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Testing and 5G NR transmission flexibility: a brief overview

Irina Cotanis
Aug. 25 2021

One of the key enablers of 5G NR is its flexible transmission characteristic, which is the flexible slot structure with self-contained transmission and scalable frequency-division multiplexing (OFDM) multi-tone numerology.

This characteristic provides significant benefits for 5G NR drive testing. But what are they? And what does this testing regime require of operators keen to tap into this way of working as 5G rollouts hot up?

In this blog post, which is Part 5 in a series dedicated to 5G NR drive testing, we discuss the key factors you should familiarize yourselves with.

What are the benefits?

A flexible slot-based framework allows network operators to efficiently multiplex the envisioned 5G services on the same frequency. A key technology to deliver this flexible framework is the 5G NR self- contained slot structure. With this, each 5G NR transmission is a modular transaction with the ability to independently decode slots and avoid static timing relationships across slots.

By confining transmissions in time and frequency, the flexible design simplifies the process of adding new 5G NR features and services in the future, consequently delivering a more forward-compatible design than previous generations.

The 5G NR self-contained slot structure also delivers significantly lower latency than LTE thanks to support for fast uplink (UL) and downlink (DL) turn-around, and scalable slot durations of 500µs at 30kHz frequency spacing up to 125µs at 120kHz frequency spacing.

This slot structure framework includes the opportunity for UL/DL scheduling, data and acknowledgement to occur in the same slot. Beyond lower latency, this modular slot structure design enables more adaptive test-drive development UL/DL configuration (in time division duplex – or TDD – mode), advanced reciprocity-based antenna techniques (such as downlink mMIMO steering based on fast uplink sounding), as well as additional use cases enabled by adding subframe headers (such as contention resolution headers for shared/unlicensed spectrum). Consequently, the self-contained transmission enables several of the 5G NR requirements to be met.

The 5G NR scalable frequency-division multiplexing (OFDM) multi-tone numerology enables the support of diverse spectrum bands, types and deployment models. For example, 5G NR must be able to operate in mmWave bands that have wider channel widths (for example, hundreds of MHz). 3GPP 5G NR Rel-15 specification utilizes scalable OFDM numerology with 2N scaling of subcarrier spacing that can scale with the channel width, so the fast Fourier transform (FFT) size scales such that processing complexity doesn’t increase unnecessarily for wider bandwidths.

Consequently, the flexible and scale NR transmission enables spectrally efficient NR support for use cases (network slices) with different, extreme and even contradictory performances. The complexity of the relationship between these NR technologies, as well as the required optimization algorithms supporting them, are dependent on devices’ capabilities and performances. Thus, the expected latency and throughput gains to be achieved by NR need to be evaluated at device-level for different scenarios, per service and application within a slice and/or per slice.

What are the testing requirements?

In order to ensure optimized operability of the NR flexibility, as described above, involves some minimum testing requirements. A few are listed below.

  • Numerology with scalable sub-carrier spacings and time division multiplexing (TDM) numerology needs to be evaluated in different test phases (for data and initial access), for different frequency bands (< 1GHz, 1-6GHz, > 6GHz) and for different UE / client type (machines) requirements.
  • The allocation of bandwidth parts (BWPs) (up to a maximum of four; Rel 15 up to two only), as aggregated spectrum bands or virtualized ‘BWPs’ with their own numerology, requires monitoring of the dynamic activation / deactivation of BWPs for different UE types.
  • The mini-slot scheduling with different possible configurations (all DL/UL, mixed DL and UL) needs to be evaluated for low latency applications.
  • Evaluation of latency and throughput at device level, per service within each network slice. Analysis of RAN performance (latency, throughput) within the context of service/network slice configuration.

To find out more about NR transmission flexibility/scalability, its benefits and performance within the context of services and network slices, as well as details on its optimization and troubleshooting, read our white paper, Initial 5G NR Drive Testing with Infovista.

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