JP2002171202A - Synchronous controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To practically improve the reception characteristics of a mobile com munication system by balancing the characteristics with path selecting capabili ties by relating the threshold of a correlation power with the receiving situation. SOLUTION: This synchronous controller for controlling the signal synchronization of received signals when one radio station communicates with the other radio station while searching a communication path with the other radio station is provided with a rake receiving means for selecting fingers whose correlation voltages exceed a threshold from the delay profile of the received signals, and realizing signal synchronization by performing rake synthesis by the selected finger group, a number of finger deciding means for deciding the scale of the fingers by comparing the number of fingers used for the rake synthesis with a prescribed number of fingers, and a correlation power threshold updating means for reducing the threshold of the correlation power when it is determined that the number of fingers is less than the prescribed number of fingers by the number of finger deciding means, and increasing the threshold of the correlation power in the other case. In this case, the update control of the threshold is performed according to the signal intensity of the received signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronization control device for a communication system, and more particularly to a synchronization control device for dynamically controlling a correlation power threshold of a communication signal when searching for a communication path between wireless stations. is there.

[0002]

2. Description of the Related Art Generally, C based on a spread spectrum method is used.
In a DMA (Code Division Multiple Access) mobile communication system, the propagation path constantly changes while having a multipath, and communication between mobile stations interferes with each other. In addition, since the communication content has been diversified despite the increasing number of users, high frequency use efficiency within a limited band is required. Therefore, using the RAKE reception method, which is one of the multipath diversity techniques, for the base station,
Various techniques for improving communication characteristics in the spread spectrum method have been proposed. In the RAKE receiving method, signal synchronization is performed between optimal paths using a maximum ratio combining technique with respect to noise power, while performing chip synchronization for each signal path and evaluating correlation. As a result, a diversity effect can be obtained between paths having low correlation with each other, so that required transmission quality can be achieved while reducing transmission power and suppressing interference.

[0003] The technical literature "CDMA Principles of Sprea"
d Spectrum Communication '' by Andrew J. Viterbi, Add
According to the ison-Wesley Wireless Communications Series), a technology has been described in which chip synchronization is conventionally performed in two stages: initial synchronization acquisition (search) and synchronization tracking (tracking) for a received signal spread with a pseudo random code spreading code. I have. In the initial synchronization acquisition, the signal component is searched serially while shifting the reception timing at a half chip interval until the correlation power value of the received signal exceeds a certain threshold value. By determining the delay profile of the path candidate group, one or more optimal paths are always selected.

[0004]

However, when the threshold value of the correlation power is set to be constant according to the above-mentioned conventional example, there are the following problems. If this threshold is always set high, only path candidates with large correlation power can be obtained, so that improvement in reliability in path selection can be expected. But RAKE
If the number of path candidates that can be combined by the receiver decreases too much,
The diversity effect during communication may be suppressed and the reception characteristics may not be improved as expected. Also, if it is set to be always low, even if a sufficient diversity effect can be obtained, the error rate in path selection may be increased and the required reception characteristics may not be expected. As described above, there is a problem that the error rate of the path selection and the diversity effect trade off.

[0005] Therefore, a synchronization control apparatus capable of solving the problem flexibly by focusing on associating the threshold value of the correlation power with the reception state and balancing the reception characteristic of the mobile communication system with the path selection ability to improve practically. Is required.

[0006]

In order to solve the above-mentioned problems, the present invention provides a mobile communication system in which a base station communicates with a mobile station while searching for a communication path with the mobile station while receiving a signal of a received signal. In a synchronization control device for controlling synchronization,
A rake receiving means for selecting a finger whose correlation power exceeds a threshold value in a delay profile of a received signal, performing rake combining by the selected finger group to obtain signal synchronization, and a predetermined number of fingers provided for the rake combining. Finger number determining means for comparing and determining the magnitude, and a correlation power threshold updating means for reducing the correlation power threshold when the number of fingers is smaller than a predetermined number and increasing the correlation power when the number of fingers is smaller than a predetermined number in the finger number determining means, The update control of the threshold value is performed based on the signal strength of the received signal.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) First Embodiment (A-1) Configuration of First Embodiment Hereinafter, an example of an embodiment in which a synchronization control device according to the present invention is applied to a CDMA mobile communication system will be described. This will be described in detail with reference to FIG. The synchronization control device 100 according to the present embodiment is provided in each base station 200 of the mobile communication system,
The function can be shown in the block diagram of FIG.

In FIG. 2, the synchronous control device 100
Is a correlator 120 for a multipath received signal, and a finger assigned / deleted by the correlator 120
1 (111), Finger 2 (112) ...
Finger N + 1 (119), RAKE receiver 130 for performing signal synthesis by finger 1 (111), finger 2 (112)... Finger N + 1 (119), and each finger 1 (111), finger 2 (1
12) ... a finger information collecting unit 140 for collecting finger information to be described later from the finger N + 1 (119);
It has a control unit 150 that controls these units 120 to 119, 130, and 140 as a whole. The demodulation unit demodulates the radio wave arriving at the antenna or detects and AD-converts the received signal to finger 1 (111) and finger 2
(112) ... Introduced to the finger N + 1 (119). The description and illustration of the transmission system to the mobile station are omitted.

The finger 1 (111) and the finger 2 (11
2)... Finger N + 1 (119) is a signal processing unit that aligns the time and phase of the received signal separated into each path for each path. The output signals are transmitted to the RAKE receiver 130 and the finger information associated with the allocation / deletion to the finger information collection unit 140 while forming each output signal in accordance with the allocation / deletion by the correlator 120 described later. As the finger information, each finger 1 (1
11), finger 2 (112) ... finger N + 1
For each (119), there is information on a finger state indicating whether each is assigned or deleted, a reference timing, and each reception timing. This reference timing is the timing of the “0” offset frame of the received signal, which is used as the head detection position in multipath. In addition, a delay time Δt of the reception timing is set in advance, and synchronization tracking is performed, and respective correlation power values are obtained at timings earlier and later by an amount corresponding to the delay time Δt. Then, the delay profile of the path candidate group obtained by synchronization acquisition is reported to the correlator 120 while finely adjusting the timing so that the difference between these power values becomes “0” by the delay locked loop (DLL) technique. .

The correlator 120 evaluates the delay profile to assign fingers 1 (111), fingers 2 (112),..., Finger N + 1 (119) necessary for multipath during communication, and unnecessary This is a searcher for deleting an object, and the control unit 150 sets a threshold signal of the correlation power for this purpose.

The RAKE receiver 130 converts the output signal group of the assigned finger 1 (111), finger 2 (112)... Finger N + 1 (119) into a signal-to-noise power ratio of each path by, for example, a maximum ratio combining technique. This is a receiver that combines while weighting according to (SN ratio). The finger information collecting unit 140 is notified of the SIR of the combined received signal as SIR information.

The finger information collecting section 140 checks the introduced finger state information, totals the number of assigned fingers, and calculates the delay from the head detection position from the deviation between each reception timing and the reference timing from the reception delay of the most advanced wave. A calculation unit that calculates the value, and causes the control unit 150 to report calculation information that is the result of the aggregation / calculation. That is, the calculation information includes the number of fingers currently assigned, the leading delay time of each finger, the SIR information, and the like.

The control unit 150 is a logical operation unit for executing the synchronization control algorithm, and may be constituted by, for example, a microprocessor (MPU) system, and its function can be shown in the block diagram of FIG. The control unit 150 includes a finger information collection unit interface (collection unit IF) 152, a finger number determination unit 153, an SI
R determination section 154, most-preceding-wave reception delay determination section 155, storage section 151 of each information described above, correlation power threshold update section 15
6. It has a correlator interface (correlator IF) 157.

The storage unit 151 stores the specified number of fingers N,
It has a memory that stores reference information such as an initial threshold value Pini, a lower threshold value Lmin, and an update step of the correlation power, a sensitivity point Q that is a target SIR value, and a most advanced wave reception delay reference value Dlim. . Further, there is a register group for storing variable information such as the number of fingers to be allocated, the current SIR at the present time, the result of determination by each determination unit, the current threshold value P of the correlation power at the present time, and the current latest preceding wave reception delay value at the present time. are doing.
The initial threshold value Pini is a unique value set based on terrain information and the like in the zone under the jurisdiction when the base station is installed.

The finger number determining unit 153 includes a collecting unit IF1.
A logic unit that compares the current finger number information obtained through 52 with the specified finger number N information, and stores the magnitude of the comparison in the storage unit 151 as a determination result.

The SIR determination unit 154 also includes a collection unit IF
This is a logic unit that compares the current SIR information obtained via the 152 with the sensitivity point Q information, and the result of the comparison is stored in the storage unit 151.

The most-preceding-wave reception-delay determining unit 155 is a logic unit that compares the current most-preceding-wave delay value information, also acquired via the collecting unit IF 152, with the most-preceding-wave delay reference value information.
The magnitude of the comparison is stored in the storage unit 151 as the determination result.

The correlation power threshold update unit 156 also acquires the current threshold information of the correlation power via the collection unit IF 152,
This is a logic unit that updates the current finger information by a predetermined threshold update logic when the update of the current finger information is completed, and causes the correlator 428 to set a new current threshold associated with the update via the correlator IF.

(A-2) Operation of the First Embodiment The content of the logic processing of the threshold update logic by the control unit 150 having the above configuration can be shown in the flowchart of FIG. In the preparation stage, the initial threshold value Pini is read from the storage unit 151 in advance and initialized in the register of the current threshold value P (ST110). Then, control unit 150 sets the set (updated) current threshold P (initial threshold Pini) information in correlator 428 (ST12).
0).

When the finger information collecting section 427 notifies the number of allocated fingers, first, the finger number determining section 153 reads out the specified finger number N from the storage section 151 and compares this with the allocated finger number to determine which is smaller. (ST130). At this time, if the number of allocated fingers is smaller than the specified finger number N, the lower limit threshold value Lmin of the correlation power is read from the storage unit 151, and this is compared with the current threshold value P to determine which is the higher value (ST140). If the current threshold value P is higher than the lower threshold value Lmin, the update step value Pstep is read from the storage unit 151, and is subtracted from the current threshold value P to obtain a new current threshold value P (ST150).

If the number of allocated fingers is equal to or exceeds the specified number of fingers N, the current threshold value P is compared with the initial threshold value Pini to determine which one is lower (ST160).
At this time, if the current threshold value P is lower than the initial threshold value Pini, the sensitivity point Q of the correlation power is read from the storage unit 151 and the current SIR is read.
(ST170). If the current SIR is higher than the sensitivity point Q, the reference value Dlim of the most advanced wave reception delay is read and compared with the current most advanced wave reception delay value (ST18).
0). If the current most advanced wave reception delay value is smaller than the most advanced wave reception delay reference value Dlim, the updated step value Pstep is read out and added to the current threshold value P to obtain a new current threshold value P (ST190).

Then, the new current threshold value P is set to the correlator IF
157, and the current threshold value P (set value) of the correlator 428 is updated (ST1).
20). The above logical processing is repeated until the communication ends.

For example, if the current most advanced wave reception delay value is within a predetermined most advanced wave reception delay reference value Dlim and the current SI
If R is a sufficiently large value, there is sufficient margin in the dynamic range of the number of fingers that can be allocated during communication. For this reason, if the transmission power control of the closed loop or the outer loop is performed with the mobile station, it is possible to sufficiently withstand transient fading. The current SIR is the sensitivity point Q
If the current delay time is less than the reference delay time Dlim, the current threshold value P of the correlation power is used.
Leave as is.

(A-3) Effects of the First Embodiment Therefore, by dynamically updating the current threshold value P of the correlation power in this way, the RAKE receiver 130
The number of reception paths to be input to the base station is controlled according to the communication state with the base station, and the reception characteristics can be improved by effective path diversity.

For example, when a mobile station is connected to both base stations 1 and 2 in two ways while moving from base station 1 to base station 2 as shown in the explanatory diagram of FIG. In some cases, it is desired that both base stations 1 and 2 perform transmission power control. At this time, one base station 2 (for example, FER1
%), A power reduction instruction is transmitted because the reception level increases due to the approach of the mobile station, and in response to this, the mobile station (FE)
R1%) lowers the transmission power. Thus, even if the reception level is weakened at the other base station 1 (for example, FER 30%) and a power increase instruction is transmitted, the mobile station is governed by the power control of the base station 2 and also issues a power reduction instruction to the base station 1. Will continue to send. For this reason, the base station 1 becomes more difficult to communicate with the mobile station and loses the balance between the transmission power in the downlink direction and the transmission power in the uplink direction.

As described above, even if sufficient reception power cannot be obtained from the mobile station, the base station 1 performs dynamic control on the current threshold value P and actively receives a reception signal via the multipath. As a result, the communication quality of the entire mobile communication system can be improved.

(B) Second Embodiment (B-1) Configuration of Second Embodiment In the first embodiment, the relative distance to the base station is estimated from the reception delay value of the most-preceding wave, and a certain distance ( The current threshold value P of the correlation power was increased when the value was within the reference value of the preceding wave. In addition, as a second embodiment, a configuration may be employed in which the most advanced wave reception delay reference value Llim is set based on the reception intensity regardless of the distance from the base station. For example, SIR
In the vicinity of the sensitivity point Q, a statistical table in which the current most-preceding-wave reception delay values measured each time are arranged is created, and the statistical mode is defined as the most-preceding-wave reception delay reference value Llim. It is stored in a predetermined register of the storage unit 240 while updating.

(B-2) Operation of the Second Embodiment The logic processing of the measurement logic of the most advanced wave reception delay reference value Llim by the control unit 150 having this configuration can be shown in the flowchart of FIG. . As a preparation stage, the most advanced wave reception reference value L which is an initial value is set in advance.
The lim is read from the storage unit 240 and initialized in the statistical table, and the sensitivity measurement width ΔQ for SIR and the delay measurement width ΔL for the most advanced wave reception delay value are set in each register (ST210).

When finger information collecting section 427 reports the current SIR, SIR determining section 154 determines whether or not the value of the current SIR is within the range of sensitivity point Q ± sensitivity measurement width ΔQ (ST220, ST230). ). If it is within this range, it is determined whether or not the most advanced wave reception delay value obtained at that time is within the range of the current most advanced wave reception delay value ± delay measurement width ΔL (ST240, ST250). If it is also within this range, the most advanced wave reception delay value is registered (additionally registered) in the registration table (ST260).

However, if it is out of these ranges (for example, when the reception quality is temporarily deteriorated due to a rapid change due to fading or the like), it cannot be set as the target of the reference value and is excluded from being registered in the statistics table ( ST29
0). Then, when registration (additional registration) occurs, the mode on the statistics table is calculated and a new first preceding reception delay reference value L is calculated.
lim is stored in a predetermined memory of the storage unit 240 (ST270).

(B-3) Effects of the Second Embodiment In a cell under the control of one base station, as shown in the explanatory diagram of FIG. 6, the closer the SIR at the base station exceeds the sensitivity point Q, the shorter the distance. If there is a mobile station, the base station instructs the mobile station to lower the power and suppresses the transmission power of the mobile station. Conversely, if the mobile station moves farther away as the SIR falls below the sensitivity point Q, the control capability of the mobile station exceeds its limit, and the SIR must be gradually reduced. For example, there is a case where a base station has gone out of a cell under its jurisdiction or a connection has been switched to another base station (soft handoff). In any case, the required S
Since an IR cannot be obtained stably, a reliable reference value cannot be calculated from these SIRs.

However, at the sensitivity point Q of the SIR, the SIR targeted by the base station can be stably obtained, so that the reference value may be calculated from the reception delay value of the most advanced wave at that time. That is, if the current SIR is below the upper limit in the vicinity of the sensitivity point Q when the base station issues the power drop instruction, or is above the lower limit when the base station issues the power increase instruction, the current most advanced wave within this range The reception delay value group is collected. Among these, the value measured most frequently is set as the most advanced wave reception reference value. Therefore, since the controllable cell configuration and the terrain are different for each base station, even if the reception path with the mobile station is greatly different, it is possible to perform highly accurate measurement corresponding to the difference in the threshold value of each correlation power. .

Although the present apparatus 100 has been applied to a base station of a CDMA mobile communication system, it can be applied to a mobile station if it has a sufficient storage capacity and a statistical calculation function. Alternatively, the present invention may be applied to a car telephone, a train telephone, a marine radio, and a satellite communication system with a higher-speed signal processing function.

[0034]

As described above, according to the present invention, when a base station communicates with a mobile station in a mobile communication system, synchronization control for controlling signal synchronization of a received signal while searching for a communication path with the mobile station. In the apparatus, a finger whose correlation power exceeds a threshold value in a delay profile of a received signal is selected, rake receiving means for performing rake combining by the selected finger group to achieve signal synchronization, and the number of fingers provided for the rake combining. A finger number determining means for determining a magnitude compared with a predetermined number; and a correlation power threshold updating means for decreasing the correlation power threshold if the number of fingers is smaller than the predetermined number, but increasing the correlation power if the number of fingers is smaller than the predetermined number. Since the threshold update control is performed based on the signal strength of the received signal, the base station dynamically adjusts the threshold of the correlation power and adjusts the number of reception paths according to the reception state. You can control Te. For this reason, even if sufficient reception power cannot be obtained from the mobile station, the base station can actively receive a reception signal via multipath. In addition, the reception characteristics have been improved by effective path diversity,
The communication quality of the entire mobile communication system can be improved.

[Brief description of the drawings]

FIG. 1 is a functional block diagram illustrating a configuration example of a main part of an embodiment.

FIG. 2 is a functional block diagram illustrating an example of application to a base station.

FIG. 3 is a flowchart illustrating an example of a characteristic operation according to the first embodiment.

FIG. 4 is an explanatory diagram showing an example of an operation associated with a threshold decision logic of a characteristic operation.

FIG. 5 is a flowchart illustrating an example of a characteristic operation according to the second embodiment.

FIG. 6 is an explanatory diagram showing an operation example of the characteristic operation associated with the most advanced wave reception delay reference value measurement logic.

[Explanation of symbols]

100: Synchronous control device, 120: Correlator, 140: Finger information collecting unit, 150: Control unit, 151: Storage unit, 1
52 ... Finger information collection unit interface, 153 ...
Finger number determination section, 154 SIR determination section, 155 most advanced wave reception delay determination section, 156 correlation power threshold update section,
157: correlator interface, 200: base station (radio station), 300: mobile station (radio station).

Claims (3)

[Claims] 1. A synchronization control device for controlling signal synchronization of a received signal while searching for a communication path with another wireless station when one wireless station communicates with another wireless station. A rake receiving means for selecting a finger whose correlation power exceeds a threshold value and performing rake combining by the selected finger group to obtain signal synchronization, and comparing the number of fingers provided for the rake combining with a predetermined number to determine a magnitude And a correlation power threshold updating means for reducing the correlation power threshold if the number of fingers is smaller than a predetermined number and increasing the correlation power threshold if the number of fingers is larger than a predetermined number. A synchronization control device for performing threshold update control by using 2. The correlation power threshold updating unit according to claim 1, wherein the correlation power threshold is increased when a reception delay value of a leading signal of the received signal is larger than a reference value. Synchronous control device. 3. The correlation power threshold updating means updates a reference value based on a reception delay value of a most advanced wave when a desired signal to interference wave power ratio of a received signal is near a sensitivity point. The synchronization control device according to claim 2, wherein: