King-Yuen Wong

A dynamic call admission policy with precision QoS guarantee using stochastic control for mobile wireless networks

Call admission control is one of the key elements in ensuring the quality of serivce in mobile wireless networks. The traditional trunk reservation policy and its numerous variants give preferential treatment to the handoff calls over new arrivals by reserving a number of radio channels exclusively for handoffs. Such schemes, however, cannot adapt to changes in traffic pattern due to the static nature. This paper introduces a novel stable dynamic call admission control mechanism (SDCA), which can maximize the radio channel utilization subject to a predetermined bound on the call dropping probability. The novelties of the proposed mechanism are: 1) it is adaptive to wide range of system parameters and traffic conditions due to its dynamic nature; 2) the control is stable under overloading traffic conditions, thus can effectively deal with sudden traffic surges; 3) the admission policy is stochastic, thus spreading new arrivals evenly over a control period, and resulting in more effective and accurate control; and 4) the model takes into account the effects of limited channel capacity and time dependence on the call dropping probability, and the influences from nearest and next-nearest neighboring cells, which greatly improve the control precision. In addition, we introduce local control algorithms based on strictly local estimations of the needed traffic parameters, without requiring the status information exchange among different cells, which makes it very appealing in actual implementation. Most of the computational complexities lie in off-line precalculations, except for the nonlinear equation of the acceptance ratio, in which a coarse-grain numerical integration is shown to be sufficient for stochastic control. Extensive simulation results show that our scheme steadily satisfies the hard constraint on call dropping probability while maintaining a high channel throughput.

High-performance AlGaN∕GaN lateral field-effect rectifiers compatible with high electron mobility transistors

A high electron mobility transistor (HEMT)-compatible power lateral field-effect rectifier (L-FER) with low turn-on voltage is demonstrated using the same fabrication process as that for normally off AlGaN∕GaN HEMT, providing a low-cost solution for GaN power integrated circuits. The power rectifier features a Schottky-gate-controlled two-dimensional electron gas channel between the cathode and anode. By tying up the Schottky gate and anode together, the forward turn-on voltage of the rectifier is determined by the threshold voltage of the channel instead of the Schottky barrier. The L-FER with a drift length of 10μm features a forward turn-on voltage of 0.63V at a current density of 100A∕cm2. This device also exhibits a reverse breakdown voltage (BV) of 390V at a current level of 1mA∕mm and a specific on resistance (RON,sp) of 1.4mΩcm2, yielding a figure of merit (BV2∕RON,sp) of 108MW∕cm2. The excellent device performance, coupled with the lateral device structure and process compatibility with AlGaN∕GaN...

Single-Chip Boost Converter Using Monolithically Integrated AlGaN/GaN Lateral Field-Effect Rectifier and Normally Off HEMT

We demonstrate a single-chip switch-mode boost converter that features a monolithically integrated lateral field-effect rectifier (L-FER) and a normally off transistor switch. The circuit was fabricated on a standard AlGaN/GaN HEMT epitaxial wafer grown with GaN-on-Si technology. The fabricated rectifier with a drift length of 15 mum exhibits a breakdown voltage of 470 V, a turn-on voltage of 0.58 V, and a specific on-resistance of 2.04 mOmegaldrcm2. The L-FER exhibits no reverse recovery current associated with the turn-off transient because of its unipolar nature. A prototype of GaN-based boost converter that includes monolithically integrated rectifiers and transistors is demonstrated using conventional GaN-on-Si wafers for the first time to prove the feasibility of the GaN-based power IC technology.

Monolithic integration of lateral field-effect rectifier with normally-off HEMT for GaN-on-Si switch-mode power supply converters

A lateral field-effect rectifier (L-FER) that can be fabricated with normally-off transistor on the same AlGaN/GaN HEMT with the same fabrication process has been demonstrated. The L-FER exhibits low turn-on voltage, low specific on-resistance and high reverse breakdown. A prototype of switch-mode dc-dc boost converter that features monolithically integrated L-FER and normally-off HEMT is demonstrated for the first time using industry-standard GaNon-Si epitaxial wafers to prove the feasibility of GaN power integrated technology.

Integrated Voltage Reference Generator for GaN Smart Power Chip Technology

GaN smart power chip technology has been realized using a GaN-on-Si HEMT platform, featuring monolithically integrated high-voltage power devices and low-voltage peripheral devices for mixed-signal functional blocks. In particular, this brief presents the imperative analog functional block-voltage reference generator for smart power applications with wide-temperature-range stability. The circuit is capable of proper functions within a wide temperature range from room temperature up to 250°C , illustrating the unique advantage of the wide-bandgap GaN in high-temperature operation. The voltage reference generator was designed with an AlGaN/GaN HEMT and Schottky diodes, and the devices were operated in the subthreshold regime to obtain low power consumption. The voltage reference generator achieved an average drift of less than 0.5 mV/°C and can be used as a reference voltage in various biasing and sensing circuits.

Optimal call admission control with QoS guarantee in a voice/data integrated cellular network

This paper addresses the issue of call admission control with the necessary quality-of-service (QoS) guarantee for an integrated service mobile cellular network. Specifically, we extend the limited fractional guarded channel (LFGC) scheme to incorporate the multiple traffic types, and derive the set of parameters that leads to the optimal call admission control. The key challenges are the state-dependent nature of the admission control, and the increasing complexity of the state space in a multi-services environment. We propose a novel control mechanism that only uses a few parameters (2-5) to characterize the optimal control planes, and use the simulated annealing technique to obtain the optimal control parameters.

Surface acoustic wave device on AlGaN/GaN heterostructure using two-dimensional electron gas interdigital transducers

Surface acoustic wave (SAW) devices using two-dimensional electron gas (2DEG) as interdigital transducers (IDTs) on AlGaN∕GaN heterostructure has been demonstrated using a planar isolation technique based on the fluoride-based (CF4) plasma treatment technique. The rf characteristics of the SAW filters with planar 2DEG IDTs are compared with SAW devices that are made of metal IDTs or hybrid metal/2DEG IDTs.

Integrated voltage reference and comparator circuits for GaN smart power chip technology

GaN smart power chip technology has been realized using GaN-on-Si HEMT platform, featuring monolithically integrated high-voltage power devices and low-voltage peripheral devices for mixed-signal functional blocks. Two imperative functional blocks for smart power applications with wide-temperature-range stability are demonstrated. The first one is a voltage reference generator, and the second one is a temperature-compensated comparator. These circuits are capable of proper functions within a wide temperature range from room temperature up to 250 °C, illustrating the unique advantage of the wide-bandgap GaN. The voltage reference generator was designed with an AlGaN/GaN HEMT and Schottky diodes, and the devices were operated in the subthreshold regime to obtain low power consumption. The voltage reference generator achieved an average drift of less than 70 ppm/°C and can be used as a reference voltage in various biasing and sensing circuits. The temperature-dependent performance of a conventional comparator is characterized and a new temperature-compensated comparator circuit is proposed. The positive limiting level of the temperature-compensated comparator is less than 450 ppm/°C drift compared to 1350 ppm/°C in the conventional comparator.

Wide-Dynamic-Range Zero-Bias Microwave Detector Using AlGaN/GaN Heterojunction Field-Effect Diode

An AlGaN/GaN HEMT-compatible lateral field-effect diode has been used for zero-bias microwave detector application. Using the versatile fluorine plasma ion treatment technique, we have been able to realize a diode that exhibits strong nonlinearity near zero bias, thus, eliminating DC supplies in microwave detector circuits. The AlGaN/GaN microwave detectors deliver high sensitivity, wide dynamic range and high temperature operating capability. The maximum zero-bias curvature coefficient (¿) measured are 11.6 V -1 and 3.2 V -1 at 50°C and 250°C, respectively, yielding a directly-measured sensitivity (ßv) of 1027 mV/mW at 50°C and 466 mV/mW at 250°C. The peak conjugately-matched sensitivity (ßv,opt) is projected to be 9030 mV/mW at 2 GHz at 50°C. At room temperature, the wide dynamic range of 53 and 54 dB at 2 and 5 GHz are observed, respectively, both of which are the highest values reported so far.

Optimizing call admission control with QoS guarantee in a voice/data integrated cellular network using simulated annealing

This paper addresses the issue of call admission control with the necessary QoS guarantee for a voice/data integrated wireless cellular network. Specifically, we propose a new call admission control policy called dual-threshold call admission control (DT-CAC) policy. It uses two thresholds, one to reserve channels for narrow-band voice handoff calls, and the other for wideband data handoff traffic. Its unique features are: (1) it adopts the complete sharing (CS) approach that maximizes the channel efficiency; (2) it derives the optimal set of thresholds that satisfies the QoS target on handoff dropping probabilities for both voice and data traffic, while at the same time minimizing the maximal new call blocking probability (voice or data). Its performance is well supported by simulation results.