Method and system for combining OFDM and transformed OFDM
View Patent ↗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 comprising, within an available spectral resource:
transmitting with OFDM multiplexing on selected sub-carriers and selected OFDM transmission durations;
transmitting with T-OFDM (transformed OFDM) multiplexing or direct multiple sub-carrier multiplexing on selected sub-carriers and selected OFDM transmission durations that do not overlap with OFDM transmissions;
wherein transmitting with OFDM multiplexing and transmitting with T-OFDM multiplexing comprises transmitting a respective signal from each of a plurality of antennas, each signal comprising OFDM multiplexing or T-OFDM multiplexing, each signal using a distinct frequency resource for each antenna of the plurality of antennas.
2. The method of claim 1 wherein transmitting a respective signal from each of a plurality of antennas comprises transmitting from a plurality of transmitters.
3. The method of claim 1 wherein transmitting a respective signal from each of a plurality of antennas comprises transmitting from a single transmitter.
4. The method of claim 1 further comprising:
mapping symbols to the selected sub-carriers for OFDM multiplexing using a sub-band mapping or a diversity mapping;
transforming symbols to be transmitted with T-OFDM to produce transformed symbols and mapping the transformed symbols to the selected sub-carriers for T-OFDM using a sub-band mapping or a diversity mapping.
5. The method of claim 1 wherein transmitting with OFDM multiplexing and T-OFDM multiplexing comprise:
for each of at least one frequency resource allocation comprising a plurality of sub-carrier frequencies:
selecting transmitting using OFDM multiplexing and transmitting using T-OFDM multiplexing.
6. The method of claim 5 wherein the at least one frequency resource allocation comprises a plurality of resource allocations each consisting of a respective contiguous set of sub-carrier frequencies or a distributed set of sub-carrier frequencies.
7. The method of claim 5 wherein for each of at least one frequency resource allocation consisting of a plurality of sub-carrier frequencies selecting transmitting using OFDM multiplexing and transmitting using T-OFDM multiplexing comprises:
multiplying a respective set of symbols by a selected one of two different transform matrices that result in OFDM multiplexing and T-OFDM multiplexing respectively.
8. The method of claim 1 wherein T-OFDM multiplexing comprises multiplying an input set of symbols by an FFT matrix prior to IFFT processing.
9. The method of claim 1 further comprising transmitting pilots.
10. The method of claim 1 further comprising transmitting pilots from each antenna on sub-carriers selected from sub-carriers being utilized by that antenna.
11. A method comprising, within an available spectral resource:
transmitting with OFDM multiplexing on selected sub-carriers and selected OFDM transmission durations;
transmitting with T-OFDM (transformed OFDM) multiplexing or direct multiple sub-carrier multiplexing on selected sub-carriers and selected OFDM transmission durations that do not overlap with OFDM transmissions;
wherein transmitting with OFDM multiplexing and transmitting with T-OFDM multiplexing comprises transmitting a respective signal from each of a plurality of antennas, each signal comprising OFDM multiplexing or T-OFDM multiplexing;
wherein transmitting a respective signal from each of a plurality of antennas comprises transmitting a respective signal from each of a plurality of transmit antennas using common frequency resources for at least two antennas such that MIMO processing will be required to separate the signals upon receipt.
12. The method of claim 11 wherein transmitting a respective signal from each of a plurality of antennas comprises transmitting from a single transmitter.
13. The method of claim 11 wherein transmitting a respective signal from each of a plurality of antennas comprises transmitting from a plurality of transmitters so as to implement a virtual MIMO transmission.