The DL scheduler is spit into 3 functional parts:
1.The Static Scheduler:
Which assigns a fixed amount of Transport Blocks as well as PDCCH and PDSCH resources for the BCCH over the DL-SCH Transport Channel.Those resources are permanently allocated.
2.The Semi-static Scheduler:
Which assigns Transport Blocks as well as PDCCH and PDSCH resources for PCCH and CCCH over the PCH and DL PDSCH SCH Transport Channels. The semi-static scheduler also assigns a regular set of Transport Blocks for all established VoIP bearers.
3.The Dynamic Scheduler:
Which assigns Transport Blocks as well as PDCCH and PDSCH resources for DCCH & DTCH over the DL-SCH Transport Channels.
The dynamic scheduler is also in charge of sending the MAC Control Timing Advance control messages in order to keep the UE in the connected mode, synchronized with the network
The LTE DL scheduler is composed of 2 main algorithms:
A pre-booking stage which reserve resources over the PDSCH for the static and semistatic schedulers. A scheduling stage which assign the resources over the PDSCH for effective traffic.
What is the DL Scheduler in LTE?
The Downlink (DL) Scheduler in LTE is responsible for allocating radio resources to users in the downlink direction (from the eNB to the UE). It ensures that data is transmitted efficiently, based on the available radio resources and the quality of service (QoS) requirements of the users.
Key Functions of the DL Scheduler
- Resource Allocation: The DL scheduler allocates resources to different users based on the channel conditions, QoS requirements, and priority levels. It decides which user gets access to the radio resources, like frequency and time slots, in each transmission.
- Channel Quality Estimation: The scheduler estimates the channel quality of each UE based on feedback received from the devices. This helps in determining how much data can be transmitted to each user with minimal errors.
- Fairness and Efficiency: The scheduler ensures fair distribution of resources while also optimizing the usage of available resources. It balances between providing good service to high-priority users and maximizing overall network capacity.
Types of DL Scheduling Algorithms
- Proportional Fair Scheduling: This algorithm allocates resources to users based on both their channel quality and the amount of data they have already received. It aims to provide a balance between fairness and high throughput.
- Round Robin Scheduling: Resources are allocated to users in a cyclic manner, ensuring each user gets a fair share of resources over time. It is simple but may not be efficient in cases with varying channel conditions.
- Maximizing Throughput Scheduling: This method prioritizes users with the best channel conditions, aiming to maximize the overall throughput. It is efficient but can lead to unfair resource allocation in certain scenarios.
How the DL Scheduler Works
The DL scheduler operates at the eNB, and it continuously monitors the channel conditions for each user. When the scheduler receives information about the channel quality (such as from CQI reports), it calculates the optimal resource allocation. Then, it assigns radio resources to each UE accordingly, ensuring the data transmission is as efficient as possible.
Why the DL Scheduler Matters
The DL scheduler is essential for optimizing network performance in LTE. By managing resource allocation efficiently, it ensures that users experience good performance based on their needs and channel conditions, while also maximizing the overall throughput of the network.