CDMA Interview Questions and Answers
Q1. What is CDMA?
Ans: CDMA stands for Code Division Multiple Access. It is a wireless generation used in transmission of alerts from locations with high Security and noise discount. The principle of Spread Spectrum is used to paintings with CDMA. Spread sign is below the noise stage and noise has no impact at the signal. CDMA isn't a frequency precise to every person, instead, each channel uses the whole available spectrum. Individual conversations are encoded with a pseudo-random virtual series. A precise code is received by using all mobile community customers and is allowed continuous network get right of entry to as opposed to intermittent or timed get admission to.
Q2. How Many Channels Are There In Cdma Forward Channels?
Ans: Forward channel includes four channels which includes:
Pilot Channel
Sync Channel
Paging Channel and
Forward Traffic Channels.
Q3. What is FDMA? Explain?
Ans: Frequency Division Multiple Access (FDMA) is one of the maximum commonplace analogue multiple get admission to methods. The frequency band is divided into channels of equal bandwidth so that each conversation is carried on a unique frequency. Guard bands are used between the adjoining signal spectra to minimize crosstalk between the channels.
Advantages:
In FDMA whilst the channel isn't used, it's far the channel bandwidth even as rest without a doubt is relatively narrow (30 KHz), called System narrowband. Little or no equalization is needed. For broadcasting, time symbols are suitable analogue hyperlinks. Framing for FDMA or synchronization bits are not wanted for the tight filter streaming. It is needed to reduce the blended interference of FDD.
Disadvantages:
It does not range appreciably from analog structures; enhancing the capacity relies upon at the sign-to-interference discount, or a sign-to-noise ratio (SNR).
The maximum flow rate in line with channel is constant and small.
Guard bands result in a waste of ability.
Hardware implies narrowband filters, which can't be found out in VLSI and therefore increases the fee.
Q4. Differentiate among CDMA and FDMA?
Ans:
CDMA:
Same frequency is used by every consumer and simultaneous transmission happens
Every narrowband sign is elevated through wideband spreading sign, normally referred to as codeword
Every user has a separate pseudo-codeword, i.E., orthogonal to others
Only the favored codeword is detected via the receivers and others seem as noise
It is mandatory for the receivers to recognize about the transmitter’s codeword
FDMA:
When the channel is not in use, it sits surely idle
Bandwidth of Channel is relatively narrow (30 KHz), referred to as narrowband system
Little or no equalization is needed for spreading image time
Analog links are suitable for FDMA
Framing or synchronization bits aren't wished for continuous transmission
Tight filtering is wanted to limit interference
Combined with FDD for duplexing
Q5. Explain the subsequent two kinds of hand off in CDMA system: a.) Soft handoff b.) Softer handoff.
Ans: Soft handoff
Soft handoff is a characteristic in which a mobile smartphone is concurrently connected to two or greater cell phones throughout a unmarried call
It is he overlapping of repeater insurance ones, which permits every cellular smartphone set is always nicely in the range of a specific repeater.
More than one repeater can send and receive indicators to transmit alerts to and from mobiles.
All repeaters are used with the equal frequency channel for every cell smartphone set.
Practically no dead zones and as result, the connections seldom interrupted or dropped.
Softer handoff
Softer handover is a good sized gentle handover wherein the added and eliminated hyperlinks belong to the equal node
Macro range with most ratio combining could be achieved inside the same node
The motion of handoff, while a user may be served in some other cellular greater effectively (much less strength emission, much less interference), is the most apparent cause for higher performance.
Q6. What is Forward Channels in CDMA?
Ans: The forward channel CDMA is the course of the conversation or cellular-to-cellular downlink route.Forward channel consists of four channels which includes:
Pilot Channel: Pilot channel is a reference channel the use of the cellular station to accumulate the time and as a section reference for coherent demodulation. It is continuously transmitted through each base station on each lively CDMA frequency. Each cell station tracks this sign constantly.
Sync Channel: Synchronization channel consists of a unmarried repeating message and transmits the synchronization configuration statistics and the machine of the cell station inside the CDMA gadget.
Paging Channel: Paging Channels’ fundamental objective is to send out pages, that is, notifications of incoming calls, to the cell stations. The base station uses these pages to transmit device overhead facts and cell station particular messages.
Forward Traffic Channels: Forward Traffic Channels are code channels and used to assign calls, usually voice and signaling visitors to the character customers.
Q7. What is Scrambling Code?
Ans: Scrambling-code identification
During the 0.33 and remaining step of the cellular seek procedure, the UE determines the exact primary scrambling code utilized by the found cellular. The primary scrambling code is normally identified via image-by using-symbol correlation over the CPICH with all codes within the code institution identified inside the 2d step. After the number one scrambling code has been diagnosed, the Primary CCPCH can be detected and the system- and mobile particular BCH facts may be study. If the UE has obtained statistics about which scrambling codes to look for, steps 2 and three above may be simplified.
Q8. Do you realize What is the primary difference among 1x RTT and 1X EVDO?
For 1xRTT has four ahead and two reverse channels, where as in EVDO channel structure is one-of-a-kind.
1x RTT supports upto 153.2 kbps of statistics, wherein as EVDO supports upto 3.1Mbps.
In 1x RTT throughout size pilot electricity ratio , Traffic strength ratio are also considered; where as in EVDO FTAP , RTAP with Slots are taken into consideration
Q9. Which is the weaker Link: FWD or Reverse in CDMA?
Ans: Reverse hyperlink is weak in CDMA because of use of PN Long codes as compared to Walsh codes inside the ahead link. Since, walsh codes are perfectly orthogonal in nature there is much less interference within the ahead hyperlink. PN long codes however are non-orthogonal in nature. However, we cant use walsh codes for the opposite link as it is able to appear from the above because the quality viable answer. This is because walsh codes are very small in quantity (sixty four/128/512 max), and as a result are not enough for identity of big wide variety of customers in the reverse hyperlink for which the PN lengthy codes are hired.
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Q10. Explain the underlying purposeful concept of gsm and cdma?
Ans: GSM refers to Global System for Mobile communications even as CDMA refers to Code Division Multiple Access. Both are diffrent technologies in Telcommunications and
behave diffrently in terms of giving voice and records offerings to the consumer.Though GSM is globally used teschnology - CDMA era has greater advantages in terms of call clarity, quicker facts speeds etc at the same time as GSM covers maximum of the network areas and has got type of handsets to select from, humans choose this era. Other than these 2 technologies we've got other technologies like TDMA, WCDMA and so on.
Q11. Describe the Centralized Methods in CDMA?
Ans:
The band used in CDMA is 824 MHz to 894 MHz (50 MHz + 20 MHz separation)
Frequency channel is divided into code channels
1.25 MHz of FDMA channel is divided into sixty four code channels.
Q12. What is Sync. Channel?
Ans:
A base station transmits a Sync-Channel that spreads with Walsh code 32.
The body of synch channel is 80/3ms lengthy with frame boundary is aligned to the pilot.
Sync channel transmits a single message usually, known as Sync Channel Message.
The Sync Channel Message carries community statistics, along with the PN offset this is used by the Base Station zone.
The length and content material of the message is depending on the P_REV.
The message transmission rate is 32 bits / frame.
The message is encoded to 128 symbols.
The message yielding price is 1200 bits / s.
