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Re: [Discuss-gnuradio] Introducing noise/ considerable BER

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Introducing noise/ considerable BER
Date: Tue, 9 Aug 2011 20:05:52 -0400

On Mon, Aug 8, 2011 at 11:34 AM, shantharam balasubramanian
<address@hidden> wrote:
> Hello people,
> Thanks a lot for the reply. So, you are saying that the packet loss at
> low transmitter amplitude in benchmark_Tx.py and benchmark_Rx.py come
> from the loss of packet synchronization data, i.e., a part of the
> packet synchronization data gets lost or degraded due to low SNR. I
> know that packet loss also occurs if the queue length is not long
> enough to hold incoming traffic or if the data reaches the receiver
> after a long time. I want to ensure that these things don't happen.
> Basically, we are trying to transmit a random binary sequence between
> two nodes using the benchmark_Tx.py and benchmark_Rx.py programs.
> Since both these programs use packets, we convert the whole binary
> sequence into a number of packets and then transmit each packet using
> the benchmark programs. Let us say, we have 2000 bits in total. We
> convert it to 20 packets (100 bits/packet) and then transmit 20
> packets from one node to the other. We want to calculate the bit error
> rate for different levels of transmitter amplitude.
> Based on our objectives, I have the following questions.
> 1. Is there any upper limit on the no. of binary bits per packet in
> benchmark_Tx.py program?
> 2. Overall can I take other steps to get rid of the packet loss
> scenario ? Adam, can you please describe the generation of long
> preamble in further details ?
> Your help and feedback will be highly appreciated.
> Thanks,
> shantharam

Keep in mind the old information theorist's adage: if you don't have
bit errors, you're using too much power! (ok, I don't know how old
that is; fred harris always quotes it, but he credits someone else
with it, probably Tony Constantinides).

In other words, we normally design our systems around having bit
errors, and indeed we recognize that they are unavoidable except under
extreme SNR conditions. To compensate, you really want to you some
kind of channel coding. The way things are in our benchmark code, a
single bit error means that an entire packet is lost.


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