Uplink ranging system and method in OFDMA system

1. A ranging system in an OFDMA (orthogonal frequency division multiple access) system, comprising:

complex exponential twiddle storage units for respectively storing complex exponential twiddle factors corresponding to a timing error;

complex multipliers for respectively complex-multiplying the complex exponential twiddle factors by received uplink ranging data;

code correlators for respectively correlating the outputs of the complex multipliers and ranging codes; and

threshold comparators for respectively comparing the outputs of the code correlators with a threshold.

2. The ranging system as claimed in claim 1 , wherein the complex multipliers perform complex multiplications of as many as the number obtained by multiplying the number of the complex exponential twiddle factors by the number of sub-carriers.

3. The ranging system as claimed in claim 1 , wherein the number of complex multipliers, code correlators, and threshold comparators are as many as the number of the complex exponential twiddle factors, and they process ranging in parallel.

4. The ranging system as claimed in 1 , wherein the threshold comparators select a value that exceeds a threshold from values output from the code correlators to detect a corresponding ranging code and a complex exponential twiddle factor.

5. A ranging system in an OFDMA (orthogonal frequency division multiple access) system, comprising:

complex exponential twiddle storage units for storing complex exponential twiddle factors corresponding to a timing error;

address increasers for increasing sub-carrier indexes and outputting them to the complex exponential twiddle factor storage units; complex multipliers for respectively complex-multiplying the complex exponential twiddle factors by received uplink ranging data;

code correlators for respectively correlating the outputs of the complex multipliers and ranging codes; and

threshold comparators for respectively comparing the outputs of the code correlators with a threshold,

wherein the complex exponential twiddle factor storage units and the address increasers are as many as the number of the complex exponential twiddle factors, they are arranged in parallel, and a plurality of sub-carrier index groups are serially input to the address increasers.

6. The ranging system as claimed in claim 5 , further comprising an adder that is located before each of the address increasers arranged in parallel, and that outputs the sum of a sub-carrier index input thereto and a specific multiple of the sub-carrier index.

7. The ranging system as claimed in claim 6 , wherein the number of the complex exponential twiddle factors and address increasers corresponds to the value obtained by dividing the number of the complex exponential twiddle factors by the number of times of processing serial ranging.

8. The ranging system as claimed in claim 6 , wherein each of the address increasers includes a plurality of shift registers of as many as the number of the sub-carrier indexes, and an adder for adding up a sub-carrier index input to the address increaser and a value stored in the last shift register.

9. The ranging system as claimed in claim 5 , wherein each of the code correlators includes:

binary multipliers for respectively multiplying the ranging data by ranging codes in parallel;

registers for respectively storing the output values of the binary multipliers; and

adders for respectively adding up the values stored in the registers and the output values of the binary multipliers.

10. A method for processing uplink ranging in an GEDMA (orthogonal frequency division multiple access) system, comprising:

a user terminal transmitting ranging data to a base station;

complex-multiplying the ranging data by a complex exponential twiddle factor corresponding to a timing error;

correlating the complex-multiplied value with a plurality of ranging codes; and

comparing the correlation values with a threshold to detect a corresponding ranging code and complex exponential twiddle factor.