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Polarization diversity in MIMO radio channels: experimental validation of a stochastic model and performance assessment
Abstract
A stochastic MIMO radio channel considering (i) polarization diversity and (ii) unbalanced branch power ratio (BPR) is being validated by comparing Monte-Carlo simulations and experimental results using the eigenanalysis as benchmark. Based on results generated by the model, the influence of the BPR on the power gain of the parallel subchannels is presented.
... In the indoor environment, there exist abundant multipaths with different polarizations. Thus, the evenly distribution of the orientations of the monopoles on the icosahedron is expected to sufficiently use the polarization diversity [15], [29] of the MIMO system and thus improve the MIMO capacity. Each of these examples are meshed into quadrilaterals using the commercial software ANSYS [30]. ...
... Fig. 15(a) and (b) shows the transmit correlation and receive correlation respectively. To ignore the effects of the RF circuits, we set the source impedances and the load impedances in (5) to be zeros and infinite respectively, and hence (29) The correlation coefficients results of the four cases listed in Table III are shown in these figures. For all these cases, the path losses are modeled using (15-b) with Monte Carlo method instead of using ray tracing method. ...
... In Case 3 and Case 4, the transmit correlation coefficients are different from the receive correlation coefficients. This is caused by the non-symmetry of the channel matrix in (29). From these figures, we see that the polarization of the radiation patterns has little effects on the correlation coefficients of the 2-by-2 monopole array MIMO system, when and are set to be uniform distribution. ...
Some MIMO applications require antennas to be closely spaced, and it will cause the mutual coupling among antennas and high spatial correlation which will harmful for enhanc-ing the system capacity. In order to solve this problem, many methods have been developed. The antenna array design is a feasible way to enhance the MIMO system performance. We developed the regular polyhedron antenna arrays. Regular polyhedron has excellent spatial sym-metry, and it is vital in 3D environment. This kind of regular polyhedron antenna arrays exhibit lower mutual coupling effect and spatial correlation then the antenna array fixed on a plane. In numerical simulation, the efficient integral method MGLFIM is employed to fast calculate the input admittance and radiation pattern. Each regular polyhedron antenna array demonstrates excellent efficiency in enhancing the MIMO system capacity. To obtain the same system capacity, the distance between two monopoles can be smaller using regular polyhedron than using planar antenna array. With the same volume, the regular polyhedron antenna array can exhibit better performance.
... In the indoor environment, there exist abundant multipaths with different polarizations. Thus, the evenly distribution of the orientations of the monopoles on the icosahedron is expected to sufficiently use the polarization diversity [15], [29] of the MIMO system and thus improve the MIMO capacity. Each of these examples are meshed into quadrilaterals using the commercial software ANSYS [30]. ...
... Fig. 15(a) and (b) shows the transmit correlation and receive correlation respectively. To ignore the effects of the RF circuits, we set the source impedances and the load impedances in (5) to be zeros and infinite respectively, and hence (29) The correlation coefficients results of the four cases listed in Table III are shown in these figures. For all these cases, the path losses are modeled using (15-b) with Monte Carlo method instead of using ray tracing method. ...
... In Case 3 and Case 4, the transmit correlation coefficients are different from the receive correlation coefficients. This is caused by the non-symmetry of the channel matrix in (29). From these figures, we see that the polarization of the radiation patterns has little effects on the correlation coefficients of the 2-by-2 monopole array MIMO system, when and are set to be uniform distribution. ...
In this paper, the effects of the antenna shapes on the indoor MIMO channel capacity are analyzed based on a rigorous numerical model. Based on network theory, we first give the rigorous MIMO channel transfer function using the admittance matrices of the transmitter and receiver, and the admittance matrix between them. Consequently, we use the multilevel Green's function interpolation method (MLGFIM) to solve for the input admittance matrices and the radiation patterns of the transmitter and the receiver and employ the ray tracing method to obtain the mutual admittance matrix between the transmitter and the receiver. Using this procedure, we rigorously analyze the channel capacity of a newly devised MIMO array system, i. e. the 20-by-20 icosahedron array MIMO. We also compare this system with a 20-by-20 planar array MIMO and find that the icosahedron array MIMO system can gain high MIMO channel capacity than the 20-by-20 planar array MIMO with relatively small effective volume size. This kind of system is suitable for indoor wireless communication environments.
... With appropriate dissimilarity in the antenna patterns, large MIMO channel capacity can be achieved [49,50]. Recent studies on the MIMO systems have sought to exploit the MIMO channels by using polarisation diversity [51][52][53][54]. These studies mostly ignore the mutual coupling effect between the multiple antennas. ...
... with part of the physical parameters. Gesbert et al[51] proposed a distributed scattering narrowband MIMO model to describe an outdoor MIMO propagation channel. These studies have provided important references for the design of MIMO systems. ...
... The aim of the measurements was to colocate two orthogonal dipole antennas (i.e., with equal to 90 ) as far as is practical so that their capacity potential could be compared with that of the spatial case while at the same time exploiting the polarization diversity available as much as possible from the above analysis. Other investigations into polarization diversity have been based on more ideal assumptions or they have only concentrated on directional antennas at the access point or mobile [2]- [4]. This particular investigation will focus on obtaining decorrelated branches at the mobile end with a wide angle of arrival by which omnidirectional antenna branches will always apply both angular and polarization diversity due to practicalities of the antennas. ...
... Thus, the channel is normalized as (1) To evaluate the scattering effects of the crossed dipoles compared to the spaced dipoles, the same normalizing factor used for the spatial case is applied so that when evaluating these two antennas any degradation in gain as well as difference in scattering is taken into account. Thus a fair evaluation is made of the antennas' comparison and two channels for the crossed dipoles, , are defined as (2) Consequently, using these normalized channels it is possible to resolve the eigenvalue decomposition, where represents the eigenvalues and the eigenvectors of a channel (3) Thus, one can calculate the Shannon capacity for a fixed signal to noise ratio (SNR) as follows: ...
Indoor multiple-inputmultiple-output (MIMO) channel measurements undertaken with spatially separated dipoles are compared with crossed dipoles at 2.4 GHz. This essentially analyses how polarization can be exploited at the mobile using practical antennas where polarization diversity is an inherent feature within an angular diversity system. Results are encouragingly comparable between the two scenarios in terms of capacity and diversity order, which indicates that polarization could be exploited within an angular based MIMO antennas that are more compact than spatially separated antennas.
... Based on that study, receiving antenna elements with orthogonal polarizations are equally effective with the copolarized elements in capacity comparison. As mentioned in [4], the dual polarized elements can be compact solutions to add diversity dimension with low correlation between antenna ports. In some cases, dual-polarized elements result in relatively high power unbalance between antenna ports that deteriorates the power gain in MIMO channel [4]. ...
... As mentioned in [4], the dual polarized elements can be compact solutions to add diversity dimension with low correlation between antenna ports. In some cases, dual-polarized elements result in relatively high power unbalance between antenna ports that deteriorates the power gain in MIMO channel [4]. ...
In this paper, measurements are used as the experimental basis for evaluation of MIMO antenna configurations at 2.15 GHz. At the transmitting fixed station, the effects of increasing the number of channels and increasing the inter-element spacing in MIMO systems are studied. The goal of the paper is to find out how MIMO channels could be exploited better. We have performed radio channel sounder measurements using antenna arrays of directive and dual-polarized elements. Three potential MIMO environments have been included in the study. We found that increasing the distance between transmitting antenna elements or increasing the number of elements decreases eigenvalue spread and improves MIMO performance.
... Correlation between channel coefficients results from insufficiently spaced antenna elements. According to [6], correlated channels can be described and modeled using separate correlation matrices RT and RR for the transmitter and the receiver, respectively. The overall correlation matrix R, describing correlation between all transmit and receive antennas, can be obtained as a Kronecker product ...
... For the combined spatial and polarization multiplexing approach, the LOS component H in (2) For the fading component H in (2) we also define a ccinelation matrix R which describes correlation between all ccand cross-polar channel coefficients. According to [6]. an approximation consist in separating the correlation matrix RT and RR. ...
Exploiting the radio channel in mobile communications systems in a multiple-input multiple-output (MIMO) manner has been shown to highly increase the system capacity. The access to such a MIMO channel usually involves spatially separated antennas of the same polarization at the transmitter and the receiver side. In this paper, we focus on the potential of dual-polarized antennas in mobile radio systems, which avoid undesired antenna spacings and promise increased system performance for certain environments. Therefore, a channel model is presented for data transmission over Ricean fading channels using antenna arrays with spatially separated antenna elements of the same polarization and spatially separated dual-polarized antenna elements, respectively. The performance of these MIMO channels is evaluated based on multiplexing data streams over the available antenna branches and a joint detection of these data streams at the receiver.
... The root mean square (rms) sum of the two standard deviations yields a standard deviation of 8 dB corresponding to the composite distribution. From our measurements, we found that the standard deviation of the composite distribution of the copolarized -factor is dB, which we may now decompose into the rms sum of two identical components, as suggested by [10] (4) The result is dB. Since we found earlier from our experimental data analysis that the frequency standard deviation is 2.93 dB, the time standard deviation , can be easily calculated using the following equation (where all three standard deviations add on an rms basis, assuming statistical independence): ...
... 11) Generate a 2 2 matrix of correlated, complex Gaussian distributed random variables with zero mean and unit variance, where the correlation is obtained by using the complex envelope correlation coefficient and where represents the number of observation time samples at a given user location. To correlate these variables, either the method that uses transmit and receive correlation matrices [3], [4] or the method described in iii) can be used. An additional time correlation of samples can be achieved by using the Doppler spectrum of the fixed wireless channel [8]. ...
This paper presents outdoor propagation measurements together with derivative analysis, modeling, and simulation of the 2×2 fixed wireless multiple-input multiple-output (MIMO) channel. Experimental data were collected in the suburban residential areas of San Jose, CA, at 2.48 GHz by using dual-polarized antennas. Measurement results include the estimation of path loss, Rician K-factor, cross-polarization discrimination (CPD), correlation coefficients, and the MIMO channel capacity. An elaborate K-factor model that assumes variation over location, time, and frequency is developed. Distance-dependent CPD models of the variable and constant signal components are proposed. A generalized 2×2 MIMO channel model is then derived based on the correlation among the path loss, the copolarized K-factor, and the CPD's distribution of the constant and scattered signal components. Finally, the MIMO channel response is simulated using the newly developed model, and results are found to be well in agreement with measurements.
... This low correlation is achieved when each antenna provides a unique weighting to each individual multipath component based on its DOD/DOA. This weighting can be on the arrival phase due to antenna location (spatial diversity), or on magnitude and phase due to antenna pattern (angle diversity) or polarization characteristics (polarization diversity) [5], [16]. Many systems use some combination of these mechanisms. ...
... Finally, in the common case where two polarizations are used, typical scattering leads to a co-polarized received signal that is 4 to 10 dB higher than the cross-polarized signal level [129]. The result is a transfer matrix that exhibits low correlation (high diversity) coupled with weak channel gain between the two orthogonally polarized channels (reduced SNR) [16], [20], [130]- [133]. Experimental results demonstrate capacity gains of around 10-20% from using dual-polarization over single-polarization spatially-separated elements in an indoor environment [20]. ...
Multiple-input-multiple-output (MIMO) wireless systems use multiple antenna elements at transmit and receive to offer improved capacity over single antenna topologies in multipath channels. In such systems, the antenna properties as well as the multipath channel characteristics play a key role in determining communication performance. This paper reviews recent research findings concerning antennas and propagation in MIMO systems. Issues considered include channel capacity computation, channel measurement and modeling approaches, and the impact of antenna element properties and array configuration on system performance. Throughout the discussion, outstanding research questions in these areas are highlighted.
... Another example is using orthogonal polarization, such as horizontal and vertical polarization. By using them, space diversity can be achieved with uncorrelated channels [6]. Conventionally, these problems are considered independently and the optimal antenna to achieve the best performance has not been found yet. ...
This paper proposes a new methodology to design optimal antennas for MIMO (Multi-Input Multi-Output) communication systems by using spherical mode expansion. Given spatial channel properties of a MIMO channel, such as the angular profile at both sides, the optimal MIMO antennas should provide the largest channel capacity with a constraint of the limited implementation space (volume). In designing a conventional MIMO antenna, first the antenna structure (current distribution) is determined, second antenna directivity is calculated based on the current distribution, and thirdly MIMO channel capacity is calculated by using given angular profiles and obtained antenna directivity. This process is repeated by adjusting the antenna structure until the performance satisfies a predefined threshold. To the contrary, this paper solves the optimization problem analytically and finally gives near optimal antenna structure (current distribution) without any greedy search. In the proposed process, first the optimal directivity of MIMO antennas is derived by applying spherical mode expansion to the angular profiles, and second a far-near field conversion is applied on the derived optimal directivity to achieve near optimal current distributions on a limited surface. The effectiveness of the proposed design methodology is validated via numerical calculation of MIMO channel capacity as in the conventional design method while giving near optimal current distribution with constraint of an antenna structure derived from proposed methodology.
... C'est la solution la plus simple, la moins coûteuse et la plus utilisée pour effectuer des mesures de caractérisation spatiale. Afin de créer un réseau virtuel, nous utiliserons une antenneélémentaire (antenne omni directionnelle dans la plupart des cas), un sondeur de canal SISO et un positionneur, nous permettant de déplacer cette antenne sur différents points d'une grille dans l'espace suivant une géométrie arbitraire et d'acquérir le signal sur chaque position [39,79,80,[117][118][119][120][121][122][123][124][125][126][127][128]. Une géométrie arbitraire peutêtre créée en prédéfinissant la structure de l'échantillonneur spatial utilisé, son nombre d'éléments et l'espacement inter-élément. ...
DIOURIS Jean-François - Professeur à l'Ecole Polytechnique de l'Université de Nantes (Rapporteur)
VAUZELLE Rodolphe - Maître de conférences - HDR à l'Université de Poitiers (Rapporteur)
SYLVAIN Michel Professeur à l'Université de Marne-la-Vallée (Examinateur)
BARBOT Jean-Pierre - Maître de conférences à l'E.N.S. de CACHAN (Examinateur)
CITERNE Jacques Professeur des Universités à l'INSA de Rennes (Président)
EL ZEIN Ghaïs - Professeur des Universités à l'INSA de Rennes (Examinateur)
PAJUSCO Patrice - Ingénieur, France Telecom R&D (membre invité)
LOSTANLEN Yves - Directeur du département Radio de SIRADEL (membre invité)
... Understanding the channel polarisation behaviour is necessary to choose antennas with the proper polarisation characteristics. In addition, the information is valuable to evaluate the performance of either polarisation diversity to decrease the effect of multipath or of multiple input multiple output (MIMO) systems to increase the capacity by employing dual-polarised antennas [37][38][39] In spite of much work on the characterisation of the received signal variation for different on-body channels, in terms of slow and fast fading [11][12][13][14][15][16]40] and path gain measurement [8][9][10], few publications are available on the polarisation behaviour of channels in body area networks, including on-body, off-body and in-body. In on-body channels, the depolarisation phenomena can be very significant due to the body movement, as well as the scattering of the wave from the body and surrounding environment. ...
... This correlation model has also been validated against measurement results in a narrowband perspective [16]. Its extension to polarisation diversity is presented in [42]. Finally, this model is the core of the 3GPP link-level MIMO model proposal [43]. ...
This document gives an overview of recent achievements of various research teams, both academic and industrial, in the characteri- sation and the exploitation of the essential properties of multiple antenna systems. It is organised into two main parts. The first part looks at re- cent modelling activities of Multiple-Input Multiple-Output (MIMO) radio channels, while the second tackles advanced antenna processing suggested in the Multiple-Input Single-Output (MISO) and MIMO perspectives. In the second part, a strong emphasis is given to the standardisation of the evolution of the Third Generation (3G) cellular systems within the Third Generation Partnership Project (3GPP).
... Hence a natural alternative would be to use dual-polarized configurations, which could use the additional dimension of polarization to sufficiently decorrelate the channel even for small inter-element spacing. It should be noted that the Kronecker product model is not valid for dual-polarized configurations [13]. We have calculated the correlation between the elements of the channel matrix for 2 × 2 dual-polarized and hybrid configurations. ...
In this paper, we analyze the impact of polarization diversity on the capacity of multiple-input multiple-output (MIMO) channels in indoor environments. A channel measurement campaign was conducted at 2.4 GHz to measure the co-polarized and cross-polarized subchannels under line-of-sight (LOS) and non-line-of-sight (NLOS) channel conditions. We analyze the measured data in terms of Ricean K-factor, cross-polar discrimination (XPD) and subchannel correlations. A major contribution of this paper is that in these measured channels, we observe a coincidence of low K factors and high XPD. In such channels, MIMO systems employing polarization diversity incur SNR and diversity deficits, when compared to spatial configurations. On the other hand, our results indicate that polarization diversity can substantially lower the subchannel correlations for compact configurations, even in a LOS scenario. We draw a fair comparison in terms of capacity, between spatial MIMO configurations and systems using polarization diversity. We analyze the performance of 2times2 and 4times4 MIMO configurations for a range of values of inter-element spacing
... The gain of polarization antenna diversity on MIMO channel with LOS components has been studied and reported in [18], [27], [21]. However, their measurement experiments are performed in small indoor environments or even more controlled anechoic chambers using custom tailored antenna and devices because their main focus was to validate their theoretical models by measurements. ...
We present an experimental performance evaluation study of WiFi links in an open-space outdoor environment. We consider a large scale wireless sensor network scenario of seismic data collection from sensors that are buried in ground and as et of access points (APs) form the hierarchical aggregation layer and the backbone of the network. We conduct two different link characterization studies. First, we evaluate the links between the sensor nodes and a wireless AP using IEEE 802.11a/b/g. We construct the path loss model and investigate the reachability distance of this link for different protocols and different sensor node antenna heights. We then characterize the long distance wireless backhaul links between the APs. We use 802.11n and high gain directional antenna for high throughput and long distance. We evaluate how different PHY and MAC layer enhancements of 802.11n impacts its performance in an open outdoor environment. We observed up to 148 Mb/s throughput at 800 meter line-of-sight links without sophisticated tuning of antenna orientation. We believe our findings can be a benchmark for WiFi based outdoor network deployment, especially for high throughput long distance links.
... The Kronecker model still applies for the co-polar submatrices H V V and H HH , but not for the cross-polar submatrices H V H and H HV . For a detailed discussion of correlation modeling for dualpolarized MIMO, we refer the interested reader to [28]. Polarization diversity results in low values of correlations between the subchannels, even in environments where the spatial channels are highly correlated. ...
This thesis deals with dual-polarized multiple input multiple output (MIMO) channels, an important issue for the practical deployment of multiple antenna systems. The MIMO architecture has the potential to dramatically improve the performance of wireless systems. Much of the focus of research has been on uni-polarized spatial MIMO configurations, the performance of which, is a strong function of the inter-element spacing. Thus the current trend of miniaturization, seems to be at odds with the implementation of spatial configurations in portable handheld devices. In this regard, dual-polarized antennas present an attractive alternative for realizing higher order MIMO architectures in compact devices. Unlike spatial channels, in the presence of polarization diversity, the subchannels of the MIMO channel matrix are not identically distributed. They differ in terms of average received power, envelope distributions, and correlation properties. In this thesis, we report on an indoor channel measurement campaign conducted at 2.4 GHz, to measure the copolarized and cross-polarized subchannels, under line-of-sight (LOS) and non-line-of-sight (NLOS) channel conditions. The measured data is then analyzed, to draw a fair comparison between spatial and dual-polarized MIMO systems, in terms of channel characteristics and achievable capacity. The main drawback of the MIMO architecture is that the gain in capacity comes at a cost of increased hardware complexity. Antenna selection is a technique using which we can alleviate this cost. We emphasize that this strategy is all the more relevant for compact devices, which are often constrained by complexity, power and cost. Using theoretical analysis and measurement results, this thesis investigates the performance of antenna selection in dual-polarized MIMO channels. Our results indicate that, antenna selection when combined with dual-polarized antennas, is an effective, low-complexity solution to the problem of realizing higher order MIMO architectures in compact devices. M.S. Committee Chair: Ingram Mary Ann; Committee Member: Durgin, Gregory David; Committee Member: Williams, Douglas B
... In [5] wideband spatial MIMO channels were characterized. MIMO systems employing dual-polarized antennas were investigated in [6, 7]. A tri-polarized MIMO system was reported for narrowband in [8] and wideband in [9]. ...
We investigate the performance of an ultra-wideband multiple-input multiple-output (UWB-MIMO) system that employs three colocated, orthogonally polarized antennas at both ends of the communications link. Results show that, at 1% outage probability, such a system can achieve 24 b/s/Hz spectral efficiency, which indicates a predicted capacity of up to 180 Gb/s for a full-band (3.1-10.6 GHz) UWB-MIMO communications system
... Hence, these quantities and their effects need to be modeled accurately to generate models that closely resemble the true wireless channel. Models for MIMO communication channels which discuss specific modeling and performance aspects such as time and angle of arrival [2], [3], [4], correlation properties [5], [6], polarization diversity [7], [8], [9] can be found in existing literature. However, a unified study of a MIMO channel that encompasses different parameters and especially a multipath channel has rarely been reported. ...
We present measurement results of indoor multiple-input multiple-output (MIMO) multipath wireless channels in the unlicensed national information infrastructure (U-NII) 5.25 GHz band for wireless local area network (WLAN) applications. MIMO channel impulse responses were measured at different locations using co-polarized (copol) and cross-polarized (crosspol) antennas under line-of-sight (LOS) and non-line-of-sight (NLOS) channel conditions in office and cafeteria type environments. Ricean k-factors, correlations, crosspol discriminations (XPD), pathloss (PL) and RMS delay spread (τrms) were computed for different antenna configurations (copol/crosspol) and different channel conditions (LOS/NLOS). Models were developed to characterize the distance dependent variation and the statistical deviations of these parameters.
... The structure of the correlation matrix is the same as the one proposed in [11]. This simple Kronecker product rule is, however, only a special case. ...
Several diversity techniques employing multiple antennas in the base station have been developed for mobile communication systems. However, the performance of diversity methods strongly depends on the correlation between antenna elements. When multiple copolarized antennas are used in base station, the practical factor limiting the number of diversity branches is the required antenna separation, because large antenna separation makes the antenna array unfavourable large while small antenna separation may result in high correlations between the antennas. Therefore, dual-polarized antennas are commonly used to implement two diversity branches. If more than two diversity branches are needed, spatially separated dual-polarized antennas provide an attractive solution alternative. In this paper we propose a model for calculating the correlations between the cross and copolarized antennas when employing spatially separated dual-polarized antennas with nominal ±45° inclination to vertical linear polarization. Results are of theoretical nature and show the relationship between base station antenna correlations and the properties of the physical channel, base station, and mobile station antennas.
... In designing MIMO systems correlation has to be taken into account, since in small mobile terminals such as portable computers, wireless personal digital assistants, and mobile phones, the antenna elements have to be closely spaced. Antenna configurations consisting of either omnidirectional or directive elements can be used in MIMO systems [12]. Polarization diversity has been suggested as an attractive solution for obtaining uncorrelated antenna elements [13]. ...
This paper presents the results achieved with a dual-polarized multiple-input multiple-output (MIMO) measurement system in the 2 GHz range. Results from continuous measurement routes were used in evaluating and comparing different MIMO antenna configurations. Different pattern and polarization diversity possibilities were studied using two methods: elements were selected from the antenna arrays used in measurements, and as another option, in the mobile station the incident waves were estimated and used in different dipole antenna arrays. The capacity limit seems to be higher in an indoor picocell than in an outdoor microcell environment. At the mobile station, directive elements result in 35% higher average capacities than those of the omnidirectional elements; however, the capacity of the directive elements also depends on the azimuth direction of arrival of the incident field. Dual-polarized antenna configurations have approximately 14% higher capacities than copolarized configurations. Increasing the number of mobile antenna elements increases the capacity in those environments where the angular spread of the incident field is large. Increasing the distance between elements at the fixed station increases the capacity - especially in microcells where signals arrive from specific directions.
This paper analyses the experimentally-assessed dual-polarized (DP) mobile channel in a tunnel environment under traffic conditions. We investigate the impact of antenna polarization and radiation pattern on the non-stationary vehicle-to-infrastructure (V2I) channel. Basic channel evaluation metrics are examined including path gain, co-polarization ratio (CPR), and cross-polarization discrimination (XPD). In addition, the stationarity region is estimated using the channel correlation function approach, and used to calculate the time-varying delay and Doppler power profiles. Statistical models are presented for parameters like CPR, XPD, RMS delay and Doppler spreads, where the lognormal distribution provides the best fit. The polarization and the opening angle of the antennas into the propagation channel are found to strongly influence the observed non-stationarity of the channel. They impact the degree of multipath richness that is captured, thus providing different path gain, delay and Doppler spreads. Based on our analysis, the directional antenna with vertical polarization provides the longest stationarity time of 400 ms at 90 km/h, as well as the lowest path loss and dispersion. Furthermore, the DP channel capacity is calculated and its dependence on different normalization approaches is investigated. We propose a more accurate normalization for the DP channels that takes the conservation of energy into account. Moreover, the subchannels correlation coefficients are determined. While the condition number is found to be low on average, the correlation results show high correlation among the DP subchannels. As conclusion, we show how the CPR and XPD play the main role in providing multiplexing gain for DP tunnel channels.
Although the characterization of wireless channels started several decades ago, and has since been the subject of intense research activities, it still attracts lots of interest. One of the main reasons for this continuing interest is the fact that, until some years ago, most of the modeling activities had focused on the time-domain aspects. This had led to a large set of models, which can be sorted according to the outdoor vs. indoor dichotomy. Usually, in outdoor scenarios, the fixed Node B1 is located much higher than the mobile User Equipment (UE2), such that the scatterers which account for the diffuse transmission of the signals are mostly lying close to the UE. On the contrary, in indoor scenarios, the environment surrounding UE and Node B is much more similar which introduces symmetry to the propagation phenomena. The outdoor vs. indoor dichotomy led to the development of two sets of models, the first one accounting for outdoor, mobile scenarios, while the second one describes indoor, portable ones. The models proposed by (COST 207 1989, ITU 1997) are among the most widely accepted for the outdoor environments. They account for the time dispersion and the time variation of the mobile channel. On the other hand, the model proposed in (Saleh and Valenzuela 1987) focuses on indoor phenomena.
Rapporteurs : Gilles Burel, Luc Vandendorpe
Examinateurs : Hikmet Sari, Jean-François Hélard, Rodolphe Le Gouable
Massive-multiple input multiple output (MIMO) was recently proposed as a key solution for improving the performance of multi-user MIMO in future cellular generations. The main paradigm in this novel MIMO technique is to use a very large number of antenna elements at the base station (BS), which was shown to drastically increase capacity while saving transmission power. However, envisioning indoor BS with such number of antennas it is essential to assess the implementation of compact arrays based on different antenna candidates, which constitutes the main objective of this work. Antenna solutions ranging from miniaturised patches to triple-polarised radiators are proposed. Characteristics such as return loss and mutual couplings are obtained via full-wave electromagnetic simulations and as a function of elements density in a given limited BS real estate. The different antenna candidates are compared by computing the signal-to-interference plus noise ratio in both noise and interference-limited regimes and for different multi-user MIMO precoding strategies. This analysis allows reporting on optimal antenna densities above which performance degrades despite an increasing number of antennas, and identifying the main cause of this limitation for the different antenna types and scenarios. Finally, practical considerations such as antenna miniaturisation, bandwidth and cost are included in the discussion.
A desirable characteristic of a multiple element antenna (MEA) is to be compact, but a smaller size tends to lead to higher ohmic and mutual coupling losses. A metric for the efficiency of the MEA would help clarify the tradeoffs between compactness and performance. In a MIMO/diversity antenna, the total efficiency seen at each port directly affects the signal-to-noise ratio (SNR) in the diversity branch. The SNR after diversity combining governs the performance of the diversity antenna system. In this paper, MEA efficiencies is therefore discussed and formulated in the context of mutual coupling and diversity combining. The impact of MEA efficiency on the diversity gain and the information theoretical capacity is also formulated and demonstrated using measurements of example MEAs. With these formulations, an equivalent number of idealized (lossless, uncorrelated, uncoupled, equal power) branches can be found for an MEA, and this defines the diversity order and the capacity order of the MEA. With this metric, the performance of different MEAs can be compared.
This paper describes an investigation into the polarization behavior of on-body wireless communication channels at 2.45 GHz. The effect of the polarization of an antenna on the channel path gain has been studied and the channel cross-polarization discrimination (XPD) has been quantified, using both simulation and measurement. In simulation, short dipole antennas, which significantly reduce the simulation time, were used to investigate path gain behavior in different channels for vertically and horizontally polarized antennas. Measurements were taken in an indoor environment using a novel dual-polarized antenna, producing normal and parallel polarizations to the body surface. The measured signals were also analyzed to extract the Rician K-factor which was defined as the ratio of the power in the line of sight (LOS) signal to the scattered power for various polarization combinations.
Multiple-Input Multiple-Output (MIMO) wireless system is one of the most promising technologies for providing a large transmission capacity without expanding the frequency band in cellular mobile systems. This paper focuses on 2×2 MIMO capacity estimation through propagation measurements at 2GHz band. The authors conducted the measurement campaign in two regions in Fujimino (Saitama prefecture) and Yokohama (Kanagawa prefecture) Japan. The former is a typical residential area and the latter is an urban area. The paper compares MIMO spatial multiplexing efficiency in terms of the eigenvalue ratio between the single and orthogonal dual-polarization antenna configurations. The eigenvalue ratio is characterized by two parameters. One is cross-polarization discrimination (XPD) and the other is the normalized received signal strength indicator (RSSI), which represents the difference from the RSSI when free space propagation is assumed. It is verified that the MIMO capacity of the dual-polarization can be estimated from just the SNR because the dependency of the eigenvalue ratio on the propagation environment is small. In contrast, that of the single-polarization needs to consider both the eigenvalue ratio and the SNR because the eigenvalue ratios change significantly due to the propagation environment.
This paper presented a simple polarization diversity technique that used in MIMO system. The polarization diversity is achieve by manipulated the antenna polarization between horizontal and vertical plane. The measurements based on receive power in line of sight (LOS) environment. Different types of polarization have been done and all results will be shown and discuss.
The dependence of channel capacity on cross-polarization and the branch power ratio is established over a wide range of both realistic and idealized values. An existing empirical model is adjusted to avoid self-contradictory results for cross-coupled, but uncorrelated energy. Typical ranges are highlighted for realistic channel measurements from the literature, and extreme cases are identified. The value of a peak capacity measure is established and compared with the outage and average capacities. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1384–1388, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23360
This paper presents results of a tri-polarized multiple-input multiple-output (MIMO) channel measurement campaign in typical room-room and floor-floor micro-cellular environments. By implementing the MIMO channels in the polarization rather than conventional spatial domain, we are able to co-locate the antenna elements at both ends of the communications link. This results in a compact system that would be a good candidate for future designs of mobile communications systems including handsets. Benchmarking against the spatial technique, demonstrates that a polarized MIMO system can offer approximately the same 10% outage capacity. In terms of ergodic capacity, the tri-polar outperforms the spatial technique by up to 2 b/s/H/z
We develop a novel three-dimensional (3D) numerical model for rigorously simulating mutual coupling effects on the channel capacity of the multiple input multiple output (MIMO) systems. In this model, the efficient integral equation method mutlilevel Green's function interpolation method (MLGFIM) is for the first time employed to calculate the input admittances and radiation patterns of the transmit and receive antennas of MIMOs. Comparing with the method of moments whose complexity is O(N2) , MLGFIM has an efficiency of O(NlogN) and is suitable for efficiently solving antenna arrays problems. To accurately model the EM wave propagation, we (1) use the ray tracing method to obtain the multi-paths and (2) rigorously obtain the dyadic path loss factor model from which a novel stochastic path loss model that is flexible for both the environments with PEC walls and that with infinite thick lossless dielectric walls is devised. Using the proposed model, we successfully analyze mutual coupling effects on the 3D correlation of a 2-by-2 monopole array and the indoor channel capacity of a 20-by-20 planar array and a 20-by-20 icosahedron array. The numerical examples in this paper demonstrate the efficiency of our model for simulating the MIMO system with complex radiators.
Polarization diversity is an efficient alternative to space diversity as it cuts the antenna spacing requirements in half, but comparable results to spatially separated antennas need to be realized for practical implementation to take place. A dual feed square patch antenna has been chosen to demonstrate a complete system evaluation from the antenna design to symbol error rate (SER) performance of polarization diversity. The patch antenna has been designed with vertical and horizontal polarizations, which are well isolated at 2.4 GHz. The beam patterns were measured in the anechoic chamber on The University of Texas at Dallas (UTD) campus. The nature of the beam patterns greatly influenced the results, which have been reported in line-of-sight (LOS) and nonline-of-sight (NLOS) indoor environments in the Erik Jonsson Engineering and Computer Science North (ECSN) building at UTD. Performance evaluation has been developed for 1 × 1, 2 × 1, and 2 × 2 systems based on channel gain, channel correlation, and SER. The dual feed patch antenna performs more consistently as the environment changes from LOS to NLOS due to the low channel correlation and the complementary nature of the vertical and horizontal beam patterns.
Multiple-Input Multiple-Output (MIMO) technology is ready for deployment in the near future. A variety of MIMO antenna types including cross-polarized antennas, uniform linear arrays, and remote radio heads will be available. While theoretical MIMO performance gains have thoroughly been investigated, one of the major tasks of network operators, the selection process of an optimal MIMO antenna type for every sector in cellular network planning and optimization workflows, has rarely been treated so far. Consequently this paper presents a method on how advantages of different MIMO antenna types can be analyzed in coverage and capacity studies based on a MIMO gain benchmark. We show by simulations in a sample planning environment that the meaningful deployment of a variety of MIMO antenna types can increase the overall cellular network capacity and how mobile user positions influence the results.
The performance of multiple-input multiple-output MIMO systems strongly depends on the correlation between antenna elements. In this paper, we propose a model for calculating the correlation between multi-polarized Rayleigh fading MIMO channels, which takes into account not only the gain patterns of both transmitting and receiving antennas, but also the polarization matrix of the propagation channel, array configurations and joint three-dimensional power angular spectrum on both transmitting and receiving side. The proposed model is then used to investigate the channel capacity for various 3�?3 MIMO configurations in different propagation environments. It is found that when the antenna array size is limited, angular spread and cross-polarization ratio is small, the ergodic capacity of a multi-polarized configuration performs better than that of a single-polarized configuration.
Multiple Input Multiple Output (MIMO) wireless system is the most promising technology for next generation cellular mobile systems due to its high-speed data transmission capability. This paper focuses on the MIMO propagation characteristics in 2GHz bands. From the viewpoint of cell coverage planning of OFDMA-MIMO systems, it is important to know the key parameters required to estimate MIMO capacity. This paper shows the difference in the propagation characteristics of dual and single polarized MIMO by conducting experimental measurements. It emerged that the ratios of the eigenvalues of the channel matrix, which represent the channel capacity, depend on cross-polarization discrimination (XPD). It was confirmed that there is a positive correlation between XPD and the eigenvalue ratio for dual polarization and a negative correlation for single polarization respectively.
Not available Electrical and Computer Engineering
Fast development of new mobile communications equipment results in demand for fast and reliable evaluation methods to estimate the performance of mobile terminals because the performance of antennas located on the terminals varies in different multipath propagation environments. Two methods presented in this thesis provide new possibilities in antenna design because, from now on, the performance of new antennas can be tested already before a prototype antenna is constructed by using existing radio channel libraries and simulated radiation patterns of the antennas. The performance can be estimated by calculating the mean effective gain (MEG) of the antenna using the elevation power distribution or by a plane wave -based method using sets of incident plane waves and the radiation pattern of an antenna. In addition to different propagation environments, the effects of the user on performance can be included in the evaluation. In this thesis, estimating the MEG of different antennas using the elevation power distribution and the power patterns of the antennas is shown to be an accurate and fast method by comparing the results with direct radio channel measurements. The mean difference between the methods is −0.18 dB with standard deviation of 0.19 dB. The usefulness of the evaluation method is demonstrated by evaluating the performance of several antennas located on mobile terminals. The antenna evaluation provided important and unique knowledge of the effect of both the environment and the user on performance. Because in calculating the radiation efficiency of the antenna we assume uniform incident field, the efficiency can result in a performance estimation that does not correspond to real usage situations. Therefore, including the environmental effects in the evaluation procedure is important, although the effect of the antenna is more important than the effect of the environment on MEG. It was noticed with calculated Gaussian-shaped beams that tilting or changing the beamwidth of a mobile terminal antenna has an effect of about 2 dB on MEG in multipath environments. Matching the polarization of the antenna to that of the environment can improve the performance more. A novel incident plane wave -based tool has been developed for evaluating the performance of antenna configurations designed for diversity and Multiple-Input Multiple-Output (MIMO) systems. In this thesis, the instantaneous joint contribution of incident field consisting of a number of extracted plane waves and the complex three-dimensional radiation pattern of the antenna is shown to be accurate and extremely fast way to estimate the diversity advantages of different antenna configurations in time-variable radio channels. The difference between the diversity gains achieved by the plane wave -based method and by the direct radio channel measurements is on average less than 0.9 dB. Moreover, the radio channel can be exactly the same for all antenna configurations under test. Furthermore, this thesis includes evaluation of the performance of different MIMO antenna configurations. The studied antenna configurations have been selected from the 16×64 MIMO channel measurement data. A novel way of using one omnidirectional reference antenna in a normalization procedure is shown to be reasonable especially in cases of antenna arrays consisting of directive elements. Three different propagation environments are used as evaluation platforms. The azimuth orientation of mobile terminal antennas may influence the performance of a MIMO antenna configuration significantly. In MIMO configurations compact dual-polarized receiving antennas provide capacity performance almost equal to the arrays employing single polarization. Helsinki University of Technology Radio Laboratory publications. S, ISSN 1456-3835; 265
This paper proposes a novel internal multi-antenna configuration employing folded dipole elements for notebook PCs. We take particular note of the properties of the folded dipole antennas that eliminate the undesired current on the ground plane. Employing folded dipole antennas in a multi-antenna configuration, mounted at the four corners of the upper ground plane of a notebook PC model, resulted in an approximate 5 dB increase in the pattern averaging gain compared to that for inverted-L antennas, which are popularly used as internal antennas equipped in mobile equipment. Furthermore, evaluated results of the multi-antenna performance showed that the proposed quad folded dipole antenna configuration achieves an approximate 6 dB higher beamforming gain and approximately double the MIMO channel capacity, respectively, compared to those for a quad inverted-L antenna configuration with a low correlation coefficient of less than 0.2.
Extensive measurements have been carried out in a straight road tunnel to study co-polar and cross-polar field behaviour versus frequency and antenna positions. The tunnel has approximately a semi-circular shape cross section that is quite usual for road and railway tunnels. Since MIMO techniques can be used for improving communication performances, even in tunnels, polarization diversity must be carefully studied for optimizing the antenna array configuration.
This paper assesses the performance of polarization MIMO in an indoor ultra-wideband communications system using measured channel data. The orthogonality of the polarization subchannels is established through correlation analysis and eigenvalue decomposition. The performance advantage is quantified in terms of the gain in Shannon capacity and is compared with narrowband and unipolar systems. It is shown that the fading correlation of the polarized subchannels is lower than 0.3, and the system can achieve spectral efficiencies as high as 17.5 b/s/Hz, providing a channel capacity of over 130 Gbps on a full-band dual-polar UWB system.
This work investigates the fundamental monopole antenna array arrangement for actual mobile terminals that satisfies the requirements for beam-steering, diversity and multiple-input-multiple-output (MIMO) transmission. We take particular note of the range below 0.5 λ for the element spacing. Using an element spacing of greater than 0.2 λ, mounted on the mobile terminals, simulated by card-type and laptop PC type terminals, resulted in approximately 2.5 dB and 5.0 dB more power in two- and four-element configurations, respectively, compared to the single-antenna configuration. Furthermore, the two- and four-element configurations yield a correlation coefficient of less than 0.7, and achieve 1.6 and 3.2 fold higher MIMO capacity, respectively, compared to the single-antenna configuration. From a comprehensive perspective, multiple monopole antennas mounted on an actual mobile terminal with an element spacing of greater than 0.2 λ can operate at high gain according to the array size with the desired diversity gains and acceptable MIMO channel capacity.
This paper presents a comparative analysis of three multiple-input multiple-output (MIMO) techniques. It is observed that the spatial MIMO technique slightly out-performs both the polarisation and joint spatial and polarisation MIMO systems. But, owing to the fact that the orthogonal polarisation MIMO antennas are co-located, the resulting compact set makes the polarisation MIMO technique attractive for future designs of high-speed high-capacity mobile communications systems.
In this paper we present the performance of DSP implementation for VBLAST receiver design used in our previously proposed enhancement of a P2P radio system. The system proposed uses a cochannel dual spatial dual polarisation mode allowing the transmission of 622 Mbps STM4 signals on four subchannels. Previously we have presented results using a LMS interference canceller at the receiver which, although it successfully cancelled the major interference effects, it did not fully utilise the possible diversity gains offered by this novel system configuration, or included the effects of fading in the channel. In this paper we present results from DSP implementations of both the existing system and a new receiver structure which employs both a MRC and ZF-VBLAST. The results show that a fixed point arithmetic implementation of the ZF-VBLAST receiver is able to give a 10 dB improvement in system performance for an increase in complexity of 1.2 times that of the floating point arithmetic LMS receiver.
The key objective of this work was to obtain a MIMO model for a line of sight (LOS) channel component as well as the covariance matrix for a non-LOS deployment. A maximum likelihood criteria is applied to obtain a LOS spatial signature vector and a NLOS covariance matrix derived from channel measurements taken in the 2 GHz UMTS spectrum for an urban deployment in Bristol (UK). Different user equipment deployments were considered to represent both LOS and NLOS, as well as static and dynamic (motion) situations. The parameters of interest were estimated from these data and the fitness model was satisfactorily evaluated in all cases. Further, the Kronecker product between transmitter and receiver matrices was evaluated in order to simplify the model, for both, LOS and NLOS cases, including polarization diversity cases.
First Page of the Article
This paper presents a simple multiple-input-multiple-output (MIMO) channel model that predicts the eigenvalue distribution and hence, the capacity of MIMO systems using vertically polarized and dual-polarized transmit-antenna configurations with dual-polarized receive antennas. The channel model is verified using broadband outdoor channel measurements taken by a 2 x 3 MIMO system in the 2.5 GHz band.
This paper provides an analytical framework useful for assessing the use of all six electric and magnetic electromagnetic field polarizations for multiantenna communications systems. The approach uses a mapping between the induced signal currents and the received electromagnetic field in order to formulate a diversity interpretation of the six-polarization problem. Application of the framework to a simple, yet representative, channel model demonstrates that for full multipath elevation and azimuthal angle spread, six communication modes are theoretically possible. However, to implement the system requires more antenna design work since a straightforward implementation is found to reduce the potential number of modes to three.
Multiple-input-multiple-output (MIMO) systems have the potential to achieve very high capacities, depending on the propagation environment. Capacity increases as signal correlation decreases. We present the measurements of a MIMO system under strong and weak line-of-sight conditions. The system capacity decreases as the distance from the transmitter increases. Indeed the transmitter correlation increases as the distance increases. The receiver correlation is lower than the transmitter correlation under both propagation conditions.
A simple framework for Monte Carlo simulations of a
multiple-input-multiple-output radio channel is proposed. The derived
model includes the partial correlation between the paths in the channel,
as well as fast fading and time dispersion. The only input parameters
required for the model are the shape of the power delay spectrum and the
spatial correlation functions at the transmit and receive end. Thus, the
required parameters are available in the open literature for a large
variety of environments. It is furthermore demonstrated that the Shannon
capacity of the channel is highly dependent on the considered
environment
Two arrays with M and N elements are connected via a scattering
medium giving uncorrelated antenna signals. The link array gain relative
to the case of one element at each end is treated for the situation
where the channels are known at the transmitter and receiver. It is
shown that the maximum mean gain achieved through adaptive processing at
both the transmitter and the receiver is less than the free space gain,
and cannot be expressed as a product of separate gains. First, by
finding the singular values of the transmission matrix, fundamental
limitations concerning the maximum gain and the diversity orders are
given, indicating that the gain is upper bounded by (√M+√N)
2 and the diversity order is MN. Next an iterative technique
for reciprocal channels which maximizes power at each stage transmitting
back and forth is described. The capacity or spectral efficiency of the
random channel is described, and it is indicated how the capacity is
upper bounded by N parallel channels of gain M(N<M) for large values
of N and M
A “Software” Testbed for Performance Evaluation of Adaptive Antennas in FH GSM and Wideband-CDMA
- F Frederiksen
- P Mogensen
- K I Pedersen
- P Leth-Espensen