Method and system for combining OFDM and transformed OFDM
Methods and systems are provided that enable an OFDM transmitter to be used for transmitting conventional OFDM or a form of transformed OFDM. A technique is provided for transforming a coded and modulated sequence of samples prior to an IFFT that enables the transformed sequence of samples to be transmitted using conventional OFDM or transformed OFDM. The selection of a transform function for transforming the coded and modulated sequence of samples may be based on optimizing the transform function for particular operating conditions between the transmitter and receiver. In some embodiments of the invention OFDM and time transformed OFDM are multiplexed in time and/or frequency in a transmission frame. In some embodiments of the invention a pilot pattern is provided in which the pilot are sent using OFDM and data is sent using OFDM and/or transformed OFDM.
1. A method for operating a transmitter, the method comprising:
adaptively selecting one of a plurality of transforms to be a selected transform, wherein no two of the transforms are equal, wherein a first of the transforms is an identity transform;
applying the selected transform to a sequence of input symbols to produce a transformed sequence of samples;
performing an inverse fast Fourier transform (IFFT) on the transformed sequence of samples to produce an output sequence; and
transmitting one or more signals onto a transmission medium based on the output sequence.
2. The method of claim 1 , wherein a second of the transforms is a Fast Fourier Transform (FFT).
3. The method of claim 1 , wherein a second of the transforms is a fast Hadamard transform.
4. The method of claim 1 , wherein a second of the transforms is a discrete cosine transform (DCT).
5. The method of claim 1 , wherein a second of the transforms is a wavelet transform.
6. A transmitter comprising:
a transform unit configured to apply a selected transform to a sequence of input symbols to produce a transformed sequence of samples, wherein the selected transform is adaptively selected from a plurality of transforms, wherein no two of the transforms are equal, wherein a first of the transforms is an identity transform;
an inverse fast Fourier transform (IFFT) unit configured to perform an IFFT on the transformed sequence of samples to produce an output sequence; and
transmission circuitry configured to transmit a signal onto a transmission medium based on the output sequence.
7. The transmitter of claim 6 , wherein a second of the transforms is a Fast Fourier Transform (FFT).
8. The transmitter of claim 6 , wherein a second of the transforms is a fast Hadamard transform.
9. The transmitter of claim 6 , wherein a second of the transforms is a discrete cosine transform (DCT).
10. The transmitter of claim 6 , wherein a second of the transforms is a wavelet transform.