2 Single site conventional PLMR system – A single-site system is defined as one site with a fixed base transmitter(s)/repeater(s) – no automated processing of calls. – Two frequencies (one pair) are required per repeater. Many administrations around the world have mandated that PLMR applicants use DLMR systems when applying for new authorizing or renewing existing ones. In addition, digital private land mobile radios many advantages over analog, including improved voice quality with greater coverage, better privacy, better battery life and more. In a normal analog radio, every sound that’s picked up by the microphone is transmitted. If there’s a lot of background noise, it can be very difficult to understand the message. Digital technology uses software that focuses purely on voice or data, paying no attention to the machine clatter or the crowd noise around the users. The result is exceptional voice clarity. Radio interference creates static on an analog radio and makes the conversation less intelligible. Voice gets garbled and the message must be repeated. Because a digital radio has automatic error correction, it rebuilds voice sounds and maintains the clarity of the voice, even if a signal is badly corrupted. And since speech is digitally-encoded, the users benefit from smarter capabilities, such as advanced software algorithms that can deliver clear voice in the most extreme conditions. See Figure 3 below. Editor´s note: To be enhanced and Complemented 3 Conceptual diagram showing improvements in audio quality with digital PLMR 4 General technical and operational considerations In cases where existing analog PLMR systems are upgraded to digital PLMR using existing channel arrangements the technical and operational considerations for digital PLMR are similar to that for analog PLMR. The same channel assignment plan may be used as the frequency separation for multiple transmitters located at a site is the same. A more efficient of the existing PLMR spectrums could be achieved with the systematic utilization of 12.5 kHz and 6.25 kHz channel spacing together with digital modulation. The use of 12.5 or 6.25 kHz channels with digital technologies can provide up to 4 times the capacity compared with traditional 25 kHz system. With the same infrastructure, digital PLMR can work as robustly and stable as analogue PLMR systems but provides additional useful features as well as better communication quality. Interference between analogue systems is the same situation as
network. Tables 1a and 1b below provide an example of an assignment criteria based on the number of mobile/portable terminals and the annual spectrum fees. Assignment criteria based on number of mobile/portable terminals. Type of PLMR system Minimum number of portable radios Maximum permitted transmit power Type of frequency assignment Single Frequency 5 1 Watt ERP Shared frequency Single Frequency 30 5 Watts ERP Shared frequency Two Frequency 50 25 Watts ERP Exclusive frequency Spectrum fee for Private PLMR Category of frequency usage Frequency band Occupied bandwidth per frequency Fee per frequency per year. Frequency used on an exclusive basis All PLMR frequency bands ≤ 25 kHz 400 units Frequency used on a shared basis All PLMR frequency bands ≤ 25 kHz 300 units 2 Assignment criteria based on light regulation for shared frequencies and based on area of coverage and popularity of frequency band for exclusive frequencies. In this example, the licensing of shared frequencies is lightly regulated. It consists of two types: a) Simple licence: 15 frequencies are shared by licensees hand-portable radios only. b) Simple site licence: The operation of a base station is permitted and a pool of frequencies is shared among licensees. A summary of the simple licensing is given in Table 2a. Simple licence using shared frequencies Type of PLMR system Frequencies Maximum transmit power of devices Licence criteria Licence fee Simple licence 15 shared 5 Watts ERP Licensee must with other Simple licences. Base station use not permitted 75 for 5 years Simple Site A pool of frequencies 2 Watts ERP for mobile station and base station Licensee must with other Simple Site licences. 75 units for 5 years