Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1999-09-02
2003-10-28
Le, Thanh Cong (Department: 2684)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S014000, C455S561000, C455S523000
Reexamination Certificate
active
06640111
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cellular wireless communications systems generally and more particularly to apparatus and methods for cellular communications with base stations.
BACKGROUND OF THE INVENTION
Cellular multiple access communications date back to the early eighties. The nineties witnessed an outburst of this type of service throughout the world and the introduction of digital technologies. The market is expected to soar and expand into Personal Communication Services (PCS), offering personal service, a host of value added features, and total personal mobility, indoors and outdoors. Broadband services are expected to emerge at the beginning of the next century. These may require a partial renewal of the network infrastructure.
Cellular mobile communication attempts to provide mobility, multi-user capacity (many independent users access the system), coverage (service is offered over a large contiguous area) and grade and quality of service.
Cellular communications are generally limited by local codes to a range of frequencies. A widely used technique of cellular communications employs spatial isolation in order to be able to reuse the same frequencies beyond a given range called a guard zone. The communications of each user is maintained with a base station, whose antenna is elevated above the scenery in order to achieve a well defined and controlled coverage are. Sectorization is achieved by directive antennas that illuminate only one sector, thereby reducing interference, enhancing performance and reducing a pattern of frequency reuse.
Each sector of cellular communications is characterized by a number of calls per unit area, also called area capacity. Area capacity may be increased by reducing the cell size. Small cells that are positioned below roof tops in urban areas are called microcells. These use lower and smaller antennas. The cell hardware is more compact, and in some cases has less circuits. Another technique for microcells involves the antenna and RF circuitry only, remote from the cell equipment and connected via RF, fiber or microwave link, to the cell. Such an arrangement is especially attractive for operators in possession of RF or fiber trunking, like CATV companies.
A future trend to increase the capacity of large cells involves smart antennas. These are multibeam array antennas at the base stations, controlled to form narrow beams that are matched to the disposition of the desired user and the sources of interference. These are expected to enhance the coverage and the capacity. The complexity involved in this technology is expected to be relieved with new cell architectures, including, among others, active antenna modules.
The network infrastructure of a typical modern cellular communications system includes a number of base stations, the actual number being related to the capacity required (measured in Erlangs, which is the number of fully occupied circuits), and to the coverage area. The base stations generally constitute about 80% of the network cost. A typical cost for a full capacity large cell base station is $500,000-$1,000,000. The infrastructure also includes interconnect trunking, which depends mainly on the total length of interconnect lines, and switching fabric, which depends on the number of cells and calling load (measured in BHCA—Busy Hour Call Attempts). The cost of the basic service of providing airtime depends mainly on the number of base stations and on their cost.
One of the problems of cellular communications systems is transmission losses. The transmit chain of a first generation base station consists of single carrier HPA's, filtered, combined and relayed by a high power cable to the mast. The losses involved in the chain amount to 8-10 dB. The carrier spacing is restricted by the combiner to at least 600 KHz.
In an effort to cut down losses, second generation base stations were developed. A second generation base station includes a MCLPA—Multi Carrier Linear Power Amplifier. This reduces the losses and adds flexibility to the design of the carriers (frequency allocations). A low noise amplifier (LNA) is used in the receive chain in the base station. The LNA reduces cable losses which degrade the system noise figure. An additional receive antenna is typically used for diversity. Recent installations place the LNA on the mast.
However, the MCLPA is an expensive part, running from $10,000 for a minicell to over $100,000 for a full capacity cell. Furthermore, MCLPA's are currently supplied to the whole market by a limited number of vendors. The MCLPA's from these vendors are available only in a power range of about 25 to 500 W.
SUMMARY OF THE INVENTION
The present invention seeks to provide a novel base station for cellular wireless communications based on a modular structure.
The present invention includes an active radiator module (ARM) that serves as a basic transmit/receive module in a variety of cellular base station configurations. The active radiator modules follow the trend of cellular architecture development and are designed to meet both current and future needs. It is a novel approach that may reduce the cost of the base station while providing desired flexibility.
In the active radiator module system, a combined signal is transmitted in low power through a cable to a mast, where it redistributes to the active radiator modules. The number of active radiator modules needed is a function of both the total effective radiated power (ERP) and gain required. The receive chain includes an LNA in each element, which reduces the noise figure of the system. The same active radiator module can serve in microcells that require small power and low gain antennas.
A remote RF unit is the least expensive solution for microcells. Its applicability is limited by the cost of RF trunking. It is the preferred solution for operators that have an access to the CATV or to fiber trunking already laid. This unit includes an amplifier, an LNA, and a transformer to the trunking band. This same module may be a part of a microcell or a picocell, but the RF is included inside the package, while the antenna is typically separate. The modular structure of the base station of the present invention provides readily upgradable base station performance at relatively low cost.
By way of example only, the present invention is described herein for certain commonly-used frequency ranges, such as for cellular telephones or PCS. However, it is appreciated that the present invention is not limited to these frequency ranges and may be applied to any set of frequencies.
There is thus provided in accordance with a preferred embodiment of the present invention, a modular cellular wireless communication base station including a plurality of active radiator modules located at a desired antenna location, each module including at least one antenna for transmitting and receiving, a transmitter including a power amplifier, and a receiver, a beam forming network controlling the relative amplitudes and phases of each of the modules, and an RF front end transmitting over a low power link with the plurality of active radiator modules via the beam forming network and receiving over a lower power link via a low noise amplifier.
In accordance with a preferred embodiment of the present invention, the RF front end is located remote from the plurality of modules. Preferably each module is self-enclosed.
Additionally in accordance with a preferred embodiment of the present invention at least one of the active radiator modules comprise two separate transmit and receive antenna elements. Preferably the transmit and receive antenna elements are isolated from each other by about 15-30 dB, most preferably by about 20 dB.
Further in accordance with a preferred embodiment of the present invention the beam forming network is located adjacent the plurality of active radiator modules, one for transmit and one for receive.
Still further in accordance with a preferred embodiment of the present invention, the modular cellular wireless communication base
Celletra Ltd.
Cong Le Thanh
Nguyen Thuan T.
Pillsbury & Winthrop LLP
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