Mobile Communication &Mobile Computing_lecture_note

8/9/2019 Mobile Communication &Mobile Computing_lecture_note

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Note for Mobile Communication

&Mobile Computing



Mobile Communication● Definition

– A form of communications which does not depend on a physical

connection between sender/receiver and who may move from 1 physical

location to another during communication.

●

hat!s the main challenge in mobile communication" – #eneral$ Mobility

● %ser Mobility$

– A user who has access to the same or similar telecommunicationservices at different places roaming

– 'roblem$ (nterrupt connection or change of access point

● Device 'ortability$

– )he device moves while the communication is still possible.



Mobile Communication

● )echnologies

– ways to provide mobile and wireless service"

● *or mobile$ Cellular networ+ ,e-$ #M %M)0

– ,ase tation0covers at least 1 cell. – cellular structure 2 a combination of multiple cells




● )echnologies

– hile 3urope and %A faces insufficiency for high userdensities in cites they have different policies

●

3urope – 1 common standard$ #M %M) ,by ()%0

● 4oaming is possible even to other non53uropean countries● %ses techni6ues of )DMA7CDMA

● 8ater #M,with better CDMA0 7 satellite technology 9 %M)

– ()% drop single standard

● %A$ mar+et forces$ AM'

– Develop : different system$ AM' )DMA CDMA

● truggles with incompatible systems

● ;apan$ )'

– Developed while ()% drop single standard (5mode became atremendous success




● #uide$ be careful

– Many research efforts in mobile computing and wireless

networ+s try to hide the fact that

<the networ+ access has been changed=● from mobile phone to 8AN or between different access

points

– Mobile (' tries to hide the fact of changing access points byredirecting pac+ets but +eeping the same (' address ,"0

● a wireless lin+ is more error prone than a wired one.

– many protocols try to improve lin+ 6uality using encodingmechanisms or retransmission so that applications made forfi-ed networ+s still wor+.



Mobile Communication● >ow cellular networ+ solve main challenges"

– 'roblem1 between sender/receiver

● Change of user location$ leaving the transmission range of a cell

– %ser peed$ up to ?@+m/hr for #M

●

Cell *ailure$ overloading or brea+down of the used cell – olution$ handover mechanism

● Class

– (ntra5cell$ witch inside a cell onto other time5slot/fre6uency.

– (nter5cell$ witch over to a neighbor cell – (nter5system$ witch to other technologies roaming

● Difficulty

– >ard/oft$ Active connection disconnected before/after

the connection to a new cell is established ● 3-$ phone/radio ,only 1 at a time/enable ? at a time0



Mobile Communication● >ow cellular networ+ solve main challenges"

– 'roblem?$ limited fre6uency 9 interference

– (dea$ reuse fre6uency channels in remote cells

● maller cells

– Adv$ more fre6uency reused less transfer power needed local

interference only more robust

– Con$ more e-pensive more often handover happened

– tructure of cellular networ+$ honeycomb5li+e

● Cluster of N cells with cell radius 4 and reuse distance D

N 2 iBi7iB7B D 2 s6rt,:BN0B4 – *re6uency distribution

N2: N2




● >ow cellular networ+ solve main challenges"

– 'roblem?$ medium always shared 9 interference

– Approach$ tructure 7 Multiple- Methods

– Multiple- Methods$ concurrent usage of medium without interference

● pace

● *re6uency

● )ime

● Code




● Multiple- Methods

– DMA ,pace Division Multiple Access0● 4euse fre6uency channel by separated cells far enough so

that we can assign optimal base stations to users.

● ecure distance$ physical distance

● 3-$ geometric distribution of *M station

● Must combine with other multiple- methods for efficiency

– *DMA ,*re6uency Division Multiple Access0● ubdivide the fre6uency band into disoint sub5bands and

allocate fre6uency statically/dynamically to users.

● ecure distance$ guard band

● 3-$ turn to different fre6uency go to different radio channels



Mobile Communication● Multiple- Methods

– )DMA ,)ime Division Multiple Access0

● eparate on the same channel by time5slots,)DM0 allocateusers to certain timeslot/dynamically assigned

● ecure distance$ time gap

● hich time5slot must be synchroniEed.

– CDMA ,Code Division Multiple Access0

● pread the spectrum using orthogonal codes

● hich code to use must be synchroniEed.

● ecure distance must be chosen properly

● >ow to choose the codes"

● Codes must be orthogonal$ inner product of ? codes 2

– A sent a bit code with +ey +a+b sent signal 2 A,+a0 ,+b0 receive message C2 A,+a07,+b0 decode A2CB+a 2CB+b ,inner product0 if F 9 1 G 9




● CDMA is highly sensitive to faults ,Amplitude must be precisely e6ual0

● pread pectrum )echni6ue

– spread bandwidth over larger fre6uency range

9 narrow interference only destroy a small fraction of signal – benefits

● 'ower flu- density could be lower than natural noise

9 could prevent detection and amming

– Cons● 8arger fre6uency band

● (ncreased comple-ity of receiver to despread signals




● Combination

– *DMA 7 )DMA

● #M D3C) '> 'AC (ridium (CH satellite system

– #M combines the ? for better use of narrow resources● Down/uplin+ use different channel 9 down/up at the same time

– CDMA$ all :#● 5CDMA ,*HMA %M)0 cdma?



Mobile Communication● Comparison$ DMA/*DMA/)DMA/CDMA

– CDMA● oft capacity 9 oft handover

– no hard limit to add a user ● )DMA/*DMA$ hard upper limit e-ists

● Difficult to plan cells● >ave to adapt power often

– Near/far effect matters● )DMA doesn!t care

– *DMA

● Must do modulation

– )DMA

● *i-ed )DMA is the only 1 which guarantees on time delay




● Modulation Methods ,signal encode0

– )o transmit digital data via certain fre6uencies



Mobile Communication●

asic +nowledge of networ+ layers● 'hysical$ bit stream I signal

generate fre6uency detect signal modulation of data onto a carrier fre6uency encryption

● Data lin+$ reliable point5to5point point5to5many connectionsaccess the medium multiple- of different data streams correction of transmission errors

synchroniEation recover from collision

● Networ+$ routing/establish connection Address routing device location handover

● )ransport$ end5to5end connection6uality of service flow/congestion

control)C'/%D'

● Application

closest to user and provides networ+ servicesto user may deal with some synchroniEationstuff between applications e-$ DN *)'

)38N3) M)'




● )elecommunication ystems




● #M ,#lobal ystem for Mobile communications0

– Cellular radio networ+ of ?nd generation

– Data communication rate up to J.K+b/s ,@.?+bs for >CD0

– Aim to provide large number of participants with

● ecure mechanisms to avoid being identified by unauthoriEed ones

– Authentication encryption stolen5blac+list ...

● eing able to locate M with optimiEed mechanism

– 3volution

● #M target at voice transmission9data5oriented,>CD #'40

– Normal mobile user M trains emergency ...etc

– )echnical things

● Media Access$ *DMA7)DMA

●

eparate uplin+ and downlin+ by fre6uency●



Mobile Communication● #M$ structure

● 4,4adio ubsystem0● ,ase tation ubsystem0$ C,ase tation Controller0 7 cells

● C$ handover management Mapping channel● Cell$ ),ase )ransceiver tation0 7 M,Mobile tation0

● )$ radio transmission 5 antennas signal processing amplifiers

● C multiple- radio channels to fi-ed channel● M$ typically a cell phone ,hard/software0

● (M,ubscriber (dentity Module0● '(N,personal identity number0$ unloc+ M

● rong '(N : times 9 loc+ (M● '%L,'(N unbloc+ing +ey0$ unloc+ (M

● (M(,(nternational Mobile ubscriber (dentity0● tores dynamic information while logged onto #M system

● ecurity stuff ● )M(,temporary Mobile ubscriber (dentity0$ assigned by 84

● 8ocation information● 8A(,8ocation Area (dentification0




● N,Networ+ and witching ubsystem0$ heart of #M● Connect wireless networ+ with standard public networ+s● perform handovers between different s● comprises functions for worldwide localiEation of users● support charging accounting and roaming of users between

different providers in different countries● MC,Mobile services witching Center0

● ,tandard ignaling ystem0 to handle all signaling forconnection setup/release handover to MCs

● #ateway,#MC0 to other fi-ed networ+,(DN')N0● %sing (*,(nterwor+ing *unction0 MC could connect to

'DN,'ublic Data Networ+0

● >84,>ome 8ocation 4egister0$ most important database in #M

● <%ser contract with networ+ provider =● tatic$ M(DN,Mobile ubscriber (DN Number0

(M(,(nternational Mobile ubscriber (dentity0● Dynamic$ current 8A,8ocation Area of M0 M4N,Mobile

ubscriber 4oaming Number0 current 84/MC● >84 is updated by 84 as soon as a scriber into/out of a 8A● 4eal5time re6uirement

●

84,isitor 8ocation 4egister0$ dynamic database

● #enerate temporary stuff li+e$ M4N for >84 )M( for M

●

M4N$ describes information ofcurrent MC which is responsible




● H,Hperating ubsystem0$ necessary function for networ+ operation/maintenance

● HMC,Hperation and Maintenance Center0● Monitors and controls all other networ+ entities via H5interface● Management functions$ traffic monitoring status reports of networ+

entities subscriber/security management accounting/billing● AuC,Authentication Center0

● 4adio interface and M are vulnerable 9 user identity and datatransmission need stronger protection

● Algorithms for authentication +eys for encryption generates thevalue needed for user authentication in >84

● 3(4,36uipment (dentity 4egister0$ a database for all (M3(s● Maintain a blac+list of stolen,loc+ed0 devices.●

>owever different networ+ providers usually notsynchroniEed9change provider of stolen M9wor+ed



Mobile Communication● #M$ localiEation and Calling

– #M always +nows currently a user is and number is uni6ue

– >ow to provide this service"

● 'eriodically update user location using ?5level location algorithm$ >84784

– >84 for authentication 84 for updating M then informs >84● 'ro$ >84 could reduce the load for updating information of M with help of 84●

4oaming$ changing 84s with uninterrupted availability of all services● )o locate and address Ms we need some numbers

– M(DN,Mobile tation international (DN number0$ phone number ● CC,country code07NDC,national destination code07N,subscriber number0

● 7OJ 1K :1K1@O? NDC$ address of networ+ provider

– (M(,(nternational Mobile ubscriber (dentity0$ another form of phone number ● MCC,mobile country code07MNC,mobile networ+ code07M(N,mobile subscriber identification number0

– )M(,)emporary Mobile ubscriber (dentity0$ to hide (M(

● elected by current 84 and invalid outside 84 – M4N,Mobile tation 4oaming Number0$ temporary address to hide identity and location

● MC let 84 generate M4N 9 store on >84●

CC,visitor ..07NC,visitor ..07N,subscriber number0● M4N help >84 find a subscriber for an incoming call



Mobile Communication● #M

– M)C,Mobile )erminated Call0$ station call mobile station

,10 ')N notices a #Mcall by loo+ing at destinationcode

,?0 forward to gateway

,:0 identify the >84 for the subscriber

,O0 >84 chec+ contract ofthis subscriber ,if number e-ists

and is allowed to use this service0then as+ current 84 forM4N

,@0 >84 received M4N,K0 with M4N >84 coulddetermine which MC isresponsible for this M andforward to #MC

,0 #MC forward setup callto MC

,P0 MC as+ for the state of M at 84,J0 84 inform MC if M is active,10 Call to all cells of the 8A,110 earching for the right cell,1?0 Answered from M,1:0,1O0 84 do security chec+

,1@05,10 84 signal MC to set up connection to M




● #M

– MHC,Mobile Hriginated Call0

,10 M send a connection re6uest,via random access channel0,?0 forward re6uest to MC,:0,O0 AuthoriEation control,84 chec+ if user is allowed to set up a call with re6uest service0,@0,K0 if HL chec+ availability to ')N,0,P0 if HL set up connection between M and ')N




● #M

– ecurity

● Access control and Authentication

–

alid user for (M$ %ser need '(N to access the (M – 8ocation registration location update with 84 call setup M

– A: for authentication

● Confidentiality

– All user5related data is encrypted

– AP 9 A@ for encryption between M and )● Anonymity

– )o provide user anonymity all data is encrypted beforetransmission

● %se )M( which is assigned by 84



Mobile Communication● #M$ ecurity

– 'roblem$ +ey length of only 1?P5bit is small

● 15way5auth$ fa+e networ+ provider for possible

● Authentication$ 84 generates 4AND

send 4AND to (M then 84 and M do A: M send bac+ generated 43 to 84

– Auth chec+ done at your phone locally,+ey is stored in phone 9 no need to sync +ey0

● 3ncryption$ use AP to generate cipher+ey use A@ to encrypt all data totransmit



Mobile Communication● #M

– >CD ,high speed circuit switched data0

● Asymmetric transmission for down/uplin+$ up to @.K+b/s

– Changes needed only in M and MC● )o split traffic stream into several traffic stream each using a separate )C>

then combine these streams again

● *le-ible usage of several time slots,)0 of 1 fre6uency

– #'4 ,general pac+et radio service0$ 1+b/s

● More efficient and cheaper transfer service by bundling channels

– uitable for internet applications,A'0 that usually rely on solely pac+ettransfer,fre6uent small transfers0

– Can allocate 15P time slots within )DMA frame on demand

– >owever 6uality limited to traffic load

● Charge on volume not on connection time,#M >CD0

● Change in software and hardware to provide <always5on= networ+ service

● >ard to attac+ M from outside networ+




–

New component● ##N,gateway#'4 supportingnode0

● #N,serving#'4 supporting

node0● 'C%,pac+et

control unit0




● #'4

– 'ro$ hides M from outside networ+ not easy to attac+

– Con$ hard for M to offer globally fi-ed (' address




● D3C) ,digital enhanced cordless telecommunications0$ @@?+b/s

– pecified by 3)( replaces older analog cordlessphone systems ,C)1 C)17$ security limit0

–

%sed in offices campus trade show● offer cheaper telephone services in railway stations large

government buildings compared to #M

– Compared to #M

●

Cell diameter $ D3C) Q :m #M Q +m ,designed foroutdoors0

● Cell capacity$ due to diameter D3C) Q 1 people/+mR?

● Cell setup cost$ D3C) Q 1euro/base station #M Q 1

● peed tolerant$ #M better D3C) has lots of handover



Mobile Communication● %M)$ from 1OO+b/s ,macro cell0 up to ?Mb/s ,pico cell0

– provide bearer services non5/real5time circuit/pac+et networ+

– >ow %M) speed up"

Asymmetric up5/downlin+ 7 CDMA 7 new modulation scheme,KOSAM07smaller cell

– ervice"

● >3,virtual home environment0

– *reely configurable on traffic load,bottlenec+ of data rates ..etc0

– election of service 6uality and corresponding cost

– Dynamic adaptation according to connection 6uality

● %'D,universal personal telecommunication service0

– 1 phone number for several devices subscriber localiEation – Call forwarding virtual mobility by changing between devices

,'ublished under 3)( under #MM re6uirements0




● %M) – %)4A5*DD ,5CDMA0$ symmetric

● )imeslots in %M) is not used to separate users,li+e#M0 instead to support periodic functions

– %se CDMA to separate users

● >ard/soft handover mode

– oft handover$ macro diversity

– %)4A5)DD ,)D5CDMA0$ a5/symmetric

● Can combine up5/downlin+ at any combination

● Need #',guard period0 due to comple-scheme,synchroniEation for CDMA )DMA0

● Hnly hard handover mode




● >andover types – (ntra node intra 4NC$ soft

– (nter node intra 4NC$ soft

– (nter 4NC$ hard – (nter MC$ hard – (nter system$ hard




● %M) Q enhancement – >'A ,high5speed pac+et access0 2 >D'A7>%'A

● >'DA$ up to 1O.OMb/s ,1.PMb/s with 3CC0 on downlin+ channel

– Combination of channel bundling,)DMA0 wideband codemultiple-,5CDMA0 improved coding,adaptive modulation andcoding with advanced scheduling0

– Adaptive switch between OSAM,6uadrature amplitudemodulation0 and 1KSAM based on channel 6uality

● >%'A

– >'A7 up to ?PMb/s on downlin+ channel

● peedup reached via KOSAM and M(MH,miltipleinput/multiple output0 others same as >'A



Mobile Communication● 8)3 ,long term evolution0 up to :Mb/s ,D0 @Mb/s ,%0

– tandardiEed by 3)( for

● fle-ible fre6uency assignment

● mall latency of @m between mobile phone and conventionaltelephone networ+

● HptimiEed for travel speed of up to 1@+m/h ,@+m/h still possible with reduced 6uality0

– )echnology

● %se of H*DM,orthogonal fre6uency division multiple-ing0 for multiple-ing

– Data is distributed over a large number of closely spaced

orthogonal subcarriers● ? subcarrier si orthogonal if the ma-imum amplitude of 1 subcarrier is

reached while the other is Eero

– 'ro$ robust against interference ,since interference on subcarrier doesnot influence the whole fre6uency band0

– Con$ e-pense for de5/coding power consumption increases with

Tsubcarrier

M bil C i i




● 8)3 Q enhancement of H*DMA – H*DMA for downlin+

● A set of subcarriers are assigned to individual users sosimultaneous transmissions are enabled for several

concurrent users without interference

– C,single carrier05*DMA for uplin+

● (nsert user5specific coefficients by the sender before*ourier transformation ,need decoding0 9 more energy5

efficient for battery5driven mobile devices

M bil C i ti




●

8)3 advanced$ up to 1#b/s – (mproved performance$ end5to5end delay ?5: ms

– 3nhancements

● Carrier aggregation

– %p to @B?M>E 9 1M>E

– 'ossible in non5/contiguous spectrum allocations

● M(MH – %p to O 8)3 antennas in 8)3 devices to use M(MH also for %plin+

– ase stations can be e6uipped with up to P antennas

● upport for relay node base stations – Additional intermediate base stations

– (mprove signal 6uality at cell borders

● upport of low power nodes for picocells and femtocells for

crowded areas

M bil C i ti




● iMa-/(333 P?.1K ,worldwide interoperability for microwave access0

– Ley feature$ 8ast mile in remote neighborhoods with wee+lydeveloped infrastructure

an e-tension of P?.1K to have ,N8H0No 8ine5of5ide effect capabilities.)his is archive due to H*DM and H*DMA. better support for So and the use of calable H*DMA

M bil C i ti




● iMa- Q adaptive modulation

M bil C i ti



Mobile Communication● iMa- Q medium access

– )DMA$ each channel gets fi-ed slot for transmission

– DAMA$ reservation phase 9 transmission phase

– Duple- connection$ *DD7)DD

,10 point to point$ 8ast mile

,?0 point to multipoint$ Connection of M

to is characteriEedvia Channel (D,C(D0

,:0 Mesh networ+$thin+ of p?p structure

M bil C i ti



Mobile Communication● MA,mobile broadband wireless access0/(333 P?.?

– #oal$ specification of '>U and MAC for pac+et5based MA system

● hould close gap between 8AN and slower but highly mobilenetwor+s,%M)0 but never reached 9 failed

● O# characteristics

–

>igh mobility 9 handover roaming ,up to :+m/h0 – witching techni6ue 9 pure pac+et switching

– (ntegrated multi5media service 9 o(' )o(' oD treaming

– >igh data rate,up to 1#b/s0 9 even at high mobility should be li+e D8

– iEe of cell 9 variable and scalable

– calability 9 available and reliable with many users

– Air interface 9 H*DM ,better spectrum efficiency0

– ecurity 9 up to data standards

– 3-tension/integration of %M) 8)3 8AN approaches

– uilt5in So




● 8AN – hat is 8AN"

● Networ+ types – 'AN,private0 8AN,local0 MAN,metropolitan0 AN,wide0 #AN,global0

● ireless versions$ 'AN,bluetooth0 8AN,P?.110 MAN,P?.1K0 AN,P?.?0

– Advantage● *le-ibility widely available (nternet access at low cost ad5hoc5

networ+s no cable problems

– 'roblem● >igher error rate on transmission lin+ in comparison to tandard5

8ANs security aspects shared medium some national restrictionsconcerning the used fre6uency bands,(M5and0

–

Application$e-tension of e-isting wired local area networ+s



Mobile Communication● 8AN Q problems and solution

– 'hysical problem● (nterference$ spread spectrum techni6ues fre6uency hopping

● >idden )erminal problem$ use of 4)/C)5mechanism

– Data security

● 3',wired e6uivalent privacy0 service

● Current improvements$ 'A,i*i 'rotected Access0 'A? P?.??i

– CMA/CA,Carrier ense Multiple Access with collision avoidance0

● CMA/CA doesn!t wor+ in wireless networ+s

– Due to no collision detection

● 'rinciple$ <listen before tal+ing= ,CMA without CD0

● 'rocedure

1. a station intends to send is listening before sending

?. if medium is free then send

:. if medium is busy wait until the <bac+ off= interval is over then begin

at 1,repeat until ma-imum number of attempts0





● 8AN Q problem and solution – Medium access problem

● >idden terminal9not detected each other9collision

● 3-posed terminal9cannot tell if one sends another signal will

cause collision to me9 not necessary waiting

– olution$ 4)/C)5Mechanism,re6uest to send/clear to send0

● >idden terminal

– C received C)

● (s not allowed to send to

● 3-posed terminal

– C independent to





● 8AN Q problem and solution – 8ow security of 3',wired e6uivalent privacy0

● ymmetrical cryptography small +ey lengths same +ey for multiple clients

– olution Q 'A/'A? ,i*i protected access P?.11i0

● Authentication

– ession +ey generated by 're5hared5Ley7long password,P5KOcharacters0

● 3ncryption$ integrity chec+

– )L(',temporal +ey integrity protocol0 generates dynamic +ey per pac+et,'A0

– 4CO,'A0/A3,'A?0 for encryption

– 4emaining security problem

● imple 'L allows brute5force/dictionary attac+



ob e Co u ca o

● luetooth Q functionality

● 'ossible Configuration

● Application

– May replace infrared forperipherals wireless headsetsdigital image transmissionbetween cameras control ofhome applications by networ+edsensors



● atellite roadcast Q #'

– Accuracy$ up to 1m ,normal 1m0

– *unctionality principle$ triangulation

● #' receiver calculates distance to satellite based on

)ime of Arrival of the received signal strength● #iven F2: distances to satellites9determine position

– ignal based on CDMA

● 3ach satellite has a uni6ue code '4C,'seudo 4andom Code0

● %ser devices +nows all codes to identify satellites

– )as+s for signal

● 3ncode information into signal,@b/s0

● Determine signal propagation delay

satellite send : components @times/s,10 (dentification component$ '4C,?0 'osition component$ e-act position

,:0)ime component$ timestamp when transmitted




● atellite roadcast Q #'

– ource of errors

● *i-ed error$ Cloc+s atellite position

● Miscellaneous error sources$ atmospheric faults multi5path propagation

● atellite roadcast Q D#',differential #'0 – >ow to determine position" Add <stationary receiver =

● tationary receiver calculates <correction factor =9mobile receiver

– 'osition of stationary receiver is e-actly +nown

– Application● Accuracy G 1cm$ meteorology

● Accuracy G 1m$ traffic control systems agriculture

● Accuracy G 1m$ railway car navigation




● atellite roadcastQ)3)4A ,terrestrial trun+ed radio0

– best choice for emergency can wor+ in an ad hoc networ+

● without base station fast connection set5up

– tandardiEed by 3)($ ? standards

● 'DH ,pac+et data optimiEed0$ pac+et data transmission

– 'oint5to5point point5to5multipoint non5/connection5oriented

– Delay$ short message G 1ms

– tatical multiple-ing

● 7D ,voice7data0$ circuit5switched voice and data transmission

– Connection mode$ unicast/broadcast

–

Delay$ short message F @ms depending on priority – )DMA channels for voice

– earer service$ up to ?P.P+b/s ,J.K+bs protected0

– Architecture$ similar to #M

– Compare to #M$ )3)4A provide group call emergency call fast dialing

cost5efficient




●

atellite roadcast Q roadcast ystem ,)DMA0 – DA ,digital audio broadcast0

● 4obust against multi5path propagation

● %se of *N,single fre6uency networ+0 – All senders of some broadcast5program wor+ on the same fre6uency as a rule

● Modulation method$ DS'L,Differential S'L0

● Hptionally CH*DM,coded orthogonal *DM0

● 3rror correction$ *3C,forward error correction0

● >igh transmission rates at high velocities ,:+m/h0● 3ncoding$ M'3#? 'CM OP+>E

● 'roblems$ acceptance in practice,its future is 6uestionable0



● ired )C'/('

– )o have networ+ you got to get (' assigned by networ+ provider

– 'roblem$ change of ('9reconfiguration re6uired

● rea+age of established connection

● Mobile device not reachable without further support – olution$ D>C',dynamic host configuration protocol0

● upport automatic assignment of (' address

– Auto5config of all networ+ parameters,router subnetmas+

DN07optional parameters,web server mail server0● %se of lease$ lease is valid for a period of time

– Client want to continuous use networ+ 9 gain ne-t lease

● Could try twice before lease e-pires

● 'roblem$ cannot support fre6uent change,DN need time to update0



● Mobile (' Q *orwarding

– *oreign Agent CoA



Mobile CommunicationM bil (' i



● Mobile (' Q issues

– )riangle 4outing ,CN5>A5MN5CN0● CN doesn!t +now where >A is so it sends to >A to forward to MN

● 9 (f CN and MN is in the same *A9not necessary route through >A

– HptimiEation$ CN +eeps cache to +now locations of MN● >A tell CN where MN is CN could be optimiEed later on

● mooth handover can be supported$ CN may be able to send data to MN before >A isupdated with newest CoA

– Micromobility in cellular networ+s

● *re6uent cell/CoA changes 9 fre6uent updates in home agent

– olution$ cellular ('

● >ierarchical updates

– cellular (' for managing cell changes in 8A,location area0

– Mobile (' u dated onl for chan es of 8A



Mobile Computing b b d M bil A li ti



● eb5based Mobile Application

– Devices comes with different siEe● Adaptive screen siEe layout design optional content

– (mage in multiple resolutions audio/video in different format

– >ow could you do with that"

● 4esponsive eb Design – ingle >)M8 mar+up 9 adapts to screen siEe through C

● *luid grids● siEe of components are relevant to its parent

● *le-ible images● force image match siEe of its container

● Multi5resolution images● Choose image resolution based on device5pi-el5ratio

● C Media Sueries● Conditionally apply styles based on browser attributes

Mobile Computing



● eb5based Mobile Application Q 4esponsive eb Design

– *luid grid● 'age5layout based on grid system$ start by ma- layout width

● All layout width are proportional to its parent layout width

– element siEe / parent siEe 2 relative siEe



Mobile Communication b b d M bil A li ti



● eb5based Mobile Application

– Mobile Device 8ayout 'atterns

Mobile Computing

M bil 'l tf t t



● Mobile 'latform ystem upport

– Android

● Corss5platform e-ecutable$

– ;ava5based application development ,HptimiEed virtual machine0

● 8ifecycle of process controlled by runtime system

– Can stop/restored at anytime

● Main concepts for application programming

– Activity,%( support runtime system0

– (ntent,message between Activity0

●

roadcast4eceiver$pecial intent filter for system messages

● battery low screen off boot completed ..etc

– ervice,bac+ground thread independent from %(0

– Content'rovider$ sharing data between applications

– 4esources$● non5code files used in code and compiled into application at build time



Mobile Computing

● Conte-t and 8ocation Awareness



asic Abstraction● ensor$ collect analog data

● idget$ abstract sensor data 9 singleconte-t value

● (nterpreter$ generate higher5level conte-t

● Aggregator$ for easier management

Conte-t$ any information that can be used to characteriEe the situationof an entity – an entity could be a person place or obect that is considered

relevant to the interaction between a user and an application

Conte-t and 8ocation Awareness



Mobile Computing



●

Conte-t Models Q Hntology5based Models – e-ample



Mobile Computing● 8ocation5base services



8ocation base services

– Determine geometric position● Measurement of certain properties of electromagnetic signals

– 4epresentation to geometric position

● 8ocation (D – Calculate distance between sender and receiver

● ignal strength )ime of arrival – Determine direction of the signal

● Angle of arrival

– Approach

● 'ositioning ,client5based positioning0 – 8ocated device under control of location information

– Need hardware and computing power at device

● )rac+ing ,infrastructure5based positioning0

– imple devices



Mobile Computing● 'ositioning/)rac+ing ystem



–

#M$C#(,cell global identity0 7 )DMA B O 555 M' ,mobile position system0

– (ndoor 'ositioning/)rac+ing

● tand5alone infrastructure approaches – Need additional hardware 9 high setup cost

– 3-$ (nfrared ultrasonic radio 4*(D

● (ntegrated infrastructure approaches

– 8AN ,cell5id lateration fingerprinting0

● 8ateration$ a method to determine position need : points to determine a ?D point

Mobile Computing



● 'ositioning/)rac+ing ystem$ #M5fingerprinting

– 1st phase$ Create radio map

● define and collect information of reference points

– ?nd phase$ %se radio map$

● *ingerprint of current position is ta+en by – earch for closest matching reference points

Mobile Computing



●

'ositioning/)rac+ing ystem Q summary




● Suestions



● Suestions – hy not use low fre6uency for data transmission in computer networ+s"

● 8ower fre6uency 9 lower data rates DM hard to apply

– >ow to avoid narrow interference"

● Dynamic fre6uency election *re6uency hopping spread spectrum

– hy MAC in wired scheme fails in wireless scheme"● Hnly sender needs to detect collision in wired scheme but many collision is

undetectable by sender of wireless

– Compare >CD and #'4

● )hey both use channel bundling on multiple timeslots ,O 15P0

● #'4 transmits data pac+et by pac+et and uses time slotseffectively 9 cheaper and charge on traffic usage while >CD isconnection5oriented and charge on connection time

– (n #M you use what channel for M"

● 3ither traffic/control channel since the receiver needn!t be connected

Mobile Communication● hat is circuit5switched"



–

A type of networ+ in which a physical path is re6uired for and dedicated to asingle connection between ? end5points. Hrdinary voice phone service is circuit5switched. )he telephone company reserves the specific physical path to thenumber you!re calling for the duration of your call. 9 inefficient

● hat is transparent/non5transparent modes of channel"

– )ransparent means no error5correction 9 higher data/error rate

● hat has to be changed for the implementation of >CD"

– e have to change the usage of channels 9 MC and M

● Compare >CD and #'4

– oth use the line ,always P channel vs based on what your application need0 cost ,settingbilling0 handover/connection setup/release ,re6uire n signals for n channel vs cansetdown0 scaling,bad good0 change needed,only M&MC vs e-tra gateway channel$C MC chec+ for data rate$ AuC >840 So,yes no0

● hat!s overboo+ing in #'4"

– A new user comes and there!s not enough resource available 9 overboo+ingsometimes leads to a connection brea+




● >ow is authentication and encryption wor+ in #M"



● >ow is authentication and encryption wor+ in #M"

– Auth$ (M,by '(N0 I AuC but neither the ? change secret

– encryption$ only happens between M and

● >ow can higher data rate increased in #M"

–

#'4$ Change timeslot usage 3D#3$ use another modulationscheme,'L0 9 increase capacity of #M cells

● hat #M elements are needed for #'4"

– Auth user services but for data transfer$ MC not needed ,replaced by routers #N ##N0

● Advantages and disadvantages of 8AN

– Adv$ fle-ible widely available at low cost Cons$ high error rate securityproblem no international standards for used fre6uency bands

● Compare 8AN and %M)

– 8AN is cheaper and faster %M) is more mobile

Mobile Communication &Mobile Computing_lecture_note

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