Time Precoding Enabled Non-Orthogonal Frequency Division Multiplexing

Abstract

In this paper, we propose a time precoding scheme for cancelling inter-carrier interference in non-orthogonal frequency division multiplexing for the first time. Achieving high spectral efficiencies is a recurring and key challenge in wireless communications systems and researchers generally use high order and advanced modulation formats to approach this problem, in particular, non-orthogonal modulation formats are a topic of particular interest. Fast orthogonal frequency division multiplexing (F-OFDM) doubles the throughput of conventional OFDM by violating orthogonality of the quadrature carrier, causing interference in the real and imaginary domains. Here, we propose a precoding scheme that enables self-interference cancellation without the need of the interference level calculation. The proposed scheme is implemented in the context of a narrowband internet-of-things (NB-IoT) system and verified on a software define radio (SDR) testbed with realistic AWGN and multiple path channels from channel emulator for concept proving. By comparing with the standard OFDM transmission, the time precoded F-OFDM outperforms around 3dB by BER with same signal-to-ratio (SNR) level.

Zero Padding or Cyclic Prefix: Evaluation for Non-Orthogonal Signals

“…Simulations are carried out based on the narrowband internetof-things (NB-IoT) standard [12] appropriately modified to accommodate the bandwidth compression factor (α) [16], [17]. The system parameters are: N = 12 data subcarriers, Q = 128 [16] and the modulation format is quadrature phase shift keying.…”

Using Zero Padding for Robust Channel Estimation in SEFDM Systems

“…System parameters in the computer simulations are carried out based on the narrowband internet-of-things (NB-IoT) standard [19]. The NB-IoT system parameters are appropriately modified to accommodate the bandwidth compression factors ranging between = 0.5 − 0.9 [16], [20], [21]. The system parameters are: = 12 data subcarriers, = 128 [20] and the modulation format is quadrature phase shift keying (QPSK) [16].…”

Experimental Validation of Zero Padding in SEFDM Systems Using Over-the-Air Transmission

“…The experimental system parameters are configured using the narrowband internet-of-things (NB-IoT) standard [14]. In order to accommodate the bandwidth compression factor in NB-IoT systems, the standard parameters are appropriately modified following the work in [4], [15]. The system parameters are given in Table I.…”