Coexistence in 5G: Analysis of Cross-Interference between OFDM/OQAM and Legacy Users

TL;DR

This paper provides an exact analysis of cross-interference between OFDM/OQAM and legacy CP-OFDM in 5G, revealing that OFDM/OQAM offers only marginal interference reduction, challenging previous assumptions.

Contribution

It presents the first exact closed-form expressions for cross-interference between OFDM/OQAM and CP-OFDM, demonstrating limited interference mitigation capabilities.

Findings

OFDM/OQAM marginally reduces interference to legacy users

Previous PSD-based interference measurements are not representative

New analytical results challenge existing beliefs about OFDM/OQAM's effectiveness

Abstract

To optimize the use of the spectrum, it is expected that the next generation of wireless networks (5G) will enable coexistence of newly introduced services with legacy cellular networks. These new services, like Device-To-Device (D2D) communication, should require limited synchronization with the legacy cell to limit the amount of signaling overhead in the network. However, it is known that Cyclic Prefix-Orthogonal Frequency Division Multiplexing (CP-OFDM) used in Long Term Evolution-Advanced (LTE-A) is not fit for asynchronous environments. This has motivated the search for a new waveform, able to enhance coexistence with CP-OFDM. Namely, it has been widely suggested that new devices could use OFDM/Offset-Quadrature Amplitude Modulation (OFDM/OQAM) to reduce the interference they inject to legacy cellular users. However, values of interference are usually measured at the input antenna of the receiver, based on the PSD of the interfering signal. We showed in previous works that this measurement is not representative of the actual interference that is seen after the demodulation operations. Building on this finding, we provide in this paper the first exact closed forms of cross-interference between OFDM/OQAM and CP-OFDM users. Our results prove that using OFDM/OQAM only marginally reduces interference to legacy users, in contradiction with many results in the literature.