Nessun titolo diapositiva

1
Satellite Personal Communications Systems
(S-PCS) the Globalstar System and evolutionary
paths towards 3G
SCHOOL ON DIGITAL AND MULTIMEDIA COMMUNICATIONS
USING TERRESTRIAL AND SATELLITE RADIO LINKS
27th February 2001
Giovanni De Maio Telit Mobile Terminals S.p.A. P
roject Manager - System Engineering
Satellite User Terminal Division
Via Vitorchiano, 81 - Rome giovanni.demaio_at_telita
l.com
2
Globalstar System Overview
3
Globalstar service aspects
Globalstar is a system that provide digital
telephony with a global coverage, by means of a
satellite constellation working in a Low Earth
Orbit (LEO). Globalstar allows access to the te
rrestrial networks, both fixed and mobile,
interworking with them in a complementary way.
In areas not covered by the terrestrial networks
, the Globalstar Terminal can be set to switch
automatically from the terrestrial to the
satellite mode. The system is designed in orde
r to maximise coverage in the temperate areas.
Globalstar System Overview
4
Globalstar System Architecture
Globalstar System Overview
GOCC Ground Operations Control Center
SOCC Space Operations Control Center
GDN Globalstar Data Network GBO Globalstar Bus
iness Office
5
Space Segment
Globalstar constellation
Globalstar System Overview
6
Space Segment
Earth Surface Coverage
Globalstar System Overview
The system is designed in order to maximise
coverage in the temperate areas.

7
Space Segment
Multiple Coverage (48 SATELLITES 10 ELEVATION)

• At LATITUDE 40
• At least 4 satellites for 38 of time
• At least 3 satellites for 87 of time
• At least 2 satellites always visible

Globalstar System Overview
At least one satellite always visible for
LATITUDE
8
Space Segment
User and feeder links
immagini
Globalstar System Overview
immagini
Satellites are of the non regenerative type they
simply perform a transparent relay of the signals
in both Forward and Reverse links
9
Space Segment
Frequency channels
Globalstar System Overview
10
Space Segment
Forward and Reverse User links channels or
Sub-Beams
L-Band Reverse User Link channels (Sub-Beams)
Globalstar System Overview
S-Band Forward User Link channels (Sub-Beams)
11
Sub-Beams to Gateways Assignment
Space Segment
Globalstar System Overview
Overlapping Beams will transmit Sub-Beams for
both Gateways
12
Space Segment
Globalstar Air Interface Channels
Globalstar System Overview
ACCESS slotted random access channel for call
originations, responses to pages and registrations
PILOT unmodulated DS SS signal transmitted by
the Gateway (employed to acquire the timing, as
phase reference for demodulation and to handoff)
TRAFFIC communication path between a UT and a
Gateway, which implies a Forward and a Reverse
Traffic Channel pair for voice, data, signaling
(when in a call)
SYNC channel carrying a repeating message for
terminal synchronization
13
Space Segment
Example of a Forward CDMA Channel
Globalstar System Overview
The above example shows a particular assignment
of the overall 128 channels (codes) within a 1.23
MHz Forward Channel to Pilot, Sync, Paging and
Traffic functionalities
14
Space Segment
Acquisition Search Space
Globalstar System Overview
The acquisition process consists of a research of
the pilot signal in a three dimensional search
space its dimensions are PN Code, PN Timing and
Frequency Doppler Shift. Note that the Frequency
Doppler Shift is actually a quite minor issue for
acquisition in a terrestrial environment (e.g.
IS-95). Less acquisition times could be achieved
in the Warm Start case by exploiting information
acquired during the previous start up.
15
Space Segment
Diversity Operation
Globalstar System Overview
Spatial diversity in the forward link is
illustrated combining is performed on up to
three received signal replicas
Diversity operation provides significant
advantages in both forward and reverse link
transmission (combining is carried out by the
user terminal and by the Gateway, respectively)
16
Globalstar Handoffs
Space Segment
Globalstar System Overview
Hard Handoff Intrabeam Handoff (change of
frequency)
17
Ground Segment
Components
TTC Tracking, Telemetry and Command
GDN Globalstar Data Network GCC Globalstar Con
trol Center (incorporates GOCC, SOCC an
d GBO into a single facility)
Globalstar System Overview
GOCC Ground Operations Control Center
SOCC Space Operations Control Center
SPCC Service Provider Control Center

GBO Globalstar Business Office (for financial
and administrative aspectsbusiness a
rrangements with SPs, billing, marke
ting and sales efforts
18
Ground Segment
Gateway - PLMN Interconnection
Globalstar System Overview
19
User Segment
Globalstar User Terminals Status Telit SAT 550
Globalstar System Overview
20
Globalstar User Terminals Status Telit SAT 650
User Segment
Shield
Radio board
Shield
Controller board
Front shell
Globalstar System Overview
Rear shell
21
GS User-to-GS User Operation
Call Processing
Globalstar System Overview
In this case satellites in view offer, as usual,
bent-pipe relays between users and relevant
Gateways whilst the Gateway-to-Gateway
connection relies onto the PSTN backbone
22
Simplified Call Procedure
Call Processing
Globalstar System Overview
User tries to place a call through the
Globalstar Satellite service
if the called party is a wireline or terrestrial
cellular-based end user ( ), the call is
routed through either the PSTN or PLMN
if the called party is a satellite-based end user
( ) the call is routed back through the
Gateway up to the Globalstar Satellite and down
to the user
23
3G S-PCS The Next Step
24
Wireless Evolution through the Generations series
3G
UMTS/IMT 2000 Global Standard for wireless
multimedia
Digital voice, low data rate applications GSM,
IS-54 (TDMA), IS-95 (CDMA), GLOBALSTAR, IRIDIUM
2G
3G S-PCS The Next Step

1G
Analogue voice (AMPS- Advanced Mobile Phone
Standard, TACS-Total Access Communications
System,... )
25
IMT 2000
International Mobile Telecommunications-200
0 (IMT-2000) are third generation mobile systems
which are scheduled to start service around the
year 2000 subject to market considerations. They
will provide access, by means of one or more
radio links, to a wide range of
telecommunications services supported by the
fixed telecommunication networks (e.g.
PSTN/ISDN/IP), and to other services which are
specific to mobile users A range of mobile
terminal types is encompassed, linking to
terrestrial and/or satellite based networks, and
the terminals may be designed for mobile or fixed
use As a strategic priority of ITU, IMT-20
00 provides framework for worldwide wireless
access by linking the diverse system of
terrestrial and/or satellite based networks.
3G S-PCS The Next Step
IMT is a result of the collaboration of many
entities, inside the ITU (ITU-R
Radiocommunication Sector and ITU-T
Telecommunication Standardization Sector ), and
outside the ITU (3GPP, 3GPP2, etc.)
26
Satellite Air interface selection - ITU Process
(ESA RTT) Commonalities with ETSI UTRA TDD.
Attractive for regional systems (HEO/GEO). (SRI-B)
Formerly TTA- SAT. (SRI-C)
Harmonization on going
Satellite Wide Band CDMA (ESA RTT- Radio
Transmission Technology). Adaptation of UMTS UTRA
W-CDMA to the satellite environment. Suited for
global systems (LEO/MEO). (SRI-A)
3G S-PCS The Next Step
27
First set of ETSI Technical Specs approved (1/2)
S-UMTS stands for the Satellite component of the
Universal Mobile Telecommunication System. S-UMTS
systems will complement the terrestrial UMTS
(T-UMTS) and inter-work with other IMT-2000
family members through the UMTS core network.
S-UMTS will be used to deliver 3rd generation
mobile satellite services (MSS) utilizing either
low (LEO) or medium (MEO) earth orbiting, or
geostationary (GEO) satellite(s). S-UMTS systems
are based on terrestrial 3GPP specifications and
will support access to GSM/UMTS core networks.
Due to the differences between terrestrial and s
atellite channel characteristics, some
modifications to the terrestrial UMTS (T-UMTS)
standards are necessary. Some specifications are
directly applicable, whereas others are
applicable with modifications. Similarly, some
T-UMTS specifications do not apply, whilst some
S-UMTS specifications have no corresponding
T-UMTS specification.
3G S-PCS The Next Step
28
First set of ETSI Technical Specs approved (2/2)
Satellite Component of UMTS/IMT 2000 A-family
Part 1 Physical channels and mapping of transpo
rt channels into physical channels
(S-UMTS-A 25.211) Part 2 Multiplexi
ng and channel coding (S-UMTS-A 25.2
12) Part 3 Spreading and modulation
(S-UMTS-A 25.213) Part 4 Physical layer pro
cedures (S-UMTS-A 25.214)
3G S-PCS The Next Step
29
S-UMTS Air Interface transport and physical
channels
3G S-PCS The Next Step
The mapping of transport channels onto physical
channels is a fundamental function performed by
the physical layer
30
Worldwide Frequency Bands
2X30 MHz in S-Band allocated to MSS, adjacent to
spectrum allocation for terrestrial systems
3G S-PCS The Next Step
ERC (European Radiocommunications Committee)
assignments to MSS 2 x 30 MHz (1980 - 201
0 MHz and 2170 - 2200 MHz) 15 MHz availabl
e from 2000 (1995 - 2010 MHz and 2185 - 2200
MHz) 30 MHz available from 2005 (1980 - 20
10 MHz and 2170 - 2200 MHz) 15 MHz assigne
d TDMA systems (S-PCS) (1995 - 2010 MHz and 2185
-2200 MHz)
31
Spectrum Needs
More bandwidth requested
Terrestrial PCS are competing for spectr
um allocation WRC2000 (2000 World Radio
communications Conference) postponed a decision
on satellite phone frequencies until 2003, which
means that before 2003 a viable satellite
consortium needs to be established or else the
already allocated spectrum will be lost and
available in favour of T-UMTS
3G S-PCS The Next Step
32
From 3GPP 3G TS 22.105 UMTS Service aspects,
Services and Service Capabilities
3G S-PCS The Next Step
33
Again from 3GPP 3G TS 22.105
3G S-PCS The Next Step
34
UMTS QoS Classes (1/2)
3G S-PCS The Next Step
Differently from systems belonging to the
previous generations, UMTS allows to enjoy the
use of bearers, defined by means of bearer
service attributes, and not of end-services/applic
ations directly. To aid the application-to-bearer
mapping, QoS classes for homogeneous end-services
have been devised, which are themselves service
attributes, characterized by a set of specific
service attributes, as from the following
viewgraph.
35
UMTS QoS Classes (2/2)
Attributes for UMTS Bearer Services
3G S-PCS The Next Step
36
The Satellite Access Network
3G S-PCS The Next Step
The access network infrastructure for the S-UMTS
is here envisaged with minimal differences
compared to the terrestrial 3G infrastructure.
The satellite should play the role of the T-UMTS
Node B (Base Station) but its to be deepened
whether the same terrestrial Iur and Iub
interfaces could be employed, which have been
devised for T-UMTS between RNCs and between RNC
and Node B, respectively.
37
S-UMTS Terminal envisaged architecture
The Control Processor manages the exchange of
data/addressing information between the DSP and
the ASIC
A digital predistortion in the TX path is
envisaged, performed by the loop DSP-Up
conversion path-Antenna set-Feedback. The same
feedback line, shown in figure, is used to
perform a dinamic adjustment, to improve the
linearity of the receiving section.
3G S-PCS The Next Step
The core of the system is the DSP, responsible of
most of the baseband processing the support of
dedicated ASICs for particular heavy
computational operations like rake-decoding/Interf
erence mitigation can be necessary depending on
DSP computational power. In this last case, a
dedicated bus between the DSP and the ASIC could
also be needed, or the ASIC should directly
communicate with the AD/DA converters and then
with the DSP.