Top 50 Mobile Computing Interview Questions You Must Prepare 02.Oct.2022

  1. Prioritization: Determine the highest priority of a data packet ready to be sent on competing nodes.
  2. Contention: Eliminate all but one of the contenders, if more than one sender hasthe highest current priority.
  3. Trmission: Finally, trmit the packet of the remaining node.

The General Packet Radio Service provides packet mode trfer for applications that exhibit traffic patterns such as frequent trmission of small volumes.

In FDMA, the base station and the mobile station establish a duplex channel. The two directions, mobile station to base station and vice versa are separated using different frequencies. This Scheme is called Frequency Division Duplex (FDD)

Moving between access point is called roaming. Even wireless networks may require more than one access point to cover all rooms. In order to provide uninterrupted service, we require roaming when the user moves from one access point to another.

The goal of DVB is to introduce digital TV broadcasting using satellite trmission (DVB-5) cable technology (DVB-c) and terrestrial trmission (DVB-7).

GEO me Geostationary or Geosynchronous earth orbit. GEO satellites have a distance of almost 36000 km to the earth. Examples are almost all TV and radio broadcast satellites, many weather satellites and satellites operating as backbone for the telephone network.

The primary goal of the standard was the specification of a simple, robust, WLAN which offers time bounded and asynchronous services also it should be able to operate with multiple physical layers.

  • Access point control function
  • Call control and connection control function
  • Network security agent
  • Service control function
  • Mobility management function

  1. Data rates planned for users are 6-38mbit/s for the downlink and 33-100kbit/s for the uplink.
  2. Trmitted along with TV programmes and doesn’t require additional lines or hardware per customer.
  3. Can be used in remote areas and developing countries where there is no high band width wired network.

  • Radio subsystem (RSS)
  • Network & Switching subsystem(NSS)
  • Operation subsystem(OSS)

DAB can repeat objects several times. If an object A consists of four segments (A1, A2, A3, A4) a single repetition pattern would be A1A2A3A4A1A2A3A4A1A2A3A4……..

  1. Intra cell Handover
  2. Inter cell Intra BSC Handover
  3. Inter BSC Intra MSC handover
  4. Inter MSC Handover

  1. Home Location Register (HLR).
  2. Visitor Location Register (VLR).
  3. Satellite User Mapping Register (SUMR).

  • Intra-cell handover
  • Inter-cell ,intra- BSC handover
  • Inter-BSC, intra-MSC handover
  • Inter MSC handover

  • User identification
  • Call redirection
  • Call forwarding
  • Closed user groups
  • Multiparty Communication

Advantages:

  1. Simple and extremely cheap senders and receivers which integrated in almost all mobile devices
  2. No licenses are needed for infrared technology and shielding is very simple.
  3. Electrical devices do not interfere with infrared trmission.

Disadvantages:

  1. Low bandwidth
  2. Quite easily shielded
  3. Cannot Penetrate

The Fast Information Channel(FIC) contains Fast Information Block(FIB) with 256bits each(16 bit checksum). An FIC carries all control information which is required for interpreting the configuration and content of the MSC.

In, non-persistent CSMA, stations sense the carrier and start sending immediately if the medium is idle., if the medium is busy, the station pauses a random amount of time before sensing the medium again and repeating this pattern.

  • Multimedia and Hypermedia information coding experts    group(MHEG)
  • Join photograph’s experts group(JPEG)
  • American standard code for information interchange(ASCII)
  • Moving pictures expert group(MPEG)
  • Hypertext markup language(HTML)
  • Hypertext trfer protocol(HTTP)
  • Bitmap(BMP)
  • Graphics interchange format(GIF)

Code Division Multiple Access systems use codes with certain characteristics to separate different users. To enable access to the shared medium without interference. The users use the same frequency and time to trmit data. The main problem is to find good codes and to separate this signal from noise. The good code can be found the following 2 characteristic

  1. Orthogonal.
  2. AutoCorrelation.

SIFS me Short Inter Frame Spacing. The shortest waiting time defined for short control message such as acknowledgements or polling response.

The satellite is the base station in satellite communication systems and that it self is moving. So, additional instance of handover are necessary due to the movement of the satellite

  1. Intra Satellite handover:
  2. Inter Satellite handover.
  3. Gateway handover.
  4. Inter System handover.

  • Data rate is 2400 bit/s
  • Packet delay is relatively low
  • Smaller footprints of LEO allows frequency reuse
  • Provide high elevations

A beacon contains a timestamp and other management information used for power management and roaming. e.g., identification of the base station subsystem (BSS).

Digital Video Broadcast Containers are basically MPEG-2 frames. DVB sends service information. This information is, 

  1. Network information table(NIT).
  2. Service Description Table(SDT).
  3. Event Information Table(EIT).
  4. Time and Date Table(TDT)

  • Traffic channel (TCH)
  • Control channel (CCH)

Event Information Table (EIT) contains status information about the current trmission and some additional information for set-top boxes.

Three GEO satellites are enough for a complete coverage of almost any spot on earth, senders and receivers can use fixed antennas positions, and no adjusting is needed. Therefore GEO’s are ideal for T.V and radio broadcasting.

Even if the location of a terminal is known to the system, it still has to route the traffic through the network to the access point currently responsible for the wireless terminal. Each time a user moves to a new access point, the system must reroute traffic. This is known as mobile routing.

Spread Aloha Multiple Access is a combination of CDMA and TDMA. The CDMA better suits for connection oriented services only and not for connection less bursty data traffic because it requires to program both sender and receiver to access different users with different codes.

TETRA (Terrestrial Trunked Radio) systems use different radio carrier frequencies, but they assign a specific carrier frequencies for a short period of time according to demand. 

Passive Scanning Simply me listening into the medium to find other networks, i.e. receiving the beacon of another network issued by the synchronization function within an access point.

SCO-stands for Synchronous Connection Oriented Link Standard telephone (voice) connection require symmetrical, circuit-switched, point-to-point connections. For this type of link, the master reserves two consecutive slots at fixed intervals.

Main Service Channel(MSC) carries all user data. eg. Audio, multimedia data.

  1. Object Repetition.
  2. Interleaved Objects.
  3. Segment repetition.
  4. Header repetition.

  • Bearer services
  • Tele services
  • Supplementary services

Logical Link Control(LLC)
Media Access Control(MAC)

Space Division Multiple Access (SDMA) is used for allocating separated spaces to users in wireless networks. The basis for the SDMA algorithm is formed by cells and sectorized antennas which constitute the infrastructure implementing space division multiplexing (SDM)

Polling is a strictly centralized scheme with one master and several slave stations. The master can collect the list of stations during the contention phase and can poll these slaves according to many schemes like round robin, random access, reservation scheme etc.

  • Flexibility,
  • Planning,
  • Design,
  • Robustness,
  • Quality Service,
  • Cost,
  • Proprietary Solution,
  • Restriction,
  • Safety and Security

The elevation angle is defined as the angle between the centre of satellite beam and the plane tangential to the earth’s surface. The foot-print can be defined as the area on earth where the signals of the satellite can be received.

There are several versions in CSMA, they are as follows

  • non-persistent CSMA
  • p-persistent CSMA
  • 1-persistent CSMA

  • Weather forecasting satellites
  • Radio & TV broadcast satellites
  • Military satellites
  • Satellites for navigation
  • Mobile communication

  • card type, serial no, list of subscribed services
  • Personal Identity Number (PIN)
  • Pin Unlocking Key (PUK)
  • An Authentication Key (KI)

  1. DAB can offer sound in CD like quality.
  2. DAB can use single frequency network where all senders trmitting the same radio program can operate at the same frequency.
  3. DAB use VHF and UHF frequency bands.
  4. DAB uses DQPSK modulation scheme.
  5. DAB user COFDM and FEC.
  6. DAB can trmit up to six stereo audio programmes with a data rate of 192kbit/s each.

Elimination yield –Non Pre-emptive Multiple Access (EY-NMPA) is a scheme which uses several phases to sense the medium. Access the medium and for contention resolution... Priority schemes can also be included. This is actually used in HIPERLAN1 specification.

  • Global Operation
  • Low Power
  • License-free Operation
  • Robust trmission technology
  • Simplified spontaneous co-operation
  • Easy to use
  • protection of investment
  • Safety and Security
  • Trparency for application

The function of Medium Access Control Layer is responsible for establishes, maintains, and releases channels for higher layers by activating and deactivating physical channels.

The inclination angle is defined as the angle between the equatorial plane and the plane described by the satellite orbit. An inclination angle of 0 degrees me that the satellite is exactly above the equator. If the satellite does not have a circular orbit, the closest point to the earth is called the perigee.