Background of invention WLAN is gaining popularity in many electronic based applications. Any user equipped with a WLAN device or card is able to access information wirelessly within a radius of up to 100m from the WLAN base station. As more WLAN networks are being deployed, there is a need to find out whether a particular location has WLAN coverage. Currently, the WLAN network either occupies the 2.45 GHz band for 802. 1 b/g standard or 5. 8 GHz for 802. 1 la standard. Existing WLAN detecting device are readily available. An example of such a WLAN detecting device can be assembled using a WLAN card, proprietary software and computer (e. g. Personal Digital Assistant or notebook). The WLAN detecting device can decode the WLAN data using the high processing power of the computer and thus is able to give detailed information on the detected WLAN network. However, device of this nature takes time to start up. Furthermore, it consumes large amount of power due to the high processing means.

Therefore, there is clearly a need for an effective WLAN detecting device that can gives instant result and consumes little battery power. The WLAN detecting device can also be incorporated with a Universal Serial Bus (USB) memory to provide a two- in-one device.

Summary of Invention A WLAN detector that makes use of envelope detection technique is disclosed. The WLAN detector extracts the transmission pulse widths (instead of decoding the data) of a received signal. By using a micro-processor, this method can differentiate WLAN signal from non-WLAN signal operating in the same frequency band. In a first aspect of the invention, a WLAN detector which continuously detects WLAN signals is disclosed. In a second aspect of the invention, a power saving WLAN detector which intermittently detects WLAN signals is disclosed. In a third aspect of the invention, an affordable WLAN detector without requiring a dedicated microprocessor is disclosed.

In a fourth aspect of the invention, the WLAN detector can be incorporated with USB memory to provide a two-in-one device.

Brief Description of the Drawing Figure 1 shows a block diagram of the WLAN detector that detects WLAN signal operating in a continuous detecting mode according to an embodiment of the invention.

Figure 2 shows a block diagram of the WLAN detector that detects WLAN signal operating in a intermittent detecting mode according to an embodiment of the invention.

Figure 3 shows a block diagram of the WLAN detector that detects WLAN signal and non-WLAN signal in continuous detecting mode according to an embodiment of the invention Figure 4 shows a block diagram of WLAN detector incorporated with USB memory according to an embodiment of the invention.

Figure 5 shows the transmission pulse widths of various transmission devices which are extracted by an envelop detector according to an embodiment of the invention.

Detailed Description of Invention A simple WLAN detector according to embodiments of the invention is proposed.

Consider the case of a WLAN detector detecting for 802.11 b/g network operating in the 2.45 GHz frequency spectrum or band. A typical WLAN Access Point (AP) or base station will sends out WLAN signal in pulse mode using modulation scheme such as Differtial Binary Phase Shift Key (DBPSK) or Quadrature Phase Shift Key (QPSK) or Quadrature Amplitude Modulation (QAM). The conventional WLAN detector needs to decode the WLAN data depending on the modulation scheme used and thus consumes more battery power as it involves 2 way communication and needs more processing power for data decoding. The proposed WLAN detector is a receiver that comprises of an envelope detector which extracts the pulse transmission width of the WLAN signal instead of decoding the actual data. The"peak to peak voltage"of the extracted pulse is a measure of signal strength while the"pulse width"is used to determine if the detected signal is from a WLAN Access Point (AP), microwave oven, bluetooth device or cordless phone. This is possible because these devices have different pulse data transmissions width and/or beacons characteristics. It is noted that high computing power is not needed to decode the actual WLAN data and transmitting power is not needed to communicate with the WLAN base station. As a result, the WLAN detector of the invention is an intelligent receiver which gives instant result and consumes much less power than existing devices in the market.

Embodiments of the invention are described hereinafter with reference to the respective figures 1-5.

Figure 1 shows a block diagram of the WLAN detector 100 that detects WLAN signal in the operating frequency band according to a first embodiment of the invention. When the switch 118 is turned on, the battery 116 will supply voltage Vb continuously to the amplifier 106 and comparator circuit) ! 0 and the microprocessor 114. Antenna 102 and Filter 104 will pick up the radio wave in the desired operating band. The Antenna 102 can be directional or omni directional depending on the applications. The received radio wave is subsequently amplified by amplifier 106.

An Envelop Detector 108 which preferably comprises of a radio frequency diode and capacitor (both not shown) extracts the transmission pulse width of the received signal. As shown in Figure 5, if the radio wave is a continuous frequency, the extracted pulse is a DC line as shown in graph 502. If the radio wave is that from a microwave oven, the extracted pulse width is about 10 ms as shown in graph 504. If it is a WLAN beacon from an Access Point (AP), the extracted pulse is tbeacon as shown in graph 506. (Note: As defined in the MAC layer of 802.11 standards, tbeacon is bounded by tmin<tbeacon<tmax. For example, tbeacon may range from 84 us to <BR> <BR> 470 us. ) The extracted pulse is then fed into the comparator circuit 110 to determine the signal strength of the radio wave. The output of the comparator with the lowest reference voltage V I will be fed into Microprocessor 114 (Note: V4>V3>V2>V1).

By analysing the pulse width, the Microprocessor 114 will know if the extracted pulse originates from a WLAN signal. Microprocessor 114 will supply power Vs to the light Indicators 112 only if the pulse width originates from a WLAN signal. In this way, the light indicators will only lights up if the radio wave is a WLAN signal. The more number of light indicators lights up, the stronger the WLAN signal. The light indicators 112 can be replaced by sound indicators or contain a combination of both.

It is noted that the microprocessor can also differentiate the WLAN signal of an Access Point (AP) from a normal station by analysing the tbeacon and tbeaconspace of the beacon.

Figure 2 shows a block diagram of the WLAN detector 200 that detects WLAN signal in the operating frequency band according to a second embodiment of the invention. When the switch 218 is turned on, the battery 216 supplies voltage Vb continuously to the Microprocessor 214. Intermittingly, Microprocessor 214 will control the supply of voltage Vc to amplifier 206 and comparator Circuit 210 (For example, Vs is supplied for 1 second for every 60 seconds.) In the event that Microprocessor 214 confirmed that the detected wave is a WLAN signal, it will continuously supply power Vc to amplifier 206 and comparator Circuit 210. At any one time, if the WLAN signal is not detected, the supply Vs to the amplifier 206 and comparator circuit 210 will be intermittingly again. WLAN detector 200 will conserve more power than WLAN detector 100.

Figure 3 shows a block diagram of the WLAN detector 300 that detects WLAN signal and non-WLAN signal in the operating frequency band according to a third embodiment of the invention. When the switch 316 is turned on, the battery 314 supplies voltage Vb continuously to an amplifier 306 and comparator Circuit 310 and Light Indicator Circuit 312. In this manner, the cost of the WLAN detector 300 is kept low as it does not need a microprocessor.

The WLAN detectors according to embodiments of the invention described in the foregoing can be considered as standalone devices that are battery operated. When the battery power is low, the battery needs to be charged or change. It gives convenience to the user if a WLAN detector is incorporated into a USB memory; so that when the battery of the detector is low, it can be automatically recharged when the USB memory is in use. All the user needs to do is to connect the WLAN detector incorporated with the USB memory to a computer via the USB connector. In a fourth embodiment of the invention, Figure 4 shows the resulting WLAN detector incorporated with USB memory 400. It has a WLAN detector 402, battery Charging Module 408 for recharging an internal rechargeable battery (not shown), a USB Connector 406 and memory module 404. The WLAN Detector 402 may be in any one of the WLAN detectors according to embodiments of the invention described in the foregoing with reference to Figure 1-3 and 5.. The 2-in-1 device can be used as a standalone device for WLAN detection, to activate it, you need to turn on the switch in the 2-in-1 device [400]. When you need to access the portable memory with the 2- in-1 device, you need to connect it to the computer via its USB connector 406. When this happens, the computer will be able to access the portable memory 404 as normal.

At the same time, the battery charging Module 408 will draw power from the external computer via its USB Connector 406 to produce a charging current. The charging current is used to charge up the internal battery of WLAN detector 400.