Internet access traffic follows hourly patterns that depend on various factors, such as the periods users stay on-line at the access point (e.g. at home or in the office) or their preferences for applications. The clustering of Internet users may provide important information for traffic engineering and billing. For example, it can be used to set up service differentiation according to hourly behavior, resource optimization based on multi-hour routing and definition of tariffs that promote Internet access in low busy hours. In this work, we propose a methodology for clustering Internet users with similar patterns of Internet utilization, according to their hourly traffic utilization. The methodology resorts to three statistical multivariate analysis techniques: cluster analysis, principal component analysis and discriminant analysis. The methodology is illustrated through measured data from two distinct ISPs, one using a CATV access network and the other an ADSL one, offering distinct traffic contracts. Principal component analysis is used as an exploratory tool. Cluster analysis is used to identify the relevant Internet usage profiles, with the partitioning around medoids and Ward's method being the preferred clustering methods. For the two data sets, these methods lead to the choice of 3 clusters with different hourly traffic utilization profiles. The cluster structure is validated through discriminant analysis. It is also evaluated in terms of several characteristics of the user traffic not used in the cluster analysis, such as the type of applications, the amount of downloaded traffic, the activity duration and the transfer rate, resulting in coherent outcomes.

The electrical parameters (88 LRGC matrices) of 8-coupled uniform lossy transmission lines were extracted from 40 S-parameter values measured by using 2-port VNA measurements, where all the ports other than 2 VNA ports were terminated by 50 ohm chip resistors. It was assumed in the extraction step that the transmission lines are weakly-coupled, and that the resistance values of all the termination chip resistors are exactly 50 ohms with the second reflections neglected. Comparison of the extracted LRGC matrix components with those from a commercial 3D field solver revealed on average and a maximum relative difference of 2.45% and 7.66%, respectively. In addition, the time-domain crosstalk voltage waveforms in the measured data and those in the SPICE simulation results using the extracted LRGC parameters agreed very well with the average difference and the maximum relative difference in peak crosstalk voltages of 4.15% and 9.68%, respectively.

A simple, novel and low cost optical device with the possibility of being integrated into a network of wireless sensors has been developed for the colorimetric detection of iron (II). The proposed device used is based on two light emitting diodes (LEDs) configured so that one acts as an emitter and the other as a light detector, and a simple threshold detection/timer circuit to measure the photocurrent at the detector LED. The colorimetric reaction is based on the chelating reaction of divalent iron with the ligand 1,10-phenanthroline. The calibration graph shows that the detection limit (DL) of iron (II) using this approach is 5 ppb with a RSD of 0.08%. All experiments were carried out in triplicate (N = 3). The effect of some cations on the determination of Fe (II) using the proposed method was also studied. Results found showed that the system is relatively free from interferences.

The oscillation characteristics of a 40 GHz, 1-3 ps regeneratively and harmonically mode-locked erbium-doped fiber laser have been investigated in detail with respect to stability, linewidth, and mode hopping. We show that because the Q value of the microwave filter in the feedback loop is limited to around 1000, which is almost the same as that in a 10 GHz laser, the cavity length should not be greatly increased as this would result in as much as a fourfold increase in the number of longitudinal beat signals. We undertook a detailed stability analysis by using three cavity lengths, 60, 80, and 230 m. The 80 m long cavity greatly improved the long-term stability of the laser because the supermode noise was suppressed and there were not too many longitudinal modes. We measured the linewidth of the longitudinal mode of the laser using a heterodyne method, and it was less than 1 kHz. We also point out that there is a longitudinal mode hopping effect with time that is induced by very small changes in temperature.

We have shown that a photonic sensor can be used as an electric-field probe for planar near-field measurements of X-band antennas. Because an antenna on the photonic sensor is small (about 0.1 λ) compared to the wavelength, the photonic sensor can directly measure the amplitude and the phase of the electric field close (about 0.3 λ) to the apertures of antennas without disturbing the electric field to be measured. Therefore we can obtain the antenna pattern by transforming the measured electric field without probe compensation. To verify the merits of the photonic sensor, we have evaluated the antenna patterns of a standard gain horn antenna and a microstrip array antenna at 9.41 GHz. Comparing the results obtained using the photonic sensor with those obtained using the conventional open-ended waveguide probe and other methods, we have shown that the antenna patterns agree with each other within 1 dB over wide ranges of directivity.

IEEE 802.11 standard and the enhanced amendments have defined several transmission rates for mobile stations to transmit and receive data frames. With the characteristic of modulation schemes, a higher network throughput can be expected by using higher level modulation scheme, but frame error probability will also become higher. Doubtlessly, it is an open issue of selecting a proper modulation scheme for a pair of mobile stations in time-varying indoor environment. This paper proposes a safe multiple access-rates transmission (SMART) scheme to enhance the reliability of data transmission in IEEE 802.11 multi-rate infrastructure wireless networks. SMART scheme provides reliable transmission by reserving a retransmission period which immediately follows the transmitted frame and is estimated by a lower transmission rate according to the transmitted frame. The performance of SMART scheme is evaluated by analytical model and simulation experiment, which show that the proposed scheme is significantly better than the IEEE 802.11 standard under the real environment with asymmetric traffic load. An enhanced SMART (ESMART) scheme is also proposed especially to improve bandwidth waste for long packet length at access point (AP). The performance measurements, such as goodput, throughput, average access delay, and service rate, are obtained and compared for the different schemes.

The architecture and implementation of a novel processor suitable wireless terminal applications, is introduced. The wireless terminal is based on the novel dual-mode baseband processor for DECT and GSM, which supports both heterodyne and direct conversion terminal architectures and is capable to undertake all baseband signal processing, and an innovative direct conversion low power modulator/demodulator for DECT and GSM. The state of the art design methodologies for embedded applications and innovative low-power design steps followed for a single chip solution. The performance of the implemented dual mode direct conversion wireless terminal was tested and measured for compliance to the standards. The developed innovative terminal fulfils all the requirements and specifications imposed by the DECT and GSM standards.

This review paper addresses an emerging aspect of the relationship between optics and microwave electronics: the application of short pulses of laser light to the sensing and measurement of continuous-wave microwave fields. In particular, very short duration optical pulses can take on the role of ultrafast sampling gates within the framework of the electro-optic sampling technique in order to realize unprecedented temporal resolution, measurement bandwidth, and probing flexibility. As a result, in numerous instances electro-optic sampling has been demonstrated, primarily within the research laboratory, to be an effective tool in the field of diagnostic testing and the determination of the electrical characteristics of microwave components. Recently, with the emergence of new applications such as microwave electric-field mapping in wireless and radar environments, and as the ultrafast time domain has gained in importance for the area of optical telecommunications, added attention has been directed to electro-optic sampling. Herein, an abbreviated historical perspective of the history of electro-optic field mapping is presented, along with the fundamental concepts that are utilized in the technique. The effectiveness of an optical-fiber-mounted electro-optic probe in a scanning electric-field-mapping system is highlighted in several diagnostic measurements on microwave and millimeter-wave antenna arrays, and a combined electric-field and thermal-imaging capability is also introduced.

Since the deployment of base stations (BS's) is far from optimum in 3-dimensional (3-D) space, i.e., the vertical baseline is relatively shorter than the planar baseline, the geometric degradation of precision of the altitude estimate is larger than that of the planar location. This paper considers the problem of 3-D range location and attempt to improve the altitude estimate. We first use a volume formula of tetrahedron to transform the range measurements to the volume measurements, then a novel pseudo-linear solution is proposed based on a linear relationship between the rectangular and the volume coordinates. Theory analysis and numerical examples are included to show the improved accuracy of the altitude estimate of mobile location. Finally, an improved estimate of 3-D mobile location is given by solving a set of augmented linear equations.

This contribution discusses which information can be derived from estimated directions of arrival (DOAs) and directions of departure (DODs) from a multiple-input multiple-output (MIMO) radio system, and establishes two new parameters describing the multipath spread at both link ends. We find that the multipath component separation, MCS, combines delay, (double-) angular and Doppler dispersion, as appropriate. MCS provides a system-independent radio characterization of propagation environments and aids in selecting optimum positions for smart-antenna deployment. Evaluation of double-directional measurements (antenna arrays at both link ends) in indoor environments show the usefulness and the limits of the multipath component separation concept.

A correlation-based technique for measuring Brillouin gain spectrum distribution along an optical fiber is proposed, which employs frequency-modulated pump and probe lightwaves. The spatial-resolution of about 40 cm is demonstrated, which cannot be realized by the conventional pulse-based technique.

In this paper, we describe the properties of an external cavity modelocked semiconductor laser with a tunability of wavelength, pulse width and repetition rate. This modelocked laser generates optical pulses with pulse widths down to 180 fs and with repetition rates up to 14 GHz in a 120 nm wavelength range near 1. 55 µm or 1. 3 µm. The generated pulses are close to the transform limit and are therefore suitable for very high speed communication systems. In addition to the tunability, this pulse source is a compact and mechanically stable device. We report on two applications of this pulse source in optical time division multiplexing experiments. In the first example the modelocked laser is used as an all-optical clock recovery. In the second example the modelocked laser was used to characterize an interferometric switch by pump-probe experiments.

A full confocal Gaussian beam open resonator system that determines the dielectric properties of low-loss materials in the 60-GHz band is developed. To achieve high Q values a quasi-optical coupling method is used to feed the resonator. It is connected to a computer-controlled HP 8510C vector network analyzer for automatic measurement. The frequency variation method is used and the data are processed using the open resonator scalar theory. Results from 96% and 99.5% alumina samples with thicknesses ranging from 0.38 mm to 1 mm, are presented in the V band, with loss tangent values of the order of 100 µ radians. This system should be able to measure substrates as thin as less than 0.1 mm to 0.3 mm, which are the thicknesses of substrates in practical use.

Efficiency of network resource can be improved by statistical multiplexing in ATM networks. If cell traffic characteristics of each connection could be obtained beforehand, we could admit maximum connections while satisfying the QoS (Quality of Service) objective. Since such traffic characteristics as an average rate and a mean burst length are difficult to anticipate, only peak rate will be used for CAC (connection admission control). The peak rate assignment strategy will, however, lead to inefficient network utilization for bursty traffic. This paper proposes an adaptive admission control using real-time traffic measurements to overcome the above problem. This scheme is based on two-state cell stream model composed of overload and underload states. The two-state model simplifies the measuring algorithm, which is suited for online processing. Performance of this scheme is investigated through simulation study for multiplexing of on-off sources with a wide spectrum of traffic characteristics. Since the proposed control scheme exploits measurements of cell streams, it achieves nearly optimum bandwidth efficiency.

Theoretical and experimental investigations of dipole antenna factors were carried out with special interest in their height patterns, since difference between them is a main cause of disagreement in EMI measurement results obtained with different antennas types. Antenna factors were expressed by matrix representation and their dependence on antenna dimensions and balun construction were numerically evaluated with the moment method. Those analyses revealed that antenna dimensions and balun characteristics have little effect on antenna factor height patterns. Slight influence was observed only at frequencies around 30MHz, when an antenna was placed less than 1.5m above a metal ground plane.

Results of an empirical investigation of the shielding properties of a small pre-fabricated reinforced concrete building are presented. The electric field attenuation was measured in the frequency range of approximately 20kHz to 500MHz. The experiments were performed in collaboration with the Italian National Board of Post an Telecommunications (ISPT). An equivalent stick model has been analyzed in frequency domain by numerically solving a set of electric field integral equations. The influence of the real reinforcement mesh (dimensions, spatial disposition, electrical parameters) on the attenuation of the electric field has been investigated. A comparison between computed and measured results is presented.

To increase the accuracy of a near field antenna measurement system, it is necessary to know radiation characteristics of a probe to detect near field data. Open ended waveguide used as a near field probe in our system was analyzed using Transmission Line Matrix (TLM) method which is a time domain electromagnetic solver. Validity of this analysis has been confirmed by comparison with experimental data and existing theoretical approximation. Frequency dependence of a complex reflection coefficient at the waveguide aperture has been derived and is shown to agree with measured values. The radiation pattern of the open ended waveguide with mounting structure is also calculated. Ripples on both the amplitude and phase patterns are correctly predicted by our simulation. This method can be applied to accurately model the effect of probe antennas to enhance the accuracy of near field antenna range.

A simple method for separating the dissipation factors associated with both conductor losses and dielectric losses of printed circuit boards in microwave frequencies is presented. This method utilizes the difference in dependence of two dissipation factors on the dimensions of bounded stripline resonators using a single printed circuit board specimen as a center strip conductor. In this method, the separation is made through a procedure involving the comparison of the measured values of the total dissipation factor with those numerically calculated for the resonators. A method, which is based on a TEM wave approximation and uses Green's function and a variational principle, is used for the numerical calculation. Both effective conductivity for three kinds of industrial copper conductor supported with a substrate of polymide film and dielectric loss tangent of the substrates are determined using this method from the values of the unloaded Q measured at the 10 GHz region. Radiation losses from the resonator affecting the accuracy of the separation are discussed, as well as the values of the effective conductivity of metals on the polyimide substrate which is calculated using the above method. The resulting values of the effective conductivity agree with those using the triplateline method within 10%.

Some results are presented of a one-year measurement period on an INTELSAT down link at Ku band with elevation of 14 for concurrent measurements of beacon attenuation, sky noise and point rainfall rate. Also some results are presented of line-of-sight (LOS) link fading characteristics at the same place. The projection of the down link trajectory on earth has nearly the same direction as the LOS path trajectory. The measurement results are compared with the theoretical values according to the CCIR recommended procedures of rain attenuation predictions for tropical regions, especially Surabaya, Indonesia. A record rain attenuation value of 80dB was observed.

A new superresolution technique is proposed for antenna pattern measurements. Unwanted reflected signals often impinge on the antenna when we measure it outdoors. A time-domain superresolution technique (a MUSIC algorithm) has been proposed to eliminate the unwanted signal for a narrow pass-band antenna. The MUSIC algorithm needs many snapshots to obtain a correlation matrix. This is not preferable for antenna pattern measurements because it takes a long time to obtain the data. In this paper, we propose to reduce a noise component (stochastic quantity) using the FFT and gating techniques before we apply the MUSIC. The new technique needs a few snapshots and saves the measurement time.