Ece-cdma-system

3059/12B

Roll No.:

M. Tech. (ECE), III-Semester Examination, Nov.-Dec.-2012 CDMASYSTEM Paper: MEEC-603 Time: 3:00 Hours

Max. Marks:

100

Note: Attempt any five questions.

1 (a)

Explain the principle behind spectrum and dispreading and how this is used in minimize interference in a CDMA system.

(10)

(b) Define the term chip, in the context of direct sequence system and in the context of a frequency hoping system.

2 (a) Explain

acquisition

and

(10)

tracking

in

diagram.

DS-SS CDMA system using block (10)

(b) Why is CDMA most secure than other multiple access techniques explain basic operation of CDMA.

3 (a)

(l0)

What is the near-far problem? Find out the methods of power control to eliminate this problem in DS-SS.

(10)

(b) What is frequency selective fading? How can minimize the fading effect using DS-CDMA techniques?

4 (a)

A speech

(10)

signal band limited to 4 KHz and 256 quantization level is to be

transmitted by DSSS transmitter. Find out the required chip rate to obtain gain of 6400.

(12)

(b) Explain the performance of FH-SS system.

(1)

(08)

·3059/12B

5 (a) Explain the effect of imperfect power contr610n DS- CDMA performance. (b) How handoff is done in COMA? Also explain, soft hando'ffs.

6 (a)

A frequency hopping spread :spectrum is to have the following parameters.

(08) (12)

(I 0)

Message bit sale = 2400 bps Hopper message bit = 16 Frequency multiplication = 8 Processing gain (i)

2:

45 dB

Find out the smallest number of frequencies required if this number is to power of2.

(ii)

Find out the B. W of the FH spread of spectrum signal.

(b) Compare

the DSSS and FHSS types of system.

systems/standards in which these schemes are utilized.

7 (a)

(10)

What do you mean by partial correlation? Why is partial correlation important for the sake receiver rather than full correlation?

8 (a)

(l0)

Discuss the frequency and channel specification of CDMA digital cellular standard IS-95 and explain the forward CDMA channel.

(b)

Find out the existing

(10)

Discuss the generation of CDMA system. Also explain the third generation CDMA system.

(10)

(b) Write short notes on any three of the followings: (i)

Multi-user detection

(ii)

Capacity estimation

(iii) .

Error probability for DS-CDMA

-,.---* *--.,..,.-

(2)

(10)