JP2015226237A - Distributed antenna system and delay correction method in distributed antenna system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform delay correction reflected with a variation of a radio environment in a distributed antenna system.SOLUTION: The distributed antenna system includes a base unit which relays a signal from a base station, and a plurality of antenna units which are connected to the base unit by optical fibers and wirelessly transmit the signal to a mobile terminal. Each of the antenna units measures an actual length of a guard interval on the basis of the exchange of the signal with the mobile terminal, calculates a delay time between the base unit and the mobile terminal on the basis of a measurement of the guard interval, and notifies the base unit of the calculated delay time. The base unit determines a maximum delay time among the delay times acquired from the plurality of antenna units, determines a difference between the maximum delay time and each of the delay times as a delay correction amount of each antenna unit and notifies each of the antenna units of the delay correction amount. In each of the antenna units, a delay amount is corrected on the basis of the delay correction amount reported from the base unit.

Description

  The present invention relates to the field of mobile communications, and more particularly to a delay correction technique in a distributed antenna system.

  In order to strengthen indoor and outdoor high-speed packet communication areas, a distributed antenna system (ADS) has been studied. The distributed antenna system is an integrated system in which a plurality of antenna devices are dispersedly arranged by optical fibers in an area spatially separated from a base station, and transmission / reception signals are collectively processed by the base station.

  As an indoor base station facility of a distributed antenna system, there is an IMCS (In-building Mobile Communication System). In the IMCS, an optical transmission device called Radio on Fiber (RoF) is used. The RoF is a device that relays an RF (radio frequency) signal of a base station via an optical fiber. As shown in FIG. 1, a RoF is a base unit (hereinafter referred to as “master unit”) 120 and an antenna. The unit 130 is referred to as a “slave unit” in the following description. One or more slave units 130-1 and 130-2 are connected to the master unit 120, and each form a wireless communication area.

  In RoF, the slave unit 130 is arranged at various positions in the indoor facility, and a transmission delay difference occurs due to a difference in fiber length between each slave unit 130 and the master unit 120. Delay correction is performed in order for the master unit 120 to synchronously receive signals from each slave unit 130.

  In general, delay correction is performed based on measurement of signal transmission time in an optical fiber (wired section). For example, in FIG. 1, base unit 120 measures the round trip time (RTT) between slave units 130-1 and 130-2 (process (101)), and calculates the delay difference (process (102). ), The delay amount is notified to each slave unit 130 (process (103)). The subunit | mobile_unit 130 performs delay correction | amendment based on the notified delay amount (process (104)), and adjusts the reception timing in the main | base station 120. FIG. That is, in this method, the delay between each slave unit 120 is adjusted to be equal to the maximum signal transmission time between the master unit 120 and each slave unit 130. This method is referred to as “actual delay measurement method” for convenience.

  Note that, in a TDD (Time Division Duplex) type distributed antenna system, a round-trip propagation delay between a base station and a subscriber terminal is based on a base station turnaround based on a ranging burst transmitted from the subscriber terminal. It has been proposed to determine whether or not the difference between the time and the minimum allowable subscriber turnaround time is greater and to adjust the time slot in the TDD frame if the round trip propagation delay is greater than the turnaround time difference. (For example, refer to Patent Document 1).

Special table 2012-520016 gazette

  As shown in FIG. 1, the delay correction method using the RTT in the wired section requires delay correction between almost all the parent devices 120 and the child devices 130. In addition, no consideration is given to radio sections that are affected when the base unit 130 receives signals synchronously. In particular, for the latter, the master unit 120 cannot know the radio environment between each slave unit 130 and the mobile terminal (hereinafter simply referred to as “terminal”), and there is a delay amount to be set due to a change in the radio section. Even if it fluctuates, it is impossible to respond. For example, the problem becomes apparent when an uplink signal of a terminal under the slave 130-1 is received by the slave 130-2.

  Therefore, it is an object to provide a delay correction technique that takes into account the propagation state of the radio section.

  In order to solve the above problems, in the present invention, a delay amount in consideration of a wired section and a wireless section is calculated from a signal transmission / reception time in a slave unit (antenna unit) in a special subframe defined in the TDD frame configuration. . Based on the calculated delay amount, the base unit (base unit) determines a delay correction amount based on the maximum delay amount, and notifies each slave unit. By performing delay correction based on the delay correction amount notified by each slave unit, signals from each terminal are synchronously received by the master unit. Alternatively, the delay time calculation method using the signal transmission / reception time in the wireless section is combined with the wired measurement method to narrow down terminals that need delay correction.

In one aspect of the invention, the distributed antenna system comprises:
A base unit that relays signals from the base station;
A plurality of antenna units that are connected to the base unit by optical fibers and wirelessly transmit signals from the base station to mobile terminals;
Each of the antenna units is
A guard interval measurement unit that measures the actual length of the guard interval based on transmission and reception of signals with the mobile terminal;
A delay time calculating unit that calculates a delay time between the base unit and the mobile terminal based on the measured value of the guard interval;
An optical signal transmitting / receiving unit for transmitting the calculated delay time to the base unit;
Have
The base unit is
A delay information acquisition unit for acquiring the delay time from the plurality of antenna units;
A delay correction amount determining unit that determines a difference between the maximum delay time in the delay time and each delay time as a delay correction amount of the antenna unit;
An optical signal transmitting / receiving unit for notifying each antenna unit of the determined delay correction amount;
Have
The antenna unit corrects the delay amount based on the delay correction amount notified from the base unit.

In another aspect of the invention, the distributed antenna system comprises:
A base unit that relays signals from the base station;
A plurality of antenna units that are connected to the base unit by optical fibers and wirelessly transmit signals from the base station to mobile terminals;
Each of the antenna units is
A guard interval measurement unit that measures the actual length of the guard interval based on transmission and reception of signals with the mobile terminal;
A delay time calculating unit that calculates a first delay time between the base unit and the mobile terminal based on the measured value of the guard interval;
Have
The base unit is
A wired section delay measurement unit that determines a second delay time between the base unit and each of the antenna units from a round trip time;
Have
In any one of the base unit and the antenna unit, or in a delay correction unit arranged at an arbitrary position between the base unit and the antenna unit, the first delay time is compared with the second delay time, and the first delay time is compared. When one delay time is larger than the second delay time, a difference between the first delay time and the second delay time is determined as a delay correction amount.

  Delay correction can be performed in consideration of changes in the wireless environment. By combining the method of the embodiment with the wired measurement method, it is possible to individually perform delay correction control on a slave unit that requires delay correction due to changes in the wireless environment.

It is a figure which shows the procedure of the delay correction | amendment by a general wired measurement method. 1 is a schematic configuration diagram of a distributed antenna system 1A to which the present invention is applied. It is a figure explaining a TDD frame structure. It is a figure explaining the delay measuring method of an embodiment. It is a figure which shows the procedure of the delay correction | amendment of 1st Embodiment. It is a flowchart of the delay correction method of the first embodiment. It is a figure which shows the avoidance of the uplink interference by delay correction of 1st Embodiment. It is a figure which shows the structure of a TDD special sub-frame. It is a figure which shows the relationship between the fiber length and the guard area which can be ensured in each special sub-frame structure. It is the schematic which shows the delay correction procedure at the time of receiving the signal from the terminal of an adjacent subunit | mobile_unit area. It is a flowchart of delay correction when receiving interference from a terminal in an adjacent slave unit area. It is a figure which shows the convergence of the delay setting error corresponding to each step of FIG. It is a figure explaining the problem at the time of a subunit | mobile_unit new installation. It is a figure which shows the procedure of the delay correction | amendment of 2nd Embodiment. It is a schematic block diagram of the optical transmission apparatus used by embodiment. It is a figure which shows the example of shared operation with FDD.

  FIG. 2 is a schematic diagram of a distributed antenna system 1A to which the present invention is applied. The distributed antenna system 1A includes a master unit 20 that relays an RF signal from the base station 10 and a plurality of slave units 30-1 and 30-2 connected to the master unit 20 through the optical fiber 2 (hereinafter referred to as "slave unit" 30 ”). An optical transmission device (RoF: Radio on Fiber) is configured by the master unit 20 and the slave units 30-1 and 30-2 connected via the optical fiber 2.

  Base unit 20 performs analog / digital (AD) conversion and electric / optical (E / O) conversion on the RF signal from base station 10, and outputs an optical signal to optical fiber 2. The base unit 20 also optically / electrically (O / E) converts the upstream signal from each slave unit 30, converts it to digital / analog (D / A), and transmits it to the base station 10.

  The subunit | mobile_unit 30-1 carries out radio | wireless communication with the terminal 40-1 located in the communication area 31-1 of an own station, and the subunit | mobile_unit 30-2 is a terminal 40-2 located in the communication area 31-2 of an own station. Wirelessly communicate with. Each slave unit 30 O / E converts the downlink signal from the master unit 20 and radiates it from the antenna after D / A conversion. In addition, an upstream signal is received from the terminal 40 located in the area, A / D converted, E / O converted, and transmitted to the base unit 20 via the optical fiber 2. The transmission / reception switching time when each slave unit 30 operates in the TDD mode is, for example, 17 μs.

  A one-way delay (STD: Single Trip Delay) between the parent device 20 and the child device 30-1 is STD1, and a one-way delay between the parent device 20 and the child device 30-2 is STD2. The one-way delay STD combines the delay based on the fiber length between the master unit 20 and the slave unit 30 (0.5 μs per 100 m) and the collection processing time (tens of μs) between the master unit 20 and each slave unit 30. It is a thing.

  As another delay element of the distributed antenna system 1A, there is a propagation delay (t2) in the radio section between the handset 30 and the terminal 40. The propagation delay t2 in the wireless section is 0.3 microsecond per 100 m area radius.

  In the distributed antenna system 1A of FIG. 2, timing advance (TA) control is performed so that upstream signals from the terminals 40-1 and 40-2 are received by the base unit 20 at the same timing. In general, uplink TA control is to control uplink transmission timing of a mobile station according to a propagation delay in order to match reception timings from a plurality of mobile stations at a base station. In the embodiment, this TA control is applied to delay control between the terminal 40 and the parent device 20.

  The terminal 40-1 operates with TA based on the delay time STD1 of the slave unit 30-1, which is the serving station. Similarly, terminal 40-2 operates with TA based on delay time STD2 of handset 30-2 that is the serving station. When the sum of the propagation delay amounts of STD2 and terminal 40-2 is smaller than the sum of the propagation delay amounts of STD1 and terminal 40-1, the TA value of terminal 40-2 is smaller than the TA value of terminal 40-1. The terminal 40-1 transmits an uplink signal at an earlier timing than the terminal 40-2. Here, the propagation delay t2 in the radio section is small enough to be ignored as compared with STD1 or STD2. Through the TA control, the transmission signal from each terminal 40 is received by the parent device 20 at the same timing.

  However, for example, as shown in FIG. 2, when the communication areas 31-1 and 31-2 partially overlap, uplink signals from the terminals 40-1 and 40-2 set with different TA values are transmitted from the same slave unit 30. May be received. The subunit | mobile_unit 30-1 receives an upstream signal with a certain timing from the terminal 40-1 located in the communication area 31-1 of an own station, and another timing from the terminal 40-2 of the adjacent communication area 31-2. Receive upstream signal. Similarly, the subunit | mobile_unit 30-2 receives an upstream signal at a different timing from the terminal 40-1 and the terminal 40-2.

  In such a situation, when the difference between TAs exceeds the cyclic prefix (CP), the orthogonality is not maintained and inter-user interference occurs. That is, signals cannot be separated within the FFT window of the base station 10, and uplink intersymbol interference occurs. The CP length is 4.7 μs, which corresponds to a fiber length difference of 940 m.

Therefore, in the embodiment, the amount of propagation delay between the base unit and the terminal is determined based on signal transmission / reception in the radio section, and the delay correction is performed so that the difference in TA value set in each terminal 40 is equal to or less than the CP length. I do. Specific delay correction will be described below.
<First Embodiment>
FIG. 3 shows a frame structure of TDD. As the frame structure of TDD, for example, as shown in FIG. 3B, seven subframe structures are defined. TDD is a communication method that temporally switches between uplink communication and downlink communication using the same channel band. A special subframe (labeled “S”) is inserted at a location where the downlink (labeled “D”) switches to the uplink (labeled “U”).

  FIG. 3A shows the configuration of the special subframe SP. The special subframe includes a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS). DwPTS is an extension area of downlink data. UpPTS is an extension area of uplink data and is used for transmission of a random access channel (RACH) or a sounding reference signal (SRS). The guard section is not used in the up or down section. The length of the guard section is known. This known guard section is referred to as “specified GP”.

  FIG. 4 is a diagram for explaining a delay time calculation method according to the first embodiment. In 1st Embodiment, the subunit | mobile_unit 30 measures the delay time between the main | base station 20 and the terminal 40 by measuring the substantial guard area length between a downlink transmission end and an uplink reception start. For example, the timer is started at the end of downlink transmission Tx, and the timer is stopped at the start of uplink reception Rx. The time from the start to the stop of the timer is the actual guard interval (referred to as “substantial GP”).

  The end of the downlink transmission Tx is delayed from the transmission end point in the special subframe by the time D1 corresponding to the downlink propagation delay due to the propagation delay with the base unit 20. On the other hand, the uplink reception Rx received from the terminal 40 by TA control is received earlier by the time D2 than the end point of the specified GP.

  Since the TA value is set based on STD (one-way delay), D1 and D2 are almost equal when the propagation delay is negligible for STD. Therefore, half of the difference between the “prescribed GP” that is a known guard interval and the measured “substantial GP” corresponds to the delay time D 1 between the parent device 20 and the terminal 40.

  According to this method, the slave unit 30 does not use a special measurement signal from the end of downlink signal transmission to the start of uplink signal reception using a transmission / reception switching period of normal communication in TDD. Can be measured. Moreover, the delay time between the main | base station 20 and each terminal 40 can be calculated | required by simple calculation of Formula (1).

Delay time = (specified GP−real GP) / 2 (1)
Here, the delay time includes not only the wired section between the parent device 20 and the child device 30, but also the propagation delay of the wireless section between the child device 30 and the terminal 40, and can be measured in a normal communication process. It can follow radio fluctuations in real time.

  FIG. 5 is a diagram illustrating a delay control procedure in the distributed antenna system 1A according to the first embodiment. First, each slave unit 30 measures a real GP with the terminal 40 using a special subframe (processing (1)). Each slave unit 30 calculates a delay amount between the master unit 20 and the terminal 40 based on the formula (1), and notifies the master unit 20 of the calculated delay amount (processing (2)). Base unit 20 determines the maximum delay difference based on the delay amount collected from each handset 30, and calculates a difference from the maximum delay difference for each handset 30 (process (3)). In FIG. 5, only two slave units 30 are illustrated for simplification of illustration, but in reality, a large number of slave units 30 are connected to the master unit 20. The base unit 20 notifies each slave unit 30 of the obtained difference as a delay correction amount in each slave unit 30 (process (4)). The subunit | mobile_unit 30 performs delay correction | amendment based on the notified delay difference.

  FIG. 6 is a flowchart of delay control according to the first embodiment. Since there is an overlapping part with FIG. 5, it will be described briefly. First, the actual GP length is measured by the slave unit 30 that configures the distributed antenna system and can operate by the TDD method, and the delay time including the wired section to the master unit 20 is calculated (S11). As described above, the actual GP length is obtained by measuring the time from the end of transmission of the downlink signal to the terminal 40 to the start of reception of the uplink signal from the terminal. The delay time between base unit 20 and terminal 40 is 1 / of the difference between the known guard interval (“specified GP”) set in the special subframe and the actually measured GP length based on equation (1). 2 is required.

  Next, the calculated delay time is notified from the child device 30 to the parent device 20, and the parent device 20 collects each delay time (S12). Base unit 20 detects the maximum delay time in the aggregated delay time (S13), and calculates the difference between the maximum delay time and the notified delay time for each slave unit 30 (S14). The parent device 20 notifies each child device 30 of the difference as a correction amount (S15). The subunit | mobile_unit 30 correct | amends the delay amount currently set based on the notified delay difference (S16). Alternatively, each slave unit 30 is notified of the maximum delay time detected in (S13), the difference from the maximum delay time is calculated in each slave unit 30 (S14), and each slave unit 30 performs delay correction. (S16). Further, if the maximum delay time equivalent is defined in advance, the maximum delay time equivalent is notified or set to each slave unit 30, and the difference from the maximum delay time is calculated in each slave unit 30 (S14). Alternatively, delay correction may be performed in each slave unit 30 (S16).

FIG. 7 is a diagram illustrating the effect of the delay correction according to the first embodiment. As a premise of FIG. 7, it is assumed that the base station 10 and the base unit 20 are time-synchronized and have no delay. Further, it is assumed that the delay amount in the child device 1 is the largest among the plurality of delay amounts collected by the parent device 20. As the timing advance (TA), a one-way delay (STD) between the master unit 20 and the slave unit 30, a propagation delay (t2) between the slave unit 30 and the terminal 40 (wireless section), and the master unit 20 (uplink synchronization point) ), The sum of up / down switching time (RTG (B): Receive / transmit gap (B)) is set. TA = STD + t 2 + STG (B) (2)
The downstream signal 3a transmitted from the master unit 20 by the DwPTS of the special subframe is wirelessly transmitted from the slave unit 1 with a one-way delay STD1 between the master unit 20 and the slave unit 1, and further delayed by t2 to the terminal 1 Received at.

  In the uplink, TA1 for terminal 1 is set from Equation (2). The terminal 1 transmits the uplink signal 4a at a timing earlier by TA1 than the start point of the UpPTS of the special subframe. The upstream signal 4 a is received by the slave unit 1 with a delay of t 2 and transmitted to the master unit 20 through the optical fiber 2. After STD1, base unit 20 receives uplink optical signal 4a of terminal 1 at the start point of UpPTS. The reception timing R1 from the terminal 1 is synchronized with the reception timing R2 from the terminal 2, as indicated by a broken line in the figure.

  On the other hand, the one-way delay STD2 in the wired section between the parent device 20 and the child device 2 is actually smaller than STD1, but since the delay correction δ is made in accordance with the maximum delay amount determined by the parent device 20, The device 2 wirelessly transmits the downstream signal 3b at the same timing as the child device 1. Here, it is assumed that the propagation delays (t2) of the radio sections of the terminal 1, the terminal 2, and each slave unit are equal. Terminal 2 receives downlink signal 3b after propagation delay t2. In the uplink, TA2 for terminal 2 is set based on delay correction matched to the maximum delay amount. At this time, TA2 has substantially the same value as TA1. The terminal 2 transmits the upstream signal 4b at a timing earlier by TA2 than the start point of the UpPTS of the special subframe. The upstream signal 4b is received by the slave unit 2 after the propagation delay t2. The STD 2 between the slave unit 2 and the master unit 20 is small, but since the delay correction amount according to the maximum delay amount is set in the slave unit 2, the master unit 20 outputs the upstream signal 4b at the start point of the UpPTS. Receive. The reception timing R2 from the terminal 2 is synchronized with the reception timing R1 from the terminal 1 as indicated by a broken line.

  In this way, the delay amount including both the wireless section and the wired section is calculated by the slave unit and collected by the master unit 20, and the master unit 20 determines the delay correction amount according to the maximum delay amount. The TA difference can be kept within the range of the CP length. Even when the communication areas of adjacent slave units 30 overlap, signals from terminals located in different slave units in the overlapping area are synchronously received within the CP length range, so that uplink interference can be prevented. .

  FIG. 8 shows a configuration example of the special subframe, and FIG. 9 shows the relationship between the fiber length and the guard interval that can be secured in each special subframe configuration of FIG. In FIG. 8, ten types of special subframe configurations are defined, and different guard sections are defined for each. An appropriate guard section GP can be selected according to the area radius. For example, the guard interval is shortened in a narrow area to increase the data extension area to improve the throughput. In the case of a wide area, it is possible to deal with the perspective problem by lengthening the guard section.

  In FIG. 9A, the delay STD between the master unit 20 and the slave unit 30, the propagation delay t2 in the radio section, and the transmission / reception switching time RTG (B) of the master unit 20 (uplink synchronization point) are necessary. The length of the guard section GP is expressed by Expression (3).

GP length> 2 × (STD + t2) + RTG (B) (3)
As shown in FIG. 9B, assuming that the guard interval determined by each special subframe configuration is a function of the fiber length, the special subframe configuration # 0 or # 1 is used to correspond to a fiber length of 20 km. Delay correction is possible. Incidentally, TA in this example is 3500T _s.

Here, if the uplink reception Rx is not started even if the specified GP is exceeded, it is determined that there is no terminal 30 communicating with the corresponding slave station 30, and the corresponding slave station is set to the sleep mode, While reducing power consumption, noise power at the input of the master 20 can be reduced.
<Modification 1>
10 to 12 show a modification of the first embodiment. FIG. 10 shows error correction when the terminal 40-1 newly starts communication in the adjacent area of the slave unit 30-2 and the slave unit 30-2 receives an uplink interference signal from the terminal 40-1. The overall processing procedure is similar to that of FIG. 5, and the same processing is indicated by the same reference numeral. A difference from FIG. 5 is a delay time notified from the slave unit 30 to the master unit 20 (process (2) ′). Eventually, the master unit 20 determines the delay correction amount of each of the slave units 30-1 and 30-2 so as to match the maximum delay amount, but the slave unit 30 until the delay correction amount is determined. An error occurs in the delay time calculated by -2. Therefore, processing for converging the error to a range smaller than the CP length is performed.

  FIG. 11 shows a processing flow when the slave unit 30-2 (slave unit 2) receives an upstream signal from the terminal 40-1 (terminal 1) in FIG. FIG. 12 is a diagram showing error correction of the delay time in each step of FIG.

  In FIG. 11, the slave unit 30-2 receives the uplink signal of the terminal 40-2 located in the communication area of the local station (S21). The delay time calculated at this time is (specified GP−substantially GP) / 2, as can be seen from FIG. This is consistent with equation (1).

The slave unit 30-2 receives the uplink signal of the terminal 40-1 at a timing earlier by Δd than the reception of the uplink signal from the terminal 40-2.
Delay time = (specified GP−real GP + Δd) / 2 (4)
Is reported (S22). As shown in FIG. 12 (B), the error Δd between the reception timing from the terminal 40-2 and the reception timing from the terminal 40-1 is corrected, and the delay time to be reported to the parent device 20 is set. This is a calculation process.

  In this case, in the slave unit 30-2, a delay correction amount shorter by Δd / 2 than the maximum delay amount is set (S23). As a result, the delay setting error is halved as shown in FIG.

  The TA of the terminal 40-2 is updated with a delay correction amount that is shorter by Δd / 2, and the transmission timing of the terminal 40-2 is set earlier by Δd / 2 (S24). This corresponds to the change of the transmission timing shown in FIG. By updating the TA, the delay amount given to the maximum delay amount at the timing of the next uplink signal reception becomes Δd / 4, and the setting error becomes Δd / 4.

S23 and S24 are repeated until the delay error Δd / ²ⁿ becomes smaller than the CP length (Δd / ²ⁿ <CP length). As long as the reception timing difference between the terminal 1 and the terminal 2 is within the range of the CP length, uplink symbol interference does not occur. Therefore, until the new delay correction amount by the base unit 20 is notified, uplink interference is not generated. Can be prevented.
<Modification 2>
FIG. 13 is a diagram illustrating a problem associated with the extension of the slave units in the first embodiment. When each slave unit 30 measures the delay time between the master unit 20 and the terminal 40 and the delay correction amount of each slave unit 30 is set to be equal to the maximum delay amount in the master unit 20, the delay time Loss of synchronization occurs when a large amount of handset is connected.

  In FIG. 13, a slave unit 30-3 having a fiber length of 10 km is added to a distributed antenna system including a slave unit 30-1 having a fiber length of 8 km from the master unit 20 and a slave unit 30-2 having a fiber length of 5 km. . When the delay correction amount of each slave unit is set in accordance with the maximum delay amount, a delay correction of 2 km (10 μs) is set in the slave unit 30-1, and a delay of 5 km (25 μs) is set in the slave unit 30-2. Correction is set.

  In this case, since the delay correction amount of the slave unit 30-2 exceeds the TA adjustment range (−16.15 μs ≦ Delay ≦ 16.66 μs) when uplink synchronization is established, the slave unit 30-2 loses synchronization. On the other hand, since the delay correction amount of the slave unit 30-1 is within the TA adjustment range, the TA is adjusted by the delay correction amount notified from the master unit 20.

In order to cope with this problem, it is desirable to limit the delay correction amount determined by the parent device 20 within the TA adjustment range. That is, when the delay correction amount determined in accordance with the maximum delay amount exceeds the TA adjustment range, the maximum TA adjustment value is notified as the delay correction value. In the example of FIG. 13, a delay correction amount of 10 μs corresponding to 2 km is set for the slave unit 30-1, and the delay correction of 16.55 μs which is the maximum value of the TA adjustment range is set for the slave unit 30-2. The amount is set. As a result, it is possible to perform appropriate delay correction while avoiding loss of synchronization.
Second Embodiment
FIG. 14 is a schematic diagram illustrating a delay correction procedure of the distributed antenna system 1B according to the second embodiment. In the first embodiment, the delay time between the parent device and the terminal is obtained by using only the measurement of the wireless section between the child device 30 and the terminal 40, and the delay correction amount in each child device 30 is determined. In this method, since the correction is uniformly performed to the maximum delay amount, the TA value may become larger than necessary and the guard interval may be wasted. Therefore, it is desirable to cause only the slave unit that needs delay correction to perform the delay correction.

  In the second embodiment, the wireless measurement method of the first embodiment is combined with the wired measurement method to identify a slave unit that requires delay correction.

Specifically, the delay measurement result (t _r ) obtained by the wired measurement method is compared with the delay measurement result (t _s ) obtained by the wireless measurement method in the master unit 20 or the slave unit 30, and the radio measurement method delay measuring result of the is larger than the delay measurement result by wired measurement _(t r _<t s), sets the delay difference _(t s -t _r) as the delay amount of the handset 30.

14, each child device 30 - 1 to 30 - is a normal communication process, and measure the actual guard interval in the special subframe, and calculates the delay time _{t s} based on equation (1) (processing (1-a)). On the other hand, the master unit 20 calculates the optical fiber 2 from the RTT of a signal propagating, way delay time t _r between the own station and each slave 30 (processing (1-b)).

In the master unit 20 or slave unit 30 compares _{t r} and _{t s,} in the case of t r _{<t s,} to calculate the difference (2). In the example of FIG. 14, since the calculated difference in base unit 20, each child device 30 is assumed to be notified of the delay measurement results t _s by the radio measurement to the parent machine.

In FIG. 14, the slave unit 30-2 calculates the delay amount between the master unit 20 and the terminal 40-2 as being equivalent to the optical fiber 8 km because of the uplink interference signal from the terminal 40-1. However, the actual amount of delay in the wired section is equivalent to 5 km of optical fiber. Accordingly, the difference _(t s -t _r) delay correction amount of the optical fiber 3km corresponds a is notified to the slave unit 30-2 (process (3)), this delay correction value in the slave unit 30-2 is set (Process (4)).

In handset 30-1 and the slave device 30-3, and the delay measurement results t _r wired assay, unless the interference signal from the no difference (other areas between the delay measurement results t _s by the radio measurement The propagation delay t2 in the radio section itself is negligibly small). According to this method, since the delay correction is performed only for the slave unit 30 that needs the delay correction, an efficient delay correction is performed for the entire system.

When the slave unit 30 determines whether or not delay correction is necessary, each slave unit 30 receives a notification of the delay measurement result ( _tr ) by the wired measurement method from the master unit 20, and each slave unit 30 calculates by the wireless measurement method. To the measured delay measurement result (t _s ). In this case, each slave unit 30 can autonomously perform delay correction.

Alternatively, a delay correction unit or an aggregation unit (see the delay correction function unit 70 in FIG. 16) may be arranged at an arbitrary position between the parent device 20 and the child device 30. In the delay correction unit (or aggregation unit), the delay amount (t _s ) calculated by the wireless measurement method and the delay amount (t _r ) calculated by the wired measurement method are compared, and the delay correction amount is calculated. Also good.

In the second embodiment, a delay error convergence process (FIG. 11 and FIG. 12) when an uplink interference signal is generated due to the start of communication of a new terminal 40 or a process for limiting the delay adjustment range to the TA adjustment range ( FIG. 13) may be combined.
<Device configuration>
FIG. 15 is a schematic block diagram of the optical transmission device 5 used in the distributed antenna systems 1A and 1B according to the first and second embodiments. The optical transmission device 5 includes a base unit (base unit) 20 and a plurality of antenna units (slave units) 30 connected to the base unit 20 via the optical fiber 2. Base unit 20 includes optical signal transmission / reception unit 21, delay information acquisition unit 22, delay correction amount determination unit 23, and RF signal transmission / reception unit 25. Further, the wired section delay measuring unit 24 may be included. The optical signal transmission / reception unit 21 includes a conversion unit 27 that converts a downlink signal from the base station 10 into an optical signal and converts an uplink signal from the slave unit 30 into an electric signal.

  The slave unit includes an optical signal transmission / reception unit 31, a radio transmission / reception unit 32, a guard interval measurement unit 33, a delay time calculation unit 34, a delay correction unit 35, and an antenna 36. The optical signal transmission / reception unit 31 includes a conversion unit 37 that converts a downlink signal from the parent device 20 into an electrical signal and converts an uplink signal received from the terminal into an optical signal.

The guard interval measuring unit 33 of the slave unit 30 includes, for example, a timer, and measures an actual guard interval from the end of downlink signal transmission to the start of uplink signal reception in a TDD special subframe. The delay time calculation unit 34 calculates the propagation delay time between the parent device 20 and the terminal 40 based on the equation (1) as described above. The delay correction unit 35 corrects the delay amount based on the delay correction amount notified from the parent device 20 and updates the TA value notified to the terminal. When delay correction is performed by combining the wireless measurement method and the wired measurement method as in the second embodiment, the delay time calculation unit 34 obtains the calculation result (T _s ) by the wired measurement method acquired from the parent device 20. When the calculation result of the delay time calculation unit 34 is larger than the measurement result (T _r ), the delay correction may be performed based on the difference.

The delay information acquisition unit 22 of the parent device 20 receives a delay measurement result between the parent device and the terminal using wireless measurement from each child device 30 connected to the own station. The delay correction amount determination unit 23 determines the delay correction amount for the slave unit 30 so that each delay measurement value matches the maximum delay amount (first embodiment). Alternatively, the delay measurement result (T _r ) obtained by the wired section delay measurement unit 24 is compared with the acquired delay measurement result (T _s ), and when the acquired delay measurement result is large, the difference is corrected for delay. The amount may be determined (second embodiment).

  FIG. 16 shows an application example of the delay correction of the present invention. A system error due to an optical transmission delay difference can also occur in an FDD distributed antenna system. Therefore, an FDD / TDD shared antenna system 1C as shown in FIG. 16 is provided. The distributed antenna system 1 </ b> C includes a parent device 20 that relays the RF signal of the base station 10 and a plurality of child devices 60-1 to 60-3 connected to the parent device 20 through the optical fiber 2. Each slave unit 60 can operate in both the FDD mode and the TDD mode. The delay correction function unit 70 may be inserted in any place between the parent device 20 and the child device 60 and set in the parent device 20 or may be set in the child device 60. The process performed by the delay correction function unit 70 may be the process of the first embodiment or the process of the second embodiment. The measurement of the delay time using the radio section is performed by the slave unit 60 using the guard section when operating in the TDD mode, but the TA control based on the set delay correction amount is performed in the FDD mode. Sometimes done. By adopting the FDD / TDD shared configuration as shown in FIG. 16, system errors in the FDD scheme can be reduced.

1, 1A to 1C Distributed antenna system 2 Optical fiber 5 Optical transmission device 10 Base station 20 Base unit (base unit)
DESCRIPTION OF SYMBOLS 21 Optical signal transmission / reception part 22 Delay information acquisition part 23 Delay correction amount determination part 24 Wired section delay measurement part 25 RF signal transmission / reception part 27 E / O and O / E conversion part 30, 30-1, 30-2, 30-3 Slave unit (antenna unit)
Reference Signs List 31 Optical signal transmission / reception unit 32 Wireless transmission / reception unit 33 Guard interval measurement unit 34 Delay time calculation unit 35 Delay correction unit 36 Antenna 37 O / E and E / O conversion units 40, 40-1, 40-2 Terminal (mobile terminal)
60 FDD / TDD common handset 70 Delay correction function part

Claims (10)

A base unit that relays signals from the base station;
A distributed antenna system including a plurality of antenna units connected to the base unit by an optical fiber and wirelessly transmitting a signal from the base station to a mobile terminal,
Each of the antenna units is
A guard interval measurement unit that measures the actual length of the guard interval based on transmission and reception of signals with the mobile terminal;
A delay time calculating unit that calculates a delay time between the base unit and the mobile terminal based on the measured value of the guard interval;
An optical signal transmitting / receiving unit for transmitting the calculated delay time to the base unit;
Have
The base unit is
A delay information acquisition unit for acquiring the delay time from the plurality of antenna units;
A delay correction amount determining unit that determines a difference between the maximum delay time in the delay time and each delay time as a delay correction amount of the antenna unit;
An optical signal transmitting / receiving unit for notifying each antenna unit of the determined delay correction amount;
Have
The distributed antenna system, wherein the antenna unit corrects a delay amount based on the delay correction amount notified from the base unit. A base unit that relays signals from the base station;
A distributed antenna system including a plurality of antenna units connected to the base unit by an optical fiber and wirelessly transmitting a signal from the base station to a mobile terminal,
Each of the antenna units is
A guard interval measurement unit that measures the actual length of the guard interval based on transmission and reception of signals with the mobile terminal;
A delay time calculating unit that calculates a first delay time between the base unit and the mobile terminal based on the measured value of the guard interval;
Have
The base unit is
A wired section delay measurement unit that determines a second delay time between the base unit and each of the antenna units from a round trip time;
Have
In any one of the base unit and the antenna unit, or in a delay correction unit arranged at an arbitrary position between the base unit and the antenna unit, the first delay time is compared with the second delay time, and the first delay time is compared. A distributed antenna system, wherein when one delay time is larger than the second delay time, a difference between the first delay time and the second delay time is determined as a delay correction amount. When the length of the measured guard interval is substantially GP and the length of a known guard interval specified by the system is a specified GP, the delay time calculation unit is a delay time (specified GP−substantive GP) / 2
The distributed antenna system according to claim 1, wherein the distributed antenna system is calculated. When the delay time calculation unit receives an uplink signal from a second mobile terminal located in an adjacent area at a different timing from an uplink signal from the mobile terminal located in the local station, the delay time calculation unit calculates a reception timing difference. If Δd,
(Regulated GP-Real GP + Δd) / 2
The distributed antenna system according to claim 3, wherein the delay time is calculated as a delay time.   The variance according to claim 2, wherein when the difference between the first delay time and the second delay time exceeds a timing advance adjustment range, the delay correction amount is limited to the timing advance adjustment range. Antenna system. A delay correction method in a distributed antenna system, comprising: a base unit that relays a signal from a base station; and a plurality of antenna units that are connected to the base unit via an optical fiber and wirelessly transmit a signal from the base station to a mobile terminal There,
In each of the antenna units, the actual length of the guard interval is measured based on signal transmission / reception with the mobile terminal,
Calculate a delay time between the base unit and the mobile terminal based on the measured value of the guard interval,
Notifying the base unit of the calculated delay time;
In the base unit, determine a maximum delay time among the delay times acquired from each antenna unit,
The difference between the maximum delay time and each delay time is determined as a delay correction amount for each antenna unit,
Notifying each antenna unit of the delay correction amount,
Each of the antenna units corrects a delay amount based on the notified delay correction amount. A delay correction method in a distributed antenna system, comprising: a base unit that relays a signal from a base station; and a plurality of antenna units that are connected to the base unit via an optical fiber and wirelessly transmit a signal from the base station to a mobile terminal There,
In each of the antenna units, the actual length of the guard interval is measured based on signal transmission / reception with the mobile terminal,
Calculating a first delay time between the base unit and the mobile terminal based on the measured value of the guard interval;
In the base unit, a second delay time between the base unit and each antenna unit is determined from the round trip time,
In the delay correction unit disposed in any one of the base unit and the antenna unit, or between the base unit and the antenna unit, the first delay time and the second delay time are compared,
A difference between the first delay time and the second delay time is determined as a delay correction amount when the first delay time is greater than the second delay time;
The delay correction method characterized by the above-mentioned. In the antenna unit, when the length of the measured guard interval is substantially GP and the length of a known guard interval specified by the system is a specified GP, the delay time is (specified GP−substantially GP) / 2.
The delay correction method according to claim 6, wherein the delay correction method is calculated. When the antenna unit receives an uplink signal from a second mobile terminal located in an adjacent area at a timing different from the uplink signal from the mobile terminal located in the local station, the reception timing difference is Δd Then
(Regulated GP-Real GP + Δd) / 2
The delay correction method according to claim 8, wherein the delay time is calculated as a delay time.   The delay according to claim 7, wherein when the difference between the first delay time and the second delay time exceeds a timing advance adjustment range, the delay correction amount is limited to the timing advance adjustment range. Correction method.

Images