The Concept of Reference Carrier in iDX 3.2

The concept of a Reference Carrier was introduced in iDX Release 3.2 to account for per-carrier differences in transmit power required for remote acquisition bursts. The Reference Carrier is defined in iBuilder on the Remote Information tab and includes the following parameters:

  • Symbol Rate
  • MODCOD
  • TDMA Initial Power
  • Spreading Factor
  • Payload Size

The TDMA Initial Power is configured in relation to the remaining Reference Carrier parameters. The correct setting for the TDMA Initial Power is typically determined during remote commissioning. The TDMA Initial Power determines the transmit power of the remote’s acquisition bursts.

A remote that has not yet acquired the network is continuously assigned acquisition slots on upstream carriers until the hub line card receives an acquisition burst from the remote in an assigned slot. The upstream carrier on which the remote is invited to transmit an acquisition burst can change at any time. It is important that all bursts on a given carrier (including acquisition bursts) are received by the hub line card at a similar Carrier to Noise ratio (C/N). For in-network remotes, the Uplink Control Process (UCP) at the hub regulates the transmit powers of each remote’s traffic bursts such that all bursts are received within the optimal C/N range. However, UCP is not active for remotes transmitting acquisition bursts. Therefore, the system relies on the configured TDMA Initial Power to set the correct transmit power for acquisition bursts.

Prior to Adaptive TDMA, all carriers in an Inroute Group had the same symbol rate, MODCOD, and Spreading Factor. In those earlier releases, the TDMA Initial Power was the absolute IF power at which the remote transmitted all acquisition bursts. Beginning with iDX Release 3.2, the symbol rate, MODCOD and Spreading Factor may vary among upstream carriers in the same Inroute Group. In an Inroute Group containing a mix of upstream carrier configurations, transmitting acquisition bursts at the same power on all carriers is not sufficient to ensure the correct C/N of the received burst. If the transmit power of the acquisition bursts were held constant for all carriers, the C/N of the received burst would vary depending on the carrier definition. This variation in C/N could make it difficult for the remote to join the network; cause interference; violate satellite power limits; or skew the UCP algorithm running at the hub.

The Reference Carrier was introduced to address this problem. In iDX Release 3.2, the TDMA Initial Power only represents the absolute IF power at which the remote transmits acquisition bursts when the assigned upstream carrier matches the configured Reference Carrier. When the remote transmits an acquisition burst on a carrier that does not match the Reference Carrier, the remote adjusts the power of the burst so that it is received by the hub line card at the correct C/N regardless of the carrier definition.

When a network is upgraded from an earlier release to a release that supports Adaptive TDMA, the Reference Carrier parameters (including the TDMA Initial Power) are automatically configured to match the TDMA carriers that were defined for the remote’s Inroute Group in the earlier release. This allows the remote to operate with the new release without re-commissioning. Note that there is no requirement that the configured Reference Carrier parameters match the configuration of an actual carrier in the Inroute Group. However, when commissioning a new remote, iDirect recommends setting the Reference Carrier parameters to match the remote’s expected clear sky carrier.

Because of the reduced operating power margins in an Adaptive network it is important to correctly set each remote’s TDMA initial power. For a description of the Adaptive TDMA feature, see the Technical Reference Guide.

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