Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-08-20
2004-05-04
Gelin, Jean (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S442000
Reexamination Certificate
active
06731936
ABSTRACT:
BACKGROUND
1. Field
The present invention relates to broadcast communications, otherwise known as point-to-multipoint, in a wireline or a wireless communication system. More particularly, the present invention relates to a system and method for a handoff in such a broadcast communication system.
2. Background
Communication systems have been developed to allow transmission of information signals from an origination station to a physically distinct destination station. In transmitting information signal from the origination station over a communication channel, the information signal is first converted into a form suitable for efficient transmission over the communication channel. Conversion, or modulation, of the information signal involves varying a parameter of a carrier wave in accordance with the information signal in such a way that the spectrum of the resulting modulated carrier is confined within the communication channel bandwidth. At the destination station the original information signal is replicated from the modulated carrier wave received over the communication channel. Such a replication is generally achieved by using an inverse of the modulation process employed by the origination station.
Modulation also facilitates multiple-access, i.e., simultaneous transmission and/or reception, of several signals over a common communication channel. Multiple-access communication systems often include a plurality of subscriber units requiring intermittent service of relatively short duration rather than continuous access to the common communication channel. Several multiple-access techniques are known in the art, such as time division multiple-access (TDMA), frequency division multiple-access (FDMA), and amplitude modulation multiple-access (AM). Another type of a multiple-access technique is a code division multiple-access (CDMA) spread spectrum system that conforms to the “TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wide-Band Spread Spectrum Cellular System,” hereinafter referred to as the IS-95 standard. The use of CDMA techniques in a multiple-access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE-ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee of the present invention.
A multiple-access communication system may be a wireless or wireline and may carry voice and/or data. An example of a communication system carrying both voice and data is a system in accordance with the IS-95 standard, which specifies transmitting voice and data over the communication channel. A method for transmitting data in code channel frames of fixed size is described in detail in U.S. Pat. No. 5,504,773, entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION”, assigned to the assignee of the present invention. In accordance with the IS-95 standard, the data or voice is partitioned into code channel frames that are 20 milliseconds wide with data rates as high as 14.4 Kbps. Additional examples of a communication systems carrying both voice and data comprise communication systems conforming to the “3rd Generation Partnership Project” (3GPP), embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), or “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard).
An example of a data only communication system is a high data rate (HDR) communication system that conforms to the TIA/EIA/IS-856 industry standard, hereinafter referred to as the IS-856 standard. This HDR system is based on a communication system disclosed in application Ser. No. 08/963,386, entitled “METHOD AND APPARATUS FOR HIGH RATE PACKET DATA TRANSMISSION,” filed Nov. 3, 1997, now U.S. Pat. No. 6,574,211, issued on Jun. 3, 2003, assigned to the assignee of the present invention. The HDR communication system defines a set of data rates, ranging from 38.4 kbps to 2.4 Mbps, at which an access point (AP) may send data to a subscriber station (access terminal, AT). Because the AP is analogous to a base station, the terminology with respect to cells and sectors is the same as with respect to voice systems.
In a multiple-access communication system, communications between users are conducted through one or more base stations. A first user on one subscriber station communicates to a second user on a second subscriber station by transmitting data on a reverse link to a base station. The base station receives the data and can route the data to another base station. The data is transmitted on a forward link of the same base station, or the other base station, to the second subscriber station. The forward link refers to transmission from a base station to a subscriber station and the reverse link refers to transmission from a subscriber station to a base station. Likewise, the communication can be conducted between a first user on one subscriber station and a second user on a landline station. A base station receives the data from the user on a reverse link, and routes the data through a public switched telephone network (PSTN) to the second user. In many communication systems, e.g., IS-95, W-CDMA, IS-2000, the forward link and the reverse link are allocated separate frequencies.
When a subscriber station travels outside the boundary of the base station with which the subscriber station currently communicates, it is desirable to maintain the communication link by transferring the call to a different subscriber station. The method and system for providing a communication with a subscriber station through more than one base station during the soft handoff process are disclosed in U.S. Pat. No. 5,267,261, entitled “MOBILE ASSISTED SOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEM,” assigned to the assignee of the present invention. The method and system for providing a softer hand-off is described in detail in U.S. Pat. No. 5,933,787, entitled “METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMON BASE STATION,” assigned to the assignee of the present invention. Using these methods, communication between the subscriber stations is uninterrupted by the eventual handoff from an original base station to a subsequent base station. This type of handoff may be considered a “soft” handoff in that communication with the subsequent base station is established before communication with the original base station is terminated. When the subscriber unit is in communication with two base stations, the subscriber unit combines the signals received from each base station in the same manner that multipath signals from a common base station are combined.
In accordance with the above-cited inventions, each base station transmits a pilot signal of a common PN spreading code offset in code phase from pilot signals of other base stations. A subscriber station assisted soft handoff operates based on the pilot signal strength detected by the subscriber station. To streamline the process of searching for pilots, four distinct sets of pilot offsets are defined: the Active Set, the Candidate Set, the Neighbor Set, and the Remaining Set. The Active Set identifies the base station(s) or sector(s) through which the subscriber station is communicating. The Candidate Set identifies the base station(s) or sector(s) for which the pilots have been received at the subscriber station with sufficient signal strength to make them members of the Active Set, but have not been placed in the Active Set by the base station(s). The Neighbor Set identifies the base station(s) or sector(s), which are likely candidates for the establishment of communication with the subscriber station. The Remaining Set identifies the base station(s) or sector(s) having all other possible pilot offsets in the current system, excluding those pilot offsets currently in the Active, the Candidate and Neighbor sets.
The sub
Butler Brian K.
Chen Tao
Sinnarajah Ragulan
Tiedemann Jr. Edward G.
Wang Jun
Baker Kent D.
Gelin Jean
Kalousek Pavel
Qualcomm Incorporated
Wadsworth Philip
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