Wireless Technology

This essay has a total of 5019 words and 32 pages.

Wireless Technology



Wireless Technology applied to Computer Processing


I. Abstract


Wireless technology can provide many benefits to computing including faster response to queries, reduced time spent on paperwork, increased online time for users, just-in-time and real time control, tighter communications between clients and hosts. Wireless Computing is governed by two general forces: Technology, which provides a set of basic building blocks and User Applications, which determine a set of operations that must be carried out efficiently on demand. This paper summarizes technological changes that are underway and describes their impact on wireless computing development and implementation. It also describes the applications that influence the development and implementation of wireless computing and shows what current systems offer.


II. Introduction


Wireless computing is the topic of much conversation today. The concept has been around for some time now but has been mainly utilizing communication protocols that exist for voice-based communication. It is not intended to replace wired data communication but instead to be utilized in areas that it would be otherwise impossible to communicate using wires. Only recently has the industry been taking steps to formulate a standard that is more suitable to data transmission. Some the problems to be overcome are:

a. Data Integrity - relatively error free transmission,
b. Speed - as close as possible to the speed of current wired networks,
c. Protection - making sure that the data now airborne is encoded and cannot be tapped by unwelcome receivers,
d. Compatibility - ensuring that the many protocols that sure to be created subscribe to a standard to allow inter-operability,
e. Environmentally safe - strengths of electromagnetic radiation must be kept within normal levels. In our study of the theories and implementation concerns of wireless computing, we found that it is being treated in an object-oriented fashion. Scientists and development crews, including the IEEE, are doing their best to implement wireless connectivity without changing the existing computer hardware.

As a result, a lot of focus is on using existing computer hardware and software to convert data to a format compatible with the new hardware, which will be added to the computer using ports, or PCMCIA connections that already exist. This means that wireless communication will be transparent to the user if and when wireless computing is utilized on a wide scale.






Wireless computing applications covers three broad areas of computing today. Replacement of normal wired LAN’s need to retain the speed and reliability found in wired LAN’s. Creation of semi permanent LAN’s for quick and easy setup without the need for running wires. This would be necessary for events such as earthquakes. The last category is that of mobile computing. With advent of PCMCIA cards, notebook computers are being substituted for regular desktop machines with complete connectivity of the desktop machine. However, you lose the connectivity when out of the office unless you have a wireless means of communicating. On the compatibility issue, the ability to mix wireless brands on a single network is not likely to come soon. The IEEE Standards Committee is working on a wireless LAN standard -- 802.11, which is an extension of the Ethernet protocol. Because the field of wireless communication is so broad, the IEEE was not able to set a standard by the time private researchers were ready to test their theories hoping to set the standard for others to follow.


II. Methods

There are a few methods of wireless communication being theorized and tested.

Radio:
This is the method that makes use of standard radio waves in the 902 MHz to 928 MHz frequency range. Although these frequencies are well used, methods have been developed to ensure data integrity. Spread spectrum transmission of data is a method where the transmitter will send information simultaneously out over many frequencies in the range increasing the change that all data will eventually reach the receiver. Frequency hopping is an additional measure that also enables data security. The 26 MHz ranges of frequencies is further divided in to channels. The transmitter then sends out data hopping from one channel to the next in a certain pattern known to the receiver. Within each channel, spread spectrum transmission can be used to maintain interference avoidance. Some of this transmission manipulation can be avoided by transmitting at a frequency that is less used. Some developers have tried transmitting in the gigahertz range. The disadvantages here are:

a. Higher frequencies mean shorter wavelengths and shorter wavelengths do not penetrate solid objects like walls and floors;
b. The same transmission strength employed by lower wavelength transmitters yields a shorter range at higher frequencies. This means that transmission strength will need to be boosted something hard to accomplish using portable tools and potentially dangerous to humans; 3) Transmission frequencies of 3 GHz and higher are licensed by the Federal Communications Commission. Developers in the range have the additional hassle of obtaining a license every time an installation is done.
c. Laser: Laser-based communication is the fastest way to communicate without wires. Information travels at the speed of light. The drawbacks however far outweigh the speed advantage and prevent this method from becoming the standard. The major drawback is that communication is restricted to line of sight. Also, very thick fog or blizzard conditions will diffuse the laser beam and causing interference and reducing data integrity.




d. Infrared: This method is similar to Laser. High-speed communications are easy to achieve using this method. However, it suffers from the same problems that plague laser communications. It requires line of sight transmission and can be disrupted by strong ambient light. Infrared wireless computing exists more commonly in the form of peripheral connections in a small area.
e. Cellular connections although expensive to use now is the area of much development by private companies. Cellular computing can be likened to the current wire-based Internet network. Data is packaged in to units, size of the unit is dependent on the actual hardware, and is sent to the nearest participating cell. That cell then forwards the packet to the next cell and so forth until the packet reaches its destination.
f. Microwave: This method of communication has been utilized for quite some time now. However this method has makes little provision for data aware transmission. It used extensively in Europe where wired transmission of any type including voice is poor. For data transmission, a lot of technology is utilized in packaging the data into a form that is compatible to voice communication. On the receiving end, the process is reversed. The advantage of this method however is that communication can be accomplished using existing satellite connections making worldwide connectivity possible.


3 Standards

The IEEE 802.11 committee has voted to create a minimum requirement for wireless computing connections. In their consideration:

(1) Use the frequencies 2.4 to 2.5 GHz. This is in the low end of the high frequency spectrum and is currently not licensed by the FCC.

(2) Use spread spectrum technology. Compared to the current bandwidth 26 MHz, 902 MHz to 928 MHz, the range 2.4 to 2.5 GHz yields a bandwidth of 100 MHZ. Spread spectrum transmission now gives 385% percent increase in data reliability.

(3) Many more sub-channels can be formed in a bandwidth of 100 MHZ. This increases the capability of frequency hopping which in turn yields greater data security.

(4) Utilize Gaussian Frequency Shift-Keying. Frequency shift-keying is a form of frequency modulation in which binary signaling is accomplished by using two frequencies separated by some Df Hz. The frequency duration is small compared with the carrier frequency, fc. A signal received at frequency fc, would represent a digital low and signals received at frequency fc Df, would represent a digital high. Note that this does not interfere with spread spectrum or frequency hopping capabilities since those function on frequencies separated by 1 MHz or more.

As part of setting a wireless standard some modifications of the standard set by the IEEE 802.3 committee have been adopted. The most significant of these is the modification to the carrier sense multiple access / collision detection, or CSMA/CD, protocol used in wired networks today. This is a method whereby any machine at any time, wishing to send a message on the net, will first send a token out to ensure that a carrier exists (network ready). After establishing this, the message will be sent.
Because any machine may send at any time, collisions of information will occur. If any machine detects a collision, it will send out a jamming signal to all the others. All machines will then wait on a random interval timer after which they will try to send again.

For wireless networks however, since a machine is not in constant communication with the rest of the LAN, detecting a collision and notifying all other machines on the net is impossible. A modification in the way of the collision handling had to be made. A method known as collision avoidance is employed to create the CSMA/CA standard. In a collision avoidance strategy, the net estimates the average time of collisions and sends a jamming signal at that time. A wireless transceiver will not only sense a carrier but will also listen for the jamming signal. When all is clear it then send its message. This collision avoidance method has two drawbacks:


1) It cannot completely filter all collisions since it operates on estimated times of collisions;
2) -If it did, it slows the network significantly by sending jamming signals whether or not a collision actually occurs.



IV. Physical Layer


Much of the focus of wireless computing development is centered on the physical and media access control layers of a system. It is on this level of the LAN protocol of which wireless products like modems and transceivers. On the physical layer issue, the 802.11 is focusing on the one proposed by Apple Computer Corporation. The Apple physical-layer protocol appears the most robust of any considered to date in 802.11. Apple’s system is a full-duplex, slow frequency-hopping protocol. By using a frequency-hop spread-spectrum radio, the system fits with the spread-spectrum methods of virtually all 802.11 specifications.

Apple splits the data-transport protocol into two layers:


•The RF Adoption Layer is similar in some respects to cell-based data protocols, such as Asynchronous Transfer Mode and IEEE 802.6 Switched Multi-megabit Data Services; like ATM and 802.6, the RF Adoption Layer includes segmentation/reassembly functions and Protocol Data Unit generation functions, and it also includes Forward Error Correction (FEC) generation and verification functions which substantially increase packet integrity in wireless environments but adds FEC overhead.

•The RF Hopping Protocol Physical Layer consists of a transmission convergence sublayer including header generation, RF framing, and RF hopping protocol functions and the physical- medium-dependent sublayer, in which the actual characteristics of the RF channel are handled. In the RF Adoption Layer, a Protocol Data Unit is split into three segments, and two error-correcting data units are added. The RF Hopping segments, and two error-correcting data units are added. The RF


Hopping Physical Layer builds special Burst Protocol Data Units out of the data and FEC units and uses


carrier-sense methods borrowed from Ethernet to determine whether an RF Hop Group is clear for transmission. Each hop group consists of five separate radio channels. The controller scans hop groups via state-machine operation with four states: scan, receive, carrier-sense, and transmit. In early tests at Apple, the hop system showed 80-microsecond hop times, 57-microsecond clock recovery, and a 5-microsecond lapse between the time an empty channel is sensed and transmission begins. Since each cluster of wireless LANs can use different hop groups, multiple LANs could operate in the same area without interference. One concern is whether the overhead for error correction for each packet, which can be as much as 50% is too high to give the proposal a chance.

The safety of those operating new equipment now plays a larger role in determining the direction of technological growth now more that ever. Factors under consideration are the effect of infrared and strong electromagnetic radiation that would pervade the workplace on the workers. This limits the strength of and communication device that would be used in accomplishing transmission.

For the Personal Computer;The adapters have a small attached antenna through which they send and receive network traffic as radio signals. Some wireless products are small boxes that attach to your PC’s parallel port. In either case, the signals may travel from PC to PC, forming a wireless peer-to-peer network, or they may travel to a network server equipped with both wireless and standard Ethernet adapters, providing notebook users a portable connection to the corporate network. In either case, wireless LANs can either replace or extend wired networks.

Standards are lacking. Wireless networking is still a technology looking for a standard, which is why very few wireless products can work with one another. Each vendor uses a different protocol, radio frequency, or signaling technology. If wired networks still operated like wireless, you would have to use the same brand of network interface card throughout your network. Right now you are, for the most
part, tied to whichever brand of wireless LAN you pick. Most of the products in this comparison listed their wireless protocol as Ethernet carrier sense multiple access/collision avoidance (CSMA/CA), a variation of standard Ethernet. Unfortunately, each vendor has put its own spin on CSMA/CA, which means even their protocols are incompatible.


5 Wireless services

As technology progresses toward smaller, lighter, faster, lower power hardware components, more computers will become more and more mobile. For space concerns this paper will exclude any further discussion of the hardware developments toward mobility except for devices directly related to wireless
connectivity such as modems.


A wireless computer is not connected via a wireline and thus has mobility and convenience. A wireless LAN provides the convenience of eliminating the wires, yet is not necessarily mobile.


(What is mobility?)


Mobility is a characteristic where the wireless computer may connect, loose the physical communication (possibly due to interference) and reconnect (possibly to another sub-network) and retain its virtual connections and continue to operate its applications. The network protocols will be discussed later.


(Then, what is portable?)

Portable is defined that the wireless computer may connect, loose the connection and then re-connect, as well. However, the mobile unit will have to restart if it is reconnected to another sub-network, requiring that running processes be shut-down and windows closed.


Mobility may be limited by the wireless service subscribed. Four basic service zones are described: Global/National service zone: Ubiquitous radio coverage throughout a region, country or the entire globe, low user densities, and minimal bandwidth requirements. Typically satellite systems.

Mobile service zone: Radio coverage in urban, suburban and populated rural areas,
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