CHAPTER TWO LIERATURE REVIEW 2.1 Introduction: 2.2Wimax

LIERATURE REVIEW

CHAPTER TWO

LIERATURE REVIEW

2.1 Introduction:

This chapter defines the project problem and reviews the related literature, in order to provide a frame work for the thesis. In this chapter the historical background, the undergoing studies and the promised research methods and approaches are reviewed and evaluated

On October 8th 2008 Baltimore [2] (Maryland state, USA) became the first city in the country where a full-scale commercial wireless broadband rollout (offered by Sprint and XOHM) means people can roam wherever they want and connect to the Internet with notebook computers and Mobile Internet Devices.

Dirik Williamson – Vice president of Nokia North American carrier sales- mentioned:

“The experience has been fantastic today in Baltimore just to walk out and be able to have that truly high speed experience without having to be in a hotspot”.

Also they stated in the grand opening that Baltimore is not the last and others cities are to follow up like Chicago, Washington DC and Boston.

2.2WiMAX Technology:

“The desire for bandwidth-intensive Internet access and other voice and data services has never been greater across all geographies and market segments despite the economic downturn of recent years and the air of uncertainty in the global telecommunications industry.” [3]

The number of internet users has increased hastily and therefore the demand as shown in Fig. 2.1.

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Fig. 2.1: Internet users

Wimax can provide the same high speed intensive applications that other traditional means of transmission provide for broadband applications like high speed data rates, voice, video and streaming media and now it can reach everyone. Generally for high speed access, there are three main alternatives, Fig. 2.2; each has its own limitations and challenges, these alternatives are:

Fig. 2.2: Broadband Access Alternatives

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1. E1 line:

The line data rate for E1 is 2.048 Mbit/s (full duplex) which is split into 32 time slots, each being allocated 8 bits in turn. It is a ideal for voice traffic because voice is sampled at the same 8khz rate so E1 line can carry 32 simultaneous voice conversions.

Expensive compared to other alternatives for the cost of installation and maintenance cost, problem with this type of broadband access is that the E1 line was originally developed to carry voice data with the advances of technology compromises were made but it’s not the most efficient, also the technology and the customers nowadays are favoring wireless access alternatives.

2. DSL (Digital subscriber line):

DSL or xDSL, is a family of technologies that provides digital data transmission over the wires of a local telephone network POTS (Plain Old Telephone Service) however it’s known that voice doesn’t occupy the entire bandwidth that the line provides in fact it only occupies a fraction therefore the bandwidth is divided into bands.

DSL typically works by dividing the frequencies used in a single phone line into two primary bands. The ISP data is carried over the high-frequency band 25 kHz and above whereas the voice is carried over the lower-frequency band 4 kHz and below

This type of broadband access is widely used in Sudan.

Mobility with DSL is an issue one cannot move freely (the issue was resolved with mDSL) but it is still an issue for other customers who are using different types of DSL another challenge is distance if one goes beyond a specified distance the speed will dramatically falls down i.e one must stay within coverage areas. Same as the above technology it is not satisfactory and the customers still need higher data rate with Quality of Service

3. Cable:

In this type of access television cables are used instead which provides a wider bandwidth and hence a higher data rate, cable modem is used.

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Cable modem is a type of modem that provides access to a data signal sent over the cable television infrastructure. Cable modems are primarily used to deliver broadband Internet access in the form of cable internet, taking advantage of the high bandwidth of a cable television network.

Challenges to be faced in this type of broadband access is the initial cost 1st Cable companies must buy the rights to provide the service and 2nd the cable has mobility restriction.

Andy Abramson [4] (editor of voip watch magazine) stated “With Wimax we create a ubiquitous access what does it mean? Basically meaning it goes everywhere and for everyone”

Wimax comes in to fill in the gaps by providing the ability of accessing anywhere one goes without restriction. It is developed to cover just about a circle of 50 km radius coverage area with a maximum data rate of 75Mb/s, it helps reducing the boundaries, meaning that instead of going to a particular place to access internet- Wi-Fi hotspots- one can get it everywhere. So in other words wimax is developed for a fast, reliable, un-restricted internet access anywhere within coverage areas.

2.3Operation Band:

The 802.16-2005 standards support the frequency range of 2 to 6 GHz, although other frequency bands can also be tolerated.

WiMAX operates in a mixture of licensed and unlicensed bands. The unlicensed bands are typically the 2.4 GHz and 5.8 GHz bands. Licensed spectrum provides operators control over the usage of the band, allowing them to build a high-quality network. The unlicensed band, on the other hand, allows independents to provide services for hotspots.

3.5 GHz and higher are defined as higher frequency bands.

Spectral allocations for wireless broadband vary by region; groundwork profiles focus on 2.3 GHz, 2.5 GHz, 3.5 GHz.

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Examples for frequency bands in different regions are presented in table 2.1[4]

Table2.1 WiMax bands of operation by regions

Region Frequency bands

Canada 2.3,2.5,3.5GHz

United states 2.3,2.5GHz

Latin America 2.5,3.5GHz

Middle East & Africa 3.5GHz

Europe 2.5,3.5GHz

Asia & Pacific 2.3,2.5,3.3,3.5GHz

Russia 2.3,2.5,3.5GHz

2.4 Wimax definition:

The new WiMAX radio technology – worldwide interoperability for microwave access – is based on wireless transmission methods defined by the IEEE 802.16 standard. WiMAX has been developed to replace broadband cable networks such as DSL and to enable mobile broadband wireless access.

The IEEE 802.16 standard for MAN (Metropolitan Area Network) consists of many technical concepts and the differences between the 802.16 standard and the other IEEE standard 802.11 – concerning Wi-Fi application can be summarized in table 2.2.

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Table 2.2: WiMax IEEE Standards [5]

802.11 (Wi-Fi) 802.16 (WiMax)

Range Optimized for users within a Up to 50 km range 100 meter radius But optimized for typical 7-10 km

Coverage Indoors Out doors

Channel 20MHz and fixed 1.5 MHz to 20MHz flexible bandwidth with frequency reuse

Bit rate 2.7 bps up to 54 Mbps 3.8 bps up to 75Mbps

2.5 Fading in WiMax:

All wireless communications techniques are subjected to suffer from the dilemma of fading even WiMax that uses OFDM (Orthogonal Frequency Division Multiplexing), although OFDM has resistance to self-symbol interference; still other problems are to be faced.

This project is mainly interested in fading. From the physics point of view, fading can be classified as:

a. Small-scale fading:

This type of fading can be observed over short distances along the receiving route and it is caused by the destructive and constructive addition of different multipath components. Large cities and indoor environments with much more reflecting surfaces will create a large number of multipath components, increasing thus the effects of this type of fading. On the other hand, in rural and suburban environments, small-scale fading is not as intense. Modern telecommunication systems such as WiMAX , can exploit the presence

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of small-scale fading by making use of antenna diversity schemes to increase channel throughput.

b. Large-scale fading:

This type of fading appears over much larger distances and it is typically caused by the shadowing introduced by obstacles such as buildings (outdoor) or people (indoor). Its amplitude is typically modeled in indoor environments by means of a lognormal distribution and it can be more or less overcome by using large fading margins in the receiver.

2.6 Throughput In WiMax:

Wimax uses OFDM (256) which is a technique for increasing the amount of information that can be carried over a wireless network. Using OFDM has many advantages, including high spectrum efficiency, resistance against multipath interference particularly in wireless communications, and ease of filtering out noise, the theoretical intensive explanation of OFDM will be intensively explained in the chapters that are yet to come.

Terry Wason Regional -Sales Director, India and S Asia, Wi-LAN Inc- [6] claimed that the throughput of Wimax is about 75Mbps on a 50 km radius and on a moving vehicle with the speed 160 kmps video streaming and file transfer can be at a speed of 20Mbps, on the other hand according to recent ‘’WiMAX system performance studies’’[7] WiMax throughput is found to be just a little over 7 Mbps at best when measured on a regular city area.

The reality in this discussion it is an either/or situation meaning that one can’t get both high data rate and distance at the same time.

In other words one will get high speed data rate while one is closer inside the coverage area where strong signals are received, but or if one is relatively far away from the center of the coverage area, high speed data rate cannot be maintained, one can still get a reasonable rate but not the same as before, data rate will decrease with distance due to the signal fading

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The truth is that WiMax provides an average on 2-4 Mbps on the down link and 0.5-1 Mbps on the uplink and of course it varies from one geographic position to another and it achieves its best performance when the antenna is in Line OF Sight (LOS) with the location, therefore WiMax antennas are usually installed on highest appropriate positions that can be found.

2.7 WiMax point to point & point to multi-points:

There are two types for a wireless WiMax connectivity: point-to-point and point-to- multipoint.[8]

2.7.1 Point-to-point (P2P) Point to point is used where there are two points in need for direct transmission between them; one is sender and one is receiver. P2P is designed 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.

2.7.2 Point-to-Multipoint (PMP) As seen in the fig (2.3), point-to-multipoint can be used for distribution. One base station can service hundreds of subscribers in terms of bandwidth and services offered

Fig2.3 P2P and PMP

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2.8WiMAX in today’s world:

Some heated arguments about the need of WiMAX and is it really going to replace Wi-Fi and other high Speed Data transfer technologies for example

“I don't need WiMAX for end delivery, I need it for fixed wireless Delivery, Wi-Fi works fine for that purpose” argued Graeme Gibson, CEO of Computers & Tele-Comm and he continued “ISP was able to provide 1.5 megabits-per-second service without suffering undue performance degradation in town” but Roger Marks, chairman of the IEEE 802.16 stated that “sure, you could use it as a WISP (Wireless ISP), but you have a real problem with scaling. As the number of users goes up, the efficiency goes down because the MAC(Media Access Control) wasn't designed for that environment” and he claimed that mobile WiMAX technology has received a huge boost in Asia, where the South Korean government announced that 802.16 work would be based on the portable Internet standard in that nation.[9]

The fact is Wimax as a new technology is promising to be very applicable in the few next years but it’s not coming into existence to replace the already working technologies and standards but to complement them and fill the missing gaps.

2.9 Channel modeling in WiMax:

2.9.1 Multi path modeling:

Multipath propagation is caused by multiple reception of the same signal; each replica of the signal takes a different path these different replicas arrive slightly delayed from one another, as an illustration fig 2.4

Fig 2.4 multi path phenomena

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When these replicas are combined at the receiver it results a signal that varies In amplitude and phase and polarization.

2.9.2 Multipath fading:

When signals are added it can be one of the following:

i. Constructive addition: This results in larger amplitude of the signal at the receiver.

ii. Destructive addition: it happens due to the phase difference of the combined signal which results in very small amplitude.

We can consider the radio channel as a system that converts the input signal into an output signal for that purpose a multi-path fading channel can be thought of as linear time variant.[10]

Now we should have a clear picture of what to do next on this project, shall follow the following steps:

1. To develop a simplified model of a fading channel.

Taking into account multipath effect.

These effects are very complex, so statistical models are used

Bear in mind that implementation of these models in the time domain is very computationally intensive.

2. Implement the above in wireless network simulation software.[10]

2.10 Simulation as a study methodology:

Computer simulation is used when there is intensive computational work is required to implement a mathematical model to study and observe the behavior of the system in hand.

Another advantage of simulation is that it is cheaper so instead of obtaining an expensive equipments and run tests on them easily computer simulation can be used to obtain results close enough to the actual results.

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Computer simulators can run for several minutes others can run for hours and even days. [11]

2.11 G=U Octave:

Octave is high level language that was created for intensive numerical computations using a command line interface for solving linear and nonlinear problems numerically, and for performing other numerical experiments using a language that is mostly compatible with Matlab software program.

Octave is an open source it can be modified easily and redistributed without licensing problem. [12]

2.11 Summary:

Technical terms were defined in this chapter and the undergoing studies were considered and evaluated a clear picture was drawn and models for the project were determined, now the project can be taken into the next chapter hence the frame work had been provided.