Wireless & Mobile Communications Questions & Answers – Second Generation (2G) Cellular Networks
This set of Wireless & Mobile Communications Interview Questions and Answers focuses on “Second Generation (2G) Cellular Networks”.
1. Popular 2G CDMA standard IS-95 is also known as ______________
Explanation: The popular 2G CDMA standard, Interim Standard (IS-95) is also known as CdmaOne. The 2.5G CDMA standard, IS-95B is called CdmaTwo. And IS-136 is a TDMA standard for 2G.
2. How many users or voice channels are supported for each 200 KHz channel in GSM?
c) Sixty four
Explanation: GSM is a circuit switched system in which each 200 kHz channel is divided into eight 25 kHz time slots, resulting in eight speech channels per radio channel.
3. How many voice channels are supported for each 30 KHz radio channel in IS-136?
Explanation: The North American Digital Cellular (NADC) system was based on Interim Standard 136 (IS-136). It divides each 30 kHz radio channel into three 10 kHz time slots.
4. How many users are supported in IS-95 for each 1.25 MHz?
b) Sixty four
d) Twenty five
Explanation: IS-95 may accommodate up to 64 users who are orthogonally coded and transmitted at the same time on each 1.25 MHz channel. Short messaging service, slotted paging, over-the-air activation, upgraded mobile station identification, and other services are included in the IS-95 standard.
5. Which modulation technique is used by GSM?
Explanation: GMSK is a type of modulation used by GSM (Gaussian Minimum Shift Keying). It is a type of modulation that has no phase discontinuities and allows for efficient spectrum usage while transmitting data.
6. IS-95 uses which modulation technique?
Explanation: IS-95 employs quadrature spreading and BPSK (Binary Phase Shift Keying). It is used for long-distance wireless communication and is considered one of the most reliable digital modulation techniques.
7. IS-136 uses which modulation technique?
a) π/4 DQPSK
Explanation: IS-136 uses π/4 DQPSK modulation technique. This technique allows a bit rate of 48.6 Kbit/s with 30 KHz channel spacing which gives a bandwidth efficiency of 1.62 bit/s/Hz.
8. Which is one of the disadvantages of 2G standards?
a) Short Messaging Service (SMS)
b) Digital modulation
c) Limited capacity
d) Limited Internet Browsing
Explanation: Circuit switched data modems are used in 2G technologies, limiting data users to a single circuit switched voice channel. The advantages of a 2G network are that it is digital and can send SMS messages.
9. GSM (Global System for Mobile) was earlier also known as _____________
a) Group System Mobile
b) Global Special Meaning
c) Group Special Mobile
d) Global Special Mobile
Explanation: Previously, GSM stood for Group Special Mobile. The meaning of the acronym was altered to Worldwide System for Mobile as it got more global.
10. 2G CDMA standard, IS-95, was proposed by which company?
a) Nippon Telephone and Telegraph (NTT)
c) Bellcore and Motorola
d) AT&T Bell Laboratories
Explanation: IS-95 was proposed by Qualcomm in early 1990s. Later it was adopted as a standard by Telecommunications Industry Association in TIA/EIA/IS-95 release published in 1995.
11. Which one of the following 2G standard is used in Japan?
Explanation: In 1991, the Japanese Ministry of Posts and Telecommunication standardised PDC (Personal Digital Cellular). It’s similar to IS-136, but with 25 KHz speech channels to match the analogue channels in Japan.
12. The 2G GSM technology uses a carrier separation of _____________
a) 1.25 MHz
b) 200 KHz
c) 30 KHz
d) 300 KHz
Explanation: Each channel in the Global System for Mobile (GSM) supports up to eight users and has a carrier separation of 200 KHz.
13. Which of the following multiple access techniques are used by second generation cellular systems?
a) FDMA/FDD and TDMA/FDD
b) TDMA/FDD and CDMA/FDD
c) FDMA/FDD and CDMA/FDD
d) FDMA/FDD only
Explanation: FDMA/FDD techniques were employed in the first generation of cellular systems. Multiple access mechanisms such as TDMA/FDD and CDMA/FDD are used in second-generation standards. Digital networks are used in 2G networks.
14. Which one is not a TDMA standard of second generation networks?
Explanation: The three most widely used second generation TDMA standards are GSM (Global System Mobile), IS-136 (Interim Standard 136), and PDC (Pacific Digital Cellular). The AMPS standard is the first of its kind.
15. Which of the following is a CDMA standard of second generation network?
Explanation: The most widely used CDMA standard for second generation networks is Interim Standard 95 (IS-95). IS-136 is a two-gigabit TDMA standard. ETACS is a 1G standard, while EDGE is a 2.5G standard.
Second-generation wireless telephony technology (2G) refers to telecom network technologies that were first introduced in 1991 by Radiolinja in Finland using the Global System for Mobile Communications (GSM) standard. In addition to SMS text messaging, 2G introduced mobile data services. The most widely used CDMA standard for second generation networks is Interim Standard 95 (IS-95). IS-136 is a two-gigabit TDMA standard. ETACS is a 1G standard, while EDGE is a 2.5G standard. AT&T’s 2G network was decommissioned in 2017. Verizon Wireless’ 2G CDMA network will be phased out by the end of 2020. Sprint’s 2G CDMA network was decommissioned in December 2021.