Satellite diversity scheme

Details Satellite diversity scheme Satellite diversity scheme

1997-04-14

2002-12-10

Nguyen, Chau (Department: 2663)

Multiplex communications

Diagnostic testing

Determination of communication parameters

C370S331000, C370S336000

Reexamination Certificate

active

06493322

ABSTRACT:

FIELD OF THE INVENTION
The present invention generally relates to mobile communications. More particularly, the present invention relates to a satellite mobile communications method and system in which a mobile unit can selectively exchange signals with multiple satellites.
BACKGROUND OF THE INVENTION
Referring to
FIG. 1
, a typical cellular mobile radiocommunication system is shown. The typical system includes a number of base stations similar to base station
110
and a number of mobile units or stations similar to mobile
120
. Voice and/or data communication can be performed using these devices or their equivalents. The base station includes a control and processing unit
130
which is connected to the MSC (mobile switching center)
140
which in turn is connected to the public switched telephone network (not shown).
The base station
110
serves a cell and includes a plurality of voice channels handled by voice channel transceiver
150
which is controlled by the control and processing unit
130
. Also, each base station includes a control channel transceiver
160
which is typically capable of exchanging control signals on more than one control channel. The control channel transceiver
160
is controlled by the control and processing unit
130
. The control channel transceiver
160
broadcasts control information over the control channel of the base station or cell to mobiles locked to that control channel. The voice channel transceiver broadcasts the traffic or voice channels which can include digital control channel location information.
When the mobile
120
first enters an idle mode, it periodically scans the control channels of base stations like base station
110
for the presence of a paging burst addressed to the mobile
120
. The paging burst informs mobile
120
which cell to lock on or camp to. The mobile
120
receives the absolute and relative information broadcast on a control channel at its voice and control channel transceiver
170
. Then, the processing unit
180
evaluates the received control channel information which includes the characteristics of the candidate cells and determines which cell the mobile should lock to. The received control channel information not only includes absolute information concerning the cell with which it is associated, but also contains relative information concerning other cells proximate to the cell with which the control channel is associated. These adjacent cells are periodically scanned while monitoring the primary control channel to determine if there is a more suitable candidate. Additional information relating to specifics of mobile and base station implementations can be found in U.S. patent application Ser. No. 07/967,027, now U.S. Pat. No. 5,745,523 entitled “Multi-Mode Signal Processing” filed on Oct. 27, 1992 to P. Dent and B. Ekelund, the entirety of which is incorporated herein by reference. It will be appreciated that the base station may be replaced by one or more satellites in a satellite-based mobile radiocommunication system.
To increase radiocommunication system capacity, digital communication and multiple access techniques such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA) may be used. The objective of each of these multiple access techniques is to combine signals from different sources onto a common transmission medium in such a way that, at their destinations, the different channels can be separated without mutual interference. In a FDMA system, users share the radio spectrum in the frequency domain. Each user is allocated a part of the frequency band which is used throughout a conversation. In a TDMA system, users share the radio spectrum in the time domain. Each radio channel or carrier frequency is divided into a series of time slots, and individual users are allocated a time slot during which the user has access to the entire frequency band allocated for the system (wideband TDMA) or only a part of the band (narrowband TDMA). Each time slot contains a “burst” of information from a data source, e.g., a digitally encoded portion of a voice conversation. The time slots are grouped into successive TDMA frames having a predetermined duration. The number of time slots in each TDMA frame is related to the number of different users that can simultaneously share the radio channel. If each slot in a TDMA frame is assigned to a different user, the duration of a TDMA frame is the minimum amount of time between successive time slots assigned to the same user. CDMA combines FDMA and TDMA. In a CDMA system, each user is assigned a unique pseudorandom user code to uniquely access the frequency time domain. Examples of CDMA techniques include spread spectrum and frequency hopping.
In a TDMA system, the successive time slots assigned to the same user, which are usually not consecutive time slots on the radio carrier, constitute the user's digital traffic channel, which is considered to be a logical channel assigned to the user. The organization of TDMA channels, using the GSM standard as an example, is shown in FIG.
2
. The TDMA channels include traffic channels TCH and signalling channels SC. The TCH channels include full-rate and half-rate channels for transmitting voice and/or data signals. The signalling channels SC transfer signalling information between the mobile unit and the satellite (or base station). The signalling channels SC include three types of control channels: broadcast control channels (BCCHs), common control channels (CCCHs) shared between multiple subscribers, and dedicated control channels (DCCHs) assigned to a single subscriber. A BCCH typically includes a frequency correction channel (FCH) and a synchronization channel (SCH), both of which are downlink channels. The common control channels (CCCHs) include downlink paging (PCH) and access grant (AGCH) channels, as well as the uplink random access channel (RACH). The dedicated control channels DCCH include a fast associated control channel (FACCH), a slow associated control channel (SACCH), and a standalone dedicated control channel (SDCCH). The slow associated control channel is assigned to a traffic (voice or data) channel or to a standalone dedicated control channel (SDCCH). The SACCH channel provides power and frame adjustment and control information to the mobile unit.
The frequency correction channel FCH of the broadcast control channel carries information which allows the mobile unit to accurately tune to the base station. The synchronization channel SCH of the broadcast control channel provides frame synchronization data to the mobile unit.
The random access channel RACH is used by the mobiles to request access to the system. The RACH logical channel is a unidirectional uplink channel (from the mobile to the base station or satellite), and is shared by separate mobile units (one RACH per cell is sufficient in typical systems, even during periods of heavy use). Mobile units continuously monitor the status of the RACH channel to determine if the channel is busy or idle. If the RACH channel is idle, a mobile unit desiring access sends its mobile identification number, along with the desired telephone number, on the RACH to the base station or satellite. The MSC receives this information from the base station or satellite and assigns an idle voice channel to the mobile station, and transmits the channel identification to the mobile through the base station or satellite so that the mobile station can tune itself to the new channel. All time slots on the RACH uplink channel are used for mobile access requests, either on a contention basis or on a reserved basis. Reserved-basis access is described in U.S. patent application Ser. No. 08/140,467, now, U.S. Pat. No. 5,420,864 entitled “Method of Effecting Random Access in a Mobile Radio System”, which was filed on Oct. 25, 1993, and which is incorporated in this application by reference. One important feature of RACH operation is that reception of some downlink information is required, whereby mobile stations

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