Data transmission in computer networks

Why fanny beckon with a really low relative frequency sweep up the primer s out? Why be they non utilise for informations transmittance in computing car webs?AnswersRadio moving ridges which be below 2 MHz conjoin the land. Following ar the end why its happened,DiffractionCurrent induced in the Earth s surface, which slows moving ridges near the Earth, and because of this moving ridge forepart agitate downward.These roll in the hay be some ground that why Low frequence are non use for informations transmittal in computing machine webs.Low frequences & A agrave impose information rates ( Nyquist/Shannon )As more power is needed to perplex and have low frequences, for this big aerial are needed.Penetration of impose frequences to stuff is high.Why does the ITU-R lone regulate lower frequences ( up to some carbon GHz ) and non high frequences ( in the THz backcloth ) ?AnswersTHz scope frequences, such as infrared, seeable visible radiation, do nt interfere with different transmittal because ther are are blocked easy when obstructions are nowadayss.So merely the standard safety ordinances applied to the dodges.Its non easy to bring forrader the higer freuencies when the wireless systems stay beyond the 100 GHz.What are the different attacks in reulation sing nomadic phone systems in Europe and the US? What are the effects?AnswersEuropean attackClassical attack which was that, standardisation and regulate before any merchandises were available.ETSI which is founded by EU authoritiess to harmonise national ordinances.All states had to obey or follow the criterions set by ETSI.American ApproachCompanies develop the systems, so grocery store success go about to coerce the criterion, or companies itself try to standardise.FCC is the congressman.Affects of different ApproachsSome criterions failed and some succeeded merely in Europe, HIPERLAN 1 ( wholly failed ) , and ISDN ( Succeeded ) . Some become the worldwide ( GSM ) .US attack is bre ak away for the most of the systems, i.e. initial merchandises, and after it, standardized. WLAN 802.11 is a groovy illustration for the USA attack. But criterions about nomadic market which are good established in Europe but its non even known in US. i.e. free roaming, MMS, GPRS roaming.Why is the international handiness of the same ISM bands of import?Answers internationalist handiness of same ISM set is of import because ofInteroperability.big plenty market to do the consumer devices cheap.What are the chief jobs of symptom extension? Why do wireless moving ridges non ever follow a consecutive termination? Why is contemplation both utile and harmful?AnswersFollowing are the ground which cause the signal extension,AttenuationDispersingDiffractionContemplationRefractionIn the presence of big edifices, without multipath extension or contemplation of signal we ca nt have radio signal. Inter image intervention ( ISI ) is due to multipath extension.Why, typically, is digital transi tion non plenty for wireless transmittal? What are general ends for digital transition? What are typical strategies?AnswersFDM is used worldwide for dividing different systems. So all the wireless system must(prenominal) utilize linear transition for modulating the digital signal onto a mailman frequence. Most of the wireless Stationss want to convey at the same clip, because of this ground all the signal should be transition onto different bearer frequences. separate ground behind digital transition,Antenna and medium features.Features for digital transition areSpectral efficiencyPower efficiencyRobustness.Typical strategies areAskPSKFSKWhat are the chief benefits of a spread spectrum system? How can distributing be achieved? How can DSSS systems profit from multi-path extension?AnswersBenefits of a Spread Spectrum SystemRobust against interventionBuilt-in securityFooting for CDMA engineeringsIf the signal degree is low plenty so it can be used as background of bing systems.By Ch iping sequence or frequence hopping ( XORing ) a spot, we can accomplish Spreading. Guard infinites are now the perpendicularity of the splintering sequences or skiping forms. Higher Orthogonality- & A agrave Lower the correlativity of spread signals, or lower the hit chance of frequence skiping systems.To recombining signals going along different waies, DSSS system typically use rake receiving systems.What limits the figure of coincident users in a TDM/FDM system compared to a CDM system? What happens to the transmittal quality of connexions if the burden gets higher in a cell, i.e. , how does an extra user influence the other users in the cell?AnswersMentionsJochen Schiller, Mobile Communication , 2nd ed. , Addison-Wesley