Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1997-12-22
2001-08-14
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Repeater
Reexamination Certificate
active
06275480
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to satellite communication systems, and more particularly to satellite cellular communication systems.
BACKGROUND OF THE INVENTION
Mobile cellular communication systems have become of increasing importance, providing mobile users the security of being able to seek aid in case of trouble, allowing dispatching of delivery and other vehicles with little wasted time, and the like. Present cellular communication systems use terrestrial transmitters, such as fixed sites or towers, to define each cell of the system, so that the extent of a particular cellular communication system is limited by the region over which the towers are distributed. Many parts of the world are relatively inaccessible, or, as in the case of the ocean, do not lend themselves to location of a plurality of dispersed cellular sites. In these regions of the world, spacecraft- or satellite-based communication systems may be preferable to terrestrial-based systems. It is desirable that a spacecraft cellular communications system adhere, insofar as possible, to the standards which are common to terrestrial systems, and in particular to such systems as the GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS system (GSM), which is in use in Europe.
The GSM system is a cellular communications system which communicates with user terminals by means of electromagnetic transmissions from, and receptions of such electromagnetic signals at, fixed sites or towers spaced across the countryside. The GSM system is described in detail in the text
The GSM System for Mobile Communications
, subtitled
A Comprehensive Overview of the European Digital Cellular System
, authored by Michel Mouly and Marie-Bernadette Pautet, and published in 1992 by the authors, at 4, rue Eliseée Reclus, F-91120 Palaiseau, France. Each fixed site or tower (tower) of the GSM system includes transmitter and receiver arrangements, and communicates with user terminals by way of signals having a bandwidth of 50 MHz., centered at about 900 Mhz., and also by way of signals having a bandwidth of 150 Mhz. Centered at about 1800 Mhz.
In cellular communications systems such as GSM, associated and dedicated control signaling is required for sending information messages about the system between the terrestrial mobile user terminal and the base station. Such information messages serve two purposes: (1) call “Set-Up”, for which standalone dedicated control channels, such as the SDCCH channel in the GSM system, are used during the setup of the call, and (2) Call Maintenance, for which slow and fast associated channels, such as SACCH and FACCH in the GSM system, are used to provide signaling during the call. Mobile Satellite Systems based upon the GSM architecture use similar dedicated and associated control channels to send system information messages as part of call set-up and “in-call signaling.”
“In-Call Signaling” in a satellite system, must occur during a call, or while a call is currently in place, much as in FACCH. The “in-call” signalling is accomplished by “stealing” or commandeering portions of TDMA traffic slots from the ongoing call. The TDMA burst structure for GSM uses two bits designated with information-carrying capacity to indicate when traffic data is being overridden by in-call signaling. The use of these two bits as an in-call-signalling flag reduces the available traffic throughput, and reduces the available error-correction capability for traffic.
Allowed patent application serial U.S. Pat. No. 5,717,686 filed Jan. 21, 1997 in the SPACECRAFT TDMA COMMUNICATIONS SYSTEM WITH CALL INTERRUPT CODING SYSTEM FOR MAXIMIZING THROUGHPUT, describes a communication system illustrated in
FIG. 1
, which is a simplified block diagram of a spacecraft or satellite cellular communications system
10
. In system
10
, a spacecraft
12
includes a transmitter (TX)
12
t
, a receiver (RX)
12
r
, and a frequency-dependent channelizer
12
c
, which routes bands of frequencies from the receiver
12
r
to the transmitter
12
t
. Spacecraft
12
also includes an array of frequency converters
12
cv
, which convert the uplink frequency to an appropriate downlink frequency. Antenna
12
a
generates a plurality
20
of spot beams, one spot beam for each frequency band. Some of the spot beams are illustrated as
20
a
,
20
b
,
20
c
, and
20
d
. Each spot beam
20
x
(where x represents any suffix) defines a footprint on the earth
1
below. Two of the spot beam footprints are illustrated as
20
bf
and
20
cf
. It will be understood that those spot beams which are illustrated in “lightning bolt” form also produce footprints. As is known to those skilled in the art, the footprints of spot beams from a spacecraft may overlap, to provide continuous coverage of the terrestrial region covered by the spot beams.
As illustrated in
FIG. 1
, a group
16
of mobile terrestrial user terminals or stations includes two mobile user terminals, denominated
16
a
and
16
b
, each of which is illustrated as having an upstanding whip antenna (not separately designated). User terminal
16
a
lies within the footprint
20
bf
, and user terminal
16
b
lies within footprint
20
cf
. User terminals
16
a
and
16
b
provide communications service to users, as described below. Each user terminal
16
a
and
16
b
is illustrated as including an access signal generator
16
aa
and
16
ab
, respectively.
FIG. 1
also illustrates a terrestrial gateway terminal (fixed site, tower, or station)
24
, which lies in a footprint (not designated) of spot beam
20
a
. Gateway terminal
14
communicates with spacecraft
12
by way of electromagnetic signals transmitted from an antenna
14
a
, and receives signals from the spacecraft by way of the same antenna. Gateway terminal
14
provides communication by way of a path
9
between spacecraft cellular communications system
10
and a land-line network illustrated as a block
8
. While a single gateway
14
is illustrated, the system
10
may contain many gateways at spaced-apart locations.
A network control center (NCC)
18
in
FIG. 1
is a terrestrial terminal which includes an antenna
18
a
for communication with the spacecraft, and by way of the spacecraft to the mobile user terminals
16
and the gateway(s)
14
. NCC
18
also includes a GPS receiving antenna
18
g
for receiving global positioning time signals, to provide an accurate time clock. The network control center performs the synchronization and TDMA control which the spacecraft cellular communications network requires. There may be a plurality of such NCCs throughout the system, adapted for providing control for particular sets of channels of the system. While NCC
18
is illustrated as being separate from gateway
14
, those skilled in the art will recognize that the NCC includes functions, such as the antenna, which are duplicated in the gateway
14
, and it makes economic sense to place the NCC(s) at the sites of the gateway(s), so as to reduce the overall system cost by taking advantage of the redundancies to eliminate expensive subsystems.
It should be understood that the normal operation of a TDMA transmitter inherently performs an interleaving function, in that a plurality of messages constituting different information are transmitted over a plurality of different “channels”, each of which is represented by a non-continuous sequence of bursts, interleaved with other sequences of bursts, which carry the other information. Thus, the data of the various messages is broken into packets which are temporally interleaved onto the channel to form “virtual” channels. The function of block
234
of
FIG. 2
b
substitutes the interrupt message in one virtual channel for the current message data which would otherwise flow in that virtual channel. In effect, the interleaved messages are then further interleaved by the TDMA system.
As so far described, the satellite communication system is generally similar to that described in a Provisional patent application filed on or about Sep. 3, 1997 in the name of Hudson, and entitled SPACECRAFT CELLULAR COMMUNICATION
Kwoh Jasper
Lockheed Martin Corp.
Meise W. H.
Nguyen Chau
LandOfFree
Fast associated control channel coding for speech channel does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fast associated control channel coding for speech channel, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fast associated control channel coding for speech channel will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2533834