To loosely define the term wireless networking is to say that it is any connection between two point for the purpose of transmitting information without any physical connection, i.e. fiber optics, copper wires, phone lines, etc....  Such wireless modes of information exchange could be as common as  visual, auditory and olfactory.  In the world of information exchange wireless communication is often referred to the transmission and reception via laser/infrared, micro-wave and radio signals.  Also, when discussing wireless networking it is most often referred to Local Area Networks (LANs) and Personal Area Networks (PANs).  While communication over longer distances, such as Wide Area Network (WANs) and Metropolitan Area Networks (MANs), are possible.  However, it will greatly reduces the efficiency of wireless transmission and, at the same time,  increase the required power and cost of operation tremendously.  Much longer distances are achievable, such as satellites.

    Wireless LANs (WLAN) frequently augment rather than replace wired LAN networks-often providing the final few meters of connectivity between a backbone network and the mobile user. The WLAN  is a flexible data communction system that makes new applications possible, thereby adding new flexibility to networking. collaborate with other users, or move to other campus locations. But the benefits of WLANs extend beyond user mobility and productivity to enable portable LANs-with WLANs, the network itself is movable. WLANs have proven their effectiveness in vertical markets and are now experiencing broader applicability in a wide range of business settings.

    Over the last seven years, WLANs have gained strong popularity in a number of vertical markets, including the health-care, retail, manufacturing, warehousing, and academic arenas. These industries have profited from the productivity gains of using hand-held terminals and notebook computers to transmit real-time information to centralized hosts for processing. Today WLANs are becoming more widely recognized as a general-purpose connectivity alternative for a broad range of business customers. The Yankee Group, a market research firm, predicts a sixfold expansion of the U.S. wireless LAN market by the year 2000, reaching more than $1 billion in revenues.
 

Laser/Infrared

    Both laser and infrared transmission fall under that same category in that the method of transmission and  reception are similar.  Networks are created when optical transmitter and receiver are in the line-of-sight and are able to make the hand shake. In much the same way that your CD player reads the 1's and 0's on the disk data is sent and received by way of packets (packs) of 1's and 0's.  Below is a diagram that will explain how information is exchanged between local networks.
 

                                                                        Ref:  http://www.eagleopt.com/omi.htm
 
        Implementation of such a system can be very cheap or very costly.  Just transceivers themselves can range from thousands of dollars for infrared systems to much higher for laser.  Of course price is strongly dependent on the utility requirements.  Therefore it's crucial for management to weigh the many different factors:

        Pros:

• Very high data transfer rate, up to Gbps for laser and 155Mbps for infrared(1.25 miles)
• Long range in data transfer:  hundreds of miles for laser and upto 2.5 miles for infrared (10Mbps)
• Multiple channel access
• Digital transmission
• Low cost device (cheap IR-LEDs)

• Data transfer rate is inversly proportional to distance
• Large and bulky units prevents mobile networking
• Must have direct-line-of-sight
• Greatly affected by the change in the transmitting medium (air, stray sunlight, clouds)
 

Article links: Laser/infrared networking Research and Technology,  FAQs

Micro-Wave (mW)
 

    Microwave radios have traditionally had a perception of being reliable and fast, but also complicated to install and maintain. Some of today's newer microwave systems have made significant improvements. They are light weight, compact and easy to install and maintain. In fact, the some of the smaller microwave systems require only a 2.5 inch post mounted on the roof or inside an office window to operate effectively. These factors reduce the time it takes to install as well as the related cost. In most cases, all that is required to physically install a microwave system are details such as placement of the antennas, type of mount to be used, and placement of the cable runs from the outdoor radio unit to the indoor data interface unit.

    Microwave systems require a clear line-of-site between the two locations. This implies that there can be no obstacles or obstructions in the path of the microwave signal. In order to accomplish this,
microwave antennas are located as high as possible. Generally, microwave antennas are mounted on roofs of buildings, radio towers, or other tall structures. In the event that a clear line-of-site cannot be established, systems are sometimes repeated over objects (i.e., other buildings) or reflected around an object using specific microwave passive repeaters. In many cases it is necessary to perform a site survey in order to assure a clear line-of-site.

    Microwave system performance can be affected by environmental and atmospheric factors. The most irevalent factor that affects microwave signals is rain, especially in the higher frequency bands (above 18 GHz). Rain has the adverse property of absorbing microwave energy and attenuating the signal path. Other factors such as snow, fog, smog, temperature inversions, etc., have minimal effects on microwave performance.

    Even with these environmental factors, microwave communications can offer greater than 99.995 %availability. In order to assure reliable communications, microwave systems are designed to
accommodate the rain factor in several ways. First, the worst case rain rate is identified for a specific region. Most often, microwave path designers plan for rainfalls that exceed the 0.01 % rain rate. This amount can range anywhere from one inch per hour in Arizona to four inches per hour in Florida. Second, the maximum path distance is calculated with the worst case rainfall. This means that systems that can operate up to three miles in Arizona may only be able to operate up to one mile in Florida. Third, antenna size is determined to achieve the desired reliability factor. The larger the antenna size, the higher the focusing factor, or gain. A 99.995 % availability translates into about 26 total minutes of statistical outage in one year.

    Most microwave LAN systems operate in the 23 GHz band and require licensing by the Federal
Communications Commission (FCC). This licensing procedure is a simple process and assures the
user of interference free operation. The licensing process consists of two steps: First, a frequency
coordination is performed to determine an available frequency. Many search firms are available in the U.S. that can perform this task. They basically have access to a regularly updated database that
identifies other existing microwave users in various geographic areas. The geographic coordinates of
your intended site is submitted to one of these search firms to allow them to accurately recommend a unique frequency that has minimal interference potential. Site coordinates are generally obtained from a site survey. Second, a License Request form 402 is filed with the FCC along with the frequency coordination report. After reviewing your submittal, the FCC grants your station the license to operate that specific microwave system at that specific site using the requested frequencies. The process takes about two weeks for frequency coordination and 60 days for the FCC license approval. This entire process can be handled by most search firms.

                Pros:

• Operating at 24GHz frequency domain, not FCC regulated.
• Can relocate system without relicencing through FCC
• Moderate data transfer rate of up to 20Mbps
• Up to 10 miles transmission range with 2feet high antennae
     Cons:

•  Microwaves are like sound waves which can have interference problem under
•  high traffic condition.
•  Large antennae prevents hand held mobile units
•  Must operate within same room, cannot penetrate walls
 

Microwave Networking,
Wireless Networking over Microwave,
10 Questions on Microwave Networking

Radio Frequency (RF)
 

 Narrowband Technology

    A narrowband radio system transmits and receives user information on a specific radio frequency. Narrowband radio keeps the radio signal frequency as narrow as possible just to pass the information.Undesirable crosstalk between communications channels is avoided by carefully coordinating different users on different channel
frequencies.

Spread Spectrum

    Most wireless LAN systems use spread-spectrum technology, a wideband radio frequency technique developed by the military for use in reliable, secure, mission-critical communications systems. Spread-spectrum is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband transmission, but the tradeoff produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to the right frequency, a spread-spectrum signal looks like background noise. There are two types of spread spectrum radio: frequency hopping and direct sequence.

    A private telephone line is much like a radio frequency. When each home in a neighborhood has its own private telephone line, people in one home cannot listen to calls made to other homes. In a radio system, privacy and noninterference are accomplished by the use of separate radio frequencies. The radio receiver filters out all radio
signals except the ones on its designated frequency.

    An interesting note to the development history of Spread Spectrum is that the idea of didn't really come from the think tank of the armed forces or its affiliates.  Instead, the idea of spreading the signal into this wideband to guide
long range missiles without being intercepted by enemies came as a result of a dinner discussion between an actress and a composer.  Check this story out at the Secret Communications System link.

Frequency Hopping

Frequency-Hopping Spread Spectrum Technology

Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise.
 
 

 
 Figure 2a. Frequency Hopping Spread Spectrum

(Ref:  http://www.wlana.com/intro/introduction/wirels.html)

Direct Sequencing

Direct-Sequence Spread Spectrum Technology

Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered (and, of course, the more bandwidth required). Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low-power wideband noise and is rejected (ignored) by most narrowband receivers.

 

 

                                     (Ref:   http://www.wlana.com/intro/introduction/wirels.html)

How Does Wireless Networks Work
 

    Wireless LANs use electromagnetic airwaves (radio, micro and infrared) to communicate information from one point to another without relying on any physical connection. Radio waves are often referred to as radio carriers because they simply perform the function of delivering energy to a remote receiver. The data being transmitted is superimposed on the radio carrier so that it can be accurately extracted at the receiving end. This is generally referred to as modulation of the carrier by the information being transmitted. Once data is superimposed (modulated) onto the radio carrier, the radio signal occupies more than a single frequency, since the frequency or bit rate of the modulating information adds to the carrier.

    Multiple radio carriers can exist in the same space at the same time without interfering with each other if the radio waves are transmitted on different radio frequencies. To extract data, a radio receiver or augment networks without installing or moving wires. Wireless LANs tunes in (or selects) one radio frequency while rejecting all other radio signals on different frequencies.

    In a typical WLAN configuration, a transmitter/receiver (transceiver) device, called an access point, connects to the wired network from a fixed location using standard Ethernet cable. At a minimum, the access point receives, buffers, and transmits data between the WLAN and the wired network infrastructure. A single access point can support a small group of users and can function within a range of less than one hundred to several hundred feet. The access point (or the antenna attached to the access point) is usually mounted high but may be mounted essentially anywhere that is practical as long as thedesired radio coverage is obtained.

    End users access the WLAN through wireless-LAN adapters, which are implemented as PC cards in notebook computers, ISA or PCI cards in desktop computers, or integrated within hand-held computers. WLAN adapters provide an interface between the client network operating system (NOS) and the airwaves (via an antenna). The nature of the wireless connection is transparent to the NOS.

    Wireless LANs provide all the functionality of wired LANs, but without the physical constraints of the wire itself. Wireless LAN configurations include independent networks, offering peer-to-peer connectivity,and infrastructure networks, supporting fully distributed data communications. Point-to-point local-area wireless solutions, such as LAN-LAN bridging and personal-area networks (PANs), may overlap with some WLAN applications but fundamentally address different user needs. A wireless LAN-LAN bridge is an alternative to cable that connects LANs in two separate buildings. A wireless PAN typically covers the few feet surrounding a user¹s work space and provides the ability to synchronize computers, transfer files, and gain access to local peripherals. Below are some configurations of WLAN accrording to the different utility requirements of WLAN:
 

    The simplest WLAN configuration is an independent LAN that connects a set of PCs with wireless adapters. Any time two or more wireless adapters are within range of each other, they can set up an independent network (Figure 3). These on-demand networks typically require no administration or preconfiguration.

 

  Fig. 3.  Independent WLAN

 

Access points can extend the range of ad hoc LANs by acting as a repeater, effectively doubling the distance between wireless PCs.

 

  Fig. 4. Extended-Range Independent WLAN Using Access Point as Repeater

 

In infrastructure WLANs, multiple access points link the WLAN to the wired network and allow users to efficiently share network resources. The access points not only provide communication with the wired network but also mediate wireless network traffic in the immediate neighborhood. Multiple access points can provide wireless coverage for an entire building or campus.
 

 

                                                         Fig. 5. Infrastructure WLAN
 
 

    Wireless communication is limited by how far signals carry for given power output. WLANs use cells, called microcells, similar to the cellular telephone system to extend the range of wireless connectivity. At any point in time, a mobile PC equipped with a WLAN adapter is associated with a single access point and its microcell, or area of coverage. Individual microcells overlap to allow continuous communication within wired network. They handle low-power signals and "hand off" users as they roam through a given geographic area.

 

                                Fig. 5.  Handing off the WLAN Connection Between Access Points

                                Figures references:  http://www.wlana.com/intro/introduction/config.html

    Wireless LANs also should not be confused with wireless metropolitan-area networks (WMANs), packet radio often used for law-enforcement or utility applications, or with wireless wide-area networks (WWANs), wide-area data transmission over cellular or packet radio. These systems involve costly infrastructures, provide much lower data rates, and require users to pay for bandwidth on a time or usage basis. In contrast, on-premise wireless LANs require nousage fees and provide 100 to 1000 times the data transmission rate.
 

      Like all technologies that have gone through infancy there must be some standards and regulations by which the wireless networking industry can follow to develop products and services using these sets of protocols.  The main concerns for standardization are network operators, service providers, manufacturers, administrators, users and the research community.  These are points are shared amongst agencies from the IEEE, FCC, European Telecommunications Standards Institute (ETSI), as well as the Asian countries.  The collaborative efforts between continents only goes to show how important and how vast the wireless communication industry can be.

    In the past radio frequencies were strictly monitored and are required to meet Industry, Service and Medical (ISM) regulation for reason that certain wavelengths in the RF bandwidth will intefere with existing devices, i.e. medical devices and airplane computers, and also for the fact that some of these waves will generate heat much like the effect of the microwave oven.  However, there has been little regulation on the digital signal transmission over the RF band until recently.  Now FCC is, again, taking their roles in monitoring and allocating the freqeuncies for digital transmission.
 

     The widespread strategic reliance on networking among competitive businesses and the meteoric growth of the Internet and online services are strong testimonies to the benefits of shared data and shared resources. With wireless LANs, users can access shared information without looking for a place to plug in, and network managers can set up or augment networks without installing or moving wires. Wireless LANs offer the following productivity,    convenience, and cost advantages over traditional wired networks:

                     Installation Speed and Simplicity-Installing a wireless LAN
                     system can be fast and easy and can eliminate the need to
                     pull cable through walls and ceilings.

                     Installation Flexibility-Wireless technology allows the network
                     to go where wire cannot go.

                     Reduced Cost-of-Ownership-While the initial investment
                     required for wireless LAN hardware can be higher than the cost
                     of wired LAN hardware, overall installation expenses and
                     life-cycle costs can be significantly lower. Long-term cost
                     benefits are greatest in dynamic environments requiring
                     frequent moves, adds, and changes.

                     Scalability-Wireless LAN systems can be configured in a
                     variety of topologies to meet the needs of specific applications
                     and installations. Configurations are easily changed and range
                     from peer-to-peer networks suitable for a small number of users
                     to full infrastructure networks of thousands of users that allows
                     roaming over a broad area.

     As reliable and flexible as the WLAN may be it is still limited to short istances, such as for infrared and microwaves.  Iin some cases wireless is limited to confined areas with little obstruction to the direct line of sight.  There is yet to be significant use of wireless networking in the WAN and MAN arena where mobility and flexibility can move to the level of utility.

Managerial Considerations

    While wireless LANs provide installation and configuration flexibility and the freedom inherent in network mobility, IS/network managers should be aware of the following factors when considering wireless LAN systems.  The follow is
a list of issues that management might consider before implementing such services:
 
 

Range/Coverage:

    The distance over which RF and IR waves can communicate is a function of product design (including
transmitted power and receiver design) and the propagation path, especially in indoor environments.
Interactions with typical building objects, including walls, metal, and even people, can affect how energy
propagates, and thus what range and coverage a particular system achieves. IR is blocked by solid objects,
which provides additional limitations. Most wireless LAN systems use RF because radio waves can penetrate
many indoor walls and surfaces. The range (or radius of coverage) for typical WLAN systems varies from
under 100 feet to more than 300 feet. Coverage can be extended, and true freedom of mobility via roaming,
provided through microcells.
 
Throughput:

    As with wired LAN systems, actual throughput in wireless LANs is product and set-up dependent. Factors
that affect throughput include airwave congestion (number of users), propagation factors such as range and
multipath, the type of  WLAN system used, as well as the latency and bottlenecks on the wired portions of the
WLAN. Typical data rates range from 1 to 10 Mbps. Users of traditional Ethernet LANs generally experience
little difference in performance when using a wireless LAN and can expect similar latency behavior.Wireless LANs provide throughput sufficient for the most common LAN-based office applications, including electronic mail exchange, access to shared peripherals, and access to multi-user databases and applications.

Integrity and Reliability:

    Wireless data technologies have been proven through more than fifty  years of wireless application in both
commercial and military systems. While radio interference can cause degradation in throughput, such interference
is rare in the workplace. Robust designs of proven WLAN technology and the limited distance over which signals
travel result in connections that are far more robust than cellular phone connections and provide data integrity performance equal to or better than wired networking.
 
    Other factors which might affect the integrity of  the transmitted signals are "multipath" and micro-wave ovens.  Multipath affects occur when signals are transmitted within enclosed area where RF signals can bounce off walls
and obstructions.  This can weaken or strengthen the signal, thus, affecting data throughput.  However, most WLAN vendors designed their products to account for these effects.

Interoperability With Wireless Infrastructure:

    There are several types of interoperability that are possible between wireless LANs. This will depend both
on technology choice and on the specific vendor's implementation. Products from different vendors employing
the same technology and the same implementation  typically allow for the interchange of adapters and access
points. An eventual goal of the IEEE 802.11 specification, currently being drafted by a committee of WLAN
vendors and users, is to allow compliant products to interoperate without explicit collaboration between vendors.

Security:
 
    Because wireless technology has roots in military applications, security has long been a design criterion for
wireless devices.  Security provisions are typically built into wireless LANs, making them more secure than most
wired LANs. It is extremely difficult for unintended receivers (eavesdroppers) to listen in on wireless LAN traffic. Complex encryption techniques make it impossible for all but the most sophisticated to gain unauthorized access to network traffic. In general, individual nodes must be security-enabled before they are allowed to participate in
network traffic.

Cost:
 
    A wireless LAN implementation includes both infrastructure costs, for the wireless access points, and user
costs, for the wireless LAN adapters. Infrastructure costs depend primarily on the number of access points
deployed; access points range in price from $1,000 to $2000. The number of access points typically depends
on the required coverage region and/or the number and type of users to be serviced.  The coverage area is
proportional to the square of the product range. Wireless LAN adapters are required for standard computer
platforms, and range in price from $300 to $1,000.

    The cost of installing and maintaining a wireless LAN generally is lower than the cost of installing and
maintaining a traditional wired LAN, for two reasons. First, a WLAN eliminates the direct costs of cabling
and the labor associated with installing and repairing it.  Second, because WLANs simplify moves, adds, and
changes, they reduce the indirect costs of user downtime and administrative overhead.

Safety:

Wireless networks can be designed to be extremely simple or quite complex. Wireless networks can support
large numbers of nodes and/or large physical areas by adding access points to boost or extend coverage.