Pulse or digital communications – Synchronizers
Reexamination Certificate
2000-11-22
2002-03-05
Corrielus, Jean (Department: 2631)
Pulse or digital communications
Synchronizers
C455S522000, C455S502000, C370S510000
Reexamination Certificate
active
06353645
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to communication systems and more particularly to synchronization of mobile terminals operating in a wireless communication system.
BACKGROUND OF THE INVENTION
Public cellular networks (public land mobile networks) are commonly employed to provide voice and data communications to a plurality of subscribers. For example, analog cellular radiotelephone systems, such as designated AMPS, ETACS, NMT-450, and NMT-900, have been deployed successfully throughout the world. More recently, digital cellular radiotelephone systems such as that designated as IS-54B (and its successor IS-136) in North America and the pan-European GSM system have been introduced. These systems, and others, are described, for example, in the book titled
Cellular Radio Systems
by Balston, et al., published by Artech House, Norwood, Mass., 1993. In addition, satellite based radio communication systems are also being utilized to provide wireless communications in various regions such as the Asian Cellular Satellite System (ACeS) generated by Lockheed Martin Corporation.
FIG. 1
illustrates a conventional terrestrial wireless communication system
20
that may implement one of the aforementioned wireless communication standards. The wireless system may include one or more wireless mobile terminals
22
that communicate within a plurality of cells
24
served by base stations
26
and a mobile telephone switching office (MTSO)
28
. Although only three cells
24
are shown in
FIG. 1
, a typical cellular radiotelephone network may comprise hundreds of cells, and may include more than one MTSO
28
and may serve thousands of wireless mobile terminals
22
.
The cells
24
generally serve as nodes in the communication system
20
, from which links are established between wireless mobile terminals
22
and a MTSO
28
, by way of the base stations
26
servicing the cells
24
. Each cell
24
will have allocated to it one or more control channels and one or more traffic channels. The control channel is a dedicated channel used for transmitting cell identification and paging information. The traffic channels carry the voice and data information. Through the communication system
20
, a duplex radio communication link
30
may be effected between two wireless mobile terminals
22
or between a wireless mobile terminal
22
and a landline telephone user
32
via a public switched telephone network (PSTN)
34
. The function of the base station
26
is commonly to handle the radio communications within the cell
24
to and from the wireless mobile terminal
22
. In this capacity, the base station
26
functions chiefly as a relay station for data and voice signals.
FIG. 2
illustrates a conventional celestial (satellite) wireless communication system
40
. The celestial wireless communication system
40
may be employed to perform similar functions to those performed by the conventional terrestrial wireless communication system
20
of FIG.
1
. In particular, the celestial wireless communication system
40
typically includes one or more satellites
42
that serve as relays or transponders between one or more earth stations
44
and satellite wireless mobile terminals
23
. The satellite
42
communicates with the satellite wireless mobile terminals
23
and earth stations
44
via duplex communication links
46
. Each earth station
44
may in turn be connected to a PSTN
34
, allowing communications between the wireless mobile terminals
23
and conventional landline telephones
32
(FIG.
1
).
The celestial wireless communication system
40
may utilize a single antenna beam covering the entire area served by the system, or as shown in
FIG. 2
, the celestial wireless communication system
40
may be designed such that it produces multiple, partially-overlapping beams
48
, each serving a distinct geographical coverage area
50
within the system's service region. A satellite
42
and coverage area
50
serve a function similar to that of a base station
26
and cell
24
, respectively, of the terrestrial wireless communication system
20
.
Thus, the celestial wireless communication system
40
may be employed to perform similar functions to those performed by conventional terrestrial wireless communication systems. In particular, a celestial radiotelephone communication system
40
has particular application in areas where the population is sparsely distributed over a large geographic area or where rugged topography tends to make conventional landline telephone or terrestrial wireless infrastructure technically or economically impractical.
In both terrestrial and satellite based communication systems, it is known that a mobile terminal typically must first synchronize with a particular base station on the communication system by locating the appropriate carrier for a control channel of a base station which is capable of transmitting to and, preferably, receiving from the mobile terminal. The communication system typically transmits a synchronization burst during some repeating time portion or segment of a multi-frame of a Time Division Multiple Access (TDMA) system or at recurring intervals in an analog system. Because cellular systems typically use a variety of carriers for control channels in various cells or regions of the geographic area covered by the communication system, the mobile terminal generally searches a plurality of candidate carriers before selecting a carrier for synchronization. For example, the ACeS system includes 170 potential TDMA carriers separated 200 kHz from each other transmitting one m-sequence burst every 470 ms for use in synchronization.
It is also known to facilitate the synchronization process by providing a mobile terminal with a list of candidate carriers to consider when attempting to synchronize with a transmitter of a communication system. The mobile terminal typically tests each of the candidate carriers and selects a best candidate. The selection may be based on comparing the power of the signal received from each of the candidate carriers. A coarse synchronization followed by a fine synchronization are then typically performed with the selected carrier. For a TDMA system, this synchronization typically involves both frequency and time synchronization. After fine synchronization, the mobile terminal generally attempts to read data, such as a broadcast control channel transmission, to access the communication system.
While this approach to synchronization is effective, it can be problematic with low link margin communication systems. For example, satellite communication systems typically require a greater time for each candidate carrier to attempt to establish synchronization. This can result in an undesirable delay between a user seeking communication access, for example, by powering up the mobile terminal, and successful synchronization with the communication system. In addition, a further problem with low link margin communication systems such as satellite systems is that the mobile terminal may be in a blocked position, such as in a building, where it will not be possible for the mobile terminal to successfully receive a signal from the communication system. The synchronization system of the mobile terminal may then consume excessive battery power with repeated unsuccessful attempts to connect to the communication system. Accordingly, there is a need for improved synchronization systems and methods for mobile terminals operating in low link margin environments.
SUMMARY OF THE INVENTION
It is, therefore, an objective of the present invention to resolve the problem of slow synchronization of a mobile terminal with a low link margin communication system.
It is a further objective of the present invention to resolve the problem of battery power consumption due to unsuccessful attempts to synchronize a mobile terminal with low link margin communication systems.
These and other objects are provided, according to the invention, by providing methods and systems for synchronization of a mobile terminal to a communication system whic
Ranta Mark
Solve Torbjorn
Corrielus Jean
Myers Bigel & Sibley & Sajovec
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