---
title: '09 Cellular Mobile Networks'
disqus: hackmd
---

09 Cellular Mobile Networks
===

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## Table of Contents

[TOC]

How do Cellphones Work?
---
- mode of communication
- full duplex
- 2 channels
- speak and listen at same time
- cell phones essentially 2 way radio
- radio transmitter
- radio receiver
- phone converts voice into electrical signal then transmit via radio waves to nearest cell tower
- half duplex
- cb radios (citizen band)
- radio freq signal <-> electrical signal
- only speak one at a time
- eg. walkie talkie
- use radio waves to talk to cell tower that connects it to rest of phone network

### Cellular Layout
- phone network composed of **cell** or signal area
- cells overlap or join to form large coverage area
- users on network can cross into diff cells w/o losing conn
- phone networks allows for **freq reuse**
- below, cell 1s on same freq but wont interfere due to phy separation
- inteference called **crosstalk**


### Cellular Division
- cellular device can comm with another
- cells in hex shapes
- preferred than square or circle as covers entire area w/o overlapping


### Cell Antennas

#### Find Towers
- http://www.cellreception.com/towers

Data Transmission in Mobile Networks
---
### MTSO
- mobile telephone switching office (mtso)
- contains switching eq for routing mobile phone calls
- handles entire cell network
- controls **handoff**
- process of transferring ongoing call or data session from one channel (cell) to another channel (cell)
- comm with PSTN (public switch telephone network)
- landline network
- brain of cell phone network
- mtso evaluates signal strength between device and network
- tell device/network to make appropriate adjustments to transmission


#### How Data is Transmitted

### Wireless Frequency
- transmission of voice or data through use of electric waves set to specific freq
- num waves per second = freq
- freq measured in hz
- 1 hz = 1 complete wave length per sec


### What Happens...
- when phone turns on


- when place call

### Cellular Hand off
- if signal on channel from tower weakens during a call, another tower and handoff needed
- if no other tower with stronger signal, call dropped


### Diff between Hard and Soft hand off

Cellular Subsets
---
### Access Technologies
- how phone talks to tower
- AMPS advanced mobile phone system
- fdma
- 800 mhz
- 1g
- analog
- TDMA time division multiple access
- 2g
- digital
- iDen integrated digital multiple access
- 2g
- digital
- CDMA code division multiple access
- 2g/3g
- digital
- GSM global system mobile comm
- 2g
- digital
- W-CDMA wideband CDMA
- 3g
- digital
- OFDM orthogonal freq-div multiple access
- 4g
- digital

### TDMA
- time div multiple access
- method of digitizing and compressing
- num of equal timeslots configed for ea freq channel
- divides convos by freq and time
- outdated tech
- facilitates many users to share same freq w/o interference
- divides signal into diff timeslots and inc data carrying capacity
- breaks up freq allocation by time
- eg. 6.7ms
- 2 channels used
- decoding
- encoding

### iDen
- integrated digital enhanced network
- based on tdma
- iden phones can support sms msgs, voice mail and data networking eg. vpn, internet and intranets
- allow users to take advantage of **PTT (push to talk)** walkie talkie tech
- half duplex
- used by
- sprint
- shutdown in 2013
- at&t
- verizon

### CDMA
- code div multiple access
- uses spread spectrum tech
- spreads info contained in particular signal of interest over greater bandwidth than orig
- assigns code to ea piece of data passed across spectrum
- newer tech still uses orig tdma concept
- deemed more superior to fdma and tdma
- cannot carry voice and data at same time
- every comm channel uses full avail spectrum
- 2 channels
- encoding
- decoding
- spread spectrum
- channels spread across entire freq range instead of 1 dedicated one
- 1850 mhz - 1990 mhz


#### CDMA Family
- cdmaOne (2g)
- orig cdma system
- cdma2000
- 3g
- evolved from cdmaone
- fam of tech for 3g cellular comm for transmission of voice, data and signals
- 1xRTT (voice), 1xEV-DO (3g wireless standard data)
- W-CDMA
- 3g
- borrows ideas from cdma
- use gsm tech and evolve into UMTS (universal mobile telecomms service)

#### BitPIM Software for CDMA
- is open src cross platform that allows u to view and manipulate data on many cdma phones
- include phonebook, calendar, wallpapers, ringtones and filesystem
- analyse most qualcomm cdma chipset based phones
- PIM = personal info management

#### Qualcomm for CDMA
- founded in 1985 by multinational semiconductor and telecomms eq company
- created CDMA and components in 1990s
- orig built base stations, chipsets and phones
- owns patent on CDMA chipset tech

### GSM
- based on TDMA
- 70%-80% of phones
- digital cellular tech for transmitting mobile voice and data services
- established in 1987 as standard
- avail in >212 countries
- global systems for mobile comm with freq 850-1900mhz
- uses SIM tech


Cell Phone Identification Numbers
---
### Mobile Identity Number (MIN)
- 10 digit
- more with country code
- assigned by carrier
- used for phone identification
- eg. [phone]
- 2 parts
- MIN 1
- 24 bit number after area code
- MIN 2
- area/mobile subscriber code
- can be ported

### Electrical Serial Number (ESN)
- unique 32bit number assigned to ea TDMA or CDMA (non GSM) device
- like mac addr
- uses 14 bit code for manufacturer code
- since 8bit almost exhausted


### Mobile Equipment ID (MEID)
- rpelace soon exhausted ESN for CDMA devices
- all fields are hex vals
- RR
- regional code
- global administered
- XXXXXX
- 000000 - for small quantities of test/prototype mobiles
- 000001 - FFFFFE
- reserved for regional admin bodies or mobile manufacturers
- subject to industry agreement
- ZZZZZZ - manufacturer assigned to unique id device
- C
- check digit
- not tramistted over air


### International Mobile Equipment Identity (IMEI)
- unique 15 digit code to identify indiv GSM mobile to mobile network
- displayed on phones dy dialing code `*#06#`


#### IMEI Checksum Verification
- 3 steps
- starting from right, double every other digit
- sum digits
- note that 14 is 1 + 4 not +14
- check if sum is divisible by 10



### International Mobile Subscriber Identity (IMSI)
- global unique identifier
- 56 bit
- unique in every network
- allowed for auth of device to network
- 3 parts
- MCC
- mobile country code
- 3 digits
- all MCC is assigned by ITU internation telecomm union in recommendation E.212
- internaitonal identification plan for public networks
- MNC
- mobile network code
- 2 digits
- MSIN
- mobile station identification num
- 10 digits


###### tags: `DFI` `DISM` `School` `Notes`