Add references and minor whitespace changes

docs/physical_layer.rst

@@ -3,10 +3,13 @@ Physical Layer
 
 4FSK generation
 ---------------
-M17 standard uses 4FSK modulation running at 4800 symbols/s (9600 bits/s) with a deviation index
-h=0.33 for transmission in 6.25 kHz channel bandwidth. Channel spacing is 12.5 kHz. The symbol
-stream is converted to a series of impulses which pass through a root-raised-cosine (α=0.5) shaping
-filter before frequency modulation at the transmitter and again after frequency demodulation at the
+
+M17 standard uses 4FSK modulation running at 4800 symbols/s (9600
+bits/s) with a deviation index h=0.33 for transmission in 6.25 kHz
+channel bandwidth. Channel spacing is 12.5 kHz. The symbol stream is
+converted to a series of impulses which pass through a
+root-raised-cosine (α=0.5) shaping filter before frequency modulation
+at the transmitter and again after frequency demodulation at the
 receiver.
 
 .. graph:: modulation
@@ -132,6 +135,9 @@ re-ordered to form type 4 bits for transmission. This, along with
 Convolutional encoder
 ~~~~~~~~~~~~~~~~~~~~~
 
+.. [ECC] Moreira, Jorge C.; Farrell, Patrick G. "Essentials of
+         Error‐Control Coding" Wiley 2006, ISBN: 9780470029206
+
 The convolutional code shall encode the input bit sequence after
 appending 4 tail bits at the end of the sequence. Rate of the coder is
 R=½ with constraint length K=5. The encoder diagram and generating

docs/summary.rst

@@ -27,3 +27,16 @@ To do this, the M17 protocol is broken down into three protocol layers, like a n
    streams, control packets, beacons, etc.
 
 This document attempts to document these layers.
+
+.. [TETRA] Dunlop, John; Girma, Demessie; Irvine, James "Digital
+           Mobile Communications and the TETRA System" Wiley 1999,
+           ISBN: 9780471987925
+
+.. [NXDN] NXDN Technical Specifications, Part 1: Air Interface;
+          Sub-part A: Common Air Interface
+
+.. [DMR] ETSI TS 102 361-1 V2.2.1 (2013-02): "Electromagnetic
+         compatibility and Radio spectrum Matters (ERM); Digital
+         Mobile Radio (DMR) Systems; Part 1: DMR Air Interface (AI)
+         protocol"
+         https://www.etsi.org/deliver/etsi_ts/102300_102399/10236101/02.02.01_60/ts_10236101v020201p.pdf