OTFS: A New Generation of Modulation Addressing the Challenges of 5G(2)

2.1 OTFS in a Nutshell

2.1.1 overview

• OTFS is a modulation scheme that multiplexes QAM information symbols in a new signal representation called the delay-Doppler representation
• The delay-Doppler representation generalizes time and frequency representations

2.1.2 Three fundamental properties

• Invariance means that the coupling pattern is the same for all QAM symbols
• Separability (sometimes referred to as hardening) means that all the diversity paths are separated from one another and each QAM symbol experiences all the diversity paths of the channel.???
• orthogonality means that the coupling is localized, which implies that the QAM symbols remain roughly orthogonal to one another at the receiver

2.2 The Delay-Doppler Signal Reprsentation

• The mathematical expression of this complementarity is captured by the Heisenberg uncertainty principle which states that a signal cannot be simultaneously localized to any desired degree in time and in frequency
• As it turns out, there exists signals which behave as if they are simultaneously localized to any desired degree both in time and in frequency, a property which renders them optimal both for delay-Doppler Radar multi-target detection and for wireless communication