| MS Seminar

Name of the Speaker: Mr. R Vignesh (EE18S070)
Guide: Prof. K Giridhar
Online meeting link: meet.google.com/ewk-cyie-rfd
Date/Time: 6th August 2024 (Tuesday), 3:00 PM
Title: A reliable Fast Frequency Hopping Technique for OFDM and associated Link Synchronization at the Receiver.

Abstract :

Frequency Hopping (FH) is an effective way to ensure resilience to jamming and eavesdropping. Combined with Orthogonal Frequency Division Multiplexing (OFDM) waveforms, they provide some characteristics vital to the communication links in the strategic/defence space. We consider a baseband-based ultra-fast FH system where a contiguous set of subcarriers of an OFDM block which hold data are altered periodically based on a random code pattern. We elicit the advantages and drawbacks of this implementation against other FH schemes in baseband and passband including the conventional RF-carrier hopping. Since only a small set of subcarriers of the OFDM symbol are used in any one hop, receiver synchronization for timing and frequency is difficult since the time-domain auto-correlation properties degrade. Time-domain cross-correlation may not be a viable synchronization technique since the receiver cannot possibly know the current hop in case of a cold-start or a warm-start.

In this work, for such a scenario, we compare existing preamble structures and processing methods using autocorrelation for synchronization. We then propose a new preamble with a two-step improved timing estimate. This new preamble incorporates features from the existing methods with some tweaks in the Cyclic Prefix (CP) and Cyclic Suffix (CS) to improve performance. Simulation results are presented to show the effectiveness of the proposed preamble and processing scheme, especially at low Signal-to-Noise Ratios. For example, a 3 dB improvement in the probability of detection performance graphs is observed around SNR = -6 dB.