WHAT IS THE USER PLANE (UP) LATENCY IN LTE ?

First of all understand the path and structure of user plane (UP). The diagram is shown below.

Ideally for UP latency the transmission of an IP packet with 0 bytes of payload , should experience a one way User Plane latency of less than 5 msec. Therefore the round trip UP latency ought to be less than 10 msec.

The above requirements are both for the case of TDD and FDD.

However in TDD, the latency is a little bit larger than FDD, because of the finite delay between the switching points.

In particular , (if you remember the structure of TDD radio frame, if you don’t remember then you can wait until TDD Module # 3 ) since the number of switching points per frame is limited due to efficiency reasons, the delay increases.

One of the main contributor of longer delay is the increased Hybrid Automatic Repeat Requests (HARQ) round trip time (RTT).