Mobile Satellite Communications System
Mobile Satellite Communications Service
IP Network
NTT DOCOMO Technical Journal
Special Articles on WIDESTAR II High-speed Mobile Satellite Communications Service for Diverse Satellite Communications
Overview of WIDESTAR II Mobile Satellite
Communications System and Service
WIDESTAR II began mobile satellite communications service covering all of the Japan landmass and the maritime
area around it in April 2010 using four beams of the N-STAR c/d
geostationary satellites. The new system provides all of the
previous WIDESTAR services and expands data communications at lower charges. Base station equipment and mobile
stations were newly developed, and core node equipment was
developed to add only the functions specific to mobile satellite communications and incorporate IMS and other generalpurpose IP technology to allow economical operation and
provision of diverse high-speed mobile satellite communications services.
1. Introduction
Radio Access Network Development Department
Kazuichi Yamamoto
Core Network Development Department
Makoto Furukawa
Product Department
Hijin Satoh
Corporate Marketing Strategy Department
Yasuki Nishi
Network Department
Kouji Horikawa
communications by the Global Mar-
continuing the services provided by
itime Distress and Safety System
WIDESTAR, WIDESTAR II is intend-
*1
The mobile satellite communications
(GMDSS) . For land mobile use, the
ed to realize diverse satellite communi-
service offered by NTT DOCOMO has
system has served as a solution for data
cations services with higher data com-
been in operation for more than ten
communications services on distant
munications speed in order to expand
years under the name of WIDESTAR.
islands, in mountainous regions and in
data communications and the solution
The satellite telephone service [1]
other such areas where mobile phone
usage. Also, the new system developed
began in March 1996 and the satellite
signals are not available as well as a
and implemented services in accor-
packet communications service [2]
means of communications for disaster
dance with the trends in the transition
began in March 2000. WIDESTAR
response by local governments [3].
toward data-centered traffic in the use
†††
†††
†††
†††
of mobile phones and other forms of
provides an important means of com-
WIDESTAR II is a new mobile
munications for ships at sea in times of
satellite communications service that
distress, and has been certified as the
was launched simultaneously across
In this special article, we begin with
means of radio telegraphy for general
Japan in April 2010 [4]. In addition to
an overview of WIDESTAR II mobile
†
Currently Kansai Regional Office
†† Currently Consumer Services Department
††† Currently Solution Business Department
*1 GMDSS: A world-wide system for safety at
sea.
NTT DOCOMO Technical Journal Vol. 12 No.2
†††
mobile communications.
37
NTT DOCOMO Technical Journal
Overview of WIDESTAR II Mobile Satellite Communications System and Service
satellite communications system and
previous WIDESTAR, revises the pro-
the systems for smooth and step-wise
service development and go on to
vided services according to satellite
system migration from WIDESTAR.
explain the specific development of
communications use and demand, and
The frequency plan used by both the
technology in the communications
provides some other communications
new and old WIDESTAR systems has a
scheme [5], core network system [6],
services such as multicast communica-
bandwidth of 15-MHz for each satellite,
base station equipment [7], the base sta-
tions as solutions. In addition to that, it
within which all channels are config-
tion maintenance and monitoring sys-
is a necessary and sufficient require-
ured to prevent mutual interference
tem [8] and mobile station [9].
ment that the communications charges
(Figure 2). Furthermore, to serve as a
can be made more economical in order
system that can be used continuously
to promote the extensive use of data
and with high reliability even during
communications and to expand solu-
large-scale disasters, it must be possible
tions.
to change radio frequency band settings
2. Overview of
WIDESTAR II
The WIDESTAR II system outline
is shown in Figure 1.
flexibly to allow increased voice traffic
WIDESTAR II uses two geosta-
3.2 Facility Requirements
at times of disaster.
tionary satellites, N-STAR c[10] and d,
One requirement for all WIDESTAR II
whose four beams of 600-km in radius
facilities is the extensive use of general-
cover a service area that includes the
purpose technology to reduce the devel-
Japan landmass and the surrounding
opment and operation cost. Another
WIDESTAR II mobile satellite com-
maritime area. The N-STAR c/d com-
requirement is to enable both systems
munications system is shown in Figure
munications satellites, successors to the
to be accommodated by the same com-
3. Higher data communications speed is
N-STAR a/b satellites of the original
munications satellites through the use
achieved by newly developed base sta-
4. System
The
*4
WIDESTAR, feature improved repeater
of frequency division multiplexing
capability for higher data communica-
and prevention of interference between
configuration
of
the
tion and mobile station equipment and
taking advantage of the repeater capa-
tions speed. The feeder link between
the base station and the satellite uses the
N-STAR d
N-STAR c
*2
C band (6/4 GHz), and the service link
· Geostationary satellite : N-STAR c and d
· Satellite base station : 2
· Frequency band used : S band and C band
between the mobile station and the
satellite uses the S band
*3
(2.6/2.5
GHz), a radio frequency band that is
Beam 1
(Eastern Japan)
Satellite base station
robust to rain attenuation. Four beams
are used to provide the service coverage
area.
3. Requirements
3.1 Service Requirements
Beam 2
(Western Japan)
Beam 3
(Okinawa)
Beam 4
(Ogasawara)
Service link (S band)
Feeder link (C band)
WIDESTAR II continues to provide the legacy basic voice and data
Figure 1 WIDESTAR service image
communications services offered by the
*2 C band: A name for the frequency band from
4 to 8 GHz. WIDESTAR uses the 6/4 GHz frequency band.
*3 S band: A name for the frequency band from
2 to 4 GHz. WIDESTAR uses the 2.6/2.5 GHz
frequency band.
38
*4 Frequency division multiplexing: A multiple access scheme in which radio frequencies
are divided and allocated to mobile terminal
radio channels.
NTT DOCOMO Technical Journal Vol. 12 No.2
Feeder link (C band)
72 MHz
6 MHz
6 MHz
15 MHz
15 MHz
12 MHz
S3
S1
S2
S4
6,349 MHz
4,124 MHz
Downlink
Uplink
Frequency
6,421 MHz
4,196 MHz
Service link (S band)
NTT DOCOMO Technical Journal
6 MHz
12 MHz
S1 (L)
S1 (H)
S2 (L)
S2 (H)
S3 (L)
S3 (H)
S4 (L)
S4 (H)
12 MHz
12 MHz
15 MHz
S (L)
Downlink
Uplink
2,505 MHz
2,660 MHz
15 MHz
S (H)
2,520 MHz
2,675 MHz
2,535 MHz
2,690 MHz
S1 to S4 : The S and C frequency bands allocated to each beam area
H, L : High and low end of the frequency band
Figure 2 WIDESTAR frequency band configuration
Core node 1
IMS
Core node 2
MPN
MGN/S-MRN
MGN/S-MRN
S-ASN/S-CSN
S-ASN/S-CSN
AGS
SIN
S-AP1
EPC
Base
station 2
S-AP3
S-AP2
xGSN
IP router network
IP router network
Base
station 1
MGN/MRN
All-IP network
AGS
OPS
CSN/ASN
S-AP4
Antenna
IP-RNC
BTS
N-STAR d
eNode B
N-STAR c
S-MS
Existing 3G
WIDESTAR II mobile satellite communications system
LTE
Mobile communications system
Figure 3 WIDESTAR II system configuration
NTT DOCOMO Technical Journal Vol. 12 No.2
39
NTT DOCOMO Technical Journal
Overview of WIDESTAR II Mobile Satellite Communications System and Service
40
bility attained through use of the
satellites. The system maintenance con-
ment scale were achieved by develop-
N-STAR satellites and other existing
trol is the function that selects the unaf-
ing only the functions specific to
radio facilities. For the core network, an
fected base station to accommodate all
WIDESTAR II and adding them to the
economical system was developed and
of the communications, thus suppress-
established FOMA base.
realized through renovation of core
ing the effect on the service.
nodes from PDC to 3G-based equip-
3) Load Balancing
The Access Gateway for Satellite
(AGS) that accommodates base stations
ment, new development of only the
To balance the communications
is based on the FOMA Serving GPRS
functions required for mobile satellite
load over the two satellites and the core
Support Node (SGSN)/Gateway GPRS
communications, and adoption of
nodes, mobile stations autonomously
Support Node (GGSN) packet switch
equipment that applies IP Multimedia
select a satellite and core node for prior-
and adds the functions required for the
Subsystem (IMS) [11] and other such
ity use thus achieving load balancing. If
voice communication provided by
general-purpose IP technology.
the priority core node cannot be used,
WIDESTAR II.
*5
communication is conducted on the
4.1 Reliability Legacy and New
other station side.
Features
Voice call processing is handled by
the Satellite-Call Session control Node
(S-CSN), the Satellite-Application
1) System Configuration
WIDESTAR II adopts a conven-
4.2 Main Constituent Nodes
Serving Node (S-ASN) and the Satel-
1) Base Station Equipment
lite-Media Resource Node (S-MRN),
tional configuration that comprises two
The base station equipment com-
all of which are based on equipment
each of communications satellites, base
prises the Satellite Transmission and
used in FOMA and adapted to
stations and core node stations so that
Receive Equipment (STRE) and the
WIDESTAR II. The S-CSN performs
service can be continued even in the
Satellite-Access Point (S-AP). The
session control , the S-ASN performs
event that one of each type of station is
main roles of STRE are frequency con-
service control, and the S-MRN per-
damaged or destroyed in a disaster.
version and signal amplification. It is
forms guidance transmission control.
2) Base Station Redundancy Configu-
implemented with general-purpose
The Media Gateway Node (MGN),
radio equipment, without newly devel-
which performs network connection
oped hardware. The S-AP carries out
control, is shared with FOMA.
ration
Base stations are affected by the sun
*6
*7
transit phenomenon twice a year, in
digital signal processing for radio signal
The FAX communications service
spring and autumn. That phenomenon
dividing and combining, modulation
control was developed as a single func-
occurs when the communications satel-
and demodulation, and radio control
tion of the Media Processing Node
lite and sun are in alignment, temporari-
functions such as radio resource man-
(MPN) [12].
ly degrading communications quality.
agement and call control processing in
The core node equipment is
Also, because the system capacity is
a single unit of equipment to reduce
installed as specialized equipment for
reduced by half if signal transmission
communication processing load.
satellite use so as not to be affected by
from one of the base stations to a satel-
2) Core Nodes
FOMA congestion and to maintain high
lite is halted for repair work or other
The core node equipment is based
such reason, a redundant equipment
on the equipment currently operating in
configuration is used to allow both base
the FOMA service. Efficient develop-
Two types of WIDESTAR II Satel-
stations to communicate with both
ment and reduced software develop-
lite-Mobile Station (S-MS) were devel-
*5 IMS: A communication system standardized
by 3GPP for achieving multimedia services by
integrating communication services of the
fixed-line network, mobile communications
network, etc. using IP technology and SIP
(see *8) protocol as used in VoIP.
*6 Sun transit phenomenon: When the satellite is eclipsed, overlapping with the sun as
seen from the base station antenna, so that
communication quality degrades due to noise
generated by the sun. This occurs twice a year,
in spring and fall, for about one week each.
*7 Session control: A function for controlling
end-to-end IP communications over the network.
reliability.
3) Mobile Stations
NTT DOCOMO Technical Journal Vol. 12 No.2
oped, a portable type and a type for
sive use of a certain bandwidth is pro-
other such services for WIDESTAR are
ships and vehicles. For both higher data
vided for specified users or user groups,
provided as relevant service solutions.
communications speed and longer call
independently of the status of ordinary
The main services are described below.
time and standby time during battery
user traffic. WIDESTAR II also pro-
1) Voice Service
operation, digital circuit performance
vides the 64-k data communications
The G.729a voice CODEC used for
and function were improved and the
service and other data communications
IP telephony was adopted, improving
LSI integration scale was increased.
services.
the voice quality over the previous
*8
NTT DOCOMO Technical Journal
Session Initiation Protocol (SIP) was
The modem communications
WIDESTAR.
2) Data Communications Service
implemented for voice services.
between mobile stations implemented
4) Monitoring System
by circuit switching in WIDESTAR is
The data communications service
The new Satellite Access-Operation
renovated as a direct-connect Peer to
has two main categories. The packet
System (SATA-OPS) monitoring sys-
Peer (PtoP) data communications ser-
communication service has asymmetri-
tem for the base station equipment
vice between mobile stations in
cal communication speeds of a maxi-
shares a distributed data-driven archi-
WIDESTAR II. G3 FAX communica-
mum 144 kbit/s uplink and a maximum
tecture with the NW-OPS monitoring
tion is also implemented as an indepen-
384 kbit/s downlink, provided as best
system of the core node equipment for
dent FAX gateway service.
effort. The maximum data speed varies
The quality of the voice service,
with the number of users sharing the
which is the basic service, is also
radio frequency band and the communi-
improved. The services provided by
cations link quality. The 64-k data com-
by
WIDESTAR were selected and adapted
munications service provides a guaran-
WIDESTAR II are shown in Table 1.
to WIDESTAR II according to satellite
teed data rate by assigning a separate
WIDESTAR II introduces occupied
communications use and demand. The
radio channel with a fixed speed of 64
bandwidth services, in which the exclu-
multicast communications service and
kbit/s.
efficiency in development.
5. Services
The
services
provided
Table 1 WIDESTAR II services
WIDESTAR II
Communications satellite
System
Voice
Data
Service
overview
Original
satellite service
Notes
WIDESTAR (previous)
N-STAR c/d
N-STAR a/b, N-STAR c/d
IMT-2000 packet switching, IMS(CS-IP)
PDC circuit switching, PDC packet switching
· High quality voice (G.729a)
· Half-rate voice (PSI-CELP)
· Packet communication service (best effort)
Uplink: Max. 144 kbit/s; Downlink: Max. 384 kbit/s
· Packet communications service
Uplink: 4.8 kbit/s; Downlink: Max. 64 kbit/s
· 64 k data communications service (guaranteed data
rate)
· Non-telephone data modem communications
(4.8 kbit/s, up- and down-link)
· FAX gateway service (G3FAX connection service)
· G3FAX (using modem)
· Occupied bandwidth service
· Direct connect service (PtoP data communications)
· Voice, FAX multicast communications service
Improved capabilities of the N-STAR c/d
communication satellites (N-STAR c is improved by a
factor of 5 and N-STAR d is improved by a factor of
10 relative to N-STAR a/b)
Equipment capability limits advances in services
PSI-CELP : Pitch Synchronous Innovation Code Excited Linear Prediction
*8 SIP: A call control protocol defined by the
Internet Engineering Task Force (IETF) and
used for IP telephony with VoIP, etc.
NTT DOCOMO Technical Journal Vol. 12 No.2
41
Overview of WIDESTAR II Mobile Satellite Communications System and Service
WIDESTAR II mobile satellite com-
3) FAX Gateway Service
NTT DOCOMO Technical Journal
FAX gateway service was devel-
munications system that began opera-
oped to continue the G3 FAX service
tion in April 2010 and the services pro-
often used by ships. In this service, a
vided by this system. This system was
FAX adapter (FAX ADP) is connected
designed for high-speed data communi-
[3] DOCOMO Business Online: “WIDESTAR
and Services.”
[4] NTT DOCOMO Press Release: “New
WIDESTAR II satellite telephone service
and satellite portable terminal 01 are
now available,” Apr. 2010.
[5] M. Inoue et. al: “Overview of WIDESTAR
to the mobile station to convert G3
cations and to conform to the techno-
FAX to mail and to conduct data com-
logical trend toward the All-IP network
munications with the FAX gateway ser-
by equipping mobile stations with SIP
nal, Vol. 12, No. 2, pp. 43-49, Sep. 2010.
vice equipment, which is one function
for voice services over IP, IMS and
[6] T. Yamamoto et. al: “WIDESTAR II Satel-
of the MPN. Communications with the
other such functions.
G3 FAX in the general public network
®*9
The future development plan is to
II Mobile Satellite Communications
Scheme,” NTT DOCOMO Technical Jour-
lite Core Network System,” NTT DOCOMO
Technical Journal, Vol. 12, No. 2, pp. 5057, Sep. 2010.
service pro-
proceed with introduction of diverse
[7] S. Sasaki et. al: “WIDESTAR II Satellite
vided by NTT Communications Corpo-
solutions and expand the use of data
Base Station Equipment,” NTT DOCOMO
ration.
communications services. The impor-
Technical Journal, Vol. 12, No. 2, pp. 58-
4) Occupied Bandwidth Service
tance of service provision and ensuring
are done via the iFAX
63, Sep. 2010.
[8] H. Ouchi et. al: “WIDESTAR II Base Sta-
An occupied bandwidth service is
a means of communication during
provided so that specified users or user
times of emergency and disaster, a role
groups can use combinations of various
inherited from the previous mobile
Vol. 12, No. 2, pp. 64-69, Sep. 2010.
services for their dedicated use. A
satellite communications system, is
[9] Y. Kiba et. al: “WIDESTAR II Satellite
group ID is designated for each contract
increasing, so it is expected that the
for the resource management of a radio
value of the WIDESTAR II mobile
frequency band. The occupied frequen-
satellite communications system will
cy bandwidth can be used independent-
also increase.
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®
*9 iFAX : A registered trademark of NTT Communications Corporation.
42
NTT DOCOMO Technical Journal Vol. 12 No.2