TG3d Channel Modelling Document (CMD)



IEEE P802.15Wireless Personal Area NetworksProjectIEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)TitleAdditional Text on Wireless Data Centers for the TG3d Channel Modelling Document (CMD)Date Submitted11 July 2015SourceBile PengE-mail: peng@ifn.ing.tu-bs.deRe:AbstractPurposeSupporting document for the development of the amendment 3d of IEEE 802.15.3NoticeThis document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.ReleaseThe contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15. Data CenterThe wireless data center uses wireless data links to replace/complement the traditional cable connections, which brings various advantages e.g. high flexibility, low maintenance cost and favorable cooling environment. The high data rate requirement makes the THz technology a competitive candidate because of its high available bandwidth up to 50 GHz.This document provides a realistic THz wireless channel model in a typical wireless data center scenario. The results presented here are based on [x9] and [x10] and are submitted to ISWCS 2015 (currently under review).As shown in Figure 7, the scenario consists of manyseveral server chassis (we assume the standard 1U rackmount chassis in this document), 4 walls and a roof (the 2 front walls and the ceiling are set invisible to illustrate the chassis). The stack height is assumed to be 1.8 m whereas the distance between 2 chassis in the x direction is 0 and in the y direction is 0.5 m. The transmitter (Tx) and the receiver (Rx) are marked as blue circles. A ray tracing simulator is applied to generate the THz channel model. Details of this ray tracing simulator is available in [x11]. In our scenario, the material parameters of the wall and ceiling are taken from [x11] whereas the chassis is assumed to be a perfect conductor. The floor is believed to absorb the signal. Using the ray tracing simulator calibrated for the frequency 300 GHz, the propagation channel can be obtained. In figure 1, the propagation paths are illustrated as blue lines.Figure SEQ Figure \* ARABIC 7: The data center scenario Propagation Path TypesFigure 8 illustrates the possible propagation path types. When the antennas are located on the chassis roof, the signal can be transmitted in a Line of Sight (LoS) path (type 1), or reflected on the ceiling (type 2). In case that Tx and Rx are placed on identical or adjacent chassis, the antenna can be mounted below the chassis roof (type 3) and the propagation path is either LoS or via a reflector to reduce the interference on the propagation path type 1 and 2.Figure SEQ Figure \* ARABIC 8: Propagation path typesSelection Between Path TypesWhen Tx and Rx are on identical or adjacent chassis, path type 3 would have advantage over type 1 and 2 because the lower antenna position produces less interference on other channels. If Tx and Rx are further departed therefore the antennas have to be placed on the chassis roof, type 2 is favorable if the propagation distance is limited whereas type 1 shows more advantage over a longer range. This selection is based on 2 considerations: 1) a shorter distance results in less free space propagation loss and therefore allows for additional reflection loss, 2) the elevation of path type 2 deviates from the horizontal direction more significantly with a shorter horizontal direction, therefore a vertically directive antenna would cause less interference on the horizontal LoS paths (because all the chassis have the identical size). We make the general suggestion that if the AoD/AoA elevation is at least 2 times the antenna Half Power Beam Width (HPBW) in the vertical direction away from the horizontal direction, type 2 has an advantage over type 1. The criterion should be adapted for every concrete scenario.Stochastic Channel ModellingThe stochastic channel modelling is based on massive ray tracing simulations. We choose a Tx position in the room corner (Tx 1) and in the room center (Tx 2) for propagation path type 1/2. For path type 3, we selected Tx and Rx positions randomly on identical or adjacent chassis.Based on the simulation results, we derive a stochastic channel model in the following approach:Determine number of propagation paths.Assign a delay to each propagation path.Determine the pathloss of each propagation path according to its delay.Define the angular difference of each NLoS path to the LoS path.Generate uniformly distributed phase for each path.Generate frequency dispersion for each path.In the following sections, we will explain the process step by step to obtain the stochastic channel model.Path NumbersThere is always 1 LoS path. The empirical distributions of the numbers of NLoS paths are presented in Table 1. Table SEQ Table \* ARABIC 1 NLoS Path number distributionsType 1/2, Tx 1Number of paths1718192021Probability (%)273522151Type 1/2, Tx 2Number of paths161718192021Probability (%)3229121683Type 3Number of paths34567891011Probability (%)2213815817863Delay distributionFigure 9 illustrates the delay distributions. Note that the LoS delay is the absolute value whereas the NLoS delay is the relative delay, i.e. the difference between the NLoS delay and the corresponding LoS delay.(a) Type 1/2, Tx 1(b) Type 1/2, Tx 2Figure SEQ Figure \* ARABIC 9: Delay distributions(c) Type 3Table 2 lists the distribution types and the corresponding parameter values.Table SEQ Table \* ARABIC 2 Delay distributionsPathDistributionParametersType 1/2, Tx 1, LoSNormal distribution=2.26x10-8, =8.76x10-9Type 1/2, Tx 1, NLoSNegative EXP=8.76x109Type 1/2, Tx 2, LoSNormal distribution=1.20x10-8, =4.56x10-9Type 1/2, Tx 2, NLoSNormal distribution=2.98x10-8, =1.79x10-9Type 3, LoSNormal distribution=1.80x10-8, =8.60x10-9Type 3, NLoSNegative EXP=4.92x107Delay-Pathloss CorrelationThe delay has a positive correlation with the pathloss, as depicted in Figure 10. As in the last section, the pathlosses and delays for the LoS paths are absolute values whereas the NLoS carries relative pathlosses and delays. The definition of the relative pathloss is the pathloss of the considered path divided by the pathloss of the corresponding LoS pathloss.(a) Type 1/2, Tx 1(b) Type 1/2, Tx 2Figure SEQ Figure \* ARABIC 10: Delay-pathloss distributions(c) Type 3Table 3 lists the correlations between delay and pathloss. The subscript “r” stands for “relative”. The correlation for the LoS paths can be completely described by the Friss equation. Therefore the random part is 0. For the NLoS paths, the additional loss due to reflections etc. contributes to the random part.Table SEQ Table \* ARABIC 3 Delay-pathloss correlationsPathDeterministic partRandom partType 1/2, Tx 1, LoSp=-20log10(d)-71.52=0Type 1/2, Tx 1, NLoSpr=-0.294dr-17.44=4Type 1/2, Tx 2, LoSp=-20log10(d)-71.52=0Type 1/2, Tx 2, NLoSpr=-0.385dr-17.95=4Type 3, LoSp=-20log10(d)-71.52=0Type 3, NLoSpr=-0.429dr-30.30=6With delays for every path available from the last section, the pathloss can be derived from Table 3.Pathloss-angle CorrelationThe simulation shows some certain degree of correlation between pathloss and the angular difference between the considered NLoS path and the corresponding LoS path. This correlation is important because it has impact on the spatial filtering performance of the directive antennas. The correlations are depicted in REF _Ref423606906 \h Figure 11 and the numbers are listed in REF _Ref423606434 \h Table 4.(a) Type 1/2, Tx 1(b) Type 1/2, Tx 2Figure SEQ Figure \* ARABIC 11: Pathloss-angle correlations(c) Type 3Table SEQ Table \* ARABIC 4 Pathloss-angle correlationType 1/2, Tx 1Relative pathloss (dB)Angular difference ()-70-60-50-40-30-20-10000.0000.0000.0540.0620.0650.0140.2570.000100.0000.0000.0230.0290.0820.0670.2740.360200.0000.0000.0000.0200.0520.0610.0310.360300.0000.1180.0080.0580.1130.0820.1200.280400.0000.0000.0000.0310.0840.0550.0670.000500.0000.0000.0230.0360.0390.0840.0360.000600.0000.1180.0780.0160.0300.1310.0160.000700.0000.0590.0850.0620.0470.1780.0000.000800.0000.0000.1090.1020.1310.0900.0000.000900.0000.0590.1320.1220.0800.0270.0230.0001000.0000.0590.0700.0490.0490.0330.0310.0001100.2490.0590.0780.0490.0390.0270.0290.0001200.0000.0590.0620.0670.0260.0230.0200.0001300.2490.1760.1010.0840.0260.0200.0220.0001400.2490.0000.0470.0670.0250.0190.0150.0001500.2490.2350.0620.0620.0320.0170.0130.0001600.0000.0590.0390.0270.0270.0270.0150.0001700.0000.0000.0160.0290.0290.0270.0190.0001800.0000.0000.0160.0260.0240.0190.0130.000Type 1/2, Tx 2Relative pathloss (dB)Angular difference ()-70-60-50-40-30-20-10000.0530.0000.0260.0170.0540.0150.0210.000100.0530.0000.0000.0170.0700.0270.0410.051200.0530.0000.0530.0440.0930.0450.0790.039300.0530.0000.0530.0480.0750.1230.1000.000400.0530.0000.0260.0650.0740.0890.1080.100500.0530.0000.0260.0720.0500.0650.1210.248600.0530.0000.0530.0750.0600.0560.1370.129700.0530.0000.1320.1400.0550.0350.1650.000800.0530.0000.1840.1300.0510.1170.0850.003900.0530.7480.1450.1060.0930.0650.0340.0391000.0530.0000.0660.0720.0390.0540.0230.0711100.0530.0000.0000.0270.0430.0530.0200.0581200.0530.0000.0530.0410.0560.0560.0120.0581300.0530.0000.0920.0680.0450.0340.0130.0391400.0530.0000.0390.0410.0460.0350.0120.0451500.0530.2500.0260.0100.0300.0290.0130.0261600.0530.0000.0000.0000.0280.0410.0050.0581700.0530.0000.0000.0140.0230.0310.0070.0191800.0530.0000.0260.0140.0160.0270.0060.019Type 3Relative pathloss (dB)Angular difference ()-70-60-50-40-30-20-10000.0620.0450.0000.0000.0000.0000.0030.002100.0000.0910.0490.0540.0050.0060.0000.000200.1250.1360.0240.0270.0050.0040.0000.000300.0620.0910.0240.0000.0160.0000.0040.003400.0000.0910.0730.0000.0330.0130.0060.006500.0000.1360.0000.0000.0300.0060.0470.028600.0000.0000.0490.0000.0250.0110.0130.006700.0000.0000.0000.0540.0270.0320.0030.047800.0000.0000.1220.0000.0190.0150.1310.069900.0000.0910.4390.6750.6920.8770.7800.8201000.0000.1820.0490.0000.0050.0040.0040.0011100.0620.0000.0490.0810.0330.0000.0010.0021200.1250.0910.0730.0000.0330.0020.0000.0051300.1870.0000.0240.0810.0270.0040.0030.0091400.0620.0000.0240.0270.0250.0000.0030.0011500.1870.0000.0000.0000.0160.0000.0000.0001600.0620.0450.0000.0000.0050.0060.0000.0001700.0000.0000.0000.0000.0000.0190.0000.0001800.0620.0000.0000.0000.0030.0000.0010.000The angular difference can be determined given the pathloss from the last section.Phase and Frequency DispersionThe phase can be safely assumed to be uniformly distributed. The frequency dispersion can be described bygf=g0f0fwhere f0 and g0 are the reference frequency and the channel gain at the reference frequency, respectively.Reference[x9] B. Peng, “A Stochastic THz Channel Model in Wireless Data Centers“ doc.: 802.15-15-0207-003d Stochastic Channel Model for Wireless Data Center [x10] B. Peng, T. Kürner, “A Stochastic THz Channel Model for Future Wireless THz Data Centers”, 12th International Symposium on Wireless Communication Systems, Brussels, August 2015[x11] S. Priebe, M. Jacob, T. Kürner, “Calibrated broadband ray tracing for the simulation of wave propagation in mm and sub-mm wave indoor communication channels,” in European Wireless, 2012. EW. pp. 1-10, VDE, 2012.[x9] B. Peng, “A Stochastic THz Channel Model in Wireless Data Centers“ doc.: 802.15-15-0207-003d Stochastic Channel Model for Wireless Data Center [x10] B. Peng, T. Kürner, “A Stochastic THz Channel Model for Future Wireless THz Data Centers”, 12th International Symposium on Wireless Communication Systems, Brussels, August 2015[x11] S. Priebe, M. Jacob, T. Kürner, “Calibrated broadband ray tracing for the simulation of wave propagation in mm and sub-mm wave indoor communication channels,” in European Wireless, 2012. EW. pp. 1-10, VDE, 2012. ................
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