Wireless Frequently Asked Questions

Wireless Terms
What does the term “wireless” imply?
What are some wireless applications?
What is the component availability of wireless devices?
What is RFID and how does it work?
What types of modulation are used in some of the various wireless applications?
What is spread spectrum?
What are the ISM bands?
What is propagation, multipath, and fading?
What is the difference between a cordless phone, a cellular phone, and a car phone?

Wireless Capabilities
At what frequencies do wireless applications operate?
How wide is the range for wireless devices?
What are some of the major wireless standards?
What are the standards, by geographic location?

Wireless Regulations
Do I need a license to operate a wireless link?
Is RF hazardous to humans and/or the environment?
How secure is wireless communication? Can others intercept my phone calls?

Ultra Wideband
What is Ultra Wideband?
How are UWB signals generated?
What are some of the benefits of UWB over a narrowband signal?
What are the current applications of UWB?
What issues need to be resolved in UWB?

Questions and Comments
Send us your questions and comments...

 

Wireless Links

Wireless Glossary

 

 

 

 

 

 

 

 

 

 

 

What does the term “wireless” imply?

Wireless describes the products and standards that allow communications without additional electrical connections. Typically, the term wireless implies that electromagnetic waves traveling through the air carry information from one place to another. Depending on their frequency, these waves exhibit different properties. For example, microwaves (on the order of GHz) tend to bounce off walls and objects. At the opposite extreme are low frequency waves (on the order of tens of MHz) which tend to travel through walls and objects. The wireless systems designer selects the operating frequency suitable for a particular application, thereby taking advantage of some of these properties.

In some areas, powerline communication is also considered wireless because of the lack of "additional" wiring.

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What are some current wireless applications?

Wireless is quickly emerging into many new applications:

• networking computers
• allowing remote monitoring and data acquisition
• providing access control and security

Of course, wireless ideally accommodates environments where wires are impossible, such as vehicles and hand-held devices. Most wireless products can be categorized by application, some of which include the following:

·        Voice and Messaging:

• Cordless phones
• Cellular phones
• Beepers, pagers, and messaging systems
• Wireless e-mail systems
• CB Radio
• Commercial two-way business radios
• Intercom systems

·        Computer Networking:

• Wireless Local Area Networks (WLANs)
• Infrared (IR) ports on computers, printers, and other devices
• Radio modems

·        Remote Data Acquisition:

• Personal Digital Assistants (PDA's)
• Radio Frequency (RF) modems

·        Commercial Home Products:

• Security and access control
• 900 MHz stereo distribution
• Temperature control systems
• Remote control
  • Keyless entry systems
  • Garage door openers
  • Remote Controlled toys
  • TV remotes

·        Global Positioning Systems (GPS)

• Aviation navigation
• Nautical navigation
• Roadway navigation

·        Radio Frequency Identification technology (RFID)

• Tags and readers - Inventory Control, Animal migration/tracking
• Smart cards - Access control, Identification, Debit cards
• Merchant RF security tags

Many other applications exist. In fact, many companies take existing products, cluttered with wires, and make them wireless.

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What is the component availability of these devices?

While wireless communications emerge as a technology, components are readily available. In fact, integrated circuit (IC) technology enabled the placement of entire subsystems (such as a transceiver) onto a single chip. Most of the major semiconductor manufacturers own several IC packages, which work at a wide range of frequencies.

To find the components most effectively:

·        contact some of the major IC manufacturers

·        exam wireless design magazines

·        search the World Wide Web

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What is RFID and how does it work?

RFID systems are used to track and identify objects, animals, and people. A typical RFID system consists of a tag, a reader, and a data processing device (such as a computer). The tag is attached to the object, animal, or person, and stores relevant identification information. The reader communicates with the tag via a wireless radio frequency link to obtain the information stored in the tag. In many cases, the reader is attached to a data processing device such as a computer via either a wired or wireless link.

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What types of modulation are used in some of the various wireless applications?

Modulation is a technique in which a carrier wave is used to carry information from one place to another. The sine wave is modified in either amplitude, phase, or frequency, so that the information is present on the wave, and can be decoded at the receiving end. The three major types of digital modulation are:

·        Amplitude Shift Keying (ASK) - ASK is rarely used in wireless applications because multipath effects can dramatically influence the amplitude of the information-bearing signal. This causes errors when the signal is received and decoded.

·        Phase Shift Keying (PSK)

·        Frequency Shift Keying (FSK)

PSK and FSK are more common in wireless systems because of their robustness in the presence of multipath.

Many hybrid forms of ASK, PSK, and FSK exist. For example, Binary Phase Shift Keying (BPSK) is a form of PSK where only two phase states are allowed. BPSK is highly clear of multipath propagation, but is unused in high data rate applications because of bandwidth inefficiency. Other forms of PSK, such as Quadrature PSK (QPSK), allow for more phase states, which provide greater spectral efficiency at the cost of more susceptibility to multipath.

One special form of modulation that has actually become a buzzword in the wireless industry is spread spectrum. Spread spectrum and many other hybrid techniques are used in some of the major cellular and data networking standards.

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What is spread spectrum?

Spread spectrum is presently one of the biggest buzzwords in wireless. This special modulation technique spreads the transmitted signal over a frequency range much wider than the minimum bandwidth required to send the signal. Widening the signal bandwidth in this fashion increases the probability that received information will closely match the transmitted information.

There are two basic types of spread spectrum modulation:

·        Direct Sequence (DS)

·        Frequency Hopped (FH)

Some hybrid spread spectrum systems exist that combine both types.

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What are the ISM bands?

The Industrial, Scientific, and Medicine (ISM) frequency bands were allocated by the Federal Communications Commission (FCC) in the mid 1980's. The bands encompass the frequency ranges 902 - 928 Mhz, 2400 - 2483.5 Mhz, and 5725 - 5850 Mhz. The advantage of the ISM bands is that they are unlicensed as long as a device operating in the ISM bands meets special FCC regulations. While many devices operating in the ISM bands use spread spectrum modulation, the FCC does permit narrowband modulation techniques to be used (provided that the respective device meets stringent power requirements).

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What is propagation, multipath, and fading?

Propagation
Electromagnetic wave propagation describes how a wave gets from one point to another depending upon the environmental conditions it encounters along the way. For example, a low frequency wave that encounters a plaster wall will likely travel through it. On the other hand, a much higher frequency wave will bounce off the wall. And a wave of an intermediate frequency might bounce off the wall but lose a substantial amount of energy in the process. It is apparent that propagation can have severe effects on the received signal.

Multipath
In a typical wireless environment, no direct line-of-sight (LOS) path between the transmitter and the receiver exists.  In fact, the electromagnetic waves emitted by the transmitter usually take different paths to get to the receiver, depending upon the obstacles in the environment. As a result, the received signal comprises a sum of the various contributions, each of which differs in both amplitude and phase. In many cases, the signals combine in a destructive manner, thereby severely degrading the signal's strength. The receiver faces the difficult task of properly demodulating and decoding the signal into something that resembles the original. Despite the emerging receiver technologies multipath problems can still seriously inhibit a wireless system's performance.

Fading
Fading describes rapid changes in a radio signal's amplitude over a short period of time or travel distance. Fading results from multipath. In fact, fading results from interference between multiple replicas of the transmitted signal.

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What is the difference between a cordless phone, a cellular phone, and a car phone?

Cordless Phones
A cordless phone refers to a device whose range of use operates in a relatively small area, (such as within a house). In fact, when you purchase a cordless phone, you receive both the handset or mobile, and a base that connects directly to the phone line in your house. The base communicates with the mobile to ensure that phone calls are handled properly. As a result, the user can only stay within a relatively short distance of the base.

Cellular Phones/Car Phones
Cellular phones and car phones refer to the same device, and permit wireless operation over large distances. Cellular phones, like cordless phones, require that the mobile be able to communicate with a base. However, a cellular phone user does not need to be aware of the base location, which may be located miles away. The user can travel over large distances. In fact, modern cellular systems permit the user to travel from an area covered by one base to an area covered by another base. The user's call is automatically and seamlessly handed over to the new base.

Cellular systems are able to achieve wide coverage and high capacity because they employ frequency re-use. This means that a channel frequency being employed in one area can also be used in another area provided that the distance between the two areas is large enough to prevent interference.

 

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At what frequencies do wireless applications operate?

The frequency varies tremendously depending on the specific device and the application being used. Below is a general run-down of several major frequency bands, along with some common devices operating in them:

Applications	Frequency Bands
VLF band radios Beacons	170 - 190 kHz
AM broadcast communications Low power voice and data	550 - 1600kHz
CB radios Low power voice and data	27 MHz
Remote control Cordless telephones Low power voice and data	49 MHz
FM radios Low power voice and data	88 - 108 MHz
Commercial two-way voice Pager services	150 - 170 MHz
303 MHz garage door openers Keyless entry systems Security alarms	260 - 470 MHz
Cellular Phones	824 - 849 MHz and 869 - 894 MHz
ISM band Wireless LAN’s Part 15 devices (spread spectrum cordless phones, etc.) Military radiolocation systems Federal mobile communications 902 - 928 MHz	902 - 928 MHz
Pager services with a high transmitter power	930 MHz
Amateur satellite Part 15 devices Microwave ovens and systems Army packet radio development	2.4 – 2.4385 GHz
Amateur satellite Part 15 devices Naval radar systems Test range instrumentation radars	5.727 – 5.875 GHz
Radio navigation	24 – 24.25 GHz

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How wide is the range for wireless devices?

Depending on the design and application of the device, range varies tremendously. While some devices (such as RF tags) operate over a few inches, other devices (such as those used in wireless computer networking) operate over tens of miles.

Range depends on many factors, which include:

·        The environment – A highly dependent factor in the range of a device. Certain environments may cause excessive multipath, which can reduce both the range and data rate of the device.

·        The operating frequency of the device

·        The output power

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What are some of the major wireless standards?

• AMPS

 Advanced Mobile Phone System. AMPS is the first analog cellular standard in the U.S. Although AMPS is still in use, it is anticipated that it will be replaced by the United States Digital Cellular(USDC) standard.

• CDPD

Cellular Digital Packet Data is a digital standard for packet data services. CDPD was designed to overlay with existing cellular infrastructure, thereby permitting simple and inexpensive installation.

• CEBus

The Consumer Electronics Bus (CEBus) standard was created by the Electronic Industries Association (EIA). CEBus is an engineering standard for home automation products. It supports carrier current, RF, IR, coaxial cable, twisted pair, and eventually fiber optic cable.

• DECT

Digital European Cordless Telephone is a universal cordless telephone standard developed by the European Telecommunications Standard Institute (ETSI). DECT offers services for both voice and data communications.

• GSM –

Global System for Mobile . The GSM standard was developed in Europe to standardize cellular communications among European countries. GSM has demonstrated substantial success and continues as one of the world's most popular standards for new cellular radio and personal communications equipment.

• IEEE 802.11 –

This is the IEEE standard for wireless LAN's. The goal of the IEEE 802.11 committee is to standardize wireless LAN development in the ISM band. The standard focuses on the media access control (MAC) and the physical (PHY) protocol levels. The IEEE 802.11 standard is still under development, but is anticipated to become the wireless LAN standard.

• IrDA

 The Infrared Data Association (IrDA) was formed to develop a standard for wireless communication using infrared (IR) technology. Some of the chief goals of the committee are to develop a standard that permits low cost, low power, point-to-point user communications using IR as the transmission medium.

• IS-54

Interim Standard 54. See USDC.

• IS-95

IS-95 is a U.S. digital cellular standard that uses a Code Division Multiple Access (CDMA) scheme. In a CDMA system, users share time and frequency resources simultaneously. This occurs through assigning each user a distinct digital code. This code is added to the information data and modulated onto the carrier, using spread spectrum techniques. Although it anticipates providing significant capacity improvement and increased interference rejection over other digital cellular standards, IS-95 remains somewhat controversial because of its wide bandwidth requirements.

• PHS

The Personal Handphone System standard was developed in Japan specifically for indoor and microcell usage.

• USDC

United States Digital Cellular, also known as IS-54 (Interim Standard 54), was developed to replace the AMPS standard, particularly in urban areas where AMPS did not provide adequate channel capacity. USDC allows the co-existence of AMPS so that providers can gradually phase out AMPS as needed.

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What are the standards, by geographic location?

Standards by geographic region can be found in detail on the following page.

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Do I need a license to operate a wireless link?

Licensing and other legal requirements for operating any radio transmitter are established by the Federal Communications Commission (FCC). Because these alter with time, the reader should consult the FCC Regulations for the latest information.

The FCC permits unlicensed operation in portions of the spectrum called ISM (Industrial, Scientific, and Medical) bands, provided that certain technical restrictions on transmitter power and modulation are met.

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Is RF hazardous to humans and/or the environment?

Thermal waves are the only electromagnetic waves confirmed as a biological hazard. This hazard stems from the fact that radio waves can heat biological material (this is how microwave ovens work). Although observed, non-thermal effects have not proven harmful. The FCC establishes legal power limits for cellular telephones, hand-held radios, and any other transmitters the public might come in contact. These limits are well below the power levels that prove to have any harmful effects, and the legal presumption is that any transmitter operating in compliance with the FCC regulations is safe.

Readers concerned about the safety of wireless devices should consult the following references:

• EMF-Link -- A biomedical science and engineering clearinghouse of information on the biological and health effects of EMF from commonly used appliances.

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How secure is wireless communication? Can others intercept my phone calls?

The cordless (49 MHz) and cellular FM phones are not secure. If you don't want anyone to hear you, don't use cordless or cellular. The new cordless (900 MHz) spread spectrum and cellular non-FM (ie IS-95, etc.) are secure because of the spreading code used in the modulation technique. In general, spread spectrum systems provide a much higher level of security than the more traditional narrowband systems.

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What is Ultra Wideband?

Ultra Wideband is the transmission of a signal where the fractional bandwidth is greater than .25.

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How are UWB signals generated?

There are several methods of generating a UWB signal, but all involve the formation of a very short pulse in the time-domain. This pulse, typically sub-nanosecond in length, can then be transmitted directly or filtered depending on whether a DC component in the UWB signal is desired or not.

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What are some of the benefits of UWB over a narrowband signal?

• UWB signals are not as affected by multi-path as narrowband signals, due to shorter pulse widths.
• It has high data rates.
• It has increased security (low probability of detection) due to low spectral power density.
• Signals transmitted below the noise floor can be recovered due to inherent processing gain. These signals will be invisible to narrow band users allowing for more efficient use of the spectrum.
• It has multi-path resolution leading to <50ft object resolution.
• It allows Multiple User Access for a given portion of the spectrum.

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What are the current applications of UWB?

UWB RADAR has been researched for some time as a method of defeating stealth aircraft and as electronic counter measures. Because of the bandwidth occupied by UWB RADAR, it is difficult to develop a system that can jam the RADAR or can effectively appear invisible to the RADAR. Several civilian systems take advantage of these properties, including:

• Secure Communication Systems (hard to jam or detect),
• Ground Penetrating RADAR, and
• Obstacle Avoidance RADAR.

Both civilian RADAR systems take advantage of the fact that while there may be no one specific frequency that is ideal (or adequate) for the application, the UWB RADAR examines many different frequency components at the same time.

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What issues need to be resolved in UWB?

• Although UWB signals can be transmitted below the noise floor, it may be desirable to transmit with more power. If a UWB system is operated under current FCC Part 15 regulations, narrow band signals operating in the same band will be adversely affected. The narrow band users will see the UWB signal as an increase in the noise floor by about 10 dB. The FCC is currently proposing new regulations to resolve this issue. On suggested solution would be to only allow UWB operation above a certain frequency.
• Currently UWB Transmitter and Receiver must be time synchronized. GPS makes this task feasible for production systems, however a system where synchronization is not required is desirable.
• High sampling rate receivers are required.
• Efficient Pulse Shaping is required.
• Current Transmitter designs consume large amounts of power in the generation and processing of the pulses. Although the period of high power consumption is very short, and probably will not affect battery life compared to a narrow band system, it does lead to problems in designing a transmitter on a chip.