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Waveform and Basic Structure of NR

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Waveform and Basic Structure of NR

Introduction:

5G, the fifth generation of cellular technology, has been deployed in many countries worldwide. The standard for 5G is the 3rd Generation Partnership Project (3GPP) Release 15, which includes New Radio (NR). NR is a key component of 5G, and it is designed to meet the requirements of 5G networks, such as high data rates, low latency, high reliability, and massive connectivity. In this article, we will discuss the waveform and basic structure of NR in technical detail.

Waveform of NR:

NR uses a new waveform called the filtered-OFDM (f-OFDM) waveform. OFDM is a widely used modulation scheme in wireless communication systems, including 4G Long-Term Evolution (LTE) systems. In OFDM, the frequency band is divided into many subcarriers, and each subcarrier is modulated with a lower rate data symbol. The advantage of OFDM is that it can mitigate the effects of multipath propagation, which is a major challenge in wireless communication.

The f-OFDM waveform is similar to OFDM in that it also divides the frequency band into subcarriers. However, f-OFDM adds a filter to each subcarrier to reduce the out-of-band emissions. The filter is designed to have a steep roll-off, which means that the filter attenuates the signal rapidly outside the subcarrier bandwidth. The advantage of f-OFDM is that it can reduce the interference between adjacent subcarriers, which can improve the spectral efficiency.

The f-OFDM waveform has several other advantages compared to OFDM, such as:

  • Better power efficiency: The filter reduces the signal power outside the subcarrier bandwidth, which can improve the power efficiency of the system.
  • Lower peak-to-average power ratio (PAPR): The PAPR is a measure of how much the signal power can vary from the average power. High PAPR can cause distortion in the signal and reduce the efficiency of the power amplifier. The f-OFDM waveform has lower PAPR compared to OFDM, which can improve the efficiency of the power amplifier.
  • Better synchronization: The filter can improve the time and frequency synchronization accuracy of the system.

Basic Structure of NR:

The basic structure of NR is based on a flexible and modular design that allows for different deployment scenarios and use cases. The structure consists of two main parts: the radio access network (RAN) and the core network (CN). The RAN includes the base station (BS) and the user equipment (UE), while the CN includes the core network functions (CNFs).

The RAN is responsible for the wireless transmission and reception of data between the BS and the UE. The BS is connected to the CN via the X2 interface, while the UE is connected to the BS via the air interface. The air interface is divided into two parts: the downlink (DL) and the uplink (UL). The DL is the direction from the BS to the UE, while the UL is the direction from the UE to the BS.

The DL and UL use different transmission schemes, as follows:

  • DL: The DL uses a multi-antenna transmission scheme called multiple-input multiple-output (MIMO). MIMO can improve the spectral efficiency and the link reliability by transmitting multiple data streams over multiple antennas. The DL also uses beamforming, which is a technique that focuses the transmitted signal towards the UE to improve the signal quality.
  • UL: The UL uses a single-antenna transmission scheme called single-input single-output (SISO). SISO is simpler than MIMO but can still provide high data rates in low mobility scenarios. The UL also uses grant-free transmission, which means that the UE can transmit data without waiting for a scheduling grant

The NR frame structure is divided into subframes, and each subframe has a duration of 1 ms. Each subframe is further divided into slots, and each slot has a duration of 0.125 ms. The number of slots in a subframe depends on the subcarrier spacing and the cyclic prefix (CP) length. The CP is a guard interval that is added to each symbol to mitigate the effects of multipath propagation.

The NR frame structure is designed to be flexible and support different deployment scenarios and use cases. The frame structure can be configured to support different subcarrier spacings, CP lengths, and numerologies. The numerology determines the subcarrier spacing and the symbol duration, and it can be configured to support different data rates and coverage requirements.

The NR frame structure also supports dynamic scheduling, which means that the BS can allocate resources to different UEs based on their traffic demands and quality of service (QoS) requirements. The BS can use different scheduling schemes, such as time division multiplexing (TDM), frequency division multiplexing (FDM), or space division multiplexing (SDM), to allocate resources to UEs.

The NR frame structure also supports different duplex modes, such as time division duplex (TDD) and frequency division duplex (FDD). TDD is a mode in which the DL and UL share the same frequency band, and the direction of transmission is determined by the time division. FDD is a mode in which the DL and UL use different frequency bands, and the direction of transmission is determined by the frequency division.

Conclusion:

In conclusion, NR is a key component of 5G, and it is designed to meet the requirements of 5G networks, such as high data rates, low latency, high reliability, and massive connectivity. NR uses a new waveform called the filtered-OFDM (f-OFDM) waveform, which adds a filter to each subcarrier to reduce the out-of-band emissions. The f-OFDM waveform has several advantages compared to OFDM, such as better power efficiency, lower PAPR, and better synchronization.