Millimeter-wave Communication and Radar Sensing — Opportunities, Challenges, and Solutions

With the development of communication and radar sensing technology, people are able to seek for a more convenient life and better experiences. The fifth generation (5G) mobile network provides high speed communication and internet services with a data rate up to several gigabit per second (Gbps). In addition, 5G offers great opportunities of emerging applications, for example, manufacture automation with the help of precise wireless sensing. For future communication and sensing systems, increasing capacity and accuracy is desired, which can be realized at millimeter-wave spectrum from 30 GHz to 300 GHz with several tens of GHz available bandwidth. Wavelength reduces at higher frequency, this implies more compact transceivers and antennas, and high sensing accuracy and imaging resolution. Challenges arise with these application opportunities when it comes to realizing prototype or demonstrators in practice. This thesis proposes some of the solutions addressing such challenges in a laboratory environment.High data rate millimeter-wave transmission experiments have been demonstrated with the help of advanced instrumentations. These demonstrations show the potential of transceiver chipsets. On the other hand, the real-time communication demonstrations are limited to either low modulation order signals or low symbol rate transmissions. The reason for that is the lack of commercially available high-speed analog-to-digital converters (ADCs); therefore, conventional digital synchronization methods are difficult to implement in real-time systems at very high data rates. In this thesis, two synchronous baseband receivers are proposed with carrier recovery subsystems which only require low-speed ADCs [A][B].Besides synchronization, high-frequency signal generation is also a challenge in millimeter-wave communications. The frequency divider is a critical component of a millimeter-wave frequency synthesizer. Having both wide locking range and high working frequencies is a challenge. In this thesis, a tunable delay gated ring oscillator topology is proposed for dual-mode operation and bandwidth extension [C]. Millimeter-wave radar offers advantages for high accuracy sensing. Traditional millimeter-wave radar with frequency-modulated continuous-wave (FMCW), or continuous-wave (CW), all have their disadvantages. Typically, the FMCW radar cannot share the spectrum with other FMCW radars.\ua0 With limited bandwidth, the number of FMCW radars that could coexist in the same area is limited. CW radars have a limited ambiguous distance of a wavelength. In this thesis, a phase-modulated radar with micrometer accuracy is presented [D]. It is applicable in a multi-radar scenario without occupying more bandwidth, and its ambiguous distance is also much larger than the CW radar. Orthogonal frequency-division multiplexing (OFDM) radar has similar properties. However, its traditional fast calculation method, fast Fourier transform (FFT), limits its measurement accuracy. In this thesis, an accuracy enhancement technique is introduced to increase the measurement accuracy up to the micrometer level [E]

Multi-Gigabaud Solutions for Millimeter-wave Communication

With the growing number of mobile network and internet services subscriptions, faster communication will provide a better experience for users. In the next generation mobile network, the fifth generation (5G), communication data rate will achieve several Gigabits per second with ultra-low latency. The capacity enhancement of the mobile backhaul and fronthaul is a challenge. The transmission capacity can be enhanced by increasing the bandwidth, increasing the spectrum efficiency and increasing both the bandwidth and the spectrum efficiency at the same time. \ua0Millimeter-wave frequency bands have the bandwidth in the order of GHz which provide great opportunities to realize high data rate communications. In this case, millimeter-wave frontend modules and wideband modems are needed in communication systems. In this thesis, a 40 Gbps real-time differential quadrature phase shift keying (DQPSK) modem has been presented to support high-speed communications [A]. As a complete system, it aims to work together with the D-band frontend module published in [1] providing more than 40 GHz bandwidth. In this modem, the modulator is realized in a single field programmable gate array (FPGA) and the demodulator is based on analog components. Although millimeter-wave frequency bands could provide wide available bandwidth, it is challenging to generate high output power of the carrier signal. In addition, the transmitter needs to back off several dB in output power in order to avoid the non-linear distortion caused by power amplifiers. In this thesis, an outphasing power combining transmitter is proposed [B] to use the maximum output power of power amplifiers while maintaining the signal quality at the same time. This transmitter is demonstrated at E-band with commercially available components.Increasing the spectrum efficiency is an additional method to enhance the transmission capacity. High order modulation signals such as quadrature amplitude modulation (QAM) signals are commonly used for this purpose.\ua0 In this case, receivers usually require coherent detection in order to demodulate the signals. Limited by the sampling rate of the analog to digital converters (ADCs), the traditional digital carrier recovery methods can be only applied to a symbol rate lower than the sampling rate. A synchronous baseband receiver is proposed [C] with a carrier recovery subsystem which only requires a low-speed ADC with a sampling rate of 100 MSps

Variable High Precision Wide D-Band Phase Shifter

This paper proposes a new concept of designing compact high precision millimeter-wave wideband variable phase shifters. The phase shifter is implemented with a stacked shim with extremely short length of 0.9 mm and two waveguide flange adaptors with length of 0.5 mm. High precision phase shifting is achieved over entire D-band (110-170 GHz) by rotating the shim 90 degrees from aligned to perpendicular with consistent impedance matching performance. In addition, a glide-symmetric holey electromagnetic bandgap (EBG) structure is adopted to avoid wave leakage from the gap between the shim and the flange adaptors. A proof-of-concept (PoC) demonstrator is designed, manufactured, and tested. The measured results show that the designed stacked shim phase shifter with embedded EBG structure ensures return loss higher than 10 dB across 110-170 GHz with a 75 mu m airgap between waveguide flanges. The studied phase shifter provides a 0.88ffi phase shifting with each degree of mechanical rotation. The fabricated PoC phase shifter has a worst-case insertion loss of 0.92 dB and a return loss of 20 dB across the entire 110-170 GHz band and a maximum phase shift of 30 degrees. At 10 degrees phase shifting, the measured insertion loss is lower than 0.52 dB, and return loss is higher than 23 dB, respectively

Millimeter-Wave Multi-Channel Backscatter Communication and Ranging with an FMCW Radar

A multi-channel backscatter communication and radar sensing system is proposed and demonstrated in this paper. Frequency modulated continuous wave (FMCW) radar ranging is integrated with simultaneous uplink data transmission from a self-packaged active radio frequency (RF) tag. A novel package solution is proposed for the RF tag. With the proposed package, the RF tag can transmit a 32-QAM signal up to 2.5 Gbps and QPSK signal up to 8 Gbps. For a multi-tag scenario, we proposed using spread spectrum code to separate the data from each tag. In this case, tags can be placed at arbitrary locations without adjacent channel interference. Proof-of-concept simulations and measurements are demonstrated. A 625 Mbps data rate is achieved in a dual-tag scenario for two tags

Integrated-EBG Ridge Waveguide and Its Application to an E-Band Waveguide 32 732 Slot Array Antenna

A methodology of designing an E-band waveguide 32 732 slot array antenna with high-efficiency and low-cost manufacturing characteristics is proposed in this article, which is based on an integrated electronic bandgap (EBG) ridge waveguide designed by integrating a cross rectangle-hollow EBG structures in the conventional ridge waveguide. The integrated EBG structure intercepts the leakage from the unconnected gap in between the two metallic plates of the waveguide, and then it decreases the manufacturing cost without using the diffusion bonding technology and multi-layer welding assembly process. The design guideline is discussed, and then the antenna is fabricated. The measured radiation characteristics are in good agreement with predicted ones, which confirms that the proposed cross rectangle-hollow EBG structures is an attractive candidate of high-performance millimeter wave antenna

A Novel Synchronization Method in Terahertz Large-Scale Antenna Array System

We focus on the problems of the accurate time delay estimation, the design of training pilots, and hybrid matrix optimization within the large-scale antenna array Terahertz (THz) broadband communication system. In contrast to the existing researches based on narrow-band arrays, we hereby shed light on the time delay estimation of broadband arrays. In THz broadband communication systems, the data symbol duration is relatively short when comparing with the dimension of the antenna array. In large-scale antenna systems, signals received in each antenna are no longer different phase-shifted copies of the same symbol, but completely different symbols in which occasion traditional narrow-band structure is no longer suitable. Based on the above conclusion, firstly, we put forward a system model based on large-scale antenna arrays and Time delay line (TDL) structure. Secondly, we deduce the Cramer-Rao lower bound (CRLB) of the time delay estimation, and present a time delay estimation algorithm that could reach the CRLB. Thirdly, by minimizing the CRLB, we address the design of the training pilot and optimized TDL structure under the condition of constant envelope training pilot and modulus TDL structure. Finally, we disclose the numerical simulation results. According to the simulation results, the aforementioned method is workable in reaching the CRLB, the TDL structure can significantly surpass that of the traditional model, and the optimal pilot design method outperforms the pseudo-random pilot structure

Radar Cross-Section Characterization of the Car In-Cabin Environment at Sub-THz Frequencies

Radar sensors at sub-THz frequencies (100 - 330 GHz) can potentially be used in car in-cabin monitoring systems. In designing such sensors, knowledge of the in-cabin propagation conditions at the sub-THz bands is useful. Considering the rather novel use-case, such data is not readily available and must be gathered through measurements. This paper presents a Radar Cross-Section (RCS) imaging system, which has been developed in order to characterize the reflective properties of common car in-cabin objects at 243 GHz. The system produces two types of data, RCS profiles and Inverse Synthetic Aperture Radar (ISAR) images, which can be analyzed jointly to give an intuitive and detailed view of object reflectivity. The system applies range-domain processing and prove efficient in ignoring peripheral reflection points and multipath, which allows for conducting compact measurements in an enclosed lab environment. The ISAR images achieve 1-2 centimeter spatial resolution, and thus demonstrates the fine-resolution capabilities of sub-THz radar systems

Modulator and Demodulator Solutions for Real-Time Communication Toward 100 Gb/s: Realtime Modem Solution towards 100 Gb/s

Due to government and other agency regulations, microwave bands, which range in frequency from 6 to 42 GHz, often have a small bandwidth of a few hundred megahertz, which lowers the data rate for communications. On the other hand, high data rate communications can be realized in millimeter-wave (mm-Wave) frequencies (30-300 GHz). Tens of gigabits per second of bandwidth are available in mm-Wave bands, such as the D-band, from 110 to 170 GHz, and H-band, from 170 to 260 GHz

An MPSK Millimeter-Wave Point-to-Point Link With Radio Over Fiber Synchronous Baseband Receiver

This paper demonstrates a millimeter-wave point-to-point radio link of MPSK (QPSK, 8-PSK, and 16-PSK) modulation without using any analog to digital converter (ADC). The proposed point-to-point radio link, not only use the radio over fiber (RoF) concept to extend the transmit distance of the central unit and the remote radio unit, but also use the clock and data recovery (CDR) applied in the optical-electrical converter (OEC) to recover the MPSK intermediate frequency (IF) signals frequency offset. Compared with the traditional RoF link, the proposed point-to-point synchronous radio link eliminated the high-speed ADC requirement for the digital-intermediate-frequency-over-fiber (DIFoF) link, which can significantly reduce the complexity and the cost of the remote radio unit. Simultaneously, we have designed a simple symbol synchronization algorithm to realize the real-time point-to-point radio link on an Field Programmable Gate Array (FPGA). The proposed millimeter-wave radio link has successfully demonstrated 6 Gbps QPSK transmission and can tolerate a frequency offset up to 100 MHz

OFDM Radar Range Accuracy Enhancement Using Fractional Fourier Transformation and Phase Analysis Techniques

Orthogonal Frequency Division Multiplexing (OFDM) technique is obtained significant attention in radar applications for its interference resilience property. In this paper, Fractional Fourier Transformation (FRFT) and phase analysis techniques are proposed to enhance ranging accuracy of an OFDM Radar. A proof-of-concept radar is built and tested at 79 GHz and a range accuracy of 20 m at 5 MHz measurement rate was measured. The range accuracy is 500 times higher than using fast Fourier transformation (FFT) method