Modulation for broadcasting from multiple transmitters
View Patent ↗In a cellular network, randomness is introduced into a transmitted signal at each transmitter, and the resulting received signal, which is the sum of all received signals, fluctuates more in time than a signal transmitted without the introduced randomness. While the introduction of randomness can diminish reception of some parts of the signal at the receiver, the transmitted signal can be encoded using forward error correction coding techniques, which allows the receiver to recover all of the signal information despite some diminished reception. Such randomization provides time diversity so that receivers can have more consistent performance. For broadcasted data, where users with the worst channel condition dictates the overall performance, having consistent performance across users can improve the overall network performance.
1. A method comprising:
generating a first sequence of symbols;
sending the first sequence to multiple transmitters;
encoding the first sequence to produce an encoded sequence at each transmitter;
multiplying the encoded sequence at each transmitter by a second sequence of elements to produce a multiplied sequence, wherein the second sequence of elements is different at each transmitter, and wherein each element in the second sequence of elements corresponds to, and stays constant for a duration of, one or more time slots;
modulating the multiplied sequence at each transmitter to produce a modulated sequence of symbols; and
transmitting the modulated sequence of symbols at each transmitter in at least the one or more time slots.
2. The method of claim 1 , wherein the encoding comprises:
applying an outer forward error correction coding to the first sequence.
3. The method of claim 2 , wherein the encoding further comprises:
applying an inner forward error correction coding to the first sequence.
4. The method of claim 2 , wherein the outer forward error correction coding comprises a block coding.
5. The method of claim 2 , wherein the outer forward error correction coding comprises a convolutional coding.
6. The method of claim 2 , further comprising:
interleaving the encoded sequence.
7. The method of claim 3 , wherein the inner forward error correction coding comprises one or more of the following: a block coding, a convolutional coding, a turbo coding, or a low-density parity-check coding.
8. The method of claim 4 , wherein the block coding comprises a Reed-Solomon coding.
9. The method of claim 1 , further comprising:
prior to multiplying the encoded sequence, applying an inverse Fourier transform to the encoded data.
10. The method of claim 9 , further comprising:
appending a cyclic prefix to the encoded data.
11. The method of claim 1 , wherein the second sequence of elements comprises a pseudo-random sequence of elements generated at each transmitter.
12. The method of claim 11 , wherein each element of the pseudo-random sequence is a complex number.
13. The method of claim 11 , wherein each element of the pseudo-random sequence is a real number.
14. The method of claim 11 , wherein the pseudo-random sequence comprises an M-sequence.
15. The method of claim 12 , wherein complex numbers in the pseudo-random sequence have a same amplitude.
16. The method of claim 12 , wherein the complex number has one of N values in N equally spaced points on a unit circle.
17. The method of claim 15 , wherein the amplitude is one.
18. The method of claim 1 , further comprising:
generating the second sequence of elements at each transmitter using pre-configured information stored at each transmitter.
19. The method of claim 18 , wherein the pre-configured information comprises a pseudorandom noise offset, the pseudorandom noise offset being different at each transmitter.
20. The method of claim 1 , wherein modulating comprises using quadrature amplitude modulation.
21. The method of claim 1 , wherein modulating comprises using binary phase shift keying.
22. The method of claim 1 , wherein modulating comprises quadrature phase shift keying.
23. The method of claim 1 , wherein each transmitter transmits using time division multiplexing to multiplex a second signal with the modulated sequence transmitted at each transmitter.
24. The method of claim 23 , wherein the second signal comprises a pilot signal.
25. The method of claim 23 , wherein the second signal comprises a unicast signal.
26. The method of claim 1 , wherein the encoded sequence comprises encoded sequences of symbols, and wherein multiplying the encoded sequence further comprises:
rotating a phase angle of each of the encoded sequences of symbols within the encoded sequence, wherein for each of the encoded sequences of symbols a rotation of the phase angle is fixed for the duration of the one or more time slots.
27. A method for broadcasting blocks of symbols from a first transmitter and a second transmitter in a cellular system, the method comprising:
rotating a phase angle of each block of symbols according to a first pattern to produce a first sequence of rotated blocks of symbols, wherein for each block of symbols, a rotation of the phase angle according to the first pattern is fixed for a duration of the block of symbols;
transmitting the first sequence of rotated blocks of symbols from a first transmitter;
rotating a phase angle of each block of symbols according to a second pattern to produce a second sequence of rotated blocks of symbols, wherein for each block of symbols, a rotation of the phase angle according to the second pattern is fixed for a duration of the block of symbols; and
transmitting the second sequence of rotated blocks of symbols from the second transmitter.
28. The method of claim 27 , wherein the first pattern comprises a series of complex numbers that vary with time, wherein each complex number in the series is used to rotate the phase angle of a corresponding respective block of symbols of the blocks of symbols.
29. The method of claim 27 , wherein the first pattern comprises a series of pseudorandom numbers, wherein each pseudorandom number in the series is used to rotate the phase angle of a corresponding respective block of symbols of the blocks of symbols.
30. The method of claim 27 , wherein rotating a phase angle comprises:
multiplying each block of symbols with a complex number, wherein the complex number is determined according to the first or second pattern.
31. The method of claim 27 , further comprising:
prior to transmitting the first and second sequences of rotated blocks of symbols, modulating the first and second sequences of rotated blocks of symbols.
32. The method of claim 27 , further comprising:
encoding symbols in each block of symbols using a first encoder to produce encode symbols.
33. The method of claim 32 , wherein encoding symbols occurs prior to rotating the phase angle.
34. The method of claim 32 , wherein the first encoder comprises an outer encoder.
35. The method of claim 32 , further comprising:
interleaving the encoded symbols to produce interleaved encoded symbols.
36. The method of claim 35 , further comprising:
encoding the interleaved encoded symbols using a second encoder.
37. A transmitter for broadcasting a modulated sequence of symbols in a cellular network comprising multiple transmitters, the transmitter comprising:
an encoder configured to encode a first sequence of symbols to produce an encoded sequence;
a multiplier configured to multiply the encoded sequence by a second sequence of elements to produce a multiplied sequence, wherein the second sequence of elements is determined according to a pattern that is different from patterns used by other transmitters in the cellular network, and wherein each element in the second sequence of elements corresponds to, and stays constant for a duration of, one or more time slots;
a modulator configured to modulate the multiplied sequence to produce the modulated sequence of symbols; and
an antenna for transmitting the modulated sequence of symbols in at least the one or more time slots.
38. The transmitter of claim 37 , wherein the encoder comprises:
an outer encoder configured to apply an outer forward error correction code to the sequence of symbols.
39. The transmitter of claim 38 , wherein the encoder further comprises:
an inner encoder configured to apply an inner forward error correction code to the sequence of symbols.
40. The transmitter of claim 37 , further comprising:
an interleaver circuit configured to interleave the encoded sequence of symbols.
41. The transmitter of claim 37 , wherein the encoded sequence comprises encoded sequences of symbols, and wherein the multiplier is configured to multiply the encoded sequence by rotating a phase angle of each of the encoded sequences of symbols within the encoded sequence, wherein for each of the encoded sequences of symbols a rotation of the phase angle is fixed for the duration of the one or more time slots.