Many organizations have large number of substantial computers in operation often located far apart.
Key points[ edit ] The advantages and disadvantages summarized below are further discussed in the Characteristics and principles of operation section.
See also the list of OFDM key features. Claimed advantages over OFDM with time-domain statistical multiplexing[ edit ] Allows simultaneous low-data-rate transmission from several users.
Pulsed carrier can be avoided.
Lower maximal transmission power for low-data-rate users. Shorter delay and constant delay. Contention-based multiple access collision avoidance is simplified. Further improves OFDM robustness to fading and interference. Claimed OFDMA advantages[ edit ] Flexibility of deployment across various frequency bands with little needed modification to the air interface.
Interferences within the cell are averaged by using allocation with cyclic permutations. Enables single-frequency network coverage, where coverage problem exists and gives excellent coverage. Offers frequency diversity by spreading the carriers all over the used spectrum.
Allows per-channel or per-subchannel power. Few users in a base station cell are transferring data simultaneously at low constant data rate.
The complex OFDM electronics, including the FFT algorithm and forward error correctionare constantly active independent of the data rate, which is inefficient from power-consumption point of view, while OFDM combined with data packet scheduling may allow FFT algorithm to hibernate during certain time intervals.
The OFDM diversity gain and resistance to frequency-selective fading may partly be lost if very few sub-carriers are assigned to each user, and if the same carrier is used in every OFDM symbol. Adaptive sub-carrier assignment based on fast feedback information about the channel, or sub-carrier frequency hopping, is therefore desirable.
It would require dynamic channel allocation with advanced coordination among adjacent base stations. The fast channel feedback information and adaptive sub-carrier assignment is more complex than CDMA fast power control.
Characteristics and principles of operation[ edit ] Based on feedback information about the channel conditions, adaptive user-to-subcarrier assignment can be achieved.
Different numbers of sub-carriers can be assigned to different users, in view to support differentiated Quality of Service QoSi. Low-data-rate users can send continuously with low transmission power instead of using a "pulsed" high-power carrier. Constant delay, and shorter delay, can be achieved.
OFDMA can also be described as a combination of frequency-domain and time-domain multiple access, where the resources are partitioned in the time—frequency space, and slots are assigned along the OFDM symbol index, as well as OFDM sub-carrier index.Multiplexing or (muxing) - To combine multiple signals (analog or digital) for transmission over a single line or media.A common type of multiplexing combines several low-speed signals for transmission over a single high-speed timberdesignmag.com other words, we can say that Muxing is used for sharing of a medium and its link by two or more devices.
The original format for Ethernet was developed in Xerox Palo Alto Research Centre (PARC), California in Using Carrier Sense Multiple Access with Collision Detection (CSMA/CD) it had a transmission rate of Mb/s and could support devices over cable stretching for 1km.
The formal Ethernet standard known as IEEE uses a protocol called carrier sense multiple access with collision detection (CSMA/CD). This protocol describes the function of the three basic parts of an Ethernet system: the physical medium that carries the signal, the medium access control rules, and the Ethernet frame, which consists of a standardized set of bits used to carry the signal.
Carrier-sense multiple access with collision avoidance (CSMA/CA) in computer networking, is a network multiple access method in which carrier sensing is used, but nodes attempt to avoid collisions by transmitting only when the channel is sensed to be "idle".
Advantages Of Csma Cd Advantages of marginal costing (Relative to the absorption costing) Preparation of routine operating statements using absorption costing is considered less informative for the following reasons: Profit per unit is a misleading figure: in the example above the operating margin of Rs2 per unit arises because fixed overhead per unit is based on output of 5, units.
CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) is a protocol for carrier transmission in networks. Unlike CSMA/CD (Carrier Sense Multiple Access/Collision Detect) which deals with transmissions after a collision has occurred, CSMA/CA acts to prevent collisions before they happen.