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The Q channel half-symbol delay causes OQPSK phase trajectories to evolve on a half-symbol (bit) rate basis. For the particular cases of FQPSK and SOQPSK-TG, carrier phase either remains unchanged or changes by /4 or /2 radians over the pending bit interval.
The OQPSK inter‑channel delay might at first seem a difficult complication because it creates additional ambiguity; in other words, the receiver must resolve relative inter-channel delay. However, as shown below, this is not a problem.
The differential encoding rule adopted in IRIG-106 for OQPSK appears in reference
[M-4] and is therein attributed to Clewer in reference [M-5] and Weber in reference [M-6]. Bit by bit, the code symbol sets {Ek} and {Ok+1) are formed with the Boolean expressions:
Two bits are coded for each value of
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