System and method for channel scanning in wireless networks

Abstract

Channel scanning for wireless networks, such as Wireless Local Area Networks (WLANs), generally provides a wireless station with the information on the available WLAN resources, such as the frequency band and the maximum transmission power. The present invention provides safe and fast domain-aware channel scanning, enabling a wireless station to comply with applicable local regulations, in spite of the possibility of domain changes, with short channel-scanning time. Fast channel scanning is accomplished by active channel scanning if valid domain information is available and there is no possibility of domain change. Also, domain-independent channels, if any, are first scanned using active scan to get domain information faster.

Description

[0001] This application claims the benefit of Provisional Application Nos. 60 / 438,964, filed Jan. 9, 2003, and 60 / 492,689, filed Aug. 5, 2003. The present application incorporates the disclosure of these provisional applications by reference.[0002] 1. Field of the Invention[0003] The present invention relates generally to wireless stations and networks, and more particularly to a method of scanning channels in a wireless network.[0004] 2. Description of the Related Art[0005] Regulatory domains, such as individual nations, independently determine the frequency band and the maximum transmission power allowed for wireless communication systems. The conditions established by each regulatory domain may vary significantly even for the same wireless communication system. For example, while the 4.9-5.0 gigahertz (GHz) band is allowed for IEEE802.11a wireless local area network (WLAN) in Japan, the 4.94-4.99 GHz band is reserved for public safety band in the United States, and thus cannot be...

AI Technical Summary

Problems solved by technology

However, if a beacon is not received for the scanned channel within a certain time limit after a wireless station starts to listen for a beacon, then the channel is determined by the wireless station to be unavailable for one of two reasons.

However, passive channel scanning is disadvantageous because it may take a long time, which can be as much as a beacon interval of the corresponding access point.

As a result, passive channel scanning may not be appropriate for channel scanning as, for example, in a handover where fast channel scanning is particularly important.

Since an active scan involves actual transmission of a probe frame, it may violate the regulations of the residing domain.

In this sense, active channel scanning is inappropriate for safe domain-aware channel scanning.

However, neither passive channel scanning nor active channel scanning can be used for both safe and fast domain-aware channel scanning.

Although the passive channel scanning is advantageous in terms of safely observing network regulations, such as maximum transmission power, it is slow, making smooth handover difficult.

Active channel scanning, although fast, cannot be used in safe domain-aware channel scanning, since it may violate the regulations of the residing domain.

For example, scanning time for wireless stations staying within a domain is still long.

Considering the number of wireless stations staying within a regulatory domain, which would be much larger than the stations crossing the regulatory domain boundary, the scanning speed cannot be sacrificed for the domain-aware roaming capability.

Further, IEEE 802.11d does not consider domain-independent channels.

IEEE 802.11d, however, does not consider domain independent channels, and passively scans domain-independent channels.

Because of the mobility of a wireless station, it is very difficult for a wireless station to predict whether upcoming access points are in the same domain.

There would be a possibility of domain change when wireless stations attempt channel scanning.

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