The tag collection algorithm in ISO/IEC 18000-7 has difficulty in collecting data from massive numbers of active RFID tags in a timely manner, so it should be improved to allow successful application in a wide variety of industrial fields. We propose two novel methods, a reduced-message method to improve the performance of data-tag collection and an efficient-sleep method to improve the performance of ID-tag collection. The reduced-message method decreases the slot size for a tag response by reducing the response size from the tag and reduces the number of commands issued from the reader. The efficient-sleep method utilizes redundant empty slots within the frame period to transmit sleep commands to the tags collected previously. We evaluated the performance improvement of tag collection by the proposed methods experimentally using an active RFID reader and 60 tags that we prepared for this study. The experimental results showed that the reduced-message method and the efficient-sleep method decreased the average tag collection time by 16.7% for data-tag collection and 9.3% for ID-tag collection compared with the standard tag collection. We also developed a simulation model for the active RFID system, reflecting the capture effect in wireless communication, and performed simulations to evaluate the proposed methods with a massive number of tags. The simulation results with up to 300 tags confirmed that the proposed methods could improve the tag collection performance, confirming the experimental results, even with larger numbers of tags.

In this paper, we propose a simple but effective way of improving the performance of channel estimation (CE) for pilot cyclic prefixed single carrier (PCP-SC) system. The proposed method utilizes the property that the shifting signal of the PCP pilot signal can also be utilized to estimate the channel information. The receiver can continuously estimate the channel information by just shifting the received pilot signal. Regardless of the signal-to-noise ratio (SNR) and the pilot type, the proposed method can achieve about a 1.72 dB performance gain in terms of the mean squared error (MSE) of channel estimation with a slight increase in computational complexity. The BER performance with the proposed CE improvement are evaluated in a multipath fading channel using a zero-forcing (ZF) equalizer and an minmum mean squared error (MMSE) equalizer by computer simulation. It is shown that the proposed CE improvment method using an MMSE equalizer which has an unbiased vlaue of noise variance (NV) estimator gives a promising BER performance. The proposed method also benefits the estimation of the SNR for the single carrier system.

A dual-band patch antenna with a shorting wall and a U-shaped slot is presented in this paper. The shorted-patch is coupled with the aperture slot that is closely placed to the shorting wall for achieving good impedance matching. A U-shaped slot is embedded in the shorted-patch and is located near the radiating edge to yield a dual-band operation. By changing the side slot length of the U-shaped slot, the tunable frequency ratio of the proposed antenna is varied from 1.73 to 2.05.

Let p be an odd prime number. We define a family of quaternary sequences of period 2p using generalized cyclotomic classes over the residue class ring modulo 2p. We compute exact values of the linear complexity, which are larger than half of the period. Such sequences are 'good' enough from the viewpoint of linear complexity.

A novel circularly polarized antenna with square slot for broadband characteristics is proposed in this paper. The horizontal and vertical components of the L-shaped probe, which is a key element to generate circular polarization, are separated in the structure, contrary to the concept of joined probes. Another novelty, placing stubs in the slot, which are attached to the ground plane, is proposed to improve the axial ratio (AR) characteristics of the antenna by around 10%. Placing a reflector at a distance of λ0/4 from the antenna to obtain unidirectional patterns is effective when no stubs are placed in the slot. The antenna attains a < 10 dB return loss bandwidth of 47.5% (2.76-4.48 GHz) and < 3 dB axial ratio (AR) bandwidth of 42.47% (2.67-4.11 GHz) in measurement. Parametric studies on key parameters and measured results are also presented.

A novel design technique for two-dimensional (2-D) waveguide slot arrays is proposed in this paper that combines a full-wave method of moments (MoM) analysis and an equivalent circuit with the explicit restraint of input matching. The admittance and slot spacing are determined first in an equivalent circuit to realize the desired distribution of power dissipation and phase, with the explicit restraint of input matching. Secondly by applying a full-wave MoM analysis to the finite 2-D array, slot parameters are iteratively determined to realize the active admittance designed above where slot mutual coupling and wall thickness are fully taken into account. The admittance, treated as the key parameter in the equivalent circuit corresponds to the power dissipation of the slots but not to the slot voltage, which is directly synthesized from the radiation pattern. The initial value of the power dissipation is assumed to be proportional to the square of the amplitude of the desired slot voltage. This assumption leads to a feedback procedure, because the resultant slot voltage distribution generally differs from the desired ones due to the effect of non-uniformity in the characteristic impedance on slot apertures. This slot voltage error is used to renew the initial distribution of power dissipation in the equivalent circuit. Generally, only one feedback cycle is needed. Two 2427-element arrays with uniform and Taylor distributions were designed and fabricated at 25.3 GHz. The measured overall reflections for both antennas were suppressed below -18 dB over the 24.3-26.3 GHz frequency range. High aperture efficiencies of 86.8% and 55.1% were realized for the antennas with uniform and Taylor distributions, the latter of which has very low sidelobes below -33 dB in both the E- and H-planes.

In this letter, we give a generalized construction for sets of frequency-hopping sequences (FHSs) based on power-residue sequences. Our construction encompasses a known optimal construction and can generate new optimal sets of FHSs which simultaneously achieve the Peng-Fan bound and the Lempel-Greenberger bound.

Some new generalized cyclotomic sequences defined by C. Ding and T. Helleseth are proven to exhibit a number of good randomness properties. In this paper, we determine the defining pairs of these sequences of length pm (p prime, m ≥ 2) with order two, then from which we obtain their trace representation. Thus their linear complexity can be derived using Key's method.

In this letter, we generalize the binary sequence introduced by Li et al. in [S. Q. Li et al., On the randomness generalized cyclotomic sequences of order two and length pq, IEICE Trans. Fund, vol. E90-A, no.9, pp.2037-2041, 2007] to sequence over arbitrary prime fields. Furthermore, the auto-correlation distribution and linear complexity of the proposed sequence are presented.

Method of moments (MoM) is an efficient design and analysis method for waveguide slot arrays. A rectangular entire-domain basis function is one of the most popular approximations for the slot aperture fields. MoM with only one basis function does not provide sufficient accuracy and the use of higher order mode of basis functions is inevitable to guarantee accuracy. However, including the higher order modes in MoM results in a rapid increase in the computational time as well as the analysis complexity; this is a serious drawback especially in the slot parameter optimization. The authors propose the slot correction length that compensates for the omission of higher order mode of basis functions. This length is constant for a wide range of couplings and frequency bands for various types of slots. The validity and universality of the concept of slot correction length are demonstrated for various slots and slot parameters. Practical slot array design can be drastically simplified by the use of MoM with only one basis function together with the slot correction length. As an example, a linear waveguide array of reflection-cancelling slot pairs is successfully designed.

Post-wall waveguide with a linear array of reflection-canceling slot pairs and center-feed is designed to cancel the frequency dependent tilting of the main beam and enhance the bandwidth of the antenna boresight gain. The array is fed at the center of the waveguide from the backside; the length of the radiating waveguide is halved and the long line effect in traveling wave operation is suppressed. Authors establish the array design procedure in separate steps to reduce the computational load in the iterative optimization by using Ansoft HFSS simulator. A center-feed linear array as well as an end-feed equivalent with uniform excitation is designed for 25.6 GHz operation and measured. The measured performances confirm the design and the advantage of the centre-feed; a frequency independent boresight beam is observed and the frequency bandwidth for 3 dB gain reduction is enhanced by 1.5 times compared to the end-feed array.

Straight microstrip lines alternately loaded with ground slots and open-end stubs are analyzed. Fabricated samples containing slots and stubs with various length combinations demonstrate constant slow-wave factors of 1.7 to 3.0 with negligible amounts of radiation loss and larger characteristic impedance tuning range. A slow-wave band-rejection filter at 1.8 GHz is built for performance comparison with a regular microstrip-line filter.

A novel square patch antenna with reconfigurable circular polarization (CP) is presented in this letter. A circular slot with perturbation is placed beneath the patch. The circular slot that has an inner perturbation yields right-handed CP, but with an outer perturbation slot yields left-handed CP. Experiments show an antenna gain of 2.8 dBic and a 3-dB axial ratio bandwidth of 30 MHz which well match the corresponding simulation results.

In this letter, a new feedback equalization scheme to suppress inter-carrier interference (ICI) in an OFDM system using scattered pilot is investigated. On a fast fading channel severe ICI occurs due to a Doppler shift and it deteriorates a bit error rate (BER) seriously because of small subcarrier spacing. In an ISDB-T receiver the equalization is mainly processed in a frequency domain because the scattered pilot is transmitted over the subcarriers. However, the frequency domain equalization may not suppress severe ICI in the case of the fast fading channel with a large Doppler shift. The proposed equalization scheme uses the scattered pilot symbols transformed in a time domain as the reference signal for feedback taps. Numerical results through computer simulation show that the proposed scheme improves the BER performance especially with low carrier-to-noise ratio (CNR) conditions.

This paper proposes a stabilized multichannel random access protocol based on slotted ALOHA for relay deployed cellular networks. To ensure the stability of random access, the proposed protocol dynamically controls the number of random access channels in a BS and a RS and the retransmission probability of the random access packets under heavy load conditions. A mathematical formula is also developed that derives an optimal partition ratio of the shared random access channels between a base station and a relay station without and with capture effect. Numerical results show that the proposed protocol can guarantee the required utilization and delay even in high offered load, which otherwise can cause bistable problem of slotted ALOHA.

In this paper, we calculate autocorrelation of new generalized cyclotomic sequences of period pn for any n > 0, where p is an odd prime number.

In this letter, a new design of a metamaterial-based microstrip antenna is presented using triangular slots embedded on the ground plane to enhance the impedance bandwidth. To improve the impedance bandwidth of the proposed antenna, two resonant mode frequencies are closely allocated using the slotted ground without changing the radiator element. The impedance bandwidth of VSWR < 2.5 is measured at 2.43 GHz (37.6%) centered on 6.46 GHz, from 5.24 GHz to 7.67 GHz in good agreements with the simulated results.

Introducing diffusion bonding of laminated thin metal plates to the fabrication of slotted waveguide arrays enlightens the high potential and the feasibility of multi-layer antennas with high-performance. It is a promising process with low cost even for a double-layer antenna, because the number of etching patterns for thin metal plates is only five. In this paper, a double-layer antenna for broadband characteristics is designed in 39 GHz band as demonstration. A 20 20-element antenna is composed of 2 2 sub-arrays by installing a partially-corporate feed circuit in the bottom layer underneath radiating waveguides in the top layer. The five-element sub-arrays in both the feeding and radiating parts are designed first. A new structure for the last slot coupler with shortened termination is also proposed to avoid an extra slot-free region when assembling the neighbor sub-arrays. As the simulation results by HFSS, the maximum gain of 34.55 dBi with the antenna efficiency of 85.5% is estimated at 38.5 GHz. The test antenna is fabricated by the diffusion bonding of thin copper plates. As the measurement results, a very high aperture efficiency of 83.2% with the directivity of 34.5 dBi is realized at the center frequency of 38.75 GHz, where the antenna gain of 34.4 dBi with the high antenna efficiency of 81.4% is achieved. The bandwidth of 5.0% defined as 1 dB down from the maximum gain is achieved.

A spiral array radial line slot antenna (SA-RLSA) is designed in 22 GHz band. A SA-RLSA excited with a coaxial feeder suffers from aperture illumination fluctuation in amplitude and phase in the circumferential (φ-) direction while in the radial direction, reasonably uniform distribution is observed. Rotational symmetry of radiation patterns is degraded and especially the sidelobe levels are unbalanced. This fluctuation is associated with the generation of the higher order modes in the φ-direction and is the unique defect of SA-RLSA which uses oversized waveguide. In this paper, a novel feeding structure with two pairs of parasitic pins around a coaxial feeder is proposed and designed so as to compensate the rotational asymmetry of aperture illumination. A measurement using the model antenna designed in 22 GHz band demonstrates the enhancement of the rotational symmetry; the circumferential fluctuation is reduced from 5.1 dB and 33 degrees to 1.8 dB and 12 degrees, while the fluctuation in the first sidelobe level suppressed from 10.7 dB to 1.2 dB.

A new linearly tapered slot antenna (LTSA) with defected sides is proposed in this letter. Both sides are defected with half-dumbbell shape slots that may alter the surface current intensities on both sides. As the half-dumbbell size is increased, the 3-dB beamwidth of the proposed antenna is 4° and 6° lower in the E/H-plane, respectively, than these of the LTSA without defects. Accordingly, the measured gain is improved by up to 3.75 dB and the first side lobe level is lowered by about -10.8 dB and -5.8 dB in the E/H-planes, respectively.