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Forward link based rescue channel method and apparatus for telecommunication systemsRelated Patent Categories: Telecommunications, Radiotelephone System, Zoned Or Cellular Telephone System, Handoff, Handoff Initiated By Another Source (e.g., Target, User Initiated, Mobile Switching Center (msc), Or Mobile Telephone Switching Office (mtso), Etc.)Forward link based rescue channel method and apparatus for telecommunication systems description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070015512, Forward link based rescue channel method and apparatus for telecommunication systems. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a division of application Ser. No. 09/978,974 filed on Oct. 16, 2001, which claims the benefit under 35 USC 119(e) of U.S. provisional patent application Ser. No. 60/241,268 filed Oct. 17, 2000, and U.S. provisional patent application Ser. No. 60/248,900 filed Nov. 14, 2000, the contents of the prior applications which are incorporated herein by reference for all purposes. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates, generally, to communication network management and, in one embodiment, to methods and apparatus for preventing loss of signal and dropped connections between a mobile station, such as a cellular or PCS phone, and a wireless communication infrastructure (network). [0004] 2. Description of Related Art INTRODUCTION [0005] Rather than just providing a means for emergency communications, cellular telephones are rapidly becoming a primary form of communication in today's society. As cellular telephone usage becomes widespread, cellular telephone networks are becoming increasingly prevalent and are providing coverage over larger areas to meet consumer demand. FIG. 1 depicts an example of a mobile station (MS) 10 operated by a mobile user that roves through a geographic area served by a wireless infrastructure or network including a first base station (BS) 12 with wireless sectors A 14 and sector B 16, and a second BS 18, with a sector C 20. In the course of such roving, MS 10 travels from position A to position B to position C and will, as a matter of course, experience variations in signal strength and signal quality of the forward link associated with the BS(s) that it is in contact with. Signal strength and quality can be especially undependable near the edges of the sectors, such as when the MS 10 transitions from the area defined by the dotted line of Sector A 14 to the area defined by the dotted line of Sector B 16, or from Sector B 16 to Sector C 20. It is in these transition areas, as well as other areas of weak signal strength or quality, where dropped connections are likely to occur. A connection as referred to herein includes, but is not limited to, voice, multimedia video or audio streaming, packet switched data and circuit switched data connections, short message sequences or data bursts, and paging. [0006] Dropped connections can range from being a nuisance to devastating for cellular telephone users. For example, a dropped emergency 911 connection can be critical or even fatal. Dropped connections can create consumer frustration significant enough to cause the consumer to change service providers. Thus, the prevention of dropped connections is of major importance to cellular network providers. Cellular Telephone Networks [0007] FIG. 2 illustrates an exemplary communication link 22 between a MS 24 and a BS 26. Communications from the BS 26 to the MS 24 are called the forward link, and communications from the MS 24 to the BS 26 are called the reverse link. A BS 26 is typically comprised of multiple sectors, usually three. Each sector includes a separate transmitter and antenna (transceiver) pointed in a different direction. Because the term BS is often used to generally identify a transceiver, it should be understood that the terms BS and sector are used herein somewhat interchangeably. The forward and reverse links utilize a number of forward and reverse channels. For example, the BS 26 broadcasts on a plurality of forward channels. These forward channels may include, but are not limited to, one or more pilot channels, a sync channel, one or more paging channels, and multiple forward traffic channels. The pilot, sync, and paging channels are referred to as common channels because the BS 26 communicates those channels to all MSs. Generally, these common channels are not used to carry data, but are used to broadcast and deliver common information. In contrast, the multiple forward traffic channels are referred to as dedicated channels, because each forward traffic channel is intended for a specific MS 24 and may carry data. [0008] Each sector within BS 26 broadcasts a pilot channel that identifies that sector and is simple for a MS 24 to decode. Both sectors and pilot channels are distinguished by pseudo-noise (PN) offsets. The word "pilot" can be used almost interchangeably with the term sector, because a pilot channel identifies a sector. [0009] The pilot channel implicitly provides timing information to the MS, and is also used for coherent demodulation, but it otherwise typically does not contain any data. When a MS is first powered up, it begins searching for a pilot channel. When a MS acquires (is able to demodulate) a pilot channel, the timing information implicit in the pilot channel allows the MS to quickly and easily demodulate a sync channel being transmitted by the network. [0010] Because the sync channel contains more detailed timing information, once the MS acquires the sync channel, the MS is then able to acquire a paging channel being transmitted by the same BS that is transmitting the pilot channel. That BS is known as the active BS. [0011] When a cellular network is attempting to initiate communications with a MS through a particular BS, a "page" is transmitted to that MS on the paging channel of that BS. Thus, once the MS is able to demodulate the paging channel of a particular BS, the MS may then monitor that paging channel while the MS is idle and waiting for incoming connections or an incoming message. [0012] In general, each BS may utilize one pilot channel, one sync channel and one paging channel that are common for all MSs to receive. However, because there are practical limitations the number of MSs that can be simultaneously paged using one paging channel, some BSs may employ multiple paging channels. [0013] The reverse channels may include an access channel and one or more reverse traffic channels. After a MS receives an incoming page from a BS, the MS will initiate a connection setup using, in part, an access channel. [0014] The previously described channels may employ different coding schemes. In time division multiple access (TDMA), multiple channels may be communicated at a particular frequency within a certain time window by sending them at different times within that window. Thus, for example, channel X may use one set of time slots while channel Y may use a different set of time slots. In frequency division multiple access (FDMA), multiple channels may be communicated at a particular time within a certain frequency window by sending them at different frequencies within that window. In code division multiple access (CDMA), given a space of frequency and time, each channel is assigned various frequencies at various times, according to a particular Walsh code or quasi-orthogonal function (QOF). The code will define how a particular channel changes over frequency and time. In direct sequence CDMA, the data from each channel is coded using Walsh codes or QOFs and then combined into a composite signal. This composite signal is spread over a wide frequency range at a particular time. When this composite signal is decoded using the same code used to code the original data, the original data may be extracted. This recovery of the original data is possible because Walsh codes and QOFs create coded data that, when combined, don't interfere with each other, so that the data can be separated out at a later point in time to recover the information on the various channels. In other words, when two coded sequences of data are added together to produce a third sequence, by correlating that third sequence with the original codes, the original sequences can be recovered. When demodulating with a particular code, knowledge of the other codes is not necessary. However, noise and interference in the field may require error correction to determine what was actually transmitted. [0015] With further reference to CDMA for purposes of illustration only, the Walsh codes or QOFs are used to code a particular channel. Thus, as described above, the simple to decode pilot channel may be the all one coded W.sub.0 Walsh code. Similarly, the sync channel may use the alternating polarity W.sub.32 Walsh code and again, these codes are fixed and known. [0016] Each MS groups the channels into various sets, which may include, but is not limited to, an active set, a neighbor set, a candidate set, and a remaining set. [0017] The MS active set contains the pilots or PN offset identifiers that a MS is utilizing at any point in time. Thus, when a MS is idle, but monitoring a single BS for pages and overhead updates, the active set for that MS will contain that BS pilot or PN offset identifier as its only member. [0018] There may be instances, however, when a MS is being handed off from one BS or sector to another, and during this handoff may actually be in communication with multiple BSs or sectors at the same time. When this occurs, multiple active pilots will be in the active set at the same time. For example, in a "soft handoff," a MS in communication with BS "A" will begin to communicate with a BS "B" without first dropping BS "A," and as a result both BS "A" and "B" will be in the active set. In a "softer handoff," a MS in communication with sector "A" in BS "A" will begin to communicate with a sector "B" in BS "A" without first dropping sector "A," and as a result both sector "A" and "B" will be in the active set. In a "hard hand-off," however, a MS in communication with BS "A" will begin to communicate with a BS "B" only after first dropping BS "A," and as a result either BS "A" or "B" will be in the active set at any one time, but not both. [0019] During the time in which the MS is in communication with multiple BSs, the MS assigns rake receiver fingers to multiple channels from one or more sectors at the same time. When a MS is in communication with multiple BSs at the same time, the MS should be receiving the same data from both of those BSs. However, although the data may be the same, it may be communicated differently from different BSs because the channels may be different. The rake receiver will therefore receive encoded data from different sectors on different channels, demodulate those sectors independently, and then combine the data. When the data is combined, the data from a strong channel may be weighted more heavily than data from a weak channel, which is likely to have more errors. Thus, the data with a higher likelihood of being correct is given higher weight in generating the final result. [0020] When a MS is idle, a neighbor set which includes BSs that are neighbors to the active BS is received by the MS on a common channel. However, when a MS is active and communicating with a BS through a traffic channel, the neighbor set is updated on a traffic channel. Continue reading about Forward link based rescue channel method and apparatus for telecommunication systems... Full patent description for Forward link based rescue channel method and apparatus for telecommunication systems Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Forward link based rescue channel method and apparatus for telecommunication systems patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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