Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-07-20
2003-02-18
Chin, Vivian (Department: 2682)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S561000
Reexamination Certificate
active
06522897
ABSTRACT:
TECHNICAL FIELD
This invention relates to the synthesis of RF radiation pattern to create a phased array using a plurality of antennas and more particularly to a system and method for generating such RF patterns from a plurality of antennas using a number of linear power amplifiers (LPAs) less than the number of antennas and even more particularly to such systems and methods for using the same number of LPAs as are currently used in non-phased array antenna systems.
BACKGROUND
It is often desirable to provide a signal simultaneously in multiple beams of a multibeam antenna system. For example, a cellular communication system may provide communications between a base transceiver station (BTS), having an antenna system associated therewith, and a plurality of mobile units operating within a predefined area, or “cell,” defined by the antenna system's radiation pattern. Often such cells, although providing communications in a full 360° about the BTS, are broken down into three 120° sectors in order to provide more capacity and less interference over that of an omni cell 360° system. Additionally, such a sectorized cell achieves extended range as compared to an omni cell 360° system due to the greater signal gain at the sector antennas resulting from their more focused coverage.
Further advantage may be realized by providing multiple narrow beams at the BTS rather than the three 120° sectors. For example, twelve 30° narrow antenna beams may be utilized to provide the same 360° communication coverage within the cell as the 360° omni cell configuration and its 120° sectorized cell replacement. Such a multiple narrow beam arrangement is desirable because, as with the 120° sector system described above, the multiple beams provide a greater signal gain resulting from their greater focused coverage. A further advantage of the multiple narrow beams is the flexibility offered in synthesizing any desired sector size by combining/phasing such beams. Combining adjacent narrow beams provides a wider composite beam, with a beam width roughly equal to the sum of the individual beams widths. Accordingly, synthesized sectors may be formed of any size by simulcasting a signal on selected ones of the narrow beams. The sector could be as narrow as a single beam or as wide as desired by using multiple beams.
The multiple antenna beams of a communication system may be generated through use of a planar or cylindrical array of antenna elements, for example, where a signal is provided to the individual antenna elements having a predetermined phase relationship (i.e., a phased array). This phase relationship causes the signal simulcast from the various antenna elements of the array to destructively and beneficially combine to form the desired radiation pattern. There are a number of methods of beam forming using matrix type beam forming networks, such as Butler matrixes.
Controlling interference experienced in wireless communication, such as may be caused by multiple users of a particular service and/or various radiating structures of a service or different services providing communication coverage within the same or different geographical areas, is a concern. Moreover, as the use of wireless communications increases, such as through the deployment of new services and/or the increased utilization of existing services, the need for interference reduction schemes becomes more pronounced.
For example, in code division multiple access (CDMA) networks a number of communication signals, each associated with a different user or communication unit, operate over the same frequency band simultaneously. Each communication unit is assigned a distinct, pseudo-random, chip code which identifies signals associated with the communication unit. The communication units use this chip code to pseudo-randomly spread their transmitted signal over the allotted frequency band. Accordingly, signals may be communicated from each such unit over the same frequency band and a receiver may despread a desired signal associated with a particular communication unit.
However, despreading of the desired communication unit's signal results in the receiver not only receiving the energy of this desired signal, but also a portion of the energies of other communication units operating over the same frequency band. Accordingly, CDMA networks are interference limited, i.e., the number of communication units using the same frequency band, while maintaining an acceptable signal quality, is determined by the total energy level within the frequency band at the receiver. Therefore, it is desirable to limit reception of unnecessary energy at any of the network's communication devices.
In the past, interference reduction in some wireless communication systems, such as the aforementioned CDMA cellular systems, has been accomplished to an extent through physically adjusting the antenna array to limit radiation of signals to within a predefined area. Accordingly, areas of influence of neighboring communication arrays may be defined which are appreciably smaller than the array is capable of communicating in. As such, radiation and reception of signals is restricted to substantially only the area of a predefined, substantially non-overlapping, cell.
Changes in the environment surrounding a communication array or changes at a neighboring communication array may require adjustment of the radiation pattern of a particular communication array. Specifically, seasonal changes around a base transceiver station (BTS) site can cause changes in propagation losses of the signal radiated from a BTS. For example, during fall and winter deciduous foliage loss can cause a decrease in signal path loss. This can result in unintentional interference into neighboring BTS operating areas or cells as the radiation pattern of the affected BTS will effectively enlarge due to the reduced propagation losses.
Likewise, an anomaly affecting a neighboring BTS may cause an increase in signal path loss, or complete interruption in the signal, therefore necessitating the expansion of the radiation patterns associated with various neighboring BTS's in order to provide coverage in the affected areas.
One solution to the problem of creating a phased array has been to use twelve antennas arranged into three panels with each panel having four antennas thereon. A typical system of this type is shown in
FIGS. 6 and 7
where it will be noted that there are at least twelve LPAs utilized, one for each antenna column. Also, it should be noted that any reference herein to an antenna or an antenna array includes an antenna column made up of a plurality of elements. Control of such an antenna column is detailed in the above-mentioned copending application entitled SYSTEM AND METHOD FOR PER BEAM ELEVATION SCANNING.
In systems which existed prior to the system shown in
FIGS. 6 and 7
, particularly in CDMA systems, there is typically only one LPA per panel (sector) which provides RF signals to a single antenna, or to a set of antennas having a relatively fixed radiation pattern. In such systems there is no ability to control, or snythesize, the radiation pattern to maximize utilization. For such synthesis to occur and thus control the radiation pattern, it is necessary to control the power and the relative phase of the RF signals which arrive at the antenna.
Thus, in addition to the LPAs being costly, if twelve LPAs were to be used (one for each antenna), their use would require the removal, or at least the rewiring of, the existing LPAs plus the addition of at least nine additional LPAs. This is costly and inefficient.
In addition, since LPA themselves are costly items (the cost partially dependent upon the amount of power being handled) and because the amount of power delivered to the antenna is critical to the proper operation of the system, it is critically important that power not be lost (or the loss minimized) after the LPA stage.
A further difficulty arises when it is desired to change the orientation of the radiation pattern so that antennas positioned on different panels cr
Feuerstein Martin J.
Martek Gary Allen
Reudink Douglas O.
Chin Vivian
Fulbright & Jaworski L.L.P.
Metawave Communication Corporation
Nguyen Duc
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