1-persistent carrier sense multiple access in radio channels withimperfect carrier sensing

A comprehensive analysis of a 1-persistent carrier-sense multi-access (CSMA) system using a radio channel with imperfect carrier sensing is presented and discussed. It is shown that a careful optimization of the channel state detector parameters must be performed in order to get good system performance. If the threshold of the detector is too high, the system will tend to behave like an unslotted ALOHA; if the threshold is too low, the system throughput will be zero. It is also shown that for the larger average packet rate G the system throughput is decreased. This is because for the same probability of correct channel sensing, the probability of incorrect transmissions from the waiting mode is increased     

Formability of a high-strength Al–Mg6.8 type alloy sheet

Room temperature formability testing was performed on an AlMg6.8 type alloy sheet with a fully recrystallized structure (average grain diameter 18 m) and after partial annealing with a retained deformed structure. The yield strengths attained after full recrystallization and after partial annealing, were 175 and 283 MPa respectively. Such an increase in strength is followed by formability degradation, maximized around the plain strain state to either 42%, as obtained using the limiting dome height test (LDH), or 35% after using forming limit curves (FLC). A comparison with known high-strength formable alloys has shown that the tested alloy in the recrystallized condition has a better stretch formability (at the same or even higher yield stress level), while in the unrecrystallized-partially annealed condition it has a lower formability, limiting its application to moderate forming requirements for very high-strength parts. © 1998 Chapman & Hall     

Inulin-based emulsion-filled gel as a fat replacer in prebiotic- and PUFA-enriched dry fermented sausages

In order to produce fermented sausages with prebiotic fibre and improved fatty acid composition, 16% of pork back fat was replaced with inulin gelled suspension (I) and inulin linseed oil gelled emulsion (IO). Physico-chemical analysis, fatty acid profiles, lipid oxidation, microbiological, textural, colour and sensory analysis were carried out. The fat content was lower in I (31.38%) and IO (35.36%) modified sausages compared to control (44.37%) (P < 0.05). IO sausages had lower SFA and MUFA and higher PUFA content with an improved n-6/n-3 ratio (2.23) (P < 0.05) and α-linolenic acid increment (5.74 g per 100 g). Reformulation led to decrease in springiness, chewiness and hardness and increase in adhesiveness of the sausages. Modified sausages had lower L* and higher a* values, while b* values of I sausages did not differ compared to control sausages. Modified sausages were acceptable regarding all sensory attributes. Lipid oxidation parameters showed higher susceptibility to oxidation and lipolysis in IO sausages.     

Wideband CDMA network sensitivity function

We analyze capacity losses in code division multiple access (CDMA) networks due to imperfections in the operation of the system components. The main result of this work is a systematic mathematical framework for capacity evaluation of CDMA-based networks in fading channels. This should be considered as an alternative tool to extensive simulations being used for these purposes at the moment. The intention is to provide simple approximate relations that simultaneously take into account: multiple access intracell interference (MAI), intercell interference, and near-far effect, including different sources of power control imperfections. In addition to this, the efficiencies of the major receiver components are also included in the analysis. A flexible complex signal format is used which enables us to model at currently interesting proposals for wideband CDMA (W-CDMA) standards. The theory is general, and some examples of practical set of channel and system parameters are used as illustration. Further elaboration of these results, including extensive numerical analysis based on the offered analytical framework, would provide enough background for the understanding of W-CDMA system performance in a realistic environment     

Adaptive self-reconfigurable interference suppression schemes forCDMA

In this paper we present a new approach to interference suppression in code-division multiple-access (CDMA) wireless networks. Depending on the interfering signal, these schemes adaptively change not only their parameters but their structures as well. For the relevant types of the interfering signal, suppression is also possible for the wideband interference occupying the same frequency band as the CDMA signal. Probability of error in these schemes is for several orders of magnitude better than in the existing solutions described in the open literature so far. The main applications are the CDMA overlay type wireless network collocated in the same frequency band with a high bit rate microwave communication system, and the multimedia CDMA network where high bit rate signal due to lower processing gain must use a higher level in order to provide the required quality of transmission     

Modeling of the code acquisition process for RAKE receivers in CDMAwireless networks with multipath and transmitter diversity

We present models for the code acquisition process in RAKE receivers. These models include multipath diversity, multiple transmitter (base station or satellite) diversity, and multiple access interference generated by other users in the network. This results in a different probability of false alarm for each cell of the code delay uncertainty region. The analysis is based on signal flow graph theory. By using these models, we elaborate different strategies for RAKE receiver synchronization and derive exact closed-form results for the average acquisition time. These strategies differ in how they organize initial (first RAKE finger) and postinitial search algorithms. If the channel is known, the initial synchronization may organize a parallel search for all fingers simultaneously by a proper set up of the local correlators' mutual delays. If not, then a serial search of different segments (partitioned among the different fingers) can be organized. In the postinitial search, sequential or random initializations are possible. A set of approximations is also included for practical applications where a quick assessment of the system performance is needed     

Symbol synchronization in digital communication systems usingpartial response CPM signaling

The applicability of standard symbol synchronization schemes in digital communication systems using partial-response CPM (continuous phase modulation) signaling has been analyzed. Using the theory of maximum a posteriori estimation of the unknown parameter in Gaussian noise, a theoretical structure for the optimum symbol synchronizer in a system using partial-response CPM signaling is derived. As the first approximation, a closed-loop configuration, known as the early-late loop, is derived and discussed. Due to signal correlation in adjacent symbol time intervals, even this configuration is impractical for a hardware realization. For these reasons, different approximations of the general maximum-likelihood function, leading to the discrete bit timing loop realizations, are derived and discussed. The influence of the carrier phase synchronization error on these synchronizers is also discussed     

Extraction of sage (Salvia officinalis L.) by supercritical CO2: Kinetic data, chemical composition and selectivity of diterpenes

The supercritical carbon dioxide (SFE) extraction of Dalmatian sage (Salvia officinalis L.) was investigated and compared to extraction performed by Soxhlet ethanol-water (70:30) mixture extraction (SE) and hydrodistillation (HD). The supercritical extraction allowed isolation of wide spectrum of phytochemicals, while other applied methods were limited to either volatiles (HD) or high molecular compounds isolation (SE). The kinetics of the supercritical extraction and fractionation within the pressure range of 10-30 MPa at 50 °C were also analyzed as well as the chemical compositions of total extract and partial or differential fractions isolated at different CO₂ consumption. Volatile fraction could be isolated at low pressure and low CO₂ consumption, whereby the pressures between 10 and 15 MPa followed by increased CO₂ consumption were favourable for obtaining desired selectivity of diterpenes which contain compounds with expressed antioxidative characteristics.