![]() ![]() The messages are either represented by a sequence of pulses by means of a line code ( baseband transmission), or by a limited set of continuously varying waveforms ( passband transmission), using a digital modulation method. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal.Īnalog transmission is a method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable. Examples of such channels are copper wires, optical fibers, wireless communication using radio spectrum, storage media and computer buses. The advantage of the efficient Wi-Fi protocol is far greater utilization of the radio spectrum, and far lower requirements to retransmit data.For broader coverage of this topic, see Communication.ĭata communication or digital communications, including data transmission and data reception, is the transfer and reception of data in the form of a digital bitstream or a digitized analog signal transmitted over a point-to-point or point-to-multipoint communication channel. However, these complications are taken care of by the IC chip designer and due to advanced semiconductor manufacturing processes the unit cost impact is minimal. ![]() Wi-Fi devices require a computer processor and accurate time synchronization in order to adhere to the strict protocol requirements. It also uses some other smart techniques to schedule time slots for certain packets and to alleviate various other problems (such as hidden nodes). Wi-Fi uses LBT to decide when to access the radio spectrum. If they detect a packet on the spectrum they wait until it is complete before turning on their transmitter to send their packet. ![]() This is a vicious circle of deteriorating performance as the required performance increases! In practice the maximum radio spectrum utilization of ALOHA networks is around 18%įortunately a better alternative to ALOHA is Listen Before Talk (LBT).Īs the name implies, devices using this protocol first listen to the radio spectrum. At utilizations greater than 10% packets start colliding more frequently triggering more and more repeated transmission. Collisions degrade the network efficiency as packets that collide have to be resent.ĪLOHA networks operate efficiently, with reasonable low number of collisions and repeats up to around 10% utilization of the radio channel. ![]() Collisions occur more frequently as the network get more congested. The disadvantage of ALOHA based networks is that collisions occur. As such it is found in early packet based networks (like the first packet based network in Hawaii) and cheap unsophisticated technologies. If a collision is detected then try sensing the packet againĪLOHA is a super simple method which is cheap and easy to implement.If a devices has a packet to send then send it immediately.Named after one of the world’s first packet based networks in Hawaii. Here I’ll look at two common ways of determining when a device accesses the radio channel and starts transmitting its data. Previously I wrote about why high data rates are beneficial for increasing network capacity and reducing power consumption. ![]()
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