1,721,066 research outputs found
Noncoherent MLSE detection of M-DPSK for DS-CDMA wireless systems
No full textThis paper focuses on maximum-likelihood sequence estimation of noncoherent M-ary differential phase-shift keying (AT-DPSK) receivers for code division multiple-access (CDMA) systems, which make use of direct-sequence spread-spectrum modulations. A typical frequency-selective Rayleigh environment with multipath diversity at the receiver is considered. In this scenario, the optimum noncoherent decision metric, which requires an estimation of the channel tap weights envelope, is derived. Then, in order not to increase the receiver implementation complexity, a joint channel and data estimation strategy is proposed, which does not require the transmission of a known training sequence (blind estimation). In this case, the decision metric becomes a simple equal gain combining of multiple-symbol square-law detection decision metrics. For this suboptimum noncoherent detector, useful bounds on the bit error probability are provided through a theoretical analysis. Nonconstant and constant multipath intensity profiles are both considered for this purpose. Simulations are also carried out in order to verify the accuracy of the theoretical bounds
Performance bounds and codes design criteria for channel decoding with a-priori information
No full textIn this article we focus on the channel decoding problem in presence of a-priori information. In particular, assuming that the a-priori information reliability is not perfectly estimated at the receiver, we derive a novel analytical framework for evaluating the decoder's performance. It is derived the important result that a good code, i.e., a code which allows to fully exploit the potential benefit of a-priori information, must associate information sequences with high Hamming distances to codewords with low Hamming distances. Basing on the proposed analysis, we analyze the performance of random codes and turbo codes
Centralized Radio Resource Management Strategies with Heterogeneous Traffics in HAPS WCDMA Cellular Systems
No full textThis paper addresses the system throughput maximization problem for HAPS third generation cellular systems. We assume that the Stratospheric Platform is able to perform a perfect link gain estimation for all mobile terminals, such that a centralized resource allocation strategy is made possible. A classical 3G wireless scenario is considered, where traffics characterized by different bit rates coexist with Best Effort Traffic services without stringent bit rate constraints. In this scenario, we firstly envisage three Rate Assignment schemes for best effort terminals which aim at achieving the maximum system throughput subject to different bit rate constraints. For the second envisaged rate assignment scheme, which represents the hest compromise between service fairness and throughput, we then propose a simplified approach that allows to noticeably decrease the implementation complexity with a slight performance degradation
Non-Linear Equalization for Incoherent Radiomobile Channel
No full textThis paper presents the simulation study of a multiple-symbols differential demodulator for Gaussian Minimum Shift Keying (GMSK) which compensates for the heavy selective distortions caused by multipath propagation. The receiver includes a channel estimator operating in a training mode at the beginning of each burst, and a multiple-symbols differential processor which has been demonstrated in the literature to be optimum over non-coherent AWGN channels. The combination of channel estimation and differential demodulation makes the receiver robust to fast Doppler shifts and to wide time-spread. Simulation results are presented which show the performance in different multipath environments based on the recommendations established by the GSM system. Comparisons with a coherent receiver including a matched filter, an adaptive channel estimator and a Viterbi processor show that the detector proposed in this correspondence is quite attractive
Decoding with a-priori information: analysis and codes' design criteria
No full textAn analytical framework for evaluating the performance of decoding in presence of a-priori is provided. It is shown that a "good code", i.e., a code which allows to fully exploit the potential benefit of a-priori information, must be characterized by both a high minimum Hamming weight and a high minimum information weight. This is a completely novel result which may help the design of good channel codes in presence of apriori information. Basing on the proposed analysis, we derive a measure of the performance gain due to a-priori information that can be obtained by random codes with infinite length. It is then shown that turbo codes with very long interleavers approach the behavior of random codes. Finally, an effective joint source-channel decoding scheme is proposed in a wireless sensors network scenario where two nodes detect correlated sources and deliver them to a central collector
On the Analytical Evaluation of Closed-Loop Power Control Error Statistics in DS-CDMA Cellular Systems
No full textThis paper proposes an analytical study that aims at evaluating the power-control error statistics in wireless direct-sequence code-division multiple-access (DS-CDMA) cellular systems based on an ideal variable step closed-loop power-control scheme. In particular, the cumulative distribution function and the correlation coefficient of the power control error are derived through a first-order Taylor expansion of the received signal envelope. A novel power-control scheme that exploits the autocorrelation properties of the fading is also proposed, and its performance is analyzed in terms of power-control error statistics. Rayleigh and Rice frequency-selective channel models, which involve the use of a diversity RAKE receiver at the base station, have been taken into account. The proposed analytical approach specifically applies to CDMA systems. A method that aims at estimating the capacity of a DS-CDMA cellular network is given in the last part of this paper
A New Watermarking Scheme Based on Antipodal Binary Dirty Paper Coding
No full textWe investigate the performance of a watermarking system in which the encoder is forced to use a binning strategy based on antipodal binary-valued sequences. The use of antipodal binary random binning has several advantages, including the possibility of relying on simple and effective binary code constructions and the ease with which this kind of schemes can cope with amplitude scaling. By relying on a novel binning strategy, we derive a lower bound of the Gelfand-Pinsker capacity of the watermark channel when the encoder is forced to use an antipodal binary auxiliary random variable, showing that for low to moderate bit-rates, the bound coincides with Costa's capacity. We exploit the properties of the new binning strategy, to develop a practical watermarking system and show that the new scheme outperforms previous constructions, exhibiting very good performance also in the presence of gain attack. Preliminary results on audio signals show that the new scheme retains its good performance also when used for the watermarking of real multimedia data
Design of efficient convolutional and serially concatenated convolutional codes with a-priori information
No full textIn this paper, we focus on the design of optimized binary convolutional codes (CCs) and serially concatenated convolutional codes (SCCCs) in the presence of a-priori information (API) at the receiver. First, we propose a design criterion for CCs based on the minimization of the bit error proabability (BEP). In this case, relevant performance gains, with respect to previously proposed CCs, are obtained. These gains persist even in the presence of estimation errors on the API. Then, we apply the same BEP-based design criterion to SCCCs and derive good encoders' structures. In the SCCC case with API at the receiver, simulation results show substantial gains with respect to previously proposed parallel concatenated convolutional coding (PCCCing) schemes optimized under the assumption of no API at the decoder. Moreover, in the presence of strong API the proposed SCCCs allow to approach the Shannon limit (SL) more than any previously proposed turbo coding scheme
Outage Statistics in CDMA Mobile Radio Systems
No full textThe statistics of the outage events in the reverse link of a direct sequence code-division multiple access (DS/CDMA) wireless system are investigated taking into account the effects of correlated Rician fading. The outage probability and the average fade are derived by assuming a constant multipath intensity profile, which includes a direct-path component in the first-path. Simulations have been carried out which validate the analytical results
Embedded Java in a web-based teleradiology system
No full textMedinet is a Web-based solution for teleradiology currently undergoing clinical evaluation as port of the European Union's advanced communications technologies and services program. The system uses embedded Java applets to permit remote access to radiologic data and diagnostic services
- …
