A wireless cellular communication system uses a number of wireless transmitters to create a geographic service area of the system. The service area may be broken down into cells, which can be sized according to subscriber density and demand within a particular region. Cells can be added to accommodate growth, such as to create new cells in unserved areas or overlaying cells in existing areas, for example.
In the wireless communication system, the wireless transmitters send and receive electromagnetic signals through antennas (rather than or in addition to transmitting and receiving signals through a transmission line). Antennas couple electromagnetic energy from one medium (space) to another (e.g., wire, coaxial cable, etc.). Physical designs of antenna systems can vary, however it is generally desirable to focus radiation of electromagnetic energy (in the form of a wireless signal) in the direction of a receiving device to efficiently transmit wireless signals and to lessen interference to other radio communication networks.
Beamforming is one way to extend wireless coverage and reliability by employing multiple transmission and reception antennas to focus transmission and reception of signals. Beamforming is a signal processing technique used in antenna arrays for directional signal transmission or reception. Spatial selectivity is achieved by using adaptive or fixed receive/transmit beampatterns, for example. Beamforming can focus energy to a specific location to extend coverage/reliability to an area where a user is located.
Beamforming using directional antennas concentrates electromagnetic energy to produce a radiation pattern in one or more desired directions. For example, a directional antenna may produce a conical-shaped coverage pattern, similar to the light output pattern of a flashlight. An angle of a beam width of the coverage pattern specifies the antenna directionality. Typical beam width angles range from 90 degrees (somewhat directional) to 20 degrees (very directional).
A directional antenna beam provides a narrow coverage pattern, which may allow for efficient transmission of wireless signals. However, since a directional antenna provides such a localized coverage pattern, an endpoint device should be within the localized coverage pattern (or possibly within a close proximity) in order to receive transmitted signals. This is because wireless devices may require control signaling messages to establish communication links, and even if the directional antenna radiates in directions slightly off-line from the endpoint device, little if any of the signals may be received in those off-line locations. Thus, if a user is not initially located within a direction of a coverage area of the directional antenna beam, the user may not be able to receive control signals needed to acquire service from the directional antenna. As a result, gaps between the coverage areas in a directional antenna system are dead-zones where users may not receive service.