The massive multiple input multiple output (MIMO) system with large-scale antenna array at base station (BS) simultaneously communicates with many mobile stations (MSs) ensuring high reliability using the pre-coding. But, in mobile communication, the performance of the pre-coding is degraded by fast fading. For improving the performance of the pre-coding, this letter proposes the power control scheme of the new approach that has the variable step size using the statistical characteristic of fast fading and Doppler frequency. From the simulation results, it is shown that the proposed scheme improves signal-to-interference-plus-noise ratio (SINR) performance.

A novel signaling scheme is proposed for iterative channel estimation and data decoding in fast fading channels. The basic idea is to bias the occurrence probability of transmitted symbols. A priori information about the bias is utilized for channel estimation. The bias-based scheme is constructed as a serially concatenated code, in which a convolutional code and a biased nonlinear block code are used as the outer and inner codes, respectively. This construction allows the receiver to estimate channel state information (CSI) efficiently. The proposed scheme is numerically shown to outperform conventional pilot-based schemes in terms of spectral efficiency for moderately fast fading channels.

This paper studies the performance of a coded convolutional spreading CDMA system with cyclic prefix (CS-CDMA/CP) combined with the zero correlation zone code generated from the M-sequence (M-ZCZ code) for downlink transmission over a multipath fast fading channel. In particular, we propose a new pilot-aided channel estimation scheme based on the shift property of the M-ZCZ code and show the robustness of the scheme against fast fading through comparison with the W-CDMA system empolying time-multiplexed pilot signals.

We provide an efficient transmission scheme which embeds a pilot signal in the data signal for channel state information (CSI) based on the configuration of a multiple-input multiple-output (MIMO) system using space-time block coding (STBC) with an adaptive array (AA). A computer simulation and analysis show that the proposed scheme, which combines the advantage of an Alamouti-like STBC scheme and the pilot-based AA, can suppress the irreducible error due to random FM noise. The proposed scheme using a pilot minimizes the decoding delay, and is highly robust against fast fading. We show that the proposed scheme can significantly increase the data transmission rate by using the transmitter diversity based on STBC, and the accuracy of the proposed technique is exemplified by a computer simulation.

Frequency-domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, channel transition within an FDE block cannot be ignored. The ISI reduction performance of FDE degrades since the cyclicity of the channel matrix is lost. To solve this problem, a method of dividing the received data block into multiple subblocks has been proposed, where pseudo cyclic prefix (CP) processing is introduced to realize periodicity in each subblock. In this method, the performance is degraded by the inherently-inaccurate pseudo CP. In this paper, we study the application of frequency-domain turbo equalization (FDTE) to subblock processing for improving the accuracy of pseudo CP. The simulation results show that FDTE with subblock processing yields remarkable performance improvements.

This article proposes a channel estimation method for the downlink channels of a WCDMA system in a high-speed railroad setting. High mobility may cause conventional symbol-level channel estimation to yield severe errors because in conventional methods channel state has to maintain constant within one to several symbol durations. However, in high mobility environment, this assumption may not hold. Errors are particularly more dangerous when using very high spreading factors. In order to counteract the adverse effect of high mobility on channel estimation, we shorten the observation window to that of an N-chip block so that channel conditions or characteristics remain approximately unchanged. We consider channel estimation prior to dispreading the received signal. In other words, channel estimation is done at the chip level rather than the conventional symbol level. The least squares (LS) criterion is employed to acquire channel characteristics for each block of N pilot chips, and the linear interpolation method is used to determine the channel characteristics for each data chip. The LS-based estimator is selected due to its simplicity since it does not need to know channel or noise statistics. An LS-based estimator at the chip level has the further advantage that it is robust against interpath interference (IPI). The uncoded bit error rate (BER) performance of a RAKE receiver using different channel estimation schemes is evaluated and compared through simulations. The proposed scheme is found to be suitable for a high-speed railroad setting.

We propose an implementation of the tapped delay line adaptive array (TDLAA) at the base station for improving the BER performance of asynchronous multi-user mobile communication over fast fading channels using multiple antennas. The data of each user at the mobile station, which applies two transmit antennas, are encoded by Space Time Block Code (STBC). The proposed scheme transmits the pilot signal and information data in alternate time slots. We derive performance criteria for designing such a scheme under the assumption that the fading is classified as fast fading. We show that the proposed scheme can suppress co-channel interference (CCI) and defeat Doppler spread effectively.

A channel estimation method for multiple input multiple output (MIMO)-OFDM with fast fading channels is proposed to increase estimation quality and reduce the computational complexity. Specifically, we use a space-time correlation between channel coefficients, and compensate the ICI term. Since ICI compensation can be obtained without any pilot symbols for target OFDM block, our proposal is practical for real-time systems. The computational complexity is reduced by considering only dominant data symbols.

In this letter, we propose a novel signal detection method that matches maximum likelihood (ML) performance but requires much less computational complexity than ML detection. When the well-known linear decoding method is used for space-time block coded (STBC) OFDM systems in fast-fading channels, co-channel interference (CCI) as well as inter-carrier interference (ICI) occurs. A maximum likelihood (ML) method can be employed to deal with the CCI; however, its computational complexity is very high. In this letter, we propose a signal detection method for orthogonal space-time coded OFDM systems that achieves the identical error performance as the ML method, but requires much less computational complexity.

We introduce a novel configuration for a multi-user Multiple-Input Multiple-Output (MIMO) system in mobile communication over fast fading channels using space-time block coding (STBC) and adaptive array. The proposed scheme adopts the simultaneous transmission of data and pilot signals which reduces control errors caused by delay of obtaining channel state information (CSI). Data and pilot signals are then encoded using a space-time block code and are transmitted from two transmit antennas. In order to overcome the fast fading problem, implementation of adaptive array using recursive least squares (RLS) algorithms is considered at the base station. Through computer simulation, it is shown that the proposed scheme in this way can overcome Doppler spread in higher frequencies and suppress co-channel interference up to N-1 users for N receiving antennas.

This letter proposes a robust detection scheme of orthogonal space-time block codes that face very fast fading channels. The proposed detection scheme employs a QR decomposition on the channel matrix and minimizes noise enhancement and impact of channel estimation errors which occur in a conventional detection scheme. It is shown by simulations that the proposed detection scheme outperforms the conventional detection scheme when the channel fading is very fast.

Spatial despreading weight based on minimum mean square error (MMSE) criterion is derived for orthogonal space-time spreading transmit diversity (OSTSTD) in a fast fading channel, taking into account the inter-antenna interference (IAI) and the inter-code interference (ICI) caused by orthogonality distortion of time-domain spreading codes. Average bit error rate (BER) performance is theoretically analyzed and confirmed by computer simulation to show that the diversity gain can be obtained even in a fast fading.

For multilevel-coded modulation, the cut-off rate of multiple antenna systems over frequency-flat, fast fading channels is derived. Following Wozencraft's approach, a closed-form expression for the cut-off rate is obtained as a function of energy ratio per dimension It is shown that the maximum value of cut-off rate increases linearly with the number of transmit antennas.

Space-time array manifold model is usually used in a fast fading channel to estimate delay for the radio location. The existing additive white Gaussian noise (AWGN) estimation error model significantly overestimates the delay estimation. In this paper, we model the estimation error of the space-time array manifold channel impulse response (CIR) matrix as a correlated AWGN matrix and its performance is shown to be closer to the estimation error of practical systems than the existing model.

In this paper, we propose a novel array antenna-assisted adaptive modulation scheme for fast fading environments. Although adaptive modulation is an efficient technique capable of establishing high bit-rate digital transmission in a multi-path fading environment, it is sensitive to the fast time variation of the channel because of difficulties in tracking the channel state. To resolve this problem, an array antenna-based Doppler spread compensator was applied to the adaptive modulation scheme. Computer simulation results indicated that the proposed scheme can markedly improve the bit error rate and throughput performance for the region in which the maximum Doppler frequency normalized by the packet length is up to 0.1.

This letter compares orthogonal space time codes and quasi-orthogonal codes when the wireless channels are fast fading. It is well known that a orthogonal space-time code is better than a quasi-orthogonal code in high signal-to-noise ratio (SNR) range and that a quasi-orthogonal code is better in low SNR range. In this letter, we show that a quasi-orthogonal space-time code is a better choice even in high SNR range when the channels are fast fading.

This letter proposes a quadratic optimization decoding (QOD) for space-time block decoding in time-selective Rayleigh fading channels. When channels are fast fading, the simple decoding exploiting the orthogonal structure of the codes can not be used to achieve a proper error performance. In an effort to mitigate the severe performance degradation, in this letter least square decoding and QOD are considered for decoding. Simulation results show that the QOD shows a significant performance improvement compared to the least square and the conventional schemes.

Decision-directed, pilot-symbol-aided channel estimation (PSACE) for coded orthogonal frequency division multiplexing (COFDM) systems has structurally unavoidable processing delay owing to the generation of new reference data. In a fast fading environment, the channel condition which varies during the delay induces channel estimation error. This paper proposes a method of reducing this estimation error. In this method, channel equalization is performed for the received signal twice. One is done as pre-equalization with the delayed estimates of channel frequency response in order to update them periodically. At the same moment, the other is done as post-equalization for the received signal that is delayed by the processing delay time, with the same estimates as the pre-equalization. By the proposed method, more accurate channel estimation can be realized without significant output delay. Computer simulations are performed by utilizing the IEEE 802.11a packet structure of 24 Mbit/s. The result shows that the proposed OFDM transmission scheme having the delay time of 20 µs offers 2.5 dB improvement in the required Eb/N0 at PER = 10-2 in the ESTI-BRAN model C Rayleigh fading channel with fd = 500 Hz.

The design criteria for space-time trellis codes (STTC's) in fast fading channels have been proposed: the Distance Criterion and the Product Criterion. The design criteria in [1] are based on optimizing the pairwise error probability (PWEP). However, the frame error rate (FER) of STTC's depends on the distance spectrum. In this paper, we propose a new design criterion for STTC's based on the distance spectrum in fast fading channels. The proposed design criterion is based on the product distance distribution for the large signal-to-noise ratio (SNR) and the trace distribution for the small SNR, respectively. Moreover, we propose new STTC's by the computer search based on the proposed design criterion in fast fading channels. By computer simulation, we show that the proposed design criterion is more useful than the Product Criterion in [1] in fast fading channels. We also show that the proposed STTC's achieve better FER than the conventional STTC's in fast fading channels.

This paper shows the method of theoretical analysis for the bit error probability of the trellis-coded partial response continuous phase modulation (TCM-PR-CPM) over the correlated Rician fast frequency nonselective fading channel. In the analysis, the fading correlation of the channel and the effect due to finite interleaver are taken into account. By applying the method to the rate 1/2 (7, 2) trellis code with the raised cosine pulse of length 2 (2RC) partial response signaling, we show that the tighter upper bounds of the bit error rate are obtained than those in the preceding report.