Post on 01-Jun-2018
8/9/2019 Mobile Communication &Mobile Computing_lecture_note
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Note for Mobile Communication
&Mobile Computing
8/9/2019 Mobile Communication &Mobile Computing_lecture_note
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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.
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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
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Mobile Communication
● )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
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Mobile Communication
● #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+.
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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
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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
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Mobile Communication
● >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
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Mobile Communication
● 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
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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
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Mobile Communication
● 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
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Mobile Communication
● 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?
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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
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Mobile Communication
● Modulation Methods ,signal encode0
– )o transmit digital data via certain fre6uencies
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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)'
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Mobile Communication
● )elecommunication ystems
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Mobile Communication
● #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●
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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
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Mobile Communication● #M$ structure
● 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
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Mobile Communication● #M$ structure
● 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
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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
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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
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Mobile Communication
● #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
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Mobile Communication
● #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
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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
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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+
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Mobile Communication
–
New component● ##N,gateway#'4 supportingnode0
● #N,serving#'4 supporting
node0● 'C%,pac+et
control unit0
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Mobile Communication
● #'4
– 'ro$ hides M from outside networ+ not easy to attac+
– Con$ hard for M to offer globally fi-ed (' address
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Mobile Communication
● 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
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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
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Mobile Communication
● %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
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Mobile Communication
● >andover types – (ntra node intra 4NC$ soft
– (nter node intra 4NC$ soft
– (nter 4NC$ hard – (nter MC$ hard – (nter system$ hard
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Mobile Communication
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Mobile Communication
● %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
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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
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Mobile Communication
● 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
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Mobile Communication
●
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
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Mobile Communication
● 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
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Mobile Communication
● iMa- Q adaptive modulation
M bil C i ti
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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+$thin+ of p?p structure
M bil C i ti
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Mobile Communication● MA,mobile broadband wireless access0/(333 P?.?
– #oal$ 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
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Mobile Communication
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Mobile Communication
● 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$e-tension of e-isting wired local area networ+s
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Mobile Communication
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Mobile Communication● 8AN Q problems and solution
– 'hysical problem● (nterference$ 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
Mobile Communication
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Mobile Communication
● 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
Mobile Communication
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Mobile Communication
● 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+
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Mobile Communication
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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
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Mobile Communication
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● 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
Mobile Communication
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● 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
Mobile Communication
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● 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
Mobile Communication
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●
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
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Mobile Communication
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● 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
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Mobile Communication
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● Mobile (' Q *orwarding
– *oreign Agent CoA
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Mobile CommunicationM bil (' i
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● 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
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Mobile Computing b b d M bil A li ti
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● 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
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● 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
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Mobile Communication b b d M bil A li ti
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● eb5based Mobile Application
– Mobile Device 8ayout 'atterns
Mobile Computing
M bil 'l tf t t
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● 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$● non5code files used in code and compiled into application at build time
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Mobile Computing
● Conte-t and 8ocation Awareness
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asic Abstraction● ensor$ 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
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Mobile Computing
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●
Conte-t Models Q Hntology5based Models – e-ample
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Mobile Computing● 8ocation5base services
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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
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Mobile Computing● 'ositioning/)rac+ing ystem
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–
#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
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● '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
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●
'ositioning/)rac+ing ystem Q summary
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Mobile Communication
● Suestions
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● 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"
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–
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+
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Mobile Communication
● >ow is authentication and encryption wor+ in #M"
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● >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
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