Guard period

BL/CE(LTE-M1) operates in 1.4 Mhz frequency block called Narrowband. The location of the Narrowband may vary in each subframe. It means that UE should need to tune to a difference frequency at every subframe. As you may guess, every freuqency retuning would take a certain period of time. It implies that we would need a certain period of guard period when transitions from one subframe to next subframe. Guard Period is a period during which no transmission and no reception occurs.

This guard period varies depending on whether it is downlink or uplink, and varies with different situations within downlink or uplink.

Uplink Guard Period

Type of uplink guard periods varies depending on the characteristics of data carried by a subframe and next subframe as described below (Following description is based on 36.211-5.2.5).

Case 1 : PUSCH in First Subframe and PUSCH in Second Subframe

Case 2 : PUCCH in First Subframe and PUCCH in Second Subframe



 

Case 3 : Shortened PUCCH in First Subframe and PUSCH in Second Subframe



 

Case 4 : Normal PUCCH in First Subframe and PUSCH in Second Subframe



 

Case 5 : Normal PUSCH in First Subframe and PUCCH in Second Subframe

Downlink Guard Period

Downlink guard period is required as in the following condition (refer to 36.211-6.2.8).

• First Downlink Narrowband Center frequency and the second narrowband center frequency is different
• In TDD, the first uplink narrowband center frequency and the second downlink center frequeny is different

The guard period is defined as follows

Reference

[1] 3GPP TS 36.211 V13.2.0 (2016-06)