Deck 23: Paging and Wireless Data Networking

Question 1

How does the ReFLEX system differ from FLEX

Answer 1

The following are the differences between FLEX and ReFLEX system:

Question 2

What is a piconet How does it differ from a scatternet

Answer 2

Piconet is a kind of Bluetooth network which can be made by connecting two to eight devices. In this network all the devices are linked to same channel. In this network the device which initiates the transfer first acts as master and all the other devices act as slave at that particular time. All the slave devices follow the master's command with respect to frequency hopping sequence and timing. It is the Master device which decides how the available channel bandwidth divides between the slaves.
Scatternet as the word suggest it is a kind of net which is scatter over the wide area using 2 or more piconets. In Scatternet a Bluetooth device can act as master in one Piconet and can act as slave in another Piconet.
The following are the differences between Scatternet and Piconet:

Question 3

What advantages does a two-way paging system have over a one-way system

Answer 3

The following list are the advantages of two-way paging system over one-way paging system:
1. The most important advantage of two-way paging system is that its ability to reply for messages and making communication more reliable.
2. It is a two way communication hence it can reply queries which come from base station and can be easily located within a particular cell.

Question 4

What are the advantages and disadvantages of infrared wireless LAN systems, compared with radio-frequency systems

Question 5

How does the in FLEXion system transmit voice

Question 6

What is the maximum range for the IRDA system Why is it designed to have such a short range

Question 7

What frequency range is used for the IEEE 802.11 and Bluetooth wireless network standards, and why

Question 8

Why is diffused infrared preferred for an optical LAN in a situation where computers may be moved

Question 9

Why is it necessary to use spread-spectrum technology in the frequency range used by IEEE 802.11 and Bluetooth

Question 10

How does a wireless bridge differ from a wireless Ethernet card for a computer

Question 11

What data rates are possible with IEEE 802.11(b) wireless LANs

Question 12

Compare the Mobitex and ARDIS systems in terms of data rate.

Question 13

Explain the difference between a Basic Service Set, an Independent Service Set, and an Extended Service Set in the IEEE 802.11 specification.

Question 14

Calculate the efficiency of the POCSAG paging system in terms of bits/second per hertz of RF bandwidth at each of its three specified data rates.

Question 15

What two types of modulation are used for the frequency-hopping version of 802.11 Explain how they differ.

Question 16

Suppose a POCSAG system is set up so that each frame contains one address codeword and one message codeword. A certain type of page requires 500 message bits. Allowing for all the other types of bits involved, how many frames and how much time will it take to transmit this message at 1200 b/s Assume that all the required frames can be transmitted in one transmission with one preamble.

Question 17

Define the two terms CSMA/CD and CSMA/CA, describe how they differ, and state which is used in wireless LANs, and why.

Question 18

Suppose a POCSAG system at 1200 b/s is replaced with a FLEX system at 6400 b/s. Give an estimate of the increase in capacity. (The answer will not be precise because the two protocols differ in the amount of redundancy they include.)

Question 19

What modulation schemes are used for the direct-sequence version of 802.11

Question 20

Suppose that instead of four-level FSK the FLEX system used eight-level FSK. What would be the maximum bit rate, assuming the baud rate remained unchanged Would there be any disadvantage to doing this

Question 21

Why is it necessary for one-way paging systems to transmit all messages from all transmitters

Question 22

How is the spreading of the spectrum accomplished in each of the two RF variants of 802.11

Question 23

Calculate the efficiency in bits per second per hertz of bandwidth of the ReFLEX system operating at its maximum rate with three paging channels in one 50-kHz RF channel.

Question 24

What factors account for the long battery life of pagers compared with cell phones

Question 25

What is the spreading gain in the direct-sequence variant of 802.11

Question 26

Suppose two stations on a wireless LAN are 150 m apart. How long does it take one station to detect that another is transmitting

Question 27

What modulation schemes and data rates are used with the POCSAG protocol

Question 28

What is the anticipated range for devices using the Bluetooth system

Question 29

What is the spreading gain for a wireless LAN system using the frequency-hopping version of the 802.11 system

Question 30

What limits the number of pagers in a POCSAG system, and approximately what is the maximum number of pagers that can be used in such a system

Question 31

What modulation scheme and spread-spectrum technique are used for Bluetooth

Question 32

Suppose the Bluetooth system is used to connect stereo headphones to a computer. What data rate could be supported for each of the two channels

Question 33

How does the POCSAG system accommodate the differing message-length requirements of tone-only, numeric, and alphanumeric pagers

Question 34

What is the maximum bit rate for the Bluetooth system

Question 35

Prepare a table comparing the data rates delivered by the Mobitex and ARDIS systems described in this chapter with the CDPD, cellular modem, and PCS data transmission systems previously discussed.

Question 36

Compare POCSAG with FLEX in terms of data rate and modulation scheme.

Question 37

How is audio transmitted using Bluetooth

Question 38

Which of the systems described in the previous problem uses frequency spectrum most efficiently