The authors present a W-band Rotman lens (RL) beamformer with WR-10 waveguide interfaces. Radio frequency characteristics, such as phase relationships and insertion losses, including the beamforming capabilities of the RL were simulated and measured to validate the performance of generating four RF beams with ±60° field of view. Subsequently, the RL as beamformer was integrated into a transmitter setup in conjunction with the array antenna, in addition to a receiver setup that was constructed from off-the-shelf components. Both W-band transmitter and receiver were used to demonstrate a wireless link transmission in an outdoor urban - mobile user access or mobile backhauling - deployment scenario; over 85 GHz carrier frequency. The demonstration used a 5G-NR Release-15 conform waveform with 400 MHz of bandwidth and up to 256 quadrature amplitude modulation (QAM). The demonstration trial was conducted including line-of-sight (LOS), obstructed line-of-sight (OLoS), and none-line-of-sight (NLoS) scenarios; and reported a successful 16QAM over 184 meters OLoS link and 16QAM over 116 meters NLoS link. The work provides experimental evidence of the potential for high-frequency bands like the W-band to be utilized in future (6G and beyond) wireless communication networks.

Extreme multiple-input multiple-output (MIMO) is identified as a future technology trend for IMT -2030 6G, evolving from MIMO in 4G and massive MIMO in 5G. A large antenna array not only forms a high-gain narrow beam to compensate for path loss but also enables multiple layers or streams that increase channel capacity. The classical Shannon theorem evaluates the single-input single-output (SISO) channel capacity. Applying a channel transfer function (CTF) matrix to Shannon's theory ena-bles the estimation of the MIMO channel capacity. This paper compares MIMO capacity and SISO capacity in a similar propa-gation environment based on field measurement data in 6 and 37 GHz shared bands. Measurements were in fixed wireless access (FW A) like outdoor-to-indoor scenarios in a typical North Ameri-can residential neighborhood. The channel sounder consists of two transmit antennas separated by two wavelengths and a receiver antenna moving on a virtual circular array (VCA). One thousand$2\times 2$CTF matrices are extracted from the measurement to calcu-late the MIMO channel capacity and capacity gain compared with SISO channels. The measurement was completed at 136 transmit-ter-receiver positions in various line-of-sight (LOS) and non-LOS (NLOS) conditions and both frequencies. The average$2\times 2$MIMO channel capacity is 1.7 times larger than SISO in the LOS condition at 6 GHz and 1.9 in the NLOS condition with rich multipath. This MIMO channel capacity gain is 1.7 at 37 GHz in the LOS condition and 1.8 in the NLOS condition. The MIMO capacity is further compared for various receiver (mimicking a consumer premise equipment, CPE) orientations, which indicates careful se-lection of CPE orientation in a FW A scenario is essential to opti-mize MIMO capacity in LOS conditions while it is insignificant in NLOS condition. Higher frequency is more orientation dependent.

This paper introduces metrics and corresponding measurement methods for the characterization of the time-variant radio channel. The known 2-dimensional system functions, the corresponding 1-dimensional power densities, and their identification by channel measurements are introduced. Further statistical parameters like path loss, delay spread, Doppler spread, and the Ricean K-factor are derived from the system functions. Additionally, the description of the temporal evolution by means of spectrograms is presented. The developed methods are applicable for all frequency ranges and are valuable for the design and optimization of communication and sensing applications in particular. In this paper, they are illustrated by experimental channel measurements in the D-band at 160 GHz.

This paper introduces THz channel propagation measurements at 300 GHz in an outdoor roof terrace environment. The results exhibit multipath reflections of up to 1 km distance, demonstrating the extreme sensitivity of this novel measurement system. From the measured data instantaneous power delay profiles were calculated, which were analyzed with respect to path loss, as well as the fading parameters RMS delay spread, channel length, and number of multipath components. The path loss was modeled according to the log-distance law. It was observed that the path loss exponent was slightly below two, whereas all fading parameters were correlated and increased with distance.

This paper reports the development outcomes of the world's first integrated analog beamforming - transmit and receive - wireless front-ends operating in the D-band (a sub-THz band), particularly designed to operate within 150 GHz to 170 GHz frequency range. Front-end hardware development includes monolithic microwave integrated circuit (MMIC) chips of the multichannel power amplifier, multichannel low-noise amplifier, and RF switches. Moreover, the development includes an analog beamforming RF network and a low-profile microstrip 1-by-8 uniform linear antenna array, which were both developed on a resistive silicon substrate. The paper also features a successful long-range (320-meter) line-of-sight unidirectional point-to-point wireless transmission experiment, utilizing a 5G-NR orthogonal frequency division multiplexing (OFDM) waveform over a 160-GHz carrier frequency. The experiment demonstrated a successful transmission of OFDM waveforms using up to a 16-QAM (quadrature amplitude modulation) scheme in the D-band.

The Industrial Internet of Things (IIoT) enables machines to communicate robustly. High reliability, high throughput, and low latency are the critical capabilities of IIoT, which have posed great challenges to existing wireless solutions for industrial applications. Due to the vast available bandwidth, the emerging millimeter-wave (mmWave) technology is promising to address this bottleneck. However, the propagation behaviors at such high frequencies in the harsh industrial environment have yet been well understood. In this work, extensive measurements have been conducted in a representative industrial application scenario using a 2-GHz wideband directional channel sounder in the 28-GHz mmWave band. By exploiting the measurement with excellent resolution, the multipath components’ (MPCs) delay-angular space is transformed onto the scatter points (SPs) in the propagation environment. An effective clustering algorithm is then proposed to cluster the SPs without prior knowledge and iterations. Through a geometrical optics analysis, the SP clusters are classified corresponding to the reflectors. By doing this, the cluster-generating reflectors are reduced to a quasi-deterministic (QD) channel model that ensures spatial consistency and MPCs’ stochastic dispersion. Finally, it is shown that the measurement data agrees well with the proposed QD model, indicating the high fidelity of the proposed model.

This paper presents the results of several over-the-air (OTA) transmission experiments utilizing fifth-generation new-radio (5G-NR) waveforms in the W-Band (75 GHz – 110 GHz) – a candidate frequency band for the sixth-generation (6G) mobile network in the near-sub-terahertz region. These experiments were conducted in an outdoor environment, including line-of-sight, non-line-of-sight, and obstructed-line-of-sight scenarios. To perform these experiments, we constructed transmit front-end and receive front-end prototypes operating in the W-band. In addition, the components of these front-ends prototypes were developed, including a Rotman lens, power divider/combiner, sector horn antenna array, and an antenna feeder in our transmitter setup. The carrier frequency was 85 GHz, and the transmitted signal bandwidth was up to 400 MHz. The experiment reported in the line-of-sight scenario a successfully transmitted 5G-NR downlink waveforms over a 600 meters distance with 64 quadrature amplitude modulation (64 QAM) for the data channel. The experiment outcome demonstrates the W-band’s potential as a frequency band for mobile access in future 6G mobile networks.

The article discusses a radio-frequency-based self-interference cancellation (SIC) technique to handle the self-interference signal segment associated with the self-interference caused by antennas’ mutual coupling, particularly for dedicated-transmit-and-receive antenna configurations. The technique is a novel SIC technique based on antenna decoupling utilizing a lossless network in the radio frequency domain. At first, the authors present a fundamental physical and mathematical description of the self-interference radio channel, employing antenna scattering matrix representation and spherical vector wave expansion. Then, the article presents the experimental results of two antenna mutual coupling measurements – including a single-input-single-output setup and a$2\times 2$dual-polarized multiple-input-multiple-output (MIMO) setup. Afterward, the authors discuss the lossless network decoupling technique for MIMO full-duplex wireless transceivers. Finally, the authors present a generalized-$\Pi $synthesizing topology of the lossless decoupling network and empirically evaluate its SIC performance by leveraging the conducted antenna mutual coupling measurement results. The empirical evaluation validates the effectiveness of the lossless decoupling network in canceling the self-interference entirely for a specific design frequency – narrowband systems. Moreover, the evaluation reveals the degradation of the network SIC performance with respect to system bandwidth and the deviation of antennas’ separation distance from its nominal design value.

This paper presents first angle-resolved measurement results in the terahertz domain for an industrial environment. The measurement campaign carried out is to be understood as a feasibility study on terahertz communication in industrial environments. Impulse response data accumulated with a correlative time-domain channel sounder that operates at a carrier frequency of 300 GHz with a measurement bandwidth of 2 GHz is analyzed with regards to channel parameters such as path gain, path loss, delay spread and angular spread. Three distinguishing carried out industrial measurement scenarios each report a successful execution. Multipath component analysis is realised based on an exceptionally high dynamic range of about 60 dB. The analysis of the collected data shows that mentioned channel parameters can be obtained for industrial surroundings that are heavily dominated by machinery, metal cladding and concrete.

The integration of wireless communications into industrial production allows processes to be faster, more flexible and more cost effective. Fifth generation (5G) mobile networks are supposed to meet the requirements for ultra-reliable low latency communication, especially in non-public deployments. Already, spectrum around 3.7 GHz is reserved for such deployments and an expansion into millimeter wave range around 28 GHz is foreseeable. This paper presents a channel measurement campaign at both 3.7 and 28 GHz in an industrial production hall in three different relevant scenarios. Path loss, K-factor and RMS delay spread are evaluated.

In this paper, we discuss a controlled environment over-the-air verification approach for directional channel sounder receivers at millimeter-wave frequencies. The presented verification setup uses a benchtop compact antenna test range comprising two feed-reflector systems with overlapping quiet zones, thus creating two primary multipath components with well-defined angles of incidence at the receiver under test. We discuss possible verification scenarios and present initial measurement results for a virtual array/synthetic aperture-type SIMO channel sounder at 29 GHz.

In this paper a novel sampler that performs beam-forming is introduced. Several parts of the receiver chain are combined into one compact sub-sampling beam-forming summation track and hold (SSBS-TH). It directly integrates a true time delay with a phase correct summation unit. Furthermore the proposed circuit includes the sampling capacitance of a time interleaved (TI) analog-to-digital converter (ADC). The SSBS-TH operates at 12 GS/s to enable wide-band operation and cover frequencies up to 6 GHz. Therefore it is suitable for software defined radio (SDR). An overall linearity of 56 dBc and a signal-to-noise ratio (SNR) above 52.8 dB is achieved.

With the expected adoption of millimeter wave technologies for industrial communication, it is fundamentally important to properly understand the radio channel characteristics of such environments. This paper presents the setup, scenario and results of a measurement campaign at 28 GHz in a machine hall. The radio channel was measured with a bandwidth of 2 GHz and both large scale parameters and directional information were extracted. Evaluation of the power delay profiles shows that the channel contains dense multipath components. A path loss model is parameterized and blockage losses, RMS delay and angle spreads are evaluated. Comparison with the 3GPP TR 38.901 channel model shows that none of the currently defined scenarios is a fit for industrial settings. This emphasizes the need for a newly defined scenario with an industry specific parameter set.

In full-duplex wireless communication systems, transmission signals travel through self-interference radio channels before they will be received by the local receivers. This paper studies time dispersion characteristics of these channels for an indoor cross-polarized 2x2 multiple-input-multiple-output antenna (MIMO) system. Four cross- polarized radio channels - excited by two transmit antennas and captured by two receive antennas perpendicularly polarized to the transmit antennas - were measured in an indoor spacious foyer (entrance hall) environment. By means of a vector network analyzer, one gigahertz of bandwidth, which occupies 2-to-3-GHz frequency band, was swept to sound these self-interference channels. The four vector network analyzer test ports were connected to two dually- polarized magnetoelectric dipole antennas that were utilized to observe the self-interference channels. Each of the dipole antennas possesses: Two radio-frequency ports, a hemispherical radiation pattern, and an excellent cross-polarization discrimination properties. The antennas were placed at two meter height and moved in track along the room circumference to measure the self-interference channels at 27 positions. The excellent cross-polarization isolation properties of the utilized antennas has allowed to capture a time- domain instantaneous channel dynamic that exceeds 120 dB - normalized with respect to the transmit power at the antennas' physical ports. This vast dynamic has used to analyze the channel with sliding sensitivity threshold. The channel measurement reports maximum excess delays up to 689 ns. Furthermore, time dispersion parameters and their associated values are discussed and reported in this paper based on the conducted self-interference channel measurements.

For fifth generation mobile communication systems (5G) utilization of the band from 6 to 100 GHz is investigated to increase the system capacity, because it is relatively easy to ensure the wide bandwidth in these frequencies. Considering the capital investment involved in establishing 5G service areas, utilizing non-line-of-sight (NLOS) environments for service areas is desirable. Moreover, since beamforming will be utilized to compensate large path loss in higher frequencies, it is important to understand the relationship between the multipath and the city structure in a NLOS environment in which compensating for path loss is more important than LOS environment. In this report, we investigate the relationship between the multipath and the city structure around intersections based on delay profiles measured using a horn antenna in a NLOS street cell environment. The results clarify that diffraction waves from building corners and reflected waves from building walls that exist along the street on which a mobile station is deployed are dominant paths.

In this paper, novel self-interference cancellation technique is proposed. The technique addresses in particularly the transceivers where dedicated-transmit-and-receive antenna configurations are embraced. The technique, moreover, relies on a lossless decoupling network, which interconnects the transceiver's chains to the antenna elements. The values of the network's reactive components, which are the building blocks of the lossless network, can be computed to suppress the self-interference at the local receivers for the targeted frequency. Thus, the technique provides a self-interference suppression method at the radio-frequency domain, which does not waste energy for cancellation purpose. Moreover, the technique can implicitly assure optimized power delivery among the antenna array elements and the transceiver front-ends. Network analysis of a multiple-input-multiple-output antenna array in a full-duplex transceiver is presented in order to characterize the self-interference in terms of mutual coupling phenomenon among the antenna array elements. Mutual coupling measurements of two identical antennas setup are presented and analyzed. Finally, empirical assessment of the proposed self-interference cancellation technique is provided, to show that the self-interference cancellation levels can exceed 70 dB by employing the proposed technique.

Reliable connectivity between vehicles is a requirement for efficient overtaking warning systems. We investigate the 6 GHz propagation channel between oncoming vehicles with five different types of large obstructing vehicles in a poor scattering environment. The presented channel gains emphasize the advantages of different antenna positions and the difference between a straight road and curved road. We conclude that connectivity ranges on a straight road are close to the minimum distance required by a warning system. We furthermore conclude that the channel gain of antennas mounted inside the vehicle can be higher compared to antennas mounted on the roof, which can increase the connectivity range significantly.

Urban intersections constitute an important safety-critical scenario for vehicle-to-vehicle communication. Based on measurements, this paper presents detailed investigations of the radio wave propagation processes in a typical urban intersection. We focus on one time instance of the propagation process and set up hypothesis for locations of the scattering objects. Multipath components (MPCs) are identified and an MPC tracking algorithm is applied. The number of MPCs and the lifetime of MPCs for this communication scenario are analyzed. It is concluded that the lifetime of an MPC is heavily dependent on its relative power, with typical values in the range 0.05-0.3 s corresponding to 0.5-3 m travel distance of the vehicles.

The use of previously unused spectrum in the millimeter-wave band is discussed for future fifth generation (5G) mobile communications systems. The legacy frequency bands are very densely used and free spaces are rare, but the question remains, whether increasing the carrier frequency is a good idea. In this paper we derive frequency dependent link capacities and energy efficiency measures for a small cell heterogeneous network scenario.

The millimeter-wave frequency bands, especially the license free band at 60 GHz, is a candidate for future broadband access links. Path loss measurements have been performed in a typical small cell access scenario. Path loss model parameters were derived for these results, including large and small scale effects. Using this model a system level analysis was performed to evaluate the performance of a heterogeneous network using millimeter-wave access links.

Future collision avoidance systems for crossing- scenarios depend on a reliable vehicle-to-vehicle communication link. Consequently, a deeper insight into inter-vehicle communication performance at intersections is needed. This paper presents three intersection categories for non-line-of-sight communication scenarios, based on a large measurement data set. For each category, packet delivery rates with respect to a 2-dimensional distance-measure are provided, which can be used for network simulations or application evaluations. The results show performances that cannot be described with a (cumulative) 1-dimensional distance-measure. We present a new evaluation method that involves channel sounder data and transmission simulations, enabling a simultaneous analysis of both, the communication performance and the underlying propagation channel. The method can also be used for a realistic evaluation of advanced signal processing algorithms.

IEEE 802.11p was released as the standard for wireless access in vehicular communication. In this paper, we introduce an 802.11p performance evaluation method based on realistic transmission simulations in Matlab. The vehicular propagation channel was measured beforehand using the wideband HHI Channel Sounder. We conducted channel sounder measurements of oncoming traffic at two different highway sections. The proposed method allows the execution of sample-based transmission simulations with full access to the receiver signal processing and all insights of wideband channel impulse responses. We compute mean packet delivery rates for different packet sizes and discuss the effect of the time-variance in a vehicular propagation channel on the transmission success.

In this paper we present a statistical evaluation of the lifetime of multipath components for the vehicular radio channel. We introduce a new identification and tracking algorithm. The algorithm follows a geometrical approach exploiting the high scatterer resolution in the measurement data and takes as an estimation basis considerations on the relative movement of the scatterer. We subsequently apply the algorithm to evaluate the measured data. We use wideband channel measurement data collected at urban street intersections under NLOS-conditions. We sequentially evaluate weighted interrelations between detected contributions in the time-delay domain and decide on common underlying scatterers or not. We suggest a classification of distinct and diffuse contributions by means of a threshold with respect to lifetime and discuss on their temporal characteristics, based on an exemplary measurement with typical values. In specific we characterize the lifetime by means of a probability density function and further examine the relation of lifetime and power level of the multipath contribution.

A very promising technical approach for future wireless communication systems is to combine MIMO OFDM and Direct (up/down) Conversion Architecture (DCA). However, while OFDM is sensitive to Carrier Frequency Offset (CFO), DCA is sensitive to I/Q-imbalance. Such RF impairments can seriously degrade the system performance. For the compensation of these impairments, a preamble-based scheme is proposed in this paper for the joint estimation of CFO, transmitter (Tx) and receiver (Rx) frequency-selective I/Q-imbalance and the MIMO channel. This preamble is constructed both in time- and frequency domain and requires much less overhead than the existing designs. Moreover, Closed-Form Estimators (CLFE) are allowed, enabling efficient implementation. The advantages and effectiveness of the proposed scheme have been verified by numerical simulations.

In this paper we present parametrization for pathloss regarding the wideband car-to-car channel at 5.7 GHz. Furthermore, we investigate the power decay of delay-resolved multipath components, categorized in LOS and NLOS paths, and discuss the results. The results show relatively high pathloss exponents and a strong dependency of the exponent on the LOS path, which carries the main part of signal power. The parametric equations and the parametrization were derived on the basis of 2 × 2 Multiple Input Multiple Output (MIMO) channel measurements in and around the city of Berlin in Germany.

In this paper we present a measurement campaign aimed to identify important radio channel parameters for selected accident situations on urban street intersections. We focus on two scenarios, that yield a significant number of severe urban accidents: Vehicles traveling on perpendicular streets and non-traffic-light-regulated left turn. The measurements were performed in the german capital Berlin by means of the HHI-Channel-Sounder, a true 2 × 2 Multiple Input Multiple Output (MIMO) wideband radio channel sounder operating at a carrier frequency of 5.7 GHz. Having used antennas with a high spatial separation during the measurements, we discuss results for selected measurements regarding the received power at each antenna.

Recently, a strong demand on high data rate wireless communication can be observed. The development of multi-gigabit wireless transmission systems has become very attractive. For achieving such data rates, the exploitation of 60 GHz mm wave is a very promising technical approach and has been adopted in IEEE 802.15.3c. Except for physical layer (PHY) designs, the Medium Access Control (MAC) layer design is also crucial for the achievable system throughput (TP). Among the MAC functionalities, the acknowledgment (ACK) mechanism is a very important component affecting the transmission reliability and efficiency. Based on the ACK-mechanisms in 802.15.3c, this paper proposes a Hybrid Dynamic Frame Aggregation and Block-ACK (HD-FABA) scheme, which can further enhance the transmission efficiency and the system throughput. A theoretical model is developed to enable efficient parameter optimization and throughput maximization. In this way, the system can adaptively adjust its parameters according to the PHY conditions, so that the PHY data rate is exploited at best. The effectiveness of the proposed scheme was verified by numerical simulations.

The compensation of frequency selective I/Q-imbalance and modulator (MOD) offset error can improve the performance of direct-conversion transmitters significantly. For effective compensation of these two effects, the parameter estimation is crucial. In many applications, ``semi-blind'' estimation is desired i.e. not dedicated pilot signals but the communication signals are used for estimation. Conventionally, Least-Square Estimation (LSE) is applied. However, if the communication signal has spectral gaps (e.g. due to oversampling), the LSE will suffer from ill-conditioned matrix problem, which results in severe estimation error. To overcome this problem, we propose an Iterative Frequency Domain Estimation (IFDE) technique, which operates adaptively according to the spectral characteristic of the communication signal and can provide good calibration performance. The effectiveness of the IFDE and its advantage over conventional LSE are verified by numerical simulations.

MIMO OFDM is a very promising technique for high-speed wireless transmission. By applying the Direct Conversion Architecture (DCA), low-cost, low-power and fully integrated implementation of such systems is enabled. However, the performance of DCA may be seriously limited by I/Q-imbalance, which shows frequency selectivity in broadband systems. In this paper, we consider an indoor scenario and present effective preamble based joint compensation of the MIMO wireless channels (block fading) and the TX- and RX-frequency-selective I/Q-imbalance. Two low overhead preambles are proposed, which are constructed in time- and frequency domain, respectively. Both of them have their own advantages. Compared to the literature, our paper considers more practical issues and shows how to choose the adequate preamble design according to system parameters to achieve the best performance with relatively low computational complexity. Effectiveness of the proposed schemes is verified by numerical simulation.

In this paper, antenna diversity (AD) schemes are presented for frequency-domain (FD) multi-user detection (MUD) in the up-link (UL) of cellular systems which apply CP (Cyclic Prefix) assisted DS-CDMA (direct sequence code division multiple access). Alamouti-based space-time-code (STC) was applied to exploit transmitter (TX) diversity. The MUD and the diversity combining in the receiver (RX) are MMSE (minimum mean square error) based. Simulation results show that with moderate computational complexity, the SIMO and MIMO schemes have achieved better performance than the iterative block decision feedback equalization (IB-DFE) based scheme in. It was also shown that SIMO is superior to MISO in terms of diversity exploitation and achieves the best tradeoff between complexity and performance.

For communication systems with direct-conversion architecture, I/Q-imbalance can be a crucial performance limiting effect. Furthermore, as the datarates of the wireless communication systems increase, larger transmission bandwidths (BW) and high-order modulated waveforms are applied. As a result, the systems are sensitive to frequency dependent I/Q-imbalance and the corresponding calibration is more challenging. Fortunately, efficient signal equalization is possible with OFDM, which is a widespread technique for broadband high datarate systems. Moreover, OFDM transceivers may have symmetrical transmitter (Tx) and receiver (Rx) structures, typically in ad-hoc networks like WLAN. In this case, efficient and separate I/Q-imbalance parameter estimation in the Tx and the Rx is possible. Based on the considerations above, a new pilot-based self-calibration scheme is presented in this paper, which requires relatively low hardware overhead and signal processing complexity. Its effectiveness was verified by numerical simulations.

Using a channel sounder for wideband Car-to-Car 2 × 2 multiple input multiple output (MIMO) radio channel measurements at 5.7 GHz with a bandwidth of 1 GHz, we have investigated typical car-to-car communication scenarios in a variety of environments in and around the city of Berlin in Germany. Apart from the full bandwidth signal, we have additionally evaluated an extracted 10 MHz signal. Among other results, we present delay and Doppler spread statistics and spatial correlation evaluations.

In this paper we investigate the 60 GHz in-car wideband radio channel to assess the feasibility of 60 GHz high bit rate radio communication inside a car. The investigations are based on a measurement campaign comprising different application-oriented transmission scenarios and propagation conditions. We analyze the channel gain, time dispersion and frequency selectivity. Finally, we derive the achievable signal-to-noise ratio and cover interference aspects.

In this paper, the coverage of a wireless incabin transmission system is analyzed by means of ray-tracing simulations. The investigations have been performed with respect to a cellular radio system operating inside a wide-bodied aircraft. The system utilizes the 60 GHz frequency band with a signal bandwidth of 250 MHz per frequency channel. For the simulations a detailed model of the aircraft has been drawn up including passengers. Dielectric parameters of common materials have been taken from literature, unknown values of special materials like carbon fiber reinforced plastic (CRP) and glass fiber reinforced plastic (GRP) have been estimated from reflection and transmission measurements. The coverage is analyzed with respect to the signal-to-noise-ratio (SNR) and signal-to-interference-ratio (SIR) regarding a occupied and a non-occupied passenger cabin.

In this paper, channel estimation schemes as well as low crest-factor preamble construction are presented for practical MIMO OFDM systems with NULL subcarriers. In the presence of NULL subcarriers, the performance of the channel estimator in [1] degrades considerably. Therefore, Maximum-likelihood (ML) channel estimators were proposed for MIMO OFDM systems with NULL subcarriers [2], [3]. However, they have relatively high computational complexity. Thus, more efficient schemes are proposed in our paper, with regard to two different cases of NULL subcarrier usages: only DC subcarrier is null or both DC and high frequency subcarriers are null. Simulation results show that the new schemes achieve performances near the optimum error bound.

OFDM signals have sidelobes in the spectrum, causing interference to the neighboring frequency channels in a cellular system. The sidelobes can be suppressed by raised cosine (RC) windowing in time domain, while the inter-cell interference can be suppressed by reserving a guardband between neighboring frequency channels. A higher roll-off factor (ROF) of the RC window leads to better sidelobe suppression and allows a smaller guardband size, increasing the spectral efficiency. However, higher ROF implies longer symbol duration and reduced data rate. Therefore, there exist a tradeoff between the ROF and the guardband size. In this paper, a joint optimization technique for the ROF and guardband size is presented, which maximizes the data rate.

Due to the extremely high user density in in-flight entertainment (IFE) systems, the required sum data rate is in the order of several Gbit/s, which can not be provided by existing standard wireless systems. To achieve such high data rates, the 60 GHz frequency band is very well suited due to its specific advantages. In this paper, a design concept for a cellular-based wireless IFE system is presented. Furthermore, the results of system simulations using measured 60 GHz in-cabin wireless channels are shown.

A channel sounder for wideband car-to-car 2 x 2 multiple input multiple output (MIMO) radio channel measurements at 5.7 GHz with a bandwidth of 1 GHz has been developed. With the use of highly accurate synchronization units a high degree of coherence was achieved. The HHI-channel-sounder has been used in a measurement campaign in typical urban traffic scenarios in Berlin, Germany. This paper presents the basic operating concept of the system, followed by first results from the campaign.

In this paper an analytical description for the transmission between multiple antennas is developed. The method allows the determination of covariances and channel capacity with respect to physical antenna parameters as polarization, antenna pattern and mutual coupling. Furthermore the utilization of the method concerning the examination of some array configurations is demonstrated.

In this paper, we present the results of a measurement campaign regarding the 60 GHz in-vehicular wireless channel. The measurements have been performed inside an aircraft passenger cabin by the use of a modular setup covering a bandwidth of 1 GHz. We consider path loss aspects and investigate the time-dispersive nature of the channel. Additionally the influence of an obstructed line-of-sight is analyzed.