Telecommunications satellite channelizer

Details Telecommunications satellite channelizer Telecommunications satellite channelizer

2000-10-11

2003-09-30

Appiah, Charles N. (Department: 2682)

Telecommunications

Carrier wave repeater or relay system

Portable or mobile repeater

C455S013300, C455S428000, C370S316000

Reexamination Certificate

active

06628920

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to the field of satellite based telecommunications and more specifically to a satellite channelizer subsystem for relaying communications signals between earth stations and mobile terminals based on predefined frequency plans.
Satellite based telecommunications systems have been proposed in the past in which a constellation of satellites orbit the earth while relaying bi-directional communications signals between mobile terminals and earth stations. In addition to supporting communication links between mobile terminals, these systems can connect mobile terminals to standard telephone subscribers, through earth station connections to public switched telephone networks.
By way of example only,
FIG. 1
generally illustrates a subsection of a proposed system in which a satellite
10
relays radio frequency (RF) signals between mobile terminals
12
and
13
and earth stations
14
and
16
. Communications links between mobile terminals
12
and
13
and satellite
10
are generally illustrated by references
18
and
19
, while first and second feeder links between the satellite
10
and the first and second earth stations
14
and
16
are generally illustrated by references
20
and
22
, respectively. Earth stations connect mobile terminals to fixed subscribers (not shown) via public switched telephone networks. Separate wideband terrestrial networks
11
,
17
and
21
(e.g., fiberoptic cable, microwave links, etc.) carry user communications traffic and signaling information between earth stations.
The earth or ground stations
14
and
16
each transmit RF signals over forward links, via the satellite
10
, to the mobile terminals
12
and
14
. The mobile terminals
12
and
14
, in turn, transmit RF signals over return links to the earth stations
14
and
16
.
Each satellite
10
includes at least one mobile antenna array (not shown) which defines a mobile coverage area
24
upon the earth surface, and at least one feeder link antenna or array (not shown) which can be pointed independently of the mobile antenna array. Feeder links may be operated at frequencies other than those assigned to the mobile links. The satellite
10
transmits and receives RF signals to and from mobile terminals and earth stations within the coverage area
24
. The mobile antenna array divides the coverage area into multiple adjacent mobile link beams
26
. Each beam
26
contains multiple frequency subbands having staggered central frequencies. In a single beam, contiguous groups of subbands may be combined to form mobile link channels.
The satellite
10
receives and transmits RF communications signals to and from mobile terminal
12
over one of the mobile link frequency subbands associated with the beam in which the mobile terminal
12
is located. Each mobile link subband may simultaneously carry RF signals to and from multiple mobile terminals at a common center frequency through the use of code division multiple access (CDMA) techniques. Each mobile terminal is assigned a unique CDMA chip code which is embedded within RF signals transmitted to and from the mobile terminal
12
. A mobile terminal to satellite bidirectional communications link (having forward and return links) established over a predefined mobile link subband and having a predefined CDMA chip code is referred to as a “resource”. Multiple resources are associated with a single mobile link subband. Each mobile link subband may only support a limited number of resources. As noted above, mobile link subbands are processed in groups, referred to as mobile link channels for simplification. Each beam includes at least one mobile link channel. Additional mobile link channels may be assigned to a single beam when the mobile terminal demand within the beam exceeds the number of resources available within a single mobile link channel (e.g., when a beam passes over a major metropolitan area). By way of example only, four mobile link channels may be available for use with a single beam.
FIGS. 2 and 3
illustrate exemplary feeder link and mobile link channel definitions which may be utilized in connection with a satellite based telecommunications system.
FIG. 2
illustrates the feeder link frequency spectrum
50
(e.g., 300 MHz) associated with a single ground station, which may be divided into a plurality of fixed bandwidth subsections (each of which is referred to as a “channel”). The feeder link frequency spectrum may be divided into a number of channels equaling the number of beams defined by the antenna array so that each ground station can service traffic in any beam. In the example of
FIG. 2
, 61 beams are utilized and thus the feeder frequency spectrum is divided into 61 channels of equal bandwidth (e.g., 4.9 MHz in width for a feeder link of 300 MHz in width).
FIGS. 3A and 3B
illustrate exemplary channel bandwidths which may be utilized for each mobile link beam. In the example of
FIG. 3A
, the bandwidth available for use within a single beam may be divided into three equal bandwidth mobile link channels, with each channel nominally assigned to one of a plurality of ground stations. Optionally, as in the example of
FIG. 3B
the mobile link beam bandwidth may equal 16.5 MHz which may be divided into two subbands of 4.9 MHz in bandwidth and two subbands of 3.35 MHz in bandwidth. The configuration of
FIG. 3B
enables full use of the allocated mobile link band in some beams when the allocated feeder link bandwidth is not sufficient to support the full mobile link band in all beams simultaneously.
Optionally, each satellite may support multiple feeder links simultaneously and allow multiple earth stations to simultaneously share the bandwidth available to each beam. In the example of
FIG. 1
, first and second earth or ground stations
14
and
16
communicate over first and second feeder links
20
and
22
with satellite
10
. Each of feeder links
20
and
22
may include a feeder bandwidth
50
divided as illustrated in
FIG. 2
among a plurality of beams. The mobile link beam bandwidth
60
(
FIG. 3B
) associated with a single beam
26
may be divided into mobile link channels
62
-
65
optionally, each mobile link channel
62
-
65
may be mapped or assigned to a different feeder link depending upon the number of earth stations in view of, and feeder links supportable by, the satellite
10
. If it is assumed that satellite
10
supports three feeder links, then mobile link channel
63
may be assigned to a first feeder link
20
with earth station
14
, mobile link channel
64
may be assigned to a second feeder link
22
with earth station
16
and mobile link channels
62
and
65
may be assigned to a third feeder link
23
with earth station
15
.
According to the example of
FIGS. 1-3
, earth station
14
may transmit RF signals over a desired subband of first channel
52
of feeder link
20
. The satellite
10
translates in frequency the RF signals received within channel
52
of feeder link
20
to the frequency of the corresponding subband of mobile link channel
63
. The satellite transmits the RF signals over mobile link channel
63
in the beam covering the mobile terminal
12
. Satellite
10
similarly receives RF signals within a designated subband of a designated channel of the second feeder link
22
from the second earth station
16
and translates same in frequency to a corresponding subband of mobile link channel
64
for retransmission over mobile link
18
to mobile terminal
12
.
FIG. 4A
illustrates an exemplary mapping scheme correlating a feeder link to multiple beams. A portion of the frequency spectrum of the feeder link is illustrated by reference
80
. The feeder link is divided into a plurality of feeder channels
82
numbered #1-190 6.
FIG. 4A
further illustrates frequency spectra for mobile link beams
84
-
86
corresponding to beams N−1, N and N+1 within a satellites coverage area. Mobile link beams
84
-
86
are divided into mobile link channels
88
-
90
, respectively. In the example of
FIG. 4A
, each m

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