Multipath Separation and Parameter Estimation by Single RIS Antenna in Fading Channel

Channel identification and measurement accuracywill greatly affect wireless communication performance. Thebroadcasting of electromagnetic waves will produce multipath,and its superposition will lead to fading. If the multipath canbe separated and the phase of each path can be adjustedseparately, better signal transmission and reception strategiescan be designed to weaken or eliminate fading and improvesignal transmission performance. In this paper, we first analyzethe multipath structure of the wireless channel, then utilize thedynamic isomeric characteristics of the reconfigurable intelligentsurface (RIS) antenna, also called dynamic metamaterial antenna(DMA), to form differentiated patterns, and rapidly sampleswithin a period of single pilot symbol, so that a group ofmultipath signals are projected on multiple patterns and pathscan be separated and measured. We simulated and evaluated the normalized mean square error of the parameter estimates, including angle of arrival and path gain of channels underdifferent conditions. The results demonstrate that even single1-bi coding RIS antenna can achieve well multipath separationand parameter estimation effects.

Multipath Separation and Parameter Estimation by Single RIS Antenna in Fading Channel

Channel identification and measurement accuracywill greatly affect wireless communication performance. Thebroadcasting of electromagnetic waves will produce multipath,and its superposition will lead to fading. If the multipath canbe separated and the phase of each path can be adjustedseparately, better signal transmission and reception strategiescan be designed to weaken or eliminate fading and improvesignal transmission performance. In this paper, we first analyzethe multipath structure of the wireless channel, then utilize thedynamic isomeric characteristics of the reconfigurable intelligentsurface (RIS) antenna, also called dynamic metamaterial antenna(DMA), to form differentiated patterns, and rapidly sampleswithin a period of single pilot symbol, so that a group ofmultipath signals are projected on multiple patterns and pathscan be separated and measured. We simulated and evaluated the normalized mean square error of the parameter estimates, including angle of arrival and path gain of channels underdifferent conditions. The results demonstrate that even single1-bi coding RIS antenna can achieve well multipath separationand parameter estimation effects.

Improvement of Pilot Symbol Orthogonal Sequences in 2×2 to 4×4 MIMO Wireless Communication Systems with Channel State Estimation

MIMO wireless communication systems with channel state estimation, in which 2 to 4 transmit-receive antenna pairs are employed, are simulated. The channel estimation is fulfilled by the orthogonal pilot signal approach, where the Walsh Hadamard-ordered sequences are commonly used for piloting. The signal is modulated by applying the quaternary phase shift keying method. Maximum 250 000 packets are transmitted through flat-fading Rayleigh channels, to which white Gaussian noise is added. Based on simulating 10 subcases of the frame length and number of pilot symbols per frame, it is ascertained that pilot symbol orthogonal sequences in 2×2 to 4×4 MIMO systems can be improved by substituting Walsh functions with partially unsymmetrical binary functions constituting the eight known orthogonal bases. The benefit is that the bit-error rate is substantially decreased, especially for 2×2 MIMO systems. Considering three cases of the pilot signal de-orthogonalization caused by two indefinite and definite pilot sequence symbol errors, the relative decrement varies from 0.123 % to 14.7 %. However, the decrement becomes less significant as the number of transmit-receive antenna pairs is increased.

The influence of ISI on channel estimation and optimized channel estimation in PSK-chirp system

Due to the influence of filters and multipath channels, the received signal of the current symbol will be affected by the interference of the previous symbol and the next symbol, the interference will reduce the performance of channel estimation, especially when the SF is relatively low, which will affect the system throughput rate. In this paper, based on BPSK chirp spread spectrum modulation system, we first describe the channel estimation of matched filtering and FFT, and derive the influence of ISI on the channel estimation of the current pilot symbol. Then we proposed the improved channel estimation based on the estimated time delay spread and transmitted signals. Finally, we simulate the MSE performance of channel estimation under different channels and different transmitted signals. The simulation results show that the MSE performance of the improved channel estimation can be improved under different channel when the SF is low, and higher throughput can be obtained.

Pilot-Aided Frame Synchronization in Optical OFDM Systems

Efficient frame synchronization is essential for data recovery in communication systems. In this study, a single pilot sequence is used to achieve both frame synchronization and peak-to-average power ratio (PAPR) reduction. The two systems considered are direct-current biased optical orthogonal frequency division multiplexing (DCO-OFDM) and asymmetrically clipped O-OFDM (ACO-OFDM). The pilot symbol is allocated to odd indexed subcarriers only. Thus, the synchronization algorithm leverages the mirror symmetric property of the pilot symbol within a frame to detect the start of the pilot signal at the receiver. This scheme has low complexity and gives precise frame synchronization at signal-to-noise ratios as low as 4 dB in an indoor visible light communication (VLC) channel.