Basics of scheduling in LTE

Scheduling is the process through which eNB decides which UEs should be given resources to send or receive data . In LTE, scheduling is done per subframe level (i.e. each 1 ms TTI)

Before getting into basics of scheduling, it is important to understand following key terms:


CQI (Channel quality indicator) is a four digit value sent to eNB by UE as a feedback for downlink channel.CQI informs eNB about the channel quality in downlink. This helps eNB to allocate proper MCS (Modulation and coding scheme) and RB (Resource block) for UE


BSR (Buffer Status Report) is a UE way of informing network that it has certain data in its buffer and it requires grants to send this data


QoS (Quality of Service) defines how a particular user data should be treated in the network. QoS is implemented between UE and PDN Gateway and is applied to a set of bearers.  e.g. VoIP packets are prioritized by network compared to web browser traffic.

Now let's see how the scheduling works
  • UE computes the CQI value from downlink channel and sends it to the eNB
  • UE sends BSR reports to eNodeB
  • Based on BSR, CQI and UE QoS, eNodeB computes MCS value and PRB mapping information and send it to the UE in downlink

Factors that affects scheduling: 

  • Traffic Volume: Schedules those UEs with bearers waiting data in buffer
  • QoS Requirement: Schedules and allocates resources to UE to meet its QoS requirement
  • Radio Conditions: Schedules resources for UE that best suits its radio environment