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This paper presents a general space vector modulation (SVM) method for the modular multilevel converter (MMC). Compared with earlier modulation methods, the proposed SVM method not only utilizes the maximum level number (i.e., $2n+ 1$ , where $n$ is the number of submodules in the upper or lower arm of each phase) of output phase voltages, but also leads to an optimized control performance in terms of capacitor voltage balancing, circulating current suppression, and common-mode voltage reduction. The maximum level number is achieved by introducing a new equivalent circuit of the MMC, and the optimized control is obtained by selecting the optimal redundant switching states. Since the computational burden of the SVM scheme is independent of the voltage level number, the proposed method is well suited to the MMC with any number of submodules. Simulation and experimental results are presented to validate the proposed method.

The ever-increasing data rate and number of connections for mobile communication offer exciting user experiences in our everyday lives. Currently, the wireless communication frontier is shifting from the current fourth generation (4G) to the forthcoming fifth generation (5G). We expect much of society to go through a revolutionary change with the advent of the 5G era-a change that will involve not only the telecommunication industry but also a wide range of vertical sectors, including automobiles, robotics, health care, factory automation, agriculture, and education.

This work explores the use of p-diamond back-barriers (BBs) and cap layers to enhance the performance of GaN-based high electron mobility transistors (HEMTs). Diamond can offer a heavily doped p-type layer, which is complementary to GaN electronics. Self-consistent electrothermal simulations reveal that the use of p-diamond BBs and cap layers can increase the breakdown voltage of GaN-based HEMTs by fourfold, at the same time that they enhance the 2-D-electron-gas confinement and reduce short channel effects. These results highlight that p-diamond layers can improve the performance of GaN HEMTs for high-power and high-frequency applications beyond the thermal improvements pursued until now.

This paper proposes a simplified space vector modulation (SVM) scheme for multilevel converters. Compared with earlier SVM methods, the proposed scheme simplifies the detection of the nearest three vectors and the generation of switching sequences, and therefore is computationally more efficient. Particularly, for the first time, the proposed scheme achieves the same easy implementation as phase-voltage modulation techniques. Another superior characteristic of the proposed scheme over earlier methods is its potential for multiphase multilevel applications. The proposed scheme also offers the following significant advantages: 1) independence of the level number of the converter; 2) more degrees of freedom, i.e., redundant switching sequences and adjustable duty cycles, to optimize the switching patterns; and 3) no need for lookup tables or coordinate transformations. These advantages make the proposed scheme well suited to large level-number applications, such as modular multilevel converters and high voltage direct current systems. Simulation and experimental results verify this new concept.

Long-range wireless power transmission (WPT) is implemented with the beamforming using the phased array transmitter technology, which has been extensively applied in the radar systems. The cost of a conventional phased array transmitter module scales up in proportion to the number of antenna elements, as the massive number of transmit channels results in the increasing complexity of hardware and feeding antenna elements. Besides, the conventional phase-shifting transmitter architecture has lower DC to RF power conversion efficiency due to the insertion loss of power combining network at microwave frequency. In this paper, the concept of spatial power combining transmitter is utilized, and the upconversion circuit is greatly simplified to an injection locked oscillator. Our WPT system is implemented with the technology of oscillator array antenna at 2.4 GHz, which converts DC power to RF power and radiates into the air directly. The feedback voltage controlled oscillator (VCO) is implemented as the microwave source using a off-the-shelf bandpass filter, and the external signal is injected to the oscillator via a microstrip coupler. The oscillator core shows the DC-to-RF conversion efficiency of 45.87% with the injected power of 0 dBm at 2.4 GHz. Then the digital phase shifter is used to phase shifting the injected signal to extend the beam coverage. From the link budget analysis, the overall DC-to-DC efficiency of our highly-integrated system shows 1.5 times (0.22%) of the conventional phased array (0.15%) when the separation between the transmit array and the receive horn antenna is 1.2 meters. Therefore, as an modularized array, the proposed system demonstrates the promising capability of upscaling to an efficient massive array with greatly reduced bill-of-materials (BOM).

All-digital outphasing transmitter architecture using multidimensional power coding (MDPC) is proposed for noncontiguous concurrent multiband transmission with a high power efficiency. MDPC transforms multiband digital baseband signals into multibit low-resolution digital signals that drive switching-mode PAs. A prototype digital outphasing transmitter consists of two 1-GHz bandwidth GaN Class-D PAs and a Chireix power combiner. The two GaN PAs are driven by bipolar radio frequency (RF) pulse-width modulation (PWM) signals, which are transformed from a concurrent dual-band LTE signal by MDPC. The dual-band LTE signal with 15-MHz aggregate channel bandwidth at 240 and 500 MHz frequency band is transmitted with $-$ 30 and $-$ 37 dBc out-of-band emissions, respectively. Digital outphasing achieves more than two times higher coding efficiency than conventional concurrent dual-band digital transmitters with the same PAs in Class-S operation. Measured power coding efficiencies of 35.4% and 47.1% are observed with outphasing bipolar and 3-level RF PWM signals respectively, which are encoded from the dual-band LTE signal.

Design approach of wideband envelope termination (ET) for high efficiency RF power amplifiers (PAs) is discussed, considering power loss subject to design constraints including envelope bandwidth, inductor quality factor, and transistor output impedance. Analysis shows that the optimum ET topology depends on the design constraints. For LTE-advanced transmission with 80 MHz channel bandwidth, a novel wideband ET is designed using an AC-terminated third-order LC filter (LCF-ET), providing 3 dB envelope impedance bandwidth of 150 MHz. Measured results demonstrate 1.75 dB envelope power loss and −39.2 dB normalised root-mean-square error with the LTE envelope signals. For the LTE signal with 10.3 dB peak-to-average power ratio, the average power efficiency of an ideal Class-A RF PA with the LCF-ET prototype is calculated as 33.4% from the measured 1.75 dB envelope power loss, which exceeds 4.7% and 24.0% average power efficiency of conventional Class-A and Class-B PAs without ET.

In this paper, we report a fully analog three-way sequential power amplifiers (SPA) using 10W GaN HEMTs. The proposed three-way SPA delivers Psat of 39∼40 dBm over 2.45–2.8 GHz covering a 15.4% fractional bandwidth. The three-way SPA includes a 2:1:1 multi-way splitter, a carrier amplifier, two peaking amplifiers, and a 7:1.5:1.5 combiner for power combining. The measured three-way SPA shows 41% to 44% drain efficiency (DE) at 31 dBm (9 dB backoff) output from 2.5 to 2.8 GHz under CW stimulus. To the best of the authors' knowledge, the proposed three-way SPA is the first time reported three-way SPA in literature.

This work for the first time explores the use of p-diamond as multi-functional back-barriers in GaN high electron mobility transistors (HEMTs). A well-calibrated self-consistent electro-thermal simulation has revealed that multi-functional p-diamond back-barriers can improve the performance of HEMTs, by achieving over 3 times higher breakdown voltage (BV), at least 30% higher thermal performance, enhanced 2DEG confinement and reduced short channel effects. These results indicate the great potential of the integration of GaN and diamond electronics for high-power and high-frequency applications.

In this paper, multi-channel capacitive sensor arrays based on microstrip band-stop filters are studied. The sensor arrays can be used to detect the proximity of objects at different positions and directions. Each capacitive sensing structure in the array is connected to an inductive element to form resonance at different frequencies. The resonances are designed to be isolated in the frequency spectrum, such that the change in one channel does not affect resonances at other channels. The inductive element associated with each capacitive sensor can be surface-mounted inductors, integrated microstrip inductors or metamaterial-inspired structures. We show that by using metamaterial split-ring structures coupled to a microstrip line, the quality factor of each resonance can be greatly improved compared to conventional surface-mounted or microstrip meander inductors. With such a microstrip-coupled split-ring design, more sensing elements can be integrated in the same frequency spectrum, and the sensitivity can be greatly improved.

In this paper, we propose a near field coupling based wireless power transfer (WPT) system with circularly polarized magnetic field. With a pair of orthogonal resonant coils arranged to generate a circularly polarized near field, we show that the power transfer efficiency is largely maintained in case of rotational misalignment. Furthermore, by arranging the coils close to a metal surface, the power transfer efficiency is actually improved, rather than decreased as in the case of WPT system made with conventional coils. Depending on the application, the receiving coil can be either a pair of orthogonal coils, or conventional coils with flat structures. We believe that the proposed technology offers a great option toward flexible WPT applications.

In this paper, we report a two-way sequential power amplifier (SPA) using GaN HEMTs. The proposed fully analog SPA delivers P sat of approximately 40dBm over 2–3 GHz covering 40% fractional bandwidth. The design consists of a 3dB input coupler, a main amplifier, a peak amplifier, and a 10dB output coupler for power combining. After proper designing and optimizing these critical wideband couplers in terms of both phase and amplitude alignment, the measured final SPA shows 45% to 61% drain efficiency (DE) at 35dBm (5dB backoff) output from 2.1 to 2.9 GHz under CW stimulus. A complete set of SPA with analog RF input and output network is demonstrated.

A novel non-contiguous concurrent multi-band digital-RF transmitter architecture is presented, which is based on outphasing the multi-level RF pulse-width modulated signals (MLRF-PWM) for digital Class-S power amplifiers. In order to improve the transmitter power efficiency, the outphasing modulation in the proposed architecture effectively increases the number of MLRF-PWM signal output levels. In addition, a multi-band multi-bit band-pass delta-sigma modulator (BPDSM) with a hard clipping technique is introduced, which further improves power coding efficiency by trading off distortion performance with coding efficiency. Experimental results with a dual-channel 25-GSPS arbitrary waveform generator (AWG) demonstrate non-contiguous carrier aggregation for 3-level Class-S PAs with inter-band LTE signals at 874 MHz and 1501 MHz for the channel bandwidth of 10-MHz and 20-MHz, respectively. The proposed outphasing MLRF-PWM technique achieves 59.5% power coding efficiency, which is significant improvement from the 8.6% coding efficiency of conventional 3-level BPDSM with the experimental dual-band LTE signal transmission.

This paper presents a generalized space vector modulation (SVM) method for any modular multilevel converter (MMC). The proposed SVM method produces the maximum level number (i.e., 2«+l, where n is the number of submodules in the upper or lower arm of each phase) of the output phase voltages and a higher equivalent switching frequency than other modulation methods, which consequently leads to reduced harmonics in the output voltages and currents. Compared with earlier modulation methods for MMCs, the proposed SVM method provides two more degrees of freedom, i.e., the redundant switching sequences and the adjustable duty cycles, thus offering significant flexibility for optimizing the circulating current suppression and capacitor voltage balancing. This SVM method is a useful tool for further studies of MMCs, as it can be conveniently extended for any control objectives. The demonstrated results validate the analysis.

This paper reports the recent development on power coding method of generating a 5-level intermediate frequency PWM-based high speed digital-RF bit train, which is used as the input switching signal for class-S digital RF power amplifiers in the digital transmitter. By introducing the discrete-time power coding process at an IF of around 60 MHz, digital transmitter at cellular bands then becomes feasible to implement with current FPGA technologies. It can lower the required sampling rate more than 10 times compared with RF carrier PWM. In addition, a linearizer is designed using a look-up-table to minimize the nonlinear coding effects of the power encoder. The demonstrator shows the state-of-the-art measured power coding efficiency of 70.47% and SNR>30dB for a 20 MHz LTE signals with PAPR of 10.25 dB at 1.9 GHz with our proposed approach.

This work presents a new efficient multi-level intermediate frequency pulse width modulation (ML-IFPWM) power coding algorithm for switch-mode power amplifier. The merits of high power coding efficiency with distortion correction function are demonstrated by a FPGA implemented digital front end. Measurement results have shown power coding efficiency greater than 45%. To our knowledge, this is the firstly reported implemented discrete-time domain 3-level power encoding approach with 5-MHz LTE signal at RF carrier frequency around 2 GHz. This can be used to generate multi-level digital pulse-train for advanced class-S PA in cellular digital base stations.

This paper presents a general dc-link voltage balancing control method for multilevel inverters based on a generalized space vector pulse width modulation (SVPWM) scheme, with no requirements for additional auxiliary-power circuits. The SVPWM scheme generates all the available switching states and switching sequences based on two simple mappings, and calculates the duty cycles simply as for a two-level SVPWM, thus independent of the level of the inverter. The optimal switching sequence and optimal duty cycles for dc-link voltage balancing control are provided in the paper. Because all the measured signals are instantaneous values, the dc-link voltage balancing control method in the paper is suitable for any load without any assumption on the output current waveforms. The dc-link voltage balancing control in the paper is effective even when the capacitances of the dc-link capacitors of the multilevel inverter are not strictly equal or the voltage of the dc source of the multilevel inverter is fluctuating. Simulation results for a five-level inverter are given.

We describe a wireless power transfer (WPT) system based on electromagnetic coupling of resonators in an array. The system can not only extend the effective range of a conventional resonant coupling based WPT system, but also provide power continuously to multiple moving devices, such as electric vehicles and robots. In this paper, the system is presented and analyzed with a transmission line model. The performance and characteristics of the system are studied and discussed.

A novel concept of portable charging station networks to serve Electric Vehicles is described. An optimum charging station deployment method is explained, and its performance has been simulated for single highway, two intersecting highways, and Manhattan-like grid traffic models. Outage probability and service waiting delay performances are evaluated. Impact of the number PCSs and the ratio of EVs to PCSs in the service area on outage probability and waiting delay are studied. The gained insights will be used in extending this pioneer step to a stochastic framework with more realistic traffic models.

The new mobile multi-hop relay-based (MMR) network architecture imposes a demanding performance requirement on relay stations. These relays will functionally serve as an aggregating point on behalf of the BS for traffic collection from and distribution to the multiple MSs associated with them, and thus naturally incorporate a notion of "traffic aggregation". However, the packet construction mechanism in IEEE 802.16/16e standard, which was designed for handling traffic solely on a per-connection basis, cannot apply on the relay link directly, as it may render a potential bottleneck and preponderantly limit the overall network capacity. As a solution, we propose two new efficiency-improvement schemes at the MAC layer, namely MPDU concatenation and MSDU aggregation, both of which incarnate the inherent notion of "aggregation" and alleviate the dismal efficiency degradation on the relay links. As confirmed by the performance evaluation, the proposed concatenation and aggregation schemes can achieve significant overhead reduction, and thus better prepare the 802.16e protocol for its adoption in MMR network

As mobile radio systems expand their role in global communications, there is a need for both increased efficiency and an ability to operate in a variety of arbitrary unpaired spectrum assignments. While traditional mobile systems are mostly operated with separated transmit and receive spectrum assignments, these assignments are becoming more difficult to find for new systems among the crowded radio spectrum. Developing a radio system that is suitable for an unpaired spectrum assignment and that can also provide rapid availability of channel information for adaptive transmissions is thus a significant goal. The paper introduces a novel concept, which we refer to as orthogonal division duplexing (ODD), to address these issues. The ODD technique interleaves multiple orthogonal carriers in the same band for transmission and reception. These orthogonal carriers are produced using techniques similar to those used for OFDM. Using the same channel for both transmission and reception enables the channel conditions to be rapidly and accurately estimated by each transceiver, eliminating the delays or errors associated with traditional channel reporting techniques. The ODD transmission system is particularly well suited to multimedia high-speed mobile communications and may be designed to be adaptable to asymmetric traffic flows.