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P25 equipment can operate one voice path per 12.5kHz FDMA channel (P25 Phase I) or two voice paths per TDMA 12.5kHz channel (Phase II). Phase II is for use on P25 trunked systems traffic channels only.
P25 Phase I can be used on conventional LMR or simulcast system and is used on both Phase I and Phase II trunked systems as a control channel. Direct mode talkaround between radios can only use P25 Phase I.
Most deployed P25 systems are Phase I. Phase II systems are being deployed in the USA for 700MHz where there is a mandate to migrate to 6.25kHz equivalent channel efficiency.
Phase I and Phase II trunked systems offer very similar if not the same functionality to the user.
As Phase II utilizes a linear modulation transmission from the base station to the mobile or portable, the base stations tend to be more complex.
Common call services offered by P25 Phase I include:
Key features of P25 include:
A key feature of P25 digital audio is that the quality is preserved from high received signals all the way down to weak received signals. Compared to an FM Analogue radio system where the received audio would be noisy at the end of coverage range or weaker signals, the P25 digital audio will sound the same as it would for a strong signal. As the weak signal becomes even weaker down to the limits of the radio receiver, the audio will sharply drop off and mute. Overall compared to analogue FM, the range will be as good or slightly better, with superior received audio quality.
The P25 air interface features robust error checking and error correction, so that some bit errors can be corrected on weak radio signals and audio still received.
The main feature of P25 Phase 2 is that of improved radio spectrum efficiency. In a nutshell, the spectrum efficiency on a P25 trunked system’s traffic channels is doubled, allowing two voice and/or data circuits per 12.5kHz radio carrier.
P25 Phase 1 systems use Frequency Division Multiple Access (FDMA) for the air interface, and each channel occupies a 12.5kHz bandwidth for a single voice or data user. (The air interface is the radio transmission between the base station and terminals).
P25 phase 2 employs a Time Division Multiple Access (TDMA) air interface for P25 so that two voice or data transmissions can occupy the same bandwidth as one channel in a 12.5kHz system.
A P25 trunked system uses a control channel, where radio terminals will register and wait for call activity or request a call setup amongst other things.
A P25 Phase 2 trunked system uses a P25 Phase 1 FDMA control channel, so all radio terminals must register to the trunked system using FDMA. This is required for backward compatibility with P25 Phase 1 terminals. When a Phase 2 terminal initiates a call on the Phase 2 trunked system, a Phase 2 TDMA traffic channel is allocated for the voice or data call. When a Phase 1 terminal sets up call on a Phase 2 system, a Phase 1 FDMA channel will be allocated for the voice or data call.
When a Phase 2 terminal radio communicates directly with another Phase 2 terminal, it switches back to FDMA or Phase 1 mode.
Conventional (non-trunked) P25 systems such as voted systems use Phase 1 FDMA for the air interface, as there is no TIA definition for the operation of Phase 2 TDMA in conventional P25.
P25 Phase 2 is attractive where frequency spectrum is scarce or where more channels can be utilised from the same allocated spectrum on a trunked system. Phase 2 does not offer any significant additional features or functions when compared with Phase 1 from the radio user's perspective.
Users who work in a mixture of analogue and digital environments can take full advantage of Simoco’s unique Xmode multimode operation which supports: P25 Trunked, P25 Conventional as well as fully operating in existing PMR and MPT1327 trunked analogue modes/
The various operating modes can be added on step by step without replacing the terminals, this is perfect for users who work in a mixture of analogue and digital environments and require a digital migration path. Terminals can be sold as; P25 Upgradable, P25 Ready or P25 enabled, allowing government agencies the ultimate flexibility today, while future proofing their communication investment for tomorrow.
Simoco is committed to developing its P25 product portfolio incorporating the next generation Phase II developments including TDMA. Utilising the enhanced P25 vocoder (AMBE+2) for improved performance in the presence of noise, Simoco P25 Phase II terminals pack two voice paths in one 12.5 kHz radio channel for the most efficient use of radio spectrum.
The compact, ruggedized design of the Simoco Portable range makes them the perfect handheld radios for mission critical users in the most demanding environments.
Simoco’s industry proven SRM is the ideal, robust mobile solution. With over 15 years of development, the SRMs have evolved to address the needs of the emergency service markets with a high level of functionality and customisation.
Simoco’s P25 simulcast base stations and infrastructure feature an easy to deploy compact 2RU design backed by Simoco’s industry-leading distributed architecture over IP, resulting in an easy to deploy, resilient range of base stations, perfect for a wide range of applications.
Simoco has a wealth of experience in the P25 market, recent projects include:
Department of Foreign Affairs & Trade (DFAT)
Simoco won the tender for the supply of the emergency radio network for the Australian Department of Foreign Affairs & Trade (DFAT) based in Canberra.
The contract involves the supply of radio infrastructure to over 50 embassies worldwide, located in some of the world’s most volatile environments. As a result of this, the installation of the radio infrastructure is a critical component for embassy staff if involved in any major international incidents.
A specific requirement for DFAT was the design of a secure network for each post and Simoco P25 architecture was selected as the appropriate technology to provide adequate security for their individual and complex requirements.
Victoria State Emergency Services
Simoco won a competitive tender to supply a communications solution to Victoria State Emergency Service (VICSES) and worked closely with the voluntary organisation to fully understand their needs and requirements.
The company then tailored a radio communications system that would support the challenging and varied work of VICSES, while keeping all operational information secure.
The new Simoco two-way radio solution enables a system of cross-band and cross-protocol fixed mobile repeaters, allows VICSES to utilise their existing UHF analogue portables to communicate across the Telstra network via any nearby In-Vehicle Repeater, enhancing performance and security.