Scheduling Layer

PTE Optimization

Requirement-Driven Magnetic Beamforming for MIMO Wireless Power Transfer Optimization

Motivation: In MIMO MRC-WPT system, we need to consider the scenario when different RXs have different requirements of power.

Problem formulation: weighted sum-power maximization $WSPMax = max_{{i_n^{tx}}} \sum_q w_q |i^{rx}_q|^2 r^{rx}_q $

Subject to:

$$ \sum_n \left|i_n^{tx}\right|^2 r_n^{tx} + \sum_q \left|i_q^{rx}\right|^2 r_q^{rx} \leq P_{\text{max}}, \ $$

$$ \left|i_n^{tx}\right|^2 \leq A_n^{tx}, \quad \forall 1 \leq n \leq N, \ $$

$$ \left|i_q^{rx}\right|^2 \leq A_q^{tx}, \quad \forall 1 \leq q \leq Q, \ $$

$$ \left|v_n^{tx}\right|^2 \leq V_n^{tx}, \quad \forall 1 \leq n \leq N. $$


Joint Power Routing and Current Scheduling in Multi-Relay Magnetic MIMO WPT System

Motivation: Relay’s ability to increase charging distance in practical systems is studied. A three-coil wireless power transfer system is more energy efficient than a two coil counterpart is feasible. But the relay On/Off based power routing algorithm can be optimized for system performance while considering the MIMO scenario.

Contribution:

  1. They propose an RX-independent algorithm, i.e., without any RX cooperation. RX cooperation, i.e., RX feedback communication is time/energy-consuming since it is achieved by using side-channels, e.g., Bluetooth.

  2. They propose an efficient searching algorithm other than enumerating all the possible relay On-Off states.

PDL Optimization

IMP: Impedance Matching Enhanced Power-Delivered-to-Load Optimization for Magnetic MIMO Wireless Power Transfer System

Motivation: The power delivered to load(PDL) maximization related issues and the two impedance mismatching phenomena need to be further explored. The first one is the PTE-PDL contradiction phenomenon. When RXs are closely coupled with TXs, the PTE is very high but the achieved PDL is quite limited. The second one is the isolated RX-pair phenomenon. When two RXs are closely coupled, the RX pair forms an “isolated island” where the energy can not reach, i.e., their PTE and PDL are both limited.

Contribution:

  1. First work to maximize the PDL in practical MIMO MRC-WPT systems with bounded TX voltages, together with addressing the impedance mismatching phenomena. Research about maximize the PDL in practical MIMO MRC-WPT systems is existing. Maximize the PDL and addressing the impedance mismatching phenomena in SISO systems is existing.

  2. In order to address the two observed phenomena, their basic idea is to handle the first one by tuning TX-RX coupling through special designed adjustable TX coils. To deal with the second one, they use RX grouping mechanism to select not coupled RX pairs to charge. Then, they conduct time scheduling among the chosen RX groups, i.e., each RX group is assigned a unique time slice for charging.

Thoughts: Already have many optimization methods. Ether optimize with a new variable or use more efficient algorithm.


EMR safety optimization

Shield: Safety Ensured High-efficient Scheduling for Magnetic MIMO Wireless Power Transfer System

Motivation: Ensure electromagnetic radiation (EMR) safety is important: Exposure to high EMR has its potential risks including tissue impairment, brain tumor and mental diseases. Not be investigated before: EMR safety related problems have not been thoroughly investigated. While MagMIMO and MultiSpot systems are likely to contravene EMR safety standards.

Contribution: They propose the first scheme for safety ensured charging in MIMO MRC-WPT systems.


Safety Guaranteed Power-Delivered-to-Load Maximization for Magnetic Wireless Power Transfer

Motivation: Current method is not very good: Shield has two deficiencies. On one hand, it is not a one-size-fits-all scheme, i.e., the derived EMR model can only be suitable for the special circular type of resonator coils. On the other hand, Shield focus on PTE maximization which is less meaningful than PDL maximization.

Contribution: They use a unified model to describe the EMR distribution of all the different coils.


Communication Layer

Parallel Feedback Communications for Magnetic MIMO Wireless Power Transfer System

Motivation: Communications is important: The RX feedback communication and power transfer channel estimation schemes enables the systems for charging in demand, magnetic beamforming for better power transfer efficiency, and so on. Current communication scheme is not efficient. However, most of the existing researches focus on the optimization algorithm for TX currents/voltages adjustment, and adopt simple feedback communication and channel estimation schemes. The existing schemes including omitting the communication and channel estimation stages, simply assuming the existence of communication links and pre-known channel conditions, or some naive method.

Contribution:

  1. Cluster phenomenon: two TXs’ current values are clearly clustered into four kinds, which are exactly correspondence to the four combined open-short states of the two RXs.

  2. They propose a collision-aware parallel communication scheme to identify the open-short state of all the RXs.


Camel: Context-Aware Magnetic MIMO Wireless Power Transfer with In-band Communication

Motivation: There are three different receiver (RX) information collection methods. The RX-independent method does not consider the RX information collection at all. The out-band based methods use additional out-band devices, along with extra energy consumption and spectrum occupation. For the in-band communication methods, some are not used in MIMO scenario. Hua et al.’s method need to collect enough combined states before decoding.

Contribution: investigate the signals’ feature from the view of mutual inductance.

Roland: Robust In-band Parallel Communication for Magnetic MIMO Wireless Power Transfer System

Motivation: Camel has a premise of ignoring RX-RX coupling when performing RX-level channel decomposition which may not work well under the scenarios where closely coupled RXs exist. RX-RX coupling can exist as relay phenomenon.

Application Layer

FreAuth: Novel Frequency Feature-Based Device Authentication for Magnetic Wireless Charging

Motivation: Device Authentication is important: Threats like freeloading, illegal device attacks need to be mitigated. Therefore, it is essential to identify and authenticate legitimate devices in magnetic WPT systems to prevent illegal access and ensure smooth usage. Current methods are not good: Uploading its identity is vulnerable to forgery as electromagnetic signals are exposed, and the communication protocol is unencrypted. Hardware fingerprint-based device authentication can be divided to two categories. Extracting device-specific characteristics from electromagnetic signals lacks permanence; Using temporal features such as oscillator difference caused clock skew is unstable and requires a long authentication process.

Contribution:

  1. They observed that each RX has its own frequency-related features.
  2. The proposed method is completely RX-independent, i.e., without requiring communication or cooperation from the receiver.