1. Field of the Invention
Embodiments of the present invention relate, in general, to beamforming and more particularly to beamforming in wireless communication networks.
2. Relevant Background
Beamforming is a signal processing technique used with one or more transmitters or receivers to control the directionality of, or sensitivity to, a radiation pattern. When receiving a signal, beamforming can increase gain in the direction of wanted signals and decrease gain in the direction of interference and noise. When transmitting a signal, beamforming can increase gain in the direction the signal is to be sent. This is done by creating beams and nulls in the radiation pattern. Beamforming can also be thought of as a spatial filter.
An ever increasing number of relatively inexpensive, low-power wireless telecommunications services, networks and devices made available over the past number of years promise near wire speed transmission and reliability. Various wireless technology of this type are described in detail in the 802 series Institute of Electrical and Electronics Engineers (IEEE) standards, its updates and amendments.
Wireless networks, such as a wireless personal area network (WPAN) and wireless local network (WLAN), involve the interconnection of devices that are not necessarily physically linked together. The interest and demand for particularly high data rates in such networks has significantly increased. One approach to realize high data rates in any WPAN/WLAN is to utilize the unlicensed 60 GHz band.
In general, antennas are highly directional at frequencies near or above 60 GHz. When multiple antennas are available at a transmitter, receiver, or both, it is therefore important to apply efficient beam patterns to the antennas to better exploit spatial selectivity of the corresponding wireless channel. Generally speaking, beamforming or beam-steering creates a spatial gain pattern having one or more high gain lobes as compared to the gain obtained by an omnidirectional antenna. If the gain pattern for multiple transmit antennas, for example, is configured to produce high gain lobe in the direction of the receiver better transmission reliability can be obtained over that which can be obtained by an omnidirectional transmission.
FIG. 1 depicts a beamformed antenna pattern as is known to one of reasonable skill in the art. As is shown, 3 wireless devices form a personl area network. A first device 110 communicates to a second device 120 through an access point 105. The first device 110 includes an omnidirectional antenna with the range as depicted 115. Similarly, the second device includes an omnidirectional antenna extending beyond the access point 105. Note that the range of the first device 115 intersects with the range of the second device 125, both of which encompass the access point 105. Thus, the antenna device 110 must be correctly directioned in order to directly communicate to the second device 120.
Also depicted in FIG. 1 is one possible pattern of beamforming, as illustrated with reference to the second device 120. By concentrating energy in one specific direction, the overall range of the omnidirectional antenna is extended by sacrificing range in different directions. Thus, as shown in FIG. 1, the range of the directional antenna 130 related to the second device 120 can extend beyond and encompass the first device 110. Also shown in FIG. 1 are two side lobes 140 which extend from the second device 120. While in this depiction only one main beam 130 and two side lobes 140 are shown, one of reasonable skill in the art will recognize that associated with the main beam 130 are an infinite number of side lobes 140, each of which have different and decreasing intensities. In between each side lobe is a region of diminished or zero transmission, which is called a null region 150. Thus, as each station can form its own directional beam, the first device 110 can directly communicate with the second device 120 without utilizing the access point 105.
One method of beamforming in a communication system includes applying different steering vectors for the antenna to generate a plurality of quality indicators. As the antenna sweeps through a plurality of sectors, quality data is collected to determine which sector produces the best transmission quality. The underlying assumptions to use this technique to identify the best beam are that the two stations are synchronized, and unfettered communication between the two stations exist. Unfortunately, these situations rarely occur. When beamforming occurs between two stations in a wireless area network that are not synchronized, one or more sectors of the antenna sector sweep may be missed. Accordingly, the beamforming process may omit the highest quality sector when establishing the communication beam between two communicating stations. These and other challenges of the prior art are addressed by one or more embodiments of the present invention.