Feel welcome to read our site and find out more about building modern, reliable and scalable Gigabit Wireless Networks for Wireless Metropolitan Area Networks (Wi-Man), 4G/LTE backhaul networks, Small Cell Backhaul, Corporate Networks and Campus and CCTV wireless networks.
We include technology introduction papers as well as usage cases to guide users in the very latest in Gigabit Wireless technology and deployment
Gigabit Wireless Metro Networks: CableFree MMW links deployed in the UAE
CableFree has deployed Gigabit Wireless MMW links for Public Safety networks in the UAE with regional partner CDN (Computer Data Networks). For this project a number of 1Gbps MMW links have been implemented to upgrade and extend existing network infrastructure for Safe City applications.
CableFree Millimeter Wave (MMW) links offer up to 10Gbps Full Duplex capacity and are proven to operate well in the harsh climate and conditions in regions such as the UAE, including recent record summer temperatures. CableFree worked closely with CDN to ensure high uptime and availability are ensured throughout the network.
CableFree MMW is a proven and robust high speed technology for Line of Sight links. High frequency microwave signals between 60 and 90GHz have “pencil beam” properties that avoid any interference and enable dense deployment in busy urban areas.
Applications for Millimeter Wave include 4G/LTE Mobile Backhaul, Safe Cities, Government, Corporate CCTV and ISP backbones.
Distances up to 5-15km can be deployed reliably: CableFree provide a full range of planning tools to enable customers to plan for high availability even in high rainfall regions.
CableFree MMW links are ideal for implementing wireless networks in many regions and can upgrade existing congested unlicensed and licensed microwave links, and extend the reach of fibre optic cabling. The links are rapid to deploy within hours and can provide permanent, temporary or disaster-recovery scenarios, including resilient backup to fragile fibre optic cables and leased lines.
For more information on Millimeter Wave and Wireless Metro Networks please contact the CableFree team: email@example.com
Researchers agree that slow internet can stress you out
You’re not the only one who gets frustrated when videos buffer too much and too often. Ericsson found that the stress caused by trying to load videos on a slow mobile connection is comparable to the stress you feel while watching a horror movie. The Swedish company discovered that when it conducted an experiment called “The Stress of Streaming Delays.” Sure, Ericsson did it to show brands how slow internet affects them, and it’s true it only had 30 subjects. But we don’t think anyone would disagree that having to endure several seconds to minutes of buffering is frustrating.
Researchers measured the subjects’ brain, pulse and heart activities while they were performing tasks on a phone, found that video streaming delays increase heart rate by 38 percent. They also found that a two-second buffering period can double stress levels. When the researchers observed the subjects who were subjected to longer delays (around six seconds), though, they saw their stress levels rise, then fall. The participants showed signs of resignation, including eye movements that indicated distraction — they were already giving up.
We’ll bet that’s a feeling you only know too well. Why wait around for downloads and buffering on Slow Internet? Choose a CableFree Wireless network and get into the fast lane with capacities up to 10Gbps!
On Dec. 16 2013, Ofcom—the UK telecom regulator—announced a new approach for the use of E-band wireless communications in the United Kingdom.
To summarize, the new approach, which is available for licensing after Dec. 17, 2013, splits the band into two segments. Ofcom will coordinate the lower segment of 2GHz, while the upper segment of 2.5GHz will remain self-coordinated as per the prior policy.
The segment Ofcom coordinates will follow the usual regulatory processes for all the other fixed link bands it oversees. Moreover, OFCOM has already updated all the relevant documents and forms to accommodate E-band. While wireless vendors would have preferred the larger portion of spectrum to have been granted to the Ofcom-coordinated process, we welcome this new arrangement because it provides an option for greater security and peace of mind to operators in terms of protection from interference than was envisaged for the previous all self-coordinated spectrum regime.
Latest E-Band regulation by OFCOM
For a more detailed look at the new E-band arrangement, Figure 1 shows the Ofcom-coordinated section sitting in the lower half of both the 71-76GHz and 81-86GHz bands thus allowing for the deployment of FDD systems in line with ECC/REC(05)07.
Figure 1: Segmented Plan for Mixed Management Approach (click on figures to enlarge)
In terms of channelization within the Ofcom-coordinated block, the regulator announced that it would permit 8 x 250MHz channels, 4 x 500MHz channels, 1 x 750MHz channel and 1 x 1000MHz channel as per ECC/REC(05)07. Ofcom also stated that 62.5MHz and 125MHz channels will be implemented as soon as the relevant technical standards, etc., from ETSI are published. Figure 2 shows the Ofcom channel plan:
Figure 2: Ofcom Permitted E-band Channelizations
Regarding equipment requirements, Ofcom stated that it will allow equipment that meets the appropriate sections of EN 302 217-2-2 and EN 302 217-4-2. This includes the antenna classes (e.g., classes 2-4) that will allow the deployment of solutions with flat panel antennas. We welcome this approach and hopes that other regulators—notably the FCC in terms of antenna requirements—currently considering opening up and/or revising their rules for E-band adopt similar approaches.
The license fees for the self-coordinated segment remains at £50 per link per annum, whereas in the Ofcom-coordinated segment the fees are bandwidth based as reflected in Figure 3:
Notwithstanding the current fees consultation process that Ofcom is undertaking, these “interim fees” will remain in place for five years, after which time the results of the fees review may mean that they will be amended.
Figure 3: Ofcom Bandwidth-based Fees
Also because of responses received during the consultation process, within the self-coordinated block, Ofcom will now require the following additional information for the self-coordination database: antenna polarization (horizontal, vertical or dual), ETSI Spectrum Efficiency Class and whether the link is TDD or FDD.
Fiber Cuts – The Real Cost – How to solve using Gigabit Wireless
Often you can’t avoid fiber cuts: they happen on public land or under public streets, outside your control. The vast majority of corporate LAN connections, cable, Internet and LTE backhaul, is done over fiber optic cable. In one report CNN stated that about 99 percent of all international communications occur over undersea cabling. Alan Mauldin, research director at U.S.-based research firm Telegeography, noted that while some major cabling projects can come with high price tags, fiber optics is considered more robust and more cost-effective than common wireless alternatives like satellite.
But while fiber optic cabling is traditionally seen as the safer option, that may be a misconception. When installed correctly, fiber optics is the “perfect” media, transmitting Gigabits of data without interruption. However, any disruption to the fragile fiber causes data outages which take days or weeks to locate and repair. According to data from the Federal Communications Commission. about a quarter of all network outages that happened between 1993 and 2001 were from cables being cut. Regardless of how the fiber cut occurred, such outages can be particularly damaging.
How easy is it to repair a fiber cut?
Fiber is not a “self healing” media: skilled teams with specialist fiber-splicing and terminating equipment are required to repair a broken fiber connection. Most data communication engineers do not have this equipment or training on using them. fiber repair is a specialist business and getting trained people and splicing equipment to site costs time and money. Factoring the anticipated cost of a fiber repair into a budget for “downtime” and “unproductivity” for corporates – and missing SLA’s for uptime for Service Providers – is a serious issue, including business continuity planning. For rural areas, access to sites can be limited, with some locations limited by poor weather, and for islands sometimes only with infrequent access by sea or air.
By vandalism – This type of fiber cut outage has been worryingly common of late. According to CNN, there have been 11 separate incidents involving the cutting of fiber optic cable in the Bay Area since July 2015. The FBI noted that there have been more than 12 in the region since January, and that it’s been hard to stop in part because there is so much critical cabling in the area and because cables are typically clearly marked, The Wall Street Journal reported. Authorities noted that these incidents show no sign of slowing down either, as they don’t have a clear suspect(s) or motive at this time. The Journal also noted that some instances of fiber optic-related downtime are not due to vandalism, but rather someone trying to steal metal.
By accident – This is perhaps one of the most common causes of fiber cuts, but nevertheless they are just as damaging. In one example a 75-year-old woman in the country of Georgia was digging in a field when she accidentally severed a fiber optic cable, in an article in The Guardian. As a result of the mishap, close to 90 percent of Armenia and parts of Azerbaijan and Georgia were completely without Internet for five plus hours.
By force of nature – Tornadoes, hurricanes, earthquakes and other major natural disasters all have the potential to cut or entirely destroy fiber optic cabling. Other seemingly more benign forces of nature can also cripple connectivity, as Level 3 reported that 28 percent of all damages it sustained to its infrastructure in 2010 were caused by squirrels.
Calculating the impact of a fiber outage
In some of these fiber cut outage incidents, the fallout can be relatively minor. A cut that occurs in the middle of the night on a redundant line can be easy enough to deal with, with service providers sometimes able to reroute traffic in the interim. Unfortunately however, such incidents often lead to much bigger problems for end users. For example, a cut fiber optic cable in northern Arizona in April caused many thousands of people and businesses to go about 15 hours with telephone and Internet service. This meant many shops had to either close or resort to manual tracking, and that personal Internet usage grinded to a halt, The Associated Press reported. More importantly, 911 emergency communications were disrupted in the incident.
It’s not just a hassle for end users, as cut fiber can severely impact public health when emergency services like police departments, fire stations and EMTs can’t take and receive calls. Plus, such incidents are very costly for service providers, forced to repair expensive infrastructure. They can also lead to canceled service, as customers become irate at service providers for failing to provide reliable connectivity at all times.
What’s a solution to fiber cut outages?
One easy way to avoid the problems related to cut fiber is to not have fiber at all and instead pursue a wireless dark fiber alternative. For example, after a cable snafu caused residents of Washington state’s San Juan Islands to go without telephone, Internet and cell service for 10 days in 2013, CenturyLink installed a wireless mobile backhaul option there, according to The AP.
By opting for a solution like a Gigabit WirelessMicrowave, MMW, Free Space Optics or MIMO OFDM Radio, service providers gain a wireless alternative to cabling that is just as robust and fast as fiber. With the Gigabit Wireless link in place, cut fiber optic cabling is less disruptive to end users and ISPs.
Where do I found out more information on solving fiber Cut Issues?
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.
For more information on Free Space Optics, please Contact Us
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.
For more information on wireless technology and OFDM, please Contact Us
Leased Line Alternatives and Resilience using Wireless
Leased lines are often very expensive to install, with high operating costs. Unless you already have fibre connected to your building then you will need to get fibre installed from the nearest point of presence (PoP), this involves digging a trench and laying an armoured glass fibre cable between the 2 locations.
The costs of doing these civil works be over £100 a metre in city locations. Urban areas require road closures, permits, traffic control, and repair bills to existing infrastructure such as drains. Therefore, the capital expenditure required for a wireless bridge is a fraction the cost, saving time and budget.
Millimeter Wave, also know as MMW or Millimetre Wave technology is being rapidly adopted for users ranging from enterprise level data centres to single consumers with smart phones requiring higher bandwidth, the demand for newer technologies to deliver these higher data transmission rates is bigger than ever before.
A wide range of technologies exist for the delivery of high throughput, with fibre optic cable considered to be the highest standard. However, fibre optics is not unmatched, especially when all considering economic factors. Millimeter wave wireless technology offers the potential to deliver bandwidth comparable to that of fibre optics but without the logistical and financial drawbacks of the deployments.
Millimeter waves represent the RF Signal spectrum between the frequencies of 30GHz and 300GHz with a wavelength between 1 – 10 millimetres but in terms of wireless networking and communications equipment, the name Millimeter Wave generally corresponds to a few select bands of radio frequencies found around 38, 60 and, more recently, the high potential 70 and 80 GHz bands that have been assigned for the public domain for the purpose of wireless networking and communications.
Commercial Millimeter Wave (MMW) links from CableFree feature high performance, reliable, high capacity wireless networking with latest generation features.
MM Wave Spectrum
In the UK, there have been 3 frequency bands that have been allocated for commercial Millimeter Wave usage, these are as follows:
57 – 66GHz: The 60GHz Millimeter Wave Band or V-Band is governed by OFCOM for licensed operation. The large amount of signal absorption via atmospheric oxygen and tight regulations make this frequency band more suited to short range, Point-to-Point and Point-to-Multipoint Millimetre Wave solutions. Between 57 – 64GHz the band is licensed and regulated but from 64 – 66GHz the band is unlicensed and self coordinated.
71 – 76GHz and 81 – 86GHz: The 70GHz and 80GHz Millimeter Wave Bands or E-Bands are governed by OFCOM for licensed operation only and are regarded to be the most suited band for Point-to-Point and Point-to-Multipoint, Millimeter Wave Wireless Networking and communication transmission. Each band has a 5GHz spectral range available which totals to be more than all other assigned frequency bands added together. Each 5GHz range can act as a single contiguous wireless transmission channel allowing very efficient use of the whole band and in turn these result in high throughput speeds from 1 to 3 Gbps whilst only using simple modulation techniques such as OOK (On-Off-Keying) or BPSK (Binary Phase Shift Keying). These throughput speeds are substantially higher than those found in lower frequencies using much more complex and advanced orders of modulation so even higher throughput speeds should be achieved with Millimetre Wave devices when utilising the same advanced techniques. It should be only a matter time before market demand brings these to the forefront.
In the US, an additional band is available as well as the above which is:
92 – 95GHz: The 94GHz Millimeter Wave Band or W-Band is governed by the FCC Part 15 for unlicensed operation also but only for indoor usage. It may also be used to outdoor Point-to-Point applications following the FCC Part 101 regulations but due to a range between 94 – 94.1GHz being excluded, the band is less spectrally efficient than the others.
The 71-76, 81-86 and 92-95 GHz bands are also used for point-to-point high-bandwidth communication links. These frequencies, as opposed to the 60 GHz frequency, do not suffer from the effects of oxygen absorption, but require a transmitting license in the US from the Federal Communications Commission (FCC). There are plans for 10 Gbit/s links using these frequencies as well. In the case of the 92–95 GHz band, a small 100 MHz range has been reserved for space-borne radios, making this reserved range limited to a transmission rate of under a few gigabits per second.
The band is essentially undeveloped and available for use in a broad range of new products and services, including high-speed, point-to-point wireless local area networks and broadband Internet access. WirelessHD is another recent technology that operates near the 60 GHz range. Highly directional, “pencil-beam” signal characteristics permit different systems to operate close to one another without causing interference. Potential applications include radar systems with very high resolution.
The upcoming Wi-Fi standard IEEE 802.11ad will run on the 60 GHz (V band) spectrum with data transfer rates of up to 7 Gbit/s.
Uses of the millimeter wave bands include point-to-point communications, intersatellite links, and point-to-multipoint communications.
Because of shorter wavelengths, the band permits the use of smaller antennas than would be required for similar circumstances in the lower bands, to achieve the same high directivity and high gain. The immediate consequence of this high directivity, coupled with the high free space loss at these frequencies, is the possibility of a more efficient use of the spectrum for point-to-multipoint applications. Since a greater number of highly directive antennas can be placed in a given area than less directive antennas, the net result is higher reuse of the spectrum, and higher density of users, as compared to lower frequencies. Furthermore, because one can place more voice channels or broadband information using a higher frequency to transmit the information, this spectrum could potentially be used as a replacement for or supplement to fiber optics.
Bandwidth & Scalable Capacity
The main benefit that Millimeter Wave technology has over lower RF frequencies is the spectral bandwidth of 5GHz being available in each of the E-Band ranges, resulting in current speeds of 1.25Gbps Full Duplex with potential throughput speeds of up to 10Gbps Full Duplex being made possible. Once market demand increases and better modulation techniques are implemented, spectral efficiency of the equipment will improve allowing the equipment to meet the higher capacity demands of prospective future networks.
Whereas low frequency, microwave signals have a wide beamwidth angle which reduces the reuse of transmission of the same signal within the local geographic area, Millimeter Wave signals transmit in very narrow, focused beams which allows for multiple deployments in tight proximity whilst using the same frequency ranges. This allows a density of around 15 times more when comparing a 70GHz signal to a 20GHz example making Millimeter Wave ideal for Point-to-Point Mesh, Ring and dense Hub & Spoke network topologies where lower frequency signals would not be able to cope before cross signal interference would become a significant limiting factor.
Propagation & Signal Attenuation
In general, Millimeter Wave links can range in anywhere up to 10km depending on factors such as equipment specifications and environmental conditions. The propagation properties of Millimeter Waves are much like those of the other popular wireless networking frequencies in that they are most significantly affected by air moisture levels; atmospheric Oxygen is also a large factor in the 60GHz band but almost negligible in the other ranges, under 0.2 dB per km.
Water vapour affects the signal at between 0 and 3dB/km at high humidity levels and the propagation due to clouds and fog acts in a very similar way depending on the density and amount of droplets in the air. These losses are relatively low and only play a major factor when considering links at 5km+.
Signal Loss (dB/km)
Oxygen absorption at Sea Level
Humidity of 100% at 30°C
Heavy Fog of 50m visibility
Heavy Rain Shower at 25mm/hr
At the 70 to 80GHz bands, water, in the form of rain, plays the most significant role in signal attenuation as it does with lower frequency signals too. The rate of rainfall, measured in mm/hour, is the depending factor in signal loss meaning that the harder it is raining, the lower the signal strength will be. Signal Propagation loss is also directly proportional to distance, so if the distance between transmitter and receiver is doubled, the loss in dB will be twice as much. Millimeter Wave performance is quite heavily dependent on rainfall and strongly affects Availability (discussed below), however, successful links can even be set up in areas of occasional heavy downpours.
Signal Loss (dB/km)
The reliability of a Millimeter Wave Wireless Network relies on the same principles as any other, in particular, the distance of operation, the radio’s link margin (being factors of transmit power, receiver sensitivity and beam divergence) and others such as redundancy paths. A link may be heavily affected by a period of intense rainfall but if it has a large enough margin, it will not suffer an outage.
The reliability of a network is called the availability and is measured as a percentage of time that the network will be functioning, for example, an availability of 99.999% over a year will equate to just over 5 hours of downtime. Much research by the ITU (International Telecommunication Union) has gone into collecting rainfall date from metropolitan areas around the world and how it will affect Millimeter Wave transmissions. You can see below an example of the expected availability of a widely available Millimeter Wave link for a few global cities and their respective availability for a 2km link.
Link Range (km, at 99.999% Availability)
Availability (2 km link)
Security is also an issue when dealing with wireless transmissions but due to Millimeter Wave’s inherently low beam widths (“pencil beams”) at about 0.36° radius with a 2ft. antenna along with, generally, lower peak transmit powers relative to lower frequencies the technology has a low probability of intercept and detection which is vital for the transference of confidential material.
FSO is a line-of-sight wireless communication technology that uses invisible beams of light to provide high speed wireless connections that can send and receive voice, video, and data information. Today, FSO technology – pioneered and championed by CableFree’s optical wireless offerings – has enabled the development of a new category of outdoor wireless products that can transmit voice, data, and video at bandwidths up to 1.25 Gbps. Free Space Optics connectivity doesn’t require expensive fibre-optic cable and removes need for securing spectrum licenses for radio frequency (RF) solutions. FSO technology requires light. The use of light is a simple concept similar to optical transmissions using fiber-optic cables; the only difference is the medium. Light travels through air faster than it does through glass, so it is fair to classify FSO technology as optical communications at the speed of light.
Optical communications, in various forms, have been used for thousands of years. The Ancient Greeks used a coded alphabetic system of signalling with torches developed by Cleoxenus, Democleitus and Polybius. In the modern era, semaphores and wireless solar telegraphs called heliographs were developed, using coded signals to communicate with their recipients. In 1880 Alexander Graham Bell and his assistant Charles Sumner Tainter created the Photophone, at Bell’s newly established Volta Laboratory in Washington, DC. Bell considered it his most important invention. The device allowed for the transmission of sound on a beam of light. On June 3, 1880, Bell conducted the world’s first wireless telephone transmission between two buildings, some 213 meters (700 feet) apart. Its first practical use came in military communication systems many decades later, first for optical telegraphy. German colonial troops used Heliograph telegraphy transmitters during the 1904/05 Herero Genocide in German South-West Africa (today’s Namibia) as did British, French, US or Ottoman signals.
During the trench warfare of World War I when wire communications were often cut, German signals used three types of optical Morse transmitters called Blinkgerät, the intermediate type for distances of up to 4 km (2.5 miles) at daylight and of up to 8 km (5 miles) at night, using red filters for undetected communications. Optical telephone communications were tested at the end of the war, but not introduced at troop level. In addition, special blinkgeräts were used for communication with airplanes, balloons, and tanks, with varying success. A major technological step was to replace the Morse code by modulating optical waves in speech transmission. Carl Zeiss Jena developed the Lichtsprechgerät 80/80 (literal translation: optical speaking device) that the German army used in their World War II anti-aircraft defense units, or in bunkers at the Atlantic Wall.
The invention of lasers in the 1960s revolutionized free space optics. Military organizations were particularly interested and boosted their development. However the technology lost market momentum when the installation of optical fiber networks for civilian uses was at its peak.
FSO vendor CableFree has extensive experience in this area: CableFree developed some of the world’s first successful commercial FSO links, with world-first achievements including
World’s first commercial 622Mbps wireless link: 1997
World’s first commercial Gigabit Ethernet 1.25Gbps wireless link: 1999
While fibre-optic communications gained worldwide acceptance in the telecommunications industry, FSO communications is still considered relatively new. CableFree Free Space Optical technology from Wireless Excellence enables bandwidth transmission capabilities that are similar to fibre optics, using similar optical transmitters and receivers and even enabling WDM-like technologies to operate through free space.
How Free Space Optics / Laser Communications Work
The concept behind FSO technology is very simple. It’s based on connectivity between FSO-based optical wireless units, each consisting of an optical transceiver with a transmitter and a receiver to provide full-duplex (bi-directional) capability. Each optical wireless unit uses an optical source, plus a lens or telescope that transmits light through the atmosphere to another lens receiving the information. At this point, the receiving lens or telescope connects to a high-sensitivity receiver via optical fibre. This Free Space Optics technology approach has a number of advantages: Requires no RF spectrum licensing. Is easily upgradeable, and its open interfaces support equipment from a variety of vendors, which helps enterprises and service providers protect their investment in embedded telecommunications infrastructures. Requires no security software upgrades. Is immune to radio frequency interference or saturation. FSO Can be deployed behind windows, eliminating the need for costly rooftop rights.
Choosing Free Space Optics or Radio Frequency Wireless
Optical wireless, using FSO technology, is an outdoor wireless product category that provides the speed of fibre, with the flexibility of wireless. It enables optical transmission at speeds of up to 1.25 Gbps and, in the future, is capable of speeds of 10 Gbps using WDM. This is not possible with any fixed wireless or RF technology. Optical wireless also eliminates the need to buy expensive spectrum (it requires no FCC or municipal license approvals worldwide), which further distinguishes it from fixed wireless technologies. Moreover, FSO technology’s narrow beam transmission is typically two meters versus 20 meters and more for traditional, even newer radio-based technologies such as millimeter-wave radio. Optical wireless products’ similarities with conventional wired optical solutions enable the seamless integration of access networks with optical core networks and helps to realize the vision of an all-optical network.
Free Space Technology in Communication Networks
Free-space optics technology (FSO) has several applications in communications networks, where a connectivity gap exists between two or more points. FSO technology delivers cost-effective optical wireless connectivity and a faster return on investment (ROI) for Enterprises and Mobile Carriers. With the ever-increasing demand for greater bandwidth by Enterprise and Mobile Carrier subscribers comes a critical need for FSO-based products for a balance of throughput, distance and availability. During the last few years, customer deployments of FSO-based products have grown. Here are some of the primary network uses:
Because of the scalability and flexibility of FSO technology, optical wireless products can be deployed in many enterprise applications including building-to-building connectivity, disaster recovery, network redundancy and temporary connectivity for applications such as data, voice and data, video services, medical imaging, CAD and engineering services, and fixed-line carrier bypass.
Mobile Carrier Backhaul
Free Space Optics is valuable tool in Mobile Carrier Backhaul: FSO technology and optical wireless products can be deployed to provide traditional PDH 16xE1/T1, STM-1 and STM-4, and Modern IP Gigabit Ethernet backhaul connectivity and Greenfield mobile networks.
Front-Haul: Mobile Carrier Base Station “Hoteling”
FSO-based products can be used to expand Mobile Carrier Network footprints through base station “hoteling.” using CPRI interface. Free Space Optics with CPRI enables “front haul” networks where the remote radio heads can be separated by up to 2km from the Base station with a 1.22Gbps CPRI “native” link between them.
Low Latency Networks
Free Space Optics is an inherently Low Latency Technology, with effectively no delay between packets being transmitted and received at the other end, except the Line of Sight propagation delay. The Speed of Light through the air is approximately 40% higher than through fibre optics, giving customers an immediate 40% reduction in latency compared to fibre optics. In addition, fibre optic installations are almost never in a straight line, with realities of building layout, street ducts and requirement to use existing telecom infrastructure, the fibre run can be 100% longer than the direct Line of Sight path between two end points. Hence FSO is popular in Low Latency Applications such as High Frequency Trading and other uses.
Low Latency Wireless Networks for High Frequency Trading
The need for speed: Best Practices for Building Ultra-Low Latency Microwave Networks.
To achieve the lowest end-to-end Ultra Low Latency with the highest possible reliability and network stability not only requires a wireless transmission platform that supports cutting edge low latency performance, but also must be combined with the experience and expertise necessary to design, deploy, support and operate a Millimeter wave, Free Space Optics or Microwave transmission network.
In High Frequency Trading (HFT) applications where computers can make millions of decisions in fractions of a second, receiving data even a single millisecond sooner can equate to a distinct advantage and generate significant profits. This is called Low Latency or Ultra Low Latency networking.
According to Information Week Magazine¹: “A one (1) millisecond advantage in trading applications can be worth $100 million a year to a major brokerage firm”. Currently electronic trading makes between 60% and 70% of daily volume of the New York Stock Exchange. Tabb Group, a research firm, estimated that High-frequency traders generated about $21 billion in 2008.
Financial Trading centres with HF Traders can be in locations separated by long distances for example Chicago and New York. Data communications between these locations is commonly over leased circuits on fibre optic networks. But if the data was carried over Microwave radio links between the same two locations it would arrive several milliseconds earlier. Why?
Millimeter Wave, MMW and Microwave are the best for Ultra Low Latency
Optical, Millimeter Wave and Microwave signals travel through the air about 40% faster than light through optical fiber. Latency in a data communications circuit, or the time difference between sending a request for data and receiving the reply, will consequently be longer over a fibre optic circuit than a microwave circuit of the exact same length.
Latency is largely a function of the speed of light, which is 299,792,458 meters/second in vacuum. Microwave signals travel through the air at approximately the same speed as light through a vacuum and will have a latency of approximately 5.4 microseconds for every mile of path length. Light travel in optical fibre has latency of 8.01 microseconds for every mile of cable, due to the refraction in the fibre. When data has to travel over 1400 miles from Chicago to New York and back again the latency difference due to the communications medium alone is more than 3.5 milliseconds.
Straighter Routes Microwave networks have shorter routes, reducing the total network distance and consequently further improving latency. Microwave links can overcome topographical obstacles such as rivers, mountains and highways while optical networks in many cases have to go around them or follow existing roads or bridges. In general, signals over fibre networks have to travel farther and thus take longer to get to their destination.
Total latency in any network includes additional latency due to data queuing delay, processing delay through gateways, network design, equipment configuration and extra distances due to circuitous routes.
Overall, CableFree Millimeter wave (MMW), Free Space Optics (FSO) and Microwave networks offer a better solution for Ultra Low Latency applications such as HFT in comparison to fiber optic equipment because of a combination of an advantage in transmission medium and simple geometry—shortest distance between two points is a straight line.