& Mobile Computing Mobile Computing “People and their machines should be able to access information and communicate” with each other easily and securely, in any medium or combination of media — voice, datacimage, video, or multimedia any time, anywhere, in a timely, cost-effective way.” — Dr. G. H. Heilmeier, Oct 1992 Mobile Computing Provide the services “Any where atAny Time” +A technology that allows ¢ransmission of data, via a computer, without having to be connected to a fixed physical link. Mobile Computing vs. Wireless Networking ‘ Mobile computing essentially accessing information and remote computational services while on the move “ Wireless Networking provides’the basic communication infrastructure necessary to mdbile computing‘Types of Telecommunicating Networks “& The telecommunication network classifies > Voice Network > Data Network (Text, pictures movies, sound etc.) Types of Communicating Devices Components of a Wireless Communication System “ The components of a Wireless Communication System are: > Transmitter » Receiver > Antenna > Filters > Mixer Comparison between Wired Mobile Network ob Fixed and Wired ¢ Mobile and Wired ob Fixed and Wireless * Mobile and Wireless “& Wired Networks + Mobile Nebworks > High bandwidth > Low bandwidth > Low bandwidth variability > High bandwidth variability > Can listen on wire » Hidden terminal problem > Exposed terminal problem > High power machines > High resource machings » Low power machines > Low resource machines > Need physical ° access(sceurity) > Higher delay / > Low delay: > Disconnected operation 5 - > Less Fixed Infrastructure > Total Fixed Infrastructure‘Types of Wireless Devices “> Laptops + Palmtops PDAs “Cell phones + Pagers 4 Sensors Mobility “> Termin: mobility: Terminal mobility means the ability of the network to locate a mobile terminal, route incoming or outgoing calls (or packet sessions) regardless of the point of attachment to the network, ani maintain connections while the terminal moves aroundin the network. “& There are two main options: > Wireless terminals which can be contacted even while they are in motion, > Fixed tetminals which can be moved between points of attachment + There are various degrees of mobility, Wepending on the relationships between the user, the terminal equipment, the services and the underlying. network infrastructure. 'Mobility’ therefore includes the following concepts: > Terminal mobility > Personal mobility > Service portability Mobility “ Personal Mobility: Personal mobility implies that a user can access services from any available terminal using a personal identifier and that the network cam locate the terminal and deliver services matching the user’s service profile. The identifier can be used wit! > Wireless terminals, » Fixed terminals, » Fixed (ie. not wireless), but movable terminals.Mobility “ Service Mobility: Service mobility implies that the network can provide a set of service features, defined by the user, in the home network or in a visited. network. Technical Challenges / Issues of Mobile Computing Technical Challenges / Issues of Mobile Computing “ Mobility ¥ Location Management ¥ Address Migration Technical Challenges / Issues of Mobile Computing + Wireless Medium, ¥ Disconnection ¥ Low Bandwidth ¥ High Bandwidth Variability ¥ Heterogeneous Network ¥ Security Risk ¥ Traffic + Portability ¥ Low Power ¥ Risk of Data ¥ Small User Interface ¥ Small Storage Capacity’ Small Processing CapacityCharacteristics of Mobile Elements, * Frequent disconnections + Predictable disconnections + Physical support for broadcast + Monetarily expensive + Relatively unreliable 4 High bandwidth variability + Low bandwidth Application Area of Mobile Computing Issues of Mobile communications + Limited resources “> Limited memory “ Limited computational power * Small screen “> Limited battery life “ Relatively unreliable “Variability in resources + Frequent location updates Useful Information “E-Commerce + Hospitality Industry 4 Airline and Railway Industries + Emergency Services 4 Replacement of fixed network + Location dependent services + Sensor Networks (such as tracking system) News “ IMSI: An International Mobile Subscribe? fdentity (IMSI) is a unique identification that is associated with all GSM and UMTS network mobile phones + The SIM inside the phone contains it as a 64 bit field + Used for acquiring certain details in Home Location Register or Visitor Location Register op It is presented as 1S-digit long number, where first 3 digits represent the Mobile Country Code and followed by the Mobile Network Code “ Remaining digits are mobile station identification number within the customer base networkUseful Information 4 TMSI: Temporary Mobile Subscriber‘Identity for most commonly sent between the mobile and the network + TMSI is assigned randomly by-VER to each mobile in the area “ The TMSI number is local for a specific local area, and need to be updated every time when the mobile moves to a new geographical area + Paging a mobile is the key use of the TMSI Useful Information ‘Useful Information “ The communication between the mobile aiid the base station is known as paging “The emphasis of broadcast information is top set-up channels for paging “Broadcast mechanism is: xVailable in every cellular system for distributing broadcast information to a plurality of mobiles Useful Information + IMEI: International Mobile Equipment [deatity is a number usually unique for + It is generally printed inside the battery compartment of the entifying mobiles phone “The number can be displayed on the screen by entering *#06# into the keypad on’ most of the phones + A stolen phone cam be stopped from accessing the network within the country, by using IMEI number for valid devices “ IMEI is only used for identifying the device and has no permanent relation to the subscriber “ The subscriber is identified by [MSI number, stored on the SIM card, which then canbe’ transferred to any other handsetReal life serials on Mobile Computing Application ‘Tracking ‘The concept of Cellular was developed-iihd introduced by Bell laboratories in early 1970°s “ The principal of cellular system divides a large geographical service area into cells with the diameter 2KM-100KM “ Each of which allocated a number of Radio Frequency (RF) Channels “Transmitters in each adjacent cell operate on different frequencies to avoid interferences “A cellular system has facility to provide handoff r System Advantages of Cellular System “ Mobility “> Flexibility * Convergence * Greater QoS “ Network ExpansionCordless ‘Telephony * Cordless telephone (CT) is a communication system using radio waves to connect portable hands¢é to a dedicated fixed port (base station) which is connected to PSTN as a normal telephone line (using ordinary telephone numbers) + CT provides limited range and mobility in the vicinity of the base station (100 m) Handover 4, Conversation ended ~ still within BS3's coverage Paging System +> Paging systems are wireless communication systems that send brief messages to a subscriber + A message is sent to a paging subscriber via the paging system access number by a telephone kéypad or modem + The issued message is called .a page Handover Management ‘ Handover is the procedure that transfers an ongoing call from one cell to another as the user’s moves through the coverage area of cellular systern; “ Handover Management can be: > Hard Handover or > Soft HandoverHandover Management ¢ Hard handoff: A hard handoff is essentially a “break before make” connection ¢b Here the link to the prior base station is terminated before or as the user is transferred to thé new cell’s base station + This means that the mobile is linked to no more than one base st mat a given time Handover Management Handover Management ‘A hard handoff occurs when users experience an interruption during the handover “process caused by frequency shifting “> A hard handoff is perceived by network engineers as event during the call, Theseare intended to be instantaneous in order to minimize the disruption of the ¢: “ Hard handoff can be further divided as intra and inter-cell handoffs Handover Management + Soft handoff: Soft handoff is also called\as Mobile Directed Handof? as they are directed by the mobile telephones + Soft handoff is the ability to select between the instantaneous received signals from different base stations ¢ Here the channel in the source cell is retained and used for a while in parallel witihthe channel in the target cell ‘In this the connection to the target is established before the connection to the source is broken,’hence this is called “make-before-break” “ The interval, during which tlie two connections are used in parallel, may be brief or substantial because of this the soft handoff is perceived by the network engineers as state of the call, Soft handoffs can be classified as Multiways and softer handoffs.Handover Hard Handoff Sott Handoff Analog, TDMA and GSM cDMA Break before Make Make before Break Strategies for Handoff detection Strategies for Handoff detection, + Who makes a decision for handoff? + Three handoff detection schemes: > Mobile-controlled handoff (MCHO) > Network-controlled handoif (NCHO) > Mobile-assisted handoff (MAHO) “ Advanced mobile systems follow MAHO Strategies for Handoff detection, + Mobile-controlled handoff (MCHO) : + MS continuously monitors the signal’strength and quali from the accessed BS and several handoff candidate BSs + When some handoff criteria are met, the MS checks the best candidate BS for an available traffic channel and launches a handoff request “ MCHO is used:in DECT and PACS +“ Two common handoffs in MCHO: > Automatic link transfer (ALT) -transfer between two base stations > Time slot transfer (TST) “transfer between channels of a single BSStrategies for Handoff detection, + Network-controlled handoff (NCHO) : “& BS monitors the signal strength and qaiity from the MS. “When deteriorate below some threshold, the network arranges for a handoff to another BS 4 The network asks all surrounding BSs to monitor the signal from the MS and the measurement results back to the network, “ The network then chooses a new BS for the handoff and informs both the MS (through old BS) and the new BS “& Used by Jow-tier CT-2 plus and by high-tier AMPS Strategies for Handoff detection, * Mobile-Assisted handoff (MAHO) : ‘ The network asks the MS to measure the signal from the surrounding BSs and report back told BS ‘ The network makes the handoff decision based on the reports from the MS “ Handoff process is more decentralized “ The MS and the BS supervise the quality of the link “ GSM handoff exéeution time ~ Isec “Used in GSNf, 18-136 and IS-95 Channel Assignment Strategies Channel Assignment Strategies ‘In a typical cellular system whole geographical area is divided into number of cells, which shape of these cells as hexagonal 4 Mobile users in each cell are serviced by a base station (BS) located at the center of "the cell and the BSs are interconnected via a wired network + BSs are also known as Mobile Service Station (MSS) ‘The number of base stations required 49’ service a given geographical area, is an important. factor for a cellular system “In wireless mobile system radio bandwidth is divided in to channels + Only a finite set of channels are available for one entire network a) oo “Chae! modo {cattacoa_) ee liChannel Assignment Strategies + Fixed Channel Allocation Schemes (FCA);\The simplest way to implement FCA is to allocate thé same number of channels to each cell so that the channels are allocated uniformly among the cells in system “ This strategy is good in situations when system is having uniform load distribution, as it decreases the overall average blocking probability: + However, the problem with FCA systems occurs, whenever the traffic load! in all the base stations is non-uniform. Channel Assignment Strategies ‘ Generally, a real life network has non-uniform traffic clusters “> For example, in a cellular system, there may be some clusters of heavy load such as, a Sports complex during a tournament, busy shopping inalls, market, business office area and highway etc. Channel Assignment Strategies Channel Assignment Strategies eee Do yourself: ‘Dynamic Channel Allocation Schemes) (DCA):In DCA schemes, all channels are kept in a,eentral pool and are assigned dynamically to new calls ay they arrive in the system ‘ After each call is completed, the channel is returned to the central pool It is fairly straightforward to select the most appropriate channel for any call based simply on current allocation and current traffié, with the aim of minimizing the interferenceChannel Assignment Strategies + DCA scheme can overcome the problem of FCA scheme + However, variations in DCA schemes center around the different cost functions used. for selecting one of the candidate channels for assignment Channel Assignment Strategies oe Advantages of DCA: ° oo. Do yoursel + Disadvantages of DCA: Pe * Channel Assignment Strategies Channel Assignment Strategies ‘© Hybrid Channel Allocation Schemes (H@A): HCA schemes are the combination of both FCA and DCA techniques. + In HCA schemes, the total number of channels available for service is divided into fixed and dynamic sets. + The fixed set contains a number of nominal channels that are assigned to cells as\in the FCA schemes and, in all cases, are to be preferred for use in their respective cells. “The dynamic set-is shared by all users in the system to increase flexi “ Example: When a call requires service from a cell and all of its nominal channels are busy, a channel from the dynamic set is assigned to the call,Channel Assignment Strategies * Advantages of HCA: * ° + Do yourself. * advantages of HCA: © sessseessesnssenen * © Do yourself.