JP7553709B2 - Distributed antenna radio system and method for supporting wireless communication - Google Patents

Description

The present invention relates to a system that supports wireless communication between a base station and a terminal station.

In recent years, wireless access systems have become widespread and are indispensable for living a rich life. Looking back at the first to fourth generation of mobile phones, technology has mainly evolved to increase the speed of wireless communication. In the fifth generation, in addition to high speed, ultra-low latency and multiple simultaneous connections are required. In order to achieve these, a wide bandwidth is effective, and since the usage situation of frequencies is tight, the use of high frequency bands such as the millimeter wave band is effective from the fifth generation onwards. For example, the fifth generation uses the 28 MHz band, which is close to the millimeter wave band. As the frequency increases (i.e., the wavelength becomes shorter), the receiving area of one planar antenna becomes smaller, for example, so there is a problem that the propagation loss is larger compared to the microwave band. If the propagation loss increases, the coverage area per wireless device becomes smaller, which leads to an increase in costs.

To solve this problem, the fifth generation will adopt beamforming technology (BF). BF technology arranges multiple antennas (array) and controls the amplitude and phase of the transmission signal of each antenna element to obtain sharp antenna directivity. In addition, the antenna gain can compensate for radio wave propagation loss.

In the transmission BF, the phase of the transmission signals radiated from multiple antennas is controlled and spatially combined, so that in some places the phases of the radio waves radiated from each antenna are close to the same phase, reinforcing their power, and in other places the radio waves radiated from each antenna cancel each other out. As a result, in places where the power is reinforced, a combined gain can be obtained, compensating for radio wave propagation loss and enabling long-distance transmission. Alternatively, the desired signal power to noise power ratio at the receiver increases, making high-speed transmission possible by increasing the number of multi-levels of quadrature amplitude modulation.

With reference to FIG. 1, the directivity when an antenna beam is formed by BF will be described. Here, an example is taken of a planar antenna, which is widely used in the microwave and millimeter wave bands. FIG. 1(a) is an example of one subarray (or one element), and radio waves have the directivity of a planar antenna. FIG. 1(b) is an example of four subarrays, and compared to one subarray, the directivity of the radio waves is sharper and the composite power in the front direction is larger. FIG. 1(c) is an example of 16 subarrays, and the directivity of the radio waves is even sharper and the composite power in the front direction is also even larger. FIG. 1(d) shows a 16 subarray, but is an example of a case where the phase of the transmission signal of each antenna element is different from that of FIG. 1(c), and the directivity of the radio waves is controlled to face leftward rather than forward. By making the directivity of the radio waves sharp, it is possible to reduce interference with other wireless devices, and there is also the advantage of improving the efficiency of frequency utilization. The principles of BF technology and directivity control methods are well known in many documents, so a detailed explanation will be omitted.

When combining the received signals of each antenna, the receiving BF can be maximised in the direction of arrival of the desired wave or minimised in the direction of arrival of the interference wave. It is also known that reception performance can be improved by providing multiple antennas and implementing spatial diversity. Various research and practical applications are also being carried out on algorithms that automatically select and execute the optimal method from the above receiving techniques in response to changes in the propagation environment.

Prior art in the technical field related to the present invention includes the following. For example, Patent Document 1 discloses an invention in which, in a radio relay amplification system in which a radio relay amplifier (booster) amplifies a signal communicated by a radio base station device as it is relayed, the gain of the booster is remotely controlled from the radio base station device. Furthermore, Patent Document 2 discloses an invention for a wireless communication system that can obtain highly accurate terminal position information even inside a building, on the subway, etc.

JP 2005-303613 A JP 2012-160936 A

Up until the 4th generation, which used microwave bands, it was possible to use mobile phone services indoors because radio waves could penetrate into buildings such as buildings and homes. However, it is known that the higher the frequency, the more difficult it is for radio waves to penetrate. With the 5th generation, which uses high frequencies such as the millimeter wave band, radio wave penetration is blocked by buildings, making it difficult to use mobile phone services indoors. For this reason, measures must be taken to enable mobile phone services indoors, even with the 5th generation.

The method of introducing wireless equipment using optical fiber to blind areas where radio waves cannot reach requires huge installation costs, so there is a demand for other methods of indoor wireless coverage (hereinafter referred to as "indoor coverage"). Figure 2 shows an overview of indoor coverage according to a conventional example. The building 100 in Figure 2 is an apartment building, a department store, etc., and is intended for buildings whose walls do not transmit radio waves or whose walls have a large amount of attenuation of radio waves. Windows 101 are provided in the building 100 and generally transmit radio waves more easily than walls. An indoor coverage device 102 is attached to the window 101 to allow radio waves to reach the indoor area and cover the indoor area. As the indoor coverage device 102, for example, (1) a wireless repeater, (2) a transparent glass antenna or a film antenna that can be attached to glass, or (3) an FSS (Frequency Selective Surface) can be used.

In the downlink, the base station 103 uses BF technology to control the directivity of radio waves to transmit a radio signal toward the indoor area device 102 installed on the outside or inside of the window 101. The indoor area device 102 transmits the radio waves from the base station 103 or amplifies the power and outputs the radio waves indoors, allowing the radio waves to reach a mobile station inside the room.

In the uplink, an indoor mobile station transmits a radio signal toward a window 101 or an indoor area device 102. The indoor area device 102 transmits radio waves toward the outdoors, but the directivity of the radio waves in a straight line is not necessarily in the direction where the base station 103 is located. In addition, equipping the indoor area device 102 with BF technology that can control the directivity of radio waves would be unrealistic, as the device would become expensive. Furthermore, if the indoor area device 102 is not used, radio waves that pass through the window 101 and travel straight are not necessarily transmitted in the direction where the base station 103 is located, and their power is also weak.

The problems with the conventional methods described above will be explained in more detail. (1) When a wireless repeater is used Consider a case where a wireless repeater is used as the indoor coverage device 102. For example, in a hotel or an apartment building, the walls of adjacent rooms also attenuate radio waves, so a wireless repeater is required in each room. A wireless repeater is a radio device equipped with a transmitter and a receiver, and has a problem of high introduction costs. In addition, since a wireless repeater is generally installed in a window, visibility when looking at the outdoors through the window from inside the room may be an issue.

(2) Case where a transparent glass antenna or a film antenna is used Consider a case where a transparent glass antenna or a film antenna is used as the indoor area forming device 102. In this case, visibility is improved, but a transmitter and a receiver connected to the antenna are required for each room, which still leaves a problem of high introduction costs.

(3) When FSS is used Consider the case where FSS is used as the indoor area forming device 102. Regarding FSS, active research is being conducted on transmitting radio waves of a desired frequency (e.g., 28 GHz) and blocking/reflecting other radio waves. Research is also being conducted on increasing the transmittance of "glass" used in windows in order to strengthen radio waves to indoors. In this case, although there is some problem with visibility, a relatively small indoor area (room) can be formed into an area for the downlink. However, since the power of the uplink is smaller than that of the downlink and the power of the uplink restricts the propagation distance, it is necessary to provide a transmitter for each FSS (i.e., for each room).

Experiments and service operations have revealed that a common issue for 28 GHz band 5G is the need to improve uplink performance compared to downlink, regardless of whether it is outdoors or not. This is because the base station that transmits the downlink is equipped with a multi-element antenna using BF technology, while the mobile station that transmits the uplink has low transmission power and low performance in functions such as signal processing to improve signal quality. In addition, while base stations that communicate with multiple mobile stations have a high investment return, the mobile stations used by users are required to be small and low cost.

As described above, in the downlink of indoor area formation, the base station 103 can control the directivity toward the indoor area formation device 102 using BF technology. In contrast, in the uplink, if the indoor area formation device 102 is provided with a directivity control function such as BF technology, the indoor area formation device 102, which requires installation in large numbers, becomes expensive. On the other hand, if the indoor area formation device 102 is not provided with a directivity control function, it is not possible to transmit radio waves in a directional direction that maximizes the power toward the base station, resulting in a problem of a shortened propagation distance of the uplink.

The present invention has been made in consideration of the above-mentioned conventional circumstances, and aims to achieve an expansion of the wireless area and high output power of the uplink at low cost.

In order to achieve the above object, the present invention provides a distributed antenna wireless system as follows.
That is, the distributed antenna radio system supports wireless communication between a base station and a terminal station, and is characterized by comprising a plurality of first antennas arranged in a distributed manner, an aggregation device which receives wireless communication signals from each of the plurality of first antennas and combines signals among the first antennas which are determined to be uplink signals from the terminal station to the base station, and a second antenna different from the first antenna which transmits the signal combined by the aggregation device to the base station.

Here, the aggregation device may select and combine signals having a signal strength above a predetermined threshold.

The aggregation device may also be configured to determine whether the signal received by the first antenna is an uplink signal based on information indicating the link direction contained in the signal received by the first antenna.

The aggregation device may also be configured to determine whether a signal received at a first antenna is an uplink signal based on the number of antennas among a plurality of first antennas that receive the signal, and, when a signal is received at two or more antennas, the identity of the signals received at these antennas.

In addition, when the second antenna is capable of receiving a downlink signal from the base station to the terminal station, the aggregation device may determine whether the signal received at the first antenna is an uplink signal based on information indicating the link direction contained in the downlink signal received at the second antenna.

In addition, each of the multiple first antennas may be installed at or near a window of the building, and the second antenna may be installed outside the building.

The distributed antenna radio system of the present invention makes it possible to expand the radio area and increase the uplink power output at low cost.

1A and 1B are diagrams illustrating examples of planar antennas and beamforming directivity. FIG. 1 is a diagram showing an overview of indoor wireless coverage according to a conventional example. 1 is a first diagram showing an overview of a distributed antenna wireless system according to an embodiment of the present invention; FIG. 2 is a second diagram showing an overview of a distributed antenna wireless system according to an embodiment of the present invention. FIG. 2 is a functional block diagram of a distributed antenna wireless system according to a first configuration example. FIG. 11 is a functional block diagram of a distributed antenna wireless system according to a second configuration example. FIG. 11 is a functional block diagram of a distributed antenna wireless system according to a third configuration example.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
An overview of a distributed antenna wireless system according to an embodiment of the present invention is shown in Fig. 3 and Fig. 4. Fig. 3 is a view of a building 100 performing indoor coverage viewed from the outside. Fig. 4 is a view of a building 100 viewed from the inside of the building 100 viewed from the outside. In these figures, the same components as those in the conventional system are denoted by the same reference numerals.

First, the downlink signal transmitted from the outdoor base station 103 to the indoor terminal station 104 will be described. The downlink signal transmitted by the base station 103 reaches the inside of the building 100 through the window 101 of the building 100 or through the indoor area device 102 provided in the window 101. Depending on the radio wave propagation environment inside the building 100, the indoor area device 102 may be provided or may be omitted, and the essence is that the radio waves of the downlink signal reach the inside of the building. Indoors, the terminal station 104 receives the downlink signal. The terminal station 104 may be a mobile station including a smartphone or a fixed station including a wireless terminal attached to a TV.

Next, an uplink signal transmitted from an indoor terminal station 104 to an outdoor base station 103 will be described. The terminal station 104 transmits the uplink signal toward an antenna 201 provided in a window 101. The reason for providing the antenna 201 in the window 101 is that the window 101 is in the same direction as the direction in which the radio waves of the downlink signal are received, so that the directional control of the radio waves transmitted by the terminal station 104 functions optimally, but this is not limited to this. For example, the antenna 201 may be provided near the window 101. Preferred examples of the antenna 201 include a transparent glass antenna or a film antenna that are highly visible.

The antenna 201 receives an uplink signal addressed to the base station 103. The received signal (uplink signal) by the antenna 201 is input to the receiving unit 203 through the cable 202. The receiving unit 203 converts the input received signal from an electrical signal to an optical signal and transmits it to the aggregation device 205 through the optical fiber (optical cable) 204. The antenna 201 and the receiving unit 203 are provided for each window 101 of the room to be covered by the wireless area of the building 100. When there are multiple rooms to be covered by the wireless area, as shown in FIG. 3, multiple sets of antennas 201 and receiving units 203 are provided for one building 100. The aggregation device 205 aggregates the received signals from the antennas 201 and receiving units 203 of each window 101. The aggregation device 205 converts the input received signal from an optical signal to an electrical signal and transmits it from the high gain antenna 206 to the base station 103.

Hereinafter, the transmission operation of the uplink signal will be specifically described using a first configuration example to a third configuration example.
<First Configuration Example>
5 shows a functional block diagram of a distributed antenna radio system according to a first configuration example. As a preferred embodiment, the receiving unit 203 includes an LNA (Low Noise Amplifier) 211 and an E/O (Electric to Optical) conversion unit 212. The LNA 211 amplifies a signal received by the antenna 201. The received signal amplified by the LNA 211 is converted from an electrical signal to an optical signal by the E/O conversion unit 212 and transmitted to the aggregation device 205 through the optical fiber 204. The receiving unit 203 may include a frequency filter or the like as a common method known to those skilled in the art, but this is omitted in this example.

In a preferred embodiment, the aggregation device 205 includes a signal selection and synthesis unit 213 and an O/E (Optic to Electric) conversion unit 214. The received signal transmitted from the receiving unit 203 through the optical fiber 204 is input to the signal selection and synthesis unit 213. In this example, to group multiple rooms into an indoor area, the received signals from multiple receiving units 203 are input to the signal selection and synthesis unit 213. The signal selection and synthesis unit 213 selects a signal that is determined to be an uplink signal from the multiple input received signals, and outputs the synthesized signal to the O/E conversion unit 214. The O/E conversion unit 214 converts the synthesized signal by the signal selection and synthesis unit 213 from an optical signal to an electrical signal and outputs it.

The combined signal output from the aggregation device 205 has its transmission power amplified by the power amplifier 215 as necessary, and is transmitted from the high-gain antenna 206 to the base station 103. The power amplifier 215 may be an element included in the aggregation device 205, or may be an element included in the high-gain antenna 206. The high-gain antenna 206 transmits the combined signal (uplink signal) from the aggregation device 205 to the base station 103 by controlling the directivity of the radio waves using BF technology.

Here, in the signal selection and synthesis unit 213 of this example, the received signals from each receiving unit 203 are compared with a predetermined signal strength threshold, and received signals having a signal strength equal to or greater than the threshold are selected and synthesized. This allows signals having a signal strength less than the threshold to be judged as noise and to be excluded before synthesizing the received signals, thereby suppressing deterioration of signal quality. Note that it is also possible to adopt a method of synthesizing all received signals from each receiving unit 203 by eliminating the signal selection function in order to emphasize the simplicity of the device.

<Second Configuration Example>
Here, the control of the uplink and downlink will be described. The distributed antenna wireless system of this example transmits a signal from the high gain antenna 206 at the timing of the uplink, but must not transmit a signal at the timing of the downlink. Therefore, it is necessary to know the timing of the uplink and downlink.

Figure 6 shows a functional block diagram of a distributed antenna wireless system according to a second configuration example. The antenna 201 installed at or near the window 101 receives not only uplink signals but also downlink signals. Therefore, the aggregation device 205 of this example is equipped with an uplink/downlink discrimination unit 216 for discriminating between uplink and downlink as one of the components of the signal selection/combination unit 213. When the aggregation device 205 determines that the signal is an uplink by the uplink/downlink discrimination unit 216, the aggregation device 205 outputs a composite signal from the signal selection/combination unit 213 and supplies it to the high gain antenna 206. On the other hand, when the aggregation device 205 determines that the signal is a downlink by the uplink/downlink discrimination unit 216, the aggregation device 205 does not output a composite signal from the signal selection/combination unit 213.

One example of a method for determining whether a signal is an uplink or downlink is to demodulate a signal received by antenna 201 and determine whether the received signal is an uplink signal based on information indicating the link direction contained in the demodulated signal.
Another example is a method of controlling the device as an IAB (Integrated Access and Backhaul) device.

As another example, in the downlink, since a large number of antennas 201 can receive downlink signals, the same received signal is input to the aggregation device 205 from multiple receivers 203, whereas in the uplink, the received signal is often input to the aggregation device 205 from one or a small number of receivers 203. That is, whether or not the received signal is an uplink signal is determined based on the number of antennas that receive the signal among the multiple antennas 201, and the identity of the signals received by two or more antennas 201 when the signal is received by these antennas 201. For example, when a signal is received by only one antenna 201, it is determined to be an uplink signal. For example, when a signal is received by two or more antennas 201, if the received signals have the same content, it is determined to be a downlink signal, and if not, it is determined to be an uplink signal.

<Third Configuration Example>
7 shows a functional block diagram of a distributed antenna radio system according to a third configuration example. In the third configuration example, an antenna capable of not only transmitting uplink signals but also receiving downlink signals is used as the high-gain antenna 206. The aggregation device 205 includes a power amplifier 215 in addition to a signal selection/combination unit 213 and an O/E conversion unit 214, a TDD switch 217 for switching between transmitting and receiving operations of the high-gain antenna 206, and an uplink/downlink switching control unit 218 for controlling the TDD switch 217 according to the timing of the uplink and downlink.

The downlink signal received by the high gain antenna 206 is input to the uplink/downlink switching control unit 218 via the TDD switch 217. The uplink/downlink switching control unit 218 determines whether the signal received by the antenna 201 is an uplink signal or not based on information indicating the link direction contained in this downlink signal. If the uplink/downlink switching control unit 218 determines that the signal received by the antenna 201 is an uplink signal, it transmits an instruction to the signal selection/combination unit 213 to combine and output the signal received by the antenna 201.

In addition, the uplink/downlink switching control unit 218 identifies the timing of each of the uplink signal and the downlink signal, and controls the switching of the TDD switch 217. That is, at the timing of the downlink signal, the TDD switch 217 is controlled to the receiving side so that the signal received by the high gain antenna 206 is supplied to the uplink/downlink switching control unit 218. On the other hand, at the timing of the uplink signal, the TDD switch 217 is controlled to the transmitting side so that the combined signal by the signal selection and combination unit 213 is supplied to the high gain antenna 206 via the O/E conversion unit 214 and the power amplification unit 215.

As described above, the distributed antenna radio system of this example comprises a plurality of antennas 201 arranged in a distributed manner to support wireless communication (particularly, uplink) between the base station 103 and the terminal station 104, an aggregation device 205 which receives wireless communication signals from each of the plurality of antennas 201 via a receiving unit 203 and combines signals that are determined to be uplink signals from the terminal station 104 to the base station 103, and a high-gain antenna 206, different from the antennas 201, which transmits the signal combined by the aggregation device 205 to the base station 103.

According to this configuration, an uplink signal transmitted from an indoor terminal station 104 to an outdoor base station 103 is received by an antenna 201 in a window of the room, aggregated in an aggregation device 205, and then transmitted from a high-gain antenna 206 to the base station 103. This makes it possible to efficiently transmit the uplink signal transmitted from the indoor terminal station 104 to the outdoor base station 103.

Therefore, the propagation distance between the base station and the building to be converted into an indoor area can be expanded, and one base station can convert many buildings into indoor areas. In particular, in a building environment where many indoor area conversion devices are required, the introduction cost can be reduced, and indoor area conversion is promoted. In addition, only a receiver needs to be connected to the antenna of each window, and a device equipped with a transmitter and a receiver (so-called radio) is not required. In addition, in order to aggregate the uplink signals received by the window antenna of each room, only one power amplifier and one high-gain antenna are required, and introduction costs and power consumption can be reduced. In this way, according to the distributed antenna wireless system of this example, it is possible to realize the expansion of the wireless area and the high output of the uplink at low cost.

The present invention has been described above based on one embodiment, but it goes without saying that the present invention is not limited to the configuration described here and can be widely applied to systems with other configurations.
Furthermore, the present invention can also be provided as, for example, a method including technical procedures related to the above-mentioned processing, a program for causing a processor to execute the above-mentioned processing, or a storage medium for storing such a program in a computer-readable manner.

The scope of the present invention is not limited to the exemplary embodiments shown and described, but includes all embodiments that have equivalent effects to those intended by the present invention. Furthermore, the scope of the present invention can be defined by any desired combination of specific features among all the respective features disclosed.

This application claims the benefit of priority to Japanese Patent Application No. 2021-090135, filed on May 28, 2021, the entire disclosure of which is incorporated herein by reference.

The present invention can be used in a system that supports wireless communication between a base station and a terminal station.

100: Building, 101: Window, 102: Indoor area device, 103: Base station, 104: Terminal station, 201: Antenna, 202: Cable, 203: Receiver, 204: Optical fiber, 205: Aggregator, 206: High gain antenna, 211: LNA, 212: E/O converter, 213: Signal selection and synthesis unit, 214: O/E converter, 215: Power amplifier, 216: Uplink/downlink discrimination unit, 217: TDD switch, 218: Uplink/downlink switching control unit

Claims (4)

A distributed antenna wireless system supporting wireless communication between a base station and a terminal station, comprising:
A plurality of first antennas each arranged in a distributed manner;
an aggregation device that receives wireless communication signals received from each of the plurality of first antennas and combines signals that are determined to be uplink signals from the terminal station to the base station;
a second antenna different from the first antenna, the second antenna transmitting the signal combined by the aggregation device to the base station ;
A distributed antenna radio system characterized in that the aggregation device determines whether the signal received at the first antenna is an uplink signal based on the number of antennas among the multiple first antennas that received the signal, and based on the identity of the signals received at two or more antennas when the signal is received at these antennas . 2. The distributed antenna wireless system according to claim 1,
The aggregation device selects and combines signals having a signal strength equal to or greater than a predetermined threshold. 3. The distributed antenna radio system according to claim 1,
Each of the plurality of first antennas is installed at or near a window of a building;
The second antenna is installed outdoors of the building. A method for supporting wireless communication between a base station and a terminal station, comprising:
Each of the plurality of first antennas, which are disposed in a distributed manner, outputs a received wireless communication signal to the aggregation device;
the aggregation device determines whether the signal received at the first antenna is an uplink signal from the terminal station to the base station based on the number of antennas that received a signal among the plurality of first antennas and, when signals are received at two or more antennas, the identity of the signals received at these antennas, and combines the signals that are determined to be uplink signals from the terminal station to the base station among the signals input from each of the plurality of first antennas;
A wireless communication support method, comprising: a second antenna different from the first antenna transmitting a signal synthesized by the aggregation device to the base station.

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