This article proposes a scheme to enable wideband and beam-reconfigurable transmitarray (TA) antennas with flexible bidirectional beams for Internet of Things (IoT) applications. The proposed scheme primarily consists of a polarization-rotation-based (PR-based) phase-shifting surface (PSS), a dielectric lens, and a feed source. By leveraging distinct frequency responses of the PR-based PSS and dielectric lens to electromagnetic (EM) waves, the proposed scheme can achieve exceptional beam reconfigurability. To validate the scheme, a bidirectional beam-reconfigurable TA antenna is developed. By mechanically rotating the feed source to tune its polarization from x-to y-polarization, the beam of the developed TA antenna transitions from a single forward beam, through a bidirectional beam, and finally to a single rearward beam, all remaining the same polarization. Notably, when the feed source is rotated to be 45-deg polarization, the forward and rearward beams exhibit comparable gains. The gain variation of the forward/rearward beam approximately follows cos(h), where h is the rotation angle of the feed source. Simulated results reveal that the developed TA antenna works well from 24 GHz to 28.5 GHz, exhibiting robust continuous and adaptive bidirectional beam reconfigurability with sidelobe levels below -15 dB and cross-polarization levels below -20 dB. A prototype is characterized, where the measured results align well with the simulated ones. With versatile beam-steering capabilities, the developed TA antenna is well-suited for 5G millimeter-wave (mm-wave)-enabled IoT applications, such as smart transportation systems, dual-side railway/roadway communication networks, and tunnel-based communication infrastructures.

Modulation recognition (MR) plays a pivotal role due to its application in the spectrum sensing of 5G industrial cognitive communications and radio interference detection at the physical layer of the Internet of Things (IoT). Previous works have mainly focused on simulated fourth-generation (4G) multicarrier systems and ideal radio frequency (RF) scenarios. To bridge the gap between practice and theory, we propose a viable MR algorithm on all-physical testbeds, with nonlinear impairments of 28 GHz active phased arrays (APA). Specifically, our testbed is built on the Rohde&Schwarz (R&S) vector signal generation R&S-SMBV100B and spectrum analyzer R&S-FSW 67 GHz. To extract salient modulation patterns, we develop a physical-informed scattering transform (SCT) MR network (SCTMR-Net). With SCT modules, SCTMR-Net produces the translation-invariant and deformation-stable representations of 5-G signals by wavelet convolution, nonlinear modulus and low-pass filters. Extensive experiments on real-world measurement verify the viability of SCTMR-Net for high robustness to APA impairments.

Unmanned aerial vehicle (UAV) millimeter wave (mmWave) technologies can provide flexible link and high data rate for future communication networks. By considering the new features of three-dimensional (3-D) scattering space, 3-D velocity, 3-D antenna array, and especially 3-D rotations, a machine learning (ML)-integrated UAV-to-Vehicle (U2V) mmWave channel model is proposed. Meanwhile, an ML-based network for channel parameter calculation and generation is developed. The deterministic parameters are calculated based on the simplified geometry information, while the random ones are generated by the backpropagation-based neural network (BPNN) and generative adversarial network (GAN), where the training data set is obtained from massive ray-tracing (RT) simulations. Moreover, theoretical expressions of channel statistical properties, i.e., power delay profile (PDP), autocorrelation function (ACF), Doppler power spectrum density (DPSD), and cross-correlation function (CCF), are derived and analyzed. Finally, the U2V mmWave channel is generated under a typical urban scenario at 28 GHz. The generated PDP and DPSD show good agreement with RT-based results, which validates the effectiveness of proposed method. Moreover, the impact of 3-D rotations, which has rarely been reported in previous works, can be observed in the generated CCF and ACF, which are also consistent with the theoretical and measurement results.

The new generation of 5G mobile and inter-satellite communication systems are using mmWave active phased array (APA) which have up to hundreds of individual analog transmitter and receiver chains and antennas. When moving to high integration scenarios, the isolation between the array and the power amplifiers (PAs) is often removed. Since the array elements are electromagnetically coupled, the waves fed to the antennas are also driving the output ports of the PAs. This effect creates a possible variable load at the output of each PA, depending on steering angle and radiated power at each element in the array. In this system, the behavior of each PA cannot be fully described solely as a function of its input, as it will change according to the coupled signal. In this paper the inter-element coupling of a 4x4 planar patch antenna array and the resulting variation in output impedance of the PA connected to each patch is simulated by using computer simulation tool (CST). The impact of the interelement coupling has been verified on linearization procedure of the active array.

In this paper, we demonstrate how a deep neural network (DNN) can be used to compensate for nonlinearities and distortion effects introduced by the latest technology of 5G transmitters. A linearization approach based on neural networks can successfully cope with the challenges introduced not only by the high nonlinearity, wide bandwidth, and high frequency but also with challenges due to inter-PA crosstalk and load modulation. The device-under-test used in this experiment, is a state-of-the-art $5\mathrm{G} 4 \times 4$ active phased array (APA) operating in highly nonlinear regions at 28 GHz with a 100 MHz wide 3GPP base station signal and with OTA measured signals used for training. Using the proposed DNN based linearization technique, an improvement of 11 % in error vector magnitude (EVM) and 10 dB suppresion in adjacent channel leakage ratio (ACLR) are achieved which demonstrates the promising potential of this technique for emerging broadband communication systems such as 5G/6G and low earth orbit (LEO) satellite networks.

This paper presents an electrical impedance characterization and measurement method for monitoring bone fracture healing progress after osteosynthesis, for cases applying an intramedullary nail. While existing solutions fail due to the presence of the nail, the proposed method makes active use of the nail to achieve accurate healing progress monitoring. The proposed method captures variations in the electrical impedance at the fracture site as body tissues transform from the blood (hematoma) to fully recovered intact bone during healing. The proposed method, therefore, has the potential to be used for data acquisition of bone healing and pave the way for digitized diagnosis and treatment of bone fractures.

In this contribution, a recently conducted measurement campaign for indoor millimeter-wave (mm-wave) propagation channels is introduced. A vector network analyzer (VNA)-based channel sounder was exploited to record the channel characteristics at the frequency band from 28-30 GHz. A virtual uniform circular array (UCA) with a radius of 0.25 m was formed using a rotator with 360 steps. Moreover, by taking advantage of fiber-optic technique applied in the channel sounder, measurements at 50 positions were performed from an indoor hall to an indoor corridor along a long pre-defined route. A low-complexity high-resolution propagation estimation (HRPE) algorithm is exploited to estimate the propagation parameters of multipath components (MPCs). Based on the HRPE estimation results, a novel clustering identification and tracking algorithm is proposed to trace clusters. Composite channel characteristics, cluster-level characteristics and dynamic (or birth-death) behaviours of the clusters are investigated, which constitute a dynamic model for the indoor mm-wave channel.

This paper presents a new SIW horn antenna with high performance in the mm-wave bands for the next generation mobile devices. The proposed antenna is integrated in a double layer of Rogers RO4003C substrate and requires a clearance of only 3 mm. Air vias are etched in the substrate in a specific portion of the horn aperture, in order to correct the phase of the electromagnetic wave and allow the beam pointing in the desired direction. Moreover, a tapered ladder transition is placed at the horn aperture to improve the impedance matching and enhance the radiation performance. Simulation results prove that the 6 dB bandwidth is wider than 40 GHz in the frequency range 24-64 GHz. In particular, the same beam pointing is guaranteed over the whole bandwidth with realized gain of 6.4, 8.5 and 8.7 dBi at 28, 38 and 60 GHz respectively. Simulations including two symmetric elements pointing opposite directions and a central element show that the angle of 90° can be covered with peak gain of 7.5 dBi at 28 GHz.

In this paper, a millimeter-wave (mm-wave) bow-tie antenna array is proposed to be integrated with a low-frequency Planar Inverted F-Antenna (PIFA) at the top edge of a handset. A layer of grating strips with pin diodes is added between the low and high-frequency antennas to provide reconfigurable radiation patterns. The proposed 5G array is matched from 24-30 GHz and can steer the beam in both configurations with a realized gain higher than 8 dBi in the broadside case, and more than 6 dBi when the radiation pattern is endfire.

A wideband endfire array considering the glass influence at 28 GHz is proposed in this paper. The array element is a bow-tie slot antenna above a ground plane, which has the endfire radiation pattern. A glass layer, which has the same size as the ground plane, is attached on the front side of the array. A trapezoid slot is made on the edge of the ground plane to compensate the influence of the glass layer. The simulated -10dB bandwidth is 11.3% from 25 GHz to 28 GHz and -6-dB bandwidth is 30.3% from 21 GHz to 28.5 GHz. The horizontal polarized endfire gain of the 4 element array ranges from 7.08 dBi to 8.36 dBi over the operating band. The array covers from -100° to 100°, when the realized gain is above 0 dBi on the XOY plane.

The aim of this work is to evaluate amplitude distributions of narrow-band channels based on sounding measurements made at 26 GHz. The setup is with an omni-directional antenna moving in different indoor environments with an access point (AP). Rician channel model parameters are obtained via maximum likelihood (ML) estimation and the k-factors are obtained as well as mean power levels. Depending on the type of environment and the location of the mobile with respect to the used AP, the found k-factors varies from about −10 dB up to about 9 dB.

Wideband large-scale array systems operating at millimeter-wave bands are expected to play a key role in future communication systems. It is recommended by standardization groups to use spherical-wave models (SWMs) to characterize the channel in near-field cases because of the large array apertures and the small cell size. However, this feature is not widely reflected in channel models yet, mainly due to the high computational complexity of SWMs compared to that of the conventional plane-wave model (PWM), especially when ultrawideband signals are considered. In this paper, a maximum likelihood estimator of low computational complexity is implemented with an SWM for ultrawideband signals. The measurement data obtained from an ultrawideband large-scale antenna array system at 28-30 GHz are processed with the proposed algorithm. The power azimuth-delay profiles estimated from the SWM and the PWM are compared to those obtained from rotational horn antenna measurement, respectively. It shows that the multipath components (MPCs) are well-estimated with the proposed algorithm, and significant improvement in estimation performance is achieved with the SWM compared to the PWM. Moreover, the physical interpretation of the estimated MPCs is also given along with the estimated scatterers.

Millimeter wave (mmWave) communication works in the frequencies above 6 gigahertz (GHz), with the system bandwidth up to 500 megahertz (MHz) or wider. In this case, the channel situations are dramatically different from the existing wireless channels in Third Generation/Fourth Generation (3G/4G) communication systems, and the stationarity of mmWave channels could be very different from our former knowledge. The focus of this paper is to study the frequency and spatial stationarities of mmWave channels. For better understanding, we compare the stationarity regions between mmWave channels and the channels below 6 GHz. First, the general average power delay profile (APDP) method is introduced as a metric to determine the size of the stationarity regions in time, frequency, and spatial domains. Then, the general APDP method is applied in the data analysis of a channel measurement. We find that the frequency stationarity regions of the channels are much larger in mmWave bands above 6 GHz than those in conventional bands below 6 GHz, while the spatial stationarity regions of the channels are much smaller in mmWave bands above 6 GHz than those in conventional bands below 6 GHz.

Channel characterization of multipath channels at centimetre and millimetre wave bands is of interest from both academia and industry, especially for the frequency bands that are under consideration for 5G mobile communication systems. In this paper, we first demonstrate the limitations of an existing vector network analyzer (VNA) based channel sounding system in terms of frequency range and measurement range. After that, an improved system is proposed to address these limitations. The proposed system is capable of measuring from 2 to 50 GHz at 30 meters distances. A measurement campaign utilizing the proposed setup equipped with rotational directive horn antennas, with a focus on multi-band power-angle-delay profiles, was performed. The measured frequency bands are 18-20 GHz, 25-27 GHz, 28-30 GHz and 38-40 GHz.

In this paper, we investigate the performance of a massive MIMO system using the time-reversal beamforming technique. The massive MIMO channels are simulated with ray-tracing at 3.5 GHz with a 200 MHz-bandwidth. We use a 64-element uniform cylindrical array as base station (BS) and we equip two users with single omnidirectional antennas. By applying convenient weights to the emitted signals, we expect to improve the useful signal level by both classic beamforming and time-focusing gains, while decreasing the inter-user interferences (IUI). The performance of the system is evaluated by the signal-to-noise (SNR) and signal-to-interference-plus-noise ratio (SINR) in a 10-path channel with line-of-sight (LOS). We compare the performance with the case where the BS is equipped with an omnidirectional antenna and without pre-processing. In this situation, the results show an SNR improvement up to 25 dB yet the output SINR is limited by the inter-symbol interferences (ISI), especially caused by the ground reflection.

This work presents results based on wideband radio channel measurements at 26 GHz. Three widely different indoor environments were measured; a cluttered laboratory, a corridor with a bend, and a large entrance hall. Power angular spectra were obtained for both vertical polarization (VP) and horizontal polarization (HP) at many different Rx locations, using both VP or HP for the fixed Tx. The results show that a quite rich channel may exist with several propagation paths. Further, coupling between the VP and HP was found in a non line of sight (NLOS) scenario.

This paper discusses multi-probe anechoic chamber setups for evaluating MIMO capable terminals with emphasis on generating spatial channel models. The multi-probe anechoic chamber method is a promising method for over the air testing. The reason can be attributed to its potential for enabling evaluating MIMO terminals in realistic propagation environments. The focus of the paper is on investigating how to create desired spatial- temporal channel models with the multi-probe anechoic chamber setups. Simulation results have shown that with the discussed methods, the number of probes and probe power weights determine to which level the spatial characteristics of the target channel models can be accurately approximated, while the other channel parameters, e.g. power delay profile, field distribution, Doppler spectrum and temporal correlation are irrelevant to the probe weighting and number of probes.

In this paper, we are proposing a dual feed compact antenna for a mobile phones that is capable of supporting the latest features of LTE, Carrier Aggregation (CA), which has been introduced to satisfy the ever increasing demand for data-rate. The antenna makes use of a dual resonator design to cover the low bands used in Long Term Evolution (LTE) from 699 to 960 MHz. The design of the RF Front End(FE) is simplified by the dual feed design which can have distributed components of the FE to relax its design and packaging requirements. The main antenna switch design can be relaxed and the high isolation between the two antennas removes the need for a diplexer. The antenna supporting the high bands (from 1710 to 2700 MHz) is fed through a matching network to increase the bandwidth while having a small volume. Inductive loading is used for the minimization of both elements. Even though the antenna occupies only an area of 30×10mm2, many combinations of low and high band are available for CA. Despite the small volume it has a good efficiency which is close to -3 dB. The design principle has been evaluated through simulations and measurement with good agreement between them.

Antenna volume has become a critical parameter in mobile phone antenna design, as broader bandwidths are required for high connectivity between users. Shrinking the antenna size affects its efficiency, if one does not sacrifice bandwidth. This paper proposes an architecture to address the need for small and wide-band antennas. The study focuses on the low-frequencies (700 MHz - 960 MHz) in order to address a tough scenario for small platforms. A tunable design of the front-end and the antennas of the mobile phone is proposed and investigated. Operation is achieved on all low-bands with an efficiency of -3 dB at 700 MHz.

MIMO OTA testing methodologies are being intensively investigated by CTIA and 3GPP, where various MIMO test methods have been proposed which vary widely in how they emulate the propagation channels. Inter- lab/inter-technique OTA performance comparison testing for MIMO devices is ongoing in CTIA, where the focus is on comparing results from various proposed methods. Channel model verification is necessary to ensure that the target channel models are correctly implemented inside the test area. This paper shows that the all the key parameters of the SCME models, i.e., power delay profile, temporal correlation, spatial correlation and cross polarization ratio, can be accurcately reproduced in a multi-probe anechoic chamber based MIMO OTA setup.

This paper presents a new channel reconstruction technique for 3D geometry-based channels in a multi- probe based MIMO OTA setup. The proposed method provides a general channel reconstruction framework for any spherical power spectrum. The channel reconstruction is formed as convex optimization problems, which give global optimal reconstruction accuracy and allow for a relatively low computational complexity.

In this work is presented a discussion on the challenges in 4G Long Term Evolution (LTE) smartphone antennas' design, also providing measurement results of the most representative devices. Both Total Radiated Power (TRP) and Total Isotropic Sensitivity (TIS) are measured for different frequency bands, showing that the newest phones tend to underperform when compared with less recent devices. The implications of these results are discussed and possible countermeasures are suggested.

The paper sheds light on the beamforming (BF) performance of large (potentially unconstrained in size) as well as dense (but physically constrained in size) antenna arrays when equipped with arbitrarily many elements. Two operational modes are investigated: Single-layer BF and multi-layer BF. In the first mode, a realistic BF criterion namely the average BF gain is revisited and employed to understand the far-field and the near-field effects on the BF performance of large-scale antennas above a clutter. The diminishing throughput returns in a single-layer BF mode versus the number of antennas necessitate multi-layering. In the multi-layer BF mode, the RF coverage is divided into a number of directive non-overlapping sector-beams in a deterministic manner within a multi-user multi-input multi-output (MIMO) system. The optimal number of layers that maximizes the user's sum-rate given a constrained antenna array is found as a compromise between the multiplexing gain (associated with the number of sector-beams) and the inter-beam interference, represented by the side lobe level (SLL).

The paper proposes a novel approach for securing the wireless communication by designing the signal in a way that makes its modulation format direction-dependent. The idea is to exploit the multi antennas at the transmitter to superimpose a space-time varying interfering component (at the modulation rate) while staying orthogonal to the desired receiver's direction. Unlike conventional interference or artificial noise injection techniques, the proposed approach impedes an arbitrary eavesdropper from blindly separating the information data symbols from the injected interference due to its space-time varying nature.

This paper presents measurements of the first MIMO handset on the market. It investigates the correlation coefficient computed from coaxial cable measurements and from optical fiber measurements. The results are compared and discussed. The question of the actual feasibility of low correlation for the LTE-700 band in small terminals is raised.

The influence of the user's body degrades small antenna performances. This paper investigates the detuning and the losses on high-Q planar antennas for small devices due to user proximity. The results at low frequencies for the Long Term Evolution (LTE) standard are compared to the results for a low- Q antenna. Two hand grips are studied and combined to a SAM(Specific Anthropomorphic Mannequin)phantom. It is shown that using the high-Q antennas the loss due to the mismatch is reduced but the absorption loss is increased.

This paper gives an overview of the techniques published over the past years to address continuous frequency tuning. It presents the challenges that have been encountered and relates to each other the parameters that influence the losses of the resulting antenna structure. A mock-up is made with a PIFA and a packaged RF-MEMS tunable capacitor to measure its efficiency as the resonance is tuned towards the LTE-700 band.

Standardization work for MIMO OTA testing methods is currently ongoing, where a multi-probe anechoic chamber based solution is an important candidate. In this paper, the probes located on an OTA ring are used to synthesize a plane wave field in the center of the OTA ring. This paper investigates the extent to which we can approach the synthesized plane wave in practical measurement systems. Both single plane wave with certain AoA and multiple plane waves with different AoAs and power weightings are synthesized and measured. Deviations of the measured plane wave and the simulated plane wave field are presented in terms of phase and power. Possible reasons for the deviations are also investigated.

In this paper both normal-band and narrow-band PIFA antennas for small terminals are compared through numerical simulations and measurements for different UMTS bandwidths. It is found that using different antennas for the transmitting and receiving regions of the frequency duplex it is possible to achieve a significant improvement in terms of isolation. Measurement results show also that ohmic losses lower the total efficiency in the narrow-band case especially at low frequencies.

Long Term Evolution (LTE) requires Multiple Input Multiple Output (MIMO) antenna systems. Consequently a new over-the-air (OTA) test methodology need to be created to make proper assessment of LTE devices radiated performance. The antenna specific parameters i.e. total antenna efficiency, gain imbalance and correlation coefficient, are essential for a proper MIMO antenna system design. However it can't be use directly to assess the LTE device system performance, since a multiplicity of other factors are involved, e.g. power amplifier load- pull, low noise amplifier source-pull, self interference noise, baseband algorithm and other factors. Several standard organizations are working towards a consensus over the proper OTA MIMO test method, however so far results of measurement campaigns have ambiguous results not allowing a desirable progress [1]. Initially presented at one of several MIMO OTA standard meetings [2], the reference antenna was conceived considering the special case of uniform distribution of incoming power. This paper shows an antenna system that will aid standard organizations and research labs adopting anechoic or reverberation chambers to proper investigate OTA radiated performance, ruling out the LTE devices unknown MIMO 2x2 antenna performance.

In this paper we present a novel method for estimating the inclination of passive UHF RFID tags, for use in supply chains to monitor the handling of tagged items. Based on observations of the polarization, a Bayesian estimator of the tag inclination is constructed. The Bayesian estimator has been analyzed and evaluated in a experimental setup. The results shows great potential as the estimator is very robust when determining the inclination.

This paper presents an Equivalent Circuit Model (ECM) for a high Quality factor (Q) tunable Planar Inverted F Antenna (PIFA). A PIFA is described and simulated with the Finite-Difference Time-Domain (FDTD) method. The resonance behavior of the proposed ECM is compared to the FDTD results and shows a match. The ECM is also valid when the PIFA is made tunable with an additional capacitor.

This paper presents a Planar Inverted F Antenna (PIFA) tuned with a fixed capacitor to the low frequency bands supported by the Long Term Evolution (LTE) technology. The tuning range is investigated and optimized with respect to the bandwidth and the efficiency of the resulting antenna. Simulations and mock-ups are presented.

The room electromagnetics (RE) theory describes the radio propagation in a single room assuming diffuse scattering. A main characteristic is the exponential power-delay profile (PDP) decaying with the so-called reverberation time (RT) parameter, depending only on the wall area, the volume of the room and an absorption coefficient. The PDP is independent on the location in the room, except for the arrival time. Based on measurements in a room with a spherical array of 16 dual- polarized wideband horn antennas, the current work studies how the RE parameters depend on the receiver (Rx) antenna polarization and orientation. Also the frequency dependence is investigated, with measurements done at both 2.3 GHz and 5.8 GHz center frequencies. The RE theory was found to fit well to the measurements with a RT in the range 22- 25 ns. Only small differences were found due to the polarization and the channel gain was depending approximately as expected with frequency.

This paper exemplifies future trends in handset antenna systems, contextualizing their historical evolution and anticipating novel paradigms. It is shown through numerical simulation how narrow-band antennas used in transceiver separation mode can reduce the total loss in presence of the user's hand, improving at the same time the antenna isolation.

This paper presents an improved method to isolate the ports for a MIMO antenna in hand-held devices using lumped components. It has been analyzed through simulation and measurement. The total efficiency and the envelope correlation have been evaluated. Compared to the case with no decoupling mechanism, the efficiency from the scattering parameters increases significantly and the envelope correlation coefficient decreases dramatically. Nevertheless, when choosing the components, the ohmic losses must receive extra consideration in order to maximize the system's total efficiency. Furthermore, the use of lumped components has the potential to make the presence of other components in the mobile device or the user, less harmful to the decoupling mechanism.

This paper presents a practical method to increase the isolation between two ports of a Multiple Input Multiple Output (MIMO) antenna for mobile hand-held devices. The method consists in a connecting strip containing lumped components placed in between the low impedance zones of the two antennas. The lumped components modify the impedance of the connecting strip so that, together with the mutual coupling impedance, it acts as a band-stop filter between the two ports. As a consequence, the efficiency due to scattering parameters almost doubles and the envelope correlation coefficient decreases dramatically. Furthermore, the use of lumped components makes this method less susceptible to the presence of other components in the mobile device or the user. This method has been verified on two antenna configurations, through simulation and measurements.

Long haul transport can be considered an obvious deployment scenario for communication between vehicles travelling in convoy, where environments will be comparable to that of a rural highway. Therefore this paper addresses antenna array techniques applicable to such circumstances, which provide little scattering to the propagation channel and little support for diversity. Only beamforming is realistically suited to increase the capacity in the vehicle to vehicle link. However, the possibility to enable multi user channels is limited in such environments since the propagation channels are highly correlated when more than two vehicle to vehicle links are in close proximity. The deliberate introduction of delay spread through wide spaced and combined multiple antenna topology thus creating an artificial wideband fading channel is proposed in this paper, which results in de-correlated vehicle to vehicle links. Measurements and experimental results are presented that demonstrate the means by which uncorrelated wideband channels between separate vehicle to vehicle links can be formed to enable multi user capabilities specific to vehicles on a rural highway.

Thanks to a recent grip study, CAD models of the human hand have been generated, investigating user's impact on PIFA antennas in mobile phones. The simulation results show that the hand and especially the index finger exhibit a major contribution in determining the total loss when compared to the upper torso alone, while the influence of the position of the fingers on the handset is found to be more important when close to the antenna. The palm-handset gap and the index finger location are the main responsible for both absorption and mismatch loss.

A random non-line-of-sight environment with stationary transmitter and receiver is considered. In such an environment movement of a scatterer will lead to perturbations of the otherwise static channel with a resulting Doppler spectrum. This is quite a general situation in outdoor environments with moving traffic or indoor situations with moving people. Here we study the latter situation in detail with experimental results from a large office environment. A general theory of Doppler spectra is developed. The impact of a scatterer depends on the angular distribution of scattered energy, and uniform as well as sharply peaked distributions are considered in the theory. The Doppler spectra are in all cases sharply peaked at zero frequency due to forward scattering, but the actually measured distribution depends on the degree and type of activity in the environment, as well as the spectrum estimation accuracy.

Preliminary results on the use of the vehicle to vehicle MIMO channel in a rural highway environment are presented. This is looked at both in terms of the available spatial multiplexing through singular value decomposition and also angular distribution within the channel. Results indicate a strong predominant line of sight link in general while instances of scattering from other vehicles will cause changes in the Doppler spectrum as well as beamforming jitter.

Outdoor radio propagation experiments are presented at 2.4 GHz, using a handset MIMO antenna with two monopoles and two planar inverted-F antennas (PIFAs), adjacent to a human phantom in browsing stance. The propagation test was performed in an urban area of a city, which resulted in non line-of-sight (NLOS) situations. In our investigation, the 4-by-4 MIMO and SISO channel capacities for the reception signals were evaluated. These measurements show that the handset MIMO antenna, close to the human operator, is capable of MIMO reception.

Interference caused by other users in a multi-user environment degrades the system performance significantly. Conventionally, user separation in a multi-user environment is achieved by signal separation in time, frequency or code. The use of multiple elements antenna (MEA) systems can apply separation of the users in space by targeting the transmitted power to the user of interest. Inevitably in that case, the separation is not ideal and there is interference on the other users in the systems. Moreover in a wideband transmission, frequency selective fading causing inter symbol interference (ISI) is a big challenge for point to point wireless communications. In this paper, we study the feasibility of applying the time reversal technique (TR) in multiple input single output (MISO) systems to alleviate the effect of ISI. The ability of TR to focus the signal on the receiver of interest in a multi-user environment is also considered. The studies are supported by measured complex channel impulse responses with 10 MHz bandwidth centered at 2.14 GHz. For an 8/spl times/1 MISO system, using TR the root mean square delay spread is reduced by a factor of 2. To evaluate the capability of the TR in reducing the ISI, simulation of the bit error rate (BER) was made. The irreducible BER of the TR-MISO system was shown to be lower than that of the SISO system by at least an order of magnitude. By using TR and assuming that two users are communicating simultaneously with the same BS the two signals have 17 dB of isolation.

Multiple input multiple output (MIMO) systems promise better performance and significant increases in channel capacity by utilizing the rich scattering environment to obtain diversity gain and spatial multiplexing. Maximum system capacity and performance can be achieved if the instantaneous channel state information (CSI) is known at both sides of the transmission link. In order to have such improvements, the CSI at both link ends must be updated timely. However, the updating process is always subject to non-ideality. We investigate the effect of delay in updating CSI on the MIMO spectral efficiency and performance with system capacity and BER as benchmarks.

We propose a spatio-temporal model for narrowband indoor non line of sight (NLOS) MIMO channel. The model bases on the parameterization from measured 8/spl times/4 MIMO radio channel. Validation of the model performance is made by comparing the estimated capacity and the temporal characteristic with these obtained from measurement. The results show that our model is capable of capturing the essential characteristics of a temporally correlated multipath MIMO radio channel.

We study a multi-antenna single-receiver mobile terminal for interference reduction in a TDMA system. The antenna system consists of two antenna elements where the phase and amplitude of one antenna signal is altered prior to RF combining. The system therefore requires only a single receiver chain. We propose a new basis expansion method for predicting the combiner weight and we show that the proposed algorithm has improved performance compared to a recently proposed method. The evaluation of the algorithm by simulation is based on measurements at 1.8 GHz by a two-antenna mobile terminal carried by different users.

The next generation GSM terminals will include EGPRS, offering high data rate services and packet data services. Data rates up to 473.6 kbits/s are theoretically possible, but only at very high SNR (signal-to-noise ratio) and CIR (channel impulse response) levels. Using an antenna system (i.e. more than one antenna port) in the handset, it is possible to combine the signals from the antennas in such a way that both the SNR and CIR level is improved. For data services, an improvement in the SNR and CIR level directly translates into an increased data throughput. This paper investigates the possible data throughput increase for EGPRS that can be obtained by using antenna systems in a handset with two antennas.

We obtained results on the capacity of a mobile MIMO channel and on the influence of the user. Measurements were done in a configuration with three distributed transmitters equipped with single antennas and with a small wireless handset with four antennas, creating a 4Rx /spl times/ 3Tx configuration. We express the quality of the radio channel in terms of the effective degree of freedom (EDOF). From our measurement it follows that fitting a small handset with multiple antennas still makes sense in an outdoor-to-indoor mobile MIMO scenario. The channel capacity can be excellent, comparable with fully uncorrelated Rayleigh fading branch signals. However, on average the user should be satisfied with less favourable conditions amounting to a loss in EDOF of 0.16 at 50% complementary cumulative distribution function (CCDF) level. Systems operating without power control will suffer from an extra degradation in EDOF of 0.10 with an increased spread in channel quality both at the high and low end of the EDOF curve.

Attaching cables to mobile terminals for accurate measurements is progressively influencing the radiation characteristics with the diminishing size of the terminals. Simulations show the large influence of cables and their exact curvature on the radiation properties of mobile terminals that are small with respect to the wavelength. These results are confirmed by measurements in an anechoic chamber. As corrections for these almost irreproducible influences are hardly feasible, we propose to omit conducting cables completely. Instead, optical fibres are used for transparent transport of the RF signals. Off-the-shelf system components allow for two channels in a box of size comparable to modern small terminals. When driven at an appropriate level this set-up shows ample dynamic range for mobile radio channel sounding.

This paper investigates the body loss when a mobile handset is carried on the user's body, e.g., when a hands-free kit is used and the handset is carried in a pocket. A number of measurements were carried out in a live GSM network, using logging of data from the Abis interface of the network. Four commercially available handsets were tested and 18 test users were involved. In addition a full body phantom mimicking the user's body was tested.

Measurements of radiation efficiency for a handheld phone equipped with a patch and a helical antenna operated near the human user have been performed. Both measurements include a simple head plus hand phantom and live persons are considered. The position of the hand on the phone is found to be the main reason for the large variation in radiation efficiency among persons. The tilt angle of the phone and the distance between the head and phone only play a minor role.

An investigation of the radiation from 5 different phones next to two head phantoms proposed for radiation measurements has been carried out and the radiation has been evaluated through the total radiated power, the total receiver sensitivity and the mean effective gain. The investigation is based on measurements of the far field patterns measured in an anechoic room using a system tester to avoid any disturbance of the radiation patterns. The results shows that the losses due to the phantom heads are twice as high in dB values, at 900 MHz compared to 1800 MHz. Even though the two head phantoms are rather different in shape it is concluded that the influence by the phantom on the radiation is the essentially same.

Mobile terminals are often used indoor with the base station outdoors. At the mobile terminal the major part of the signal energy comes through openings in the building such as windows. Typically, only one of the sides in a room has windows, and seldom does a room have windows on all sides. Hence, the dominating signal can be expected to arrive at the mobile terminal from a narrow range of angles. Mobile terminal antennas used next to the head in the speaking position will be directional due to the fact that part of the radiation pattern facing the head will be attenuated and reflected. Having a directive antenna in a directive environment, the performance will depend on the orientation of the antenna in the radio environment. A new statistical spherical outdoor to indoor power spectrum model has been proposed to be able to calculate the directional performance of mobile terminals with a single or multiple antennas. The model consists of a major scattering area in one direction and more uniformly distributed minor scatterers in the other directions. A verification of the proposed model was performed and 60 data sets of spherical power spectrum measurements were collected in a typical urban environment. Using the new model, the directional performance of mobile terminal antennas including a human operator has been investigated through directional mean effective gain, branch power ratio, and correlation calculations using spherical radiation pattern measurements of a mobile terminal including the effect of 42 different persons. The accuracy of the calculated values was verified by directly measured values using 200 persons walking with the mobile terminal in the same office-like environments as where the spherical power spectrum measurements were performed.

The diversity gain obtained by employing antenna diversity on handheld phones are investigated for the two branch case in the presence of the human head. The envelope correlation coefficient is calculated from measurements of angular distributions of multipath field and complex radiation patterns. The mean effective gain (MEG) and diversity gain is calculated for a 360/spl deg/ rotation of the phone in the environments. The calculated correlation, MEG and diversity gain are compared to measured values in the same environments. It is demonstrated that low correlation and nearly equal branch powers can be obtained on small handhelds even when operated near the human head, and it is concluded that a high return can be expected from antenna diversity on realistic handhelds. Furthermore good agreements is shown between both measured correlation and MEGs and calculated values based on measured angular power densities and complex antenna patterns.

Antennas for hand-held telephones must have high efficiency due to the limited power available, and recent demands call for integrated antennas in hand-held telephones. A full short circuit planar inverted-F antenna (FS-PIFA) is investigated, which concentrates the current near the antenna, and has a relatively higher gain directed away from the user's head thereby reducing the losses in the human body, which is important from the point of view of efficiency and possible health hazards. For design and analysis of the antenna including parts of the human body the finite difference time domain (FDTD) method is employed, and measurements of average received power and spatial peak specific absorption rate, SAR, values were performed, to verify simulation results. Measurements of the antenna gain in realistic environments with a person showed a gain about 2 dB less than a half wavelength whip on the same telephone, while the local SAR was typically 0.1-0.2 mW/cm/sup 3/, a factor of ten smaller than present standards and handportables.>