Moving Cell Solution to Provide Wireless Access to

Moving Cell Solution to Provide Wireless Access to Sonic Speed Vacuum Train (REV. 0)

Soon-Gi Park Principal Research Staff/Ph. D. E-mail: [email protected]

ETRI (Electronics and Telecommunications Research Institute) https://etri.re.kr/eng/main/main.etri 218, Gajeong-ro, Yuseong-gu, Daejeon, 34129, KOREA 01/29/2017

Introduction Existing trains generate air resistance proportional to the square of train speed and they consume energy proportional to the cube of train speed. On the other hand, the vacuum train, which runs in a vacuum tube, can travel at a speed of sound or higher while consuming a relatively small amount of energy. Through Robert Goddard's patent (1945), we can see that he first started the research on vacuum train in 1909 and it was Robert M. Salter's engineering papers (1972 thru 1978) that began to gain public attention afterwards. At the time, it was impossible to commercialize due to limitations of technology and huge cost. In 2013, Elon Musk conducted a conceptual design for a vacuum train called Hyperloop, which could generate two-thirds of the cost, three times faster speed and 3.5 to 4 times more utility than the existing high-speed train (HST). The company (Virgin Hyperloop One), established to commercialize Hyperloop by Shervin Pishevar, succeeded in driving a full-scale vehicle at a speed of 386 km/h in a vacuum tube in December 2017, and continues to increase its speed. If a vehicle can travel at a speed of sound in a vacuum test route by 2020, it will be used first for freight and then for passengers. For such commercialization, it is necessary to increase the transportation efficiency (i.e. the operation density of vehicle) and at the same time to secure safety. The underlying element for that is to provide wireless access between the ground and the vehicle driving at a sonic speed. This document proposes a new communication method between the ground and vehicles traveling at high speeds such as a sonic speed.

Motivation Wireless communication of vacuum train encounters the driving at a sonic speed of the vehicle and the enclosed vacuum tube environment that have not been experienced in existing land transportations. The vehicle requires wireless communication ensuring low delay and high reliability in the vehicle control aspect while it can run at a sonic speed in a closed tube environment. To ensure the safety of Hyperloop, there is a need to monitor the outside or inside of the vehicle in real time and hence gigabit data transmission is required in the wireless communication between the vehicle and the ground. Additionally, data transmission for passengers in the vehicle may be required.

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Current Technologies Long Term Evolution (LTE) communication claims to support communications for vehicles traveling at 350 km/h and GSM-R/LTE-R/5G are known to support communications for vehicles traveling at 500 km/h (GSM: Global System for Mobile communications, -R: -Railway). However, these conventional cellular communication schemes are operated based on the concept of fixed cell planning, and as the vehicle speed is higher, the data transmission speed is lowered. When the position of the vehicle is located at the center of cell, the data rate is highest. The farther its position is from the center of the cell, the lower the data transmission speed. Additionally, performance degradation due to handover (cell change) occurs at cell boundary. There were communication methods based on a Leakage Coaxial Cable (LCX) or Distributed Unit (DU) to support vehicles traveling at 500 km/h or 600 km/h in HST, MAGnetic LEVitation (MAGLEV). However, there are no examples yet that support higher speeds (such as sonic speeds or higher). LCX communication method is advantageous in that it can maintain a constant data transmission rate within one segment regardless of the position and speed of vehicle, but it is difficult to guarantee a data transmission speed of 10 Mbps or more due to the limit of leakage propagation, and it has performance degradation due to handover (segment change) and a restriction on the segment length due to cable power loss. In the DU-based communication scheme, the data transmission rate can be improved by narrowing the interval between DUs grouped into one cell, and it is possible to reduce the number of handovers by expanding the coverage of the cell assuming that the vehicle travels at the same speed. However, performance degradation due to handover (cell change) still occurs at the cell boundary. That is, since all the above-mentioned methods are operated as fixed cells (or fixed segments), as the speed of the vehicle increases, the number of handovers increases, which inevitably leads to performance degradation. Further, in a tube environment in which the entire path is closed instead of the open environment, a fixed cell having a constant coverage cannot exist due to the waveguide phenomenon, and hence communication may not be possible in the entire route.

Seed Idea If the base station (BS) can be moved in accordance with the moving direction and speed of the user equipment (UE) as shown in the left side of , the communication between UE and BS is similar to

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the fixed communication environment and then can support large data transmission regardless of the moving speed of the UE. The question mark in the center of means that there are various ideas about the way to move BS in Hyperloop. The right of claims that the picturized answer is the pace maker communication method (PMCM), which will be described in detail in the next section. In fact, it is impossible to physically move a BS, so a moving BS is called a virtual BS, a ghost BS, or a moving cell. PMCM has a similar effect as a moving BS. The role of pace maker that run together with runner's pace in marathon and support him is similar to moving cell concept (where runner corresponds to UE/capsule (vehicle)).

The Concept of Pace Maker Communication Method (PMCM)

PMCM PMCM is a method to support mass data transfer regardless of the moving direction and speed of the vehicle. The key concept is to move the BS together according to the moving direction and speed of the vehicle. In this section, an example of a system structure for realizing this is presented, and features about moving cell operation, hardware and software are described based on this structure. The PMCM is a communication technology for sonic speed vehicles running in a closed tube environment like Hyperloop,

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but it can also be used for the existing land transportations (e.g. subway, HST, MAGLEV, etc.) in open-site scenarios and tunnel scenarios.

Architecture We can select either the radio (LCX or DU) or the Free Space Optic (FSO) methods in realizing PMCM. That is, the PMCM is a technology applicable to both the radio method and the FSO method. shows an example of a DU-based PMCM system architecture applied to Hyperloop. DUs are arranged at regular intervals on the ceiling inside the tube, and one physical group of DUs is called the Linear Active Antenna Module (LA2M). These multiple LA2Ms are connected to a single Virtual Active Antenna Controller (VA2C). Compared to LTE(-Advanced), the Tube Side Unit (TSU) is the entity corresponding to the eNB, the Central Communication Unit (CCU) is the entity corresponding to the Evolved Packet Core (EPC), and the Capsule Active Antenna Module (CA2M) and Equipment (CE) is the entity corresponding to the UE (CA2M corresponds to the antenna of the UE). The Capsule Control Network (CCN) on the ground is connected to the CCN inside all vehicles to manage the operation control of the vehicle. The passenger service network (PSN) on the ground is connected to the PSN inside all vehicle to provide communication services for passengers. For example, a CCN inside a vehicle can be a WiFi AP or a Small Cell BS, allowing passengers to use the Internet and existing cellular services using their laptops or smartphones while on board. The STAR or RING topology can be used for the connection between VA2C and LA2M, as shown in and . STAR topology is a structure that connects a VA2C and each DU of LA2Ms to 1: 1 respectively, and RING topology connects DUs belonging to LA2Ms and a VA2C together on the same physical line. When fiber is used in the same physical line in the RING topology, if different wavelengths are used between each DU belonging to the LA2M and VA2C, VA2C has the effect of having an independent communication path with each DU. An important part of configuring the ground communication infrastructure is the connection between the inside of the tube and the outside of the tube because the inside of the tube is vacuum, and this connection may be selected as wired or wireless. In the case of wired, the fiber penetrates through the lid cover to connect the outside and the inside of tube, the perimeter portions of the fiber in contact with the cover is filled by the seal materials, the cover is placed in its hole on the tube surface, and the space between the tube and the cover is airtight by tightening the screw. In the case of wireless, this quartz window are used to penetrate the laser, and two devices placed in inside and outside the lid convert the optical signal to a 5

laser and vice versa. is an example of installing LA2M inside the tube and installing the remaining entities (VA2C/ TSU/ CCU) outside the tube and is an example of installing the LA2M/VA2C/TSU inside the tube and installing only CCU outside the tube. The choice can be made based on the system reliability and total cost for ownership (TCO). Choosing one of two installation methods can be done by taking into account the system reliability and the total cost for ownership (TCO) aspect. In , the core of the DU-based PMCM system architecture is to set up a sliding window dedicated to each capsule (e.g. a sliding window for CAPSULE 1, a sliding window for CAPSULE 2) and to move the sliding window according to the direction and speed of capsule (vehicle). The movement of the sliding window is possible by STAR or RING topology connected to DUs, VA2C and TSU.

DU-based PMCM System Architecture for Hyperloop

Connection Topology between VA2C and LA2M (DU) – Type 1

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Connection Topology between VA2C and LA2M (DU) – Type 2

Moving Cell Operation shows three types of fixed cell method to explain the difference between the existing fixed cell method and the moving cell method in PMCM. a is a case where one antenna is used to form a cell having a coverage of 1.2 km and these cells are slightly overlapped. In this case, the difference between the maximum and minimum signal strengths is very large, and each unique antenna has one unique fixed cell identity. As the vehicle travels, nine cells (cell 1 thru 9) are used and eight handovers occur in a. b is a case where five antennas are arranged in a section of 1.2 km and one cell is formed by grouping them. The difference between the maximum and minimum signal strengths is relatively reduced because the minimum signal strength is increased, and handover in b occurs eight times like a. c is a case in which 10 antennas are grouped into one cell for each 2.4 km section. The signal intensity difference between maximum and minimum in c is the same as the one of b, but there are four handovers and the performance degradation due to handover is relatively small. That is, compared to a, the minimum signal strength in b and c is improved through antenna densification and cell grouping and hence the signal variation becomes small. c shows that cell expansion can reduce the occurrence speed of the handover when assuming the same vehicle speed. Additionally, minimum cell strength can be slightly improved by grouping cells by two antennas in the antenna arrangement of a, and the occurrence number of handover is 4 as in c. In this document, moving cell method adopts antenna densification, cell grouping and cell expansion, and then moves the cell to obtain a similar effect to fixed communication without handover. By doing so, deterioration in performance due to Doppler spreading can be prevented. 7

, and show examples of moving cell operation over time (e.g. T1, T2, T3, …). is the example of non-overlapping moving cell operation, and and are classified into examples of overlapping moving cell operation. The non-overlapping moving cell operation of forms a cell (cell 1) dedicated to one vehicle and move the previous cell and the current cell so that they do not overlap. It is a way of jumping without reusing the antenna provided for the dedicated cell at a specific point so that the dedicated cell is not overlapped when moving in the movement direction and speed of the vehicle. The overlapping moving cell operation in and forms a dedicated cell (cell 1) for one vehicle, and it is moved in accordance with the moving direction and speed of the vehicle where the antennas that are served in the previous dedicated cell to overlap (reuse). shows that only one antenna is moved while overlapping the moving cell (i.e., shift(+1)), and shows moving every three antennas while overlapping the moving cell (i.e., shift(+3)). Reflecting the vehiclededicated cell and its overlapping movement characteristics, the moving cell is also referred to as the sliding window. The moving cell method must require information on the current position, moving direction and speed of the vehicle, and it provides superior and stable signal quality compared to the fixed cell method since the dedicated cell is moved based on this information. Temporary performance degradation may occur at a jump boundary point when the dedicated cell dedicated to the vehicle jumps without overlapping in , and it can be larger depending on the inaccuracy of the position of the vehicle, so this non-overlapping moving method is very important to the accuracy of the position of the vehicle. On the other hand, there is no performance degradation at boundary point like since the vehicle-dedicated cell are moved in a superimposed manner such as and , and relatively good signal quality can be obtained and the accuracy of the vehicle location may be relatively low. The moving cell method (sliding window) in and can also be used in open-site and tunnel scenarios, and it can also be used in a fully enclosed tunnel environment (i.e., a closed vacuum tube), such as Hyperloop. However, the characteristics that are different from the existing communications should be considered because the sonic speed vacuum train travels only within a closed vacuum tube with a diameter of 3.3 m. Since the vehicle is only in a closed tube, placing the antenna outside the tube cannot provide radio access between the ground and the vehicle due to the signal blocking effect of the tube and hence the antenna has to be placed inside the tube, and cell coverage of 1.2 km cannot be guaranteed with only one antenna considering the diameter of the tube is about 3.3 m. Assuming that a radio propagation method is used for communication between the ground and the vehicle, it is possible to provide radio access through a cell grouping and a cell expansion about the antennas on the ceiling of the vacuum tube. Due to radio propagation characteristics in a closed vacuum tube, fixed cell methods like cannot 8

be used. It is very difficult for one cell to have a unique cell identity and to form a fixed service area because it acts as an extensive interference of other neighboring cells due to the waveguide effect of radio waves within the enclosed tube environment.

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Fixed Cell Methods (3 cases)

Non-overlapping Moving Cell - Jumping 10

Overlapping Moving Cell – Sliding (Type 1)

Overlapping Moving Cell – Sliding (Type 2)

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Hardware Compared with the LTE mobile communication system in terms of hardware (HW), the new HW entity in PMCM system is VA2C, and its role is to simultaneously transmit one downlink signal from TSU to DUs belonging to LA2Ms under the control of the VA2C and to select one of the uplink signals from DUs of LA2M or to perform a soft combination of all or part of them. The choice of whether to group all DU ports within one LA2M into one, or to group some DU ports, or to process each DU port individually on the uplink or downlink side will be determined by the system performance requirements and system CAPEX/OPEX. and show the role of VA2C on the downlink side and uplink side respectively based on the STAR topology mentioned above (Even with the above RING topology, the processing concept is the same). In the a, the downlink signal of TSU 1 is transmitted to the B port of VA2C 2 and the VA2C 2 simultaneously connects to the DU ports (d, e, f, g, h, i) of VA2C to send it to the specific DUs belonging to LA2M 3 and LA2M 4. In this case, wireless access service section made by the continuous DUs in which the downlink transmission is performed is referred to as downlink sliding window. In b, DU ports for the downlink signal of TSU 1, which has arrived at port B of VA2C 2, is moving from ‘d, e, f, g, h, i to ‘c, d, e, f, g, h’. In c, the downlink traffic in the CCU must be processed in both TSU 1 and TSU 2. In this case, the downlink signal in all DUs of sliding window should be the same. In order to do that, the same content is transmitted over the same radio resource area in the same subframe. The downlink signal of TSU 1 is received at B port of VA2C 2, and the downlink signal of TSU 2 is received at A port of VA2C 3, and the downlink sliding window is moved by adding b port and by leaving h port. In d, the DU transmission port of VA2C 2 is changed to ‘c, d, e, f’ and the DU transmission port of VA2C 3 is changed to ‘a, b’ to move the downlink sliding window. In a, an uplink sliding window is defined as a radio access service interval in which the uplink signal of the vehicle is significantly received in specific DU ports of LA2M 3 and LA2M 4. These DUs are only included in VA2C 2 and their ports are ‘d, e, f, g, h, i’. VA2C 2 transmits the uplink signal to TSU1 through port B of VA2C 2. At this time, all uplink signals may be transmitted to TSU 1, or one or a part of uplink signal(s) selected by the upper layer’s command may be transmitted to TSU 1, or soft-combining result for some uplink signals may be send to TSU 1. For example, it is possible to raise only one uplink signal having the greatest reception strength, or to raise a plurality of uplink signals having a predetermined reception strength threshold and higher, or to raise a soft-combined uplink signal about all or some of the uplink signals belonging to a sliding window. In b, the DU receiving ports of

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VA2C 2 for the uplink sliding window have been changed to ‘d, e, f, g, h, i’ from ‘c, d, e, f, g, h’. In c, the receiving ports for the uplink sliding window is changed to the port b of VA2C 3 and the ports ‘c, d, e, f, g’ of VA2C 2. In this case, the uplink signal(s) is also transmitted to both TSU 2 and TSU 1, and CCU may receive a number of identical uplink traffic and must choose one of them. As an example for any of the methods by which CCU selects the uplink traffic, CCU may give the control information about the pretraffic filtering condition for raising the uplink traffic to the TSU. If the condition is satisfied, TSU raises uplink traffic as well as related information (e.g., system frame/subframe and received strength, etc). When CCU receives the same uplink traffic (s) from multiple TSUs or one TSU, it selects one uplink traffic among them based on their information. As an additional method, TSU send the control message including the reception information related to uplink traffic (s) to CCU before actually raising them, CCU selects uplink traffic based on this control message and this CCU’s selection information is sent to the TSU, and then TSU only uploads uplink traffic (s) corresponding to it. In d, the receive ports for the uplink sliding window have been changed to ports ‘a, b’ of VA2C 3 and ports ‘c, d, e, and f’ of VA2C 3. In summary, the sliding window must be managed for each vehicle and it also may be managed differently for the uplink and the downlink and it can move in accordance with the moving direction and speed of the vehicle. VA2C is the HW entity that enables this physical movement and it can multiplex the downlink signal to multiple DUs and select or softly combine multiple received uplink signals.

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Role of VA2C - Downlink Aspect 14

Role of VA2C - Uplink Aspect 15

Software Compared to LTE mobile communication system in terms of software (SW), PMCM system is described in three aspects (function relocation, sync protocol, radio resource management) in this section.

Function Relocation (CP/UP Aspect)

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Function Relocation In order to explain the function relocation of PMCM system based on the functional layout of each node in the LTE mobile communication system, shows horizontal division of control plane (CP) and user plane (UP) together with vertical node classification of CCU, TSU, VA2C, LA2M. All entities are synchronized (node synchronization) and IP multicast can be used in the transport layer for control and data transmission between nodes. In case of CP, CP-TSU can be controlled by CP-CCU control and CP-TSU can control CP-VA2C and CP-LA2M. This control is as shown in Fig. (1), (2), and (3), and these controls are responsible for controlling UP as well as CP itself. The radio resource control protocol (RRC) is relocated to CCU rather than TSU and PDCP/RLC may be relocated to CCU rather than TSU. In terms of UP, there are three options. In UP-1, there is MAC/PHY function in TSU and RF function in LA2M. In UP-2, TSU has a MAC function and LA2M has a PHY/RF function. There are MAC/PHY/RF functions in LA2M in case of UP3. We can select one of the three choices (PHY-RF (UP-1), MAC-PHY (UP-2), and RLC (Relay) -MAC (UP-3)) mentioned above in function split between LA2M and TSU. Assuming the same user traffic processing, there is an advantage in that the transmission/reception data capacity between LA2M and TSU is reduced in order of UP-1/UP-2/UP-3 but there may be a disadvantage that the product cost for LA2M increases. In addition, UP-1 only may be capable of uplink soft combining for DUs belonging to different LA2Ms. CCU can also provide the ability to match the Internet and the Small Cell Gateway/EPC, and it especially may support voice and video calling between the ground CCN and the vehicle CCN or between the vehicle CCN and the vehicle CCN by adding functions such as IP Multimedia Subsystem (IMS).

Sync Protocol Design SYNC protocol of supports three functions. SYNC protocol located in the CCU is responsible for the de facto master MAC function in cooperation with the RRC, and it synchronizes the downlink content on the same radio resource area at the same time in cooperation with the SYNC protocol in other entities (e.g. TSU, LA2M). It also serves to support uplink content selection of the upper node. Firstly, PROBE SYNC Packet function transmits the probe packet to the lower nodes and collects each delay time for the intermediate and the end node to which the final contents are to be delivered. Based on this information, scheduling for simultaneous transmission is performed considering the maximum delay in achieving content synchronization. Secondly, DL SYNC data packet function is used to support joint transmission in nodes corresponding to a sliding window on the downlink. MAC function buffers transmitted packets

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considering the maximum delay factor measured through PROBE SYNC packet and MAC functions in all nodes belonging to a sliding window can transmit the same content at the pre-defined radio resource area and the pre-defined time by using the control information including DL SYNC data packet. Thirdly, UL SYNC packet function is for transmitting uplink contents to the upper node, and it supports the selection of the best uplink content by including various information (whether soft combining or not, receiving power and time information, etc.).

Radio Resource Management The characteristics of radio propagation in a vacuum tube are that the path loss, the delay spread, the spectral power density, and the spectral delay spread depending on the distance can be varied by various factors such as frequency wavelength, transmission power, etc. An example of them is shown in . In , downlink or uplink radio propagation characteristics depending the distance are classified into three areas: good window (GW), dead window (DW), and interference window (IW) respectively, and these three areas are collectively referred to as capsule radio zone (CRZ). GW (Good Window) is a section where wireless communication between the ground and the vehicle is possible. In DW (Dead Window), the path loss and delay are the largest due to the interference of radio waves, and the communication is impossible. In IW (Interference Window), due to the waveguide effect, the path loss decreases then gradually increases with distance, and the delay is little and gradually increases with distance, which is an interval that can interfere with other vehicles. For example, if you are using a 60GHz frequency in a particular environment, the Good Window, the Dead Window and the Interference Window in downlink CRZ aspect can be 500m, 500m, and 6km, respectively. This result depends on which frequency is used. Even if the frequency is the same, radio propagation characteristics may be different depending on various factors such as the tube diameter and its material, transmission power, and BR (ratio of tube cross-section to vehicle cross-sectional area), etc. From the results of simulations or measurements of radio propagation characteristics such as under certain environmental conditions, GW 500 m means that the maximum possible distance of the sliding window (i.e., the distance of service section of the moving cell that can group DUs) is 500 m in actual operation, and sliding window cannot be more than 500 m due to dead window and it should be managed within 500 m. DW may be equal to the length of the set sliding window (GW), and DW and IW may act as interference of the preceding and following vehicles. In a closed vacuum tube, due to the radio propagation characteristics shown in a, the fixed cell concept of (ensuring continuity of wireless communication service area through continuous fixed 18

cell placement) cannot be established. If the concept of fixed cell is applied to the whole driving range of the vehicle in a closed vacuum tube, interference occurs in the control region, so that the scheduling itself cannot be performed. Even if scheduling is performed, interference occurs in the data region. In other words, wireless communication may be impossible on all routes. From the uplink CRZ view in b, Good Window, Dead Window and Interference Window are all present. In uplink GW, the strength of the uplink received signal can be increased through joint reception (JR) on the ground, but it may be difficult to perform JR for all DUs corresponding to GW in the uplink CRZ due to hardware limitations. As a result, uplink GW may have one or more uplink content (s) received from each DUs or processed via JR, and hence it is necessary to select the best uplink content based on the additional radio information. The radio propagation characteristics such as in a closed vacuum tube means that new radio resource management concept is needed instead of that used in fixed cell concept. This new radio resource management is shown in and . Assuming that the route length of the vacuum tube from the A station to the B station is 413 km and a capsule runs according to the capsule operation profile of , a vehicle can arrive from station A to station B in 25 minutes. Each capsule arrives at the B station starting from station A through an acceleration/constant velocity/deceleration predefined in its own operation profile. In the 413 km vacuum tube section from station A to station B, a number of capsules (1thru 8 over) can be operated and hence each capsule operation profile is planned in advance so that these capsules do not collide with each other. When a capsule operation profile is updated, the operation profiles of other capsules are also updated. New communication systems such as PMCM require radio resource management from the CRZ point of view in the context of . The key concept of the new radio resource management is that each vehicle has its own CRZ, and its first judgment is to confirm whether such CRZs are overlapping or non-overlapping. In , a vehicle-specific moving cell (sliding window) is created for each vehicle and it is moved according to the moving direction and speed of the vehicle. If CRZs of the vehicles is non-overlapping, each vehicle can use the entire frequency band at all times. If CRZs of the vehicles is overlapping, interference between CRZs is avoided by allocating resources separately on the frequency axis and by preventing overlapping time on the time axis. All vehicles (3, 4, 5, 6) corresponding to non-overlapping CRZ in do not cause interference even when using the entire transmission time interval (TTI) time of the entire frequency resource as shown in a. On the other hand, if there are capsules (1 and 2, 7 and 8) corresponding to overlapping CRZ in , interference can be avoided by separating the control and data regions from the frequency-domain or the time-domain as shown in b.

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Downlink and Uplink Capsule Radio Zone (CRZ)

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Non-overlapping and Overlapping CRZ

Radio Resource Management in Non-overlapping and Overlapping CRZ 21

Conclusion The moving cell method (sliding window) presented in this document has no performance degradation due to Doppler phenomenon no matter how fast the vehicle speed is, and it can realize data rates higher than gigabit because it provides an environment similar to fixed communication. This method can be used for the existing land transportations (e.g., subway, HST, MAGLEV, etc.) as well as for new land transportation like Hyperloop. In addition, air mobile objects moving at predetermined altitudes and routes can be applied by extending this concept. In this document, moving cell method (sliding window) is described based on the DU-based radio method. However, this method can be used for the radio method such as LCX or for the optical communication method like FSO. In particular, there may be four considerations when this method is used in Hyperloop. The first is the frequency selection problem in terms of CRZ. The length of the CRZ may be shorter as millimeter wave frequencies (frequency region 2 (FR2): 24250 MHz to 52600 MHz) are used than the existing cellular frequencies (frequency region 1 (FR1): 450 MHz to 6000 MHz). As a result, the shorter the wavelength of the frequency, the smaller the length of the CRZ. Secondly, the enclosed vacuum tube environment corresponds to a large radio chamber considering that the frequency is only present within a sealed vacuum tube and the actual transmission power is very small. Therefore, licensing and regulation of the frequency may not be necessary from the technical point of view. Thirdly, the safety is more important than cost in case of transporting passengers, so redundant communication systems are essential. In the redundancy scheme, the same type of redundancy or heterogeneous redundancy can be considered. Fourthly, this method requires the position of the vehicle. This location information can be obtained from various existing methods and the vehicle location awareness function may be embodied in the communication function. Most of the technologies that can realize the PMCM system called moving cell method (sliding window) have already been developed through the Giga KOREA Projects (GK13thru18N0100 and GK13thru18N0330) sponsored by the Korean government. It is possible to develop a PMCM system that can be applied to Hyperloop by recycling the results from the two projects (80%), by developing the additional SW and by relocating the existing SW functions (20%) (Refer to ANNEX. A).

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References [1] Elson Musk, ‘Hyperhelop Alpha’, 2014. [2] Paular Fraga-Lamas, Tiago M. Fermandez-Carames, Luis Castedo, ‘Towards the Internet of Smart Trains: A Review on Industrial IoT-Connected Railways’, Sensors, June 2017. [3] Bart Lannoo, Didier Colle, Mario Pickavet, and Piet Demeester, ‘Radio-over-Fiber-Based Solution to Provide Broadband Internet Access to Train Passengers’, IEEE Communication Magazine, February 2007. [4] Charles D. Gavrilovich, ‘Broadband Communication on the Highways of Tomorrow’, IEEE Communication Magazine, April 2001.

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ANNEX. A Giga KOREA Project’s Results (that can be recycled for PMCM system) PMCM System Moving Cell Method (Sliding Window)

Giga KOREA Project GK17thru18N0100

Giga KOREA Project GK13thru18N0330

CCU

NGC (Next Generation Core)

-

TSU

gNB (5G BS)

-

VA2C

-

IFoverFiber (IFoF)

LA2M

BS Antenna (FR2, 28GHz)

CA2M

UE Antenna (FR2, 28GHz)

-

UE

-

~10Gbpsmax (per UE)

-

ETRI SAMSUNG, INNOWIRELESS, ELUON, TECHFLEX

ETRI

CE

Performance

Main Participant

-

* Giga KOREA Project [GK13thru18N0100]: 5G mobile communication system development based on mmWave (5 years) * Giga KOREA Project [GK13thru18N0330]: Development of Indoor DAS Technology based on IFoF for 5G Mobile Communication (5 years) * FR2 (Frequency Region 2): 24250MHz ~ 52600 MHz * IF: Intermediate Frequency

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 Giga KOREA Project [GK13thru18N0330] - Results

 Giga KOREA Project [GK13thru18N0330] - Results

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