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Adds physical layer diagram 

Clarifies details about the upsampler and RRC filter.
pull/101/head
Jay Francis 2022-03-24 19:29:47 -04:00
parent 315b5acfb5
commit f69621c9ff
2 changed files with 34 additions and 3 deletions
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11
pages/02.part-1/03.physical-layer/docs.md
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@ -12,13 +12,16 @@ media_order:
M17 standard uses 4FSK running at 4800 symbols/s (9600
bits/s) with a deviation index h=0.33 for transmission in 9 kHz
channel bandwidth. Channel spacing is 12.5 kHz. The symbol stream is
converted (upsampled) to a series of impulses which pass through a
channel bandwidth. Channel spacing is 12.5 kHz.
The symbol stream is converted (upsampled) to a series of impulses which pass through a
root-raised-cosine (alpha=0.5) shaping filter before frequency modulation
at the transmitter and again after frequency demodulation at the
receiver.
!!! Do we need to specify minimal/recommended upsampling rates and minimal/recommended number of RRC taps? !!!
Upsampling by a factor of 10 is recommended (48000 samples/s).
The root-raised-cosine filter should span at least 8 symbols (80 samples, 81 taps).
[mermaid]
graph LR
@ -81,6 +84,8 @@ In the case of dibits, the most significant bit is sent first. When four dibits
A complete transmission shall consist of a preamble, a synchronization burst, data, and an end of transmission marker.
![physical_layer_transmission](phy_layer.svg?classes=caption "Physical Layer Transmission")
### Preamble
Every transmission shall start with a preamble, which shall consist of 40 ms (192 symbols) of alternating outer symbols (+3, -3) or (-3, +3). To ensure a zero crossing prior to a synchronization burst, the last symbol transmitted within the preamble shall be opposite the first symbol transmitted in the synchronization burst.

26
pages/02.part-1/03.physical-layer/phy_layer.svg 100644
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@ -0,0 +1,26 @@
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<text transform="matrix(1 0 0 1 57.1884 59.7264)"><tspan x="0" y="0" class="st3 st4">40ms</tspan><tspan x="-21.7" y="14.4" class="st3 st4">(192 Symbols)</tspan></text>
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