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 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
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 |
NB-IoT Related Stuff
LTE and LTE-M RELATED LINKS
This tutorial section on LTE basics covers following sub topics:
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
Difference between LTE Advanced vs LTE Advanced Pro vs 5G Links
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OFDM vs OFDMA
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