Peak to average power ratio reduction methodology for QAM communications systems

• US 5,381,449 A
• Filed: 11/01/1991
• Issued: 01/10/1995
• Est. Priority Date: 06/12/1990
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Birchler, Mark A., Jasper, Steven C.
• Primary Examiner(s): Chin, Stephen
• Application Number:
  US07/786,681
• Time in Patent Office: 1,166 Days
• Field of Search: 375/38, 375/39, 375/42, 375/59, 375/60, 370/9, 370/10, 370/12, 370/18, 370/19, 370/20, 332/103, 332/144
• US Class Current: 375/298
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26134 Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
• CPC Class Codes: H04L 27/262 Reduction thereof by selection of pilot symbols
• CPC Class Codes: H04L 27/2637 with direct modulation of individual subcarriers
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/3411 reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set
• CPC Class Codes: H04L 27/3455 in order to facilitate carrier recovery at the receiver end, e.g. by transmitting a pilot or by using additional signal points to allow the detection of rotations
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

The ratio of peak power level to average power level in a power amplifier used in a QAM communication system transmitter can be reduced by preselecting magnitudes and phase angles of complex-valued pilot symbols used in multi-channel, N-level QAM.

Claims

1. In an quadrature amplitude modulation (QAM) communication system comprised of a composite signal, having a peak power level and an average power level, for transmission on a communication channel, which composite signal is comprised of a plurality of QAM subchannel signals combined together, at least one;

of which QAM subchannel signals includes;

a) a plurality of complex-valued QAM information symbols, each of which information symbols are located substantially on one of n where n is an integer constellation points of a complex plane, each constellation point being defined by a discrete magnitude and discrete phase angle from a predetermined reference point in the complex plane; and

b) a plurality of predetermined complex-valued pilot symbols, each having a magnitude and phase, each of said plurality of QAM subchannel signals having an average power level and having a peak power level over a finite length of time, a method of reducing the ratio of the peak power level to average power level in said composite signal comprised of;

combining at least one of said complex-valued QAM information symbols, with at least one, complex-valued, non-constellation-based pilot symbol, to form at least a first QAM subchannel signal;

combining said QAM subchannel signal with at least one other QAM subchannel signal to form a composite signal; and

transmitting, said composite signal on said communication channel.

2. The method of claim 1 including the step of pulse shape filtering said QAM subchannel signal prior to transmission on said communication channel to form filtered QAM subchannel signals.

3. The method of claim 2 including the step of modulating each filtered QAM subchannel signal to a predetermined subchannel center frequency.

4. The method of claim 3 including the step of combining each of the modulated filtered QAM subchannel signal to produce said composite signal.

5. In an quadrature amplitude modulation (QAM) communication system comprised of a composite signal having an average power level and a peak power level, for transmission on a communication channel, which composite signal is comprised of a plurality of QAM subchannel signals combined together, each of said QAM subchannel signals being comprised of:

a) a plurality of complex-valued QAM information symbols, each of which information symbols are located substantially on one of n where n is an integer constellation points of a complex plane, each point being defined by a discrete magnitude and phase angle from a predetermined reference; and

b) complex-valued pilot symbols combined with said QAM information symbols at predetermined pilot symbol times over a predetermined time period, each pilot symbol having a magnitude and phase;

a method of reducing the ratio of the peak power level to average power level in said composite signal comprised of;

during a finite time period during which a plurality of QAM subchannels has at least one, pilot symbol;

at least one of said QAM subchannel signals, has a first-valued pilot (fixed pilot QAM subchannel signals);

in at least one other QAM subchannel signal, combining with said QAM information symbols, a second-valued pilot symbol to form a second QAM subchannel signal;

combining said fixed pilot QAM subchannel signals with said second QAM subchannel signal to form a composite signal; and

transmitting said composite signal on said communication channel.

6. In an n-level quadrature amplitude modulation (QAM) communication system comprised of a composite signal having an average power level and a peak power level, for transmission on a communication channel, which composite signal is comprised of a plurality of QAM subchannel signals combined together, each of said QAM subchannel signals being comprised of:

a) a plurality of complex-valued QAM information symbols, each of which information symbols are, located substantially on one of n where n is an integer constellation points of a complex plane; and

b) complex-valued pilot symbols combined with said QAM information symbols at predetermined pilot symbol times, each pilot symbol having a magnitude and phase;

a method of reducing the ratio of the peak power level to average power level in said composite signal comprised of;

in a first QAM subchannel signal, combining with QAM information symbols thereon, at said pilot symbol times, at least one pilot symbol selected from a first set of complex, non-fixed-values, to form said first QAM subchannel signal;

in a second QAM subchannel signal, combining with QAM information symbols thereon, at said pilot symbol times, at least one pilot symbol selected from a second set of complex, non-fixed-values, to form said second QAM subchannel signal;

combining said first and second QAM subchannel signals with at least one other QAM subchannel signal to form a composite signal; and

transmitting said composite signal on said communication channel.

7. In a quadrature amplitude modulation (QAM) communication system comprised of a composite signal for transmission on a communication channel, which composite signal is comprised of a plurality of QAM subchannel signals combined together, of which each QAM subchannel signal includes:

a) QAM information symbols (QAM symbols), said QAM symbols having an average power level and having a peak power level over a finite length of time; and

b) a plurality of predetermined complex-valued pilot symbols, each having a magnitude and phase, and that are combined with said QAM symbols, said complex-valued pilot symbols having an average power level and having a peak power level over a finite length of time, a method of reducing the ratio of the peak power level to average power level in said composite signal comprised of;

selecting phase angles for a plurality of fixed-amplitude pilot symbols for a plurality of said subchannels, which pilot symbols can include both constellation based, and non-constellation-based pilot symbols (preselected pilot symbols), to minimize the peak-to-average power ratio of the composite signal over a finite length of time;

combining said preselected pilot symbols for each subchannel with QAM symbols on said subchannel to form piloted QAM subchannel symbol streams; and

transmitting combined preselected pilot symbols and QAM symbols on said communication channel.

8. The method of claim 7 including the step of pulse shape filtering said piloted QAM subchannel symbol streams prior to transmission on a communication channel to form filtered QAM symbol streams.

9. The method of claim 8 including the step of modulating each filtered QAM symbol stream to a predetermined subchannel center frequency.

10. The method of claim 9 including the step of combining each of the modulated filtered QAM symbol streams at their respective subchannel center frequencies to produce said composite signal.

11. In a quadrature amplitude modulation (QAM) communication system comprised of a composite signal for transmission on a communication channel, which composite signal is comprised of a plurality of QAM subchannel signals combined together, of which each QAM subchannel signal includes:

a) QAM information symbols (QAM symbols), said QAM symbols having an average power level and having a peak power level over a finite length of time; and

b) a plurality of complex-valued pilot symbols, each having a magnitude and phase, and that are combined with said QAM symbols, said complex-valued pilot symbols having an average power level and having a peak power level over a finite length of time, a method of reducing the ratio of the peak power level to the average power level in said composite signal comprised of;

selecting phase angles for a plurality of fixed-amplitude pilot symbols for a plurality of said subchannels, which pilot symbols can include both constellation based, and non-constellation-based pilot symbols (preselected pilot symbols), to minimize the peak-to-average power ratio of the composite signal over a finite length of time;

combining said preselected pilot symbols for each subchannel with QAM symbols on said subchannel; and

transmitting the combined preselected pilot symbols and QAM symbols on said communication channel.

12. The method of claim 11 including the step of pulse shape filtering said piloted QAM subchannel symbol streams prior to transmission on a communication channel to form filtered QAM symbol streams.

13. The method of claim 12 including the step of modulating each filtered QAM symbol stream to a predetermined subchannel center frequency.

14. The method of claim 13 including the step of combining each of the modulated filtered QAM symbol streams at their respective subchannel center frequencies to produce said composite signal.

15. In a quadrature amplitude modulation (QAM) communication system comprised of a composite signal for transmission on a communication channel, which composite signal is comprised of a plurality of QAM subchannel signals combined together, of which each QAM subchannel signal includes:

a) QAM information symbols (QAM symbols), said QAM symbols having an average power level and having a peak power level over a finite length of time; and

b) a plurality of complex-valued pilot symbols, each having a magnitude and phase, and that are combined with said QAM symbols, said complex-valued pilot symbols having an average power level and having a peak power level over a finite length of time, a method of reducing the ratio of the peak power level to the average power level in said composite signal comprised of;

selecting magnitudes and phase angles for a plurality of pilot symbols for a plurality of said subchannels, which pilot symbols can be both constellation based, and non-constellation based, (preselected pilot symbols) to minimize the peek-to-average power ratio of complex-valued composite signals over a finite length of time;

combining said preselected pilot symbols for each subchannel with QAM symbols on said subchannel;

transmitting the combined preselected pilot symbols and QAM symbols on said communication channel.

16. The method of claim 15 including the step of pulse shape filtering said piloted QAM subchannel symbol streams prior to transmission on a communication channel to form filtered QAM symbol streams.

17. The method of claim 16 including the step of modulating each filtered QAM symbol stream to a predetermined subchannel center frequency.

18. The method of claim 17 including the step of combining each of the modulated filtered QAM symbol streams at their respective subchannel center frequencies to produce said composite signal.

19. In an quadrature amplitude modulation (QAM) communication system comprised of a composite signal for transmission on a communication channel, which composite signal is comprised of a plurality of QAM subchannel signals combined together, at least one of which QAM subchannel signal includes:

a) a plurality of complex-valued information symbols, each of which information symbols are located substantially on one of n where n is an integer constellation points of a complex plane, each constellation point being defined by a discrete magnitude and discrete phase angle from a predetermined reference point in the complex plane; and

b) a plurality of predetermined complex-valued pilot symbols, each having a magnitude and phase, each of said plurality of QAM subchannel signals having an average power level and having a peak power level over a finite length of time, a method of reducing the ratio of the peak power level to average power level in said composite signal comprised of;

selecting phase angles for a plurality of fixed-amplitude pilot symbols for a plurality of said subchannels (preselected pilot symbols) such that at least one of said complex-valued pilot symbols is a non-constellation-based pilot symbol;

combining said preselected pilot symbols for each subchannel with QAM symbols on said subchannel to form piloted QAM subchannel symbol streams; and

transmitting the combined preselected pilot symbols and QAM symbols on said communication channel.

20. In an quadrature amplitude modulation (QAM) communication system comprised of a composite signal, having a peak power level and an average power level, for transmission on a communication channel, which composite signal is comprised of a plurality of QAM subchannel signals combined together, at least one of which QAM subchannel signal includes:

a) a plurality of complex-valued QAM information symbols, each of which information symbols are located substantially on one of n where n is an integer constellation points of a complex plane, each constellation point being defined by a discrete magnitude and discrete phase angle from a predetermined reference point in the complex plane; and

b) a plurality of predetermined complex-valued pilot symbols, combined with the QAM information symbols over a finite length of time, each having a magnitude and phase, each of said plurality of QAM subchannel signals having an average power level and having a peak power level over a finite length of time, a method of reducing the ratio of the peak power level to average power level in said composite signal comprised of;

combining at least one of said complex-valued QAM information symbols, with a plurality of complex-valued, non-constellation-based pilot symbols, having a plurality of phase angles, to form at least one QAM subchannel signal;

combining said QAM subchannel signal with at least one other QAM subchannel signal to form a composite signal; and

transmitting said composite signal on said communication channel.