Introduction to Mobile Computing

• Unit 01 provides an introduction to Mobile Computing.

Evolution of Computing Devices

• A graph illustrates the evolution of computing devices over time.
• The volume of different devices (Mainframe, Workstation, Laptop, Mini-Computer, Personal Computer, and Smartphone) in cubic millimeters (mm³) has decreased from 1960 to 2020.
• The X-axis represents the year of introduction of different computing devices.

Mobile Computing

• Mobile computing involves technologies that allow the transmission of data, voice, and video.
• This happens through a computer, smartphone, or any wireless-enabled device.
• The connection doesn't require a fixed physical link which enables users to access data regardless of their location.
• Mobile computing consists of mobile communication, mobile devices/hardware, and mobile software.
• Mobile communication refers to the infrastructure for seamless and reliable communication which includes devices, protocols, services, and bandwidth.
• Mobile devices or hardware includes components that receive or access the service of mobility, like portable laptops, smartphones, tablet PCs, and Personal Digital Assistants (PDAs).
• These devices have a receptor medium for sensing and receiving signals, operate in full-duplex mode, and use existing networks, mostly wireless.
• Mobile software is the actual program that runs on the mobile hardware.
• The software's main factor is portability, allowing users to operate from anywhere.

Mobile and Wireless Devices

• Sensors are simple wireless devices represented by a sensor transmitting state information.
• Pagers are simple receivers that display short text messages, but cannot send any messages and are virtually replaced by mobile phones
• Mobile phones/smartphones send/receive voice or short messages and now have color graphic displays, touch screens, and internet browsers.
• They can run multiple programs concurrently and have high-speed data access via Wi-Fi and cellular broadband.
• Personal Digital Assistants (PDAs) act as electronic organizers, comprising simple versions of office software.
• Pocket computers are a step towards full computers that have tiny keyboards, color displays, and simple versions of programs.
• Notebooks/laptops offer similar performance to desktop computers with the only difference being size, weight, and the ability to run on battery.

Applications of Mobile Computing

• Vehicles/Traffic applications use wireless communication for mobility-aware systems.
• These systems receive music, news, road conditions, and weather reports via digital audio broadcasting (DAB).
• UMTS are used for personal communication with voice and data connectivity.
• Satellite communication provides a connection in remote unknown areas and uses GPS to find the exact position.
• Cars in the same location can form an ad-hoc network for quick information exchange.
• Emergency applications include ambulances with high-quality wireless connections.
• These systems share vital information about injured persons from the accident scene with the hospital.
• Specialist suggestions can be prepared in advance and doctors can be consulted early for diagnosis.
• Wireless networks are used for communication when hurricanes or earthquakes happen.
• Decentralized, wireless ad-hoc networks and mobile phone systems may be the only systems that survive, if the fixed telephone system fails.
• Business applications allow CEOs to call distant video conferences and allow travelling salesman to access the database.

More Applications for Mobile Computing

• Wireless networks can replace wired networks in certain situations like remote sensor locations, where deploying weather forecasts or earthquake detection is impossible due to deployment costs.
• Tradeshows may need to dynamically setup an infrastructure for the show.
• Cabling takes a long time and inflexible in historic buildings when a lot of cabling can destroy valuable walls or floors.
• A wireless access point can be setup in the corner of a room as a solution.
• In Entertainment, Apps will provide travel guides and building information for the user Users can pay for goods via their card on their phone.

Location Dependent Services

• These services can follow the user location or detect the user's location for custom services to be provided.
• If a conference call starts, then it will be forwarded to the location of the current user.
• Email services will follow the location of the user to the current location
• Information services will allow you to search for local businesses, like ATM's.
• Important information must be secure when transferred to the user such as bank information, and video calls.

Challenges in Mobile Computing

• Challenges in mobile computing include wireless communication, mobility, and portability due to having fewer resources to stationary machines.
• This means devices need to be smaller, lighter and consume less.
• Obstacles make the wireless connection difficult to implement due to the errors the wireless connection causes.
• Wireless communication is more susceptible to disconnection. Resources need to be allocated to handle disconnection.
• Wireless networks deliver lower bandwidth than wired and mobile designs must be concerned about bandwidth consumption.
• User experience must be of good quality.

Additional Challenges in Mobile Computing

• Security risks are greater with wireless. Security is further complicated if users allowed to cross security domains, secure communication over insecure channels is accomplished by encryption.
• A mobile computer needs a mechanism for determining which server to use as a mobile computer's network address keeps changing.
• Mobility requires an update to what the current "address" of a user is at all times in conjunction to local name servers, printers, and more.
• Weight should be minimal, and batteries should still have long lives.
• Breaches of data can happen easier as mobile devices get lost easier.

Portability Challenges

• Smaller devices have inadequate techniques to show windowing. Surface areas of devices are smaller making other forms of input difficult.
• Smaller Storage occurs as it's limited by physical size in comparison to larger desktop computers.

Simplified Reference Model

• There are 5 components to this reference model: Physical, Data Link, Network, Transport, and Application.
• The physical Layer is responsible for managing the transfer of of all information that is going to be transmitted. This includes signals, frequency, detecting signals, generating them, modulation, and more.
• Data Link is responsible for transferring data by synchronizing different streams, correcting transmission errors, and more.
• Network is responsible for sending packets through a given network.
• Transport is responsible for providing the service that the networks provides.
• Application is responsible for ensuring all prior layers can interact with the world wide web (www)

Wireless Transmissions

• Wireless transmission occurs between 2 points without any physical media.
• The distances of transmission can range from meters, to thousands kilometers. The frequencies used are regulated.
• Wireless has hurdles that wired transmission typically does not.
• IR is commonly used in fiber optics as well in wireless communication.
• Radio transmission frequency: Very Low, Low, Medium, High, Very High, Ultra High.

Wireless Transmission: Frequencies Regulation

• Mobile phones generally transmit using: NMT, AMPS, TDMA, CDMA, GSM, UMTS (FDD), and W-CDMA.
• Cordless telephones generally transmit using: UMTS (TDD), CT1+, CT2, DECT, and PACS.
• Wireless LANS generally transmit using: IEEE 802.11, HIPERLAN2, and IEEE 802.11a.
• Others can transmit using RF-Control, and Satellites.
• Signals can be the physical representations of data when the user exchanges it.
• Signal function parameters = Amplitude A, Frequency f, and Phase Shift φ

Wireless Transmission: Signals

• The signal parameters are: Amplitude A, Frequency f, and Phase Shift.
• Amplitude, A is measured in Volts (V). The value is displayed versus the frequency f(Hz).
• Transmissions can be manipulated in 3 directions. Amplitude, Frequency and Phase shift.
• Antennas couple electromagnetic energy to and from a medium
• Some antennas transmit Omni directionally in communications for ulticast communications like radio, TV and some paging systems.
• Others are unidirectional for unicast communications such as telephone and satellites.

Wireless Transmission: Signal Propogation

• Signal Propagation means that wired/wireless networks have senders/receivers. However, transversal has some differences.
• Wireless networks only transmit if there are no wires in the selected direction.
• Line of Site: Emitted waves follow on the ground for distances and direct communication.
• When a transmission is being sent, the range can be: Transmission, Detection, Interference
• Signals that travel like light are known as "Line Of Sight"

Wireless Transmission: Multipath Propgation

• Signals can take many paths between the sender and receiver, such as reflection, scattering, and diffraction.
• When multiple signals arrive to the receiver it can cause interferences, creating a delay in the signal sent to the receiver.
• Some signals follow an irregular path, creating sky waves/ground waves.
• Signals follow ground waves which allow the earth's surface transmissions to propagate for a long time, for the use of submarines.
• Distant communication also makes use of short waves that follow the earth/ionosphere.

Wireless Transmission: Multiplexing

• Mutliplexing means a common medium can be shared by other users with the use of different techniques to avoid interference.
• Users use a highway, or lane, with the lanes providing the space.
• Multiplexing can use four dimensions, time, space frequency and code.
• Using guard spaces is important, this gives the users time to start their transmissions.
• Criteria to ensure quality:
  • Minimum interference
  • Max utilisation of the medium
• Multiplexing can also divide space into three dimensions (SDM.)
• Different senders must be wide enough from one another to isolate the other user.
• Some channels may establish to close, which creates issues leading to radio interference.
• Different senders use a certain space to their own frequency band so they continuously transmit data. A well known example of this is Radio.
• Multiple transmissions leads to waste and is very inflexible.

More Detailed Information on Wireless Transmission Channels

• Each channel has it's own individual frequency band for data to continuously be transmitted and uses radios (FDM.)
• TDM can be used to create a full bandwidth line with guard spaces.
• Time-Division Multiple Access (TDM): can be used when each kᵣchannel gives a certain bandwidth for a certain length of time (GSM.)
• Different radio channels talk to each other, but use a code to identify them by their code division (CDM.)
• Coding assigns a certain code to a channel creating a code division.
• Since you're assigning codes to different channels, this causes a good protection against data interference.
• With each channel being able to use the same spectrum and separation being coded, channels can interfere creating background static in the line .
• This means better signal regeneration is critical for good code division, while also making the data lower.

Modulation Systems: Digital, and Analog System

• Digital modulation requires analogizing it. By amplitude or frequency (FSK.)
• Analog modulation requires shifting the frequency to act as the receiver. This includes smaller antennas/multiplexing using radio and more.
• Signals can be manipulated in three different methods. Digital can be modified, or used as amplitude by shifting it.

Modulation Systems Digital Details

• Amplitudes is where the system can be zero, which represents the binary.
• With FSK the frequency is either increased or decreased as an indicator for changing the signal. Implementers can use an alternate or two separate signals with slightly different paths.
• Finally, with phase, the signal phase is given with a signal shifting data.
• When data is set with "1", a +1 is set to multiply the frequency. When "0" is set, a one (1) is implemented.

Spread Spectrum

• Spread spectrum creates bands around the signal to broadcast the signal around a certain portion of a code.
• The original data can be built even if the interference occurs.
• Two transmission techniques used for SS are: DSS, and FHSS
• DSS spreads the signals throughout the code.
• HHSS splits transmissions between channels.

More Detailed Information on Spread Spectrums

• It's common to XOR the signal with a chipping sequence to encrypt a spread.
• The higher the chipping sequence means a wider system.
• These systems are commonly used with many factors to consider,
  • civil app are set for factors of 10-100
  • Military is set as 10,000 and higher
• The bandwidth of these transmissions is important.
• With FHSS frequencies are split among channels. The transmitter and receiver typically stay on one of these channels. The dwell time is the time the signal spends on one channel. The signal is faster at running different routes, also known as fast hopping.
• Signals can be used at one channel for several periods.

Additional Topics in Transmission and Cellular Networks.

• The frequency synthesizer creates a chain to find the right bandwidth and modulate it. Once the receiver comes, the signal can be demodulated and show.
• Cellular System design allow mobile communications to connect and implement SDM.
• These are called base stations. The Radius is also determined by weather, building, and load of a phone network.
• Mobile telemetry has cell around a location to communicate in vice versa.

Cellular System Benefits

• Cellular systems install thousands of base stations rather than one massive transmitter.
• SDM increase capacity of a signal and ensure it can connect.
• Less Transmission occurs from nearby base stations sending energy to it.
• Distance between sender and receiver increase, then that means the interferences will increase. Having a shorter range will only have the mobile or base deals with local areas.
• Using signals can be decentralized across certain segments, causing the whole signal is good. The influences will be smaller as well.
• Small cells have Infrastructure costs, but are required for better speeds and overall services. Handovers depend on cell size and speed.
• When two frequencies interfere with one another frequencies have to be handled delicately.

Summary of Different Network Operations

• A mechanism requires a user to access a medium using SDM, TDM, FDM and CDM.
• MAC regulates the highway for example.
• Wireless systems require multiple forms of authentication to create a good connection.
• CSMA/CD scheme detects a collision every time.
• Problems with wireless
  • Signal is not always in range
  • Objects attenuate the signal
  • Receiver may receive collisions from far senders.

Multiple Access Control

• Multiple Access Control needs to be configured to support what is happening and if it's exposed during collision scenarios can cause an issue when devices wants to transmits, creating an idle medium.
• The signal strength is drowned from B, making C unable to receive at all.
• There needs to be a power control of sensors to allow the end user to use the full strength and medium around one receiver.
• There should be different access methods in use, such as: MDMA, FDMA.
• Different cells provide different quality in connection.

Medium Access Control Methods

• SDMA allows different separated devices in users in wireless.
• The MAC algorithm decides its cell is associated with terminal station code.
• FDMA allows the radio stations to act as transmitters over time.
• Allocation is configured to assign all the same time points, or even combining FDMA with TDMA for better transmission.
• Channel transmissions are limited to what the sender does. You can always listen on the frequency, what's flexible is the wired based networks which are also designed on TDMA.
• Fixed TDM occurs where a time slot can be created as a static channel in fixed patterns typically in bandwidth, used to implement duplexes/etc, TDD assigns uplink/downlink frequencies.

More Info on Time Division Multiple Access (TDMA)

• The protocol in this, ALOHA, was invented at the University of Hawaii where there was no access. If two stations access, there would be created issues and destroy data. The works only for the light, and require complicated access.

• New systems implement time slots to handle the lack of connections, such as slotted ALOHA. These schemes introduce time slots. Senders must synchronize while transmission can create some collisions to some degree.

• A has already started the process, as the message sends in real time.

• A is hidden from C for it is already communicating with A. However, after the connection with STS C can no longer create a connection.

• Exposed terminal problems can result in a system by which one station has multiple ways of communicating at a certain point of time.

Better Forms of Connection Control

• Busy tone signaling is the best method for sensing connections and transmissions.
• Better forms of this rely on multiple systems, and can even come from other data sources.

Code Division Multiple Access

• CDMA uses code to split access by creating very certain characteristics to handle the transmission. These systems used exact codes. Good codes can be separated from noise by two code categories. autocorrelation or have to be orthogonal. The vectors have to create inner products for this to workout.