Browse Prior Art Database

FAST SIGNAL QUALITY VOLER

IP.com Disclosure Number: IPCOM000005687D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2001-Oct-26
Document File: 2 page(s) / 116K

Publishing Venue

Motorola

Related People

Brian K. Johnson: AUTHOR [+2]

Abstract

This article relates to a multi-user low power communication system in which a plurality of remote receivers are used to relay information from portable transceivers. Since even the low power signals may be detected by more than one remote receiver, a voting protocol has been establishe'd.

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MOlYlROLA Technical Developments October 1987

FAST SIGNAL QUALITY VOLER

by Brian K. Johnson and Stelios Patsiokas

   This article relates to a multi-user low power communication system in which a plurality of remote receivers are used to relay information from portable transceivers. Since even the low power signals may be detected by more than one remote receiver, a voting protocol has been establishe'd.

   A known voting controller device selects the best quality audio signal from a number of remote receivers, which are positioned in different locations. It includes a number of quality modules, each of which deals with the audio signal from one remote receiver. When the remote receiver is squelched, it sends a 2175 Hz signal over the audio path to the controller which recognizes this specific frequency. The corresponding audio quality module indicates to the controller that it is receiving no audio and should not be selected.

   When a remote receiver is unsquelched, its audio signal is processed by its respective quality module and the noise present in the speech silent periods is sampled. The controller selects the signal which has the lowest level of this background noise, and connects only this audio signal to the controller interconnection line. Thus best quality signal is interpreted by the controller to be the signal with the lowest noise content. The various levels have to be very carefully set at each receiver to ensure equal levels of signal at the quality modules, with standard modulation, otherwise the controller may inadvertently choose the lowest signal which may not be the best quality signal.

   Due to the random nature of noise, the controller has to average the noise over a period of about 200 msec in order to make a choice This delay may.be a problem for onsite distributed systems having portable transceivers and a plurality of receivers, since it can cause miss steering of the transmitter in the next remote site and thus degrade the quality of the signal ultimately received by the portable transceiver.

   Figure 1 shows the difference between the new voter system and the prior art. In this new voter, each remote receiver must have an RSSI (received signal strength indicator). This is asignal voltage that varies in proportion to the power in dBm (log.) of the received RF signal. This output is available on many Motorola IC's which can be designed into the remote receiver. The RSSI output voltage is connected to the control port of a voltage-to- frequency converter. This device generates a sinusoidal output, with a frequency which is proportional to the voltage on its control port. By adjusting the gain and DC offset in the RSSI signal path to the...