In the context of Long-Term Evolution (LTE) networks, an "LTE channel" refers to the distinct communication pathways used for transmitting data and control information between the user equipment (such as your smartphone) and the network (the eNodeB or base station). These channels are fundamental to how information flows through the LTE protocol stack, facilitating communication between different layers.
Based on the reference provided, a key concept is that there are three different channel types defined in LTE - logical channels, transport channels, and physical channels, each associated with a service access point (SAP) between different layers. These channels are used by the lower layers of the protocol stack to provide services to the higher layers.
Understanding these channel types is crucial to grasping how LTE efficiently manages data and control signals. They represent different levels of abstraction in the communication process.
The Three Pillars of LTE Channels
LTE defines a layered architecture for its communication protocols. The channels provide the interfaces between these layers.
h3>1. Logical Channels
Logical channels are defined by the MAC (Medium Access Control) layer and specify what type of information is being transferred. They represent the services offered by the MAC layer to the Radio Link Control (RLC) layer.
- Examples:
- Dedicated Traffic Channel (DTCH): Used for transmitting user plane data (your actual data traffic).
- Dedicated Control Channel (DCCH): Used for transmitting control plane information for a specific user equipment (e.g., connection setup, mobility information).
- Broadcast Control Channel (BCCH): Carries system information broadcast to all UEs in a cell.
- Paging Control Channel (PCCH): Used for paging UEs when the network needs to reach them.
2. Transport Channels
Transport channels are defined by the physical layer and describe how the information is transferred over the radio interface. They are the interface between the MAC layer and the Physical layer.
- Characteristics: They are characterized by how the data is transported, including aspects like transport block size, modulation, coding, and HARQ (Hybrid Automatic Repeat Request) information.
- Examples:
- Downlink Shared Channel (DL-SCH): Used for most downlink data and control information, supporting dynamic scheduling and HARQ.
- Uplink Shared Channel (UL-SCH): Used for most uplink data and control information, also supporting dynamic scheduling and HARQ.
- Broadcast Channel (BCH): Carries the Master Information Block (MIB).
- Paging Channel (PCH): Carries paging information.
- Random Access Channel (RACH): Used by UEs to initiate communication with the network.
3. Physical Channels
Physical channels are defined by the physical layer and correspond to specific sets of resource elements (time-frequency resources) on the radio interface over which the transport channels (or control information directly from the physical layer) are mapped. They are the actual signals transmitted over the air.
- Mapping: Transport channels are mapped onto physical channels for transmission.
- Examples:
- Physical Downlink Shared Channel (PDSCH): Carries the DL-SCH and PCH transport channels.
- Physical Uplink Shared Channel (PUSCH): Carries the UL-SCH and RACH transport channels.
- Physical Downlink Control Channel (PDCCH): Carries downlink scheduling assignments and uplink grant information.
- Physical Broadcast Channel (PBCH): Carries the BCH transport channel.
- Physical Uplink Control Channel (PUCCH): Carries uplink control information (like HARQ feedback, Channel State Information).
- Synchronization Signals (PSS/SSS): Used by UEs for cell search and synchronization.
These three channel types work in concert, passing data and control information down through the protocol layers for transmission and up through the layers upon reception, ensuring efficient and reliable communication in the LTE network.
