Sign in Subscribe

UCI (Uplink Control Information)

Last updated on 


Uplink Control Information (UCI) is a crucial component in wireless communication systems, especially in the context of cellular networks like LTE (Long-Term Evolution) and 5G (Fifth Generation). UCI is responsible for carrying control information from the user equipment (UE), also known as the mobile device, to the network.

In the LTE and 5G standards, UCI is transmitted in the uplink direction, meaning it travels from the UE to the base station (eNodeB in LTE or gNB in 5G). The UCI is embedded within the physical uplink control channel (PUCCH) or the physical uplink shared channel (PUSCH), depending on the type of information being conveyed.

Here's a technical breakdown of UCI in the LTE and 5G context:

  1. Types of UCI:
    • PUCCH (Physical Uplink Control Channel): In LTE, PUCCH is dedicated to carrying UCI. It's used for transmitting control information related to uplink scheduling, acknowledgments (ACK/NACK) for downlink data, and channel quality indicators (CQI).
    • PUSCH (Physical Uplink Shared Channel): In both LTE and 5G, UCI can also be transmitted on the PUSCH, especially for scenarios where dynamic scheduling is applied. This allows the UE to send both data and control information on the same channel.
  2. UCI Formats:
    • ACK/NACK (Acknowledgment/Negative Acknowledgment): UCI is commonly used to transmit acknowledgments or negative acknowledgments for received downlink data. This information helps the network scheduler understand whether the transmitted data was successfully received or not.
    • CQI (Channel Quality Indicator): The UE provides feedback on the quality of the radio channel through CQI. This information aids the base station in optimizing the allocation of radio resources for improved data transmission.
  3. Modulation and Coding Scheme (MCS):
    • The UCI bits are modulated and coded using specific schemes, such as Quadrature Amplitude Modulation (QAM) or Binary Phase Shift Keying (BPSK), depending on the modulation and coding scheme selected for the transmission.
  4. Frequency of Transmission:
    • The frequency at which UCI is transmitted depends on the specific configuration and network conditions. In LTE, PUCCH is often associated with specific subframes, and in 5G, UCI on PUSCH is dynamically scheduled based on the network's requirements.
  5. Dynamic Scheduling:
    • In 5G, UCI transmission on PUSCH is often part of dynamic scheduling, where the network adapts the scheduling of UCI based on the real-time channel conditions and traffic demands.

UCI plays a vital role in enabling efficient and reliable communication between the UE and the network by conveying important control information. It is transmitted over specific physical channels, and its format and scheduling depend on the type of information being communicated and the characteristics of the wireless network.