Haeseong Jeong

Wireless repeater with adaptive equalizer and phase noise compensator for LTE-Advanced uplink

In this paper, we propose adaptive equalizer and phase noise compensator in order to effectively cancel feedback channel and phase noise in wireless repeater system based on LTE-Advanced uplink system. In a repeater system, the performance got worse caused by feedback channel and phase noise. In order to cancel feedback channel, we use adaptive equalizer such as NLMS and RLS. And block type pilot is a common pilot pattern in LTE-Advanced uplink standard. So the phase noise compensator exploits block type pilot. Instead of estimating phase noise in other algorithms, the proposed method directly estimates the interference components caused by phase noise and improves estimation accuracy. After that, we reconstruct the interference matrix and suppress the interferences by the inverse matrix method. BER performance of proposed method is satisfied with 12.5dB at 10−4.

Doppler spread and its compensation by FDE and turbo code

In the satellite communication system, Doppler spread is caused by the movement of the mobile receiver such as high speed aircraft, vessel, and so on. To overcome Doppler spread in the satellite communications, we propose the novel FDE (Frequency Domain Equalizer) and turbo code in order to compensate Doppler spread efficiently in this paper. And we adapt single carrier system in order to save power in satellite system. Also, in order to guarantee channel capacity, we have to reduce interference such as Doppler spread by using FDE. To overcome such shortcomings and secure high SINR (Signal to Interference and Noise Ratio), we propose FDE and turbo code. If we reduce interference and secure high SINR by using FDE and turbo code, the Shannons channel capacity is guaranteed. Therefore, the purpose of this paper is to improve system performance with low BER (Bit Error Rate) and high SINR. In this paper, we adapt comb type pilot in order to estimate and compensate Doppler spread. As the simulation results, the proposed algorithm has high performance which is satisfied with 2.5dB at 10-4 where the number of iterations is 4.

Adaptive equalizer and compensation of ICI in the wireless repeater system

In this paper, we propose adaptive equalizer and compensation of ICI (Inter carrier interference) in the wireless repeater system based on OFDM in order to effectively cancel feedback channel and phase noise. When the gain of a wireless repeater is larger than the isolation between transmit and receive antennas of the repeater, the feedback signal that comes into the receive antenna from the transmit antenna of the repeater causes the repeater to go into feedback oscillation regardless of the input signal. And the phase noise effect can exist on up and down converter of wireless repeater. Thus, in order to cancel feedback channel and phase noise, we suggest an adaptive equalizer such as NLMS (Normalizer least mean square), RLS (Recursive least square) and a phase noise compensator. In case of phase noise compensator, because phase noise has random characteristic, comb type pilot is used for estimation and compensation phase noise in wireless communication systems. First, we remove CPE (Common phase error) by received pilot symbol. After that, we use the obtained error power as a MMSE (Minimum mean square error) detection criterion factor and a forgetting factor to compensate ICI caused by phase noise. BER performance of proposed method is satisfied with 13.5dB at 10−4.

Combination of QAPM and OFDM for high power efficiency and spectral efficiency

In this paper, we analyze performance of low power consumption modulation scheme such as Phase Shift Position Modulation(PSPM), Phase Silence Shift Keying(PSSK) and Quadrature Amplitude Position Modulation(QAPM) using OFDM transmission in AWGN channel. A PSPM, PSSK and QAPM modulation scheme are decrease in bandwidth efficiency but improved power efficiency than existing PSK and QAM. These modulation schemes can achieve power efficiency because every symbol of modulations has a zero-envelope period like PPM techniques. The OFDM system is high bandwidth efficiency than single carrier system. In this paper, we compare PSPM, PSSK and QAPM modulation using OFDM transmission regard to BER performance, throughput and PAPR.

Adaptive Phase Noise Compensator in Wireless ICS Repeater

In this paper, we study a novel wireless interference cancellation system(ICS) repeater based on OFDM system with phase noise analysis and performance evaluation. Recently, there were many researches about wireless repeater. The previous study is just considering the feedback channel cancellation algorithm. But, in wireless repeater system, the phase noise effect can exist at up and down converter of wireless repeater. In wireless repeater system, if there are phase noise effects, the performance of system will get worse. So, the phase noise compensator is needed in wireless repeater. Therefore, we propose adaptive phase noise compensator based on OFDM system in order to effectively cancel phase noise. In order to cancel interference, we adapt adaptive phase noise compensator in wireless repeater system. The adaptive phase noise compensator compensates phase noise effect. Therefore, in this paper, we analyze phase noise of wireless repeater based on OFDM system. In this paper, when phase noise power is -15 dBc and phase noise cutoff frequency is 100 kHz at 4QAM, the BER performance of propose algorithm is better about 4 dB than with adaptive equalizer and without phase noise compensator at .

A Fast ICI Suppression Algorithm with Adaptive Channel Estimation for the LTE-Advanced Uplink System

In this paper, we propose a fast ICI suppression algorithm with adaptive channel estimation for the LTE-Advanced uplink system. In order to effectively remove phase noise and carrier frequency offset at time varying channel, we use the comb type pilot. The purpose is to improve performance by reducing computational complexity than conventional PNFS(Phase Noise & Frequency offset Suppression) algorithm. We reduce computational complexity by decreasing overlapping computation or unnecessary computation at conventional PNFS algorithm. Also, we propose an effective channel estimation method. We estimate and compensate multipath channel through the proposed adaptive channel estimation method. The BER performance of the proposed method is better about 0.5 dB than the conventional method at the Vehicular A channel.

Efficient Doppler Spread Compensation with Frequency Domain Equalizer and Turbo Code

In the satellite communication system, Doppler spread is caused by the movement of the mobile receiver such as high speed aircraft, vessel, and so on. To overcome Doppler spread in the satellite communications, we propose the novel FDE (Frequency Domain Equalizer) and turbo code in order to compensate Doppler spread efficiently in this paper. And we adapt single carrier system in order to save power in satellite system. Also, in order to guarantee channel capacity, we have to reduce interference such as Doppler spread by using FDE. To overcome such shortcomings and secure high SINR (Signal to Interference and Noise Ratio), we propose FDE and turbo code. If we reduce interference and secure high SINR by using FDE and turbo code, the Shannon’s channel capacity is guaranteed. Therefore, the purpose of this paper is to improve system performance with low BER (Bit Error Rate) and high SINR. In this paper, we adapt comb type pilot in order to estimate and compensate Doppler spread. As the simulation results, the proposed algorithm has high performance which is satisfied with 2.5dB at 10− 4 where the number of iterations is 4.

Suppression of carrier frequency offset and phase noise in adaptive bit loading OFDM system

Introduce adaptive bit loading technique into orthogonal frequency division multiplexing (OFDM) system can highly improve system performance in frequency selective fading channel. However, similar with ordinary OFDM system, this system is very sensitive to carrier frequency offset (CFO) and phase noise. When CFO and phase noise exist, common phase error (CPE) as well as inter carrier interference (ICI) will be generated to disturb the received signal and system performance will be seriously degraded. In this paper, we analyze the interferences caused by CFO and phase noise in adaptive bit loading OFDM system when the channel condition is frequency selective fading channel. Then the suppression method based on block type pilots is introduced to overcome the interferences simultaneously. From the simulation results, it can be seen that CFO and phase noise will cause serious system performance degradation. But after we perform the suppression processing, system performance can be significantly improved.