JP2005328231A - Wireless terminal device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless terminal device capable of stably reducing power consumption by suppressing the strength of transmitting power to low and proper strength with high stability and flexibility. <P>SOLUTION: The wireless terminal device is provided with a distance estimator 303 which estimates a distance in-between an access point AP1 on the basis of the radio field intensity of a beacon signal received from the access point AP1, a transmitting power determining part 305 for determining the strength of the transmitting power of a wireless signal on the basis of the estimated distance, and a transmitting power control unit 307 for gradually increasing the strength of the determined transmitting power from a low level. The transmitting power control unit 307 detects the strength of the transmitting power at the time of receiving a signal which shows the completion of link establishment from the access point AP1 when a wireless LAN is established, and makes the wireless terminal device to execute data communication by using the strength of the transmitting power. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless terminal device having a configuration for reducing power consumption by suppressing transmission power of a wireless signal to a low level for a station terminal (wireless terminal device) that establishes a wireless LAN via an access point.

  For example, a wireless LAN device defined in IEEE 802.11 has an infrastructure mode for communicating between station terminals via an access point such as a router and an ad hoc mode for directly communicating between station terminals.

  Generally, when constructing a wireless LAN environment, the infrastructure mode is often used. In data transmission / reception via the access point, data communication is performed after establishing a link between the station terminal and the access point. The link establishment referred to here includes authentication and association.

  An area composed of a plurality of or a single station terminal in one access point is called a BSS (Basic Service Set). When establishing a link for one BSS, a station terminal generally attempts to connect to an access point with maximum transmission power. This is to make it easy for the access point to pick up the radio wave by any station terminal emitting a strong radio wave.

  However, radio wave transmission at the maximum level is not always desirable in terms of reducing power consumption of the station terminal, and it is desirable that radio waves can be transmitted with the minimum necessary.

  As a conventional example, for example, the master station transmits a signal with a predetermined transmission power, and the slave station detects the electric field strength of the signal received from the master station. If the electric field strength is high, the transmission power is reduced. On the other hand, a TDD wireless communication system that increases transmission power when the transmission power is small is known (see, for example, Patent Document 1).

  For example, a router connected to the LAN via a wireless link stores a table indicating the MAN topology, receives information indicating the quality of the wireless link and the traffic load of the network, and based on the information. There is known a so-called wireless MAN network device that optimizes a transmission method and a transmission path, thereby efficiently using cost, power, and bandwidth (see, for example, Patent Document 2).

JP 2000-261392 A Special table 2001-520480 gazette

  The former conventional example describes that transmission power is controlled while determining the strength of the received signal from the master station and the data error rate, but according to this method, it changes dynamically according to the received signal strength. Therefore, for example, when radio wave interference such as fading occurs, it is not always possible to control to the optimum transmission power, and there is a problem in stability.

  The latter conventional example has a feature that the transmission data is switched using means for determining the received signal quality. However, the configuration is insufficient from the viewpoint of flexibly responding to the degree of signal quality. There is a problem of lack of flexibility.

  The present invention solves the above-mentioned problems, and when building a wireless LAN, the strength of the transmission power is kept low to an appropriate strength with high stability and flexibility, thereby stably reducing power consumption. It is an object of the present invention to provide a wireless terminal device that can be used.

  In order to achieve the above object, the present invention provides a distance estimation unit that estimates a distance from an access point based on the radio field intensity of a beacon signal received from the access point, and a wireless communication based on the distance estimated by the distance estimation unit. A transmission power determination unit that determines the strength of the transmission power of the signal, and a transmission power control unit that gradually increases the transmission power strength determined by the transmission power determination unit from a low level, Detecting the strength of the transmission power at the time when a signal indicating completion of link establishment is received from the access point when establishing a wireless LAN, and thereafter performing data communication using the strength of the transmission power. Features.

  The transmission power determining unit sets an intensity of a level that is lower by a predetermined value than the intensity of the transmission power corresponding to the distance estimated by the distance estimating unit, and the transmission power control unit includes: The strength of the transmission power is gradually increased from the value of the transmission power strength that is lower by the set predetermined value.

  The transmission power control unit performs data communication using a transmission power intensity that gives a predetermined margin (that is, a predetermined enhancement) in the transmission power intensity set by the completion of the link establishment. To do.

According to the present invention, the wireless terminal device that constructs the wireless LAN does not need to increase the strength (level) of transmission power more than necessary based on the reception level determined in establishing the wireless link with the access point. A wireless LAN environment can be constructed with power consumption.
Furthermore, when a predetermined margin is provided for the intensity (level) of transmission power, data communication becomes more stable, so a wireless LAN environment with high performance and low power consumption can be constructed.
The wireless LAN environment configured as described above has low power consumption and is very advantageous in terms of cost as compared with a wireless terminal device that transmits a wireless signal at a conventional fixed level.
In particular, wireless link establishment can be started with a setting farther than the estimated distance (low level setting), and link establishment with an access point can be performed with lower transmission power. .

  Hereinafter, a radio terminal apparatus according to an embodiment of the present invention will be described with reference to FIG. 1 to FIG. FIG. 1 is a block diagram showing a schematic configuration of the main points (wireless signal transmission / reception system) of the wireless terminal device 11 of the present embodiment.

  As shown in FIGS. 3 and 4, the wireless terminal device 11 includes, for example, station terminals STA1 and STA2 such as a personal computer equipped with a wireless signal transmission / reception system, as well as an audiovisual device equipped with a wireless signal transmission / reception system. Any terminal device such as an air-conditioning device, cooking-related device, or hot-water supply device is included.

(Specific example of configuration)
As the wireless terminal device 11, for example, station terminals STA1 and STA2 switch two antennas 101 and 102 and connections between the antennas 101 and 102 and an RF (Radio Frequency) 13 as shown in FIG. Two switches 103 and 104 are provided. The baseband processing circuit 115 controls the switching of the switches 103 and 104, for example. One switch 103 is switched to select one of the antennas 101 and 102 which has a better radio signal reception state, and one switch 104 is switched to a radio signal reception system in the RF 13, Alternatively, there is any switching of switching to a radio signal transmission system.

  First, the RF 13 receiving system includes a low-noise amplifier 105 that amplifies a radio signal (beacon signal) from an access point (see FIG. 3 and FIG. 4: a router that constructs a wireless LAN, for example) AP1, a radio signal, and a predetermined signal. A baseband signal is generated by mixing (for example, 1 / 2.cos (α ± β)) with an oscillation signal from a VCO (not shown: oscillator) of. A mixer 106, a bandpass filter 107 that filters the baseband signal, a variable amplifier 109 that variably amplifies the baseband signal, a mixer 110 that mixes the amplified baseband signal and an oscillation signal from a predetermined VCO, Bandpass filter 111 for filtering the baseband signal after mixing, and the baseband signal after filtering ADC (A / D converter) 113 that performs A / D conversion on the signal and outputs the converted signal to the baseband processing circuit 115. The baseband processing circuit 115 that has received the filtered baseband signal performs predetermined signal processing not closely related to the technical idea of the present invention, and the operation of the station terminals STA1 and STA2. Preprocessing (for example, including conversion into a predetermined bit string) or the like is also performed.

  Second, the RF 13 receiving system performs A / D conversion on the DET (detector) 108 that detects the signal strength of the baseband signal filtered by the bandpass filter 107, that is, the voltage value, and the detected voltage value. An ADC (A / D converter) 112 that outputs to the baseband processing circuit 115. The baseband processing circuit 115 that has acquired the voltage value of the baseband signal performs processing according to the technical idea of the present invention as shown in detail in FIG. 2 and described later.

  The RF 13 transmission system includes a DAC (D / A converter) 207 for D / A converting a predetermined output signal based on the intensity of transmission power set by the baseband processing circuit 115, and filtering the output signal after digital conversion. A band-pass filter 206 to perform, and a mixer 205 that mixes an output signal and an oscillation signal from a predetermined VCO (for example, 1/2 · cos (α ± β) is processed; α: output signal, β: oscillation signal) , A variable amplifier 204 that variably amplifies the output signal after mixing in accordance with processing to be described later of the baseband processing circuit 115, a bandpass filter 203 that filters the output signal after amplification, and amplifies the output signal after filtering And a low-noise amplifier 201 that transmits from the antenna 101 and the like via the switches 103 and 104.

  On the other hand, as shown in FIG. 2, the baseband processing circuit 115 determines the signal strength of the baseband signal detected by the DET 108 of RF13, that is, the electric field strength of the radio signal (beacon signal) received from the analog amount of the signal voltage value. Based on the value of the distance between the estimated access point AP1, the distance estimation unit 303 that estimates the distance to the access point AP1 based on the field strength of the determined radio signal, and the estimated access point AP1. A transmission power determining unit 305 that determines the strength of the transmission power of the radio signal, and the transmission system of the RF 13 in order to gradually increase the determined transmission power strength, for example, from a slightly lower level to a higher level. And a transmission power control unit 307 that controls the variable amplifier 204. These may be configured by hardware or may be configured by software. These operation timings are controlled by, for example, a CPU (not shown: central processing unit).

  That is, when the transmission power control unit 307 establishes a wireless LAN link by interactively transmitting and receiving wireless signals between the station terminal STA1 and the like and the access point AP1, a signal indicating completion of link establishment from the access point AP1. The strength of the transmission power at the time of receiving a response (eg, a response signal indicating response or an acknowledge signal) is detected, and thereafter, basically, data communication for relaying the access point AP1 using the strength of the transmission power is performed. Let RF13 do it. However, in this example, as described above, the transmission power control unit 307 should increase the intensity of the transmission power determined by the transmission power determination unit 305 from, for example, a low level slightly lower than the intensity to a gradually higher level. The variable amplifier 204 is controlled. When the intensity of transmission power is gradually increased to a high level, there is a mode in which the level is maintained at the time when link establishment is completed, and thereafter boosting is not performed.

  On the other hand, the transmission power control unit 307 controls the variable amplifier 204 in accordance with the timing of outputting a predetermined output signal to the RF 13 transmission system by driving other circuit systems of the baseband processing circuit 115. is there. Note that after the link establishment is completed, the electric field strength determination unit 301, the distance estimation unit 303, and the transmission power determination unit 305 may be maintained in an inoperative state.

  On the other hand, the transmission power determination unit 305 sets a strength that is lower than the transmission power strength corresponding to the distance estimated by the distance estimation unit 303 by a predetermined value, and the transmission power control unit 307 transmits the transmission power determination unit 305. A mode (mode 2) in which the variable amplifier 204 is controlled so as to gradually increase the strength of the transmission power from the value of the transmission power level that is lower by the predetermined value set by the above. Also in this case, there is a mode in which the increase in transmission power is stopped when link establishment is completed.

  The transmission power control unit 307 is a variable amplifier that performs data communication using the transmission power intensity that gives a predetermined margin (that is, a predetermined enhancement) in the transmission power intensity set upon completion of link establishment. A mode in which 204 is controlled is also preferable. Needless to say, this control mode may be applied to the above-described mode 2.

(Specific example of operation)
In the wireless LAN device, first, in order for the station terminal STA1 and the like to link to a BSS (basic service set) of a certain access point AP1, it is necessary to detect a beacon signal periodically transmitted from the access point AP1. The beacon signal is a signal that serves as a reference for performing ID detection, authentication, and the like within the BSS at the same time as the presence of the access point AP1 is notified to the station terminal STA1 and the like. The station terminal STA1 or the like that has received the beacon signal transmits a radio signal for establishing a link such as authentication and association to the nearby access point AP1 from the received beacon signal and data.

  For example, a PA (not shown: Power Amplifier) such as a station terminal STA1 amplifies an output signal at the time of transmission to such an extent that it is not distorted and sends it to the end of the antenna 101 or the like. PA is generally composed of a semiconductor element using a compound such as GaAs or InGaP, but its efficiency is not always good, and PA alone requires power consumption of about 0.5 W to 2 W. In order to keep the power consumption of the PA low, the PA bias signal may be lowered. This means that the transmission power from the end of the antenna 101 or the like is reduced, and this is equivalent to a narrow range of radio waves.

  Thus, if the power consumption of the PA can be kept low without degrading the connection performance, for example, most of the power consumption of the entire system such as the station terminal STA1 can be kept low. If it is known in advance that a necessary minimum signal can be transmitted to the transmission partner, there is no problem, but it is impossible in practice. Therefore, power consumption can be kept low unless the transmission power of the transmission signal is unnecessarily increased as estimated from the signal strength at the time of establishing the radio link. In particular, when the station terminal STA1 or the like is placed in the immediate vicinity of the access point AP1, it is possible to access even if the transmission power is reduced, and it is possible to reduce the low power consumption.

  As shown in FIG. 3, when the station terminal STA1 or the like is to be activated in the vicinity of a certain access point AP1, the station terminal STA1 enters the reception mode and determines whether or not it is within a range where radio waves reach from the access point AP1. In the case of this figure, since the station terminal STA1 can detect a beacon signal from the access point AP1, it tries to establish a radio link with the access point AP1. At this time, the electric field strength determination unit 301 of the station terminal STA1 measures the radio field strength (or electric field strength) from the beacon signal received from the access point AP1. The measurement of the radio wave intensity may be performed with a training signal included in the transmission signal. For example, in IEEE802.11a, if a long training signal of a preamble signal is used, all subchannels of OFDM are transmitted, so that power detection can be performed with higher accuracy.

  The distance estimation unit 803 estimates the distance to the access point AP1 using the measurement result of the electric field strength and distance measurement means such as a correspondence table (table) that can estimate the distance prepared in advance. From this estimation result, in order to establish a radio link this time, a signal is transmitted from the baseband processing circuit 115 of the station terminal STA1. At this time, since the distance to the access point AP1 can be estimated to some extent, the transmission power level of the station terminal STA1 can be controlled to some extent. That is, if the access point AP1 and the station terminal STA1 are close, weak transmission power is sufficient, and if the estimated distance is long, the transmission power is set to be strong corresponding to the distance.

  However, since the estimated distance may not always be correct, the transmission power control unit 307 attempts to establish a link with the access point AP1 while gradually increasing the transmission power from a certain low level. When the transmission level is increased to some extent, link establishment with the access point AP1 is completed, and data communication between the access point AP1 and the station terminal STA1 becomes possible.

  At this time, the transmission power transmitted by the station terminal STA1 and the like can be recognized by the access point AP1, but as shown in FIG. 4, the radio signal of the station terminal STA2 may not reach the station terminal STA1 directly (hidden). Terminal problem). This problem is likely to occur particularly when the transmission voltage of the station terminal STA2 is set to a low level. However, in the access using the access point AP1, if only the access point AP1 can recognize the station terminal STA1, there is no problem in transmission / reception, and this can be solved by the RTS / CTS control according to the IEEE 802.11 standard. .

  Next, an example of the operation of the baseband processing circuit 115 will be described with reference to the flowchart shown in FIG. First, when the station terminal STA1 is activated in step 501, it is determined in step 502 whether or not a beacon signal from the access point AP1 is detected. When a beacon signal is detected, the electric field strength determination unit 301 is activated in step 503 and the electric field strength is measured. Subsequently, in step 504, the distance measuring unit 303 is activated, and the distance to the access point AP1 is estimated from the electric field strength value. In step 505, the transmission power determination unit 305 is activated to determine the initial transmission power of the transmission signal.

  In step 506, the baseband processing circuit 115 sends a radio link establishment signal to the RF 13 transmission system. If this signal reaches the access point AP1 with the initial transmission power, the access point AP1 responds. Should return. Therefore, in step 507, it is determined whether or not there is a wireless link establishment response from the access point AP1. If it is determined here that there is no response for establishing a radio link (No), a predetermined increase value is added to the initial transmission power in step 508, and the transmission power (transmission power slightly higher than the initial transmission power) is present. Send a signal. In other words, here, it is assumed that the response to the establishment of the radio link has not arrived, and the transmission signal is transmitted waiting for the next radio link establishment signal transmission timing. In step 509, it is determined again whether there is a response to the establishment of a radio link from the access point AP1.

  Thus, if it is determined in step 509 that there is a wireless link establishment response from the access point AP1 (Yes), the process proceeds to step 506 and the above-described processing is repeated. In this way, the processing from step 506 to step 509 is repeated until there is a response from the access point AP1. If it is determined in step 507 that there is a response to establishment of a radio link from the access point AP1 (Yes), the transmission power determination unit 305 and the transmission power control unit 307 are activated in step 510 to determine the transmission power level. And after transmitting the radio signal of this transmission power, it transfers to the data communication process with the transmission power. That is, data communication is started using the strength (level) of transmission power when there is a response from the access point AP1.

  In the present embodiment, when establishing a wireless LAN, the transmission power control unit 307 basically performs data communication using the intensity of transmission power at the time when a signal indicating link establishment completion is received from the access point AP1. Therefore, it is possible to suppress the transmission power intensity to an appropriate intensity with high stability and flexibility, thereby stably reducing power consumption.

  Further, in one aspect, the transmission power determining unit 305 sets a strength that is a level lower by a predetermined value than the strength of the transmission power corresponding to the distance to the access point AP1 estimated by the distance estimating unit 303, and Since the transmission power control unit 307 gradually increases the transmission power intensity from the transmission power intensity level that is lower by the predetermined value set by the transmission power determination unit 305, the transmission power control unit 307 realizes a lower transmission power level. In this case, there is an advantage that stability is further increased and flexibility is further improved.

  Also, in one aspect, the transmission power control unit 307 sets the transmission power that gives a predetermined margin (that is, a predetermined enhancement) in the intensity of the transmission power set by the completion of link establishment with the access point AP1. Since the data communication is performed using the strength, there is an advantage in that the stability is further increased and the flexibility is further improved in realizing the low transmission power level.

It is a block diagram which shows the structure of the principal point of the radio | wireless terminal apparatus which concerns on one embodiment of this invention. It is a block diagram which shows the structure of the principal point of the baseband processing circuit in the radio | wireless terminal apparatus which concerns on one embodiment. It is explanatory drawing explaining an example at the time of building wireless LAN with the radio | wireless terminal apparatus which concerns on one embodiment. It is explanatory drawing explaining another example at the time of constructing | assembling wireless LAN with the wireless terminal device which concerns on one Embodiment. It is a flowchart which shows the operation example of the radio | wireless terminal apparatus which concerns on one embodiment.

Explanation of symbols

AP1 access point 11 wireless terminal device STA1, STA2 station terminal 13 RF (high frequency circuit)
101, 102 Antenna 103, 104 Switch 105, 201 Low noise amplifier 106, 110, 202, 205 Mixer 107, 111, 203, 206 Bandpass filter 109, 204 Variable amplifier 108 DET (detector)
112,113 ADC (A / D converter)
115 Baseband processing circuit 207 DAC (D / A converter)
301 Field strength determination unit 303 Distance estimation unit 305 Transmission power determination unit 307 Transmission power control unit

Claims (3)

A distance estimation unit that estimates the distance to the access point based on the radio field intensity of the beacon signal received from the access point;
A transmission power determination unit that determines the strength of the transmission power of the radio signal based on the distance estimated by the distance estimation unit;
A transmission power control unit that gradually increases the strength of the transmission power determined by the transmission power determination unit from a low level,
The transmission power control unit detects the strength of the transmission power at the time of receiving a signal indicating completion of link establishment from the access point when establishing a wireless LAN link, and thereafter uses the strength of the transmission power. A wireless terminal device for performing data communication. The transmission power determination unit sets a strength of a level that is lower by a predetermined value than the strength of transmission power corresponding to the distance estimated by the distance estimation unit,
2. The transmission power control unit according to claim 1, wherein the transmission power control unit gradually increases the transmission power intensity from a transmission power intensity level that is lower by the predetermined value set by the transmission power determination unit. Wireless terminal device. The transmission power control unit performs data communication using a transmission power intensity that gives a predetermined margin (that is, a predetermined enhancement) in the transmission power intensity set by the completion of the link establishment. The wireless terminal device according to claim 1 or 2.

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