I am using xbee pro 2.4GHz module for my project. I am experimenting it in the environment of a train coach. it works for a 3 coach distance when the train is stationary but doesnt even work a 2 coach distance when the train is in motion at 60-80kmph. The data rate which i am aiming at is not very huge. just minimum. I also do not want to use the wire antenna which is given by default. I want a bidirectional antenna without reducing (if it increases then i do not mind) the current range.
Can anyone please suggest me which antenna i should go with?
Also i need some ideas on what all parameters do i have to consider in such a dynamic environment such as a train for a reliable data transfer? My confirmation and testing process for the feasibility of using it in a inter coach communication is still ON…
First, I imagine the metal structure of the rail car will make it difficult to get good RF communications between the interiors of cars. Second, as to why the communication range is so much worse when the train is in motion, I wonder if it is due to interference (EMI) or something like that. At least, I can’t think of another logical explanation right now.
If you want to build an 802.15.4 network covering multiple rail cars, I would consider how the XBee nodes can be placed close together and used for routing to create a robust RF network. For instance, put one XBee on the rear interior of each car and one on the front interior of each car so that the signal is at maximum strength when it has to travel through the car wall to the next car.
I am using xbee pro 2.4GHz module for my project. I am experimenting it in the environment of a train coach. it works for a 3 coach distance when the train is stationary but doesnt even work a 2 coach distance when the train is in motion at 60-80kmph. The data rate which i am aiming at is not very huge. just minimum. I also do not want to use the wire antenna which is given by default. I want a bidirectional antenna without reducing (if it increases then i do not mind) the current range.
Can anyone please suggest me which antenna i should go with?
Also i need some ideas on what all parameters do i have to consider in such a dynamic environment such as a train for a reliable data transfer? My confirmation and testing process for the feasibility of using it in a inter coach communication is still ON…
If the stationary train signal to noise ratio (SNR) is good, for 802.15.4 at 2.4GHz that would be about 6dB or more, then in motion, I can’t imagine why there’d be serious difference. Multipath off the walls at 2.4GHz is a tiny fraction of the period of the symbols. So the question is what is the SNR and received signal strength indicator (RSSI)? Again, for 2.4GHz 802.15.4, you’d want -90dBm or more positive (stronger).
When in motion, are there more “people” as attenuators? Is the RF path different due to curves vs. windows?
If this is all on 900MHz, I’d be concerned with multipath effects due to the frequency.
The physical conditions were similar,when stationary & in motion , w.r.t the position where the module was kept and the density of people in the train . I have not measured the SNR & RSSI. I do not have any range analysis modules . I tested it using the normal xbee pro modules by doing some data transfer. I probably have to study how the SNR & RSSI varies in dynamic condition and only then I can comment something on that. What else do you think would be the other parameter affecting the range and throughput?
Reg the RF path… Its an omni directional wire antenna which comes by default. It would increase the perpendicular distance between the modules in a curve. There are curves i wouldn’t say it was an ideal straight track.
colinb:
First, I imagine the metal structure of the rail car will make it difficult to get good RF communications between the interiors of cars. Second, as to why the communication range is so much worse when the train is in motion, I wonder if it is due to interference (EMI) or something like that. At least, I can’t think of another logical explanation right now.
If you want to build an 802.15.4 network covering multiple rail cars, I would consider how the XBee nodes can be placed close together and used for routing to create a robust RF network. For instance, put one XBee on the rear interior of each car and one on the front interior of each car so that the signal is at maximum strength when it has to travel through the car wall to the next car.
The challenge is all about if i can use one module per coach and still achieve a fail safe system. Fail safe in the sense even if module in one coach fails the modules on either side of this failed module must be able to communicate with each other.If it doesnt work that way then i would consider using 2 modules as a last option. Because the RSSI staying at the center of each coach is of prime importance to me in order to recognize if any new coaches are dynamically attached to a train i.e not and including it in the network of the particular train which it is attached to. The challenge is also like how do we make sure a new coach is attached to my train and not to the train on the track beside.
The physical conditions were similar,when stationary & in motion , w.r.t the position where the module was kept and the density of people in the train . I have not measured the SNR & RSSI. I do not have any range analysis modules . I tested it using the normal xbee pro modules by doing some data transfer. I probably have to study how the SNR & RSSI varies in dynamic condition and only then I can comment something on that. What else do you think would be the other parameter affecting the range and throughput?
Reg the RF path… Its an omni directional wire antenna which comes by default. It would increase the perpendicular distance between the modules in a curve. There are curves i wouldn’t say it was an ideal straight track.
The XBee will tell you the received signal strength - in an AT command register and in the header of each API mode packet.
Are these XBee PRO or non-PRO modules? The PRO have much more transmitter power.