Patent Grant
7642988
This application is related to the application “Multi-link antenna array that conforms to cellular leasing agreements for only one attachment fee” and “Hybrid architecture that combines a MAN fiber system with a Multi-link antenna array” that were filed on the same day as the current application and are hereby incorporated by reference.
Not applicable
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1. Field of the Invention
The invention is related to the field of communications, and in particular, to communication antennas.
2. Description of the Prior Art
Most cellular backhaul uses Incumbent local exchange carrier (ILEC) T1 circuits. ILEC circuits are expensive and do not scale economically as cell backhaul demand increases, especially for wireless data and video. Using point-to-point or point-to-multipoint radio or microwave links for cellular backhaul links can be costly. One of the cost drivers is the cost of real estate on cell towers. In this application the term “cell tower” includes all manner of cellular mounting structure, for example building sites, towers, treelike structures, and the like. Cell tower leasing agreements typically charge a fee for each antenna element mounted to the tower, and a fee based on the number of cables running up the tower that attach to the antenna elements.
Therefore there is a need for a system and method that allows multiple antenna elements to be mounted onto a cell tower at a minimum cost.
The spectrum available for the radio and microwave point-to-point and point-to-multipoint links is also restricted. Common carrier bands at 2, 4 and 6 GHz, especially the 4 GHz band, are under utilized today. The original and primary use of the bands was for long distance telecommunication across the US. The long distance links were typically operated by AT&T, MCI and other telephone companies. The long distance radio frequency (RF) links had link distances of 30 miles or more. These long distance links require large antennas. These antennas had to be mounted individually on cell towers and the leasing cost on cell towers is based, in part, on the number of mountings used. The large microwave antennas also created wind loading problems on cell towers. Today these companies and new operators typically utilize fiber optic transcontinental networks for Long Distance telecommunications. Deployment of fiber networks has rendered the 4 GHz band as highly under utilized and available for other uses.
Therefore there is a need for a system and method that utilizes these common carrier bands for point-to-point links.
A system and method for mounting a plurality of antenna elements onto a cell tower is disclosed. The plurality of antennas are mounted into a radome enclosure. The radome enclosure has an outer size and shape that matches the outer size and shape of a cellular antenna element. The radome enclosure is configured to attach to a cellular tower using the same physical mounting system as the cellular antenna elements. The plurality of antennas provide multiple point-to-point links that may be used for wireless backhaul links or other applications.
a and 5b are isometric views of two prior art cellular mounting decks.
A Multi-link antenna array is a new concept to conserve the mounting space available on cell towers and minimize antenna leasing expenses. In this application the term “cell tower” includes all manner of cellular mounting structure, for example building sites, towers, treelike structures, and the like. In one embodiment of the current invention, an array of small antennas are mounted inside a radome enclosure. The size and shape of the radome enclosure matches the general size and shape of cellular antenna elements. This enables the array of small antennas, known as a multi-link antenna array, to be mounted onto cell towers or building rooftops in a similar fashion as a cellular antenna element and conform to present cell antenna leasing agreements. By matching the size and shape of the cellular antenna element, the multi-link antenna array will also have essentially the same wind loading as the cellular antenna element.
In one example embodiment of the invention, the antenna mounting system 204 is a vertical post fixed inside the radome enclosure 202. The plurality of antennas 206 are mounted along the vertical post. The vertical post allows the plurality of antennas 206 to be aimed over the full 360 degree azimuth range. Other antenna mounting systems that allow the full 360 degree azimuth range are possible and include a series of horizontal slots built into the radome enclosure, where each antenna mounts to the radome using one or more slots, a series of stackable disks, where each disk contains one antenna and where the disks can be rotated on top of each other, or the like. In another example embodiment of the invention, the antenna mounting system may limit the aim of the antennas to a subset of the full 360 degree azimuth range.
In one example embodiment of the invention, each of the plurality of antennas 206 is configured to operate at one of the common carrier bands, for example the 2, 4, 6, 10, 11, 18, 23, or 28 GHz band. When operating at one of the common carrier bands, antenna 206 may be a small patch antenna. Using a small sized patch antenna that fits into the form factor of the radome enclosure 202 may still allow an effective range of up to 10 miles for some of the common carrier bands. The small patch antennas handle all weather conditions without link path failures and operates through foliage albeit with some reduction in range when operating at the 2, 4, or 6 GHz frequencies. The higher frequency common carrier bands (10-28 GHz) may have a reduction in link distance and less tolerance for adverse weather conditions using the small patch antennas. Patch antennas are common for many bands but there are currently no commercially available certified small form factor patch type directional antennas that can be used with common carrier bands such as the 2, 4, 6, 10, 11, 18, 23, and 28 GHz common carrier point to point microwave (MW) bands. Matching a patch antenna to a given wavelength band is well known in the arts.
One of the costs for utilizing cellular towers is the number of cables or wires that run up the tower. In one example embodiment of the invention, the signal lines for each of the plurality of antennas mounted inside the radome enclosure are bundled into one cable that exits the radome. The cable may also include a power lead, a ground path, control lines or the like.
In one example embodiment of the invention, each of the plurality of antennas mounted inside the radome include a radio frequency (RF) head. The RF head converts an intermediate frequency (IF) into the actual frequency used by the antenna. In this way an IF signal can be sent up the tower and into the radome enclosure, instead of the RF signal. The signal lines used to transmit IF signals are typically smaller than lines designed to carry microwave RF signals. By bundling all the signal lines, and possibly the power line, ground path, and control lines into only one cable, the cost under the current cellular lease agreements may be minimized.
In one example embodiment of the invention, all the antennas inside a radome enclosure would be similar and would operate at essentially the same wavelength. In another example embodiment of the invention, a variety of different antennas, operating over a wide range of frequencies, would be mounted inside one radome enclosure. The variety of antenna types include: small patch type antennas, yagi antennas, parabolic antennas, circular polarizing elements, helical antennas, and the like. The multi-link antenna array may operate at one of, or a combination of, the following carrier bands: common carrier bands of 4, 6, 10, 11, 18, 23, 28 GHz; unlicensed bands ISM 2.4, UNII 5.8, 3.6 GHz; E-band 71-91 GHz and auctioned carrier bands applicable with PTP (point to point) radios: 700, 800, 1900 MHz, broadband radio service (BRS) 2.5 GHz and all LMDS bands (28 GHz through 39 GHz), Millimeter Wave radio bands, or any frequency where point to point microwave and millimeter wave radios are authorized to operate. One or more multi-link antenna arrays may be mounted onto a cellular tower, depending on the number of point-to-point links required at that site.
The multi-link antenna array of the current invention enables multiple point to point links to be supported from a single enclosure on a cell tower antenna mounting system or building mounting system. The small sized antennas permit the use of existing common carrier bands, such as the 4 GHz band, as cell site backhaul links. The common enclosure holding multiple antennas avoids the high leasing costs associated with mounting individual antennas. The individual antenna rotary mounting provides support of multiple microwave paths having full azimuth range of MW link propagation from a single host array and tower mounting.
Using the common carrier bands creates a lower one-way transmission delay than point to multi-point fixed wireless system or mesh wireless topologies. Transmission delay and differential delay for cell site backhaul are a particular challenge, especially as they relate to CDMA soft hand-offs and the ongoing migration to all IP end to end transmission for cellular originated and/or terminated traffic. In one example embodiment of the invention, the RF modems per link maybe also be incorporated into each antenna to improve S/N (signal to noise margin) and further increase link ranges.
Cellular tower lease agreements may vary in the detail that describes the size and shape of a cellular antenna element that may be mounted onto a cellular tower under the lease agreement. The detail level may vary between one lease agreement that specifies the exact size and shape of the cellular antenna element, to a lease agreement that only specifies the physical distance between cellular antenna elements 412. The size and shape of a cellular antenna element may be specified indirectly in the lease agreement by specifying the operating wavelength band and the output power for the cellular antenna element. In one example embodiment of the invention, the multi-link antenna array is configured to fit within the maximum size and space allowed under a cellular tower leasing agreement for a cellular antenna element. The size and shape allowed may vary depending on the leasing agreement for each tower. In one example embodiment of the invention, the width 412 of the multi-link antenna array 406 may be limited to the width 410 of a cellular antenna element 404. In another example embodiment of the invention, the width 412 of the multi-link antenna array 406 may be just smaller than the minimum spacing allowed between cellular antenna elements. At this size, two multi-link antenna arrays mounted side-by-side would almost touch. In one example embodiment of the invention, the width 412 of the multi-link antenna array would be limited to two feet. Multi-link antenna array 406 would mount to the mounting deck 402 using the same mounting system that the cellular antenna elements 404 use. Cellular antenna element mounting systems come in a variety of configurations.
In another example embodiment of the invention, each antenna in the antenna array may contain motors that allow the individual antenna's to be aligned without having someone on the cell tower. In one example embodiment of the invention, the motors could be used by a technician that would adjust the direction the antenna pointed while looking at the current signal strength from the antenna. The technician may be on the ground near the tower, or may be at a site remote from the tower. In another example embodiment of the invention, the antennas could be re-positioned automatically using an automated servo system that would optimize the signal strength received by the antenna. The motors may be deployed in a one axis configuration or in a two axis configuration. In the one axis configuration, the motors would be configured to adjust the antennas in the azimuth direction. Having motors attached to the antennas in the antenna array allows the antennas to be adjusted or completely re-pointed without the aid of a tower crew.
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