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2010 Edition, March 2010

Complete Document

Project 25 Two-Slot TDMA Overview

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Description / Abstract:

Scope of the P25 Two-Slot TDMA Standard

This document describes the P25 Phase 2 Two-Slot TDMA Standard in a general way. The P25 Phase 2 Two-Slot TDMA Standard is a suite of P25 standards documents. The high level technical scope of the P25 Two-Slot TDMA Standard includes the following major items.

• Interface Description of the Um2 interface designated for the P25 Phase 2 TDMA Two-Slot CAI.

• TDMA CAI for Two-Slots operating at a gross bit rate of 12 kb/s with Harmonized-Continuous Phase Modulation (H-CPM) for the inbound link and Harmonized-Differential Quadratrure Phase Shift Keying (H-DQPSK) modulation for the outbound link. The P25 Two-Slot TDMA CAI is divided into a Physical layer (PHY) and a Media Access Control layer (MAC) to facilitate TDMA operation.

• Dual Rate Vocoder at a gross bit rate of 7.2 kb/s for the full rate for use with Phase 1 and 3.6 kb/s for the half rate for use with Phase 2.

• Trunking control signals using MAC Protocol Data Units (PDUs).

o The MAC PDUs are compatible with Phase 1 addressing and trunking functions.

o The Phase 1 trunking control channel also has additions to address TDMA calls and control TDMA operation for ease of migration.

• Encryption for voice messages uses the Message Indicator (MI), Key ID (KID), and Algorithm ID (ALGID) combined into an Encryption Sync Signal (ESS) that is compatible with the definitions used in Phase 1.

• Use of FDMA for Phase 1 trunking interoperability and direct mode (talkaround).

• Standardized signaling allowing optional synchronization of FDMA Control Channel (CCH) and TDMA Traffic Channel (TCH) for better access time.

Future work:

• Harmonized-Differential 8 Phase Shift Keying (H-D8PSK) modulation for downlink for improved simulcast delay spread.

• Slotted control channel:

o Single slot TDMA CCH (either one of the Two-Slots running CCH protocol) – allows control and voice on a single RF channel.

o Composite Control Channel (dynamically running one or no slots with CCH protocol) – allows voice operations on both slots of a single RF channel implementation.

o Full TDMA CCH where both slots run the CCH protocol.

• Slotted data channel for OTAR or other data applications.

• Scrambling of the TDMA CCH and the Data Channel (DCH).

• Development of a vehicular repeater tp support TDMA.

• Development of a P25 Four-Slot TDMA Standard, including specification of P25 defined Four-Slot TDMA protocols for a P25 Four-Slot TDMA CCH, TCH, and DCH.