JP2008187552A - Communication system with inter-base-station control channel, and base stations - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively accomplish a SFN (Single Frequency Network) without using any expensive device such as a GPS. <P>SOLUTION: A plurality of base stations having network addresses comprise a master base station and slave base stations, wherein the master base station includes a base station information transmitting unit for transmitting a network address of the master base station via a radio, each slave base station includes a base station information receiving unit for receiving the network address transmitted from the master base station via radio, and the plurality of base stations are capable of communicating with one another via a wired network using the network addresses. The master base station then includes a synchronizing signal transmitting unit for transmitting a synchronizing signal via radio, each slave base station includes a synchronizing signal receiving timing measuring unit for receiving the synchronizing signal transmitted by the master base station and measuring a receiving timing of the synchronizing signal, and synchronizing timing to synchronize the base station to the wired network is determined based on a result of measuring the synchronizing signal receiving timing. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is used in a cellular system or a base station apparatus. In particular, it is effective for a system utilizing TDD (Time Division Duplex).

  In OFDMA (Orthogonal Frequency Domain Multiple Access), information on base stations placed in the vicinity is input in advance, or information on base stations that are geographically close to the wired network is not input. Stations autonomously broadcast each other's backbone wired network address and receive them to recognize nearby base stations and assist in synchronization correction and handover between base stations via the backbone wired network By exchanging information for doing so, efficient wireless control can be established without using precious frequency resources.

  FIG. 2 is a diagram showing a temporal arrangement (frame format) of wireless lines (or channels) in the prior art (PHS: Personal Handy phone System). 120 is a unit of time called a slot, and is composed of a plurality of signal symbols.

  In FIG. 2, four slots gather to form an uplink or downlink burst. One frame is composed of 8 slots including the uplink and downlink. Furthermore, a super frame is composed of 80 frames.

  Here, the uplink and downlink are multiplexed by a time multiplexing method called a TDD method. The point is that the same frequency is used and the uplink and downlink are secured by dividing time. The uplink is a radio channel from the terminal to the base station, and the downlink is a radio channel from the base station to the terminal.

  In the wireless system, a plurality of base stations cover each other an area called a cell, thereby realizing a planar cover area. In the TDD scheme, the uplink and the downlink are divided in time.

  Devices that transmit radio waves are divided into base stations and terminals. For this reason, as shown in FIG. 8, for example, in the uplink, in addition to the signal from the terminal in communication, the base station also receives interference from the adjacent base station or a terminal in communication with the adjacent base station. There is concern about interference. If the TDD frame is accurately taken between a plurality of base stations in the system, all the base stations are in a receiving state at the timing of reception by the base station. Does not occur. Therefore, interference resulting from this can be reduced.

  In addition, as shown in FIG. 9, in the downlink, in addition to signals from the communicating base station, the terminal has interference from neighboring terminals and interference from neighboring base stations communicating with neighboring terminals. It is thought to occur. Also in this case, if the TDD frame is accurately protected, interference between terminals can be prevented, so that interference can be reduced.

  As described above, in the TDD system, synchronization between a plurality of base stations is accurately performed, and by synchronizing with the terminal, the structure of interference can be suppressed to a specific pattern, and interference can be suppressed.

  In recent years, a wireless communication system based on OFDMA has become important. In OFDM, the influence of multipath is reduced by attaching a CP (Cyclic Prefix) to an OFDM symbol. If this feature is used, it becomes possible to synthesize signals output from a plurality of base stations in a space, and a site diversity effect can be obtained. For example, by simultaneously transmitting the same information from a plurality of base stations, it is possible to realize an SFN (Single Frequency Network) that receives a spatially synthesized signal on the terminal side.

  Non-Patent Document 1 describes the configuration of a system based on OFDMA.

  With the implementation of SFN, for example, even in an area where the sensitivity deteriorates due to interference from signals from a plurality of base stations, such as a cell boundary, the reception sensitivity can be improved by the site diversity effect.

  In order to realize SFN, it is required that the difference in arrival time of signals transmitted from a plurality of base stations is within the CP length. If so, spatial synthesis can be realized by taking out a FFT (Fast Fourier Transform) size sample from the received signal at an appropriate timing and subjecting the taken signal to FFT processing. Accordingly, each base station needs to be synchronized between base stations with an accuracy sufficiently shorter than the length of the CP length.

  Incidentally, as a method for ensuring synchronization between base stations with high accuracy, a method using GPS shown in FIG. 3 is known. Each base station is equipped with a GPS receiver and an oscillator that synchronizes with it, and establishes synchronization of each base station by synchronizing with the transmitter.

  Each GPS receiver receives a GPS satellite signal and obtains position information such as latitude and longitude and time information such as timing. It is possible to generate a highly accurate clock by correcting the above-mentioned transmitter using this time information as a trigger. While this method can easily establish synchronization, each base station needs to be equipped with an expensive GPS oscillator, and is difficult to adopt in a small base station where the unit price of the base station is low.

  Now, in PHS, a wired network is connected to an ISDN line that can distribute a highly accurate clock. Therefore, synchronization between base stations is possible without having a GPS oscillator if phase synchronization is performed based on a signal transmitted over the air based on a clock distributed from a wired network.

  As shown in FIG. 4, a base station (100-1) serving as a master is provided, and a mechanism in which surrounding base stations (100-2) are synchronized with a timing signal distributed by the master base station using radio waves is practical. It has become.

  FIG. 1 shows a configuration of the entire system including a base station and a terminal. In FIG. 1, a base station 100-1 is a base station having a GPS receiver 111.

  Patent Document 1 discloses a base station of a radiotelephone system that can generate a timing clock that is frequency-synchronized with a line clock and phase-synchronized with a PPS, and can synchronize a large number of base stations in a short time.

  In accordance with the reference signal generated by the GPS receiver 111, the clock generator 112 generates a reference clock. This becomes the master clock, and the RF unit 104 and the modem unit 105 operate. Since the master clock is synchronized with GPS, the base station can be synchronized with the reference time of the system. The terminal 101 that receives the signal transmitted by the base station 100-1 and synchronizes with it can also synchronize with the system.

  A base station 100-2 illustrated in FIG. 1 is a slave base station. Has a function to synchronize with a separately prepared master base station.

  In Patent Document 2, a radio base station receives a frame signal including a control CH signal from a reference radio base station (reference station) in accordance with a preset synchronization mode, and transmits the control CH signal in the frame signal. A method is disclosed in which the reception timing of the local station is matched with the position, and frame synchronization is established in the wireless section between the local station and the reference station.

  In Patent Document 3, in order to synchronize a plurality of base stations, a reference clock and a system frame signal supplied from a wired transmission path are used and frame synchronization transmitted from other base stations is also used. An inter-base station synchronization signal correction method is disclosed in which a signal is received, a delay of the synchronization signal with respect to the frame signal is calculated by the reference clock, and system synchronization correction is possible.

  Assuming that the base station 100-1 is a master base station, the modem unit 105 of the base station 100-1 generates a reference signal. The signal is sent to the RF unit and converted to a radio frequency. The converted signal is transmitted from the antenna 103-1. The transmitted signal is received by the antenna 103-2 of the slave base station 100-2. The received signal is converted into a baseband frequency in the RF unit.

  The signal converted into the baseband is extracted in the modem unit as a reference signal. In accordance with the reference signal, the clock unit generates a reference signal. The wired network 108 to which these base stations are connected has a mother clock unit 109 that generates a reference clock in addition to the base station control unit 115, and the generated mother clock is distributed over the wired network.

  The wired network interface unit 107 extracts a mother clock distributed over the wired network. Then, the reference clock is distributed from the clock unit 112 synchronized with this to the RF unit and the modem unit. Since the mother clock of the wired network is a standard on the wired network, synchronization is ensured in the system.

  However, when distributing the mother clock, a transmission delay occurs due to the transmission distance, and this causes a phase shift. For this reason, it is necessary to detect the phase for synchronizing the system. This is performed by the master base station signal received by the slave base station via the antenna 103-2. By detecting the phase of the received signal, the slave base station can correct the timing deviation from the master base station.

  FIG. 5 is a diagram for explaining the above-described phase synchronization. In BaseStation # 1, which is a master base station, for example, a clock (GPS_CLK) synchronized with GPS is used as a reference. A clock (Gene_CLK) is generated in synchronization with the clock (NW_CLK) distributed from the wired network. Frequency correction (AFC) works with the rise of NW_CLK as a trigger to generate a stable clock. Then, a radio signal burst is generated and transmitted in synchronization with GPS_CLK (Wireless Burst Tx in the figure).

  Next, in BaseStation # 2, which is a slave base station that does not have a reference signal such as GPS, a clock (Gene_CLK) is generated in synchronization with a clock (NW_CLK) that is also distributed from the wired network.

  However, the phase of NW_CLK of BaseStation # 1 and # 2 is shifted by T0 ′ (1) −T0 ′ (2) due to the delay difference generated in the wired network. The slave base station can identify the phase within the delay of the radio propagation instead of the wired network delay by detecting the head of the radio burst transmitted by the master base station.

  The slave base station adjusts the frame timing so that the head of the received radio burst coincides with the head of the radio burst transmitted by itself. Once the adjustment is completed, the master station and the slave station are synchronized with the clock of the same wired network, and therefore synchronization is ensured unless a phase slip occurs.

JP2001-285177 JP2006-211016 JP 9-69811 A IEEE C802.20-06 / 04.

  However, in order to realize SFN, synchronization between base stations is required with high accuracy. As a prior art, there is a method in which each base station has a GPS receiver and synchronizes depending on its accuracy.

  Now, in broadband communication that is expected to develop in the future, terminals need to output broadband signals, so services such as PHS (Personal Handy phone System) in Japan that install small base stations at intervals of several hundred meters Form is also considered to be influential.

  In such a case, it is necessary to provide a GPS receiver incorporating a stable oscillator for a small base station. However, although the base station is small and inexpensive, the GPS receiver is very expensive. Therefore, providing the GPS receiver has been a problem in terms of cost.

  Further, the conventional PHS incorporates a mechanism for preventing a synchronization error between base stations by having a high-accuracy clock supplied from a wired network and synchronizing it with a normal time. Then, a mechanism has been incorporated in which a signal issued by a specific master base station is received during a quiet communication period such as at night, and the surrounding slave base stations correct the absolute timing.

  Even in this method, the signal has to be transmitted from the master station to the slave station with sufficient strength. For this reason, there existed problems, such as the distance between a master-slave station being limited from the point of a measurement precision and the point which cannot correct a propagation delay.

  In order to provide the timing correction method at a low cost, it is difficult to provide an expensive GPS receiver for each base station. Therefore, the conventional master-slave timing correction method is desirable from the viewpoint of cost.

  However, in the conventional method, the first problem is that “correction between remote base stations is difficult from the viewpoint of reception sensitivity”, and the second problem is that “by increasing the distance between base stations, The error associated with the propagation delay increases. "

In order to solve the above-described problems, the present invention is characterized by including the following (1) to (3).
(1) A mechanism for acquiring wired network addresses of base stations that are adjacent in an autonomous distributed manner is provided. For this purpose, a base station serving as a master is provided with a mechanism for transmitting a radio wave having wired network address information at a specific timing of a specific frequency in a quiet period such as at night.

The slave base station receives the signal and makes it possible to obtain the wired network address of the master base station. As a result, each base station can acquire a communication means using a wired network of neighboring base stations without inputting the base station arrangement information in advance. (This process corresponds to the first stage described below.)
(2) The slave base station that has acquired the wired network address uses the acquired network address to access the master base station via a wired line, informs the master base station of the presence of the slave base station, and transmits from the slave base station. A process of receiving the transmitted signal and requesting preparation for measuring the propagation time. (This process corresponds to the second stage described below.)
(3) By using a feedback-type timing correction method that returns information from the slave station to the master station, the influence of the delay due to propagation is measured, the timing deviation between slave stations due to the propagation delay is corrected, and the master station -It is possible to increase the distance between slave stations. (This process corresponds to the third stage described below.)
Furthermore, the present invention adds at least one of the following processes (4), (5), (6), and (7) to the processes of (1), (2), and (3) above, thereby Further effects such as increasing the distance between the station and the slave base station and improving the timing measurement accuracy can be expected.
(4) The master station or slave station is not a single unit, but a mechanism that transmits a signal for synchronization multiple times and combines it on the receiver side so that the reception timing can be measured even with weak radio waves It comprises.

Furthermore, in order to support it, it is equipped with a mechanism that enables direct or indirect communication between base stations via a wired network, and between remote base stations that cannot send significant signals (information) wirelessly. Can also implement a synchronization sequence.
(5) A mechanism for transmitting and receiving a broadband synchronization signal exceeding 5MHz enables highly accurate timing measurement and guarantees the synchronization performance required for SFN implementation.
(6) In order to assist in searching for a master station in the vicinity, a mechanism for wirelessly broadcasting an IP address or alternative information for periodically accessing the master station using a multi-hopping technique is provided.
(7) A slave station that satisfies a certain condition is defined as a reliable slave station and operated as a semi-master station. By performing a synchronization sequence using a plurality of master stations or quasi-master stations, the slave station can avoid the influence of obstacles and establish stable synchronization.

  The number of GPS-equipped base stations can be reduced compared to the conventional one, and an inexpensive system can be constructed. In addition, synchronization with high accuracy (<0.5 us) is possible, and SFN can be realized without GPS. In addition to synchronization, PHS requires an autonomous distributed interference control function. However, if multi-hop is used, it is possible to grasp surrounding interfering stations, so it can be used for channel assignment by cooperation between base stations.

  Hereinafter, a communication system to which the present invention is applied will be described in detail with reference to the drawings. The configuration of the wired network includes a base station having a clock unit that is synchronized with the clock that serves as a reference from the wired network.

  Each base station receives clock distribution from the same mother clock existing in the wired network and controls the oscillation frequency of the local oscillator. For this reason, the frequency is stabilized with the accuracy of the clock distributed from the wired network, and jitter does not occur. However, since the transmission distance from which the clock is distributed from the mother clock differs depending on each base station, the phase of the distributed clock will vary.

  Now, in the base station made of the prior art, a known burst signal is transmitted wirelessly from the master station, and each slave station receives the burst signal and synchronizes with the burst signal, thereby suppressing phase variations. However, the synchronization with the burst signal transmitted wirelessly has a problem that the propagation delay of the burst signal remains as a fixed error factor (phase shift).

  Therefore, the communication system to which the present invention is applied includes means for correcting a fixed error factor generated for each base station.

  FIG. 6 is a diagram showing a procedure in the first embodiment to which the present invention is applied. The embodiment is roughly divided into three stages.

  First, the first stage (Stage # 1) is a stage in which a “synchronization signal” is transmitted from the master base station using radio. The “synchronization signal” to be transmitted is classified into three types.

  The first signal is a pilot signal (Sync Signal in the figure) for measuring the reception timing. The pilot signal is known information including a scramble code unique to the master station or a phase of the scramble code.

  The surrounding slave base stations can measure the reception timing by matching the received signal with the scramble code. The accuracy of measurement is inversely proportional to the bandwidth of the pilot signal. For example, for a signal transmitted in a 10 MHz band, timing can be measured with a resolution of light speed / bandwidth = 299792458 [m / s] / 10000000 [Hz] = about 30 m.

  The second information is assist information (Sync Signal Assist in the figure) for receiving the pilot signal.

  The assist information includes information related to the scramble code itself. The slave station performs timing measurement by matching the received pilot signal with the scramble code, but uses assist information to identify the scramble code to be matched.

  When the master station transmits a scramble code, the scramble code is generated from, for example, a PN sequence. However, the longer the PN sequence period (sequence length), the lower the autocorrelation on the receiving side. A long period can be taken. As a result, the timing can be measured even with a weak signal.

  However, the longer the scramble code period, the more difficult it is to specify the type and phase of the scramble code to be matched. Therefore, by using the assist information and transmitting the scramble code generation polynomial and the current phase information, it is possible to generate a scramble code in accordance with the reception timing, and to reduce the time required for timing measurement.

  The third information is IP address information of the master station (note that IP address information is a kind of wired network address information). As will be described later, in the system according to the present invention, information for timing measurement is not only transmitted wirelessly but also via a wired network. As a result, timing measurement can be performed without using limited radio resources as much as possible. In order to ensure communication via such a wired network, the IP address of the master station is required.

  This slave station has a mechanism for retransmitting the received “synchronization signal” to other slave stations by multi-hop (retransmission). The information to be retransmitted includes the second (assist information), the third (master station IP address), and the number of multi-hops. The base station that has received the transmitted information can know the IP address of the master station based on this information.

  The slave base station retransmits the obtained information if the number of multi-hops is less than a predetermined value and the surrounding base stations are not performing multi-hop. The timing of retransmission is determined by a random number and is retransmitted several times.

  By this retransmission operation, it is possible to transmit the scramble code information of the master station and the IP address of the master station to a distant base station.

  As described above, the pilot signal itself is a signal composed of a known scramble code. By matching using a long code length, even a weak signal can be detected, and the measurable distance is long. On the other hand, information such as assist information and IP address is a signal including information unknown to the receiving side, and the receivable distance is shortened. The multi-hop function is a technique for filling the gain difference between the two.

  In the above description, the signal transmitted from the master station and the signal retransmitted from the slave station may be OFDM modulated signals or CDM signals.

  Next, in the second stage (Stage # 2), the slave base station sends a “measurement request” to the master station via the wired network, informs the master station of the existence of the slave station, and reduces the round trip delay. This is the stage to request to start measurement preparation. The request includes assist information (information regarding a scramble code unique to the slave station) for receiving the pilot signal of the slave station.

  The master station notifies the slave station of the completion of preparation by transmitting an ACK signal. This ACK signal is also transmitted through a wired network.

  Next, the third stage (Stage # 3) is a stage in which a synchronization signal is transmitted from the slave base station using radio. The slave base station enters this stage when receiving an ACK signal from the master station.

  The slave station in the third stage transmits its own IP address information and a pilot signal based on the assist information notified to the master station in the second stage. The master station measures the reception timing of the signal transmitted by the slave station by using a scramble code known in advance and its phase and matching the received signal.

  The measurement result is returned to the slave station that transmitted the signal via the wired network. Since the slave station has already transmitted ACK information in the wired network, the result of the reception timing can be notified without error.

  In the third stage, the slave station also broadcasts the IP address. Other base stations in the vicinity receive the IP address of the slave station in the third stage described above, thereby making the slave station exist and obtaining information on the IP address.

  Since the IP address information cannot be received at a distance, only the master or slave base station around the slave station can obtain the IP address of the base station. The IP address obtained here is used for operations such as cooperation between base stations.

  Now, when exchanging information using radio, valuable frequency resources are consumed. Especially for communication between distant base stations, it is necessary to increase the energy density for transmitting 1 bit, and a large frequency resource is required. On the other hand, in wired transmission via a wired network, information can be transmitted almost certainly without using wireless resources.

  Therefore, in the first embodiment to which the present invention is applied, the first stage, the second stage, and the third stage described above are provided, and the radio delay is used for the measurement of the propagation delay, and control information for performing such a measurement. By using a wired network for the exchange, and constructing a communication system, the effect of being able to perform timing measurement while minimizing the consumption of valuable radio resources is achieved.

  Next, a mechanism for generating a transmission signal according to the present embodiment will be described.

  In the case of an OFDM signal, the configuration of the transmitter (radio base station information transmitter) is shown in FIG. FIG. 13 shows a configuration of a transmitter that transmits scramble code information. For example, the PN generation unit 1001 generates a PN code sequence seed based on a wired network ID.

  For example, when the wired network ID is a 32-bit address, the LSB 24 bits are set as the MSB, and the value obtained by padding the lower 4 bits and 0 is set as the initial phase of the PN code sequence consisting of 32 taps. As for the initial phase, the time determined by the system is set to 0:00, and the phase is updated based on this time.

  In this way, a PN sequence having a phase independent from surrounding base stations can be created. The subsequent MAP unit 1002 maps the scramble code generated according to the seed to a two-dimensional resource composed of a time axis and a frequency axis. The mapped information is converted into a time signal in IFFT section 1003. A CP (Cyclic Prefix) is added as necessary. The output of the IFFT unit is converted into a radio frequency by the RF unit 1004 and transmitted from the antenna.

  Further, the receiver (radio base station information receiving unit) of the embodiment according to the present invention is realized by the configuration shown in FIG. In this configuration, two types of delay profile creation methods can be realized.

  A signal received by the antenna is amplified and frequency-modulated by the RF unit 1101 and converted to a baseband frequency.

  The converted signal is used for detection of reception timing by detecting a pilot signal necessary for reception in the matched filter unit 1105 and a specific pattern (scramble code and its phase) inserted to detect timing. (First method).

  In the case of the first method, a matched filter unit 1105 is used as a synchronization signal reception timing measurement unit.

  In accordance with the obtained timing, the FFT unit 1102 performs FFT processing on the baseband signal output from the RF unit 1101 and converts it to a frequency domain signal. Information on a specific frequency and time is extracted from the converted signal and input to the correlator 1106.

  In the correlator 1106, descrambling is performed with a pattern such as a pilot signal prepared in advance, and a delay profile is created by IFFT calculation (second method).

  In the case of the second method, a matched filter unit 1106 is used as a synchronization signal reception timing measurement unit.

  If the peak of the delay profile exceeds a predetermined level, a signal corresponding to the prepared pattern is detected. Time measurement of the detected signal is completed from the delay amount of the delay profile.

  Although two delay profile creation methods are presented here, the effects of the present invention can be obtained as long as other methods are used to create a delay profile. For example, the delay profile obtained by the first method can be synthesized to detect even a weak signal. Information such as a wired network ID is extracted from the output of the FFT unit 1102 by the demapping unit 1103 and is demodulated and extracted by the demod unit 1104.

  In the above embodiment, the scramble pattern and information are divided and sent in a specific frequency and time domain, but matching with the scramble pattern obtained in the delay profile creation process by incorporating information such as the network ID into the scramble pattern itself. The method of extracting information from the above is also within the scope of this patent. From the obtained network ID, the corresponding base station can know the network ID of the surrounding master base station.

  The slave station also has the configuration of FIG. 13 to transmit the master station information to the surrounding base stations by multi-hop, and can use this to generate and transmit the transmission information.

  FIG. 12 shows a frame format according to the first embodiment to which the present invention is applied. The vertical axis represents the frequency, and in this example, the occupied band of the normal signal is 1.275 MHz. The horizontal axis represents time, and in this example, the frame is a TDMA frame obtained by dividing a unit of 5 ms into eight.

  If the divided unit is called a slot, the first four slots are for the downlink and the latter four slots are for the uplink. N TDMA frames are combined to form one base frame, and the first slot at the head of the base frame is a downlink synchronization signal and a common control channel slot. The fifth slot is a slot for transmitting an access probe for uplink.

  When the radio channel of the control signal that sends the signals for timing adjustment between the base stations, which is a feature of the present invention, is called the inter-base station cooperation channel (BSCCH), the BSCCH transmitted by the master base station is: It is placed in the first slot of the second TDMA frame.

  On the other hand, a timing measurement signal transmitted from the slave base station to the master base station is placed in the first slot of the third TDMA frame. In addition, a signal in which the slave base station multi-hops a signal transmitted from the master base station is placed in the first slot of the fourth TDMA frame.

  In this way, by transmitting information using a plurality of subbands in a specific slot, time synchronization can be performed while avoiding the influence of frequency selectivity and avoiding interference with normal communication. Furthermore, if a series of measurement operations are pre-programmed so as to be performed in a quiet communication period such as at night, the influence on normal communication can be almost eliminated.

  In a normal time, as shown in FIG. 11, the inter-base station cooperation channel (BSCCH) is allocated to the data transmission channel (DCH).

  The procedure of the first embodiment will be described with reference to FIG. First, the master base station (BaseSation # 1) transmits a pilot signal which is a synchronization signal or a prescribed signal and assist information for receiving its own IP address, synchronization signal or pilot signal (S201-1 or S202). ).

  In the case of multi-hop, the slave base station (BaseStation # n) receives the information and retransmits it (S201-2). The information to be retransmitted is assist information for receiving the IP address of the master base station and the synchronization signal. Here, the assist information is information such as the type and phase of the scramble code, and is used to reduce the amount of calculation for receiving the synchronization signal.

  The slave base station (BaseStation # 2) receives the synchronization signal, and if it can be received, transmits a “measurement request” of the synchronization signal to the master base station via the wired network interface (NW-IF) (S203). , S204). The request information includes assist information for receiving a synchronization signal that the slave base station will send in the future. Since the request (S204) is transmitted via the wired network, there is no consumption of radio resources.

  When the master station receives a request through a wired network interface (NW-IF) (S205, S206), it determines whether there is an obstruction factor such as a collision with another request and determines when measurement is possible. To do. When it is possible, ACK (S206, S207, S208) is transmitted through the wired network interface.

  When receiving the ACK, the slave base station transmits a synchronization signal by radio (S209). Since the master base station receives the assist information of the synchronization signal at the reception stage of the request, the master base station receives the synchronization signal using this information. The master station measures the time (D304) from when the master base station sends the synchronization signal until the slave base station receives the synchronization signal.

  This time measurement may be a relative amount with respect to a reference clock. The measurement result is returned to the slave base station via the wired network (S210, S211, S212). The slave base station measures the time (D302) from when the master base station synchronization signal is received to when the slave station synchronization signal is transmitted (this time can also be relative to the reference clock). The propagation delay time (D301 = D303) is calculated by subtracting D302 from the measurement result (D304) returned from the master base station and dividing it by 2.

  The time after the propagation delay time measured with respect to the timing at which the synchronization signal is received is the transmission timing of the synchronization signal, and the slave base station synchronizes the frame in accordance with the transmission timing. Therefore, timing synchronization considering propagation delay is possible, and the problem is solved.

  FIG. 15 is a schematic diagram of a propagation path when frequency selectivity exists. The horizontal axis represents frequency, and the vertical axis represents frequency quality.

  Due to the multipath effect, frequency selectivity occurs in the propagation path as shown in FIG. At this time, for example, if the signal is transmitted only in the subband # 1, the signal cannot be transmitted from the quality of the propagation path. In particular, what is discussed here is transmission between base stations, and the quality of the propagation path hardly changes with time.

  Therefore, it is necessary to transmit in a wide band in order to convey information stably. In addition, if broadband information is used, the resolution in the time direction is increased. For example, with a 1 MHz bandwidth, the temporal resolution is about 1 us, but with a 10 MHz bandwidth, it can be improved to 0.1 us.

  FIG. 16 is a flowchart showing the operation of the master base station. The base station enters this process at a specific time zone. First, it is determined whether it is a master station (2001). If it is a master station, a base station cooperation channel (BCSCCH) is transmitted.

  The slot to be transmitted is 500 in FIG. Next, after waiting for a “measurement request” from the wired network and receiving the measurement request, preparations are made for receiving the inter-base station cooperation channel from the slave station based on the information (scramble pattern) (2002).

  The slot to receive is 501 in FIG. When received, the measurement result is returned to the slave station via a wired network (2003). It is checked whether the cooperation between base stations during the off-traffic period is permitted (2004). If it is within the time, observation is continued. If it is overtime, transmission of the inter-base station cooperation channel is stopped.

  FIG. 17 is a flowchart showing the operation of the slave base station. The base station enters this process at a specific time zone.

  First, it is determined whether it is a slave station (2101). If it is a slave station, a base station cooperation channel (BCSCCH) is received (2102). The slot to receive is 500 in FIG. The relationship between the own frame and the received signal is measured (2103).

  When the measurement is completed, a “measurement request” is transmitted to the master station through the wired network at an arbitrary timing (2104). Then, the inter-base station cooperation channel is transmitted at an appropriate timing according to the ACK from the master station, and the transmission is stopped at an appropriate timing (2105).

  The slot to be transmitted is 501 in FIG. It waits for the measurement result sent from the master station via the wired network (2106), and calculates the correction time using the result (2107).

  As described above, according to the first embodiment to which the present invention is applied, wirelessly arranged in the surroundings without being notified of network address information of a nearby wireless base station in advance or via a wired network. It becomes possible to collect network addresses of base stations and perform information communication between adjacent wireless base stations via a wired network using the network addresses.

  In the first embodiment, the relationship between the master base station and the slave base station is uniform, but the slave base station synchronized by the correct method synchronizes with the system with the same degree of accuracy as the master base station. ing. Therefore, a slave base station that has finished a series of operations can operate as a master base station.

  This is the second embodiment. In the second embodiment, there are also slave base stations that can measure a plurality of master base stations. In that case, it is possible to increase the synchronization accuracy by using the least square method. FIG. 10 shows the procedure when the slave base station becomes a quasi-master base station as the fourth stage, and uses the results measured using a plurality of base stations (master or quasi-master station) to minimize the base station. One synchronization timing can be obtained using the square method.

  The present invention can be utilized for a wireless communication infrastructure. This is particularly effective in wireless communication employing the TDD scheme.

The block diagram of the radio system which consists of a prior art. The frame structure of the wireless system which consists of a prior art. A wireless system synchronization method according to the prior art. A wireless system synchronization method according to the prior art. A wireless system synchronization method according to the prior art. The figure which shows the step of the 1st Example which consists of this invention. The flow of the 1st Example which consists of this invention. The figure which shows the interference of a radio | wireless system. The figure which shows the interference of a radio | wireless system. The figure which shows the step of the 2nd Example which consists of this invention. The frame structure of the normal period of 1st Example which consists of this invention. The frame structure at the time of the synchronization process of 1st Example which consists of this invention. 1 shows a transmitter according to a first embodiment of the present invention. The receiver of the 1st Example which consists of this invention. The schematic diagram which shows the frequency selectivity of a radio | wireless system. The flow of the master station of 1st Example which consists of this invention. The flow of the slave station of 1st Example which consists of this invention.

Explanation of symbols

100 ... Base station device 101 ... Terminal device 102 ... Antenna 103 ... Antenna 104 ... RF unit 105 ... Baseband modem unit 106 ... MAC processing unit 107 ... Wired Network interface 108 ... Wired network 109 ... Mother clock 110 ... Synchronization unit 111 ... GPS receiver 112 ... Clock generation unit 113 ... Control unit 114 ... Storage unit 115 ... Base station controller.

Claims (18)

A plurality of base stations having network addresses comprise a master base station and a slave base station,
The master base station has a base station information transmitter that transmits the network address of the master base station via radio,
The slave base station has a base station information receiving unit that receives a network address transmitted by the master base station via radio,
A communication system, wherein the plurality of base stations can communicate with each other via a wired network using a network address.   The communication system according to claim 1, wherein the slave base station retransmits the received network address of the master base station to another slave base station via radio. The communication system according to claim 1, wherein the master base station includes a synchronization signal transmission unit that transmits a synchronization signal via radio,
The slave base station has a synchronization signal reception timing measurement unit that receives the synchronization signal transmitted by the master base station and measures the reception timing of the synchronization signal,
A communication system, wherein a synchronization timing at which a base station synchronizes with a wired network is determined based on a reception timing measurement result of a synchronization signal. The communication system according to claim 3, wherein the base station information transmission unit of the master base station further transmits assist information for assisting reception of the synchronization signal,
The base station information receiving unit of the slave base station receives the network address and assist information of the master base station, and outputs the received network address and address information to the synchronization signal reception timing measuring unit,
The synchronization signal reception timing measurement unit receives a synchronization signal transmitted from a master base station using the input assist information, and measures the reception timing.   5. The communication system according to claim 4, wherein the slave base station retransmits the received network address and assist information of the master base station to another slave base station via radio as input to the base station information transmitting unit. A communication system characterized by the above.   6. The communication system according to claim 5, wherein a plurality of base stations create broadcast information using information of other base stations obtained autonomously and broadcast the information on a radio channel. The communication system according to claim 3, wherein the slave base station requests assist information for assisting reception of the synchronization signal with respect to a network address of an adjacent master base station obtained by the base station information receiving unit,
The proximity master base station that has received the assist information request transmits assist information including at least information of the code sequence of the synchronization signal to the slave base station that requests the assist information via a wired network.
The slave base station takes the assist information obtained from the wired network into the synchronization signal reception timing measurement unit,
The synchronization signal reception timing measurement unit receives a synchronization signal transmitted from a master base station using the obtained assist information, and measures the reception timing. The communication system according to claim 3,
Timing measurement request in which the slave base station requests reception timing measurement of a synchronization signal transmitted by the slave base station via a wired network, with respect to the network address of the adjacent master base station received by the base station information receiving unit The steps of
When the slave base station receives an acknowledgment signal (ACK) from the master base station, the synchronization signal transmission unit of the slave base station transmits a synchronization signal having a specific modulation pattern in a specific frequency band at a specific timing;
The master base station uses the synchronization signal reception timing measurement unit, receives the synchronization signal transmitted by the slave base station, measures the reception timing of the synchronization signal, and notifies the slave base station of the measurement result via a wired network And steps to
The slave base station includes a step of determining a synchronization timing to synchronize with the wired network using the notified result. A base station with a network address
A base station information transmitter that transmits the network address of the base station itself via wireless;
It has a base station information receiving unit that receives the network address of another base station via radio,
A base station, which can communicate with another base station via a wired network using the network address.   10. The base station according to claim 9, wherein the received network address of the other base station is input to the base station information transmitting unit and retransmitted to the other base station via radio. The base station according to claim 9, further comprising: a synchronization signal transmitting unit configured to transmit a synchronization signal having a specific modulation pattern in a specific frequency band at a specific timing via wireless communication;
It has a synchronization signal reception timing measuring unit that receives a synchronization signal transmitted by another base station and measures the reception timing of the synchronization signal,
A base station that determines a synchronization timing at which a base station synchronizes with a wired network by using a reception timing measurement result of a synchronization signal. The base station according to claim 11, wherein the base station information transmitting unit further notifies assist information for assisting reception of the synchronization signal,
The base station information receiving unit receives network address and assist information in other base stations, and notifies the received network address and assist information to the synchronization signal reception timing measuring unit,
The synchronization signal reception timing measuring unit receives a synchronization signal transmitted from another base station using the obtained assist information, and measures the reception timing.   13. The base station according to claim 12, wherein a network address and assist information transmitted by another base station received by the base station information receiving unit are input to the base station information transmitting unit and retransmitted to other base stations. A base station characterized by   14. A base station according to claim 13, wherein broadcast information is created using information of other base stations obtained autonomously, and the base station information is broadcast to a terminal using a broadcast channel. Bureau. The base station according to claim 11, requesting assist information for assisting reception of the synchronization signal for a network address of another adjacent base station obtained by the base station information receiving unit,
Assist information obtained from the wired network is taken into the synchronization signal reception timing measurement unit,
The synchronization signal reception timing measuring unit receives a synchronization signal transmitted from another base station using the obtained assist information, and measures the reception timing.   12. The base station according to claim 11, wherein when an assist information request is received from another base station via a wired network, at least a synchronization signal code sequence is transmitted to the other base station requesting assist information via the wired network. A base station that transmits assist information including the following information. 12. The base station according to claim 11, wherein a reception timing of a synchronization signal transmitted by the base station via a wired network is measured with respect to a network address of another adjacent base station obtained by the base station information receiving unit. Make a timing measurement request,
Upon receiving an acknowledgment signal (ACK) from another base station, the synchronization signal transmitting unit transmits a synchronization signal having a specific modulation pattern in a specific frequency band at a specific timing,
A base station that determines a phase (or synchronization timing) when a base station synchronizes with a wired network using a measurement result notified via the wired network. The base station according to claim 11, when receiving a timing measurement request transmitted from another base station via a wired network, reserves a timing measurement,
When the timing measurement is possible, send an acknowledgment signal (ACK) to the other base station that sent the timing measurement request via the wired network.
Measure the reception timing of the synchronization signal consisting of a specific modulation pattern in the specific frequency band of the specific timing transmitted from another base station using the synchronization signal reception timing measurement unit,
A base station that notifies a base station of a measurement result via a wired network.

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