In the context of fading channels it is well established that, with a constrained transmit power, the bit rates achievable by signals that are not peaky vanish as the bandwidth grows without bound. Stepping back from the limit, we characterize the highest bit rate achievable by such non-peaky signals and the approximate bandwidth where that apex occurs. As it turns out, the gap between the highest rate achievable without peakedness and the infinite-bandwidth capacity (with unconstrained peakedness) is small for virtually all settings of interest to wireless communications. Thus, although strictly achieving capacity in wideband fading channels does require signal peakedness, bit rates not far from capacity can be achieved with conventional signaling formats that do not exhibit the serious practical drawbacks associated with peakedness. In addition, we show that the asymptotic decay of bit rate in the absence of peakedness usually takes hold at bandwidths so large that wideband fading models are called into question. Rather, ultrawideband models ought to be used.

Training over sparse multipath noisy channels is explored. The energy allocation and the optimal shape of training signals that enable communications over unknown channels are characterized as a function of the channels' statistics. The performance of training is evaluated by the reduction of the mean square error of the channel estimate and by the decrease in the the mutual information due to the uncertainty of the channel. The performance of low dimensional training signal is compared to the performance of a full dimensional one. Especially, The trade-off between the number of required measurements (signal dimensions) and the energy allocation is calculated, and it is proven that if the signal to noise ratio of the received training signal is low, reducing the number of channel measurements using compressed sensing is as efficient as training over the entire frequency band.

This work suggests to quantify and analyze tremorusing an Ultra Wide-Band (UWB) Wireless Sensor Network(WSN). WSN based on UWB technology provides a new technology for non contact tremor assessment with extremely low radiation and penetration through walls. Tremor is the target symptom in the treatment of many neurological disorders such as Parkinson's disease (PD), midbrain tremor, essential tremor (ET) and epilepsy. The common instrumental approaches for the assessment of tremor are motion capture devices and video tracking systems. The new tremor acquisition system is based on transmission of a wideband electromagnetic signal from multiple sensor nodes placed indifferent locations in a home and analysis of the received signal in each sensor node. The sensors can exchange information between each other with a coded transmission or send the raw data to a UWB hub for further analysis. The data can be then sent by an internet gateway to a health care center for monitoring and for medical care. This paper describes the basic system and gives a fundamental detection technique. For a feasibility test we built an UWB based sensor node prototype and examined its performance with an arm model that fluctuated in the range of clinical tremor frequencies (3-12 Hz). A future development of this work can lead to a low cost monitoring system installed at any home, hospital or school to continuously assess and report tremor conditions during daily life activities.

The multipath components of wideband (2-17 GHz) non line of sight channel responses measured inside several buildings are stable along sections that are 9.5 cm long on average with a standard deviation of 8.1 cm. An analysis of measured channels that explicitly includes finite spatial areas of stability of the multipath components is superior to the classic analysis that attributes spatial dynamics to interference of the multipath. The spatial stability of responses with 1 GHz bandwidth decreases as the center frequency increases, i.e. the size of the typical area of stability of each multipath component tends to decrease with increasing carrier frequency.

Key factors of indoor NLoS radio channels are examined, namely the number of channel taps, the mean delay, the RMS delay spread and the channel gain. We analyze wideband (2-11 GHz) results in bands of 528 MHz and examine the mean behavior of the parameters vs. transmitter-receiver separation, with separations of up to 30 meters, as well as the parameterspsila correlation across sub-carrier frequency. The mean dependence of the parameters on terminal separation is approximated by a simple linear fit. The measurements were taken in three office buildings in the Givat Ram campus of the Hebrew University with the terminals in the same and in adjacent floors.

Channel uncertainty limits the achievable data rates of certain ultra-wideband systems due to the need to estimate the channel. The use of bursty duty-cycled transmission reduces the channel uncertainty because the receiver has to estimate the channel only when transmission takes place, but the maximum amount of burstiness and hence the possible reduction of channel uncertainty both depend on the spectral efficiency of the modulation scheme used. This general principle is demonstrated by comparing the channel conditions that allow duty-cycled direct-sequence spread spectrum (DSSS) and pulse position modulation (PPM) to achieve the additive white Gaussian noise (AWGN) channel capacity in the wideband limit. We show that duty-cycled DSSS systems achieve the wideband capacity as long as the number of independently faded resolvable paths increasessublinearlywith the bandwidth, while duty-cycled PPM systems can achieve the wideband capacity only if the number of paths increasessublogarithmically. The difference is due to the fact that DSSS is spectrally more efficient than PPM and hence allows more bursty transmission.

The acquisition, or synchronization, of a multipath channel profile for ultra-wideband pulse position modulation (PPM) communication systems is considered. The rate of increase of the number of paths as the bandwidth grows determines whether acquisition can occur. If the number of independent Gaussian paths increases without bound, but slower than the bandwidth, then the system cannot acquire in the limit. Acquisition is not possible on multipath channels with deterministic path amplitudes, if the number of paths diverges but not too fast. These results hold for exponential or uniform power delay profiles

A preponderance of ultrawideband radio communication systems under current study employ the use of pulse position modulation (PPM). However, there are significant issues related to the synchronization of PPM systems in multipath. If the multipath scattering is rich i.e. the number of reflections (paths) increases without bound as the bandwidth increases, then synchronization is impaired. In particular, it is shown that a threshold-type detector fails in synchronizing, for any possible threshold, in the limit of large bandwidth. The maximum likelihood detector can synchronize under some severely constrained scenarios which do not appear to reflect reality in light of recent propagation measurements

A new model for UHF propagation in large buildings is presented. This model relies on knowledge of the interior arrangement of the building without requiring much detail. The guiding of radiation along hallways is the most significant propagation process at distances of more than 10 m from the transmitter. The waveguide model predicts the power loss rate along the hallways, which is affected by the coupling among the propagating modes. The coupling results from the roughness of the surfaces in the building; it is predicted in an average manner using the average deviation of the walls from perfect smoothness. The model predictions are compared to measurements in an office building and to ray tracing predictions.

A new model for UHF propagation in large buildings is presented. This model relies on knowledge of the interior arrangement of the building without requiring much detail. The guiding of radiation along hallways is the most significant propagation process at distances of more than 10 m from the transmitter. The waveguide model predicts the power loss rate along the hallways, which is affected by the coupling among the propagating modes. The coupling results from the roughness of the surfaces in the building; it is predicted in an average manner using the average deviation of the walls from perfect smoothness.

Channel capacity in a waveguide with mode coupling is limited by a keyhole effect caused by the propagation mechanism. The coupling among the propagating modes reduces the channel rank, and at sufficient distances between the transmitter and receiver, the channel rank converges to 1. Measurements of the received power and channel capacity along a hallway and in rooms beside it, show a decrease of capacity with distance, which is explained by the keyhole effect in the hallway.

Waveguide theory is suggested for the analysis of UHF radiation in urban microcellular environments, where both the transmitter and the receiver are below rooftop level. The delay profile is calculated from the steady state power distribution among the modes of the waveguide. The delay profile is very asymmetrical because most of the power is contained in the low order (faster) modes, and because the differences between the group velocities of the modes tend to be smaller for the low order modes.