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LTE-M channel types | LTE-M downlink channel, uplink channels

This page mentions LTE-M channel types and their functions.It covers both LTE-M downlink channels and uplink channels.

Introduction:
LTE-M follows 3GPP specifications similar to LTE technology. LTE-M stands for Long Term Evolution for Machine-Type Communications. It is mainly developed to fulfill cellular IoT device objectives such as low device cost, deep coverage, longer battery life, higher cell capacity and so on. There are different categories of LTE-M devices viz. Cat-0, Cat-M1 and Cat-M2 as per different 3GPP releases. LTE-M Cat-0, Cat-M1 and Cat-M2 follow 3GPP TS 36 series of rel.12, rel.13 and rel.14 respectively. Let us understand functions of LTE-M channel types.

LTE-M Channel Types

The LTE-M Channel Types are categorized into downlink channels and uplink channels. There are signals also which are used for synchronization and channel estimation/equalization purposes.

LTE-M downlink channels and signals

LTE-M Downlink Channels

LTE-M supports set of downlink and uplink channels and signals. The mapping between logical channels, transport channels and physical channels is also shown. As mentioned PSS, SSS and RS are used as downlink signals where as PDSCH, MPDCCH and PBCH are used as downlink channels.

Location:
• PSS, SSS, and PBCH are transmitted periodically in the center of the LTE carrier.
• MPDCCH and PDSCH are transmitted in narrowband.
• DL Reference Signals (RS) are transmitted in all PRBs.

Synchronization Signals

Following table mentions useful parameters of synchronization signals.

Details Description
Subframes in FDD #0 and #5 for both PSS and SSS
Subframes in TDD #1 and #6 for PSS, #0 and #5 for SSS
Subframe periodicity 5 ms for both PSS and SSS
Sequence pattern periodicity 5 ms for PSS, 10 ms for SSS
Subcarrier spacing 15 KHz
Bandwidth 62 subcarriers (DC not included)
Frequency Location At the center of LTE system BW

Downlink Reference Signals

Following table mentions useful parameters of downlink reference signals.

Details Description
Subframe Any
Subcarrier spacing 15 KHz
CRS (Cell-specific reference) Bandwidth Full System Bandwidth
DMRS (Demodulation Reference Signal) Bandwidth Same as associated MPDCCH/PDSCH
CRS Frequency location In every PRB
DMRS frequency locationn In affected PRBs

PBCH

Following table mentions useful parameters of PBCH channel used to deliver the MIB that provides essential information for the device to operate in the network.

Details Description
Subframes in FDD #0 for core part, #9 for repetitions
subframes in TDD #0 for core part, #5 for repetitions
TTI 40 ms
Repetitions Core part plus 0 or 4 repetitions
Subcarrier spacing 15 KHz
Bandwidth 72 subcarriers (excluding DC)
Frequency location At center of LTE system BW

MPDCCH

Following table mentions useful parameters of MPDCCH channel used to carry Downlink Control Information (DCI).

Details Description
Subframe Any
Basic TTI 1 ms
Repetitions 1, 2, 4, 8, 16, 32, 64, 128, 256
Subcarrier spacing 15 KHz
Bandwidth 2, 4, or 6 PRBs
Frequency location Within a Narrowband
Frequency hopping Between 2 and 4 narrowbands (if configured)

PDSCH

Following table mentions useful parameters of PDSCH channel primarily used to transmit unicast data.

Details Description
Subframe Any
Basic TTI 1 ms
Repetitions Max. 32 in CE mode-A, Max. 2048 in CE mode-B
Subcarrier spacing 15 KHz
Bandwidth 1 to 6 PRBs in CE Mode-A, 4 or 6 PRBs in CE Mode-B
Frequency location Within narrowband
Frequency hopping Between 2 or 4 narrowbands(if configured)

LTE-M Uplink Channels and signals

LTE-M Uplink Channels

PRACH, PUSCH and PUCCH are used as uplink channels as shown in the figure. RS and DMRS are used as reference signals in uplink.

PRACH

Following table mentions useful parameters of PRACH channel. The PRACH is used by the device to initialize connection and allows the serving base station to estimate the time of arrival of UL transmission.

Details Description
Subframe Any
Basic TTI 1, 2 or 3 ms
Repetitions 1, 2, 4, 8, 16, 32, 64, 128
Subcarrier spacing 1.25 KHz
Bandwidth 839 subcarriers ( equivalent to 1.05 MHz)
Frequency location Any
Frequency hopping Between two frequency locations (if configured)

Uplink Reference Signals

Following table mentions useful parameters of Uplink Reference Signals (SRS, DMRS). RS signals are used by eNB (i.e. Base station) to perform channel estimation, to perform UL quality measurements and to issue timing advance commands.

Details Description
Subframe Any
Subcarrier spacing 15 KHz
DMRS bandwidth Same as associated with PUSCH/PUCCH
SRS Bandwidth 4 PRBs
DMRS frequency location Same as associated PUSCH/PUCCH
SRS frequency location Configurable

PUSCH

Following table mentions useful parameters of PUSCH channel used to transmit unicast data primarily.

Details Description
Subframe Any
Basic TTI 1 ms
Repetitions Maximum 32 in CE mode A, Max. 2048 in CE mode B
Subcarrier spacing 15 KHz
Bandwidth 1 to 6 PRBs in CE mode A, 1 or 2 PRBs in CE mode B
Frequency location Within narrowband
Frequency hopping Between 2 narrowbands (if configured)

PUCCH

Following table mentions useful parameters of PUCCH channel. The PUCCH is used to carry the following types of Uplink Control Information (UCI).
• UL scheduling request (SR)
• DL HARQ feedback (ACK or NACK)
• DL CSI

Details Description
Subframe Any
Basic TTI 1 ms
Repetitions in CE mode A 1, 2, 4, 8
Repetitions in CE mode A 1, 2, 4, 8
Repetitions in CE mode B 4, 8, 16, 32 (Rel. 14 supports 64 and 128 also)
Subcarrier spacing 15 KHz
Bandwidth 1 PRB
Frequency location Any PRB
Frequency hopping Between 2 PRB locations


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LTE tutorial  LTE-M tutorial  LTE features  LTE terminologies  Frame  TDD FDD  Channel types  PHY  stack  throughput  CA   cell search  network entry  Timers  PSS vs SSS  Security   LTE Bands  EARFCN  Hotspot  router  What is VoLTE  VoLTE originating call flow  VoLTE UE attach and registration procedure 


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