The next-generation wireless systems are expected to support data rates of more than 100 Mbps in outdoor environments. In order to support such large payloads, a polarized antenna may be employed as one of the candidate technologies. Recently, the third generation partnership standards bodies (3GPP/3GPP2) have defined a cross-polarized channel model in SCM-E for MIMO systems; however, this model is quite complex since it considers a great many channel-related parameters. Furthermore, the SCM-E channel model combines the channel coefficients of all the polarization links into one complex output, making it impossible to exploit the MIMO spatial multiplexing or diversity gains in the case of employing polarized antenna at transmitter and receiver side. In this paper, we present practical and simple 2D and 3D multipolarized multipath channel models, which take into account both the cross-polarization discrimination (XPD) and the Rician factor. After verifying the proposed channel models, the BER and PER performances and throughput using the EGC and MRC combining techniques are evaluated in multipolarized antenna systems.
The next-generation wireless systems are required to possess high voice quality and high data rate services compared to the current cellular mobile radio standards and also provide seamless data service. Recent work has shown that independent spatial channels can be used to greatly enhance capacity under situations subject to scattering, such as urban areas or indoor environments [
A great deal of research is in progress in regard to spatial MIMO channel models; however, models regarding the polarized antenna channel are still in their early stages. Existing polarized antenna channel models can be divided into two categories: two-dimensional (2D) channel models where all of the scatterers are located in a 2D plane and three-dimensional (3D) channel models where all the scatterers are located in 3D space. One of the well-known 2D polarized antenna channel models is the one defined by the spatial channel model extended (SCM-E) [
In our preliminary work [
The remaining parts of this paper are organized as follows. Section
This section describes the propagation characteristics of polarized antenna systems. Usually there are multiple scatterers, such as buildings, cars, and trees, uniformly located around the MS in urban environments. The propagation characteristics of polarized antenna systems can be determined through XPD, which quantifies the separation between two transmission channels that use different polarization orientations as
The larger the XPD, the smaller the amount of energy coupled between the cross-polarized channels. When a horizontally polarized antenna receives a signal sent from a vertically polarized antenna (and vice versa), the received signal strength is reduced in proportion to the XPD value. XPD values have been found to decrease with an increase in the distance [
For polarized channel modeling in macro and micro cell environments, we use the same number of scatterers, six, as laid out in the 1st and 2nd mid rays of the SCM-E urban channel model [
As shown in Figure
2D scatterer model parameters.
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Scatterer signal projected to |
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Scatterer signal projected to |
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Distance between scatterers and MS |
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Phase rotation of received signal at MS |
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Updated phase rotation according to MS movement |
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Moving distance of MS |
2D scatterer model.
We extend the 2D scatterer model to the 3D scatterer model by adding a new parameter,
3D scatterer model parameters.
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Scatterer signal projected to |
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Scatterer signal projected to |
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Scatterer signal projected to |
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Distance between scatterers and MS |
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Phase rotation of received signal projected in |
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Updated phase rotation projected in |
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Phase rotation of received signal projected in |
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Updated phase rotation projected in |
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Moving distance of MS |
3D scatterer model.
The analytical performance under Rician polarized channel environment was discussed in [
The elements of polarized channel matrix
The Rician factor for a fading channel is defined as the ratio of the power in the fixed component to the power in the variable components. Under the definitions of
The practical and simple (PS) multipolarized channel models are presented in this section; they are categorized into the Rayleigh channel model and the Rician channel model through the consideration of the wireless channel statistical properties. In addition, according to the scatterer environments, they are further classified into a 2D channel model and a 3D channel model.
The PS multipolarized channel models are based on SCM-E channel model given by (
The SCM-E channel model is very complex for use in imitating the practical wireless propagation channel since it employs a pseudoray tracing model. Another drawback is that there is only a single output of complex channel gain from the SCM-E polarized channel model for each instant in time, which makes the exploiting of MIMO spatial multiplexing or Rx combining techniques impossible. Moreover, it is not convenient to observe the characteristics of each of the polarized channel links (e.g.,
PS 2D dual-polarized Rayleigh channel is modeled as depicted by (
Instead of the independent consideration of the channel parameters used in the SCM-E channel model, all the contributions mentioned above are jointly coupled in order to build a complete channel matrix in our proposed polarized channel model, which results in the simple and practical channel model.
Based on these principles, the PS 2D dual-polarized Rayleigh channel is modeled as described in (
The PS 3D dual-polarized Rayleigh channel is modeled as described in (
We expand the 2D scatterer model to the 3D scatterer model by adding an elevation angle parameter
Since a dual-polarized antenna on the
The PS 3D triple-polarized Rayleigh channel is modeled as seen in (
This channel model generates a (
Similar to the Rayleigh channel model described above, the PS dual-polarized Rician channel for both the 2D and 3D cases can be generated by introducing the Rician factor [
The dual-polarized case is extended into a (
The PS multipolarized channel models are designed for use in macro and micro cell environments. Therefore, the power delay profile of ITU-R M.1224 Veh. A from [
The multipolarized antenna system is designed to be used in macro and micro cell environments; therefore we use 64 scatterers by setting the scatterer radius to 10 m and the MS mobility to 0, 30, and 60 km/h. The carrier frequency is set to 1.8 GHz in order to use the measured
System parameters.
System parameters | Values |
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Target cell | Macro, micro |
Carrier frequency | 1.8 GHz |
System BW | 20 MHz |
Scatterer radius | 10 m |
Rician factor | 9 dB |
LoS XPD value | 14 dB |
NLoS XPD value | 5.8 dB |
Number of symbols in packet | 100 symbols |
Modulation | QPSK |
Combining techniques | EGC, MRC |
Equalizer | 1-tap time-domain equalizer |
The system bandwidth is 20 MHz, resulting in a symbol duration of 0.05
Figure
Normalized fading envelope of the PS 3D triple-polarized channel model: (a) MS mobility = 0 km/h and (b) MS mobility = 60 km/h.
Figure
Phase response of the PS 3D triple-polarized channel model.
Figure
PSD of the PS 3D triple-polarized channel model.
Equal gain combining (EGC) and maximum ratio combining (MRC) are performed at the MS in order to combine the signals of the polarized channel links [
We vary the
The BER performances for antennas and XPD values under a flat PS 3D fading Rician channel.
Figures
The BER and PER performances using EGC in the PS 3D multipolarized multipath Rician fading channel.
The BER and PER performances using MRC in the PS 3D multipolarized multipath Rician fading channel.
The throughput in the PS 3D multipolarized multipath Rician fading channel.
The proposed channel model in [
In this paper, PS 2D and 3D multipolarized multipath fading channel models have been presented based on the polarized characteristic of the SCM-E channel model. In order to verify and evaluate our proposed channel models, the measured
The authors declare that there is no conflict of interests regarding the publication of this paper.
This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2013R1A1A2010287) and the project “Development of marine RF based ad hoc network for ship” from Ministry of Oceans and Fisheries (MOF), Korea. This work was also supported by Inha University Research grant. Part of this work has been published with preliminary form in the proceeding of the International Conference on Information Networking (ICOIN) in February 2012.