What is Wireless Communication?
Transmitting / receiving voice and data using Electromagnetic wave in open Space.
---The signal from transmitter to receiver is carrier over a well-defined frequency channels or band .
---Every channel has a certain frequency bandwidth and capacity.
---Apart channels can be used to transmit signal in parallel and independently.
Type of Wireless Communication?
1.Mobile:-Cellular Phone GSM/ CDMA.
2.Portable:-IEEE 802.11b WI-FI
IEEE 802.15.3 UWB
3.Fixed:- IEEE 802.16 Wireless MAN
Typical Frequencies:-
1.FM Radio:- 88MHz
2.TV Broadcast:- 200MHz
3.GSM Phone:- 900MHz
4.GPS:- 1.2GHz
5.PCS Phone:- 1.8GHz
6.Bluetooth:- 2.4GHz
7.Wi-Fi:- 2.4GHz and 5GHz
2.4GHz and 5GHz is a free Licence band used in colleges or home. Higher the Frequency band Smaller the Wavelength.
Types of Wireless Communication in GSM:-
1.Radio Transmission
a.easily generated,omni-directionaly travel long distances,easily pentrate building
Problem:-
a.Frequency depentents.
b.relative low bandwidth for data communication.
c.Tightly Licenced by the governments.
2.Microwave Transmission:-
a.Widely used for long distance communication.
b. Gives a high S/N ratio,relatively inexpensive.
b. Gives a high S/N ratio,relatively inexpensive.
Problem:-
a.Don't pass through building well.
b.Weather and frequency dependent.
Some other types of wireless communication:-
1. Infrared and millimete waves
a. Widely used for short rage communication.
b. Unable to pas through solid object.
c.Used for indoor wireless LAN's,Not for outdoors.
2.Light wave transmission
a.Unguided optical signal such as laser.
b.Connect two LAN's in two building via laser mounted on their roof.
c.Unidirectional easy to install, do not required licence.
Problem:-
a.Unable to penetrate rain or thick fog.
b.Laser beam can be easily diverted by turbulent air.
Current Wireless Systems:-
1. Cellular systems.
2. Wireless LAN.
3. Satellite system.
4. Paging system
5. PANs.
About Cellular system:-
Reuse the Channels to maximize capacity.
a.Geographic region divided into cells.
b. Frequency/Time slots/ codes reused at spatially separated location.
c. Base station/Mobile telephone switching offices(MTSOs) coordinates handoff and control function.
About Wireless LAN(WLAN):-
a. WLAN connect "Local" computers 100 mtr range.
b. Breaks data into Packets.
c. Channels access is shared.
d. Backbone interface provide best-effort service.
e. Poor per formation in same application.
f. Low mobility.
Wireless LAN standards:-
Bit rate Frq Range
1. IEEE 802.11b 5.5 - 11 Mbps 2.4GHz 100meter
2. IEEE 802.11a 54 Mbps 5GHz 100 meter
3.Hiper LAN 20 Mbps 5GHz 50 meter
4. Hiper LAN/2 54 Mbps 5GHz 50meter
About Satellite Systems:-
a. Cover very large area (Globle Coverage).
---very useful in sparsely populated areas rural,sea,mountains etc.
b. Different orbit height
----GEOs(39000Km) versus LEOs(2000Km).
c. Optimized for one-way transmission
-----Radio and movies broadcasting set TV.
d. Expensive base stations
e. Limited quality voice/data transmission.
f. Traditional applications
---Weather satellite
---Radio and Tv broadcasting,
---military satellites
g. Telecommunication application,
----Global telephone connection.
----Backbone for global network
----GPS.
About Paging systems:-
1.Broad coverage for short messaging.
2. Message broadcast for all base station.
3. Simple terminals.
4.Optimized for one way transmission.
5. Answer back hard,
6. Overtaken by cellular.
About Personal Area Network(PAN):-
1.Cable replacement Rf technology(low cost).
2. Short range(10m to 100m).
3. 2.4GHz band (crowded).
4. One data and 3 voice channels.
5. 1 Mbps data rate shared between 7 devices.
7. TDD duplex scheme.
8.Polling based multiple access.
9. Widely supported by telecommunication,pc,electronics devices.
Cellular Standards :-brief survey
1. 2G System:-Voice Channels
----IS-136 TDMA combined FDMA/TDMA
---GSM combined FDMA/TTDMA most widely used.
---IS-95 CDMA
2. 2.5G System :Voice and Data channels
---For those who can't wait for 3G services
---General packet radio service(GPRS)
a.evolved from GSM.
b.data sent on multiple channels.
---Enhanced data rates for global evolution(EDGE).
a.also evolved from GSM using enhanced modulation.
b.data rate upto 384kbps.
---CDMA-2000
a.data rate up to 144kbps
b.evolved from IS-95
3.3G System:Voice/Data
---Universal Mobile Telecommunication Service(UTMS).
---CDMA-2000.
Types of Cell used in telecommunication networks.
1.Femto Cells:-
Smallest unit of the cellular network hierarchy. These cells cover only a few meters where all devices are in range of the user.
2.Pico Cells:-
The Size of these cellular networks is in the range of a some tens of meters .
3. Micro Cells:-
It covers a range of more than hundred of meters.
4. Macro Cells:-
It cover areas in the range of several kilometers.
5. Mega Cells:-
Cover national wide areas with range of hundreds of kilometers.
What is Frequency Reuse in Cellular Communication:-
--Radio Spectrum is one of the scarcest resources available in frequency band.
--Employ architectures that can support many uses as possible with the available spectrum.
--Some spectrum can support multiple users separated by a distance and thus efficiently using the spectrum.
--Frequency reuse has its foundation in the attenuation of the signal strength of e.m wave with distance.
--Distance separating the transmitters should be sufficiently large.
--Transmit power should be reasonable small.
--The Cellular concept is work on the concept of frequency reuse.
What is Global System for Mobile Communication(GSM)
1.A GSM System has 124 pair of Simplex channels.
2. Each 200kHz wide.
3. Supports eight separate connections on it using TDM.
4. Each active station is assigned one time slot on one channel pair.
5. each cell can be supported 992 channels ,but several of them are not available,to defer frequency conflict with neighboring cells.
6. Transmitting and receiving does not happen in the same time slot because the GSM radio can not transmit and receive at the same time and it takes time to switch from one to the other.
7. A data frame is transmitted in 547 micro second,but a transmitter is only allowed to send one data frame every 4.615 micro sec,since it is sharing the channel with seven other station.
About Control Channels (CC) of Mobile Communication:-
1. The broadcast control channel(BCC) is a continuous stream of out put from the BS containing the BSs identity and the channel status.All MS monitor their signal strength to see when they moved into a new cell.
2.The dedicated control channel(DCC) is used for location updating, registration and call setup in particular each BS maintains a database of MS,information needed to maintain this data base and is sent on the dedicated control channel
What is Mobile Communication or Cellular Communication?
Location Managements
3.Three logical sub-channels:-
--Is the paging channel,if the BS used to advertised incoming calls each MS monitors it continuously to watch for call it should answer.
--Is the random access channel This allows users to request a slot on the dedicated control channel if two request colloids they are garbled and have to be retired later.
--Is the access grant channel the announced assigned slot.
What is Mobile Communication or Cellular Communication?
GSM
Channel Multiplexing:- FDM + 8 TDM slots
Uplink(GSM 900) :- 890-915 MHz 125 channels
(1800) :- 1710-1785 MHz
Downlink(GSM 900) :- 935-960 MHz; 125 channels
(1800) :- 1805-1880 MHz
Channel Bandwidth :- 200KHz
FDD separation :- 45(900)/95(1800 MHz
Modulation :- FSK
Channels :- Broadcast control;dedicated control channel;paging;
TDM frame :-24 frame,120m sec each.
Time Slots :- 8 slots;0.577msec each(24x8=192)
What is Handoff in GSM networks.
Change of radio connection from one base station to other is known as Handoff.
Types of Handoff:-
1.Hard handoff.
2. Soft handoff.
What is Hard Handoff:-
Break before make:-MS connects to BS station-2 after link with BS-1 break used in GSM System.
Difficulty in Handoff Detection:-
--Signal Strength fluctuates;Scattering,reflection and diffraction results in fading of received signal.
--False handoff requirement at the boundary results in ping pong effect at the boundary.
--Number of un necessary handoff must be reduced.
What is Soft Handoff:-
Soft Handoff is make before break;MS connected to BS-2 before connection to BS-1 breaks.Soft Handoff used in CDMA System.
Merits and Demerits of soft Handoff:-
Merits:-
1.Mobile station does not loose contact during handoff.
2. The effects of ping pong is reduced.
3. Easy to implements for CDMA system.
Demerits:-
1.It is a complex process.
2. Hardware requirement is more.
3. utilizes extra resource during handoff.
Location Managements
Location updates:-
1.Messages are sent by MS regarding its changing points of access to the fixed network.
2. Each time the MS makes an update to its location a database in the fixed part of the network has to be updated to reflect the new location information.
2.Response from the paged terminal enables the network to locate the MS.
2. Each time the MS makes an update to its location a database in the fixed part of the network has to be updated to reflect the new location information.
Paging:-
1.Required to deliver an incoming message to the MS.2.Response from the paged terminal enables the network to locate the MS.
Location information dissemination:-
1.Procedures to store and distribute the location information related to MS serviced by the networks.Location Update Algorithms
Static Location Updates:-
1. Initiation of location update is decided by the topology of the network.
2. Location Area(LA) based location updates(Commonly used)
3. Distance-based performs location update after crossing certain number of cells.
4. Timer-based performs location update after a certain time has elapsed.
Dynamic Location Updates:-
1. Uses mobility of the user and cal pattern for location update.
2. State-based performs location update based on the currents state information such as distance traveled the number of LAs etc.
3. User-profile-based maintains a list of LAs that the MS located in at different points of time.
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