The transmission media

1.0 Introduction

1.1 Brief Description

        Nowadays, information technology especially in computer is growing rapidly. As we can see, from hardware to software and from local area network to internet, every aspects is improving. For example, hardware nowadays is getting smaller in size and portable, such as USB storage media. The Transmission media for local area network and internet are also improving from solid cable to wireless and microwave.

        One of the hot issues in Information Technology today is Wireless Local Area Network (WLAN). WLAN was created in the early 1980s and slowly extend to today various version of Institute of Electrical and Electronics Engineering (IEEE) 802.11 family, radio technology, Bluetooth technology, infrared technology and cellular service. As Wireless LAN technology is rapidly becoming crucial component of computer networks and is growing by leaps and bound, today, Wireless LAN is one of the important technology in vertical markets, including health-care, retail, manufacturing, warehousing, academia, communications, government, and also home user. Wireless LAN is created to counter the disadvantages of wired LAN. Wireless LAN has become popular due to the mobility, ease installation in difficult-to-wire areas, reduced installation time, increased reliability and long term cost saving

        I, as a final year student majoring Data Communications & Networking is assigned to this project WirelessLAN Performance : Bandwidth & Coverage as for the final year project title. The main objective of the project is to understand what is Wireless LAN, how does Wireless LAN work, performance, factors that affect the performance and solutions to the performance on bandwidth and coverage. In order to complete this project, I need to

  • search for WirelessLAN technology informations
  • read and document methods of WirelessLAN performance
  • implement the solution

1.2 Objectives

        The objectives of this projects are to:-

  • Brief explanation on the WirelessLAN performance factors
  • Stated all the factors that affect the performance, such as throughput, interference, bandwidth, coverage, antenna type, system design, etc

  • Performance factor caused by bandwidth and coverage
  • Description on how bandwidth and coverage affect the performance of WirelessLAN

  • Solutions to increase the performance in bandwidth and coverage

1.3 Project Scope

        This research topic on wireless performance: bandwidth and coverage only applicable on bandwidth and coverage limitation base on IEEE 802.11 standard. The bandwidth range are base on industrial, scientific, and medical (ISM) band which range from 902-928MHz, 2.400-4.835GHz, and 5.725-5.850GHz..

1.4 Problem Statement

        After some research on the project WirelessLAN Performance: Bandwidth & Coverage, there are few problems that I able to identify as follows :-

  • Low speed and unreliable WirelessLAN connection due to bandwidth issue
  • Bandwidth with greater capacity are likely to perform better in data transmission. Bandwidth performance is distinguished by actual and theoretical output. The number of users in a particular medium will affects the performance as the medium is shared. Some applications may be more demanding in terms of bandwidth compare to others.

  • Low speed and unreliable WirelessLAN connection cause by coverage issue
  • Distance between Access Point (AP) and client will affect the efficiency. The further the distance, the lower data rate. This could also be affected by the orientation of the client depending on the location of the antenna and also the location of access point.

2.0 Background & Literature Review

        In this chapter, we will briefly do some research about the final year project topic, searching articles, news, journals, from various source, summarize and analyze all the reading materials and then come out with own review and opinion.

2.1 Wireless Local Area Network ( WLAN)

        Wireless Local Area Network (WLAN) is the linking of two or more devices via wireless distribution method. Wireless LAN also as known as a flexible data communications system implemented as an extension to or as an alternative for a wired LAN. Wireless LAN utilizes spread-spectrum technology based on radio waves to enable communication between devices in a limited area, also known as the basic service set, giving users the mobility to move around within a broad coverage area and still be connected to the network. In the past few years, wireless LAN have occupy a significant niche in the LAN market. Organizations found that wireless LANs are an indispensable adjunct to traditional wired LANs, to satisfy the requirement for mobility and flexibility, ease and speed of deployment, and ad hoc networking. In the earlier use of wireless LAN, even there are benefits that leads to the usage of wireless LAN, but due to the reason such as high prices, low data rates, occupational safety concerns, and licensing requirements. However, wireless LANs has grown rapidly after these problems have the solutions.

2.2 Wireless LAN Requirements

        In order to start a wireless LAN, one need to consider and meet the requirement of wireless LAN. This is important as one can assure to install a solution which does not fully meet the needs or effectively interface with other systems. The common wireless LAN requirements are as follows :-

* Coverage Areas

This describes where users will need access to the wireless LAN. They might only need connectivity in their offices and conferences rooms, but they might be able to do without wireless connectivity inside power utility rooms and the cafeteria. By properly specifying coverage area, you'll avoid the unnecessary expense of installing access points where they're not needed. Unless obvious, also identify which country where the wireless LAN will operate. This impacts channel planning and product availability.

* Facility

Provide a facility description that includes the floor plan, type construction, and possible locations for mounting access points. Find or create building drawings and walk through the facility to verify accuracy. Also, consider taking photos if the building has multiple floors or has a complex layout, such as a five story multi-wing hospital. In addition to a visible inspection, consider performing an RF site survey to complete the facility assessment. All of this will capture the environment in a way that will help you choose the right design alternatives.

* Battery Longevity

Mobile workers use battery-powered workstations that need to have a long battery life when used with wireless adapters. An 802.11 Network Interface Card (NIC) will draw current at a couple hundred milliamps. Batteries under this load will last from a couple hours to a day or so, depending on the size of the battery. In the design, one must decide whether to activate power management, specify larger batteries or implement effective battery-charging plan.

* Transmission Robustness and Security

Wireless LAN may be interference prone and easily eavesdropped. The design of a wireless LAN must permit reliable transmission even in a noisy environment and should provide some level of security from eavesdropping especially transmitting sensitive information such as credit card numbers. Additional firewalls can be added to ensure the security in wireless LAN.

* Applications

Wireless LAN typically must support user applications which generally includes web browsing, email, file transfer, or certain real-time data monitoring. The information types for example, data, video, or voice will enable one specify throughput and data rates during the system designing.

2.3 History and Type of Wireless LAN

In 1970 University of Hawaii, under the leadership of Norman Abramson, developed the world's first computer communications network using low-cost ham-like radios, named ALOHAnet. The bi-directional star topology of the system connected seven computers deployed over four islands to communicate with the central computer on the Oahu Island without using phone lines. The first generation of wireless data modems were with data rates below 9600-bit/s, to an existing short distance radio system, typically in the two meter amateur band. The second generation of wireless modems was developed immediately after the Federal Communications Commission (FCC) announcement in the experimental bands for non-military use of the spread spectrum technology. These modems provided data rates on the order of hundreds of kbit/s. The third generation of wireless modem then aimed at compatibility with the existing LANs with data rates on the order of Mbit/s. Several companies developed the third generation products with data rates above 1 Mbit/s and a couple of products had already been announced by the time of the first IEEE Workshop on Wireless LANs.

The committee of Institute of Electrical and Electronic Engineers (IEEE) started to develop a standard for wireless LANs and created primarily the various versions of IEEE 802.11 (Wi-Fi). With the IEEE 802.11 standards, wireless LANs were emerging in various market such as trading, hospitality, academia and others. Later, an alternative ATM-like 5 GHz standardized technology, High Performance Radio LAN (HiperLAN),which is a European alternative of IEEE 802.11 standards, has so far not succeeded in the market, and with the release of the faster 54 Mbit/s 802.11a (5 GHz) and 802.11g (2.4 GHz) standards, almost certainly never will.

Wireless LAN technology were extend to several categories as below :-

  • IEEE 802.11 family
  • Radio Network
  • Infrared Network
  • Bluetooth Network
  • Mobile / Cellular Network

2.4 IEEE 802.11 Architecture

IEEE 802.11 is a set of standards that carry out wireless LAN communication in 2.4Ghz, 3.6Ghz and 5Ghz frequency band. 802.11 standard specifies a single Medium Access Control (MAC) layer and several physical layer. MAC layer enable the sharing of the common air medium while physical layers proved the actual transmission of data. The standard defines two kinds of services, which is Basic Service Set (BSS) and Extended Service Set (ESS).

Basic Service Set (BSS)

        IEEE 802.11 defines the BSS as the building block of a wireless LAN. Figure 2.4a show the BSS without Access Point (AP). A basic BSS consists of at least two stations ( stationary or mobile wireless stations). A BSS that without AP is a stand-alone network is also known as Independent Basic Service Set (IBSS) or is referred as an Ad-Hoc network. This network only allows peer-to-peer station communications. IBSS networks are characteristically limited both temporally and spatially. Figure 2.4b show the BSS with AP are as known as Infrastructure network. AP is needed when stations are required to perform network.

ESS is made up of two or more BSSs with APs. BSSs are connected using Distribution System (DS). When this happened, each BBS becomes a component of an extended and larger network. AP is function as the traffic director when data moves between BSS and DS. ESS make the entire network looks like an independent basic service set to Logical Link Control layer (LLC) which means stations within ESS can communicate or move between BSS's transparently to LLC.

2.4.1 IEEE 802.11 Services

The 802.11 defines a number of services that need to be provided by the wireless LAN to provide functionality equivalent to that which is inherent to wired LANs. These services are divided into two groups.

  • Station Services
    • Authentication
    • Deauthentication
    • Privacy
    • MAC Service Data Unit (MSDU) delivery
  • Distribution System Services
    • Association
    • Disassociaiton
    • Distribution
    • Integration
    • Reassociation

Station Services

The 802.11 standard defines services for providing functions among stations. A station may be within any wireless element on the network, such as a handheld PC or handheld scanner. In addition, all access points implement station services. To provide necessary functionality, these stations need to send and receive MAC Service Data Unit (MSDUs) and implement adequate levels of security. Among the services in station services, Authentication, Deauthentication and Privacy are more important.

* Authentication

Wireless LANs have limited physical security to prevent unauthorized access, hence 802.11 defines authentication services to control LAN access to a level equal to a wire link. The authentication service is used by stations to establish their identity with stations they wish to communicate with. The standard do no t mandate any particular authentication scheme, which could range from relatively unsecure handshaking to public-key encryption schemes.

* Deauthentication

This service is invoke when a station wants to disassociate from another station. Deauthentication is a notification and cannot be refused. A station performs deauthentication by sending an authentication management frame (or group of frames to multiple stations) to advise of the termination of authentication.

* Privacy

Used to prevent the contents of messages from being read by other than the intended recipient. The standard provides for the optional use of encryption to assure privacy.

Distribution System Services

802.11 defined this service as it provide functionality across a distribution system. Access points provide distribution services.

* Association

Establishes an initial association between a station and an access point before it can send information through a distribution system. Each station can associate with only a single access point, but each access point can associate with multiple stations.

* Disassociaiton

Upon terminate an existing association, dissasociation is invoke. This service is a notification which should be given before a station leave an area or shut down. However, the MAC management facility protects itself against stations that disappear without notification.

* Distribution

Distribution service is invoke when a station sends MAC frames across a distribution system. The 802.11 standard does not specify how the distribution system delivers the data. The distribution service provides the distribution system with only enough information to determine the proper destination BSS.

* Integration

The integration service enables the delivery of MAC frames through a portal between a distribution system and a non-802.11 LAN. It performs all required media or address space translations. The details of an integration function depend on the distribution system implementation and are beyond the scope of the 802.11 standard.

* Reassociation

Reassociation service enables an established association to be transferred from one access point to another, allowing a mobile station to move. Reassociation provides additional functionality to support BSS-transition mobility for associated stations. This keeps the distribution system informed of the current mapping between access point and station as the station moves from one BSS to another within an ESS.

2.4.2 IEEE 802.11 MAC Layer

        The distributed coordination function (DCF) is a mandatory form of medium access for 802.11 standard. The DCF implements a carrier-sense protocol and supports only asynchronous communications. The DCF is suitable for sending information such as bar codes, and data files, but is not every efficient for sending broadband, time-critical information such as video. Besides DCF, 802.11 standard provide another option, which is point coordination function (PCF) medium access mechanism that is implemented in the access point. PCF provides delivery of time-bounded data via synchronous communications using station-polling mechanisms. This mechanism is capable of transporting video more effectively which DCF cannot do. Another optional method is by using wired equivalent (WEP). WEP offers frame transmission privacy by generating secret shared encryption keys for source and destination stations. WEP only encrypts the payload of MAC layer frames, but not the headers.

The physical layer of the original 802.11 standardized three wireless data exchange techniques:

  • Infrared (IR);
  • Frequency hopping spread spectrum (FHSS);
  • Direct sequence spread spectrum (DSSS).

The 5 GHz band is sub-divided into 52 subbands. 48 subbands is use for sending 48 groups of bits at a time and 4 subbands for information control. This will diminished the effects of interference. OFDM use PSK and Quadrature Amplitude Modulation (QAM) for modulation and with the data rates of 18Mbps (PSK) and 54 Mbps (QAM).

IEEE 802.11b DSSS

IEEE 802.11b DSSS describe the high -rate direct sequence spread spectrum (HR-DSSS) method in the 2.4GHz ISM band. Besides the encoding method, or known as complementary code keying (CCK), HR-DSSS is almost similar to DSSS. The CCK enable IEEE 802.11b to achieve 5.5Mbps and 11Mbps transmit rate. This standard provide a new option to transmit , physical layer convergence procedure (PLCP) header with a short preamble (56 bits). The Synchronization and Start Frame Delimiter fields are transmitted at 1Mbps in this short preamble mode. The rest of PLCP header are transmitted at 2Mbps by using DSSS differential quadrature phase-shift keying (DQPSK) and the data payload at either 2Mbps, or at 5.5Mbps or 11Mbps using CCK. CCK modulation is based on the use of polyphase complementary codes. This modulation encodes 4 or 8 bits to one CCK symbol. Four data rates: 1, 2, 5,5 and 11Mbps are define by HR-DSSS in order to be backward compatible with DSSS. Data rates of 1 and 2Mbps use the same modulation techniques as DSSS. Binary phase-shift keying (BPSK) is use in 5.5Mbps data rate and transmits at 1.375 Mbaud/s with 4-bit CCK encoding. Lastly, the 11Mbps version uses quadrature phase-shift keying (QPSK) and transmit at 1.375 Mbps with 8-bit CCK encoding.

IEEE 802.11g OFDM

New 802.11g standard is introduced to solve the problems of decreasing operational range when upgrade from 802.11b to 802.11a and also the problem of upgrading whole network. This new standard defines forward error correction and using orthogonal frequency-division multiplexing (OFDM) at the 2.4GHz ISM band. This standard achieve a 22 or 54Mbps data rates using OFDM modulation techniques. This standard is said to be backward compatible with 802.11b and 802.11 by meaning 802.11g access points will works well with 802.11b wireless network adapters and vice versa. The reason to use this 802.11g standard is because of it fast maximum speed and the signal range is not easily obstructed and good compare to other standards. Anyhow, 802.11g standard are more costly and appliances may interfere on the unregulated signal frequency.

IEEE 802.11n

This is the newest IEEE standard which designed with the purpose of improving 802.11g in the way of the bandwidth amount supported which utilizing multiple wireless signals and antennas or as known as multiple input, multiple output (MIMO). Figure 2.4.2f Shows how 802.11n solve the problems of radio receiver dealing with multipath propagation. 802.11n enable two transmitters and two receivers work at the same time, and thus making the data can be sent through two channels and the 54Mbps rate of 802.11g standard equipment is doubled. 802.11n increase the signal intensity and having the fastest maximum speed. However, this standard is not finalized yet and the cost would be expect to be much more expensive than 802.11g.

2.5 IEEE 802.11 Family

The following table shown the whole IEEE 802.11 family standard :-

  • 802.11a - 54 Mbps standard, 5 GHz signaling (ratified 1999)
  • 802.11b - 11 Mbps standard, 2.4 GHz signaling (1999)
  • 802.11c - operation of bridge connections (moved to 802.1D)
  • 802.11d - worldwide compliance with regulations for use of wireless signal spectrum (2001)
  • 802.11e - Quality of Service (QoS) support (not yet ratified)
  • 802.11F - Inter-Access Point Protocol recommendation for communication between access points to support roaming clients (2003)
  • 802.11g - 54 Mbps standard, 2.4 GHz signaling (2003)
  • 802.11h - enhanced version of 802.11a to support European regulatory requirements (2003)
  • 802.11i - security improvements for the 802.11 family (2004)
  • 802.11j - enhancements to 5 GHz signaling to support Japan regulatory requirements (2004)
  • 802.11k - WLAN system management (in progress)
  • 802.11l - skipped to avoid confusion with 802.11i
  • 802.11m - maintenance of 802.11 family documentation
  • 802.11n - 100+ Mbps standard improvements over 802.11g (in progress)
  • 802.11o - skipped
  • 802.11p - Wireless Access for the Vehicular Environment
  • 802.11q - skipped
  • 802.11r - fast roaming support via Basic Service Set transitions
  • 802.11s - ESS mesh networking for access points
  • 802.11T - Wireless Performance Prediction - recommendation for testing standards and metrics
  • 802.11u - internetworking with 3G / cellular and other forms of external networks
  • 802.11v - wireless network management / device configuration
  • 802.11w - Protected Management Frames security enhancement
  • 802.11x - skipped (generic name for the 802.11 family)
  • 802.11y - Contention Based Protocol for interference avoidanc

2.5.1 Bluetooth, IEEE 802.15

The name "Bluetooth" comes from the Danish king Harald I (910-986), nicknamed Harald I Blåtand ("the blue-toothed"), who is credited with uniting Sweden and Norway, as well as introducing Christianity to Scandinavia. (Kioskea ,2008)

Bluetooth is a wireless LAN technology designed to link devices (mainly such as printers,mobile phones, wireless headsets, mouse, keyboards and others) to another without a hard-wired connection. The aim of this 802.15 standard is to transmit voice or data between devices which use low-cost radio circuits, over a range of about 10 metres. Bluetooth version 1.2 can reach 1 Mbps in transfer speeds, with corresponds to 1600 hops/s in full-duplex mode, with the range of 10 metres under class II transmitter and merely a little under one hundred metres using class I transmitter. Bluetooth 2.0 + Enhanced Data Rate (ERD) manage to have 2.1Mbits with lower power consumption through a reduced duty cycle.

Bluetooth uses radio waves ( 2.4 GHz frequency band) to communicate. During exchange data, Bluetooth devices don't have to be in visual communication. Thus, two Bluetooth devices can communicate to each other even they are on either side of the wall. Bluetooth detection can be done without user's involvement in any within range of each other.

IEEE 802.15 are extended to following's multiple norms:

  • IEEE 802.15.1 defines Bluetooth 1.x, which can reach speeds of 1 Mbps;
  • IEEE 802.15.2 recommends practices for using the 2.4 GHz frequency band (the frequency also used by WiFi). However, this standard has not yet been approved;
  • IEEE 802.15.3 is a standard currently being developed, which would offer broadband speed (20 Mbps) with Bluetooth;
  • IEEE 802.15.4 is a standard currently being developed for use with low-speed Bluetooth applications.

2.6 WirelessLAN Performance

WirelessLAN had gained popularity due to the capability and advantage that been carried out in various market in the world. With wirelessLAN, it provide a wide mobility and availability to many industries and also end user which really bring much of convenience to the world. WirelessLAN applications works through spread spectrum. In order to get a efficiency wirelessLAN, many factors should be take into consideration. Below are some of the factors or parameters that should be taken into account.

* Interference

Since wirelessLAN are so popular in the market and it is common that a major cities are able to see in excess of more than twenty wirelessLAN from a single spot. The different wireless LAN which consists of various transmission medium all under frequency spectrum are interfering each other.

* System Design

Every receiver has a minimum received power threshold that the received signal must achieve certain bit rate. The maximum bit rate would be decreased if the received signal power is lower than the threshold, hence, performance affected. A good performance from transmitter is important too as higher transmit output power can provide better performance.

* Antenna Type

Antenna gain is the power gain in comparison to an isotropic antenna which is measured in decibels (dBl). Omnispherical antenna is the most suitable device as it allows operation in any position. Antenna diversity is important in preventing multi-path fading.

* Coverage

Coverage play an important role in determining the speed. The distance between nodes, resistance to interferences and ability to keep connectivity in a wide range must take into consideration. The propagation of spectrum frequency and radio transmission may influenced by many factors. Discrete object such as wall or building may decrease the reflect signal. Environment can easily affect radio transmission and it is hard to predict the comportment of the system and define a range. One should have a good area which as closer as possible in order to get good signal.

* Bandwidth

Also known as the data rate supported by a network connection or interface. Bandwidth is not the only factor that contribute to speed in a network, but is considered a primary measure of network speed. Bandwidth represent the overall capacity in networking. The greater capacity of bandwidth will result in better performance result. Bandwidth is measure by the amount of data that pass through a network over a period of time which measure in bits per second (bps). Bandwidth can be distinguish between Actual Throughput and Theoretical Throughput.

* Theoretical Throughput

This is the bandwidth that every device was designed to be. For example, a standard dialup modem can reach the peak bandwidth of 56kbps. Ethernet network are theoretically build to support 100 Mbps of bandwidth.

* Actual Throughput

But, in practical, a standard modem or Ethernet network are unable to get their peak bandwidth respectively. This is due to the physical limitation and defective of telephone lines or LAN cable, signal leakage during transmission and others.


3.1 Bandwidth Measurement

In order to have efficient wireless LAN, there are some parameter that we need to take into consideration from time to time. This research topic took bandwidth and coverage as the two important parameters to keep a reliable, consistent and efficient wireless LAN.

Bandwidth Monitoring Software

It is difficult to determined the low quality of a network without any appropriate data. It might be the problem from company department switch, slow server, application software that consumed a big amount of bandwidth and others. With bandwidth monitoring software, one can solve the problem in much easier way. Bandwidth monitoring software can keep tracking bandwidth usage of network connections, devices or leased lines. It does not only allows to discern the actual amount of bandwidth being used, but also can track connectivity errors and trace usage trends, making network administrators life easier in order to balance and reroute the traffic. Administrator can also get alerted whether there are bandwidth threshold or network load issue through bandwidth monitoring software. Besides, bandwidth monitoring software is a helper and reminder to an network administrator to find out the problem of the connections, deliver better quality of service to user by being proactive and also avoid bandwidth and server performance bottlenecks.

In this research, a bandwidth monitoring software, namely PRTG Network Monitor had been tried out. PRTG Network Monitor provide a 30days free trial for the potential customer to have a clear survey or testing on their products for customers satisfaction. This is rather easy use of software with friendly interface.

There's a total of 12 notification can be shown. Different alert such as status alert, multiple condition alert, escalation alerts, alert scheduling, acknowledged alarms and others can be shown to alert user. Upon monitoring is done, PRTG will summarize the report in both HTML or PDF format. Specific sensor reports or overall sensor reports can be produce and exported for further usage.

3.2 Coverage Measurement

Many unreliable wirelessLAN are cause by throughput and coverage issues. The rate of user experience at variety of distances and locations is very important. Therefore, measurement in throughput and coverage in WLAN is a must to solve the problems.

Wireless LAN environment are divided into three categories:

  • Outdoor : A direct line of sight between access point and client, included outdoor campus coverage, large open buildings, or public area.
  • Open Office : not a direct line of sight between access point and client where at least two to three obstructions like wall or partition board. Examples include warehouse or meeting areas.
  • Closed Office : no direct line of sight between access point and client where at least one obstruction , which included buildings with a number of office or rooms with walls.

Above three categories have differ WirelessLAN coverage significant. Closed Office WLANs provide shortest range while outdoor WLANs provide longest range. Different construction architecture have differ impact on WLAN coverage issue. To benchmark a product performance, the same products need to be testing in several range and there different environment. This is to ensure the accurate and fair result. Many benchmark software can be use to measure Transmission Control Protocol (TCP) throughput either in uplink direction or downlink direction. Downlink TCP performance is most important metric as it reflects the common usage, such as web browsing and accessing email. Other application like video streaming used User Datagram Protocol (UDP) which the performance number will be higher than TCP performance number as there is lesser protocol involve in UDP.

Measurement Test Setup

In order to get the accurate and fair result, the same manufactured access point must pair with the same manufactured client.

  • Test example of same manufacturer pairing:
    • Test 1 : Vendor 1 access point with Vendor 1 client
    • Test 2 : Vendor 2 access point with Vendor 2 client
  • Test example where client device are tested with 3rd-party access point:
    • Test 1 : Vendor 3 access point with Vendor 1 client
    • Test 2 : Vendor 3 access point with Vendor 2 client
  • Test example where test configuration is interoperability being tested:
    • Test 1 : Vendor 1 access point with Vendor 1 client
    • Test 2 : Vendor 1 access point with Vendor 2 client.
    • Test 3 : Vendor 2 access point with Vendor 1 client.
    • Test 4 : Vendor 2 access point with Vendor 2 client.

The next step to determine a more fair measurement is to choose a set of test locations.

  • Choose one of the three environment and marked down the same access point and client location where they are tested.
  • Select a channel for testing and very the radio frequency environment on the selected channel is clear. Use a sniffer or client device to check that there are no access points or ad-hoc networks located on the same channel at the test area. For 802.11b and 802.11g, there will be no overlapping channel; channels with number spacing of 4 or less overlap and cause significant in-band interference. In 2.4GHz channel 1 overlap with channels, 2,3,4,5 and channel 6 overlaps with channels 2,3,4,5,6,7,8,9 and 10. There will be no overlap for 802.11a as the standard is 54 Mbps channels
  • Select at least 8 test locations at variety of locations and distance form the access point in the same environment. At least one of the test location should be at the limit of the coverage.
  • All wireless LAN have limit on signals that are too strong. Some WLAN products may actually produce low data rates at very close range, therefore the closest test point should not less than 5 feet apart.

The key of the measurement is repeatability. For every product tested, the access point, client locations, software setup, channel used, environment, test procedure must be the same.

4.0 Propose Solution

WirelessLAN technology is a surprising diffusion in telecommunications. WLAN hotspots is increasing and most of the mobile devices, like laptops, Personal Device Assistant (PDA) are equipped with IEEE 802.11 adapters. This indirectly increase the demand of wireless connectivity in the market.

4.1 Coverage and physical installation restrictions

Part of the end-user requirement is a desired coverage area, and possibly some physical restriction to go along with it. Physical restrictions, such as a lack of available electrical power and network connections, can be mundane. Some institutions may also require than their access points and antenna are hidden, this is simply to preserve the aesthetic appeal of the building.

It is often desirable to mount access points as high as possible. Access Points (APs) work best when they are above the obstruction that live on the floor. By mounting them above cubicles and other objects, it may make their signal go father more reliable. Some APs are mount on the wall or the ceiling tile.

Many commercial buildings are "dropped" ceilings, where the ceiling tile is suspended from the actual ceiling. Network wiring and electrical cables are placed above the ceiling tile, along with air ducts. In addition to APs, this would include any support equipment mounted up above the ceiling as well. Power injectors are often not plenum-rated because they usually be located safely in wiring closets.

4.2 The Fallback of 802.11b Interoperability

The 802.11b standards integrates a complex protocol for authentication of new devices on wireless network and for roaming between stations. The radio preamble sent at the beginning of every 802.11 packet is sent at the lowest radio speed due to interoperability requirements. or small packets, this preamble makes up a large percentage of the transmission time. As many small packets are sent to support roaming, authentication, acknowledgement of packets, utilization drops to a fraction of what would be available if larger chunks of data were being transmitted.

Since interoperability, high quality and low cost of 802.11b devices are strong incentives for using this technology in outdoor environments, several research organizations have studied ways to resolve the hidden node and effective bandwidth problems. One company, Karlnet Inc., has its TurboCell, which resolves the hidden node problem by centralizing control of the wireless network at the TurboCell access point or base station. The TurboCell access point uses a highly-optimized polling technique to tell remote wireless stations when they can transmit. To avoid problems associated with pure polling schemes, TurboCell also employs a "free for all" period to enable stations that have data available but are low in the polling queue to transmit without much delay. The "free for all" period allows a station that may not have transmitted for a long period of time to begin transmitting once again and move to a higher priority in the polling scheme. The determination of polling intervals based on a complex combination of factors is finely tuned and the result of years of research into wireless performance in production environments.

For performance-critical outdoor point-to-mulitpoint environments, optimal bandwidth usage is crucial. The TurboCell protocol remedies the effective bandwidth problems associated with roaming, authentication and long preamble by aggregating many small packets into a single SuperPacket for transmission over the wireless link.

5.0 Gantt Chart

6.0 Conclusion

Through this research topic, I have better understanding in how WirelessLAN especially in IEEE 802.11 operates. With all the special architecture of each 802.11 standards, each of them are useful in different time and place. Due to the popularity gain in WirelessLAN, therefore more studies on how to make wirelessLAN a more perfect and reliable should be carried out. Since this is a phase 1 in this project, there will be more methods or solutions to be discuss in order to solves all the imperfectness of the WirelessLAN.

7.0 Reference

  • Wireless Local Area Network (WLAN)
  • Kuran, M & Tugcu, T. (2007) A Survey on Merging Broadband Wireless Access Technologies, Computer Network.
  • Kanoksri Sarinnapakorn (March,2001) "High Rate" Wireless Local Area Networks
  • Valadas, R.T. Tavares, A.R. Duarte, A.M.deO. Moreira, A.C. Lomba, C.T. Aveiro Univ.; (Dec ,1998) Infrared physical layer of IEEE 802.11 standard for WLAN, Comunications Magazine, IEEE Ir.J.Mill, Spread Spectrum (SS) applications
  • Bradley Mitchell, The 802.11 family explained, Guide "About the Bluetooth SIG". Bluetooth SIG. Retrieved 2008-02-01.
  • Bluetooth (Oct, 2008) Kioskea,
  • Joseph Kahn (1997) Proceedings of the IEEE , Network Monitoring Company
  • E. Amaldi, A. Capone, M. Cesana, F. Malucelli, F. Palazzo Politecnico di Milano - DEI, WLAN Coverage Planning : Optimization Models and Algorithms
  • Jean-Paul Saindon (May,2002) Techniques to Resolve 802.11 and Wireless LAN Technology in Outdoor Environments
  • Matthew S.Gast (Apr, 2002) 802.11 Wireless Networks: The Definitive Guide, Second Eddition

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