Orthogonal time frequency space (OTFS) modulation is a two-dimensional signaling technique that has recently emerged in the literature to tackle the time-varying (TV) wireless channels. OTFS deploys the Doppler-delay plane to multiplex the transmit data where the time variations of the TV channel are integrated over time and hence the equivalent channel relating the input and output of the system boils down to a time-invariant one. This signaling technique can be implemented on the top of a given multicarrier waveform with the addition of precoding and post-processing units to the modulator and demodulator. In this letter, we present discrete-time formulation of an OFDM-based OTFS system. We argue against deployment of window functions at the OTFS transmitter in realistic scenarios and thus limit any sort of windowing to the receiver side. We study the channel impact in discrete-time providing deeper insights into OTFS systems. Moreover, our derivations lead to simplified modulator and demodulator structures that are far simpler than those in the literature.

Spatial-multiplexing multiple-input multiple-output (MIMO) systems have been developed and enhanced over the past two decades. In particular, a great amount of effort has gone towards development of capacity achieving detectors with affordable computational complexity. The developed detectors may be broadly divided into two classes: (i) deterministic sampling, such as list sphere decoding detector; and (ii) stocastic sampling, such as those based on Markov chain Monte Carlo (MCMC) search schemes. This paper proposes a novel detection scheme that is based on stochastic sampling, but is fundamentally different from the MCMC detectors. While MCMC follows a set of sequential sampling steps, hence, the sample sets obtained are highly correlated, the method proposed in this paper takes stochastic samples that are completely independent. This new approach of stochastic sampling leads to a detector with significantly reduced complexity. It also allows reduction in the detector latency.

Future mobile networks not only envision enhancing the traditional link quality and data rates of mobile broad band (MBB) links, but also development of new control channels to meet the requirements of delay sensitive use cases. In particular, the need for ultra-reliable low-latency communications (URLLC) for many internet of things (IoT) users is greatly emphasized. In this paper, we present a novel spread spectrum waveform design that we propose for transmission of control signals to establish URLLC communications. These control signals are transmitted over the spectral resources that belong to the MBB communications in the network, but at a level that minimally affects these data channels. The proposed waveform, although a direct sequence spread spectrum (DSSS) technique, is designed to take advantage of symbol synchronization available to the OFDM broad band communications in the network. This allows simple synchronization with the rest of the network. The proposed DSSS method can transmit single and multiple bits within each OFDM time frame and can serve many user equipment (UE) nodes simultaneously.

This letter presents a capacity analysis of filter bank multicarrier offset quadrature amplitude modulation (FBMCOQAM) systems. In FBMC-OQAM receivers it is common to preserve the real part of the demodulated signal samples for information recovery. The imaginary part of these samples, which are called intrinsic interference, are simply ignored. This letter provides a theoretical answer to the following fundamental question. Does the ignored imaginary interference in FBMCOQAM contain any information beyond what could be obtained from the preserved real parts?

This paper presents a comparison of the conventional filter bank multicarrier (FBMC) with the generalized frequency division multiplexing (GFDM) and cyclic FBMC (C-FBMC) that have recently been proposed as waveforms candidates for 5G. We identify situations where FBMC outperforms GFDM/C-FBMC, as well as the cases where GFDM/C-FBMC provide more flexibility than FBMC.

An analog adaptive notch filter implementation at 54.1 MHz is presented in this paper. The analog circuit is implemented using discrete components. Implementation issues such as components phase shift and DC offset are discussed and solution for them are proposed. In addition, effect of frequency offset between reference and input signal is discussed. The implemented circuit has -3 dB bandwidth of 300 Hz and a null depth of 45 dB or better.