Difference between CE Mode A and CE Mode B

Difference between CE Mode A and CE Mode B | LTE-M

This page compares CE Mode A Vs CE Mode B in LTE-M and describes difference between CE Mode A and CE Mode B used in LTE-M technology.

Introduction: These modes have been introduced in 3GPP Release 13 for coverage enhancement. Following sections mention unique features of LTE-M under these modes developed to address below mentioned challenges.
• LTE-M devices reduces complexity by adopting simple techniques such as single antenna for reception, low max. transmit power and so on. These modifications lead to performance degradation which results into coverage loss compare to LTE technology.
• LTE-M devices require to work under challenging coverage conditions. Moreover they need to support higher coverage compare to LTE.

LTE-M CE Mode A

• This mode supports 32 subframe repetitions of the data channel. This information is carried by PDSCH as well as PUSCH channels.
• Both PDSCH and PUSCH use bandwidth of 1 to 6 PRBs in CE mode A.
• This mode provides sufficient CE (Coverage Enhancement) to compensate for all the simplifications which can be implemented by low-cost LTE-M devices. Moreover this mode provides some additional CE beyond normal LTE coverage.
• This mode is optimized for moderate CE which can be achieved through a small amount of repetition.
• This mode supports both periodic and aperiodic SRS transmission.

LTE-M CE Mode B

• This mode supports 2048 subframe repetitions of the data channel. This information is carried by PDSCH as well as PUSCH channels.
• PDSCH uses bandwidth of 4 to 6 PRBs in CE mode B. PUSCH uses bandwidth of 1 or 2 PRBs.
• It provides deep coverage compare to CE mode A which may be needed in more challenging coverage conditions.
• It is optimized for substantial CE achieved through a large amount of repetition.
• If a device supports CE mode B, this means it also supports CE mode A.
• This mode does not support SRS transmission but will use shortened formats for PUSCH / PUCCH.

Table-1: PDSCH Modulation and Coding Schemes and TBS in LTE-M

MCS-and-TBS-for-PDSCH-CE-Mode-A-and-Mode-B-LTE-M

Table-2: PUSCH Modulation and Coding Schemes and TBS in LTE-M

➤Tables above mentions modulation and coding schemes (MCS) and TBS values for PDSCH and PUSCH channels.
➤All the low-cost LTE-M devices (with categories Cat-M1 and others) have mandatory support for CE mode A. They can also support CE mode B optionally.
➤These modes capable devices operate in CE mode only if it is required to stay within coverage i.e. when they are outside the normal LTE coverage range.
➤When these devices are in normal LTE coverage range they will use normal LTE operation instead of CE mode. This allows them to leverage benefits of high performance of normal LTE technology with respect to latency and data rates.

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