Fixed collision rate back-off scheme for collision resolution in wireless networks

This investigation proposes a fixed collision rate (FCR) back-off algorithm for wireless networks. The proposed scheme takes advantage of the central unit (CU) in a wireless network to broadcast a common back-off window size to all the users, significantly alleviating the unfairness of bandwidth utilization in conventional binary exponential back-off (BEB) algorithms. It is shown that, when maximum throughput is achieved, collision rate is almost a constant for any traffic load. In the operation of the FCR, the CU dynamically adjusts the back-off window size to keep the collision rate at a constant level for maximum throughput. Simulation results demonstrate that the unfairness of bandwidth utilization in the BEB is significantly lessened and the throughput can be maintained at e^-1≈0.368 when the number of users approaches infinity. The capture effect even further improves system performance.     

On the Power Allocation and System Capacity of OFDM Systems Using Superimposed Training Schemes

Channel estimation in multipath environments is typically performed using the pilot-symbol-assisted modulation (PSAM) scheme. However, the traditional PSAM scheme requires the use of dedicated pilot subcarriers and therefore leads to a reduction in the bandwidth utilization. Accordingly, this paper investigates a channel-estimation approach for orthogonal frequency-division multiplexing (OFDM) systems using a superimposed training (ST) scheme, in which the pilot symbols are superimposed onto the data streams prior to transmission. By using equally spaced pilot symbols of equal power and assuming that the number of pilots is larger than the channel order, it is shown that the channel-estimation performance is independent of the number of pilots used. The optimal ratio of the pilot symbol power to the total transmission power is analyzed to maximize the lower bound of the channel capacity. Overall, the current results show that the ST-based channel estimation schemes have a slightly poorer performance than the PSAM scheme but yield higher system capacity.     

Immobilization of <Emphasis Type="Italic">Escherichia coli</Emphasis> novablue γ-glutamyltranspeptidase in Ca-alginate-<Emphasis Type="Italic">k</Emphasis>-carrageenan beads

The recombinant Escherichia coli gamma-glutamyltranspeptidase (EcGGT) was immobilized in Ca-alginate-kappa-carrageenan beads. Effects of alginate concentration, amount of loading enzyme, and bead size on the entrapped activity were investigated. Optimum alginate concentration for EcGGT immobilization was found to be 2% (w/v). Using a loading enzyme concentration of 1.5 mg/g alginate, maximum enzyme activity was observed. With increase in bead size from 1.9 to 3.1 mm, the immobilization efficiency was decreased significantly because of mass transfer resistance. Thermal stability of the free EcGGT was increased as a result of the immobilization. Ca-alginate-kappa-carrageenan-EcGGT beads were suitable for up to six repeated uses, losing only 45% of their initial activity. Upon 30 days of storage the preserved activity of free and immobilized enzyme were found as 4% and 68%, respectively. The synthesis of L: -theanine was performed in 50 mM Tris-HCl buffer (pH 10) containing 25 mM L: -glutamine, 40 mM ethylamine, and 1.5 mg EcGGT/g alginate at 40 degrees C for 12 h, and a conversion rate of 27% was achieved.     

Efficient RC low-power bus encoding methods for crosstalk reduction

In on-chip buses, the RC crosstalk effect leads to serious problems, such as wire propagation delay and dynamic power dissipation. This paper presents two efficient bus-coding methods. The proposed methods simultaneously reduce more dynamic power dissipation and wire propagation delay than existing bus encoding methods. Our methods also reduce more total power consumption than other encoding methods. Simulation results show that the proposed method I reduces coupling activity by 26.7-38.2% and switching activity by 3.7%-7% on 8-bit to 32-bit data buses, respectively. The proposed method II reduces coupling activity by 27.5-39.1% and switching activity by 5.3-9% on 8-bit to 32-bit data buses, respectively. Both the proposed methods reduce dynamic power by 23.9-35.3% on 8-bit to 32-bit data buses and total propagation delay by up to 30.7-44.6% on 32-bit data buses, and eliminate the Type-4 coupling. Our methods also reduce total power consumption by 23.6-33.9%, 23.9-34.3%, and 24.1-34.6% on 8-bit to 32-bit data buses with the 0.18, 0.13, and 0.09 μm technologies, respectively.     

Super-Imposed Training Scheme for Timing and Frequency Synchronization in OFDM Systems

In this paper, a super-imposed scheme for timing and frequency synchronization is proposed for orthogonal frequency division multiplexing (OFDM) systems. The proposed architecture includes a pre-defined pseudo-noise (PN) sequence, which is added to both the OFDM symbol and the cyclic prefix (CP) in time domain. In contrast to existing synchronization schemes, the proposed architecture has the advantage of better bandwidth utilization since it does not require extra pilot symbols. The peak-to-average power ratio (PAPR) is also significantly decreased. Both the timing and frequency offset estimators are derived using the maximum likelihood (ML) criterion. Efficiencies of the estimators are analyzed mathematically in AWGN channels. Simulation experiments are also conducted in frequency selective fading channels. Moreover, the optimal power allocation factor of the PN sequence is determined by minimizing the bit error rate using simulation experiments     

Macrodiversity technique for improvement in BER in wireless systems

The authors analyse a novel macrodiversity scheme, the multiply-detected macrodiversity (MDM) scheme, which relies on post-detection combining, as opposed to the traditional macrodiversity techniques, which are selection-based. The average fraction of the cell area is evaluated with an improved bit error rate (BER) performance, average BER improvement, and improvement in the average outage probability, relative to three other selection-based macrodiversity schemes. As a point of reference, the average improvement in BER is always at least one order of magnitude throughout at least 25%, of the cell area, when the probability of the co-channel interferer's presence is not >70%     

The multiply-detected macrodiversity scheme for wireless cellularsystems

The multiply-detected macrodiversity (MDM) scheme is proposed for wireless cellular systems. As opposed to the traditional macrodiversity schemes, in which at any time a signal from only one base station is selected, in the MDM scheme there is no selection, but all the received signals are detected, and a maximum-likelihood decision algorithm is employed to maximize the probability of correct decision. We study the performance of the MDM scheme and compare it with the performance of the traditional selection-based macrodiversity schemes. Depending on the propagation parameters, our results show that through the use of the MDM scheme, significant improvement in the bit-error rate (BER) can be achieved. For instance, if the outage probability is defined as BER above 10^-4 the outage is eliminated at least 45% of the time as compared with signal-to-interference (S/I) diversity, for a propagation attenuation exponent of 4.0 and shadowing standard deviation of 4.0 dB. Furthermore, as compared with the (S/I) diversity, the MDM scheme reduces, on the average, the BER at least two orders of magnitude throughout more than 60% of the cell area for a propagation attenuation exponent of 3.5, shadowing standard deviation of 4.0 dB and system loading of less than 50%     

Electrophoretic deposition of mesoporous TiO2 nanoparticles consisting of primary anatase nanocrystallites on a plastic substrate for flexible dye-sensitized solar cells

A film of mesoporous TiO(2) nanoparticles (MTNs) consisting of anatase nanocrystallites was electrophoretically deposited and compressed on a plastic substrate for the corresponding DSSC that gave an excellent conversion efficiency (η) of 5.25% under illumination of 100 mW cm(-2).     

Prediction of NMR order parameters in proteins using weighted protein contact-number model

In the NMR experiment, the protein backbone motion can be described by the N–H order parameters. Though protein dynamics is determined by a complex network of atomic interactions, we show that the order parameter of residues can be determined using a very simple method, the weighted protein contact number model. We computed for each Cα atom the number of neighboring Cα atoms weighted by the inverse distance squared between them. We show that the weighted contact number of each residue is directly related to its order parameter. Despite the simplicity of this model, it performs better than the other method. Since we can compute the order parameters directly from the topological properties (such as protein contact number) of protein structures, our study underscores a very direct link between protein topological structure and its dynamics.