Baseband Interference Research Articles

Baseband linearity and interference effects in intensity modulated and direct detected optical MIMO systems

Abstract In short reach intensity modulated and direct detected (IM/DD) optical multiple-input multiple-output (MIMO) systems linear equalization strategies are commonly applied. However, the square-law detector inherently is a non-linear system element. This work investigates this discrepancy and shows for which laser types and under which mode coupling conditions baseband linearity applies for the first time. Based on a system model that integrates a multitude of aspects, e.g. the phase state of each fiber mode and mode coupling, it is shown that the received signal consists of a linear component and one that can be considered as interference. The simulation and measurement results highlight that only MIMO setups with weak and no mode cross-talk can be considered as linear. Systems with high mode cross-talk are impaired by significant interference, resulting in a highly degraded bit-error rate performance.

Built-In Test of Phased Arrays Using Code-Modulated Interferometry

This paper presents a built-in self-test technique for phased arrays that applies code modulation to each element within the array to allow parallel in situ measurements and a built-in distribution network to allow injection or extraction of test signals. The aggregated test response is downconverted from radio-frequency or millimeter-wave frequencies using a direct (power) detector, resulting in a baseband interference signal composed of code-modulated complex cross correlations between all elemental signals. Using orthogonal code products, each cross correlation can be extracted from the interference signal, and then the full set of cross correlations can be used to obtain amplitude and phase data of each element. A four-element 60-GHz phased-array receiver front end that includes this code-modulated embedded test (CoMET) infrastructure has been fabricated in SiGe BiCMOS technology. The BIST overhead is less than 2% of the total die area. Comparisons between our built-in test technique and measurements using a vector network analyzer show that CoMET can be used to extract amplitude with 1 dB accuracy and phase with four degree accuracy. Furthermore, measurements confirm that CoMET can be used to extract the phase-step response of each element in parallel across all settings as well as phase offset introduced by the built-in test network.

Modeling and Analysis of Cellular Networks Using Stochastic Geometry: A Tutorial

This paper presents a tutorial on stochastic geometry (SG) based analysis for cellular networks. This tutorial is distinguished by its depth with respect to wireless communication details and its focus on cellular networks. The paper starts by modeling and analyzing the baseband interference in a basic cellular network model. Then, it characterizes signal-to-interference-plus-noise-ratio (SINR) and its related performance metrics. In particular, a unified approach to conduct error probability, outage probability, and rate analysis is presented. Although the main focus of the paper is on cellular networks, the presented unified approach applies for other types of wireless networks that impose interference protection around receivers. The paper then extends the baseline unified approach to capture cellular network characteristics (e.g., frequency reuse, multiple antenna, power control, etc.). It also presents numerical examples associated with demonstrations and discussions. Finally, we point out future research directions.

Calibrated Monolithically Integrated 90 <named-content content-type="math" xlink:type="simple"> <inline-formula> <tex-math notation="TeX">$^{\circ} $</tex-math></inline-formula></named-content> Downconverter for Colorless Operation in the C+L Band

We propose a 90 $^{\circ} $ hybrid-based monolithically integrated coherent receiver suitable for colorless operation in the complete C- and L-band (1530–1625 nm). In-phase and quadrature (IQ) signal components are obtained from a calibrated analog IQ recovery circuit, which adequately combines all the four photocurrents at the output of the 90 $^{\circ} $ hybrid nearly cancelling the baseband interference from the self-beating of adjacent wavelength division multiplexing channels. We numerically demonstrate that the proposed downconverter supports colorless reception of 128 channels with 16-quadrature amplitude modulation at 112 Gbps in the C+L band. Aside from this, this receiver exhibits a noticeable dynamic range, thereby not requiring a variable optical attenuator on the signal path, and it is pretty robust under realistic fabrication errors of the optoelectronic chip.

System study on nonlinear suppression of varying-envelope local interference in multimode transceivers

In multimode transceivers, a local transmitter may induce a strong interference in a local receiver, often several orders of magnitude stronger than the desired received signal. To suppress this interference linearly, the receiver would need a very large dynamic range, resulting in excessive power consumption. A potentially much more power-efficient approach involves a memoryless nonlinearity that can strongly suppress the interference when accurately adapted to the envelope of the interference. This approach has so far been limited to constant-envelope interferers owing to the difficulty of extracting accurate interference envelope information from the compound received signal. In this paper, we observe that in multimode transceivers the locally available baseband interference enables accurate adaptation for varying-envelope interferences. The paper performs a system study to explore the resulting performance. Specifically, we show that for varying-envelope interferences, nonlinear distortion products emerge that are negligible for constant-envelope interferences. We analyze these products, identify the conditions for which adequate interference suppression is combined with negligible distortion, and show that these conditions are met in most cases of practical interest. Simulations for a broad set of modulation schemes corroborate this analysis.

Analysis of an Adaptive Nonlinear Interference Suppressor for Wireless Multimode Transceivers

In multimode transceivers, the transmitter for one communication standard may induce strong interference in the receiver for another standard, often exceeding the desired signal by many tens of decibels. To linearly suppress this interference, the receiver requires a very large linear dynamic range, resulting in excessive power consumption. In a recent paper, a nonlinear block, which requires an adaptation signal proportional to the envelope of the received interference, has been used to strongly suppress the interference. In that work, the required adaptation signal for the nonlinear block has been determined analytically. In this paper, we quantify the required accuracy for the adaptation signal to properly suppress the interference while keeping the degradation to the receiver symbol error rate (SER) negligible. To provide the required accuracy, we propose a closed-loop method that calculates the adaptation signal based on a model, which describes the received interference in terms of the locally available baseband interference. We propose a method to adapt this model during the operation of the transceiver such that the power of the residual interference at the output of the nonlinear block is minimized. Our analysis shows that the proposed method can strongly suppress the interference while a SER close to that of an exactly linear receiver is achieved. Simulation results for a practical scenario validate this analysis.

MEASUREMENTS OF THE TIME STATISTICS OF FMTV SPECTRA AND TV INTERFERENCE INTO FDM/FM CARRIERS

AbstractWhen computing the amount of interference from FMTV signals in satellite systems, it is customary to consider that the only effective TV modulation is the energy dispersal signal (EDS). This leads to a sufficient but highly conservative system design, since for most of the time the wanted demodulated signal may experience interference levels well below that computed using this approach. If the time statistics of the interference can be determined through measurement, then a grade‐of‐service approach can be taken in which interference can be guaranteed not to exceed a certain level for more than a prescribed fraction of the time. This approach will lead to more efficient use of orbit/spectrum resources as a result of the implementation of less conservative system designs.This paper presents a simulation approach used to ‘measure’ FMTV power spectra with and without EDS and the corresponding interference powers into the basebands of FDM/FM carriers. Time statistics in the form of FMTV spectral masks and FDM baseband interference power time distributions have been derived from the measured data of 1000 off‐air TV frames for co‐channel TV and standard FDM/FM carrier sets (12 to 1200 channels) deployed by INTELSAT. Sample results are given.

A method for estimating the protection ratio in fm television transmission

AbstractA calculation method for estimating the protection ratio in FM‐TV transmission is described. The interference between two FM carriers modulated by the NTSC or TCI color bar signal is analyzed and the baseband interference is expressed in a simple form as beat interference. Applying several weighting functions of the visual system to the beat interference, a subjective interference index which expresses the degree of subjective impairment is defined and then a method for estimating the protection ratio using this index is proposed. The protection ratios calculated by this method for various signaling systems and modulation parameters agree well with the results of subjective assessment tests. The method permits determination of the protection ratio in any FM‐TV system without subjective assessment tests for various parameters. It can be used to estimate the protection ratio in introducing new services to existing satellite broadcasting channels and to develop new channel plans.

A New Demodulation Method Improving FM System Interference Immunity

As a result of investigation of interference into FM systems, a new algorithm for the process of demodulation is proposed. When compared to the method using the conventional limiter-discriminator, it offers better immunity against the baseband interference noise. Desired signal processing is performed by the functional devices added to the conventional limiter-discriminator in such a way that this new demodulator can be optimized in the sense of the minimum baseband interference noise. The statistics of the wanted and interfering signals must be known. Several examples involving interference problems in FDM-FM radio-relay systems carrying multichannel telephone signals are elaborated to illustrate the performances of the proposed demodulator. FDM-FM, PSK, or FSK systems are considered the cause of the interference. The noise power ratio (NPR) at the output of the conventional limiter-discriminator and the improvement factor offered by the new demodulator, obtained on digital computer, are presented versus baseband frequency in the form of diagrams. Different IF filters in FDM-FM receiver and transmit filters in the interfering systems are taken into account. The improvement offered by the proposed demodulator is of such a degree that some of the important restrictions in planning different radio systems could be relaxed.