Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1997-10-28
2001-08-14
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S335000, C455S562100, C342S375000
Reexamination Certificate
active
06275482
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to antenna systems utilized in mobile radio communication systems, and more particularly to a radio cell site antenna architecture which is capable of producing higher gain for improved communication performance.
BACKGROUND ART
Generally, wireless radio communication systems are employed to connect mobile radio/telephone users together. Implementation of such systems, also known as “cellular” telephone services or Personal Communication Services “PCS,” has become commonplace, particularly in metropolitan areas. As shown in
FIG. 1
, typical system configurations divide up a particular geographic service area
10
into several smaller geographic cell sites
12
. Communication within each cell site is provided by a fixed base station
14
, and communication between the cell sites or between a cell site and a land based telephone network is controlled by a control call processor
16
located in a mobile telephone switching center
18
. The mobile telephone switching center
18
is connected to a public switched telephone network
20
.
The respective boundaries of each cell site
12
are generally defined by the transmission and reception range of the respective base stations. These cell boundaries typically overlap at adjoining edges to enable communication throughout the total service area by permitting mobile users
22
to move among the different cells without disrupting communication capabilities, i.e., cell site hand-offs.
In order to allow a large number of users to have simultaneous access to an otherwise limited band-width, typical cellular systems employ either frequency division multiple access (FDMA), time division multiple access (TDMA), or code division multiple access (CDMA) as a system access protocol. Of particular concern to the present invention is a CDMA protocol.
In contrast to FDMA and TDMA, CDMA allows multiple users to simultaneously share all time and frequency resources of the system. This is generally achieved by assigning each user a unique pseudo-random code or identification code which is then used during modulation and demodulation of transmitted signals. An identical code is used at the other end of the transmission to only allow receipt of data that has a matching code sequence. Because the unique code effectively spreads the spectrum of the transmitted signal beyond that which is needed for transmitting the baseband signal, CDMA facilitates rejection of unwanted signals, thereby enhancing system performance in highly noisy environments.
Each base station employs an antenna system arranged to be capable of communicating signals throughout a particular cell's coverage area. One important aspect in the operation of a base station antenna system is to optimize of the strength of signals communicated with mobiles located at the outer boundary. With respect to signals transmitted from the base station to a mobile user, i.e., a downlink channel, weakness of the signal can be overcome merely by increasing the level of power for the base station's transmitter. However, reliable base station reception of signals sent by mobile users, i.e., via an uplink channel, are more problematic due to typical low gain designs of conventional mobile transceivers.
In addition, because of the inherently noisy environment and potential for multi-path signal fading, known CDMA base station antenna systems generally employ spatial or frequency diversity as a mechanism for improving transmission reliability. More specifically, with spatial diversity, the antenna system includes at least two downlink antennas physically separated either horizontally or vertically by an appreciable number of wavelengths. The respective outputs of the antennas are supplied to a processor for determining which antenna is receiving the best quality signal. The best signal path is subsequently connected to the receiver subsystem of the base station. With a wideband signal like that used in CDMA systems, different frequencies will selectively fade in the 1.25 Mhz channel. This frequency diversity arrangement mitigates signal outages due the effects of Rayleigh or “fast” fading.
While spatial and frequency diversity arrangements improve uplink channel performance, a need still exists for a base station antenna architecture which improves uplink performance, particularly in congested metropolitan areas. While it is possible to provide higher gain simply by increasing the size of the respective antennas, such a solution may not be feasible due to physical space constraints or cost.
DISCLOSURE OF THE INVENTION
It is therefore an object of the present invention to provide an improved method and system for reception of CDMA transmitted signals which increases reverse link budget and therefore reverse link coverage.
It is another object of the present invention to provide an improved method and system for diversity reception of CDMA transmitted signals in a cellular or PCS system.
It is a further object of the present invention to provide a base station for use in a CDMA cellular or PCS system which improves reverse link coverage by utilizing a combined angular, spatial, and temporal diversity antenna arrangement.
It is still a further object of the present invention to provide a base station for use in a CDMA cellular or PCS system which includes an antenna architecture having a combined 45-60° angular and spatial diversity to improve reverse link coverage.
It is still another object of the present invention to provide a base station for use in a CDMA cellular or PCS system which includes an antenna architecture having a combined 45-60° angular, spatial, and temporal diversity to improve reverse link coverage.
In accordance with these and other objects, a proffered embodiment of the present invention provides a base station for a CDMA mobile radio communication system having a combined diversity antenna architecture formed from a first and second narrow beamwidth antenna element arranged to receive CDMA signals transmitted from mobile transceivers located in a predetermined geographic coverage area. Each antenna element is oriented so a peak boresight forms a 45-60° angle with respect the other element, and slanted 22.5 to 30° from a boresight of the sector coverage area. The first and second antenna elements are separated in distance by a multiple number of wavelengths. A signal combiner is provided for combining the outputs of the antenna assemblies, and is operative to provide the best qualitative signal to a receiver.
In accordance with another aspect of the present invention, a method for providing diversity reception of signals at a base station used in a CDMA mobile radio communication system comprises the steps of positioning a first and a second diversity narrow beamwidth antenna element so as to receive CDMA signals transmitted from mobile transceivers located in a predetermined geographic coverage area, and orienting each element so that a peak boresight forms a 45-60° angle with respect to the other element. The second antenna element is separated in distance from the first antenna element by a multiple number of wavelengths. All real time outputs of the first and second antenna elements are combined, and the path receiving the best qualitative signal is detected by a RAKE receiver in the CDMA base station.
In accordance with other aspects of the present invention, the method and system provide for delaying the outputs of one of the antenna assemblies to provide temporal diversity, and also providing a separation between the first and second antenna assemblies of a distance within the range of 10-20 wavelengths. In addition, a second redundant pair of antenna elements can be utilized.
The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
REFERENCES:
patent: 5581260 (1996-12-01), Newman
patent: 5596329 (1997-01-01), Searle et al.
p
Jevremovic Vladan M.
Perini Patrick L.
Brooks & Kushman P.C.
Hyun Soon-Dung
Nguyen Chau
Qwest Communications International Inc.
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