Sectorized cell having non-redundant broadband processing unit

Details Sectorized cell having non-redundant broadband processing unit Sectorized cell having non-redundant broadband processing unit

1998-07-09

2001-06-26

Nguyen, Lee (Department: 2683)

Telecommunications

Transmitter and receiver at same station

Radiotelephone equipment detail

C455S103000, C455S132000, C455S137000, C455S277100, C370S334000, C370S347000, C370S362000

Reexamination Certificate

active

06253094

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention relates to wireless communication systems, but more particularly, to a method and system for attaining sectorization in a cellular communication system utilizing a single broadband processing unit.
2. Discussion of the Prior Art
In order to provide multi-channel voice and data communications over a broad geographical area, wireless communication providers currently install base station transceivers in protected and maintainable structures, known as cell sites. A cell site encompasses an antenna, a tower or building upon which the antenna is mounted, high-power amplifiers, duplexers, transmitters, receivers and broadband processing equipment. The broadband processing equipment channelizes and combines digital signals on multiple channels that are associated with respective subscribers. The digital signals, however, are communicated over the air with subscribers in the analog domain. Thus, the base station equipment further includes analog-to-digital and digital-to-analog converters, depending on the direction of information flow, as described in commonly owned U.S. Pat. Nos. 5,535,240 and 5,592,480 which issued Jul. 9, 1996 and Jan. 7, 1997, respectively, to Ronald R. Carney, et al., incorporated herein by reference.
The cell itself is an area on the ground that is generally depicted as a hexagon. This is the simplest way to illustrate the cellular idea, but in reality, the actual shape of the cell and the coverage provided by the radiated signal from the cell site is rarely as regular, uniform and clearly defined. The actual shape of the cell depends upon the contours and the condition of the terrain surrounding the cell site. Factors such as the size and number of trees and/or the degree of urbanization determine how large an area one cell can cover. The cell may itself be sectorized wherein it is provided with an antenna designed to concentrate energy in an arc of 120 degrees rather than the usual 360 degrees. Different frequencies may be used for each sector, and these frequencies may be repeated among cells. Using the sectorization, the cell site is able to accommodate communication for a greater number of subscribers. The instant application is directed to sectorization which is sometimes referred to as cell-splitting.
Each sector is configured to provide two-way (duplex) multi-channel communication capability for only a limited portion of the frequency spectrum that is allotted to the wireless communication service provider. A typical cellular communication channel consists of a pair of frequencies, one for each direction of transmission, used for full-duplex operation. A typical transceiver consists of multiple sets of discrete receiver and transmitter signal processing components in order to service a particular portion of the frequency spectrum, usually 400 30 Khz channels within a 12 MHZ bandwidth. The receiver section of a typical transceiver includes a dedicated set of signal processing components, including a front end, an intermediate frequency (IF) section and a baseband section.
A primary limitation in current cellular communication systems is that a service provider is only allocated a fixed number of frequencies with which to handle subscriber calls. Typically, there must be a 35 mile separation between cells using the same frequency set, so that subscribers communicating on the same frequencies do not interfere with one another. Frequency reuse allows subscribers to use the same frequencies in adjoining cells without interference, thereby allowing a service provider to accommodate more subscribers.
Whenever a base station employs sectorization, however, each sector requires its own broadband processing unit to perform digital combining and channelizing. Unfortunately, such replication of digital processing equipment increases the complexity and expense of the base station.
SUMMARY OF THE INVENTION
It is a general objective of the present invention to increase the channel capacity of a cell using existing broadband processing equipment.
It is a more specific objective of the invention to provide a scheme for sectorizing a cell without replication of broadband processor units.
It is another object of the invention to provide a sectorized communication cell using lower power transmitters for the respective sectors.
In accordance with the invention, the improvement comprises a technique in which a non-sectorized cell is converted to a sectorized cell having multiple sectors. In a preferred embodiment, the spectrum of given frequency band having a center frequency ′&OHgr;
o
is divided into multiple bands (three, for example) having center frequencies ′&OHgr;
o
, ′&OHgr;
o
−&agr; and ′&OHgr;
o
+&agr; (in the case where three sectors are employed). In the receive path, respective sub-bands are used to convey analog RF signals in respective sectors to a transceiver. Each of the transceivers include a front end for receiving incoming RF signals and an analogto-digital converter for converting the analog signal to a digital data stream. The digital data streams from transceivers are combined, i.e., processed by digitally adding, and supplied to a single channelizer which, in turn, supplies the data to a TDM bus. In the reverse path, TDM digital data signals emanating from TDM bus are supplied to a combiner which feeds each of the respective transceivers, which select the appropriate data from the combiner by digital filtering or processing. The transceivers convert the digital signal to analog form. After conversion, power amplifiers associated with the respective sectors effect emission of radiated power in the respective sectors.
Advantageously, amplifiers in the sectorized improvement operate at lower power levels than the single high power amplifier of a non-sectorized cell thereby providing substantial cost savings. More importantly, instead of deploying multiple broadband processing units, the improved sectorized cell requires only a single broadband processing unit, thereby providing further economies. The invention only requires software modification of the broadband processing unit used in a single cell site to handle information distributed in different spectral bands associated with the sectors.
These and other objects of the invention will become apparent upon review of the accompanying disclosure when read in conjunction with the accompanying drawing figures, wherein like reference numerals designate the same of corresponding parts throughout the several views.


REFERENCES:
patent: 5832389 (1998-11-01), Dent
patent: 5893033 (1999-04-01), Keskitalo et al.
patent: 6006113 (1999-12-01), Meredith

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