Comments on “Relationship between group delay and storedenergy in microwave filters”

For original paper, see ibid., vol.49, no.1, p.192-6 (2001). In the original paper, it is shown that the time-averaged stored energy in a passive lossless reciprocal symmetrical or antimetrical two-port is proportional to the group delay. The authors point out that some of their results were previously reported in a book by Penfield et al. (1970) and apologize for claiming credit for the work     

Comments on “Applications of simulated annealing for thedesign of special digital filters”

For original paper see ibid., vol.40, p.323 (1992). Discusses the performance measurement of a discrete coefficient filter which is designed by scaling optimization     

Comments on “Comments on the peak factor of sampled andcontinuous signals”

The author comments that a signal, which does not satisfy the conditions of the sampling theorem, is used as a basis for the proof in the paper of Wulich (see ibid., vol.4, no.7, p.213-14, 2000). Therefore, the presented proof is incorrect     

Comments on “Shielding effectiveness of conductivepolymers”

The authors comment that K. Naishadham (see ibid., vol.34, no.1, p.47-50, 1992) calculated the plane-wave shielding effectiveness of conductive polymers as a function of frequency. As indicated, a comparison to the measured result of the DC conductivity indicates that the microwave conductivity at room temperature is within a small percentage of the DC result, and therefore can be used for a wide frequency range. The conductivity of the polymers is given by σ=2πf₀ϵ₀ϵ" and is assumed invariant for all frequencies. Based on the invariability of polymers' conductivity for all frequencies, they calculated the shielding effectiveness of the polymers. Discrepancies are found by comparing these figures to those of Naishadham. It is concluded that shielding effectiveness calculated by Naishadham was done under the assumption of frequency-invariant ϵ" instead of σ     

Comments on “Partial parallel interference cancellation forCDMA”

We comment on partial parallel interference cancellation as discussed in the paper by Divsalar et al. (see ibid. vol.46, p.258-68, 1998). The aforementioned work showed that by multiplying the symbol estimates by a factor less than unity in the early stages of cancellation, the performance of parallel cancellation can be improved relative to full (“brute force”) cancellation. In this paper we analyze the improvement of parallel cancellation when using partial cancellation, and provide additional insight into the gains. Specifically, we show that the decision statistic is biased when linear (soft) estimates of the symbol or channel are used for cancellation. Partial cancellation improves the performance in this case by reducing the decision statistic bias     

Comments on “Radial line planar monopulse antenna”

The author points out that Miyashita and Katagi (IEEE Trans. Antennas Propagat., vol.44, p.1158-65, Aug. 1996) claim a new type of planar monopulse antenna, without reference to Kelly and Goebels (1964) that described their “invention” of the radial line planar monopulse antenna. Further, scant mention is made of the pioneering work by Goebels and Kelly (1961) and by Kelly and Goebels (1964) in various other papers by Goto, Ando, Nakano and others     

Comments on “Nonblocking property of reverse banyannetworks”

It is shown that the nonblocking property of reverse banyan networks mentioned in the above paper follows directly from the fact that banyan networks can realize permutations characterized by bitonic sequences     

Comments on “transient radiation of traveling-wave wireantennas”

Wu and Ruan (see ibid., vol.41, p.120-23, 1999), based on the formalism of Podosenov, Svckis and Sokolov (1995), tried to calculate the electromagnetic radiation field from the current of a traveling wave propagating along a thin curvilinear wire with free ends. In this article the author tries to prove that in the paper of Wu et al. one problem was substituted by another. In fact, another problem, but not that which was formulated by the authors, was solved. It is not the problem of radiation from a curvilinear antenna of finite length, but the problem of radiation from part of an infinite antenna and two external sources emerging under a forcible requirement of satisfying the Lorentz condition for a subsystem, where this condition does not operate a fortiri. The proof is based on the following easily verifiable facts: (1) a coincidence of the expressions for the magnetic field; and (2) a dissimilarity of the expression for the electric field from the formula to a forcible imposing of the Lorentz condition being invalid for subsystems. The author comments on the second point in more detail     

Comments on “Capture and Retransmission Control in Mobile Radio”

For original paper by Zorzi and Rao, see IEEE J. Sel. Areas Commun., vol.12, no.8, p.1289-98 (1994 October)     

Comments on “Probability estimation in arithmetic andadaptive-Huffman entropy coders”

This comment points out some omissions in the work of Duttweiler and Chazmas (see ibid., vol.4, p.237, 1995) on credit related to scaled-count estimators that perform count-scaling when the count of the less probable symbol (LPS) reaches a limiting value     

Comments on “Minimum Duration Outages in Rayleigh Fading Channels“

Closed-form expressions are derived for the minimum duration outage and the probability of outage considered by Lai and Mandayam in the above paper.     

Comments on “Subband coding of images using asymmetricalfilterbanks”

In the above paper Egger and Li (see ibid., vol.4, p.478-85, Apr. 1995) presented a set of two-channel filterbanks, asymmetrical filterbanks (AFB's), for image coding applications. The basic properties of these filters are linear-phase, perfect reconstruction, asymmetric lengths for dual filters, and maximum regularity. In this correspondence, we point out that the proposed AFB's are not new in the sense that the proposed construction is equivalent to the factorization of Lagrange halfband filters, which has been reported by other researchers. In addition, we correct an error in the formulation of constructing AFBs in their paper.     

Comments on “Minimum-latency transport protocols withmodulo-N incarnation numbers”

The authors comment on a class of minimum-latency transport protocols that have been analyzed by Shankar and Lee (see ibid., vol.3, no.3, p.255, 1995). The protocols use unique incarnation numbers and caching schemes to reduce the latency of connection setup whenever possible. They discuss three modifications to the protocol. (1) A modification to the opening procedure which eliminates some constraints for the correctness of the protocol. (2) A modification which allows data messages in the opening state of the client to be sent. This reduces the latency in some situations for the price of stricter constraints for correctness. (3) An alternate way of closing connections. Apart from these modifications, they also show that the proofs can be refined to get somewhat less restrictive constraints for the correctness of the protocol     

Comments on “modified K-means algorithm for vector quantizerdesign”

Previously a modified K-means algorithm for vector quantization design has been proposed where the codevector updating step is as follows: new codevector=current codevector+scale factor (new centroid-current codevector). This algorithm uses a fixed value for the scale factor. In this paper, we propose the use of a variable scale factor which is a function of the iteration number. For the vector quantization of image data, we show that it offers faster convergence than the modified K-means algorithm with a fixed scale factor, without affecting the optimality of the codebook.     

Comments on “On the resonant frequencies of microstripantennas”

The resonant frequencies of equilateral triangular microstrip antenna calculated by Gang (see ibid. vol.37, no.2, p.245, 1989) are compared with the experimental results of Dahele and Lee (1987). When computing the resonant frequencies of equilateral triangular microstrip antenna, using the same equations proposed by Gang, we obtained different results, which are given, from Gang's results. For an equilateral triangular microstrip antenna, the resonant frequencies obtained from the cavity model with perfect magnetic walls are given by the formula shown. In this work, we suggest a new closed-form expression. We compared our computed values of the resonant frequencies for the first five modes of the equilateral triangular patch antenna with theoretical and experimental results reported by other scientists     

Comments on “New dynamic flip-flops for high-speeddual-modulus prescaler”

For the original paper see ibid., vol. 33, no. 10, p. 1568-1571 (1998). In the aforementioned paper a fast true single-phase clocking (TSPC) ratioed D-flip-flop is proposed by C. Yang et al. It is claimed by the commenters that the proposed flip-flop violates the edge-triggering characteristic. However, it is shown that high clock frequency and the propagation delay of the transistor enable the flip-flop to operate normally in the dual-modulus prescaler     

Further improvements in digitizing continuous-time filters

A new method for digitizing a linear continuous-time filter has improved stability characteristics and reduced implementation requirements while retaining the accuracy of the higher order rules recently appearing in the literature. This method approximates the sampled input by a polynomial of degree q fitted to the latest (q+1) samples. The value of q is selected by the designer; values of q up to 14 have been tested successfully. The exact response of the original continuous-time filter to the polynomial input is computed analytically. The method has been formulated using matrices, which lends itself well to machine computation and greatly simplifies the effort needed to obtain numerical results     

Comments on “On the use of ρ-algorithm in seriesacceleration”

The author draws the attention of the readers to the paper of Singh and Singh (see ibid., vol.39, p.1514-16, Oct. 1991) that an extremely simple and elegant method of handling this age-old problem may be found in Morse and Feshbach (1953). Suggested by the geometry of the original problem for the Helmholtz equation, one first determines the solution of the Poisson's equation (setting the wavenumber to zero) with appropriate boundary conditions and sources in closed form, as well as an infinite series. A useful feature of the series solution is that each term resembles a corresponding term in the original series solution of the Helmholtz equation, and for large values of the summation index, term by term, equality is approached. By adding the closed form answer, subtracting the series solution, and rearranging, one realizes fast convergence. Yet another gratifying feature is that convergence of the transformed series can be easily proven