local area networks-wimax

8/8/2019 Local Area Networks-WiMAX

1/47

Lappeenranta University of Technology 9.2.2009

Faculty of Technology Management

Department of Information Technology

Laboratory of Communications Engineering

Local Area Networks special course seminar

IEEE 802.16 WiMAX

Antti Knutas / 0279186 Jussi Laakkonen / 0237801

Ruotsalaisenraitti 3 B 16

53850 Lappeenranta 53850 Lappeenranta

GSM: 0408270139 GSM: 050 324 7642


2/47

ABSTRACT

Lappeenranta University of TechnologyFaculty of Technology Management

Department of Information Technology

Laboratory of Communications Software Engineering

Antti Knutas and Jussi Laakkonen

IEEE 802.16 WiMAX

Local Area Networks special course seminar.

2009

47 pages, 8 figures and 3 tables.

Keywords: WiMAX, 802.16, performance, applications

WiMAX, a wireless Metropolitan Area Network technique that has been released in 2001 and

developed actively since. WiMAX is developed by Institute of Electrical and Electronics Engineersand devices are certified by WiMAX Forum. Current version of WiMAX is 802.16e that was

released in 2005, it supports full mobility while previous version, 802.16d supported only fixedconnections.

WiMAX provides connectivity over very long distances when direct point-to-point links are usedon high frequencies. With point-to-multipoint networking on lower frequencies WiMAX can be

used on over ten kilometer radius and therefore can compete with other techniques that are meantfor similar purposes. The actual throughput of WiMAX is also fairly high when compared to other

techniques providing mobile broadband connections. Differences between WiMAX and ADSL,

Flash-OFDM, UMTS and WLAN are explained and some real life performance comparisonbetween WiMAX and these techniques is presented.

In this document the layer model of WiMAX is introduced in detail and the possibilities of WiMAX

are being explained. The real life performance that is based on research results is compared to

numbers presented by developing and certifying organizations.

The possibilities that mobile WiMAX can provide are explained and some analysis about possibleusages of WiMAX are presented including replacement and addition scenarios. In addition to these

some real life applications and usages of WiMAX are explained, using WiMAX as backhaul

network is one of the most used applications of WiMAX.

ii


3/47

Table of Contents

ABBREVIATIONS..............................................................................................................................3

1 INTRODUCTION............................................................................................................................6

2 WIMAX OPERATION....................................................................................................................7

2.1 Standards...................................................................................................................................7

2.2 Network topologies...................................................................................................................8

2.3 Layer architecture.....................................................................................................................9

2.3.1 Convergence sublayer.....................................................................................................10

2.3.2 Medium Access Control Common Part Sublayer...........................................................10

2.3.3 Security Sublayer............................................................................................................11

2.3.4 Physical layer..................................................................................................................13

2.3.5 Multiple Input, Multiple Output antenna techniques .....................................................14

2.3.6 Duplexing methods.........................................................................................................15

2.3.7 Modulation in licenced frequencies between 10 and 66 GHz.........................................16

2.3.8 Modulation in licenced frequencies between 2 and 11 GHz...........................................16

2.3.9 Modulation in licence free frequencies between 2 and 11 GHz.....................................17

2.4 Network reference model........................................................................................................17

3 LIMITATIONS OF WIMAX.........................................................................................................19

3.1 Distances and speeds of different network topologies............................................................19

3.2 Actual performance.................................................................................................................20

3.3 Base station coverage..............................................................................................................21

3.4 Currently available frequencies..............................................................................................22

4 WIMAX VERSUS OTHER TECHNIQUES.................................................................................23

4.1 Competing techniques.............................................................................................................23

4.1.1 ADSL..............................................................................................................................24

4.1.2 Flash-OFDM...................................................................................................................24

4.1.3 UMTS..............................................................................................................................25

4.1.4 WLAN.............................................................................................................................26

4.2 Mobile WiMAX compared to other techniques.....................................................................27

4.2.1 Performance and usage comparison................................................................................28

4.2.2 Comparison of network efficiency..................................................................................29

4.2.3 Mobile WiMAX, replacement or addition......................................................................30

5 APPLICATIONS............................................................................................................................32

1


4/47

5.1 Last Mile Broadband Connectivity Potential......................................................................32

5.2 WiMAX Backbones................................................................................................................33

5.3 WiMAX and 3GPP Interworking...........................................................................................34

5.4 WiMAX Around the World....................................................................................................34

6 CONCLUSION..............................................................................................................................37

7 REFERENCES...............................................................................................................................38

2


5/47

ABBREVIATIONS

3G 3rd Generation

3GPP 3rd Generation Partnership Project

AAS Adaptive Antenna System

ADSL Asymmetric Digital Subscriber Line

AES Advanced Encryption Standard

AK Authorization Key

AP Access Point

ARQ Automatic Repeat reQuest

ASN Access Service Network

ASP Application Service Provider

ATM Asynchronous Transfer Mode

BPSK Bit Phase Shift Keying

BE Best Effort

BS Base Station

CAP Carrierless Amplitude Phase Modulation

CPS Common Part Sublayer

CS Convergence Sublayer

CSN Connectivity Service Network

DAMA Demand Assigned Multiple Access

DES Data Encryption Standard

DFS Dynamic Frequency Selection

DMT Discrete Multi-tone

DoS Denial of Service

DSL Digital Subscriber Line

DSLAM Digital Subscriber Line Access Multiplexer

EAP Extensible Authentication Protocol

EBF Eigen Beamforming

ErtPS Extended real-time Polling Services

EVDO Evolution Data Optimized

FDD Frequency Division Duplex

FICORA Finnish Communications Regulatory Authority

3


6/47

Flash-OFDM Fast Low-latency Access with Seamless Hand-off, Orthogonal Frequency

Division Multiplexing

FFT Fast Fourier Transform

HSPA High Speed Packet Access

IEEE Institute of Electrical and Electronics Engineers

IP Internet Protocol

ISM Industry, Science and Medical

LAN Local Area Network

LOS Line-of-sight

MAC Medium Access Control

MAN Metropolitan Area Network

MIMO Multiple Input, Multiple OutputMiTM Man in The Middle

MRT Maximum Ratio Transmission

MS Mobile Station

NAP Network Access Provider

NLOS Non line-of-sight

nrtPS Non real-time Polling Services

NSP Network Service Provider

OFDM Orthogonal Frequency Division Multiplexing

OFDMA Orthogonal Frequency Division Multiple Access

P2P Point-to-point

PAN Personal Area Network

PDU Protocol Data Unit

PKCS Public-key Cryptography Standard

PKM Privacy Key Management

PMP Point-to-multipoint

QoS Quality of Service

QAM Quadrature Amplitude Modulation

QPSK Quadrature Phase Shift Keying

RSA Rivest, Shamir & Adleman

RSSI Received Signal Strength Indication

rtPS Real-time Polling Services

S-OFDMA Scalable Orthogonal Frequency Division Multiple Access

4


7/47

SAP Service Access Point

SC Single Channel

SM-MIMO Spatial Multiplexing Multiple Input, Multiple Output

SS Subscriber Station

STBC Space Time Block Coding

TDD Time Division Duplex

TDM Time Division Multiplexing

TDMA Time Division Multiple Access

UGS Unsolicited Grant Services

UMTS Universal Mobile Telecommunications System

VoIP Voice over Internet Protocol

W-CDMA Wideband Code Division Multiple AccessWAN Wide Area Network

WiBro Wireless Broadband

WiMAX Worldwide Interoperability for Microwave Access

WLAN Wireless Local Area Network

5


8/47

1 INTRODUCTION

WiMAX stands for Worldwide Interoperability for Microwave Access, in general WiMAX is a

Metropolitan Area Network (MAN) technology that provides wireless access for last-mile solutions

providing layer-2 connectivity. Operational range of WiMAX is 50 km at maximum with fixed

connections with visual connections and roughly 20 km without visual connection. Current versions

of WiMAX support full mobility and handovers including data transmissions at vehicular speeds.

Nowadays in addition to higher frequency ranges of 10 to 66 GHz there is a mobile standard for use

of frequencies beneath 6GHz. Technical details of WiMAX will be shown in the next section of this

document. In some cases WiMAX is referred as third generation mobile broadband technique.

WiMAX is defined in IEEE (Institute of Electrical and Electronics Engineers) 802.16 standard,

devices are certified by WiMAX Forum that is a non-profitable organization similar to Wi-Fi

Alliance. WiMAX Forum includes companies such as Intel, Cisco and several others.

Overall WiMAX performance can be considered good, the figures presented by standard and

WiMAX Forum promise a lot. But the real performance isn't always what the standard states.

Multiple different research results about performance and operating distances (and conditions) have

been published. The results are presented in section 3.2 of this document and the actual

performance is compared to other similar techniques in section 4.2.

The security of WiMAX (with IEEE 802.16e additions) can be considered to be good. It is not very

prone to DoS (Denial of Service) attacks, MiTM (Man in The Middle) attacks could be prevented

and data is encrypted with proper methods. Key exchange and authentication methods that are

currently used can also be considered to be good (at least no research results proving otherwise was

found). These will be explained in section 2.3.3 of this document.

Currently there are multiple ways to use WiMAX, like connecting two networks to each other and

providing wireless broadband for users. Connections can be with or without line-of-sight, with

direct point-to-point links or the base station can provide connections for multiple subscribers on

certain area. WiMAX can be used to form the whole network infrastructure or it can be used as an

backhaul network for other network technologies to use. This will be presented in detail on further

sections of this document.

6


9/47

2 WIMAX OPERATION

In following sections the standard versions and WiMAX functionality (layer model) is explained

along with some research results concerning security of WiMAX. Possible networking topologies

are also explained and a reference model provided by WiMAX Forum is presented.

2.1 Standards

WiMAX is defined in IEEE 802.16 standard [1], first version was released in 2001. This standard

introduced the usage of licenced frequencies from 10 to 66 GHz for WiMAX operation. Due to the

short wavelength of the selected frequency range it was necessary to have direct visual contact

between devices, in other words line-of-sight (LOS) was required. Also the multipath propagation

was not allowed. The possible usages of WiMAX were broadened with 802.16a standard [2] in

2003 that introduced licenced frequencies below 11 GHz for WiMAX operation. This removed the

requirement for LOS due to the longer wavelength that allows the signals to pass through solid

objects, also the multipath propagation was seen as a possible benefit for WiMAX operation. At this

point the standard contained only point-to-point specification for fixed WiMAX .

Throughout years the standard was gradually updated and in 2004 the first standard introducing real

usage of WiMAX was released, 802.16-2004 [3] (or 802.16d). This standard was an replacement

for older standards, it introduced the usage of WiMAX in fixed systems only. This standard is

currently considered as the first release of WiMAX standard and is regarded as basis for WiMAX

compatibility. New frequencies for WiMAX were introduced: licence free frequencies below 11

GHz (most commonly frequencies from 5 to 6 GHz). In addition new mechanisms for physical and

Medium Access Control (MAC) layers are introduced, also new network topologies: point-to-multipoint and mesh were introduced at this point of standard development.

In 2005 WiMAX standard got its most important amendment, 802.16e [4] that introduced

mechanisms and protocols that allow mobility (proper handover mechanisms with re-authentication

support and power saving methods for mobile devices) in WiMAX networks. This updated also the

previous standard to support Subscriber Stations (SS) that move at vehicular speeds (120 km/h).

This standard is called as mobile WiMAX and it operates on frequencies from 2 to 6 GHz that are

7


10/47

not licenced. Also new security mechanisms were introduced, these fixed the vulnerabilities that

were found from IEEE 802.16d.

2.2 Network topologies

WiMAX supports three different network topologies: point-to-point (P2P), point-to-multipoint

(PMP) and Mesh. Each of these is used for different purposes on different frequency ranges, these

topologies are defined in IEEE 802.16d [3]. In figure 1 there are examples of P2P link and PMP

topology, in this figure P2P link is used to connect two Base Stations (BS) to each other and the

another BS uses PMP topology to make the connection available for multiple users in certain area.

P2P is used when WiMAX operates on higher licenced frequencies (10 66 GHz) and also on

lower licenced frequencies (2 11 GHz). As it is named it is used for direct connections only,

connected devices must have a visual connection to each other and the transmitting antennas must

be directional. Normally this means that there can be only 2 devices connected to each other, it is

possible to add multiple antennas to one BS that could provide connections to more than one BS or

SS. P2P topology is used only in fixed WiMAX networks and there is a single channel reserved for

every connection.

Point-to-multipoint is used when multiple subscriber stations are needed to be connected to a single

BS and they do not have visual connection with BS (non line-of-sight, NLOS). PMP is used in both

8

Figure 1: WiMAX P2P links and PMP topology example [5]


11/47

fixed (licenced frequencies between 2 and 11 GHz) [3] and mobile WiMAX (licence free

frequencies between 2 and 11 GHz) that is defined in IEEE 802.16e [4]. One channel is reserved for

each device that is transmitting, channel width is dependant of the used frequency .

Mesh topology is a scalable network topology where all nodes in the network are connected to each

other as presented in figure 2 and traffic is routed through nodes or sent directly to a certain node.

There exists a Mesh BS in the network that is actually an SS that provides connection to external

network (the red node with label 2 in figure 2), to Internet through fibre for instance. Other SSs

register themselves (black nodes in figure 2) with this Mesh BS and the traffic to external network

is routed to this Mesh BS through other SSs (as in figure 2). Mesh topology sets some limitations to

channel usage, simultaneous transmissions of devices that are near to each other must be on

separate channels. For example if node number 7 wants to access external network it has to rely itstraffic through its neighbour node, number 6 that forwards data to node number 2. Mesh topology

can be used in both fixed and mobile WiMAX on licence free frequencies (from 5 to 6 GHz). This

kind of network requires that every node has a roof-mounted antenna. It is encouraged to use

multiple directional antennas instead of one omnidirectional antenna (with fixed connections)

because it will result in more interference.

2.3 Layer architecture

WiMAX [3] contains two main layers: physical and Medium Access Control layers. These layers

exchange information with each other through special Service Access Points (SAP). Layer model of

WiMAX is shown in figure 3, MAC layer contains three separate sublayers, each sublayer has its

9

Figure 2: Example of Mesh topology


12/47

own responsibility and scope.

Figure 3: WiMAX layer model [3]

2.3.1 Convergence sublayer

Convergence sublayer (CS) is an adaptation layer that adapts higher layer protocols into WiMAX

[3] architecture. It transforms and classifies data that is received from MAC SAP into form that is

used by upper layer protocols, synchronous data when using ATM (Asynchronous Transfer Mode)

protocol and packet data when using Ethernet and/or IP (Internet Protocol) version 4 or 6 protocols.

CS works for another way around, all that is received from CS SAP is classified and transformed

into form that is used by MAC Common Part Sublayer (CPS) and then sent to MAC SAP.

2.3.2 Medium Access Control Common Part Sublayer

MAC Common Part Sublayer is the control layer that operates as an interface between adaptation

layer (convergence sublayer) and physical layer in WiMAX [3]. Its responsibility is to make sure

that all resources that are provided by transmission path are used effectively and the quality of

10


13/47

connection stays at as high level as possible (Quality of Service). In addition to these MAC CPS

contains transmission error control (Automatic Repeat reQuest, ARQ) method and methods for

forming Protocol Data Units (PDU), packaging and fragmentation are used for forming PDUs.

Support for different network topologies is also located at MAC CPS.

ARQ provides reliable data transmission with timeouts and acknowledgements. The functionality is

based on repeat requests that will be sent automatically when an error is detected in some packet.

This will continue until an authentic packet is received or the maximum amount of repeat requests

is reached.

Quality of Service (QoS) method in WiMAX [3] allows to change QoS packet parameters

individually for different devices and services. It contains four different levels of QoS parametersfor different usages.

Highest level is Unsolicited Grant Services (UGS) that require specific unchangeable

amount of bandwidth and the data transmission is continuous [3]. An example of this kind

of application is VoIP (Voice over Internet Protocol) [6].

Second highest level of QoS is real-time Polling Services (rtPS) and is meant for services

that have real time requirements and do not have any specific bandwidth requirements (size

and amount of transferred data/packets varies) [3]. Audio and video streams are examples of

this kind of usage [6].

Third highest level of QoS is Extended real-time Polling Services (ErtPS) and is meant for

similar services than in rtPS that allow some jitter in connections [3]. VoIP with Activity

Detection is an example of service that can be used with ErtPS QoS level [6].

Second lowest level of QoS is non-real-time Polling Services (nrtPS), this level is for

services that transmit data as bursts and do not have real time requirements [3]. File Transfer

Protocol is an example of nrtPS service [6].

Lowest level of QoS is Best Effort (BE) and is meant for services that don not require full

reliability. Examples of BE services are web browsing and data transfer [6].

2.3.3 Security Sublayer

Security Sublayer is responsible of making sure that connections are secured and data is properly

encrypted. Because all data is transferred with wireless methods strong encryption methods are

11


14/47

needed, wireless connections are easy to eavesdrop if not properly protected. Security Sublayer int

WiMAX [3] contains means for authentication, exchange of encryption keys in a secure manner and

encryption methods for securing connections and transmissions. Security sublayer consists of two

protocols, encapsulation protocol and key management protocol (Privacy Key Management, PKM).

Encapsulation protocol contains definitions for encryption methods and algorithms required for

authentication. In addition to these it contains the rules about how to apply these methods into MAC

PDU payload.

PKM provides authentication of network nodes, authorization of nodes for service access and

keying data distribution and synchronization between BS and SS. PKM supports usage of EAP

(Extensible Authentication Protocol) along with digital certificates (X.509) for authentication ofdifferent nodes. It also supports authentication with digital certificates only, digital certificates are

required also by used encryption method, RSA (Rivest, Shamir, & Adleman) PKCS (Public-key

Cryptography Standard) #1 for providing the public keys of RSA key pairs, these keys are needed

for message validity check.

In PKM v1 (IEEE 802.16d [3]) the authentication was defined to be one sided; BS was never

authenticated and this was considered as a great security risk in Johnston's and Walkers article

about WiMAX security [7], this design flaw made it possible to use rogue BSs. This issue was fixed

in IEEE 802.16e [4] with new version of PKM (version 2) by adding mandatory mutual

authentication (with RSA) of both BS and SS. The authentication (and overall security) is

improved with IEEE 802.16e [4] by enhancing the maintenance of keys and adding better security

contexts for keys. It was also introduced in IEEE 802.16e [4] that the authentication procedure

could be enhanced by applying EAP with RSA or double EAP (prevents MiTM attacks since EAP

authentications are cryptographically bound).

WiMAX uses multiple different keys for different kind of connections (unicast, broadcast and

multicast), in IEEE 802.16d [3] most important keys (Authorization Key, AK) were created with

random number generator (usage of random number generator was only suggested, no requirement

for key creation was set) that is a great security risk [7]. In IEEE 802.16e [4] this issue was fixed by

adding a new method for key creation, keys are generated from the results of successful

authentications. Additionally the SS is required to re-authenticate always when the security context

is lost. Security context is lost when lifetime of certain key has passed, re-authentication is

12


15/47

requested or SS has moved to coverage area of another BS (when using mobile WiMAX). After re-

authentication the previously used security context is replaced with new one, new keys are derived

from the results of re-authentication procedure. The key exchange in PKMv1 was considered to be

unsafe by Eren in his research about WiMAX security architecture [8] and it was fixed by adding a

3-way handshake procedure in IEEE 802.16e [4] that is performed after every authentication or re-

authentication. For the actual data encryption DES (Data Encryption Standard) was used in in IEEE

802.16d [3], the key size (56 bits) and the protocol itself were considered as a security risk [7] and it

was replaced later by more secure AES (Advanced Encryption Standard) in IEEE 802.16e [4].

Additionally with improvements in IEEE 802.16e [4] WiMAX should be less prone to DoS attacks,

because management messages are protected with proper method: Message Authentication Code.

Packet numbers are used for management messages and when the number space has been ran outre-authentication is requested and as said, this provides new security context thus making it almost

immune to DoS attacks. Although it was mentioned in research of Maccari et. al. [9] that with large

amount of false authentication requests DoS attack could be successful because public key

encryption and decryption procedures require a lot of computational power for validity checking.

Their research is targeted mainly towards IEEE 802.16e with Mesh topology and introduces

problems that are detected in Mesh topology only but some will also apply to other topologies too.

The problems they've addressed are mainly towards DoS attacks, it was introduced that the sleep

mechanism that was introduced in IEEE 802.16e could make it possible to conduct a DoS attack

with the identifier of sleeping victim SS, also the unencrypted management frames were seen as a

possible threat.

2.3.4 Physical layer

Physical layer contains everything that is related to signal handling, it is responsible of modulating

the signal with correct method and using right channel for signal transmissions. IEEE 802.16 [3],

[4] contains five different modulation schemes that can be used in different frequency ranges.

Modulation schemes are Single Channel (SC), SCa, OFDM (Orthogonal Frequency Division

Multiplexing), OFDMA (Orthogonal Frequency Division Multiple Access) and HUMAN. In all of

these BPSK (Bit Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16-QAM

(Quadrature Amplitude Modulation) and 64-QAM can be used for signal modulation except in SCa

where only QPSK can be applied. The speed and operating distances that can be provided with

13


16/47

different methods is directly dependant on the modulation method (symbol rates). 64-QAM

provides the best speed with shorter distances and with BPSK it is possible to cover longer

distances with lowered bit rates. These signal modulation methods can be dynamically changed

during transmission but only one can be in use at a time. The dynamic changing of modulation

methods comes necessary when using mobile WiMAX, when moving further away from BS the

next modulation method can be applied that provides longer operating distance. The procedure for

modulating the signal is [3] :

1. Data block to be encrypted is randomized. The data to be sent is always encrypted.

2. Randomized data block is Forward Error Correction coded. Possible encoding methods (and

their combinations) after this are: Reed-Solomon coding, Convolution coding, Block Turbo

Code and Convolution Turbo Code.

3. Signal modulation with selected modulation method.

Physical layer of IEEE 802.16 [3] contains a special method for detecting and avoiding interference

on selected frequency. This method is called Dynamic Frequency Selection (DFS). DFS works in a

way that it changes the actual channel frequency based on the measurement data (transmit and

receive activity) gathered from the channel and therefore minimizes the interference to connections

of others while providing the best channel for the device at all times. The frequency change can

happen dynamically during connections.

Transmission power management and distance measuring are also located on physical layer in IEEE

802.16 [3]. With these methods every node can adjust the transmission power for its needs and in

addition with AAS (Adaptive Antenna System) the signal can be aligned with BS and SS, in IEEE

802.16e [4] more advanced MIMO (Multiple Input, Multiple Output) techniques were introduced.

Distance measurement and power adjustment are done at the beginning of the connection

establishment or when re-registering the connection or when connection is lost. This can be also

done as timed event at any point during connection.

2.3.5 Multiple Input, Multiple Output antenna techniques

Mobile WiMAX (IEEE 802.16e [4]) introduced new MIMO antenna techniques that can be

classified into two categories: open and closed loop MIMO [10]. When open loop is used the

transmitter doesn't utilize channel fading information for channel selection, closed loop transmitters

14


17/47

adapt their functionality based on the information they receive of channel condition.

Open loop MIMO [10] contains three techniques; Space Time Block Coding (STBC), and Spatial

Multiplexing MIMO (SM-MIMO) and an adaptive mode selection between STBC and SM-MIMO.

STBC transmits every OFDM symbol once per antenna and maps each subcarrier wave for each

transmit antenna signal. SM-MIMO can double the peak performance and increase the system

performance by reserving 2 downlink and uplink data streams for each receiver, symbols are

divided between these two streams and sent on different antennas.

Closed loop MIMO [10] techniques take advantage of reciprocity of both downlink and uplink

transmissions, two techniques are available: Maximum Ratio Transmission (MRT) and Eigen

Beamforming (EBF). MRT tries to maximize the signal-to-noise ratio for each receiver by trackingchannel responses, it requires accurate information about channels. The algorithm that is used in

MRT tries to maximize the performance with given physical hardware and sets no constraints for

for antenna techniques. EBF uses statistical information (different weighs are computed for every

subcarrier) about channels and is more robust than MRT when signal-to-interference-plus-noise

ratio is low. EBF suits better for mobile networks where receivers are moving on high speeds since

accurate channel information is hard to use because of larger delays in connections, therefore

statistical information is better in this situation.

2.3.6 Duplexing methods

WiMAX [3] supports two different duplexing methods, TDD (Time Division Duplex) and FDD

(Frequency Division Duplex). Both of these can be used with modulation schemes supported by

WiMAX. The selection of duplex method is based on usage needs, network type and choices made

by operator or the person deploying the network.

TDD in WiMAX works in a way that uplink and downlink transmissions are sharing the same

frequency but have different amount of timeslots (separated in time). The allocation of timeslots for

uplink and downlink is adaptive, this allows the BS to operate in a more dynamic way, different

amount of time slots can be assigned for different SSs operating on different ranges.

In FDD both uplink and downlink transmissions have their own channels (separate frequencies).

15


18/47

The downlink channel allows the data to be sent in short bursts, this allows the BS to support both

Full (send and receive simultaneously) and Half Duplex (send or receive) SSs at the same time.

2.3.7 Modulation in licenced frequencies between 10 and 66 GHz

SC modulation scheme can be used on fixed WiMAX [3] when using licenced frequencies from 10

to 66 GHz. Used channels for transmission are normally 25 or 28 MHz wide. To allow flexible

usage of the whole spectrum TDD or FDD channeling is used.

Transmit channel of SC uses a combination of TDMA (Time Division Multiple Access) and

DAMA (Demand Assigned Multiple Access) and is divided into time slots (TDD) for different

usage needs (for example registration of connections and user traffic). The channel that receives

transmissions from others is based on TDM (Time Division Multiplexing) in Full Duplex mode and

in Half Duplex TDMA is used.

2.3.8 Modulation in licenced frequencies between 2 and 11 GHz

SCa, OFDM and OFDMA modulation schemes are used in licenced frequency bands between 2 and11 GH in fixed WiMAX [3]. Channels that are used on this frequency range are from 1.25 MHz to

20 MHz wide. TDD and FDD can be used for channeling.

SCa modulation scheme is similar to SC in higher licenced frequencies, same methods are used.

OFDM modulation scheme is based on OFDM and it utilizes Fast Fourier Transform (FFT) for

waveform creation, sizes for FFT are from 128 to 2048. OFDM is immune to interference of

multipath propagation, orthogonality of the tones can be maintained and multipath propagation can

be exploited but not utilized in OFDM modulation scheme. The size of the FFT that is to be used is

defined by the amount of subcarrier waves, there are three different types of subcarrier waves:

transmission, measurement and empty. Symbols for OFDM are created by using this subcarrier

waves. OFDMA modulation scheme is an enhanced version of OFDM, active subcarrier waves

have been divided into smaller parts (allows better scalability) and multipath propagation is

exploited to support more advanced antenna techniques (MIMO).

16


19/47

2.3.9 Modulation in licence free frequencies between 2 and 11 GHz

On licence free frequencies from 2 to 11 GHz (normally 2 to 6 GHz in nowadays implementations)

a modulation scheme called HUMAN is used [3], [4]. Fixed connections [3] use only TDD

channeling and channels are 10 or 20 MHz wide. In mobile WiMAX [4] channels are between 1.25

and 20 MHz and it uses TDD and FDD, only TDD was introduced in first mobile WiMAX profiles

[6].

Previously mentioned DFS technique is applied in HUMAN modulation scheme because used

frequencies are not licenced, i.e. there might be some other devices with different techniques using

same frequencies and it is necessary to avoid interfering with these connections. In fixed WiMAX

[4] network the operation is based on a hybrid of OFDM and SC. Mobile WiMAX [ 4] uses ScalableOrthogonal Frequency Division Multiple Access (S-OFDMA) [6] that supports different

frequencies which can be used when needed and is also scalable. The scalability of S-OFDMA [ 6]

is based on dynamic adjustment of the FFT size while scaling the subcarrier accordingly (between

10.94 KHz intervals).

2.4 Network reference model

The reference model for WiMAX networks was presented by WiMAX Forum [11] and is shown in

figure 4. This model shows how the WiMAX network could be built and what parts are needed. It

also explains the functional entities and reference points between components (interworking etc.).

The terms that are used in figure 4 in alphabetical order:

ASN (Access Service Network) is the part that provides radio access for WiMAX

subscriber. It includes connectivity (layer-2, WiMAX and layer-3, e.g. IP), authentication

and authorization, network discovery and radio resource management.

ASP (Application Service Provider) is a entity that provides applications or services for

WiMAX subscribers via visited or home NSPs (Network Service Provider).

CSN (Connectivity Service Network) provides IP connectivity to different services for

WiMAX subscribers.

MS (Mobile Station) is a mobile WiMAX subscriber device.

NAP (Network Access Provider) is a entity that provides infrastructure for radio access to

17


20/47

one or more NSPs, multiple ASNs can be used.

NSP provides IP connectivity and services for WiMAX subscribers, it establishes

contractual and roaming agreements with NAP(s) in order to provide these even when

WiMAX subscriber moves away from home NSP.

Figure 4: WiMAX network reference model [11]

The R1, R2, R3, R4 and R5 are reference points that explain the protocols and procedures that are

needed between different parts of network:

R1: WiMAX connection as stated in standard (physical and MAC specifications).

R2: Authentication and authorization and IP host management between SS and home or

visited NSP.

R3: Authentication, authorization, policy and mobility management between ASN and CSN.

R4: Interworking of ASNs when MS is moving between ASNs.

R5: Interworking between visited and home NSP when SS is in visited network.

18


21/47

3 LIMITATIONS OF WIMAX

The performance of WiMAX has been quite intensively tested and researched. In this section some

research reports and results of those researches are introduced. The claims that are introduced by

standards and certifying organizations are compared to real life results. Additionally currently

available frequencies in Finland are introduced at the end of this section.

3.1 Distances and speeds of different network topologies

WiMAX [3] is intended to be used in four multiple scenarios; fixed with LOS (P2P), fixed with

NLOS (P2P and PMP), mobile (PMP) and mesh networks. Different modulation schemes are also

used for different purposes. The reported speeds are downlink speeds, WiMAX connections are

asynchronous, uplink speed is always lower than downlink.

When the devices have LOS to each other direct P2P links can be used on licenced high frequencies

[3], SC modulation is used. It will provide connections over long distances (up to 50km in best

circumstances, generally 30 km) with adequate speeds (2 Mbps) and decent speeds (over 10 Mbps)

up to 20 km. In theory [3] it could be possible to achieve speeds up to 120 Mbps and the maximum

range could be as high as 100 km with P2P connections. But in practice the maximum throughput

of a WiMAX base station is 72 Mbps and the maximum range is 50 kilometers [5].

Without LOS and fixed connections it is possible to use either P2P links or PMP topology on

licenced frequencies (2 11 GHz) [3], this allows to use SCa, OFDM and OFDMA modulation

schemes. SCa is used with P2P links and for PMP topology OFDM or OFDMA schemes can be

used. The maximum distance for connections with adequate speeds (2 Mbps) is 10 km [12]. Themaximum speed for one channel is reported to be 40 Mbps and current implementations are

expected to provide 30 Mbps connections within 3 km radius [12].

On licence free frequencies (usually 2 to 6 GHz [4]) PMP and Mesh topologies can be used with

HUMAN modulation scheme that uses S-OFDMA for modulation [4]. Both fixed and mobile

connections can be used and no LOS is required. The maximum distance that provides decent

speeds (over 3 Mbps) is 5 km and maximum throughput [5] and with MIMO techniques the

19


22/47

maximum transfer speed could be as high as 63 Mbps [6].

The latency on connections between a SS and BS are reported to be 5 ms at minimum [5]. The

actual latency of the connection depends on the connection between SS and the other end. The

latency is claimed to be same when moving, even at high speeds [5].

3.2 Actual performance

The fading model of WiMAX is assumed to be similar to Cost 231 Hata model. But Grnsund et.al.

[13] derived a Path Loss model based on their empirical tests on fixed WiMAX connections (on

licence free frequency, 3.5 GHz) that approaches Free Space Loss model more than Cost 231 Hata

models. It was also noted in research of Grndalen et. al. [14] that the RSSI (Received Signal

Strength Indication) curve is better than Cost 231 Hata model for urban environments. Their tests

were conducted on actual deployment of hundreds of WiMAX SSs and ten WiMAX BSs. Tests of

Grnsund et.al. [13] also showed that on this frequency the range with decent connection quality

can be as high as 10 km while adequate connections could be delivered as far away as 16 km from

BS.

Palade et. al. [15] found out in their performance analysis that the size of the transmitted packet

does not affect network parameters (latency, jitter). Their tests involved fixed networks and also

mobility performance of WiMAX was tested. Mobility tests showed that even with fairly high

speeds (15 m/s, 54 km/h) the performance was almost as good as when the device was stationary,

with very high speeds (30 m/s, 108 km/h) the network performance started to slightly deteriorate

(handover delay doubled).

As for performance connection to channel width, Mach and Bestak [16] found out in their research

(with fixed WiMAX) that with channel width of 3.5 MHz the overall bitrate was 7 Mbps of the

theoretical maximum 13 Mbps. With 20 MHz wide channels the performance was even poorer

when comparing to theoretical maximum, 75 Mbps. Bitrate that was achieved in tests was only 15

Mbps. Tests of Mach and Bestak were conducted on 3.5 GHz frequency, for comparison

Shcwengler and Pendhakar [17] did their tests on 5.8 GHz frequency with fixed network in PMP

topology using same modulation scheme and 20 MHz wide channels. Their tests showed that the

maximum throughput in laboratory environment for PMP was slightly less than 20 Mbps, both used

20


23/47

similar parameters. The difference might be caused by different environments and amount of

devices used in testing, also there might be some deviation between devices that are implemented

by different manufacturers. Shcwengler and Pendhakar also tested the performance of P2P links, the

maximum performance was roughly 40 Mbps, which is fairly good considering the actual

throughput maximum of a BS (72 Mbps [5]). With least robust modulation (BPSK) the throughput

with both, P2P and PMP was roughly 5 Mbps [17]. This means that with longer distances the speed

can be considered fairly good but most likely deteriorates to level of 1 Mbps at the maximum range

of 50 km [5]. The outdoor tests conducted by Shcwengler and Pendhakar [17] with fixed WiMAX

(PMP topology) showed similar speeds to results presented by Mach and Bestak [16], both used

same modulation scheme (OFDM).

The actual performance of a deployed mobile WiMAX network was measured by Kim et. al. [ 18] inSeoul, the network that was used in tests is a Korean version of IEEE 802.16e system (WiBro,

Wireless Broadband). WiBro in Seoul uses 2.3 GHz frequency with OFDMA modulation scheme

and TDD channeling with 10 MHz wide channels. Their results show that the performance is fairly

good, when stationary speeds are close to 10 Mbps and at the edge of the cell speeds as high as 5

Mbps can be reached. When on the move (bus and metro) the average speed is close to 2 Mbps.

3.3 Base station coverage

In throughput analysis of WiMAX by Mach and Bestak [16] it was found out that if there are

multiple users (10) near BS the overall throughput starts to diminish greatly. Mobile network with

PMP topology and OFDM modulation scheme at 3.5 GHz frequency was used for testing. It was

also noted that when wider channels are used, the performance and throughput with multiple users

will increase. Based on their research results Mach and Bestak suggested that when there are

multiple users near BS higher modulation type and smaller coding rate (less robust burst types)

could be used for improved performance.

WiMAX forum claims that a single BS could handle thousands of subscribers [12] but the results

provided by research of Mach and Bestak [16] suggests otherwise. The absolut maximum number

of subscribers in the area of a single BS is closer to 40. It has been proposed by Mach and Bestak

that the throughput could be increased by adding relay stations to BS cell area, this would provide

better channel quality for more distant users.

21


24/47

3.4 Currently available frequencies

As previously mentioned WiMAX can operate on licenced and licence free frequencies. In order to

deploy a WiMAX network that uses licenced frequencies a deal must be made with authorities that

manage the frequencies in the country where the network could be deployed. In Finland FICORA

(Finnish Communications Regulatory Authority) regulates the frequencies.

The WiMAX forum has introduced different profiles [6] for different frequencies for mobile

WiMAX to use. The frequencies that can be used and are being used with mobile WiMAX are 2.3,

2.5, 3.5 and 5.8 GHz [6].

A workgroup that is working on dividing the frequencies for new technologies in Finland has

proposed in 2008 that frequencies from 2570 to 2620 MHz (with 5 MHz guard bands) could be

used for mobile WiMAX for commercial purposes [19]. Currently also the 3.5 GHz frequency band

(from 3410 to 3600 MHz) is available for operators to use with fixed WiMAX and there are 50

active licences that are valid until the end of the year 2010 [20]. It has been also mentioned that

these frequencies could be used not only for fixed but mobile WiMAX networks too [20]. For

comparison Sweden uses frequencies from 3.6 to 3.8 GHz and Norway uses 2 and 2.6 GHz

frequencies for mobile WiMAX [21].

22


25/47

4 WIMAX VERSUS OTHER TECHNIQUES

WiMAX can be and is often considered as a 3rd generation mobile technique (with IEEE 802.16e

amendment), there are multiple different competing techniques that offer almost the same

functionality with different transmission and operating speeds. The wireless techniques that overlap

each other are presented in figure 5. There is not much competition on MAN area but since MAN

area technologies can be used in LAN (Local Area Network) and even in PAN (Personal Area

Network) area and WAN (Wide Area Network) area techniques overlap the with the coverage of

MAN area techniques they can be seen as competitors of WiMAX. In following sections some

competitors are briefly introduced and then compared against WiMAX.

4.1 Competing techniques

There are multiple techniques available for similar purposes that WiMAX has been designed for.

From nowadays technologies that are in use there is ADSL (Asymmetric Digital Subscriber Line)

for broadband usage, Flash-OFDM (Fast Low-latency Access with Seamless Hand-off, Orthogonal

Frequency Division Multiplexing), 3rd generation phone networks (UMTS, Universal Mobile

Telecommunications System) for wireless broadband and WLAN (Wireless Local Area Network)

can be considered as similar technique. ADSL and WLAN can be considered as so called last mile

technologies since they provide connections to the edges of the cell range. Flash-OFDM and UMTS

are wireless broadband techniques (actually UMTS is a mobile phone network technology but can

be considered as a wireless broadband), ADSL is a broadband technique that requires cables

23

Figure 5: Global wireless standards [22]


26/47

(twisted pair copper lines i.e. phone lines).

4.1.1 ADSL

ADSL [23] is a broadband communications technology that provides connections via copper wire

(phone lines). Basically ADSL is similar to WiMAX because it provides a mean for transferring

data for upper layer techniques, like ATM or IP. It is an coding technology that handles the traffic

and transforms it into right form for correct technology to use (from IP to ADSL ATM data and

vice versa for instance). ADSL uses different frequencies than phone traffic (0 4 KHz) so both can

coexist in same cable. ADSL uses frequencies from from 25.875 to 1104 KHz. Newer standards,

like ADSL2+ uses the frequency spectrum up to 2.2 MHz [24]. For modulation the physical layer of

ADSL [23] uses Carrierless Amplitude Phase Modulation (CAP) or Discrete Multi-tone (DMT)

modulation. CAP uses frequencies between 25 and 160 KHz for uplink traffic and frequencies

above 240 KHz for downlink, this minimizes the interference. DMT divides the frequency band

into channels that are 4.3125 KHz wide and uses the channel that has best signal for transmissions.

ADSL [23] connections require a subscriber station (stationary, registered to one line) at consumer

end and DSLAM (Digital Subscriber Line Access Multiplexer) equipped centrals at service

provider end . The need for multiple DSLAMs comes for relatively short operating distances that

are shown in table 1, same table also shows the maximum speeds for different ADSL versions. The

maximum operating range for ADSL is close to 6 km [24], at this distance only lower speeds can be

achieved. The latencies for ADSL connection are generally low on connections that are within the

range [24] and are mostly dependant on connections of the operator.

ADSL version Maximum distance Maximum downlink speed Maximum uplink speed

ADSL 1.8 km 8 Mbps 1 Mbps

ADSL2 2.5 km 12 Mbps 3.5 Mbps

ADSL2+ 2.5 km 24 Mbps 3.5 Mbps

Table 1: ADSL distances and speeds [23] [24]

4.1.2 Flash-OFDM

Flash-OFDM [25] was originally developed by Flarion (that was later bought by Qualcomm) [26],

24


27/47

it is a wireless and fully mobile technology for broadband communications that supports

450/700/800/1900/2100 MHz frequency bands, currently the 450 MHz band is the most used.

Flash-OFDM [25] uses OFDM for modulation and uses the whole spectrum that is available and

divides it into equally spaced channels, width is implementation specific, usually 1.25 MHz. The

overhead for messages is claimed to be zero because of the dynamic resource allocation attributes

on physical layer and the latencies should be really low [26], it has been said that in tests the latency

has been measured to be from 35 to 55 ms [25].

Flash-OFDM [25] operates as WiMAX from the layer model point of view, it provides MAC and

physical layers for upper layers to use, this means that for example IP-based traffic can be directly

used on top of Flash-OFDM. Flash-OFDM supports seamless connectivity (handover process is fast

between BSs), the movement from one BS to another shouldn't be noticeable by user (latencies arevery small). Flash-OFDM is dependant on operator [26], new network infrastructure will have to be

built and currently there is no possibility for user to form own networks with Flash-OFDM. User

needs only a Flash-OFDM subscriber station and maybe an external antenna for better connections.

Speeds that consumer can achieve with Flash-OFDM [25] are around 1.5 Mbps, in theory it is

possible to reach data rates of 5 Mbps in downlink and 1.8 Mbps in uplink. The overall throughputs

of Flash-OFDM are 2500 / 800 kbps (downlink / uplink). Flash-OFDM was designed to operate

when user moves very fast, it is said that the maximum speed for a moving SS is 250 km/h. Due to

low frequency it is possible to cover wide areas with one BS when using 450 MHz band, in rural

environment cell radius is 25 km and in urban environments it is 5 km.

4.1.3 UMTS

UMTS [27] is developed by 3rd Generation Partnership Project group, UMTS is a general term for

standards that are being used in 3rd generation (3G) mobile phone networks. It covers the original

3G W-CDMA (Wideband Code Division Multiple Access) and HSPA (High Speed Packet Access)

modulation schemes. W-CDMA uses QPSK modulation, HSPA uses 16QAM modulation and the

upgrade, HSPA+ introduced 64QAM modulation to standard. Originally it was designed to use

bandwidth around 2 GHz but there are implementations that support already existing mobile phone

frequencies of 2nd generation (2G) mobile phone networks (850/900/1900/2100 MHz), the channel

width is 5 MHz. 3G phone network operation requires an central operator that provides the network

25


28/47

and BSs for subscribers to use (with mobile phone or UMTS modem), it is not possible to form own

networks with UMTS technology. UMTS technologies are designed to support direct IP-based

traffic.

The transfer rates of original W-CDMA are 384 kbps, with newer techniques introduced by HSPA

the maximum downlink transfer rate is 14 Mbps and uplink transfer rate 5.8 Mbps. Additionally

with newest upgrade to HSPA, HSPA+ introduces speeds as high as 42 / 11 Mbps (downlink /

uplink). Qualcomm has reported [28] that in their tests maximum speed for downlink that was

achieved was 20 Mbps. The cell radius of one UMTS [27] BS is roughly 1.5 km in urban areas and

4 km in rural areas. Seamless roaming between BSs is supported (also backwards compatible with

2G networks, vertical are handovers supported). As previous mobile phone networks, also 3G

networks support data transfers at very high speeds (up to 500 km/h in urban areas and up to 120km/h in urban areas) when the data rates are lower. The latencies for connections with W-CDMA

are 150 ms and with HSPA from 50 to 100 ms.

4.1.4 WLAN

WLAN is a wireless technology for local area connections and can be used as a wireless extension

of an existing LAN. It is also developed by IEEE and defined in IEEE 802.11 standard [ 29]. With

WLAN the range of the network can be increased without applying any cables and it is fully

compatible with existing LAN. Additionally WLAN supports full mobility and handover between

Access Points (AP). This allows to cover a large area with multiple APs that are connected to each

other so users can move freely in the coverage area without noticing a significant delay between

handovers. WLAN works at amazingly high speeds, Morioka and Mano [30] tested the maximum

speed on race track and found out that it is possible to use WLAN at over 200 km/h speed. There is

no need for operator and anyone can deploy their own WLAN [29] networks at home, at office or in

public places like parks for instance. The standard supports also forming of dynamic networks (Ad

Hoc), these Ad Hoc networks can be formed between any device that supports same standards.

There are multiple standards developed and will be developed further, table 2 shows the frequencies

that WLAN uses, modulations in different standard versions and speeds of those standards. The

current approved standard is IEEE 802.11g [29] that The IEEE 802.11n standard hasn't yet been

published but there are devices based on standard drafts [31]. According to Wang and Refai [32] the

26


29/47

maximum throughput that can be achieved with IEEE 802.11g is 20 Mbps. They also conducted

some research related to delay measurement model in IEEE 802.11g and the minimum delay that

they reached was around 5 ms.

The indoor range of WLAN [29] with current standard is 100m and in practice the range is

somewhere between 50 and 70 meters depending on the environment, outdoors the range can be

nearly 300 m in ideal situations but with normal conditions the range is roughly 200 m at maximum

[31]. Used frequency band is divided into 14 channels that are 5 MHz wide, there are some

limitations about channel uses in different countries since unlicensed ISM (Industry, Science and

Medical) band is used in WLAN [29]. In most of the European countries 13 different channels can

be used (from 1 to 13).

Standard Frequency band(s) Modulation Max. speed

IEEE 802.11 2.4 GHz Frequency Hopping Spread Spectrum 2 Mbps

IEEE 802.11b 2.4 GHz OFDM 11 Mbps

IEEE 802.11a 5 GHz Direct Sequence Spread Spectrum 54 Mbps

IEEE 802.11g 2.4 GHz OFDM/Direct Sequence Spread Spectrum 54 Mbps

IEEE 802.11n 2.4 and 5 GHz OFDM 300 Mbps

Table 2: WLAN standards, modulations and speeds [31]

4.2 Mobile WiMAX compared to other techniques

WiMAX is quite different from other techniques that were presented in previous sections, after all it

is meant to be used in different kind of network (MAN) than the others. Table 3 in next section

shows the differences between mobile WiMAX (selected because is designed for similar purposes)

and other techniques, the differences that are shown are quite necessary to be known by end users

and network operators. As previously mentioned, all but ADSL are techniques that use wireless

media for transmissions. The mobility preferences of wireless techniques are almost the same, there

might be some differences between handover delays and handover types (for example UMTS

supports vertical handovers).

27


30/47

4.2.1 Performance and usage comparison

As the table 3 shows, WiMAX is very competitive with other presented techniques, it is slower than

UMTS but offers a better coverage and cannot work on as high speeds as Flash-OFDM but provides

a lot better throughput and also latencies are better. Although Flash-OFDM provides a lot better

operating range and thus is a hard competitor for WiMAX since less BSs are required. In order to

cover 129 m area with UMTS (HSPA) it would require almost 60 BSs and with mobile WiMAX

(with MIMO antenna technique) the same area could be covered with 20 BSs [ 33]. Mobile WiMAX

cannot compete with the speed provided by WLAN but the coverages are nearly from different

planets. ADSL can only compete with mobile WiMAX in throughput but since it requires cables in

order to work the mobility of WiMAX takes points from that quarrel.

Technique Operating range Throughput Maximum velocity

of SS

Connection latencies

at minimum

ADSL 2.5 km Theory: 24 Mbps No mobility 5 ms

Flash-

OFDM

Rural: 25 km

Urban: 5 km

Theory: 5 Mbps

Practice: 2.5 Mbps

250 km/h 35 ms

UMTS Rural: 4 km

Urban: 1.5 km

Theory: 42 Mbps

Practice: 20 Mbps

Rural: 500 km/h

Urban: 120 km/h

50 ms

Mobile

WiMAX

Rural: 10 km

Urban: 2 km

Theory: 40 Mbps

Practice: 10 Mbps

120 km/h 5 ms

WLAN Outdoors: 200 m

Indoors: 70 m

Theory: 54 Mbps

Practice: 20 Mbps

200 km/h 5 ms

Table 3: Comparison of technique parameters

The actual performance comparison was performed by WiMAX Forum [34], their released white

paper shows that the performance of mobile WiMAX is far more better than its worst competitor at

that moment. Tests were conducted with similar parameters and traffic amounts as simulation. As it

can be seen from figure 6, HSPA cannot compete with mobile WiMAX in downlink speeds but

uplink speeds are almost the same. The analysis was performed in 2006 and after that HSPA+ has

been introduced which increases the speeds of UMTS network to the same level (as stated by

QualComm [28]). The third technique present in the figure, EVDO (Evolution Data Optimized)

uses CDMA2000 modulation with multiple carriers (revision B), EVDO is used for similar

purposes than mobile WiMAX; mobile broadband [35].

28


31/47

Figure 6: Sector throughput comparison (Mbps) [34]

4.2.2 Comparison of network efficiency

Previously mentioned white paper published by WiMAX Forum [34] also contains analysis about

the spectral efficiency of mobile WiMAX compared to others. The results are shown in figure 7 and

as it can be seen, mobile WiMAX is twice as much efficient than HSPA. The efficiency is evaluated

by comparing the bit rates that can be achieved with frequencies used by selected technique.

Figure 7: Spectral efficiency comparison (bps/Hz) [34]

29


32/47

4.2.3 Mobile WiMAX, replacement or addition

It isn't a easy to choose a replacement for older working technology since new investments are

required almost in all cases. WiMAX is a good replacement for old wired networks, like ADSL

since it can provide decent speeds to places where phone wires cannot be put (mountains for

instance) or it would cost too much. This is because of the good range that mobile WiMAX (and

fixed) provides and the range can be extended with multiple BSs without any cables (P2P links

between BSs as show in figure 1). There is no use to replace local (indoor) WLAN networks with

mobile WiMAX because WLAN devices are much cheaper to use. WLAN networks that are built to

cover large outdoor areas can benefit from WiMAX since it is possible to connect WiMAX BSs to

existing IP-based network, mobile WiMAX could be used as an extension to existing WLAN that

greatly enhances the range (coverage per BS ratio is better) and provides better coverage. Theremight not be a need to replace the whole network with WiMAX since devices cost quite much.

With techniques that are meant for really similar purposes than mobile WiMAX (Flash-OFDM and

UMTS) the struggle is harder because full mobility at high speeds is supported. As previously said,

WiMAX can compete with them but the real competition is solved by the real need of the user. If

there is a need to access network at adequate speeds and low latencies WiMAX is the choice but if

the coverage per BS is required to be higher and the speed of connection doesn't matter that much

Flash-OFDM is the right one. Or if there is need for very high speed connections and the money is

no problem UMTS would satisfy the needs. When thinking of the moving speed of SS all of the

techniques mentioned would fit for the purposes.

WiMAX can be seen as replacement for some networks but it can be also seen as a extension to

existing network or as a backhaul network. As it was mentioned IP-based data can be sent in

WiMAX network and therefore it is compatible with others that expect the data to be transferred as

IP packets. WiMAX comes in handy because it supports both P2P links with high data rates on

fairly long distances and allows to for example form small clusters with specified smaller area

network technology and to connect these networks to each other or to internet. There are multiple

white papers published by WiMAX forum that present the usage of WiMAX (mobile and fixed)

with different existing networking techniques, like DSL (Digital Subscriber Line) techniques [36]

(ADSL is a DSL technique) and 3G mobile phone networks [37]. These papers introduce example

architectures for using WiMAX with these techniques (similar approaches could possibly be used

with other techniques too). There exists a recently published article [38] in IEEE Communications

30


33/47

Magazine that introduces a good way to integrate WiMAX and 3G mobile phone networks, this

article presents issues with integration process and presents the architecture for integrating these

two techniques. The issues related to integration, like handovers and seamless connectivity are also

addressed in the article [38].

31


34/47

5 APPLICATIONS

WiMAX has practically two types of applications: Non-line of sight broadband user access for

mobile and stationary clients, which is the newer part of the standard and various applications of

WiMAX as the backbone of networks or for point to point connections. These two technologies use

different equipment, and often different frequency ranges as well [39]. Therefore it is required to

examine the various applications of WiMAX from several perspectives: Which sort of advantages

WiMAX can bring over existing backbones and how it can be used to bridge existing wireless

networks, and how WiMAX can be used in the so called last mile which concerns connecting the

end user to the service provider network node. There is a lot of development going on all fronts, and

WiMAX has practical potential to be used in both roles. One of the latest developments in utilizing

WiMAX is the Third Generation Partnership Project (3GPP) where a client device equipped with

several radio devices can utilize seamless hand-off between different wireless networks [40]. For

example, a compact laptop or a PDA (Personal Data Access Device) could seamlessly switch from

a faster mobile WiMAX connection to a UMTS cell when leaving the WiMAX hotspot area.

WiMAX is still an evolving set of techniques with several separate evolution projects started in the

IEEE 802.16 Working Group seeking to both improve the current release of Mobile WiMAX and to

develop a new set of standards incorporating newer technology. The most recent standard under

development, Mobile WiMAX 1.5 [10] should reduce hand-off latency, add persistent allocation to

improve efficiency for VoIP data traffic and include improvements for the MIMO radio technology.

5.1 Last Mile Broadband Connectivity Potential

As established earlier in the report, WiMAX has sufficient speed and range to cover significantareas of cities and towns with a pattern of access points and thus provide end user access whether to

stationary or mobile users at speeds which are acceptable at least by 2008 Scandinavian standards.

However, this far wired DSL has been the most popular broadband access method globally, being

dominant and having 60% of broadband lines in OECD countries and 80% broadband lines in

Europe. For many years, fixed wireless access networks have been proposed as an alternative to

DSL and cable networks. Still, they have not reached mass markets, mostly because of standards

and interoperability, low economies of scale and resulting high pieces of equipment. [41]

32


35/47

In the paper Competitive Potential of WiMAX In The Broadband Access Market: A Techno-

Economic Analysis [41] Timo Smutra analyses the competitive potential of 3.5GHz WiMAX-

based network deployment where fixed network access is provided to residential and small-to-

medium sized enterprises in a five-year study period in several types of areas. The result is that in

the economic model the most proved profitable, and in suburban areas only the most dense area

turned out profitable. In rural areas, satisfying the customer needs requires a heavy initial

investment, but gives the operator a significantly larger subscriber base and annual revenues as

opposed to the urban and suburban areas. However, in all models operation as possible and

eventually profitable without external influences like government sponsorship.

5.2 WiMAX Backbones

This far wireless network usually use some sort of cabled connection, whether it is 3G or Wi-Fi but

with licensed frequencies of WiMAX and higher speeds of stationary point to point links it would

be possible to use WiMAX to extend these end-user networks from single wired but faster by using

point to point backhauls [42]. Because the higher frequencies 802.16d WiMAX [3] uses to achieve

fast point to point links are in the licensed band, its use is most often envisioned to serve as

backbone for networks instead of servicing companies or individual network subscribers directly.

Also, when compared to WiFi, the more common current wireless technology, WiMAX has reliable

QoS features and it can operate on exclusive licensed bands which means the links are more reliable

and this is one of the reasons it could be the favored wireless backhaul technology in the future

[43]. One more advantage to WiMAX operating on the licensed bands is its excellent bandwidth

efficiency: Both the operator and the licensing authority benefit as much as possible from the

licensed frequency area. The licensing authority is able to enable more operators to operate in the

area, and the operator is able to get more performance and thus serve more subscribers [34].

One recent area of research is using the 802.16e [4], Mobile WiMAX, and its lower frequency

ranges for P2P backhaul [44]. While still operating in the licensed frequency ranges, it is proposed

[44] that one advantage of lower frequencies come with less strict line of sight requirements. The

disadvantages are that because it was originally designed for mobile broadband wireless access its

overhead is relatively large and while this makes the network more robust, it also makes the link

33


36/47

less efficient.

5.3 WiMAX and 3GPP Interworking

One of the largest challenges in upgrading networks to the next generation and new technologies is

interoperability: With the ubiquity of old network infrastructure, it is no longer possible to

completely replace old network technologies [40]. Also, with new networking technologies like

WiMAX being introduced, there are different strengths and weaknesses in different wireless

network technologies. It would be both economically reasonable and more convenient to the end

user to seamlessly integrate several levels of wireless networking into one cohesive whole, where

the end user might not be always aware of the hand-off between different networking layers [38].

The seamless integration [38] has several requirements, the most important of which are:

Appropriate authentication infrastructure, minimize the interruption caused by the handover and

preserve the QoS levels and features when the device moves between access technologies. One

solution to the seamless integration is to use the new features of Mobile WiMAX to integrate within

an evolved IP backhaul inside a third generation mobile phone network, like UMTS. This would

allow a hand-off from a faster Mobile WiMAX hotspot or network to a wider but older UMTS

coverage when leaving the metropolitan area. This would be accomplished by using the

interworking features of the Mobile WiMAX to connect it to the 3GPP access network by an

exposed generic IP interface.

5.4 WiMAX Around the World

While currently WiMAX might not be able to match Wi-Fi in the commonplaceness and the

affordability of the devices, WiMAX does match Wi-Fi in performance. It is expected that

standardization will not only reduce equipment and component costs, but it will also allow

interoperability between the equipment of different vendors [45]. The vendors and service providers

of WiMAX Forum [12] believe that it will eventually be as widely deployed as Wi-Fi is today, with

the 2,4GHz Wi-Fi being the most common unlicensed data access method.

While reliable statistics were not available from academic databases about the current market

34


37/47

situation in modern countries, a quick independent study revealed that current WiMAX networks

available for resale are centered around metropolitan or suburban areas in Finland [46]. The

situation in Northern America appears similar: Service for rural America is not current in

consideration, and in Canada WiMAX service is only now considered for more distant parts [47],

[48].

While older generation wireless networks are currently in use in developing countries, there is a lot

of potential for WiMAX outside the Western countries. Compared to wireless technologies, wired

networks do give the same or better performance but only to selected places and initial deployment

costs might be high and they lack the ubiquity and affordability: In a country with no initial

infrastructure it can be cheaper to skip the copper or fiber-laying stage completely because while

some of the equipment and electronic costs have declined, the cost of civil engineering, site

acquisition and the cable costs remain high. Taking these factors into account, it can be predicted

that the first viable infrastructure to serve rural and underdeveloped areas will be wireless

technology. [45]

The needs for communications infrastructure do not vary just from country to country but also from

one part of the country to other. Also, there isn't necessarily need for an uniform infrastructure since

the needs of cities and the more rural villages are different. Because of that it is necessary to

identify determine appropriate architectures for each tier of economy according to a strategic vision.

City-wide Wi-Fi/WiMAX is one high-tech economic development tools in use in developed

countries and it also could be used in developing nations. [45]

When considering implementing a large scale wireless network it is important to think of the social

and economical values of a network: These values are governed by three following assumptions.

The value of the network is proportionate to the number of customer it reaches, to the square

number of users it has and to the number of groups. [45]

One possible model is a three-layered one presented in figure 8 that separates the country into three

different zones: A metropolitan zone that is composed of large cities and would be covered by a

WiMAX backhaul and a mesh Wi-Fi network with the backhaul connecting the most important

portions of the mesh. The Wi-Fi mesh itself would cover most if not all portions of the city. In sub-

urban areas it is important to consider an affordable infrastructure where the subscriber base might

35


38/47

not be large enough to warrant full coverage of the area. Instead subscribes could reach access

points by using directional high gain antennas from the existing hotspots or utilizing long range

WiMAX coverage. That way the suburban areas would have a distribution of hotspots which cover

optimal zones such as neighborhoods or campus areas, with an option for longer range connectivity.

The most rural and remote areas that are hundreds of kilometers removed from fiber backbone

could be served by a satellite connection that it is commercially resold to a group of other access

points and users within the community such as entrepreneurs, community centers and schools. [45]

Figure 8: Tiered Communications Infrastructure [41]

36


39/47

6 CONCLUSION

WiMAX is a widely spreading networking technique that can be used in multiple different ways. At

the moment probably the most used application of WiMAX is a third generation broadband,

networking can be provided with fixed or mobile connections. Other newly emerging application of

WiMAX is the usage of WiMAX as a backhaul (or backbone as some call it) network for

applications like third generation mobile phone networks.

The current version of WiMAX can compete with other techniques that provide similar

functionality. These techniques are 3G mobile phone networks (UMTS) and Flash-OFDM.

Currently the throughput of WiMAX is on the same line with UMTS while WiMAX networks can

cover larger areas with less base stations. Flash-OFDM cannot compete with WiMAX when it

comes to transfer speeds but the coverage of one Flash-OFDM BS is far more better. But the

latency of the connection that is provided by WiMAX can be as low as in WLAN networks and

none of the existing mobile techniques can compete with that. Although UMTS and Flash-OFDM

can be used in higher speeds (the movement speed of a SS) WiMAX is a real tough competitor for

these techniques. The next version (or amendment) of WiMAX is being developed at the moment

and is rumoured to be more efficient providing better performance that can compete with any

available technology in transmission speeds [12]. It has been mentioned that next version of

WiMAX could provide speeds up to 300 Mbps [12].

Security of WiMAX can also be considered to be good, the actual method (cipher) for encrypting

the data is the same as used in current WLAN networks (AES) but the actual protocol that ensures

security is very different. PKM v2 that is used in modern WiMAX networks can be considered to

be secure since it fixes all vulnerabilities that were found from previous version.

WiMAX techniques hold a lot of potential for developing the state of wireless technology in use

today, with it being able to form both backhaul networks, fast point to point links to subscribers,

mobile use and hybrid solutions where those are more economical with new possibilities still being

developed as of now. Still, the mobile WiMAX seems to be most commonly in use as of early 2009

with providing mobile and stationary wireless Internet access to subscribers near suburban and

metropolitan areas.

37


40/47

7 REFERENCES

[1] IEEE 802.16-2001 Standard. Part 16: Air Interface for Fixed and Mobile Broadband

Wireless Access Systems [IEEE standard]. Institute of Electrical and Electronics

Engineers.

Available: http://ieeexplore.ieee.org/xpl/tocresult.jsp?isNumber=21532


Wireless Access Systems. Amendment 2: Medium Access Control Modifications and

Additional Physical Layer Specifications for 2-11 GHz [IEEE standard]. Institute of

Electrical and Electronics Engineers.

Available: http://ieeexplore.ieee.org/xpl/tocresult.jsp?isNumber=26891


Wireless Access Systems [IEEE standard]. Institute of Electrical and Electronics

Engineers.

Available: http://standards.ieee.org/getieee802/download/802.16-2004.pdf


Wireless Access Systems Amendment 2: Physical and Medium Access Control Layers

for Combined Fixed and Mobile Operation in Licensed Band [IEEE standard]. Institute

of Electrical and Electronics Engineers.

Available: http://standards.ieee.org/getieee802/download/802.16e-2005.pdf

[5] WiMAX Book Overview Learn about WiMAX [intenet page]. Wimax.com [retrieved

8.1.2009].

Available: http://www.wimax.com/education/wimax/wimax_overview

[6] Mobile WiMAX Part I: A Technical Overview and Performance Evaluation [White

paper].

Wimax Forum. 2006. [retrieved 2.2.2009].

Available: http://www.wimaxforum.org/documents/downloads/Mobile_WiMAX_Part1

_Overview_and_Performance.pdf

38


41/47

[7] David Johnston, Jesse Walker. Overview of IEEE 802.16 Security.

IEEE Security & Privacy Magazine. Volume 02, Issue 3, May-June 2004. Pages: 40 -

48.

ISSN: 1540-7993

[8] Evren Eren. WiMAX Security Architecture Analysis and Assessment.

4th IEEE Workshop on Intelligent Data Acquisition and Advanced Computing Systems:

Technology and Applications. IDAACS 2007. Dortmund, Germany. Pages: 673-677.

2007.

ISBN: 978-1-4244-1347-8

[9] Leonardo Maccari, Matteo Paoli, Romano Fantacci. Security analysis of IEEE 802.16.IEEE International Conference on Communications. ICC 2007. Glasgow, Scotland.

Pages: 1160-1165. 2007.

ISBN: 1-4244-0353-7

[10] Fan Wang, Amitava Ghosh, Chandy Sankaran, Philip J. Fleming, Frank Hsieh, Stanley

J. Benes. Mobile WiMAX Systems: Performance and Evolution.

IEEE Communications Magazine. Volume: 46, Issue: 10, October 2008. Pages 41-49.

ISSN: 0163-6804

[11] WiMAX End-to-End Network Systems Architecture. Stage 2: Architecture Tenets,

Reference Model and Reference Points. Part 1. [White paper].

WiMAX Forum. 2006. [retrieved 2.2.2009].

Available: http://www.wimaxforum.org/documents/documents/WiMAX_Forum_

Network_Architecture_Stage_2-3_Rel_1v1.2.zip

[12] Wimax Forum Frequently Asked Questions [internet page]. Wimax Forum [retrieved

8.1.2009].

Available: http://www.wimaxforum.org/documents/faq/

[13] Pl Grnsund, Paal Engelstad, Torbjrn Johnsen,Tor Skeie. The Physical Performance

and Path Loss in a Fixed WiMAX Deployment.

International Conference On Communications And Mobile Computing. Proceedings of

39


42/47

the 2007 international conference on Wireless communications and mobile

computing. IWCMC07. Honolulu, Hawaii, USA. Pages: 439 444. 2007

ISBN: 978-1-59593-695-0.

[14] Ole Grndalen, Pl Grnsund, Tor Breivik and Paal Engelstad. Fixed WiMAX field

trial measurements and analyses.

16th IST Mobile and Wireless Communications Summit. Budapest, Hungary. Pages: 1

5. 2007.

ISBN: 963-8111-66-6

[15] Tudor Palade, Emanuel Puschita, Ion Bogdan. Performance evaluation of Wireless

Systems implementing IEEE 802.16 standard.12th WSEAS International Conference on Communications. Heraklion, Greece. 2008.

ISBN: 978-960-6766-84-8

[16] Pavel Mach, Robert Bestak. WiMAX Performance Evaluation

Sixth International Conference on Networking, 2007. ICN '07. Martinique, Caribbean,

Sea, France. Pages: 17-17. 2007.

ISBN: 0-7695-2805-8

[17] Thomas Schwengler and Niranjan Pendharkar. Testing of fixed Broadband Wireless

systems at 5.8 GHz.

IEEE Region 5 and IEEE Denver Section Technical, Professional and Student

Development Workshop. Pages: 32 38.

ISBN: 0-7803-8898-4

[18] Dongmyoung Kim, Hua Cai, Minsoo Na, and Sunghyun Choi. Performance

Measurement over Mobile WiMAX/IEEE 802.16e Network.

International Symposium on a World of Wireless, Mobile and Multimedia Networks.

WoWMoM 2008. Newsport Beach, California, USA. Pages: 1-8. 2008

ISBN: 978-1-4244-2099-5

[19] Markkinalhtinen taajuushallintomalli Tyryhmn ehdotus [pdf document].

Ministry of Transport And Communications Finland. Helsinki, Finland. 2008. [retrieved

40


43/47

2.2.2009].

Available: http://www.lvm.fi/fileserver/1908.pdf

[20] Taajuuksien kehittmistyryhm, Vliraportti 27.11.2007 [pdf document].


2.2.2009].

Available: http://www.lvm.fi/fileserver/upl114-Taajuustyryhmn%20vliraportti.pdf

[21] Radiotaajuuksien kaupallistamisen mallit EU-maissa [pdf document].


2.2.2009].

Available: http://www.lvm.fi/fileserver/LVM08_08.pdf

[22] IEEE 802.16 and WiMAX Broadband Wireless Access for Anyone [White paper].

Intel. 2003.

[23] David Ginsburg. ADSL. 2000. 282 s. ISBN 951-826-181-4

[24] Asymmetric DSL [internet page]. Howstuffworks.com [retrieved 10.1.2009].

Available: http://www.howstuffworks.com/dsl.htm

[25] Flash-OFDM technology [internet page]. CroCopil project [retrieved 10.1.2009].

Available: http://www.cdt.ltu.se/projectweb/42c13bdf2e759/Flash%20OFDM.html

[26] Flash-OFDM overview [internet page]. Qualcomm [retrieved 10.1.2009].

Available: http://www.qualcomm.com/products_services/networks/flashofdm/

overview.html

[27] 3GPP Keywords-WCDMA-HSPA-LTE-etc [internet page]. 3rd Generation Partnership

project [retrieved 11.1.2009].

Available: http://www.3gpp.org/Keywords-WCDMA-HSPA-LTE-etc

[28] Qualcomm Achieves World's First HSPA+ Data Call [internet page]. Qualcomm.com

[retrieved 12.1.2009].

41


44/47

Available: http://www.qualcomm.com/news/releases/2008/080731_Qualcomm_

Achieves_Worlds_First_HSPA_Data_Call.html

[29] IEEE 802.11-2007 Standard. Part 11 Wireless LAN Medium Access Control (MAC)

and Physical Layer Specifi

local area networks-wimax

Documents