Why is spread spectrum transmission important

Frequency hopping was used by the German military as early as World War I in an attempt to prevent the British from listening in on transmissions. Spread spectrum technology saw further development and deployment during World War II. Probably the most famous developer of spread spectrum technology was the actress Hedy Lamarr, who co-patented a frequency hopping technique in to prevent radio-controlled torpedoes from being detected and jammed.

Today, spread spectrum is an important component of code division multiple access CDMA technology, which used in cellular telecommunications. In CDMA, a pseudo-random spreading code is used to spread the signal within the available bandwidth. By: Justin Stoltzfus Contributor, Reviewer.

By: Satish Balakrishnan. Dictionary Dictionary Term of the Day. Natural Language Processing. Techopedia Terms. Connect with us. Constant-frequency signals may also be readily intercepted by eavesdroppers with the right equipment, and are therefore unsuitable for transmissions of confidential or sensitive data. With spread spectrum communications, so long as the spreading algorithm remains known only to those authorized to use it, the interception of a signal is a difficult task for any potential hacker.

An eavesdropper would have to know or have equipment capable of determining the exact spread spectrum function being used, and its specific starting time, so as to create variations in the frequency of their receiver that exactly match those of the spread spectrum transmission. The frequency hopping pattern or direct sequence spreading code effectively encrypts each transmitted signal. Further protection for data transmission may be assured by using cryptographic ciphers on the messages themselves.

Spread spectrum techniques may be employed to enhance the security of cognitive or self-learning radio system transmissions, where the dangers of signal jamming or eavesdropping may be reduced not only by frequency hopping and direct sequence deployments, but also the lesser known time-hopping and chirp spread spectrum techniques, or hybrid transmissions combining elements of two or more of these variants.

In addition to being hard to intercept or jam, spread spectrum transmissions are also difficult to spoof or exploit. Spread spectrum messages may also be encrypted to any level necessary for maintaining confidentiality. This is certainly true of sniffing.

What Is Spread Spectrum? Spread Spectrum Functions To qualify as a spread spectrum signal, the signal bandwidth has to be much greater than the information bandwidth. Common carrier refers to services that allow the transmission of messages—mainly by telephone or telegraph, but today even by digital transmissions. The FCC regulates these services similar to the manner in which public utilities are regulated, more so than in the case of broadcasters.

Heavy regulation is involved here to protect the public good, including control of rates, routes, charges, and quality of service. The safety and special radio services are treated differently as well, mainly due to the number of different services involved.

They allow for non-broadcast private users to communicate over walkie-talkies, CBs and the like. The non-broadcast public includes the safety officials mainly police , fire, local government, and special emergency services. Thinking about these different services in terms of what is offered to the user results in two distinctions. The broadcast realm offers programs and entertainment, venues for the public to express themselves.

Common carrier and emergency services provide a different service, the ability to directly communicate with another person. Examples of past regulation in these two realms will be reviewed with the hopes of further understanding how the FCC uses regulation to combat scarcity and utilize new technology.

AM broadcasting has had its ups and downs since the Communications Act of There was a stall in growth during the Second World War, followed by another boom. New AM stations were appearing everywhere and the Commission soon had another problem on its hands. Shortly after the War, the FCC casually approved licenses for new stations just by waging the cost of some interference with the benefit the station may provide.

The consequences of this type of deliberation were not immediate, but around interference again became an unavoidable problem. The resulting regulation from the Commission practically killed AM. Starting in , every broadcaster applying for an AM license had to prove they could not put their service on FM first! This inevitably led to the broadcasting landscape we now have today where FM is more widely used.

What is important here is that the FCC was using a non-technical restriction on licenses; in order to decrease spectrum scarcity in the AM band, regulation was put into effect that ignored technology as a viable solution.

With broadcasting, the damage was compounded with the possibility of infringing on First Amendment rights. In this situation the regulation of the FCC further restricted access to the AM band and violated the rights of some broadcasters who were denied licenses. One possible way to decrease the scarcity of the AM band was to decrease the frequency spacing between the channels. This was in direct conflict with the 9kHz spacing used in other countries.

Major broadcasting areas had documented that their 9kHz channel spacing eliminated most of the interference found between close broadcast frequencies. Even more importantly, the new spacing would result in a more efficient use of the spectrum in the United States. More stations would be allowed in the AM band and the thought was that this would increase diversity and loosen the regulation concerning AM allocation.

The interesting thing about the proposal was that all of the major broadcasting groups were behind it, even though it clearly threatened broadcasters with direct competition. The possibility of acquiring more spectrum for commercial or noncommercial use just seemed too attractive. One of the few groups in the industry that was not so excited about the move to 9kHz spacing was the manufacturers of AM receivers.

They were upset that their digital receivers would not work correctly with the new spacing and claimed they were not given fair advanced notice. These digital receivers, however, comprised less than one percent of the existing AM receivers, and the FCC had no problem in approving the move to 9kHz in Very soon afterwards, studies were issued to allay the fears that existing technology would not cooperate with the new spacing.

Directional antennas had been used in broadcasting at times to have more control over a frequency, to steer it away from interfering with nearby channels. The changes in frequencies did cause very minor attenuation with some of the antennas, barely noticeable with expert measuring equipment.

There was also the threat of increased interference with AM receivers because of the spacing, but this proved to be a similar case where the problem was barely noticeable, and that was in only a few units. Partly due to the regulation of AM, we have a situation today where FM is very popular and becoming very crowded.

There were excited demonstrations of comparison between AM and FM, but the listeners were at a loss regarding the significance of the new signal. The engineers immediately recognized that the higher frequency of FM required less power to transmit, which could make entry more affordable.

Perhaps due to the stronghold that AM had on the broadcasting industry and its success at the time, the FCC was actually reluctant to allow a permit for experimental FM operation. It was only around that FM was allowed into an experimental band, and a boom quickly followed. Since the band was moved in the spectrum, the old receivers could not tune into the stations. This is a recurring problem where equipment becomes instantly outdated because of changing spectrum regulation.

Despite this, FM has since become more popular than AM to both broadcasters and listeners. FM receivers quickly picked up on the high fidelity of FM even though similar technology was used in some AM transmissions. Also, there is a greater ability for FM to disregard unwanted signals and prevent interference. Receivers are able to grab the strongest signal and "lock onto" it. In contrast, different AM signals which are close together just compound themselves and produce interference. When the FM band started to become crowded in the early s, the FCC was eager to prevent the allocation disaster they had just experienced with AM.

In , the Commission offered a solution by drawing up an allocation table for all of the FM channels. Spectrum slices of predetermined size were allocated to broadcasters in an area with the goal of preventing interference. Unfortunately, the table was rather inflexible because it did not take into account the possible use of directional antennas and the fact that all stations did not use the same amounts of power.

The pleas for the ability to use directional antennas were denied by the FCC in favor of the allocation table. What was missing was an explanation by the Commission as to why they preferred the table scheme. One reason was that a similar allocation table had been used in the allocation of TV channels with some success.

Also, the tables were easy to administer and maintain while providing an almost sure way to provide some quality of service to the users. There were a couple of problems regarding the FM allocation plan, which allowed for spectral inefficiency. A number of stations which got their start on FM could not afford the type of equipment powerful enough to take advantage of the broadcast area their license provided.

According to the allocation plan, the FCC had to treat this station similar to all others in its class, allowing it to grow into their spectrum assignment. There were only three different classes of FM licenses, each having their own power specifications. The complaint in the late s was that more classes were needed in order to increase spectral efficiency.

Spectrum was being wasted by stations that only met the low end requirement for a class. More classes with smaller power ranges would eliminate the problem of weaker stations not using part of their allocation. As of , the FCC was leaning more towards a five class system as a possible solution.

The other problem with the FM allocation plan was that it ignored the potential of directional antennas. This serves as another good example of a regulatory scheme that ignores technological solutions to spectrum scarcity. In fact, other than TV and FM, the technology was used in almost all other services. The reason behind this blind eye towards directional antennas may have involved TV in another way as well. The broadcast industry immediately wanted to know the exact demand for more FM stations and whether or not the market could support more stations.

They also rumored that the directional antennas would be costly and susceptible to lightening damage even though this proved not to be the case. In the s, a number of new technologies were still being developed regarding both AM and FM.

AM stereo is a technology that has been around for some time but has never really caught on, probably because simple AM receivers do not support it.

Unfortunately, putting AM stereo capability in new receivers today will not bring people to the stores because FM stereo is so readily available. Likewise, FM may have the ability to add channels to their signals with the advent of FM quad technology. This is an attempt by FM to join the surround-sound technology movement. The same question still applies as to who will manufacture the receivers and who will purchase them.

The two bands are also continuously trying to better utilize or increase their portion of the spectrum. The AM industry proposed to extend their band from kHz to kHz, but at what advantage? Sure the move would open up the spectrum to more broadcasters, but there is still the question of the manufacturing of receivers. On the FM side, the industry is trying to increase spectrum use by reducing channel spacing as well. Besides the receiver manufacturing question, there are other more serious concerns as well.

Questions regarding the effects on FM fidelity and the proposed FM quad technology are definitely warranted. There is another radio service that has a similar history to standard broadcast radio. Land mobile radio LMR is a specialized service that enables communication between mobile users with portable devices. The service started simply as a one-way communication between a base-station and a receiver.

Today, the expansion of the service has led to paging and cellular communications. By , the technology had become popular as 29 other cities were already involved. The first license was issued in allowing for a portable transceiver that enabled two-way communications. Technology further improved leading up to the War because of military requirements for mobile communication.

Spectrum scarcity became an issue with LMR almost immediately, and regulation was necessary. Since the growth of the service was so fast around this time, different categories of LMR were devised. These categories included a number of private services dealing with land transportation and emergency services.

A major ruling in addressed the serious allocation issues arising from increased use. In addition, the new mobile telephone service was given consideration.

The Bell system had for some time been asking for spectrum in order to experiment with their new technology. A decision by the Commission in created another new service and, in effect, increased the number of licenses available for LMR. The business radio service experienced immediate exponential growth concerning the number of licenses handed out.

Around this same time, the Bell system was experimenting with another one-way LMR service that used very small personal receivers. In , the FCC recognized this new service by reallocating some channels in the spectrum, but the growth was so fast that another ruling in equally allocated channels to the RCCs and WCCs specifically for paging. LMR usage was exploding with these new services and the FCC had to find a way to accommodate the new users in the spectrum, which seemed to have no room.

There was little time to wait for technology to solve the problem, which would include better receivers to parse through more precise more narrow LMR frequencies. UHF was an easy target in the s because most of their allocated spectrum was not being used. UHF providers, including educational broadcasters, felt that the lack of spectrum for LMR was due more to poor utilization than mere lack of room.

Other users of spectrum around the MHz range were looked at and the technology was studied as well, only to determine that the under-utilization of the UHF band was the only answer. Infighting immediately began among the different services of LMR who each wanted a big slice of the newly allocated spectrum. The Bell system stated that it needed a larger part of the new spectrum in order to provide a more efficient common carrier service that would have room to expand.

Providers of other LMR services such as land transportation and public safety believed that their usage was going to grow the most. They chided the Bell system for trying to steal spectrum away from the more efficient and standard mode of dispatch.

The FCC would struggle for some time to satisfy all groups in allocating the new spectrum channels. The only thing left for the Commission was to choose the technology that would enable the LMR services to better utilize the new allocation. To increase the broadcast area, repeaters could be used which were placed on tall buildings or hills.

There was a cost advantage here because the repeaters could be shared by broadcasters and even a single channel could be shared within an area. Another technology involved computer control and promised more efficient use of the newly allocated spectrum. Called a multi-channel trunked system, it takes advantage of the fact that in any one area usually some frequencies are used more than others.

For example, in urban areas the frequencies for dispatch taxi cabs will be used more than say the forestry frequencies. Computer control of the spectrum takes advantage of this by placing a user in an unused part of the spectrum, or if the spectrum is full places the user in a queue. How the technology works should be familiar to many today. An area is divided into hexagonal cells that mesh rather nicely.

In each of these cells are transceivers and receivers that communicate with base stations where there is a connection to the landline. The activity in these cells is controlled by a computer at the base station. The benefit of all of this is again better spectral efficiency. The smaller area that the cells cover, the more a particular channel is used.

For instance, just imagine the Commission ignoring common carrier or land transportation services when spectrum was being handed out. Cellular would have been killed if common carriers were not given any consideration. The telephone monopoly at the time constantly had to be kept in check as well. With the Bell system involved in LMR, they needed to be constrained as to the amount of resources they could use to further their cellular service. In , an important ruling was made by the FCC to allocate certain amounts of spectrum according to the technologies previously discussed.

This was significant because it was the first time the Commission recognized the different technologies in an allocation, not the services involved. All of the eligible groups then could grab a part of the allocated band in a first-come, first-serve basis. In the end, another ruling adjusted competition by prohibiting wireline common carriers WCCs from manufacturing, providing or maintaining LMR equipment.

Looking at the history of radio broadcasting and LMR shows the types of issues that the FCC has to deal with concerning spectrum use. The most recurrent problem is that there is never enough room for any service in the spectrum. On the one hand, the Commission has to prevent this scarcity in an expedient but pro-competitive manner.

On the other hand, the FCC has to be forward-thinking enough to recognize important new technologies that may alleviate scarcity or provide better service. The Commission has always tried to be fair to corporations, mainly because of the fear of monopoly. What was seen in this review was that the FCC can more easily stifle private broadcasters through strict regulation which inhibits free speech.

The goal of course is to prevent scarcity, but having regulatory measures which ignore technology seem wasteful and detrimental. Many radical ideas were discussed regarding broadcasting that aimed at helping alleviate the lack of spectrum.

Since improved technology has allowed the possibility of spread spectrum, it would make sense to allow users a part of the spectrum that would be more efficient and would make more room in other bands. At the conclusion of the LMR study, the Commission began thinking of spectrum allocation toward technologies and not services. It seems that spread spectrum technology should be thought of this way as well.

In some areas the new technology may end up being a better regulator than the Commission itself. While the Telecommunications act of marks a significant turning point in the legislation of wireline communications, wireless law has emerged relatively unchanged from its inception in the Radio Act of The Telecommunications Act modified the Communications Act of Title 47 of the Code of Federal Regulations contains the regulations related to telecommunications, with Chapter 1 pertaining to the FCC.

The values leading to the interpretation of the Communications Act are indicated in the very first section of the radio title. Among the purposes of this Act is the maintenance of the control of the United States over all radio transmission and for the use of such channels for limited periods of time. Moreover, this Act declared that such use has to be granted by licenses issued by the FCC, permitting specific people to operate the apparatus for the transmission of energy, communications, or signals by radio.

The FCC has the general power to regulate radio communications and the spectrum. Led by public demand, interest, or necessity requirements, its purpose is to make a rapid and efficient radio communication service with adequate facilities at reasonable charges. This mechanism has been established for several reasons, such as national defense, the safety of life and property, and interstate and foreign commerce.

The FCC exercises its power in various manners. It is important to underline, however, that all of these provisions are clearly inspired by the spectrum scarcity theory, a very different approach than the possibility of using the spectrum without allocation. Along these lines, the FCC classifies radio stations and prescribes the nature of the service to be rendered by each class of licensed stations and each station within any class.

Likewise, the FCC assigns bands of frequencies to the various classes of stations, in addition to assigning frequencies and determining the power that each station shall use and the time during which it may operate. The licenses cannot be granted for periods longer than eight years. Furthermore, the FCC has the power to define the location of stations and regulate the kind of apparatus to be used, based on its external effects and the purity and sharpness of the emissions from each station and its apparatus.

This provision concerning the regulation of standards of the apparatus is critical in developing spread spectrum technology.

Nevertheless, the intention of the FCC power as written does not relate to the new technologies being developed. It is merely contemplated among the tools needed for an efficient use of the allocated spectrum. The FCC also has the power to establish areas to be served by any station, to prescribe the qualifications of station operators, and to classify them according to the duties being performed.

In the same manner, the FCC has the authority to suspend the license of any operator if there is sufficient proof to satisfy the Commission that the licensee has violated the act or license provisions.

Besides this, the FCC has express power to study new uses of radio, to provide for experimental uses of frequencies, and to generally encourage the larger and more effective use of radio in the public interest.

This is consistent with the idea that spread spectrum technology is the future solution for spectrum management. The FCC uses licenses to allocate the spectrum.

However, such licenses have specific limitations imposed by the Communications Act. From these parameters, the FCC also develops other kinds of limitations to the licenses. Further, the FCC has the mandate and the ability to impose sanctions and specific limitations to specific operators. It is clear that no license shall be construed to create any right, beyond the terms, conditions, and validity period of the license. These limitations have quality and quantity considerations.

Regarding quality, the operators have to comply with technical standards to avoid interference with other operators. Similarly, the operators have to transmit in accordance with power levels imposed by the FCC, preventing the obstruction of weaker signals by stronger ones. Quantity considerations basically refer to the number of years for which a license can be granted. However, a renewal of the license may be granted for a term not to exceed 8 years from the date of expiration of the preceding license.

When there was more than one application for a license, the FCC would grant licenses based on a "random selection" system. In this case, the FCC had to determine that the main use of the spectrum would not involve the licensee receiving compensation from subscribers in return for which the licensee enables those subscribers to receive or transmit communications signals, such as in a cellular service.

Nevertheless, the criteria that the FCC employed was that the use of the spectrum always had to be in the public interest, convenience, and necessity. However, if the use involved receiving compensation from subscribers, the FCC would use a competitive bidding system, rather than random selection. The random selection criteria seem to respond to the concept of fairness and equality of opportunities.

If two or more persons want to have access to the spectrum, and there is only one frequency to assign, the idea of a random selection avoids the specter of preferences. Further, it helps soothe the constitutional concerns of denying spectrum access to some and granting it to others. However, the "popular" system is that of "competitive bidding", a practice that led the FCC to recognize that the spectrum belongs to the public, and the public should get some compensation for its use.

At the same time, this system aims to grant the license to the user who values it the most. The FCC has provided small allocations for unlicensed uses that have been used to develop wireless internet access and mobile communications services. Unfortunately, due to the limited nature of these experiments, the global impact has been small. However, the most promising of these experimental allocations seems to be the recent FCC order permitting the operation of the "Unlicensed National Information Infrastructure.

However, these devises do not themselves have legal protection from interference. The FCC regulation for unlicensed operations is focused basically on general requirements regarding equipment. This is a convenient approach to a new understanding of spectrum management. Rather than regulate the spectrum itself, the FCC can lay down basic rules and standards for the devices to be used in a common spectrum or open access system.

In such a way, the people who need access to the spectrum will not have to ask for licenses or any kind of permissions. They will simply have to use a given technology that allows the communal use of the spectrum, avoiding interference. This experimental band that opens the door for a new concept of spectrum management is commonly known as the "U-NII band.

The importance of this U-NII band is that it provides the opportunity to observe the management of the spectrums as a commons, rather than the traditional understanding that required allocations. This is well explained by Professor Benkler:. It gives users of U-NII devices no "rights. It is this prohibition that necessitates an FCC license, or permission from a licensee, before one can transmit.

The U-NII band opens a legal space for multilateral coordination of communications to develop as a mechanism for avoiding interference. It also raises the possibility that unlicensed wireless devices will provide a component of the information infrastructure that is not owned by anyone.

No other communications facility currently offers that promise. However, the range of frequencies assigned to this experimental system of spectrum management is so limited that the outcome will not be as ambitious as it could be. The new technologies have been relegated to a "dark corner" of the spectrum.

It is necessary to provide a wider part of the spectrum to this experiment toward the goal of providing the next generation with a more accessible and communal spectrum. The FCC commissioners have recently had several opportunities to express their views about spectrum regulations, the scarcity rationality, and the future of spectrum management. There were two strong speeches recently, presenting the possibility of drastically changed paradigms. Besides those, however, most of the statements have been related to the status quo of the scarcity theory.

However, some of the arguments expressed by the commissioners indirectly endorse the new paradigm. An illustrative example is the theory of spectrum management expressed by Commissioner Susan Ness. Some of these points will be discussed below:. Commissioner Ness indicates that the spectrum is a national asset. This principle expressed by Ness responds simply to the basic provisions of the Communications Act of The basic concern is the scarcity of spectrum, far from other more proactive considerations.

Nevertheless, the concept of spectrum as a national asset is not in contradiction with the new spectrum access paradigm.

Innovation can be developed in the concept of spectrum management consistently with this view. Moreover, Ness supports this principle by expressing concern at the possibility of spectrum controlled by a few operators: "spectrum is our prime communications link.

It should not be controlled by a few—a bottleneck that can silence other voices. According to Commissioner Ness: "The Commission has not always responded as rapidly as we should to accommodate advances in technology.

We must move expeditiously if we are to stay in the forefront in the development of new technologies and services. This is a natural duty of any government agency in charge of the management of a public asset that is the subject of rapid technological changes. Furthermore, this principle demonstrates how allocation is understood as a non-questionable system of spectrum management. However, the idea that the FCC is willing to review and reallocate spectrum is a necessary step towards new paradigms.

Naturally, the idea of the spectrum as a commons, somehow, will require the FCC to review the present allocation, before the final step of minimum or no allocation. The interest in the advancement in technology also directly supports the use of spread spectrum and other digital radio technology. Commissioner Ness argued the possibility of infinite capacity of the spectrum, despite its being a scarce resource. Further, she pointed out that the trade-off is between using additional spectrum that could support other services and the cost of developing and deploying new, more efficient technology in the existing spectrum.

Along these lines, Ness concluded that unlicensed bands must share the spectrum with a wide assortment of other unlicensed services. There, parties must share spectrum with a wide assortment of other unlicensed services, frequently adapting their technologies to avoid interference. This principle is without a doubt the most unreceptive to the new paradigm of spectrum management. She understood the prospect of a new concept of spectrum—scarce, but infinite in its capabilities.

Nevertheless, she does not discuss the probability of an entire spectrum without allocation. The idea of dividing and licensing the spectrum still dominates this rationale. In addition, the tragedy of the commons seems to be an eternal concern with new technologies in a non-licensed environment. Commissioner Ness has said that the FCC "should provide greater service flexibility, particularly for emerging technologies.

Generally, licensees should not need Commission approval to adjust their services to meet market demand where there is no interference. Allowing greater flexibility will enable the licensee to respond rapidly to market conditions. This argument again supports the idea of spread spectrum technology leading to a new paradigm of spectrum management. If the market demands new and broader solutions, the FCC and the current regulation should not be the obstacle to better services and more extensive and greater access to the spectrum.

Commissioner Ness indicated that the marketplace should resolve the debate between competing technologies. The free market will work better if the FCC avoids setting standards where the technology is an extension of an established service. However, after being disfavored for so long in comparison to licensed services, spread spectrum and other digital radio technology probably need some active assistance in order to share the spectrum without either allocation or interference.

While a system of open spectrum access generally means less regulatory involvement, it may actually necessitate larger governmental involvement in standard setting. Ness suggested that there is greater efficiency if spectrum users bear some relationship to the propagation characteristics of the spectrum.

But not even a Wireless Summit can by edict eliminate the laws of physics. The higher the frequency, the shorter the wavelength and the shorter the distance the signal is carried. Mobility is best achieved in bands 2 GHz and below.

This is a critical point when looking at the actual stage of new technology experiments. The frequency ranges assigned to develop the spread spectrum services and others similar are very limited. In order to create a global impact using the new paradigm, it is necessary to have a broader part of the spectrum, and not simply a "black corner" as is the case today.

Somehow, Ness decided to express her sympathy for the auction methodology while developing this principle. However, she pointed out that there are times when the public is better served by not auctioning licenses. For example, she said that the FCC has set aside bandwidth for unlicensed services, such as cordless telephones, remote home and auto security devices, and wireless access to the Internet. This idea, among others, indirectly gives support to a new concept of spectrum management.

The judicial and legislative authorities of the United States presume that spectrum is scarce. They founded all the norms and jurisprudence on the spectrum scarcity presumption.