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From: | Marcus Müller |
Subject: | Re: [Discuss-gnuradio] Decoding constellation (0, 1-1) using gnuradio |
Date: | Wed, 11 Nov 2015 21:27:47 +0100 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 |
The point is that what you're effectively doing is using the front
11 as a kind of preamble, and 01 or 10 being the symbol you send. That doesn't sound like much. To be honest, PPM in an environment like that without lots of redundancy simply sounds unstable -- you just miss one of your preamble symbols, and your whole PPM symbol will be lost. You just misinterpret two "no-signal" 0s, and get a preamble. Make your contiguous packets longer. The average PPM transceiver -- old garage door openers etc -- would use something 10s of symbol durations worth of preamble, and then 10s of repititions of the symbol. PPM isn't very popular these days, because with the same transmitter energy you can usually get better performance, as it doesn't work very well on the typical radio channels: It's sensitive to multipath (which is pretty obvious) or non-flat fading (which, is, for many practical aspects, usually equivalent to multipath), and timing recovery is unnecessarily hard if you don't have a lot of symbols. So, maybe we should take a step back and ask: *what* is the *data* you're trying to transmit? Transmitting a single bit at a time sounds so unlikely. Best regards, Marcus On 11/11/2015 08:26 PM, abhinav narain
wrote:
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