Basic CS (Samsung Papers): Sample Questions 1 - 2 of 4

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Question number: 1

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What is Umbrella cell?


  • A freeway crossing very small cells produces an important number of handovers among the different small neighboring cells. In order to solve this problem, the concept of umbrella cells is introduced. An umbrella cell covers several microcells. The power level inside an umbrella cell is increased comparing to the power levels used in the microcells that form the umbrella cell. When the speed of the mobile is too high, the mobile is handed off to the umbrella cell. The mobile will then stay longer in the same cell (in this case the umbrella cell). This will reduce the number of handovers and the work of the network.
  • A too important number of handover demands and the propagation characteristics of a mobile can help to detect its high speed.
     Umbrella cell approach

    Umbrella Cell Approach

    Umbrella cell approach is used for both low speed and high speed users. High speed vehicles crosses the cellular boundary very rapidly. So, using umbrella approach one big tower is placed at the centre of area to provide network connectivity to high speed users to minimize the number of handoffs. Same way it is useful to low speed vehicles also. As it moves in one cell only, microcell tower is also provided for them for network connectivity.

Question number: 2

» Basic CS » Networks



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


Choice (4) Response












  • 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.