Cellular Communication

Reading Time: 6 minutes
Electromagnetic Spectrum.
Why Micro-waves?
Why Cellular?-Frequency Reuse.
Basic Structure.
How do you call your friends?
Spectrum crunch
Cognitive radio
Cell breathing
Green communication.
Research in this domain.
Why micro-waves?

Microwaves are widely used

for point-to-point communications because their small wavelength allows conveniently-sized antennas to direct them in narrow beams, which can be pointed directly at the receiving antenna.
Less attenuation to water vapour,oxygen molecules,etc.

Range roughly from 800MHz-30GHz

}Method used by service providers to improve the efficiency of a cellular network and to serve millions of subscribers using a limited radio spectrum.
}Based on the fact that after a distance a radio wave gets attenuated and the signal falls bellow a point where it can no longer be used or cause any interference.
}Transmitter transmitting in a specific frequency range will have only a limited coverage area
}Beyond coverage area frequency is reused by another transmitter.
}the entire network coverage area is divided into cells based on the principle of frequency reuse


• basic geographical unit of a cellular network
• Represented graphically as a hexagonal shape, but in reality it is irregular in shape
• Width of cells changes as demand changes.


• is a group of adjacent cells, usually 7 cells; no frequency reuse is done within a cluster.
BTS (Base Transceiver Station)
• Main component of a cell
• Connects the subscribers to the cellular network
•Transmission/reception of information; it uses several antennas spread across the cell
BSC (Basic Station Controller)
• Interface between BTSs and it is linked to BTSs by cable or microwave links; it routes calls between BTSs; it is also connected to the MSC
MSC (Mobile Switching Center)
• Coordinator of a cellular network
• Connected to several BSCs,
• Routes calls between BSCs;
• Links the cellular network with other networks like PSTN through fiber optics, microwave or copper cable

 Home Location Register (HLR)

– maintained by the service provider

– permanent data about each subscriber (i.e. location, activity status, account status, call forwarding preference, caller identification preference)

  Visitor Location Register(VLR)

–stores temporary data about a subscriber; it is kept in the MSC of the of the area the subscriber is located in; when the subscriber moves to a new area the new MSC requests this VLR from the HLR of the old MSC

 Equipment Identity Register(EIR) –

-database located near the MSC and containing information identifying cell phones which are stolen or which are cloned.

Authentication unit:-

-This unit holds the security concerns that hover around the all channels, authenticating even the correct base station not the ones held for data recovery by some external agents.

Control channel

-dedicated channel for sending ack,tracking call,tracking messages,other control signals

-only control data ;no voice

Voice channel

-for only voice transmission




-the subscriber dials the receiver’s number and sends it to the BTS
-the BTS sends to its BSC the ID, location and number of the caller and also the number of the receiver
-the BSC forwards this information to its MSC
-the MSC routes the call to the receiver’s MSC which is then sent to the receiver’s BSC and then to its BTS
-the communication with the receiver’s cell phone is established
-when the receiver’ phone is in an idle state it listens for the control channel of its BTS
-if there is an incoming call the BSC and BTS sends a message to the cells in the area where the receiver’s phone is located
-the phone monitors its message and compares the number from the message with its own
-if the numbers matches the cell phone sends an acknowledgement to the BTS
after authentication, the communication is established between the caller and the receiver
-when the phone needs to make a call it sends an access request (containing phone identification, number) ; if another cell phone tries to send an access request at the same time the messages might get corrupted, in this case both cell phones wait a random time interval before trying to send again
-then the BTS authenticates the cell phone and sends an acknowledgement to the cell phone
-the BTS assigns a specific voice channel and time slot to the cell phone and transmits the cell phone request to the MSC via BSC
-the MSC queries HLR and VLR and based on the information obtained it routes the call to the receiver’s BSC and BTS
 the cell phone uses the voice channel and time slot assigned to it by the BTS to communicate with the receiver.



Calling & Receiving Continued:-

-When a request to deliver a call is made in the network, the MSC or the receiver’s home area queries the HLR; if the cell phone is located in its home area the call is transferred to the receiver; if the cell phone is located outside its home area, the HLR maintains a record of the VLR attached to the cell phone

– Based on this record, the MSC notes the location of the VLR and indicated the corresponding BSC about the incoming call

-The BSC routes the call to the particular BTS which uses the paging channel to alert the phone.

-The receiver cell phone monitors the paging channel periodically and once it receives the call alert from the BTS it responds to the BTS

-The BTS communicates a channel and a time slot for the cell phone to communicate

– Now the call is established




-Why Hand-off?
-How to do Hand-off?
-What factors determine handoff?
-Types of hand-off
First generation Hand-off
MAHO-In 2g phones
First generation Hand-off:-
-In this signal strength measurements are made by base station & supervised by MSC.
-Each base station monitors the signal strengths of all the control channels to determine the relative location of each      mobile user with respect to the base station tower.
 The locator receiver is controlled by the MSC & is used to monitor the signal strength of users in need of hand-off.
  Based on the locator receiver signal strength info from each base station ,the MSC decides whether hand-off is      necessary or not.
MAHO-In 2g phones:-
Every mobile station measures the received power from surrounding base stations &  continually reports the results to these measurements to the serving base station.
A hand-off is initiated when power received from base station of a neighbouring cell begins to exceed the power received from current base station by a certain level or for a certain period of time.
Cell breathing:-

is a mechanism which allows overloaded cells to offload subscriber traffic to neighbouring cells by changing the geographic size of their service area. Heavily loaded cells decrease in size while neighbouring cells increase their service area to compensate. Thus, some traffic is handed off from the overloaded cell to neighbouring cells, resulting in load balancing.



Why green Communication?

-Use of solar panels in place of diesel in base station.

-Dynamic Power Assignment based on load detection,

-A fixed control channel scans number of mobile users in an area of a cell & tells neighbouring bts whether or not to expand.

-if the minimum requirement fails then bts expand & area is served by that neighbouring bts. While the bts of that cell remains off.



Methods for Efficient Hand-off with same quality of service. (QOS)
Tackling Spectrum Crunch – Software defined Radio-cognitive radio.
Maintaining the QOS within a cell at specified power level.
Security in software defined radio.
Green wireless communication-focussing cell breathing techniques even in high traffic zones.
Basic electronics.(1st year).-Websearch.
Signal & System.(2nd year).-Prof.S.C Dutta Roy IITD NPTEL
Analog Modulation.(2rd year)-Prof. Surendra Prasad IITD NPTEL
Digital Modulation.(3rd Year)-Taub –Communication Engineering.
Speech Coding(no year)-Rabiner;Rappaport;Youtube-E amberkairajah-video.
Wireless Communication(Final Year).-Rappaport;Prof.Ranjan K Bose-IITD NPTEL
Wireless Communication “Rappaport”-Pearson Publications.
NPTEL Videos-Prof.Ranjan K Bose-IIT Delhi.
IEEE Papers.
https://www.youtube.com/watch?v=KymIDyQiXZI-basic building block call transfer Mr. Vishwendra Choudhary.


Download materials:-


Basic Communication:-

Types of Hand-offs:-


Mindbend Indeaz -Some Problems & Basic & Best Solution

Reading Time: 6 minutes

Artificial Growth of algae & subsequent drain of nitrogen based chemicals.

  • While searching for technical solution, one has to keep in mind that technology should not induce other problems while solving one problem.
  • Also when we say water management it’s not controlling our limit of use but to artificially induce natural recycle process by studying nature. The best way to tackle waste is to match it with waste utilization. Manipulation of waste is like shifting it from one system to another without actually reducing the same.
  • Here I will be talking on a method that study natural water recycling method and adoption of the same instead of chemical processes which solve one problem and create another.


  • Eutrophication can be human-caused or natural. Untreated sewage effluent and agricultural run-off carrying fertilizers are examples of human-caused eutrophication. However, it also occurs naturally in situations where nutrients accumulate (e.g. depositional environments), or where they flow into systems on an ephemeral basis. Eutrophication generally promotes excessive plant growth and decay, favoring simple algae and plankton over other more complicated plants, and causes a severe reduction in water quality. Phosphorus is a necessary nutrient for plants to live, and is the limiting factor for plant growth in many freshwater ecosystems. The addition of phosphorus increases algal growth, but not all phosphates actually feed algae. These algae assimilate the other necessary nutrients needed for plants and animals. When algae die they sink to the bottom where they are decomposed and the nutrients contained in organic matter are converted into inorganic form by bacteria. The decomposition process uses oxygen and deprives the deeper waters of oxygen which can kill fish and other organisms. Also the necessary nutrients are all at the bottom of the aquatic ecosystem and if they are not brought up closer to the surface, where there is more available light allowing for photosynthesis for aquatic plants, a serious strain is placed on algae populations. Enhanced growth of aquatic vegetation or phytoplankton and algal blooms disrupts normal functioning of the ecosystem, causing a variety of problems such as a lack of oxygen needed for fish and shellfish to survive. The water becomes cloudy, typically colored a shade of green, yellow, brown, or red.
  • Naturally Algal blooms occur when excess of plant nutrient (Nitrates & Phosphates) is available in the water-A natural cleansing process.
  • These blooms have been found to destroy fishes in fresh water because of the low oxygen level initiated by planktons feeding on algae after death at the lower water level.
  • It has been found that the root cause of imbalance in water is excess of nitrates & phosphates. So the target should be root cause.
  • Thus we could encourage algal growth for nitrate reduction outside the fresh water body & thereby decrease the nitrate & phosphate level and also increase food for planktons /phosphorous fixating bacterias/nitrogen fixating bacterias-which are then eaten by marine life-A natural phenomenon initiated artificially.
  • The excess of algae may be used as a bio-diesel or may be fed by phytoplankton to zooplanktons to small fishes to large fishes & the eco-logic continues.
  • Well traditionally ion exchange methods used in industries are used for nitrate reduction however nitrates do not go away from system they are just removed from water source & they appear in other system.eg:-

In ion-exchange resins the nitrate ion is removed from water source by exchanging with chloride ions. After the exchange the nitrates present in the resin bed are exchanged with HCL to regenerate resin producing HNO3 .thus we see that still overall system –the eco-system has nitrates still left & will somehow or other reappear. Also the chlorides that we exchanged are also as dangerous as nitrates if present in large quantity. So any chemical process is a curtain to existing problem it no longer solves problem as a whole. A bio-chemical process is therefore best by observing nature.

  • Also biological dentrification is used in which nitrates are converted to Nitrogen gas.
  • The process is similar to denitrification done by anaerobic bacterias but those require organic food in plenty to convert nitrates ultimately each natural process comes down to bacteria and microbes level as they are natural scavengers but those attract pests and rodents bad odor etc.


  • The time algal growth requires, the time planktons & other organism requires to complete a food-web is high .hence this system may be only used in areas where there is no continuous addition of nitrates-small industries letting off waste in 5 days, a farming site where agricultural run-off carries phosphates & nitrates during rainy season, a waste water treatment plant having large base for each pond for cultivation.

Use of reflectors as flyers controlled by the control station to reflect the amount of power in a cellular structure:-

  • In a cellular structure the transmitting & receiver (duplex antenna) is one that radiates micro-waves for mobile communication. Generally in urban areas where concentration of mobile phones is very high the towers are placed on residential towers or offices or shops etc.
  • There is a growing debate on whether the electromagnetic exposure can cause tumors or cancer. Although few researchers have shown the opposite but practically over exposure to micro-waves can definitely lead to a disorder because these waves tend to heat the body temperature when they pass through our body. The tissues break in to cells creating disorder in the body due to high temperature.
  • Even though limits of radiation are standardized by government ,continuous exposure is dangerous for all of us. people living near towers face high dangers of exposure while people far away likely do not .since power density of the antenna is high near the antenna & starts reducing as the distance increases.
  • So we can direct a high powered beam of radiations towards a secondary tower flying in the sky over a cellular structure at heights calculated for power required & that can be used as a transmitter receiver to be communicated with the base station.
  • This will always ensure uniform power spread & the affect of heat effect of micro-waves would be reduced.
  • This will ensure constant power density on surface of earth (exceptions hills, mountains etc.) to be used for purpose of communication rather than concentrated power density.



  1. Mobile base station makers will have to share extra costs for making new equipment controllable from control tower as well.
  2. Finding out space in the sky for installing each such station over which we can place the flying station which will not be interfered by birds, airplanes, ionosphere reflection, etc.


A free wireless internet service for developing economies called “Project Loon” was announced by Google & initially was surveyed in New-Zealand by a farmer for wireless internet by sending balloons carrying transponders receptors & efficient mechanism for looming around a particular region just like a geo-synchronous satellite. This will also be in India, South-Africa.

An ICT model for empowering rural population:-

Our government spends 60000 crore in Nrega-a scheme which is aimed at providing opportunities for employment in 100 days. A worker from rural area is made to toil for breaking stones & he gets his income from that. With bundles of corruption, this scheme neither utilizes individual potential of a farmer, a child, a painter, a porter goldsmith etc. to meet their expenses rural public do .Instead of this each village can have a “centre of internet” where everything that an urban Indian gets rural India also has.


  • Healthcare:

Supply of generic medicines as when needed, supply essential supplements for maternal ,child health through a WLAN connections each in one village, asking possible diagnostic questions to doctors who are unwilling to go to rural side, people will tell their day to day activities & doctors would suggest diseases that can occur or a database of diseases in different languages.

  • Entrepreneurship:

Popularity of village & direct details of those involved in sale of those materials online.

  • Current trends of market:

Current Wheat, Rice, Moong, etc. to give farmers a fare share of their products

Giving their new inventions on web may be integrated with National Innovation Foundation (NIF).

  • Education.


CEV - Handout