Non-Coherent Multiuser Massive MIMO-OFDM with Differential Modulation

Abstract

Massive multiple-input multiple-output (MIMO) and orthogonal frequency division multiplexing (OFDM) are wireless technologies adopted by the Fifth Generation (5G) of mobile communications. The channel estimation and pre/postequalization processes in coherent detection schemes for massive MIMO-OFDM are a challenging task, where several issues are faced, such as pilot contamination, channel calibration, matrix inversions, among others. Moreover, they increase the energy consumption and latency of the system. A non-coherent technique relying on DPSK constellation has been proposed for a singlecarrier scheme, assuming flat-fading. In our paper, we extend this technique to be combined with OFDM, where the channel is doubly dispersive (time and frequency). We will show that the differential modulation can be performed either in the time or frequency domain, where the latter suffers from an additional phase rotation, which should be estimated and compensated. We provide the analytical expression of the signal-to-interferenceand-noise ratio (SINR) for both cases, and we show numerical results in order to verify our analysis.

Differential Data-Aided Channel Estimation for Up-Link Massive SIMO-OFDM

“…We will use the frequency domain implementation of the NCDS presented in [16]. This method has the advantage of involving a lower processing delay.…”

“…On the other hand, NCDS is suitable for these extreme cases where resources are not wasted to transmit reference signals. Indeed, [14]- [16] showed that NCDS has a great robustness against high Doppler scenarios, no matter the delay spread when OFDM is used. On the contrary, for low mobility or fixed communication scenarios with low or moderate values of delay spread, the number of reference signals can be greatly reduced ( ↓ and ↓) since the channel remains quasi-static in both dimensions.…”

“…Though traditionally dismissed due to the SNR loss with respect to coherent approaches, the combination of non-coherent detection with massive MIMO has recently gained attention, since this SNR loss may become negligible when considering the gains in spectral efficiency and complexity reduction. A significant number of works in the literature focus on the up-link (UL) [13]- [16], where single antenna users transmit to a base station (BS) equipped with an array of a very large number of elements, which corresponds to a multi-user single-input multiple-output (SIMO) scenario. The large number of elements at the receiver can leverage spatial diversity, improving the link performance.…”

“…References [14], [15] proposed the use of differential phase shift keying (DPSK), where the BS receiver non-coherently combines two contiguous symbols for each antenna and performs an averaging process over the antennas to mitigate the channel effects. Later, the combination of [14] with OFDM is studied in [16] assuming a doubly dispersive channel model. Moreover, the differential modulation showed great robustness against extremely high Doppler shifts, significantly outperforming the traditional coherent schemes in these scenarios.…”

“…The idea is to maintain the SNR efficiency of coherent demodulation schemes (CDS) while not wasting resources for pilot transmission thanks to NCDS, even for those scenarios which suffer from high values of Doppler and/or delay spread. We focus on the particular case of UL since the recent literature has shown that the NCDS can make use of the large number of antennas at the BS to improve its performance [14]- [16]. Besides, most massive MIMO systems are based on a time division duplex (TDD) where training is performed in the UL, making the UL CSI estimation indispensable.…”