What is a scheduler and what does it do in a 5G network?

Resource allocation in a 5G network is managed by a scheduler, which dynamically assigns time, frequency, and power to user equipment (UEs) connected to a base station (gNB). Providing high-quality service (QoS) to various 5G use cases is crucial, including ultra-reliable Low-Latency Communication (uRLLC), Massive Machine-Type Communication (mMTC), and Enhanced Mobile Broadband (eMBB).

While scheduling is not explicitly outlined in the 3GPP 5G standards, processes like measurement collection are defined to assist in scheduling algorithms. The responsibility of defining and implementing the scheduling algorithm lies with the gNB manufacturer. Some essential considerations for scheduling include:

Utilizing measurements to make real-time adjustments based on changing channel conditions and user demands.

Using power headroom reports to support power-aware packet scheduling by measuring the transmit power requirements.

Considering buffer status reports to determine the amount of data queued for transmission by a user.

Taking into account QoS requirements, such as priority, delay, and throughput, based on specific use cases and data types.

Differentiating between default and dedicated radio bearers that support different QoS levels or flow requirements.

Figure 1. A scheduler uses various data inputs to optimize resource allocation and enhance overall QoS. (Image: ShareTechnote)

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Downlink considerations

The downlink allocates resources dynamically to UEs and adjusts schedules in real-time to prioritize latency-critical data in the buffer.

Ensuring that each UE receives its guaranteed bit rate (GBR) is essential, delivering the required level of service without exceeding processing capabilities or causing network congestion.

Uplink considerations

Uplink resource allocation relies on reports from UEs, with the scheduler prioritizing latency-critical data in the buffer for immediate transmission.

UEs utilize an uplink rate control function to manage resource sharing between logical channels, with the scheduler serving logical channels based on their prioritized bit rates to ensure critical applications are addressed first.

Bit rate classifications

Bit rate requirements play a significant role in scheduling, with Non-GBR, GBR, and Delay Critical GBR classifications offering different levels of priority and performance guarantees.

Table 1. Non-GBR, GBR, and Delay Critical GBR classifications in 5G scheduling. (Table: LinkedIn)

Conclusion

Efficiently scheduling radio traffic is vital for maintaining the desired QoS in 5G networks. While the 3GPP standards offer guidelines on scheduler operation, the specific implementation of scheduling algorithms is left to individual gNB manufacturers.