Interview Questions.

Question 1. What Is Cdma?

Answer :

CDMA stands for Code Division Multiple Access. It is a wi-fi generation used in transmission of alerts from locations with excessive Security and noise discount. The precept of Spread Spectrum is used to work with CDMA. Spread sign is beneath the noise degree and noise has no effect on the sign. CDMA is not a frequency specific to every person, instead, every channel uses the total to be had spectrum. Individual conversations are encoded with a pseudo-random virtual series. A particular code is acquired by way of all cellular community customers and is allowed non-stop community get admission to in place of intermittent or timed get admission to.

Question 2. Explain Cdma Development Group (cdg)?

Answer :

CDG is made out of carrier vendors, infrastructure manufacturers, tool companies, check system providers, utility developers, and content providers. Its contributors jointly outline the technical requirements for the development of complementary systems CDMA2000 and 4G and interoperability with different emerging wireless technology to boom the availability of wireless services and products to consumers and corporations worldwide.

GSM Interview Questions
Question three. What Is Forward Channels In Cdma?

Answer :

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

Question four. How Many Channels Are There In Cdma Forward Channels?

Answer :

Forward channel includes 4 channels which includes:−

Pilot Channel
Sync Channel
Paging Channel and
Forward Traffic Channels.
GSM Tutorial
Question 5. Explain Pilot Channel?

Answer :

Pilot channel is a reference channel the usage of the mobile station to collect the time and as a segment reference for coherent demodulation. It is constantly transmitted by each base station on every active CDMA frequency. Each cellular station tracks this sign continuously.

UMTS Interview Questions
Question 6. Explain Sync Channel?

Answer :

Synchronization channel contains a single repeating message and transmits the synchronization configuration statistics and the system of the cellular station within the CDMA gadget.

Question 7. Explain Paging Channel?

Answer :

Paging Channels’ fundamental goal is to ship out pages, that is, notifications of incoming calls, to the mobile stations. The base station uses those pages to transmit system overhead data and cell station unique messages.

UMTS Tutorial Wideband Code Division Multiple Access (WCDMA) Interview Questions
Question 8. Explain Forward Traffic Channel?

Answer :

Forward Traffic Channels are code channels and used to assign calls, normally voice and signaling traffic to the character users.

Question nine. What Is Reverse Channels In Cdma?

Answer :

The Reverse CDMA channel is the mobile-to-mobile course of the conversation or uplink course.

3G Interview Questions
Question 10. How Many Channels Are There In Cdma Reverse Channels?

Answer :

Reverse channel is includes two channels which includes:−

Access Channels and
Reverse Traffic Channels.
General Packet Radio Service (GPRS) Tutorial
Question eleven. Explain Access Channels?

Answer :

Access channels are used by cellular stations to establish communications with the bottom station or to answer Paging Channel messages. The get right of entry to channel is used for short signaling message exchanges consisting of call-ups, responses to pages, and registrations.

General Packet Radio Service (GPRS) Interview Questions
Question 12. Explain Reverse Traffic Channels?

Answer :

Reverse visitors channels are used by individual users of their actual calls to transmit visitors from a unmarried mobile station to at least one or extra base stations.

GSM Interview Questions
Question thirteen. Explain The Cdma Capacity?

Answer :

The factors finding out ability are:−

Processing Gain
Signal to Noise Ratio
Voice Activity Factor and
Frequency Reuse Efficiency.
Capacity in CDMA is smooth, CDMA has all customers on each frequency and customers are separated by using code. This means, CDMA operates inside the presence of noise and interference. In addition, neighboring cells use the equal frequencies, which means no re-use. So, CDMA potential calculations need to be very simple. No code channels in a cellular, improved by using no cells. But it isn't always that simple. Although now not to be had code channels are sixty four, it is able to now not be feasible to apply a single time, because the CDMA frequency is the equal. Flexible functionality way that every one the code channels can be pursued at a time, however at the price of fine.

CDMA Tutorial
Question 14. Describe The Centralized Methods In Cdma?

Answer :

The band utilized 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.

Question 15. Explain Processing Gain In Cdma?

Answer :

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

W is Spread Rate

R is Data Rate

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

= 21dB

Actual processing gain = P (advantage) - SNR

= 21 – 7 = 14dB

CDMA uses variable charge coder

The Voice Activity Factor of 0.4 is taken into consideration = -4dB.

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

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

Adobe Edge Interview Questions
Question sixteen. What Are The Cdma Identities?

Answer :

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
Question 17. What Is Permuted Esn?

Answer :

CDMA is a spread spectrum technique wherein more than one customers to get right of entry to the device at the identical example in a cellular, and of course at the identical frequency. Therefore, discriminate the users at the reverse hyperlink (i.E. Statistics from MS to the bottom station). It spreads statistics using codes which are precise to the cellular station in all the CDMA mobile structures. This code has an detail that is the ESN. But it doesn’t use the ESN in the identical format; rather, it uses an ESN swapped.

Embedded firmware software Interview Questions
Question 18. What Is The Function Of Imsi?

Answer :

The mobile stations are identified with the aid of the identity of the worldwide cellular station (IMSI). The IMSI consists of up to 10 heaps - 15 numerical characters (zero- nine). The first three digits of the IMSI is the u . S . Code of the cell (MCC), the ultimate digits are the National NMSI cell station identity.
The NMSI includes the cell network code (MNC) and the cellular station identification range (SIDS). An IMSI is 15 digits in length is referred to as a class zero IMSI (NMSI is the 12 digits in length). IMSI, that is less than 15 digits in length, is a class known as IMSI (NMSI the length is much less than 12 counts).
For CDMA operation, the identical IMSI may be registered in more than one cellular stations. Individual structures may additionally or won't allow these skills. The management of those features is a characteristic of the bottom station and the system operator.
UMTS Interview Questions
Question 19. What Is Fdd And What Are The Frequencies It Uses?

Answer :

Frequency Division Duplex is one of the a couple of access techniques in wireless technology; it uses following frequency bands −

Uplink: 1920 MHz - 1980 MHz and

Downlink: 2110 MHz - 2170 MHz.

Question 20. What Is Tdd And What Are The Frequencies It Uses?

Answer :

TDD is Time Division Duplex. A duplex method by using which the Uplink and the Downlink transmissions are carried over the identical frequency the usage of synchronized time intervals. The provider makes use of a five MHz band, despite the fact that there may be a low chip fee solution beneath have a look at with the aid of the 3GPP (1.28 Mcps). The available frequency bands for TDD can be 1900-1920 MHz and 2010-2025 MHz.

Firmware Development Interview Questions
Question 21. What Is Fdma?

Answer :

Frequency Division Multiple Access (FDMA) is one of the most common analogue multiple get admission to methods. The frequency band is divided into channels of identical bandwidth in order that every conversation is carried on a extraordinary frequency. Guard bands are used between the adjacent sign spectra to reduce crosstalk among the channels.

Question 22. What Are The Advantages Of Fdma?

Answer :

In FDMA whilst the channel isn't always used, it's miles the channel bandwidth whilst relaxation simply is highly slender (30 KHz), called System narrowband. Little or no equalization is wanted. For broadcasting, time symbols are suitable analogue links. Framing for FDMA or synchronization bits aren't needed for the tight clear out streaming. It is required to decrease the combined interference of FDD.

Question 23. What Are The Disadvantages Of Fdma?

Answer :

It does now not fluctuate significantly from analog structures; improving the ability depends at the sign-to-interference reduction, or a signal-to-noise ratio (SNR).
The maximum float rate consistent with channel is fixed and small.
Guard bands result in a waste of ability.
Hardware implies narrowband filters, which cannot be realized in VLSI and consequently increases the cost.
Question 24. What Is Tdma?

Answer :

Time Division Multiple Access (TDMA) is a complicated technology, because it calls for a very accurate synchronization among the transmitter and the receiver. The TDMA is used in digital mobile radio systems. The man or woman cell stations are assigned cyclically a frequency for distinctive use at some point of a time c programming language.

Wideband Code Division Multiple Access (WCDMA) Interview Questions
Question 25. What Are The Advantages Of Tdma?

Answer :

It allows bendy prices (i.E., numerous slots can be assigned to a consumer, as an example, every time c language interprets 32Kbps, a consumer is assigned two 64 Kbps slots in keeping with frame).
It can face up to gusty or variable bit fee visitors. Number of slots allocated to a user may be modified body by body (for instance, two slots of the body 1, body 2 of the 3 slots, one slot within the body three, frame zero of the notches four, and many others.)
No shield bands required for the wideband device.
No narrowband filters required for the wideband gadget.
Question 26. What Are The Disadvantages Of Tdma?

Answer :

The high records prices of broadband structures require complex equalization.
Due to the burst mode, a huge number of extra bits for synchronization and supervision are wanted.
Call time is needed in each slot to deal with time to inaccuracies due to clock instability.
Electronics operating at excessive bit charges growth power intake.
Complex signal processing is needed to synchronize within short slot.
Question 27. What Is Cdma? Explain.

Answer :

Code Division Multiple Access system may be very exceptional from time and frequency multiplexing. In this machine, a user has get entry to to the whole bandwidth for the whole duration. The fundamental precept is that exclusive CDMA codes are used to differentiate between extraordinary customers. Forms usually used are direct collection spread spectrum modulation (DS-CDMA), frequency hopping or combined CDMA detection (JD CDMA). Here, a sign is generated which extends over a extensive bandwidth. A code known as spreading code is used to perform this action. Using a set of codes, that are orthogonal to each other, it is feasible to choose a sign with a given code within the presence of many different alerts with distinct orthogonal codes.

3G Interview Questions
Question 28. What Are The Advantages Of Cdma?

Answer :

CDMA has a tender capacity. The more the wide variety of codes, the greater number of customers. However, many codes are used S/I drops and the BER (Bit Error Rate) will increase for all users.
CDMA requires a good strength control because it suffers from close to-a ways effect. In other phrases, a user close to the base station transmits the same electricity as a person later will drown the latter signal. All indicators have to have greater or much less identical strength on the receiver.
Rake receivers can be used to enhance sign reception. Delayed versions of time (a chip or later) of the signal (multipath indicators) may be gathered and used to make choices at the bit stage.
Flexible transfer can be used. Mobile base stations can switch with out changing operator. Two base stations receive cellular signal and the mobile gets from  base stations.
Transmission Burst - reduces interference.
Question 29. What Are The Disadvantages Of Code Division Multiple Access?

Answer :

The code length should be carefully decided on. A massive code length can result in postpone or may additionally purpose interference.
Time synchronization is needed.
Gradual switch will increase the use of radio resources and can reduce capacity.
As the sum of the strength received and transmitted from a base station wishes consistent tight energy manage. This can bring about several handovers.
Question 30. What Is Spread Spectrum Technique?

Answer :

Spread spectrum is a form of wireless communications wherein the frequency of the transmitted signal is intentionally numerous. This effects in a far extra bandwidth than the signal might have, if its frequency were now not various. In other words, the transmitted sign bandwidth is more than the minimum facts bandwidth had to efficiently transmit the signal. Some function apart from the data itself is being employed to determine the ensuing transmitted bandwidth.

Question 31. How Many Types Of Spread Spectrum Techniques Are Used In Cdma?

Answer :

Following two kinds of spread spectrum techniques are used:−

Direct Sequence and
Frequency Hopping.
Question 32. What Is Frequency Hopping?

Answer :

Frequency hopping is a ramification spectrum in which the propagation takes area by means of hopping in frequency over a extensive band. The particular order wherein the spoil occurs is decided by way of a hopping desk generated by means of using a pseudo-random code sequence.

Question 33. What Are The Advantages Of Spread Spectrum?

Answer :

Since the signal is unfold over a wide frequency band, the power spectral density will become very low, so other communications systems do not be afflicted by this form of conversation. However, the Gaussian noise will increase.
Multipath can be agreed with, as a massive number of codes may be generated, permitting a massive range of customers.
The maximum range of users have no longer limited spectrum or resource, as different get right of entry to systems such as FDMA, right here they have got simplest constrained interference.
Security − with out understanding the spreading code, it's far almost impossible to get better the transmitted records.
Descending rejection − as huge bandwidth is used the machine, it's far less at risk of deformation.
General Packet Radio Service (GPRS) Interview Questions
Question 34. What Is Pn Sequence In Cdma?

Answer :

The DS-CDMA gadget uses  forms of spreading sequences − PN sequences and orthogonal codes. The PN sequence is generated by way of the pseudo-random noise generator that is sincerely a binary linear feedback shift check in, such as XOR gates and a shift check in. This PN generator has the capacity to create a sequence identical for both the transmitter and the receiver, and while keeping the appropriate properties of the noise randomness bit collection.

Question 35. What Is Multi-route Fading?

Answer :

In wireless communications, fading is the deviation of the sign attenuation affecting a certain propagation media. Discoloration may additionally vary with time, the geographical function or frequency of the radio, that is regularly modeled as a random technique. A fading channel is a conversation channel experiencing fading. In wireless systems, fading can be because of multipath,and multi-route fading.

Question 36. What Is Rake Receiver?

Answer :

CDMA gadget makes use of a signal rapid chip price for spreading spectrum and it has a excessive time decision. For this purpose, CDMA is able to recognize via decomposing each of the direction to reach with the time distinction. From this, it gets a extraordinary paths of signal each one one at a time, with the aid of summing later, it could prevent signal degradation. This is known as because the RAKE receiver.

Adobe Edge Interview Questions
Question 37. What Is Walsh Code?

Answer :

Walsh Codes are most normally utilized in CDMA programs orthogonal codes. These codes correspond to strains of a special rectangular matrix known as the Hadamard matrix. For a fixed of Walsh codes of duration N, it includes n traces to shape a square matrix of n × n Walsh code. The IS-ninety five device makes use of 64 Walsh characteristic matrix sixty four. The first line of this matrix contains a string of all zeros with every of the following lines containing one of a kind mixtures of bit 0 and 1. Each line is orthogonal and identical illustration for binary bits. When implemented with the CDMA device, each cellular person makes use of one of the 64 sequences of rows within the matrix as a spreading code, imparting zero move-correlation among all of the other customers.

Question 38. What Is Soft Handover/handoff?

Answer :

Cellular device tracks cell stations so that you can maintain their communication hyperlinks. The cellular station is going to neighbor cell and communication hyperlink switches from modern mobile to the neighbor cellular that's referred to as as soft handover.

Soft handoff is a characteristic in which a mobile cellphone is concurrently linked to two or extra cell telephones throughout a single call.
It is the overlapping of repeater insurance ones, which allows each mobile cellphone set is continually nicely in the variety of a selected repeater.
More than one repeater can ship and acquire indicators to transmit indicators to and from mobiles.
All repeaters are used with the equal frequency channel for every cell phone set.
Practically no lifeless zones and as end result, the connections seldom interrupted or dropped.
Question 39. What Is Hard Handover?

Answer :

In FDMA or TDMA cell machine, new communication establishes after breaking contemporary verbal exchange for the time being doing handoff. Communication among MS and BS breaks for the time being switching frequency or timeslot that is known as difficult handover.

Question forty. What Is Power Control?

Answer :

Power control is the wise selection of transmit energy in a communication device for achieving nice performance inside the machine. The performance depends on context and there are chances to encompass optimizing metrics like hyperlink records charge, community capability, geographic coverage, and variety. A higher transmit power interprets right into a higher signal energy on the receiver.

Embedded firmware software Interview Questions
Question forty one. What Is Reverse Link Power Control?

Answer :

The strength of closed loop control is used to atone for the fast Rayleigh discoloration. This time, the cell transmitted power is managed by way of the bottom station. For this reason, the base station constantly video display units the reverse hyperlink sign pleasant. If the first-rate of the relationship is negative then the base station will increase the power. Similarly, if the quality of the hyperlink may be very excessive then the mobile base station controller reduces the strength. This is called as reverse hyperlink power control.

Question forty two. What Is Forward Link Power Control?

Answer :

Similar to opposite hyperlink energy manage, ahead link energy control is also vital to preserve the ahead hyperlink nice to a specific level. This time, the cellular video display units the ahead hyperlink pleasant and shows to the bottom station to show on or off, this energy manipulate has no impact at the near-a ways trouble because all the alerts are blurred collectively the identical stage of strength after they get to the mobile. In brief, there is no close to-a ways hassle inside the forward link.

Firmware Development Interview Questions
Question forty three. Explain The Effects Of Power Control?

Answer :

Power control is capable of compensating the fading fluctuation.
Received strength from all MS are controlled to be same.
Near-Far problem is mitigated via the power control.
Question forty four. Explain The Frequency Allocation Concept?

Answer :

In FDMA or TDMA, radio aid is allocated now not to intervene among neighbor cells:−

Neighbor cells can't use the same (same) frequency band (or timeslot).
The left parent suggests the easy cellular allocation with seven bands of frequency.
In real scenario, due to complicated radio propagation and irregular cell allocation, it isn't easy to allocate frequency (or timeslot) appropriately.
CDMA system is against this, seeing that all users percentage the identical frequency, the arrangement of the frequency is not an problem. This is in designing the machine, which will be a very big advantage.

Question 45. What Are The Interferences In Cdma?

Answer :

There are four principal interferences in CDMA as given underneath:−

Noise resources
Signal processing
Frame errors rate and
Power in line with Walsh code.
Question forty six. Explain The Cmda Interference “body Error Rate.”?

Answer :

The quantity of transmission mistakes, measured in phrases of a frame mistakes fee (FER). It increases with the variety of calls. To triumph over this hassle, the minicell and cell website online can growth the strength until either the cellular or the minicell site can power up greater further to reduce FER to an acceptable amount. This occasion presents a gentle restrict calls from a specific minicell.