Bernhard Rembold

Far-region electromagnetic radiation with a vertical magnetic dipole in sea

Great attention has been paid to conveniently calculating the electromagnetic (EM) field due to a vertical magnetic dipole (VMD) buried in stratified media. It is quite difficult because this topic involves the computation of Sommerfeld (1949) type integrals (SI). In this paper closed-form expressions for the far field of a VMD embedded below the sea surface are obtained easily by using a new technique to evaluate the SI with the aid of complex image theory. The present approach can be also used to get the far field formulas for other similar cases.

SABA: a testbed for a real-time MIMO system

The growing demand for high data rates for wireless communication systems leads to the development of new technologies to increase the channel capacity thus increasing the data rate. MIMO (multiple-input multiple-output) systems are best qualified for these applications. In this paper, we present a MIMO test environment for high data rate transmissions in frequency-selective environments. An overview of the testbed is given, including the analyzed algorithms, the digital signal processing with a new highly parallel processor to perform the algorithms in real time, as well as the analog front-ends. A brief overview of the influence of polarization on the channel capacity is given as well.

Unified spatio-temporal frequency domain equalization for multi- and single-carrier CDMA systems

Single carrier (SC-) and multi carrier (MC-) CDMA transmission are compared. Spreading and pulse shaping processes are shown to be identical in both systems. Based on this equality, a unified frequency domain system model is derived for a multiuser system with multiple base station antennas. The system model includes the effects of spreading, oversampling, pulse shaping, the MIMO (multiple input multiple output) channel and selection filter. Linear spatio-temporal joint detection is proposed for the uplink and an appropriate predistortion for the downlink. Predistortion offers efficient downlink transmission with spatial diversity and uses a signal processing very similar to the joint detection. Similarities of uplink and downlink processing of SC and MC-CDMA argues for a unified hardware implementation. This idea is discussed and some implementation issues like variable FFT sizes, conflicts in resource sharing, different resolution requirements and computational complexity are addressed.

Adaptive MIMO techniques for the UTRA-TDD mode

In this paper, MIMO techniques for suppression of ISI and MAI in frequency-selective fading channels are evaluated analytically and by means of link level computer simulation in a UTRA-TDD like system. Equalization of the spatio-temporal channel matrix is either performed at the transmitter via joint predistortion (JP), at the receiver via zero-forcing block linear equalization (ZF-BLE) combined with symbol cancellation (ZF-B-BLAST), or balanced at both sites of the channel via space-time vector coding (STVC). The computational complexity of all presented approaches is reduced by the introduction of blocked block-circulant system matrices.

Optimum Modulation Efficiency and Sideband Backscatter Power Response of RFID-Tags

The paper defines the efficiency of a transponder-modulatedRFID-tag andderives an expression for the sideband backscatter response. The modulation is assumed to be generated by switched transponder input impedances, delivering modulation sidebands. An optimum antenna impedance is derived for given transponder impedances for maximum modulation efficiency. Using this result, the sideband backscatter power response of a tag is given. Some examples demonstrate the practical meaning of the derived expressions. Index Terms – RFID, back scatter, sideband modulation

Investigations on UHF RFID wave propagation using a Ray Tracing Simulator

This paper focuses on the use of RFID technology in the UHF 868 MHz band for identification of consumer items in a distribution center, warehouse or packing station. Wave propagation between RFID transmitters, passive transponder tags and receivers are simulated with ray tracing in order to analyze the functionality of the system in a realistic environment. Index Terms – RFID, ray tracing, wave propagation, simulation, consumer goods, distribution center, packing station, warehouse, tagging, identification

Joint Detection and Joint Pre-Distortion Techniques for SD/TD/CDMA Systems

Abstract In this paper, the trade-off between combined multiple access interference suppression in the spatial domain, i.e. by means of an antenna array with M elements, and in the code domain, i.e. by means of orthogonal spreading with spreading gain Qb, is examined for a Space Division/Code Division/Time Division Multiple Access (SD/ TD/CDMA) mobile communications system. With Joint Detection (JD) being applied at a multi-antenna receiver and Joint Pre-Distortion (JP) being employed at a multi-antenna transmitter, establishment of up to K^ MQh concurrent data channels is possible. For both JD and JP, sparse system models are developed allowing for an efficient computation of Zero-Forcing or Minimum Mean Square Error Block Linear Equalization (ZF/MMSE-BLE) procedures. Expressions for the uncoded BER in frequency-flat line-of-sight and Rayleigh fading channels are derived for the case of ZF-BLE. For frequency-selective channels, JD and JP system performance is evaluated by means of Monte-Carlo simulation. The promising results reveal that in multi-antenna TD/CDMA systems, the normalized spreading gain Ob/Kb can be reduced below 1, leading to an obvious increase in the supportable data rate per user. If a larger number of antenna elements is available, the loss of spatial diversity sacrificed for user separation becomes negligible.

A 3-Port Antenna for MIMO applications

As well known, the capacity of a radio frequency channel can be enlarged by multiple input multiple output (MIMO) antenna system. By using identical antennas with the same orientation, a certain antenna distance must be respected for achieving the full MIMO gain. On mobile terminals, usually only a limited surface area for antennas is available. Therefore multiport antennas with small dimensions are requested, which offer sufficient decoupling between the ports. The present paper describes a 3-port antenna, operating at 5.6 GHz, which can be used e.g. for MIMO-WLAN applications. The design is outlined and simulated and measured results are given.

Radar cross section of long wires

Using a continuous wave (CW) Doppler radar at 60 GHz, the radar cross sections of long metallic rods were measured. The results show linear increase with growing distance between radar and rods. A new expression for the radar cross section, which was also derived, demonstrates good agreement with the measured data.

Evaluation of MIMO Systems with Respect to Front-End Imperfections

In multiuser multiple-input multiple-output (MIMO) systems the performance of joint detection and joint predistortion techniques highly depends on the quality of radio-frequency (RF) components. Therefore, the focus of this paper is on front-end imperfections. We demonstrate the influence of erroneous calibration (which is essential for downlink predistortion), phase noise and nonlinear amplifiers. For all issues we elaborate on the different disturbances that arise, analyse the impact on symbol estimation and evaluate system performance in ierms of coded bit error ratio (BER). A general result for all examined front-end imperfections is that their influence increases with the number of spatially multiplexed data streams culminating in unacceptable performance degradation in fully loaded systems. Moreover, Wiener-based detection and predistortion reduces the degradation due to front-end imperfections in low SNR regimes compared to zero forcing.