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`EXHIB}T 5
`WILLIAMS
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`Anne Torreano, CSR 10520
`
`Sierra Wireless EX 1018 p 1
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`

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`MOBILE HAI{DSE,T
`DESIGI\
`
`Sa.ial Kumar Das
`Nokia R&D Center, Indict
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`copyright @ 2010
`
`John wiley & sons (Asia) pte Lrd, 2 clementi Loop. # ()2-0t,
`Singapore 129809
`
`Visit our Home Page on wwwwiley.cont
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`John Wiley & Sons lnc., I I I River Streer, Hoboken, NJ 07030, USA
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`
`Library of Congress Cataloging-in- publication Data
`Das, Sajal K.
`Mobile handset design / Sajal Kurnar Das.
`p. cm.
`ISBN 978-0-470 -8246't -2 (ctoth)
`l Mobile communication systems. 2. wireless communication systems. 3. cellular telephones. I. Title.
`TKós70.M6D35 2009
`621.3845'64c22
`
`2009018?t4
`
`rsB N 978-0-470 _fa246.7 _? (HB)
`
`Typeset in 9/l lpt Times by Thomson Digital, Noida, Inc.lia.
`l:rlt:d and bound in Singapore by Markono prinr Mectia pte Ltd, Singapore.
`This book is printed on acitl-fiee paper responsibly nranut'actured tiom sustainable f<lrestry in which at least
`two trees are planted for each one used i.or paper procluction.
`
`Sierra Wireless EX 1018 p 3
`
`

`
`20
`
`Mobile Handset Des lgn
`
`power P, is spl'ead over the surt'ace o{'a sphele whose raclius is r., so the power density will be p,/.lnrr.
`Taking this energy, the fìux lines will nrove away fionr the transmitting on,.nnn. Now, as they move away
`tì.onttheantenua'thesizeofthesphereincrea.es.rincreasesbutthesarnepower(p,)iscontaineclwithinit.
`Thus the porver density Pr/4n'i clecreases as it travels firr tì'onr the transnritting antenna (tìlr exarnple.
`increase in r )' and the problenr of transnrission of electrical energy via air/fiee-space is solvecl.
`How ís Ettcrgy Receioed on the olher síde? - Again, the anteina helps to solve this pr.oblem too. It
`transfirrms the received EM wave into an electrical signal. when the transmittecl wave arrives at the
`receiving end' it tries to penetrate via anothel the nletallic antenna. we know that the EM wave consists of
`an electl'ic fìeltl and a nlagnetic fìekl and that these are perpendicular to each other, and also that they are
`perpendicular to the direction of propagation. Thus when the EM wave touches the metallic antenna (fio'r
`Maxwell's third equation) the rragnetic tìeld (É/ )will generate a surf.ace current on the nletallic antenna,
`which will try to penetrate via the lnetal (as it is a sood conductor). Hr¡wever. it will die clown afÌer
`traveling a thickness ofthe skin clepth, ancl. the EM wave will generate an electrical current in the rnetal
`body of the antenna. Similarly (fì.orn Maxwell's fourth equation). the electric fìeld will generare an electric
`voltase in tlte antenna. as shown in Figure Ll9.
`This phenrmenon can be experience<l by pracing a radio inside a crose, metal
`that it does not play. as the EM wave can noip.n.,roì. uia the thick meta¡ jc wa'.
`through a concrete wall' For the same ,.n.n,,. o mobile telephone call disconnects inside an enclosecl
`"'.',t-ti:iiîrîi#ÍÏ:
`nretallic lifÌ due to the <iegradation of the signal strength.
`Thus we have convertecl the transmittecl energy {which was transmitted using the carrier of the EM
`waves) back into the electrical signal through the help of another antenna. so the antenna helped in
`transmitting and receiving the infbrnlation through the air. As the user wants to sencl and receive the
`infonnation' ideally the user should have both tranJnitting and receiving onr.nnor. However, in general. in
`a ntobile device' the sanle antenna is usecl fìrr transmission as well as r.eceìving purposes ( ret'er to chapter 4).
`Thus we ntlw kltow how to transmit and receive the infbrmation uio tt. nî, tft)r example. via a wireless
`nredium) using antenna However. the problem at this stage is whether the baseband signal is transmittecl
`its lrequencv is low (-KHz), ancl so it can nor be senr directly via the air clue ro rhe rbilowing
`iïi::íìl'
`
`A lalger antenna length (-1./4) is required.
`Much less BW is available at the lower frequency region.
`
`I 2
`
`The soltrtion kl this is to up-convert the baseband signal to a high frequency RF signal at the transmitter.
`and then sirnilarly down-convert at the receiver fbr exanrple. *rricrr råqul,-e. RF conver.sion techniqr:es.
`How is the baseband signal up-converted/down-converted'J The solution fbr up-conversion is the use of
`analog or digital modulation and nrixing techniques (on a transmitter block) and the solution lbr down-
`conversio¡r is the use of demodulation_ nrixing techniques (on a receiver block). These wi ll be discussed in
`nrore detail in chapter 4' Next we will establish whaì else, apaff from the anten¡ra, is require¿ insi¿e the
`transmitter and receiver to franstnit or receive the information.
`
`1.2.3 Bqsic: Building Blocks of ct wireless Transmiîter (tnd Receiver
`we know that a iligital system is more imnune to noise, and that in adclition to this thele are rnany such
`advantages ol'digital systems over the olcl analog systems. So, from th. r..nnd g.n"ration onwarcls *ir.l"rl
`systems have been designed with digital technology. However, there is o i-ur.r, in that voice and
`video signals are inherently analog in nature. so ¡o*.on these signals be interf'aceil with a ¿igital system,l
`These signals have to be brought into the digital domain. for procelsing ,ring on onurog-to-digital converter
`( ADC) and then again reverred back into an analog signal using a aigita't-to-aiaiof lonu.n., inAC) ancl rhen
`sentviaanantenna'Atypical
`transmitterblockãiagranrol'awirelesssysternisshownintheFigure
`
`1.20.
`
`Sierra Wireless EX 1018 p 4
`
`

`
`lntroduction to Mobile Handsets
`
`t',l
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`
`to digital
`converslon
`(AUDTO CODEC)
`
`Date source
`
`Digital modulation
`(convert digital
`data to analog
`signal)
`
`Channel coding
`(EFìFIOR coding)
`
`Data
`segmentation
`
`Analog
`modulation
`(RF up
`convertion)
`
`Power ampl
`
`Antenna
`
`EM waveltt/
`
`lnterleaving
`
`Ciphering
`
`Duplexer
`
`Digital baseband unil
`
`Transmltter
`
`RF frontend
`
`Irigure 1.20 Transrnitter system block tliagrarn
`
`As sht>wn in the Figure 1.20, on the transmitter side, when the user speaks in front of a rnie ruphotrc, it
`generates an electrical signal. This signal is sampted and converted into digital data and then tèd to the
`i..,¡rce coclec, for ex¿mple. a speech codec unit (this is discussed in more details in Chapter tì)' which
`rcrnoves the reclgndant ciata and generates the intbrmation bits. These data are then tècl into the channel
`coder unit. When the signal travels via the metlium, during this time it can be ¿ffected by signal noise, so
`rve need sorre type of protection against this. The channel coder unit inserts some extra redundant clat¿ bits
`tusing an algorithm, which helps the receiver to detect and correct the receivecl data (this is cliscussecl in
`n¡,r.",l.tnil in Chapter 3). Next. it is fèd to nn interleaving block. When data pass through the channel. this
`tirne there miry be some type of burst noise in the channel. which can acttlally colrupt the entire clata during
`rhis b¡rst period. Although the burst lasts tbr only a short duration, its anrplitude is very high. so it corrupts
`the clata enf irely fbr that duration. In order to protect the tlata tìrrm btrrst en'of, we rreed to randomize the
`tlata signal (separate consecutive bits¡ over the entire data tïlinle, so th¿tt dûta citn be recovel'ed' althottgh
`sorne p¿ìrt will be corrupted completely. An interleaving block helps in this respect (this is (liscussed in
`tlctail in Chapters -3 untl 8). Next, it is passetl to a ciphering block, rvhere the clata ale cipherecl using a
`spec'ifìc algorithrr. This is basically clone for rlata security purposes, so that un¿tuthorizecl boclies cannot
`.leõíicle tlre intbrrnation (ciphering is rliscussecl in Chapters 7 and 9). Then the data are put together in a
`hlock and segnrentecl tccorcling to the dlltx frame length.
`T¡e clata processing is now over, and next we have to pass it fbr transmission. This tlata signll can lrot he
`scnt dir.ectly using an ¿lntenn¿ì. becuuse, it will be conrpletely distorted- Also, the lrctlttcncy and anlplitucle
`olthe clata signal is less. as we know the length olthe transmitting iìntenna shotrld bc ¿ nlinimurï ol'the
`orrler of Z/4. So, the ret¡uirecl size of the antenn¿ will have to he very large, which is not t'easible. This is
`tvhy we neetl t1¡ co¡vert it into a high tiequency analog signal usiltg rnodulation techniclues.'Ihe digital
`rloclulator h|rck transt'ers the digitîl signal into a krw anrplittrde lnalog signal. As the fiec¡trency ol this
`arrakre siqnal n-ray be less. lve therefbre rray need to convert it into a hi-uh fret¡uency IìF signal. where tlre
`rvavelength is slrlll ancl the requirecl antenna length will also be snlall. The analog lltotlulittor block helps
`to up-convert the analog signal frequency to rì high RF carrier fret¡rtcncy (the nloclulation technitlue is
`tliscussetl in Chapter 5). It is then t'ed into ¿r power amplilìer to increase the porver olthe signal. ittrtl al'ter
`that it is passed to rluplexer unit. We know that uur telephr)ne ilcts as ir transmitter as well its a rcceiver. so it
`
`Sierra Wireless EX 1018 p 5
`
`

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`+ !
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`
`Mobile Handset Design
`
`should have both a transmission and a reception block inside. As we wa¡lt Jo use the same antenna for
`transmission and for reception purposes, so we c<-rnnect a duplexer unit to separare out the transrnitting and
`receiving signals' The transmitted signal goes to an antenna and this antenna racliates the signal through
`airltiee space.
`As shown in Figure l'21, the reverse sequence happens in the receiver, once it receives the signal. The
`antenna actua¡ly receives many such EM waves. which are ofdifferent frequencies. Now, ofthese signals,
`the receiver should receive oly
`lh: desired frequency band signal that is transmitted by rhe transmirrer.
`This is done by passing the signal fiom the dupËxer uia a bunã-puss fìlter. This filrer will allow only rhe
`desired frequency band signal to pass through ii and the remiander will be blocked. Afrer rhis, ir passes via
`the low noise amplifìer to increase the power of the feeble signal that is received. Then it is RF down-
`converted (analog demodulated)' digital demodulated, de-interleaved, a"-"ipi.."a, decoded and the
`information blocks are recovered. Next, it is passed to the source decoder and ulrirnutaly converted back
`into ¿rn analog voice signal by the DAC andpassed to the speaker to create the speech signal.
`
`1',
`
`Antenna
`
`l'
`d
`
`Digital to analog
`conversion
`(AUDtO CODEC)
`
`Channel decoding
`
`Digital
`demodulalion
`(generate
`data)
`
`Data
`concatenation
`
`De-interleaving
`
`De-ciphering
`
`Dig¡tal baseband unit
`
`Receiver
`
`Analog
`demodulation
`(RF down
`conversion)
`
`Low noise
`ampl
`
`filter
`
`Duplexer
`
`BF fronfend
`
`Figure 1.21 Receiver system block diagram
`
`In this figure the front blocks dealswith the analog signals. This fiont-encl part that deals with the analog
`signal is called the RF front-end or RF transceiver. Sometimes the digital modulation/de-modulation unit
`is also put together with the RFtransceiverunit (the design of the RF tiansmitterand receiver are discussed
`in detail in chapter4)' The back-end part, where the baseband cligital signal (baseband signal) is processed
`and the signaring and protocol aspects are dealt with is known as the baseband module.
`
`1.2.4 The Need for e Communication protocol
`we have seen how the sender and receiver communicate via a wireless channel using a transmitter an¿ a
`receiver To set up, maintain and release any communication between the users, we need to follow certain
`
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`
`Sierra Wireless EX 1018 p 6
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`

`
`Introduction to Mobile Handsets
`
`23
`
`protocols, which will govern the communication between the various entities in the system. The Open
`Sysrem Interconnection (OSI) retèrence model was specified by ITU, in cooperation with ISO (lntema-
`tional Organization for Standardization) and IEC (International ElectrochemicaI Commission). The OSI
`reference model breaks down or separates the communication process into seven independent layers, as
`shown in Figure 1.22. Generally, in wireless communication systems, similar to the ISO-OSI model, a
`tayered protocol architecture is used. However, in most instances, only the lower three layers (physical.
`data link and netwofk) are modified according to the needs of the various wireless systems. A layer is
`composed of subsystems of the same rank of all the interconnected systems. The functions in a l¡yer are
`perfbrmed by hardware or software subsystems, and are known as entities. The entities in the peer layers
`(sender side and receiver side) communicate using a defìned protocol. Peer entities communicate using
`peer protocols. Data exchange between peer entities is in the tbrm of protocol data units (PDUs)' All
`messages exchanged between layer N and layer (N - I ) are called primitives. All message exchange on
`the sâme level (or layer) between two network elements, A and B, is <letermined by what is known as peer-
`to-peer protocol.
`
`SYSTEM.A
`
`Applicat¡on
`
`Presentation
`
`Session
`
`Transport
`
`Network
`
`Data link
`
`Physical
`
`Communicalion link
`
`SYSTEM.B
`
`Application
`
`Presentation
`
`Session
`
`Transport
`
`Network
`
`Data l¡nk
`
`Physical
`
`Figrre 1.22 Peer to peer protocol layers
`
`Various wireless standarcls, such as CSM (Clobal Systems fbr Mobile Communication) and UMTS
`(Universal Mobile Telecommunications System) have been developed tbllowing ditlerent sets of protocols
`as required for the communications. This is discussed later in more detail in the appropriate chapters.
`
`1.3 Evolution of Wireless Communication Systems
`Since the invention of the radio, wireless communication systems have been evolving in various w¿Iys to cater
`to the neecl tbr communications in a virriety ol segments. These are broadly t.tivided into two categories:
`
`Broadcast communication systems - This is typically simplex in nature, which Ineans that one sicle
`transmits and other side receives the infbrmation, and there is no ièedback from the receiver sitle.
`Typically raclio lnd TV transmissions are of this nature. This is generally point-to-rnulti-point in
`nature. The transnlitter broadcasts the inibrmation and all the intended receivers receive that
`inlbrmation by tuning the receiver.
`
`Sierra Wireless EX 1018 p 7
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`

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`256
`
`Mobile Handset Design
`
`User process
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`Device drivers
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`Linux kernel
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`Figure E.2 RT-Linux kernel
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`
`8.3 Device Driver Software
`Protocol software, radio modem processing software (layer-l part), and application software usually run
`on processors on top of an RTOS and there are several hardware blocks, which are meant to perform
`specific tasks (such as keypad, microphone, display, RF HW module, etc.). These hardware blocks are
`configured and controlled by the processors að required. It is risky to work with bare hardware and also
`difficult to make the hardware work according to the command. Device driver is a software program that
`controls devices such as the keyboard, LCD, camera, USB, and so on. A device driver acts like a translator
`between the device and programs that use the device. Each device has its own set of specialized commands
`that are known to its driver. In contrast, most programs access devices by using generic commands. The
`driver, therefore, accepts generic commands from a program and then translates them into specialized
`commands for that device. Now, instead of putting code in each application, we write conrols for each
`device and then share the code between different applications in order to share the same hardware among
`the various applications.
`
`8.4 GSM System Protocol Software
`As mentioned earlier, for various reasons (for example, to connect to the Retwork, to set up, maintain,
`release a call, and to route a call seamlessly), there is a need to define a set of rules or protocols between
`various network entities, which should be followed for communicating or passing infonnation among the
`entities. For the GSM system these are called GSM protocols. The protocol stack for GSM follows the
`same basic concepts ofISO OSI-7 layer architecture, but this has been modified at the lower three layers to
`sui-t the specific requirements. The very first aim of communication is to transport user information, but in
`order to suppott this, in parallel there is also a need for signaling data transmission. We have discussed
`earlier, for GSM, that the TCH is used for user specific traffic information sending and the SACCH and
`FACCH channels are mainly used to transmit the signaling information during the call (for example, along
`with the TCH) and SDCCH is used outside a call, for example, when the call is not established.
`The overall protocol architecture can be broadly divided into three planes: ( I ) userplane (speech, data);
`(2) control plane (signaling); and (3) management plane (management of network elements, such as
`configuration, faults, and so on). Within a GSM network, different protocols are needed to enable the flow
`ofdata and signaling between the varioust GSM subsystems. Figure 8.3 shows the interfaces that link
`different GSM subsystems and the protocols used to communicate on each interface. The GSM protocol
`
`Sierra Wireless EX 1018 p 8
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`

`
`ilgn
`
`GSM Mobile Phone Software Design
`
`257
`
`Um
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`Figure 8.3 GSM system entities and protocol interfaces
`
`architecture is designed such that the MS communicates with various protocol entities at different levels
`of abstraction.
`CSM speciflc protocols are mainly divided into three layers:
`a. Layer-L is the physical layer, which uses the channel structures over the air interface (Um) as discussed
`in chapter ó, Section o.r.i on¿ chapter 7. This is responsible lor channel encoding/decoding''
`interleaving, ciphering, burst fbrming, for example, bit (or symbol) transmission and reception over
`the air link.
`b. Layer-Zis the data link layer. The functionalities of this layer are: multiplexing of one or more layer-2
`connections on controvsignaling channels, error detection (based on HDLC), flow control' transmis-
`sion quality assurance, routing, and so on I l l'
`c. Layer-3 is the network layei. the functionalities of this layer are: connection management (air
`interface),subscriberi<lentification,managementoflocationdata,andmanagementofadtiedserviccs
`(SMS. call fbrwarding, conference calls. etc')'
`
`The user plane protocol architecture is much simpler ancl involves only physical layer and data-link layers'
`
`8.4.1 GSM Mobile Hctncl,set (MS) Protocol Stack
`Insicle a GSM mobile handset, enrities tbr all the layers are resicling and interacting with their
`corresponcÌing counterparts, which are spread across the GSM subsystems as shown in Figure 8'3'
`Different sub-layers in layer-2 ancl layer-3 of the GSM phone protocol stack are shown in Figure 8'4'
`Layer-Zand tayer-3 consists of r"veral entities ancl generally, entities run as sep¿ìrate threacls in an OS
`environment ancl use a queue basecl communication motlel, where the primitive contents are stored in
`tlynamically allocated partition fnemory sections. Generally, the interf'ace to L I consists of the primitive
`based service access ptlints.
`
`DL (data link layer) - This provides layer-2 f unctionality to the RR on clitferent logical GSM channels'
`RR (radio resource) -This .sub-layer makes sure that a suitable cell is selected, the surrounding neighbor
`cells are observed and the serving cell with the best radio quality is used. in iclle mode ancl in a call or
`rlata connection.
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`Sierra Wireless EX 1018 p 9
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`

`
`2-slì
`
`Mobilc Handset Design
`
`GSM
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`stack
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`l'igure 8.4 Mobile phone CSM prorocol srack (L2lL-1) archirecrurc
`
`ALR (adaptation layer) - TIris is an adaptation sub-layer that exists between the RR and L I lncl h'el¡rs ro
`support the RR in cell-selection/r'e-selecrion, sl pre-processing, aniì paging detection.
`MIVI (mobility managenrent) * This is ¿ì user protocol between the mobile station ancl the network
`switching subsystem (NSS ). fbr which the base station subsystem (BSS) is transparent. This sub-layer.
`makes sure that the mobile stavs in the registered state in the honle or roaming network. It is
`responsible for the fìrnctions relating to location registration, paging. attachrnent/detachlnent.
`handover. dynanric channel allocation ancl nranagement. MM nraintains the full or limited servicc
`of the phone. The niessages defined in MM allow lbr roaming and security funcrions in GSM.
`CC (call control) - This is in charge of circuit switched call handling. It perfbrms the required signaling
`between MS and network in order to establish, receive, maintain, and end a call. Han<Jling ol
`conferences and a second call is also in the scope of this entity. CC is part of the connection
`lnanagement (cM) layer.
`SS (supplementary service) - This is in charge of getting/setting ancl querying services in the
`network. such as call-fbrwarding, call-deflection, and call-barring. SS is part of rhe connecrion
`munagement layer'.
`Si\{S lsh¡rrt message service) - This provides the capability kr send and reccive SMS. The rcception ol a
`cell bl'oadcast messages (CBM) is also handled here. SMS is part of the connection lnanagement layer'.
`SII (sr:ssion management) - This sub-layer controls the activation/deactivation and nroditication of rlre
`PDP (packet data profìle) context in the CPRS system (discussed in Chapter I3). A context clefìnes the
`QoS fbr a packet oriented connection. the used NSAPVSAPI (service access point identifìer'), the IP
`adclresses of the MS, gateway and the DNS. Up to seven contexts carì be handled by SM. It is part of tlre
`connectiorì nranagernent layer.
`
`Each entity consists of several state machines, which process incorning events such as primitives,
`tilneouts, events. and use static storage to stoÍe state relevant data between events. Entities can intelact
`with other entities by sending events or prirnitives and they could lnaintain their own timers. Several
`entities could be grouped and run in a single OS thread as: CC - SMS - SS - SM.
`As the real-ti lne requirentelrts and the protocol itselfallow that only one entity of the gloups is active at a
`p¿ìrticular time. the entities can thus share tlre same input queue and the sanle stack.
`
`SIM (st¡bscriber identity module) * This entity controls the SIM dlivel that manages the âccess to
`different SIM data fields and provides an SAP (service access point is the interfirce point between two
`layers) towards MM. GMM. ancl ACI.
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`ACI (application control interface) - The application conrrol intertàce consists of several srate
`machines. which are triggered by AT-commands or incoming primitives from the underlying L23
`entities. ACI cont¡ols theL23 functions also by primitive exchange on rhe connected SAps.
`ùIMI (man-machine interface) - MMI is used to inreract with the user. It takes the input from the
`user through a touch screen or key pad and displays the output on the LCD screen or invokes the
`proper operations.
`
`In the next sections, the protocols and message structure used in different layers for communication
`among different entities in the system are described.
`
`8.4.2 Air Interface (IJm) Protocol
`In the Figure 8'5, the interfaces between Ll,Lz,and L3 layers are shown. In the signaling plane, as RR is
`an L3 enrity, it can interact with Ll and L2.
`
`User plane
`(data)
`
`Traffic channel
`TCH
`
`Physlcal fayer
`
`(,
`
`oC
`
`)
`
`I
`
`Signaling plane
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`Flad¡o resourc6 managemgnl
`L3
`
`Data
`
`layer
`
`L2
`
`+
`
`Figure 8.5 Ll, L2, and L3 interfhces
`
`8.4.2,1 Layer-l
`The physical properties of the um intert'ace have already been described in cletail in the previous chapter
`
`8.4.2.2 Layer2
`The main functionalities of the link layer are structuring in the frame, segmentation and reassembly, error
`detection and correction. multiplexing and flow control. Across the um intert'ace, the data Iink layer usecl
`is the LAPDm (modified LAPD). This is a modifìecl version of the LAPD (link access protocol fbr ISDN
`"D" channel) protocol' which is used in ISDN. This LAPDm protocol is related to two other layer-2
`protocols, such as HDLC and LAPB. For the clevelopment of the LAPDm prorocol. rhe LApD protocol is
`taken and all dispensable parts were removed to save resources. The frame f'onnats defined for LApDm
`are based on those clefined f'or LAPD. However, there are some important ilitl'erences between LApDm
`and LAPD, in particular with regarcl to fiame clelimitation methods ànd trnnsparency mechanisms. These
`dif'ferences are necessary fbr operation within the constraints set by the ra.tio path. LApDm supports
`tivo modes of operation: (l) unacknowleclgecl mode operation using UI tiames (no flow control and
`error control); and (2) acknowledged mocle operation using the multiple tiame procedure (positive
`
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`260
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`Mobile Handset Design
`
`acknowledgment, error co¡rection based on ARQ). For BCCHs and CCCHs only the unacknowledged
`mode of operation is implemented. LAPDm is used for information sent on the control channels BCCH,
`AGCH, NCH, PCH, FACCH, SACCH, and SDCCH as defined in the GSM standard.
`LAPDm use$ three frame formats:
`
`t . A'format - This lrame format can be used for any DCCH and it does not carry any higher layer data (no
`information field), but is is used for filling.
`2. B-format - This frame carries the actual signaling data on the radio interface. It is transmitted in every
`DCCH and ACCH. The maximum length of layer-3 information is restricted based on the logical
`channel and is defined by parameter N201. A-format and B-format frames are sent both in uplink and
`downlink. SACCH, FACCH, SDCCH uses frame types A or B.
`3. Bbis-format - This frame does not have any address field, as this is not required on a broadcast channel
`and this frame format is used for transmission on BCCH, PCH, and AGCH. These frames are only sent
`on the downlink.
`The maximum frame length is 23 bytes : 184 bits, which is the length of the layer-2 data block passed
`to the layer- I channel coding unit. Figure 8.6 shows the LAPDm frame format and coding of fields for
`the several message types used by the protocol. The LAPDm address field has as its main element the
`SAPI, through which the layer-3 message is received. On the radio interface rwo values of SApI are
`
`Bit number
`<-
`876 54321
`
`Address
`
`Control
`
`Length ind¡cator
`
`lnlormation
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`k+f
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`n+1
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`TYPE'B
`Bit number
`87654321
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`Length ind¡cator
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`m
`m+1
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`PIõl
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`N2O1+m
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`F¡ll bits
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`Type-Abis
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`Bil number
`a-
`876 84321
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`Address
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`Control
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`Length ¡ndicator
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`Fill bits
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`TYPE.A
`Bit number
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`7654321
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`I
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`indicator
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`lnformation
`
`Fill bits
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`Type-Bbis
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`1
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`k
`k+1
`k+2
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`n
`n+l
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`ooo
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`N2O1+n
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`EIrlclõl
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`Y
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`m
`m+1
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`tv
`fV+1
`
`N2O1+m
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`Figure 8.ó LAPDm frame formar
`
`¡ 1 I I t i II
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`GSM Mobile Phone Software Design
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`261
`
`used: (l) sAPI : 0 for messages from the radio resource management (RR)' mobility management
`(MM), and call control (cc); un¿ (z) sepl = 3 for messages from the sMS and supplementary services
`iSS¡ ,nr.rug"r. The control freld is used in the same fashion as in HDLC or LAPB and contains the
`à"qi"n." aid retransmission counters N(S) andN(R), respectively. The frame length freld contains the
`tengttr of the layer.3 message within the information field of the LAPDm frame' If the message is less
`thaã the length specified inlarameterN201 ofthe radio interface, frll-in octets are used to make up for
`the space. tithe iayer-l message to be transmitted is longer than N201, segmentation occurs. Whether
`segmentation has occurred or not, is indicated in the M-bit of the length field.
`îor ünk layer signaling, two physical layer channels are used (SACçH and FACCH). The frame
`structure of the SACCH *"rrug" it iho*n in Figure 8.7. The important functionality of a link layer is to
`improve the quality of transmisiion, by detecting frames that have been subjected to transmission errors'
`anå probably asking for repetition. It supports both acknowledgment (acknowledged back indicating
`conectly reached) and un-acknowledgment modes. The link layer offers the possibility of multiplexing
`indepenient flows on the same channil. On theradio interface, two independent flows can co-exist' The
`first Lne is devoted to transfer of signaling messages and the second one is for SMS- These two flows are
`distinguished by a link identifier SAPI, as discussed earlier'
`
`Bit number
`t-
`87 6 5 4321
`Power level
`Free
`
`Free
`
`Timing advance
`
`Layer 2 data (2'l octets)
`
`El 1
`EIel 2
`-td, I8+i
`
`23
`
`Figure 8.7 Frame structure for SACCH block
`
`8.4.2.3 Layer-3
`Layer-3 contains several sub-layers (Figure 8.8), which control signaling channel functions (BCH'
`C|CU, and dedicated channels). These sub-layers are radio resoufce management (RR), mobility
`management (MM), call control (CC) as well as short message service (SMS) management, and
`supplementary services (SS) management.
`
`l. Radio Resource (RR) Sub'LaYer
`RR is the heart ofthe protocol. This controls the setup, maintenance, andtermination ofradio and fixed
`phannels, supporß measurements and handovers. The main procedures in anRR layer are:channel
`àlrigo*"nr, l|unnet release; channel change and handover, change of channel frequencies, hopping
`,.q,i.n.., (algorithms) and frequency tables, measurement reports from the MS, power control
`ctiscontinuous transmission reception, time advance, modification ofchannel modes (speech and data)'
`and cipher mode setting.
`An RR session is always initiated by an MS, tt[ough the access procedure, either for an outgoing call, or
`in response to a paging message. The access and paging procedure