Multi-carrier transmission systems and methods using subcarrier relocation and guard interval insertion

1. A multi-carrier transmission system comprising:

an encoder that converts a data sequence into encoded symbols corresponding to respective sub-carriers;

a first shifter that rearranges the encoded symbols to define a guard interval length;

an inverse fast Fourier transform (IFFT) unit that inverse fast Fourier transforms the rearranged encoded symbols;

a second shifter that multiplies respective ones of the transformed symbols by multipliers that are a function of a frequency shift effected by the IFFT unit to generate respective processed symbols; and

a guard interval inserter that interleaves symbol replicas with the processed symbols according to the guard interval length.

2. The multi-carrier transmission system according to claim 1 , wherein the first shifter comprises:

a plurality of phase shifters that shift an angular frequency of at least one of the encoded symbols;

a counter that increases a count value in response to a clock signal; and

a multiplexer that outputs one of the encoded symbols and the phase-shifted symbols in response to the count value.

3. The multi-carrier transmission system according to claim 2 , wherein each of the plurality of phase shifters comprise a multiplier that multiplies the encoded symbols according to the equation x(n−i)⇄X(k)e j2πki/N , wherein N is the length of the data sequence and i is the length of the guard interval in terms of N.

4. The multi-carrier transmission system according to claim 1 , wherein the guard interval length is one-fourth the length of the data sequence, and wherein the first shifter comprises:

a first phase shifter that shifts an angular frequency of at least one of the encoded symbols by −90°;

a second phase shifter that shifts an angular frequency of at least one of the encoded symbols by −180°;

a third phase shifter that shifts an angular frequency of at least one of the encoded symbols by 90°;

a counter that increases a count value in response to a clock signal; and

a multiplexer that outputs one of the encoded symbols and the phase-shifted symbols output from the first, second and third phase shifters in response to the count value.

5. The multi-carrier transmission system according to claim 4 , wherein the first, second and third phase shifters each comprise a multiplier that multiplies the encoded symbols according to the equation x(n−i)⇄X(k)e j2πki/N , wherein N is the length of the data sequence and i is N/4.

6. The multi-carrier transmission system according to claim 1 , wherein the guard interval length is one-half the length of the data sequence, and wherein the first shifter comprises:

a first phase shifter that shifts an angular frequency of at least one of the encoded symbols by 180°;

a counter that increases a count value in response to a clock signal; and

a multiplexer that outputs one of the encoded symbols and the phase-shifted symbols in response to the count value.

7. The multi-carrier transmission system according to claim 6 , wherein the first phase shifter comprises a multiplier that multiplies the plurality of symbols output from the encoder according to the equation x(n−i)⇄X(k)e j2πki/N , wherein N is the length of the data sequence and i is N/2.

8. The multi-carrier transmission system according to claim 1 , wherein the second shifter comprises:

a multiplier that multiples the transformed symbols according to the equation x(n−i)⇄X(k)e j2πki/N , wherein N is the length of the data sequence and m is N/2;

a counter that increases a count value in response to a clock signal; and

a multiplexer that outputs one of the transformed symbols and the multiplied symbols in response to the count value.

9. The multi-carrier transmission system according to claim 1 , wherein the guard interval inserter comprises:

a controller that determines whether symbols output from the second shifter correspond to the guard interval;

a shift register that stores symbols determined by the controller to correspond to the guard interval; and

a multiplexer that outputs the symbols output from the second shifter and the symbols stored in the shift register.

10. A method of transmitting a multi-carrier signal, the method comprising:

converting a data sequence into encoded symbols corresponding to respective sub-carriers;

rearranging the encoded symbols to define a guard interval length;

inverse fast Fourier transforming the rearranged encoded symbols;

multiplying respective ones of the transformed symbols by multipliers that are a function of a frequency shift effected by the inverse fast Fourier transformation to generate respective processed symbols; and

interleaving symbol replicas with the processed symbols according to the guard interval length.

11. The method of transmitting a multi-carrier signal according to claim 10 , wherein converting a data sequence into encoded symbols further comprises:

converting the data to be transmitted into a plurality of symbols arranged in series;

converting the plurality of symbols arranged in series into a plurality of symbols arranged in parallel;

rectangular pulse-shaping the plurality of symbols arranged in parallel; and

modulating the plurality of rectangular pulse-shaped symbols with a plurality of sub-carriers.

12. The method of transmitting a multi-carrier signal according to claim 10 , wherein rearranging the encoded symbols to define a guard interval length comprises:

receiving the encoded symbols;

determining the index associated with each of the received symbols;

shifting an angular frequency of at least one of the received symbols based on the index associated with each symbol.

13. The method of transmitting a multi-carrier signal according to claim 12 , wherein shifting an angular frequency of at least one of the received signals is performed according to the equation x(n−i)⇄X(k)e j2πki/N , wherein N is the length of the data sequence, k is the index of the symbol, and i is the length of the guard interval in terms of N.

14. The method of transmitting a multi-carrier signal according to claim 10 , wherein the length of the data sequence is N (a positive integer), and wherein the guard interval length is G (a positive integer less than N).

15. The method of transmitting a multi-carrier signal according to 14 , wherein the guard interval corresponds to the last G symbols of the data sequence.

16. The method of transmitting a multi-carrier signal according to claim 15 , wherein the first shifter shifts the encoded symbols to position the last G symbols, corresponding to the guard interval, in the front of the data sequence.

17. The method of transmitting a multi-carrier signal according to claim 14 , wherein U is one-fourth of N, and wherein rearranging the encoded symbols to define a guard interval length comprises:

receiving the encoded symbols;

determining the index associated with each of the received symbols;

shifting an angular frequency of at least one of the received signals according to the equation x(n−i)⇄X(k)e j2πki/N , wherein k is the index of the symbol and i is N/4.

18. The method of transmitting a multi-carrier signal according to claim 14 , wherein G is one-half of N, and wherein rearranging the encoded symbols to define a guard interval length comprises:

receiving the encoded symbols;

determining the index associated with each of the received symbols;

shifting an angular frequency of at least one of the received signals according to the equation x(n−i)⇄X(k)e j2πki/N , wherein k is the index of the symbol and i is N/2.

19. The method of transmitting a multi-carrier signal according to claim 10 , multiplying respective ones of the transformed symbols by multipliers that are a function of a frequency shift effected by the inverse fast Fourier transformation to generate respective processed symbols comprises:

receiving the transformed symbols;

determining the index associated with each of the received symbols;

multiplying certain of the received symbols by 1 according to the equation x(n−i)⇄X(k)e j2πki/N , wherein N is the length of the data sequence, k is the index of the symbol and m is N/2.

20. The method of transmitting a multi-carrier signal according to claim 10 , wherein interleaving symbol replicas with the processed symbols according to the guard interval length comprises:

receiving the processed symbols;

determining whether each of the processed symbols corresponds with the guard interval;

storing guard interval symbols in a shift register;

outputting the processed symbols not corresponding with the guard intervals and replicas of the guard interval symbols; and

outputting the guard interval symbols stored in the shift register at the rear of the output symbols.