Ee463 cellular comm & cdma - comm 2 presentation - loren schwappach

Introduction to Cellular
Communications & CDMA
Prepared for Dr. John Santiago
CTU EE463 Communications II
Loren Karl Schwappach
15 December 2010

CTU : EE463 Communications II : Introduction to Cellular Communications & CDMA : Loren K. Schwappach 1

Objectives:
 Cellular Communications
 Brief History of Mobile Phones
 The Cellular Concept
 Frequency Reuse
 Handoffs
 G1-G3 Explained
 Frequency Division Multiple Access (FDMA)
 Time Division Multiple Access (TDMA)
 Frequency and Time Division Multiple Access (F/TDMA)

 Code Division Multiple Access (CDMA)
 G4 and Beyond
 Final Conclusions
 References
 Questions

NOTE: If you would like to explore any information on this presentation outside of class I
have used reference blocks “[ ]” throughout this presentation to indicate a recommended
source (see references slide).

CTU : EE463 Communications 2 : Cellular Communications & Introduction to CDMA : Loren K. Schwappach 2

Cellular Communications
 Cellular technology:
 Fastest growing technology on the planet and utilized by billions of
people around the world.

 No longer limited to voice:
• Cell phones are now capable of providing: Calculators, alarm clocks, contact
databases, appointment reminders, day-to-day organizers, Short Message Service
(SMS) a.k.a. texting services (used by 74% of all subscribers), games, e-mail, internet
browsers, radio, MP3 players, streaming video players, Bluetooth, digital cameras, GPS
receivers, and more.

 First handheld mobile phone (invented by Martin Cooper) was
demonstrated in 1973 by Motorola. [1]
• Motorola released the first commercially available mobile phone (DynaTAC 8000x in
1983), by 1990, 12.4 million people worldwide had cellular subscriptions. [3]

 There were approximately 4.6 billion worldwide cellular phone
subscriptions by the end of 2009. [4]


History
 1837 – Samuel Morse patents the electromagnetic telegraph. [5]
 1843 - Michal Faraday performs studies to see if space could conduct electricity.
[6]
 1860s – James Clerk Maxwell predicts the existence of radio waves (Publishes
Treatise on Electricity and Magnetism {Maxwell’s Equations} in 1873).
 1865 – Dr. Mahlon Loomis becomes the first person to communicate through the
atmosphere wirelessly (14-18 miles) using a wireless telegraph (awarded
50,000 for his research). [7]
 1876 – Alexander Bell invents the telephone. [5]
 1887 – Heinrich Hertz generates radio waves and demonstrates they share the
same properties as light. [5]
 1896 – Guglielmo Marconi files patents on wireless transmission by radio.
 Although the actual inverter of the radio is highly debatable and most historians credit the invention
to either Guglielmo Marconi, Nikola Tesla, Alexander Popov, Sir Oliver Lodge, Reginald Fessanden,
Heinrich Hertz, Amos Dolbear, Mahlon Loomis, Nathan Stubblefield, and/or James Clerk Maxwell.
[8]


History Continued..
 1902 – Reginald Fessenden invents AM radio broadcasting. [5]
 1919 – Edwin Armstrong invents the super heterodyne radio receiver. [5]
 1933 – Edwin Armstrong invents FM for radio transmission. [5]
 1938 – H.A. Reeves invents pulse code modulation (PCM). [5]
 1940s – Radiotelephones were introduced in the United States. [8]
 1973 – Martin Cooper invents the first Mobile phone (previous slide). [5]
 1970s – Advanced mobile phone system (AMPS) is launched as a 1G FDMA
mobile phone system.
 1980s – 2G digital systems are developed. Global System for mobile
Communication (GSM) was the first commercially operated 2G system based on
TDMA.
 2001 – The first 3G network (actually 2.5G network) using TDMA was developed
in Japan.
 2000s – True 3G networks appear based on advanced CDMA technology.
 Today – pre-4G networks are in the market and true 4G networks in
development .
 Tomorrow – Nearly instant Terabit per second wireless audio/video data
transfers changing the world as we know it today.


The Cellular Concept
 In an analog cell-phone system in the US, the cell-
phone carrier receives about 832 frequencies to use
across the city. [9]
 The carrier chops up the city into a grid of large (10
square mile, 26 square kilometer) hexagonal cells. [9]
 Each cell has a base station consisting of a small
building and a tower. [9]


Frequency Reuse
 A single Analog cell-phone system
 Uses one-seventh of the available duplex (2-way) voice channels
for a unique set of frequencies without collisions. [9]
 As mentioned a cell-phone carrier typically gets 832 radio
frequencies. [9]
• Since each cell phone uses two frequencies per call there are typically 395 voice
channels per carrier (42 are used as control channels).
• Therefore each cell has about 56 channels in an analog system.
• Common 2G TDMA based systems can carry approximately three times as many
channels per cell. Newer 3G CDMA based systems carry even more.
 Cell phones have low-power transmitters in them and typically
have two signal strengths (0.6W and 3W). [9]
 The Base Station performs power balancing and also transmits at
low power allowing frequency reuse. [9]
• This cellular approach requires a large number of bases (hundreds in most
cities).
 Each Base Station also has communication with the Mobile
Telephone Switching Office (MTSO). [9]


Handoffs
 All Cell phones have special codes associated to them.
These codes are used to identify the phone, the
phones owner and the service provider. [10]
 System Identification Code (SID) – A unique 5-digit number
assigned to each carrier by the FCC (Programmed into the phone).
[10]
 Mobile Identification Number (MIN) – A 10-digit number derived
from you phone’s number. [10]
 Electronic Serial Number (ESN) – A unique 32-bit number
programmed into the phone when it is manufactured. [10]


Handoffs
 When you power up the phone it begins listening for
a SID using a control channel (freq used by phone and
base station to communicate). [10]
 If no control channels are available you receive a “no service”
indication.
 When the phone receives a SID, the phone compares
it to the SID programmed into the phone. [10]
 If correct it begins communication with the base station.
 If not correct then the phone knows it is roaming (using another
carrier) and you may be subject to large roaming fees.
 Along with the SID the phone transmits a registration
request (consisting of the SID, MIN, and ESN) to the
connected base station. [10]
 This lets the MTSO keep track of your phone in it’s database. This
allows the MTSO to know which cell you are in.


Handoffs Continued..
 Now the MTSO picks a frequency pair for your phone to
use and communicates it to your phone from the base
station over the control channel. [10]

 Now that your phone and base station are using the
frequency pair your call is connected and the base station
keeps track of the signal strengths of your frequency pair.
[10]

 As you move toward the edge of your cell, you cell’s base
station reports to the MTSO that your signal strength is
diminishing. Meanwhile the base station you are
approaching detects your signal strength increase and
both stations report to the MTSO to coordinate a new
frequency pair for your phone and the approaching base
station. [10]


Handoffs Continued..
 After some time your phone gets a signal on a control
channel informing your phone to change frequencies.
[10]
 This process is called Handoff and attempts to keep
you connection intact while traversing through cells.


G1 – G3 Explained
 1G – 1st Generation Wireless Telephone Technology
 Unencrypted analog system for mobile communications.
 1970s technology using Frequency Division Multiple Access (FDMA) technology.

 2G – 2nd Generation Wireless Telephone Technology
 Digitally encrypted phone conversations.
 Initially launched in 1991 on the GSM standard using TDMA technology.
 GSM (TDMA based) accounts for approximately 80% of worldwide subscribers.
 IS-95 (CDMA based) a newer standard than GSM accounts for the majority of US
subscribers and approximately 17% of worldwide subscribers.
 2.5G standards using GPRS (uses a modified form of TDMA) for up to 115 Kbps.
 2.75G standards using EDGE supports data rates up to 236.8Kbps using 8PSK
encoding.

 3G – 3rd Generation Wireless Telephone Technology [11]
 Digital Standards launched initially by Japan in 2001.
 Provides mobile broadband access of several Mbps.
 CDMA2000 (CDMA based) supports up to 14.7Mbps.
 Uses 1.8 – 2.5GHz Frequency Band.

 4G – 4th Generation Wireless Telephone Technology
 I’ll talk about this later.


Frequency Division Multiple Access (FDMA)
 Used by Analog mobile phones.
 Band of Frequencies is broken up into smaller bands.
 Each transmitter transmits using radio waves in its own
sub-band.
 AMPS the first 1G implementation used 30KHz for each
user.
 Pros:
 Simple Design
 No Inter-symbol Interference (ISI)
 No interference among users in a cell.
 Cons:
 Narrowband interference
 Static spectrum allocation (less secure)
 Freq. reuse problems
 Requires High Q analog filters or large guard bands.


Frequency Division Multiple Access
(FDMA)


Time Division Multiple Access (TDMA)
 In pure TDMA, the base station does not split up its
allocated frequency band into smaller sub-bands.
 Communicates with users one at a time through time
partitioning.
 Pros:
 Suited for digital.
 Higher capacity than FDMA.
 High Q filters are not required.
 Cons:
 Very susceptible to jamming, and other-cell interference.
 Requires equalizers.


Time Division Multiple Access (TDMA)


Frequency and Time Division Multiple Access
(F/TDMA)
 F/TDMA is the real TDMA implemented by most providers
(2G technology).
 IS-54 (2G) used 30 KHz channels with three users sharing
them (3 slots).
 GSM (2G) uses 270KHz channels with eight users sharing
them (8 slots).
 Pros:
 Better suited for digital.
 Higher capacity than FDMA and TDMA alone.
 High Q filters are not required.
 Cons:
 Strict synchronization and guard time needed.
 Still susceptible to jamming, and other-cell interference.
 Requires equalizers.


Frequency and Time Division Multiple
Access (F/TDMA)


Code Division Multiple Access (CDMA)
 All users communicate with the receiver at the same
time and using the same set of frequencies.
 This means all users interfere with each other.
 How would you separate the users from interfering
with each other?...

 CDMA controls this interference by assigning each
user a unique code.


Code Division Multiple Access


Why use CDMA?
 Higher capacity than TDMA and FDMA.
 CDMA systems can reuse frequencies in every cell.
 No guard bands or guard times are typically required.
 No equalizer is typically required.
 Improved performance due to diversity. [12]
 Lower mobile transmit power . [12]
 Longer battery life.
 Variable transmission rate with voice activity detection.


Why use CDMA?
 Allows soft handoff. [15 ]
 Combats user interference. [12] & [13]
 If a user doesn’t have anything to send, it causes less interference
to other users of the system.
 Is a form of Spread-Spectrum technology making it
usable for military use.
 Cells can use directional antennas to “sectorize” the
cell. [14]
 120 degree antennas can create 3-sector cells which
is very common (triples capacity).
 All 3G Systems use CDMA!


Why use CDMA?
 Cons:
 Requires tight synchronization to use orthogonal codes.
 Quasi-orthogonal codes cause self-interference.
 Near-far problem is a serious hindrance, requiring fast and
accurate power control measures.

 Near-far Problem:
 Users near the base receive high power
 Users far from the base receive low power


Low-Bandwidth Signal:

High-Bandwidth Spreading Code:

Mix is a simple multiply

… and transmit.


To Decode / Receive, take the signal:

Multiply by the same Spreading Code:

… to get ...



Don’t ask me to explain this:
However, this ones for Dr. Santiago..
It uses the Welsh coding scheme.


 Direct Sequence CDMA (DS-CDMA) [16]
 Classical DS-CDMA uses binary pseudo-noise (PN) codes.
• Synchronization problem solved using an acquisition search by searching all
phase delays (accomplished with a delay lock loop (DLL)), and a
 Chaotic signals can offer very attractive properties such as the
security of transmission and low probability of interception .
 Chaos-based DS-CDMA with additive pilot signals
(ACAS-A)
 1 2 x
2
 Uses chaotic generator function, for example: k 1 k x
 Uses Gold sequence codes. Sounds cool right? See referenced IEEE
paper for more. [16]


G4 and Beyond
 Must meet speed requirements of 100s of Mbps.
 Pre-4G technologies include: mobile WiMAX, and LTE
 4G standards in development: IEEE 802.16m (1 Gbps), Flash-
OFDM (uses OFDM system, remember a presentation on OFDM
this November?)
 iBurst and MBWA (uses High Capacity Spatial Division Multiple
Access (HC-SDMA) a technology beyond my current level of
understanding)

 Standard beyond the 4G standard expected to be finalized by 2013.
 Implementation expected around 2020
 Who knows what kind of throughputs and technologies the new
standard will introduce..


Final Conclusions
 TODAY WE LEARNED LOTS ABOUT:
 The History of Mobile Phones
 The Cellular Concept
 Frequency Reuse
 Handoffs
 G1-G3 Technologies
 Frequency Division Multiple Access (FDMA)
 Time Division Multiple Access (TDMA)
 Frequency and Time Division Access (F/TDMA)
 Code Division Multiple Access (CDMA)
 Chaos Based DS-CDMA
 G4 and Beyond


References
 [1] Teixeira, Tania. “Meet Marty Cooper – the inventor of the mobile phone." BBC News. 23 April
2010. Retrieved 15 December 2010. Website:
http://news.bbc.co.uk/2/hi/programmes/click_online/8639590.stm

 [2] Teixeira, Tania. Photograph of Martin Cooper, Inventor of the mobile phone. BBC News. 23 April
2010. Retrieved 15 December 2010. Website:
http://news.bbc.co.uk/2/hi/programmes/click_online/8639590.stm

 [3] “Cellular Subscribers 1990“. Worldmapper the world as you’ve never seen it before.
WorldMapper. 23 April 2010. Retrieved 15 December 2010.
http://www.worldmapper.org/display.php?selected=333

 [4] “Number of Cell Phones Worldwide Hits 4.6B”. CBS News. GENEVA. 15 February 2010.
Retrieved 15 December 2010. Website:
http://www.cbsnews.com/stories/2010/02/15/business/main6209772.shtml

 [5] Ulaby, F., “Fundamentals of Electromagnetics Fifth Edition”. Pearson Prentice Hall, Upper Saddle
River, NJ, 2007.

 [6] “The History of Cell Phones”. ORACLE ThinkQuest Projects by Students for Students. Retrieved
15 December 2010. Website: http://library.thinkquest.org/04oct/00047/historycell.htm

 [7] “Mahlon Loomis”. CBS News. GENEVA. 15 February 2010. Retrieved 15 December 2010.
Website: http://www.smecc.org/mhlon_loomis.htm

 [8] Burande, Abhay. “History of the Radio – Who Invented the Radio”. Buzzle.com Retrieved 15
December 2010. Website: http://www.buzzle.com/articles/history-of-radio-who-invented-the-
radio.html


References:
 [9] “HowStuffWorks Cell Phone Frequencies”. HowStuffWorks.com Retrieved 15 December 2010.
Website: http://electronics.howstuffworks.com/cell-phone1.htm

 [10] “HowStuffWorks Cell Phone Codes”. HowStuffWorks.com Retrieved 15 December 2010.
Website: http://electronics.howstuffworks.com/cell-phone3.htm

 [11] Degada A., Channel Estimation and Rake Reception for 3G Air Interface Wideband Coded
Division Multiple Access. IEEE (2009). Accessed 15 Dec 2010.

 [12] Brown T., Ghazi-Moghadam V., Kaveh M., Detection of Code Division Multiple Access Signals in a
Multiuser Environment Using Antenna Arrays. IEEE (1995). Accessed 15 Dec 2010.

 [13] Jeng W., Su T., Hsieh W., Using Code Division Technique to Improve the Performance of Ad Hoc
Wireless Network. IEEE (2005). Accessed 15 Dec 2010.

 [14] Haghighi S., Varadharajan K., Varadharajan V., Mohammadi-Nodooshan V., Overhearing Gain
Analysis in Low-Traffic CDMA Wireless Sensor Networks. IEEE (2010). Accessed 15 Dec 2010.

 [15] He Z., Ye F., Wang C., Junyao M., Li W., Tao Z. Huang D. A Quick Distributed Soft Handoff Method
in CDMA System Based on Mobile Agent. IEEE (2010). Accessed 15 Dec 2010.

 [16] Kaddoum G., Roviras D., Charge P., Fournier-Prunaret D., Signal Processing 89. ScienceDirect
Journal (2008). Accessed 15 Dec 2010.


Questions


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