OFDM Multiple Sub-Channel Communication System

• US 20070183308A1
• Filed: 04/16/2007
• Published: 08/09/2007
• Est. Priority Date: 06/11/2001
• Status: Abandoned Application

• Current Assignee: Unique Broadband Systems, Ltd.
• Original Assignee: Unique Broadband Systems, Inc.
• Inventors: Dolgonos, Alex, Howell, Randy, Korobkov, Dmitri
• Application Number:
  US11/735,786
• Publication Number:
  US 20070183308A1
• Time in Patent Office: Days
• US Class Current: 370/208
• CPC Class Codes: H04L 1/004 by using forward error control H04L1/0618 takes precedence; coding, decoding or code conversion, for error detection or correction H03M13/00
• CPC Class Codes: H04L 27/2637 with direct modulation of individual subcarriers
• CPC Class Codes: H04L 27/2653 with direct demodulation of individual subcarriers
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0037 Inter-user or inter-terminal allocation
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/0046 Determination of how many bits are transmitted on different sub-channels
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver

Abstract

A transmitter for transmitting an OFDM signal in a communications channel, including: (a) a plurality of base-band OFDM modulators, each for modulating a respective baseband data signal onto a plurality of orthogonal sub-carriers and outputting a respective baseband sub-channel OFDM signal, and (b) a fast convolution filter and up-converter for applying fast convolution filtering and digital up-conversion to the sub-channel OFDM signals to output a combined OFDM signal that includes each of the sub-channel OFDM signals, the fast convolution and up-converter filtering each of the sub-channel OFDM signals and frequency shifting all of the sub-channel signals to respective designated frequencies within the combined OFDM signal.

Claims

1. A transmitter for transmitting an OFDM signal in a communications channel, including:

(a) a plurality of base-band OFDM modulators, each for modulating a respective baseband data signal onto a plurality of orthogonal sub-carriers and outputting a respective baseband sub-channel OFDM signal; and

(b) a fast convolution filter and up-converter for applying fast convolution filtering and digital up-conversion to the sub-channel OFDM signals to output a combined OFDM signal that includes each of the sub-channel OFDM signals, the fast convolution and up-converter filtering each of the sub-channel OFDM signals and frequency shifting all of the sub-channel signals to respective designated frequencies within the combined OFDM signal.

2. The transmitter of claim 1 wherein said fast convolution and up-converter includes:

a plurality of processing chains each associated with a sub-channel and including a frequency domain filter for applying a sub-channel spectral mask to one of the sub-channel OFDM signals to output a filtered sub-channel OFDM signal;

a common buffer for receiving the filtered sub-channel OFDM signals from each of the processing chains and shifting each of the sub-channel OFDM signals to the respective designated frequencies within the combined OFDM signal; and

an IFFT for converting the combined OFDM signal output by the common buffer from a frequency domain signal to a time domain signal.

3. The transmitter of claim 2 further including a fast convolution output buffer for removing filter transients from the time domain signal output by the IFFT.

4. The transmitter of claim 1 wherein the fast convolution filter and upconverter applies overlap-and-save fast convolution filtering to the sub-channel OFDM signals.

5. The transmitter of claim 1 wherein the fast convolution filter and upconverter applies overlap-and-add fast convolution filtering to the sub-channel OFDM signals.

6. The transmitter of claim 1 wherein said fast convolution and up-converter includes:

a plurality of processing chains, each for processing one of the sub-channel OFDM signals received from an associated one of the OFDM modulators, each processing chain including;

i) an input buffer for breaking the sub-channel OFDM signal into a plurality of processing blocks;

ii) an FFT for performing and FFT on the processing blocks to convert the sub-channel OFDM signal into a frequency domain signal; and

iii) a digital filter for applying a spectral mask to each of the processing blocks, the spectral mask corresponding to a band-width assigned to the sub-channel;

a common buffer for receiving the filtered sub-channel OFDM signals from each of the processing chains and shifting each of the sub-channel OFDM signals to the respective designated frequencies within the combined OFDM signal; and

an IFFT for converting the combined OFDM signal output by the common buffer from a frequency domain signal to a time domain signal.

7. The transmitter of claim 6 wherein the fast convolution filter and upconverter applies overlap-and-save fast convolution filtering to the sub-channel OFDM signals and includes an output buffer for discarding from each processing block in the combined OFDM signal output from the IFFT a portion that overlaps in time with a portion of a preceding processing block.

8. The transmitter of claim 6 wherein the fast convolution filter and upconverter applies overlap-and-add fast convolution filtering to the sub-channel OFDM signals and includes an output buffer for adding portions of the processing blocks in the combined OFDM signal output from the IFFT to portions of preceding processing blocks that overlap in time.

9. The transmitter of claim 1 including a data splitter for receiving a block of data and segmenting the block of data into the respective baseband data signals for input to the plurality of base-band OFDM modulators.

10. The transmitter of claim 1 wherein each base-band OFDM modulator includes:

(i) a forward error correction block for receiving the respective baseband signal and introducing error-correcting redundancy into the baseband signal;

(ii) spectrum builder and Inverse Fast Fourier Transform blocks for segmenting portions of the signal into sub-segments represented as complex values and modulating the complex values onto respective OFDM sub-carriers to output an OFDM symbol; and

(iii) a cyclic extension block for inserting a guard time into the OFDM symbol.

11. The transmitter of claim 1 comprising a controller that receives time-varying medium access control (MAC) layer information for an OFDM system in which the transmitter operates and in dependence thereon provides sub-channel and frequency position information to the fast convolution filter and up-converter for use in dynamically setting the respective designated frequencies.

12. A method for transmitting an OFDM signal including a plurality of sub-channel OFDM signals in a communications channel, comprising, at a transmitter:

(a) receiving data and segmenting the data into a plurality of parallel baseband data signals;

(b) generating in parallel a plurality of baseband sub-channel OFDM signals, each baseband sub-channel OFDM signal including a respective one of the baseband data signals modulated onto a plurality of orthogonal sub-carriers; and

(c) applying fast convolution filtering and digital up-conversion to the baseband sub-channel OFDM signals to output a combined OFDM signal that includes each of the sub-channel OFDM signals, including filtering each of the baseband sub-channel OFDM signals and frequency shifting each of the sub-channel baseband OFDM signals to respective designated frequencies within the combined OFDM signal.

13. The method of claim 12 including dynamically setting the respective designated frequencies in dependence on medium access control (MAC) information for the communications channel.

14. A transmitter for transmitting an OFDM signal in a communications channel, including:

a data splitter receiving a block of data and segmenting the block of data into a plurality of baseband data signals;

a plurality of base-band OFDM modulators, each receiving a respective one of the baseband data signals and modulating the respective baseband data signal onto a plurality of orthogonal sub-carriers and outputting a respective baseband sub-channel OFDM signal; and

a fast convolution filter and up-converter applying fast convolution filtering and digital up-conversion to the baseband sub-channel OFDM signals to output a combined OFDM signal that includes each of the sub-channel OFDM signals, the fast convolution and up-converter filtering each of the sub-channel OFDM signals and frequency shifting all of the sub-channel signals to respective designated frequencies within the combined OFDM signal.

15. The transmitter of claim 14 comprising:

a controller that receives time-varying medium access control (MAC) layer information for the communication channel and outputs frequency position information in dependence thereon, and

wherein the fast convolution and up-converter includes;

(a) a plurality of processing chains, each for processing one of the sub-channel OFDM signals received from an associated one of the OFDM modulators, each processing chain including;

i) an input buffer for breaking the sub-channel OFDM signal into a plurality of processing blocks;

ii) an FFT for performing and FFT on the processing blocks to convert the sub-channel OFDM signal into a frequency domain signal; and

iii) a digital filter for applying a spectral mask to each of the processing blocks, the spectral mask corresponding to a band-width assigned to the sub-channel;

(b) a common buffer for receiving the filtered sub-channel OFDM signals from each of the processing chains and shifting each of the sub-channel OFDM signals to the respective designated frequencies within the combined OFDM signal, wherein the common buffer dynamically sets the respective designated frequencies in dependence on the frequency position information output by the controller; and

(c) an IFFT for converting the combined OFDM signal output by the common buffer from a frequency domain signal to a time domain signal.

16. The transmitter of claim 14 wherein each base-band OFDM modulator includes:

(i) a forward error correction block for receiving the respective baseband signal and introducing error-correcting redundancy into the baseband signal;

(ii) spectrum builder and Inverse Fast Fourier Transform blocks for segmenting portions of the signal into sub-segments represented as complex values and modulating the complex values onto respective OFDM sub-carriers to output an OFDM symbol; and

(iii) a cyclic extension block for inserting a guard time into the OFDM symbol.