Adaptive transmit beamforming for frequency division duplexing systems
Embodiments of a method and apparatus for performing an adaptive transmission scheme in a frequency division duplexing communication system based on channel state information estimated using an open-loop mode are described herein. In one example, the method includes estimating an impulse response of a channel using a signal received over a first frequency band of the channel from a device, transforming the impulse response into a frequency response of the channel, and subsequently performing the adaptive transmission scheme using the frequency response to transmit a signal to the device over a second frequency band of the channel that is different from the first frequency band.
1. A method for performing an adaptive transmission scheme in a frequency division duplexing communication system, the method comprising:
estimating a first impulse response of a channel using a signal received over a first frequency band of the channel from a device;
transforming, by a processor, the first impulse response into a first frequency response of the channel; and
performing the adaptive transmission scheme using the first frequency response of the channel to transmit a signal to the device over a second frequency band of the channel,
wherein the first frequency band is different from the second frequency band.
2. The method of claim 1 , wherein performing the adaptive transmission scheme further comprises:
using state information of the channel determined based on feedback received from the device.
3. The method of claim 2 , wherein using the state information of the channel further comprises:
adjusting the state information based on the first impulse response or the first frequency response.
4. The method of claim 1 , further comprising:
estimating a second frequency response of the channel using a signal received over a third frequency band of the channel from the device; and
solving for a third impulse response that, when transformed into a third frequency response, approximates both the first frequency response and the second frequency response.
5. The method of claim 4 , wherein solving for a third impulse response comprises:
using a linear algebra technique to fit the first frequency response and the second frequency response to the third frequency response.
6. The method of claim 4 , further comprising:
determining a quality of the third impulse response by evaluating the third frequency response at one or more frequencies of components that make up the first frequency response or the second frequency response.
7. The method of claim 1 , further comprising:
determining a quality of the first impulse response based on a change in a radiation pattern of an antenna used to transmit the signal to the second device.
8. The method of claim 1 , further comprising:
determining a quality of the first impulse response based on a doppler shift of a signal transmitted over the channel.
9. The method of claim 1 , further comprising:
determining a quality of the first impulse response of the channel based on a doppler spread of a signal transmitted over the channel.
10. The method of claim 1 , further comprising:
determining a quality of the first impulse response based on a number of positive and negative acknowledgements received for packets transmitted to the device using the adaptive transmission scheme.
11. The method of claim 1 , further comprising:
estimating a second impulse response of the channel using a signal received from the device over a third frequency band; and
determining a quality of the first impulse response by comparing a delay spread of the first impulse response to a delay spread of the second impulse response.
12. The method of claim 1 , wherein the adaptive transmission scheme is beamforming.
13. The method of claim 1 , wherein the adaptive transmission scheme is antenna selection, hybrid switching, or smart cyclic delay diversity.
14. A method for performing an adaptive transmission scheme in a frequency division duplexing communication, the method comprising:
estimating a first frequency response of a channel using a signal received over a first frequency band of the channel from a device;
estimating a second frequency response of the channel using a signal received over a second frequency band of the channel from the device;
solving, by a processor, for an impulse response that approximates both the first frequency response and the second frequency response when the impulse response is transformed into a third frequency response; and
performing the adaptive transmission scheme using the third frequency response to transmit a signal to the device over a third frequency band of the channel,
wherein the first frequency band, the second frequency band, and the third frequency band are different.
15. The method of claim 14 , wherein solving for the impulse response comprises:
using a linear algebra technique to fit the first frequency response and the second frequency response to the third frequency response.
16. The method of claim 14 , further comprising:
determining a quality of the third impulse response by evaluating the third frequency response at one or more frequencies of components that make up the first frequency response or the second frequency response.
17. The method of claim 14 , wherein the adaptive transmission scheme is beamforming.
18. A transmitter for performing an adaptive transmission scheme in a frequency division duplexing communication system comprising:
a channel estimator, implemented at least in part using a processor, configured to estimate an impulse response of a channel using a signal received over a first frequency band of the channel from a device;
a discrete Fourier Transform (DFT) hardware block configured to transform the impulse response into a frequency response of the channel; and
an adaptive transmission scheme hardware module configured to perform the adaptive transmission scheme using the frequency response to transmit a signal to the device over a second frequency band of the channel.
19. The transmitter of claim 18 , wherein the adaptive transmission scheme is beamforming.
20. The transmitter of claim 18 , wherein the adaptive transmission scheme is antenna selection, transmit switching, hybrid switching, or smart cyclic delay diversity.
21. A method for performing an adaptive transmission scheme in a frequency division duplexing communication system, the method comprising:
estimating a first frequency response of a channel using a signal received over a first frequency band of the channel from a device;
performing, by a processor, extrapolation on the first frequency response to determine frequency response information for frequencies outside the first frequency band; and
performing the adaptive transmission scheme using the frequency response information to transmit a signal to the device over a second frequency band of the channel,
wherein the first frequency band is different from the second frequency band.