AMJohny Learns

What is Wi-Fi ,FSO,LMDS,MMDS?

Johny: Dad, we have purchased wireless router in our school. What is the use of this Router?

Dad: This image shows  a wireless router. This router has one ethernet port for connecting the adsl modem. In addition, it has 4 ethernet ports to connect any pc. Other PCs can be connected wirelessly if they have wifi adapter.

Johny: How to configure the router.

Dad : You can connect a pc in any of the four ethernet  ports and configure the router. View this  video to know how to connect a PC to the router. 

Johny: How to connect the ADSL modem into the Wireless Router.

Dad: View this Video.

Johny : How to configure the PC having wi-fi adapter.

Dad:  View this video.

Johny : What are the important points I should remember about Wi-Fi?

Dad : 1) The IEEE standard for wifi is 802.11 (and 802.11a,802.11b,802.11g)

         2) It uses 2.4GHz band (Mr.a is using 5 Ghz band)

         3) Its speed is upto 2Mbps (Mr. a & g are 54 Mbps. Mr.b is 11Mbps)

         4) It uses the FHSS or  DSSS modulation (Mr.a uses OFDM, Mr.b uses only DSSS)


Johny : But who is better? whether Mr.a or Mr.b or Mr.g?

Dad :  Mr.a is very good when coverage is within a room

 Johny: What is FSO?

Dad : FSO stands for Free Space Optics. If light goes through a cable, it is Fibre Optics. If the light goes between two antennaes, tghen it is FSO. If two places are in the light of sight, why you are wasting time,money and energy by laying optical fibre.Straightway send the light from one building to the other.

               1) Its coverage is about 6.4 km (In a fog area, reduce the distance to 500m)

                2) Speed is upto  1.25 Gbps ( now it is 2.5Gbps. In future it will be 10Gbps by using WDM)

                3) Light used is INFRA RED ( Now laser is used)

Johny : What is LMDS?


        2)  Its RF is 28 GHz ( and 31 GHz,etc). Because of high frequency, Line of Sight is must.

        3)  Coverage is upto 8 km (now 32km)

        4) Modulation :  64QAM,16QAM,4QAM,QPSK,DPSDK,BPSK

        5) Good for wireless cable TV. Good for telephone service also

         6) Frequency sharing is by TDMA and FDMA

         7) To have a speed of 2mbps, you need 2.8 MHz,if you use BPSK (just 0.4MHz for 64QAM)

          8) Spectral efficiency is 5 bits per second per cycle for 64QAM.


Johny: What is MMDS?

Dad :  1) it is Multichannel Multipoint Distribution system.

           2) Speed is 9Mbps down and 2Mbps Up

           3) Multiplexing is OFDM

            4) Coverage is much larger than LMDS

Johny: What is 2G,2.5G and 3G?

Dad : 1) 2G GSM was having the speed of 14kbps. But 2.5G GSM (called as GPRS) is 115kbps

          2)2G CDMA was 14kbps, 2.5G CDMA (called as CDMA 2000 1x) is 170kbps......needs correction

          3) 3G CDMA (called as WCDMA) is 384kbps...............needs correction