UL-SCH (uplink shared channel)

Last updated on Jul 21, 2023

Uplink Shared Channel (UL-SCH):

The Uplink Shared Channel (UL-SCH) is an essential component in the 3GPP (3rd Generation Partnership Project) specifications for cellular communication systems, particularly in the context of LTE (Long-Term Evolution) and 5G NR (New Radio) networks. UL-SCH is a logical channel used for transmitting user data and control information from the User Equipment (UE) to the base station (eNB in LTE, gNB in 5G NR) over the uplink direction.

Background:

In mobile communication networks, data transmission occurs between the user equipment (UE), such as a smartphone or modem, and the base station (eNB or gNB), which connects to the core network and the internet. The uplink direction refers to data transmission from the UE to the base station, while the downlink direction refers to data transmission from the base station to the UE.

Purpose of UL-SCH:

The primary purpose of the Uplink Shared Channel (UL-SCH) is to carry user data and uplink control information from the UE to the base station. User data includes various types of information, such as internet traffic, voice calls, video streams, and other application data, while uplink control information includes feedback and control signaling from the UE, which is used by the base station to manage the radio resources effectively.

Data and Control Information on UL-SCH:

The UL-SCH can carry both user data and uplink control information simultaneously. The data and control information are multiplexed in time, meaning they are transmitted in different time slots or time intervals, allowing efficient use of the available radio resources.

The uplink control information includes:

Acknowledgment/Negative Acknowledgment (ACK/NACK): The UE sends ACK/NACK signals to indicate the successful or unsuccessful reception of downlink data from the base station.
Channel Quality Indicators (CQI): The UE sends CQI reports to provide feedback on the channel quality, which helps the base station adapt its transmission parameters to improve data rates and performance.
Scheduling Requests (SR): The UE sends SRs to request uplink resources for transmitting user data to the base station.

Resource Allocation and Grant-Based Access:

The UL-SCH uses grant-based access, where the base station assigns uplink resources to the UE for transmission. The base station sends a UL grant to the UE, specifying the time-frequency resources and other transmission parameters that the UE should use for UL-SCH transmission.

Flexible Resource Allocation in 5G NR:

In 5G NR, the UL-SCH is further enhanced to support flexible resource allocation. 5G NR introduces various numerologies and slot formats, allowing different time and frequency configurations for different services and user scenarios. This flexibility improves spectral efficiency and accommodates diverse use cases with varying QoS requirements.

Conclusion:

The Uplink Shared Channel (UL-SCH) is a critical channel in LTE and 5G NR mobile communication networks, responsible for transmitting user data and uplink control information from the User Equipment (UE) to the base station. By using grant-based access and multiplexing user data with uplink control information, the UL-SCH ensures efficient utilization of uplink radio resources and supports diverse services and applications with varying QoS requirements.