Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-11-06
2003-01-28
Vo, Nguyen T. (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S450000, C370S329000
Reexamination Certificate
active
06512927
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to communication network management and, in one embodiment, to methods and apparatus for simultaneously preventing loss of signal and dropped connections between multiple mobile stations, such as cellular or PCS telephones, and a communication infrastructure (network).
2. Description of Related Art
Introduction
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.
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
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.
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.
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.
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.
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.
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.
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.
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, channels are defined by codes such as Walsh codes or quasi-orthogonal functions (QOF) such that the channels have minimal interference with one another even though they may be transmitted in the same frequency band and during the same 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. The CDMA wireless communication system is fully described by the following standards, all or which are published by the TELECOMMUNICATIONS INDUSTRY ASSOCIATION, Standards & Technology Department, 2500 Wilson Blvd., Arlington, Va. 22201, and all of which are herein incorporated by reference: TIA/EIA-95B, published Feb. 1, 1999; and TIA/VEIA/IS-2000, Volumes 1-5, Release A, published Mar. 1, 2000.
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
Denso Corporation
Moore James K
Morrison & Foerster / LLP
Vo Nguyen T.
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