Fast SRS antenna port switching for frequency-division duplexing

1. A mobile device comprising:

a baseband processor;

first and second antennas; and

a front end including a transmit power amplifier, a first transmit path, a second transmit path, and a receive path, the front end configurable in a frequency division duplex operation mode to transmit via the first transmit path within a transmit band of a frequency division duplex band and to receive via the receive path within a receive band of the frequency division duplex band, the front end further configurable in a channel modeling mode to transmit via the second transmit path over the first antenna within a receive band of the frequency division duplex band, and further configurable in the channel modeling mode to transmit via the second transmit path over the second antenna within the receive band of the frequency division duplex band.

2. The mobile device of claim 1 wherein in the channel modeling mode the baseband processor generates a first sequence of symbols for transmission within the receive band via the second transmit path, the first sequence including one or more sounding reference signal symbols.

3. The mobile device of claim 1 wherein the front end includes a frequency division duplex filter having a transmit portion configured to pass signals within the transmit band and a receive portion configured to pass signals within the receive band, the transmit portion positioned within the first transmit path.

4. The mobile device of claim 3 wherein the front end includes a second filter positioned within the second transmit path configured to pass signals within at least the receive band of the frequency division duplex band.

5. The mobile device of claim 4 wherein the second filter is configured to pass signals within a time division duplex band that encompasses the receive band of the frequency division duplex band.

6. The mobile device of claim 4 wherein the front end includes an antenna switch configured to switch between connecting an output of the frequency division duplex filter to an antenna of the mobile device and connecting the output of the second filter to the antenna.

7. The mobile device of claim 1 wherein the front end includes a frequency division duplex filter including a first portion configured to pass signals within the transmit band and a second portion configured to pass signals within the receive band, the first portion positioned within the first transmit path and the second portion positioned within the second transmit path.

8. The mobile device of claim 7 wherein the second portion is a bi-directional filter positioned within both the second transmit path and a frequency division duplex receive path.

9. The mobile device of claim 8 wherein the second portion receives when the front end operates in the first frequency division duplex operation mode, and the second portion transmits when the front end operates in the second channel modeling mode.

10. A radio frequency module comprising:

a substrate;

a power amplifier supported by the substrate;

a first transmit path, a second transmit path, and a receive path, the radio frequency module configurable in a frequency division duplex operation mode to transmit, via the first transmit path, within a transmit band of a frequency division duplex band and to receive via the receive path within a receive band of the frequency division duplex band, the radio frequency module further configurable in a channel modeling mode to transmit, via the second transmit path, within a receive band of the frequency division duplex band; and

an antenna switch, the radio frequency module further configurable in the channel modeling mode to control the antenna switch to selectively connect the second transmit path to either of a first antenna of a plurality of antennas or a second antenna of a plurality of antennas.

11. The radio frequency module of claim 10 wherein in the channel modeling mode the second transmit path transmits a first sequence of symbols for transmission within the receive band, the first sequence including one or more sounding reference signal symbols.

12. The radio frequency module of claim 10 wherein the module includes a frequency division duplex filter having a transmit portion configured to pass signals within the transmit band and a receive portion configured to pass signals within the receive band, the transmit portion positioned within the first transmit path.

13. The radio frequency module of claim 12 further comprising a second filter positioned within the second transmit path, the second filter configured to pass signals within a frequency band that includes at least the receive band of the frequency division duplex band.

14. The radio frequency module of claim 10 further comprising a frequency division duplex filter including a first portion configured to pass signals within the transmit band and a second portion configured to pass signals within the receive band, the first portion positioned within the first transmit path and the second portion positioned within the second transmit path, the second portion being a bi-directional filter configured to receive when the radio frequency module operates in the frequency division duplex operation mode and transmit when the radio frequency module operates in the channel modeling mode.

15. A method of operating a mobile device, comprising:

causing the mobile device to enter a frequency division duplex operating mode in which the mobile device transmits, via a first transmit path of the mobile device, within a transmit band of a frequency division duplex band, and in which the mobile device receives, via a receive path of the mobile device, within a receive band of the frequency division duplex band;

causing the mobile device to enter a channel modeling operating mode in which the mobile device transmits, via a second transmit path of the mobile device, within the receive band of the frequency division duplex band; and

when the mobile device is in the channel modeling operating mode, transmitting one or more first sounding reference symbols to a base station via the second transmit path via a first antenna of the mobile device and, subsequent to transmitting the one or more first sounding reference symbols, transmitting one or more second sounding reference symbols to a base station via the second transmit path via a second antenna of the mobile device.

16. The method of claim 15 wherein the first transmit path extends between a transmit power amplifier of the mobile device and an antenna of the mobile device and the second transmit path extends between the transmit power amplifier of the mobile device and the antenna of the mobile device via a different connection pathway.

17. The method of claim 15 wherein the first transmit path includes a filter with a pass band about as wide as the receive band of the frequency division duplex band and the second transmit path includes a filter with a passband that encompasses and is substantially wider than the receive band of the frequency division duplex band.

18. The method of claim 15 wherein in the frequency division duplex operating mode a first filter of the mobile device is within the receive path, and in the second channel modeling operating mode the first filter is within the second transmit path.