Optimum Combining Research Articles

Adaptive radial basis function diversity combiner for multipath channels

The Letter demonstrates the advantages of applying nonlinear signal processing to the problem of spatial diversity combining in digital communication channels suffering from severe intersymbol interference (ISI) due to multipath propagation. It is shown that a radial basis function (RBF) network can outperform an optimum linear combiner by approximating a Bayesian classification operation. Such a network can rapidly adapt to an unknown channel using a simple adaptive algorithm.

Postdetection optimal diversity combiner for DPSK differential detection

Postdetection diversity reception weights and combines all the detector outputs before symbol decision to combat the effects of multipath fading. A theoretical analysis of a postdetection optimal diversity combiner that can minimize the symbol error probability for differential phase shift keying (DPSK) differential detection in the presence of multiplicative Rayleigh fading, and co-channel interference (CCI) is presented. The effect of unequal average powers among diversity branches is taken into account. It is shown that the postdetection maximal-ratio combiner (MRC) described previously by the author is not optimal unless all branches have the same average power. It is also found that the combiner optimized for the effect of CCI (fading induced random FM noise) should weight each branch detector output in inverse proportion to the average CCI power (desired signal power). Assuming two-branch diversity, calculated BER (bit-error-rate) performance of pi /4-shift QDPSK due to AWGN, CCI, and random FM is presented. In addition, the BER due to multipath channel delay spread (which is not treated in the theoretical analysis) is also computed to find the optimal combiner.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Compound strategies of coding, equalization, and space diversity for wide-band TDMA indoor wireless channels

Compound strategies of equalization and space diversity in the form of an optimum baseband combiner are attractive for wideband time division multiple access (TDMA) portable communication radio links in order to combat dispersive fading and cochannel interference. The authors investigate the performance of such a scheme in conjunction with convolutional coding and soft-decision Viterbi decoding via a semianalytical technique based on the method of moments. Such an approach avoids a Gaussian characterization of interference and yields results for both ideal interleaving and no interleaving. With dual space diversity, three taps per forward filter, and a data rate of 10 Mb/s, it is shown that, although a third space diversity branch remains preferable in terms of performance, channel coding can be a viable alternative, particularly in terms of outage rate, to increasing the space diversity order, even in the absence of interleaving, provided the signal-to-interference ratio is sufficiently high. >

Optimal partial decision combining in diversity systems

The optimal partial decision combiner is derived, and its performance is analyzed and compared to majority voting and selection diversity using binary noncoherent frequency-shift keying on a Rayleigh-faded additive white Gaussian noise channel. The degradation in the probability of bit error is evaluated when the channel state estimate is imperfect due to parameter quantization, AWGN, and cochannel interference. It is demonstrated that the optimal partial decision combiner can provide a simple means for improving performance on channels with limited cochannel interference.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Impact of Forecast Uncertainty on Feeder-Cable Sizing

This paper estimates the forecast error distribution for outside plant using data from the central office forecast measurement plan. We then determine the impact of the forecast errors on feeder-cable sizing by using this distribution to estimate the conditional distribution of engineered cable size with respect to optimum cable size. The marginal distribution of optimum cable size is estimated from a growth rate distribution which in turn is estimated from cable shipment data. We then use the resulting joint distribution to weight the percentage cost penalty of each possible combination of optimum and forecast size. The impact analysis is done separately for each gauge. By weighting by the million conductor feet of each gauge shipped, we then obtain an estimate of overall sizing-error cost penalty. The resulting penalty estimate is about 0.5 percent of the annual feeder-cable-construction program.

Intracellular distribution of α-galactosidase in leaves of Cucurbita pepo

The intracellular distribution of α-galactosidase in leaves of Cucurbita pepo was studied at different developmental stages using tissue strips, homogenates, and isolated protoplasts. About 85% of the total activity was found in the 500 g supernatant after tissues were homogenized either in water, in buffer at pH 5.6 or at pH 7.0, or in buffer containing 0.8 M KCl. Isolated protoplasts contained less than 10% of the total activity which was confined to the 20 000 g supernatant after lysis. p-Nitrophenyl-α-D-galactoside was readily hydrolysed when incubated with leaf strips but less than 3% of α-galactosidase could be leached from strips held for 4 h in 100 mM phosophate buffer or in buffer containing either 0.8 M KCl, 1 mM EDTA, or 1 mM dithioerythritol. It is concluded that at all stages of leaf development a high proportion of α-galactosidase is located in the exocellular region, not strongly bound either to the outer surface of the plasmalemma or to the cell wall but prevented from diffusing through the wall matrix by some physical attribute such as molecular size. Enzyme release occurred only following breakage or enzymatic digestion of the wall. The in vivo properties of the exocellular enzyme in leaf strips were compared with those of three molecular forms of α-galactosidase (LI, LII, and LIII) which were partially purified from mature leaves. The exocellular enzyme was active over a broad pH range with optima at pH 3.0 and pH 6.0; this resembles a combination of pH optima for LI and LIII. Inhibition by Cu2+ and p-chloromercuribenzoate resembled that for LIII and LII, respectively. Galactose and galactinol at a 5 mM concentration were 25–30% inhibitory for all enzyme preparations; melibiose, raffinose, and stachyose were very weakly inhibitory. The function of an exocellular α-galactosidase and its bearing on the transport of galactosylsucrose oligosaccharides to and from the minor veins of C. pepo are discussed.

Investigation of the diagonal-flow turbines of the Zeya hydroelectric station under low heads

1. The optimal combiner relationships of the diagonal-flow turbines in the Zeya hydrostation differ considerably from those calculated. Realization of the optimal combiner relationship for a turbine head of 46 m makes it possible to increase the efficiency of the unit by about 8% at loads close to the maximum for this head. 2. The maximum capacity of the unit under low heads is limited by the limiting opening of the guide apparatus with a considerable margin with respect to the runner-blade angle. 3. At heads close to the start-up head the maximum output of the turbine is slightly below the output on the line of limitation of the factory operating characteristic. 4. The operation of the turbine in nonoptimal regimes is accompanied by a considerable increase of pressure fluctuations under the runner and vertical vibrations of the supporting elements of the unit. Therefore a careful adjustment of the optimal combiner relationship is necessary. 5. The maximum output of the turbine at heads greater than 50 m exceeds the value on its line of limitation on the factory operating characteristic. 6. The diagonal-flow turbines made a good showing with respect to vibrations during operation at reduced heads; there is no need to introduce operating regime limitations. 7. The diagonal-flow turbines of the Zeya hydrostation have good cavitation properties, thanks to which there is little need to protect them from cavitation.

Parametric Linear Programming: Some Extensions*

AbstractThis paper considers a special version of the general problem of imputing regions in the space of parameters to optimal solutions and/or to optimal values Z* of the problem: Optimize the scalar-valued function subject to the constraints Inthe special version, the constraints are linear arid the objective function is i.e., a “mixture” of linear objective functions with undetermined “weights” λi. It is shown that the set of values of λi which allow finite optima, as well as those subsets of it for which basic feasible solutions are also optimal feasible, are convex polyhedra. The set of finite optima associated with each feasible basis is convex. Even when the values of some of the parameters are held fixed, the set of those values of the others whichmaintain a given optimum is a convex polyhedron. Furthermore, a convex combination of basic feasible solutions produces the same combination of optima only for those (vectors of) parameter values which are common to the polyhedra in the parameter space....

Plurality-Count Diversity Combining for Fading M-ary Transmissions

The performance of a plurality-count diversity combiner for fading M -ary transmissions is analyzed, and calculated error probabilities are presented graphically for alphabet sizes of 2, 8, and 32. The performance is shown to be within 3 dB of that of an optimum square-law combiner for moderate alphabet sizes when there is no restriction on the allowable number of diversity branches. It is shown that a worthwhile saving in transmitted power can be effected by using nonbinary alphabets with plurality-count combining for the transmission of binary data. The availability of extra information from the combiner for use with error-correction is discussed.

Multiple Diversity with Nonindependent Fading

Previous analyses of diversity techniques are extended to include the performance of an optimum (maximal-ratio) combiner in the case of nonindependent signal fading fluctuations, for an arbitrary number of diversity branches. The analysis includes the general possibility of correlations among the quadrature components of the various signals. Some computational simplifications for certain cases of physical interest are given, as well as a specific application to two problems in digital communications.