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The extrinsic information and the received systematic observations exert different influence on decision-making with the change of SNR values for turbo iterative decoding. By multipling a weighted coefficient for the priori information, this paper proposed a novel adaptive iterative soft decoding algorithm for turbo codes, which alters the proportion of the extrinsic information and the received systematic...
A novel timing offset estimator for orthogonal frequency division multiplexing (OFDM) systems is proposed. The estimator is a modification to Schmidl method by a kind of new preamble. The performance of the estimator is presented in terms of mean and variance by simulation in multipath fading channel. The results show that the proposed estimator has smaller variance than Schmidl and Minn's estimators,...
To investigate the blind symbol rate estimation of any linear base-band digital modulation scheme with square root raised cosine filter, an algorithm based on cyclic correlation and Haar wavelet transform estimator is proposed. First we use FFT to estimate the bandwidth roughly. Then we set the sampling frequency and range scale of wavelet transform according to bandwidth. Using the signals filtered...
In this paper, an optimal signal-to-noise ratio (SNR) which is independent from correlation-interval and mobile speed is analyzed, which is on the basis of the channel auto-correlation Doppler shift estimation algorithm. And then an optimized SNR tracking (OSNRT) algorithm on the basis of Rake receiver under multi-path fading channel is proposed. The improved algorithm calculated Doppler shift by...
Channel estimation and data detection are investigated for OFDM systems over time- and frequency-selective (doubly selective) channels. Relying on the complex exponential basis expansion channel model, a pilot embedded channel estimation scheme with low computational complexity and high data rate efficiency is proposed. An iterative edition exploiting recovered data to enhance the performance is also...
In orthogonal frequency division multiplexing (OFDM) systems, channel power delay profile can be acquired by an IFFT of pilot-aided channel estimate which is used for fine timing. However, an ambiguous channel impulse response (CIR) estimate is induced by coarse timing errors. In this paper, a simple CIR adjustment algorithm is proposed to correct the CIR order which can hold with large coarse timing...
As is well known, the robust and reliable acoustic communication in adverse littoral water is a very challenging task. Orthogonal frequency division multiplexing (OFDM) is a promising technique for achieving high speed rate and combating multi-path fading in underwater acoustic communication. In this paper, the basic principle of OFDM system is firstly introduced. Then a channel estimation method...
This paper provides three channel estimations including LS (least square) estimation, LMMSE (linear minimum mean square error) estimation and Lr-MMSE (low rank minimum mean square error) estimation utilized to the relay channel to approximate the optimal solution in OFDM system. The simulation results show that LMMSE estimation outperforms the other two estimations, but it is too complicated. The...
In this paper, an improved expectation-maximum (IEM) frequency estimation algorithm is discussed, in which the unknown data symbols and the known pilot symbols are exploited jointly in a recursive way. Compared with the data-aided ML estimation, the IEM algorithm can improve the performance without increasing the number of pilot symbols, and is superior in performance to the non-data aided blind estimator...
This paper reports on investigations into the effects of spatial correlation on channel estimation and capacity of a multiple input multiple output (MIMO) system. Minimum mean square error (MMSE) method is applied for channel estimation under a correlated channel scenario. Simulation results for a 4 times 4 MIMO system with the Jakes model describing a channel between a base station and a mobile station...
This paper analysis the performance of the ad-hoc network with a base station, a mobile and a third station acting as a relay. Three combining methods for the Amplify-and-Forward (AF) protocol and the Decode-and-Forward (DF) protocol are compared. Simulations indicate that the Amplify- and-Forward (AF) protocol beats the Decode-and-Forward (DF) protocol under all these three combining methods. To...
A new algorithm based on pilots for the joint carrier frequency offset (CFO) and channel estimation of the uplink of MC-DS-CDMA systems is presented. As with the specially designed pilots, the inter-user interference (IUI) among user specific sub-matrix of received signal matrix in time domain does not exist any more, CFO and channel estimations are easily obtained for all users with single user CFO...
High peak-to-average power ratio (PAPR) is a disadvantage of comb-type frequency-domain training pattern (FDTP) in MIMO OFDM system. To deal with such problem, an excellent orthogonal time-domain training pattern (TDTP), based on circularly shifting Chu sequence and satisfying that optimal condition derived by us, is proposed for maximum likelihood (ML) channel estimation. From theory analysis and...
The detection of V-BLAST system always requires an optimal ordering procedure, and also it requires knowledge of the channel state information (CSI) while in practice accurate CSI may not be available. In this paper, we investigate the system with two transmit antennas to evaluate its performance, considering both the effects of channel estimation error and optimal ordering procedure. Based on the...
Doubly-selective channel estimator for orthogonal frequency division multiplexing (OFDM) systems is proposed in this paper. Based on the generalized complex exponential basis expansion model (GCE-BEM), we describe the time-variant channel with time-invariant coefficients over multiple OFDM blocks. The time variation of channel destroys the orthogonality between subcarriers. The resulting channel matrix...
The SC-FDE (single carrier-frequency domain equalizer) is a field that gathers more and more interest as a modulation scheme for the broadband wireless communications, for simple channel equalization, SC-FDE systems perform equalization in frequency domain instead of time-domain using FFT,IFFT and CP (cyclic prefix) like it user for example in OFDM (orthogonal frequency division multiplexing). In...
We examine the ergodic capacity of beamforming over a multiple-input single-output (MISO) time-selective channel with channel estimation error and delayed limited feedback. At each frame, the receiver obtains the minimum mean squared error estimation of the channel, chooses a transmit beamforming vector, according to the error channel estimation, from a codebook based on random vector quantization...
Real time Video transport over ad hoc network poses a great challenge due to the high variability of the network bandwidth. In this paper, to adjust rate in time according to the change of the quality of the channel of ad hoc network, we propose a scheme which judge the quality of the wireless channel proactively. The value of signal strength is used to be an important factor for judging the quality...
Because the high DFO (Doppler Frequency Offset) of aviation channel causes much ICI (Inter-Channel Interference) among subcarriers of AMBC (Aviation Mobile Broadband Communication) based on OFDM technology, which degrades the performance badly, a new method, ANTI-D (ANTI-Doppler by information aid), aiming at eliminating ICI and improving the performance, is presented with a view to the characteristics...
Multi-band orthogonal frequency division multiplexing (MB-OFDM) is a suitable solution to implementation of high speed data transmission in ultra wideband (UWB) spectrum by dividing the spectrum available into multiple bands. MB-OFDM system structure and transmitted signal is introduced in this paper. Channel models are fundamental to the study and design of communication systems. A survey on indoor...
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