01.Introduction:-There is requirement of Cellphone detection is prisons. The prisoner use
the mobile phones make extortion calls to business man or to law abiding citizens through
their proxies while siting inside the prisons. The prison authorities have requirement of such
kind device which when installed inside prison barracks gives them alert when ever there is
unauthorized use of mobile phones inside prison barracks.
02.Frequency Bands of phone operation:-The mobile operators offer their mobile services
in different frequency bands.Following frequency bands are being used in India

1 2G Capabilities: GSM900,GSM1800
2 3G Capabilities: UTMS900,UMTS 2100
3 4G Capabilities: LTE 850,LTE900 LTE1800,TDD-LTE2100(1),TDD-LTE
2300(40),LTE2500(41)
There is full duplex communication between mobile tower and mobile phone.In frequency
duplex mode the uplink frequency(Mobile to Tower) and downlink frequencies(Tower to
Mobile phone) are different while In TDD-LTE the uplink and downlink frequencies are same
03.Business potential:- There is huge business potential of these mobile detector not only in
prisons but in conference rooms, examination halls or offices where use of mobile phone is
banned.

04.Component selection :
For prototype design the ST micro electronics NuCLEO-WL55JC1 development board is
chosen due to following reasons.
01.Low power consumptions of Micro Controller
02.Integrated Radio transceiver
03.The easy availability of following development tools from ST micro electronics
        (a)STM32CubeIDE :for compiling, linking and programming 
         (b) STM32CubeMX for Graphical interface for configuration
         © Example codes for running our first startup code.
04.Free availability of evaluation Boards(NUCLEO-WL55JC1) from Elektor
05.Frequency Band of interest available in Transceiver  of NUCLEO-WL55JC1 board

05.Design Concept:-
We will try to detect mobile phone which uses GSM900 technology as its uplink
frequency falls within radio transceiver of NuCLEO-WL55JC1 Board and same
concept can be used for other technology bands.
(a) in FDD the communication between mobile phone to Tower take place on uplink
frequency band where as communication from tower to mobile phone take place on
downlink frequency band. 
(b) When ever user wants to communicate with anyone he dials his phone number and in
back ground the mobile phone communicates with Tower on uplink frequency band
of that Technology, our goal is to use NuCLEO-WL55JC1 Board do detect this uplink
communication between mobile phone and tower and glow/blink a LED when ever
the communication is detected.

06.Software Flow:
01.Initilize the Board
02 Initialize the Radio Trans reviver
03 Put the transceiver in Receive mode
04 Initialize the Channel spacing to 200Khz
05 Set the start frequency of transceiver to start Frequency=915Mhz
06Check The RSSI at start Frequency and store
07If RSSI is received then Glow /Blink the LED
08Increament the frequency to Frequency +200Khz
09 Repeat steps 6,7,9 till end of frequency band is reached that is 935Mhz
This whole process will repeat continuously inside while loop

07.Future improvements:
01. Instead of blinking LED on frequency detection we can use audio alert
02.The LORAWAN communication can be used to send the alert to prison official if distance
between barracks and prison official is large.
03.Same concept can be used to detect mobile phone of other frequency bands by addition
of other RF components for frequency translation which NuCLEO-WL55JC1 Board can handle