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Following is the detailed description of the diagram:

Optical Transmitter - Infrared LED driver:

The heart of the Optical transmitter is the HSDL4220 infrared LED exclusively suitable for the 10Mb/s operation in this Transmitter. The HSDL-4200 series of emitters are the first in a sequence of emitters that are aimed at high power, low forward voltage, and high speed.

These emitters utilize the Transparent Substrate, double heterojunction, Aluminum Gallium Arsenide (TS AlGaAs) LED technology. These devices are optimized for speed and

efficiency at emission wavelengths of 875 nm. This material produces high radiant efficiency over a wide range of currents up to 500 mA peak current. The HSDL-4200 series of emitters are available in a choice of viewing angles, the HSDL-4230 at 17° and the HSDL-4220 at 30°. It has a bandwidth of 9 MHz, where 10 Mbit/s Manchester-modulated systems need bandwidth of around 16 MHz . Operation in a usual circuit with current drive would lead to substantial signal corruption and range reduction. Therefore a special driving technique consisting of driving the LED directly with 15-fold 74AC04 gate output in parallel without any current limitation is implemented. As the voltage to keep the nominal LED average current (100mA) varies with temperature and other component characteristic, an AC-bypassed current sense resistor is put in series with the LED. A feedback loop measures voltage on this resistor and keeps it at a preset level by varying supply voltage of the 74AC04

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gates. Therefore the 74AC04 is operating as a structured power CMOS switch completely in analog mode.

This way the LED junction is flooded and cleared of carriers as quickly as possible, basically by short circuit discharge. This pushes the speed of the LED to maximum, which makes the output optical signal fast enough so that the range/power ratio is the same as with the faster red HPWT-BD00-F4000 LED. The side effects of this brutal driving technique are: 1) the LED overshoots at the beginning of longer (5 MHz/1 MHz) impulses to about 2x brightness.

This was measured to have no adverse effect on range. 2) A blocking ceramic capacitor bank backing up the 74AC04 switching array is crucial for correct operation, because charging and discharging the LED is done by short circuit. Under dimensioning this bank causes the leading and trailing edges of the optical output to grow longer.

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Optical Receiver - Preamplifier stage:

The usual approach in FSO (Free Space Optics) preamplifiers is to employ a transimpedance amplifier. A transimpedance amplifier is a very sensitive broadband high-speed device featuring a feedback loop.

Following is the brief scrutiny of a transimpedance amplifier:

The transimpedance amplifier as shown above presents a low impedance to the photodiode and isolates it from the output voltage of the operational amplifier. In its simplest form a transimpedance amplifier has just a large valued feedback resistor, Rf. The gain of the

amplifer is set by this resistor and because the amplifier is in an inverting configuration, has a value of -R_f. There are several different configurations of transimpedance amplifiers, each suited to a particular application. The one factor they all have in common is the requirement to convert the low-level current of a sensor to a voltage. The gain, bandwidth, as well as current and voltage offsets change with different types of sensors, requiring different configurations of transimpedance amplifiers.

This transimpedance amplifier inside a ronja system also makes use of a PIN diode.

A PIN diode is a diode with a wide, undoped intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region. The p-type and n-type regions are

typically heavily doped because they are used for ohmic contacts. A PIN diode operates under what is known as high-level injection. In other words, the intrinsic "i" region is flooded with charge carriers from the "p" and "n" regions.

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Its function can be likened to filling up a water bucket with a hole on the side. Once the water reaches the hole's level it will begin to pour out. Similarly, the diode will conduct current once the flooded electrons and holes reach an equilibrium point, where the number of electrons is equal to the number of holes in the intrinsic region. When the diode is forward biased, the injected carrier concentration is typically several orders of magnitude higher than the intrinsic level carrier concentration. Due to this high level injection, which in turn is due to the depletion process, the electric field extends deeply (almost the entire length) into the region. This electric field helps in speeding up of the transport of charge carriers from P to N region, which results in faster operation of the diode, making it a suitable device for high frequency operations.

Ronja however uses a feedback-less design where the PIN has a high working electrical resistance (100 kilohms) which together with the total input capacitance (roughly 7 pF, 5 pF PIN and 2 pF input MOSFET cascade) makes the device operate with a passband on a 6 dB/oct slope of low pass formed by PIN working resistance and total input capacitance. The signal is then immediately amplified to remove the danger of contamination by signal noise, and then a compensation of the 6 dB/oct slope is done by derivator element on the

programming pins of an NE592 video amplifier. The NE592 video amplifier is a monolithic, two-stage, differential output, and wideband video amplifier. It offers fixed gains of 100 and 400 without external components and adjustable gains from 400 to 0 with one external resistor. The input stage is designed so that with the addition of a few external reactive elements between the gain select terminals, the circuit can function as a high-pass, low-pass, or band-pass filter.

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This feature makes the circuit ideal for use as a video or pulse amplifier in

communications, magnetic memories, display, video recorder systems, and floppy disk head amplifiers. It is available in an 8-pin version with fixed gain of 400 without external components and adjustable gain from 400 to 0 with one external resistor.

Due to this implementation, a surprisingly flat characteristic is obtained in the receiver section of the RONJA. If the PIN diode is equipped with 3 kΩ working resistor to operate in flat band mode, the range is reduced to about 30% due to thermal noise from the 3 kΩ resistor.

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Transceiver - Ronja Twister:

An optical transceiver module configured for long wave optical transmission is disclosed.

Significantly, the transceiver module utilizes components formerly used only for shortwave optical transmission, thereby reducing new component production and device complexity. In one embodiment, the transceiver module includes a transmitter optical subassembly including a laser capable of producing an optical signal. A consolidated laser driver/post amplifier including a first bias current source provides a bias current to the laser for producing the optical signal. A means for amplifying the bias current provided to the laser by the first bias current source is also included as a separate component from the laser driver/post amplifier.

The means for amplifying in one embodiment is a field-effect transistor that is operably connected to the laser driver/post amplifier and configured to provide an additional bias current to the laser diode such that sufficient lasing operation of the laser is realized.

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Physical Layer:

In the seven-layerOpen Systems Interconnection model (OSI) of computer networking, the physical layer or layer 1 is the first (lowest) layer. The implementation of this layer is often termed PHY. The physical layer consists of the basic networking hardware transmission technologies of a network. It is a fundamental layer underlying the logical data structures of the higher level functions in a network. Due to the plethora of available hardware

technologies with widely varying characteristics, this is perhaps the most complex layer in the OSI architecture. The physical layer defines the means of transmitting raw bits rather than logical data packets over a physical link connecting network nodes. The bit stream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a hardware transmission medium. The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium.

The major functions and services performed by the physical layer are:

 Bit-by-bit or symbol-by-symbol delivery

 Providing a standardized interface to physical transmission media, including

 Mechanical specification of electrical connectors and cables, for example maximum cable length

 Electrical specification of transmission line signal level and impedance

 Radio interface, including electromagnetic spectrum frequency allocation and specification of signal strength, analog bandwidth, etc.

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 Specifications for IR over optical fiber or a wireless IR communication link

 Modulation

 Line coding

 Bit synchronization in synchronous serial communication

 Start-stop signaling and flow control in asynchronous serial communication

 Circuit switching

 Multiplexing

 Establishment and termination of circuit switched connections

 Carrier sense and collision detection utilized by some level 2 multiple access protocols

 Equalization filtering, training sequences, pulse shaping and other signal processing of physical signals

 Forward error correction for example bitwise convolutional coding

 Bit-interleaving and other channel coding

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Data link layer:

The data link layer is the protocol layer that transfers data between adjacent network nodes in wide area network or between nodes on the same local area network segment. The data link layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the layer.

Examples of data link protocols are Ethernet for local area networks (multi-node), the Point-to-Point Protocol (PPP), HDLC and ADCCP for point-to-point (dual-node) connections. The data link layer is concerned with local delivery of frames between devices on the same LAN.

Data-link frames, as these protocol data units are called, do not cross the boundaries of a local network. Inter-network routing and global addressing are higher layer functions, allowing data-link protocols to focus on local delivery, addressing, and media arbitration. In this way, the data link layer is analogous to a neighborhood traffic copy; it endeavors to arbitrate between parties contending for access to a medium, without concern for their ultimate destination. When devices attempt to use a medium simultaneously, frame collisions occur.

Data-link protocols specify how devices detect and recover from such collisions, and may provide mechanisms to reduce or prevent them.

Delivery of frames by layer 2 devices is effected through the use of unambiguous hardware addresses. A frame's header contains source and destination addresses that indicate which device originated the frame and which device is expected to receive and process it. In contrast to the hierarchical and routable addresses of the network layer, layer-2 addresses are flat, meaning that no part of the address can be used to identify the logical or physical group to which the address belongs.

The data link thus provides data transfer across the physical link. That transfer can be reliable or unreliable; many data-link protocols do not have acknowledgments of successful frame reception and acceptance, and some data-link protocols might not even have any form of checksum to check for transmission errors. In those cases, higher-level protocols must provide flow control, error checking, and acknowledgments and retransmission.

In some networks, such as IEEE 802 local area networks, the data link layer is described in more detail with media access control (MAC) and logical link control (LLC) sub layers; this means that the IEEE 802.2 LLC protocol can be used with all of the IEEE 802 MAC layers, such as Ethernet, token ring, IEEE 802.11, etc., as well as with some non-802 MAC layers such as FDDI. Other data-link-layer protocols, such as HDLC, are specified to include both sub layers, although some other protocols, such as Cisco HDLC, use HDLC's low-level framing as a MAC layer in combination with a different LLC layer. In the ITU-T G.hn

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standard, which provides a way to create a high-speed (up to 1 Gigabit/s) local area network using existing home wiring (power lines, phone lines and coaxial cables), the data link layer is divided into three sub-layers (application protocol convergence, logical link control and medium access control).

Within the semantics of the OSI network architecture, the data-link-layer protocols respond to service requests from the network layer and they perform their function by issuing service requests to the physical layer.

Data link layer services:

 Encapsulation of network layer data packets into frames

 Frame synchronization

 Logical link control (LLC) sublayer.

 Error control (automatic repeat request, ARQ), in addition to ARQ provided by some transport-layer protocols, to forward error correction (FEC) techniques provided on the physical layer, and to error-detection and packet canceling provided at all layers, including the network layer. Data-link-layer error control (i.e. retransmission of erroneous packets) is provided in wireless networks and V.42 telephone network modems, but not in LAN protocols such as Ethernet, since bit errors are so uncommon in short wires. In that case, only error detection and canceling of erroneous packets are provided.

 Flow control, in addition to the one provided on the transport layer. Data-link-layer error control is not used in LAN protocols such as Ethernet, but in modems and wireless networks.

 Media access control (MAC) sub layer.

 Multiple access protocols for channel-access control, for example CSMA/CD

protocols for collision detection and re-transmission in Ethernet bus networks and hub networks, or the CSMA/CA protocol for collision avoidance in wireless networks.

 Physical addressing (MAC addressing)

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40 MODELS

 Ronja Tetrapolis: Range of 1.4 km (0.87 mi), red visible light. Connect with 8P8C connector into a network card or switch.

 Ronja 10M Metropolis: Range of 1.4 km (0.87 mi), red visible light. Connects to Attachment Unit Interface.

 Ronja Inferno: Range of 1.25 km (0.78 mi), invisible infrared light.

 Ronja Bench-press: A measurement device for developers for physical measurement of lens/LED combination gain and calculation of range from that

Ronja Tetrapolis:

Ronja Tetrapolis is a device for optical communication with 10Mbps full duplex speed over 1.4km. The device terminates an optical path. To operate a complete link, two devices are necessary.

Ronja Benchpress:

This is a Ronja model that is not a communication device, but a bench for measuring lens properties. You insert a combination of LED and lens into the bench and measure exact transmitter gain of the lens+LED combination in decibels. You can then use this value to calculate precise range of the device. This is handy for evaluating new types of LEDs, new types of lenses or if you have doubts if your lens is of adequate quality for the device (for example due to greenish haze).

Ronja 10M Metropolis:

This is another variant of Ronja similar to Ronja Tetropolis, but varying in its technical specifications.

Ronja Inferno:

Ronja Inferno is a device for optical communication with 10Mbps full duplex speed over 1.25 km using infrared light. The device terminates an optical path. To operate a complete link, two devices are necessary

41 Technical specifications:

Ronja Inferno:

Gross data rate 10 Mbps

Transmission

mode Full duplex (half duplex also supported)

Nominal range 1.25 km with 130mm RX loupe lenses and 90mm TX loupe lenses. The switch or cad has to have well implemented PLL.

Minimum operating distance

1/4 of nominal range. Further manual reduction possible by change of two passive components in receiver.

Data interface

 Connects with RJ45 jack into IEEE 802.3 UTP interface. Must be plugged directly into data terminal equipment (DTE, PC or a switch) using the integral 1m cable. Auto negotiation not supported, not transparent for auto negotiation signals.

 The preamble is chopped off more than specified by IEEE 802.3 which could cause a problem when Ronja is connected into a cascade of pure hubs. However hubs almost don't exist today anymore so it is not a problem.

 Doesn't comply to IEEE 802.3 regarding not transmitting when link integrity is not yet established. This violates page 303 14.2 g) - but IEEE 802.3 compliant devices must work with it. Complying to it would make Ronja Tetrapolis more complicated

Power consumption

335mA @12VDC (4.02W) from wall cube, 2W from external heating power supply (switchable off).

Typical Maximum

Idle 225mA 285mA

Full data load (both directions) 275mA 335mA

Operating

wavelength Infrared, 875nm wavelength, 37nm spectral width

Optical output 30mW

42 Ronja Tetrapolis:

Gross data rate 10 Mbps

Transmission

mode Full duplex (half duplex also supported)

Nominal range 1.4km with 130mm lenses. The switch or cad has to have well implemented PLL.

Minimum operating distance

1/4 of nominal range. Further manual reduction possible by change of two passive components in receiver.

Data interface

 Connects with RJ45 jack into IEEE 802.3 UTP interface. Must be plugged directly into data terminal equipment (DTE, PC or a switch) using the integral 1m cable.

Auto negotiation not supported, not transparent for auto negotiation signals.

 The preamble is chopped off more than specified by IEEE 802.3 which could cause a problem when Ronja is connected into a cascade of pure hubs. However hubs almost don't exist today anymore so it is not a problem.

 Doesn't comply with IEEE 802.3 regarding not transmitting when link integrity is not yet established. This violates page 303 14.2 g) - but IEEE 802.3 compliant devices must work with it. Complying to it would make Ronja Tetrapolis more complicated

Power consumption

285mA @12VDC (3.42W) from wall cube, 2W from external heating power supply (switchable off).

Typical Maximum

Idle 185mA 245mA

Full data load (both directions) 225mA 285mA

Operating

wavelength visible, 625nm, 100nm spectral width (618nm perceived wavelength, red-orange)

Optical output 17.2mW

Divergence cone

half angle 1.9mrad (130mm aperture transmitter lens)

Estimated Optical

EIRP 20kW (130mm aperture transmitter lens, HPWT-BD00-F4000)

43 Operating

temperature -30...+70degC (outdoor part - optical heads, RX, TX), 0...+55degC (indoor part - Twister2)

Operating humidity

Up to 100% (condensing) with lens heating on (outdoor part), up to 95% with lens heating off (and indoor electronics).

Weight 15.5kg (one side of a link, on a welded parallel console)

Required visibility 4km at maximum range.

Optical modulation

BPSK (as on AUI aka Manchester) plus 1MHz asynchronous 50% duty cycle square wave between packets. The transmitter appears to shine permanently and steadily no matter if data pass or not.

Indicators LEDs Power, Receive Packet, Transmit Packet

Aiming system Visual, retro reflector for transmitter and DC voltage signal strength monitor port for receiver.

Mechanical Installation Constraints

 Possible mount places:

Place Is drilling

necessary?

Railing, round or rectangular No

Wall Yes

Corner of wall Yes

Chimney No

Horizontal or tilted surface of masonry or

masonry covered with tin, foil etc. Yes

Ceiling Yes

 Max. 1m from RJ45 connector is a grounded metal box with dimensions 180x123x62 mm.

 Cable distance between RJ45 connector and optical head mounting points is max.

100m

44 Ronja Benchpress:

Operating ambient temperature 0…+55°C

Usage environment Indoor

Operating humidity 0-95% noncondensing

Ronja 10M Metropolis:

Gross data rate 10 Mbps

Transmission

mode Full duplex only

Nominal range 1.4km with HPWT-BD00-F4000 and 130mm lenses. The switch or cad has to have well implemented PLL.

Minimum operating distance

1/4 of nominal range. Further manual reduction possible by change of two passive components in receiver.

Data interface

IEEE 802.3 Attachment Unit Interface (AUI). Connector male DB-15 with screws instead of AUI mechanical latch. AUI cable not supported - integrated cable length 1m. The preamble is chopped off more than specified by IEEE 802.3 which could cause a problem when Ronja is connected into a cascade of pure hubs. However hubs almost don't exist today anymore so it is not a problem.

Power

consumption 300mA @12VDC (3.6W) from AUI, 2W from external heating power supply (switchable off)

Operating

wavelength visible, 625nm, 100nm spectral width (618nm perceived wavelength, red-orange)

Optical output 17.2mW

Divergence

cone half angle 1.9mrad (130mm aperture transmitter lens)

Estimated

Optical EIRP 20kW (130mm aperture transmitter lens, HPWT-BD00-F4000)

45 Operating

temperature -30…+70°C (outdoor part - optical heads, RX, TX), 0…+55°C (indoor part - AUI interface)

Operating

humidity Up to 100% (condensing) with lens heating on, up to 95% with lens heating off.

Weight 15.5kg (one side of a link, on a welded parallel console)

Required

visibility 4km for uninterrupted operation at full range.

Optical modulation

BPSK (as on AUI) plus 1MHz asynchronous 50% duty cycle square wave between packets.

BPSK (as on AUI) plus 1MHz asynchronous 50% duty cycle square wave between packets.

In document UNIVERSIDAD COMPLUTENSE DE MADRID (página 134-151)