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What Is Converged Scheduling?

The converged scheduling algorithm employs different methods to improve the downlink and uplink transmission efficiency: pre-scheduling based on multi-user multiple-input multiple-output (MU-MIMO) for downlink traffic; orthogonal frequency division multiple access (OFDMA) scheduling for uplink small TCP ACK packets. This algorithm is mainly applicable to multi-user concurrent services in high-density scenarios.

How Does Converged Scheduling Come into Being?

In high-density scenarios such as enterprise offices and educational institutions, there are typically a large number of STAs, with high concurrency and severe interference. As such, enterprise WLANs urgently need a solution to improve multi-user concurrency efficiency in high-density scenarios. On live networks, service packets are typically bursty and discrete, and a large number of small packets are sent in single-user (SU) mode. This increases the number of signal collisions on the air interface and reduces the downlink transmission efficiency. Additionally, TCP packets are mostly used to carry high-concurrency services on the live network. Although TCP can ensure highly reliable information transmission, yet the upper-layer TCP ACK mechanism usually performs multiple uplink and downlink interactions over the air interface. As a result, uplink and downlink transmission collisions are severe in multi-user concurrency scenarios, causing packet loss. This further deteriorates the downlink wireless transmission efficiency. To address these issues, the converged scheduling algorithm is introduced.

For multi-user concurrent services in high-density scenarios, the converged scheduling algorithm employs different methods to improve the downlink and uplink transmission efficiency: pre-scheduling based on MU-MIMO for downlink traffic; OFDMA scheduling for uplink small TCP ACK packets.

How Does Pre-scheduling Based on MU-MIMO Work?

Compared with SU-MIMO, MU-MIMO usually provides throughput performance gains in large-packet transmission scenarios. However, a burst of service packets will prevent simultaneous scheduling of packets of multiple users. Even if the packets can be scheduled, the packet buffers of these users are insufficient, failing to achieve the air interface performance gains of MU-MIMO. For greedy services characterized by unlimited bandwidth requirements and long transmission duration, downlink pre-scheduling based on MU-MIMO reduces the packet scheduling frequency and allows more packets to stay in the scheduling buffer. This extends the single-frame transmission duration, increases the MU-MIMO packet transmission opportunities, and reduces the number of small-packet transmissions over the air interface. This ultimately improves the downlink transmission efficiency,

Downlink pre-scheduling based on MU-MIMO
Downlink pre-scheduling based on MU-MIMO

How Does OFDMA Scheduling Work?

Unlike MU-MIMO, OFDMA provides throughput performance gains in small-packet transmission scenarios. This technology saves air interface overheads such as the channel access and backoff time, time for sending PPDU PHY frame headers, and Block Ack (BA) time. Additionally, OFDMA helps to mitigate collisions caused by multi-user channel contention. When STAs run TCP services concurrently, an AP schedules small TCP ACK packets using OFDMA to control the unordered, free channel contention in the uplink direction. This in turn reduces uplink and downlink transmission collisions, and ensures high efficiency in sending downlink TCP packets.

Uplink OFDMA scheduling for small packets
Uplink OFDMA scheduling for small packets
References
About This Topic
  • Author: Wang Yibo
  • Updated on: 2024-10-21
  • Views: 496
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