Systems and methods for channel based beamforming for stacked carrier multiple access
View Patent ↗Methods and systems that enhance interference cancellation are described. Samples are obtained from stacked carriers in a received signal and a data vector is created from the samples. Stacked carriers are selected using a steering vector received during synchronization of the receiver. The steering vector is calculated to obtain cancellation of interference from another receiver and is calculated based on time domain channel estimation. Specialized time domain training sequences and simple cross correlation are used to obtain a channel estimate for use in stacked carrier beamforming and/or for use in OFDM based spatial beamforming. State space or filter based modeled interpolators in the frequency domain or time domain to interpolation of the channels, or whitening matrix-filters over time or frequency are used for maintaining linear beamforming weights as a function of time or frequency. Space time adaptive processing facilitates beamforming of communications signals OFDM and 802.16 (WiMax) systems.
1. A method for enhancing interference cancellation, comprising:
receiving a signal including stacked carriers at a receiver;
obtaining samples from two or more of the stacked carriers;
creating a data vector from the samples, wherein the two or more stacked carriers are selected using a steering vector received during a synchronization of the receiver;
wherein the steering vector is calculated based on a time domain channel estimate, and wherein the steering vector enables frequency domain interference cancellation.
2. The method of claim 1 , wherein spacing between the stacked carriers is variable.
3. The method of claim 1 , wherein the steering vector is calculated to obtain cancellation of co-channel interference in the signal.
4. The method of claim 1 , further comprising obtaining the time domain channel estimate using Yule Walker equations, wherein one or more time domain training sequences are used to solve the Yule Walker equations.
5. The method of claim 1 , further comprising
obtaining the time domain channel estimate based on one or more predefined time domain training sequences; and
using the channel estimate for stacked carrier beamforming.
6. The method of claim 1 , further comprising
obtaining the time domain channel estimate based on one or more predefined time domain training sequences; and
using the channel estimate for orthogonal frequency-division multiplexing (OFDM) based spatial beamforming.
7. The method of claim 4 , further comprising removing estimated interference prior to solving the Yule Walker equations.
8. The method of claim 7 , wherein the Yule Walker equations are solved using at least one of fast convolution and a Fast Fourier Transform.
9. The method of claim 5 , wherein the stacked carrier beamforming is obtained by computing beamforming weights for a plurality of subcarriers using one or more of a data process and an interference process autoregressive model, wherein the computing step reduces the effects of frequency dispersion.
10. The method of claim 1 , further comprising performing depermutation on a number of code repetitions in the received signal for the time domain channel estimate.
11. An interference cancellation system, comprising:
a receiver including:
at least one antenna configured to receive a signal that includes stacked carriers, wherein the receiver is configured to create a data vector from samples obtained from two or more of the stacked carriers selected using a steering vector received during synchronization of the receiver,
wherein the steering vector is calculated based on a time domain channel estimate, and wherein the steering vector enables frequency domain interference cancellation.
12. The system of claim 11 , wherein the steering vector is selected to enable cancellation of co-channel interference in the signal.
13. The system of claim 11 , wherein the antenna receives the signal from a first emitter, and wherein the steering vector is selected to enable cancellation of interference received from a second emitter.
14. The system of claim 13 , wherein the receiver is coupled to a plurality of antennas.
15. The system of claim 11 , further comprising a Fast Fourier Transform processor configured to obtain the channel estimate by solving Yule Walker equations.
16. The system of claim 11 , wherein the receiver generates the channel estimate based on one or more predefined time domain training sequences and uses the channel estimate for beamforming.
17. The system of claim 11 , wherein the channel estimate is used for spatial beamforming.
18. The system of claim 15 , wherein one or more time domain training sequences are used to remove estimated interference prior to solving the Yule Walker equations.
19. The system of claim 11 , wherein the receiver is configured to extract a set of subcarriers from the signal.
20. The system of claim 19 , wherein the subcarriers are selected from an arbitrary set of frequency bins.
21. A method for enhancing interference cancellation, comprising:
receiving a signal including stacked carriers at a receiver;
obtaining samples from two or more of the stacked carriers, wherein the two or more stacked carriers are selected using a steering vector received during a synchronization of the receiver;
creating a data vector from the samples; and
obtaining a time domain channel estimate using Yule Walker equations, wherein one or more time domain training sequences are used to solve the Yule Walker equations, and wherein the steering vector is calculated based on the time domain channel estimate.
22. The method of claim 21 , further comprising removing estimated interference prior to solving the Yule Walker equations.
23. The method of claim 22 , wherein the Yule Walker equations are solved using a fast convolution or a Fast Fourier Transform.
24. The method of claim 21 , wherein the steering vector is calculated based on a time domain channel estimate, and wherein the steering vector enables cancellation of co-channel interference in the signal.
25. The method of claim 24 , further comprising
obtaining the time domain channel estimate based on one or more predefined time domain training sequences; and
using the channel estimate for stacked carrier beamforming.
26. An interference cancellation system, comprising
a receiver including:
at least one antenna configured to receive a signal that includes stacked carriers, wherein the receiver is configured to create a data vector from samples obtained from two or more of the stacked carriers selected using a steering vector received during synchronization of the receiver; and
a Fast Fourier Transform processor configured to obtain a channel estimate by solving Yule Walker equations;
wherein the steering vector is calculated based on the channel estimate.
27. The system of claim 26 , wherein one or more time domain training sequences are used to remove estimated interference prior to solving the Yule Walker equations.
28. The system of claim 26 , wherein the steering vector is selected to enable cancellation of co-channel interference in the signal.
29. The system of claim 26 , wherein the steering vector is calculated based on a time domain channel estimate, and wherein the steering vector enables frequency domain interference cancellation.
30. The system of claim 26 , wherein the receiver generates the channel estimate based on one or more predefined time domain training sequences and uses the channel estimate for beamforming.