802.15.4 2.4ghz range extension

[NicoP]

I've found some reference design to extend range of at128rfa1 transceiver but would like to have some feedback of edaboard members. Does someone here work on such a design ?
The keys of my design are:
- 100meters range at non 802.15.4 compliant rate of 2.5Mbps (why I need a PA and maybe LNA )
- bypass of the PA when devices are close enough.

I plan to use CEL PA upg2314 for amplified Tx path and a bidirectionnal RxTx path.

Any comments to help me ?

 

[kspalla]

YES.

you need LNA to improve sensitivity of the receive. this helps in reverse direction.

you need PA if the target is too faraway. this can be calculated from link budget.

tell us more on bidirectional rxtx path. using CEL PA on tx path is ok to me.

 

[NicoP]

The bidirectional rxtx path will be a direct link from balun filter to antenna matching network through 2 spdt switches. The reference design can be found here. This path could just be considered as a ~1dB insertion loss path.

I wonder if someone already worked on such a design where SP3T switches are used to choose between a PA txpath, a LNA rx path or a direct bidirectional TxRx path ?

 

[kspalla]

oh.. its common port for TX and RX by the RF231 chip set. if the chip set performance is not enough then you need to have the external PA, LNA and Filter.
In the app note it is used PA. i.e. improved in Tx path.
Please LNA in RX path to further improvement.

 

[NicoP]

Using this design with a LNA in the Rx path, it's no more a bidirectional path. Keep in mind my goal is to be able to bypass the PA when range extension is not needed.

 

[kspalla]

so what is the problem now. i am unable to understand please explain.
In my view range extension will not solve by just increasing the Tx power. Range and reach has to met.

 

[NicoP]

Depending on the application, I want to be able to choose (in software) between an amplified Tx Path (with PA) and a non amplified tx path.

 

[kspalla]

The current application note holds good which is software controlled. what help you further require?

 

[NicoP]

The application note does not specify whether the Rx path can be used as a TXpath.

 

[kspalla]

the app note suggest in one way only.
Rx path will be RX path only can not be used as tx path

 

[NicoP]

Yes but i don't see a reason why Rx path can't be used as Tx path in this design. Am I wrong ?

 

[kspalla]

the concept bidirectional loses once you keep switches and amplifier. it becomes directional and is controlled by the external processor. You need SP3T switches to have controlled RX path. but you need to define when you need range extension etc.

 

[NicoP]

Sure I understand that I will have to modify the control of switches and define when I need range extension, it shouldn't be a hard task . From this point, the Rx path can be used as Tx path, i have no reason to consider that SPDT switches used on the ref design are unidirectional.