Guobing Li

Silicon-on-insulator asymmetric optical switch based on total internal reflection

Based on the large cross-section single-mode rib waveguide condition, total internal reflection (TIR) and the plasma dispersion effect, a silicon-on-insulator (SOI) asymmetric optical waveguide switch with transverse injection structure has been proposed and fabricated, in which the SOI technique utilizes silicon and silicon dioxide thermal bonding and back-polishing. The device performance is measured at a wavelength of 1.3 /spl mu/m. It shows that the extinction ratio and insertion loss are less than -18.1 and 6.3 dB, respectively, at an injection current of 60 mA. Response time is 110 ns.

Zero-gap directional coupler switch integrated into a silicon-on insulator for 1.3-μm operation

A silicon-on insulator (SOI) zero-gap directional coupler switch is studied based on the large-cross-section singlemode rib waveguide condition, the dual-mode interference principle, and the free-carrier plasma dispersion effect, in which the SOI technique uses silicon and silicon dioxide thermal bonding and backpolishing. The SOI is fabricated by potassium hydroxide anisotropic etching. Its insertion loss and cross talk are measured to be less than 4.81 dB and 218.6 dB, respectively, at a wavelength of 1.3 microm and a switching voltage of 0.91 V. Response time is ~210 ns.

High-Throughput Multi-Source Cooperation via Complex-Field Network Coding

Physical-layer network coding over wireless networks can provide considerable throughput gains with respect to traditional cooperative relaying strategies at no loss of diversity gain. In this paper, a novel cooperation protocol is developed based on complex-field wireless network coding. Sources transmit efficiently information symbols linearly combined with symbols from other sources. Different from existing wireless network coding protocols, transmissions are not restricted to binary symbols, and do not have to be received simultaneously. In a network with N sources, the developed protocol can achieve throughput up to approximately 1/N symbols per source per channel use, as well as diversity of order N. To deal with decoding errors at sources, selective- and adaptive-forwarding protocols are also developed at no loss of diversity gain. Analytical results corroborated by simulated tests show considerable performance gains with respect to distributed space-time coding, and bit-level network coding protocols.

Multi-Band Cognitive Radio Spectrum Sensing for Quality-of-Service Traffic

Cognitive radios (CRs) are capable of sensing the RF spectrum to identify idle bands dynamically, and transmit opportunistically so as not to interfere with cohabiting primary users (PUs) over the same bands. In this work, spectrum sensing algorithms for CRs that support quality-of-service (QoS) traffic are investigated. Multiple bands are sensed in parallel to reduce the sensing delay, while ensuring a fixed minimum rate for CR transmissions with a given outage probability. Interference constraints are also imposed to protect PU transmissions. Both fixed sample size (FSS) as well as sequential sensing algorithms are developed to minimize the sensing delay. In the sequential sensing case, a bank of sequential probability ratio tests (SPRTs) are run in parallel to detect PU presence in all bands concurrently. Notably, the parameters for the detectors can be obtained via convex optimization. Numerical tests demonstrate that sequential sensing yields average sensing delays significantly smaller than those of FSS sensing.

Distributed Power Allocation Schemes for Amplify-and-Forward Networks

In this paper, distributed power allocation schemes are studied for amplify-and-forward (AF) cooperative relay networks, where only partial channel state information (CSI) is available at the source and relays. Aiming at minimizing the total transmit power while providing a target outage probability, a scheme is first investigated in which the source decides transmit power and a relay-forwarding threshold, and each relay makes individually the transmit decision based on the threshold and its own CSI. Then a single relay power allocation scheme is proposed to simplify the implementation complexity, in which only one relay is selected to forward messages. Simulation results illustrate the performance improvement of the proposed schemes.

High-Diversity Cooperative Spectrum Sensing in Cognitive Radio Networks

This paper develops a cooperative scheme among cognitive radios (CRs) to increase the spectrum sensing performance. CRs adaptively transmit local binary decisions to a fusion center (FC), which in turn uses a simple maximum-likelihood detector to decide the presence of absence of the primary user (PU). The diversity order of the probability of false alarm and miss-detection is studied under both Neyman-Pearson and minimum-error-probability criteria. In particular, it is shown that under the Neyman-Pearson criterion, the probability of miss- detection can achieve diversity order up to the number of CRs for a bounded probability of false alarm. Under the minimum-error-probability criterion, both the probability of false alarm and miss-detection can achieve diversity order up to the number of CRs. Compared to existing cooperative sensing approaches, this novel scheme is robust to fading effects in both PU-to-CR and CR-to-FC links. Simulated tests verify the analytical claims, showing considerable performance gains compared to non-cooperative and non-adaptive hard-decision schemes.

Design of system-level simulation platform for 5G networks

The Fifth Generation (5G) of mobile communications systems have been proposed and researched globally, and are expected to be launched in 2020. Aside from diverse exciting air-interface innovations for 5G systems, the networking design plays the critically important role to support the massive mobile traffics. It is widely recognized that the core features of 5G networking lie in the heterogeneous accesses, which are not confined to coexistence of small and macro cells, but generalized to access over multiple air-interfaces with utterly different networking fashions, such as LTE-A and WLAN. The heterogeneous feature not only complicates the network design, but also imposes significant challenges in system-level simulations and evaluations. Lack of innovation in simulation techniques will no doubt slow down the evolving and standardization process of 5G systems. To tackle these problems, we in this paper present a novel design of system-level 5G simulation platform. The unique features of our design include two-fold. 1) Simultaneous simulation of different types of networks are supported. In particular, cellular networks run in a well time-aligned fashion while WiFi operates entirely based on asynchronous random access mechanism. 2) Our platform offers the simulation of concurrent transmissions over multiple radio-access technologies for each single user, supporting either single or multiple services. We elaborate on the core ideas of our design embedding the aforementioned features as well as the details for building the entire platform. We also discuss the future innovative efforts and directions in simulation techniques for 5G networks.

High-rate cooperative beamforming for physical-layer security in wireless cyber-physical systems

The vast interconnectivity of devices in the Internet of Things (IoT) and Cyber-Physical systems under wireless environments facilitates information exchange, but challenges network security. In this paper, cooperative beamforming for secure communications is studied in wireless cyber-physical systems, where two legitimate devices communicate with the help of amplify-and-forward (AF) relays, and the eavesdropping devices around purpose to intercept the information. To achieve high secrecy sum rate, a secrecy sum rate maximization problem via cooperative beamforming with or without artificial noise is formulated under individual relay power constraint. The problem is shown to be non-convex. We then reformulate it into a difference of convex programming problem, relax it by a tight semidefinite relaxation (SDR), and approximate it into sequential convex problems by first-order Taylor expansion, which eventually leads to a high-rate beamforming solution. The simulations show that our developed beamforming scheme can achieve high secrecy sum rate and fast convergence.

Minimum-Delay Spectrum Sensing for Multi-Band Cognitive Radios

Spectrum sensing algorithms are developed for cognitive radios to support real-time traffic. Multiple bands are sensed in parallel to reduce sensing delay, while meeting a minimum rate requirement with a prescribed outage probability. Interference constraints are also imposed to protect primary user (PU) transmissions. Both fixed sample size (FSS) and sequential sensing algorithms are developed. In the FSS sensing, a series of convex feasibility problems are solved to minimize sensing delay. In the sequential case, a bank of sequential probability ratio tests (SPRTs) is employed to detect PU presence, where the detector parameters are optimized via convex optimization. Numerical tests demonstrate that the (average) sensing delay of sequential sensing is considerably smaller than that of FSS sensing.

Silicon raised strip waveguides based on silicon and silicon dioxide thermal bonding

Si raised strip waveguides on SiO/sub 2/ have been proposed and fabricated, which are based on silicon-on-insulator (SOI) material. In the waveguides, the SOI technique utilizes silicon and silicon dioxide thermal bonding and back-polishing. An anisotropic etchant is used to produce the trapezoidal Si raised strip waveguides by etching the Si film down to the SiO/sub 2/ etch-stop buried layer. The transmission losses of the Si waveguides are measured to be less than 0.2 dB/cm at the 1.3 /spl mu/m wavelength for the lowest mode TE-like mode.