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IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 6, 2007
Correlations of Wide-Band Channel Parameters in Street Canyon at 2.45 and 5.25 GHz Xiongwen Zhao, Senior Member, IEEE, Lassi Hentilä, Member, IEEE, Juha Meinilä, Member, IEEE, Tommi Jämsä, Member, IEEE, Pekka Kyösti, and Jukka-Pekka Nuutinen
Abstract—The correlation between channel parameters root mean square delay spread (DS), shadow fading, number of clusters, and Rician factors (K-factors or K) is investigated based on wide-band channel measurements. The channel measurements were performed at 2.45 and 5.25 GHz in long line-of-sight (LOS) and non-LOS (NLOS) street canyons. The relation of the channel parameters to distance is illustrated. Very high correlation between channel parameters was found in the LOS street canyon, while much lower correlation was found in the NLOS street canyon. The linear relationship between the DS and the other channel parameters is derived in the LOS case, thus allowing the use of one channel parameter (e.g., the DS) to predict the others. Index Terms—B3G, channel parameters, correlation, street canyons, wide-band measurements.
I. INTRODUCTION
II. CORRELATIONS OF CHANNEL PARAMETERS
I
N Europe, IST WINNER (Wireless World Initiative New Radio) is an ongoing project for B3G wireless systems. The WINNER phase I work package 5 (WP5) and phase II work package 1 (WP1) focus on radio channel measurements and modeling. For the purpose of the B3G link and system-level simulations, suburban measurements were carried out by WP1 in the city center of Oulu, Finland, with 100 MHz bandwidth at 2.45 and 5.25 GHz. The measurements were executed with the Propsound CS, Elektrobit multidimensional radio channel sounder.1 The heights of the base station (BS) and mobile station (MS) were 8 and 1.7 m, respectively. The street widths varied from 15 to 20 m and the average building height was around 12 m. The measurements analyzed in this paper were performed along the same line-of-sight (LOS) and non-LOS (NLOS) street canyons for both carrier frequencies, 2.45 and 5.25 GHz. The channel parameters of root mean square delay spread (DS), shadow fading (SF), number of clusters (NCs) and Rician factors (K) were derived independently at 2.45 and 5.25 GHz as a function of distance between the MS and BS along the street canyons. The observation and investigation of correlation between channel parameters provided interesting results. Currently much literature exists on the extraction of wideManuscript received January 30, 2007; revised April 4, 2007. This work was supported in part by the European Union under the framework of IST projects IST-4-027756 WINNER II and IST-2003-507581 WINNER I. X. Zhao is with Elektrobit Corporation, Espoo 02150, Finland (e-mail:
[email protected]). L. Hentilä, J. Meinilä, T. Jämsä, P. Kyösti, and J.-P. Nuutinen are with Elektrobit Corporation, Oulu 90570, Finland. Digital Object Identifier 10.1109/LAWP.2007.898545 1http://www.propsim.com.
band radio channel parameters, their relationships, and their frequency dependencies [1]–[6]. The correlation coefficients of the channel parameters were derived for different environments in [1]. In [2]–[4], the scatter plots of DS and K factors were given based on wide-band channel measurements. The results show that as DS increases, there is high likelihood of encountering low K-factors. However, to the best of our knowledge, the comparison of correlation between channel parameters and the derivation of correlation relationships have not yet been presented comprehensively. Note that in this paper, the correlations of the channel parameters are derived and discussed at 2.45 and 5.25 GHz independently. Correlation between the frequencies is not included due to the limitations of the measurements.
The channel parameters investigated in this letter are defined as follows. The DS is calculated as the second moment of a power delay profile (PDP). The SF is the difference of the decibel values between the measured path loss and the calculated path loss; the latter is from the regression line of path loss. A positive SF translates to path attenuation, while a negative SF translates to path gain. The NC is defined as the number of local peaks in a PDP and is derived in the delay domain. The K factors were derived by using the moment method described in [6]. The parameters were averaged by grouping the measured impulse responses (IRs) in drops (or segments). The drop size was about 2.5 m, in which the channel can be regarded as wide-sense stationary. We use dynamic ranges of 20–25 dB and 15–17 dB for noise cut in LOS and NLOS measured IRs, respectively. Comparable drop size and dynamic ranges can also be found in [1]. Fig. 1(a) and (b) shows the variations of the channel parameters in the LOS street canyon with respect to distance between the MS and BS at 2.45 and 5.25 GHz, respectively. It is seen that the peaks and valleys of the SF, DS, and NCs always appear at the same time or positions, which shows that they have excellent positive correlation. Additionally they have excellent negative correlation with K-factors. In simple terms, Fig. 1 shows that the higher SF is, the higher DS and NCs, and the lower K-factors are. As K-factor increases (meaning a strong LOS component), lower SF, DS, and NCs are observed in the street canyon. The correlation coefficients can be found in Table I and the maximum and minimum absolute correlation coefficients are 0.88 and 0.43, respectively. The fading of the channel parameters is either in phase or completely out of phase in the LOS street canyon, and their relationships are derived and shown in Table II
1536-1225/$25.00 © 2007 IEEE
ZHAO et al.: CORRELATIONS OF WIDE-BAND CHANNEL PARAMETERS IN STREET CANYON AT 2.45 AND 5.25 GHZ
Fig. 1. Variation of channel parameters with respect to distance between the MS and BS in the LOS street canyon. (a) 2.45 and (b) 5.25 GHz.
TABLE I CORRELATION COEFFICIENTS OF THE CHANNEL PARAMETERS
by linear regression. The mean value and the standard deviation are offered in the same table as well. Fig. 2(a) and (b) shows the variations of the channel parameters in the NLOS street canyon with respect to distance between the MS and BS at 2.45 and 5.25 GHz, respectively. Table I also shows the correlation coefficients. It is seen that in the NLOS street canyon the similar correlation rules as in the LOS case can be found, but the positive and negative correlations are much
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Fig. 2. Variation of channel parameters with respect to distance between the MS and BS in the NLOS street canyon. (a) 2.45 and (b) 5.25 GHz.
lower. Therefore, in the NLOS street canyon, a linear relationship with small regression errors can no longer be obtained as was possible in the LOS case. It can be seen from Figs. 1(a) and (b) and 2(a) and (b) that the variation rules of the channel parameters at 2.45 and 5.25 GHz are different due to different propagation mechanisms. In LOS street canyon, multipath components that arrive and are combined in the MS include direct, reflected, and scattered rays caused by building surfaces and moving cars, etc. However, the amplitude and phase of the multipath components are frequency dependent, resulting in different fading characteristics of the channel and also the channel parameters. As mentioned in the previous section, the frequency correlations of the parameters between 2.45 and 5.25 GHz are not discussed. However, a relative close linear relationship between the channel parameters, e.g., between SF and DS, at both of the frequencies can be found and pairs are quite in Table II. It is seen that the close at both frequencies. This might also be due to the relative small difference in carrier frequencies.
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IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 6, 2007
TABLE II LINEAR RELATIONSHIPS OF THE CHANNEL PARAMETERS IN THE LOS STREET CANYON
presented in Table II. Fig. 3(a) presents the measured and predicted channel parameters with respect to distance between the MS and BS. Fig. 3(b) compares the measured and predicted cumulative distribution functions (cdfs) in the LOS street canyon showing good agreement between the measurements and predictions. The fit standard deviations can be found in Table II. Therefore, we can now use one known or easy derived channel parameter, e.g., the DS, to predict the others (SF, NCs, and K-factors) rather than deriving them all independently. Fig. 3 presents such predictions.
IV. CONCLUSION High positive and negative correlations between channel parameters are observed in the long LOS street canyon. Linear relationships are derived and can be used to predict one parameter from another without necessarily deriving them all. Similar correlations can also be found in the NLOS street canyon; however, the absolute correlation coefficients are much lower than in the LOS case. Comparable linear relationships between the DS and the other channel parameters were derived at 2.45 and 5.25 GHz, respectively, which might be due to the relative closer carrier frequencies.
REFERENCES
Fig. 3. Measured and predicted channel parameters in the LOS street canyon at 2.45 GHz. (a) Variations with distances between the MS and BS. (b) CDF.
III. USING ONE CHANNEL PARAMETER TO PREDICT THE OTHERS As an example, here we use the DS at 2.45 GHz to predict the SF, NCs, and K-factors using the linear relationships
[1] Final Report on Link Level and System Level Channel Models, IST2003-507581, WINNER D5.4 ver 1.4. [2] M. A. Beach et al., “European technological advances in smart antennas,” in Proc. 3rd IST Mobile Wireless Commun. Summit, Nice, France, Nov. 6–8, 2000. [3] G. Del Galdo, J. Lotze, M. Haardt, and C. Schneider, “Advanced geometry-based modeling for MIMO scenarios in comparison with real measurements,” in Internationales Wissenschaftliches Kolloquium, Ilmenau, Germany, Sep. 22-25, 2003. [4] H. Yang, P. F. M. Smulders, and M. H. A. J. Herben, “Frequency selectivity of 60 GHz LOS and NLOS indoor radio channels,” in Proc. IEEE 63rd Veh. Technol. Conf., Melbourne, Australia, May 7–10, 2007. [5] Z. Irahhauten and H. Nikookar, “On the frequency dependence of wireless propagation channel’s statistical characteristics,” in Proc. IEEE 57th Veh. Technol. Conf., Jeju, Korea, Apr. 21–24, 2003. [6] L. J. Greenstein, D. G. Michelson, and V. Erceg, “Moment-method estimation of the Ricean K-factor,” IEEE Commun. Lett., vol. 6, pp. 175–176, Jun. 1999.
