Browse Prior Art Database

System for Increased Trunked Frequency Usage Efficiency

IP.com Disclosure Number: IPCOM000126858D
Original Publication Date: 2005-Aug-03
Included in the Prior Art Database: 2005-Aug-03
Document File: 6 page(s) / 103K

Publishing Venue

Motorola

Related People

John Gilbert: AUTHOR

Abstract

Lack of radio frequency channel capacity within trunked radio systems is often a problem for radio system designers. In many urban areas, additional radio channels are simply not available. Radio system designers would like every possible opportunity to maximize the efficient use of the radio channels that are available to them.

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System for Increased Trunked Frequency Usage Efficiency

By John Gilbert

Background

Lack of radio frequency channel capacity within trunked radio systems is often a problem for radio system designers. In many urban areas, additional radio channels are simply not available.  Radio system designers would like every possible opportunity to maximize the efficient use of the radio channels that are available to them.

Problem

Radio talkgroup calls within a SmartZone (SZ) trunked radio system typically include multiple sites. A single talkgroup call might involve three or more sites, depending on where receiving radios are located. Sites within land mobile trunking systems have historically assigned radio channels as pairs of transmit and receive frequencies. When a call is made within a SZ system with four affiliated sites, 8 individual frequencies would be assigned (F1, F2, F3, F4, F5, F6, F7, F8 as seen in figure 1.). Of these 8 frequencies, only 5 (F1, F2, F3, F5, F7 in our example). are actually active during any single radio transmission. The four base to mobile frequencies (F1, F3, F5, F7). are needed, as is the single mobile to base frequency (F2) for the radio sourcing the audio. The base receive frequencies at the sites where no subscriber to base audio is being received at the moment are not actually used (F4, F6, F8) during the single radio transmission. If we could free these three channels for the use of the system with other base to mobile calls, we could increase overall site capacity. The capacity increase becomes greater as the number of participating sites in the call increases. 

Fig 1. Current Operation: Multisite Call with four radio sites busies 8 separate frequencies

Solution

When paired channels are no longer required in the system design, additional calls can be made using previously idle frequencies (F4, F6, F8, in our example) located at sites that are not sourcing audio (site 2, site 3 and site 4) for the call. In our example of figure two, frequencies F4, F6, and F8 would be available for assignment to other calls.

This improved channel assignment method allows higher channel utilization at destination sites and will allow calls to be granted that would previously have been busied due to lack of assignable channels at sites 2, 3 and 4. Figure 2 shows frequencies previously used only for inbound communication (F4, F6, F8) being used for additional outbound talkgroup calls.

Fig 2.    New Operation: Multisite call with four radio sites busies only 5 frequencies.

Three additional frequencies are available for other calls.

Base station configuration at the site on the old "inbound" receive frequencies (F4, F6, F8, in our example) would need to be changed so that the base station is now also able to transmit as well as receive on these frequencies. In order to do this, RF filtering, RF switching and possibly additional antennas would be required to segregate a portion of the inbound frequency spectrum to be used for outbou...