Wimax technology for broadband wireless access 2007 phần 1 ppt

The digest is calculated over an entire MAC management message with the exception of the HMAC-Digest or HMAC Tuple attributes.15.4.1 Message Authentication Keys The authentication keys u

The digest is calculated over an entire MAC management message with the exception of the HMAC-Digest or HMAC Tuple attributes.

15.4.1 Message Authentication Keys

The authentication keys used for the calculation of HMAC keyed hash included in some MAC management messages (see above) are:

• the downlink authentication key HMAC_KEY_D used for authenticating messages in the downlink direction;

• the uplink authentication key HMAC_KEY_U used for authenticating messages in the uplink direction.

As for PKMv1, the PKMv2 MAC message for the uplink is C/HMAC_KEY_U and the MAC message for the downlink is C/HMAC_KEY_D HMAC_KEY_D and HMAC_KEY_U are derived from the AK, as mentioned in Section 15.3 above The HMAC/CMAC/KEK deri- vation from the AK is illustrated in Figure 15.14.

AK-160 bits Authentication

Figure 15.14 HMAC/CMAC/KEK derivation from the AK (Based on Reference [2].)

The BS uses HMAC_KEY_D and HMAC_KEY_U for the following:

• Verify the HMAC-Digest attributes in Key Request MAC management messages received from that SS, using HMAC_KEY_U.

• Calculate, using HMAC_KEY_D, the HMAC-Digest attributes it writes into Key Reply, Key Reject and TEK Invalid MAC management messages sent to that SS.

• When receiving MAC messages containing the HMAC Tuple attribute, the BS uses the HMAC_ KEY_U indicated by the HMAC Key Sequence Number to authenticate the messages HMAC_KEY_S is used in the Mesh mode HMAC-Digest calculation.

15.5 Other Security Issues

The procedures seen in this chapter are all about device authentication (SS or BS) level protocols, such as the higher-level EAP, may be used for this purpose This type of authentication is part of a WiMAX network specifi cation.

Comparisons and Conclusion

16.1 Comparison Between Fixed WiMAX and Mobile WiMAX

In this chapter, some comparisons and then the conclusion are proposed It is rather risky to give comparisons in a time where the broadband wireless access is at the eve of great changes and innovations However, based on technical background, many news reports and confer- ence analyses, some comparisons are given A start is made by comparing Fixed WiMAX and Mobile WiMAX.

Which technology must be chosen? Fixed WiMAX products are already here The problem

is that they can only propose a fi xed wireless access, although at rather long distances, up to

20 km Is it better for an operator to wait some time, until the end of 2007 or the beginning

of 2008, according to present expectations, to have Mobile WiMAX? It is up to each tor to decide, taking into account the market targeted In places where telecommunication infrastructure is well developed, it seems that Fixed WiMAX cannot compete with wired technologies such as DSL Indeed, it would be surprising to have a wireless (unlimited) Mb/s cheaper than a wired (unlimited) Mb/s in London or Paris one day soon However, what if this wireless (unlimited) Mb/s includes nomadicity (‘your PDA Internet connection works everywhere in the city, although you have to restart your session’) and, even more, mobility (‘your session is uninterrupted when you move’)?

opera-WiMAX has some strong advantages: the same infrastructure can have Fixed and Mobile WiMAX access; the operator can start by covering a small area (if regulatory requirements do not forbid it) in order to adapt the deployment evolution to the busi- ness case This is sometimes known as the ‘pay as you grow’ model More generally, the business case must be adapted to the market profi le: fi gures of business travellers, remote (fi xed) subscribers, urban technophiles, applications expected (such as Internet, games), etc This could make, in some cases, Fixed WiMAX a good starter before wide deploy- ments of Mobile WiMAX This could also give the Fixed WiMAX operator a leading position (reputation, market knowledge, client database, technical teams, etc.) before the deployment of Mobile WiMAX Mobile WiMAX should normally occupy a majority of the WiMAX landscape for some years However, a precise estimation of the number of years is thought to be very diffi cult to give today This may well leave a market share for Fixed WiMAX, at least for ‘some’ years Some applications are, by nature, fi xed

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(e.g telemetering) On the other hand, it must be kept in mind that Mobile WiMAX can also be used for fi xed access from the technical point of view, not taking into account the cost parameter An important parameter is the spectrum and the cost of this spectrum for each of Fixed and Mobile WiMAX As of today, these spectrums do not have overlapping zones.

16.2 Comparison Between WiMAX and WiFi

A start can be made by saying that comparing WiMAX and WiFi is comparing two ent frameworks WiMAX has much longer distances and may (or will) also include mobility between cells In fact, WiFi and WiMAX are complementary, specifi cally if WiMAX is used for the backhauling of WiFi (see Chapter 1).

differ-There is also a difference in the chronology WiFi is a WLAN, based on the IEEE 802.11 standard, published in 1997, and the 802.11b variant, published in 1999 WiMAX is a BWA system, including mobility, based on the IEEE 802.16-2004 standard [1], published in 2004, and the 802.16e variant [2], published in February 2006 (in addition to other 802.16 amend- ments) Hence, if we consider the standard or the products, there is a difference of about six years between the two In Table 16.1, some comparison elements between WiFi and WiMAX and proposed.

Some precision must be given for the data rate The one expressed in Table 16.1 is the PHYsical data rate, i.e the data rate of coded bits The highest data rate mode is displayed in the table For all these packet-type transmissions, there is no fi xed value for a data layer data rate value due to retransmission, link adaptation, variable header sizes, etc Standardisation efforts are going on in order to have a higher data rate for IEEE 802.11/WiFi, specifi cally with the 802.11n variant.

WiMAX has a much better performance than WiFi (range, QoS management, spectrum use effi ciency, etc.) but this comes at the price of a higher cost in frequencies and in equip- ment complexity (and then cost) Consequently, it is defi nitely not certain that WiMAX could one day soon replace WiFi for some applications.

Table 16.1 Some comparison points between WiFi WLAN and WiMAX BWA

Data rate (PHY Layer,

optimistic)

54 Mb/s /20 MHz channel 26.2 Mb/s / 7 MHz channel

QoS management Best Effort, unless for the seldom (until

now) implemented 802.11e variant

Five classes of QoS

Multiple access CSMA/CA (MAC Layer common

to 802.11, 802.11a, 802.11b and 802.11g); TDD

TDMA: TDD and FDD Sophisticated bandwidth reservation mechanisms

(indoor CPE)

portability, mobility, etc

Comparisons and Conclusion 253

16.3 Comparison Between WiMAX and 3G

Table 16.2 gives some comparison elements between major wireless systems: the generation cellular system GSM, in its EDGE evolution, 3G UMTS, WiFi in its two variants, 802.11b (the original WiFi) and 802.11a (including OFDM transmission), and WiMAX.

second-In order to compare with cellular 3G networks, only Mobile WiMAX is considered, since Fixed WiMAX represents a market completely different from 3G The advantages of each of the two systems are highlighted, starting with the older one, cellular 3G.

16.3.1 Advantages of the 3G Cellular System

• WiMAX uses higher frequencies than Cellular 3G, which mainly operates in the 1.8 GHz range Received power decreases when frequency increases and wireless system transmit- ted powers are often limited due to environmental and regulatory requirements WiMAX ranges are globally smaller than 3G ranges This is the case for outdoor and indoor equip- ments However, the cell range parameter is often not the most limiting one in high-density zones, where the main part of a mobile operator market is located.

• 3G is already here Its equipment including the high-data rate High-Speed Downlink Packet Access (HSDPA) networks and products are already used, since 2005 in some countries Globally, 3G has a fi eld advance of two to three years with regard to WiMAX Will it be enough for 3G to occupy a predominant market share?

• The WiMAX spectrum changes from one country to another For example, a WiMAX user taking equipment from country A to country B will probably have to use a different WiMAX frequency of the operator of country B On the other hand, making multifrequency mobile equipment, for a reduced cost, is now becoming more and more easy for manufacturers.

Table 16.2 Some comparison elements between major wireless systems

Operating frequency

Licensed One channel

(frequency carrier) bandwidth

Number of users per channel

magnitude:

25); data rate decreases

5 km (up to, often less)

3.5 MHz,

7 MHz,

10 MHz, other

Many (100, …) 20 km

(outdoor CPE)

• Some countries have restrictions on WiMAX frequency use, i.e WiMAX operators can be forbidden to deploy mobility by the regulator.

• Cellular 3G has long had the exclusive support of leading manufacturers, such as Nokia These companies now seem to be interested in WiMAX while also still remaining very interested in 3G.

16.3.2 Advantages of the (Mobile) WiMAX System

• The frequency spectrum of WiMAX should be cheaper than 3G system frequencies in many countries The UMTS licence sales in Europe, and specifi cally in Germany and the

UK, reached surprisingly high amounts.

• WiMAX is a very open system as frequently seen in this book: many algorithms are left for the vendor, which opens the door to optimisation, and connections between different busi- ness units operating on different parts of the network (core network, radio access network, services providers, etc.), possibly in the same country, are made easy (see Chapter 13) This

is probably an advantage, but perhaps it might create some interoperability problems in the

fi rst few years?

• The WiMAX PHYsical Layer is based on OFDM, a transmission technique known to have

a relatively high spectrum-use effi ciency (with regard to SC CDMA) There are plans to upgrade 3G by including OFDM and MIMO in it This evolution is called, for the moment, LTE (Long-Term Evolution) This gives a time advance for WiMAX in the implementation

of OFDM.

• WiMAX is an all-IP technology This is not the case for the 3G system where many mediate protocols (tunnelling, etc.) made for the fi rst versions of 3G are not all-IP How- ever, evolution of 3G should provide end-to-end IP (or all-IP).

inter-• WiMAX has a strong support of some industry giants, such as Intel, KT, Samsung and many others.

Taking into account all these observations, it is very diffi cult to decide between the two tems However, if we want to make a guess, it could be said that there is a place for both of these two technologies, depending on the market, the country and the application … at least for a few years to come!

sys-16.4 Final Thoughts and Conclusion

In this book, an attempt has been made to give a global picture of this new and exciting WiMAX technology WiMAX is based on two sources: the IEEE 802.16 standard, includ- ing its amendments, and the WiMAX Forum Group documents Evidently, this book does not replace these documents, but it is hoped that it will provide a clear introduction to the subject.

WiMAX has a large number of mechanisms and is expected to be used for many tions The near future will tell which of these mechanisms will be implemented, how they will

applica-be implemented and the mechanisms that will applica-be updated by the standardisation bodies.

Multiple access and burst profi le defi nition Messages

in addition to other uplink channel parameters

Broadcast

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Mesh network (confi guration, entry and scheduling) messages

is an embedded data of the MSH-NCFG message

The Network Descriptor contains many channel parameters (modulation and coding schemes, threshold values, etc.) which makes it similar to UCD and DCD

to inform all the neighbours of the schedule of the transmitting station

Sent by the SS in response to an MCA-REQ

Contains mainly the Confi rmation Code, indicating whether the request was successful

Primary management

Transmitted by the SS at initialisation It can also be used

at other periods to determine the network delay and to request a power and/or downlink burst profi le change

Initial ranging

RNG-Initial ranging

Transmitted by the BS on the SS Basic CID in response

to a DBPC-REQ message from the SS If the (required) DIUC parameter is the same as requested in the DBPC-REQ message, then the request was accepted

Otherwise, the DIUC parameter of DBPC-RSP is the previous DIUC at which the SS was receiving downlink data

Basic

SS basic capability negotiation messages

Basic

Basic Capability Response

Transmitted by the BS in response to an SBC-REQ Indicates the intersection

of the SS and the BS capabilities

Sent by an SS or BS to create a new service

fl ow Service fl ow attributes, including QoS parameters are indicated

Primary Management

DSA-Primary management

Primary management

Sent by the SS in order to register with the BS

Indicates supported management parameters,

CS capabilities, IP mode, etc

Primary management

it again, use it with restrictions, etc.) Unsolicited

or in response to an SS DREG-REQ message

Basic

De-registration

Request message

Sent by the SS to the BS in order to notify the BS

of the SS de-registration request from the BS and the network

Radio resource management messages

Basic

(continued overleaf)

A.1 The MAC Management Messages added by 802.16e

The following MAC management messages were defi ned in 802.16e They are about bility, power-save modes, power control, MBS and MIMO.

mo-AAS (Adaptive Antenna System) messages

Type

(8 bits)

Message name Description (related to AAS operations) Type of connection

Primary management

Implementation of the FPC is optional Power control

is normally realised by periodic ranging

Broadcast

(continued)

Power control mode messages

62 MBS_MAP Sent by the BS, on an MBS portion to describe the MBS

connections serviced by this MBS portion If MBS_MAP

is not sent, these connections are described in the DL-MAP

Broadcast, Primary management

Basic

Scanning interval

allocation Response

Sent by the BS to start MS scan reporting with

or without scanning allocation

Basic

(continued overleaf )

Sleep mode messages

Basic

MOB_SLP-RSP, Sleep

Response

Sent from the BS to an MS on Broadcast CID or on the

MS Basic CID in response to an MOB_SLP-REQ message, or unsolicited May contain the defi nition

of a new Sleep Mode Power Saving Class or signal activation

Sent from the BS to an MS in a Sleep mode that has one

or more Sleep Mode Power-Saving Class Type I This message, sent during those MS listening intervals, indicates whether there has been traffi c addressed to any MS that is in Sleep mode

The MS transmits a MOB_SCN-REP message

to report the scanning results to its serving

BS after each scanning period at the time indicated in the MOB_SCN-RSP message

Primary management

ASC-REP message, which the Serving BS then sends to the MS

Primary management

or rejects the handover, it also transmits the MOB_HO-IND message with a proper indication

Basic

(continued)