The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An ever-increasing number of relatively inexpensive, low power wireless data communication services, networks and devices have been made available over the past number of years, promising near wire speed transmission and reliability. Various wireless technology is described in detail in the 802 IEEE Standards, including for example, the IEEE Standard 802.11a (1999) and its updates and amendments, the IEEE Standard 802.11n, and the IEEE draft standards 802.15.3, and 802.15.3c now in the process of being finalized, all of which are collectively incorporated herein fully by reference.
As one example, a type of a wireless network known as a wireless personal area network (WPAN) involves the interconnection of devices that are typically, but not necessarily, physically located closer together than wireless local area networks (WLANs) such as WLANs that conform to the IEEE Standard 802.11a or the IEEE Standard 802.11n. Recently, the interest and demand for particularly high data rates (e.g., in excess of 1 Gbps) in such networks has significantly increased. One approach to realizing high data rates in a WPAN is to use hundreds of MHz, or even several GHz, of bandwidth. For example, the unlicensed 60 GHz band provides one such possible range of operation.
In general, antennas and, accordingly, associated effective wireless channels are highly directional at frequencies near or above 60 GHz. As a result, the distance separating a pair of communicating devices has a significant impact on the data rate that the pair of communication devices can support. Further, when multiple antennas are available at one or both communicating devices, an efficient beam pattern allows the devices to better exploit spatial selectivity of the wireless channel and, accordingly, increase the data rate at which the devices communicate. Generally speaking, beamforming or beamsteering creates a spatial gain pattern having one or more high gain lobes or beams (as compared to the gain obtained by an omni-directional antenna) in one or more particular directions, with reduced the gain in other directions. If the gain pattern for multiple transmit antennas, for example, is configured to produce a high gain lobe in the direction of a receiver, better transmission reliability can be obtained over that obtained with an omni-directional transmission.
In general, communication devices develop an efficient beam pattern through an exchange of information such as beamforming training data (one such technique is described in U.S. patent application Ser. No. 12/548,393, filed on Aug. 26, 2009 and entitled “Beamforming by Sector Sweeping,” and U.S. Provisional Patent Application No. 61/091,914 entitled “Beamforming by Sector Sweeping,” filed Aug. 26, 2008, both of which are expressly incorporated by reference herein in their entireties). However, when a device attempts to discover other devices active on a communication channel, a beamforming pattern is not yet available. As a result, a communication device scans the channel in an omni-directional mode, and generally does not detect all activity occurring on the communication channel.
Activity occurring on a communication channel can include data transmissions such as broadcasts of beacons by a piconet central point (PCP), for example. On the other hand, activity can also include interference from such sources as adjacent stations in the same Basic Service Set (BSS) or a different BSS, other systems operating in the same frequency range (e.g., 60 GHz), radar pulses, etc. Some interference sources may be highly directional, especially at frequencies near or above 60 GHz.