Receivers incorporating uniform and non-uniform constellations and adaptive selection
Communication systems are described that use unequally spaced constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. One embodiment is a digital communications system including a transmitter transmitting signals via a communication channel, the transmitter including a coder capable of receiving user bits and outputting encoded bits at a rate, a mapper capable of mapping encoded bits to symbols in a constellation, and a modulator capable of generating a modulated signal for transmission via the communication channel using symbols generated by the mapper, wherein the constellation is unequally spaced and characterizable by assignment of locations and labels of constellation points to maximize parallel decode capacity of the constellation at a given signal-to-noise ratio so that the constellation provides a given capacity at a reduced signal-to-noise ratio compared to a uniform constellation that maximizes the minimum distance between constellation points of the uniform constellation.
1. A communication system, comprising:
a receiver capable of receiving signals via a communication channel having a channel signal-to-noise ratio (SNR), wherein the receiver comprises:
a demodulator capable of demodulating a received signal into a demodulated signal;
a demapper, coupled to the demodulator, capable of determining likelihoods using the demodulated signal and a symbol constellation selected from a set of symbol constellations; and
a decoder, coupled to the demapper, capable of using the likelihoods determined by the demapper to provide a sequence of received bits based upon a low density parity check (LDPC) code having a code rate;
wherein each symbol constellation in the set of symbol constellations is utilized in combination with a code rate;
wherein the set of symbol constellations comprises a group of symbol constellations, where each symbol constellation in the group of symbol constellations has the same number of constellation points that have amplitude and phase values;
wherein the group of symbol constellations includes:
a symbol constellation in which constellation points that share an amplitude value are evenly spaced with respect to phase; and
a plurality of symbol constellations, where each symbol constellation of the plurality of symbol constellations is utilized in combination with a code rate that is different from the code rates utilized by the other symbol constellations in the plurality of symbol constellations and comprises:
constellation points that have a shared amplitude value; and
the constellation points that have the shared amplitude value are unevenly spaced with respect to phase; and
wherein the receiver is capable of sending a request to modulate the signals received via the communication channel using a specific symbol constellation from the set of symbol constellations and a specific code rate, where the specific symbol constellation and the specific code rate are selected by the receiver based on a quality measurement made by the receiver.
2. The communication system of claim 1 , wherein:
each of the set of symbol constellations is associated with a different SNR;
the symbol constellations within the group of symbol constellations contain sixteen constellation points; and
each of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is associated with SNRs less than 14.8 dB.
3. The communication system of claim 1 , wherein:
each of the set of symbol constellations is associated with a different SNR;
the symbol constellations within the group of symbol constellation are thirty-two point symbol constellations;
the plurality of constellations comprises at least one thirty-two point symbol constellation associated with an SNR less than 20.4 dB;
the set of symbol constellations further comprises at least one eight point symbol constellation, where
the at least one point symbol constellation comprises constellation points that have a shared amplitude value and the constellation points that have the shared amplitude value are unevenly spaced with respect to phase; and
the at least one eight point symbol constellation is associated with an SNR less than 8.4 db.
4. The communication system of claim 1 wherein:
each of the set of symbol constellations is associated with a different SNR; and
at least one symbol constellation from the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is characterized by the assignment of labels and spacing of constellation points such that the at least one symbol constellation is capable of providing greater parallel decoding capacity when operated at its associated SNR than any of the other symbol constellations in the plurality of symbol constellations when operated at the same SNR.
5. The communication system of claim 1 , wherein at leat one of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is characterized by the assignment of labels and spacing of constellation points so as to maximize parallel decoding capacity at a specific SNR subject to at least one constraint.
6. The communication system of claim 1 , wherein each of the set of symbol constellations is a multi-dimensional symbol constellation having multiple degrees of freedom.
7. The communication system of claim 1 , wherein:
the receiver is capable of selecting the specific symbol constellation and the specific code rate from a plurality of predetermined LDPC code rate and symbol constellation pairs based at least in part on the quality measurement;
each of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is only included in one of the plurality of predetermined LDPC code rate and symbol constellation pairs; and
the receiver is capable of sending a request to a remote transmitter to use a selected LDPC code rate and symbol constellation pair.
8. The communication system of claim 1 , wherein the receiver is capable of substituting the set of symbol constellations by an upgrade to at least one of the receiver software and firmware.
9. The communication system of claim 1 , further comprising a transmitter capable of transmitting signals via the communication channel, where the transmitter comprises:
a coder capable of receiving bits and outputting encoded bits using a Low Density Parity Check (LDPC) code;
a mapper, coupled to the coder, capable of mapping the encoded bits to symbols in the selected symbol constellation; and
a modulator, coupled to the mapper, capable of generating a signal for transmission via the communication channel based upon symbols selected by the mapper.
10. The communication system of claim 1 , wherein the plurality of symbol constellations that each comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase are symbol constellations having constellation points that are non-uniformly spaced in each degree of freedom available to the symbol constellation.
11. A communication system, comprising:
a receiver that receives signals via a communication channel having a channel signal-to-noise ratio (SNR), wherein the receiver comprises:
a demodulator that demodulates a received signal into a demodulated signal;
a demapper that determines likelihoods using the demodulated signal and a symbol constellation selected from a set of symbol constellations; and
a decoder that uses the likelihoods determined by the demapper to provide a sequence of received bits based upon a low density parity check (LDPC) code having a code rate;
wherein each symbol constellation in the set of symbol constellations is utilized in combination with a code rate;
wherein the set of symbol constellations comprises a group of symbol constellations, where each symbol constellation in the group of symbol constellations has the same number of constellation points that have amplitude and phase values;
wherein the group of symbol constellations includes:
a symbol constellation in which constellation points that share an amplitude value are evenly spaced with respect to phase; and
a plurality of symbol constellations, where each symbol constellation of the plurality of symbol constellations is utilized in combination with a code rate that is different from the code rates utilized by the other symbol constellations in the plurality of symbol constellations and comprises:
constellation points that have a shared amplitude value; and
the constellation points that have the shared amplitude value are unevenly spaced with respect to phase; and
wherein the receiver sends a request to modulate the signals received via the communication channel using a specific symbol constellation from the set of symbol constellations and a specific code rate, where the specific symbol constellation and the specific code rate are selected by the receiver based on a quality measurement made by the receiver.
12. The communication system of claim 11 , wherein:
each of the set of symbol constellations is associated with a different SNR;
the symbol constellations within the group of symbol constellations contain sixteen constellation points; and
each of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is associated with SNRs less than 14.8 dB.
13. The communication system of claim 11 , wherein:
each of the set of symbol constellations is associated with a different SNR;
the symbol constellations within the group of symbol constellation are thirty-two point symbol constellations;
the plurality of constellations comprises at least one thirty-two point symbol constellation associated with an SNR less than 20.4 dB;
the set of symbol constellations further comprises at least one eight point symbol constellation, where
the at least one point symbol constellation comprises constellation points that have a shared amplitude value and the constellation points that have the shared amplitude value are unevenly spaced with respect to phase; and
the at least one eight point symbol constellation is associated with an SNR less than 8.4 db.
14. The communication system of claim 11 wherein:
each of the set of symbol constellations is associated with a different SNR; and
at least one symbol constellation from the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is characterized by the assignment of labels and spacing of constellation points such that the at least one symbol constellation is capable of providing greater parallel decoding capacity when operated at its associated SNR than any of the other symbol constellations in the plurality of symbol constellations when operated at the same SNR.
15. The communication system of claim 11 , wherein at least one of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is characterized by the assignment of labels and spacing of constellation points so as to maximize parallel decoding capacity at a specific SNR subject to at least one constraint.
16. The communication system of claim 11 , wherein each of the set of symbol constellations is a multi-dimensional symbol constellation having multiple degrees of freedom.
17. The communication system of claim 11 , wherein:
the receiver selects the specific symbol and the specific code rate from a plurality of predetermined LDPC code rate and symbol constellation pairs based at least in part on the quality measurement;
each of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is only included in one of the plurality of predetermined LDPC code rate and symbol constellation pairs; and
the receiver sends a request to a remote transmitter to use a selected LDPC code rate and symbol constellation pair.
18. The communication system of claim 11 , wherein the receiver can substitute the set of symbol constellations by an upgrade to at least one of the receiver software and firmware.
19. The communication system of claim 11 , further comprising a transmitter that transmits signals via the communication channel, where the transmitter comprises:
a coder that receives bits and outputs encoded bits using a Low Density Parity Check (LDPC) code;
a mapper that maps the encoded bits to symbols in the selected symbol constellation; and
a modulator that generates a signal for transmission via the communication channel based upon symbols selected by the mapper;
wherein the mapper is interposed between the modulator and the coder and the mapper receives information from the coder and provides information to the modulator.
20. The communication system of claim 11 , wherein the plurality of symbol constellations that each comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase are symbol constellations having constellation points that are non-uniformly spaced in each degree of freedom available to the symbol constellation.
21. A communication system, comprising:
a receiver that receives signals via a communication channel having a channel signal-to-noise ratio (SNR), wherein the receiver uses a symbol constellation selected from a set of symbol constellations to transform the received signals into received bits based upon a low density parity check (LDPC) code having a code rate;
wherein each symbol constellation in the set of symbol constellations is utilized in combination with a code rate;
wherein the set of symbol constellations comprises a group of symbol constellations, where each symbol constellation in the group of symbol constellations has the same number of constellation points that have amplitude and phase values;
wherein the group of symbol constellations includes:
a symbol constellation in which constellation points that share an amplitude value are evenly spaced with respect to phase; and
a plurality of symbol constellations, where each symbol constellation of the plurality of symbol constellations is utilized in combination with a code rate that is different from the code rates utilized by the other symbol constellations in the plurality of symbol constellations and comprises:
constellation points that have a shared amplitude value; and
the constellation points that have the shared amplitude value are unevenly spaced with respect to phase; and
wherein the receiver is capable of sending a request to modulate the signals received via the communication channel using a specific symbol constellation from the set of symbol constellations and a specific code rate, where the specific symbol constellation and the specific code rate are selected by the receiver based on a quality measurement made by the receiver.
22. The communication system of claim 21 , wherein:
each of the set of symbol constellations is associated with a different SNR;
the symbol constellations within the group of symbol constellations contain sixteen constellation points; and
each of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is associated with SNRs less than 14.8 dB.
23. The communication system of claim 21 , wherein:
each of the set of symbol constellations is associated with a different SNR;
the symbol constellations within the group of symbol constellation are thirty-two point symbol constellations;
the plurality of constellations comprises at least one thirty-two point symbol constellation associated with an SNR less than 20.4 dB;
the set of symbol constellations further comprises at least one eight point symbol constellation, where
the at least one point symbol constellation comprises constellation points that have a shared amplitude value and the constellation points that have the shared amplitude value are unevenly spaced with respect to phase; and
the at least one eight point symbol constellation is associated with an SNR less than 8.4 db.
24. The communication system of claim 21 wherein:
each of the set of symbol constellations is associated with a different SNR; and
at least one symbol constellation from the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is characterized by the assignment of labels and spacing of constellation points such that the at least one symbol constellation is capable of providing greater parallel decoding capacity when operated at its associated SNR than any of the other symbol constellations in the plurality of symbol constellations when operated at the same SNR.
25. The communication system of claim 21 , wherein at least one of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is characterized by the assignment of labels and spacing of constellation points so as to maximize parallel decoding capacity at a specific SNR subject to at least one constraint.
26. The communication system of claim 21 , wherein each of the set of symbol constellations is a multi-dimensional symbol constellation having multiple degrees of freedom.
27. The communication system of claim 21 , wherein:
the receiver selects the specific symbol constellation and the specific code rate from a plurality of predetermined LDPC code rate and symbol constellation pairs based at least in part on the quality measurement;
each of the plurality of symbol constellations that comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase is only included in one of the plurality of predetermined LDPC code rate and symbol constellation pairs; and
the receiver sends a request to a remote transmitter to use a selected LDPC code rate and symbol constellation pair.
28. The communication system of claim 21 , wherein the receiver can substitute the set of symbol constellations by an upgrade to at least one of the receiver software and firmware.
29. The communication system of claim 21 , further comprising a transmitter that transmits signals via the communication channel, where the transmitter uses the selected symbol constellation to transform encoded bits into the transmitted signals.
30. The communication system of claim 21 , wherein the plurality of symbol constellations that each comprise constellation points that have a shared amplitude value and are unevenly spaced with respect to phase are symbol constellations having constellation points that are non-uniformly spaced in each degree of freedom available to the symbol constellation.