Preamble and embedded synchronization for RF carrier frequency-hopped OFDM

In this work, we apply RF carrier frequency hopping to orthogonal frequency-division multiplexing (FH-OFDM). Achievable hop rate and bandwidth efficiency are determined based on signal acquisition/synchronization and data demodulation performance in the presence of unknown time-frequency offsets, and channel gain/phase perturbations. We compare performance using two different data-aided synchronization approaches. The first method sends synchronization information in a preamble before the OFDM payload symbol, whereas the second method embeds the synchronization information directly into the OFDM symbol stream. In the embedded technique, superposition of the synchronization information causes interference onto the OFDM data information. Thus, the sync information must be removed before satisfactory bit-error rate (BER) performance can be achieved. Consequently, embedded interference cancellation (EIC) is utilized which requires accurate estimation of the synchronization offsets and channel perturbations. Using coherent quadrature phase-shift keying-OFDM modulation, performance comparisons are presented using the COST207 multipath fading channel model. Fading channel BER performance results indicate that the embedded technique incurs only a slight signal-to-noise ratio penalty (less than 1 dB) compared with the preamble method. However, the embedded method offers the potential for improved hop rate and bandwidth efficiency because no dedicated slot is required for a synchronization field.

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