Methods for transceiving data in multi-band orthogonal frequency division multiple access communications system and communications apparatuses utilizing the same

1. A communications apparatus in a communications system, comprising:

a receiving module, receiving a signal with a predetermined signal bandwidth, wherein the signal comprises a plurality of regular sub-carrier frequency components and a plurality of guard sub-carrier frequency components, and the signal carries data on both the regular and the guard sub-carrier frequency components;

a low pass filter, filtering the signal to obtain a filtered signal, wherein a filter bandwidth of the low pass filter is wide enough to pass the regular sub-carrier frequency components and at least half of the guard sub-carrier frequency components of the signal;

an analog to digital converter (ADC), sampling the filtered signal with a sampling rate exceeding a standard sampling rate defined in accordance with the predetermined signal bandwidth of the signal to obtain a plurality of digital samples;

a Fast Fourier Transform (FFT) module, performing a fast Fourier transform on a predetermined number of points of the digital samples to obtain a plurality of transformed samples, wherein the predetermined number exceeds a standard number defined in accordance with the predetermined carrier bandwidth; and

a sub-carrier collector, collecting the data from the transformed samples.

2. The communications apparatus as claimed in claim 1 , wherein the transformed samples comprises a plurality of regular sub-carrier tones and a plurality of guard sub-carrier tones, and the sub-carrier collector collects the data from both the regular and the guard sub-carrier tones.

3. The communications apparatus as claimed in claim 1 , wherein the data is transmitted over a plurality of radio frequency (RF) carrier bands, and each RF carrier band comprises the regular sub-carrier frequency components and the guard sub-carrier frequency components located between adjacent RF carrier bands within the predetermined signal bandwidth.

4. The communications apparatus as claimed in claim 3 , wherein the filter bandwidth of the low pass filter is wide enough to pass both the regular sub-carrier frequency components and the guard sub-carrier frequency components of an RF carrier band.

5. The communications apparatus as claimed in claim 1 , wherein the sampling rate of the ADC is a multiple of the standard sampling rate.

6. The communications apparatus as claimed in claim 1 , wherein a first ratio of the sampling rate of the ADC to the standard sampling rate is a power of 2.

7. The communications apparatus as claimed in claim 6 , wherein a second ratio of the predetermined number of a FFT point to the standard number relates to the first ratio.

8. The communications apparatus as claimed in claim 1 , wherein the communications system is an Orthogonal Frequency Division Multiple Access (OFDMA) communications system.

9. A method for transceiving data in a multi-band Orthogonal Frequency Division Multiple Access (OFDMA) communications system comprising:

transmitting the data through a plurality of radio frequency (RF) carrier bands to an air interface, wherein each RF carrier band has a predetermined signal bandwidth and comprises frequency components of N sub-carrier tones, comprising a plurality of regular sub-carrier tones and a plurality of guard sub-carrier tones located between adjacent RF carrier bands, and wherein the data is carried by both the regular sub-carrier tones and the guard sub-carrier tones;

receiving an RF signal comprising the frequency components of at least one of the RF carrier bands from the air interface;

processing the RF signal to obtain a plurality of digital samples, wherein the digital samples are obtained according to a sampling rate exceeds the predetermined signal bandwidth; and

retrieving the data from the digital samples.

10. The method as claimed in claim 9 , wherein the processing step further comprises:

down converting the RF signals to a baseband signal;

low pass filtering the baseband signal by using a filter bandwidth wide enough to pass the regular sub-carrier tones and at least half of the guard sub-carrier tones of the received RF carrier band to obtained a filtered signal; and

oversampling the filtered signal with the sampling rate to obtain the digital samples.

11. The method as claimed in claim 9 , wherein the sampling rate is a multiple of the predetermined signal bandwidth.

12. The method as claimed in claim 10 , wherein the retrieving step further comprises:

performing a K×N points of Fourier transform on the digital samples to obtain a plurality of transformed samples, wherein K relates to a ratio of the sampling rate to the predetermined signal bandwidth; and

collecting the data from the transformed samples.

13. The method as claimed in claim 10 , wherein a ratio of the sampling rate to the predetermined signal bandwidth is a power of 2.

14. The method as claimed in claim 10 , wherein the filter bandwidth of the low pass filtering is wide enough to pass both the regular sub-carrier tones and the guard sub-carrier tones of the received RF carrier band.

15. A method for receiving data in a multi-band Orthogonal Frequency Division Multiple Access (OFDMA) communications system comprising:

receiving a signal from an air interface, wherein the signal carries data within a radio frequency (RF) carrier band, and comprises a plurality of regular sub-carrier frequency components and a plurality of guard sub-carrier frequency components located at the edges of the RF carrier band, wherein the signal carries data on both the regular and the guard sub-carrier frequency components;

low pass filtering the signal by using a filter bandwidth wide enough to pass the regular sub-carrier frequency components and at least half of the guard sub-carrier frequency components of the signal to obtain a filtered signal;

sampling the filtered signal with a sampling rate exceeding a predetermined signal bandwidth of the RF carrier band to obtain a plurality of digital samples; and

retrieving the data from the digital samples.

16. The method as claimed in claim 15 , wherein the signal has been modulated by using N points of Inverse Fast Fourier Transform (IFFT) to carry data within the RF carrier band, and the method further comprises:

performing M points of Fast Fourier Transform (FFT) on the digital samples to obtain a plurality of transformed samples, wherein M is a positive integer and exceeds N; and

collecting the data from the transformed samples.

17. The method as claimed in claim 15 , wherein a ratio of M to N is a positive integer and relates to a ratio of the sampling rate to the predetermined signal bandwidth.

18. The method as claimed in claim 15 , wherein a ratio of the sampling rate to the predetermined signal bandwidth is a power of 2.

19. The method as claimed in claim 15 , wherein the filter bandwidth is wide enough to pass both the regular sub-carrier frequency components and the guard sub-carrier frequency components of the signal to obtain the filtered signal.

20. The method as claimed in claim 15 , further comprising:

performing a fast Fourier transform on a predetermined number of points of the digital samples to obtain a plurality of transformed samples, wherein the predetermined number exceeds a standard number defined in accordance with the predetermined carrier bandwidth, and wherein the transformed samples comprise a plurality of regular sub-carrier tones and a plurality of guard sub-carrier tones, and the sub-carrier collector collects the data from both the regular and the guard sub-carrier tones.