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In this paper, we propose and analyze a multi-level acknowledgement scheme for hybrid ARQ (H-ARQ) systems, which modifies a general ACK/NAK signals to represent multilevel information. For instance, the other signals except the ACK/NAK signals may be used for scheduling of retransmission in H-ARQ scheme, which results in increasing the resolution of uplink channel estimation signals. Simulation results...
Evolutionary particle swarm algorithm is proposed for blindly identifying the communication channels. The channel coefficients vector candidates are evaluated by scoring positions of a swarm of particles flying through the multimodal problem space based on their values of the higher order cumulant cost function. The flying is constituted by the interaction of these particles and the alteration arrangement...
Sparse multi-path is encountered in OFDM and Ultra-wideBand (UWB) communications. Conventional channel estimation methods ignore the prior knowledge of the sparseness, and estimates have higher MSE. We introduced two approaches: Lp norm constraint method and LASSO method which are related to Bayesian model. The two approaches exploit the sparse a priori and obtain better performance.
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,...
NC-OFDM is OFDM-based spectrum pooling technique and also a transmission mode of cognitive radio. The paper models and analyzes NC-OFDM stochastic process, then designs stochastic comb-pilot pattern and analyzes its characteristics in detail. At the end of the paper simulation results prove the feasibilities of the stochastic comb-pilot strategies in NC-OFDM system.
It is shown in the paper that by employing a maximum ratio combining (MRC) pre-equalizer, the complexity of the receiver in an Interleave-Division Multiple-Access (IDMA) downlink is reduced, while similar or even slightly better performance is achieved, compared to that using Log Likelihood Ratio Combining (LLRC).
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...
The aeronautical wireless channel can be modeled as a sparse double-selective channel, which includes a strong line-of-sight (LOS) path and a weak reflected diffuse path Compared with the LOS path's, delay and Doppler shift of the reflected path are more difficult to be estimated, which are time-varying and non-stationary. With equalization using non-sufficient delay and Doppler shift estimation,...
Adaptive channel tracking algorithms are studied based on LMS and KALMAN in MIMO-OFDM system. A novel adaptive channel tracking algorithm, which combines the LMS and KALMAN filter to make use of the stabilization of LMS and the accuracy of KALMAN filter, is proposed. On the one side, the algorithm can track and estimate the channel with the optimal MSE, and on the other hand, the algorithm conquers...
Because noise subspace estimation for blind channel estimation can't achieve a good trade-off between convergence speed and steady-state error, and an ambiguous complex coefficient exists between estimated and actual channel impulse response. In this paper, we propose a blind channel estimation algorithm based on noise subspace estimation algorithm with adaptive variable step-size and ambiguous complex...
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...
Multiantenna wireless systems have been well studied in achieving high data rates. In this paper, we improve a subspace-based blind channel estimation technique for multi- input multi-output (MIMO) orthogonal frequency-division multiplexing (OFDM) approach based on tracking the subspace recursively. The recursive subspace algorithm has a computational complexity of O(J2) , where the J is the input...
This paper mainly focus on methods for obtaining the CIR by performing the IFFT of CFR, which are heuristic or direct to improve channel estimation and tracking in MIMO- OFDMA systems. When FUSC mode is used, pilot signal are uniformaly inserted into the carrier sets during preamble and the FFT size over pilots spacing is an integer in mobile WiMAX. Therefore, it is possible to obtain CPR based on...
In this paper, the downlink zero-forcing beamforming strategy under perfect channel state information at the transmitter (CSIT) for the case of random packet arrivals is investigated. Under this setting, the relevant fairness criterion is the stabilization of all buffer queues which guarantees a bounded average delay for all users. In case of queue stability is the goal, it can be shown that allocating...
Multiple-input multiple-output (MIMO) receive antenna selection without channel state information (CSI) for linear detection is proposed in the presence of unknown interferences. This antenna selection technique is implemented based on training sample sequence by minimizing the Least Squares (LS) estimation error, which avoids the channel estimation. Since the high complexity of the exhaustive search,...
This paper proposes a novel channel estimation for filtered multitone (FMT) systems which is called FPEA. It implements an estimation in frequency domain with pilot sequences in subchannels. The analysis then is given for estimation and anti-frequency-offset performance. Finally, simulation results of the performance achieved by FPEA are presented and compared with other algorithms.
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...
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