Method and apparatus for providing signal acquisition and frame synchronization in a hierarchical modulation scheme
An approach is provided for supporting signal acquisition and frame synchronization in a digital broadcast system utilizing Low Density Parity Check (LDPC) codes. Hierarchical modulation is utilized to provide backward compatibility, whereby the lower layer signal is encoded using LDPC coding. A signal is received, whereby the signal is modulated according to the hierarchical modulation scheme including an upper layer and a lower layer. The signal includes a data pattern and a coded frame. The dependency of the received signal on the upper layer modulation is removed. The modulation removed signal is correlated with multiple predetermined data patterns to determine the data pattern of the signal. The code rate of the coded frame is derived based on the determined data pattern. The above arrangement is particularly suited to a digital satellite broadcast system.
1. A method for generating a signal in a communication system, the method comprising the steps of:
receiving, via circuitry, an upper layer data stream associated with a first modulation scheme and a lower layer data stream associated with a second modulation scheme;
coding the lower layer data stream according to a sequence among a plurality of sequences specifying respective data patterns corresponding to different code rates;
modulating the upper layer data stream and the coded lower layer data stream according to respective ones of the first and second modulation schemes;
multiplying the modulated upper layer data stream and lower layer data stream to generate a multiplied signal; and
transmitting the multiplied signal over a communications channel.
2. A method according to claim 1 , wherein the data patterns are of equal length.
3. A method according to claim 1 , wherein the lower layer data stream is encoded according to Low Density Parity Check (LDPC) coding.
4. A method according to claim 3 , wherein the upper layer data stream is encoded according to convolutional coding.
5. A method according to claim 1 , wherein the first modulation scheme is of a higher order than the second modulation scheme.
6. A method according to claim 5 , wherein the first modulation scheme is Quadrature Phase Shift Keying (QPSK) and the second modulation scheme is Binary Phase Shift Keying (BPSK).
7. A method according to claim 1 , wherein the data patterns include:
100100001110100111101101000110000011011000000010001100000101111010110010001010100111001010
111101011000001010101011000110100011010010001100000110011010110010001111001000011011000000
010100111001010100010011010111101000001100010000000110110000011000101101111001011100001001
000000110110000100111100010011010110011000001100010010110001011000110101010100000110101111.
8. A method according to claim 1 , wherein the upper layer data stream has a first Digital Video Broadcast (DVB) format, and the lower layer data stream has a second DVB format that is different from the first DVB format.
9. A method according to claim 1 , wherein the communication system is a satellite network.
10. A method according to claim 1 , wherein the code rate is derived based on a corresponding one of the data patterns without an explicit field being designated to specify the code rate.
11. An apparatus for generating a signal in a communication system, the apparatus comprising:
hierarchical modulation circuitry configured to receive an upper layer data stream associated with a first modulation scheme and a lower layer data stream associated with a second modulation scheme, to code the lower layer data stream according to a sequence among a plurality of sequences specifying respective data patterns corresponding to different code rates, to modulate the upper layer data stream and the coded lower layer data stream according to respective ones of the first modulation scheme and the second modulation scheme and to multiply the modulated upper layer data stream and lower layer data stream to generate a multiplied signal; and
transmit circuitry configured to transmit the multiplied signal on a communications channel.
12. An apparatus according to claim 11 , wherein the data patterns are of equal length.
13. An apparatus according to claim 11 , wherein the lower layer data stream is encoded according to Low Density Parity Check (LDPC) coding.
14. An apparatus according to claim 13 , wherein the upper layer data stream is encoded according to convolutional coding.
15. An apparatus according to claim 11 , wherein the first modulation scheme is of a higher order than the second modulation scheme.
16. An apparatus according to claim 15 , wherein the first modulation scheme is Quadrature Phase Shift Keying (QPSK) and the second modulation scheme is Binary Phase Shift Keying (BPSK).
17. An apparatus according to claim 11 , the data patterns include:
100100001110100111101101000110000011011000000010001100000101111010110010001010100111001010
111101011000001010101011000110100011010010001100000110011010110010001111001000011011000000
010100111001010100010011010111101000001100010000000110110000011000101101111001011100001001
000000110110000100111100010011010110011000001100010010110001011000110101010100000110101111.
18. An apparatus according to claim 11 , wherein the upper layer data stream has a first Digital Video Broadcast (DVB) format, and the lower layer data stream has a second DVB format that is different from the first DVB format.
19. An apparatus according to claim 11 , wherein the communication system is a satellite network.