Jens Timmermann

Estimated performance of UWB impulse radio transmission including dirty RF effects

For studying the performance of an ultra-wideband (UWB) system, either measurements or simulations can be performed. Simulations for performance predictions are more flexible, but they require an accurate system modeling that takes into account the non-ideal hardware. This paper presents the UWB indoor channel modeling, including relevant, non-ideal hardware components for the UWB impulse radio technique. As a performance measure the estimated bit error rate versus distance and versus signal-to-noise ratio for Time Hopping Pulse Position Modulation (TH-PPM) in a line of sight indoor scenario is presented. The influence of the data rate on the bit error rate is investigated as well.

Investigating the influence of the antennas on UWB system impulse response in indoor environments

UWB applications will primarily be used in indoor environments due to the power constraints given by the FCC in 2002. Therefore, investigating and modeling the indoor propagation of ultra wideband signals is of great interest. It has been shown, how a narrowband ray tracing tool developed at the Institut fur Hochstfrequenztechnik und Elektronik describing indoor wave propagation can be extended to ultra wideband channels, and first simulation results describing the channel impulse response without antenna influence have already been reported. In this paper, antennas are taken into consideration by combining data of measured complex antenna patterns with the extended Ray Tracing method whereas the antennas are typical UWB antennas. The impulse response of the UWB system including antennas is called system impulse response. Since frequency dependent complex pattern information is used, the system impulse response includes the transient response of the antennas in the time domain. After determining the UWB system impulse response, the differences between channel impulse response and system impulse response are investigated. Furthermore, in both cases, a distance estimation between transmitter and receiver is performed to investigate the impact of antennas in UWB localization applications.

Simulation of the Impact of Antennas and Indoor Channels on UWB Transmission by Ray Tracing and Measured Antenna Patterns

During the development stage of a UWB system, system simulations are helpful to evaluate the system performance. System simulations demand for accurate description and modeling of the entire system, whereas the computation time must be small. In many cases, system simulators are based on idealized assumptions and neglect effects of non-ideal hardware. In reality however, real UWB antennas can corrupt signal transmission. This paper presents a system simulator that can deal with non-ideal, measured complex antenna patterns. It is shown how antenna patterns impact signal transmission in typical indoor scenarios. To describe multipath propagation within small computation time, full-wave solutions of Maxwells equations cannot be performed. Instead, a UWB Ray Tracing tool developed at the Institut fur Hochstfrequenztechnik und Elektronik is used and expanded by complex pattern information to take into account the influence of antennas. The system simulator determines the distorted signal and reconstructs the bit sequence by a conventional correlation receiver.

Investigations on the Applicability of Diversity Techniques in Ultra Wideband Radio

This paper presents an investigation on the achievable gain in ultra wideband (UWB) indoor propagation channels through the application of diversity and multiple input multiple output (MIMO) techniques. Both, signal to noise ratio and channel capacity are investigated based on simulation results from a ray-optical simulator. In particular the different behavior of classic diversity approaches and spatial multiplexing MIMO is regarded.

Lowdin Transform on FCC Optimized UWB Pulses

In this contribution we present a novel method for constructing orthogonal pulses for UWB impulse radio transmission under the FCC spectral mask constraint. In contrast to previous work we combine a convex formulation of the spectral design with Lowdins orthogonalization method [1], which delivers a shift--orthogonal basis optimally close (in energy) to the initial pulse, which generates (in a stable way) the shift--invariant space. The convex formulation of the spectral design is achieved by approximating the FCC mask with a finite--order filter matched to Gaussian monocycles as input. The output pulse then has high energy concentration in the passband (NESP value). Using Lowdins orthogonalization we compute the corresponding shift--orthogonal pulse. We show that our approach is able to generate for finitely many shifts, orthogonal equal energy pulses with nearly the same NESP value. Furthermore, we show that the orthogonalization procedure can be well approximated using the Zak transform allowing for an efficient implementation with the discrete Fourier transform. Surprisingly, we could observe, that for certain parameters, this approximation yields almost the same performance as the exact Lowdin method.

Comparing UWB Freespace Propagation and Indoor Propagation Including Non-ideal Antennas

Electromagnetic wave propagation of UWB signals can be interpreted as a superposition of narrowband electromagnetic wave propagation for a large set of frequencies. Since channel and antenna radiation patterns depend on frequency, describing and modeling the system transfer function of a UWB system including channel and antennas is more challenging compared to a narrowband system. This paper compares mathematical modeling of UWB freespace propagation to the more realistic case of UWB multipath propagation in indoor scenarios. Simulation results based on 3D Ray Tracing visualize the effect of both indoor channel and antennas on the UWB transmit signal in an indoor scenario, and finally, it is demonstrated, how signal distortions can be compensated by inverse filtering using an estimated system transfer function.

Löwdin's approach for orthogonal pulses for UWB impulse radio

In this contribution we present a novel orthogonalization method for ultra-wideband (UWB) impulse radio transmission. Contrary to other work we utilize Löwdins orthogonalization method which delivers a shift-orthogonal basis optimally close (in energy) to the initial pulse generating the shift-invariant space. We show that the shift-orthogonal basis can be well approximated using the Zak transform whenever the initial pulse fulfils certain conditions. This method can be efficiently implemented with the discrete Fourier transform. Furthermore we discuss the existence of compactly supported shift-orthogonal pulses, which are desirable for pulse position modulation.

Application of Optimal Pulse Design in Non-ideal Ultra-wideband Transmission

The performance of an impulse radio system depends on the pulse shape, modulation, coding, the front-end components, the channel and the receiver structure. In this contribution, a Time Hopping Pulse Position Modulation (TH-PPM) system is investigated that operates in an indoor scenario and consists of non-ideal frontend components and a correlation receiver. The question arises how the pulse shape influences the system performance, namely the bit error rate. Classical pulse shapes do not fully exploit the power spectral density regulation and lead to reduced transmit power and performance. Therefore, optimal pulse shapes are of great interest. This contribution first summarizes how optimal pulse shapes can be obtained and demonstrates in a second step how they improve the system performance if the system is assumed to be non-ideal which is neglected in most contributions.

Bit Error Rate of a Non-ideal Impulse Radio System

The development of a UWB impulse radio front end for commercial indoor applications is a challenging task, since its components must have constant characteristics over an ultra-wide bandwidth to achieve high performance. In reality, non-ideal behavior cannot completely be cancelled out. For the estimation of the performance of such a non-ideal system by a system simulation, dedicated modeling of the components is important. This contribution shows the modeling of non-ideal components like oscillator, UWB antennas, indoor channel, and low noise amplifier, based on rigid assumptions. A system simulation of the (simplified) non-ideal impulse radio system is performed with the advanced design system (ADS) showing the achievable bit error rate. To improve the performance, optimal pulse shaping in the presence of non-ideal components is discussed.

Signal Optimization in UWB Systems

In this article an optimization of the on-air transmitted UWB signal is performed. This is achieved by designing an adapted filter, that not only restricts the signal to the mask given by the regulations, but also allows to compensate the non-ideal behavior of the UWB components at the transmitter side. Since for UWB transmission the power spectral density is limited, by optimizing the on-air transmitted UWB spectrum it will be possible to have an improvement of the transmitted power and hence of the transmission performance.