Method and apparatus for efficient digital time delay compensation in compressed bandwidth signal processing

• US 5,051,991 A
• Filed: 10/17/1984
• Issued: 09/24/1991
• Est. Priority Date: 10/17/1984
• Status: Expired due to Term

• Current Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson GE Mobile Communications Inc (Telefonaktiebolaget LM Ericsson)
• Inventors: Szczutkowski, Craig F.
• Primary Examiner(s): Kuntz, Curtis A.
• Application Number:
  US06/661,740
• Time in Patent Office: 2,533 Days
• Field of Search: 370/109, 370/185, 370/108, 370/110.1, 370/118, 381/29-35, 375/122, 358/133, 358/260, 333/14
• US Class Current: 370/519
• CPC Class Codes: H04B 1/667 using a division in frequency subbands for TV signals H04N19/63
• CPC Class Codes: H04K 1/00 Secret communication

Abstract

Time delay compensation is inserted into a digital signal processing channel having compressed bandwidth portions at a point where the bandwidth is compressed. Since a smaller number of bits per unit of information is present at such a point, this reduces the number of bits which must be buffered to achieve a given amount of time delay compensation. For example, in a subband coder/decoder using a non-symmetrical QMF filter tree, the necessary time delay compensation in the various subband channels is effected subsequent to a digital bandwidth compression encoding step on the transmitter side. On the receiver side, similar time compensation may be provided in the subband channels prior to a digital bandwidth expansion decoding step. By implementing the necessary digital time delay compensation at a point in the system where the signals are bandwidth compressed to a maximum degree (i.e. using a minimum number of bits per second to transmit given information), digital memory requirements for implementing the digital time delay compensation are minimized.

Claims

1. A digital time delay compensated subband signal processor comprising:

filter means for separating a digitized input signal into plural subband channels of digital signals having different respective time delays therein and representing corresponding subbands of signal frequency components;

digital coding means connected to said plural subband channels for separately coding the digital signals in each subband channel in a digitally compressed form to provide compressed coded digital signals in each of said subband channels;

time delay compensation means connected to at least one of said subband channels for time delaying said compressed coded digital signals in said at least one subband channel for a predetermined time period to provide substantially time synchronous coded compressed digital signals at a predetermined point in each of said subband channels; and

multiplex means connected to said plural subband channels for combining said substantially time synchronous coded compressed digital signals into an output stream of coded compressed digital signals.

2. A digital time delay compensated subband signal processor as in claim 1 further comprising:

demultiplexing means connected to receive said output stream for separating a received bit-serial input stream of said coded compressed digital signals into plural received subband channels of received digital signals;

second time delay compensation means connected to at least one of said received subband channels for time delaying said received digital signals in said at least one received subband channel by a predetermined time period;

decoding means connected to said plural subband channels for separately decoding the received time-delayed digital signals in each received subband channel to provide an expanded set of digital signals therein; and

inverse filter means connected to receive said expanded set of received digital signals for combining said expanded digital signals from each received subband channel with differing respective time delays which, in combination with the time delays introduced by said second time delay compensation means produces a time synchronous output stream of decoded expanded digital signals.

9. A digital time delay compensated subband signal processor as in claim 1 wherein said filter means comprises a quadrature mirror filter.

3. A digital time delay compensated signal processor comprising:

demultiplexing means for separating a received bit-serial input stream of coded compressed digital signals into plural received subband channels of received digital signals;

time delay compensation means connected to receive the received digital signals in at least one of said received subband channels for time delaying said received digital signals in said at least one received subband channel by a predetermined time period;

decoding means connected to said received subband channels for separately decoding the received time-delayed digital signals to provide an expanded set of digital signals therein; and

inverse quadrature mirror filter means connected to receive said expanded set of digital signals for combining said expanded digital signals from each received subband channel with differing respective time delays to produce a time synchronous output stream of decoded expanded digital signals.

4. A digital time delay compensated subband signal processing method comprising:

separating a digitized input signal into plural subband channels of digital signals having different respective time delays therein and representing corresponding subbands of signal frequency components;

separately coding the digital signals in each subband channel in a digitally compressed form to provide compressed coded digital signals in each of said subband channels;

time delaying said compressed coded digital signals in at least one of said subband channels for a predetermined time period to provide substantially time synchronous digital signals in each of said subband channels; and

combining said substantially time synchronous digital signals into an output stream of coded compressed digital signals.

5. A digital time delay compensated subband signal processing method as in claim 4 further comprising:

separating a received bit-serial input stream of said coded compressed digital signals into plural received subband channels of received digital signals;

time delaying said received digital signals in at least one of said received subband channels by a predetermined time period;

separately decoding the received time-delayed digital signals in each received subband channel to provide an expanded set of digital signals therein; and

combining said expanded received digital signals from each received subband channel with differing respective time delays which, in combination with the time delays introduced by said second time delay compensation means produces a time synchronous output stream of decoded expanded digital signals.

6. A digital time delay compensated signal processing method comprising:

separating a received bit-serial input stream of coded compressed digital signals into plural received subband channels of received digital signals, said subband channels each time delaying said digital signals;

further time delaying said received digital signals in at least one of said received subband channels by a predetermined time delay compensation period;

separately decoding the received time-delayed digital signals to provide an expanded set of digital signals in said at least one subband channel; and

combining said expanded received digital signals from each received subband channel with differing respective time delays to produce a time synchronous output stream of decoded expanded digital signals.

7. A digital time delay compensated digital processor using non-symmetrical quadrature mirror filter technique, said processor including:

means for defining plural subband channels of digital signals which are coded into a bit-compressed digital format for transmission over a communication channel; and

time delay compensation means operating in said subband channels for time delaying said coded bit-compressed digital signals, for compensating for unequal time delays encountered in said non-symmetrical quadrature mirror filter technique and for minimizing digital memory requirements for effecting such time delay compensation.

8. A digital time delay compensated signal processing method including the following steps:

using a non-symmetrical quadrature mirror filter technique to define plural subband channels of digital signals which are coded into a bit-compressed digital format for transmission over a communication channel; and

time delaying said coded bit-compressed digital signals in said subband channels and compensating for unequal time delays encountered in said non-symmetrical quadrature mirror filter technique while also minimizing digital memory requirements for effecting such time delay compensation.

10. A digital signal subband processing system including:

means for separating a digitized input signal into first and second subband channels of digital signals encoded into bit-compressed digital format, said first and second subband channels having different respective time delays therein; and

time delay compensation mean operating in said first subband channel fur further time delaying said first subband coded bit-compressed digital signals by a predetermined compensation delay time period so as to substantially time synchronize said first and second coded bit-compressed subband digital signals.

11. A system as in claim 10 further including multiplexing means connected to receive said first and second subband channel digital signals for combining said substantially time synchronous digital signals into an output stream of coded compressed digital signals.

12. In a digital signal processing system providing time delay in a channel transmitting digital signals encoded into a bit-compressed digital format, the improvement comprising:

subband filter means connected to said channel for providing bit-compressed digital subband signals; and

time delay compensation means operating in said channel and connected to said subband filter means for further time delaying said received bit-compressed digital signals by a predetermined compensation delay time period and for time synchronizing said bit-compressed digital signals with further subband digital signals also encoded in a bit-compressed digital format, said time delay compensation means including a digital signal storage device.

13. A digital signal subband processing system including:

filter means for separating a digitized input signal into first and second subbands of digital signals encoded into bit-compressed digital format, said first and second subbands having different inherent respective signal propagation time delays; and

time delay compensation means connected to receive said first subband digital signals for further time delaying said first subband bit-compressed digital signals by a predetermined compensation delay time period so as to equalize the time delays of said first and second bit-compressed subband digital signals.