Introduction to Mobile Computing

UNIT-I INTRODUCTION TO MOBILE COMPUTING Mobile Computing is an umbrella term used to describe technologies that enable people to access network services anyplace, anytime, and anywhere. Mobility means moving from one place to another either r information or device. There are two types of mobility. One is User Mobility and another one is Device Portability. User Mobility means who has access to the same or similar telecommunications services at different places. Device Portability means communication devices moves from one place to another A communication device can exhibit any one of the following characteristics:  Fixed and wired: This configuration describes the typical desktop computer in an office. Neither weight nor power consumption of the devices allow for mobile usage. The devices use fixed networks for performance reasons.  Mobile and wired: Many of today’s laptops fall into this category; users carry the laptop from one hotel to the next, reconnecting to the company’s network via the telephone network and a modem.  Fixed and wireless: This mode is used for installing networks, e.g., in historical buildings to avoid damage by installing wires, or at trade shows to ensure fast network setup.  Mobile and wireless: This is the most interesting case. No cable restricts the user, who can roam between different wireless networks. Most technologies discussed in this book deal with this type of device and the networks supporting them. Today’s most successful example for this category is GSM with more than 800 million users. Mobile computing is a process of computation on a mobile device. A set of decentralized (distributed) computations on diversified devices, systems, and networks, which are mobile, synchronized, and interconnected via mobile communication standards and protocols. Mobile device does not restrict itself to just one application, such as, voice communication Pervasive means ‘existing in all parts of a place or thing’. Pervasive computing means The next generation of computing which takes into account the environment in which information and communication technology is used everywhere, by everyone, and at all times. 1. NOVEL APPLICATIONS Smart Phones: It is a mobile phone with additional computing functions so as to multiple applications • A mobile phone with additional computing functions so as to enable multiple applications • SMS (short message service), MMS (multimedia messaging service), phone, e-mail, addres book, web browsing, calender, task-to-do list, pad for memos. • Compatibility with popular Personal Information Management (PIM) software • Integrated attachment viewing. • Sure Type keyboard technology with QWERTY-style layout. • Dedicated Send and End keys 1 UNIT-I • Bluetooth® capability for hands-free talking via headset, ear buds, and car kits. • EvDO* support enabling the device as a wireless modem use for laptop or PC. • Speaker phone • Polyphonic ring tones • 64 MB memory • Bright, high-resolution display, supporting over 65,000 colors Enterprise Solutions Enterprises or large business networks have huge database and documentation requirements. The term Enterprise Solutions refers to Business solutions for corporations or enterprises. They may include specialized hardware or software programming to help an enterprise in finding solutions for needs such as management of storage, security, revision, control, retrieval, distribution, preservation and destruction of documents and contents etc. Music, Video and E-books: • Example─ Apple iPods enables listening to one’s favourite tunes anytime and anywhere • View photo albums • Slide shows • Video clips Mobile Commerce: • Stock quotes in real time or on demand. • The stock purchases or selling • Bank transactions • Retail purchases • Supply chain management • e-Ticketing─ booking cinema, train, flight, and bus tickets Mobile Cheque: It is a mobile based payment system employed during purchase. This service is activated through text message exchange between customer, merchant and mobile service provider. Mobile based Supply Chain Management: 2 UNIT-I The producer consumer problem is also called Supply Chain Management problem. IT companies have developed mobile device software for Supply Chain Management systems. The sales force and manufacturing units use mobile devices to maintain the supply chain. 2. LIMITATIONS OF MOBILE COMPUTING  Resource constraints: Battery needs and recharging requirements are the biggest constraint in mobile computing. New processors have been developed, which consume less power, reduces battery power requirement.  Interference: Radio transmission cannot be protected against interference using shielding and result in higher loss rates for transmitted data or higher bit error rates respectively  Bandwidth: Although they are continuously increasing, transmission rates are still very low for wireless devices compared to desktop systems. Researchers look for more efficient communication protocols with low overhead.  Dynamic changes in communication environment: variations in signal power within a region, thus link delays and connection losses  Network Issues: discovery of the connection-service to destination and connection stability  Interoperability issues: the varying protocol standards  Security constraints: Not only can portable devices be stolen more easily, but the radio interface is also prone to the dangers of eavesdropping. Wireless access must always include encryption, authentication, and other security mechanisms that must be efficient and simple to use. 3. MOBILE COMPUTING ARCHITECTURE Mobile computing Architecture contains the following components • Programming languages used for mobile system software • Operating system functions to run the software components onto the hardware • Middleware components deployment • Layered structure arrangement of mobile computing components • Protocols and layers used for transmission and reception Programming Languages: One of most popular language used in mobile computing is Java. Because it is platform independent means independent of CPU and OS. Java2 has Standard Edition called J2SE. It has two limited sized editions. -- J2ME (Java2 Micro edition) and JavaCard (Java for smart card. These two are used for developing applications in mobile computing. The Java enterprise edition (J2EE) used for web and enterprise server based applications of mobile services C and C++ gives compact machine specific codes. Visual C++ and Visual Basic are also used for developing applications for pocket PC with a windows platform. 3 UNIT-I Functions of Operating System OS Offers the user to run an application without considering the hardware specifications and functionalities. OS also provides functions which are used for scheduling the multiple tasks in a system. It provides the functions required for the Synchronization of multiple tasks in the system. OS provides multiple threads synchronization and priority allocation. OS also provides Management functions (such as creation, activation, deletion, suspension, and delay) for tasks and memory. It Provides Interfaces for communication between software components at the application layer, middleware layers, and hardware devices. It also facilitates execution of software components on diversified hardware. OS Provides Configurable libraries for the GUI (graphic user interface) in the device. OS provides User application’s GUIs, VUI (voice user interface) components, and phone API. OS provides the device drivers for the keyboard, display, USB, and other devices Functions of Middleware for Mobile Systems Middleware are the Software components that link the application components with the network-distributed components. Examples of middleware applications are • To discover the nearby device such as Bluetooth • To discover the nearby hot spot • For achieving device synchronization with the server or an enterprise server • For retrieving data (which may be in Oracle or DB2) from a network database • For service discovery at network • For adaptation of the application to the platform and service availability Mobile Computing Architectural Layers: 4 UNIT-I Mobile Computing Architecture refers to defining various layers between user applications, interfaces, devices and network hardware. An application deploys the software components. The client APIs can be considered at a layer in the architecture. The middle ware components which discover the service , link the client and network service, update database, manage the device using remote server software, perform client server synchronization and adapt the application to the given platform and server. An OS is a layer between application and hardware. It facilitates running the program and providing many OS functions. Protocols Mobile Computing services uses no of mobile communication protocols • Such as GSM 900, GSM900/1800/1900, UMTS, and I-Mode • WPAN protocols─ (Bluetooth, IrDA, and Zigbee) • WLAN protocols ─ (802.11a and 802.11b) • WAP Layers: The OSI seven layer format is follows 1. Physical for sending and receiving signals (for example, TDMA or CDMA coding) 2. Data-link (for example, multiplexing) 3. Networking (for linking to the destination) 4. Wireless transport layer security (for establishing end-to-end connectivity) 5. Wireless transaction protocol 6. Wireless session protocol 7. Wireless application environment (for running a web application, for example, mobile ebusiness) 4. MOBILE DEVICES Handheld Mobile Phones with multimedia functionalities: Mobile phones are handheld devices with large functionalities. Each mobile device essentially includes computer. Smart phones are hybrid cellular phones that possess advanced functionalities of multiphones or multimedia phones besides the functions of regular mobile phones. They can also play MP3and MP4 in addition to the smart phone Smart Cards: A mobile computer chip sandwiched with a very small space between the layers of the card Smart Sensors: Sensors in a mobile device enable it to interact with its better surroundings. For example a sensor for background noise can be used to control voice amplification while receiving a call 5. LIMITATIONS OF MOBILE DEVICES AND SYSTEMS Quality of Service constraints • Technical restrictions and practical considerations─ difficulties in mobile device uninterrupted operations • Maintaining quality of service along with the provisioning of seamless access to all users 5 UNIT-I Accessibility constraints • Smart labels on packages limited access─ transmitted signals low power • Labels can only be read from very short ranges • RFID access limited to ranges within line of sight • RFID transmissions require hotspots close by due to low transmitted signal strength. Range Constraint • Signal strength inversely proportional to the square of the distance • Degradation of signal quality due to reflection, scattering, and diffraction • Access range limited to the range up to which the signal strength is such that it can be separated from the noise • Up to which multi-path delays can be compensated for by digital signal processing techniques to restore signal quality Connectivity • Connectivity loss or intermittent connectivity in certain situations • The atmospheric conditions changes in environment affect signal strength • Water attenuation of UHF and near microwave • For example, in the event of heavy rain, there may be complete loss of connectivity Security Constraints • Unsolicited advertisements and unwanted messages • Virus attacks • Hackers render it functionless or threaten integrity and security of the data stored on the device • Noise signals transmitted by an attacker can jam a mobile device • Repeated transmission of unwanted signals by an attacker can drain the resources of the device • Energy resources depleted fast when computations are forced and authentication algorithms are run repeatedly Mobility constraints • Non-availability of an access point or base station • Infrastructural issues • No base stations or Wi-Fi hotspots providing connectivity and access to the Internet to sensors, labels, automotive systems, RFID tags, and cell phones • Use of different standards in different regions limits the operability • GSM phone may not be operable in all continents hence hampering global roaming for the user • Some service providers may not be able to provide connectivity in all parts of the country or in other continents, etc. Energy Constraints in Devices • Limited energy in battery • Battery size and power limited due to considerations such as size, weight, and bulk of mobile devices • The devices need to be recharged after short periods of time. In this way energy availability also limits device mobility. 6 UNIT-I • Some devices such as smart cards, smart labels, remote sensors, and actuators do not even have a battery of their own. Mobile Computing Strategy in view of constraints • Processor circuit dissipates higher energy when its clock frequency higher • Computational speed higher at higher clock frequency • A device is, therefore, programmed so that only computations such as graphic image processing run at full processor speed • The clock frequency reduced for the other computations to save power. • The clock is activated only when a device interrupts or starts processing instructions. • Many innovative mobile computing strategies adopted to mitigate the effects of energy constraints on mobile computing • Use ZigBee protocol─ a lesser stack size as compared to Bluetooth so less energy dissipation due to lesser computational requirements • Use of a communication protocol that has less protocol stack overheads reduces the energy requirement. Processor Design • Innovative circuits of mobile device processors have been designed and are continuously improved upon so that the same program instructions process with lesser energy dissipation per unit computational speed • Examples of energy efficient processors─ ARM and TigerSharc Hardware Limitations • Constraints on memory • Innovative forms of memory designed and are continuously improved upon. • Internal flash drives and the card slots for external memory used • Memory stick used to enhance the memory in the device • Large memory capacity─ 30GB video memory in mobile devices in a recent enhancement of the Apple iPod Bandwidth Constraints • Limited by the frequency spectrum that a regulator allots to a service provider • The service must use the frequency spectrum allotted to it in an efficient manner • Multiplexing and coding techniques help in achieving efficient transmission. • The technology in use also limits the spectrum efficiency • For example, CDMA has higher spectrum efficiency as compared to GSM 6. GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS (GSM) 7 UNIT-I GSM is a mobile communication standard. GSM communication uses cellular networks. The GSM standard operates in the frequency ranges of 900, 1800, and 1900 MHz. Tri-band (operable in GSM 900/1800/1900) phones enable easy international roaming in GSM networks GSM is a second generation (2G) communication standard. Services: • Teleservices • Supplementary services • Bearer services Connection A mobile station, MS, has a mobile terminal, MT. A mobile terminal acts as an interface between a communications network (e.g., a GSM public land mobile network) and a terminal, TE. The TE is used by a caller to connect and talk (communicate). The MT is responsible for mobile communication and TE is the source or destination of the service. A connection is established between two TEs – the source and the destination. The destination TE may or may not belong to a GSM network. It depends on the sourcedestination which may be a GSM, PSTN (public-switched telephone network), ISDN (integrated service digital network), PSPDN (public-switched public data network), or any other network carrying the data to the end point TE. Following are the teleservices in GSM: 1. Point to point Cellular broadcast 8 UNIT-I  Telephone/Fax  Voice Full 13 kbps  SMS up to 160 characters  Emergency number 112  MMS gif, jpg, wbmp  Teletext  Videotext access  Fax group 3 2. Half data rate speech 3. Enhanced full rate speech Following are the supplementary services in a GSM system:  Call forwarding  Caller line ID  Connected line ID  Closed user group  Multiparty groupings  Call hold, waiting  Call barring,  Operator restrictions  Call charge service Following are the bearer services in a GSM system: Bearer means a set of data which is transmitted from or received by a TE i.e., the voicedata or data set that has been formatted in certain specified formats. This data is then transmitted at certain standardized rates through the interfaces. (Voice-data is data that obtained after digitizing, coding, encoding and appending error detection and correction bits, and encrypting of a voice signal.)  The transparent data transfer for bearer services is at rate 2.4 to 9.4 kbps.  The transparent/non-transparent data transfer 300 bps to 9.6 kbps. Bearer services are responsible for transmission of data (voice signals are also transmitted as data) between two user network interfaces [(1, 8) and (4, 5) in Fig. 3.1] using the intermediate interfaces [(2, 7) and (3, 6) in Fig. 3.1] at a mobile network. Landline phone connect to a GSM phone A landline phone connects to a GSM phone. The source TE at the caller end interfaces the PSTN network. The destination for the call (and source for the reply) is a mobile station TE, which interfaces a GSM public land network in this case. It uses connection path 2, 3, 4, 5, 6 and 7 Transparent Data Transfer Transparent means that the interface for the service is using only physical layer protocol. Physical layer means the layer which transmits or receives data after formatting or multiplexing using a wired (wire or fibre) or wireless (radio or microwave) medium. 9 UNIT-I The physical layer protocol in a GSM bearer service also provides for FEC (forward error correction). FEC entails insertion of redundant bits along with the data to be transmitted. This redundant data allows the receiver to detect and correct errors. FEC requires higher bandwidths but is advantageous in situations where retransmission is not convenient. Non-transparent Data Transfer Non-transparent means that the service interface uses physical layer, data link layer, and flow control layer protocols. Data link layer is the layer which frames the data and appends additional bits to ensure very small error rate. Framing refers to combining and appending additional bits and header. The data link layer performs other functions too Flow control layer controls the flow of data by selecting or rejecting erroneous data transmitted and by re-transmitting erroneous data. The protocols for data link and flow control layers provide for (a) error detection and correction and (b) selecting, rejecting, retransmitting the data, respectively. When data transmits at 9.6 kbps the data error rates are high. This is because when nontransparent data is transmitted at 9.6 kbps, there is no retransmission and erroneous data just gets rejected. The data error rate becomes negligibly small at slow data rates (300 bps). This is because when non-transparent data transmits at 300 bps, then the erroneous data is corrected or gets retransmitted at data link and flow control layers. A special error correction facility called RLP (radio link protocol), used in GSM networks, is an example of a non-transparent communication protocol. RLP results in more robust transmission with very small BER (bit error rate). Synchronous Transmission Synchronous data transmission means that data is transmitted from a transceiver at a fixed rate and constant phase differences (and thus time intervals) are maintained between data bursts or frames Example A voice data is transmitted in synchronous transmission mode. A data frame transmits in 4.615 ms. 51 frames will take how much time? 51 × 4.615 ms = 235.4 ms. The receiver must synchronize the clock rate according to the incoming data bits. The receiver must also synchronize data bits coming in from multiple paths or stations and compensate for the varied delays in received signals. Handshaking is not required in synchronous transmission of data. Synchronous data transmission is fast because there is no waiting period during data transfer. Some examples of synchronous data transfer in a GSM system are as follows: Example Voice is converted into bits after coding in a GSM system and the bits are transferred at data rates of 13 kbps as synchronous data. There are no in-between acknowledgements or waiting periods in this faithful transmission of bits. An SMS is transmitted through a GSM channel as synchronous data. There are no inbetween acknowledgements and any transmission errors are corrected using FEC. Asynchronous Data Transfer 10 UNIT-I Asynchronous data transmission means data is transmitted by the transceiver at variable rates and constant time intervals are not maintained between consecutive bursts or frames. There is usually handshaking or acknowledgement of data in asynchronous data transfer. But even if there is no acknowledgement, even if data flow is maintained by using the FEC but the buffers are used during transmission then the transmission can still be asynchronous. Use of buffers causes variable delays in reception. Synchronous packet Transmission Synchronous packet transmission takes place after formation of packets. Different packets during are transmitted through different interfaces, routes, channels, or time-slots to reach a common destination. At the destination, various packets are arranged in their original sequence. A sequence number transmitted along with each packet helps in sequential arrangement of packets at the receiver. Each packet flow is transmitted as synchronous data. There is no handshaking or acknowledgement of the data during the flow of packets. Assume that there are N packets and only M paths at an instance. A packet along a path takes time = T. Then M packets will flow simultaneously and time taken will be just T. Balance (N – M) packet will flow in next slots of time T each. Example Assume only three paths are available for the packets. Suppose M = 3 and N =9, then time taken will be 3 × T . Suppose M = 3 and N = 10 or 11 or 12, then time taken will be 4 × T . GSM System Architecture GSM network divided into 3 subsystems namely • Radio subsystem (RSS) • Network subsystem (NSS) • Operation subsystem (OSS) 11 UNIT-I Radio subsystem (RSS): The RSS contains all radio specific entities in GSM network. RSS contains no of MSs, BTSs and BSCs Mobile Station (MS): A mobile device or phone. It connects to the GSM network. MS consists of Mobile Terminal(MT). It has Hardware and software to transmit and receive GSM data, and a user terminal (TE) through which the user receives and sends the data. MT Transmits through the interface Um at a power of 1–2 W Subscriber Identity Module (SIM): Each MS has a SIM. It is inserted card into MS. It is provided by the GSM service provider Functions of SIM: • Information which does not change when the MS moves into another location (i) International mobile subscriber identity (IMSI) (ii) Card serial number and type 12 UNIT-I • SIM Contains a PIN (personal identification number). Using the PIN, the MS is unlocked when it seeks connection to another MS. The user can use the PIN to lock or unlock the MS • Stores the PUK (PIN unblocking key) which enables the subscriber to unlock the SIM if it is accidentally locked due to some reason • Stores a 128-bit authentication key provided by the service provider • Also stores the international mobile subscriber identity (IMSI). IMSI has a unique 15 digit number allocated to each mobile user. IMSI three parts— a three digit mobile country code (MCC), a mobile network code (MNC) consisting of two digits, and the mobile subscriber identity number (MSIN) with up to 10 digits Base Transceiver station (BTS): BTS Connects to a number of mobile stations (MSs).Each MS establishes connection through the user interface Um [(1,8)].Um is the ISDN U interface for mobile. The BTS to MS connection through Um. A BTS is also connected to a BSC at through the Abis interface Functions of BTS: • Formation of cells using appropriately directed antennae • Processing of signals • Amplification of signals to acceptable strength so that they can be transmitted without loss of data • Channel coding and decoding • Frequency hopping so that multiple channels for various mobile stations can operate simultaneously using different channel band frequencies • Encryption and decryption of data • Paging Base Station Controller (BSC): BSC manages a number of BTSs. It Uses the Abis interface to connect to BTSs. BSCs reserve radio frequencies for communication and manage handovers between BTSs. A BSC along with the BTSs connected to it and the mobile stations managed through it forms a base station system (BSS) Functions of BSC: • Processing of signals • Controlling signals to the connected BTSs and control of handover of signals from one BTS to another within a BSS 13