WiMAX has the potential to replace a number of existing telecommunications infrastructures. In a fixed wireless configuration it can replace the telephone company's copper wire networks, the cable TV's coaxial cable infrastructure while offering Internet Service Provider (ISP) services. In its mobile variant, WiMAX has the potential to replace cellular networks. How do we get there?

What is WiMAX or Worldwide Interoperability for Microwave Access? WiMAX is an Institute of Electrical and Electronics Engineers (IEEE, see http://www.ieee.org) standard designated 802.16-2004 (fixed wireless applications) and 802.16e-2005 (mobile wire-less). The industry trade group WiMAX ForumTM (http://www.wimaxforum.org ) has defined WiMAX as a "last mile" broadband wireless access (BWA) alternative to cable modem service, telephone company Digital Subscriber Line (DSL) or T1/E1 service.


Fixed WiMAX


Figure 2 Fixed WiMAX offers cost effective point to point and point to multi-point solutions

What makes WiMAX so exciting is the broad range of applications it makes possible but not limited to broadband internet access, T1/E1 substitute for businesses, voice over Internet protocol (VoIP) as telephone company substitute, Internet Protocol Television (IPTV) as cable TV substitute, backhaul for Wi-Fi hotspots and cell phone towers, mobile telephone service, mobile data TV, mobile emergency response services, wireless backhaul as substitute for fiber optic cable.

WiMAX provides fixed, portable or mobile non-line-of sight service from a base station to a subscriber station, also known as customer premise equipment (CPE). Some goals for WiMAX include a radius of service coverage of 6 miles from a WiMAX base station for point-to-multipoint, non-line-of-sight (see following pages for illustrations and definitions) service. This service should deliver approximately 40 megabits per second (Mbps) for fixed and portable access applications. That WiMAX cell site should offer enough bandwidth to support hundreds of businesses with T1 speeds and thousands of residential customers with the equivalent of DSL services from one base station.


Mobile WiMAX


Figure 3 Mobile WiMAX allows any telecommunications to go mobile

Mobile WiMAX takes the fixed wireless application a step further and enables cell phone-like applications on a much larger scale. For example, mobile WiMAX enables streaming video to be broadcast from a speeding police or other emergency vehicle at over 70 MPH. It potentially replaces cell phones and mobile data offerings from cell phone operators such as EvDo, EvDv and HSDPA. In addition to being the final leg in a quadruple play, it offers superior building penetration and improved security measures over fixed WiMAX. Mobile WiMAX will be very valuable for emerging services such as mobile TV and gaming.

WiMAX is not Wi-Fi


Figure 4 Where Wi-Fi covers an office or coffee shop, WiMAX covers a city

One of the most often heard descriptions of WiMAX in the press is that it is "Wi-Fi on steroids". In truth, it is considerably more than that. Not only does WiMAX offer exponentially greater range and throughput than Wi-Fi (technically speaking 802.11b, although new variants of 802.11 offer substantial improvements over the "b" variant of 802.11), it also offers carrier grade quality of service (QoS) and security. Wi-Fi has been notorious for its lack of security. The "b" variant of 802.11 offered no prioritization of traffic making it less than ideal for voice or video. The limited range and throughput of Wi-Fi means that a Wi-Fi service provider must deploy multiple access points in order to cover the same area and service the same number of customers as one WiMAX base station (note the differences in nomenclature). The IEEE 802.11 Working group has since approved upgrades for 802.11 security and QoS.



Converged voice and data easy as FM radio?


Figure 5 With WiMAX, converged voice and data can be as easy as FM radio

Visualize turning on an FM radio in your office. You receive information (news, weather, sports) from that service (the FM radio station) and hardware (the FM radio with attached antenna). WiMAX can be described as being somewhat similar. In place of a radio station there is a base station (radio and antenna) that transmits information (internet access, VoIP, IPTV) and the subscriber has a WiMAX CPE that receives the services. The major difference is that with WiMAX the service is two-way or interactive.


Wireless Architectures
by Carl Townsend — last modified 2006-08-14 09:45 PM
The following section will provide a simple overview of wireless concepts and nomenclature to help the reader understand how WiMAX works and will assist the reader in com-municating with the WiMAX industry.


Wireless architecture: point-to-point and point-to-multipoint

There are two scenarios for a wireless deployment: point-to-point and point-to-multipoint.


Figure 7: Point-to point and point-to-multipoint configurations

Point-to-point (P2P)

Point to point is used where there are two points of interest: one sender and one receiver. This is also a scenario for backhaul or the transport from the data source (data center, co-lo facility, fiber POP, Central Office, etc) to the subscriber or for a point for distribution using point to multipoint architecture. Backhaul radios comprise an industry of their own within the wireless industry. As the architecture calls for a highly focused beam between two points range and throughput of point-to point radios will be higher than that of point-to-multipoint products.

Point-to-Multipoint (PMP)

As seen in the figure above, point-to-multipoint is synonymous with distribution. One base station can service hundreds of dissimilar subscribers in terms of bandwidth and services offered.


Line of sight (LOS) or Non-line of sight (NLOS)?




Figure 8: The difference between line of sight and non-line of sight

Earlier wireless technologies (LMDS, MMDS for example) were unsuccessful in the mass market as they could not deliver services in non-line-of-sight scenarios. This limited the number of subscribers they could reach and, given the high cost of base stations and CPE, those business plans failed. WiMAX functions best in line of sight situations and, unlike those earlier technologies, offers acceptable range and throughput to subscribers who are not line of sight to the base station. Buildings between the base station and the subscriber diminish the range and throughput, but in an urban environment, the signal will still be strong enough to deliver adequate service. Given WiMAX's ability to deliver services non-line-of-sight, the WiMAX service provider can reach many customers in high-rise office buildings to achieve a low cost per subscriber because so many subscribers can be reached from one base station.

WiMAX Radios
by Carl Townsend — last modified 2006-08-14 09:50 PM
At the core of WiMAX is the WiMAX radio. A radio contains both a transmitter (sends) and a receiver (receives). It generates electrical oscillations at a frequency known as the carrier frequency (in WiMAX that is usually between 2 and 11 GHz). A radio might be thought of as a networking device similar to a router or a bridge in that it is managed by software and is composed of circuit boards containing very complex chip sets.

WiMAX architecture, very simply put, is built upon two components: radios and antennas. Most WiMAX products offer a base station radio separate from the antenna. Conversely, many CPE devices are also two piece solutions with an antenna on the outside of the building and subscriber station indoors as illustrated in the figure below.



Figure 9: Most WiMAX solutions use radios separate from antennas

The chief advantage of this is that the radio is protected from extremes of heat cold and humidity all of which detract from the radio's performance and durability. In addition, having the antenna outdoors optimizes the link budget (performance of the wireless connection) between transmitter and receiver especially in line of sight scenarios. The antenna is connected to WiMAX radio via a cable known as a "pigtail". One simple rule for wireless installations: keep the pigtail as short as possible. Why? The longer the pigtail the more signal is lost between the antenna and the radio. The popular LMR-400 cable, for example will lose about 1 dB (pronounced "dee-bee" for decibel, a measure of signal strength) for every 10 feet of cable. Very simply put, if an antenna is placed at the top of a 20-story building and the radio in the wiring closet on the ground floor, one may lose all signal in the cable.


Radios and Enclosures


Radio placement

The photo above shows the WiMAX radio deployed in an enclosure. Note from left to right: a) copper grounding cable on the inside of the enclosure b) Ethernet connection to the data source c) Heliax "pigtail" to the antenna (Heliax is a heavy duty, lightning resistant cable) d) 110v power via an APC UPS (note black box in top right hand corner of enclosure.
What are some strategies to ensure the antenna can be as high as possible to take advan-tage of line-of-sight topologies where ever possible while keeping the pigtail as short as possible? One approach is to co-locate the radio on or near the roof with the antenna in an enclosure. Considerations for enclosures include: a) security and b) weather resistance-how hot or cold can your radio gets and still function?

Sheet metal or fiberglass enclosures with a lock provide security. Next, it is necessary to determine how well suited the radio is for local atmospherics (hot or cold). Most Wi-MAX radios are rated as operating between -20 degrees Fahrenheit to 120 degrees F at the upper end. If you will be operating in locations that will exceed those parameters you need an enclosure that will shield your radio form those extremes. As the radio will generate its own heat, surrounding it with insulation will ensure the temperature of the radio will not suffer from sub-zero temperatures.


WiMAX Antennas
by Carl Townsend — last modified 2006-08-14 09:51 PM




WiMAX antennas, just like the antennas for car radio, cell phone, FM radio, or TV, are designed to optimize performance for a given application. The figure above illustrates the three main types of antennas used in WiMAX deployments. From top to bottom are an omni directional, sector and panel antenna each has a specific function.

Omni directional antenna



Figure 12: An omni-directional antenna broadcasts 360 degrees from the base station

Omni directional antennas are used for point-to-multipoint configurations. The main drawback to an omni directional antenna is that its energy is greatly diffused in broad-casting 360 degrees. This limits its range and ultimately signal strength. Omni directional antennas are good for situations where there are a lot of subscribers located very close to the base station. An example of omni directional application is a WiFi hotspot where the range is less than 100 meters and subscribers are concentrated in a small area.

Sector antennas



Figure 13: Sector antennas are focused on smaller sectors

A sector antenna, by focusing the beam in a more focused area, offers greater range and throughput with less energy. Many operators will use sector antennas to cover a 360-degree service area rather than use an omni directional antenna due to the superior per-formance of sector antennas over an omni directional antenna.


Panel antennas



Figure 14: Panel antennas are most often used for point-to-point applications

Panel antennas are usually a flat panel of about one foot square. They can also be a configuration where potentially the WiMAX radio is contained in the square antenna enclosure. Such configurations are powered via the Ethernet cable that connects the ra-dio/antenna combination to the wider network. That power source is known as Power over Ethernet (PoE). This streamlines deployments as there is no need to house the radio in a separate, weatherproof enclosure if outdoors or in a wiring closet if indoors. This configuration can also be very handy for relays.

Subscriber Stations
by Carl Townsend — last modified 2006-07-23 04:36 PM
The technical term for customer premise equipment (CPE) is subscriber station. The gen-erally accepted marketing terms now focus on either "indoor CPE" or "outdoor CPE". There are advantages and disadvantages to both deployment schemes as described below.

Outdoor CPE


Figure 15: An outdoor CPE device. Note mounting brackets for outdoor mounting on roof or side of building
Source Airspan

Outdoor CPE, very simply put, offers somewhat better performance over indoor CPE given that WiMAX reception is not impeded by walls of concrete or brick, RF blocking glass or steel in the building's walls. In many cases the subscriber may wish to utilize an outdoor CPE in order to maximize reception via a line of sight connection to the base sta-tion not possible with indoor CPE. Outdoor CPE will cost more than indoor CPE due to a number of factors including extra measures necessary to make outdoor CPE weather re-sistant.


Indoor CPE


Figure 16: Indoor WiMAX CPE (Airspan EasyST)- object on left) with telephone handset and VoIP adapter

The most significant advantage of indoor over outdoor CPE is that it is installed by the subscriber. This frees the service provider from the expense of "truck roll" or installation. In addition, it can be sold online or in a retail facility thus sparing the service provider a trip to the customer site. Indoor CPE also allows a certain instant gratification for the subscriber in that there is no wait time for installation by the service provider. Currently, many telephone companies require a one month wait between placement of order and in-stallation of T1 or E1 services. In addition, an instant delivery of service is very appeal-ing to the business subscriber in the event of a network outage by the incumbent service provider


Objections to WiMAX
by Carl Townsend — last modified 2006-07-23 04:50 PM
A discussion of WiMAX is not complete without taking on objections to the technology. Before any one can sell a high technology product, they must first sell the customer on the technology.



Figure 20: Objections to WiMAX are best understood via the provisions built into the WiMAX Physical and MAC layers
Source: IEEE

Technology sales people invariably encounter objections to the technology they are sell-ing.
The primary objections to WiMAX are:
1. Interference: Won't interference from other broadcasters degrade the quality of the WiMAX service?
2. Quality of Service (QoS): Wireless is inherently unstable so how can it offer voice and video services?
3. Security: Is WiMAX secure? Can anything wireless be secure?
4. Reliability: Nothing can be as reliable as the telephone company's service (rumored to offer "five 9s" of reliability or 5 minutes of downtime per year).

The answers to those objections are best understood via the Physical (known as the PHY, pronounced "fi") and Medium Access Control (MAC pronounced "mac") Layers. The WiMAX Working Group no doubt were aware of these objections based on experiences with earlier wireless technologies (Wi-Fi, LMDS, MMDS, CDMA, GSM) and have en-gineered WiMAX to fix failures of past wireless technologies.

Purpose
The purpose of Wi-Fi is to hide complexity by enabling wireless access to applications and data, media and streams. The main aims of Wi-Fi are the following:
• make access to information easier
• ensure compatibility and co-existence of devices
• eliminate cabling and wiring
• eliminate switches, adapters, plugs, pins and connectors.

Uses
A Wi-Fi enabled device such as a PC, game console, mobile phone, MP3 player or PDA can connect to the Internet when within range of a wireless network connected to the Internet. The coverage of one or more interconnected access points — called a hotspot — can comprise an area as small as a single room with wireless-opaque walls or as large as many square miles covered by overlapping access points. Wi-Fi technology has served to set up mesh networks, for example, in London.[1] Both architectures can operate in community networks.
In addition to restricted use in homes and offices, Wi-Fi can make access publicly available at Wi-Fi hotspots provided either free of charge or to subscribers to various providers. Organizations and businesses such as airports, hotels and restaurants often provide free hotspots to attract or assist clients. Enthusiasts or authorities who wish to provide services or even to promote business in a given area sometimes provide free Wi-Fi access. Metropolitan-wide Wi-Fi (Muni-Fi) already has more than 300 projects in process.[2] There were 879 Wi-Fi based Wireless Internet service providers in the Czech Republic as of May 2008.[3][4]
Wi-Fi also allows connectivity in peer-to-peer (wireless ad-hoc network) mode, which enables devices to connect directly with each other. This connectivity mode can prove useful in consumer electronics and gaming applications.
When wireless networking technology first entered the market many problems ensued for consumers who could not rely on products from different vendors working together. The Wi-Fi Alliance began as a community to solve this issue — aiming to address the needs of the end-user and to allow the technology to mature. The Alliance created the branding Wi-Fi CERTIFIED to reassure consumers that products will interoperate with other products displaying the same branding.
Many consumer devices use Wi-Fi. Amongst others, personal computers can network to each other and connect to the Internet, mobile computers can connect to the Internet from any Wi-Fi hotspot, and digital cameras can transfer images wirelessly.
Routers which incorporate a DSL-modem or a cable-modem and a Wi-Fi access point, often set up in homes and other premises, provide Internet-access and internetworking to all devices connected (wirelessly or by cable) to them. One can also connect Wi-Fi devices in ad-hoc mode for client-to-client connections without a router.
As of 2007 Wi-Fi technology had spread widely within business and industrial sites. In business environments, just like other environments, increasing the number of Wi-Fi access-points provides redundancy, support for fast roaming and increased overall network-capacity by using more channels or by defining smaller cells. Wi-Fi enables wireless voice-applications (VoWLAN or WVOIP). Over the years, Wi-Fi implementations have moved toward "thin" access-points, with more of the network intelligence housed in a centralized network appliance, relegating individual access-points to the role of mere "dumb" radios. Outdoor applications may utilize true mesh topologies. As of 2007 Wi-Fi installations can provide a secure computer networking gateway, firewall, DHCP server, intrusion detection system, and other functions

Advantages and challenges


A keychain size Wi-Fi detector.
[edit] Operational advantages
Wi-Fi allows LANs (Local Area Networks) to be deployed without cabling for client devices, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.
In 2008, wireless network adapters are built into most modern laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in even more devices. Wi-Fi has become widespread in corporate infrastructures.
Different competitive brands of access points and client network interfaces are inter-operable at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards compatible. Wi-Fi is a global set of standards. Unlike mobile telephones, any standard Wi-Fi device will work anywhere in the world.
Wi-Fi is widely available in more than 220,000 public hotspots and tens of millions of homes and corporate and university campuses worldwide.[5] WPA is not easily cracked if strong passwords are used and WPA2 encryption has no known weaknesses. New protocols for Quality of Service (WMM) make Wi-Fi more suitable for latency-sensitive applications (such as voice and video), and power saving mechanisms (WMM Power Save) improve battery operation.

Limitations
Spectrum assignments and operational limitations are not consistent worldwide. Most of Europe allows for an additional 2 channels beyond those permitted in the U.S. for the 2.4 GHz band. (1–13 vs. 1–11); Japan has one more on top of that (1–14). Europe, as of 2007, was essentially homogeneous in this respect. A very confusing aspect is the fact that a Wi-Fi signal actually occupies five channels in the 2.4 GHz band resulting in only three non-overlapped channels in the U.S.: 1, 6, 11, and three or four in Europe: 1, 5, 9, 13 can be used if all the equipment on a specific area can be granted not to use 802.11b at all, even as fallback or beacon. Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (0.1 W).

Reach
Due to reach requirements for wireless LAN applications, power consumption is fairly high compared to some other low-bandwidth standards. Especially Zigbee and Bluetooth supporting wireless PAN applications refer to much lesser propagation range of <10m (ref. e.g. IEEE Std. 802.15.4 section 1.2 scope). Range is always making battery life a concern.
Wi-Fi networks have limited range. A typical Wi-Fi home router using 802.11b or 802.11g with a stock antenna might have a range of 32 m (120 ft) indoors and 95 m (300 ft) outdoors. Range also varies with frequency band. Wi-Fi in the 2.4 GHz frequency block has slightly better range than Wi-Fi in the 5 GHz frequency block. Outdoor range with improved (directional) antennas can be several kilometres or more with line-of-sight.

Wi-Fi performance decreases roughly quadratically as the range increases at constant radiation levels.

Mobility


Speed vs. Mobility of wireless systems: Wi-Fi, HSPA, UMTS, GSM
Because of the very limited practical range of Wi-Fi, mobile use is essentially confined to such applications as inventory taking machines in warehouses or retail spaces, barcode reading devices at check-out stands or receiving / shipping stations. Mobile use of Wi-Fi over wider ranges is limited to move, use, move, as for instance in an automobile moving from one hotspot to another. Other wireless technologies are more suitable as illustrated in the graphic

Threats to security
The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be easily breakable even when correctly configured. Wi-Fi Protected Access (WPA and WPA2), which began shipping in 2003, aims to solve this problem and is now available on most products. Wi-Fi Access Points typically default to an "open" (encryption-free) mode. Novice users benefit from a zero-configuration device that works out of the box, but this default is without any wireless security enabled, providing open wireless access to their LAN. To turn security on requires the user to configure the device, usually via a software graphical user interface (GUI). Wi-Fi networks that are open (unencrypted) can be monitored and used to read and copy data (including personal information) transmitted over the network, unless another security method is used to secure the data, such as a VPN or a secure web page. (See HTTPS/Secure Socket Layer.)

Channel pollution
Standardization is a process driven by market forces. Interoperability issues between non-Wi-Fi brands or proprietary deviations from the standard can still disrupt connections or lower throughput speeds on all user's devices that are within range, to include the non-Wi-Fi or proprietary product. Moreover, the usage of the ISM band in the 2.45 GHz range is also common to Bluetooth, WPAN-CSS, ZigBee and any new system will take its share.
Wi-Fi pollution, or an excessive number of access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other access points by others, caused by overlapping channels in the 802.11g/b spectrum, as well as with decreased signal-to-noise ratio (SNR) between access points. This can be a problem in high-density areas, such as large apartment complexes or office buildings with many Wi-Fi access points. Additionally, other devices use the 2.4 GHz band: microwave ovens, security cameras, Bluetooth devices and (in some countries) Amateur radio, video senders, cordless phones and baby monitors, all of which can cause significant additional interference. General guidance to those who suffer these forms of interference or network crowding is to migrate to a Wi-Fi 5 GHz product, (802.11a, or the newer 802.11n if it has 5 GHz support) as the 5 GHz band is relatively unused and there are many more channels available. This also requires users to set up the 5 GHz band to be the preferred network in the client and to configure each network band to a different name (SSID). It is also an issue when municipalities,[6] or other large entities such as universities, seek to provide large area coverage. This openness is also important to the success and widespread use of 2.4 GHz Wi-Fi.


Standard devices


An embedded RouterBoard 112 with U.FL-RSMA pigtail and R52 mini PCI Wi-Fi card widely used by wireless Internet service providers (WISPs) in the Czech Republic.


OSBRiDGE 3GN - 802.11n Access Point and UMTS/GSM Gateway in one device.


USB wireless adaptor
A wireless access point connects a group of wireless devices to an adjacent wired LAN. An access point is similar to a network hub, relaying data between connected wireless devices in addition to a (usually) single connected wired device, most often an ethernet hub or switch, allowing wireless devices to communicate with other wired devices.
Wireless adapters allow devices to connect to a wireless network. These adapters connect to devices using various external or internal interconnects such as PCI, miniPCI, USB, ExpressCard, Cardbus and PC card. Most newer laptop computers are equipped with internal adapters. Internal cards are generally more difficult to install.
Wireless routers integrate a WAP, ethernet switch, and internal Router firmware application that provides IP Routing, NAT, and DNS forwarding through an integrated WAN interface. A wireless router allows wired and wireless ethernet LAN devices to connect to a (usually) single WAN device such as cable modem or DSL modem. A wireless router allows all three devices (mainly the access point and router) to be configured through one central utility. This utility is most usually an integrated web server which serves web pages to wired and wireless LAN clients and often optionally to WAN clients. This utility may also be an application that is run on a desktop computer such as Apple's AirPort.
Wireless network bridges connect a wired network to a wireless network. This is different from an access point in the sense that an access point connects wireless devices to a wired network at the data-link layer. Two wireless bridges may be used to connect two wired networks over a wireless link, useful in situations where a wired connection may be unavailable, such as between two separate homes.
Wireless range extenders or wireless repeaters can extend the range of an existing wireless network. Range extenders can be strategically placed to elongate a signal area or allow for the signal area to reach around barriers such as those created in L-shaped corridors. Wireless devices connected through repeaters will suffer from an increased latency for each hop. Additionally, a wireless device connected to any of the repeaters in the chain will have a throughput that is limited by the weakest link between the two nodes in the chain from which the connection originates to where the connection ends.


Distance records
Electronics portal

Distance records (using non-standard devices) include 382 km (237 mi) in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about 3 MB of data between mountain tops of El Aguila and Platillon.[7][8] The Swedish Space Agency transferred data 310 km (193 mi), using 6 watt amplifiers to reach an overhead stratospheric balloon. [9]

Embedded systems


Embedded serial-to-Wi-Fi module
Wi-Fi availability in the home is on the increase.[10] This extension of the Internet into the home space will increasingly be used for remote monitoring.[citation needed] Examples of remote monitoring include security systems and tele-medicine. In all these kinds of implementation, if the Wi-Fi provision is provided using a system running one of operating systems mentioned above, then it becomes unfeasible due to weight, power consumption and cost issues.
Increasingly in the last few years (particularly as of early 2007), embedded Wi-Fi modules have become available which come with a real-time operating system and provide a simple means of wireless enabling any device which has and communicates via a serial port.[11] This allows simple monitoring devices – for example, a portable ECG monitor hooked up to a patient in their home – to be created. This Wi-Fi enabled device effectively becomes part of the internet cloud and can communicate with any other node on the internet. The data collected can hop via the home's Wi-Fi access point to anywhere on the internet. [12]
These Wi-Fi modules are designed so that designers need minimal Wi-Fi knowledge to wireless-enable their products.


Network security
Main article: Piggybacking (internet access)
During the early popular adoption of 802.11, providing open access points for anyone within range to use was encouraged to cultivate wireless community networks;[13] particularly since people on average use only a fraction of their upstream bandwidth at any given time. Later, equipment manufacturers and mass-media advocated isolating users to a predetermined whitelist of authorized users—referred to as "securing" the access point.[dubious – discuss]

Wikinews has related news:
Florida man charged with stealing WiFi
Measures to deter unauthorized users include suppressing the AP's SSID broadcast, allowing only computers with known MAC addresses to join the network, and various encryption standards. Suppressed SSID and MAC filtering are ineffective security methods as the SSID is broadcast in the open in response to a client SSID query and a MAC address can easily be spoofed. If the eavesdropper has the ability to change his MAC address, then he can potentially join the network by spoofing an authorized address.
WEP encryption can protect against casual snooping, but may also produce a misguided sense of security since freely available tools such as AirSnort or aircrack can quickly recover WEP encryption keys. Once it has seen 5-10 million encrypted packets, AirSnort can determine the encryption password in under a second;[14] newer tools such as aircrack-ptw can use Klein's attack to crack a WEP key with a 50% success rate using only 40,000 packets. The newer Wi-Fi Protected Access (WPA) and IEEE 802.11i (WPA2) encryption standards resolve most of the serious weaknesses of WEP encryption.
Attackers who have gained access to a Wi-Fi network can use DNS spoofing attacks very effectively against any other user of the network, because they can see the DNS requests made, and often respond with a spoofed answer before the queried DNS server has a chance to reply.[15]
One serious issue with wireless network security is not just encryption, but access to the network (signal reception). With wired networking it is necessary to get past either a firewall or the security guard & locked doors. With wireless it is only necessary to get reception and spend as long as you want, comfortably out of (easy) reach of the network owner. Most business networks protect sensitive data and systems by attempting to disallow external access. Thus being able to get wireless reception (and thus possibly break the encryption) becomes an attack vector on the network as well.[16]
Recreational logging and mapping of other people's access points has become known as wardriving. It is also common for people to use open (unencrypted) Wi-Fi networks as a free service, termed piggybacking. Indeed, many access points are intentionally installed without security turned on so that they can be used as a free service. These activities do not result in sanctions in most jurisdictions, however legislation and case law differ considerably across the world. A proposal to leave graffiti describing available services was called warchalking. In a Florida court case, owner laziness was determined not to be a valid excuse. [17]
Piggybacking is often unintentional. Most access points are configured without encryption by default, and operating systems such as Windows XP SP2 and Mac OS X may be configured to automatically connect to any available wireless network. A user who happens to start up a laptop in the vicinity of an access point may find the computer has joined the network without any visible indication. Moreover, a user intending to join one network may instead end up on another one if the latter's signal is stronger. In combination with automatic discovery of other network resources (see DHCP and Zeroconf) this could possibly lead wireless users to send sensitive data to the wrong middle man when seeking a destination (see Man-in-the-middle attack). For example, a user could inadvertently use an insecure network to login to a website, thereby making the login credentials available to anyone listening, if the website is using an insecure protocol like HTTP, rather than a secure protocol like HTTPS


City wide Wi-Fi
Further information: Municipal wireless network

Wikibooks has a book on the topic of
Nets, Webs and the Information Infrastructure
Sunnyvale, California became the first city in the United States to offer city wide free Wi-Fi, [20]Corpus Christi, Texas had offered free Wi-Fi until May 31, 2007 when the network was purchased by Earthlink.[21] Philadelphia is also trying to save the Earthlink wifi for its city.[22] New Orleans had free city wide Wi-Fi shortly after Hurricane Katrina.[23] City wide Wi-Fi is available in nine cities in the UK, Newcastle Upon Tyne being the first UK city host, others include Leeds, Liverpool, Norwich and London.[24] Other cities, such as the Minneapolis metro area, have a large number of Wi-Fi hotspots so you can receive good signals anywhere, even if from different sources. In Europe, the City of Luxembourg has a city-wide Wi-Fi network.
In Latin America, Mexico City downtown has a public Wi-Fi network. Also, many public squares in towns of Puerto Rico are offering Wi-Fi Internet access.
As compared to Wireless Mesh, WiMax provides over 4 times the number of subcarriers over a variable bandwidth of 1 to 28 MHz. With more subcarriers and a variable length guard interval, the spectral efficiency has increased from 15% to 40% compared to Wireless Mesh. The error vector magnitude of Wireless Mesh is higher than WiMax. This makes WiMax have a longer range. Wireless Mesh transmits and receives functions on the same channel where as WiMax transmits and receives functions at a different channel and at a different time. In Wireless Mesh the output power is virtually fixed however in WiMax the devices closer to the base stations emit less output power whereas the ones further away emit maximum output power.
Wi-Fi can overpower WiMax if the city is meshed with hot spots. A very easy way to do it would be if mobile carriers integrate hot spots with their mobile base stations as WiMax chips are not as integrated as the Wi-Fi chips.

] Origin and meaning of the term "Wi-Fi"
The term "Wi-Fi" suggests "Wireless Fidelity", comparing with the long-established audio recording term "High Fidelity" or "Hi-Fi", and "Wireless Fidelity" has often been used in an informal way, even by the Wi-Fi Alliance itself, but officially the term does not mean anything.
"Wi-Fi" was coined by a brand consulting firm called Interbrand Corporation that had been hired by the Alliance to determine a name that was "a little catchier than 'IEEE 802.11b Direct Sequence'."[25][26][27]Interbrand invented "Wi-Fi" as simply a play-on-words with "Hi-Fi", as well as creating the yin yang style Wi-Fi logo.
The Wi-Fi Alliance initially complicated matters by stating that it actually stood for "Wireless Fidelity", as with the advertising slogan "The Standard for Wireless Fidelity",[26] but later removed the phrase from their marketing. The Wi-Fi Alliance's early White Papers still held in their knowledge base: "… a promising market for wireless fidelity (Wi-Fi) network equipment."[28] and "A Short History of WLANs." The yin yang logo indicates that a product had been certified for interoperability.[29]
The Alliance has since downplayed the connection to "Hi-Fi". Their official position is that it is merely a brand name that stands for nothing in particular, and they now discourage the use of the term "Wireless Fidelity".


Wi-Fi Alliance
Main article: Wi-Fi Alliance
The Alliance promotes standards with the aim of improving the interoperability of wireless local area network products based on the IEEE 802.11 standards. The Wi-Fi Alliance, a consortium of separate and independent companies, agrees on a set of common interoperable products based on the family of IEEE 802.11 standards.[30] The Wi-Fi Alliance certifies products via a set of defined test-procedures to establish interoperability. Those manufacturers with membership of Wi-Fi Alliance and whose products pass these interoperability tests can mark their products and product packaging with the Wi-Fi logo.[31]

1. If you’re annoyed by Internet Explorer’s incessant barking that you’ve lowered your security settings (like, if you’re a non-paranoid expert), launch “gpedit.msc” from either the Run command or Start Search field, navigate through Local Computer Policy / Computer Configuration / Administrative Templates / Windows Components / Internet Explorer. In the rightmost pane, double-click “Turn off the Security Settings Check feature” and set it to Enabled.
2. If Internet Explorer’s Information Bar also annoys you, you can turn it off (again) in the Group Policy Object Editor (gpedit.msc) through Local Computer Policy / Computer Configuration / Administrative Templates / Windows Components / Internet Explorer / Security Features. In the rightmost pane, double-click “Internet Explorer Processes” and set it to Disabled. Hallelujah!
3. I’ve just mentioned two tweaks that are buried inside the Group Policy Editor. Jim Allchin pointed out that there’s a Group Policy Settings Reference spreadsheet available. Makes for great weekend reading.
4. Read the Background on Backgrounds if you’re a performance junkie. Don’t set your wallpaper through Internet Explorer ever again! Now that Windows supports JPG wallpapers, there’s absolutely no need (or excuse) for using BMPs anymore.
5. If you insist on keeping UAC (User Account Control) turned on for yourself, you might care to make the elevation prompts a bit less visually jarring. Brandon told me about this one, even though I have UAC turned off. Launch the Local Security Policy manager (secpol.msc), and navigate through Security Settings / Local Policies / Security Options. In the rightmost pane, scroll to the bottom and double-click “User Account Control: Switch to the secure desktop when prompting for elevation.” Disable it, and you can keep UAC turned on without getting turned off by the embarrassingly craptacular Aero Basic theme.
6. Vista can send you emails! The Computer Management tool can still be accessed by right-clicking “Computer” and selecting “Manage” from the menu. However, now you can attach a task to any event. Try navigating through System Tools / Event Viewer / Windows Logs / Application. Now, go ahead and select an event - then look to the rightmost pane and click “Attach Task to This Event.” Name it whatever, describe it however, click through the next step, then in the Action step, you’ll see the “Send an e-mail” option.
7. The Windows Task Manager gives you a lot more troubleshooting information in Vista. Flip to the Processes tab, and in the View menu, click “Select Columns” and add Description, Command Line, and Image Path Name. Moreover, when you right-click a process, you can select either “Go to Service(s)” or “Open File Location.” These are all long overdue options.
8. This one’s interesting. Open up the Date and Time Control Panel applet. Flip to the “Additional Clocks” tab. There, you can configure two more clocks from different time zones. They’ll appear in the tooltip when you hover over the Taskbar clock. No additional software (or silly sidebar widgets) necessary.
9. Applicable in other versions of Windows, I’m going to throw it in here for good measure. Create a shortcut to RegSvr32.exe in your SendTo folder. To get there quickly, enter “shell:sendto” in the Run command dialog or Start Search field. Now, when you wanna register a DLL or OCX file with the system, you can select it/them and “Send To” the RegSvr32 shortcut.
10. I figured I’d round out my first set of Windows Vista tips and tricks with a tiny bit of eye candy. It doesn’t beat Picasa, but the Windows Photo Gallery is better than nothing. Once it’s indexed all your photos, click the icon next to the Search field and turn on the “Table of Contents.” That’s kinda nifty.

Lucent Technologies - Unleashing the CDMA advantage in WCDMA
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Unleashing the CDMA advantage in
WCDMA
Lucent Technologies - Unleashing the CDMA advantage in WCDMA
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Unleashing the CDMA advantage in WCDMA
The air interface selected for UMTS is Wideband Code Division Multiple Access (WCDMA). This
solution offers operators a number of significant advantages over alternative technologies,
including increased network capacity, longer battery life for terminals and enhanced privacy for
users. However, such benefits come at the cost of additional network complexity. This is why a
background in GSM deployment is no guarantee of success in UMTS. However, many of the
complexities associated with UMTS are familiar to those with a background in CDMA
deployment. Operators moving to UMTS need to draw on the experience of technicians and
vendors with a track record in CDMA.
Lucent estimates that operator spending on the radio access component of UMTS networks will
account for more than 60 per cent of total capital expenditure. For this reason a robust
network implementation is critical if operators are to maximise infrastructure investment. Such
an approach will allow them to optimise capacity levels and enable the multimedia services
that are a key element of the UMTS value proposition.
CDMA is the industry’s most sophisticated air interface. WCDMA adds to its complexity.
However, high performance radio access is critical to the success of UMTS and code division
schemes allow network operators to make the most of their scarce radio spectrum allocation.
For example, in the context of 2G systems, it is estimated that a cdmaOne network can offer
30 per cent more capacity than a GSM network with the same spectrum allocation. The history
of wireless has repeatedly demonstrated that capacity is invariably consumed faster than the
industry predicts. With the imminent arrival of bandwidth hungry high-speed data applications,
the advantages of the efficiencies inherent in code division technology become apparent.
Such efficiencies can best be grasped when we contrast CDMA with GSM - the most successful
implementation of time division and frequency division technology.
Imagine you are making a mobile call via a GSM network. If another individual were making a
call in a neighbouring cell on the same frequency, the co-channel interference created would
disrupt your call. The task of frequency planning is therefore of high importance in GSM: it
ensures that channels using similar frequencies are kept apart and interference minimised.
GSM allows cell capacity to be readily determined and this means that GSM network planning
is relatively straightforward. The downside is that, unless the available radio frequencies can be
re-used closer together and repeatedly within the network, spectral efficiency can be limited.
In contrast to the frequency planning requirements of GSM, CDMA networks employ universal
frequency re-use. This means that all subscribers using a UMTS network transmit
simultaneously within the same wideband radio channel. This removes the restriction that each
cell employs only a limited number of channels, although it creates the potential for significant
co-channel interference.
In CDMA networks ‘spread spectrum’ techniques combine the transmission from an individual
user with a much faster signal. This process distributes the user’s signal over the whole of the
available wideband radio channel. Individual transmissions are identified by means of a unique
spreading code allocated by the radio network controller. Each transmission is ultimately
Lucent Technologies - Unleashing the CDMA advantage in WCDMA
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reassembled using an identical code to that used in the spreading process.
This spread spectrum solution offered by CDMA has no impact on other transmissions on the
same network, each of which is allocated its own unique spreading code. As far as other users
are concerned, such signals simply appear as low-level noise. So while there is the potential for
increased co-channel interference, the spread spectrum technique actually makes the CDMA air
interface more robust than other air interfaces.
However, it is much more difficult to determine cell capacity in CDMA networks than in their
GSM counterparts. The problem is evident in the term ‘soft capacity’ that is often used to
describe CDMA cells. This is because in a CDMA network, capacity is dependent on the
average level of interference between users. As more connections are made into the network
the overall level of interference increases; this in turn affects the call quality of every user
connected to the network. Those users furthest from the base station tend to receive the
greatest amount of interference and, at some point, could be forced below a signal-to-noise
threshold that would normally guarantee acceptable service.
This is a feature of CDMA networks known as ‘cell breathing’: the effective service area
expands and contracts according to the number of users connected. Overlap-regions between
cells (which are known as ‘handover areas’) need careful planning and management. Cell
translations and databases must be configured to ensure that handover areas are of optimal
size and users furthest from base stations can be successfully ‘handed over’ to neighbouring
cells with lighter traffic loads. If these handover areas are too small, mobiles at the edge of a
cell will not receive support from the neighbour cells in time. This will result in too much
interference and ultimately a dropped call. If the handover area is set too large then too many
mobiles will receive multi-cell support, creating unnecessary links into the network that strain
call processing resources and reduce capacity.
In a CDMA network, mobiles operating at the edge of a cell must be simultaneously supported
by the surrounding cells. In this way they become a source of signal strength rather than of
interference. Such support – which is known as a ‘soft handover’ - is not required in GSM,
where only one cell at a time is required to support a call. However, GSM network planners
face a different challenge in the shape of what is known as a ‘hard handover’. In a GSM
network, the mobile terminal must change frequencies during the handover between cells.
When the terminal is instructed to re-tune to a new frequency there is a momentary period
during which the user is disconnected from a traffic channel. This is the point at which the call
is most vulnerable to being dropped by the network.
Handover complexity in CDMA networks is further increased when multiple wideband carriers
are involved. In dense urban areas, several wideband channels may be employed to increase
capacity. A lower capacity region utilising only one wideband channel (a ‘common carrier’)
often surrounds such an area. In this situation there is a need for a cross-carrier handover - the
CDMA version of hard handover. To avoid dropped calls, handovers must be triggered very
precisely at the boundary of the handover region. Lucent’s experience with cdmaOne (IS-95)
networks has demonstrated that successful handovers are crucial to realising CDMA network
performance. This equally applies to WCDMA in UMTS, which must optimally execute soft and
hard handovers in order to deliver uninterrupted services.
Lucent Technologies - Unleashing the CDMA advantage in WCDMA
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CDMA network performance is highly dependent on the quality of several fundamental
algorithms. Handover is one. Further examples include speech compression and power control:
Speech compression is used to lower the bit rate at which information must be transmitted on
the traffic channel while still being understood at the receiving end. Lower bit rates are
important because they correlate directly with lower transmission power that in turn reduces
interference. Speech is compressed to the lowest possible link bit rate while still maintaining
voice quality. Lucent led the industry in defining the initial vocoder for the IS-95 standard in
cdmaOne networks. It also made significant contributions to the enhanced variable rate coder
deployed in today’s CDMA networks.
Power control over mobile terminal transmissions is a crucial factor in a system that allows all
users to share a common radio channel. Power control must be both fast and accurate to cope
with continually changing conditions on a network. UMTS will yield enhanced voice capacity in
relation to that found in 2G networks. It will also supply a mix of voice and data services, and
data users must be allowed to receive brief, controlled bursts of interference in order to achieve
higher data rates. IS-95 power control is only partly dictated by standards, so Lucent has
continually refined its proprietary algorithms to enhance network performance: this expertise
has led to further refinements for UMTS.
However sophisticated the air interface, capacity will be lost if the radio access network is not
correctly planned and optimised. Antenna orientation, forward power adjustments, handover
translations and neighbour lists are all part of this tuning process. Cell planning and
optimisation tools like Lucent’s Ocelot take into account propagation effects, irregular network
layout and traffic distribution to work out the best antenna configuration for each cell.
It has been found that network coverage can be improved by up to 12 per cent and capacity
by up to 60 per cent over traditional design techniques. In reality, a trade-off between better
coverage and capacity is likely to be the strategy applicable to most situations. The key benefit
to operators is that the optimisation can be carried out before deployment, virtually eliminating
the need for drive testing. Such a process normally involves weeks of taking measurements and
making antenna adjustments in the field. By contrast, Ocelot™ allows networks to be brought
on-line much sooner, so that an operator can start generating revenue from the earliest
opportunity.
To conclude, CDMA air interface technology, basic algorithms and cell planning techniques are
radically different to those used in GSM. Operators must expect their potential UMTS vendor to
demonstrate both technical leadership and deployment experience in today’s CDMA markets.
Only then can they expect to fully realise the levels of radio performance required by
tomorrow’s 3G services.

THIS IS ABT CDMA


CDMA Introduction

CDMA Cellular Radio Systems Research

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	Cellular services are now being used every day by millions of people worldwide. The number of customers requiring such services is increasing exponentially, and there is a demand for integration of a variety of multimedia services. The range of services includes short messaging, voice, data, and video. Consequently, the bit rate required for the services varies widely from just 1.2 kbps for paging up to several Mbps for video transmission. Furthermore, supporting such a wide range of data rates with flexible mobility management increases network complexity dramatically. The CDMA is a digital modulation and radio access system that employs signature codes (rather than time slots or frequency bands) to arrange simultaneous and continuous access to a radio network by multiple users. Contribution to the radio channel interference in mobile communications arises from multiple user access, multipath radio propagation, adjacent channel radiation and radio jamming. The spread spectrum system’s performance is relatively immune to radio interference. Cell sectorisation and voice activity used in CDMA radio schemes provide additional capacity compared to FDMA and TDMA. However, CDMA still has a few drawbacks, the main one being that capacity (number of active users at any instant of time) is limited by the access interference. Furthermore, Near-far effect requires an accurate and fast power control scheme. The first cellular CDMA radio system has been constructed in conformity with IS-95 specifications and is now known commercially as cdmaOne.
	Packet Data over GSM, GPRS, and EGPRS There is increasing demand for data traffic over mobile radio. The mobile radio industry has to evolve the current radio infrastructures to accommodate the expected data traffic with the efficient provision of high-speed voice traffic. The General Packet Radio Service (GPRS) is being introduced to efficiently support high-rate data over GSM. GPRS signalling and data do not travel through GSM network. The GPRS operation is supported by new protocols and new network nodes: Serving GPRS support node (SGSN) and Gateway GPRS support node (GGSN). One prominent protocol used to tunnel data through IP backbone network is the GPRS tunnel protocol (GTP). GPRS obtains user profile data using location register database of GSM network. GPRS supports quality of service and peak data rate of up to 171.2 kbps with GPRS using all 8 timeslots at the same time. GPRS uses the same modulation as that used in GSM, that is Gaussian Minimum Shift Keying (GMSK) with 4 coding schemes. GPRS packetises the user data and transports it over 1 to 8 radio channel timeslots using IP backbone network. The Enhanced Data Rates for GSM Evolution (EDGE) employs an Enhanced GPRS (EGPRS) to support data rate up to 384 kbps through optimised modulation. EGPRS support 2 modulation schemes, namely GMSK with 4 coding schemes and 8-PSK with 5 coding schemes. Unlike GPRS where header and data are encoded together, headers are encoded separately in EGPRS.
	Packet Data over CDMA: IS-95B, and W-CDMA The IS-95 CDMA system is a narrow band radio system. Bandwidth is limited to 1.25 MHz and a chip rate of 1.2288 Mcps. The system is intended to provide voice and low bit rate data service using circuit-switching techniques. Data rate varies from 1.2 kbps to 9.6 kbps. Forward (base station to mobile) and reverse (mobile to base station) link structures are different and each is capable of distinctive capacity. Forward transmission is coherent and synchronous while the reverse link is asynchronous. The 'chanellisation' in each link is achieved by using 64- chip orthogonal codes, including provision for pilot, synchronisation, paging, and network access. Consequently, the number of active users able to simultaneously access the network is limited by the level of interference, service provisions and the number of 'channels' available. In IS-95B, an active mobile always has a fundamental code channel at 9.6 kbps and when high data rate is required, the base station assign the mobile up to 7 supplementary code channels. Thus peak data rate is up to 76.8 kbps. Data rate is controlled at the base station and conveyed to mobile through the supplementary channel assignment message. The Wideband CDMA (W-CDMA) system is the major standard in the next-generation Global Mobile Telecommunications standard suite IMT-2000. The W-CDMA supports high data rate transmission, typically 384 kbps for wide area coverage and 2 Mbps for local coverage for multimedia services. Thus W-CDMA is capable of offering the transmission of voice, text, data, picture (still image) and video over a single platform. However, in addition to the drawbacks arising from the mobile environment and multiple access interference, high bit rate transmission causes Inter-symbol interference (ISI) to occur. The ISI therefore has to be taken into account during transmission. The W-CDMA has 2 versions: frequency division duplex (FDD) and time division duplex (TDD). The FDD version of W-CDMA will operate in either of the following paired bands: Uplink: 1920 - 1980 MHz Downlink: 2110 - 2170 MHz Uplink: 1850 - 1010 MHz Downlink: 1930 - 1990 MHz The 3GPP architecture of the Universal Mobile Telecommunications System (UMTS) is composed of IP-based core network (CN) connected to the user equipment through UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN consists of a set of radio network subsystem comprising a radio controller and one or more node base station. The network controller is responsible for the handover decisions that require signalling to the user equipment. Each subsystem is responsible for the resources of its set of cells and each node B has one or more cells. 3GPP Release 2000 on the architecture for an all IP mobile networks proposed 2 reference architectures. The 1st option is based on packet technologies and IP telephony for simultaneous real time and non real time wireless mobile services. The 2nd option support the IP based services and also support the release 99 circuit switched terminals.
	Multi-Carrier CDMA system Multi-carrier modulation (MCM) is a data transmission technique where several subcarriers are employed to transport the user’s data stream signal. Originally this technique was implemented using a bank of analogue Nyquist filters which provide a set of continuous-time orthogonal basis functions. Today using very fast and cost effective digital signal processors, multi-carrier modulation can be implemented using discrete Fourier transform (DFT) as the set of orthogonal subcarriers. This makes the technique very attractive. Multi-Carrier Modulation (MCM) improves system capacity by making transmission more robust to frequency selective fading and enhances user spectral efficiency. The main drawbacks are: Difficult subcarriers' synchronisation in fading transmissions. Sensitivity to frequency offset is more pronounced than for a single carrier. Sensitivity to non-linear amplification (peak factor problem). To gain the advantages of both schemes (CDMA & MCM), a combination known as multi-carrier CDMA ( MC-CDMA ) was proposed in 1993 taking after both CDMA & MCM schemes. An MC-CDMA transmitter spreads the original data stream in the frequency domain over different subcarriers using a given spreading code. In this system the subcarriers convey the same information at one time. The MC-CDMA offers better frequency diversity to combat frequency selective fading. Figure 1. MC-CDMA transmitter Figure 2. Spectrum of MC-CDMA signal The simplicity of the multi-carrier system is an important aspect in a cellular system especially for the down link receiver (mobile station). The modulation-demodulation is done by IDFT - DFT. A wavelet-based system can be used instead of DFT for the multi-carrier modulation. Wavelet transform has a property of time-frequency multi resolution. By choosing the right wavelet function and scaling function, the system can achieve the optimum resolution according to need. Digital communication systems can be viewed as general transmultiplexer systems, which consist of synthesis part and analysis part. The element, which plays an important role in characterisation of the system, is the filter set used in both synthesis and analysis parts. The time-frequency properties of these filters, i.e. time spread and frequency spread, will determine the type of communication systems (TDMA, FDMA, CDMA, OFDM, MC-CDMA, MC-DS-CDMA). Consequently, the key decision is how to design and optimise this set of filters according to their applications. One of the optimisation results for multi-carrier systems is to use one of perfect reconstruction quadrature mirror filter (PR-QMF) types which is called discrete wavelet multi tone (DWMT). Using this DWMT system for MC-CDMA cellular system, yields the following advantages: lower interchannel interference more robust against multipath fading more robust against narrow band interference or jamming signal From the above advantages, it can be expected that this wavelet-based MC-CDMA system will provide higher spectral efficiency and more capacity.
	Figure 3. A PSD Comparison of WB-MC-CDMA and FB-MC-CDMA
	Reference [1] A. Fukusawa, et.al, "Wideband CDMA system for Personal Radio Communication", IEEE Comm. Magazine, Oct 1996, p.116 - 123. [2] K. Rajan et.al, Wireless PCS, McGraw Hill, 1997. [3] TIA, TIA/EIA/IS-95 interim standard, July 1993. [4] William C.Y.Lee. Mobile Cellular Telecommunications, McGraw Hill, 2nd Edition, 1995. [5] T Novosad, "A New Family of Quadriphase Sequences for CDMA", IEEE Trans. on Information Theory, Vol. 39, No.3, p. 1083 - 1085, May 1993. [6] PV Kumar et.al, " Large Families of Quaternary Sequences with Low Correlation", IEEE Trans. on information Theory, Vol. 42, No.2, p. 579 - 592, May 1993. [7] N Zhang, SW Golomb, "Polyphase Sequence with Low Correlation", IEEE Trans. on Information Theory, Vol. 39, No.3, p. 1085 - 1089, May 1993. [8] S Moshavi, "Multi-User Detection for DS-CDMA Communication", IEEE Comm. Magazine, Oct 1996, p.124 - 136. [9] ES Sousa. Spread Spectrum for PCS. IEEE GTC, London, 1996. [10]AJ Viterbi. CDMA Cellular Systems. New York, McGraw Hill, 1995. [11] EA Sourour, M Nakagawa, "Performance of Orthogonal Multicarrier CDMA In A Multipath Fading Channel", IEEE Transaction on Communication, Vol. 44 No.3, Mar 1996. [12] S Kondo , LB Milstein, "Performance of Multicarrier DS CDMA System", IEEE Transaction on Communication, Vol. 44 No.2 Feb 1996. [13] R. Prasad, S. Hara. "An Overview of Multi-Carrier CDMA", Proc. IEEE ISSSTA‘96, Mainz, Germany, Sept 1996. [14] JG. Proakis. Digital Communications. New York, Mc Graw Hill, 1995. [15] K Fazel, GP. Fetweiss. Multi-Carrier Spread Spectrum. Dordrecht (Netherland), Kluwer Academic Publishers, 1997. [16] TM Schmidl , DC Cox. "Robus Frequency and Timing Synchronisation". IEEE Transaction on Communication, Vol.45 No.12. December 1997 [17]KH. Chang et. al. "Performance Analysis Of Wavelet Based MC-CDMA". Proc. IEEE ISSSTA'96, Sept 1996. [18]K. Fazel et.al. "A Flexible And High Performance Cellular Mobile Communications System Based On Orthogonal Multi-Carrier SSMA". Wireless Personal Communications 2, Kluwer Academic Publisher, 1995. [19] A. Fukasawa et.al. "Wideband CDMA System For Personal Radio Communications", IEEE Communications Magazine, October 1996. [20]S. Kaiser. "Trade-Off between Channel Coding and Spreading in Multi-Carrier CDMA Systems". Proc. IEEE ISSSTA'96, Sept 1996. [21] M. Luise , R. Reggiannini. "Carrier Frequency Acquisition and Tracking for OFDM Systems". IEEE Trans. on Communications, Vol.44 No.11 November 1996. [22]N. Yee , JP. Linnartz. "MC-CDMA: A New Spreading Technique for Communication over Multipath Channel". Final Report, 1993-1994. [23] GW. Wornell. "Signal Processing with fractals : A Wavelet-based Approach", Prentice Hall , 1996. [24] A.N. Akansu, M.V. Tazebay, M.J. Medley and P.K. Das, "Wavelet & Subband Transforms: Fundamentals & Communication Applications", IEEE Comm. Magazine, Dec 1997. [25] P. Steffen, P. Heller, R. A. Gopinath and C. S. Burrus, "Theory of Regular M-band Wavelet Bases", IEEE Trans. On Signal Processing, Special Issue on Wavelets, Dec 1993. [26] R. Gross, M. Tzannes, S. Sandberg, H. Padir and X. Zhang, "Discrete Wavelet Multitone (DWMT) System for Digital Transmission over HFC Links", Proc. SPIE, Vol. 2609, Nov 1995. [27] S. Hara and R.Prasad, "An Overview of Multi-Carrier CDMA", IEEE Comm. Magazine, Dec 1997. [28] J.G. Proakis, Digital Communications, New York, Mc Graw Hill, 1995. [29] N. Yee , J.P. Linnartz and G. Fettweis, "Multicarrier CDMA In Indoor Wireless Radio Networks", Proc. IEEE PIMRC’93, Yokohama, Japan, Sept 1993. [30] K.H. Chang, X.D. Lin and M.G. Kyeong, "Performance Analysis of Wavelet Based MC-CDMA", Proc. IEEE ISSSTA'96, Sept 1996. [31] S.D. Sandberg and M.A. Tzannes. "Overlapped Discrete Multitone Modulation for High Speed Copper Wire Communications", IEEE Journal on Selected Areas in Communications, Vol.13 No.9, Dec 1995. [32] M.A. Tzannes, M.C. Tzannes and H.L. Resnikoff, "The DWMT: A Multicarrier Transceiver for ADSL Using M-band Wavelet Transforms'', ANSI T1E1.4 Committee Contribution No. 93-067, Miami, FL, Mar 1993. [33] M.A. Tzannes, M.C. Tzannes, J.G. Proakis and P.N. Heller, "DMT Systems, DWMT Systems, and Digital Filter Banks'', Proc. IEEE ICC'94, New Orleans, USA, 1994. [34] A.N. Akansu, P. Duhamel, X. Lin and M de Courville, "Orthogonal Transmultiplexers in Communication: A Review", IEEE Trans. on Signal Processing, 1998. [35] A.N. Akansu, M.V. Tazebay and R.A. Haddad. "A New Look at Digital Orthogonal Transmultiplexers for CDMA Communications", IEEE Trans. on Signal Processing, pp. 263-267, Jan. 1997. [36] S.B. Weinstein and P.M. Ebert. "Data Transmission by Frequency Division Multiplexing Using the Discrete Fourier Transform", IEEE Trans. on Communication Tech, Vol. Com-19, Oct. 1971. [37] A. Scaglione, G. B. Giannakis and S. Barbarossa. "Minimum Redundancy Filterbank Precoders for Blind Channel Identification Irrespective of Channel Nulls'', Proc. IEEE WCNC'99, New Orleans, USA, Sept. 1999. [38] G. Strang and TQ Nguyen, Wavelets and Filter Banks, Wellesley-Cambridge Press, 1997. [39] TQ Nguyen, "Biorthogonal Cosine-Modulated Filter Banks'', Proc. ICASSP'96, 1996. [40] S Nanda, K Balachandran, and S Kumar, "Adaptation techniques in wireless packet data services", IEEE Comm. Magazine, Jan 2000, Vol. 38, No.1, P.54 – 64.

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Hi I Am Student of B.sc(IT) from St Xavier College