Transmitter and receivers using resource sharing and coding for increased capacity

• US 4,495,619 A
• Filed: 02/13/1984
• Issued: 01/22/1985
• Est. Priority Date: 10/23/1981
• Status: Expired due to Term

• Current Assignee: AT&T, Inc.
• Original Assignee: AT&T, Inc.
• Inventors: Acampora, Anthony
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Chin, Stephen
• Application Number:
  US06/579,521
• Time in Patent Office: 344 Days
• Field of Search: 375/39, 375/57, 375/58, 375/60, 375/99, 370/104, 370/105, 370/106, 370/107, 371/41, 371/49, 371/50, 370/104, 370/105, 370/106, 370/107, 455/50, 455/53, 328/165
• US Class Current: 370/207
• CPC Class Codes: H04B 7/212 Time-division multiple access [TDMA]
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0015 characterised by the adaptation strategy
• CPC Class Codes: H04L 1/0059 Convolutional codes

Abstract

The present invention relates to transmitters and receivers in a digital time division multiple access (TDMA) communication system wherein the resource sharing concept is generalized by fully exploiting the available clear air carrier-to-noise ratio (CNR) of a transmission link to achieve very high transmission capacity while maintaining low rain outage. Transmission is accomplished by using a first predetermined redundancy code and a first predetermined signal constellation for quadrature amplitude modulation during clear air conditions to permit a high rate of information transfer. When the fade depth exceeds the built-in fade margin, a second predetermined redundancy code and a second predetermined signal constellation is used while using time slots borrowed from a resource sharing reserved time slot pool to maintain the data rate at the fade site. Either one of the first redundancy code or signal constellation can equal either one of the second redundancy code or signal constellation.

Claims

1. A transmitter capable of transmitting each of one or more digital message burst input signals in at least one separate assigned time slot of a time division multiple access (TDMA) frame sequence which is destined for a separate one of a plurality of remote, spaced apart, receivers of a TDMA communication system, the transmitter comprising:

encoding means (12) capable of receiving each of the one or more digital message burst input signals to be transmitted, the encoding means comprising a plurality of redundancy encoders (33) which generate different redundancy codes and a control means (32) connected to the plurality of redundancy encoders for selecting one of said redundancy encoders and associated redundancy code to be used in encoding each of the one or more digital message burst input signals; and

modulating means (14) comprising a signal constellation encoder (42) capable of selectively generating any one of a plurality of signal constellations, where each signal constellation comprises a plurality of points and is not a scalar replica of another signal constellation, and converting each of the encoded digital message burst input signals from the encoding means into a selected one of the plurality of signal constellations, and control means (44) for causing the signal constellation encoder to selectively use a predetermined one of the plurality of signal constellations for each of the redundancy encoded digital message burst input signals;

the encoding means control means and the modulating means control means being capable of selecting a first pair combination of a predetermined redundancy code and a predetermined signal constellation for encoding a digital message burst input signal for transmission in a single time slot of the frame sequence when the transmission between the transmitter and remote receiver destined to receive said transmitted message burst input signal is equal to or above a predetermined carrier-to-noise ratio (CNR), and selecting a second pair combination of a predetermined redundancy code and a predetermined signal constellation for encoding a digital message burst input signal for transmission in more than one time slot of the frame sequence when the transmission between the transmitter and a remote receiver destined to receive said transmitted message burst signal is below said predetermined CNR, the first pair combination being a fixed pair of a predetermined redundancy code and a predetermined signal constellation and the second pair combination comprising a selectively different pair of a predetermined redundancy code and a predetermined signal constellation than used for said first pair combination for achieving a high transmission capacity while maintaining low fade condition outage for each of the one or more message burst signal transmissions.

2. A transmitter according to claim 1 wherein the signal constellation encoder is a quadrature amplitude modulation (QAM) encoder and each of the signal constellations is derived from a different value of M phase shifts than used with each of the other signal constellations.

3. A transmitter according to claim 2 wherein the QAM encoder is capable of selectively generating any one of a plurality of different signal constellations for use with said second pair combination and said modulating means control means is capable of selectively causing the QAM encoder to use one of said plurality of different signal constellations each time a redundancy encoded message burst signal is being modulated for transmission to a remote receiver experiencing a fade condition, where each of said plurality of different signal constellations is associated with a predetermined separate depth of fade range.

4. A transmitter according to claim 1 wherein the transmitter further comprises scrambling means (13) for scrambling the output signal of the encoding means to insure independence of contiguous encoded symbols.

5. A transmitter according to claim 1, 2, 3 or 4 wherein the encoding means control means is capable of selectively enabling one of said plurality of redundancy encoders for use during each time slot of the frame sequence where a message burst signal is to be transmitted, the redundancy encoder being selectively enabled to achieve a predetermined bit error rate in the transmission of the message burst to the remote receiver and maintain the rate of bit transmission at a value less than a random coding band which varies with the carrier-to-noise ratio.

6. A receiver capable of receiving digital message burst signals transmitted by a remote transmitter in separate time slots of a time division multiple access (TDMA) frame sequence and destined for the receiver, where the transmitter uses (a) a first pair combination of a predetermined redundancy code of a plurality of different redundancy codes and a predetermined signal constellation of a plurality of different signal constellation for encoding each message burst signal for transmission in one time slot of the TDMA frame sequence when the carrier-to-noise ratio (CNR) is equal to or above a predetermined CNR in transmissions between the transmitter and receiver corresponding to a predetermined clear air condition, where each different signal constellation includes a set of points which is different and not a scalar replica of the set of points for each of the other signal constellations, and (b) a second pair combination of a predetermined redundancy code and a predetermined signal constellation for encoding each message burst signal for transmission in more than one time slot of the TDMA frame sequence when the transmission between the transmitter and receiver is below said predetermined CNR, the first pair combination being a fixed pair of a predetermined redundancy code and a predetermined signal constellation and the second pair combination comprising a selectively different pair of a predetermined redundancy code and a predetermined signal constellation than used for said first pair combination for achieving a high transmission capacity while maintaining low fade condition outage;

the receiver comprising;

filtering means (21) for generating an output signal comprising only signals received within a predetermined frequency band;

demodulating means including a signal constellation demodulating means capable of translating a signal constellation comprising a predetermined set of points, received in each of the message burst signals destined for the receiver into an output signal indicative of a vector value of the output signal from the filtering means; and

sequence estimating means including a decoding means capable of decoding the output signal of the demodulating means wherein each originally encoded message burst signal was encoded using a predetermined one of a plurality of redundancy codes to derive each remotely transmitted message burst signal in its original form.

7. In a time division multiple access (TDMA) communication system comprising a plurality of remote, spaced apart, stations which communicate with one another using digital message burst signals transmitted in assigned time slots of a frame sequence, a method of providing maximum data transmission and rain margin in transmissions between two stations of the system which are experiencing either one of a fade or non-fade condition, the method comprising the steps of:

at a transmitting station

(a) encoding a message burst signal using a first pair combination of a predetermined redundancy code of a plurality of redundancy codes and a predetermined signal constellation of a plurality of signal constellations and transmitting said encoded message burst signal in a single time slot of the frame sequence when the transmission between the transmitter and the remote receiver destined to receive the message burst signal is equal to or greater than a predetermined carrier-to-noise ratio (CNR), where each signal constellation of the plurality of signal constellations comprises a plurality of points and is not a scalar replica of another signal constellation; and

(b) encoding a message burst signal using a second pair combination of a predetermined redundancy code of a plurality of redundancy codes and a predetermined signal constellation of a plurality of signal constellations and transmitting said encoded message burst signal once in more than one time slot of the TDMA frame sequence when the transmission between the transmitter and the remote receiver destined to receive the message burst signal is below the predetermined CNR, where the first pair combination and the second pair combination are a different pair of the plurality of redundancy codes and the plurality of signal constellations.