Variable sectorization tower top applique for base stations

Communications: radio wave antennas – Antennas – With support for antenna – reflector or director

Reexamination Certificate

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Details

C343S853000, C343S893000

Reexamination Certificate

active

06504517

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to wireless communication systems and, in particular. to antenna arrays used in wireless communication systems.
BACKGROUND OF THE RELATED ART
Sectorization of cells is a well-known technique for reusing logical channels in order to enhance the capacity of wireless communication systems.
FIG. 1
depicts a conventional sectorized cell
10
in accordance with the prior art. Cell
10
includes three 120° sectors A, B, C, and has an associated base station
12
for providing wireless communication services to mobile-telephones within cell
10
. Base station
12
includes, for each sector, a set of base station radios
13
, converters
15
, and an antenna configuration
14
comprising of two antenna elements
16
-
1
,
16
-
2
. The set of base station radios
13
performs digital base-band signal processing and provides wireless communication services to mobile-telephones in its sector over associated antenna elements
16
-
1
,
16
-
2
. Converters
15
are connect to base station radios
13
, and include an D/A-A/D converter and base band/RF-RF/base band converter for converting digital base band signals outputted from base station radios
13
into analog RF signals for transmission over antenna configuration
14
, and vice-versa for analog RF signals received over antenna configuration
14
. Each antenna element
16
-
1
,
16
-
2
is connected to a converter
15
via a separate cable, wire or optical fiber, not shown, and produces a beam of approximately 120° for providing wireless communication coverage (or beam coverage) to mobile-telephones within its associated sector.
The beams produced by antenna elements
16
-
1
,
16
-
2
are non-variable or fixed beamwidths and, thus, the associated sectors, in effect, are fixed in size. Fixed size sectors are undesirable because traffic distribution and loading patterns may not be uniform across each sector resulting in inefficient utilization of base station radio resources. For example, the number of mobile-telephones in one sector may exceed the capacity (or capability to process signals being transmitted to and from the mobile-telephones) of the associated set of base station radios
13
, whereas the number of mobile-telephones in another sector may not exceed the capacity of the associated set of base station radios
13
resulting in unused excess capacity. Or the loading pattern at one time of day may differ from the loading pattern at another time of day due to, for example, commuter traffic resulting in inadequate base station radio resources in one sector and excess base station radio resources in another sector.
To overcome these problems associated with fixed size sectors, adaptive or variable sectorization has been proposed. Adaptive sectorization allows for sector sizes to be adjusted by varying the associated beam coverage.
FIG. 2
depicts an adaptive sectorized cell
20
in accordance with the prior art. Cell
20
includes three sectors A, B, C, and has an associated base station
22
for providing wireless communication services to mobile-telephones within cell
20
.
FIG. 3
depicts a more detailed illustration of base station
22
, which includes a set of base station radios
23
per sector, butler matrices
25
, converters
21
and an antenna configuration
24
. Butler matrices
25
are connected to base station radios
23
for shifting phases of digital base band signals outputted by base station radios
23
to obtain phase shifted digital base band signals. Converters
21
are connected to butler matrices
25
for converting the phase shifted digital base band signals into phase shifted analog RF signals for transmission over antenna configuration
24
.
Antenna configuration
24
comprising of an antenna array
27
per butler matrix
25
, wherein each antenna array
27
includes four antenna elements
26
. Each antenna element
26
in antenna array
27
is connected by a separate cable, wire or optical fiber to converters
21
, and produces a beam of approximately 120°. Thus, twelve cables are required for connecting the twelve antenna elements to converters
21
. The 120° beams produced by antenna elements
26
of antenna array
27
are combined and manipulated via associated butler matrix
25
to produce four 30° beams over which downlink signals may be transmitted, wherein a downlink signal intended for a particular mobile-telephone is only transmitted over the 30° beam covering the area in which that mobile-telephones is currently positioned.
Each set of base station radios
23
has an associated set of 30° beams (hereinafter referred to as “beam set”). The number of 30° beams in each beam set determines the size of each sector A, B, C. Accordingly, the size of each sector A, B, C may be adjusted by varying the number of 30° beams in the associated beam set. Suppose each beam set initially includes four adjacent 30° beams, thus, each sector A, B, C had a size corresponding to 120°. If the traffic in sector A of cell
20
exceeds the capacity of the associated set of base station radios, sector A may be adjusted to correspond to the coverage area of three adjacent 30° beams to reduce the load of sector A, and either sector B or C may be adjusted to correspond to the coverage area of five adjacent 30° beams to increase its load if there exist unused base station radio resources in that sector.
The architecture of cell
20
, however, would not be easy to implement in wireless communication systems based on Code Division Multiple Access (CDMA) techniques because a pilot signal is required to be transmitted along with other downlink signals such that coherent demodulation of downlink signals can be performed at the mobile-telephones. If only one antenna element
26
in antenna array
27
is used to transmit the pilot signal, the pilot signal will be transmitted over a 120° beam formed by that antenna element
26
and, thus, a phase difference may exist between the pilot signal and downlink signals transmitted over the 30° beams making it difficult to coherently demodulate such downlink signals using the pilot signal. Alternately, if a pilot signal is transmitted over every antenna element
26
in antenna array
27
, the pilot signal will only be transmitted over a resulting 30° beam formed by all the antenna elements
26
through butler matrix
25
and, thus, the pilot signal cannot be used to demodulate downlink signals transmitted over other 30° beams. Accordingly, there exists a need for an adaptive sectorization technique that would amiable to CDMA environments.
SUMMARY OF THE INVENTION
The present invention is an adaptive sectorization technique that is amiable to CDMA environments using an antenna configuration and a phase shifter network that can form a variable width beam over which a pilot signal and other downlink signals may be transmitted. The antenna configuration having at least an antenna sub-array with two or more antenna elements. The phase shifter network having a plurality of switches for adjusting beam width by directing signals to be transmitted over one or more of the antenna elements, and phase shifters for shifting phases of the signals to be transmitted over the one or more antenna elements. In one embodiment, the phase shifter network is at the RF front end allowing for phase adjustment at the RF front end instead of at digital base band signal processing. Adjusting the phases at the RF front end enables transmission of the pilot signal and downlink signals in a same beam pattern generated by one of the antenna sub-arrays in the antenna configuration, thereby eliminating pilot error resulting when the pilot signal and downlink signals are transmitted over different beams.


REFERENCES:
patent: 4414550 (1983-11-01), Tresselt
patent: 4918458 (1990-04-01), Brunner et al.
patent: 4962383 (1990-10-01), Tresselt
patent: 5327147 (1994-07-01), Caille et al.
patent: 5552798 (1996-09-01), Dietrich et al.
patent: 5581583 (1996-12-01), Conti et al.
patent: 5694498 (1997-12-01), Manasson et al.
patent: 5841388 (1998-11-01), Yasuda et al.
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