5G Field Trials: OFDM-Based Waveforms and Mixed Numerologies

Service diversity is expected in the upcoming fifth-generation (5G) cellular networks, which poses great challenges to the underlying waveforms to accommodate heterogeneous service requirements in a flexible way. By dividing the bandwidth into several subbands, each having a different numerology, this paper reports a field trial in time division duplex downlink conducted on a configurable test bed in a real-world environment for the performance evaluations of orthogonal frequency-division multiplexing (OFDM)-based 5G waveform candidates, i.e., cyclically prefixed OFDM (CP-OFDM), windowing OFDM (W-OFDM), and filtered OFDM (f-OFDM), in the presence of mixed numerologies. Field trial results confirm the feasibility of mixed numerologies and reveal the impact of several important system parameters, e.g., guard bandwidth, data bandwidth, signal-to-noise ratio (SNR), and transmit power. The results also suggest that f-OFDM outperforms CP-OFDM and W-OFDM in terms of both the spectrum efficiency and robustness in a high SNR regime, and the gain increases with a higher inter-numerology out-of-band interference. In some specific scenarios, ideal spectrum utilization can be realized by f-OFDM which completely removes the guard band.

I. Introduction

Currently, research, development and standardization activities for the fifth generation (5G) of cellular networks are in full action. Critical capability objectives, such as 20 Gbits/s peak data rate, connection density and 1 ms latency for enhanced mobile broadband (eMBB), massive machine-type communications (mMTC) and ultra-reliable and low-latency communications (URLLC) services respectively [1], present serious challenges on 5G commercial deployments. On the other hand, wide available spectrum in millimeter-wave bands [2], as well as numerous emerging advances in waveforms, modulation and coding schemes, multiple access schemes, antenna technologies, network technologies and system architectures, are considered as key enablers for 5G [1], [3], [4]; filtered orthogonal frequency-division multiplexing (f-OFDM) [5]–[7], sparse code multiple access (SCMA) [8], polar code [9], massive multiple-input multiple-output (MIMO) [10], cloud radio access network (C-RAN) [11], network densification, to name a few.