DDM or Digital Diagnostic Monitoring is a management technology which allows operators to monitor several parameters of a fibre optic transceiver, such as optical input/output levels, temperature, laser bias current and supply voltage. All of these parameters can be monitored in real-time.
Examples of optical modules supporting DDM are the Small Form Factor Pluggable modules such as SFP and SFP+ for 1Gbps to 10Gbps and up to 25Gbps capacity
What does the DDM do exactly?
DDM is capable of providing component monitoring on transceiver applications in great detail. The system that is used is an extension of the interface defined in GBIC specification (GBIC being a type of transceiver).
The interface itself is capable of generating alarms and warning flags which alert the host system when operating parameters fall outside of a set of ‘normal operating’ rules. This allows the end user to isolate faults and predict failure.
What is DOM?
DOM or Digital Optical Monitoring is used to monitor certain parameters of an optical transceiver in real-time. This helps operators to identify the location of a fiber link failure which in turn helps to simplify the maintenance process and improve overall system reliability.
DOM gives you the ability to monitor the transmit and receive power of the optical transceiver module, its temperature and supply voltage. Each system can be configured to monitor transceivers that are in operation either globally or by specific port.
With DOM console message and syslog messages are sent if operation falls below or rise above the specific transceivers manufacturer thresholds.
Under its naming convention, the WiFi alliance calls 802.11ax Wi-Fi 6. 802.11ac is now WiFi 5, and 802.11n is WiFi 4. The idea, according to the WiFi Alliance, is to make matching endpoint and router capabilities a simpler matter for the rank-and-file user of WiFi technology.
Meanwhile it’s important to know that the Wi-Fi Alliance has not made up simpler names for all the 802.11 standards, so it’s important to be familiar with the traditional designations. Also, the IEEE, which continues to work on newer versions of 802.11, has not adopted these new names, so trying to track down details about them using the new names will make the task more complicated.
Released in September 1999, it’s most likely that your first home router was 802.11b, which operates in the 2.4GHz frequency and provides a data rate up to 11 Mbps. Interestingly, 802.11a products hit the market before 802.11a, which was approved at the same time but didn’t hit the market until later.
The first following the June 1997 approval of the 802.11 standard, this standard provided operation in the 5GHz frequency, with data rates up to 54Mbps. Counterintuitively, 802.11a came out later than 802.11b, causing some confusion in the marketplace because customers expected that the standard with the “b” at the end would be backward compatible with the one with the “a” at the end.
Approved in June 2003, 802.11g is the successor to 802.11b, able to achieve up to 54Mbps rates in the 2.4GHz band, matching 802.11a speed but within the lower frequency range.
802.11n (WiFi 4)
The first WiFi standard to specify MIMO, 802.11n was approved in October 2009 and allows for usage in two frequencies – 2.4GHz and 5GHz, with speeds up to 600Mbps. When you hear the term “dual-band”, it refers to being able to deliver data across these two frequencies.
802.11ac (WiFi 5)
802.1ac-compliant devices operate in the 5 GHz frequency space. With Multiple Input, Multiple Output (MIMO) – multiple antennas on sending and receiving devices to reduce error and boost speed – this standard supports data rates up to 3.46Gbps. Some router vendors include technologies that support the 2.4GHz frequency via 802.11n, providing support for older client devices that may have 802.11b/g/n radios, but also providing additional bandwidth for improved data rates.
802.11ax (Wi-Fi 6)
Also called High Efficiency WLAN, 802.11ax aims to improve the performance in WLAN deployments in dense scenarios, such as sports stadiums and airports, while still operating in the 2.4GHz and 5GHz spectrum. The group is targeting at least a 4X improvement in throughput compared to 802.11n and 802.11ac., through more efficient spectrum utilization.
60GHz (V-Band) is now becoming a popular frequency band in wireless world, with both short-range and wider area applications ahead for the tiny beams of this unlicensed millimeter radio technology.
The frequency — part of the V-Band frequencies — is considered among the millimeter radio (mmWave) bands. Millimeter wave radios operate using frequencies from 30GHz to 300GHz. Until recently, 60GHz has typically been used for military communications as well as some commercial applications.
Major technology vendors show growing interest in the technology and the associated patents. Qualcomm Inc. (Nasdaq: QCOM) bought Wilocity recently to combine 60GHz WiGig technology with WiFi. Google (Nasdaq: GOOG) bought Alpental, a startup that, according to one of its founders, is using 60GHz to develop a “hyper scalable mmWave networking solution for dense urban nextGen 5G & WiFi.”
Why 60GHz, and why now? Here are a few reasons the market is expanding:
A short-range wireless specification — using the Institute of Electrical and Electronics Engineers Inc. (IEEE) 802.11ad specification — that can link devices at up to 7 Gbit/s over a distance of up to 12 meters. That’s 10 times faster than the current 802.11n WiFi, though with less range. This makes the technology ideal for wirelessly delivering high-definition video in the home. The Wi-Fi Alliance is expecting WiGig-certified products to arrive in 2015. (See Wi-Fi Alliance, WiGig Align to Make WiFi Super Fast.)
Particularly for small cells, operators can use the 60GHz radios to connect small cells to a fiber hub. (See More Startups Target Small-Cell Backhaul.)
These are useful for providing extra capacity at events, ad-hoc networks, and private high-speed enterprise links. (See Pushing 60.)
Wireless video: Some startups have jumped the gun on the WiGig standard and plowed ahead with their own 60GHz video connectivity using the Sony-backed WirelessHD standard.
A global unlicensed band exists at 57-64GHz. It is largely uncongested compared to the 2.5GHz and 5GHz public bands currently used for WiFi. (See FCC to Enable Fast Streaming With New 60GHz Rules.)
There’s also a lot of it. “The 60 GHz band boasts a wide spectrum of up to 9GHz that is typically divided into channels of roughly 2GHz each,” Intel Corp. (Nasdaq: INTC)’s LL Yang wrote in an article on the prospects for the wide-area and short-range use of the technology. Spectrum availability is “unmatched” by any of the lower-frequency bands.
The spectrum is now open and approved for use across much of the world. This includes the US, Europe, and much of Asia, including China.
As we’ve already seen, 60GHz technology is expected to offer blazing wireless transmission speeds.
Issues with 60GHz
No technology is ever perfect, right?
Transmissions at 60GHz have less range for a given transmit power than 5GHz WiFi, because of path loss as the electromagnetic wave moves through the air, and 60GHz transmissions can struggle to penetrate walls. There is also a substantial RF oxygen absorption peak in the 60GHz band, which gets more pronounced at ranges beyond 100 meters, as Agilent notes in a paper on the technology. Using a high-gain adaptive antenna array can help make up for some of these issues with using 60GHz for wider area applications.
Some vendors have also argued that there are potential advantages for the technology over omnidirectional systems. “The combined effects of O2 absorption and narrow beam spread result in high security, high frequency re-use, and low interference for 60GHz links,” one vendor notes
Many users own FSO links including Geodesy / LaserBit which are old and sometimes problematic. Often, users require higher reliability, uptime, capacity or distance than their older FSO laser links can provide.
The Need for Reliability and High Availability
Modern IP networks demand higher capacity and uptime, and as FSO links are installed outdoors often in harsh conditions where they age faster than indoor mounted IT equipment such as switches and routers, which are installed in nice airconditioned environments. Modern Carrier Class wireless equipment is designed for all-outdoor use including harsh environments and can ensure ultra-high availability and reliability in practical use.
Alternatives to Geodesy and FSO
There are many alternatives available including Carrier Class FSO from other vendors, MMW links with 10Gbps+ capacity, Microwave links and MIMO radio. These have different characteristics, capabilities and price points. Modern links can offer up to 40Gbps capacity and for low-end solutions, MIMO radios at lower price points than FSO for sites where budgets are tight.
If the customer requires a direct replacement FSO link, there are relatively few FSO vendors currently available with reliable shipping products.
Other FSO vendors currently offering carrier grade FSO:
Geodesy – LaserBit – FSO Laser Links – Free Space Optic laser links – Manufacturer information
Established in 1996, Geodesy (formerly LaserBit) provides optical communications at the speed of light which operate license-free. With products capable of sending up to 1 Gbps full duplex of data, GeoDesy offers reliable, fibre-optic connections without the need for expensive physical fibre.
GeoDesy – LaserBit – Manufacturer information
Geodesy (formerly LaserBit in Hungary) is a Manufacturer of FSO bridges with claimed over 20,000 lasers installed
Geodesy claim 15 years experience of building wireless bridges
Geodesy claim Risk free 100% satisfaction guarantee on all laser products
Affordable solutions costing from £2,995 installed
Built for line of site (LOS) with ranges suitable up to 5km
Ultra secure connections using narrow beams of light are secure from RF packet sniffers
Reliable availability with five nines availability
Licence free operation using FSO technology
Upgrading from GeoDesy FSO AT Series
Geodesy state that the Auto tracking series is a 8th generation series that maintains precise beam alignment, even when environmental factors cause movement to the device. The AT series is also the most recommended solution from the GeoDesy range.
Beam Tracking System
Gigabit Ethernet connectivity up to 2500m
Full duplex connectivity
Secure and error free data transmission
Built-in automatic failover
License free operation
Upgrading from GeoDesy FSO AF Series
Geodesy state that the AF series is a 5th generation build, offering laser transmission using a unique modulation technique that ensures error free data transfer over distances up to 1000 meters.
Point to point communications up to 1 Gbps
Wireless Ethernet range up to 1000m
Error free data transfer
Secure data transmission
Built-in automatic failover
Upgrading from a GeoDesy FSO PX Series
Geodesy state that the PX 5th generation series offers speeds from 100 Mbps to 1 Gbps and ranges of connectivity up to 5000 meters, and suited for installations to solid structured buildings on budget constrained projects.
Point to point communications up to 1 Gbps
Wireless Ethernet range up to 5000m
Full duplex connectivity
Secure data transmission
Built-in automatic failover
Licence free operation
The technical specifications listed above are those advertised by the manufacturer. No warranty is made to the accuracy of this information, which may vary widely in practical installations. Many vendors are known to exaggerate or mis-state the capability of the equipment which they offer.
For More Information on Wireless Upgrades
If you would like more information on upgrading a GeoDesy AT/AF/PX wireless solutions please Contact Us and our experienced team of wireless experts will be delighted to assist.
A new standard for 60GHz Wi-Fi goes beyond 802.11ad wireless speed & range
A new standard for high speed multi-gigabit WiFi is emerging. Though products based on the IEEE 802.11ad (WiGig) standard have really only begun rolling out, an effort to deliver an enhancement called IEEE 802.11ay that promises to deliver faster and longer range Wi-Fi networks is gaining steam.
The up-coming 802.11ay is as an enhancement of 802.11ad in the unlicensed 60 GHz millimeter wave band of spectrum, and should be a natural upgrade. The upgrade will offer significant speed and range improvements.
802.11ay is a type of WLAN in the IEEE 802.11 set of WLANs. It will have a frequency of 60 GHz, a transmission rate of 20–40 Gbit/s and an extended transmission distance of 300–500 meters. It has also been noted that it is likely to have mechanisms for channel bonding and MU-MIMO technologies. It is expected to be released in 2017. 802.11ay will not be a new type of WLAN in the IEEE 802.11 set, but will simply be an improvement on 802.11ad.
Where 802.11ad uses a maximum of 2.16 GHz bandwidth, 802.11ay bonds four of those channels together for a maximum bandwidth of 8.64 GHz. MIMO is also added with a maximum of 4 streams. The link-rate per stream is 44Gbit/s, with four streams this goes up to 176Gbit/s. Higher order modulation is also added, probably up to 256-QAM. 802.11ay applications could include replacement for Ethernet and other cables within offices or homes, and provide backhaul connectivity outside for service providers.
What is the difference between ad and ay?
The 802.11ad standard was published in 2012 and the technology gives devices access to the unlicensed and relatively unclogged 60 GHz millimeter wave spectrum band for multimedia streaming, VR headset connectivity, computer-to-monitor wireless links and other apps that don’t require more than say 30 or 40 feet of unimpeded space. It has been adopted by chipmakers as well as vendors of routers, access points and other devices. The Wi-Fi Alliance runs a WiGig certification program for vendors, and the early 11ad gear on the market most commonly supports data transfer rates of 4.6Gbps – way faster than 802.11n and 11ac, but more limited in range and unable to penetrate solid objects.
The backwards compatible 802.11ay amendment to 802.11ad is designed to boost speeds several-fold. That initially would amount to a transmission rate of 20 to 30Gbps and a range of 33 to 100 feet with 11ay-to-11ay device setups, but once channel bonding, MIMO and other capabilities are exploited, you could be getting closer to 200Gbps and reaching distances approaching 1,000 feet, according to industry players.
11ay, as the specs are being developed, “is really allowing for a wider range of products than you’d get with ad, which has one set of data rates that everyone supports… ay has a lot more parameters to play with in channel bonding, MIMO and features at the MAC level to allow a far greater range of performance and products” according to one chipset vendor.
Other up-coming Fast WiFi standards: 802.11ax
Users should not confuse 802.11ay with 802.11ax, which will work in the 2.5 and 5 GHz bands. The lower frequency bands for 11ax will penetrate walls. 11ay will not.
What will 802.11ay be used for?
It remains to be seen how soon the high speeds of 11ay will really be needed for internal uses, as 802.11ac — including Wave 2 products — are already pretty robust. But experts say that if 11ad doesn’t quite do it for you given its distance limitations, “11ay will finally be the technology that would let you snip that Ethernet cord – you no longer have to run Ethernet cables to everyone’s desk… there’s enough wireless bandwidth in ay.”
Many are enthusiastic about 802.1ay’s potential as a fixed point-to-point or point-to-multipoint outdoor backhaul technology, especially in light of scaled back fiber rollout plans by providers like Google and Verizon in the face of extraordinary costs associated with such implementations. “I’m more bullish on using ad & ay for backhaul (instead of mesh) in the case of campus & city networks — provided that it has a useful range” according to one industry expert
But it’s possible that 802.11ay could find a role in internal mesh and backbone networks as well as for other uses such as providing connectivity to VR headsets, supporting server backups and handling cloud applications that require low latency. “I believe that eventually, there will be enterprise applications for this – but it’s probably a few years into the future, given that we will have 802.11ax fairly soon & because there’s still a lot of 5 GHz band available for that (and ac).
When will 802.11ay become reality?
The 802.11ay task group had its initial meeting in 2015 and the spec only hit the Draft 0.1 stage in January. Though it is expected to reach Draft 1.0 by July 2017, according to the IEEE task group. If that mark is hit, expect pre-standard 11ay products to start rolling out within a year of that time.
Who is behind 802.11ay?
The IEEE task force leading the 11ay work includes representatives from major equipment and chipsets vendors. The group states its goal as this: “Task Group ay is expected to develop an amendment that defines standardized modifications to both the IEEE 802.11 physical layers (PHY) and the IEEE 802,11 medium access control layer (MAC) that enables at least one mode of operation capable of supporting a maximum throughput of at least 20 gigabits per second (measured at the MAC data service access point), while maintaining or improving the power efficiency per station. This amendment also defines operations for license-exempt bands above 45 GHz while ensuring backward compatibility and coexistence with legacy directional multi-gigabit stations (defined by IEEE 802.11ad-2012 amendment) operating in the same band.”
The new standard 802.11ax for Wi-Fi goes beyond 802.11ac wireless
A new standard for high speed multi-gigabit WiFi is emerging. Current WiFi products use chips based on the IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, IEEE 802.11 and IEEE 802.11ac standard have really only begun rolling out, an effort to deliver an enhancement called IEEE 802.11ax that promises to deliver faster and longer range Wi-Fi networks.
The up-coming 802.11ax is as an enhancement of 802.11ac in the unlicensed 2.4 and 5GHz bands of spectrum, and should be a natural upgrade. The upgrade will offer significant speed and range improvements.
IEEE 802.11 ax is a type of WLAN in the IEEE 802.11 set of types of WLANs. It is designed to improve overall spectral efficiency especially in dense deployment scenarios. It is still in a very early stage of development, but is predicted to have a top speed of around 10 Gb/s, it works in 2.4 and/or 5 GHz, in addition to MIMO and MU-MIMO it introduces OFDMA technique to improve spectral efficiency and also higher order 1024 QAM modulation support for better throughputs. Though the nominal data rate is just 37% higher comparing with 802.11ac, the new amendment will allow achieving 4X increase of user throughput thanks to more efficient spectrum usage. It is due to be publicly released in 2019.
Modulation and coding schemes for single spatial stream
Data rate (in Mb/s)
20 MHz channels
40 MHz channels
80 MHz channels
160 MHz channels
1600 ns GI
800 ns GI
1600 ns GI
800 ns GI
1600 ns GI
800 ns GI
1600 ns GI
800 ns GI
The 802.11ax amendment will bring several key improvements over 802.11ac. 802.11ax addresses frequency bands between 1 GHz and 6 GHz. Therefore, unlike 802.11ac, 802.11ax will also operate in the unlicensed 2.4 GHz band. To meet the goal of supporting dense 802.11 deployments the following features have been approved.
Other up-coming Fast WiFi standards: 802.11ay
Users should not confuse 802.11ax with 802.11ay, which will work in the 60GHz bands. The lower frequency bands 1-6GHz for 11ax will penetrate walls. 11ay will not.
What will 802.11ax be used for?
802.11ax is an upgrade for existing 802.11a, 802.11b, 802.11g, 802.11n and 802.11ac networks, Many are enthusiastic about 802.1ax’s potential as a fixed point-to-point or point-to-multipoint outdoor backhaul technology, especially in light of scaled back fiber rollout plans by providers like Google and Verizon in the face of extraordinary costs associated with such implementations. Therefore 11ax will find applications outdoors as well as indoors.
Who is behind 802.11ax?
The IEEE task force leading the 11ax work includes representatives from major equipment and chipsets vendors.
In 2012 and 2013, IEEE 802.11 received various submissions in its Standing Committee (SC) Wireless Next Generation (WNG) looking at issues of IEEE 802.11ac and potential solutions for future WLANs. Immediately after the publication of IEEE 802.11ac in March 2013, the IEEE 802.11 Working Group (WG) established Study Group (SG) High Efficiency WLAN (HEW)
5G radio access technology will be a key component of the Networked Society. It will address high traffic growth and increasing demand for high-bandwidth connectivity. It will also support massive numbers of connected devices and meet the real-time, high-reliability communication needs of mission-critical applications. 5G will provide wireless connectivity for a wide range of new applications and use cases, including wearables, smart homes, traffic safety/control, critical infrastructure, industry processes and very-high-speed media delivery. As a result, it will also accelerate the development of the Internet of Things. ITU Members including key industry players, industry forums, national and regional standards development organizations, regulators, network operators, equipment manufacturers as well as academia and research institutions together with Member States, gathered as the working group responsible for IMT systems, and completed a cycle of studies on the key performance requirements of 5G technologies for IMT-2020.
The Aim of 5G
The overall aim of 5G is to provide ubiquitous connectivity for any kind of device and any kind of application that may benefit from being connected. 5G networks will not be based on one specific radio-access technology. Rather, 5G is a portfolio of access and connectivity solutions addressing the demands and requirements of mobile communication beyond 2020.
The specification of 5G will include the development of a new flexible air interface, NX, which will be directed to extreme mobile broadband deployments. NX will also target high-bandwidth and high-traffic-usage scenarios, as well as new scenarios that involve mission-critical and realtime communications with extreme requirements in terms of latency and reliability.
In parallel, the development of Narrow-Band IoT (NB-IoT) in 3GPP is expected to support massive machine connectivity in wide area applications. NB-IoT will most likely be deployed in bands below 2GHz and will provide high capacity and deep coverage for enormous numbers of connected devices.
Ensuring interoperability with past generations of mobile communications has been a key principle of the ICT industry since the development of GSM and later wireless technologies within the 3GPP family of standards.
4G to 5G Evolution
In a similar manner, LTE will evolve in a way that recognizes its role in providing excellent coverage for mobile users, and 5G networks will incorporate LTE access (based on Orthogonal Frequency Division Multiplexing (OFDM)) along with new air interfaces in a transparent manner toward both the service layer and users. Around 2020, much of the available wireless coverage will continue to be provided by LTE, and it is important that operators with deployed 4G networks have the opportunity to transition some – or all – of their spectrum to newer wireless access technologies.
For operators with limited spectrum resources, the possibility of introducing 5G capabilities in an interoperable way – thereby allowing legacy devices to continue to be served on a compatible carrier – is highly beneficial and, in some cases, even vital. At the same time, the evolution of LTE to a point where it is a full member of the 5G family of air interfaces is essential, especially since initial deployment of new air interfaces may not operate in the same bands. The 5G network will enable dual-connectivity between LTE operating within bands below 6GHz and the NX air interface in bands within the range 6GHz to100GHz. NX should also allow for user-plane aggregation, i.e. joint delivery of data via LTE and NX component carriers. This paper explains the key requirements and capabilities of 5G, along with its technology components and spectrum needs.
In order to enable connectivity for a very wide range of applications with new characteristics and requirements, the capabilities of 5G wireless access must extend far beyond those of previous generations of mobile communication. These capabilities will include massive system capacity, very high data rates everywhere, very low latency, ultra-high reliability and availability, very low device cost and energy consumption, and energy-efficient networks.
MASSIVE SYSTEM CAPACITY
Traffic demands for mobile-communication systems are predicted to increase dramatically. To support this traffic in an affordable way, 5G networks must deliver data with much lower cost per bit compared with the networks of today. Furthermore, the increase in data consumption will result in an increased energy footprint from networks. 5G must therefore consume significantly lower energy per delivered bit than current cellular networks. The exponential increase in connected devices, such as the deployment of billions of wirelessly connected sensors, actuators and similar devices for massive machine connectivity, will place demands on the network to support new paradigms in device and connectivity management that do not compromise security. Each device will generate or consume very small amounts of data, to the extent that they will individually, or even jointly, have limited impact on the overall traffic volume. However, the sheer number of connected devices seriously challenges the ability of the network to provision signaling and manage connections.
VERY HIGH DATA RATES EVERYWHERE
Every generation of mobile communication has been associated with higher data rates compared with the previous generation. In the past, much of the focus has been on the peak data rate that can be supported by a wireless-access technology under ideal conditions. However, a more important capability is the data rate that can actually be provided under real-life conditions in different scenarios.
5G should support data rates exceeding 10Gbps in specific scenarios such as indoor and dense outdoor environments.
Data rates of several 100Mbps should generally be achievable in urban and suburban environments.
Data rates of at least 10Mbps should be accessible almost everywhere, including sparsely populated rural areas in both developed and developing countries.
VERY LOW LATENCY
Very low latency will be driven by the need to support new applications. Some envisioned 5G use cases, such as traffic safety and control of critical infrastructure and industry processes, may require much lower latency compared with what is possible with the mobile-communication systems of today. To support such latency-critical applications, 5G should allow for an application end-to-end latency of 1ms or less, although application-level framing requirements and codec limitations for media may lead to higher latencies in practice. Many services will distribute computational capacity and storage close to the air interface. This will create new capabilities for real-time communication and will allow ultra-high service reliability in a variety of scenarios, ranging from entertainment to industrial process control.
ULTRA-HIGH RELIABILITY AND AVAILABILITY
In addition to very low latency, 5G should also enable connectivity with ultra-high reliability and ultra-high availability. For critical services, such as control of critical infrastructure and traffic safety, connectivity with certain characteristics, such as a specific maximum latency, should not merely be ‘typically available.’ Rather, loss of connectivity and deviation from quality of service requirements must be extremely rare. For example, some industrial applications might need to guarantee successful packet delivery within 1 ms with a probability higher than 99.9999 percent.
VERY LOW DEVICE COST AND ENERGY CONSUMPTION
Low-cost, low-energy mobile devices have been a key market requirement since the early days of mobile communication. However, to enable the vision of billions of wirelessly connected sensors, actuators and similar devices, a further step has to be taken in terms of device cost and energy consumption. It should be possible for 5G devices to be available at very low cost and with a battery life of several years without recharging.
While device energy consumption has always been prioritized, energy efficiency on the network side has recently emerged as an additional KPI, for three main reasons:
Energy efficiency is an important component in reducing operational cost, as well as a driver for better dimensioned nodes, leading to lower total cost of ownership.
Energy efficiency enables off-grid network deployments that rely on medium-sized solar panels as power supplies, thereby enabling wireless connectivity to reach even the most remote areas.
Energy efficiency is essential to realizing operators’ ambition of providing wireless access in a sustainable and more resource-efficient way.
The importance of these factors will increase further in the 5G era, and energy efficiency will therefore be an important requirement in the design of 5G wireless access.
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Please Contact Us for more information on 5G and IMT-2020
FSO (Free Space Optics, Laser, Optical Wireless) Guide
Free Space Optics (FSO) communications, also called Optical Wireless (OW) or Infrared Laser, refers to the transmission of modulated visible or infrared (IR) beams through the atmosphere to obtain optical communications. Like fibre, Free Space Optics (FSO) uses lasers to transmit data, but instead of enclosing the data stream in a glass fibre, it is transmitted through the air. Free Space Optics (FSO) works on the same basic principle as Infrared television remote controls, wireless keyboards or IRDA ports on laptops or cellular phones.
History of Free Space Optics (FSO)
The engineering maturity of Free Space Optics (FSO) is often underestimated, due to a misunderstanding of how long Free Space Optics (FSO) systems have been under development. Historically, Free Space Optics (FSO) or optical wireless communications was first demonstrated by Alexander Graham Bell in the late nineteenth century (prior to his demonstration of the telephone!). Bell’s Free Space Optics (FSO) experiment converted voice sounds into telephone signals and transmitted them between receivers through free air space along a beam of light for a distance of some 600 feet. Calling his experimental device the “photophone,” Bell considered this optical technology – and not the telephone – his pre-eminent invention because it did not require wires for transmission.
Although Bell’s photophone never became a commercial reality, it demonstrated the basic principle of optical communications. Essentially all of the engineering of today’s Free Space Optics (FSO) or free space optical communications systems was done over the past 40 years or so, mostly for defense applications. By addressing the principal engineering challenges of Free Space Optics (FSO), this aerospace/defence activity established a strong foundation upon which today’s commercial laser-based Free Space Optics (FSO) systems are based.
How Free Space Optics (FSO) Works
Free Space Optics (FSO) transmits invisible, eye-safe light beams from one “telescope” to another using low power infrared lasers in the terahertz spectrum. The beams of light in Free Space Optics (FSO) systems are transmitted by laser light focused on highly sensitive photon detector receivers. These receivers are telescopic lenses able to collect the photon stream and transmit digital data containing a mix of Internet messages, video images, radio signals or computer files. Commercially available systems offer capacities in the range of 100 Mbps to 2.5 Gbps, and demonstration systems report data rates as high as 160 Gbps.
Free Space Optics (FSO) systems can function over distances of several kilometres. As long as there is a clear line of sight between the source and the destination, and enough transmitter power, Free Space Optics (FSO) communication is possible.
FSO: Wireless Links at the Speed of Light
Unlike radio and microwave systems, Free Space Optics (FSO) is an optical technology and no spectrum licensing or frequency coordination with other users is required, interference from or to other systems or equipment is not a concern, and the point-to-point laser signal is extremely difficult to intercept, and therefore secure. Data rates comparable to optical fibre transmission can be carried by Free Space Optics (FSO) systems with very low error rates, while the extremely narrow laser beam widths ensure that there is almost no practical limit to the number of separate Free Space Optics (FSO) links that can be installed in a given location.
How Free Space Optics (FSO) benefits you
FSO is free from licensing and regulation which translates into ease, speed and low cost of deployment. Since Free Space Optics (FSO) transceivers can transmit and receive through windows, it is possible to mount Free Space Optics (FSO) systems inside buildings, reducing the need to compete for roof space, simplifying wiring and cabling, and permitting Free Space Optics (FSO) equipment to operate in a very favourable environment. The only essential requirement for Free Space Optics (FSO) or optical wireless transmission is line of sight between the two ends of the link.
For Metro Area Network (MAN) providers the last mile or even feet can be the most daunting. Free Space Optics (FSO) networks can close this gap and allow new customers access to high-speed MAN’s. Providers also can take advantage of the reduced risk of installing an Free Space Optics (FSO) network which can later be redeployed.
The Market. Why FSO? Breaking the Bandwidth Bottleneck
Why FSO? The global telecommunications network has seen massive expansion over the last few years. First came the tremendous growth of the optical fiber long-haul, wide-area network (WAN), followed by a more recent emphasis on metropolitan area networks (MANs). Meanwhile, local area networks (LANs) and gigabit Ethernet ports are being deployed with a comparable growth rate. In order for this tremendous network capacity to be exploited, and for the users to be able to utilize the broad array of new services becoming available, network designers must provide a flexible and cost-effective means for the users to access the telecommunications network. Presently, however, most local loop network connections are limited to 1.5 Mbps (a T1 line). As a consequence, there is a strong need for a high-bandwidth bridge (the “last mile” or “first mile”) between the LANs and the MANs or WANs.
A recent New York Times article reported that more than 100 million miles of optical fibre was laid around the world in the last two years, as carriers reacted to the Internet phenomenon and end users’ insatiable demand for bandwidth. The sheer scale of connecting whole communities, cities and regions to that fiber optic cable or “backbone” is something not many players understood well. Despite the huge investment in trenching and optical cable, most of the fibre remains unlit, 80 to 90% of office, commercial and industrial buildings are not connected to fibre, and transport prices are dropping dramatically.
Free Space Optics (FSO) systems represent one of the most promising approaches for addressing the emerging broadband access market and its “last mile” bottleneck. Free Space Optics (FSO) systems offer many features, principal among them being low start-up and operational costs, rapid deployment, and high fiber-like bandwidths due to the optical nature of the technology.
Broadband Bandwidth Alternatives
Access technologies in general use today include telco-provisioned copper wire, wireless Internet access, broadband RF/microwave, coaxial cable and direct optical fiber connections (fiber to the building; fiber to the home). Telco/PTT telephone networks are still trapped in the old Time Division Multiplex (TDM) based network infrastructure that rations bandwidth to the customer in increments of 1.5 Mbps (T-1) or 2.024 Mbps (E-1). DSL penetration rates have been throttled by slow deployment and the pricing strategies of the PTTs. Cable modem access has had more success in residential markets, but suffers from security and capacity problems, and is generally conditional on the user subscribing to a package of cable TV channels. Wireless Internet access is still slow, and the tiny screen renders it of little appeal for web browsing.
Broadband RF/microwave systems have severe limitations and are losing favor. The radio spectrum is a scarce and expensive licensed commodity, sold or leased to the highest bidder, or on a first-come first-served basis, and all too often, simply unavailable due to congestion. As building owners have realized the value of their roof space, the price of roof rights has risen sharply. Furthermore, radio equipment is not inexpensive, the maximum data rates achievable with RF systems are low compared to optical fiber, and communications channels are insecure and subject to interference from and to other systems (a major constraint on the use of radio systems).
Free Space Optics (FSO) Advantages
Free space optical (FSO) systems offers a flexible networking solution that delivers on the promise of broadband. Only free space optics or Free Space Optics (FSO) provides the essential combination of qualities required to bring the traffic to the optical fiber backbone – virtually unlimited bandwidth, low cost, ease and speed of deployment. Freedom from licensing and regulation translates into ease, speed and low cost of deployment. Since Free Space Optics (FSO) optical wireless transceivers can transmit and receive through windows, it is possible to mount Free Space Optics (FSO) systems inside buildings, reducing the need to compete for roof space, simplifying wiring and cabling, and permitting the equipment to operate in a very favorable environment. The only essential for Free Space Optics (FSO) is line of sight between the two ends of the link.
Security and Free Space Optics (FSO)
The common perception of wireless is that it offers less security than wireline connections. In fact, Free Space Optics (FSO) is far more secure than RF or other wireless-based transmission technologies for several reasons:
Free Space Optics (FSO) laser beams cannot be detected with spectrum analyzers or RF meters
Free Space Optics (FSO) laser transmissions are optical and travel along a line of sight path that cannot be intercepted easily. It requires a matching Free Space Optics (FSO) transceiver carefully aligned to complete the transmission. Interception is very difficult and extremely unlikely
The laser beams generated by Free Space Optics (FSO) systems are narrow and invisible, making them harder to find and even harder to intercept and crack
Data can be transmitted over an encrypted connection adding to the degree of security available in Free Space Optics (FSO) network transmissions.
Free Space Optics (FSO) Challenges
The advantages of free space optical wireless or Free Space Optics (FSO) do not come without some cost. When light is transmitted through optical fiber, transmission integrity is quite predictable – barring unforseen events such as backhoes or animal interference. When light is transmitted through the air, as with Free Space Optics (FSO) optical wireless systems, it must contend with a a complex and not always quantifiable subject – the atmosphere.
Attenuation, Fog and Free Space Optics (FSO)
Fog substantially attenuates visible radiation, and it has a similar affect on the near-infrared wavelengths that are employed in Free Space Optics (FSO) systems. Note that the effect of fog on Free Space Optics (FSO) optical wireless radiation is entirely analogous to the attenuation – and fades – suffered by RF wireless systems due to rainfall. Similar to the case of rain attenuation with RF wireless, fog attenuation is not a “show-stopper” for Free Space Optics (FSO) optical wireless, because the optical link can be engineered such that, for a large fraction of the time, an acceptable power will be received even in the presence of heavy fog. Free Space Optics (FSO) optical wireless-based communication systems can be enhanced to yield even greater availabilities.
Free Space Optics (FSO) and Physical Obstructions
Free Space Optics (FSO) products which have widely spaced redundant transmitters and large receive optics will all but eliminate interference concerns from objects such as birds. On a typical day, an object covering 98% of the receive aperture and all but 1 transmitter; will not cause an Free Space Optics (FSO) link to drop out. Thus birds are unlikely to have any impact on Free Space Optics (FSO) transmission.
Free Space Optics (FSO) Pointing Stability – Building Sway, Tower Movement
Only wide-beamwidth fixed pointed Free Space Optics (FSO) systems are capable of handling the vast majority of movement found in deployments on buildings. Narrow beam systems are unreliable, requiring manual re-alignment on a regular basis, due to building movement. ‘Wide beam’ means more than 5milliradians. Narrow systems (1-2mRad) are not reliable without a tracking system
The combination of effective beam divergence and a well matched receive Field-of-View (FOV) provide for an extremely robust fixed pointed Free Space Optics (FSO) system suitable for most deployments. Fixed-pointed Free Space Optics (FSO) systems are generally preferred over actively-tracked Free Space Optics (FSO) systems due to their lower cost.
Free Space Optics (FSO) and Scintillation
Performance of many Free Space Optics (FSO) optical wireless systems is adversely affected by scintillation on bright sunny days; the effects of which are typically reflected in BER statistics. Some optical wireless products have a unique combination of large aperture receiver, widely spaced transmitters, finely tuned receive filtering, and automatic gain control characteristics. In addition, certain optical wireless systems also apply a clock recovery phase-lock-loop time constant that all but eliminate the affects of atmospheric scintillation and jitter transference.
Solar Interference and Free Space Optics (FSO)
Solar interference in Free Space Optics (FSO) free space optical systems can be combated in two ways. Optical narrowband filter proceeding the receive detector used to filter all but the wavelength actually used for intersystem communications. To handle off-axis solar energy, sophisticated spatial filters have been implemented in CableFree systems, allowing them to operate unaffected by solar interference that is more than 1 degree off-axis.
Free Space Optics (FSO) Reliability
Employing an adaptive laser power (Automatic Transmit Power Control or ATPC) scheme to dynamically adjust the laser power in response to weather conditions will improve the reliability of Free Space Optics (FSO) optical wireless systems. In clear weather the transmit power is greatly reduced, enhancing the laser lifetime by operating the laser at very low-stress conditions. In severe weather, the laser power is increased as needed to maintain the optical link – then decreased again as the weather clears. A TEC controller that maintains the temperature of the laser transmitter diodes in the optimum region will maximize reliability and lifetime, consistent with power output allowing the FSO optical wireless system to operate more efficiently and reliably at higher power levels.
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What is OFDM? (Orthogonal Frequency Division Multiplexing)
OFDM: Orthogonal Frequency Division Multiplexing, is a form of signal modulation that divides a high data rate modulating stream placing them onto many slowly modulated narrowband close-spaced subcarriers, and in this way is less sensitive to frequency selective fading.
Orthogonal Frequency Division Multiplexing or OFDM is a modulation format that is being used for many of the latest wireless and telecommunications standards.
OFDM has been adopted in the Wi-Fi arena where the standards like 802.11a, 802.11n, 802.11ac and more. It has also been chosen for the cellular telecommunications standard LTE / LTE-A, and in addition to this it has been adopted by other standards such as WiMAX and many more.
Orthogonal frequency division multiplexing has also been adopted for a number of broadcast standards from DAB Digital Radio to the Digital Video Broadcast standards, DVB. It has also been adopted for other broadcast systems as well including Digital Radio Mondiale used for the long medium and short wave bands.
Although OFDM, orthogonal frequency division multiplexing is more complicated than earlier forms of signal format, it provides some distinct advantages in terms of data transmission, especially where high data rates are needed along with relatively wide bandwidths.
What is OFDM? – The concept
OFDM is a form of multicarrier modulation. An OFDM signal consists of a number of closely spaced modulated carriers. When modulation of any form – voice, data, etc. is applied to a carrier, then sidebands spread out either side. It is necessary for a receiver to be able to receive the whole signal to be able to successfully demodulate the data. As a result when signals are transmitted close to one another they must be spaced so that the receiver can separate them using a filter and there must be a guard band between them. This is not the case with OFDM. Although the sidebands from each carrier overlap, they can still be received without the interference that might be expected because they are orthogonal to each another. This is achieved by having the carrier spacing equal to the reciprocal of the symbol period.
Traditional view of receiving signals carrying modulation
To see how OFDM works, it is necessary to look at the receiver. This acts as a bank of demodulators, translating each carrier down to DC. The resulting signal is integrated over the symbol period to regenerate the data from that carrier. The same demodulator also demodulates the other carriers. As the carrier spacing equal to the reciprocal of the symbol period means that they will have a whole number of cycles in the symbol period and their contribution will sum to zero – in other words there is no interference contribution.
One requirement of the OFDM transmitting and receiving systems is that they must be linear. Any non-linearity will cause interference between the carriers as a result of inter-modulation distortion. This will introduce unwanted signals that would cause interference and impair the orthogonality of the transmission.
In terms of the equipment to be used the high peak to average ratio of multi-carrier systems such as OFDM requires the RF final amplifier on the output of the transmitter to be able to handle the peaks whilst the average power is much lower and this leads to inefficiency. In some systems the peaks are limited. Although this introduces distortion that results in a higher level of data errors, the system can rely on the error correction to remove them.
Data on OFDM
The data to be transmitted on an OFDM signal is spread across the carriers of the signal, each carrier taking part of the payload. This reduces the data rate taken by each carrier. The lower data rate has the advantage that interference from reflections is much less critical. This is achieved by adding a guard band time or guard interval into the system. This ensures that the data is only sampled when the signal is stable and no new delayed signals arrive that would alter the timing and phase of the signal.
The distribution of the data across a large number of carriers in the OFDM signal has some further advantages. Nulls caused by multi-path effects or interference on a given frequency only affect a small number of the carriers, the remaining ones being received correctly. By using error-coding techniques, which does mean adding further data to the transmitted signal, it enables many or all of the corrupted data to be reconstructed within the receiver. This can be done because the error correction code is transmitted in a different part of the signal.
OFDM advantages & disadvantages
OFDM has been used in many high data rate wireless systems because of the many advantages it provides.
Immunity to selective fading: One of the main advantages of OFDM is that is more resistant to frequency selective fading than single carrier systems because it divides the overall channel into multiple narrowband signals that are affected individually as flat fading sub-channels.
Resilience to interference: Interference appearing on a channel may be bandwidth limited and in this way will not affect all the sub-channels. This means that not all the data is lost.
Spectrum efficiency: Using close-spaced overlapping sub-carriers, a significant OFDM advantage is that it makes efficient use of the available spectrum.
Resilient to ISI: Another advantage of OFDM is that it is very resilient to inter-symbol and inter-frame interference. This results from the low data rate on each of the sub-channels.
Resilient to narrow-band effects: Using adequate channel coding and interleaving it is possible to recover symbols lost due to the frequency selectivity of the channel and narrow band interference. Not all the data is lost.
Simpler channel equalisation: One of the issues with CDMA systems was the complexity of the channel equalisation which had to be applied across the whole channel. An advantage of OFDM is that using multiple sub-channels, the channel equalization becomes much simpler.
Whilst OFDM has been widely used, there are still a few disadvantages to its use which need to be addressed when considering its use.
High peak to average power ratio: An OFDM signal has a noise like amplitude variation and has a relatively high large dynamic range, or peak to average power ratio. This impacts the RF amplifier efficiency as the amplifiers need to be linear and accommodate the large amplitude variations and these factors mean the amplifier cannot operate with a high efficiency level.
Sensitive to carrier offset and drift: Another disadvantage of OFDM is that is sensitive to carrier frequency offset and drift. Single carrier systems are less sensitive.
There are several other variants of OFDM for which the initials are seen in the technical literature. These follow the basic format for OFDM, but have additional attributes or variations:
COFDM: Coded Orthogonal frequency division multiplexing. A form of OFDM where error correction coding is incorporated into the signal.
Flash OFDM: This is a variant of OFDM that was developed by Flarion and it is a fast hopped form of OFDM. It uses multiple tones and fast hopping to spread signals over a given spectrum band.
OFDMA: Orthogonal frequency division multiple access. A scheme used to provide a multiple access capability for applications such as cellular telecommunications when using OFDM technologies.
VOFDM: Vector OFDM. This form of OFDM uses the concept of MIMO technology. It is being developed by CISCO Systems. MIMO stands for Multiple Input Multiple output and it uses multiple antennas to transmit and receive the signals so that multi-path effects can be utilised to enhance the signal reception and improve the transmission speeds that can be supported.
WOFDM: Wideband OFDM. The concept of this form of OFDM is that it uses a degree of spacing between the channels that is large enough that any frequency errors between transmitter and receiver do not affect the performance. It is particularly applicable to Wi-Fi systems.
Each of these forms of OFDM utilise the same basic concept of using close spaced orthogonal carriers each carrying low data rate signals. During the demodulation phase the data is then combined to provide the complete signal.
OFDM, orthogonal frequency division multiplexing has gained a significant presence in the wireless market place. The combination of high data capacity, high spectral efficiency, and its resilience to interference as a result of multi-path effects means that it is ideal for the high data applications that have become a major factor in today’s communications scene.
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