Unlicensed Spectrum and Wireless Networks


A recent media article stating that Steve Jobs wanted to build an unlicensed network for the iPhone peaked my interest on speaking about unlicensed spectrum and the way it has been carved out by the FCC. I have always been against licensed spectrum making wireless expensive. The recent auctions both AWS and 700MHz have shown that it is all but a numbers game and deeper the pockets of the Operator the more spectrum they have are able to garner. Spectrum has been called the oxygen for wireless operators and in many ways it is as all commercial operators. Recognizing this potential the Obama administration and the FCC has made plans to make available 300 MHz of new spectrum over 5 years and 500 MHz over the next 10 years, which is almost, doubles the 547 MHz of spectrum that we license out today.

As consumers race to embrace all that wireless broadband connectivity has to offer and U.S. mobile innovation continues to advance at an astounding pace, there is a clear and compelling national interest in ensuring adequate spectrum is available to continue this progress. Unfortunately, we cannot simply flip a switch and make more broadband spectrum available. It typically takes several years for spectrum to be repurposed and released into the marketplace. And the clock is ticking with rising demand rapidly closing the gap with existing supply. The consequences of inaction are severe, widespread and wholly negative for consumers and the U.S. economy.

European countries, which had been leading the world in mobile communications, embraced the auction to promote competition and regional integration through the entrance of international operators to many countries. When 3-G auctions were held in 2000, at the peak of the “wireless bubble”, license fees skyrocketed far above their value; the fees amounted to more than 100 billion euro for all of Europe. After the bubble collapsed, however, the expected market for “mobile multimedia” proved almost nonexistent. Mobile operators in Europe fell into a business crisis due to huge liabilities. Deployment of 3-G services was delayed – some of them were even aborted – because of technical problems and financial difficulties.

Economists offer the excuse that it was not the auction but the operators’ extremely speculative behavior that was to blame. Through auctions, at least theoretically, spectrum can be allocated efficiently if operators behave rationally. This would be better than traditional licensing by paper examinations, known as “beauty contests”, in promoting competition and in realizing the full value of spectrum. Yet it is undeniable that auctions induced the “winner’s curse”, which is not rational but regular behavior in financial markets. A more important problem is that spectrum auctions depend on the legacy systems of telephone switching. It is inefficient and expensive in the Internet age, as the tragedy of 3G evidenced.

Another problem is that very little spectrum is available for auctions. Relocation of spectrum is conducted by governments after the removal of incumbent operators by negotiation, which takes a long time. Because spectrum is allotted by licenses for specific use, even if a band is idle, nobody is allowed to use it and incumbents cannot convert it to a different use. As a result, it is estimated that, integrating space and time, more than 90 percent of the spectrum less than 6 GHz in the metropolitan area of Tokyo is not used. Rural areas must be even less efficient.

UNII bands

The Unlicensed National Information Infrastructure (U-NII) radio band is part of the radio frequency spectrum used by IEEE-802.11a devices and by many wireless ISPs.

It operates over three ranges:

U-NII Low (U-NII-1): 5.15-5.25 GHz. Regulations require use of an integrated antenna. Power limited to 50mW.

U-NII Mid (U-NII-2): 5.25-5.35 GHz. Regulations allow for a user-installable antenna, subject to Dynamic Frequency Selection (DFS, or radar avoidance). Power limited to 250mW

U-NII Worldwide: 5.47-5.725 GHz. Both outdoor and indoor use, subject to Dynamic Frequency Selection (DFS, or radar avoidance). Power limited to 250mW. This spectrum was added by the FCC in 2003 to “align the frequency bands used by U-NII devices in the United States with bands in other parts of the world”. The FCC currently has an interim limitation on operations on channels which overlap the 5600 – 5650 MHz band.

U-NII Upper (U-NII-3): 5.725 to 5.825 GHz. Sometimes referred to as U-NII / ISM due to overlap with the ISM band. Regulations allow for a user-installable antenna. Power limited to 1W. Wireless ISPs generally use 5.725-5.825 GHz.

U-NII is an FCC regulatory domain for 5- GHz wireless devices. U-NII power limits are defined by the United States CFR Title 47 (Telecommunication), Part 15 – Radio Frequency Devices, Subpart E – Unlicensed National Information Infrastructure Devices, Paragraph 15.407 – General technical requirements. Regulatory use in individual countries may differ.

The European HiperLAN standard operates in same frequency band as the U-NII.

There are 14 channels designated in the 2.4 GHz range spaced 5 MHz apart (with the exception of a 12 MHz spacing before Channel 14). As the protocol requires 25 MHz of channel separation, adjacent channels overlap and will interfere with each other. Consequently, using only channels 1, 6, 11, and 14 is recommended to avoid interference. Potential Wireless LAN uses of this range are documented by IEEE 802.11 clauses 18 (802.11b), 19 (802.11g) and 20 (802.11n). IEEE 802.11 clauses 14 and 15 also specify potential uses of this range, but did not see widespread implementation.

Countries apply their own regulations to both the allowable channels, allowed users and maximum power levels within these frequency ranges. Most of the world will allow the first thirteen channels in the spectrum. In the USA, 802.11 operations in the channels 12 and 13 are actually allowed under low powered conditions. The 2.4 GHz Part 15 band in the US allows spread-spectrum operation as long as the 50-dB bandwidth of the signal is within the range of 2400–2483.5 MHz which wholly encompasses both channels 12 and 13. A Federal Communications Commission (FCC) document clarifies that only channel 14 is forbidden and furthermore low-power transmitters with low-gain antennas may legally operate in channels 12 and 13.However, channels 12 and 13 are not normally used in order to avoid any potential interference in the adjacent restricted frequency band, 2483.5–2500 MHz, which is subject to strict emission limits set out in 47 CFR §15.205.

 Wi-Fi – 802.11x

Wi-Fi doesn’t require any special introduction as it has been the disruptive technology on which commercial wireless technologies like WiMAX/LTE have evolved. Wi-Fi is derived from the decades old term Hi-Fi that stands for the output’s type produced by quality music hardware. Wi-Fi Technology is WIRELESS FIDELITY and stands for all those technologies that fall under the specifications of IEEE 802.11 including 802.11a, 802.11b and 802.11g. The association of the term Wi-Fi with various technologies is merely because of the promotions made by the Wi-Fi Alliance. 

For those whose laptops and cell phones do not have a built-in wireless transmitter then you could purchase a wireless adaptor and inject it into USB port. A Wi-Fi hotspot is automatically discovered and connected by the transmitters. The presence of Wi-Fi in public places makes it convenient to stay connected to your official tasks or to the social networking. Wi-Fi is also associated with 802.11 networking. The reference is derived from IEEE – Institute of Electrical and Electronics Engineers uses the numbering system for classifying a range of technological protocols. Wi-Fi steps into the boots of TV and radio in order to transmit data through radio waves. The two-way radio communication: the wireless adapter translates data into a radio signal then transmits it via antenna; and the signal is received and decoded by the wireless router that uses a tangible

wired Ethernet connection to send information to the internet. The equation is reversed when wireless router receives data from the internet and translates it into a signal where the wireless adaptor receives the signal and decodes it.

 Wi-Fi communication devices are extended forms of radios used for cell phones and walkie-talkies: they simultaneously transmit and receive radio waves and convert 1s to 0s into the radio waves along with reconverting the radio waves into 1s and 0s, however the Wi-Fi radios enjoy some exceptional features. Technology has developed far more than our expectations – none of us could perceive the developments in approaching future. With features like Wi-Fi, earth would turn into a world wide web where every user is omnipresent and active. No matter where you are, you can access the world of web through your handsets and your laptops and your iPads. You might not have noticed what it is but the technology that enables you to plug in internet without any wires whether you are in a cafe, a library, a shopping mall or an airport is Wi-Fi – the wireless network also known as 802.11. The circumference where wireless technology is present and available to the users is known as Hotspot. The inexpensive, user-friendly Wi-Fi networks are also obtrusive; if you do not need one you would not know there exists any. Wi-Fi could be also installed in home or offices in order to transmit information over the air without the aid of wires. In near future you would find wireless networking available in every nook and corner.

Wi-Fi alliance – http://www.wi-fi.org/

 UWB Bands

Ultra-Wideband (UWB) is a technology for transmitting information spread over a large bandwidth (>500 MHz) that should, in theory and under the right circumstances, be able to share spectrum with other users. Regulatory settings of Federal Communications Commission (FCC) in United States are intended to provide an efficient use of scarce radio bandwidth while enabling both high data rate “personal area network” (PAN) wireless connectivity and longer-range, low data rate applications as well as radar and imaging systems.

Ultra Wideband was traditionally accepted as pulse radio, but the FCC and ITU-R now define UWB in terms of a transmission from an antenna for which the emitted signal bandwidth exceeds the lesser of 500 MHz or 20% of the center frequency. Thus, pulse-based systems—wherein each transmitted pulse instantaneously occupies the UWB bandwidth, or an aggregation of at least 500 MHz worth of narrow band carriers, for example in orthogonal frequency-division multiplexing (OFDM) fashion—can gain access to the UWB spectrum under the rules. Pulse repetition rates may be either low or very high. Pulse-based UWB radars and imaging systems tend to use low repetition rates, typically in the range of 1 to 100 megapulses per second. On the other hand, communications systems favor high repetition rates, typically in the range of 1 to 2 giga-pulses per second, thus enabling short-range gigabit-per-second communications systems. Each pulse in a pulse-based UWB system occupies the entire UWB bandwidth, thus reaping the benefits of relative immunity to multipath fading (but not to intersymbol interference), unlike carrier-based systems that are subject to both deep fades and intersymbol interference.

A significant difference between traditional radio transmissions and UWB radio transmissions is that traditional systems transmit information by varying the power level, frequency, and/or phase of a sinusoidal wave. UWB transmissions transmit information by generating radio energy at specific time instants and occupying large bandwidth thus enabling a pulse-position or time-modulation. The information can also be imparted (modulated) on UWB signals (pulses) by encoding the polarity of the pulse, the amplitude of the pulse, and/or by using orthogonal pulses. UWB pulses can be sent sporadically at relatively low pulse rates to support time/position modulation, but can also be sent at rates up to the inverse of the UWB pulse bandwidth. Pulse-UWB systems have been demonstrated at channel pulse rates in excess of 1.3 giga-pulses per second using a continuous stream of UWB pulses (Continuous Pulse UWB or “C-UWB”), supporting forward error correction encoded data rates in excess of 675 Mbit/s. Such a pulse-based UWB method using bursts of pulses is the basis of the IEEE 802.15.4a draft standard and working group, which has proposed UWB as an alternative PHY layer.

One of the valuable aspects of UWB radio technology is the ability for a UWB radio system to determine “time of flight” of the direct path of the radio transmission between the transmitter and receiver at various frequencies. This helps to overcome multi path propagation, as at least some of the frequencies pass on radio line of sight. With a cooperative symmetric two-way metering technique distances can be measured to high resolution as well as to high accuracy by compensating for local clock drifts and stochastic inaccuracies.

Another valuable aspect of pulse-based UWB is that the pulses are very short in space (less than 60 cm for a 500 MHz wide pulse, less than 23 cm for a 1.3 GHz bandwidth pulse), so most signal reflections do not overlap the original pulse, and thus the traditional multipath fading of narrow band signals does not exist. However, there still is multipath propagation and inter-pulse interference for fast pulse systems which have to be mitigated by coding techniques.

Good resource http://bwrc.eecs.berkeley.edu/Research/UWB/overview.htm

WiMAX Case study

Unlicensed WiMAX is often the technology of choice for some of today’s applications. The debate over the merits of licensed vs. unlicensed WiMAX has been raging for years, but the fact of the matter always has been, and will remain, that both licensed and unlicensed WiMAX have considerable opportunities in today’s broadband landscape. Though vendors and different industry organizations will often try to persuade otherwise, the licensed and unlicensed WiMAX solutions are not at war, and they are often not even competing for the same types of applications.

Simply put, tier one service providers that are deploying mobile WiMAX have traditionally been committed to licensed WiMAX solutions, while tier 2-3 service providers and WISPs that are providing primarily fixed wireless broadband access have traditionally championed unlicensed WiMAX solutions. Now, that’s not to say that the use of licensed or unlicensed WiMAX is ALWAYS tied to either mobile or fixed service (respectively), but for the most part that is the case.

The difference between licensed and unlicensed WiMAX technologies is subtle. So before we dive into the primary opportunities and applications for unlicensed WiMAX, let’s break down some of the key differentiators:

Primary Markets – Licensed WiMAX tends to be used primarily in urban markets, while unlicensed WiMAX is the technology of choice for the rural markets.

Primary Applications – Licensed WiMAX is most often used for Mobile WiMAX deployments such as Clearwire’s services. Unlicensed WiMAX tends to cater to the fixed broadband wireless access/last mile access markets for rural and under-served areas; connectivity/backhaul for wireless video surveillance; and connectivity/backhaul for Intelligent Traffic Systems (ITS) and transportation applications.

Interference – Licensed WiMAX is regulated so each Service Provider owns their own frequency bands so will not get interference from other Service Providers. Unlicensed WiMAX is unregulated so each Service Provider needs to be a nice neighbor and ensure they do not interfere with other networks. Having 480MHz of spectrum available in the 5GHz unlicensed band provides amble flexibility to avoid interference with other operators.

Cost – Securing frequency licenses for licensed WiMAX can cost billions of dollars. This massive up-front cost often prohibits the use of the technology for many providers. But for unlicensed WiMAX, there is no cost for frequencies. Cost of equipment is the only up-front cost.

Time to Deploy – Licensed WiMAX can take several months to apply for and acquire desired frequencies, and requires extensive pre-planning. Unlicensed WiMAX is much faster time to market due to limited restrictions.

Capacity – Lower frequency bands (such as licensed WiMAX) have smaller channel sizes(1-7 MHz max.), and thus, less total capacity available. This makes licensed WiMAX ideal for voice, but sub-optimal for data. Unlicensed WiMAX supports 480MHz of spectrum in most countries with channel sizes up to and exceeding 40MHz, thus increasing your max. Capacity by more than 5x over licensed – making it optimal for broadband data.

Last-Mile Access for Rural Areas

WiMAX has long been pegged as the saving grace for providing broadband to rural, under-served communities throughout the world. But when determining which variant (licensed or unlicensed) is better suited for deploying last-mile access to these under-served areas, it’s important to remember the primary reason why many of these areas don’t have access in the first place. Simply put, the cost of extending service via fiber or other wired technologies has outweighed the potential return the major carriers could expect based on the small populations of people in these rural areas.

With wired technologies like fiber or copper, the combination of the high cost of goods as well as the cost associated with trenching or stringing that wire for long distances to rural areas was the prohibiting factor. Similarly, with licensed WiMAX, the high cost of applying for and acquiring licensed frequencies has also made it an unrealistic option for extending broadband service to remote communities – despite the distance benefits that WiMAX links provide.

Unlicensed WiMAX, however, provides an ideal balance of high-performance, long-distance functionality at a significantly lower cost. As a result, carriers, ISPs and WISPs are able to cost-effectively extend broadband service to remote rural areas. And due to the significant upfront cost savings, these service providers are able to recognize a much quicker return on investment (ROI), even though the population of subscribers in these areas is smaller.

Unlike wireless mesh technologies, which provide unpredictable service for backhauling streaming video, WiMAX is deterministic with built in scheduled access and Quality of Service (QoS) mechanisms to ensure the reliable delivery of data. Today, however, cities and counties are turning to unlicensed WiMAX technologies to remove the cost and complexity roadblocks that have prevented greater rollout of these programs. WiMAX, originally designed as a backhaul technology, has proven ideal for the increased bandwidths required by HD video cameras. And since today’s wireless radios can not only backhaul the traffic from multiple cameras while (in some cases) powering co-located cameras directly from the radio via Power over Ethernet (PoE), unlicensed WiMAX and other high-bandwidth point-to-multipoint technologies are ideally suited to drive down the cost of traffic camera connectivity while greatly easing deployments.

This is Just the Beginning as there is definitely a huge market opportunities for both licensed and unlicensed WiMAX, but it is important to understand in which applications and opportunities each is relevant. For applications and markets where high-performance broadband access or connectivity is needed but where initial cost and a need for faster ROI are limiting factors, unlicensed WiMAX and other unlicensed PtMP technologies are the ideal solution for the following reasons:

  • Elimination of the massive costs and delays of trenching for fiber or acquiring licensed frequencies
  • Quickly deployed and configured – operational within hours
  • Deploys virtually anywhere – across rugged terrain, bodies of water and remote areas
  • Carrier-class reliability ensures non-stop security
  • High capacity, configurable and secure broadband wireless for guaranteed QoS
  • Enables real-time transmission from and control of surveillance cameras

xG – a Florida based company claims of a carrier-class cognitive radio network that operates in unlicensed spectrum called xMax (a flavor of WiMAX). xMax technology is a frequency-agile radio capable of detecting interference in real time, handing off from channel to channel 33 times a second. Rather than looking at the frequency domain for interference, xMax also senses the time domain to slice the interference even further.

The company has so far designed its network for the unlicensed 900 MHz band where Part 15 devices operate. The technology can also work in licensed bands. The unlicensed 900 MHz band is about 15 percent occupied in the time domain during at its most congested points. As such, xG Technology believes the xMax network can serve as an adjunct to commercial mobile operators looking to offload both voice and data traffic as the network comes with an ecosystem of testing and network management tools and handset capability. There are other markets the company is exploring, such as helping new entrants come into the mobile broadband market and serving segments such as the military and smart grid.

Architecture- http://www.xgtechnology.com/Technology/network-architecture.html

Company – http://www.xgtechnology.com/Company/about-xg.html