Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions

Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio (NR) and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing of 8 terminals). Coarse and even error-prone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.Comment: submitted to IEEE transactions on signal processin

Electronic dispersion precompensation of direct-detected NRZ using analog filtering

We demonstrate (in real-time) electrical dispersion compensation in direct detection links using analog transmit side filtering techniques. By this means, we extend the fiber reach using a low complexity solution while avoiding digital preprocessing and digital-to-analog converters (DACs) which are commonly used nowadays. Modulation is done using an IQ MachZehnder modulator (MZM) which allows straightforward compensation of the complex impulse response caused by chromatic dispersion in the fiber. A SiGe BiCMOS 5-tap analog complex finite impulse response (FIR) filter chip and/or a delay between both driving signals of the MZMs is proposed for the filter implementation. Several link experiments are conducted in C-band where transmission up to 60 km of standard single-mode fiber (SSMF) of direct detected 28Gb/s NRZ/OOK is demonstrated. The presented technique can be used in applications where low power consumption is critical

Architectures for RF Frequency synthesizers

Frequency synthesizers are an essential building block of RF communication products. They can be found in traditional consumer products, in personal communication systems, and in optical communication equipment. Since frequency synthesizers are used in many different applications, different performance aspects may need to be considered in each case. The main body of the text describes a conceptual framework for analyzing the performance of PLL frequency synthesizers, and presents optimization procedures for the different performance aspects. The analysis of the PLL properties is performed with the use of the open-loop bandwidth and phase margin concepts, to enable the influence of higher-order poles to be taken into account from the beginning of the design process. The theoretical system analysis is complemented by descriptions of innovative system and building block architectures, by circuit implementations in bipolar and CMOS technologies, and by measurement results. Architectures for RF Frequency Synthesizers contains basic information for the beginner as well as in-depth knowledge for the experienced designer. It is widely illustrated with practical design examples used in industrial products.\ud Written for:\ud Electrical and electronic engineer

Discrete Multitone Modulation for Maximizing Transmission Rate in Step-Index Plastic Optical Fibres

The use of standard 1-mm core-diameter step-index plastic optical fiber (SI-POF) has so far been mainly limited to distances of up to 100 m and bit-rates in the order of 100 Mbit/s. By use of digital signal processing, transmission performance of such optical links can be improved. Among the different technical solutions proposed, a promising one is based on the use of discrete multitone (DMT) modulation, directly applied to intensity-modulated, direct detection (IM/DD) SI-POF links. This paper presents an overview of DMT over SI-POF and demonstrates how DMT can be used to improve transmission rate in such IM/DD systems. The achievable capacity of an SI-POF channel is first analyzed theoretically and then validated by experimental results. Additionally, first experimental demonstrations of a real-time DMT over SI-POF system are presented and discusse

Single-Carrier Modulation versus OFDM for Millimeter-Wave Wireless MIMO

This paper presents results on the achievable spectral efficiency and on the energy efficiency for a wireless multiple-input-multiple-output (MIMO) link operating at millimeter wave frequencies (mmWave) in a typical 5G scenario. Two different single-carrier modem schemes are considered, i.e., a traditional modulation scheme with linear equalization at the receiver, and a single-carrier modulation with cyclic prefix, frequency-domain equalization and FFT-based processing at the receiver; these two schemes are compared with a conventional MIMO-OFDM transceiver structure. Our analysis jointly takes into account the peculiar characteristics of MIMO channels at mmWave frequencies, the use of hybrid (analog-digital) pre-coding and post-coding beamformers, the finite cardinality of the modulation structure, and the non-linear behavior of the transmitter power amplifiers. Our results show that the best performance is achieved by single-carrier modulation with time-domain equalization, which exhibits the smallest loss due to the non-linear distortion, and whose performance can be further improved by using advanced equalization schemes. Results also confirm that performance gets severely degraded when the link length exceeds 90-100 meters and the transmit power falls below 0 dBW.Comment: accepted for publication on IEEE Transactions on Communication