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.
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……..
Advantages:
Disadvantages:
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.
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
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
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,
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.
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.
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
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.
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.