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2026-10-22, Week 43
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main_email:seikou696@asagi.waseda.jp
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ICACT20220275 Slide.31        [Big slide for presentation]       Chrome Text-to-Speach Click!!
The formulas of the closed-form solution based on L1/L2-ball projection method.

ICACT20220275 Slide.30        [Big slide for presentation]       Chrome Text-to-Speach Click!!
A recent spread of smart phones and other wireless devices has further increased data traffic in communication networks.

ICACT20220275 Slide.29        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Thank you for your attention!

ICACT20220275 Slide.28        [Big slide for presentation]       Chrome Text-to-Speach Click!!
This is reference.

ICACT20220275 Slide.27        [Big slide for presentation]       Chrome Text-to-Speach Click!!
References

ICACT20220275 Slide.26        [Big slide for presentation]       Chrome Text-to-Speach Click!!
We are going to discuss on the switching between the L1-ball projection method and the L2-ball projection method in the power allocation optimization problem. We will also discuss on the optimal placement of IRS according to the surrounding environment using ray tracing method.

ICACT20220275 Slide.25        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Last, Future work

ICACT20220275 Slide.24        [Big slide for presentation]       Chrome Text-to-Speach Click!!
To increase the system capacity of IRS-assisted OAM communication systems, we propose the IMI cancellation method for IRS-assisted OAM multiplexing and the L2-ball projection approaches to optimize the transmit power allocation for OAM modes. The simulation of the IRS-assisted OAM communication shows that the IMI cancellation method can achieve increasing the maximum system capacity. It also shows that the L2-ball projection method can achieve increasing the maximum system capacity as compared to the L1-ball projection method, but it is limited to when the IRS is placed near the middle.

ICACT20220275 Slide.23        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Conclusion

ICACT20220275 Slide.22        [Big slide for presentation]       Chrome Text-to-Speach Click!!
This is the simulation result of System capacity vs The distance between UT and the IRS along the x-axis ZIO. As you can see this figure, system capacity increase applying IMI cancellation effectively both L1-ball projection method and the L2-ball projection method. It is also observed that the maximum system capacity can be achieved effectively applying the L2-ball projection method than the L1-ball projection method when the IRS is placed in the middle. This means that as the distance between U_T and IRS, and IRS and U_R increases, the system capacity is limited by divergence effects, but the IRS can compensate for the performance degradation.

ICACT20220275 Slide.21        [Big slide for presentation]       Chrome Text-to-Speach Click!!
This is simulation parameter of system model. We set the parameter of the number of multiplexed OAM modes to 5 and the parameter of the number of antenna elements to 8, because users cannot be equipped with many antenna elements. We also set the parameter of the distance between UT and UR to 40 meters.

ICACT20220275 Slide.20        [Big slide for presentation]       Chrome Text-to-Speach Click!!
These figures are an IRS-assisted OAM communication system model. We denote the transmitter UCA and receiver UCA by UT and UR, respectively. The radii of UT, and UR are RT and RR, respectively, and every antenna element of UT and UR is arranged equidistantly around a ring. XIO denote the distance between UT and the IRS along the x-axis. ZIO denote the distance between UT and the IRS along the z-axis. In this system, we assume that there is no direct link between UT and UR due to some obstacles blocking, so an IRS is applied to establish an alternative LoS route between them.

ICACT20220275 Slide.19        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Simulation model

ICACT20220275 Slide.18        [Big slide for presentation]       Chrome Text-to-Speach Click!!
These figures show L1 and L2 constraint regions for the same loss function. The black dot indicates the location where the loss function is minimum. Each curved contour line represents the same loss function value, and any outside of that ellipse will have higher loss. The regularized coefficients will sit on the constraint boundaries somewhere because the minimum location is outside the constraint regions. L1 and L2 constraint regions get different coefficient locations, on the diamond and circle, for the same loss function. In L1 ball projection, the optimal location (w1, w2) is the dot at the diamond tip. In L2 ball projection, the optimal location (w1, w2) is at the new dot location. At least for this case, L1 gets a zero coefficient, whereas, L2 does not.

ICACT20220275 Slide.17        [Big slide for presentation]       Chrome Text-to-Speach Click!!
The L1-ball projection has the feature of sparse representation where many weights are zero. The advantage of this is that estimation is fast, and interpretability is improved because the number of extra explanatory variables is reduced. However, there is a disadvantage that the number of explanatory variables is reduced too much. Therefore, it is used when only some features are important and fast calculation is required. The L2-ball projection does not have sparse representation, so it is used when all features 𝐰 are important and overtraining is to be prevented. Assuming that the user side cannot be equipped with many antenna elements, the number of OAM modes will be small. Therefore, the weights for all the OAM modes are important, and L2 is adopted.

ICACT20220275 Slide.16        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Next is the proposed method for optimizing the transmit power allocation. To maximize the system capacity of all OAM modes, the problem of optimizing the transmission power allocation of all OAM modes ｐ can be formulated as Formula 2. This function is Loss function that minimizes interference from other OAM modes, which is a component that becomes noise when retrieving the received signal. There are two ways to solve this loss function. L1-ball projection approaches and L2-ball projection approach.

ICACT20220275 Slide.15        [Big slide for presentation]       Chrome Text-to-Speach Click!!
In signal processing, the received signal vector after Inter-mode interference (IMI) suppression x-hat is given by Formula 1. Large w is the linear filtering based on minimum mean square error as the equalization criterion, which suppress the Inter-mode interference.

ICACT20220275 Slide.14        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Signal processing is as follows: First, QPSK modulated signals are assigned to each OAM modes. After allocation, the power is allocated for each OAM mode according to the power allocation optimization algorithm. After IDFT processing, the radio waves are emitted from the antenna elements of the UT. Next, the IRS set the phase shift according to the IRS’s reflecting phase shift optimization algorithm. Radio waves with noise coming from the UT are reflected according to the phase shift and reach the UR. After DFT, IMI suppression methods reduce the noise power. Last, the original signal is obtained by QPSK demodulation.

ICACT20220275 Slide.13        [Big slide for presentation]       Chrome Text-to-Speach Click!!
The purpose of this research is to realize NLOS IRS-Assisted OAM-Based communication with Uniformed Circular Array Antenna (UCA) in consideration of transmission quality. To increase the system capacity of IRS-assisted OAM communication systems, we propose an inter-mode interference cancellation method for IRS-assisted OAM multiplexing and a L2-ball projection method to optimize the transmit power allocation for OAM modes.

ICACT20220275 Slide.12        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Purpose and Proposed scheme

ICACT20220275 Slide.11        [Big slide for presentation]       Chrome Text-to-Speach Click!!
IRS can improve the wireless communication coverage, throughput, and energy efficiency. But, in the IRS-enhanced wireless communication system, channel state information is important for achieving the passive beamforming gain of IRS, which, however, is a challenging task due to its massive number of passive elements without transmitting/receiving capabilities.

ICACT20220275 Slide.10        [Big slide for presentation]       Chrome Text-to-Speach Click!!
IRS enables the reconfiguration of wireless propagation environment by smartly controlling the signal reflections via its massive low-cost passive elements.　By coordinating IRS’s reflections, it is possible to deliver radio waves to NLoS users and to improve the power strength of edge users by relaying them. The communication procedure between AP and User using IRS is as follows: First, A user send the uplink pilot signals to an AP via an IRS. Next, The AP estimate the concatenated user-IRS-AP channel based on the uplink pilot signals from the user. Next, IRS controller set a new reflection pattern to the IRS. Finally, the AP send signals to the user via IRS.

ICACT20220275 Slide.09        [Big slide for presentation]       Chrome Text-to-Speach Click!!
IRS is a reflector that can reflect a signal by adjusting its amplitude and phase by utilizing many low-cost reflecting passive elements.

ICACT20220275 Slide.08        [Big slide for presentation]       Chrome Text-to-Speach Click!!
OAM-based communication can significantly increase throughput in a line-of-sight (LoS) environment, because utilizing different OAM modes to encode multiple channels at the same frequency can be regarded as an implementation of space division multiplexing due to their spatial phase distributions. But Radio wave with OAM by emitted from UCA is not suitable for long distance communication and non-line-of-sight (NLoS) communication. Moving on to Intelligent Reflecting Surface.

ICACT20220275 Slide.07        [Big slide for presentation]       Chrome Text-to-Speach Click!!
OAM signal can be generated by spiral phase plates antenna and Uniformed circular array (UCA) antenna, etc. The UCA antenna can generate multiple OAM modes simultaneously in a flexible way and is expected to be used for OAM based wireless communications. To generate the OAM wave, the antenna elements in transmit UCA are fed with the same input signal but different phase shift. By simultaneously emitting radio waves of different OAM modes, many signals can be transmitted at one time without interference.

ICACT20220275 Slide.06        [Big slide for presentation]       Chrome Text-to-Speach Click!!
The main feature of EM wave with OAM is that the Poynting vector has a component rotating around the direction of propagation, which leads to be rotated phase on a vertical plane and a doughnut-shaped intensity distribution.

ICACT20220275 Slide.05        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Moving on to Related research. I’m going to introduce about OAM and IRS.

ICACT20220275 Slide.04        [Big slide for presentation]       Chrome Text-to-Speach Click!!
A recent spread of smart phones and other wireless devices has further increased data traffic in communication networks. The orbital angular momentum (OAM) mode multiplexing is attracting attention in order to respond to the demand for high-speed and large capacity. The intelligent reflecting surface (IRS)-enhanced wireless communication system is also attracting attention for improving the wireless communication coverage, throughput, and energy efficiency.

ICACT20220275 Slide.03        [Big slide for presentation]       Chrome Text-to-Speach Click!!
Let’s see Background.

ICACT20220275 Slide.02        [Big slide for presentation]       Chrome Text-to-Speach Click!!
This is outline.

ICACT20220275 Slide.01        [Big slide for presentation]       [YouTube] Chrome Text-to-Speach Click!!
Good morning/afternoon,　I'm Kosei Ono from Waseda University, Japan. Today, I will introduce about "Performance Analysis of Intelligent Reflecting Surface-Assisted Orbital Angular Momentum-Based Communication Systems. “