JP2004312159A - Carrier detection method, and terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier detection method whereby a terminal carries out no demodulation when the terminal receives only an interference signal even if a measured value of reception power by a receiver of the terminal exceeds a carrier detection threshold value. <P>SOLUTION: When a carrier detection section A302 detects a received signal with an amplitude in excess of a prescribed threshold value, a demodulation section 303 starts demodulating the received signal. When a carrier detection section B discriminates that the amplitude of the received signal is not within a prescribed range, the demodulation section 303 stops demodulation. An RSSI_sta calculation section 304 and a window setting section 306 reflect the amplitude of the received signal at which no demodulation is stopped and its arrival probability on the decision of the prescribed range. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a carrier detection method in a burst signal transmission system.
[0002]
[Prior art]
In a burst signal transmission system such as a wireless LAN (Local Area Network) employing a CSMA / CA (Carrier Sense Multiple Access With Collision Aidance) system as a wireless access system, a base station is a terminal belonging to the base station at the same time. Only one terminal in the group can communicate. In such a system, the base station normally gives identification information to each terminal when establishing a line to a group of terminals belonging to the base station. When the base station transmits a burst signal to one terminal in a terminal group belonging to the base station, the base station adds identification information for the terminal to the head of the burst signal and transmits the burst signal. All terminals measure the received signal level of the burst signal transmitted from the base station, and compare the measured value with a predetermined determination threshold (hereinafter, referred to as a carrier detection threshold). When the measured value exceeds the carrier detection determination threshold, it is determined that the carrier has been detected, and the demodulation operation is started. On the other hand, when the measured value falls below the carrier detection threshold, it is determined that no carrier is detected, and the demodulation operation is stopped. These are represented by the following equations.
[0003]
(Carrier detection conditions)
RSSI ≧ Th_CS (1)
(Carrier non-detection condition)
RSSI <Th_CS (2).
[0004]
In Equations (1) and (2), RSSI represents a measured value of received power at the receiver, and Th_CS represents a carrier detection threshold.
[0005]
By performing the above carrier detection, when no carrier is detected, unnecessary demodulation operation is omitted, so that the power consumption of the receiver can be reduced. Here, when the carrier detection threshold value Th_CS is set to a high value, the carrier detection probability decreases. Therefore, even if the received signal level can be originally demodulated, the probability of not detecting the carrier increases, and the communication efficiency deteriorates. On the other hand, when the carrier detection determination threshold value Th_CS is lowered, the probability of detecting the reception noise power and the interference power from other carriers increases, and the probability of performing unnecessary carrier detection increases. The problem is that the power consumption of the battery increases and the effective time of the battery decreases. From the above, it is desirable that the carrier detection threshold Th_CS be set to an optimal value in consideration of communication efficiency and power consumption.
[0006]
As a conventional technique relating to a method of optimizing a determination threshold, there is a method of holding an RSSI signal in advance without detecting a carrier and adaptively setting a carrier detection threshold Th_CS based on the RSSI signal ( Patent Document 1). The terminal that satisfies the equation (1) and is determined to have detected the carrier starts demodulation processing of the received signal, and determines whether the burst signal is addressed to itself according to the terminal identification information added to the head of the burst signal. Is determined. If it is addressed to itself, the demodulation operation of data subsequent to the burst signal identification information is performed, and if it is not addressed to itself, the demodulation operation of data subsequent to the burst signal identification information is stopped.
[0007]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-156666
[Problems to be solved by the invention]
In the above prior art, even when the terminal receives only the interference signal, the demodulation operation up to the terminal identification information of the burst signal is performed when the RSSI satisfies the expression (1). Therefore, there is a problem that power consumption increases due to unnecessary operation of the demodulation circuit, and the effective time of the battery is reduced. In addition, an unnecessary increase in the processing time of the demodulation circuit has a problem of reducing the communication efficiency of the system.
[0009]
An object of the present invention is to provide a carrier detection method for preventing a demodulation operation when a terminal receives only an interference signal, even if a measured value of received power in a receiver exceeds a carrier detection threshold. It is in.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a carrier detection method in which when a received signal having a magnitude exceeding a predetermined threshold is detected, demodulation of the received signal is started. If not, demodulation is stopped.
[0011]
Further, the magnitude and the arrival probability of the received signal for which the demodulation has not been stopped are reflected in the determination of the predetermined range.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 shows a configuration diagram of a burst signal transmission system according to an embodiment of the present invention. The terminal 20 and the terminal 21 belong to the base station 10 configuring the cell 30. The individual information burst signals transmitted from the base station 10 to the terminal 20 and the terminal 21 are referred to as an individual information burst signal 40 and an individual information burst signal 41, respectively.
[0014]
Hereinafter, the demodulation operation of terminal 20 and terminal 21 for the individual information burst signal will be described. As an example, consider a case where the base station 10 transmits the individual information burst signal 40 to the terminal 20. In this case, the demodulation of the individual information burst signal 40 in the terminal 20 and the terminal 21 starts with the demodulation operation of the terminal 20 and the terminal 21 when the RSSI for the individual information burst signal 40 satisfies the formula (1) The terminal identification information added to the head of the individual information burst signal identifies which terminal the individual information burst signal is addressed to. In the above example, since the individual information burst signal 40 is addressed to the terminal 20, the terminal 20 demodulates the individual information burst signal 40 with data after the terminal identification information. On the other hand, since the individual information burst signal 40 is not addressed to the terminal 21, the terminal 21 does not perform the operation of demodulating data after the terminal identification information.
[0015]
On the other hand, in the burst signal transmission system of the present embodiment, the base station 10 transmits the broadcast information burst signal 50 at regular time intervals. Since the broadcast information burst signal 50 is broadcast to the terminals 20 and 21 belonging to the base station 10, the terminals 20 and 21 demodulate the broadcast information burst signal 50. The demodulation of the broadcast information burst signal 50 in the terminal 20 and the terminal 21 starts the demodulation operation when the RSSI for the broadcast information burst signal 50 satisfies the expression (1). Based on the added terminal identification information, it is determined that the signal is a broadcast information burst signal, and both the terminal 20 and the terminal 21 demodulate data after the terminal identification information added to the head of the broadcast information burst signal 50.
[0016]
Next, the basic concept of the carrier detection method in the terminal for the burst signal transmission system of the present embodiment will be described.
[0017]
First, the terminal holds the RSSI at the time when Expression (1) is satisfied, and sets the held RSSI as RSSI_sta. Thereafter, from the terminal identification information of the individual information burst signal and the broadcast information burst signal, it is determined whether or not the received burst signal is a signal from the base station to which the terminal belongs, and to which the terminal belongs. If the signal is from the base station, the terminal sets the RSSI range for determining the start / stop of the demodulation operation of the burst signal to be received next time based on the information in which the RSSI_sta is set from the held RSSI as in the following equation. Set to.
[0018]
RSSI_sta-Th_win / 2 <RSSI <RSSI_sta + Th_win / 2 (3).
[0019]
Here, Th_win is a set value that determines the RSSI range. The relationship between Th_CS in Expressions (1) and (2) and RSSI_sta and Th_win in Expression (3) satisfies the following expression.
[0020]
Th_CS <RSSI_sta-Th_win / 2 <RSSI_sta <RSSI_sta + Th_win / 2 (4).
[0021]
The terminal starts the demodulation operation when the received RSSI satisfies Expression (3), and stops the demodulation operation when the received RSSI does not satisfy Expression (3). The basis of the present embodiment is to determine whether the RSSI of the received signal is within the range shown by Expression (3), thereby determining the start or stop of the demodulation operation of the received burst signal. is there.
[0022]
Referring to FIG. 2, there is shown a flowchart illustrating a flow of a process of the carrier detection method according to the present embodiment.
[0023]
In step 100, a communication line between a terminal and a base station is established. At the time of line establishment, it is assumed that the initial values of RSSI_sta and Th_win in Expression (3) are set.
[0024]
In step 101, a terminal measures RSSI. In step 102, it is determined whether the RSSI satisfies the conditional expression (1). When the RSSI satisfies the conditional expression (1), it is determined in step 103 that a carrier has been detected, and the RSSI measured in step 101 is held. When the RSSI does not satisfy the conditional expression (1), it is determined that the carrier is not detected, and the process returns to step 101.
[0025]
In step 130, the terminal makes a condition determination of equation (3). If the RSSI held in step 101 satisfies the condition of expression (3), the demodulation operation is started in step 120. If the condition of expression (3) is not satisfied, the demodulation operation is stopped in step 121. Return to 101.
[0026]
After step 120, in step 104, it is determined from the terminal identification information of the burst signal obtained by demodulation whether or not the received burst signal is transmitted from the base station to which the terminal belongs. If it is determined in step 104 that the received burst signal is not transmitted from the base station to which the terminal belongs, the demodulation operation is stopped in step 123 and the process returns to step 101. If it is determined in step 104 that the received burst signal is transmitted from the base station to which the terminal belongs, in step 105, RSSI_sta in equation (3) is updated using the RSSI held in step 103.
[0027]
In the setting of the RSSI_sta in step 105, for example, the past RSSI_sta may be weighted and averaged by a weighting filter having a transfer function as shown in the following equation to improve the setting accuracy of the RSSI_sta.
[0028]
RSSI_sta. avg (n) = W × RSSI_sta. avg (n-1) + (1-W) × RSSI_sta (n) (5).
[0029]
Here, RSSI_sta. avg (n) and RSSI_sta (n) represent the output and input of the weighting filter at time n, respectively. W is a weighting coefficient in the range of 0 to 1. When the weighting filter represented by the equation (5) is used, RSSI_sta. avg (n) corresponds to RSSI_sta in Expression (3) at time n.
[0030]
After step 105, it is determined in step 106 whether or not the broadcast information burst signal transmitted from the base station at regular time intervals has been received with a high probability. If the signal has been received with a certain probability or more in Step 106, the value of Th_win in Expression (3) is reduced in Step 107. If the signal has not been received with a certain probability or more, the value of Th_win in Expression (3) is calculated in Step 108. Enlarge.
[0031]
After the processing in step 107 or step 108 is completed, the process returns to step 101. The process shown in FIG. 2 is performed until the terminal releases the line establishment.
[0032]
Next, the configuration of a terminal that implements the carrier detection method of the present embodiment will be described.
[0033]
FIG. 3 shows a configuration of a receiving unit of the terminal according to the present embodiment. The terminal extracts a signal of a band used by the terminal for communication with the reception filter 300 from the signal (reception signal) received by the antenna. The RSSI measurement section 301 receives the output of the reception filter 300 and calculates a reception signal level (RSSI). The carrier detection unit A302 determines whether or not the condition of Expression (1) is satisfied with respect to the RSSI calculated by the RSSI measurement unit 301. If the condition of Expression (1) is satisfied, the measurement is performed by the RSSI measurement unit 301. The received RSSI is notified to the RSSI_sta calculating section 304, and the demodulation section 303 is notified of the start of the demodulation operation. On the other hand, when the condition of Expression (1) is not satisfied in the carrier detection unit A302, the stop of the demodulation operation is notified to the demodulation unit 303. The demodulation unit 303 performs data demodulation of the received signal.
[0034]
Based on the base station information demodulated by demodulation section 303, base station information identification section 305 determines whether or not the base station that transmitted the signal received by the terminal is the base station to which the terminal belongs. In the base station information identification unit 305, if the base station that has transmitted the signal received by the terminal is a base station to which the terminal belongs, the base station that has transmitted the signal received by the terminal to the RSSI_sta calculation unit 304 is If it is not the base station to which the terminal belongs, it notifies the demodulation section 303 of the stop of the demodulation operation. In the RSSI_sta calculating section 304, when receiving from the base station information identifying section 305 that the base station that has transmitted the signal received by the terminal is the base station to which the terminal belongs, the RSSI measurement used in the carrier detecting section A 302 is performed. Using the RSSI in the unit 301, the RSSI_sta in the equation (3) is calculated / updated.
[0035]
Window setting section 306 receives, from base station information identifying section 305, the reception notification of the broadcast information burst signal transmitted from the base station to which the terminal belongs, and uses the information to set Th_win indicated by equation (3). At the same time, the RSSI_sta value is received from the RSSI_sta calculation unit 304, and an RSSI range represented by Expression (3) is set.
[0036]
The carrier detection unit B307 receives the RSSI measurement value from the RSSI measurement unit 301, and determines whether the RSSI measurement value satisfies Expression (3). When the measured value of the RSSI received from the RSSI measuring unit 301 satisfies the expression (3), the carrier detection unit B307 notifies the demodulation unit 303 of the start of the demodulation operation, and when the measured value of the RSSI does not satisfy the expression (3), The demodulation unit 303 is notified of the stop of the demodulation operation.
[0037]
The essential part of the present embodiment is to determine the start or stop of the demodulation operation of the received burst signal by setting the RSSI range shown in Expression (3).
[0038]
Next, the operation of the present embodiment will be described with reference to FIG.
[0039]
FIG. 4 shows a general relationship between a logarithmic value (Log display) of a distance R between a terminal and a base station to which the terminal belongs and RSSI. FIG. 4 shows that the relationship between the distance R between the terminal and the base station and the RSSI correspond one-to-one, and the RSSI decreases as the distance R between the terminal and the base station increases.
[0040]
As an example, consider the case where Log (R) = Rx, and let the RSSI at this time be RSSI_x. In this case, it can be said that as the error between the RSSI and the RSSI_x actually received by the terminal (error Er in FIG. 4) increases, the possibility that the signal is not a signal received from the base station increases. This translates into a higher probability that the measured RSSI is receiving an interference signal coming from a source other than the base station to which the terminal belongs. Since the interference signal is a communication interference signal for the terminal, the terminal receiving the interference signal is forced to perform an unnecessary demodulation operation. Therefore, if the probability that the terminal receives the interference signal increases, the probability that the terminal performs an unnecessary demodulation operation increases.
[0041]
In the present embodiment, the above RSSI_x is estimated by calculating the RSSI_sta in the equation (3), and the allowable error is set by Th_win in the equation (3). Has the effect of reducing the probability of causing the terminal to perform unnecessary demodulation operations as described above by stopping the demodulation operations. In addition, by averaging the RSSI_sta setting in Equation (3) adaptively based on past information, the accuracy of estimating RSSI_sta is improved, and the probability of causing the terminal to perform unnecessary demodulation operation is further reduced. There is. Also, by making Th_win in the equation (3) adaptively variable according to the reception success probability of the broadcast information burst signal, if the probability of receiving the received signal from the base station is high, the equation (3) The reception probability of interference power is reduced by narrowing the RSSI range in the above equation, and when the probability of receiving a reception signal from the base station is low, the RSSI range in the equation (3) is expanded to obtain the reception signal from the base station. Has the effect of reducing the probability of not receiving, and improving communication efficiency. Also, adaptively controlling RSSI_sta and Th_win in equation (3) has the effect of enabling control independent of a propagation model between a terminal and a base station belonging to the terminal.
[0042]
【The invention's effect】
As described above, according to the present invention, the probability of reducing unnecessary demodulation operation when a terminal receives an interference signal, as compared with the carrier detection method using only equation (1) in the related art, is reduced. Since it can be increased, there is an effect of reducing power consumption of the terminal and improving communication efficiency. Also, by adaptively controlling RSSI_sta and Th_win in equation (3), autonomous control that does not depend on the propagation model between the terminal and the base station to which the terminal belongs becomes possible, so the set values of RSSI_sta and Th_win Has the effect of reducing the number of man-hours for the optimum design of the set value as compared with the case where is fixed.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a burst signal transmission system according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating a flow of a process of a carrier detection method according to the embodiment.
FIG. 3 is a diagram illustrating a receiver configuration of a terminal according to the present embodiment.
FIG. 4 shows a general relationship between a logarithmic value (Log) of a distance R between a terminal and a base station to which the terminal belongs and RSSI.
[Explanation of symbols]
Reference Signs List 10 base station 20, 21 terminal 30 cell 40, 41 individual information burst signal 50 broadcast information burst signal 60, 61 interference signal 101-123 step 300 reception filter 301 RSSI measurement section 302 carrier detection section A
303 Demodulation unit 304 RSSI_sta calculation unit 305 Base station information detection unit 306 Window setting unit 307 Carrier detection unit B

Claims (4)

When a received signal having a magnitude exceeding a predetermined threshold is detected, in a carrier detection method in which demodulation of the received signal is started,
If the magnitude of the received signal is not within a predetermined range, the demodulation is stopped. The method according to claim 1, wherein the magnitude and the arrival probability of the received signal for which the demodulation has not been stopped are reflected in the determination of the predetermined range. Upon detecting a received signal having a magnitude exceeding a predetermined threshold, in a terminal device having means for starting demodulation of the received signal,
The terminal device further comprising means for stopping the demodulation when the magnitude of the received signal is not within a predetermined range. The terminal device according to claim 3, further comprising: means for reflecting a magnitude and an arrival probability of a received signal for which demodulation has not been stopped in determining the predetermined range.

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