One of the problems with other forms of phase shift keying is that the sidebands extend outwards from the main carrier and this can cause interference to the other radio communication systems using nearby channels. GSM Works as follows: The entire frequency band is divided into chunks and each such chunk is divided into timeslots and each such. So, in order to differentiate, the transmission from each user.
At the receiving end, the spread information is decoded. Answer : Rx level 0 to 63 is GSM unit. While to is dbm Rxlevel unit of GSM. When we will add to Rxlevel [dbm],it will get convert into GSM unit 0 to Popular Interview Questions. All Interview Questions. Gsm Practice Test. IT Skills. Management Skills.
Communication Skills. Business Skills. Digital Marketing Skills. Human Resources Skills. Health Care Skills. Finance Skills. All Courses. All Practice Tests. Question 1. What Is Gsm? Networking Interview Questions Question 3. Is This Answer Correct? But why? What you mean by Link Budget? The speech frame is swept if even one of its most important 50 bits is observed not to be correct. The three parity bits following the 50 class Ia bits are used for error detection.
It is important to notice that BER is evaluated before channel decoding, i. Rx level 0 to 63 is GSM unit. The 26 traffic Multiframe structure is used to combine user data traffic , slow control signaling SACCH , and idle time period. The 12th frame no. Each timeslot in a cell allocated to traffic channel usage will follow this format, that is, 12 bursts of traffic, 1 burst of SACCH, 12 bursts of traffic and 1 idle.
Idle Bursts: The idle time period allows a mobile device to perform other necessary operations such as monitoring the radio signal strength level of a beacon channel from other cells. The time interval of a 26 frame traffic Multiframe is 6 blocks of speech coder data msec. Effective isotropic radiated power EIRP is the amount of power that a theoretical isotropic antenna that evenly distributes power in all directions would emit to produce the peak power density observed in the direction of maximum antenna gain.
EIRP can take into account the losses in transmission line and connectors and includes the gain of the antenna. The EIRP is often stated in terms of decibels over a reference power emitted by an isotropic radiator with equivalent signal strength. The EIRP allows comparisons between different emitters regardless of type, size or form. The polarization indicates the plane in which the wave is vibrating.
The polarization plane is taken to be that of the electric component. Vertical and horizontal are the simplest forms of polarization, and they both fall into a category known as linear polarization. However, it is also possible to use circular polarization. This has a number of benefits in areas such as satellite applications, where it helps to overcome the effects of propagation anomalies, ground reflections and the spin that occur on many satellites.
Circular polarization is a little more difficult to visualize than linear polarization; however, it can be imagined by visualizing a signal propagation from an antenna that is rotating. Another form of polarization is known as elliptical polarization. Rayleigh fading is a reasonable model when there are many objects in the environment that scatter the radio signal before it arrives at the receiver. Rayleigh fading models assume that the magnitude of a signal that has passed through such a communications channel will vary randomly, or fade, according to a Rayleigh distribution the radial component of the sum of two uncorrelated Gaussian random variables.
Rayleigh fading is most applicable when there is no dominant propagation along a line of sight between the transmitter and receiver. If there is a dominant line of sight, Rician fading may be more applicable. Multipath fading is receiving multiple copies of the signal at receiver due to reflections.
The copies reach the receiver with different phases, so summation either constructive or destructive. This affects the quality of received signal in terms of BER.
Antenna diversity increases the received signal strength by taking advantage of the natural properties of radio waves. There are two primary diversity methods: space diversity and polarization diversity.
Space Diversity: Increased received signal strength at the BTS may be achieved by mounting two receiver antennae instead of one. If the two Rx antennae are physically separated, the probability that both of them are affected by a deep fading dip at the same time is low. At MHz, it is possible to gain about 3 dB with a distance of five to six meters between the antennae. At MHz the distance can be shortened because of its decreased wavelength.
By choosing the best of each signal, the impact of fading can be reduced. Space diversity offers slightly better antenna gain than polarization diversity, but requires more space.
Polarization Diversity: With polarization diversity the two space diversity antennae are replaced by one dual polarized antenna. This antenna has normal size but contains two differently polarized antenna arrays. The two arrays are connected to the respective Rx branches in the BTS. For most applications, the difference between the diversity gain for space diversity and polarization diversity is negligible, but polarization diversity reduces the space required for antenna.
Skip to content 1. Explain Each Of Them Briefly? GSM services are categorized in three teleservices, bearer, and supplementary services. Teleservices communicate with other subscribers. Bearer service provides the underlying network capacity necessary for transmission to occur between two points in the same or different networks. The bearer services describe what the network can offer e. Supplementary service is optional which subscriber can subscribe for free.
Ex: call forwarding, call waiting. What Is Ciphering? Why Do We Need It? Networking Interview Questions 3. What Is Authentication? Define the hopping parameters in detail? The MA is a list of hopping frequencies transmitted to a mobile every time it is assigned to a hopping physical channel.
The HSN is a cell specific parameter. For the baseband hopping two HSNs exists. Reference source not found.. Example of the hopping sequence generation is presented in Error! What is the effect of frequency hopping in RXQual? A speech frame is generally discarded if after the decoding and error correction process any of the category 1a bits is found to be changed based on the three parity bits following them in a speech frame.
FER is a measure of how successfully the speech frame was received after the error correction process and it is thus a better indication of the subjective speech quality compared to the RXQUAL which gives an estimate of the link quality in terms of BER. The bit error distribution affects the ability of the channel decoding to correct the errors.
FER comparison according to the laboratory tests. Reference source not found. This may seem to be surprising since it is expected that frequency hopping improves the network quality. However, in most cases the quality is actually improved, but the improvement is more visible in the call success ratio.
The improved tolerance against interference and low field strength in FH network means that it is less likely that the decoding of SACCH frames fails causing increment in the radio link timeout counter.
Thus, it is less likely that a call is dropped because of the radio link timeout. However, at the same time the call success rate is significantly improved. In the Error! This difference is a consequence of interference and frequency diversities that affect the frequency hopping network. The successful error correction leads to less erased frames and thus improves the FER. What do you understand by idle channel measurement?
The frequency hopping has a significant effect on the idle channel interference measurement results. When the frequency hopping is used, the frequency of a hopping logical channel is changed about times in a second. The frequency of the idle time slots changes according to the same sequence.
If the interference is averaged over more than one SACCH frame, the averaging effect is even stronger. However, normally the interferers are mobiles located in interfering cells.
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