An all-digital transmitter for pulsed ultra-wideband communication

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 91-96).Applications like sensor networks, medical monitoring, and asset tracking have led to a demand for energy-efficient and low-cost wireless transceivers. These types of applications typically require low effective data rates, thus providing an opportunity to employ simple modulation schemes and aggressive duty-cycling. Due to their inherently duty-cycled nature, pulse-based Ultra-Wideband (UWB) systems are amenable to low-power operation by shutting off circuitry during idle mode between pulses. Furthermore, the use of non-coherent UWB signaling greatly simplifies both transmitter and receiver implementations, offering additional energy savings. This thesis presents an all-digital transmitter designed for a non-coherent pulsed UWB system. By exploiting relaxed center frequency tolerances in non-coherent wideband communication, the transmitter synthesizes UWB pulses from an energy efficient, single-ended digital ring oscillator. Dual capacitively-coupled digital power amplifiers (PAs) are used in tandem to generate bipolar phase modulated pulses for spectral scrambling purposes. By maintaining opposite common modes at the output of these PAs during idle mode (i.e. when no pulses are being transmitted), low frequency turn-on and turn-off transients typically associated with single-ended digital circuits driving single-ended antennas are attenuated by up to 12dB. Furthermore, four level digital pulse shaping is employed to attenuate RF side lobes by up to 20dB. The resulting dual power amplifiers achieve FCC compliant operation in the 3.5, 4.0, and 4.5GHz IEEE 802.15.4a bands without the use of any off-chip filters or large passive components. The transmitter is fabricated in a 90nm CMOS process and requires a core area of 0.07mm2. The entirely digital architecture consumes zero static bias current, resulting in an energy efficiency of 17.5pJ/pulse at data rates up to 15.6Mbps.by Patrick Philip Mercier.S.M

Guest editorial for the special issue on software-defined radio transceivers and circuits for 5G wireless communications

Yichuang Sun, Baoyong Chi, and Heng Zhang, Guest Editorial for the Special Issue on Software-Defined Radio Transceivers and Circuits for 5G Wireless Communications, published in IEEEE Transactions on Circuits and Systems II: Express Briefs, Vol. 63 (1): 1-3, January 2016, doi: https://doi.org/10.1109/TCSII.2015.2506979.Peer reviewedFinal Accepted Versio

Coherent versus noncoherent signaling for satellite-aided mobile communications

The use of coherent versus noncoherent communications is an unresolved issue for the mobile satellite community. Should one select the more robust but less efficient noncoherent strategy for communications over satellite-aided mobile channels, or does the introduction of a space platform in the mobile link improve signal stability (both amplitude and phase) such that conventional coherent schemes become attractive? This publication tries to answer some of the questions by discussing the results from experiments using a coherent QPSK receiver. The issues discussed include items such as the measured performance in Rician fading, the link error floor in a fading environment, etc. The results are compared and contrasted with that of a noncoherent limiter/discriminator FM receiver

A proof-of-concept superregenerative QPSK transceiver

In this paper we present a description and experimental verification of an HF-band proof-of-concept superregenerative transceiver for QPSK signals. We describe a simple implementation of an all-digital, FPGA-based, QPSK transmitter section. On the receiver side, the quench signal is generated in the same FPGA with a minimum of analog circuitry. As the main novelty, we present a simple synchronization scheme suitable for packetized transmissions.Peer ReviewedPostprint (author’s final draft

A 21-GS/s single-bit second-order delta-sigma modulator for FPGAs

A new high-speed delta-sigma modulator (DSM) topology is proposed by cascading a bit reduction process with a multi-stage noise shaping MASH-1-1 DSM. This process converts the two-bit output sequence of the MASH-1-1 DSM to a single-bit sequence, merely compromising the DSM noise-shaping performance. Furthermore, the high clock frequency requirements are significantly relaxed by using parallel processing. This DSM topology facilitates the designs of wideband software defined radio transmitters and delta-sigma radio-over-fiber transmitters. Experimental results of the FPGA implementation show that the proposed low-pass DSM can operate at 21 GS/s, providing 520-MHz baseband bandwidth with 42.76-dB signal-to-noise-and-distortion ratio (SNDR) or 1.1-GHz bandwidth with 32.04-dB SNDR (based on continuous wave measurements). An all-digital transmitter based on this topology can generate 218.75MBd 256 QAM over 200-m OM4 multimode fiber in real time, with 7-GS/s sampling rate and an error vector magnitude below 1.89%

Exploração de transmissores integralmente digitais em cenários C-RAN

In order to accommodate the ever-growing demand for higher transmission rates, the next generation of mobile telecommunications (5G) will need larger bandwidths, as well as, new frequencies with available spectrum capable of accommodate such bandwidths. The rise in frequency is being pointed out as a solution for this problem, however, the low coverage areas presented by these frequency bands (mmWave) will require a new way of implementing base stations. Those, in their turn, will exist in higher numbers and closer together. It is where that the new radio access network architecture, C-RAN, may allow for the ful lment of these requirements, besides also allowing for the reduction in cost of each base station as well as providing an increase in its energy e ciency. This dissertation aims to create a point-to-point optical link based on All- Digital Transmitters (ADT) capable of being used for data transmission in the fronthaul. Taking advantage of recent developments in ADT, it is now possible to create one with large bandwidths. Besides, the eld programmable gate arrays (FPGAs) have been providing each time higher processing capacity using each time less energy, making the nal product cheaper and more e cient. Recurring to delta-sigma modulation ( M), a reduction in the complexity of the remote radio head (RRH) can be achieved. In this work the optical link that will be used to transport the data through the fronthaul will be based on an SFP. However, other techniques of radio over bre (RoF) can be used to enable, for example, optical upconversion. From the conclusion of this work, a point-to-point optical link based on an ADT was achieved with an Error Vector Magnitude (EVM) always lower than 5%. Also, from this work, two optical upconversions were developed with an output frequency range from 27 GHz up to 63 GHz.De modo a acompanhar a sempre crescente exigência de maiores taxas de transmissão, a próxima geração de telecomunicações móveis (5G) irá necessitar de maiores larguras de banda, bem como novas frequências de transmissão com espectro livre capaz de acomodar tais larguras de banda. A subida em frequência é apontada como uma solução para este problema, contudo as baixas áreas de cobertura apresentadas por estas bandas de frequência (mmWave) irão necessitar de uma nova forma de implementar estações base. Estas, por sua vez, terão de existir em maior número e mais próximas. É aqui que a nova arquitetura de redes de acesso radio, C-RAN, pode permitir cumprir com estes requisitos, além de poder baixar o custo de cada estação base e aumentar a sua eficiência energética. Esta dissertação tem como objetivo a criação de uma ligação ponto a ponto baseada em transmissores integralmente digitais (ADTs) capaz de ser usada para a transmissão de dados no fronthaul. Aproveitando os desenvolvimentos recentes nos ADT, a criação de um transmissor integralmente digital com largura de banda elevada é agora possível. Além disto, os agregados de células lógicas reprogramáveis (FPGAs) têm vindo a fornecer cada vez uma maior capacidade de processamento, usando menos energia, tornando o produto final, mais barato e mais eficiente. O recurso à modelação deltasigma ( M) no ADT poderá reduzir consideravelmente a complexidade da cabeça remota de rádio (RRH). Neste trabalho a ligaçãao ótica que irá ser usada para enviar os dados no fronthaul será baseada num SFP, mas outras técnicas de rádio sobre fibra (RoF) poderão ser também usadas de forma a possibilitar, por exemplo, upconversion ótico. Da conclusão deste trabalho resulta uma ligação ponto a ponto baseada num ADT com um Error Vector Magnitude (EVM) sempre abaixo dos 5%, bem como duas arquiteturas de upconversion ótico com uma gama possível para o sinal de saída que pode variar entre os 27 GHz e os 63 GHz. uma maior capacidade de processamento, usando menos energia, tornando o produto nal, mais barato e mais e ciente. O recurso a modelação deltasigma ( M) no ADT poder a reduzir consideravelmente a complexidade da cabeça remota de radio (RRH). Neste trabalho a ligação otica que ir a ser usada para enviar os dados no fronthaul ser a baseada num SFP, mas outras t ecnicas de r adio sobre bra (RoF) poderão ser também usadas de forma a possibilitar, por exemplo, upconversion otico. Da conclusão deste trabalho resulta uma ligação ponto a ponto baseada num ADT com um Error Vector Magnitude (EVM) sempre abaixo dos 5%, bem como duas arquiteturas de upconversion otico com uma gama possível para o sinal de saída que pode variar entre os 27 GHz e os 63 GHz.POCI-01-0247-FEDER- 024539; POCI-01-0145- FEDER-016432Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Arquiteturas paralelas avançadas para transmissores 5G totalmente digitais

The fifth generation of mobile communications (5G) is being prepared and should be rolled out in the early coming years. Massive number of Radio-Frequency (RF) front-ends, peak data rates of 10 Gbps (everywhere and everytime), latencies lower than 10 msec and huge device densities are some of the expected disruptive capabilities. At the same time, previous generations can not be jeopardized, fostering the design of novel flexible and highly integrated radio transceivers able to support the simultaneous transmission of multi-band and multi-standard signals. The concept of all-digital transmission is being pointed out as a promising architecture to cope with such challenging requirements, due to its fully digital radio datapath. This thesis is focused on the proposal and validation of fully integrated and advanced digital transmitter architectures that excel the state-of-the-art in different figures of merit, such as transmission bandwidth, spectral purity, carrier agility, flexibility, and multi-band capability. The first part of this thesis introduces the concept of all-digital RF transmission. In particular, the foundations inherent to this thematic line are given, together with the recent advances reported in the state-of-the-art architectures.The core of this thesis, containing the main developments achieved during the Ph.D. work, is then presented and discussed. The first key contribution to the state-of-the-art is the use of cascaded Delta-Sigma (∆Σ) architectures to relax the analog filtering requirements of the conventional All-Digital Transmitters while maintaining the constant envelope waveform. Then, it is presented the first reported architecture where Antenna Arrays are directly driven by single-chip and single-bit All-Digital Transmitters, with promising results in terms of simplification of the RF front-ends and overall flexibility. Subsequently, the thesis proposes the first reported RF-stage All-Digital Transmitter that can be embedded within a single Field-Programmable Gate Array (FPGA) device. Thereupon, novel techniques to enable the design of wideband All-Digital Transmitters are reported. Finally, the design of concurrent multi-band transmitters is introduced. In particular, the design of agile and flexible dual and triple bands All-DigitalTransmitter (ADT) is demonstrated, which is a very important topic for scenarios that demand carrier aggregation. This Ph.D. contributes withseveral advances to the state-of-the-art of RF all-digital transmitters.A quinta geração de comunicações móveis (5G) está a ser preparada e deve ser comercializada nos próximos anos. Algumas das caracterı́sticas inovadoras esperadas passam pelo uso de um número massivo de font-ends de Rádio-Frequência (RF), taxas de pico de transmissão de dados de 10 Gbps (em todos os lugares e em todas as ocasiões), latências inferiores a 10 mseg e elevadas densidades de dispositivos. Ao mesmo tempo, as gerações anteriores não podem ser ignoradas, fomentando o design de novos transceptores de rádio flexı́veis e altamente integrados, capazes de suportar a transmissão simultânea de sinais multi-banda e multi-standard. O conceito de transmissão totalmente digital é considerado como um tipo de arquitetura promissora para lidar com esses requisitos desafiantes, devido ao seu datapath de rádio totalmente digital. Esta tese é focada na proposta e validação de arquiteturas de transmissores digitais totalmente integradas e avançadas que ultrapassam o estado da arte em diferentes figuras de mérito, como largura de banda de transmissão, pureza espectral, agilidade de portadora, flexibilidade e capacidade multibanda. A primeira parte desta tese introduz o conceito de transmissores de RF totalmente digitais. Em particular, os fundamentos inerentes a esta linha temática são apresentados, juntamente com os avanços mais recentes do estado-da-arte. O núcleo desta tese, contendo os principais desenvolvimentos alcançados durante o trabalho de doutoramento, é então apresentado e discutido. A primeira contribuição fundamental para o estado da arte é o uso de arquiteturas em cascata com moduladores ∆Σ para relaxar os requisitos de filtragem analógica dos transmissores RF totalmente digitais convencionais, mantendo a forma de onda envolvente constante. Em seguida, é apresentada a primeira arquitetura em que agregados de antenas são excitados diretamente por transmissores digitais de um único bit inseridos num único chip, com resultados promissores em termos de simplificação dos front-ends de RF e flexibilidade em geral. Posteriormente, é proposto o primeiro transmissor totalmente digital RF-stage relatado que pode ser incorporado dentro de um único Agregado de Células Lógicas Programáveis. Novas técnicas para permitir o desenho de transmissores RF totalmente digitais de banda larga são também apresentadas. Finalmente, o desenho de transmissores simultâneos de múltiplas bandas é exposto. Em particular, é demonstrado o desenho de transmissores de duas e três bandas ágeis e flexı́veis, que é um tópico essencial para cenários que exigem agregação de múltiplas bandas.Apoio financeiro da Fundação para a Ciência e Tecnologia (FCT) no âmbito de uma bolsa de doutoramento, ref. PD/BD/105857/2014.Programa Doutoral em Telecomunicaçõe

Real-time 100-GS/s sigma-delta modulator for all-digital radio-over-fiber transmission

All-digital radio-over-fiber (RoF) transmission has attracted a significant amount of interest in digital-centric systems or centralized networks because it greatly simplifies the front-end hardware by using digital processing. The sigma-delta modulator (SDM)-based all-digital RoF approach pushes the digital signal processing as far as possible into the transmit chain. We present a real-time 100-GS/s fourth-order single-bit SDM for all-digital RoF transmission in the high-frequency band without the aid of analog/optical up-conversion. This is the fastest sigma-delta modulator reported and this is also the first real-time demonstration of sigma-delta-modulated RoF in the frequency band above 24 GHz. 4.68 Gb/s (2.34 Gb/s) 64-QAM is transported over 10-km standard single-mode fiber in the C-band with 6.46% (4.73%) error vector magnitude and 3.13 Gb/s 256-QAM can be even received in an optical back-to-back configuration. The carrier frequency can be digitally tuned at run-time, covering a wide frequency range from 22.75 to 27.5 GHz. Besides, this high-speed sigma-delta modulator introduces less than 1 mu s latency in the transmit chain. Its all-digital nature enables network virtualization, making the transmitter compatible with different existing standards. The prominent performance corroborates the strong competitiveness of this SDM-based RoF approach in high-frequency RoF 5C communication