The concept behind phase modulation is that there is a fundamental waveform and to generate different symbols the phase of that fundamental waveform is changed. For instance in BPSK there are two possible symbols one being the fundamental waveform (0 degrees phase) and the other one a shifted version of the fundamental at 180 degrees.
For QPSK, basically the same concept is applied but the different phases are 0, 90, 180, 270.
At 02:58 AM 12/18/2003, you wrote:
>Hello,
>
>Im having difficulties understanding exactly what Phase means, Im
reading
>802.11 Wi-Fi handbook
>(Neil Reid&Ron Seide) which explains that frequency is the complete
cycle
>of a wave.
>Phase is where the wave begins its cycle. Makes sense I guess.
>What becomes confusing is BFSK and BPSK, BFSK sends an on or off bit
with
>each frequency,
>BPSK sends two states, a "one" with one phase and "zero" with another
phase.
>If phase just determines at what point in time a frequency begins its
>cycle, how can there be a modulation scheme based on phase?
>
>Thanks
Sanford Weinberg <[EMAIL PROTECTED]> wrote:
>Hello,
>
>Im having difficulties understanding exactly what Phase means, Im
reading
>802.11 Wi-Fi handbook
>(Neil Reid&Ron Seide) which explains that frequency is the complete
cycle
>of a wave.
>Phase is where the wave begins its cycle. Makes sense I guess.
>What becomes confusing is BFSK and BPSK, BFSK sends an on or off bit
with
>each frequency,
>BPSK sends two states, a "one" with one phase and "zero" with another
phase.
>If phase just determines at what point in time a frequency begins its
>cycle, how can there be a modulation scheme based on phase?
>
>Thanks
Sanford Weinberg <[EMAIL PROTECTED]> wrote:
Great question... you are correct in that frequency is how long it takes to
complete one cycle (cycles per second) and phase is where it
starts...Disclaimer: this explanation is simplified for the concepts -
Remember this is a digital system. we don't look at the entire wave just
if we are at a peak or baseline at specific (sample) times. If we have a
frequency of one cycle per second (1 hertz) then to send one character
would take us typically 8 - 10 seconds (bit by bit plus overhead bits).
Remember my choice of frequency is probably limited by what I want to use
it for and the FCC
If I synchronize clocks on receiver and sender and I can process faster
then my frequency (say a tenth of a second in our example) then I can send
out theoretically 10 signals on the same frequency of 1 cycle per second at
different phases and get the character in one second instead of 8-10.
Let me know if you more detail is needed
At 02:58 AM 12/18/2003, you wrote:
>Hello,
>
>Im having difficulties understanding exactly what Phase means, Im reading
>802.11 Wi-Fi handbook
>(Neil Reid&Ron Seide) which explains that frequency is the complete cycle
>of a wave.
>Phase is where the wave begins its cycle. Makes sense I guess.
>What becomes confusing is BFSK and BPSK, BFSK sends an on or off bit with
>each frequency,
>BPSK sends two states, a "one" with one phase and "zero" with another phase.
>If phase just determines at what point in time a frequency begins its
>cycle, how can there be a modulation scheme based on phase?
>
>Thanks
>
>
>--------------------
>"Computer games don't affect kids, I mean if Pac Man affected us as kids,
>we'd all run aroound in a darkened room munching pills and listening to
>repetitive music." - Kristian Wilson, Nintendo, Inc, 1989.
>
>_________________________________________________________________
>Worried about inbox overload? Get MSN Extra Storage now!
>http://join.msn.com/?PAGE=features/es
>
Alexander Tasc�n
M.S. Electrical Engineering
The future is here. It's just not widely distributed yet - WIlliam Gibson
Do you Yahoo!?
New Yahoo! Photos - easier uploading and sharing
