Telecommunications – Wireless distribution system
Reexamination Certificate
1999-04-21
2002-07-02
Maung, Nay (Department: 2744)
Telecommunications
Wireless distribution system
C455S436000, C455S442000, C455S450000, C455S453000, C725S062000
Reexamination Certificate
active
06415132
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to wireless communication systems and in particular to a technique for dynamic allocation of remotely deployed transceiving equipment.
Wireless communication networks, such as cellular mobile telephone and Personal Communications Services (PCS), continue to enjoy wide spread growth and popularity. There is often times a need in such systems to provide increasingly greater call handling capacity, as well as to accommodate higher peak usage. Emerging PCS networks, presently still in the stages of being implemented, demand additional design considerations such as low build out cost as they must compete with entrenched cellular networks.
Several approaches have been adopted for deploying such networks. One approach is to increase the coverage area afforded by a given system by increasing the antenna tower height and transmit power level beyond conventionally accepted norms. However, such solutions often increase the number of “blind” spots in areas that include a number of tall buildings, hills, or other natural obstructions to radio propagation.
Alternatively, a relatively large number of base stations may be deployed with smaller radio coverage “footprints”. While this avoids blind spots, it greatly increases the total capital cost for base station transceiving equipment which may be $200,000 or more per cell site.
Rather than deploy base station equipment in each relatively small cell (which would be relatively cost prohibitive), broadband distribution cable networks can be used to connect the antennas to centrally located base station equipment. For example, a suggestion has been made in U.S. Pat. No. 5,381,459 to use cable television networks to distribute wireless communication signals between base transceiver system (BTS) equipment and remote transceiver sites located at each cell. This approach couples the transceiver signals over an existing coaxial cable television network using time or frequency division multiplexing in order to avoid interference with other signals being carried, such as cable television signals.
Recently, other types of broadband distribution networks have also been proposed. Such networks consist of optical fiber transmission media which can directly distribute signals between centrally located base transceiver system (BTS) equipment and remotely located transceiver equipment. See, for example, our co-pending United States' patent application Ser. No. 09/256,244 entitled “Optical Simulcast Network with Centralized Call Processing,” filed Feb. 23, 1999.
There is also presently a demand by the customers of such cellular telephone systems for digital modulation techniques, such as code division multiple access (CDMA). In these CDMA systems, such as the IS-95B system being used widely in the United States a common frequency band is used to support communication between multiple mobile subscriber units and base stations. With this technique, signals occupying a common carrier frequency are discriminated at a receiving terminal (which may either be the base station or the mobile unit) based on the use of pseudo random noise (PN) codes. In particular, transmitting terminals use different PN codes or PN code phase offsets to produce signals that may be separately received. The mobile unit is then provided with a list of carrier signal codes and phase offsets corresponding to neighboring base stations surrounding the base station through which communication is established. The mobile unit is also equipped with a searching function that allows it to track the strength of the carrier signals generated from a group of the neighboring base stations.
In this CDMA system, various methods exist for switching a mobile unit from one base station to another. These methods, known as “handoff,” are an essential feature of cellular telephone systems which must support the ability to continue a telephone conversation in progress as a mobile unit moves between cells. The handoff method specified in the most popular CDMA system standards is called a “soft handoff.” This method is considered “soft” in the sense that communication with the adjacent base station is established before communication is terminated with the original base station. While the mobile unit is communicating with both base stations, a single receive signal for the remote subscriber unit is created by combining the signals from each base station within the circuits located in the mobile unit. Similarly, the signals received from the mobile unit by both base stations are combined in a centralized system controller prior to being forwarded to complete the connection.
While soft handoff solves certain problems caused by the movement of mobile units between cells, other difficulties are encountered within such systems when they use broadband distribution networks to distribute signals between remotely located transceiver equipment and the centralized base station equipment. In such networks, it is desirable to utilize the sharing or “simulcast” of radio carriers in adjacent cells. This permits the most efficient use of radio transceiving equipment when the demand for use of the system is relatively low.
However, as traffic demand increases over short periods of time, such as when traffic patterns change during the course of a day, it becomes desirable to activate additional transceiving equipment in the cells. By enabling the “blossoming” of such radio coverage, the additionally activated transceiving equipment can handle the increased traffic load. Such equipment should be deployed in a way which avoids the need for the remote units to switch between carrier frequencies. In particular, it would be desirable to avoid having to interrupt a communication in progress to command a mobile unit to perform a “hard” handoff to switch to a different carrier.
In other words, the system should operate in a simulcast mode such that adjacent cells or sectors may use the same carrier and code phase offsets when the traffic density is relatively light. It would then be desirable to disable the simulcast as new capacity is needed, and to do this in a way which does not require modification of standard remote subscriber units such which are already in use.
SUMMARY OF THE INVENTION
Briefly, the present invention is a technique for handling changes in demand over short periods of time in a is wireless communication system. An optical fiber or other available broadband distribution network is used to distribute signals between Centrally located base transceiver station (BTS) equipment and remotely located transceiver equipment referred to herein as “cable microcell integrators” (CMI). The CMIs are deployed in a configuration such as one per cell (or cell sector) to provide radio frequency coverage in a pattern which approximates the eventual expected required deployment of base stations when the system is at full capacity.
With this scenario, a single radio carrier preferably carries the channelized radio frequency (RF) signals as a simulcast for a number of different CMIs. The same active traffic channels may therefore be broadcast to multiple CMIs and hence to multiple coverage areas during time periods of low demand. In this mode, multiple adjacent CMIs are configured to communicate with the mobile subscriber units using the same RF channel. A group of CMIs arranged in this manner are referred to as a “simulcast cluster.” Simulcast clusters may also be defined by assigning other signal characteristics in common. For example, in CDMA systems, simulcast clusters are defined by assigning a common carrier frequency, common pseudonoise (PN) code, and common PN code phase offset. In comparison to traditional networks wherein the full capacity of an RF channel is not fully utilized, the coverage area of an RF channel may therefore be extended via the simulcast to provide a significant improvement in network efficiency.
In order to accommodate changes in traffic demand, such as may occur during a rush hour, a second RF channel is activated within the RF coverage
Davis Temica M.
Hamilton Brook Smith & Reynolds P.C.
Maung Nay
Transcept, Inc.
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