Reduction of Cyclic Prefix Overhead in Narrow-Band Internet of Things (NB-IoT) Systems

Repetition mechanism is widely applied in orthogonal frequency division multiplexing (OFDM) oriented narrow-band Internet of Things (NB-IoT) systems, whereas the OFDM symbols of subscribers are transmitted for multiple times repeatedly to enhance the achievable signal-to-noise ratios at the receivers. Therein, the cyclic prefix (CP) of each OFDM symbol has also been transmitted duplicately, resulting in degenerated spectral efficiency. To remedy this issue, in this letter, we develop a versatile CP-free repetition scheme. Specifically, all CP overheads are remove when symbols are repeatedly transmitted in our approach. We explicitly demonstrate that with the explored strategy, the simple single-tap equalization is still applicable for receivers, without any inter-symbol interference. Thereafter, the channel estimation approach for the developed CP-free protocol is designed as well. Numerical simulations have been done to validate the effectiveness of the devised scheme with respects to the bit error ratio (BER) and the mean square error (MSE).