An implantable WBAN path-loss model for a capsule endoscopy which is used for examining digestive organs, is developed by conducting simulations and experiments. First, we performed FDTD simulations on implant WBAN propagation by using a numerical human model. Second, we performed FDTD simulations on a vessel that represents the human body. Third, we performed experiments using a vessel of the same dimensions as that used in the simulations. On the basis of the results of these simulations and experiments, we proposed the gradient and intercept parameters of the simple path-loss in-body propagation model.

This paper proposes an ultra-wideband double-directional spatio-temporal channel sounding technique using transformation between frequency- and time-domain (FD and TD) signals. Virtual antenna arrays, composed of omnidirectional antennas and scanners, are used for transmission and reception in the FD. After Fourier transforming the received FD signals to TD ones, time of arrival (TOA) is estimated using a peak search over the TD signals, and then angle of arrivals (AOA) and angle of departure (AOD) are estimated using a weighted angle histogram with a multiple signal classification (MUSIC) algorithm applied to the FD signals, inverse-Fourier transformed from the TD signals divided into subregions. Indoor channel sounding results validated that an appropriate weighting reduced a spurious level in the angle histogram by a factor of 0.1 to 0.2 in comparison with that of non-weighting. The proposed technique successfully resolved dominant multipath components, including a direct path, a single reflection, and a single diffraction, in line-of-sight (LOS) and non-LOS environments. Joint TOA and AOA/AOD spectra were also derived from the sounding signals. The spectra illustrated the dominant multipath components (agreed with the prediction by ray tracing) as clusters.

Path loss and delay profile characteristics of the 3-GHz band are measured and compared for line-of-sight (LOS) and non-line-of-sight (NLOS) paths in a suburban residential area. For the LOS path, the path loss increases as a function of distance squared; and hence the propagation is considered as the free space propagation. For the NLOS paths, it is found that corner losses occur ranging from 28 to 40 dB, and subsequent losses increase as a function of distance squared, but in case of there are open spaces, spaces between the rows of houses or roads intersecting LOS road, the increase was small. The delay spread for the LOS path increased in proportion to power of the distance; and the exponents ranging from 1.9 to 2.9 is found smaller than in urban areas. The delay spreads for the NLOS paths were several times greater than that for the LOS path, and the rate of delay spread increase with distance was found to be several orders of magnitude greater for NLOS paths than the LOS path.

In this paper, the effects of Bragg scattering on ultra-wideband (UWB) signal transmission from periodic surfaces are reported. First, the frequency dispersive property of Bragg scattering is theoretically and experimentally confirmed. Next, the transfer function of both specular path and Bragg scattering are extracted. Then direct sequence UWB (DS-UWB) transmission simulations are conducted by using a raised cosine pulse that occupied 3.1 to 10.6 GHz and a Gaussian pulse that occupied 8.75 to 9.25 GHz. Finally, the effects of Bragg scattering on UWB systems are discussed.

This paper reports on a study of the interference effects from 2 types of ultra wideband (UWB) sources on a QPSK transmission system by simulation. The culprit UWB sources were: multi-band orthogonal frequency-division multiple-access (MB-OFDM) and direct-sequence UWB (DS-UWB), which were modeled on the proposal specifications in the IEEE 802.15.3a to standardize high-speed wireless personal area networks. Average bit error rate (BER) degradation of the victim system was evaluated under in-band interference from the UWB signals. The proposed modified equivalent baseband system was employed in the simulation in order to reduce the simulation costs. Interference effects from the UWB sources were also examined under a Rayleigh fading channel.

Ultra wideband (UWB) radar cross sections (RCSs) of several targets have been measured using various combinations of transmitting and receiving linear polarizations (V-V, H-H, and +45- -45) with a view to obtaining information on the design of vehicular short-range radars. This paper reports the UWB RCSs (σLR and σLL) of a typical passenger automobile using two circular polarization combinations (L and R denote left and right circular polarizations). The wideband measurements were carried out with use of a vector network analyzer by sweeping the frequency from 24.5 to 28.8 GHz in a radio anechoic chamber. The UWB RCSs were derived by integrating the received power in the frequency domain. Similar to the linear polarization results, fluctuations of the RCSs were smaller in the UWB than in narrowband for both L-R and L-L, because the ultra-wide bandwidth cancels out RCS plunges caused by narrowband interference among reflected waves from various facets of the target. The median of (σLR- σLL) was 2 dB, while the median of (σHH - σ+45 - -45) or (σVV-σ+45- -45) was 6 dB. This is because the body of the automobile comprises a number of smaller scattering objects yielding σ LL, either similar to the corner reflectors or asymmetrical to the radar boresight. Frequency-domain responses showed a number of notches caused by the interference between numerous reflecting waves having power levels of a similar order and different round-trip path lengths. Some representative reflective parts of the automobile were identified through analyses of time-domain responses.

This paper presents an experimental study of on-body ultra-wideband (UWB) radio propagation channels within an enclosed space. To facilitate high-speed wireless body area networks, UWB is a promising technology because of its low power consumption and anti-multipath capabilities. The motivation of this study is to examine the effects of nearby humans on the UWB channels by varying the population within an elevator cabin from one (subject alone) to 20 (full capacity of the elevator). The first domain (0 < delay, t ≤ 4ns) in the measured delay profiles was either a direct (for line-of-sight) or diffracted (for non-line-of-sight) wave, which was found almost unrelated to the population; whereas the second domain (t > 4ns) highly depended on it. Total received power and delay spreads decreased with increasing the population. In addition, by varying human population, average power delay profiles were modeled based on measurements.

Precise determination of antenna phase centers is crucial to reduce the uncertainty in gain when employing the three-antenna method, particularly when the range distances are short-such as a 3-m radio anechoic chamber, where the distance between the phase centers and the open ends of an aperture antenna (the most commonly-used reference) is not negligible compared with the propagation distance. An automatic system to determine the phase centers of aperture antennas in a radio anechoic chamber is developed. In addition, the absolute gain of horn antennas is evaluated using the three-antenna method. The phase centers of X-band pyramidal horns were found to migrate up to 18mm from the open end. Uncertainties in the gain were evaluated in accordance with ISO/IEC Guide 93-3: 2008. The 95% confidence interval of the horn antenna gain was reduced from 0.57 to 0.25dB, when using the phase center location instead of the open end. The phase centers, gains, polarization, and radiation patterns of space-borne antennas are measured: low and medium-gain X-band antennas for an ultra small deep space probe employing the polarization pattern method with use of the horn antenna. The 95% confidence interval in the antenna gain decreased from 0.74 to 0.47dB.

This paper proposes a new method which simultaneously undertakes ranging and communications based on the PHY of MB-OFDM technology. A transmitter modulated one or multiple OFDM subcarriers with a low-frequency (1.05 MHz) ranging signal; and a receiver sampled the received signal at a 3.2-MHz sampling rate to estimate the time of arrival of the ranging signal. This configuration and an additional protocol supporting bidirectional ranging achieved a 140-mm resolution (equivalent to 2.15 GHz sampling). This method does not modify the PHY but only changes the baseband signal processing. The validity of this method was demonstrated using computer simulation and prototype experiments.

The cellular-communication systems of the future will be required to provide multimedia services to users moving about in a variety of ways (on foot, in automobiles etc.). Different forms of motion have different characteristics. The characterization of the different forms of motion and their effects on telecommunications traffic is important in the planning, design and operation of mobile communication networks. The characterization of the motion of various platform types (inter-city buses, recreational vehicles, freight trucks, and taxis) based on measurements using Global Positioning System is presented in this paper. The measured characteristics of motion are then used to evaluate teletraffic statistics such as cell cross-over rate and cell dwell time by overlaying hypothetical cell systems on the measured loci of vehicles. Self-similarity was discovered in the cell dwell time characteristic of the taxis.

This paper presents an ultra wideband (UWB) channel sounding scheme with a technique for estimating time of arrival (TOA) and angle of arrival (AOA) using measurement signals. Since the power spectrum over the UWB bandwidth can be measured in advance, we propose a signal model using the measurement power spectrum to design the proper UWB signals model. This signal model is more similar to measurement signals than the flat spectrum model which is an ideal model. If more than three waves impinge on a receiver, we must determine the proper grouping of the elements of TOA vector and AOA vector. It is difficult to determine the grouping using only measurement signals because of many degradation factors. We also propose pairing the elements of TOA vector and that of AOA vector using correlation method based on measurement signals and the proposed signal model. This technique is available for more than the case of three paths if pairing the estimated TOAs and AOAs of measurement signals is not accurately determined. We evaluated the proposed techniques for a vector network analyzer (VNA) with a three-dimensional virtual antenna array.

This paper introduces the concept of measuring double directional channels in ultra wideband (UWB) systems. Antenna-independent channel data were derived by doing the measurements in a wooden Japanese house. The data were useful for investigating the impact of UWB antennas and analyzing waveform distortion. Up to 100 ray paths were extracted using the SAGE algorithm and they were regarded as being dominant. The paths were then identified in a real environment, in which clusterization analyses were done using the directional information on both sides of the radio link. Propagating power was found to be concentrated around the specular directions of reflection and diffraction. This led to the observation that the spatio-temporal characteristics of extracted paths greatly reflected the structure and size of the environment. The power in the clusters indicated that the estimated 100 paths contained 73% of the total received power, while the rest existed as diffuse scattering, i.e., the accumulation of weaker paths. The practical limits of path extraction with SAGE were also discussed. Finally, we derived the scattering loss and intra-cluster properties for each reflection order, which were crucial for channel reconstrucion based on the deterministic approach.

To obtain a high throughput for transmission control protocol (TCP) connections over the wireless links, we previously proposed a novel transmission power control method for code division multiple access (CDMA) packet communication systems. By using this transmission power control method, we developed a transmission power control method and a packet multiplexing method to transmit constant bit rate (CBR) and TCP packets over CDMA wireless systems. Our methods can guarantee the quality of service (QoS) for CBR connections and utilize bandwidth effectively without modifying the TCP protocol or using slot assignments. Evaluation of our methods by computer simulation showed that the proposed methods provide a near-maximum throughput and guarantee the packet loss ratio of CBR connections regardless of the number of connections.

To implement soft handoff in cellular communication systems that employ code division multiple access (CDMA), it is necessary to establish communication lines between the switch and multiple base stations and distribute the communication data via these multi-connections to the base stations simultaneously. This means that, when soft handoff is performed with the same amount of communication line resources as hard handoff, the blocking probability is higher than for hard handoff, and service quality is thus worse. Furthermore, handoffs occur more frequently as the size of cells becomes smaller, and this increases the probability of forced terminations. Switches must be endowed with greater processing capacity to accommodate the more frequent handoffs. The use of the queuing handoff method can be expected, in general, to mitigate forced termination probability compared with the immediate handoff method. In this regard, we propose a prioritized queuing handoff method that gives priority to fast-moving mobile stations (MSs) as a way to mitigate forced terminations even more than the non-priority queuing method without appreciably increasing the processing load. We then compare the traffic characteristics of our proposed method with these of three other methods in micro cell systems--immediate method, non-priority queuing method, and conventional hard handoff method without multi-connections--by computer simulation. Here, considering that the proposed method gives priority to fast-moving calls, traffic characteristics for these methods were evaluated separately for slow- and fast-moving MSs. The results reveal that proposed method can reduce the forced termination probability and total call failure probability more than non-priority queuing method without having an appreciable impact on slow-moving calls.