Pilot Symbol Assisted Channel Estimation Research Articles

MIMO Channel Estimation in an SDR Platform for Evaluation of D&F Relay Nodes

Relay Nodes (RNs) have received special attention as a radio access technology which can overcome channel fading and improve the channel capacity in high-speed and dense vehicle environments. RNs have been the object of standardization by the 3GPP; however, this process has not been accompanied by the development of hardware that allows for evaluation of the advantages of RNs. Software Defined Radio (SDR) has emerged as a promising technology to implement the concept of RNs at low cost. In this paper, a detailed study of the MIMO wireless channel between an evolved Node-B (eNB) and an RN is carried out. The developed algorithms are implemented in an SDR platform for Decode-and-Forward (D&F) relay node evaluation, resulting in significant improvements of its capabilities on the MIMO channel. A pilot symbol-assisted channel estimation algorithm based on combinations of the Least-Squares (LS) technique and Bi-Cubic (BCI), Bi-Linear (BLI), and Bi-Nearest Neighbors (BNNI) interpolation methods is considered. Furthermore, the Minimum Mean Square Error (MMSE) and Zero-Forcing (ZF) equalization schemes are studied. In the tests conducted, Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) scenarios are considered, demonstrating the capabilities of the developed platform. The performance measurements using different modulation schemes are compared under the same conditions. The simulation results show that the LS technique together with the BCI and MMSE methods performed the best among all evaluated channel estimation and equalization algorithms, in terms of the Error Vector Magnitude (EVM) performance of the received Resource Grid (RG). Furthermore, we show that the Bit Error Rate (BER) and throughput of the core network increase when using the 2 × 2 MIMO technique.

Effects of CEE and Feedback Error on Performance for AF-ORS with PSA-CE Schemes Over Quasi-Static Rayleigh Fading Channels

In this paper, we propose the analytical approach for amplify-and-forward (AF) opportunistic relaying schemes (ORS). When operation of AF-ORS consists of relay selection and data transmission phases based on pilot symbol assisted-channel estimation (PSA-CE) methods over quasi-static Rayleigh fading channels, we show that the relay selection phase can be implemented by pilots symbols transmission for source-relay and relay-destination. Moreover, the feedback method for the selected relay index is proposed to have a simple fashion. Then, we investigate the effects of both a channel estimation error and an estimated noise variance, which are obtained by PSA-CE methods, on the received signal-to-noise ratio (SNR). The average SNR loss is also derived in terms with the number of pilots in PSA-CE methods. Moreover, the average symbol error rate, the outage probability, and the normalized channel capacity of the ORS are derived in approximated closed-form expressions for an arbitrary link SNR when the channel state information in the source-relay-destination link is estimated based on transmitted pilots symbols. As the number of pilot symbols, the derived analytical approach is verified, and by comparing it with simulation results, the accuracy is demonstrated. In addition, it is verified that the effect of the feedback error can be neglected for PAS-CE methods over quasi-static fading channels.

A Survey on Pilot Symbol Assisted Channel Estimation in OFDM Systems*

A Survey on Pilot Symbol Assisted Channel Estimation in OFDM Systems*

Burst-by-Burst Adaptive DF Relay Systems with PSA-CE Methods over Quasi-Static Rayleigh Fading Channels

In this paper, we propose an analytical approach for adaptive decode-and-forward (ADF) relaying schemes consisting of burst data transmission based on pilot symbol assisted-channel estimation (PSA-CE) methods over quasi-static Rayleigh fading channels. At first, we focus on the error-event at relay nodes in which the transmission mode switching is carried out burst by burst, whereas previous studies assumed the transmission mode switching symbol-by-symbol, thus showing lower error rate bound. Under consideration of burst transmission for ADF relay systems, we derive exact error rate expressions which better estimate the performance of actual systems. Then, the average bit and burst error rates are derived in approximated expressions for an arbitrary link signal-to-noise ratio (SNR) related with channel estimation errors. Their accuracy is confirmed by comparison with simulation results. Furthermore, ADF relay systems with PSA-CE schemes are confirmed to select correctly decoded relay nodes without additional signaling between relay nodes and the destination node and it is verified to achieve the performance at a cost of negligible SNR loss.

Comparative Study of Bit Error Rate with Channel Estimation in OFDM System for M-ary Different Modulation Techniques

In this paper we investigate the bit error rate performance of orthogonal frequency division multiplexing system with channel estimation through least square error (LSE) and minimum mean square error (MMSE) algorithms. In this paper we are implementing the M-ary phase shift keying (M- PSK) and M-ary quadrature amplitude modulation (M-QAM) digital modulation techniques for mapping the signal in OFDM system for bit error rate evaluation with the employment of comb-type pilot symbol-assisted channel estimation algorithm over frequency selective multi-path Rayleigh fading channel. Here the performance of Least Squares method depends on not only on the signal-to-noise ratio (SNR) but also on the pilot ratio. Simulation results show that applying the LSE and MMSE channel estimation algorithm, they produce the best BER performance over the fading channel. We can consider the OFDM system as either a modulation technique or a multiplexing technique. In a single carrier system, a single fade or interferer can cause the entire link to fail, but in a multicarrier system, only a small percentage of the subcarriers will be affected [1]. Here we are using the pilot symbols as a guard band to eliminate the Inter Symbol Interference, and cyclic prefix eliminates the Inter Subcarrier Interference. Keywords Channel estimation, orthogonal frequency division multiplexing (OFDM), least square error (LSE), minimum mean square error (MMSE), pilot symbol, bit error rate (BER).

A Comparative Study of Channel Estimation Techniques for OFDM in DVB-T2

pilot symbol assisted channel estimation is a well-known multicarrier technique for high rate transmission over wireless frequency selective fading channels. In this paper a comparative study of channel estimation techniques is presented based on a pilot arrangement used in the second generation for Digital Video Broadcasting Terrestrial (DVBT2) system in time-varying frequency-selective fading channels. A modified method based on Domain Transform Least Square Estimation (DTLSE) has been proposed which reduces the computational complexity by avoiding the use of the matrix inversion .The estimation matrix size for obtaining Channel Impulse Response (CIR) depends only on the length of the channel not on the number of pilot subcarriers nor the size of OFDM symbol. Two Dimensional Linear Interpolation (2-DLI) is discussed which performs better than one Dimensional Linear Interpolation (1-DLI)but suffers from long processing delay and higher sensitivity to Doppler frequency shifts. The Minimum Mean Squared Error (MMSE) channel estimation is also considered as a reference method because it has a good performance close to the perfect estimation at the cost ofhigh computational complexity and the necessity of prior knowledge ofchannel statistics. The proposed method is compared with three other methods DTLSE, 2-DLI and MMSE.The proposed method provesto give a better performance compared to the other methods which suffer from either a much higher computational load or less robustness to Doppler shifts.

Average Error Rate Expressions for DF relay Networks with CE Error for PSA-CE schemes Over Rayleigh Fading Channels

This paper provides a framework for evaluating the error rate performance of decode and forward (DF) relay cooperative transmission in the presence of channel estimation (CE) error caused by pilot symbol assisted-channel estimation (PSA-CE) schemes over Rayleigh fading channels. Average bit error rate (BER) and average symbol error rate (SER) are expressed as the well-known closed-forms by using error-events at relay nodes and moment generating function (MGF) of the received signal-to-noise ratio (SNR), which quantifies the SNR penalty arising from CE errors. Moreover, the effects of erroneous detection and transmission at relay nodes are verified in terms of both the combined SNR and the average error rate, and cooperative diversity is observed from closed-form error rate expressions. Simulation results are finally presented to validate derived analytical performance ma-trices.

Effects of CEE on ASER performance for Cooperative AF Relay Systems with PSA-CE Schemes

In this paper, we propose the analytical approach for amplify-and-forward (AF) relay cooperative transmission in the presence of channel estimation error (CEE) generated by pilot symbol assisted-channel estimation (PSA-CE) schemes over quasi-static Rayleigh fading channels. Average symbol error rate (SER) is expressed as the well-known closed-form by using moment generating function (MGF) of the received signal-to-noise ratio (SNR), which quantifies the SNR penalty arising from CEE. Moreover, the effect of CEE on SER performance is verified based on the number of pilot symbols and the accuracy of the derived average SER expression of M-ary phase shift keying (MPSK) is confirmed by comparison with simulation results.

Pilot symbol assisted channel estimation for OFDM-based cognitive radio systems

In this article, challenges regarding the provision of channel state information (CSI) in non-contiguous orthogonal frequency division multiplexing (NC-OFDM) cognitive radio (CR) systems are addressed. We propose a novel scheme that utilizes cross entropy (CE) optimization together with an analytical pilot power distribution technique to design pilot symbols that minimizes the channel estimate mean squared error (MSE) of frequency-selective channels. The optimal selection of pilot subcarriers is a combinatorial problem that requires heavy computations. To reduce the computational complexity, the CE optimization is utilized to determine the position of pilot subcarriers. Then, for a given pilot placement obtained by the CE algorithm, a closed form expression to obtain optimal pilot power distribution is employed. Simulation results indicate that, the proposed pilot symbol design provides better channel estimate MSE as well as the bit error rate (BER) performance when compared with the conventional equal powered pilot design.

Low-complexity channel estimation for OFDM systems in high-mobility fading channels

Nowadays, multicarrier transmission is very popular because of the high data rate requirement of wireless systems. Orthogonal frequency-division multiplexing (OFDM) is a special case of multicarrier transmission. It is considered an effective technique for frequency-selective channels because of its spectral efficiency, its robustness in different multipath propagation environments, and its ability of combating intersymbol interference. Losing subchannel orthogonality causes interchannel interference, but many conventional channel estimators assume that the channel is time-invariant during one OFDM symbol. This assumption causes error floors along the OFDM symbol for high-mobility cases. In this paper, we propose 2-dimensional pilot symbol-assisted channel estimation for wireless OFDM systems by using frequency and time-domain interpolation. This method has the advantage of minimizing the system complexity and processing delay while closely approximating the actual mobile channel. The performance of our proposed method is compared to coherent modulation with perfect channel estimation as well as other conventional channel estimation methods. Different detection techniques were used to test our proposed channel estimation algorithm.

주파수 선택적 시변 채널 OFDM 시스템에서의 파일럿 심볼을 이용한 채널 예측 및 등화

본 논문에서는 주파수 선택적 시변 채널 OFDM 시스템에서 파일럿 심볼을 이용하는 채널 예측 및 등화 방식의 성능을 분석하고 문제점 및 개선 방안을 제시한다. 주파수 영역 채널 행렬의 대역폭을 제한하기 위하여 시간 영역 윈도우를 도입하며, 채널 예측에 LS(Least Square) 및 선형 MMSE(Minimum Mean Square Error) 예측 방식을 이용한다. 채널 등화에는 채널 예측에 이용되는 파일럿 심볼의 존재가 고려된 선형 MMSE 및 결정 귀환 등화 방식을 이용한다. 계산량을 감소시키기 위하여 채널 등화 알고리즘에 요구되는 선형 연립 방정식의 풀이에 band LU 행렬 분해 알고리즘을 도입하며, 컴퓨터 시뮬레이션을 통하여 기존 방식과의 성능을 비교한다. 결정 귀환 등화 방식에 시간 영역 윈도우를 적용하는 경우, 결정 귀환 관련 행렬의 대역폭이 제한되지 않아 성능이 저하되는 문제점을 분석하였다. In this paper, we analyze the performance of pilot symbol assisted channel estimation and equalization schemes for OFDM systems over frequency-selective time-varying channels and propose methods to improve the system performance. In the least square(LS) and linear minimum mean square error(MMSE) channel estimation, time domain windowing is introduced for banding the frequency domain channel matrix. The linear MMSE and decision feedback equalization schemes are employed with the pilot symbols for channel estimation taken into account in the equalization process. To reduce computational complexity, the band LU matrix factorization algorithm is introduced in solving the linear systems involved in the equalization, and the performances are compared with the known previous results by computer simulations. When time domain windowing is employed in the decision feedback equalization, the matrix related with the decision feedback process is shown to be unhanded and the resultant performance degradation is analyzed.

KINERJA PERPADUAN DETEKSI DATA DAN ESTIMASI KANAL ITERATIF PADA SISTEM KOMUNIKASI NIRKABEL ANTENA JAMAK

In iterative data-detection and channel-estimation algorithms, the channel estimator and the data detector recursively exchange the information order to improve the system performance. In this paper, maximum a posteriori based iterative data detection and pilot symbol assisted channel estimation of the single parity check product code for multiple antenna wireless communication is studied. Results show the algorithm can converge at a few iteration numbers and improve error probability performance of the system.

Pilot Symbol Assisted Channel Estimation Techniques for OFDM Systems: A Review

Orthogonal frequency division multiplexing (OFDM) Is a potential technique for transmitting high rate data over wireless channels. Satisfactory performance can be achieved by using coherent modulation techniques together with the channel estimation. For frequency selective fast fading channels, the task of channel estimation becomes quite challenging for an OFDM system because channel response appears unequal in both frequency and time domain. Therefore, an independent estimation of the channel is necessary at each of the subcarriers in each individual OFDM symbol. This article describes various pilot symbol assisted (PSA) channel estimation techniques. The Minimum mean square error (MMSE) channel estimation is superior in performance as it exploits prior information about the channel. Different models of MMSE estimator, which are based on different approximations of channel correlation matrix, are also discussed. Finally, a brief description of Kalman filter based estimation is presented for the situations where inter carrier interference (ICI) can not be neglected.

Linear Interpolation in Pilot Symbol Assisted Channel Estimation for OFDM

In this paper, we investigate several efficient interpolation techniques for pilot symbol assisted channel estimation in OFDM. The interpolation methods studied include two dimensional (2-D) separable lowpass sine interpolator with Kaiser window, 2-D separable Deslauriers-Dubuc (DD) interpolation and 2-D discrete Fourier transform (DFT) based lowpass interpolation. The performances of these interpolators are compared with those of the well known minimum mean-square error (MMSE) 2-D separable Wiener filter and the perfect channel state information. It is shown that the Kaiser window based interpolator and DD interpolation are simple, robust, and outperform the 2-D DFT based lowpass interpolation as well as several existing interpolation methods proposed in the literature. These two schemes are suitable candidates for use in 1-D and 2-D channel estimation

Channel-aware priority transmission scheme using joint channel estimation and data loading for OFDM systems

This paper presents a data-loading technique that jointly considers the effect of channel estimation and the property of encoded multimedia data in Orthogonal Frequency Division Multiplexing (OFDM) systems. We observe that OFDM subchannels experience different average bit error rate (BER) due to channel estimation inaccuracy. The leakage effect in the fast Fourier transform (FFT)-based channel estimation method or the model mismatch in the polynomial-based channel estimation method results in a variation on the decoded BER across different OFDM subchannels. Thus, we are motivated to design the Priority Transmission (PT) scheme, which utilizes this BER variation across different OFDM subchannels and provides unequal error protection (UEP) for multimedia transmission. In addition, since OFDM has been adopted in many multimedia transmission standards, we compare the different channel estimation techniques, which were compared only for generic data transmission before, in the context of multimedia transmission with the PT scheme. In particular, we extend the polynomial-based channel estimation that was previously designed for a decision-directed scenario to a pilot-symbol-assisted (PSA) channel estimation scenario. Then, we investigate the channel estimation mean square error (MSE) and BER performance of individual OFDM subchannels for both the FFT-based and the polynomial-based channel estimation. Furthermore, we design the PT scheme that achieves significant gain in peak-signal-to-noise ratio (PSNR) of the reconstructed images for both channel estimation methods. Finally, we compare different OFDM channel estimation techniques for multimedia transmission. It is shown that for generic data transmission, the polynomial-based PSA channel estimation outperforms the FFT-based method in realistic channel conditions, and both types of channel estimation have similar performance when using the proposed PT scheme for multimedia transmission.

Error Probability Minimizing Pilots for OFDM With M-PSK Modulation Over Rayleigh-Fading Channels

Orthogonal frequency division multiplexing (OFDM) with pilot symbol assisted channel estimation is a promising technique for high rate transmissions over wireless frequency-selective fading channels. In this paper, we analyze the symbol error rate (SER) performance of OFDM with M-ary phase-shift keying (M-PSK) modulation over Rayleigh-fading channels, in the presence of channel estimation errors. Both least-squares error (LSE) and minimum mean-square error (MMSE) channel estimators are considered. For prescribed power, our analysis not only yields exact SER formulas, but also quantifies the performance loss due to channel estimation errors. We also optimize the number of pilot symbols, the placement of pilot symbols, and the power allocation between pilot and information symbols, to minimize this loss, and thereby minimize SER. Simulations corroborate our SER performance analysis, and numerical results are presented to illustrate our optimal claims.

On the design of layered space-time systems for autocoding

Hochwald et al.(see IEEE Trans. Inform. Theory, Nov. 2001) have recognized that arbitrarily reliable communication is possible in multiantenna systems with coding over only a single coherence interval. In particular, they showed that reliable communication is possible for all rates R/spl les/C/sub a/ with code words that extend over a single coherence interval when the number of transmit antennas and coherence interval (n,T)/spl rarr//spl infin/. They coined the names "autocoding" for this phenomenon and "autocapacity" for C/sub a/. They also proposed a signalling scheme based on random unitary matrices that achieves a significant fraction of this capacity. The main limitation, however, is that currently no decoder of reasonable complexity is known for this signalling scheme. We investigate the application of space-time layering to autocoding. We show that properly constructed layered systems can achieve the autocapacity with a reasonable complexity receiver composed of minimum mean-square error (MMSE) decision feedback multiuser detectors and single user decoders. In addition to this asymptotic result, we propose a specific layering approach, the threaded space-time layering, that combines generalized bit interleaved space-time coded modulation, iterative signal processing and pilot symbol assisted channel estimation. We show that this approach is well suited for practical systems with limited numbers of transmit antennas and small coherence intervals. Finally, we report simulation results that demonstrate the ability of the threaded approach to achieve significant fractions of the autocapacity with a realizable receiver. The simulation results also indicate significant performance gains over the Cayley differential space-time signalling scheme in certain scenarios.

Experiments on pilot symbol-assisted coherent multistage interference canceller for DS-CDMA mobile radio

A three-stage coherent multistage interference canceller (COMSIC) employing pilot symbol-assisted (PSA) channel estimation for replica generation of multiple access interference (MAI) is implemented and its performance in the presence of frequency selective multipath fading is experimentally evaluated by a multipath fading simulator. A fast transmission power control (TPC) method suitable for COMSIC is also proposed, in which the signal-to-interference plus background noise power ratio (SIR) at the matched filter (MF) based RAKE receiver is measured to achieve a short TPC delay and the target signal-to-interference ratio value is compensated by an outer loop so that the measured block error rate (BLER) is equal to the prescribed target value. The experimental results show that as expected the COMSIC satisfactorily reduces the MAI even when the number of active users is equal to the spreading factor in a multipath fading environment, and thus, improves the bit error rate (BER) performance in a multiuser environment. The results also show that the proposed fast TPC method with a two-slot delay associated with COMSIC works satisfactorily and the combination of COMSIC and fast TPC significantly decreases the transmission power of a mobile station (required transmission power of a mobile station with COMSIC at the average BER of 10/sup -3/ is decreased by approximately 2.0 (3.0) dB compared with the MF-based RAKE receiver with (without) antenna diversity reception). This extends the cell coverage, battery life, and increases the system capacity in the reverse link.

Coherent orthogonal filter using pilot symbol-assisted channel estimation for DS-CDMA

A coherent orthogonal filter (COF) using pilot symbol-assisted channel estimation is proposed for DS-CDMA cellular mobile radio. In the proposed scheme, a complex fading envelope in the multi-path environment is estimated using pilot symbols, and tap coefficients of orthogonal filter are controlled for maximising the signal to interference ratio (SIR) of a RAKE combined signal. Computer simulation results show that the required Eb/N0 of the proposed COF is reduced by ~10.0 dB compared to a conventional matched filter receiver at an average BER of 3 × 10-2 when there are 10 users and processing gain is 31.