Page 61 - Basics of Electrical, Electronic and Communication

342 Chapter 17. Advanced communication Systems

A two channel CDMA system is shown in Figure 17.18. m(t) and
c(t) represent message and PN sequence respectively.
Advantages of CDMA
1. Increased cellular communications security.
2. Simultaneous conversations possible.

3. Increased efficiency, meaning that the carrier can serve more
subscribers.

4. Smaller phones.
5. Low power requirements and little cell-to-cell coordination needed
by operators.
6. Extended reach-beneficial to rural users situated far from cells.

17.6.4 Comparison of GSM and CDMA

A comparison between CDMA and GSM is given in table 17.2.
CDMA GSM
1. Based on spread spectrum 1. Based on TDMA
technique. technique
2. Improved privacy and 2. Less secure.
security.
3. Less probability of error 3. High probability of error
and hence high voice quality. and hence less voice quality.
4. 1.25 MHz bandwidth per 4. 200kHz bandwidth
carrier per carrier.
5. Available operating frequency 5. Available operating frequency
450, 800, 1900 MHz. 900, 1800, 1900 MHz
6. Using RUIM Card 6. Using SIM Card
(Removable User Identity (Subscriber Identity
Module). Module).
7. Soft/Softer hand-off 7. Hard hand-off
(make before break) (break before make)

Table 17.2: Comparison between CDMA and GSM

342