher subcarrier spacing allows for shorter symbol and slot durations, which leads to lower latencies. • Short physical downlink-shared channel and physical uplink-shared channel transmissions support as few as two symbols. • Support of a flexible scheduling and timing framework with different UE processing capabilities empowers a 5G NR network to optimize a downlink and uplink transmission time, which is based on the UE's processing capabilities and the latency requirements of corresponding traffic. • Support of preconfigured uplink resources (e.g., configured grant) enables the UE to transmit uplink data autonomously. Channel Coding 5G NR introduced new channel coding schemes for data and control channels with a payload of 12 or more bits: • For data channels, 5G NR supports Low-Density Parity-Check (LDPC) codes. • For control channels with a payload of 12-bits or more, 5G NR supports Polar codes. • For control channels with a payload of 3- to 11-bits, 5G NR supports Reed-Muller codes. • For control channels with 1- or 2-bits, 5G NR supports Repetition or Simplex codes respectively Massive MIMO in 5G NR 5G NR uses massive MIMO, the latest extension of the MIMO techniques, to establish a larger set of antenna arrays with a larger number of elements, thus increasing the efficiency of the 5G network infrastructure. The purpose of massive MIMO is to enhance wireless capacity by improving spectral efficiency through higher order spatial multiplexing and to enhance coverage using beamforming. 5G NR developed a flexible and scalable framework for massive MIMO, which supports: • Carrier frequencies ranging from less than 1GHz to mmWaves • Different kinds of antenna array architectures (digital, analog, and hybrid) "...exploiting shorter wavelengths with smaller antenna array elements that can be packed together more tightly, it's feasible to implement antenna arrays with tens or even hundreds of antenna elements in the mmWave band." [ C O N T ' D O N N E X T P A G E ]

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