dPMR446

This is dPMR in its simplest form, a peer to peer only operation without base stations or repeaters. As this equipment operates under licence-free status it has to follow similar limitations as for the analogue equivalent PMR446.
These limitations are that RF power is limited to 0,5 watt and only handheld equipment is permitted. The frequency allocation is just above that used by PMR446 and operates on 446,100 to 446,200 MHz. Naturally, because of the 6,25 kHz channeling, dPMR446 offers double the number or channels as PMR446.

dPMR446 equipment is capable of both voice and data modes of operation using a simplified addressing system that can be considered analogous with CTCSS use in PMR446 or with an extended addressing system as used by the fully functional TS102 658 type dPMR radios.

As well as offering voice and data, dPMR446 protocol also supports combined voice+data so it is possible to embed data into a voice call or automatically append it at the end of a call. This means that dPMR446 can offer all the usual voice services plus text messaging (SMS), status information texts, embedded data such as GPS position etc.

dPMR Mode 1

This is the peer to peer mode of dPMR (without repeaters or infrastructure) but without the limitations of the licence-free counterpart. It can operate all typical licenced PMR frequency bands and without the RF power limits of dPMR446.
As well as offering voice and data, dPMR446 Mode 1 also supports combined voice+data so it is possible to embed data into a voice call or automatically append it at the end of a call.

dPMR Mode 1 can be considered as an advanced version of dPMR446. Certainly by programming a dPMR Mode 1 radio with the same frequencies and colour codes and address mode as a dPMR446 radio it would be possible for the two radios to communicate.

Just as for dPMR446, the dPMR Mode 1 protocol also supports combined voice+data so it is possible to embed data into a voice call or automatically append it at the end of a call. This means that dPMR446 can offer all the usual voice services plus text messaging (SMS), status information texts, embedded data such as GPS position etc.

The removal of licence-free limitations means that dPMR Mode 1 can also offer such functions as priority and emergency calls and break-in.

dPMR Mode 2

In the dPMR Mode 2 level of functionality, repeaters and infrastructure are added. This brings extra functionality such as network interfaces which can be IP based or simply analogue. Coverage areas are greatly increased, even more so when multiple repeaters are used. Such multiple repeaters can be managed by dynamic channel selection or they can be co-channel wide area using that specific function from the dPMR Mode 2 protocol.

Again, dPMR Mode 2 can offer all the basic functions of the Mode 1 protocol with the extra benefit of being able to interface beyond the wireless part of the network. IP connectivity will permit user groups to include PC based terminals from other offices, areas or even countries. The same interface could provide remote control of a base station or repeater from a fixed connection.

dPMR Mode 3

dPMR Mode 3 is the final step where all the possible functionality of the protocol is available. Mode 3 can offer multichannel, multisite radio networks that are fully managed by specific beacon channels at each radio site. This ensures optimum use of spectrum and optimum density of radio traffic.

Management of the radio network starts from the authentication of radios that wish to connect. Calls are set-up by the infrastructure when both parties have responded to the call request ensuring optimum use of the radio resource. Calls may be diverted to other radios, landline numbers or even IP addresses. The infrastructure managing these beacon channels would be capable to placing a call to another radio whether that radio is using the same site or another site within the network.

As the allocation of communication channels is made dynamically, the system can further optimise traffic by dynamically modifying permitted call times. Radios that fail authentication can be blocked, either temporarily or permanently. The system will allow radios with the authority to make priority or emergency calls to pre-empt the use of channels from users making non-priority calls. Where call requests exceed capacity, these calls can be queued by the system until resources become available.

All the services and functions available in Mode 1 and 2 are possible with a few exceptions as well as several extra functions implemented by the beacon channel infrastructure.

Without getting too technical, the basic difference between FDMA (Frequency Divided Multiple Access) and TDMA (Time Divided Multiple Access) is the definition of a channel and how it is used (accessed). In FDMA a particular bandwidth (E.g. 6.25kHz) at a particular frequency (E.g. 150.000MHz) is used to define a channel. Basically, the way channels have been allocated for decades. In TDMA, the same principle applies regarding bandwidth and frequency, but the signal is divided into time slots that allow the channel to have 'extra' capacity in the same bandwidth E.g. Two 6.25kHz 'equivalent' channels in a 12.5kHz channel. See the diagram below for a graphical explanation.

Until now, TDMA was more spectrum efficient at wider channel spacing's like 25kHz, as for example, two or three users could access the same bandwidth as one FDMA channel user. However, in the case of the newly developed narrowband 6.25kHz FDMA technology like dPMR, both this and 2-slot 12.5kHz TDMA technology achieve the same result as far as spectrum efficiency is concerned.

Both TDMA and FDMA technologies achieve the same 6.25kHz narrowband capability via different methods. The difference is that the FDMA system is a 'true' 6.25kHz channel and the TDMA system provides 6.25kHz channel 'equivalence' via the time slots in 12.5kHz band-width. From the perspective that 12.5kHz is considered the current narrowband standard channel spacing, then both systems achieve so called "double capacity". The difference is that the FDMA system is ALWAYS double capacity whether it is used with or without infrastructure. For TDMA, double capacity is ONLY achieved when a repeater is synchronizing the time slots, and that two users are in the same geo-graphical area, accessing the same repeater at the same time.

Click on the thumbnail below for spectrum usage diagrams.

In theory, in identical conditions, the narrower channel width of the FDMA system would allow the signal to achieve better coverage than the12.5kHz TDMA (or FDMA) system when transmitted at the same output power. This is because the noise floor of any receiver is proportional to the filter bandwidth, therefore the smaller the bandwidth the smaller the signals that can be received. In real world use, various factors such as topography, antenna height of base stations and surrounding buildings etc. all affect coverage, so without specific comparison tests, either system cannot claim to be better than the other. What can be said is that when compared to an analog FM signal, digital easily out-performs analog at the fringes of the communication range, thus providing more reliable audio over a greater total area, even if the coverage footprint is the same as analog FM. Click on the Thumbnail below for a coverage diagram

The manufacturer of a competing TDMA system claims 40% improved battery life in digital mode as the radio is transmitting only half the time (Ie. one time slot). While only market feedback will prove this true or false, to date, we have not been able to find any figures on actual transmit power consumption in public literature to make any accurate judgments on this claim. As such, the user cannot calculate if there really is any improvement in digital mode battery life. As explained in “Coverage”, in the FDMA system, reduced noise components with the narrower channel bandwidth improves receiver sensitivity. Therefore, it could be possible to transmit at reduced power, which in turn conserves battery life and thus can prolong radio use time.