Multiplex communications – Channel assignment techniques – Combining or distributing information via code word channels...
Reexamination Certificate
1998-03-12
2001-05-15
Ton, Dang (Department: 2661)
Multiplex communications
Channel assignment techniques
Combining or distributing information via code word channels...
C370S242000, C370S320000, C370S341000, C370S342000, C370S479000
Reexamination Certificate
active
06233247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates, in general, to a method and system to be utilized with wireless communications systems having cellular architectures. In particular, the present invention relates to a method and system, to be utilized with wireless communications systems having cellular architectures which utilize Code Division Multiple Access (CDMA). Yet still more particularly, the present invention relates to a method and system, to be utilized with wireless communications systems having cellular architectures which utilize CDMA, and which increase the reliability of such wireless communications systems by avoiding communication failure.
2. Description of the Related Art
The present invention is related to wireless communication systems, and, in particular, to wireless communications systems which have both a cellular architecture (e.g., cellular telephony, personal communications systems) and which utilize CDMA (or similar technologies). Wireless communication refers to the fact that transmission between sending and receiving stations occurs via electromagnetic radiation not guided by any hard physical path (e.g. by microwave link). Cellular architecture refers to the fact that the wireless system effects service over an area by utilizing a system that can be (ideally) be pictographically represented as a cellular grid. CDMA stands for Code Division Multiple Access, which is a type of spread spectrum technology, originally developed for military application and thereafter adapted for civilian use.
Wireless cellular communication utilizing CDMA is the latest incarnation of a technology that was originally known as mobile telephone systems. Early mobile telephone system architecture was structured similar to television broadcasting. That is, one very powerful transmitter located at the highest spot in an area would broadcast in a very large radius. If a user were in the usable radius, then that user could broadcast to the base station and communicate by radio telephone to the base station. However, such systems proved to be very expensive for the users and not very profitable to the communication companies supplying such services. The primary limiting factor of the original mobile telephone systems was that the number of channels available for use was limited due to severe channel-to-channel interference within the area served by the powerful transmitter.
Counter-intuitively, engineers discovered that channel-to-channel interference effects within the service area were not related solely to the distance between stations communicating with a base station transmitter (which intuitively would seem to give rise to the interference), but were also related inversely to the usable radius of the roughly circular area being served by a base station transmitter. Engineers found that by reducing the radius of an area being served by a base station transmitter by a significant percentage, channel-to-channel interference effects were reduced such that a significant increase in the number of additional usable channels could be provided. For example, it was found that a system based on an area being served by a base station transmitter with a one-kilometer useable radius would have
100
times more usable channels than a system based on an area being served by a base station transmitter with a 10-kilometer useable radius.
Reducing the power of the central transmitter allowed a significant increase in the number of available channels by reducing channel-to-channel interference within an area. However, as the power of the central transmitter was reduced, the serviceable area was also reduced. Consequently, although reducing transmission power increased the number of available channels, the small service area provided by such reduced power did not make such radio telephone systems attractive communication options for many users. Thus, a problem arose relating to how to utilize the discovery that smaller area size (or, equivalently, reduced transmitter power) increased the available channels such that radio telephone systems based on such smaller areas would be commercially viable.
This problem was solved by the invention of the wireless cellular architecture concept. The wireless cellular architecture concept utilizes geographical subunits called “cells” and encompasses what are known as the “frequency reuse” and “handoff” concepts. A cell is the basic geographic unit of a cellular system. Cells are defined by base stations (a base station consists of hardware located at the defining location of a cell and includes power sources, interface equipment, radio frequency transmitters and receivers, and antenna systems) transmitting over small geographic areas that are represented (ideally) as hexagons. The term “cellular” comes from the honeycomb shape of the areas into which a coverage region, served via two or more base stations, is divided when the mathematically ideal hexagonal shape used to represent the usable geographic area of each of the two or more base stations. It is to be understood that, although the mathematically ideal shape of the cell is a hexagon, in practicality each cell size varies dependent upon the landscape (e.g., a base station transmitting on a flat plane will closely approximate the ideal hexagon, whereas a base station transmitting in a valley surrounded by hills will not closely approximate a hexagon due to the interference from the surrounding hills).
Within each cell a base station controller talks to many mobile subscriber units at once, utilizing one defined transmit/receive communications channel for each mobile subscriber unit with which communication is taking place. Each mobile subscriber unit (a control unit and a transceiver that transmits and receives wireless transmissions to and from a cell site) uses a separate, temporarily assigned transmit/receive wireless channel to talk to a cell site. Each wireless transmit/receive communications channel consists of a pair of frequencies for communication—one frequency for transmitting from the cell site base station controller to the mobile subscriber unit, named the forward link, and one frequency for transmitting from the mobile subscriber unit to the cell site base station controller, named the reverse link.
Wireless communication is regulated by government bodies (e.g., the Federal Communications Commission in the United States). Government bodies dictate what frequencies in the wireless spectrum can be used for particular applications. Consequently, there is a finite set of frequencies available for use with cellular communications. The frequency reuse concept is based on the assigning to each cell a group of radio channels to be used within the small geographic area (cell). Adjacent cells are assigned groups of channels that are completely different from the groups of channels assigned to neighboring cells. Thus, in the frequency reuse concept there is always a buffer cell between two cells utilizing the same set of frequencies. The cells are sized such that it is not likely that two cells utilizing the same set of frequencies will interfere with each other. Thus, such a scheme allows “frequency reuse” by non-adjacent cells. As mobile subscriber units transit adjacent cells, the mobile subscriber unit is “handed” from a cell it is leaving into a cell it is entering by directing the mobile subscriber unit to stop using frequencies appropriate to the cell it is leaving and to begin using frequencies appropriate to the cell it is entering. Thus, the cellular architecture concept, in conjunction with the frequency reuse concept, augmented by the operation of “hand-off” gave rise to the ability to utilize small cells to provide communications service over a large geographic area.
The first large-scale wireless communications system utilizing cellular architecture in North America was the Advanced Mobile Phone Service (AMPS) which was released in 1983. With the introduction of AMPS, user demand for bandwidth was initially low until users became acquainted with the power
Alami Samir
Chang Kim
Bracewell & Patterson L.L.P.
Crane John D.
Hom Shick
Nortel Networks Limited
Ton Dang
LandOfFree
Method and system for avoiding communication failure in CDMA... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for avoiding communication failure in CDMA..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for avoiding communication failure in CDMA... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2561963