Scope
[OpenAirInterface Physical Layer (PHY) Specifications]

The openair PHY consists of several protocol functions which provide the interface between the MAC and PHY for allocation MAC layer PDUs to physical resources. Physical channels are used to convey signaling, data and training information across the radio medium. OpenAirInterface implements the following physical channels:

1. The PCHSCH (Physical Clusterhead Synchronization Channel) is a pilot resource reserved to a clusterhead (CH) which is responsible for delivering synchronization information to nodes in the cluster. This channel is used by nodes to acquire timing information regarding the beginning of the TTI and to perform initial frequency offset adjustments with respect to the carrier frequency of the CH. The channel is also used by adjacent clusterheads to synchronize the network, in order to facilitate inter-cluster communication under quality-of-service guarantees.
2. The PCHBCH (Physical Cluster-head Broadcast Channel) is a signaling resrouce reserved to a clusterhead which is responsible for delivering layer 2/3 protocol information to the nodes of the cluster. It can also used by the nodes in the cluster to acquire accurate timing and frequency synchronization information.
3. the PRACH (Physical Random Access Channel) is a signaling resource used by a node to provide layer 2 protocol information to its clusterhead.
4. the PCHSCH (Physical Clusterhead Synchronization Channel) is a pilot resource used by a CH to allow the UE/MR to estimate the channel of CH and to acquire timing synchronization.
5. the PSCH (Physical Synchronization Channel) is a pilot resource used by a node to allow the CH to estimate the channel of an MR/UE.
6. the PSACH (Physical Scheduled-Access Channel) is a multi-cast data resource used by a node or CH to send MAC data PDUs to one or more destinations in parallel (using multi-antenna OFDMA).
7. the PSACCH (Physical Scheduled-Access Control Channel) is a signaling resource used by a node to provide MAC protocol information to the destinations of its transmissions as well as the CH.
8. the PMRBCH (Physical Mesh Router Broadcast Channel) is a signaling resource used by a node to provide layer 2 broadcast protocol information to neighbouring nodes outside the range of clusterheads. It is used by nodes in mesh network topologies to relay network synchronization and provide initial configuration information to

Transport channels constitute the control and user plane interfaces between the MAC and PHY layers. The are used to exchange both data and measurement information and are mapped onto the above physical channels. OpenAirInterface implements the following transport channels:

1. The CHBCH (Clusterhead Broadcast Channel) is the transport channel mapped to the PCHBCH.
2. The RACH (Random-Access Channel) is the transport channel mapped to the PRACH.
3. The DL-SACH (Downlink Scheduled-Access Channel) is the transport channel mapped to the PSACH.
4. The UL/MR-SACH (Uplink or Mesh-Router Scheduled-Access Channel) is the transport channel with components mapped to both the PSACH and PSACCH.
5. The MRBCH (Mesh-Router Broadcast Channel) is the transport channel mappted to the PMRBCH.

During reception, all transport channels convey measurement information.

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