There are major four channel in LTE Downlink trasport channel. which list below with its work in short.Paging Channel ( PCH)
- Supports UE discontinuous reception (DRX) to enable UE power saving.
- Broadcasts in the entire coverage area of the cell.
- Mapped to physical resources which can be used dynamically also for traffic/other control channels.
Broadcast Channel ( BCH )
- The LTE transport channel maps to Broadcast Control Channel (BCCH).
- Fixed, pre-defined transport format.
- Broadcast in the entire coverage area of the cell.
Multicast Channel ( MCH)
- Broadcasts in the entire coverage area of the cell.
- Supports MBSFN combining of MBMS transmission on multiple cells.
- Supports semi-static resource allocation e.g.with a time frame of along cyclic prefix.
Downlink Shared Channel ( DL-SCH )
- Main channel for downlink data transfer. It is used by many logical channels.
- Supports Hybrid ARQ.
- Supports dynamic link adaptation by varying the modulation, coding and transmit power.
- Optionally supports broadcast in the entire cell.
- Optionally supports beam forming.
- Supports both dynamic and semi-static resource allocation.
- Supports UE discontinuous reception (DRX) to enable UE power saving.
- Supports MBMS transmission.
How Many LTE Downlink Transport Channels? How Do They Work?
In LTE, there are several downlink transport channels that play crucial roles in transmitting data between the evolved NodeB (eNB) and the User Equipment (UE). These channels are designed to carry different types of data, from user traffic to control information, ensuring efficient and reliable data transmission across the network.
Types of LTE Downlink Transport Channels
- PDSCH (Physical Downlink Shared Channel): This is the primary transport channel for user data in the downlink. It carries the payload data (such as internet browsing, video streaming, etc.) from the eNB to the UE. The data is transmitted using orthogonal frequency division multiple access (OFDMA) and is scheduled by the eNB based on resource allocation.
- PBCH (Physical Broadcast Channel): The PBCH is used for broadcasting essential system information (like cell identity, network configurations, etc.) from the eNB to all UEs within the cell. This channel is used for initial access and synchronization.
- PDCCH (Physical Downlink Control Channel): The PDCCH carries control information in the downlink, such as scheduling assignments, resource allocation, and other critical signaling. It provides the necessary instructions to the UE for accessing the data on the PDSCH or other channels.
- PHICH (Physical Hybrid-ARQ Indicator Channel): The PHICH carries feedback about the status of Hybrid Automatic Repeat Request (HARQ) processes. This indicates whether the transmitted data was successfully received or needs retransmission.
How These Downlink Transport Channels Work
- PDSCH: The eNB allocates resources to the PDSCH based on the available radio resources and the user’s data requirements. The UE receives the data transmitted over the PDSCH, and the eNB uses scheduling algorithms to ensure efficient resource allocation and data delivery.
- PBCH: The PBCH is transmitted periodically and contains essential system information, allowing the UE to synchronize with the network and access the services. It provides the necessary parameters for the UE to know about the cell it is connecting to.
- PDCCH: The PDCCH carries control messages, such as information about the resources allocated for the UE’s data transmission. The PDCCH provides instructions to the UE on how to decode and access the data on the PDSCH. It also helps the UE to perform necessary actions like power control or retransmission.
- PHICH: The PHICH informs the eNB whether the data transmission over PDSCH has been successfully received by the UE. If an error is detected, the eNB can trigger a retransmission of the lost data using HARQ.
Importance of Downlink Transport Channels
Downlink transport channels are essential for ensuring the smooth and efficient delivery of data from the eNB to the UE. Each channel serves a specific purpose, from broadcasting system information and controlling resource allocation to transmitting actual user data. These channels ensure that LTE networks can manage multiple services simultaneously while maintaining high quality and reliability for users.