Method for RF output power control of a wireless communication device

The present invention discloses a method for RF output power control of a wireless communication device by switching the wireless communication device between different modes according to a state parameter corresponding to a received beacon. These modes include a normal power mode for outputting a normal RF output power and a reduced-power mode for outputting a reduced RF output power. The reduced RF output power is less than the normal RF output power.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a method for RF output power control of a wireless communication device and, more particularly, to a method for output power control by switching the wireless communication device between different modes according to a state parameter corresponding to a received beacon.

2. Description of the Prior Art

In recent years, applications in fields such as mobile communications as well as wireless local area network (WLAN) have attracted considerable attention. For wireless communication devices such as mobile phones, base stations, wireless network interface cards and access points, and so forth, it is necessary to reduce power consumption so as to prevent ageing and degradation of the components. Especially, portable wireless communication devices require batteries as power supply; therefore, it is necessary for such devices to reduce power consumption so as to prolong the battery lifetime. Moreover, in order to prevent human from absorbing the electromagnetic waves, it is required that the RF energy of the nuisance radiation from the wireless communication devices must be conserved when the devices are not operating or operating at a short distance.

In view of the power consumption, most of the power is consumed by the transmitter of wireless communication devices when the transmitter is transmitting RF signals. Accordingly, the present invention provides a method for RF output power control of a wireless communication device so as to reduce power consumption and eliminate nuisance radiation on one hand and leave the link quality of signal transmission unaffected on the other.

SUMMARY OF THE INVENTION

In view of these problems, it is the primary object of the present invention to provide a method for RF output power control of a wireless communication device by switching different modes according to a state parameter corresponding to a received beacon.

In order to achieve the foregoing object, the present invention provides a method for RF output power control of a wireless communication device, comprising steps of:

switching a wireless communication device to a normal power mode so as to output a normal RF output power;

receiving a beacon; and

switching the wireless communication device to a reduced power mode so as to output a reduced RF output power, wherein the reduced RF output power is no more than the normal RF output power.

Moreover, the wireless communication device is switched between the normal power mode and the reduced power mode according to a state parameter corresponding to the received beacon.

Other and further features, advantages and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings are incorporated in and constitute a part of this application and, together with the description, serve to explain the principles of the invention in general terms.

DETAILED DESCRIPTION OF THE INVENTION

The present invention providing a method for RF output power control of a wireless communication device can be exemplified by the preferred embodiment as described hereinafter.

Please refer toFIG. 1, which is a schematic block diagram showing four power modes of a wireless communication device in accordance with one preferred embodiment of the present invention. As shown inFIG. 1, the wireless communication device is switched from a certain power mode to another power mode. The four power modes are described hereinafter:

(1) Normal power mode—which is active at normal operation. At normal power mode, a wireless communication device outputs a normal output power, which can be a pre-determined value. In one embodiment, the normal output power is determined to be the maximum output power for the wireless communication device so that the signals output from the wireless communication device can be received by other receiving devices as faraway as possible.

(2) Scanning power mode—also referred to as “standby power mode”. At scanning power mode, a wireless communication device stops data transmitting and data receiving so that the output power is reduced to minimum to minimize power consumption. However, in order for the wireless communication device to transmit a beacon to a receiving station afar and let the receiving station be informed that the wireless communication device is still at operation, the wireless communication device has to have enough output power to transmit the beacon in each period of time. At scanning power mode, the wireless communication device outputs a scanning output power corresponding to the scanning power mode with the strength of the output power being between the maximum output power and the minimum output power of the wireless communication device. In one embodiment, the scanning output power versus time shows a pre-determined periodical function. The periodical function can be a sine function, a saw-tooth function, or even a pseudo random function.

(3) Efficiency-enhanced mode—also referred to as “semi-standby power mode”. At efficiency-enhancing mode, a wireless communication device does not transmit and receive power as frequently as the normal power mode, and thus the output power is reduced and power consumption is reduced. In one embodiment, the wireless communication device outputs a corresponding controlled output power. In order to enhance the efficiency of the output power, the controlled output power is set up according to the estimated propagation loss between the wireless communication device and a destination device. Furthermore, the controlled output power is further adjusted according to the fact whether the wireless communication device re-sends the signal.

(4) Zero-power mode. The power supply is off and thus a wireless communication device does not output any power.

The wireless communication device is switched between four modes as shown inFIG. 1. To begin with, no matter which mode the wireless communication device is at, it is switched to the zero-power mode when the power supply is turned off. The wireless communication device is switched to the normal power mode after the power is turned on.

Moreover, the wireless communication device is switched between different modes (i.e., normal power mode, scanning power mode, and efficiency-enhanced mode) according to a state parameter (such as appearing frequency, disappearing time) corresponding to a received beacon. The beacon refers to a specific signal for request and response between wireless communication devices so that one device informs the other device of its present state, thereby enabling follow-up data communication. The switching procedure is described hereinafter with reference toFIG. 1:

(1) The wireless communication device is switched between the normal power mode and the efficiency-enhanced mode according to the appearing frequency and a first pre-determined threshold of a received beacon. When the wireless communication device is at the normal power mode and the appearing frequency of a beacon is smaller than the first pre-determined threshold, it means that the working load of the wireless communication device is not heavy and the wireless communication device is then switched to the efficiency-enhanced mode. When the wireless communication device is at the efficiency-enhanced mode and the appearing frequency of the beacon is not less than the first pre-determined threshold, it indicates that the working load of the wireless communication device is heavy and the wireless communication device is then switched to the normal power mode.

(2) When the wireless communication device is at the efficiency-enhanced mode and the disappearing time of the beacon is larger than the second pre-determined threshold, it means that the working load of the wireless communication device is not heavy and the wireless communication device is then switched to the normal power mode. When the wireless communication device is at the scanning power mode and a new beacon is received, it indicates that the wireless communication device is going to perform data communication and the wireless communication device is then switched to the normal power mode. In another embodiment, the wireless communication device can also be switched to the efficiency-enhanced mode.

Hereinafter, the controlled output power of the efficiency-enhanced mode is further described. As mentioned above, the controlled output power is determined according to an estimated propagation loss from the wireless communication device to a destination device. Therefore, the estimated propagation loss is taken into consideration such that the signals can be transmitted with maintained power while being unaffected by the propagation loss.

In the embodiment shown inFIG. 1, the controlled output power is obtained from an effective isotropic radiated power (EIRP) plus an estimated propagation loss minus an antenna gain, i.e.,
controlled output power=EIRP+estimated propagation loss−antenna gain  (1-1)

In 1-1, the effective isotropic radiated power is determined according to the data rate setting, multiplex type, spreading type, coding type and modulation type of the wireless communication device. The data rate setting is the most dominant factor. A table representing the relation between these factors and the EIRP can be stored in the wireless communication device for reference.

In the present embodiment, it is assumed that the channel between the wireless communication device and the destination device is time-invariant and reciprocal. Therefore, the propagation loss along the transmitting path is equal to that along the receiving path. For simplicity, the estimated propagation loss in 1-1 can be obtained from a specified propagation loss along the receiving path minus a reference propagation loss, i.e.,

In 1-2, the receive antenna gain is referred to the antenna by which the host device is receiving signals. RSS refers to measured received signal strength of the host device. The reference values (with an index ref) are determined mean values for a plurality of devices of the same type. It is noted that the effective radiated power of the destination device is assumed to be equal to the reference effective radiated power, i.e., ERP=ERPref.

Moreover, as the above-mentioned EIRP is determined, the propagation loss has been considered and thus will not be considered again when the estimated propagation loss is to be determined.

Moreover, in the embodiment shown inFIG. 1, the wireless communication device has two diversity antennae. The antenna gain in 1-1 is a gain of transmit antenna. However, since the channel is time-invariant and reciprocal, the receive antenna is used to transmit signals and the transmit antenna gain is then equal to the receive antenna gain. Therefore, the antenna gain in 1-1 can be obtained by using the gain of the receive antenna from which a higher S/N ratio is measured.

Furthermore, in the embodiment shown inFIG. 1, the wireless communication device determines and optimizes the controlled output power according to the fact whether the frame is resent. The frame is the fundamental unit of information carriage in all modern communication networks. The aforementioned beacon is one of frame types.

Please refer toFIG. 2, which is a flow chart showing a method for optimizing the controlled output power of a wireless communication device in accordance with the present invention. The method comprises steps of:

Step21: determining whether a wireless communication device has resent a frame; proceeding with Step26if yes and Step22otherwise;

Step22: determining a resend-to-send ratio of the wireless communication device;

Step23: determining whether the resend-to-send ratio is less than a threshold; proceeding with Step24if yes and Step25otherwise;

Step24: subtracting one pre-determined unit from the controlled output power and returning to Step21;

Step25: maintaining the controlled output power and returning to Step21; and

Step26: adding the pre-determined unit to the controlled output power and returning to Step21.

The wireless communication device resends a frame when the frame is not properly received by a destination device. It is not limited in the present invention what condition the wireless communication device has met before it decides to resend a frame. It may occur when the device has received a negative-acknowledgement frame, or has not received an acknowledgement frame for a period, or other conditions. When wireless communication device is determined that the frame is to be resent, the output power of the wireless communication device has to be increased so as to enhance link quality and range. Therefore, after the wireless communication device is determined to have resent the frame, the procedure goes to Step26and adds a pre-determined unit to the controlled output power. The pre-determined unit is set according to the requirement of the wireless communication device and the control resolution and coverage of power amplifier installed therein.

In Step21, if the wireless communication device is determined not to resend the frame, the procedure proceeds with Step22and Step23and the resend-to-send ratio is thus determined and compared to the threshold. The resend-to-send ratio is the times the wireless communication device resends a frame to the times the wireless communication device sends a frame, i.e., the percentage of the resent frames out of the sent frames. If the resend-to-send ratio is less than the threshold, it means that the destination device has properly received the frames and thus the controlled output power can be subtracted by a pre-determined unit so as to reduce power consumption, as described in Step24. If the resend-to-send ratio is not less than the threshold, it means that the destination device does not have received the frames properly and thus the controlled output power must be maintained, as described in Step25. The threshold is determined according to the type of the wireless communication device.