5G roadmap

As the standardization activities are being formed to lay the foundation of 5G wireless networks, there is a common consensus on the need to replace the celebrated orthogonal frequency division multiplexing (OFDM) by a more effective air interface that better serves the challenging needs of 5G. To this end, in the recent past, a number of new waveforms have been introduced in the literature. Interestingly, and at the same time not surprising, these methods share a common fundamental principle with OFDM: each data packet is made up of a number of complex-valued sinusoidals (pure tones) that are modulated by the information symbols. In this tutorial article, we build a common framework based on the said OFDM principle and derive these new waveforms from this point of view. This derivation provides a new perspective that facilitates straightforward understanding of channel equalization and the application of these new waveforms to multiple-input multiple-output channels. It also facilitates derivation of new structures for more efficient synthesis/analysis of these waveforms than those that have been reported in the literature.

OFDM Inspired Waveforms for 5G

It has been claimed that filter bank multicarrier (FBMC) systems suffer from negligible performance loss caused by moderate dispersive channels in the absence of guard time protection between symbols. However, a theoretical and systematic explanation/analysis for the statement is missing in the literature to date. In this paper, based on one-tap minimum mean square error (MMSE) and zero-forcing (ZF) channel equalizations, the impact of doubly dispersive channel on the performance of FBMC systems is analyzed in terms of mean square error of received symbols. Based on this analytical framework, we prove that the circular convolution property between symbols and the corresponding channel coefficients in the frequency domain holds loosely with a set of inaccuracies. To facilitate analysis, we first model the FBMC system in a vector/matrix form and derive the estimated symbols as a sum of desired signal, noise, intersymbol interference (ISI), intercarrier interference (ICI), interblock interference (IBI), and estimation bias in the MMSE equalizer. Those terms are derived one-by-one and expressed as a function of channel parameters. The numerical results reveal that under harsh channel conditions, e.g., with large Doppler spread or channel delay spread, the FBMC system performance may be severely deteriorated and error floor will occur.

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FBMC System: An Insight Into Doubly Dispersive Channel Impact

In the future, many objects will communicate with each other and with human beings, enabling a vast range of possible services and applications. However, this scenario comes with stringent network requirements. This paper studies and discusses recent technologies that were proposed to achieve the requirements of the Internet of Things (IoT) and massive machine type communications (mMTC). It focuses on their physical layer characteristics and identifies gaps that 5G networks need to address to achieve full connectivity in the IoT scenario. Hence, a detailed tutorial on the possible radio access technologies for 5G networks focusing on IoT use-cases is presented. The advanced 5G waveforms discussed are: 1) orthogonal frequency division multiplexing (OFDM); 2) universal filtered multicarrier (UFMC); 3) filter bank multicarrier (FBMC); and 4) generalized frequency division multiplexing (GFDM). The features that each radio access technology should present to address the main IoT’s requirements are emphasized.

5G Waveforms for IoT Applications

A filter-bank multicarrier–quadrature amplitude modulation (FBMC-QAM) system with two prototype filters for transmitting QAM symbol is proposed, and the orthogonality conditions for the FBMC-QAM system without the intrinsic interference is derived. The proposed transmitter performs the individual filtering for the even and odd-numbered sub-carrier symbols, respectively. In order to satisfy the derived orthogonality conditions, we perform a sub-block wise reverse ordering procedure for the outputs of the odd-numbered sub-carrier filter. Also, this paper shows that the proposed FBMC-QAM system satisfies the suggested orthogonality conditions and can use the multiple-input multiple-output transmission schemes as the conventional orthogonal frequency division multiplexing (OFDM) systems. The signal-to-interference power ratio and the bit error rate (BER) for the proposed FBMC-QAM system are evaluated. Numerical results show that the proposed FBMC-QAM system has almost the same BER performance compared with the FBMC-OQAM and OFDM systems.

A New Filter-Bank Multicarrier System With Two Prototype Filters for QAM Symbols Transmission and Reception

Scenarios envisaged for mobile communication systems beyond 2020 imply that future applications and services will impose highly diverse requirements on the system design. To appropriately respond to these requirements while ensuring an efficient usage of available spectrum and system resources, the air interface of 5G system is expected to provide much more flexibility compared to today's systems. Filterbank based multi-carrier (FBMC) may be considered a potential enabler for that purpose, as it provides excellent waveform properties with additional degrees of freedom for the system design, thanks to the use of prototype filters that may be adjusted to meet desired system constraints. This paper elaborates on the challenges that still need to be solved to render FBMC an eligible candidate as fundamental technology for 5G mobile radio and presents some first approaches towards practical solutions.

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Pierre Siohan

Papers

FBMC-based air interface for 5G mobile: Challenges and proposed solutions