defined. Two environments are characterized in this report. Table x1 summarizes the two characterized environments. The scenario can be uniformed to line-of-sight (LOS) channel with transmission distance of a quite short range. Even for LOS scenario, we have to consider the case which metal chassis or metal cover exists on consumer electronics (CE) in which IEEE802.15.3d devices are implemented inside. That metal must be object for the path between the transmitter (TX) and the receiver (RX). Table 1: A Table Channel Model Scenario Environment Description CMx LOS download CMx LOS w/o File exchange CMx LOS w Metal File exchange Channel Characterization Close Proximity P2P (300 GHz): Concerning the usage model of close proximity P2P wireless communications, the channel is assumed to be line-of-sight propagation in millimeterwave, 300 GHz band. Generally, TSV model is introduced in millimeterwave PAN/LAN systems in IEEE802.15.3c and IEEE802.11ad operating both at 60 GHz. For proximity communications usage, reflections are observed inside terminals and at surface of terminals, etc. The channel model shall be modified to represent such propagation mechanisms and the frequency band at 300 GHz. The channel model shall apply at least one of the several kinds of propagation depending on the antenna configurations.
Data Center The 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 in a typical wireless data center scenario. The results presented here are based on [7.1] and [7.2]. As shown in , the scenario consists of many 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 are available in [7.3]. In our scenario, the material parameters of the wall and ceiling are taken from [7.3] 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 7, the propagation paths are illustrated as blue lines. Figure: The data center scenario Propagation Path Types 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. Propagation path types Selection Between Path When 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 Modelling The 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 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 Numbers is always 1 LoS path. The empirical distributions of the numbers of NLoS paths are presented in . Table NLoS Path number distributions Type 1/2, Tx 1 Number of paths 17 18 19 20 21 Probability (%) 27 35 22 15 1 Type 1/2, Tx 2 Number of paths 16 17 18 19 20 21 Probability (%) 32 29 12 16 8 3 Type 3 Number of paths 3 4 5 6 7 8 9 11 Probability (%) 22 8 8 8 6 3 0