Systems, methods and transceivers for wireless communications over discontiguous spectrum segments
View Patent ↗Methods of transmitting a plurality of communications signals over a plurality of discontiguous bandwidth segments in a frequency band include defining a plurality (N FFT ) of orthogonal subcarriers across the frequency band, defining a plurality (N) of available physical subcarriers from among the orthogonal subcarriers. The available physical subcarriers are distributed among the plurality of discontiguous bandwidth segments. The methods further include multiplexing the plurality of communications signals onto the plurality of available physical subcarriers. Multiplexing the plurality of communications signals onto the plurality of available physical subcarriers may include assigning the communications signals to respective ones of a plurality (N) of logical subcarriers, and mapping the plurality of logical subcarriers to corresponding ones of the plurality of available physical subcarriers. Related transmitters, receivers and communications systems are also disclosed.
1. A transmitter for a wireless communications system, comprising:
a subcarrier mapper configured to receive a plurality of input symbols, configured to assign the plurality of input symbols to N logical subcarriers, configured to map the N logical subcarriers to N available physical subcarriers out of N FFT physical subcarriers, and configured to generate N FFT transmit symbols corresponding to the N FFT physical subcarriers;
an inverse fast fourier transform (IFFT) processor configured to perform an inverse fourier transform on the N FFT transmit symbols output by the subcarrier mapper; and
a parallel to serial converter configured to convert an output of the IFFT processor to a serial output stream,
wherein the N FFT available physical subcarriers comprise orthogonal subcarriers defined across a frequency band including a plurality of discontiguous available bandwidth segments, and wherein the N available physical subcarriers are distributed among the plurality of discontiguous available bandwidth segments,
wherein the subcarrier mapper is further configured to assign at least one pilot signal to at least one of the plurality of logical subcarriers,
wherein the IFFT processor is further configured to modulate each of the available physical subcarriers with data from a corresponding logical subcarrier,
wherein the subcarrier mapper is further configured to set an input data signal corresponding to each of the plurality of unavailable physical subcarriers to zero,
wherein the subcarrier mapper is further configured to define a plurality of clusters in the discontiguous bandwidth segments, each of the clusters comprising a plurality contiguous subcarriers, configured to define an adaptive modulation and coding (AMC) subchannel comprising a plurality of contiguous clusters extending over a plurality of contiguous symbols, configured to allocate a first plurality of subcarriers within the AMC subchannel as pilot subcarriers such that the pilot subcarriers are distributed uniforml across the AMC subchannel, and configured to allocate a second plurality of subcarriers within the AMC subchannel as data subcarriers, and
wherein pilot subcarriers in an AMC channel are offset by two subcarriers in adjacent symbols.
2. The transmitter of claim 1 , wherein the AMC subchannel comprises two clusters over three symbols.
3. The transmitter of claim 1 , wherein the AMC subchannel comprises one cluster over six symbols.
4. The transmitter of claim 1 , wherein the subcarrier mapper is configured to allocate the pilot subcarriers for an AMC subchannel at locations determined by the indices of logical subcarriers.
5. The transmitter of claim 1 , wherein the pilot subcarriers for an AMC channel including nine subcarriers per cluster are determined according to the equation:
pilot_subs
(
n
,
k
)
=
9
n
+
3
m
+
1
for
n
=
0
,
1
,
…
,
⌈
N
9
⌉
,
wherein:
n is an index number of a pilot subcarrier in a symbol;
k is an index of the symbol;
m is given by k mod 3; and
┌X┐ denotes the largest integer not greater than X.
6. The transmitter of claim 1 , wherein the subcarrier mapper is further configured to assign a plurality of data symbols to data subcarriers in the AMC subchannel according to a scrambling sequence.
7. The transmitter of claim 6 , wherein the scrambling sequence is defined by a Galois field and an offset.
8. The transmitter of claim 6 , wherein the scrambling sequence is unique to a particular cell and/or sector of a wireless communications system.
9. The transmitter of claim 1 , further comprising:
a plurality of spreaders configured to spread the communications signals using a plurality of corresponding spreading codes;
a combiner configured to combine the plurality of spread communications signals to form a combined communications signal; and
a serial to parallel converter configured to convert the combined communications signal to parallel communications signals.
10. The transmitter of claim 9 , wherein the combiner is further configured to combine the plurality of communications signals with a pilot signal.
11. The transmitter of claim 9 , wherein the subcarrier mapper is further configured to assign the parallel communications signals to respective ones of a plurality (N) of logical subcarriers, and configured to map the plurality of logical subcarriers to corresponding ones of the plurality of available physical subcarriers.
12. The transmitter of claim 1 , wherein the subcarrier mapper is further configured to assign at least one pilot signal to at least one of the plurality of logical subcarriers, and wherein the IFFT processor is further configured to modulate each of the available physical subcarriers with data from a corresponding logical subcarrier.
13. The transmitter of claim 12 , wherein the subcarrier mapper is further configured to set an input data signal corresponding to each of a plurality (N FFT -N) of unavailable physical subcarriers to zero, wherein the parallel communications signals and the at least one pilot signal comprise N information signals corresponding to the available physical subcarriers; and
wherein the IFFT processor is further configured to perform an N FFT -point inverse fourier transform of the N information signals corresponding to the available physical subcarriers and the N FFT -N input data signals corresponding to each of the plurality of unavailable physical subcarriers.
14. The transmitter of claim 13 , further comprising a parallel to serial converter configured to convert an output of the N FFT -point inverse fourier transform to a serial data stream.
15. A receiver for a wireless communications system, comprising:
a serial to parallel converter configured to convert a received symbol stream to an N FFT symbol wide parallel received symbol stream;
a fast fourier transform (FFT) processor configured to perform an N FFT -point fourier transform on the parallel received symbol stream and to generate received symbols corresponding to N FFT subcarriers; and
a subchannel demapper configured to select N symbols of the received symbols corresponding to the N FFT subcarriers, wherein the N selected symbols correspond to N available physical subcarriers out of the N FFT subcarriers and configured to reconstruct a transmit data stream associated with the receiver from the N selected symbols,
wherein the N FFT available physical subcarriers comprise orthogonal subcarriers defined across a frequency band including a plurality of discontiguous available bandwidth segments, and wherein the N available physical subcarriers are distributed among the plurality of discontiguous available bandwidth segments,
wherein the subcarrier demapper is further configured to receive at least one pilot signal from at least one of the plurality of available physical subcarriers,
wherein the subcarrier demapper is further configured to receive a plurality of clusters in the discontiguous bandwidth segments, each of the clusters comprising a plurality contiguous subcarriers, and configured to extract the at least one pilot signal from an adaptive modulation and coding (AMC) subchannel comprising a plurality of contiguous clusters extending over a plurality of contiguous symbols, and
wherein the subcarrier demapper is configured to locate pilot subcarriers in an AMC channel including nine subcarriers per cluster according to the equation:
pilot_subs
(
n
,
k
)
=
9
n
+
3
m
+
1
for
n
=
0
,
1
,
…
,
⌈
N
9
⌉
,
wherein:
n is an index number of a pilot subcarrier in a symbol;
k is an index of the symbol;
m is given by k mod 3; and
┌X┐ denotes the largest integer not greater than X.
16. The receiver of claim 15 , wherein the AMC subchannel comprises two clusters over three symbols.
17. The receiver of claim 15 , wherein the AMC subchannel comprises one cluster over six symbols.
18. The receiver of claim 15 , wherein the subcarrier demapper is further configured to extract a plurality of data symbols from data subcarriers in the AMC subchannel according to a scrambling sequence.
19. The receiver of claim 18 , wherein the scrambling sequence is defined by a Galois field and an offset.
20. The receiver of claim 18 , wherein the scrambling sequence is unique to a particular cell and/or sector of a wireless communications system.
21. The receiver of claim 15 , further comprising:
a parallel to serial converter configured to convert the reconstructed transmit data stream to a parallel communications signal; and
a despreader configured to despread the parallel communications signals using a spreading code associated with the receiver.
22. A communications system, comprising:
a transmitter comprising:
a subcarrier mapper configured to receive a plurality of input symbols, configured to assign the plurality of input symbols to N logical subcarriers, configured to map the N logical subcarriers to N available physical subcarriers out of N FFT physical subcarriers wherein N FFT >N and configured to generate N FFT transmit symbols corresponding to the N FFT physical subcarriers;
an inverse fast fourier transform (IFFT) processor configured to perform an inverse fourier transform on the N FFT transmit symbols output by the subcarrier mapper; and
a parallel to serial converter configured to convert an output of the IFFT processor to a serial output stream; and
a receiver comprising:
a serial to parallel converter configured to convert a received symbol stream to an N FFT symbol wide parallel received symbol stream;
a fast fourier transform (FFT) processor configured to perform an N FFT -point fourier transform on the parallel received symbol stream and to generate received symbols corresponding to N FFT subcarriers; and
a subchannel demapper configured to select N symbols of the received symbols corresponding to the N FFT subcarriers, wherein the N selected symbols correspond to N available physical subcarriers out of the N FFT subcarriers, and configured to reconstruct a transmit data stream associated with the receiver from the N selected symbols,
wherein the N FFT available physical subcarriers comprise orthogonal subcarriers defined across a frequency band including a plurality of discontiguous available bandwidth segments, and wherein the N available physical subcarriers are distributed among the plurality of discontiguous available bandwidth segments,
wherein the subcarrier mapper is further configured to assign at least one pilot signal to at least one of the plurality of logical subcarriers,
wherein the IFFT processor is further configured to modulate each of the available physical subcarriers with data from a corresponding logical subcarrier,
wherein the subcarrier mapper is further configured to set an input data signal corresponding to each of the plurality of unavailable physical subcarriers to zero,
wherein the subcarrier mapper is further configured to define a plurality of clusters in the discontiguous bandwidth segments, each of the clusters comprising a plurality contiguous subcarriers, configured to define an adaptive modulation and coding (AMC) subchannel comprising a plurality of contiguous clusters extending over a plurality of contiguous symbols, configured to allocate a first plurality of subcarriers within the AMC subchannel as pilot subcarriers, such that the pilot subcarriers are distributed uniformly across the AMC subchannel, and configured to allocate a second plurality of subcarriers within the AMC subchannel as data subcarriers, and
wherein pilot subcarriers in an AMC channel are offset by two subcarriers in adjacent symbols.
23. The communications system of claim 22 , wherein the AMC subchannel comprises two clusters over three symbols.
24. The communications system of claim 22 , wherein the AMC subchannel comprises one cluster over six symbols.
25. The communications system of claim 22 , wherein the subcarrier mapper is configured to allocate the pilot subcarriers for an AMC subchannel at locations determined by the indices of logical subcarriers.
26. The communications system of claim 22 , wherein the pilot subcarriers for an AMC channel including nine subcarriers per cluster are determined according to the equation:
pilot_subs
(
n
,
k
)
=
9
n
+
3
m
+
1
for
n
=
0
,
1
,
…
,
⌈
N
9
⌉
,
wherein:
n is an index number of a pilot subcarrier in a symbol;
k is an index of the symbol;
m is given by k mod 3; and
┌X┐ denotes the largest integer not greater than X.
27. The communications system of claim 22 , wherein the subcarrier mapper is further configured to assign a plurality of data symbols to data subcarriers in the AMC subchannel according to a scrambling sequence.
28. The communications system of claim 27 , wherein the scrambling sequence is defined by a Galois field and an offset.
29. The transmitter of claim 1 , wherein the N available physical subcarriers do not include guard subcarriers.
30. The receiver of claim 15 , wherein the N available physical subcarriers do not include guard subcarriers.
31. The communications system of claim 22 , wherein the N available physical subcarriers do not include guard subcarriers.