Changyoung An

Design and performance evaluation of SSD (simultaneous single band duplex) system using RF cancellation and digital cancellation.

In this paper, we design SSD (simultaneous single band duplex) system using RF (radio frequency) cancellation and digital cancellation. We analyze characteristic of residual self-interference after RF Cancellation signal when error of phase shifter occur in RF cancellation. When phase shifter error of 0°, 0.5°, 1° and 2° occur in RF cancellation, residual self-interference signal power after RF cancellation is bigger than desired signal power of distant station. So, it is impossible to receive transmit data of distant station. But we confirm that it is possible to receive transmit data of distant station by digital cancellation with frame structure. Also, in digital cancellation with frame structure, if residual self-interference signal after RF cancellation is too large then LMS algorithm requires more time to estimate self-interference channel. That is, performance degradation occurs because self-interference channel estimation has not completed in estimation frame.

Design of W-OFDM and nonlinear performance comparison for 5G waveform

For the spectrum efficiency improvement of 5G mobile communication, a new waveform based on multi-carrier are important. In this paper, we like to suggest a W-OFDM(weighted orthogonal frequency division multiplex) system design and compare the nonlinear system performance with the already existing OFDM, UFMC(universal filtered multicarrier), FBMC(filter bank multicarrier) systems. At first, we describe OFDM, UFMC, FBMC, and W-OFDM(weighted OFDM). Then, we evaluate and compare the spectrum characteristics of these systems in the nonlinear HPA environment. As simulation results, OOB power of FBMC is the lowest under the linear HPA condition. But, OOB power of UFMC, FBMC, and W-OFDM is similar under the nonlinear HPA environment. In the real HPA nonlinearity, W-OFDM with low-complexity and simple structure is advantageous than the well-known strong candidates for 5G mobile system such as FBMC and UFMC.

Single RF based MIMO system using load-modulation

In this paper, we confirm that load modulation technique can support generation of high-order m-QAM symbols for LM-MIMO system. And then we evaluate performance of LM-MIMO system using load modulated symbols. A number of RF chains can cause various problems in conventional MIMO system. On the other hand, LM-MIMO system requires single RF chain only. Therefore, LM-MIMO system has low-complexity and low power consumption. As results, we can confirm that load modulation of T-model can generate high-order m-QAM symbols. Also, we can confirm that 4×4 LM-MIMO system with single RF chain has a similar performance to conventional 4×4 MIMO system with a number of RF chains.

A Novel CFO Suppression Algorithm for OFDMA Uplink Communication System

In orthogonal frequency division multiple access uplink system, orthogonal multiple subcarriers are assigned to different users for parallel high data rate communications. However, carrier frequency offset (CFO), which is due to oscillator mismatches and/or Doppler shift, will destroy the orthogonality among subcarriers and introduce intercarrier interference (ICI) as well as multiple-access interference (MAI). Thus, system performance will be seriously degraded. To overcome this problem, it is of great importance to do research on suppression of the interferences caused by CFO. Especially, for the application services of the fast time-varying WiMAX, LTE and vehicular communication, the most important property of the suppression algorithm of the multiple CFOs effects is the efficient and high speed processing to compensate the ICI as well as MAI due to the multiple CFOs effects. In this paper, we propose a novel fast time domain inverse matrix receiver to suppress the interference of multiple CFOs. Compared with the conventional frequency domain direct ZF inverse matrix method, which has high complexity in obtaining the ICI matrix and its inverse matrix, the proposed method has very low complexity in obtaining the interference matrix. Furthermore, the signal after interference suppression is a frequency domain signal. Thus the FFT processing in conventional receiver can be skipped and receiver complexity can be simplified. Simulation results show that the proposed simple system works very fast and it does not show the serious error floor phenomenon in high SNR range and this algorithm has almost the same performance to the frequency domain direct ZF inverse matrix method.

Robust Digital Retrodirective Beamforming Technique for Multipath Channel Environment

Abstract In this paper, we describe the effect of temporal and spatial focusing obtained by using the digital retrodirective beamforming (DRDB) system and analyze BER performance of DRDB in multipath channel. There is a problem with reception performance degraded due to inter symbol interference (ISI) in multipath channel. In order to reduce ISI, the existing communication system use complex equalizer. In order to reduce ISI, we propose a DRDB system which can retransmit data information toward direction as the received signal without any prior information. Also, we explain ISI mitigation by temporal and spatial focusing of the proposed system. Simulation results show that the proposed system has better BER performance than that without DRDB becauseof ISI mitigation effect in multipath channel environment.

Spectrum Efficient and Power Efficient Communication System for Satellite Applications

For the satellite application, the spectrum efficient and power efficient communication is very important. However, there is a big trade-off between the spectrum efficiency and power efficiency in the communication system design. 4D-8PSK-TCM (4 dimensional 8 phase shift keying trellis coded modulation) communication system could be the one strong candidate for the best solution to this trade-off problem, which was recommended in Consultative Committee for Space Data Systems (CCSDS) satellite communication. However, the detailed design and performance evaluation of the 4D-8PSK-TCM communication system has not been clearly studied and reported. So, in this paper, the design method of the 4D-8PSK-TCM communication system will be described at first. Secondly, the characteristics of peak to average power ratio (PAPR), spectral characteristic, and constellation characteristic according to the square root raised cosine (SRRC) filtering are determined for each transmission efficiency mode. Finally, bit error rate (BER) performance according to each reception processing step is evaluated and analyzed. With the simulation results, the PAPR characteristic and the spectral characteristic can be obtained to evaluate. Good PAPR characteristics can be shown when the roll off factor values are 0.35 and 0.5, and the spectral waveforms have been confirmed.

Design and Performance Comparison of W-OFDM Under the Nonlinear HPA Environment

Recently, the spectral efficiency improvement of wireless and cellular communications is very important. Several waveforms have been proposed in order to satisfy key performance indicators of the 5th generation (5G) cellular communication. Universal filtered multi-carrier (UFMC) and filter bank multi-carrier (FBMC) and the filtered orthogonal frequency division multiplexing are typical candidate for 5G waveform, but they have some advantages and problems as well. In this paper, a weighted orthogonal frequency division multiplexing (W-OFDM) is considered since W-OFDM has pretty low complexity and comparable merits. In this paper, at first, we describe the system model and operation principle about UFMC, FBMC, and W-OFDM system. Next, we evaluate the out-of-band (OOB) power spectrum and bit error rate (BER) performance of these systems in the linear or nonlinear HPA. Simulation results show that OOB power spectrum and BER performance of UFMC, FBMC, and W-OFDM are similar in the linear operation. From the implementation point of view, if these performance and characteristics are similar, low-complexity is very decisive for the communication processing speed that is very important to the low latency and ultra-fast processing in the receiver. Additionally, under the nonlinear HPA environment, W-OFDM system is more advantageous because W-OFDM system uses a simple time-domain windowing technique in order to reduce OOB power.

WR-OFDM system and OOB spectrum comparison

The most important figure-of-merit for the 5G waveform is the spectrum efficiency. Especially, OOB (out-of-band) spectrum must be reduced to increase the spectrum efficiency and decrease the guard band between the channels. In the filtering methods, UFMC (universal filtered multi-carrier) and FBMC (filter bank multi-carrier) were suggested for the new waveform for 5G mobile communication system. Similar to OFDM system, they are based on the multi-carrier, but they have sharper OOB spectrum. Due to the very complicated process and some serious difficulty to the realization, windowing method has been enlightened. In the windowing method, WOLA-OFDM (weighted overlap and add — orthogonal frequency division multiplexing) system is the most famous and representative windowing method among the many possible conventional windowing methods. However, the WOLA-OFDM system has serious problems. Due to the copy and addition processes, time resource will be slightly sacrificed and the other is that the left part of the copied and added parts will invade into the right part of the previous OFDM symbol. This is very serious data damage even before the transmission. In this paper, we like to suggest a WR (windowing and restructuring)-OFDM system that shows competitive OOB spectrum characteristics and is designed by simple some modification of the conventional OFDM system. Basically this is similar to the conventional OFDM system, but windowing process has to be included after the CP (cyclic prefix) addition stage. By adding this windowing process, we can get the desirable OOB (Out-Of-Band) spectrum characteristics that are very important to save the frequency resources and competitively similar shape to the OOB spectra of FBMC and UFMC system. From the simulation results, it is confirmed that OOB power spectrum of WR-OFDM is quite comparable with the existing waveforms.

Design and Performance Evaluation of W-OFDM System for 5G Mobile Communication

본 논문에서는 5세대 이동통신을 위한 OFDM(Orthogonal Frequency Division Multiplexing)을 기반으로 하고 Window 함수을 적용한 W-OFDM 시스템 모델을 제시하고 그 성능을 평가한다. 제안하는 시스템은 기존의 OFDM 시스템의 높은 OOB 전력을 가지는 문제점을 해결하기 위해 CP를 추가하는 부분에 Window 함수를 함께 적용한다. 이는 시간영역에서 연속성을 갖게 만들고 OOB 전력을 저감시킨다. 그리고 수신기에서는 Window 함수를 적용함으로써 생긴 데이터 손실을 CP의 일부를 이용하여 재구성함으로써 데이터 손실을 막는다. 이로 인해서 Window 함수의 길이는 CP길이의 절반이하로 정한다. 제안하는 시스템 모델을 Window 함수의 종류와 길이의 따라 시뮬레이션을 진행하였다. 비교한 Window 함수 중에서는 Kaiser Window 함수가 가장 OOB 저감 효과가 컸다. 또한 Window 함수의 길이를 늘일수록 OOB 전력 저감 효과가 더 크게 나타났으며 동일한 BER성능을 얻으면서 기존 OFDM 시스템 대비 OOB전력을 저감시킬 수 있는 것을 확인 하였다. 즉 제안하는 시스템은 다가올 5세대 이동통신에 적합하다고 할 수 있다.

WF-OFDM (windowing and filtering OFDM) system for the 5G new radio waveform

The 2 approaches for the 5G new radio waveform design are the filtering and windowing for the spectrum efficiency improvement by reducing the OOB(out-of-band) power spectrum. As filtering method, UFMC (universal filtered multicarrier), FBMC (filter bank multicarrier) and f-OFDM (filtered orthogonal frequency division multiplexing) waveforms are the potential candidates for a new waveform for 5G system. Another possible approach is to use the windowing in the conventional CP-OFDM system in order to reduce the OOB power spectrum. W-OFDM (window orthogonal frequency division multiplexing) is typical and show comparable performance. Each approach has some advantages and disadvantages together. The best OOB reduction performance can be shown in FBMC system. However, FBMC system is the most complicated and cannot support the general M-QAM (M-ary quadrature amplitude modulation) format. So, it is very important to design a novel OFDM-based waveform that has the similar OOB power spectrum to the FBMC and support the general M-QAM modulation as well. In this paper, we like to propose a WF-OFDM System for the 5G and 5G beyond mobile system waveform design. This WF-OFDM system uses a combination method of the filtering and windowing to get the synergy effect, so that the spectrum efficiency may be increased by reducing the OOB (out-of-band) power spectrum. 4 kinds of WF-OFDM systems are devised depending on the filtering and windowing positions for the OOB performance improvement. Simulations results show that the proposed WF-OFDM system has comparable or better OOB spectrum reduction characteristics to FBMC system. Especially, the proposed system WF-OFDM # 3 and #4 show the remarkable OOB reduction performance even in the short window length of 6 or 8.