Essential CDMA Interview Questions & Answers:

1. Please post questions on cdma, gsm?

2. Can cdma sim be used in gsm mbile?

3. Do you know What is the main difference between 1x RTT and 1X EVDO?

1) For 1xRTT has four forward and two reverse channels,
where as in EVDO channel structure is different.

2) 1x RTT supports upto 153.2 kbps of data, where as EVDO
supports upto 3.1Mbps.

3)In 1x RTT during measurement pilot power ratio , Traffic
power ratio are also taken into consideration; where as in
EVDO FTAP , RTAP with Slots are taken into consideration

4. what is cdma technology?
What was its origin ?
How it works?
How it is different from gsm?

1> cdma stands for code division multiple access; its
frequency 800 mhz and 1900 mhz
2>channel bandwidth 12mhz with 1.25mhz for spread spectrum
3>in cdma we allocate a unique code to the user separately
and allocate the total bandwidth to the user.
4>in gsm we divide the bandwidth into many time slots and
allocate each time slot to the user.

5. What is Scrambling Code?

Scrambling-code identification

During the third and last step of the cell search
procedure, the UE determines the exact primary scrambling
code used by the found cell. The primary scrambling code is
typically identified through symbol-by-symbol correlation
over the CPICH with all codes within the code group
identified in the second step. After the primary scrambling
code has been identified, the Primary CCPCH can be detected
and the system- and cell specific BCH information can be
read.
If the UE has received information about which scrambling
codes to search for, steps 2 and 3 above can be simplified

6. Do you know For CDMA, which is the weaker Link: FWD or Reverse? Why?

Reverse link is weak in CDMA because of use of PN Long codes compared to Walsh codes in the forward link. Since, walsh codes are perfectly orthogonal in nature there is less interference in the forward link. PN long codes on the other hand are non-orthogonal in nature. However, we cant use walsh codes for the reverse link as it may seem from the above as the best possible solution. This is because walsh codes are very small in number (64/128/512 max), and hence are not sufficient for identification of large number of users in the reverse link for which the PN long codes are employed.

7. Explain the underlying functional concept of gsm
and cdma?

GSM refers to Global System for Mobile communications while
CDMA refers to Code Division Multiple Access.
Both are two diffrent technologies in Telcommunications and
behave diffrently in terms of giving voice and data
services to the customer.
Though GSM is globally used teschnology - CDMA technology
has more benefits in terms of call clarity, faster data
speeds etc while GSM covers most of the network areas and
has got variety of handsets to choose from, people prefer
this technology.
Other than these 2 technologies we have other technologies
like TDMA, WCDMA etc