8.1
Bosch & Airspan
Bosch
and Airspan are the 2 Point to Multi Point systems used by MTT in
its Access Network.
8.2
Air Span (
AS4000 )
AS4000
Wireless Fixed Access System is a digital point to multipoint
radio access system providing wireless access for fixed
subscribers to the telecommunication network. Normally it is
referred to as Airspan, which is the trade name of the company.
This system is widely used in MTT as well as in other
telecommunication companies such as Suntel and Lanka Bell. This is
comparatively cheaper than MDS because one setup can serve several
customers. AS4000 delivers telephony, voice band facsimile/data,
and leased line Data, providing the same functionality as
“copper pairs” and is therefore a direct alternative to the
use of copper cabling for the delivery of these services to
customers.
The AS4000 DA system comprises the following major sub-systems:
·
The Subscriber Terminals (STs)
·
The Central Terminal (CT)
·
The Access Concentrator (AC)
·
The AS8100 Sitespan Management System
The Subscriber Terminals (STs)
The AS4000 Subscriber
Terminal (ST) portfolio includes 2 subscriber terminal types
called internal radio unit and external radio Unit. In general,
the customer has access to the same range of facilities that are
supported by a conventional copper pair.
The Central Terminal (CT)
The
Central Terminal (CT) is the AS4000 Base Station. This is
deployed in omni or sectored cell configurations supporting
variable numbers of Subscriber Terminals (ST) per cell. The CT is
a multi-service platform-hosting single and dual line telephony,
multi-line telephony; digital data leased lines and ISDN basic
rate interfaces.
The Access
Concentrator
The Access Concentrator (AC) is required when AS4000
is operating in “Demand Assigned” mode to de-multiplex the
traffic concentrated on the air-interface for presentation to the
network switching equipment. The Access Concentrator provides CAS,
V5.1 or V5.2 network interface with the Local Exchange. Also in
system versions using 32kbit/s compression the decompression to
64kbit/s is performed within the AC.
The Management
System
The Sitespan Manager is a
scaleable, distributed PC based management system. monitors, tests
and configures the WFA system. All elements of the AS4000 System
(AC, CT and ST) can be managed from a single Sitespan server
connected at the Access Concentrator.
8.3 BOSCH
BOSCH is a digital point to multi point system (DMS)
used in MTT Access network and is available for the following
frequency ranges:
·
3.5 GHz
(DMS 3.5), 45, 15
·
10.5 GHz (DMS
10.5)
·
26 GHz
(DMS 26)
·
The
DMS supports a point-to-multipoint topology with the possibility
of a cellular area coverage. To achieve a very high capacity, a
cell cay be divided up into several sectors. Sectorization angles
of 90,
45, 15 degrees (DMS 10.5 and DMS 26) and 60 degrees (DMS 3.5) are
available as standard values.
Fig
8.1 shows the example of a possible cell configuration. It
includes a Radio Base Station (RBS) with a total of 8 sectors (45
deg. sectorization)
Fig 8‑1
Example of a cell with 8 sectors
Architecture of
the radio base station (RBS)
A Radio Base Station (RBS)
without redundancy is composed of the following two subrack types:
·
Central Shelf
·
Extension Shelf
All
sectors of a cell are completely independent of each other, so
that each sector needs its own sub racks. The following subracks
are necessary for each sector as shown in the Fig
3-15.
·
Only
one central shelf is required for up to six RNUs (Remote Network
Units)
·
In case of more than six RNUs, an additional extension shelf
is needed for every group of 16 RNUs.
·
Up to 100 RNUs can be operated per sector. For this maximum
configuration, one central shelf with six modems and the
corresponding number of extension shelves with up to 16 modems
each are required.
The
IF combiners combines the signals supplied by the modems or by the
IF combiners of the extension selves. The IF unit converts the
combined signal into an IF signal and passes it on to the RF unit.
In the RF Outdoor Unit, the IF signal is then converted into RF
signal. In the MTT network 10.5 GHz range is used. BOSCH network
is used in MTT for 2 Mbit/s data transmission.
Bosch
Customer Site Equipments
Fig 8.2 BOSCH Customer premises
arrangement
The CPE (Customer Premises Antenna) transmits
horizontally polarized waves and it receives vertically polarized
waves. That is the base station antenna transmits in vertical
polarization and it receives in horizontal polarization. This
technique reduces interference but increases the frequency band
requirements.
Chapter
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