Effective as of January 2021, all new radios added to ALMR must be TDMA capable/enabled.  NOTE:  Additionally, no previously approved models currently authorized to operate on ALMR will be added if they are not TDMA capable.

An exciting new capability will be coming to ALMR with the GTR upgrade project that will help bring additional capacity to ALMR sites across the state.  As part of this upgrade, sites will transition from Phase 1 frequency-division multiple access (FDMA) to Phase 2 time-division multiple access (TDMA).

Member organizations are reminded, it will be necessary to reprogram TDMA-enabled radios, update firmware (referred to as “flashing”), and program TDMA-capable radios currently operating on the system.  Additionally, agencies should already be planning for the eventual life-cycle replacement of non-TDMA capable radios in the next three to five years.

Some of the features include:

P25 Phase II TDMA and Dynamic Dual Mode (DDM) at all State of Alaska sites.  The DDM feature allows a single channel to either operate in FDMA or TDMA mode depending on the affiliated talkgroup and user radio capabilities.  Dynamic Transcoding is also included, which enables efficient communication between FDMA and TDMA sites without downgrading the channel to its lowest common denominator, FDMA.  Although the included P25 infrastructure will support TDMA, to function it will also require TDMA subscribers.

With Dynamic Dual Mode (DDM), the voice channel is capable of either FDMA or TDMA, and the system will smart select based on the users on that talkgroup.  For DDM capable RF sites and subsystems, the system determines which mode is used to assign calls over-the-air in a dynamic manner.  The P25 site control channel and IV&D data continues to operate in FDMA mode.  From an end user perspective, FDMA and TDMA calls will operate the same.

Dynamic Dual Mode offers several advantages with the implementation of Phase 2 TDMA software:

  • Provides flexible migration to Phase 2 TDMA with support for both Phase 1 and Phase 2 TDMA user radios.
  • Ensures continued compatibility with neighboring Phase 1 systems and sites.
  • Minimizes system resources – other systems partition channels for exclusive operation in either the Phase 1 or Phase 2 mode which increases the number of base stations and frequencies necessary to operate the system effectively.

Dynamic Transcoding enables communication between FDMA and TDMA.  Because the call type is determined on a site-by-site basis, more sites can operate in TDMA – even in a mixed fleet of FDMA and TDMA radios.  This means you get a more efficient use of channels and frequencies, and all sites and radios can participate in a call regardless of the originating call type.  Dynamic transcoders reside in each zone core, translating between FDMA and TDMA audio formats.  Each site operates in the best mode based on the channel resources available and capabilities of the radios at that site.  Radio users communicate without a console patch or the need to downgrade the call.  Radio users from TDMA and FDMA-only sites are able to join a Dynamic Talkgroup without changing the call type at either site.

If all TDMA resources at a site are busy, the call can still go through because ASTRO 25 with transcoding will switch the call at that site to available FDMA resources, rather than wait for TDMA resources at that site to free up.  When TDMA resources are freed up, subsequent calls will switch back to TDMA at that site, so you gain higher efficiencies.

TDMA Transition Checklist for Members

TDMA Transition Plan/Policy



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