Re: Large Wireless networks?

On Thu, 24 Apr 2008 00:53:45 -0400, CBFalconer <cbfalconer@xxxxxxxxx>
wrote:

Polling 10k items in 15 minutes
from a single point leaves an absolute max of 9000 / 10k ~= 1 sec
per poll. That ignores any retransmissions needed.

You must have short seconds where you live, if you managed to get 9000
into 15 minutes :-).

In any half-duplex protocol, the Rx/Tx turnaround delay is critical in
order to get a decent throughput. Any receiver with ordinary IF and a
single PLL frequency synthesizer should be avoided, since the PLL
would have to swing from the Rx local oscillator frequency to the
transmit frequency, which can take a quite long time, before the
transmission can begin. Using a zero-IF receiver or separate PLLs for
Rx and Tx would be OK.

One way to reduce the effects of Rx/Tx delays would be to use a TDMA
system, in which the master sends a common sync message and each slave
has a time slot based on the node-ID in which it has to transmit. The
distances in the OP's case are so small, that the two-way propagation
delay is only a few microseconds, so you do not have to leave large
guard bands into the slot or use some GSM style propagation delay
compensation.

In TDMA or ordinary master/slave systems, in order to reduce the slave
power consumption, the master should use a fixed poll cycle, thus the
slave receiver could be turned of for most of the polling cycle and
be activated just slightly prior to the expected poll to this slave
(as in DVB-H).

Paul

.

Relevant Pages

  • Re: one Devicenet Question please
    ... >> I have been working on IO control application. ... >> decide what will be the data send by the master in the Poll command ... If your slave device has ...
    (comp.arch.embedded)
  • Re: one Devicenet Question please
    ... I wanted to implement the Poll support. ... The Poll Command message sent from the master to the slave ...
    (comp.arch.embedded)
  • Re: On I2C protocol
    ... have the SCL clock stretching from the slave. ... the clock stretching not only applies ... of the master to introduce a delay. ...
    (comp.arch.fpga)
  • At least Bush has one thing to celebrate . . .
    ... And the Democrats just may pick up DeLiar's Congressional seat!!!!!!! ... DeLay's Poll Numbers Sink to Lowest Levels ... re-elect DeLay or vote for the Democratic Party's candidate for Congress? ...
    (alt.politics)
  • Re: 8ms Timer for serial port access
    ... You can use 'poll' to tell when there's data ready ... >> 3) Repeat. ... >> 2) Read as many bytes as are ready without blocking. ... > Then I will have another delay before I can process the data. ...
    (comp.os.linux.development.apps)