Liang Wu

Towards indoor localization using Visible Light Communication for consumer electronic devices

Indoor localization is the fundamental capability for indoor service robots and indoor applications on mobile devices. To realize that, the cost of sensors is of great concern. In order to decode the signal carried out by the LED beacons, we propose two reliable solutions using common sensors available on consumer electronic devices. Firstly, we introduce a dedicated analog sensor, which can be directly connected to the microphone input of a computer or a smart phone. It decodes both the signal pattern and signal strength of a beacon. Secondly, we utilize rolling-shutter cameras to decode the signal pattern, providing potential solutions to the localization of hand-held devices with cameras. In contrast to existing widely-applied indoor localization approaches, like vision-based and laser-based methods, our approach reveals its advantages as low-cost, globally consistent and it retains the potential applications using Visible Light Communication(VLC). We also study the characteristics of the proposed solutions under typical indoor conditions by experiments.

Analysis and Design of a 0.6 V 2.2 mW 58.5-to-72.9 GHz Divide-by-4 Injection-Locked Frequency Divider With Harmonic Boosting

A locking-range enhancement technique is proposed for divide-by-4 injection-locked frequency dividers (ILFDs) at millimeter-wave frequencies. The working principle of the conventional divide-by-4 ILFDs is analyzed and verified with simulations to show that the limited locking range is mainly attributed to low efficiency of harmonic mixing. Based on the observation, an enhancement technique is developed by employing a properly-designed 4th-order LC tank to boost the 3rd-order harmonic tone at the output to increase the injection efficiency and thus the locking range. Implemented in a 65-nm CMOS process, a divide-by-4 ILFD prototype with the proposed harmonic boosting technique measures a locking range of 21.9% from 58.53 GHz to 72.92 GHz while consuming 2.2 mW from a 0.6 V supply, which corresponds to FoM of 6.54.

A 4-Path 42.8-to-49.5 GHz LO Generation With Automatic Phase Tuning for 60 GHz Phased-Array Receivers

Millimeter-Wave (MMW) phased-array receivers are used not only to overcome the large path loss and thus to relax the link budget but also to electrically steer the beam direction to suppress unwanted signals. Each element of the array requires a variable phase shift to compensate for the time difference between adjacent elements depending on the angle of the incident signals such that a maximum gain is achieved in that particular direction. Conventionally, this phase shift is controlled by the baseband with exhaustive tuning algorithms resulting in very long tuning time as the beam direction is changed, which grows exponentially with the number of elements used. This paper proposes an LO generation scheme with automatic successive phase tuning to achieve a resolution of 22.5° and an RMS error of 0.93°.

Visible Light Communication System Design and Link Budget Analysis

This paper presents, for the first time, a systematic approach to visible light communication (VLC) transceiver design based on an analytical optical wireless link budget study. To obtain the signal-to-noise ratio at the receiver, the received signal power is predicted by modeling the transmitted optical power and the channel path loss, while the input-referred noise is estimated by characterizing the noise contribution from each of the receiver building blocks. Based on the targeted bit error rate (BER) and communication distance, a VLC transceiver using discrete components and a fully integrated CMOS VLC transmitter compliant with the IEEE 802.15.7 Standard have been designed and tested. Experimental results show that the measured BER agrees well with the proposed model for both the systems, validating our design approach and the link budget analysis.

A 41-mW 30-Gb/s CMOS optical receiver with digitally-tunable cascaded equalization

This paper presents a 65-nm CMOS, 1-V, 1.37-pJ/bit optical receiver with embedded equalizer, enabling adaptability to overcome channel losses and component variations. The digitally-controlled continuous-time linear equalizer (CTLE) consists of three cascaded tunable peaking stages offering 16-dB of adjustable low-frequency gain. Optical measurement results with a 30-Gb/s photodetector (PD) show that the receiver achieves 10-12 BER at 30 Gb/s for a 215-1 PRBS input with a -5.6-dBm input sensitivity. Using a lower bandwidth 14-Gb/s PD, the receiver can still reach 30 Gb/s at 10-12 BER with only a 0.6-dB degradation in input sensitivity. These measurement results demonstrate the effectiveness of the proposed receiver and the programmable cascaded CTLE.

A 49-to-62GHz CMOS quadrature VCO with bimodal enhanced magnetic tuning

A transformer-based enhanced-magnetic-tuning technique is presented to tune the frequency of millimeter-wave oscillators. By switching the polarity of the phase shift of the coupling currents, both of the two intrinsic modes in a quadrature VCO (QVCO) are exploited to achieve ultra-wide frequency tuning range. Designed and implemented in 65nm CMOS process, the QVCO with proposed bimodal enhanced-magnetic-tuning measures a continuous tuning range of 24% from 48.8 to 62.3 GHz and phase noise of -90 to -94 dBc/Hz at 1MHz offset while drawing 13 to 25 mA from 1.2-V supply, corresponding to FoM from 173 to 176 dBc and FoMT from 181 to 184 dBc.

A 24-GHz and 60-GHz dual-band standing-wave VCO in 0.13µm CMOS process

By exploiting the intrinsic multiple oscillation modes of a standing-wave oscillator, a dual-band millimeter-wave VCO is designed. Implemented in 0.13µm CMOS with an area of 0.05mm2, the VCO prototype measures a dual-band operation at 24 GHz and 60 GHz with tuning range of 10.8% and 7.2%, phase noise of −120dBc/Hz and −114dBc/Hz at 10MHz offset, power consumption of 11mW and 24mW, corresponding to FoM of −177dB and −176dB, respectively.

A Fully Integrated IEEE 802.15.7 Visible Light Communication Transmitter With On-Chip 8-W 85% Efficiency Boost LED Driver

This paper presents the first IEEE 802.15.7 PHY-I standard compliant visible light communication (VLC) transmitter and LED driver SoC for location-based applications using standard white LED lights as beacons or broadcasters. Implemented in a 0.35μm CMOS process with 20-V high-voltage device, the mixed-signal SoC integrates a baseband DSP unit, a VLC modulator, and a switching boost converter with an on-chip power MOSFET. Designed to drive an array of up to 4×5 LEDs using batteries, the boost converter generates an output at 6-20 V from an input at 3-5V with a 92% peak efficiency and an 8-W rating. Measured VLC data rate up to 266 kb/s with 211-1 PRBS inputs is achieved at a PER of <;10% and transmission efficiency of 5 nJ/bit. The LED driver can simultaneously support nine dimming levels and VLC.

Design and Characterization of Active Matrix LED Microdisplays With Embedded Visible Light Communication Transmitter

This paper presents the design and characterization of the first active matrix light-emitting diode (AMLED) microdisplay with an embedded visible light communication (VLC) transmitter, enabling LED digital signage for location-based applications such as information broadcasters and indoor positioning beacons. The driver system-on-a-chip (SoC) integrates four identical macro-cells, each containing a pixel driver array, a row driver, a column driver, and a first-in first-out memory, to drive a wide quarter-VGA (WQVGA) display featuring 400 × 240 blue micro-LED (μLED) pixels fabricated on a single gallium nitride (GaN) substrate. The size of each μLED pixel is 30 × 30 μm2. At the system level, pulse-width modulation (PWM) superimposed with on-off keying modulation is proposed to accomplish grayscale control for display and simultaneously transmit VLC signal by modulating the μLED array. At the circuit level, a pixel driver cell composed of three transistors and one capacitor (3T1C) with a novel VLC function is employed to implement the control scheme. Flip-Chip bonding is adopted to establish connections between the WQVGA microdisplay and the AMLED driver SoC. Implemented in a 0.5-μm 2P3M CMOS process, the driver SoC enables a high-resolution microdisplay module to achieve 4-bit grayscale at a 100-Hz frame rate, while supporting 1.25-Mb/s VLC for a bit error rate <;10-5 up to 25-cm distance without a lens. When using optical lenses, the VLC distance is extended to >500 cm.

A fully integrated IEEE 802.15.7 visible light communication transmitter with on-chip 8-W 85% efficiency boost LED driver

This paper presents an IEEE 802.15.7 Physical Layer I (PHY-I) standard compliant visible light communication (VLC) transmitter system-on-a-chip (SoC), enabling the use of ordinary white LED lights as beacons or broadcasters for location-based applications. The mixed-signal SoC integrates a baseband digital signal processing (DSP) unit, a VLC modulator, and a switching boost LED driver with an on-chip power MOSFET. The DSP unit supports various coding schemes as well as both the on-off keying (OOK) modulation and the variable pulse-position modulation specified in the aforementioned standard. The boost LED driver is designed to power a matrix of 4 × 5 LEDs using Li-ion batteries for portable applications. The SoC simultaneously supports VLC and LED illumination with nine dimming levels. Implemented in a 0.35-μm CMOS process with 20-V devices, the SoC achieves a measured VLC data rate of up to 266 kb/s at a package error rate (PER) <; 10% using a 211 -1 PRBS (pseudo random binary sequence) input. The communication distance measured is more than 2 m using no optical lens with the link efficiency of 5 nJ/bit. From an input at 3-5 V, the boost converter generates an output at 6-20 V with a 92% peak efficiency and an 8-W rating.