619,180 research outputs found
Performance Evaluation of Distributed-Antenna Communications Systems Using Beam-Hopping
No full textDigital beamforming (DBF) techniques are capable of improving the performance of communications systems significantly. However, if the transmitted signals are conflicted with strong interference, especially, in the direction of the transmitted beams , these directional jamming signals will severely degrade the system performance. In order to efficiently mitigate the interference of the directional jammers, in this contribution a beam-hopping (BH) communications scheme is proposed. In the proposed BH communications scheme, only one pair of the beams is used for transmission and it hops from one to the next according to an assigned BH pattern. In this contribution a range of expressions in terms of the average SINR performance have been derived, when both the uplink and downlink are considered. The average SINR performance of the proposed BH scheme and that of the conventional single-beam (SB) as well as multiple-beam (MB) assisted beam-processing schemes have been investigated. Our analysis and results show that the proposed BH scheme is capable of efficiently combating the directional jamming, with the aid of utilizing the directional gain of the beams generated by both the transmitter and the receiver. Furthermore, the BH scheme is capable of reducing the intercept probability of the communications. Therefore, the proposed BH scheme is suitable for communications, when several distributed antenna arrays are available around a mobile
Iterative channel equalization, channel decoding and source decoding
No full textThe performance of soft source decoding is evaluated over dispersive AWGN channels. By employing source codes having error-correcting capabilities, such as Reversible Variable-Length Codes (RVLCs) and Variable-Length Error-Correcting (VLEC) codes, the softin/soft-out (SISO) source decoder benefits from exchanging information with the MAP equalizer, and effectively eliminates the inter-symbol interference (ISI) after a few iterations. It was also found that the soft source decoder is capable of significantly improving the attainable performance of the turbo receiver provided that channel equalization, channel decoding and source decoding are carried out jointly and iteratively. At SER = 10-4, the performance of this three-component turbo receiver is about 2 dB better in comparison to the benchmark scheme carrying out channel equalization and channel decoding jointly, but source decoding separately. At this SER value, the performance of the proposed scheme is about 1 dB worse than that of the ½-rate convolutional coded non-dispersive AWGN channel.<br/
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Multinuclear Cd-2, Cd-3 and 1-D Framework Structures of Cd(II) Schiff Base Complexes
Full text linkReactions of the "salen" type Schiff bases H2L1 and H2L2 with Cd(OAc)(2)center dot 2H(2)O gave complexes with Cd-2 and Cd-3 cores and an extended 1-D framework architecture [H2L1 = N,N'-(1,2-phenylenyl)bis(5-bromo-2-hydroxy-3-methoxybenzaldimine; H2L2 = N,N'-(propyl)-bis(5-bromo-2-hydroxy-3-methoxybenzaldimine)].Agapiou, Kyriacos, Michelle L. Mejía, Xiaoping Yang, and Bradley J. Holliday. "Multinuclear Cd 2, Cd 3 and 1-D framework structures of Cd (II) Schiff base complexes." Dalton Transactions 21 (Apr., 2009): 4154-4159.Chemistr
Assessing Ageing Condition of Mineral Oil-Paper Insulation by Polarization/Depolarization Current
No full textAccurately assessing the ageing status of oil-paper insulation in transformer is essential and important. Polarization and Depolarization Current (PDC) technique is effective in assessing the condition of oil-paper insulation system. Though the PDC behaviour of mineral oil-paper insulation has been widely investigated, there is no report about how to make the quantitative analysis of mineral oil-paper insulation ageing condition by PDC. The PDC characteristics of mineral oil-paper insulation samples were investigated over the ageing period at 110°C. A new method for assessing the ageing condition of mineral oil-paper insulation by calculating the depolarization charge quantity was proposed. Results show that the depolarization charge quantity of mineral oil-paper insulation sample is very sensitive to its ageing condition. The stable depolarization charge quantity could be used to predict the ageing condition of mineral oil-paper insulation
Downlink Space–Time Spreading Using Interference Rejection Codes
No full textIn this paper, the authors will investigate the performance of a loosely synchronized (LS) code-based space–time spreading (STS) scheme in comparison to that of classic Walsh code and pseudonoise code-based STS when communicating over dispersive Nakagami-m multipath channels. Closed-form formulas are derived for characterizing the bit-error-rate performance as a function of the number of resolvable paths L and the number of users K. Our numerical results suggest that the employment of LS code-based STS scheme is beneficial in a low-user-load and low-dispersion channel scenario, where a near-single-user performance can be achieved without a multiuser detector. Index Terms—Code-division multiple access (CDMA), Gaussian approximation, interference-free window (IFW), large area synchronized (LAS) codes, loosely synchronized (LS) codes, Nakagami-m fading
Joint Iterative Decoding of Trellis-Based VQ and TCM
No full textA joint video and channel coded system employing an iteratively decoded serial concatenation of a Vector Quantization (VQ) based video codec and a Trellis-Coded Modulation (TCM) scheme is proposed. The video codec imposes VQ-induced code constraints, which may be completely described by a trellis structure, which is employed as the basis for optimal minimum mean-squared-error VQ-encoding and -decoding. In the latter case, the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm is employed to facilitate the iterative exchange of soft information between the VQ and TCM decoder. An error-free video reconstruction quality is supported using 16-level Quadrature Amplitude Modulation (16QAM) based TCM for transmission over Rayleigh-fading channels at a Signal-to-Noise Ratio (SNR) per bit of 5.25 dB. This value is within 1.29 dB of the Rayleigh channel’s capacity at our system’s effective bandwidth-efficiency of 2 bits/s/Hz. Owing to its ability to exploit the VQ-induced code constraints during iterative decoding, the joint video and channel coding approach is found to consistently outperform the Shannonian source and channel separation philosophy. This is achieved at the cost of a 1.6 times higher computational complexity. Finally, the convergence of the iterative decoder is investigated with the aid of a novel so-called EXtrinsic Information Transfer (EXIT) chart
[Letter from Arthur S. Rosichan to J. L. Zuber - August 11, 1944]
No full textLetter from Arthur S. Rosichan to J. L. Zuber: August 11, 1944. Subject of the letter is the author moving to Houston to work for the Jewish Community Council
Intersystem soft handover for converged DVB-H and UMTS networks
Full text linkDigital video broadcasting for handhelds (DVB-H) is the standard for broadcasting Internet Protocol (IP) data services to mobile portable devices. To provide interactive services for DVB-H, the Universal Mobile Telecommunications System (UMTS) can be used as a terrestrial interaction channel for the unidirectional DVB-H network. The converged DVB-H and UMTS network can be used to address the congestion problems due to the limited multimedia channel accesses of the UMTS network. In the converged network, intersystem soft handover between DVB-H and UMTS is needed for an optimum radio resource allocation, which reduces network operation cost while providing the required quality of service. This paper deals with the intersystem soft handover between DVB-H and UMTS in such a converged network. The converged network structure is presented. A novel soft handover scheme is proposed and evaluated. After considering the network operation cost, the performance tradeoff between the network quality of service and the network operation cost for the intersystem soft handover in the converged network is modeled using a stochastic tree and analyzed using a numerical simulation. The results show that the proposed algorithm is feasible and has the potential to be used for implementation in the real environment
Evidence for the decay B0→J/ψω and measurement of the relative branching fractions of meson decays to J/ψη and J/ψη′
Full text linkFirst evidence of the B 0 → J / ψ ω decay is found and the B s 0 → J / ψ η and B s 0 → J / ψ η ′ decays are studied using a dataset corresponding to an integrated luminosity of 1.0 fb -1 collected by the LHCb experiment in proton-proton collisions at a centre-of-mass energy of sqrt(s) = 7 TeV. The branching fractions of these decays are measured relative to that of the B 0 → J / ψ ρ 0 decay:frac(B (B 0 → J / ψ ω), B (B 0 → J / ψ ρ 0)) = 0.89 ± 0.19 (stat) - 0.13 + 0.07 (syst),frac(B (B s 0 → J / ψ η), B (B 0 → J / ψ ρ 0)) = 14.0 ± 1.2 (stat) - 1.5 + 1.1 (syst) - 1.0 + 1.1 (frac(f d, f s)),frac(B (B s 0 → J / ψ η ′), B (B 0 → J / ψ ρ 0)) = 12.7 ± 1.1 (stat) - 1.3 + 0.5 (syst) - 0.9 + 1.0 (frac(f d, f s)), where the last uncertainty is due to the knowledge of f d / f s, the ratio of b-quark hadronization factors that accounts for the different production rate of B 0 and B s 0 mesons. The ratio of the branching fractions of B s 0 → J / ψ η ′ and B s 0 → J / ψ η decays is measured to befrac(B (B s 0 → J / ψ η ′), B (B s 0 → J / ψ η)) = 0.90 ± 0.09 (stat) - 0.02 + 0.06 (syst)
An Iterative Detection Aided Irregular Convolutional Coded Wavelet Videophone Scheme Using Reversible Variable-Length Codes and Map Equalization
No full textIn this paper, we characterize the achievable performance of a wavelet encoding-based videophone system, which further compresses and protects the wavelet-based video codec's bit-stream with the aid of Reversible Variable-Length (RVLC) codes. More specifically, the video codec uses RVLC codes for compressing and protecting the video frame header. By constrast, Irregular Convolutional Codes (IRCCs) are used for Unequal Error Protection of the video bitstream generated from the wavelet-subbands, when communicating over InterSymbol Interference (ISI) contaminated channels. At the receiver, the turbo-equalizer, the IRCC decoder and the RVLC decoder all employ the Maximum APosteriori (MAP) algorithm and their operations are performed in an iterative turbo-detection style. The proposed system was designed for maintaining a near-unimpaired video reconstruction quality for channel Signal-to-Noise Ratios (SNR) in excess of about 5dB, when communicating over a five-path dispersive AWGN channel
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