Infrared Optical Wireless Systems
Background Information
BOV-2M & BOS-EM
Wireless Systems
What is an optical wireless communications system?
An optical wireless (OW) system is similar to a fixed wireless (microwave or
RF) system except that information is carried by optical or infrared beam
rather than by a microwave or RF carrier.
OW systems generally have smaller transceiver units and much
smaller/sharper beam widths. They are also referred to as Free Space Optical or
Infrared communications systems.
Sceptre’s OW transmitters use light-emitting diodes (LEDs) instead of
lasers to generate the infrared beam.
Like fixed wireless, OW requires a direct line of sight between
locations.
Are the beams visible?
The systems are designed to work in the infrared region of the electromagnetic
spectrum, a region invisible to the eye.
The operating wavelength is typically in the region of 850 Nm
corresponding to a frequency of 340,000 GHz, which is 4 to 5 orders of
magnitude greater than that used for microwave links.
Will multiple OW systems converging on one site interfere with one
another?
Multiple OW systems can be co-located on the same roof or building without
interference. This gives OW datacom
systems a major technical advantage over 2.4GHz wireless LAN/spread radio in
computer networking (LAN, WAN) applications – an outdoor 11Mbps direct sequence
spread radio/wireless LAN system cannot be used if more than 3-4 similar
systems have already been or are likely to be installed in the same area. To overcome problems of interference a low
bandwidth (2Mbps) spectrum hopping wireless LAN system must be installed
instead.
System Description
Sceptre
is currently selling 2 OW systems:
The
BOV-2M 2.048Mbps G.703/E1 (telecom) OW system can be used to transmit
voice and data from a few meters to a maximum distance in
The
BOS-EM 10Mbps Ethernet (datacom) OW system can be used to transmit data
from a few meters to a maximum distance in
Both
LED systems are full duplex and to ensure the highest quality and reliability
in all atmospheric conditions, Sceptre’s OW systems use two independent
wireless channels (one working in reserve like a satellite communications
system).
Each OW system consists of 2 Optical Transmitters, 2
Optical Receivers,
2
Optical Switches/Modems*, 2 Sighting Scopes, power supplies and up to 100
meters of Coax Cabling at each end.
The
systems all use LED for the OW transmission source.
Infra-Red
OW equipment can be installed and operated anywhere in the world without a
license. No right of way permit is
required to beam an infrared channel over land.
The systems are small and low profile, allowing them to be installed in
architecturally sensitive areas.
* The optical switch/modem shown on the front page has now been
re-designed to conform to standard European rack mount dimensions.
Applications
Sceptre’s
OW systems are available for a wide number of applications:
1.
Telecommunications
2.
Computer Networking
-
Local Area and Metropolitan Area Networks for companies, educational
and health authorities, the military, emergency services, local government, etc
3.
Last Mile Broadband Access
-
A cost-effective alternative to leased lines and fixed wireless for
operators and service providers.
-
Fast installation of high-bandwidth services to offices, hotels, shops,
apartment buildings, etc
4.
High-quality video transmission
-
Broadcast – sporting events, concerts, etc
-
Security – CCTV, traffic monitoring cameras
-
Video conferencing
5.
Temporary/Disaster Recovery Engineering
-
Natural disaster disruption
-
Link establishment before fiber optic installation
-
Temporary replacement for broken fiber optic cable
6.
Elimination of Right of Way & Access Problems
-
Motorways and major roads
-
Rivers
-
Lakes
-
Urban areas
-
Land with no right of way permit
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Sceptre’s
BOS-EM datacom system can support the following broadband multimedia
applications: |
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• Video/programming on
demand |
• On-line computer games
& gambling |
Ease of Use
For
carriers and service providers we can offer a reliable wireless system with no
licensing issues, no Health & Safety issues, no planning issues and no
frequency re-use or spectrum issues.
This means less administration, no expensive RF software, less back-room
staff.
Improved Network Connections
OW
systems offer a seamless interconnection of hardware – they are totally
transparent to the network and act in the same way as a section of fibre optic
cable.
Mounting Information
The
optical head can be mounted on a roof, wall or window ledge in exactly the same
way as a CCTV camera. A number of
standard mounting brackets are available from Sceptre, including Wall, Plinth
and Pole mounting brackets. In addition
Sceptre has a working relationship with an engineering works any type of
bracket or tower can be constructed.
In
order to pass the optical data between the two link heads line-of-sight must be
available at all times during the data transmission period. Therefore,
consideration must be taken to future obstacles such as tree growth, cranes,
erection of new buildings etc.
Microwave
and wireless LAN/spread radio wireless systems require a wide, clear line of
sight to prevent interference – this is often difficult to find in towns and
cities where buildings and trees may reduce the diameter of the line of
sight. Sceptre’s OW system will work in
areas where microwave/spread radio will not since it needs a line of sight with
a gap of just 30 mm between buildings or other obstacles.
A
system must not be installed above its maximum rated transmission distance, as
this will affect availability performance.
Alignment Information
Installation
(or de-installation) of the mounting structures and OW equipment takes just a
few hours. Once installed, actual
alignment of the OW equipment takes just a few minutes. The procedure for alignment is
straightforward and involves an installer using a standard telescopic scope to
align the equipment. The first operation is to point the two link heads roughly
at each other using the human eye and then the scope until the
receiver/transmitter indicator lights up on each optical switch/modem. A final, more accurate, alignment is then
found by moving the link heads very slightly (one at a time). No specialist skills are required for
installation and oscilloscopes and other technical equipment are not used. Once final alignment has been achieved the
adjustment fastenings are then fully tightened to provide a completely rigid
system. Because the system uses a wide
LED beam instead of a narrow laser beam, the installers have a 10-meter
diameter at either end within which to place the beam.
Performance Specifications
The systems offer an industry accepted performance
availability figure which, through field trials, independent laboratory testing
and through two years of commercial deployment in Moscow, have achieved a
continuous operational availability of 99.998% in all weather conditions at
operating distances of up to 1.5 km
(BOV-2M) and 1000 metres (BOS-EM):
Sceptre’s OW systems have been designed with margins
to accommodate path losses due to rain, snow and fog.
We have set out below the rain, snow and fog Attenuation
figures for Sceptre’s OW systems and compare these with the published data from
a leading US
Company |
Rain Attenuation |
Snow Attenuation |
Fog Attenuation |
|
Sceptre BOV-2M, BOS-EM LED infrared |
10 dB/km |
10 dB/km |
20 dB/km |
Company |
Rain Attenuation |
Snow Attenuation |
Fog Attenuation |
|
Air Fiber Optimesh TM Laser Infrared |
20-50 dB/km |
50-150 dB/km |
30-300 dB/km |
Unlike
microwave, LED OW is not affected by heavy rain.
Sceptre’s
OW systems offer a bit error rate (BER) of 10-10.
Reliability Statement
The main LED component has a guaranteed lifespan of
250,000 hours or 28 years.
Sceptre’s OW systems have been
designed to simply and cheaply solve two major technical problems that affect
competing laser OW:
·
Temporary Obstacles Blocking
Transmission - the systems have been designed in the same way as a
satellite link with two separate transmitters and receivers at each end of the
link which allow the packet data stream to be confirmed, on receipt, by a
separate data stream going in the opposite direction on a different vector in
space. This provides a fault tolerant (always-on)
two-way communications link between two points that are exclusive of one
another. This effectively deals with the
common problem of birds, leaves and other temporary obstacles affecting data
transmission by blocking the beam.
Building Movement & Vibration –
Buildings twist and bend under windy conditions or they contract and expand in heat and cold. As a result, the orientation of an OW system can swing through changes of a degree or more. As a result, OW systems that have a narrow (i.e. less than 1 degree) beam spread will lose the signal unless they are equipped with expensive tracking systems. Sceptre’s OW products are highly resistant to this problem as
the light beam has a one degree
projection pattern at source, similar to that of a flashlight. The beam can be adjusted to have a diameter
of up to 10 metres by 1km. Where optical
units are located on a swaying structure, a wireless connection data will be
retained because even the tallest building will not be expected to move by more
than a few metres – i.e. the signal from the units will always remain within
the projected 10 metre pattern of the paired transceivers.
Sunlight – OW systems have been traditionally affected by sunlight and on bright days, a sunlit background will result in a reduction of margin. Sceptre’s OW systems have a small receiving area (d=100 mm) and the range is normally set with more than sufficient margin to allow for a reduction of margin. There will be no impact on performance caused by sensitivity to sunlight.