KR102327817B1 - Method and apparatus for transmission and reception signal in high speed train communication network - Google Patents

Abstract

Transmitting an uplink signal to the base station during the duration of the UpPTS of the special subframe, and after uplink transmission, performing signal transmission and reception through the step of waiting for a guard time before receiving a downlink signal from the base station. To move to, a terminal and a signal transmission and reception method of a mobile communication system are provided.

Description

Method and apparatus for transmitting and receiving signals in a high-speed train communication network

The present disclosure relates to an apparatus and method for transmitting and receiving signals in a high-speed train communication network.

Many efforts are currently underway to improve LTE systems for high-speed scenarios by targeting potential uses of 5G communication systems. And one of the main purposes is to provide an optimal quality of service (QoS) to a user riding in a moving body moving at a speed of up to 500 km/h.

However, the frame of the conventional LTE system is not suitable for a high-speed scenario with directionality for several reasons. First, since the frame of the conventional LTE system is suitable for providing a service to a plurality of user equipment (UE) placed in a cellular environment, a terminal equipment (TE) including a plurality of passengers having one or more UEs ) and RU are not suitable for communication. In addition, in the LTE system, timing advance (TA) must be estimated and TA must be updated to obtain uplink synchronization of a plurality of UEs, but in a high-speed scenario, it is not necessary to individually estimate TA for each UE. , it is difficult to timely update the TA. In addition, preamble transmission and TA estimation of random access (RA) inevitably take a lot of time in consideration of a system delay due to a high speed of a train and frequent synchronization. Finally, in a high-speed scenario, the number of TEs simultaneously accessing the network is limited, and a situation in which multiple simultaneous network access requests are generated is also rare. Therefore, the long preamble of the random access channel (RACH) of the LTE system is also inappropriate, and the performance of the Zadoff-Chu sequence, which is sensitive to frequency offset, is also very poor under severe Doppler spread.

An embodiment provides a terminal and a method of transmitting and receiving a signal of a terminal waiting for a guard time before receiving a downlink signal from the base station after transmitting an uplink signal to the base station during the duration of the uplink pilot time slot of a special subframe to provide.

Another embodiment provides a base station for transmitting and receiving a signal based on a transmission delay determined through a random access channel including a special symbol only at a special symbol position.

According to one embodiment, a terminal of a mobile communication system that moves at a high speed is provided. The terminal includes a processor, a memory, and a wireless communication unit, and the processor executes a program stored in the memory to uplink to the base station during the duration of an uplink pilot time slot (UpPTS) of a special subframe. After transmitting the signal, and after transmitting the uplink signal, the step of waiting for a guard time (GT) before receiving the downlink signal from the base station is performed.

Prior to the step of transmitting the uplink signal from the terminal, the processor executes a program, and receives the downlink signal from the base station during the duration of a downlink pilot time slot (DwPTS) of a special subframe. Further, when performing the step of transmitting the uplink signal, the processor may perform the step of directly transmitting the uplink signal without waiting time after receiving the downlink signal.

In the terminal, the transmission of the downlink signal from the base station may be performed by the base station before the reception of the uplink signal by the base station by a round-trip transmission delay.

In the terminal, when performing the step of transmitting the uplink signal, the processor may perform the step of transmitting the uplink signal to the base station during the duration of the UpPTS and the duration of the uplink subframe.

In the terminal, the sum of the duration of the DwPTS, the duration of the UpPTS, the duration of the uplink subframe, and the guard time may be equal to the length of two subframes of the LTE system.

In the terminal, after the step of waiting for the guard time, the processor may further perform the step of receiving a downlink signal from the base station during the duration of the downlink subframe by executing a program.

According to another embodiment, a method for transmitting and receiving a signal of a terminal of a mobile communication system, which moves at a high speed, is provided. The method includes transmitting an uplink signal to a base station for a duration of an uplink pilot time slot (UpPTS) of a special subframe, and after transmitting the uplink signal, the downlink from the base station and waiting for a guard time (GT) before receiving a signal.

The signal transmission/reception method further includes, before transmitting the uplink signal, receiving a downlink signal from a base station during a duration of a downlink pilot time slot (DwPTS) of a special subframe, and , transmitting the uplink signal may include transmitting the uplink signal immediately without waiting time after receiving the downlink signal.

In the signal transmission/reception method, the transmission of the downlink signal from the base station may be performed by the base station prior to the reception of the uplink signal by the base station by a round-trip transmission delay.

Transmitting the uplink signal in the signal transmission/reception method may include transmitting the uplink signal to the base station during the duration of the UpPTS and the duration of the uplink subframe.

In the signal transmission/reception method, the sum of the duration of DwPTS, the duration of UpPTS, the duration of the uplink subframe, and the guard time may be equal to the length of two subframes of the LTE system.

The signal transmission/reception method may further include, after the step of waiting for the guard time, receiving a downlink signal from the base station during the duration of the downlink subframe.

According to another embodiment, a base station of a mobile communication system, which moves at a high speed, is provided. The base station includes a processor, a memory, and a wireless communication unit, and the processor executes a program stored in the memory, estimating a transmission delay based on a random access channel including a special symbol, received from the terminal, a special sub Transmitting a downlink signal to the terminal during the duration of a downlink pilot time slot (DwPTS) of the frame, and after transmitting the downlink signal, an uplink pilot time slot of a special subframe time slot, UpPTS), a step of waiting for a round-trip transmission delay is performed until an uplink signal is received from the terminal.

In the base station, the special symbol may be located in at least one of n special symbol positions included in the random access channel.

If the special symbol is located at two or more special symbol positions among n special symbol positions in the base station, the two or more special symbol positions may be consecutive in the random access channel.

The number of special symbol positions in the base station, the length of the special symbol positions, and the number of special symbols that can be transmitted by the terminal may be adaptively determined according to system parameters and environments.

In the base station, the processor executes a program, and after a round trip transmission delay, an uplink signal from the terminal during an uplink pilot time slot (UpPTS) duration of a special subframe and a duration of an uplink subframe The step of receiving , and the step of waiting for a time equal to the amount of time obtained by subtracting the round-trip transmission delay from the guard time may be further performed.

In the base station, the guard time may be equal to the maximum round trip transmission delay.

Since the base station and the TE do not perform UL synchronization in the high-speed scenario, the contention-based RA procedure of the LTE system can be further simplified to a contention-free RA procedure by using a new frame structure and PRACH structure.

1 is a conceptual diagram illustrating a directional network for train communication according to an embodiment.
2 is a diagram illustrating cell coverage of a directional network having a directional beam according to an embodiment.
3A and 3B are diagrams illustrating a directional network in which two trains are connected to different RUs, respectively, according to an embodiment.
4 is a conceptual diagram illustrating a transmission delay between a base station and a terminal using LTE TDD frame configuration 2;
5 is a conceptual diagram illustrating a hybrid TDD frame structure of a directional network according to an embodiment.
6 is a flowchart illustrating operations of a base station and a terminal using a hybrid TDD frame structure according to an embodiment.
7 is a conceptual diagram illustrating PRACH signaling of a directional network according to an embodiment.
8 is a block diagram illustrating a wireless communication system according to an embodiment.

Hereinafter, with reference to the accompanying drawings, it will be described in detail for those of ordinary skill in the art to which the present invention pertains to easily implement the embodiments of the present disclosure. However, the present description may be embodied in various different forms and is not limited to the embodiments described herein. And in order to clearly explain the present description in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, a train terminal (terminal equipment, TE) is a terminal, a mobile station (MS), a mobile terminal (MT), an advanced mobile station (AMS), a high reliability mobile station (high reliability mobile station, HR-MS), subscriber station (SS), portable subscriber station (PSS), access terminal (AT), user equipment (UE), machine It may refer to a machine type communication device (MTC device) and the like, and may include all or some functions of MT, MS, AMS, HR-MS, SS, PSS, AT, UE, and the like.

In addition, the base station (base station, BS) is an advanced base station (advanced base station, ABS), a high reliability base station (high reliability base station, HR-BS), a Node B (node B), an advanced node B (evolved node B, eNodeB), an access point (AP), a radio access station (RAS), a base transceiver station (BTS), a mobile multihop relay (MMR)-BS, a relay serving as a base station station, RS), a relay node (RN) serving as a base station, an advanced relay station (ARS) serving as a base station, and a high reliability relay station (HR) serving as a base station -RS), small base station [femto base station (femto BS), home node B (home node B, HNB), home eNodeB (HeNB), pico base station (pico BS), macro base station (macro BS), micro base station (micro BS) ), etc.], etc., may include all or part of the functions of ABS, NodeB, eNodeB, AP, RAS, BTS, MMR-BS, RS, RN, ARS, HR-RS, small base station, etc. have.

1 is a conceptual diagram illustrating a directional network for train communication according to an embodiment, and FIG. 2 is a diagram illustrating cell coverage of a directional network having a directional beam according to an embodiment.

Referring to FIG. 1 , a directional antenna is installed in a radio unit (RU) of a base station of a high speed train (HST) installed in the front and rear parts of the TE and on the ground, respectively. The functions of the HST base station include digital units (DUs) and RUs. The TE may function as a mobile relay and provide a wireless backhaul link to passengers. The reason for using the TE instead of forming a separate direct link from the RU to the individual passenger is to avoid the group handover problem. As shown in FIG. 1 , each TE includes two antennas (a first antenna and a second antenna), and the TE is located in front of the traveling direction through each of the two antennas, RU(RU _{n +1} ) and the traveling direction. It is possible to perform communication with the RU (RU _{n ) located behind the.} That is, the first antenna forms a radio link D _{1 with RU n ,} and the second antenna forms a radio link D _{2 with RU n +1} . Each link also acts as an _{interfering link I 1} and I ₂ with respect to each other.

The directional network shown in FIG. 2 includes four cells, and one cell is formed by each RU. The first cell _{represents the coverage of RU n} , the second cell represents the coverage of RU _{n +1} , the third cell represents the coverage of RU _{n +2} , and the fourth cell represents the coverage of RU _{n +3} . That is, all RUs form cells in only one of the TE's moving directions or the opposite direction to the moving directions, and the boundary of each cell touches the position of the next RU.

Considering the wireless backhaul link between the TE and the RU, the TE acts like a super UE from the point of view of the network and the RU. In this case, the time division duplex (TDD) frame of the conventional LTE system is not suitable for the directional network as shown in FIGS. 1 and 2 .

3A and 3B are diagrams illustrating a directional network in which two trains are connected to different RUs, respectively, according to an embodiment.

In the present description, since the speed of the train is high and the coverage of the RU is generally not large, each RU performs communication using the same radio resource at the same time as one TE. For example, if the millimeter wave (mmWave) frequency band is used to provide ultra-high data rates as a wireless backhaul link, the coverage of the RU is less than 1000 m, in which case the safety between two consecutive trains running on the same railway line is not guaranteed. The two trains do not fall within the coverage of the same RU because they are far enough apart for Referring to FIG. 3A , the second TE is _{connected to RU n} , and the first TE is connected to _{RU n +1 .} That is, even if both TEs are located between RUs, an antenna connected to each TE performs communication with one RU.

When trains intersecting on opposite tracks exist in the coverage of the same RU, different resources in terms of space, frequency, time, or code, etc. may be used (that is, grant freedom) to avoid multiple connections to the same RU.

For example, since each TE includes two antennas, a service can be provided to a plurality of trains through the degree of freedom of the antenna, and a prerequisite of this description that a service is provided to a TE using the same radio resource at the same time This can be guaranteed.

4 is a conceptual diagram illustrating a transmission delay between a base station and a terminal using LTE TDD frame configuration 2;

In the LTE system, in the TDD subframe, there is a special subframe between a downlink (DL) subframe and an uplink (UL) subframe, and the special subframe is a downlink pilot time slot (downlink pilot time slot). , DwPTS), a _{guard time of τ GT} , and an uplink pilot time slot (UpPTS). From the base station side, the frame structure is fixed. However, since there are multiple UEs that want to connect to the network through the UL, UL synchronization for all UEs is required so that all UL data of different UEs can reach the base station at the same time. In the ideal case, as shown in FIG. 4 , if the DL transmission delay is τ _d (t) for a specific UE, then the TA for the UL transmission of the specific UE is τ _d (t). Depending on the location of the UE, TA values for different UEs are also different. Therefore, in terms of the base station, the timing of the DL subframe and the UL subframe is fixed. However, since one TE is provided by an RU in a high-speed scenario, UL synchronization for a plurality of TEs is not required. That is, no estimation of TA is required, and all related transmission/reception and processing are not required.

5 is a conceptual diagram illustrating a hybrid TDD frame structure of a directional network according to an embodiment.

From the point of view of TE, the frame structure according to an embodiment has a fixed DL subframe duration and a fixed UL subframe duration. According to an embodiment, the guard time of the hybrid frame structure is located after the DL subframe and the UL subframe. In FIG. 5, (a) is a frame structure for when a TE is located in a cell interior, and (b) is a frame structure for when a TE is located at a cell edge. In both (a) and (b), the total duration of the special subframe + UL subframe is equal to the duration of 2 subframes as in the case of LTE. That is, from the point of view of TE, the TDD frame structure according to one embodiment is fixed for both DL and UL. However, since the LTE system is a centralized system, the UL reception timing of the HST base station in HST communication varies with time. That is, from the perspective of the HST base station, the TDD frame structure according to an embodiment has a fixed DL duration and a time-varying UL duration.

_{In (a) of FIG. 5 , the base station waits for τ GT} - 2τ _d (t) after receiving the uplink signal from the TE during the durations of the UpPTS and UL subframes. However, in (b), the base station transmits the downlink signal to the terminal through the DL subframe without waiting after receiving the uplink signal from the terminal because _{τ GT} - 2τ _{d (t) is 0.} That is, the guard time τ _GT is twice the maximum transmission delay τ _MAX (ie equal to the maximum round-trip transmission delay).

6 is a flowchart illustrating operations of a base station and a terminal using a hybrid TDD frame structure according to an embodiment.

Referring to FIG. 6 , the base station transmits a downlink signal during the DL subframe and DwPTS (S110), and the terminal receives the downlink signal during the DL subframe and DwPTS (S120). Unlike the LTE system, the base station does not transmit TA-related information when transmitting a downlink signal. The base station waits for 2τ _d (t) (ie, round trip transmission delay) after downlink transmission (S130). According to an embodiment, the base station may know the boundary of the UL subframe through several methods, and may know the transmission delay through the determined boundary of the UL subframe. For example, the base station may use SRS to find out the boundary of the UL subframe. Alternatively, the base station may know the boundary of the UL subframe by calculating auto-correlation of the cyclic prefix of the OFDM symbol transmitted in the uplink. Alternatively, the base station may know the boundary of the UL subframe using a special symbol or a short preamble sequence included in the PRACH according to an embodiment. In this case, the base station may determine the transmission delay before the downlink signal transmission step (S110) of the base station.

Thereafter, in the UpPTS immediately following DwPTS and the UL subframe following the UpPTS, the UE transmits an uplink signal (S140), and the base station receives the uplink signal (S150). Accordingly, the time point at which the base station performs uplink reception is a time point that has _{elapsed by 2τ d} (t) from the downlink transmission of the base station. Finally, the base station _{transmits the downlink signal after τ GT} - 2τ _d (t) from the uplink reception (S160), and the terminal can receive the downlink signal from the base station after _{τ GT has elapsed from the uplink transmission.} There is (S170).

Meanwhile, in a high-speed scenario, since the number of TEs connected to an RU is very small and a TA is not required, a physical random access channel (PRACH) of an LTE system optimized for a cellular network is not optimal. In the RA procedure of the LTE system, the preamble is transmitted in the PRACH, 1) notifies the base station that there is RA by the UE, and 2) the base station is used to estimate TA. Since TA estimation is not required in the high-speed scenario, the LTE preamble is used to indicate the RA to the base station in the high-speed scenario. Also, the Zadoff-Chu sequence of the LTE system, which is very sensitive to the frequency offset, is not suitable in the high-speed scenario with severe Doppler spread due to high-speed mobility. In addition, the LTE preamble is designed to be very long in the time domain to ensure sufficient energy for decoding, but in a high-speed scenario, a long duration for preamble transmission is also not required because the number of TEs simultaneously connected to the RU is very small. .

7 is a conceptual diagram illustrating PRACH signaling of a directional network according to an embodiment.

Because the radio channel changes rapidly in a high-speed scenario due to the high mobility of the train, a sounding reference signal (SRS) may be frequently transmitted in UpPTS. If the SRS is transmitted by the TE in all UpPTS, the SRS may be used by the HST base station to detect the boundary of the UL subframe. In the LTE standard, the preamble is defined in five different formats having different lengths and positions. Since UpPTS is occupied by SRS, format 4 among preamble formats of the LTE standard is not used in HST communication.

Referring to FIG. 7 , preamble format 0, which is one subframe long in the time domain, is used for comparison. According to an embodiment, instead of transmitting the Ginzadorf-Chu sequence as a preamble, the TE uses a special symbol for the RA. According to one embodiment, the special symbol includes connection request information for network connection, such as TE identification. The location of the special symbol transmitted from different TEs may be randomly selected during the PRACH duration to avoid collision of multiple RA requests. 7, the PRACH according to an embodiment includes n (n is a natural number) special symbol positions. Each TE may use at least one special symbol location to transmit network connection request information. And when the TE uses two or more special symbol positions, each special symbol position may be contiguous in the PRACH.

Referring to FIG. 7 , a second special symbol location is used by the TE for the initial RA for the HST communication network. When a plurality of TEs perform RA for a network, a special symbol position is randomly selected by the plurality of TEs. In addition, n, which is the number of special symbol positions included in the PRACH, the length of each special symbol position, and the number of special symbols that can be transmitted by one TE may be adaptively determined according to system parameters and environments.

As described above, since the base station and the TE do not perform UL synchronization in the high-speed scenario, the contention-based RA procedure of the LTE system can be further simplified to a contention-free RA procedure by using a new frame structure and PRACH structure.

8 is a block diagram illustrating a wireless communication system according to an embodiment.

Referring to FIG. 8 , a wireless communication system according to an embodiment includes a base station 810 and a TE 820 .

The base station 810 includes a processor 811 , a memory 812 , and a radio frequency unit (RF unit) 813 . The memory 812 may be connected to the processor 811 to store various information for driving the processor 811 or at least one program executed by the processor 811 . The wireless communication unit 813 may be connected to the processor 811 to transmit and receive wireless signals. The processor 811 may implement the functions, processes, or methods proposed in the embodiments of the present disclosure. In this case, in the wireless communication system according to an embodiment of the present disclosure, the air interface protocol layer may be implemented by the processor 811 . The operation of the base station 810 according to an embodiment may be implemented by the processor 811 .

The TE 820 includes a processor 821 , a memory 822 , and a wireless communication unit 823 . The memory 822 may be connected to the processor 821 to store various information for driving the processor 821 or at least one program executed by the processor 821 . The wireless communication unit 823 may be connected to the processor 821 to transmit and receive wireless signals. The processor 821 may implement the functions, steps, or methods proposed in the embodiments of the present disclosure. In this case, in the wireless communication system according to an embodiment of the present disclosure, the air interface protocol layer may be implemented by the processor 821 . The operation of the TE 820 according to an embodiment may be implemented by the processor 821 .

In the embodiment of the present disclosure, the memory may be located inside or outside the processor, and the memory may be connected to the processor through various known means. The memory is a volatile or non-volatile storage medium of various types. For example, the memory may include a read-only memory (ROM) or a random access memory (RAM).

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improved forms of the present invention are also provided by those skilled in the art using the basic concept of the present invention as defined in the following claims. is within the scope of the right.

Claims (19)

As a terminal of a mobile communication system moving at high speed,
a processor, a memory, and a wireless communication unit;
The processor executes the program stored in the memory,
Receiving a first downlink signal from a base station through the wireless communication unit during a duration of a downlink pilot time slot (DwPTS) of a special subframe;
Immediately after receiving the first downlink signal, without waiting time, an uplink signal is transmitted to the base station through the wireless communication unit during the duration of an uplink pilot time slot (UpPTS) of the special subframe step, and
After transmitting the uplink signal, waiting for a guard time (GT) before receiving a second downlink signal from the base station
A terminal that performs a. delete In claim 1,
The transmission of the first downlink signal from the base station is performed by the base station before the reception of the uplink signal by the base station by a round-trip transmission delay. In claim 1,
When the processor performs the step of transmitting the uplink signal,
Transmitting the uplink signal to the base station during the duration of the uplink subframe
Further performing, the terminal. In claim 4,
The sum of the duration of the DwPTS, the duration of the UpPTS, the duration of the uplink subframe, and the guard time is equal to the length of two subframes of the LTE system, the terminal. In claim 1,
After waiting for the guard time, the processor executes the program,
Receiving the second downlink signal from the base station during the duration of the downlink subframe
Further performing, the terminal. A method of transmitting and receiving a signal of a terminal of a mobile communication system moving at high speed, the method comprising:
Receiving a first downlink signal from a base station during a duration of a downlink pilot time slot (DwPTS) of a special subframe;
Immediately after receiving the first downlink signal, transmitting an uplink signal to the base station during the duration of an uplink pilot time slot (UpPTS) of the special subframe without waiting time, and
After transmitting the uplink signal, waiting for a guard time (GT) before receiving a second downlink signal from the base station
A signal transmission and reception method comprising a. delete In claim 7,
The transmission of the first downlink signal from the base station is performed by the base station before the reception of the uplink signal by the base station by a round-trip transmission delay. In claim 7,
Transmitting the uplink signal comprises:
Transmitting the uplink signal to the base station during the duration of the uplink subframe
Further comprising, a signal transmission and reception method. In claim 10,
The sum of the duration of the DwPTS, the duration of the UpPTS, the duration of the uplink subframe, and the guard time is equal to the length of two subframes of the LTE system. In claim 7,
After waiting for the guard time, receiving the second downlink signal from the base station for the duration of the downlink subframe
Further comprising, a signal transmission and reception method. As a base station of a mobile communication system moving at high speed,
a processor, a memory, and a wireless communication unit;
The processor executes the program stored in the memory,
estimating a transmission delay based on a special symbol included in a random access channel received from the terminal;
transmitting a downlink signal to the terminal through the wireless communication unit during a duration of a downlink pilot time slot (DwPTS) of a special subframe;
Waiting for a round-trip transmission delay determined based on the transmission delay before receiving an uplink signal from the terminal during an uplink pilot time slot (UpPTS) of the special subframe;
Receiving the uplink signal from the terminal through the wireless communication unit during the duration of the UpPTS of the special subframe and the duration of the uplink subframe, and
Waiting for a time equal to the maximum round-trip transmission delay minus the round-trip transmission delay
A base station that performs In claim 13,
The special symbol is located in at least one of n special symbol positions included in the random access channel. 15. In claim 14,
If the special symbol is located at two or more special symbol positions among the n special symbol positions, the two or more special symbol positions are consecutive in the random access channel. 15. In claim 14,
The number of special symbol positions, the length of the special symbol positions, and the number of special symbols that can be transmitted by the terminal are adaptively determined according to system parameters and environments. delete delete In claim 13,
The special symbol includes connection request information for network access, the base station.

Images