What is User Plane Latency

The transmission of an Internet Protocol (IP) packet with 0 byte payload should experience a one-way UP latency of less than 5 ms. For FDD it was concluded that for a typical case with an initial Hybrid Automatic Repeat Request (HARQ) error rate of 0.3, a total average UP latency of 4ms + S1-U transfer delay can be achieved.

For TDD frame structure type 2, the requirements on UP delay can be reached for a 4- DL/3-UL configuration and no re-transmission assumed for the first transmission.

In general, the latency in TDD is larger than in FDD, because of the finite delay between the switching points. In particular, since the number of switching points per frame is limited due to efficiency reasons, the delay increases. The main contributor to the longer delay is the increased HARQ Round Trip Time (RTT).