Interview Questions.

Q1. Explain The Effects Of Power Control?

Power manipulate is able to compensating the fading fluctuation.

Received electricity from all MS are managed to be identical.

Near-Far trouble is mitigated by the energy control.

Q2. Explain Forward Traffic Channel?

Forward Traffic Channels are code channels and used to assign calls, typically voice and signaling visitors to the character customers.

Q3. What Is Cdma?

CDMA stands for Code Division Multiple Access. It is a wireless generation used in trmission of alerts from places with excessive Security and noise reduction. The principle of Spread Spectrum is used to paintings with CDMA. Spread sign is under the noise degree and noise has no impact at the signal. CDMA isn't a frequency specific to every user, alternatively, each channel uses the entire available spectrum. Individual conversations are encoded with a pseudo-random digital series. A unique code is acquired by using all mobile community customers and is allowed continuous community get entry to instead of intermittent or timed get entry to.

Q4. What Is Soft Handover/handoff?

Cellular device tracks mobile stations a good way to keep their communication hyperlinks. The cellular station is going to neighbor cell and communication hyperlink switches from cutting-edge mobile to the neighbor cellular that is called as soft handover.

Soft handoff is a characteristic wherein a mobile telephone is simultaneously connected to two or more cellular telephones at some point of a unmarried name.

It is the overlapping of repeater insurance ones, which enables every cell cellphone set is usually nicely inside the range of a particular repeater.

More than one repeater can send and receive indicators to trmit indicators to and from mobiles.

All repeaters are used with the same frequency channel for each cell cellphone set.

Practically no useless zones and as end result, the connections seldom interrupted or dropped.

Q5. Explain Processing Gain In Cdma?

P (gain) = 10log (W/R)

W is Spread Rate

R is Data Rate

For CDMA P (benefit) = 10log (1228800/9600)

= 21dB

Actual processing benefit = P (gain) - SNR

= 21 – 7 = 14dB

CDMA makes use of variable price coder

The Voice Activity Factor of 0.Four is considered = -4dB.

CDMA has a hundred% frequency reuse. Use of same frequency in surrounding cells causes a few extra interference.

In CDMA, frequency reuse performance is 0.Sixty seven (70% eff.) = -1.73dB

Q6. What Is Fdma?

Frequency Division Multiple Access (FDMA) is one of the most not unusual analogue more than one get admission to strategies. The frequency band is split into channels of identical bandwidth in order that every communication is carried on a different frequency. Guard bands are used between the adjacent signal spectra to reduce crosstalk between the channels.

Q7. What Is Reverse Link Power Control?

The strength of closed loop manipulate is used to compensate for the rapid Rayleigh discoloration. This time, the mobile trmitted power is controlled through the base station. For this motive, the bottom station continuously video display units the opposite hyperlink sign fine. If the high-quality of the connection is bad then the bottom station increases the strength. Similarly, if the excellent of the link may be very excessive then the cell base station controller reduces the power. This is referred to as as reverse hyperlink energy manipulate.

Q8. What Is Permuted Esn?

CDMA is a spread spectrum technique wherein more than one customers to access the device on the identical example in a cell, and of course on the equal frequency. Therefore, discriminate the users on the opposite hyperlink (i.E. Statistics from MS to the base station). It spreads information the use of codes which are precise to the cellular station in all the CDMA cellular structures. This code has an detail this is the ESN. But it doesn’t use the ESN in the equal layout; as an alternative, it uses an ESN swapped.

Q9. What Is Rake Receiver?

CDMA machine uses a signal rapid chip charge for spreading spectrum and it has a high time decision. For this reason, CDMA is able to recognize by means of decomposing each of the direction to reach with the time distinction. From this, it receives a exceptional paths of sign every one one after the other, through summing later, it can save you signal degradation. This is known as as the RAKE receiver.

Q10. Explain Sync Channel?

Synchronization channel includes a single repeating message and trmits the synchronization configuration statistics and the machine of the mobile station in the CDMA system.

Q11. Explain Access Channels?

Access channels are used by mobile stations to set up communications with the base station or to wer Paging Channel messages. The get entry to channel is used for brief signaling message exchanges which includes name-ups, responses to pages, and registrations.

Q12. What Is Tdma?

Time Division Multiple Access (TDMA) is a complicated generation, because it calls for a completely accurate synchronization between the trmitter and the receiver. The TDMA is utilized in digital mobile radio structures. The man or woman cell stations are assigned cyclically a frequency for different use in the course of a time c programming language.

Q13. What Is Power Control?

Power manipulate is the wise selection of trmit electricity in a communication device for achieving satisfactory performance inside the machine. The performance depends on context and there are chances to include optimizing metrics like link data rate, community capability, geographic coverage, and variety. A better trmit energy trlates right into a better signal electricity at the receiver.

Q14. What Are The Advantages Of Fdma?

In FDMA when the channel isn't always used, it's miles the channel bandwidth at the same time as relaxation definitely is fairly slim (30 KHz), referred to as System narrowband. Little or no equalization is wanted. For broadcasting, time symbols are suitable analogue links. Framing for FDMA or synchronization bits aren't wanted for the tight filter streaming. It is required to minimize the blended interference of FDD.

Q15. What Is Hard Handover?

In FDMA or TDMA cell machine, new verbal exchange establishes after breaking contemporary verbal exchange at the moment doing handoff. Communication between MS and BS breaks in the intervening time switching frequency or timeslot that is called difficult handover.

Q16. Explain Pilot Channel?

Pilot channel is a reference channel using the cellular station to gather the time and as a segment reference for coherent demodulation. It is continuously trmitted by using each base station on each lively CDMA frequency. Each cell station tracks this signal continuously.

Q17. What Are The Disadvantages Of Fdma?

It does now not range drastically from analog systems; improving the potential relies upon on the signal-to-interference reduction, or a sign-to-noise ratio (SNR).

The most waft price in line with channel is fixed and small.

Guard bands lead to a waste of capacity.

Hardware implies narrowband filters, which can not be realized in VLSI and consequently will increase the fee.

Q18. Explain Cdma Development Group (cdg)?

CDG is made from carrier carriers, infrastructure producers, tool companies, test device companies, software builders, and content providers. Its contributors together outline the technical necessities for the development of complementary structures CDMA2000 and 4G and interoperability with other rising wireless technologies to increase the provision of wireless products and services to clients and companies worldwide.

Q19. What Is Walsh Code?

Walsh Codes are maximum typically used in CDMA programs orthogonal codes. These codes correspond to strains of a special rectangular matrix referred to as the Hadamard matrix. For a hard and fast of Walsh codes of duration N, it consists of n strains to shape a square matrix of n × n Walsh code. The IS-95 system makes use of 64 Walsh function matrix 6@The first line of this matrix consists of a string of all zeros with each of the following traces containing one of a kind combos of bit 0 and @Each line is orthogonal and equal representation for binary bits. When applied with the CDMA system, each cellular user uses one of the sixty four sequences of rows within the matrix as a spreading code, offering zero go-correlation amongst all the different customers.

Q20. What Is Forward Channels In Cdma?

The ahead channel CDMA is the path of the conversation or cellular-to-mobile downlink route.

Q21. What Is Pn Sequence In Cdma?

The DS-CDMA system makes use of two types of spreading sequences − PN sequences and orthogonal codes. The PN collection is generated via the pseudo-random noise generator that is certainly a binary linear feedback shift register, such as XOR gates and a shift register. This PN generator has the capacity to create a chain equal for both the trmitter and the receiver, and whilst maintaining the desirable properties of the noise randomness bit collection.

Q22. Describe The Centralized Methods In Cdma?

The band used in CDMA is 824 MHz to 894 MHz (50 MHz + 20 MHz separation);

Frequency channel is split into code channels; and

1.25 MHz of FDMA channel is split into sixty four code channels.

Q23. How Many Channels Are There In Cdma Reverse Channels?

Reverse channel is consists of  channels which includes:−

Access Channels and

Reverse Traffic Channels.

Q24. What Are The Advantages Of Cdma?

CDMA has a gentle ability. The greater the quantity of codes, the more range of customers. However, many codes are used S/I drops and the BER (Bit Error Rate) will growth for all customers.

CDMA calls for a decent energy manipulate because it suffers from close to-a ways impact. In other words, a consumer near the base station trmits the same electricity as a user later will drown the latter sign. All signals must have greater or much less same power on the receiver.

Rake receivers may be used to improve sign reception. Delayed variations of time (a chip or later) of the sign (multipath alerts) can be accumulated and used to make decisions on the bit level.

Flexible trfer may be used. Mobile base stations can switch with out changing operator. Two base stations receive cellular signal and the cell gets from  base stations.

Trmission Burst - reduces interference.

Q25. What Are The Disadvantages Of Code Division Multiple Access?

The code length have to be cautiously decided on. A large code period can set off delay or can also purpose interference.

Time synchronization is required.

Gradual trfer increases using radio resources and might reduce capacity.

As the sum of the energy obtained and trmitted from a base station wishes consistent tight energy manage. This can bring about numerous handovers.

Q26. What Are The Advantages Of Spread Spectrum?

Since the signal is unfold over a wide frequency band, the strength spectral density turns into very low, so different communications structures do no longer suffer from this kind of verbal exchange. However, the Gaussian noise increases.

Multipath can be agreed with, as a large variety of codes can be generated, allowing a large range of customers.

The most variety of users have now not limited spectrum or useful resource, as different get entry to structures including FDMA, right here they have best constrained interference.

Security − without knowing the spreading code, it's miles almost impossible to recover the trmitted records.

Descending rejection − as large bandwidth is used the machine, it's miles much less at risk of deformation.

Q27. What Is Frequency Hopping?

Frequency hopping is a diffusion spectrum in which the propagation takes vicinity via hopping in frequency over a extensive band. The specific order in which the ruin occurs is decided through a hopping table generated by means of the use of a pseudo-random code series.

Q28. Explain The Cdma Capacity?

The factors deciding ability are:−

Processing Gain

Signal to Noise Ratio

Voice Activity Factor and

Frequency Reuse Efficiency.

Capacity in CDMA is gentle, CDMA has all customers on every frequency and customers are separated by way of code. This me, CDMA operates inside the presence of noise and interference. In addition, neighboring cells use the same frequencies, which me no re-use. So, CDMA capability calculations need to be very simple. No code channels in a cell, elevated by using no cells. But it is not that easy. Although no longer available code channels are 64, it can no longer be feasible to use a unmarried time, for the reason that CDMA frequency is the same. Flexible functionality me that all the code channels may be pursued at a time, however at the price of excellent.

Q29. What Is The Function Of Imsi?

The cellular stations are recognized by using the identification of the worldwide cellular station (IMSI). The IMSI includes up to ten heaps - 15 numerical characters (zero- nine). The first 3 digits of the IMSI is the u . S . A . Code of the cellular (MCC), the closing digits are the National NMSI mobile station identification.

The NMSI includes the cellular community code (MNC) and the mobile station identity wide variety (SIDS). An IMSI is 15 digits in length is called a category zero IMSI (NMSI is the 12 digits in length). IMSI, that's much less than 15 digits in period, is a category called IMSI (NMSI the length is much less than 12 counts).

For CDMA operation, the same IMSI can be registered in more than one cell stations. Individual systems may additionally or won't allow these talents. The control of those features is a function of the bottom station and the device operator.

Q30. Explain Paging Channel?

Paging Channels’ foremost objective is to send out pages, this is, notifications of incoming calls, to the cell stations. The base station makes use of those pages to trmit gadget overhead data and mobile station particular messages.

Q31. Explain The Frequency Allocation Concept?

In FDMA or TDMA, radio useful resource is allocated no longer to intervene amongst neighbor cells:−

Neighbor cells cannot use the equal (same) frequency band (or timeslot).

The left determine shows the simple cell allocation with seven bands of frequency.

In actual scenario, because of complicated radio propagation and irregular cellular allocation, it isn't always smooth to allocate frequency (or timeslot) accurately.

CDMA machine is against this, on account that all customers proportion the equal frequency, the arrangement of the frequency isn't always an difficulty. This is in designing the machine, so that you can be a completely massive gain.

Q32. What Are The Advantages Of Tdma?

It lets in bendy rates (i.E., numerous slots may be assigned to a consumer, for example, each time interval trlates 32Kbps, a user is assigned two sixty four Kbps slots in line with body).

It can withstand gusty or variable bit price visitors. Number of slots allotted to a user can be changed body by way of body (as an example,  slots of the frame 1, frame 2 of the three slots, one slot inside the body three, body 0 of the notches 4, and many others.)

No guard bands required for the wideband device.

No narrowband filters required for the wideband machine.

Q33. What Is Forward Link Power Control?

Similar to opposite link strength manage, forward hyperlink strength manipulate is likewise necessary to keep the ahead hyperlink excellent to a unique stage. This time, the mobile monitors the forward link best and shows to the base station to turn on or off, this strength manage has no effect on the close to-a long way hassle due to the fact all the alerts are blurred together the equal stage of power when they get to the mobile. In short, there may be no close to-some distance trouble in the ahead link.

Q34. What Is Tdd And What Are The Frequencies It Uses?

TDD is Time Division Duplex. A duplex method through which the Uplink and the Downlink trmissions are carried over the same frequency using synchronized time intervals. The provider makes use of a five MHz band, although there is a low chip charge solution under observe with the aid of the 3GPP (1.28 Mcps). The to be had frequency bands for TDD will be 1900-1920 MHz and 2010-2025 MHz.

Q35. Explain Reverse Traffic Channels?

Reverse visitors channels are used by man or woman customers in their actual calls to trmit visitors from a single cellular station to 1 or more base stations.

Q36. What Are The Interferences In Cdma?

There are 4 predominant interferences in CDMA as given beneath:−

Noise assets

Signal processing

Frame mistakes price and

Power in keeping with Walsh code.

Q37. What Are The Disadvantages Of Tdma?

The excessive records costs of broadband systems require complicated equalization.

Due to the burst mode, a huge variety of additional bits for synchronization and supervision are needed.

Call time is needed in each slot to house time to inaccuracies because of clock instability.

Electronics running at excessive bit charges boom electricity intake.

Complex signal processing is needed to synchronize inside brief slot.

Q38. What Is Fdd And What Are The Frequencies It Uses?

Frequency Division Duplex is one of the more than one get right of entry to strategies in wi-fi era; it uses following frequency bands −

Uplink: 1920 MHz - 1980 MHz and

Downlink: 2110 MHz - 2170 MHz.

Q39. What Are The Cdma Identities?

Network Identities:−

SID (System Identity)

NID (Network Identity)

Mobile Station Identities:−

ESN (Electronic Serial Number)

Permuted ESN

IMSI (International Mobile Station Identity)

IMSI_S

IMSI_11_12

Station Class Mark

Q40. What Is Spread Spectrum Technique?

Spread spectrum is a shape of wi-fi communications in which the frequency of the trmitted signal is deliberately numerous. This effects in a miles greater bandwidth than the signal would have, if its frequency were now not varied. In other phrases, the trmitted signal bandwidth is greater than the minimal facts bandwidth needed to efficiently trmit the sign. Some characteristic aside from the statistics itself is being hired to determine the consequent trmitted bandwidth.

Q41. How Many Types Of Spread Spectrum Techniques Are Used In Cdma?

Following two varieties of spread spectrum strategies are used:−

Direct Sequence and

Frequency Hopping.

Q42. What Is Multi-direction Fading?

In wi-fi communications, fading is the deviation of the sign attenuation affecting a positive propagation media. Discoloration can also vary with time, the geographical position or frequency of the radio, that is often modeled as a random manner. A fading channel is a conversation channel experiencing fading. In wireless systems, fading may be due to multipath,and multi-route fading.

Q43. How Many Channels Are There In Cdma Forward Channels?

Forward channel includes four channels which incorporates:−

Pilot Channel

Sync Channel

Paging Channel and

Forward Traffic Channels.

Q44. What Is Cdma? Explain.

Code Division Multiple Access machine is very extraordinary from time and frequency multiplexing. In this system, a consumer has get right of entry to to the whole bandwidth for the complete length. The fundamental principle is that exceptional CDMA codes are used to distinguish among unique customers. Forms typically used are direct sequence spread spectrum modulation (DS-CDMA), frequency hopping or combined CDMA detection (JD CDMA). Here, a sign is generated which extends over a huge bandwidth. A code known as spreading code is used to carry out this action. Using a collection of codes, which might be orthogonal to each different, it is possible to pick out a sign with a given code in the presence of many different signals with one of a kind orthogonal codes.

Q45. What Is Reverse Channels In Cdma?

The Reverse CDMA channel is the cell-to-mobile direction of the communication or uplink route.