1xBTS 1xBTS

Channels & Acquisition

An HRPD sector runs a continuous forward link that a device acquires and reads before it can use the carrier, and a reverse link the device uses to reach the network and carry user data back. This page covers both, plus how the sector decides who gets each forward slot.

An HRPD sector continuously transmits forward-link pilot, MAC bursts, and Control Channel capsules. The Control Channel carries the information a device needs to decide whether it can use the sector:

  • Sync gives timing and the sector PN.
  • QuickConfig gives fast-changing sector indicators such as color code and active forward-traffic MAC state.
  • SectorParameters gives the sector ID, subnet mask, channel list, and neighbor information.
  • AccessParameters tells the device how to use the reverse Access Channel.
  • BroadcastReverseRateLimit advertises reverse-rate limits for active MAC indexes.

The HRPD forward slot is 2048 chips, about 1.667 ms. A Control Channel cycle is 256 slots. 1xBTS follows that structure when it builds HRPD overhead and directed control messages for Rev 0 and Rev A devices.

The reverse link starts with the Access Channel, which a device uses to make first contact with the sector — for example to request a session or open a connection. AccessParameters on the forward Control Channel tells the device how to use it.

Once a traffic connection is up, the device transmits a Reverse Traffic Channel that carries several pieces at once: a reverse pilot, the RRI (Reverse Rate Indicator), the DRC the device is requesting, an ACK channel for forward H-ARQ feedback, and the reverse data itself. The AN decodes pilot, RRI, DRC, ACK, and data, then feeds signaling and packet bytes back into the AN session logic.

Forward scheduling

HRPD does not assign a fixed-rate forward channel to a device. Instead the sector schedules forward packets slot by slot. On the reverse link the AT continuously reports a DRC value — the forward rate it can currently receive. The scheduler picks a matching physical packet size and transmits on the Forward Traffic Channel, using H-ARQ feedback from the AT’s reverse ACK channel to confirm or retransmit. This is what lets the sector spend each slot on the device that can use it best.

See also