PSK Modulation and demodulation

Hello,

I'm studying and maintaining an existing tele-communication system. I 
guess it's a BPSK modulation but not quite sure.

The transmitted data is a Chirp(up sweeping frequency)header followed by
modulated data body.

On the receiver side, the incoming data is auto-correlated with a locally
stored up-chirp waveform and then defive 2 parameters, one is the sign the
other is a delay information.

Then the incoming data body is convoluted with a Root-Raised-Cosine filter
alike waveform shown in this
link:http://en.wikipedia.org/wiki/Raised-cosine_filter. BUT, my waveform is
just UP-SIDE-DOWN! 

I'm just guessing the Root-Raised-Cosine filter alike waveform is used to
demodulate the data body, by taking use of the 2 parameters derived from
the Chirp header.

Could you help to answer these questions?
1. What kind of modulation is this?
2. Any helpful documents about it?

Thanks in advance!

Jeff

On Jan 19, 4:24�pm, "zhejunli"
<JeffLi@n_o_s_p_a_m.cathedralenergyservices.com> wrote:

>
> On the receiver side, the incoming data is auto-correlated with a locally
> stored up-chirp waveform and then defive 2 parameters, one is the sign the
> other is a delay information.
>
> Then the incoming data body is convoluted with a Root-Raised-Cosine filter
> alike waveform shown in this
> link:http://en.wikipedia.org/wiki/Raised-cosine_filter. BUT, my waveform is
> just UP-SIDE-DOWN!
>

If the estimate of the delay parameter is off by a half-period
of the carrier frequency, or if the phase-locked loop (if one
is in use) has locked onto the opposite phase (whether this
can happen does depend on the design and implementation),
then the received waveform would be upside down. Maybe
the bits are differentially encoded at the transmitter to take
into account this possibility, and if so, the demodulator
output bit stream will be the same even if the waveforms
are inverted.

Dilip Sarwate

>On Jan 19, 4:24=A0pm, "zhejunli"
><JeffLi@n_o_s_p_a_m.cathedralenergyservices.com> wrote:
>
>>
>> On the receiver side, the incoming data is auto-correlated with a
locally
>> stored up-chirp waveform and then defive 2 parameters, one is the sign
th=
>e
>> other is a delay information.
>>
>> Then the incoming data body is convoluted with a Root-Raised-Cosine
filte=
>r
>> alike waveform shown in this
>> link:http://en.wikipedia.org/wiki/Raised-cosine_filter. BUT, my waveform
=
>is
>> just UP-SIDE-DOWN!
>>
>
>If the estimate of the delay parameter is off by a half-period
>of the carrier frequency, or if the phase-locked loop (if one
>is in use) has locked onto the opposite phase (whether this
>can happen does depend on the design and implementation),
>then the received waveform would be upside down. Maybe
>the bits are differentially encoded at the transmitter to take
>into account this possibility, and if so, the demodulator
>output bit stream will be the same even if the waveforms
>are inverted.
>
>Dilip Sarwate
>

Thank you Dilip,

Do you think this is a BPSK modulation? Do you have any suggestions for
books or documents to dig into it? Thanks
Jeff

>On Jan 19, 4:24=A0pm, "zhejunli"
><JeffLi@n_o_s_p_a_m.cathedralenergyservices.com> wrote:
>
>>
>> On the receiver side, the incoming data is auto-correlated with a
locally
>> stored up-chirp waveform and then defive 2 parameters, one is the sign
th=
>e
>> other is a delay information.
>>
>> Then the incoming data body is convoluted with a Root-Raised-Cosine
filte=
>r
>> alike waveform shown in this
>> link:http://en.wikipedia.org/wiki/Raised-cosine_filter. BUT, my waveform
=
>is
>> just UP-SIDE-DOWN!
>>
>
>If the estimate of the delay parameter is off by a half-period
>of the carrier frequency, or if the phase-locked loop (if one
>is in use) has locked onto the opposite phase (whether this
>can happen does depend on the design and implementation),
>then the received waveform would be upside down. Maybe
>the bits are differentially encoded at the transmitter to take
>into account this possibility, and if so, the demodulator
>output bit stream will be the same even if the waveforms
>are inverted.
>
>Dilip Sarwate
>

Thank you Dilip,

Do you think this is a BPSK modulation? Do you have any suggestions for
books or documents to dig into it? Thanks
Jeff

On Jan 20, 9:39�am, "zhejunli"
<JeffLi@n_o_s_p_a_m.cathedralenergyservices.com> wrote:

> Thank you Dilip,
>
> Do you think this is a BPSK modulation? Do you have any suggestions for
> books or documents to dig into it? Thanks
> Jeff

Maybe try www.dsprelated.com or www.dspguru.com or
www.dsplog.com to see if they have any information that
will help.

On Jan 19, 4:24�pm, "zhejunli"
<JeffLi@n_o_s_p_a_m.cathedralenergyservices.com> wrote:
> Hello,
>
> I'm studying and maintaining an existing tele-communication system. I
> guess it's a BPSK modulation but not quite sure.
>
> The transmitted data is a Chirp(up sweeping frequency)header followed by
> modulated data body.
>
> On the receiver side, the incoming data is auto-correlated with a locally
> stored up-chirp waveform and then defive 2 parameters, one is the sign the
> other is a delay information.
>
> Then the incoming data body is convoluted with a Root-Raised-Cosine filter
> alike waveform shown in this
> link:http://en.wikipedia.org/wiki/Raised-cosine_filter. BUT, my waveform is
> just UP-SIDE-DOWN!
>
> I'm just guessing the Root-Raised-Cosine filter alike waveform is used to
> demodulate the data body, by taking use of the 2 parameters derived from
> the Chirp header.
>
> Could you help to answer these questions?
> 1. What kind of modulation is this?
> 2. Any helpful documents about it?
>
> Thanks in advance!
>
> Jeff

Since this is an existing telecommunication system, there is a good
chance it was designed to meet some sort of spec. Perhaps if you tell
us what this system does, i.e., pagers, cellphones, satellite,
telemetry etc, someone here may know the protocol.

You talk about how the received data is convolved with a RRC, but
where does this data come from? Is there a modem? Is there a radio?
These types of answers will help.

Clay