Mobile Computing Notes pdf — MC notes pdf Details Unit The rapidly expanding technology of cellular communication, wireless LANs, and satellite services will make information accessible anywhere and at any time. Regardless of size, most mobile computers will be equipped with a wireless connection to the fixed part of the network, and, perhaps, to other mobile computers. Unit The IP addresses are designed to work with stationary hosts because part of the address defines the network to which the host is attached. A host cannot change its IP address without terminating on-going sessions and restarting them after it acquires a new address. Mobile Computing Notes pdf Details Unit The advantage of hoarding is that there is no access latency delay in retrieving the queried record from the server over wireless mobile networks. The client device API has instantaneous data access to hoarded or cached data.

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It has a control unit, radio cabinets, antennas, a power plant, and data terminals. MTSO- The switching ofce, the central coordinating element for all cell sites, contains the cellular processor and cellular switch. It interfaces with telephone company zone ofces, controls call processing, provides operation and maintenance, and handles billing activities. There are two basic cellular systems; one is the circuit-switched system and the other is the packet-switched system.

In a circuit-switched system, each trafc channel is dedicated to a user until its cell isterminated. We can further distinguish two circuit-switched systems: one for an analog system and one for a digital system. A basic digital system consists of four elements: mobile station, base transceiver station BTS , base station controller BSC , and switching subsystems.

In a cellular packet-switched system. MS: Provides the voice and packet data services. It is also called UE User Equipment. Its function is similar to BSC. This includes mobility management, security, and access control functions. It interfaces to HLR. The designation of various types of channels is done by FCC which is an international organization which gives the required standards. But, the grouping of voice channels into subsets is done by each system according to its preference.

It refers to the allocation of specific channels to cell sites and mobile units. The channel assignment can be done in two ways. They are:-i Short-term assignment. Long-term assignment:-A fixed channel set consisting of one or more subsets is assigned to a cell site on a long-term basis. Short-term assignment:-During a call, a particular channel is assigned to a mobile unit on a short-term basis.

After the call, the channel will be altered. Ideally channel assignment should be based on causing the least interference in the system. Setup channels also called control channels are the channels designated to setup calls. A call always needs a setup channel. Setup channels can be classified by usage into two types: Access channels and paging channels. Access channels: it is used for the mobile originating calls Paging channels: it is used for land originating calls. In a low traffic system access channels and paging channels are the same.

FCA requires manual frequency planning, which is an arduous task in TDMA and FDMA based systems, since such systems are highly sensitive to co-channel interference from nearby cells that are reusing the same channel.

This result in traffic congestion and some calls being lost when traffic gets heavy in some cells, and idle capacity in other cells. A more efficient way of channel allocation would be Dynamic Channel Allocation or Dynamic Channel Assignment DCA in which voice channel are not allocated to cell permanently, instead for every call request base station request channel from MSC. The channel is allocated following an algorithm which accounts likelihood of future blocking within the cell.

The term handover or handoff refers to the process of transferring an ongoing call or data session from one channel connected to the core network to another. In satellite communications it is the process of transferring satellite control responsibility from one earth station to another without loss or interruption of service.

In terrestrial networks the source and the target cells may be served from two different cell sites or from one and the same cell site in the latter case the two cells are usually referred to as two sectors on that cell site.

Such a handover, in which the source and the target are different cells even if they are on the same cell site is called inter-cell handover. A special case is possible, in which the source and the target are one and the same cell and only the used channel is changed during the handover. Such a handover, in which the cell is not changed, is called intra-cell handover.

A hard handover is one in which the channel in the source cell is released and only then the channel in the target cell is engaged. A soft handover is one in which the channel in the source cell is retained and used for a while in parallel with the channel in the target cell.

Hard handovers are intended to be instantaneous in order to minimize the disruption to the call. A hard handover is perceived by network engineers as an event during the call. It requires the least processing by the network providing service. When the mobile is between base stations, then the mobile can switch with any of the base stations, so the base stations bounce the link with the mobile back and forth.

This is called ping-ponging. In this case the connection to the target is established before the connection to the source is broken, hence this handover is called make-before-break. The interval, during which the two connections are used in parallel, may be brief or substantial. For this reason the soft handover is perceived by network engineers as a state of the call, rather than a brief event.

Soft handovers may involve using connections to more than two cells: connections to three, four or more cells can be maintained by one phone at the same time. When a call is in a state of soft handover, the signal of the best of all used channels can be used for the call at a given moment or all the signals can be combined to produce a clearer copy of the signal.

The latter is more advantageous, and when such combining is performed both in the downlink forward link and the uplink reverse link the handover is termed as softer. Softer handovers are possible when the cells involved in the handovers have a single cell site.

Vertical handover or vertical handoff refers to a network node changing the type of connectivity it uses to access a supporting infrastructure, usually to support node mobility. For example, a suitably equipped laptop might be able to use both a high speed wireless LAN and a cellular technology for Internet access.

Wireless LAN connections generally provide higher speeds, while cellular technologies generally provide more ubiquitous coverage. Vertical handovers refer to the automatic fallover from one technology to another in order to maintain communication. Dropped Call Rate DCR is a term in telecommunications denoting the fraction of the calls which, due to technical reasons, were cut off before the speaking parties had finished their conversation and before one of them had hung up.

This fraction is usually measured as a percentage of all calls. A Media Access Control address MAC address is a unique identifier assigned to network interfaces for communications on the physical network segment. In the GSM cellular mobile phone standard, timing advance value corresponds to the length of time a signal takes to reach the base station from a mobile phone.

FDMA gives users an individual allocation of one or several frequency bands, or channels. It is particularly commonplace in satellite communication. In FDMA all users share the satellite simultaneously but each user transmits at single frequency.

FDMA can be used with both analog and digital signal. Since a predetermined frequency band is available for the entire period of communication, stream data a continuous flow of data that may not be packetized can easily be used with FDMA. Each user transmits and receives at different frequencies as each user gets a unique frequency slot 24 Explain TDMA? Time division multiple access TDMA is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots.

The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium e.

It is also used extensively in satellite systems, combat-net radio systems, and PON networks for upstream traffic from premises to the operator. Code division multiple access CDMA is a channel access method used by various radio communication technologies. 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. A cellular network or mobile network is a radio network distributed over land areas called cells, each served by at least one fixed-location transceiver, known as a cell site or base station.

Cellular networks offer a number of advantages over alternative solutions: 29 Explain frequency reuse? The key characteristic of a cellular network is the ability to re-use frequencies to increase both coverage and capacity. As described above, adjacent cells must use different frequencies, however there is no problem with two cells sufficiently far apart operating on the same frequency.

The elements that determine frequency reuse are the reuse distance and the reuse factor. The reuse distance, D is calculated as flexible enough to use the features and functions of almost all public and private networks[1] increased capacity reduced power use larger coverage area reduced interference from other signals where R is the cell radius and N is the number of cells per cluster.

Cells may vary in radius in the ranges 1 km to 30 km. The boundaries of the cells can also overlap between adjacent cells and large cells can be divided into smaller cells. It therefore required considerable bandwidth for a large number of users. In general terms, AMPS was very similar to the older "0G" Improved Mobile Telephone Service, but used considerably more computing power in order to select frequencies, hand off conversations to PSTN lines, and handle billing and call setup.

Frequency-hopping spread spectrum FHSS is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom sequence known to both transmitter and receiver.

A spread-spectrum transmission offers three main advantages over a fixed-frequency transmission: 1. Spread-spectrum signals are highly resistant to narrowband interference.

The process of re-collecting a spread signal spreads out the interfering signal, causing it to recede into the background. Spread-spectrum signals are difficult to intercept. An FHSS signal simply appears as an increase in the background noise to a narrowband receiver. An eavesdropper would only be able to intercept the transmission if the pseudorandom sequence was known.

Spread-spectrum transmissions can share a frequency band with many types of conventional transmissions with minimal interference. The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be utilized more efficiently. To minimize interference, a certain distance must be maintained between cells using the same frequencies.

However, this distance can be reduced without disturbing the cell reuse pattern. As the size of the cells are reduced, the same frequencies can be utilized in more cells, which in turn means more subscribers can be accommodated on the system.

Particularly in congested areas, the cellular operator often splits an existing cell into two or more smaller cells. New transceivers are placed and the power of the transmitters are reduced in order to confine the signals to the newly created cells. In cellular telephone system, co-channel interference can be decreased by replacing a single omnidirectional antenna with several directional antennas, each radiating within a smaller area.


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It has a control unit, radio cabinets, antennas, a power plant, and data terminals. MTSO- The switching ofce, the central coordinating element for all cell sites, contains the cellular processor and cellular switch. It interfaces with telephone company zone ofces, controls call processing, provides operation and maintenance, and handles billing activities. There are two basic cellular systems; one is the circuit-switched system and the other is the packet-switched system.

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