Linearity vs. Power Consumption of CMOS LNAs in LTE Systems

This paper presents a study of linearity in wideband CMOS low noise amplifiers (LNA) and its relationship to power consumption in context of Long Term Evolution (LTE) system. Using proposed figure of merit to compare 35 state-of-the-art LNA circuits published in recent years, the paper shows a proportional but relatively weak dependence between amplifier performance (that is combined linearity, noise figure and gain) with power consumption. As a result, the predicted increase of LNA performance, necessary to satisfy stringent linearity specifications of LTE standard, may require a significant increase in power, a critical budget planning aspect for both handheld devices and base stations operating in small cells

ワイヤレス通信のための先進的な信号処理技術を用いた非線形補償法の研究

The inherit nonlinearity in analogue front-ends of transmitters and receivers have had primary impact on the overall performance of the wireless communication systems, as it gives arise of substantial distortion when transmitting and processing signals with such circuits. Therefore, the nonlinear compensation (linearization) techniques become essential to suppress the distortion to an acceptable extent in order to ensure sufficient low bit error rate. Furthermore, the increasing demands on higher data rate and ubiquitous interoperability between various multi-coverage protocols are two of the most important features of the contemporary communication system. The former demand pushes the communication system to use wider bandwidth and the latter one brings up severe coexistence problems. Having fully considered the problems raised above, the work in this Ph.D. thesis carries out extensive researches on the nonlinear compensations utilizing advanced digital signal processing techniques. The motivation behind this is to push more processing tasks to the digital domain, as it can potentially cut down the bill of materials (BOM) costs paid for the off-chip devices and reduce practical implementation difficulties. The work here is carried out using three approaches: numerical analysis & computer simulations; experimental tests using commercial instruments; actual implementation with FPGA. The primary contributions for this thesis are summarized as the following three points: 1) An adaptive digital predistortion (DPD) with fast convergence rate and low complexity for multi-carrier GSM system is presented. Albeit a legacy system, the GSM, however, has a very strict requirement on the out-of-band emission, thus it represents a much more difficult hurdle for DPD application. It is successfully implemented in an FPGA without using any other auxiliary processor. A simplified multiplier-free NLMS algorithm, especially suitable for FPGA implementation, for fast adapting the LUT is proposed. Many design methodologies and practical implementation issues are discussed in details. Experimental results have shown that the DPD performed robustly when it is involved in the multichannel transmitter. 2) The next generation system (5G) will unquestionably use wider bandwidth to support higher throughput, which poses stringent needs for using high-speed data converters. Herein the analog-to-digital converter (ADC) tends to be the most expensive single device in the whole transmitter/receiver systems. Therefore, conventional DPD utilizing high-speed ADC becomes unaffordable, especially for small base stations (micro, pico and femto). A digital predistortion technique utilizing spectral extrapolation is proposed in this thesis, wherein with band-limited feedback signal, the requirement on ADC speed can be significantly released. Experimental results have validated the feasibility of the proposed technique for coping with band-limited feedback signal. It has been shown that adequate linearization performance can be achieved even if the acquisition bandwidth is less than the original signal bandwidth. The experimental results obtained by using LTE-Advanced signal of 320 MHz bandwidth are quite satisfactory, and to the authors’ knowledge, this is the first high-performance wideband DPD ever been reported. 3) To address the predicament that mobile operators do not have enough contiguous usable bandwidth, carrier aggregation (CA) technique is developed and imported into 4G LTE-Advanced. This pushes the utilization of concurrent dual-band transmitter/receiver, which reduces the hardware expense by using a single front-end. Compensation techniques for the respective concurrent dual-band transmitter and receiver front-ends are proposed to combat the inter-band modulation distortion, and simultaneously reduce the distortion for the both lower-side band and upper-side band signals.電気通信大学201

Architectures and Circuit Techniques for High-Performance Field-Programmable CMOS Software Defined Radios

Next-generation wireless communication systems put more stringent performance requirements on the wireless RF receiver circuits. Sensitivity, linearity, bandwidth and power consumption are some of the most important specifications that often face tightly coupled tradeoffs between them. To increase the data throughput, a large number of fragmented spectrums are being introduced to the wireless communication standards. Carrier aggregation technology needs concurrent communication across several non-contiguous frequency bands, which results in a rapidly growing number of band combinations. Supporting all the frequency bands and their aggregation combinations increases the complexity of the RF receivers. Highly flexible software defined radio (SDR) is a promising technology to address these applications scenarios with lower complexity by relaxing the specifications of the RF filters or eliminating them. However, there are still many technology challenges with both the receiver architecture and the circuit implementations. The performance requirements of the receivers can also vary across different application scenario and RF environments. Field-programmable dynamic performance tradeoff can potentially reduce the power consumption of the receiver. In this dissertation, we address the performance enhancement challenges in the wideband SDRs by innovations at both the circuit building block level and the receiver architecture level. A series of research projects are conducted to push the state-of-the-art performance envelope and add features such as field-programmable performance tradeoff and concurrent reception. The projects originate from the concept of thermal noise canceling techniques and further enhance the RF performance and add features for more capable SDR receivers. Four generations of prototype LNA or receiver chips are designed, and each of them pushes at least one aspect of the RF performance such as bandwidth, linearity, and NF. A noise-canceling distributed LNA breaks the tradeoff between NF and RF bandwidth by introducing microwave circuit techniques from the distributed amplifiers. The LNA architecture uniquely provides ultra high bandwidth and low NF at low frequencies. A family of field-programmable LNA realized field-programmable performance tradeoff with current-reuse programmable transconductance cells. Interferer-reflecting loops can be applied around the LNAs to improve their input linearity by rejecting the out-of-band interferers with a wideband low in- put impedance. A low noise transconductance amplifier (LNTA) that operates in class-AB-C is invented to can handle rail-to-rail out-of-band blocker without saturation. Class-AB and class-C transconductors form a composite amplifier to increase the linear range of the input voltage. A new antenna interface named frequency-translational quadrature-hybrid (FTQH) breaks the input impedance matching requirement of the LNAs by introducing quadrature hybrid couplers to the CMOS RFIC design. The FTQH receiver achieves wideband sub-1dB NF and supports scalable massive frequency-agile concurrent reception

The Experimental Design of Radio-over-Fibre System for 4G Long Term Evolution

The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) is the potential key to meet the exponentially increasing demand of the mobile end users. The entire LTE network architecture and signal processing is carried out at the enhanced NodeB (eNB) level, hence the increased complexity and cost. Therefore, it is not efficient to deploy eNB for the purpose of extending the network coverage. As a solution, deployment of relay node (RN), with radio-over-fibre (RoF) acting as the interface between eNB and RN is proposed. Due to the high path loss and multipath fading, wireless interface would not be the ideal channel between eNB and RN. A detailed investigation is carried out by comparing the Rayleigh multipath fading channel with the optical fibre channel, where the latter achieved a ~31 dB of signal-to-noise ratio (SNR) gain. The distributed feedback laser (DFB) is selected as the direct modulated laser (DML) source, where the modulation method introduces a positive frequency chirp (PFC). The existing mathematical expression does not precisely explain on how the rate equations contribute to PFC. Therefore, an expression for PFC is proposed and derived from the carrier and photon densities of the rate equations. Focusing on theoretical development of DML based RoF system, a varying fast Fourier transform (FFT) scheme is introduced into LTE-Advanced (LTE-A) technology as an alternative design to the carrier aggregation. A range of FFT sizes are investigated with different levels of optical launch power (OLP), the optimum OLP has been defined to be within the range of ~-6 to 0 dBm, which is known as the intermixing region. It is found that FFT size-128 provides improved average system efficiency of ~54% and ~65% in comparison to FFT size-64 and FFT size-128, respectively, within the intermixing region. While fixing FFT size to 128, the investigation is diverted to the optimisation of optical modulators. The author revealed that the performance of dual electrode-Mach Zehnder modulator (DE-MZM) is superior to both DML scheme and single electrode (SE)-MZM, where DE-MZM achieved a transmission span of 88 km and 71 km for 16-quadrature amplitude modulation (QAM) and 64-QAM, respectively. At the initial experimental link design and optimisation stage, an optimum modulation region (OMR) is proposed at the optical modulation index (OMI) of 0.38, which resulted in an average error vector magnitude (EVM) of ~1.01% for a 10 km span. The EVM of ~1.01% is further improved by introducing the optimum OLP region at –2 dBm, where the observed average EVM trimmed to ~0.96%. There is no deviation found in the intermixing region by transmitting the LTE signal through a varying transmission span of 10 to 60 km, additionally, it was also revealed that the LTE RoF nonlinear threshold falls above the OLP of 6 dBm. The proposed system was further developed to accommodate 2×2 multiple-input and multiple-output (MIMO) transmission by utilising analogue frequency division multiplexing (FDM) technique. The studies procured that the resulting output quality of signal at 2 GHz and 2.6 GHz is almost identical with a twofold gain in the peak data rate and no occurrence of intermodulation (IMD). In order to emulate the complete LTE RoF solution, an experimental design of full duplex frequency division duplex (FDD) system with dense wavelength division multiplexing (DWDM) architecture is proposed. It is found that channel spacing of 50 MHz between the downlink (DL) and uplink (UL) introduces severe IMD distortion, where an adjacent channel leakage ratio (ACLR) penalty of 14.10 dB is observed. Finally, a novel nonlinear compensation technique utilising a direct modulation based frequency dithering (DMFD) scheme is proposed. The LTE RoF system average SNR gain observed at OLP of 10 dBm for the 50 km transmission span is ~5.97 dB. External modulation based frequency dithering (EMFD) exhibits ~3 dB of average SNR gain over DMFD method

Radio-Communications Architectures

Wireless communications, i.e. radio-communications, are widely used for our different daily needs. Examples are numerous and standard names like BLUETOOTH, WiFI, WiMAX, UMTS, GSM and, more recently, LTE are well-known [Baudoin et al. 2007]. General applications in the RFID or UWB contexts are the subject of many papers. This chapter presents radio-frequency (RF) communication systems architecture for mobile, wireless local area networks (WLAN) and connectivity terminals. An important aspect of today's applications is the data rate increase, especially in connectivity standards like WiFI and WiMAX, because the user demands high Quality of Service (QoS). To increase the data rate we tend to use wideband or multi-standard architecture. The concept of software radio includes a self-reconfigurable radio link and is described here on its RF aspects. The term multi-radio is preferred. This chapter focuses on the transmitter, yet some considerations about the receiver are given. An important aspect of the architecture is that a transceiver is built with respect to the radio-communications signals. We classify them in section 2 by differentiating Continuous Wave (CW) and Impulse Radio (IR) systems. Section 3 is the technical background one has to consider for actual applications. Section 4 summarizes state-of-the-art high data rate architectures and the latest research in multi-radio systems. In section 5, IR architectures for Ultra Wide Band (UWB) systems complete this overview; we will also underline the coexistence and compatibility challenges between CW and IR systems

Real-Time Localization Using Software Defined Radio

Service providers make use of cost-effective wireless solutions to identify, localize, and possibly track users using their carried MDs to support added services, such as geo-advertisement, security, and management. Indoor and outdoor hotspot areas play a significant role for such services. However, GPS does not work in many of these areas. To solve this problem, service providers leverage available indoor radio technologies, such as WiFi, GSM, and LTE, to identify and localize users. We focus our research on passive services provided by third parties, which are responsible for (i) data acquisition and (ii) processing, and network-based services, where (i) and (ii) are done inside the serving network. For better understanding of parameters that affect indoor localization, we investigate several factors that affect indoor signal propagation for both Bluetooth and WiFi technologies. For GSM-based passive services, we developed first a data acquisition module: a GSM receiver that can overhear GSM uplink messages transmitted by MDs while being invisible. A set of optimizations were made for the receiver components to support wideband capturing of the GSM spectrum while operating in real-time. Processing the wide-spectrum of the GSM is possible using a proposed distributed processing approach over an IP network. Then, to overcome the lack of information about tracked devices’ radio settings, we developed two novel localization algorithms that rely on proximity-based solutions to estimate in real environments devices’ locations. Given the challenging indoor environment on radio signals, such as NLOS reception and multipath propagation, we developed an original algorithm to detect and remove contaminated radio signals before being fed to the localization algorithm. To improve the localization algorithm, we extended our work with a hybrid based approach that uses both WiFi and GSM interfaces to localize users. For network-based services, we used a software implementation of a LTE base station to develop our algorithms, which characterize the indoor environment before applying the localization algorithm. Experiments were conducted without any special hardware, any prior knowledge of the indoor layout or any offline calibration of the system

PASSIVE RF CIRCUITS FOR SIMULTANEOUS TRANSMIT AND RECEIVE AND IMPACT ANALYSIS OF RECONFIGURABLE WIDEBAND RF ELECTRONICS ON COMMUNICATIONS SYSTEM OPERATIONS

Consumer based wireless systems currently operate with a split spectrum approach. However, in order to accommodate the increased demand for high datarate services within fixed spectrum allocations a new architecture will be required. The ability to simultaneously transmit and receive data within the full spectrum allocation can alleviate this problem. Simultaneous transmission and reception within current spectrum limits could effectively double data rates. However, physical limitations on radio frequency circuits including reflections and mutual coupling currently limit the capability of systems to operate in this mode. Therefore, radio frequency circuits that cancel this self-interference must be introduced. This thesis describes the development of a self-interference cancellation circuit for simultaneous transmit and receive. The design operates by combining an out of phase signal of equal magnitude with the original self-interference signal. Design methodology for the required radio frequency circuitry, including antenna elements, directional couplers, and hairpin resonators is provided. A characterization method for determining the antenna mutual coupling and phase characteristics is implemented in commercial computer aided design software. Both a hairpin resonator and a delay line are used to match the phase and magnitude characteristics of the antenna mutual coupling. Directional couplers are designed to provide the required anti-phasing of the signal and couple the required power level from the transmit path, through the phasing element, to the receive path. The devices are fabricated on high frequency printed circuit board materials and measured. The theory of operation for a T-junction exponential power divider used in an early version of the circuit is also presented. Measured results of the self-interference cancellation circuit agree well with simulation. Future RF systems are being designed with a desire for both simultaneous transmit and receive capability and wideband operation. However, due to the nature of wideband devices, they are susceptible to out-of-band interference degrading system level performance. With this in mind, a system level analysis of a wideband low noise amplifier with both adaptive and controllable biasing current is performed. Based on a quadrature phase shift keyed communications system, simulation and measurements fundamental to the operation of such wideband devices are conducted. This analysis shows the dependence of in-band performance on power received from out-of-band interfering signals. It is shown that the out-of-band noise sources contribute to increased error vector magnitude in the receiver due to gain compression

Four-element phased-array beamformers and a self-interference canceling full-duplex transciver in 130-nm SiGe for 5G applications at 26 GHz

This thesis is on the design of radio-frequency (RF) integrated front-end circuits for next generation 5G communication systems. The demand for higher data rates and lower latency in 5G networks can only be met using several new technologies including, but not limited to, mm-waves, massive-MIMO, and full-duplex. Use of mm-waves provides more bandwidth that is necessary for high data rates at the cost of increased attenuation in air. Massive-MIMO arrays are required to compensate for this increased path loss by providing beam steering and array gain. Furthermore, full duplex operation is desirable for improved spectrum efficiency and reduced latency. The difficulty of full duplex operation is the self-interference (SI) between transmit (TX) and receive (RX) paths. Conventional methods to suppress this interference utilize either bulky circulators, isolators, couplers or two separate antennas. These methods are not suitable for fully-integrated full-duplex massive-MIMO arrays. This thesis presents circuit and system level solutions to the issues summarized above, in the form of SiGe integrated circuits for 5G applications at 26 GHz. First, a full-duplex RF front-end architecture is proposed that is scalable to massive-MIMO arrays. It is based on blind, RF self-interference cancellation that is applicable to single/shared antenna front-ends. A high resolution RF vector modulator is developed, which is the key building block that empowers the full-duplex frontend architecture by achieving better than state-of-the-art 10-b monotonic phase control. This vector modulator is combined with linear-in-dB variable gain amplifiers and attenuators to realize a precision self-interference cancellation circuitry. Further, adaptive control of this SI canceler is made possible by including an on-chip low-power IQ downconverter. It correlates copies of transmitted and received signals and provides baseband/dc outputs that can be used to adaptively control the SI canceler. The solution comes at the cost of minimal additional circuitry, yet significantly eases linearity requirements of critical receiver blocks at RF/IF such as mixers and ADCs. Second, to complement the proposed full-duplex front-end architecture and to provide a more complete solution, high-performance beamformer ICs with 5-/6- b phase and 3-/4-b amplitude control capabilities are designed. Single-channel, separate transmitter and receiver beamformers are implemented targeting massive- MIMO mode of operation, and their four-channel versions are developed for phasedarray communication systems. Better than state-of-the-art noise performance is obtained in the RX beamformer channel, with a full-channel noise figure of 3.3 d