Robert C. Qiu

Ultra-wideband for multiple access communications

Ultra-wideband wireless communications techniques have many merits, including an extremely simple radio that inherently leads to low-cost design, large processing gain for robust operations in the presence of narrowband interference, covert operations, and fine time resolution for accurate position sensing. However, there are a number of challenges in UWB receiver design, such as capturing multipath energy, intersymbol interference especially in a non-line-of-sight environment, and the need for high-sampling-rate analog-to-digital converters. In this article, we provide a comprehensive review of UWB multiple access and modulation schemes, and their comparison with narrowband radios. We also outline the issues with UWB signal reception and detection, and explore various suboptimal low-complexity receiving schemes

Time Reversal With MISO for Ultrawideband Communications: Experimental Results

Time reversal (TR) communications marks a paradigm shift in ultrawideband (UWB) communications. The system complexity can be shifted from the receiver to the transmitter, which is ideal to some applications. UWB multiple input-single output (MISO) is enabled by the use of the TR scheme. Two basic problems are investigated experimentally using short UWB radio pulses (nanosecond duration). Temporal focusing and increase in collected-energy with the number of antennas are verified. Also, the reciprocity of realistic channels, the cornerstone of TR, is demonstrated perhaps for the first time in electromagnetics

60-GHz millimeter-wave radio: principle, technology, and new Results

The worldwide opening of a massive amount of unlicensed spectra around 60 GHz has triggered great interest in developing affordable 60-GHz radios. This interest has been catalyzed by recent advance of 60-GHz front-end technologies. This paper briefly reports recent work in the 60-GHz radio. Aspects addressed in this paper include global regulatory and standardization, justification of using the 60-GHz bands, 60-GHz consumer electronics applications, radio system concept, 60-GHz propagation and antennas, and key issues in system design. Some new simulation results are also given. Potentials and problems are explained in detail.

A study of the ultra-wideband wireless propagation channel and optimum UWB receiver design

The paper addresses a crucial point in ultra-wideband (UWB) radio wave propagation, which is the spatial-temporal resolution of scattering objects into multiple frequency-dependent scattering centers. The effect contributes to the widely observed temporal dispersion of pulse-shaped transmit signals and their distortion, respectively. Particularly the latter is explained by (multiple) diffraction of the incident wave, leading to (multiple) band-limited impulse responses with characteristic frequency content, which in turn causes signal distortion and a degradation of the signal-to-noise ratio in a correlation receiver. We presented a new approach on UWB propagation modeling and optimum design of correlation receivers.

Cognitive Radio Network for the Smart Grid: Experimental System Architecture, Control Algorithms, Security, and Microgrid Testbed

This paper systematically investigates the novel idea of applying the next generation wireless technology, cognitive radio network, for the smart grid. In particular, system architecture, algorithms, and hardware testbed are studied. A microgrid testbed supporting both power flow and information flow is also proposed. Control strategies and security considerations are discussed. Furthermore, the concept of independent component analysis (ICA) in combination with the robust principal component analysis (PCA) technique is employed to recover data from the simultaneous smart meter wireless transmissions in the presence of strong wideband interference. The performance illustrates the gain of bringing the state of the art mathematics to smart grid.

Time reversal with MISO for ultra-wideband communications: experimental results

Time reversal (TR) communications marks a paradigm shift in UWB communications. The system complexity can be shifted from the receiver to the transmitter, which is ideal to UWB sensors. UWB multiple input single output (MISO) is enabled by the use of the TR scheme. Two basic problems are investigated experimentally using short UWB radio pulses (nanosecond duration). Temporal focusing and SNR increase with the number of antennas are verified. Also, reciprocity of realistic channels, the foundation of TR, is demonstrated for the first time in electromagnetics.

Multipath resolving with frequency dependence for wide-band wireless channel modeling

Multiple ray paths are resolved using high-resolution digital signal processing algorithms. The Cramer-Rao (CR) bound is used as a benchmark where a combination of the singular value decomposition method and the eigen-matrix pencil method is proven to be most successful. The conventional complex channel model for wireless propagation is extended to include the frequency-dependent feature of rays which can be used to classify the ray arrivals and provide physical insight of the channel. A novel complex-time model is used to approximate the suggested model. This approach is important to various applications such as equalizers, RAKE receivers, etc., in wireless communication systems. Five key features (noise immunity, robustness, resolution, accuracy, and physical insight) of the proposed algorithm are studied using numerical examples.

Compressed Meter Reading for Delay-Sensitive and Secure Load Report in Smart Grid

It is a key task in smart grid to send the readings of smart meters to an access point (AP) in a wireless manner. The requirements of scalability, realtimeness and security make the wireless meter reading highly challenging. On assuming that the number of smart meters is large and the data burst is sparse, i.e., only a small fraction of the smart meters are reporting their power loads at the same time, the technique of compressed sensing is applied for the wireless meter reading. The distinguishing feature of the compressed meter reading is that the active smart meters are allowed to transmit simultaneously and the AP is able to distinguish the reports from different smart meters. The simultaneous access results in uniform delays, in contrast to the possible large delay in carrier sensing multiple access (CSMA) technique. The random sequence used in the compressed sensing enhances the privacy and integrity of the meter reading. The validity of the proposed scheme is then demonstrated by numerical simulations.

Reduced-complexity UWB time-reversal techniques and experimental results

This paper presents a reduced-complexity time reversal technique for ultra-wideband (UWB) communications. Time reversal takes advantage of rich scattering environments to achieve signal focusing via transmitter-side processing, which enables the use of simple receivers. The goal of this paper is to demonstrate a UWB time reversal system architecture based on experimental results and practical pulse waveform, taking into account some practical constraints, and to show feasibility of UWB time reversal. Pre-decorrelating in addition to time reversal processing is considered for a downlink multiuser configuration. Multiple transmit antennas are employed to improve the performance.

Error performance of pulse-based ultra-wideband MIMO systems over indoor wireless channels

Multiple-input multiple-output (MIMO) techniques are applied to ultrawideband (UWB) systems to achieve high-rate communications over indoor wireless channels. The receiver employs a zero-forcing (ZF) scheme to separate N parallel transmitted data streams for each resolvable multipath component. A RAKE is then applied to combine the ZF paths carrying information of the same symbol to form the decision variable. Analytical error rate expression of an (N,M,L) system (N transmit antennas, M receive antennas, and L paths combined) over a pragmatic indoor log-normal fading channel is derived, which captures the diversity order by a single degree-of-freedom parameter.