blake_ch22.pdf

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Chapter 22: Personal Communications Systems

MULTIPLE CHOICE

1. Current PCS systems are referred to as:

a. first-generation c. third-generation

b. second-generation d. digital-generation

ANS: B

2. The frequency band designated for PCS in North America is:

a. 800 MHz c. 1.9 GHz

b. 900 MHz d. 12 GHz

ANS: C

3. The "forward" PCS channel is:a. from the base to the mobile c. from mobile to mobile

b. from the mobile to the base d. same as the uplink

ANS: A

4. Compared to AMPS, PCS cell sites are:

a. bigger c. distributed

b. smaller d. higher-power

ANS: B

5. AMPS was designed for:

a. POTS c. use built into an automobile

b. voice d. all of the above

ANS: D

6. The number of competing PCS systems in North America is:

a. 2 c. 4b. 3 d. many

ANS: B

7. CDMA technology was invented by:

a. AT&T c. Bell Labsb. Lucent d. Qualcomm

ANS: D

8. GSM is used in:

a. Asia c. North America

b. Europe d. all of the above

ANS: D


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9. In GSM, voice channels are called:

a. traffic channels c. bearer channels

b. voice channels d. talking channels

ANS: A

10. AMPS uses:

a. CDMA c. spread-spectrum

b. TDMA d. none of the above

ANS: D

11. Other things being equal, battery life in a GSM phone should be:a. less than in a TDMA phone c. greater than in a TDMA phone

b. no better than in an AMPS phone d. no better than a TDMA phone

ANS: C

12. It is necessary to send control information on traffic channels in:a. no PCS system c. TDMA onlyb. GSM only d. both GSM and TDMA

ANS: D

13. GSM uses:

a. frequency hopping c. CDMA

b. direct-sequence modulation d. all of the above

ANS: A

14. In GSM, SIM stands for:

a. Short Inbound Message c. Subscriber ID Moduleb. Subscriber-Initiated Message d. Subscriber ID Method

ANS: C

15. IMSI stands for:

a. Integrated Mobile Subscriber Identification

b. International Mobile Subscriber Identification

c. Interim Mobile Subscriber Identification

d. Intermodulation System Interference

ANS: B

16. IS-95 uses:


b. TDMA d. all of the above

ANS: C

17. IS-136 uses:


b. TDMA d. all of the above


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ANS: B

18. In CDMA:

a. all frequencies are used in all cells

b. each cell uses half the available frequencies

c. each cell is assigned a frequency by the based. the frequency is selected by the mobile phone

ANS: A

19. CDMA uses a set of PN sequences that are:

a. common c. rotating

b. unique d. orthogonal

ANS: D

20. The next generation of PCS is expected to have:

a. faster data rates c. wider roaming area

b. Internet access d. all of the above

ANS: D

COMPLETION

1. PCS stands for ____________________ Communications System.

ANS: Personal

2. Current PCS systems are called ____________________-generation systems.

ANS: second

3. In North America, PCS is assigned the ____________________-MHz band.

ANS: 1900

4. Compared to AMPS, PCS cells are ____________________ in size.

ANS: smaller

5. Besides TDMA and CDMA, ____________________ is also used in North America for PCS.

ANS: GSM

6. The spread-spectrum technique used in IS-95 PCS is ____________________.

ANS:

CDMA

direct sequence


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7. The spread-spectrum technique used in GSM is _________________________.

ANS: frequency hopping

8. Unlike AMPS, CDMA allows for a ____________________ handoff.

ANS: soft

9. The orthogonal PN sequences used in CDMA are called a ____________________ code.

ANS: Walsh

10. Unlike other systems, in CDMA ____________________ frequencies are used in all cells.

ANS: all

11. PN stands for Pseudo-____________________ Noise.

ANS: random

12. ____________________ diversity is inherent in any spread-spectrum system.

ANS: Frequency

13. RF channel S/N ratios ____________________ than zero are typical in CDMA systems.

ANS: less

14. CDMA uses a ____________________-rate vocoder.

ANS: variable

15. A phone user typically talks less than ____________________% of the time during a conversation.

ANS: 50

16. CDMA requires ____________________-loop power control to work properly.

ANS: closed

17. GPRS stands for General ____________________ Radio Service.

ANS: Packet

18. IMT stands for International ____________________ Telecommunications.

ANS: Mobile

19. UPT stands for ____________________ Personal Telecommunications.

ANS: Universal


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20. UWT stands for Universal ____________________ Telecommunications.

ANS: Wireless

21. W-CDMA stands for ____________________ CDMA.

ANS: Wideband

SHORT ANSWER

1. What is the advantage of a "soft" handoff?

ANS:

No calls are dropped.

2. If CDMA receivers hear all frequencies all the time, how do they pick a specific frequency?

ANS:

Each frequency is modulated using a separate orthogonal PN sequence. To demodulate, the receiver usesthe PN sequence specific to the channel it wants.

3. What is the effect of cochannel interference in CDMA?

ANS:

It increases the background noise level, but CDMA can tolerate a lot of such noise.

4. How does GSM achieve frequency diversity?

ANS:It uses limited frequency hopping.

5. Why was PCS assigned to 1.9 GHz instead of the 800-MHz band used for AMPS?

ANS:

The 800 MHz band was already overcrowded.

6. Why would a battery in a GSM phone be expected to last longer than a battery in a TDMA phone?

ANS:

A TDMA phone is active during one out of every three time slots. A GSM phone is active during one out

of every eight.

7. What is the advantage of using offset QPSK over standard QPSK?

ANS:

With standard QPSK, the transmitted power repeatedly goes to zero. With offset QPSK, it never goes to

zero. Linearity requirements are less strict for offset QPSK transmitters.

8. What is the "near/far" effect in CDMA, and what causes it?


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ANS:

A stronger station farther away can "drown out" a weaker station that is near. This happens when the

power transmitted by mobile units is not well controlled by the base.

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