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

Abstract

Abstract-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.Index Terms-Channel estimation, priority transmission, unequal error protection, leakage effect, wireless multimedia transmission.

Two novel noise estimation methods with low complexity for the OFDM system

“…System parameters of the OFDM system are related to the 3GPP LTE system and arranged in TA BLE I [5]. Pilot symbols are inserted into the OFDM frame for channel and noise estimation [6]- [8]. For the sake of the tradeoff between estimation accuracy and complexity, pilot symbols need not be inserted into all subcarriers of the OFDM symbol.…”

A Channel Estimation Technique for Hierarchical DVB-T System to Extract High-Priority Stream

“…Here, N is the total number of subcarriers, n is the index of subcarrier, and k is the index of OFDM symbols. The channel noise samples { w[n, k] } are modeled as Gaussian random variables with zero mean and variance &2 and are assumed to be independent for different n 's or k 's [3].…”

“…In Rayleigh fading, the sequence { YJ (t) } is modeled as zero-mean circular symmetric complex Gaussian random variable with variance a, and is assumed to be independent for different paths [3]. The channel frequency response at the OFDM subcarriers locations can be approximated by the samples of continuous channel frequency response [3], that is H [n, k] h(t, r)e-j2 fr dr f=nAf,t=kTf E yi(kT )e -j2zmAfri (4) i Where Tf is the length of an OFDM symbol, Af =Bd /N is the frequency space between two consequence subcarrier, and…”

Unequal error protection for OFDM systems in time-varying channels

“…The rationale of UEP is to provide variant resource allocation procedure corresponding to variant importance degree of information content. In [4], [5] multimedia data are rearranged to subchannels according to the feedback information of channel estimation from the receivers. Houas et al [6] assigned multimedia data of high error sensitive degree to the best subcarriers by further joint considerations in optimizing the source rate and symbol payload.…”