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Question number: 6

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Question

Which of the following is not CDMA technology? (2004)

Choices

Choice (4) Response

a.

DS

b.

DS – FH

c.

DS –FT

d.

TDMA – FS

Answer

d.

Explanation

  • CDMA is an example of multiple access, where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth). To permit this without undue interference between the users, CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code).
  • In FHSS, which stands for Frequency Hopping Spread Spectrum, RF carrier frequency is changed according to the Pseudo-random sequence (PN sequence). This PN sequence is known to both transmitter and Receiver and hence help demodulate/decode the information. Within one chip duration, RF frequency does not vary. Based on this fact there are two types of FHSS, fast hopped FHSS and slow hopped FHSS.
  • In DSSS, which stands for Direct Sequence Spread Spectrum, information bits are modulated by PN codes (chips). PN codes are Pseudonoise code symbols. This PN codes have short duration compare to information bits. Here transmitted information over the air occupies more bandwidth compare to user information bits. DSSS is the modulation technique adopted in IEEE 802.11 based WLAN compliant products. In DSSS systems entire system bandwidth is available for each user all the time.