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A METHOD OF PL SIGNALING FOR ANALOG SIMULCAST SYSTEMS USING AN ALL DIGITAL INFRASTRUCTURE

IP.com Disclosure Number: IPCOM000008534D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2002-Jun-20
Document File: 4 page(s) / 149K

Publishing Venue

Motorola

Related People

Phillip C. Hargrave: AUTHOR

Abstract

A method was developed to allow PL tone synchronization in a simulcast system that consists of packetized analog transport. The method adds phase information to the analog packets to the PL tone can be synthesized by the transmitter and summed with the analog before transmission.

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MOTOROLA Technical Developments

A METHOD OF PL SIGNALING FOR ANALOG SIMULCAST SYSTEMS USING AN ALL DIGITAL INFRASTRUCTURE

by Phillip C. Hargrave

ABSTRACT

  A method was developed to allow PL tone synchronization in a simulcast system that consists of packetized analog transport. The method adds phase information to the analog packets to the PL tone can be synthesized by the transmitter and summed with the analog before transmission.

PROBLEM

  In analog simulcast systems, it has traditionally been an expensive proposal to perform PL due to the necessary equipment to achieve the required bandwidth below 300 Hz. (See Figure I). Additionally, the advent of digital infrastructures has provided a relatively cheap mechanism for the transportation of audio between entities. This has proven very useful for digital simulcast systems. However, the audio compression algorithms typically used in digital infrastructures are similarly bandwidth limited such that PL tones cannot be transported. Therefore, the need exists for a method which allows analog simulcast systems to incorpo- rate PL signaling using digital infrastmctures.

PROPOSAL

  The difftculty in PL signaling in a digital infra- strucure revolves around the vocoders lack of response below 300 Hz and the need to maintain phase synchronization of the PL tone across multi- ple simultaneous transmitters. The phase must be maintained for link outages that occur during a call and across call boundaries. (See Figure 2.)

  A method for providing the synchronization is proposed that meets the above stated goals. Analog voice packets are sent from the simulcast central controller to the transmiter. The packets contain GPS based launch times. When the transmitter gets the analog voice packet over the infrastructure it notes the launch time and de-vocodes the voice pack back into base band audio. It then waits until the launch time and transmits the first sample of audio at the launch time. This works well except when the vocoder does not have any response below 300 Hz. To get around this, in the analog voice packet, a PL frequency and PL phase angle are added along with the current GPS simulcast launch time. This informs the transmiter where along the PL sine wave it should start generating and summing the PL tone for the current packet of voice. (See Figure 3). The phase information can be in any form. Pha...