Pilot-based Channel Estimation Technique Research Articles

3D indoor positioning with spatial modulation for visible light communications

In this paper, a novel three-dimensional (3D) indoor visible light positioning (VLP) algorithm is proposed based on the spatial modulation (SM) and its error performance assessed as compared to the conventional received signal strength (RSS)-based 3D VLP systems. As contrasted to the traditional VLP system, the proposed SM-based 3D VLP system first estimates the optical channel gain between the transmitting light-emitting diodes (LEDs) and the two photo detectors (PDs) attached to the user by a pilot-based channel estimation technique. Then, unknown 3D positions of the receiver are determined by the trilateration algorithm with distances computed from the estimates of the channel gains. Consequently, the 3D VLP system achieves an interference-free transmission with increased spectral efficiency and without the need for a demultiplexing process at the receiving end. The algorithm’s performance is evaluated regarding positioning error by applying the SM over four LEDs and the number of pilots selected as a function of the environmental signal-to-noise ratios (SNRs). The computer simulation results show that the positioning errors are obtained in an order of magnitude smaller than RSS-based techniques in an indoor industrial environment. This is mainly because the distances involved in determining the 3D positions can be determined more precisely by the pilot-aided channel estimation method without creating any data rate problem in transmission due to the higher spectral efficiency of the SM.

An embedded pilot power based channel estimation and low-complexity feedback equalization scheme for OTFS system

Orthogonal Time Frequency Space modulation (OTFS) has evolved as an astounding modulation technique for high-speed communication in a doubly dispersive channel. In any wireless communication system, channel estimation and equalization are essential at the receiver to recover the transmitted data. To accomplish this for the emerging OTFS based systems, a modified embedded pilot-based channel estimation technique and low complexity feedback equalization algorithm for integer Doppler shifts in the delay-Doppler domain are proposed in this paper. Our channel estimation scheme exploits embedded-pilot arrangement, and the symbol equalization relies on the Interference calculation and its mitigation iteratively. To achieve this we contemplate a prudent arrangement of symbols in the OTFS frame in such a way that the Guard symbols prevent the interference between data symbols and the pilot symbol at the receiver. Two distinct lumps of received data of the same OTFS frame will be engaged in channel estimation and data detection. An analytical expression of the theoretical Cramer Rao Lower Bound (CRLB) is derived and plotted for the proposed channel estimation scheme. The attained simulation results for Bit-Error-Rate (BER) under the proposed scheme show a significant error rate improvement over the Minimum Mean Squared Error (MMSE) equalization algorithm. Further, a lower computational complexity is also achieved in comparison with modified MMSE detection and MP detection algorithms.

Pilot-Assisted OFDM for Underwater Acoustic Communication

Multicarrier techniques have made it possible to wirelessly transmit data at higher rates for underwater acoustic (UWA) communication. Several multicarrier techniques have been explored in the past for wireless data transmission. OFDM is known to fight off inter-symbol interference due to the orthogonality of its subcarriers. However, due to time variations, OFDM suffers from intercarrier interference. As the UWA channel is both a time and frequency variant, channel estimation becomes complex. We propose a pilot-based channel estimation technique and explore two equalizers for improving the error performance of an OFDM-based UWA system. Both the equalizers employ pilot subcarriers to estimate the UWA channel. One equalizer is a least squares (LS) equalizer and the other is a zero forcing (ZF) equalizer. Using computer simulations, it is observed that, for an acceptable error performance, the number of pilots should be one-fourth the number of subcarriers. Moreover, if the energy of the pilots is increased without changing the overall symbol energy, the error performance degrades. It is also noted that both the LS and ZF equalizers give an acceptable error performance with the ZF performing marginally better than the LS. Furthermore, the error performance of the proposed system is evaluated as a function of the transmitter-receiver distance and an acceptable error performance is observed even at 1250 m.

Analysis of Variable Bit Rate SOFDM Based Integrated Satellite-Terrestrial Broadcast System in Presence of CFO and Phase Noise

In this paper, the exact closed-form signal-to-interference-noise ratio (SINR) expression, for the joint effect of carrier frequency offset (CFO) and phase noise (PHN) is derived for integrated satellite-terrestrial broadcast system (ISTBS), employing Walsh–Hadamard (WH) based spread orthogonal division multiplexing (SOFDM) transmission scheme at the satellite terminal. To examine that, three-state Fontan land mobile satellite (LMS) suburban environment is considered for S-band transmission. Additionally, bit error rate (BER) and spectral efficiency is analyzed based on the obtained SINR expression. Variable bit rates (VBRs) are assumed for SOFDM. This analysis is performed to support VBR quality of service (QoS) at the physical layer of digital video broadcast satellite handheld (DVB-SH)-A based ISTBS. The results disclose a continuous performance deterioration under both assessment measures with increasing doppler frequency shift or PHN. Moreover, simulation and analytical results illustrate a close match for various values of normalized CFO and PHN. Further, pilot-based channel estimation technique is carried out and the estimated error variance is evaluated for VBR WH-SOFDM.

Analysis of Variable Bit Rate SOFDM Transmission Scheme Over Multi-Relay Hybrid Satellite-Terrestrial System in the Presence of CFO and Phase Noise

In this paper, the exact closed-form signal-to-interference-noise ratio (SINR) expression, for the joint impact of carrier frequency offset (CFO) and phase noise (PHN), is derived for each channel link in a multi-relay hybrid satellite-terrestrial broadcast system, employing the Walsh Hadamard (WH) based spread-orthogonal frequency multiplexing (S-OFDM) and OFDM transmission scheme at satellite terminal and terrestrial repeaters (relays) respectively. Additionally, bit error rate and spectral efficiency are analyzed for such hybrid system with $M$ -relay, based on the obtained SINR expressions. To examine that, an adaptive decode and forward (ADF) strategy is employed at relay terminals. Also, three-state Fontan Land Mobile Satellite and six-path typical urban terrestrial channel models are considered. This analysis is performed to support variable bit rate (VBR) quality of service at the physical layer of Digital Video Broadcast Satellite Handheld (DVB-SH)-A architecture, the provision of which is absent in the DVB-SH standard. VBRs are assumed for S-OFDM. The results illustrate that both single-relay and three-relay ADF-based VBR WH-SOFDM yield an identical performance in the presence of the combined effect of CFO and PHN, under both performance measures. However, the improvement in performance for the three-relay strategy is observed in the presence of CFO only. Further, a pilot-based channel estimation technique is performed at the receiver, and the estimated error variance is evaluated for every channel link. Later, the block-by-block system computational complexity of single-relay and $M$ -relay ADF-based VBR WH-SOFDM is evaluated. It is shown that the complexity of the $M$ -relay ADF strategy is rate dependent and almost $M-1$ times the single-relay strategy. Hence, an increase in the number of relays would not yield any significant performance gain, but would enhance the system computational complexity considerably. Therefore, for high data rate transmission, the single-relay ADF-based WH-SOFDM scheme could be a suitable candidate for hybrid satellite-terrestrial communication systems in future.

Analysis of Variable Bit Rate WH/CI‐Spread OFDM based Integrated Satellite‐Terrestrial Broadcast System

In this study, the exact closed-form signal-to-interference-noise ratio (SINR) expression, for the impact of Doppler frequency shift on minimum mean square error receiver is derived for Walsh Hadamard (WH) and polyphase carrier interferometry (CI) code based multicarrier spread orthogonal frequency division multiplexing (SOFDM) transmission scheme over integrated satellite–terrestrial broadcast system. Additionally, bit error rate and spectral efficiency are analysed based on the obtained SINR expression. To examine that, three-state Fontan land mobile satellite, and six-path typical urban and rural area terrestrial channel models are employed. This analysis is performed to substantiate variable bit rate (VBR) quality of service at the physical layer of digital video broadcast satellite handheld (DVB-SH)-A architecture, the provision of which is absent in DVB-SH standard. VBR is assumed for SOFDM. The results illustrate that WH-SOFDM outperforms CI-SOFDM under both performance measures in all the three channel environments. Further, pilot-based channel estimation technique is performed and the estimated error variance is evaluated for VBR WH/CI-SOFDM. Later, block-wise system computational complexity of WH/CI-SOFDM schemes is evaluated. It is shown that, CI-SOFDM is a relatively more complex system than WH-SOFDM. Thus, a trade-off is present between the achieved performance gain and system complexity.

One-Shot Blind Channel Estimation for OFDM Systems Over Frequency-Selective Fading Channels

This paper presents a blind channel estimation (BCE) technique for orthogonal frequency division multiplexing communications systems. The proposed system is based on modulating particular pairs of subcarriers using amplitude shift keying and phase shift keying, which enables the realization of a decision-directed one-shot BCE (OSBCE), with complexity and accuracy that are comparable to pilot-based channel estimation techniques. The performance of the proposed estimator is evaluated in terms of the mean squared error (MSE), where an accurate analytical expression is derived and verified using Monte Carlo simulation under various channel conditions. The obtained results show that the MSE of the proposed OSBCE is comparable to pilot-based estimators, which confirms the efficiency of the proposed OSBCE.

Efficient Implementation of Filter Bank Multicarrier Systems Using Circular Fast Convolution

In this paper, filter bank-based multicarrier systems using a fast convolution approach are investigated. We show that exploiting offset quadrature amplitude modulation enables us to perform FFT/IFFT-based convolution without overlapped processing, and the circular distortion can be discarded as a part of orthogonal interference terms. This property has two advantages. First, it leads to spectral efficiency enhancement in the system by removing the prototype filter transients. Second, the complexity of the system is significantly reduced as the result of using efficient FFT algorithms for convolution. The new scheme is compared with the conventional waveforms in terms of out-of-band radiation, orthogonality, spectral efficiency, and complexity. The performance of the receiver and the equalization methods are investigated and compared with other waveforms through simulations. Moreover, based on the time variant nature of the filter response of the proposed scheme, a pilot-based channel estimation technique with controlled transmit power is developed and analyzed through lower-bound derivations. The proposed transceiver is shown to be a competitive solution for future wireless networks.

A Semi Blind Channel Estimation Method Based on Hybrid Neural Networks for Uplink LTE-A

The paper describes how to improve channel estimation in Single Carrier Frequency Division Multiple Access (SC-FDMA) system, using a Hybrid Artificial Neural Networks (HANN). The 3 rd Generation Partnership Project (3GPP) standards for uplink Long Term Evolution Advanced (LTE-A) uses pilot based channel estimation technique. This kind of channel estimation method suffers from a considerable loss ofbitrate due to pilot insertion; all data frame sent contains reference signal. The HANN converts data aided channel estimator to semi blind channel estimator. To increase convergence speed, HANN uses some channel propagation Fuzzy Rules to initialize Neural Network parameters before learning instead of a random initialization, so its learning phase ismore rapidly compared to classic ANN.HANN allows more bandwidth efficient and less complexity. Simulation results show that HANN has better computational efficiency than the Minimum Mean Square Error (MMSE) estimator and has faster convergence than classic Neural Networks estimators.

Two-way 증폭과 전송 릴레이 네트워크의 용량 최적화

본 논문에서는 two-way 릴레이 네트워크에서 파일롯(pilot)기반 채널 추정 기법과, 전송시 데이터 심볼과 함께 파일롯 심볼을 전송하는 기법을 제안한다. 채널상태정보(channel state information : CSI)가 없는 경우, destination은 파일롯 심볼을 사용해 채널을 추정한다. 이 시스템에서 릴레이는 파일롯 심볼과 데이터 심볼을 증폭하고 AF(amplify and forward)프로토콜을 사용하여 destination에 전송한다. 릴레이 이득이 고정되어 있어서 릴레이는 채널을 추정할 필요가 없기 때문에 destination이 채널을 추정한다. 이 채널 추정에는 이미 잘 알려진 LS(least-square)와 MMSE(minimum mean-square error)를 사용하였다.

Channel Estimation Technique for STBC coded MIMO System with Multiple ANN Blocks

In this work, a channel estimation technique based on Artificial Neural Networks (ANN) has been proposed as an alternative to pilot based channel estimation technique for Space-Time Block Coded Multiple-Input Multiple-Output (STBC- MIMO) systems over Rayleigh fading channels. ANNs, due to their high degree of adaptability, can be used for modelling the nonlinear phenomenon of channel estimation and for decoding the degraded symbols over severely faded channel. Two different ANN structures, namely Multilayer Perceptron (MLP) and Recurrent Neural Networks (RNN) have been trained and tested extensively for estimating the channel in STBC- MIMO systems with Binary Phase Shift Keying (BPSK) modulation scheme. Simulated results in terms of Bit Error Rates (BER) vs. Signal to Noise Ratio (SNR) have been used to compare the effectiveness of the learning capability of the two ANN structures over wireless fading channel. RNN structures are found to outperform the MLP, both in terms of training performance and BER results and thus proving its nonlinear dynamic adaptive behaviour. General Terms

Interference Rejection for Parametric Channel Estimation in Reuse-1 Cellular OFDM Systems

This paper proposes a joint channel-estimation method for the desired and interfering channels for cell edge users in reuse-1 orthogonal frequency-division multiplexing (OFDM) cellular systems. The following assumptions are made in proposing the algorithm: 1) the desired and interferer's channel multipath delays do not overlap; 2) the same pilot sequence is sent from the desired and interfering base stations (BSs); and 3) reuse-3 preamble symbols, as in the preamble structure in IEEE 802.16d/e (Wimax) systems, are used to obtain initial channel estimates without interference. If we make these assumptions, then it is possible to estimate the desired and interfering channels, even with reuse-1 pilots. The proposed pilot-based channel estimation technique exploits the delay subspace structure to reduce the impact of cochannel interference (CCI) on channel estimation. Delay subspace refers to the set of basis vectors spanning the frequency response of the desired and interfering multipath channels. This enables us to jointly estimate and track the desired and interfering channels with a lower mean-squared error (MSE), when compared with the conventional modified least-squares (mLS) technique, which ignores the structure of interference. The significance of accurate channel estimates in symbol detection schemes is demonstrated for systems employing two or more receiver antennas. The proposed channel estimator significantly improves the performance of symbol-detection schemes based on either interference nulling combiner (INC) or minimum MSE diversity combiner (MMSE-DC), when compared with detection schemes using mLS-based channel estimates. Analytical expressions are derived for the MSE of the estimated multipath delays. Simulation results are also provided to show the improved performance for the proposed channel-estimation method compared with the mLS-based channel estimation method, when used in conjunction with INC and MMSE-DC detectors.

Artificial Neural Network Channel Estimation Based on Levenberg-Marquardt for OFDM Systems

The many advantages responsible for the widespread application of orthogonal frequency division multiplexing (OFDM) systems are limited by the multipath fading. In OFDM systems, channel estimation is carried out by transmitting pilot symbols generally. In this paper, we propose an artificial neural network (ANN) channel estimation technique based on levenberg-marquardt training algorithm as an alternative to pilot based channel estimation technique for OFDM systems over Rayleigh fading channels. In proposed technique, there are no pilot symbols which added to OFDM. Therefore, this technique is more bandwidth efficient compared to pilot-based channel estimation techniques. Also, this technique is making full use of the learning property of neural network. By using this feature, there is no need of any matrix computation and the proposed technique is less complex than the pilot based techniques. Simulation results show that ANN based channel estimator gives better results compared to the pilot based channel estimator for OFDM systems over Rayleigh fading channel.