Re: choosing the modulation technique

On Apr 1, 3:38 pm, "barry_b" <bbuternow...@xxxxxxxxx> wrote:
Can I get some feedback on my thought process below for choosing a
modulation technique?

I am in the process of choosing the modulation and coding for the
following system:
- frequency band: 2 - 20 Hz
- bit rate: configurable 2 - 16 bps
- transmitter: battery powered
- receiver: PC based (i.e. lots of processing power)
- channel: some burst noise
- adjacent signals/channels: none
- traffic: 1 direction, single user, bursty, asynchronous
- data in payload: 1 to 150 bits

I was considering either bpsk, qpsk, msk or 4-cpfsk. The transmitter
can
accomodate psk or fsk.

I ranked the modulations as follows:
- bspk/qpsk: good error rate performance curve
- msk: smaller bandwith and same BER as bpsk; thus I can use a
narrower
filter and get better performance
- 4-cpfsk (mod index = 0.5): better BER curve than bpsk and msk
(according
to Matlab)

Given that 4-cpfsk has a better BER curve, does it make sense to use
4-CPFSK even for low bit rates? I.e which
is better:
1) bspk/qpsk
2) msk
3) 4-cpfsk (mod index = 0.5)
4) bspk with spreading
5) msk with spreading

From what I know, spreading doesn't provide any coding gain, but only
provides immunity to frequency drop-outs
frequency jamming, thus 3) should be the best. Correct?

Given the short payload, I don't think convolutional coding is
applicable.
I will be using a reed-solomon
code.

In the receiver, I will be implementing a coherent detector.

thanks,
barry

What is the channel?


The channel is:
- transmitter and receiver are not moving
- wireless
- signal is coupled to the ground with antennas
- ground acts as a low pass filter which has acceptable attenuation below
20 Hz

.

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