Design Methodology and Method and Apparatus for Signaling with Capacity Optimized Constellations

• US 20150236812A1
• Filed: 09/19/2014
• Published: 08/20/2015
• Est. Priority Date: 06/05/2007
• Status: Active Grant

• Current Assignee: Constellation Designs, LLC (SoftBank Group Corp.)
• Original Assignee: Constellations Designs, Inc.
• Inventors: Barsoum, Maged F., Jones, Christopher R.
• Granted Patent: US 9,385,832 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H03M 13/255 with Low Density Parity Check [LDPC] codes
• CPC Class Codes: H03M 13/6325 Error control coding in combination with demodulation
• CPC Class Codes: H04B 15/00 Suppression or limitation of noise or interference by means associated with receiver H04B1/10
• CPC Class Codes: H04B 17/336 Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• 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 27/3405 Modifications of the signal space to increase the efficiency of transmission, e.g. reduction of the bit error rate, bandwidth, or average power
• CPC Class Codes: H04L 27/3483 using a modulation of the constellation points
• CPC Class Codes: H04L 27/3809 Amplitude regulation arrangements
• CPC Class Codes: H04W 24/02 Arrangements for optimising operational condition
• CPC Class Codes: Y02D 30/50 in wire-line communication networks, e.g. low power modes or reduced link rate

Abstract

Communication systems are described that use geometrically shaped constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. In several embodiments, the geometrically shaped is optimized based upon a capacity measure such as parallel decoding capacity or joint capacity. In many embodiments, a capacity optimized geometrically shaped constellation can be used to replace a conventional constellation as part of a firmware upgrade to transmitters and receivers within a communication system. In a number of embodiments, the geometrically shaped constellation is optimized for an Additive White Gaussian Noise channel or a fading channel. In numerous embodiments, the communication uses adaptive rate encoding and the location of points within the geometrically shaped constellation changes as the code rate changes. One embodiment of the invention includes a transmitter configured to transmit signals to a receiver via a communication channel, wherein the transmitter, includes a coder configured to receive user bits and output encoded bits at an expanded output encoded bit rate, a mapper configured to map encoded bits to symbols in a symbol constellation, a modulator configured to generate a signal for transmission via the communication channel using symbols generated by the mapper. In addition, the receiver includes a demodulator configured to demodulate the received signal via the communication channel, a demapper configured to estimate likelihoods from the demodulated signal, a decoder that is configured to estimate decoded bits from the likelihoods generated by the demapper. Furthermore, the symbol constellation is a capacity optimized geometrically spaced symbol constellation that provides a given capacity at a reduced signal-to-noise ratio compared to a signal constellation that maximizes d_min.

Claims

1. A digital communication system, comprising:

a transmitter configured to transmit signals to a receiver via a communication channel;

wherein the transmitter, comprises;

a coder configured to receive user bits and output encoded bits at an expanded output encoded bit rate;

a mapper configured to map encoded bits to symbols in a symbol constellation;

a modulator configured to generate a signal for transmission via the communication channel using symbols generated by the mapper;

wherein the receiver, comprises;

a demodulator configured to demodulate the received signal via the communication channel;

a demapper configured to estimate likelihoods from the demodulated signal;

a decoder that is configured to estimate decoded bits from the likelihoods generated by the demapper; and

wherein the symbol constellation is a capacity optimized geometrically spaced symbol constellation that provides a given capacity at a reduced signal-to-noise ratio compared to a signal constellation that maximizes d_min.

2. The communication system of claim 1, wherein the geometrically spaced symbol constellation is capacity optimized subject to additional constraints.

3. The communication system of claim 1, wherein the geometrically shaped symbol constellation is optimized for capacity using parallel decode capacity.

4. The communication system of claim 1, wherein the geometrically shaped symbol constellation is optimized for capacity using joint capacity.

5. The communication system of claim 1, wherein the code is a Turbo code.

6. The communication system of claim 1, wherein the code is a LDPC code.

7. The communication system of claim 1, wherein the modulation scheme is a PAM scheme.

8. The communication system of claim 1, wherein the modulation scheme is a PSK scheme.

9. The communication system of claim 1, wherein the modulation scheme is a QAM scheme.

10. The communication system of claim 1, wherein the modulation scheme is a multidimensional modulation scheme.

11. The communication system of claim 1, wherein the channel is an AWGN channel.

12. The communication system of claim 1, wherein the channel is a fading channel.

13. The communication system of claim 1, wherein the constellations points of the geometrically spaced symbol constellation are variable depending on the user rate.

14. The communication system of claim 13, wherein:

the transmitter is configured to modify the rate of the code in order to change the user bit rate of the communication system;

the transmitter is configured to move the constellation points of the symbol constellation used by the mapper based upon the code rate of the coder;

the receiver is configured to receive information concerning code rate changes from the transmitter; and

the receiver is configured to modify the decoder and the constellation used by the demapper in response to receipt of a notification of a change of user bit rate.

15. The communication system of claim 14, wherein:

the receiver is configured to acknowledge receipt of a modification to the code rate and the constellation of the communication system; and

the transmitter is configured to commence transmitting using the new code rate and symbol constellation upon receipt of the acknowledgement from the receiver.

16. The communication system of claim 15, wherein:

a backchannel communication link exists between the transmitter and the receiver;

the receiver is configured to monitor receiver performance and initiate a change in code rate in response to the observed receiver performance;

the receiver is configured to transmit to the transmitter via the backchannel a change in user bit rate; and

both the mapper and the demapper are configured to move the constellation points of the geometrically shaped symbol constellation based upon the change in user bit rate.

17. The communication system of claim 1, wherein the constellations points of the geometrically spaced symbol constellation are variable depending on the channel.

18. The communication system of claim 17, wherein the constellations points of the geometrically spaced symbol constellation are variable depending on the channel SNR.

19. The communication system of claim 18, wherein:

a backchannel communication link exists between the transmitter and the receiver;

the receiver is configured to transmit information to the transmitter from which the transmitter can compute the channel SNR;

the transmitter is configured to transmit to the receiver information indicative of a symbol constellation and a code configuration; and

the demapper is configured to move the constellation points of the geometrically shaped symbol constellation based upon the information received from the transmitter.

20. A method of transmitting bits of user information over a communication channel, comprising:

encoding the bits of user information using a coding scheme;

mapping the encoded bits of user information to a symbol constellation, wherein the symbol constellation is a capacity optimized geometrically spaced symbol constellation that provides a given capacity at a reduced signal-to-noise ratio compared to a signal constellation that maximizes d_min;

modulating the symbols in accordance with a modulation scheme;

transmitting the modulated signal via the communication channel;

receiving a modulated signal;

demodulating the modulated signal in accordance with the modulation scheme;

demapping the demodulated signal using the geometrically shaped signal constellation to produce likelihoods;

decoding the likelihoods to obtain an estimate of the decoded bits.