LTE downlink channel mapping:
LTE Up link channel Mapping
LTE Uplink Information Flow:
LTE Downlink channel Information Flow:
MAC layer does multiplexing of multiple logical channel into single transport channel. So understanding of LTE channels is important.
First, what are channels in LTE?
Channels are used to transfer the data from one layer to another, channels are used.
These are used to segregate the different types of data and allow them to be transported across different layers. These channels provide interfaces to each layers within the LTE protocol stack and enable an orderly and defined segregation of the data.
How many different types channels have been divided?
On a high level it is divided into 3 types:
1. Logical Channel (What type of information)
2. Transport Channel (How the information is transported)
3. Physical Channel (Where the information is to be sent)
Logical channel defines what type of information to be sent.
Logical Channel is between RLC and MAC layers.
Logical channel is divided into 2 types:
1. Control Channel:
It will carry signaling messages in the control plane. They can be either common channel or dedicated channel.
Common channel means, common to all the users in a cell (Point to multipoint).
Dedicated channel means, channels can be used by one user only (Point to point)
2. Traffic Channel:
They will carry user plane data.
There are 7 logical channel in Downlink and 3 Logical channels in Uplink
In the list of 7 Downlink Channels: We have 5 control channels and 2 traffic channels
1. Broadcast Control Channel (BCCH) – It Used for broadcasting MIBs/SIBs
2. Paging Control Channel (PCCH) – It is used for paging the UE
3. Common Control Channel (CCCH) -It is Common to multiple UE’s.
4. Dedicated Control Channel (DCCH) – It used to transmit dedicated control information for a particular UE (BI-Directional)
5. Multicast Control Channel (MCCH) – It is used for transmit information for Multicast
Traffic Channel: In Downlink we have 2 Traffic channel
6. Dedicated Traffic channel (DTCH): Dedicated Traffic for a particular UE
7. Multicast Traffic Channel (MTCH): used to transmit Multicast data
List of 3 Uplink Channels:
We have 2 control channels and 1 traffic channels
1. Common Control Channel (CCCH) -It is Common to multiple UE’s
2. Dedicated Control Channel (DCCH) – It used to transmit dedicated control information for a particular UE
3. Dedicated Traffic channel (DTCH): Dedicated Traffic for a particular UE
Transport channels define how the information is transported.
Transport channel is between MAC and Physical Layer
Downlink Transport Channels
There are 4 downlink transport channels:
1. Broadcast Channel (BCH) :
This LTE transport channel maps to Broadcast Control Channel (BCCH).
It carries BCCH.
It will carry information like used for MIB and send information to Physical Broadcast channel (PBCH)
2. Downlink Shared Channel (DL-SCH):
This transport channel is the main channel for downlink data transfer.
It is used by many logical channels like BCCH, CCCH, DCCH DTCH,MCCH,MTCH and send its information to Physical Downlink Shared Channel (PDSCH).
Carries DCCH, DTCH, BCCH, MTCH.
The information carried by this channel is SIB, Data transfer
3. Paging Channel (PCH) :
It is used to convey the PCCH information and mapped to Physical Downlink Shared Channel (PDSCH) and carries Paging Information.
4. Multicast Channel (MCH) :
This transport channel is used to transmit MCCH information to set up multicast transmissions.
This channel is mapped to Physical Multicast Channel (PMCH) this is basically used for MBMS services.
Uplink Transport channel:
There are 2 uplink transport channels:
1. Uplink Shared Channel (UL-SCH) : This transport channel is the main channel for uplink data transfer.
It can be used by many logical channels like CCCH, DCCH DTCH.
2. Random Access Channel (RACH) : This is used for random access procedure.
It will not carry no logical channel.
This channel is further divided into 4 different types.
Transport channel is between physical Layer to UE in downlink
1. Downlink Physical Channels.
2. Uplink Physical Channels.
3. Physical Data Channels
4. Physical Control Channels.
Now lets see the downlink Physical Channels:
There are total of 6 downlink channels, divided into data and control channels.
Downlink physical Data Channel (PBCH, PDSCH,PMCH)
Downlink Physical Control Channel (PCFICH,PHICH,PDCCH)
1. Physical Broadcast Channel (PBCH)
It is used to broadcast system information with in eNB that allow UE to access the network.
It will carry only MIB information.
It transmits MIB that is 14 bits each and is split into four 10 ms frames, thus being repeated every 40 ms
Carries BCH information.
2. Physical Downlink Shared Channel (PDSCH):
It will handle the L1 data traffic transmission.
The data is transmitted in transport blocks once every 1 ms.
It also transmits paging messages or system information blocks;
carries DL-SCH and PCH information.
3. Physical Multicast Channel (PMCH)
Transmits Multimedia Broadcast and Multicast Services (MBMS);
carries MCH information.
4. Physical Downlink Control Channel (PDCCH)
Responsible for handling downlink allocation information, uplink allocation grants for the terminal, paging indications or system information.
5. Physical Hybrid ARQ Indicator Channel (PHICH)
Carries the acknowledgement signals from the uplink transmissions.
It is used to carry the Hybrid ARQ status.
6. Physical Control Format Indicator Channel (PCFICH) :
It will inform UE about the OFDM symbol used for PDCCH.
Uplink Physical Channels:
Thre are 3 uplink channels. Divided into data and control channel as below:
Uplink physical Data Channel ( PUSCH,PRACH)
Uplink Physical Control Channel (PUCCH)
1. Physical Random Access Channel (PRACH):
Does the initial access when the UE losses its uplink synchronization;
carries RACH information.
2. Physical Uplink Shared Channel (PUSCH):
It will carry the L1 uplink transport data with the control information;
carries UL-SCH information.
3. Physical Uplink Control Channel (PUCCH):
It will carry control information.
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