Why throughput of my 9XTend at 9600 baud rate is only 200+bytes/sec in broadcast mode?

XBee & XBee Gateway XTend
1
  1. I think there must be something wrong here?
    200-250 bytes per second seems too little.

My parameters are:

BR0 : 9600
DTffff ; broadcast
TX1 ; transmit only

  1. How can I disable the 2.1 KB buffer for DO, We work on real time applications, I would rather drop the old packets then deliver it late.

Thank you for your help.

2

I think there is a confusion. If you want the lowest latency, then your BR should be set to 1.

Now other than controlling the buffer on the output side to cause a buffer over run, it is impossible to disable the radios buffer.

3

Oh and Disable RR and MT.

4

The MT was my initial thought as well. 200-250bytes/sec * 10 bits = 2-2.5Kbps.

By default the MT is set to 3, which causes a total of 4 transmissions to be sent for every packet. So divide 9600 baud by 4, and that sounds about right.

Beyond that, your packetization parameters RO, RB, and PK. Can also affect timing slightly.

5

Thank you guys for your help.

First, I need more reliable broadcast for critical real time data, about 350-600 bytes per second, that is why I choose 9600 instead of 115200. Unless 115200 is as reliable as 9600 for blockage.

Second, I tried MT=0 (RR is disabled in broadcast mode) then the throughput can reach about 500bytes/sec. Then come down to the question:

Should I use 115200 with MT=9 or 9600 MT=0?
Which one is supposed to be more reliable under some blockage(Distance is within 0.5 mile).

Thank you for your help.

6

If you need reliable broadcast at a relatively short distance (I assume you’re using 1W output power (PL=4) at 1/2 mile, so your link margin is quite large), I’d go with the MT=9 @ 115200. Choosing the higher bit rate reduces your link margin by 10 dB, but you give the system 10 chances to get a packet through so it will be less sensitive to bit errors. (with MT=0 a single bit error is all that’s needed to wreck your communications link).