How Mobile Phone WorksAdaptive Power ControlFrequency Reuse in GSM System

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Presented By Sree Narayan Chakraborty

ASH1201002MMUHAMMAD TANVIR HASSAN

ASH1201058M

How Mobile Phone Works?

Setting up a call process • when powered on, the phone does not have a frequency/ time slot to it yet; so it scans for the control channel of the BTS and picks the strongest signal • then it sends a message (including its identification number) to the BTS to indicate its presence • the BTS sends an acknowledgement message back to the cell phone• the phone then registers with the BTS and informs the BTS of its exact location • after the phone is registered to the BTS, the BTS assigns a channel to the phone and the phone is ready to receive or make calls

MAKING A CALL when the phone needs to make a call it sends an access request (containing phone identification, number) using RACH to the BTS; 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

RECEIVING A CALL 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.

A microscopic microphone A speaker An LCD or plasma display A keyboard not unlike the one we saw in a TV remote control An antenna A battery Printed Circuit Board(PCB) Flash / Room

Mobile Equipments

•Transmitting Power of Mobile Station(MS):0.5watt•Transmitting Power of Base Station(BTS):10-100watt

Transmitting Power in GSM

•As cellular mobile moves power seen at BTS changed•So we use adaptive power control to maintain it

Adaptive Power Control

•Save the power of BTS &MS•Reduce the interference of the network•Increase the quality of the network

Purpose of Adaptive Power Control

•Electronic Serial Number (ESN) -Unique 32-bit number programmed in the phone •Mobile Identification Number (MIN) – 10 digit number derived from the phone’s number. •System Identification Code (SID) – unique 5 digit number that is assigned to each carrier by the FCC

Codes in the Mobile Phone

SIM card (Subscriber Identification Module (SIM)) is a type of Smart card used in mobile phone. The SIM is a detachable smart card containing the user’s subscription information and phone book. This allows the user to retain his or her information even after switching off the handset. Alternatively, the user can also change service providers while retaining the handset simply by changing the SIM. SIM card Securely stores the service subscriber key having 15 digits.The digits of the key are :

•First 3 digits – Mobile country code•Second 2 digits – Mobile network code•Third 10 digits – Mobile station identification number

Subscriber Identification Module (SIM)

There are two types of channels used in GSM :•Control channels:

These are responsible for housekeeping tasks such as telling the mobile when a call is coming in and which frequency to use. To ensure this handover works, the phone constantly monitors the broadcast control channel of up to 16 neighboring cells. In normal operation, phones continually adjust the power of the radio waves they send out to be the minimum needed for the base station to receive a clear signal. If a phone moves far away from its base station and if the signal is weak, the network consults the list and triggers a handover to a neighboring cell with best signal.

•Traffic channels:It is used to carry calls or other data from the mobile phone to the base station and vice versa. In the Traffic channel, voice or text data is carried in bursts. Each burst comprises two consecutive strings of bits (a series of signals representing 1s and 0s), each 57 bits long.

Channels used in GSM

Frequency Reuse

•GSM frequency :900 MHz•Uplink frequency :890-915 MHz•Downlink frequency :935-960 MHz•Duplex Distance:45 MHz

Frequency Band in GSM System

•Uplink & Downlink bandwidth=25 MHz•25 MHz is divided into 200KHz •Total Frequency = 25MHz / 200KHz= 125 F•Guard Band Frequency 1 F•So 124 F will be used•Suppose 124 F is divided among operators. •There fore each operator use = 124F/3 =41F •BCCH use 12F and TCH use 28 F with 1F Guard Band.

•1TDMA Frame =8 slots•1 Time slot=577 micro second•Therefore 8 time slots =8*577 micro second=4.615 ms.•

TDMA Frame

1 12 13 41

1F for Guard Band