Overcoming the SNR-wall for energy detection using the autocorrelation of cyclic prefix based OFDM signal

Abstract

Energy detection is one of the basic schemes of spectrum sensing. In case of energy detection because of the uncertainty in estimating the noise variance there exists a fundamental limit of minimum SNR, called the SNR-wall, below which the signal could not be reliably detected. In this paper, we propose a method to overcome this SNR-wall for OFDM signal by exploiting the autocorrelation property of the cyclic prefix both in AWGN and multipath fading channel. Required SNR for signal detection versus noise uncertainty for a given false alarm probability (0.01) and detection probability (0.99) has been found out in case of both energy detector and the autocorrelation based detector for OFDM signal. Our result shows that there is about 23 dB advantage with our proposed method for AWGN channel and about 12 dB advantage for multipath fading channel over conventional energy detector for noise uncertainty parameter U = 5 with ~ 5,000 signal samples.

Overcoming the SNR-Wall by Autocorrelation based Sensing of OFDM Signal

“…Autocorrelation based spectrum sensing for OFDM signal has been described in [26][27][28], but in their calculations the authors do not consider any uncertainty in the noise. This idea in [29] is already proposed, but detailed mathematical analysis has not been included there and also the results have not been validated by Monte Carlo simulation. For sufficiently large observation samples (>1000 samples) and at moderate cyclic prefix to OFDM symbol length ratio (>15%) this method provides lower SNR requirement in signal detection for given false alarm and detection probabilities at a fixed noise uncertainty.…”

Tεχνικές Για Σύγχρονα Ετερογενή Και Ευέλικτα Ραδιοσυστήματα

“…Πιο πρόσφατα, οι ερευνητικές προσπάθειες έχουν εστιάσει στον προσδιορισμό των ορίων των διαφόρων προσεγγίσεων για την ανίχνευση. Για παράδειγμα, η αβεβαιότητα στην εκτίμηση ισχύος θορύβου έχει αποδειχθεί ότι είναι ένας βασικός περιοριστικός παράγοντας στην απόδοση της ανίχνευσης ενέργειας [189] και πολλές εργασίες δημοσιεύθηκαν πρόσφατα με στόχο τη βελτίωση των επιδόσεων ενός τέτοιου ανιχνευτή ενέργειας [190], [191].…”