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 within an available spectral resource, the method comprising:
adaptively switching between:
transmitting to a receiver with orthogonal frequency-division multiplexing (OFDM); and
transmitting to the receiver with transformed orthogonal frequency-division multiplexing (T-OFDM), wherein said transmitting with T-OFDM includes:
applying a non-identity transform to a plurality of modulation symbols to obtain intermediate symbols; and
providing mapped symbols determined by the intermediate symbols to an OFDM unit in order to convert the mapped symbols into a time-domain OFDM signal.
2. The method of claim 1 , further comprising:
receiving feedback from a remote communication system, wherein said feedback is used to select between said transmitting with OFDM and said transmitting with T-OFDM.
3. The method of claim 1 , further comprising: selecting between said transmitting with OFDM and said transmitting with T-OFDM on the basis of signal-to-noise ratio and/or traffic type.
4. The method of claim 1 , further comprising: selecting between said transmitting with OFDM and said transmitting with T-OFDM on the basis of head room in a power amplifier of the transmitter.
5. A transmitter for communication within an available spectral resource, the transmitter comprising:
circuitry configured to adaptively switch between:
transmitting to a receiver with orthogonal frequency-division multiplexing (OFDM); and
transmitting to the receiver with transformed orthogonal frequency-division multiplexing (T-OFDM), wherein said transmitting with T-OFDM includes:
applying a non-identity transform to a plurality of modulation symbols to obtain intermediate symbols; and
providing mapped symbols determined by the intermediate symbols to an OFDM unit in order to convert the mapped symbols into a time-domain OFDM signal.
6. The transmitter of claim 5 , further comprising:
a transformer configured to apply the non-identity transform to the plurality of modulation symbols to obtain the intermediate symbols; and
said OFDM unit.
7. The transmitter of claim 5 , wherein said circuitry includes:
a transform unit configured to apply the non-identity transform to the plurality of symbols in order to produce said intermediate symbols; and
said OFDM unit.
8. The transmitter of claim 5 , wherein the transmitter is configured to receive feedback from a remote communication system, and to use said feedback to select between said transmitting with OFDM and said transmitting with T-OFDM.
9. The transmitter of claim 5 , wherein the transmitter is configured to select between said transmitting with OFDM and said transmitting with T-OFDM on the basis of signal-to-noise ratio and/or traffic type.
10. The transmitter of claim 5 , wherein the transmitter is configured to select between said transmitting with OFDM and said transmitting with T-OFDM on the basis of head room in a power amplifier of the transmitter.
11. The transmitter of claim 5 , wherein the transmitter is part of a base station.
12. The transmitter of claim 5 , wherein the transmitter is part of a user equipment device.
13. A non-transitory memory medium for operating a transmitter within an available spectral resource, wherein the memory medium stores program instructions, wherein the program instructions, when executed by a processor, cause the processor to implement:
adaptively switching between:
transmitting to a receiver with orthogonal frequency-division multiplexing (OFDM); and
transmitting to the receiver with transformed orthogonal frequency-division multiplexing (T-OFDM), wherein said transmitting with T-OFDM includes:
applying a non-identity transform to a plurality of modulation symbols to obtain intermediate symbols; and
providing mapped symbols determined by the intermediate symbols to an OFDM unit in order to convert the mapped symbols into a time-domain OFDM signal.
14. The non-transitory memory medium of claim 13 , wherein the program instructions, when executed by the processor, further cause the processor to implement:
receiving feedback from a remote communication system, wherein said feedback is used to select between said transmitting with OFDM and said transmitting with T-OFDM.
15. The non-transitory memory medium of claim 13 , wherein the program instructions, when executed by the processor, further cause the processor to implement:
selecting between said transmitting with OFDM and said transmitting with T-OFDM on the basis of signal-to-noise ratio and/or traffic type.
16. The non-transitory memory medium of claim 13 , wherein the program instructions, when executed by the processor, further cause the processor to implement:
selecting between said transmitting with OFDM and said transmitting with T-OFDM on the basis of head room in a power amplifier of the transmitter.