Digital FM audio processing in a dual-mode communication system

• US 6,246,885 B1
• Filed: 06/11/1998
• Issued: 06/12/2001
• Est. Priority Date: 01/31/1996
• Status: Expired due to Fees

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Lee, Way-Shing, Chang, Henry, Singh, Randeep, Black, Peter J.
• Primary Examiner(s): Urban, Edward F.
• Application Number:
  US09/095,859
• Time in Patent Office: 1,097 Days
• Field of Search: 455/550, 455/552, 455/553, 455/575, 455/34, 455/84, 455/561, 704/200, 704/201, 704/226, 704/227
• US Class Current: 455/553.1
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes
• CPC Class Codes: H04W 28/06 Optimizing the usage of the radio link, e.g. header compression, information sizing , discarding information system modifying transmission characteristic according to link quality by modifying frame length H04L1/0007; dynamic adaptation of the packet size for flow control or congestion control H04L47/365
• CPC Class Codes: H04W 4/18 Information format or content conversion, e.g. adaptation by the network of the transmitted or received information for the purpose of wireless delivery to users or terminals
• CPC Class Codes: H04W 88/06 adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals
• CPC Class Codes: H04W 88/08 Access point devices

Abstract

A novel and improved digital FM audio processor for use in a dual-mode communication system selectively operative in either FM or code division multiple access (CDMA) modes. Analog voice or voice-band data is input to a speech encoder/decoder (CODEC) which converts the analog signal to a digital signal. The digital FM signal is read from the CODEC, filtered, compressed, up-sampled and combined with a transponded SAT signal and then modulated for RF transmission. On the receive side, the FM analog signal is received, demodulated, down-sampled, expanded, and filtered before being converted to the proper format (μ-law, a-law, or linear) for the speech CODEC. The CODEC then converts the digital FM audio signal into an analog waveform for conversion to sound. By performing the FM audio processing digitally, the same digital signal processing (DSP) firmware may integrated on the same application specific integrated circuit (ASIC) which is capable of performing audio processing of both FM and CDMA audio signals.

Claims

1. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode, wherein said transmit audio processor comprises;

a compressor for digitally compressing said audio-band transmit signal, wherein said compressor comprises;

an absolute value calculator for generating an absolute energy value signal in response to measuring an absolute energy value of said audio-band transmit signal;

a digital filter, coupled to said absolute value calculator, for filtering said measured absolute energy value signal; and

a divider, coupled to said absolute value calculator and said digital filter, for dividing said audio-band transmit signal by said digitally filtered, measured absolute energy value signal;

a summer for digitally combining said compressed audio-band transmit signal with said regenerated supervisory audio tone

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode; and

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone.

2. The digital signal processor of claim 1 wherein compressor further comprises:

an interpolator, coupled to an input of said absolute value calculator, for increasing a data rate of said audio-band transmit signal; and

a decimator, coupled to an output of said absolute value calculator, for decreasing a data rate of said measured absolute energy value signal.

3. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode, wherein said transmit audio processor comprises;

a compressor for digitally compressing said audio-band transmit signal;

a summer for digitally combining said compressed audio-band transmit signal with said regenerated supervisory audio tone; and

an interpolator coupled to said compressor and said summer and interposed therebetween, said interpolator for increasing a data rate of said compressed audio-band transmit signal, wherein said interpolator comprises;

a data inserter for inserting extra data points into said compressed audio-band transmit signal;

a filter for removing aliases introduced into said compressed audio-band transmit signal by said data inserter; and

a sampler, for sampling said filtered, compressed audio-band transmit signal;

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode; and

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone.

4. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode, wherein said transmit audio processor comprises;

a compressor for digitally compressing said audio-band transmit signal; and

a summer for digitally combining said compressed audio-band transmit signal with said regenerated supervisory audio tone;

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode;

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone;

a dual-tone multi-frequency (DTMF) generator for generating digitally-encoded DTMF tones and a DTMF control signal; and

a multiplexer, coupled to said DTMF generator and said compressor, for alternately providing said compressed audio-band transmit signal and said digitally-encoded DTMF tones to said summer in response to said DTMF control signal.

5. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode, wherein said transmit audio processor comprises;

a compressor for digitally compressing said audio-band transmit signal; and

a summer for digitally combining said compressed audio-band transmit signal with said regenerated supervisory audio tone;

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode;

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone; and

an echo suppressor, coupled to said compressor, for generating an attenuation signal in response to an absolute energy value of said audio-band transmit signal; and

a transmit gain adjust element, coupled to said echo suppressor and said compressor, for attenuating said audio-band transmit signal in response to said attenuation signal.

6. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode, wherein said transmit audio processor comprises;

a compressor for digitally compressing said audio-band transmit signal; and

a summer for digitally combining said compressed audio-band transmit signal with said regenerated supervisory audio tone;

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode, wherein said receive audio processor comprises an expander for de-compressing said audio band receive signal, and wherein said expander comprises;

an absolute value calculator for generating an absolute energy value signal in response to measuring an absolute energy value of said audio-band receive signal;

a digital filter, coupled to said absolute value calculator, for filtering said measured absolute energy value signal; and

a multiplier, coupled to said absolute value calculator and said digital filter, for multiplying said audio-band receive signal by said digitally filtered, measured absolute energy value signal; and

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone.

7. The digital signal processor of claim 6 wherein expander further comprises:

an interpolator, coupled to an input of said absolute value calculator, for increasing a data rate of said audio-band receive signal; and

a decimator, coupled to an output of said absolute value calculator, for decreasing a data rate of said measured absolute energy value signal.

8. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode, wherein said transmit audio processor comprises;

a compressor for digitally compressing said audio-band transmit signal; and

a summer for digitally combining said compressed audio-band transmit signal with said regenerated supervisory audio tone;

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode, wherein said receive audio processor comprises an expander for de-compressing said audio band receive signal; and

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone; and

a dual-tone multi-frequency (DTMF) generator for generating digitally-encoded DTMF tones and a DTMF control signal;

a multiplexer, coupled to said DTMF generator and said expander, for alternately providing said expanded audio-band receive signal and said digitally-encoded DTMF tones at an output of said multiplexer in response to said DTMF control signal.

9. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode wherein said transmit audio processor comprises;

a compressor for digitally compressing said audio-band transmit signal; and

a summer for digitally combining said compressed audio-band transmit signal with said regenerated supervisory audio tone;

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode, wherein said receive audio processor comprises an expander for de-compressing said audio band receive signal; and

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone;

an echo suppressor, coupled to said expander, for generating an attenuation signal in response to an absolute energy value of said audio-band receive signal; and

a receive gain adjust element, coupled to said echo suppressor and said expander, for attenuating said audio-band receive signal in response to said attenuation signal.

10. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode;

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode; and

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone, wherein said supervisory audio tone processor comprises;

a supervisory audio tone detector for determining a frequency of said supervisory audio tone; and

a supervisory audio tone transponder for regenerating said supervisory audio tone, wherein said supervisory audio tone detector comprises;

a plurality of parallel filter banks, each filter bank for measuring an energy value of a different one of a plurality of supervisory audio tone frequencies; and

a decision element for selecting a maximum measured energy value from said plurality of measured energy values.

11. The digital signal processor of claim 10 wherein each of said plurality of filter banks comprises:

a squarer for squaring said supervisory audio tone; and

a block averager, coupled to said squarer, for averaging said squared supervisory audio tone.

12. A digital signal processor for use in a communication device which transmits and receives analog-modulated information signals when in an analog mode and which transmits and receives digitally-modulated information signals when in a digital mode, said digital signal processor comprising:

a transmit audio processor for digitally processing an audio-band transmit signal when in said analog mode;

a receive audio processor for digitally processing an audio-band receive signal when in said analog mode; and

a supervisory audio tone processor, coupled to said receive audio processor and said transmit audio processor, for digitally detecting and transponding a supervisory audio tone, wherein said supervisory audio tone processor comprises;

a supervisory audio tone detector for determining a frequency of said supervisory audio tone; and

a supervisory audio tone transponder for regenerating said supervisory audio tone, wherein said supervisory audio tone transponder comprises;

a supervisory audio tone summer for summing said supervisory audio tone with said compressed transmit audio signal;

an automatic gain control loop, coupled to said supervisory audio tone summer, for controlling a gain of said summed supervisory audio tone and compressed transmit audio signal; and

a differentiator, coupled to said automatic gain control loop, for differentiating said gain controlled, summed supervisory audio tone and compressed transmit audio signal.