Christian Carlowitz

A Millimeter-Wave Low-Power Active Backscatter Tag for FMCW Radar Systems

In this paper, a fully integrated active backscatter transponder based on the switched injection-locked oscillator (SILO) principle for frequency-modulated continuous-wave radar applications is presented. Furthermore, a method to characterize a SILO amplifier is extended and utilized to measure the system parameters of the presented backscatter tag that operates at 34.45 GHz. It is digitally tunable from 32.7 to 35.4 GHz and reaches an unpulsed output power of 5 dBm. Above injection power levels of

Precise ranging and simultaneous high speed data transfer using mm-wave regenerative active backscatter tags

-\hbox{53 dBm}

Concept for a novel low-complexity QAM transceiver architecture suitable for operation close to transition frequency

, the SILO tag responds phase coherent at its maximum output power. In system measurements, the SILO backscatter transponder was used to perform distance measurements at ranges from 0.7 to 11.5 m. A remarkably good mean distance measurement error of 7 cm with a standard deviation of 10 cm was achieved in a strong multipath environment. The single measurement precision is below 3 mm.

A mm-wave RFID system with locatable active backscatter tag

For precise ranging in dense indoor RFID applications, a large absolute bandwidth is required for effective multipath suppression. Since the bandwidth of UHF systems is severely restricted, we propose mm-wave tags combined with high volume data storage and high speed data transfer (≫10 MBit/s) as an attractive alternative - in short range (1-10 m) augmented reality and multimedia applications, for example. A regenerative active backscatter tag based on a pulsed injection-locked oscillator is suggested in order to achieve a sufficiently high reader SNR for high bandwidth communication. This paper demonstrates that a 34.3-34.8 GHz frequency modulated continuous wave (FMCW) RFID ranging approach can be integrated seamlessly with simultaneous data transmission from the modulated active backscatter tag to the reader at 37.5 MBit/s. Mutual distortions between FMCW ranging and data transmission are prevented by line encoding and quadrature mixing.

Synthesis of angle modulated ultra wideband signals based on regenerative sampling

The implementation of ultra-high speed mm-wave and THz transceivers based on homodyne concepts suffers from severe scaling issues with respect to system complexity, circuit size and power consumption as such transceivers nowadays typically need to operate close to the transition frequency of the underlying semiconductor process. In order to mitigate these severe issues, we propose a novel regenerative sampling concept based on a simple positive feedback low-gain amplifier stage. We show for the first time a concept that allows to regenerate quadrature modulated signals with minimal effort based on a simultaneous phase and amplitude regenerative sampling (SPARS) process. This concept enables attractive alternatives to the homodyne approach, e.g., a synthesizer-free self-mixing receiver, which significantly reduces the complexity of the receiver circuit. This paper provides the proof-of-concept of the novel approach by simulations and by measurements with a lumped element 22 GHz 16-QAM feasibility demonstrator.

Regenerative sampling self-mixing receiver: A novel concept for low complexity phase demodulation

Precise localization of an object with attached RFID tag is required for many future applications like the internet of things, augmented reality or distributed sensor networks. Especially precise medium range localization in dense multipath environments places high demands on the capabilities of RFID tags, which are severely limited concerning complexity and power consumption. Regarding range coverage, active backscatter transponders significantly reduce path loss in comparison to their passive counterparts. This is particularly important at high frequencies, which are attractive since their regulatory constraints offer larger allocated bandwidths compared to lower frequency bands. Therefore, with mm-wave transponders, ranging resolution, data throughput for RFID communication and multi user capability can be improved without accepting range limiting RF power restrictions like in ultra-wideband systems. In order to achieve a measurement range in the order of 10 m with a tag featuring limited complexity and power consumption, the switched injection-locked oscillator is proposed as backscatter transponder technology, which has already been successfully applied to lower frequency localization systems [2]. In contrast to a simple linear amplifier based approach, it offers much higher single stage gain in the order of about 60 dB when switched on. Furthermore, aliases caused by the switched operation allow suppressing passive reflections of the RFID readers signal completely. In this paper, a complete 34 GHz FMCW RFID ranging system concept and demonstrator implementation based on the switched injection-locked oscillator are demonstrated for the first time. The theoretical expectations regarding the operation principle are verified experimentally and the performance of the demonstrator implementation is evaluated. Measurement results in an indoor multipath indoor environment deliver an accuracy of about 3 cm within a range of 1 to 6 m.

A System Concept for Online Calibration of Massive MIMO Transceiver Arrays for Communication and Localization

For efficient low power UWB communication and ranging systems, fine grained control of the UWB signal spectral properties is desirable to maximize throughput and SNR at a given power budget and spectral mask. Simple impulse radio modulation techniques like pulse amplitude, binary phase or pulse position modulation usually do not provide the same flexibility and spectral efficiency as more complex angle modulation principles. The generation of angle modulated signals, however, is usually much more complex than for impulse radio transmitters. In this paper, a novel concept for the synthesis of pulsed angle modulated ultra wideband signals based on regenerative sampling is introduced that overcomes the above mentioned contradiction. The concept allows for generating arbitrarily phase modulated pulsed UWB signals with a low-complexity hardware. It is based on a switched injection locked oscillator that samples the phase from a high order harmonic of a phase modulated baseband signal. The signal synthesizer does not require any linear amplifiers or PLLs at RF frequency. This principle brings complex angle modulation to ultra wideband signals while at the same time retaining the feasibility of low power implementation. In this paper, this completely novel signal generation principle is introduced for the first time and its capability is theoretically and experimentally verified.

An integrated switched injection-locked oscillator for pulsed angle modulated ultra wideband communication and radar systems

In this paper, a novel low complexity receiver concept for high-order differential phase demodulation is introduced for the first time. With a first hardware demonstrator, a high data rate of 300 Mbit/s is achieved without requiring a synthesizer for downconversion. A phase sensitive regenerative sampling approach is employed that integrates both low noise amplifier and automatic gain control using a free running switched injection-locked oscillator with no need for stabilization by a phase locked loop. Differential phase detection is achieved by quadrature self-mixing the regenerated signal with one path delayed by the symbol period. This approach is particularly attractive in combination with the switched injection-locked oscillator due to its constant high output power that allows for matching the mixers best operating point. The proposed concept is demonstrated at 5.5 GHz with 8th order differential phase shift keying and a symbol rate of 100 MBaud/s. A short range data rate of 300 Mbit/s is achieved at a bit error rate below 1e-3.

Synthesis of pulsed frequency modulated ultra wideband radar signals based on stepped phase shifting

Massive multiple-input multiple-output (MIMO) techniques are being considered for the fifth generation (5G) mobile communication systems in order to deliver high multiplexing gain. However, hardware impairments like quadrature imbalance in mixers violate the requirement for channel reciprocity and may change, e.g., with temperature or while aging. In addition, advanced wireless localization techniques and the generation of predefined beam patterns require knowledge about all antenna phase center positions and the time and phase delay of all transmit and receive channels. Thus, an efficient online compensation method is needed that scales well for very large numbers of transceiver modules. We propose to extend the transmitter with a small measurement feature at the transmitter output based on one uncalibrated power detector per module as well as a single, external four-element backscatter array for the entire matrix. These enhancements facilitate a fast and efficient iterative calibration, which recognizes and mitigates all major error sources. Beside optimal communication throughput and energy efficiency, it thereby brings localization capabilities to mobile networks as an additional major benefit. For verification, a system of multiple cost-efficient 5.8-GHz massive MIMO transceivers with 150-MHz bandwidth and a backscatter array has been implemented. Measurement results demonstrate the capability of the proposed concept to efficiently compensate major error sources as well as its robustness.

Demonstration of an efficient high speed communication link based on regenerative sampling

This paper describes an integrated switched injection-locked oscillator (SILO) circuit for use in pulsed angular modulated ultra wideband communication and radar systems. The circuit consists of two active baluns for single-ended to differential and differential to single-ended conversion, a Schmitt-trigger with modified current mirror load for current peak generation and a simple cross-coupled oscillator for signal generation. It has an externally controllable pulse repetition rate and a pulse duration of approx. 1ns. During operation it consumes 33mA at 3.3V supply voltage, while generating a 370 mVpp signal. The generated signal has a 10dB-bandwidth of over 2GHz at 7.5 GHz center frequency. Measurement results with an external baseband generator are shown.