3 ms·
This is entirely wrong. OFDM is necessary for WiFi etc. in order to maximize spectral efficiency (i.e., bps per Hz for a given unit of radio spectrum) and mitig
by ooterness 2y ago
This is entirely wrong. OFDM is necessary for WiFi etc. in order to maximize spectral efficiency (i.e., bps per Hz for a given unit of radio spectrum) and mitigate multipath.
The main purpose of the GPS spreading codes is to prevent self-interference from the other satellites and to increase the effective bandwidth for the cross ambiguity function (i.e., to get a nice, sharp cross-correlation peak in the time-domain). The pre-spreading data signal is only ~50 bits per second, so spectral efficiency is not a primary concern.
- teleforce 2y ago>For GNSS on the other hand, don't care about the bandwidth because it's for location service not streaming video, but the limitations of being pseudo-orthogonal eventually got to them in the form of spoofing vulnerability. Please check my original comments as above. Granted, it's still perhaps feasible to spoof OFDM system but it'll be much harder to pull off compared to the pseudo-orthogonal spread spectrum system [1],[2]. [1] Secure OFDM System Design and Capacity Analysis under Disguised Jamming (2019): https://arxiv.org/abs/1804.07826 https://arxiv.org/abs/1804.07826 [2] OFDM-based JCAS under Attack: The Dual Threat of Spoofing and Jamming in WLAN Sensing (2025): https://arxiv.org/html/2501.06798v1 https://arxiv.org/html/2501.06798v1