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MATCHING RF CHANNEL ACCESS TO SENSITIVITY

IP.com Disclosure Number: IPCOM000005463D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 2 page(s) / 101K

Publishing Venue

Motorola

Related People

David Paldin: AUTHOR

Abstract

Initial or continued access to an RF channel for voice (or data) transmission can be accomplished through a codeword or ID exchange. This codeword may be a digital data block or it may be a tone. However, the channel sensltlvity for the codeword exchange is not necessarily the same as the channel sensitivity for the voice or data traffic, as perceived by the user. A sensitivity mismatch may cause the codeword processor to squelch an audio path even though the audio signal quality is acceptable to the user. Conversely, the codeword processor may unsquelch an audio path even though audio quality is at an unacceptable level. The codeword processor must have some flexibility and allow the designer to ad- just the codeword exchange sensitivity to a perceived audio or data transfer sensitivity.

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Technical Developments Volume 2 January 1982

MATCHING RF CHANNEL ACCESS TO SENSITIVITY

By David Paldin

   Initial or continued access to an RF channel for voice (or data) transmission can be accomplished through a codeword or ID exchange. This codeword may be a digital data block or it may be a tone. However, the channel sensltlvity for the codeword exchange is not necessarily the same as the channel sensitivity for the voice or data traffic, as perceived by the user. A sensitivity mismatch may cause the codeword processor to squelch an audio path even though the audio signal quality is acceptable to the user. Conversely, the codeword processor may unsquelch an audio path even though audio quality is at an unacceptable level. The codeword processor must have some flexibility and allow the designer to ad- just the codeword exchange sensitivity to a perceived audio or data transfer sensitivity.

   In the novel subaudible digital decoder being examined, receiver audio muting is controlled by mobile detection of a digital subaudible word. The sensitivity threshold of the digital controller must be controlled to insure the receiver does not mute until the accompanying voice is unintelligible. The stream of low speed digital data (BO, Bl,B2, . ..) is to be compared by the decoder with a known codeword (CO, Cl, C2, . ..). The codeword is kept in a codeword register (see Figure 1) and is actually compared with data samples (DO, Dl, 02, . ..) taken from the data stream. In voice traffic control, the decoder sensitivity is based on average signal strength. The effects of fading are controlled by hysteresis on recognizing loss of codeword, or by bit error correction or by adjusting codeword length. It is assumed that in this decoder the efforts made to compensate for codeword bits lost through fading, allow the decoder sensitivity to be approximately the same as audio sensitivity. The entire sensitivity range spanned by this decoder and used to match audio sensitivity is the result of the effort made to recover each individual bit. The average probab...