JP6046566B2 - Communication system, base station, and communication method - Google Patents

Description

  The present invention relates to a communication system, a base station, and a communication method including base stations that employ different communication methods.

  In a frequency band in which wireless communication is performed using a certain communication method (for example, PHS (Non-Patent Document 1)), wireless communication using a communication method other than the communication method (for example, the TD-LTE method (Non-Patent Document 2)) is performed. Is being considered to do. The PHS is assigned a frequency band of 1884.5 MHz to 1893.5 MHz and a bandwidth of 9 MHz (hereinafter referred to as 9 MHz band). For example, in the 9 MHz band, it is conceivable to perform wireless communication by the PHS method and the TD-LTE method.

The Japan Radio Industry Association, “2nd Generation Cordless Telephone System Standard RCR STD-28 Version 6.0”, March 28, 2011 3GPP TS 36.211 Ver. 9.0.0 “LTE; Evolved Universal Terrestrial Radio Access (U-UTRA); Physical channels and modulation”

  In this way, in a frequency band in which wireless communication is performed using a certain communication method, when performing wireless communication using a communication method other than the communication method and coexisting, communication devices (base stations) that employ each communication method , Mobile stations) are desired not to interfere with each other.

  An object of the present invention made in view of the above-described problems is that in the case of performing wireless communication by a communication method other than the communication method in a frequency band in which wireless communication is performed by a certain communication method, An object of the present invention is to provide a communication system, a base station, and a communication method that can reduce interference between communication apparatuses that employ a communication method.

In order to solve the above problems, a communication system according to the present invention provides:
A first base station that employs a TDD communication system, and a second base that employs a TDD communication system in which the radio frame and the arrangement configuration of uplink radio resources and downlink radio resources in the radio frame are different from those of the first base station. A communication system comprising a station,
The first base station adjusts the timing of the carrier sense for each downlink radio resource included in a radio frame when performing carrier sense for the second base station.

Moreover, the communication system according to the present invention includes:
The first base station uses a threshold value different from a threshold value used in carrier sense for another first base station that adopts the same communication method as that of the first base station in the determination in the carrier sense.

Moreover, the communication system according to the present invention includes:
The first base station employs a PHS scheme, and the second base station employs a TD-LTE scheme.

Further, the base station according to the present invention is:
A base station that employs a TDD communication scheme; and a second base station that employs a TDD communication scheme in which a radio frame and an arrangement configuration of uplink radio resources and downlink radio resources in the radio frame are different from those of the base station. A base station in a communication system,
When performing carrier sense for the second base station, the carrier sense timing is adjusted for each downlink radio resource included in the radio frame.

Further, the base station according to the present invention is:
In the determination in the carrier sense, a threshold value different from the threshold value used in carrier sense for another base station that employs the same communication method as that of the own station is used.

Further, the base station according to the present invention is:
The base station employs a PHS scheme, and the second base station employs a TD-LTE scheme.

Further, the communication method according to the present invention includes:
A first base station that employs a TDD communication system, and a second base that employs a TDD communication system in which the radio frame and the arrangement configuration of uplink radio resources and downlink radio resources in the radio frame are different from those of the first base station. A communication method in a communication system comprising a station,
When the first base station performs carrier sense for the second base station, the carrier sense timing is adjusted for each downlink radio resource included in the radio frame.

Further, the communication method according to the present invention includes:
The first base station uses a threshold value different from a threshold value used in carrier sense for another first base station that adopts the same communication method as that of the first base station in the determination in the carrier sense.

Further, the communication method according to the present invention includes:
The first base station employs a PHS scheme, and the second base station employs a TD-LTE scheme.

  According to the communication system, the base station, and the communication method of the present invention, when performing wireless communication using a communication method other than the communication method in a frequency band in which wireless communication is performed using a certain communication method, Interference between communication apparatuses adopting the method can be reduced.

1 is a schematic diagram of a communication system according to an embodiment of the present invention. It is a block diagram of the base station which concerns on one Embodiment of this invention. It is a block diagram of the mobile station which concerns on one Embodiment of this invention. It is a figure which shows the outline | summary of the timing of the carrier sense in a PHS system. It is a figure which shows the resource block and cell specific reference signal in a TD-LTE system. It is a figure which shows the kind of frame structure of a TD-LTE system. It is a figure which shows the outline | summary of each radio | wireless frame of each base station. It is a sequence diagram which shows operation | movement of the communication system which concerns on one Embodiment of this invention. It is a figure which shows the kind of special sub-frame structure of a TD-LTE system. It is a figure which shows the outline | summary of each radio | wireless frame of each base station.

  Embodiments of the present invention will be described below.

(Embodiment)
FIG. 1 is a schematic diagram of a communication system 1 according to an embodiment of the present invention. A communication system 1 according to an embodiment of the present invention includes a plurality of communication devices. For example, as shown in FIG. 1, the communication system 1 includes a communication device 10a (first base station 10a) and a communication device 10b (second base station 10b), and each includes a communication device 11a (first mobile station 11a) and communication. A device 11b (second mobile station 11b) is connected. Although FIG. 1 shows an example in which two base stations and two mobile stations are provided, the present invention is not limited to this, and there may be two or more base stations and mobile stations. In the present embodiment, the communication system 1 will be described as performing wireless communication in the 9 MHz band.

  2A and 2B are block diagrams of the first base station 10a and the second base station 10b, respectively, according to an embodiment of the present invention. As shown in FIG. 2A, the first base station 10a includes a base station communication unit 101a, a base station baseband unit 102a, and a base station control unit 103a. The base station communication unit 101a and the base station baseband unit 102a are connected to the base station control unit 103a.

  The first base station 10a shown in FIG. 2 (a) employs a TDD (Time Division Duplex) communication method and communicates with the first mobile station 11a. Preferably, the communication method is a PHS method. Hereinafter, the 1st base station 10a demonstrates as what communicates by a PHS system. The PHS method uses a radio frame having a time length of 5 ms. The radio frame has an arrangement configuration including four continuous downlink radio resources (slots) and four continuous uplink radio resources (slots). Each downlink radio resource and each uplink radio resource has a time length of 625 μs.

  The base station communication unit 101a of the first base station 10a transmits and receives radio signals (data) to and from the first mobile station 11a via an antenna. The base station communication unit 101a performs amplification and down-conversion with low noise on the received radio signal (reception signal), and sends the processed signal to the base station baseband unit 102a. Further, the base station communication unit 101a performs up-conversion and amplification on the baseband signal received from the base station baseband unit 102a, and generates a radio signal (transmission signal). Then, the base station communication unit 101a transmits the radio signal to the first mobile station 11a via the antenna.

  The base station baseband unit 102a demodulates the received signal by performing AD conversion or the like on the signal received from the base station communication unit 101a, and extracts the baseband signal. Then, the base station baseband unit 102a sends a baseband signal to the base station control unit 103a. The base station baseband unit 102a modulates the baseband signal by performing DA conversion or the like on the baseband signal generated by the base station control unit 103a. Then, the modulated baseband signal is sent to the base station communication unit 101a.

  The base station control unit 103a controls and manages the entire first base station 10a including each functional block of the first base station 10a. The base station control unit 103a is configured as software executed on any suitable processor such as a CPU (central processing unit), or by a dedicated processor (for example, DSP (digital signal processor)) specialized for each process. It can also be configured.

  The second base station 10b shown in FIG. 2B employs a TDD communication method in which the radio frame and the arrangement configuration of the uplink radio resources and the downlink radio resources in the radio frame are different from those of the first base station 10a. Preferably, the communication method is a TD-LTE method. Hereinafter, the second base station 10b will be described as adopting the TD-LTE scheme. The TD-LTE scheme uses a radio frame with a time length of 10 ms. The radio frame is composed of 10 subframes, and each subframe is assigned as a downlink radio resource or an uplink radio resource. A plurality of allocation patterns for each subframe are determined by the standard (Non-patent Document 2).

  The base station communication unit 101b of the second base station 10b transmits and receives radio signals (data) to and from the second mobile station 11b via an antenna. The base station communication unit 101b performs amplification and down-conversion with low noise on the received radio signal (reception signal), and sends the processed signal to the base station baseband unit 102b. Further, the base station communication unit 101b performs up-conversion and amplification on the baseband signal received from the base station baseband unit 102b to generate a radio signal (transmission signal). Then, the base station communication unit 101b transmits the radio signal to the second mobile station 11b via the antenna.

  The base station baseband unit 102b demodulates the received signal by performing AD conversion, fast Fourier transform, and the like on the signal received from the base station communication unit 101b, and extracts the baseband signal. Then, the base station baseband unit 102b sends a baseband signal to the base station control unit 103b. The base station baseband unit 102b modulates the baseband signal by performing inverse fast Fourier transform, DA conversion, and the like on the baseband signal generated by the base station control unit 103b. Then, the modulated baseband signal is sent to the base station communication unit 101b.

  The base station control unit 103b controls and manages the entire second base station 10b including each functional block of the second base station 10b. The base station control unit 103b is configured as software executed on any suitable processor such as a CPU (central processing unit), or by a dedicated processor (for example, DSP (digital signal processor)) specialized for each process. It can also be configured.

  FIGS. 3A and 3B are block diagrams of the first mobile station 11a and the second mobile station 11b, respectively, according to an embodiment of the present invention. As shown in FIG. 3A, the first mobile station 11a includes a mobile station communication unit 111a, a mobile station baseband unit 112a, and a mobile station control unit 113a. The mobile station communication unit 111a and the mobile station baseband unit 112a are connected to the mobile station control unit 113a.

  The mobile station communication unit 111a transmits and receives radio signals (data) to and from the first base station 10a via an antenna. The mobile station communication unit 111a performs amplification and down-conversion with low noise on the received radio signal (reception signal), and sends the processed signal to the mobile station baseband unit 112a. In addition, the mobile station communication unit 111a performs up-conversion and amplification on the baseband signal received from the mobile station baseband unit 112a to generate a radio signal (transmission signal). Then, the mobile station communication unit 111a transmits the radio signal to the first base station 10a via the antenna.

  The mobile station baseband unit 112a demodulates the received signal by performing AD conversion or the like on the signal received from the mobile station communication unit 111a, and extracts the baseband signal. Then, the mobile station baseband unit 112a sends a baseband signal to the mobile station control unit 113a. The mobile station baseband unit 112a modulates the baseband signal by performing DA conversion or the like on the baseband signal generated by the mobile station control unit 113a. The modulated baseband signal is sent to the mobile station communication unit 111a.

  The mobile station control unit 113a controls and manages the entire first mobile station 11a including each functional block of the first mobile station 11a. The mobile station control unit 113a is configured as software executed on an arbitrary suitable processor such as a CPU (Central Processing Unit), or by a dedicated processor (for example, DSP (Digital Signal Processor)) specialized for each process. It can also be configured.

  The mobile station communication unit 111b transmits and receives radio signals (data) to and from the second base station 10b via the antenna. The mobile station communication unit 111b performs amplification and down-conversion with low noise on the received radio signal (reception signal), and sends the processed signal to the mobile station baseband unit 112b. In addition, the mobile station communication unit 111b performs up-conversion and amplification on the baseband signal received from the mobile station baseband unit 112b to generate a radio signal (transmission signal). The mobile station communication unit 111b transmits the radio signal to the second base station 10b via the antenna.

  The mobile station baseband unit 112b demodulates the received signal by performing AD conversion, fast Fourier transform, and the like on the signal received from the mobile station communication unit 111b, and extracts the baseband signal. Then, the mobile station baseband unit 112b sends a baseband signal to the mobile station control unit 113b. The mobile station baseband unit 112b modulates the baseband signal by performing inverse fast Fourier transform, DA conversion, and the like on the baseband signal generated by the mobile station control unit 113b. Then, the modulated baseband signal is sent to the mobile station communication unit 111b.

  The mobile station control unit 113b controls and manages the entire second mobile station 11b including each functional block of the second mobile station 11b. The mobile station control unit 113b is configured as software executed on any suitable processor such as a CPU (Central Processing Unit), or by a dedicated processor (for example, DSP (Digital Signal Processor)) specialized for each process. It can also be configured.

  Here, the first base station 10a adopting the PHS system performs carrier sense before starting communication under the control of the base station control unit 103a. The carrier sense can be used by measuring the received power in the scheduled use slot in order to avoid communication interference with other radio apparatuses in the downlink radio resource (scheduled use slot) scheduled to be used by the first base station 10a. It is to determine whether. Carrier sense is performed for each scheduled slot and for each frequency channel.

  FIG. 4 is a diagram illustrating an outline of a U-wave detection position (carrier sense timing) of general carrier sense. Specifically, the carrier sense is performed by the first base station 10a measuring the received power at the three parts of the front edge, the center, and the rear edge shown in FIG. Then, the base station control unit 103a of the first base station 10a compares the maximum value of the received power measured at these three portions with the carrier sense determination threshold value. The carrier sense determination threshold is, for example, 26 dBμV. That is, the base station control unit 103a determines that the use-scheduled slot can be used when the carrier sense is less than 26 dBμV in all of the front edge, the center, and the rear edge. On the other hand, if the base station control unit 103a is 26 dBμV or more in at least one of the front edge part, the center part, and the rear edge part due to carrier sense, the slot to be used is already used, and is not used. Determine that it is possible.

  Preferably, when all channels exceed 26 dBμV, the carrier sense determination threshold is set to 40 dBμV. The leading edge is a period including the ramp-up of the slot to be used. The central portion is a period from the ramp-up to the ramp-down of the scheduled use slot. The trailing edge is a period including a ramp-down of a slot to be used.

On the other hand, the 2nd base station 10b communicates by a TD-LTE system. FIG. 5 shows a schematic diagram of downlink radio resources related to the second base station 10b. In the TD-LTE scheme, downlink radio resources are managed in resource block units. FIG. 5 shows two resource blocks continuous in the time direction, and is composed of 14 OFDM symbols and 12 subcarriers, that is, 168 resource elements (14 OFDM symbols × 12 subcarriers). Here, the second base station 10b periodically transmits only the cell-specific reference signal (R ₀ ) shown in FIG. 5 among the 168 resource elements. As shown in FIG. 5, the time for transmitting the cell-specific reference signal is limited to the 1st, 5th, 8th, and 12th symbols. Therefore, when the carrier sense measurement position of the first base station 10a is performed in a period in which the cell-specific reference signal is not transmitted (period other than the first, fifth, eighth, and twelfth symbols), the first base station 10a The second base station 10b may not be able to determine that the radio resource is being used. For this reason, there is a possibility that the first base station 10a performs communication using the radio resource, and communication interference occurs.

  Therefore, according to the present invention, when the first base station 10a performs carrier sense for the second base station 10b, the carrier sense timing is set in accordance with the cell-specific reference signal transmission period of the second base station 10b. By adjusting, the interference of the communication is prevented. This will be described in detail below.

  In the present invention, in order to adjust the carrier sense timing of the first base station 10a, the TD-LTE radio frame configuration (subframe allocation pattern) employed by the second base station 10b is appropriately selected. FIG. 6 is a list listing radio frame configurations defined by the TD-LTE standard (Non-Patent Document 2). In FIG. 6, “D”, “U”, and “S” mean a downlink subframe (downlink radio resource), an uplink subframe (uplink radio resource), and a special subframe, respectively. The switching point period indicates a period of switching from the downlink subframe to the uplink subframe. The configuration number “No. 1” matches the PHS radio frame length because the ratio of the downlink radio resource to the uplink radio resource is 1: 1 and the switching point cycle is 5 ms. Therefore, this configuration is optimal for the first base station 10a to perform carrier sense for the second base station 10b. Therefore, in the present invention, the configuration number “1” is selected.

  Further, the first base station 10a and the second base station 10b are set so that the head of the subframe number 4 or 9 in the configuration number “1” matches the head of the downlink frame of the first base station 10a. Synchronize. Specifically, the base station control unit 103b of the second base station 10b performs the first base station 10a so that the head of the subframe number 4 or 9 matches the head of the downlink frame of the first base station 10a. And synchronize the radio frame.

  FIG. 7 shows the case where the radio frame configuration at the second base station 10b is No. 1 and the top of the subframe number 4 or 9 matches the top of the downlink frame of the first base station 10a. A schematic diagram of each radio frame is shown. As shown in FIG. 7, the downlink radio resource transmission periods (first 2.5 ms) of the first base station 10a and the second base station 10b are the same. Here, as shown in FIG. 7, the length (slot length) of each downlink radio resource of the first base station 10a and the second base station 10b is different from 625 μs and 1 ms, respectively. Therefore, the first base station 10a adjusts the carrier sense timing to be different for each downlink radio resource (slot) so as to match the timing at which the cell-specific reference signal of the second base station 10b is transmitted. That is, the first base station 10a adjusts the carrier sense timing for each downlink radio resource included in the radio frame when performing carrier sense for the second base station 10b.

  Specifically, for example, the carrier sense for the second base station 10b during the period in which the downlink radio resource 801a is transmitted is the period during which the cell-specific reference signal is transmitted in the downlink radio resource 801b (for example, 1, Match the period of 5th symbol). The carrier sense in the period during which the downlink radio resource 802a is being transmitted is the period during which the cell-specific reference signal is transmitted (for example, the 12th symbol of the radio resource 801b or the radio resource 802b). Match the period of the first symbol). By doing in this way, the 1st base station 10a can judge appropriately whether the 2nd base station 10b is communicating.

  Next, the operation related to the carrier sense of the communication system 1 according to the present invention will be described with reference to the sequence diagram shown in FIG. First, the base station control unit 103b of the second base station 10b establishes a radio frame with the first base station 10a so that the head of the subframe number 4 or 9 matches the head of the downlink frame of the first base station 10a. Are synchronized (step S1).

  Subsequently, the base station control unit 103a of the first base station 10a adjusts the carrier sense timing for each downlink radio resource included in the radio frame in performing carrier sense for the second base station 10b. Carrier sense is performed (step S2).

  As described above, according to the present invention, in the frequency band in which wireless communication is performed using a communication method such as PHS, when performing wireless communication using another communication method such as TD-LTE other than the communication method, carrier sense is performed. By adjusting the timing, it is possible to reduce interference between communication devices that employ each communication method.

  Carrier sensing is performed in units of 300 kHz in the frequency direction. Here, since one resource block, which is a resource allocation unit of the second base station 10b, is 180 kHz, the 300 kHz always includes one resource block. Therefore, it is not necessary to adjust the carrier sense in the frequency direction.

  Note that the cell-specific reference signal transmitted by the second base station 10b occupies only 2 resource elements (2 subcarriers) out of 12 resource elements (12 subcarriers) of each OFDM symbol as shown in FIG. That is, only 1/6 of downlink radio resources at a certain time is used for communication. Therefore, preferably, for carrier sense targeted for the second base station 10b, a threshold used for carrier sense targeted for another first base station that employs the same communication method as the own station (hereinafter referred to as a normal threshold). )) And a different threshold (hereinafter referred to as a special threshold). Preferably, in carrier sense targeting the second base station 10b, a threshold value (special threshold value) for carrier sense determination is set low. Specifically, for example, the special threshold value is determined by the following formula 1.

(Equation 1)
(Special threshold value) = (Normal threshold value) + log ₁₀ (1/6) Expression (1)

  In this way, by setting the carrier sense determination threshold for the second base station 10b to be lower than the normal threshold, the first base station 10a can more reliably determine whether the second base station 10b is using radio resources. Can be determined.

If signals are transmitted and received by another communication device when switching from downlink radio resources to uplink radio resources, there is a possibility that interference will occur in communication. Therefore, the second base station 10b preferably prevents the interference by adjusting the configuration of the special subframe. FIG. 9 is a diagram illustrating a configuration of a special subframe defined by the TD-LTE standard (Non-Patent Document 2). The special subframe includes a downstream part (DwPTS), an upstream part (UpPTS), and a guard period (GP). Here, no signal is transmitted or received in the guard period. As shown in FIG. 9, the periods of the downlink part and the uplink part differ depending on the configuration of the special subframe. Note in Figure 9, _{T S} represents a basic time unit (Basic Time Unit), 307200T _S corresponds to 10 ms. Here, in the configuration of the configuration number “5”, when the normal cyclic prefix is used, the lengths of the downstream part and the upstream part are 6592 T _s (for 3 OFDM symbols) and 4384 T _s (for 2 OFDM symbols), respectively. The GP becomes the remaining 19744T _s (9 OFDM symbols).

  FIG. 10 shows a schematic diagram of each radio frame when the configuration of the special subframe is the configuration number “5”. As shown in FIG. 10, the timing of switching from the downlink radio resource to the uplink radio resource of the first base station 10a is included in the guard period of the special subframe of the second base station 10b. Therefore, preferably, the second base station 10b selects the configuration number “5” of the special subframe. Thus, by matching the guard period of the second base station 10b with the timing of switching from the downlink radio resource to the uplink radio resource of the first base station 10a, the first base station 10a and the second base station 10b Communication interference can be reduced.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, the functions included in each means, each step, etc. can be rearranged so that there is no logical contradiction, and a plurality of means, steps, etc. can be combined or divided into one. .

DESCRIPTION OF SYMBOLS 1 Communication system 10a 1st base station 10b 2nd base station 11a 1st mobile station 11b 2nd mobile station 101a, 101b Base station communication part 102a, 102b Base station baseband part 103a, 103b Base station control part 111a, 111b Mobile station Communication unit 112a, 112b Mobile station baseband unit 113a, 113b Mobile station control unit 801a, 802a, 801b, 802b Radio resource

Claims (9)

A first base station that employs a TDD communication system, and a second base that employs a TDD communication system in which the radio frame and the arrangement configuration of uplink radio resources and downlink radio resources in the radio frame are different from those of the first base station. A communication system comprising a station,
The first base station adjusts the carrier sense timing for each downlink radio resource included in a radio frame when performing carrier sense for the second base station.   The first base station uses a threshold value different from a threshold value used in carrier sense intended for another first base station that adopts the same communication method as the own station in the determination in the carrier sense. The communication system according to claim 1.   The communication system according to claim 1 or 2, wherein the first base station employs a PHS scheme, and the second base station employs a TD-LTE scheme. A base station that employs a TDD communication scheme; and a second base station that employs a TDD communication scheme in which a radio frame and an arrangement configuration of uplink radio resources and downlink radio resources in the radio frame are different from those of the base station. A base station in a communication system,
A base station that adjusts carrier sense timing for each downlink radio resource included in a radio frame when performing carrier sense for the second base station.   The base station according to claim 4, wherein a threshold value different from a threshold value used in carrier sense for another base station adopting the same communication method as that of the own station is used in the determination in the carrier sense.   The base station according to claim 4 or 5, wherein the base station employs a PHS scheme, and the second base station employs a TD-LTE scheme. A first base station that employs a TDD communication system, and a second base that employs a TDD communication system in which the radio frame and the arrangement configuration of uplink radio resources and downlink radio resources in the radio frame are different from those of the first base station. A communication method in a communication system comprising a station,
A communication method characterized by adjusting the timing of the carrier sense for each downlink radio resource included in a radio frame when the first base station performs carrier sense for the second base station.   The first base station uses a threshold value different from a threshold value used in carrier sense intended for another first base station that adopts the same communication method as the own station in the determination in the carrier sense. The communication method according to claim 7.   The communication method according to claim 7 or 8, wherein the first base station employs a PHS scheme, and the second base station employs a TD-LTE scheme.

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