Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
2000-04-29
2002-03-05
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S335000, C370S535000, C359S199200, C455S450000
Reexamination Certificate
active
06353600
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to cellular communications systems. More particularly, it relates to systems and methods for dynamically allocating centralized capacity resources to remote cells in a CDMA cellular network.
BACKGROUND ART
As cellular communications rapidly spread into every walk of modern life, there is a growing demand for ever greater service at ever lower cost.
Conventional cellular networks employ an architecture which divides a geographical area into coverage areas called cells, and a base-station is placed at the center of each cell to serve the cellular traffic. The base-station is equipped with transmitters and receivers that provide the RF radio coverage, while a fixed number of radio channels in the base-station determines the traffic handling capacity. Since each cell must be provided with an adequate number of radio channels in order to meet the peak traffic demand with a specified grade-of-service, the cost for providing such peak traffic capacity and the associated operational expenses must be paid at the outset, though the peak traffic capacity may not be fully utilized most of the time. The situation is further compounded by the non-uniform and dynamic nature of the traffic capacity demand within the cellular network, resulting in capacity shortages in some of the cells while capacity excesses others experience. Moreover, as the demand for cellular service increases within a particular area, the network must be re-engineered and more base-stations must be installed to meet the demand, which can be costly and time consuming. All in all, the dynamic nature of traffic capacity demand makes it difficult for the current cellular networks to operate efficiently and to optimize both cost and grade-of-service.
U.S. co-pending patent applications, “Adaptive Capacity Management in a Centralized Base-station Architecture” of Adam Schwartz Ser. No. 09/560,656 filed on Apr. 27, 2000, and “A Cellular Communications System With Centralized Capacity Resources Using DWDM Fiber Optic Backbone” of Woon Wong and Adam Schwartz 09/561,372 filed on Apr. 28, 2000, provide a novel cellular network architecture that de-couples the traffic capacity and the RF coverage in a cellular network by placing base-stations at a centralized location, in contrast to one base-station per cell structures in prior art networks. The RF coverage in each remote cell is independently provided by one or more RF antennae placed inside the cell. Such a centralized base-station architecture enables the cellular network to dynamically allocate traffic channels to remote cells based upon traffic demand and grade-of-service requirement in each cell, thereby enhancing overall capacity in the network. More specifically, 09/560,656 provides an adaptive capacity management method for cellular communications systems in which radio resources utilize non-interfering channels, such as frequency bands in Frequency Division Multiple Access (FDMA), or time-slot assignments in Time Division Multiple Access (TDMA). 09/561,372 provides a cellular network in which optical fibers and Dense Wavelength Division Multiplexing (DWDM) are advantageously employed to distribute multiple traffic channel groups from the centralized base-stations to different remote cells. The present invention addresses cellular communications systems in which radio resources employ wide-band Code Division Multiple Access (CDMA) channels.
In a CDMA cellular system, the basic unit of radio resource is a set of orthogonal digital codes whose frequency spectrum is spread over a given band of frequency by a pseudo-noise (PN) digital sequence (a spreading code). More than one PN sequence are used to spread the digital codes in a given frequency band. Each digital code spread by a PN sequence is referred to as a CDMA channel, hereinafter. A traffic channel group consisting of one or more CDMA channels characterized by the same PN code occupying the same frequency band is referred to as a CDMA signal, hereinafter. In CDMA technology, PN codes are used for a variety of purposes. The use of PN codes in this invention refers solely to the spreading code used to spread downlink CDMA signals for the purpose of distinguishing downlink CDMA signals of the same frequency band from one another. While CDMA channels within each CDMA signal are orthogonal to each other, CDMA channels belonging to different CDMA signals are not orthogonal to each other. Therefore, when CDMA channels belonging to different PN sequences (i.e., different CDMA signals) are used simultaneously in a cell, cross-interference will occur amongst CDMA channels, which degrades the signal-to-noise ratio of channel reception and leads to undesirable soft-handoff.
Hence, while there is no inherent limit to the number of non-interfering FDMA or TDMA channels that can be shuffled to a given cell, so long as the frequency spectrum and other physical constraints permit, there is an upper limit to the number of CDMA channels sharing a common frequency band that can be allocated to a cell. That is to say that in the current state of CDMA cellular communications, the number of users that can be supported in a cell is limited by the cross-interference amongst CDMA channels, rather than by the amount of traffic channel resources that can be devoted to it.
Sectorization has been implemented in the art to mitigate the cross-interference amongst CDMA channels as described above. That is, multiple directional antennae are used to divide a cell into multiple sectors with mutually exclusive radio coverage areas, such that different CDMA signals allocated to the cell are assigned to different antennae. However, the allotment of traffic channel resources to each sector in the prior art cellular networks has been on a fixed basis, with no provision for dynamic assignment of traffic channels based upon traffic demand and grade-of-service requirement.
What is needed in the art are therefore cellular communications systems in which traffic capacity resources are dynamically managed and optimally utilized.
OBJECTS AND ADVANTAGES
Accordingly it is a principal object of the present invention to provide a cellular network architecture in which traffic channel resources are centralized and dynamically allocated to remote cells according to the demand. It is another object of the present invention to provide a method for maximizing capacity resources by dynamically sectorizing cells in a CDMA cellular network. It is a further object of the present invention to provide a cellular communications network in which centralized traffic channel resources are distributed to remote cells by use of Wavelength Division Multiplexing (WDM) on optical fibers and remote cells are dynamically sectorized according to traffic demand and grade-of-service requirement.
The primary advantage of the present invention is that it enables a CDMA cellular network to dynamically manage and optimally utilize its capacity resources without having to change its hardware design, in contrast to the static and passive nature of the prior art cellular networks. The present invention provides a cost-effective buildout strategy for cellular network operators. Another advantage of the present invention is that as the demand for cellular service increases in a particular area, more capacity can be easily implemented without disrupting the overall operation of the entire network. A further advantage of the present invention is that the use of optical fibers and WDM provides a simple, efficient, and economical way to transmit traffic channel resources between centralized base-stations and remote cells.
These and other objects and advantages will become apparent from the following description and accompanying drawings.
SUMMARY OF THE INVENTION
The present invention provides a cellular network, including a centralized base-station site containing a plurality of base-station units, one or more remote cells, each equipped with S directional antennae, a cellular distribution means for transmitting traffic channel resources between the
Lau Kam-Yin
Schwartz Adam L.
Hsu Alpus H.
LGC Wireless Inc.
Lumen Intellectual Property Services
Qureshi Afsar M.
LandOfFree
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