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

Introduction to Cellular Communications & CDMA

Prepared for Dr. John SantiagoCTU EE463 Communications II

Loren Karl Schwappach15 December 2010

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

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).

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

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.

Code Division Multiple Access 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) Uses chaotic generator function, for example:

Uses Gold sequence codes. Sounds cool right? See referenced IEEE paper for more. [16]


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2

121

G4 and Beyond 4G – 4th Generation Wireless Telephone Technology

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)

5G – 5th Generation Wireless Telephone Technology 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


http://news.bbc.co.uk/2/hi/programmes/click_online/8639590.stm

http://news.bbc.co.uk/2/hi/programmes/click_online/8639590.stm

http://www.worldmapper.org/display.php?selected=333

http://www.cbsnews.com/stories/2010/02/15/business/main6209772.shtml

http://library.thinkquest.org/04oct/00047/historycell.htm

http://www.smecc.org/mhlon_loomis.htm

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. ScienceDirectJournal (2008). Accessed 15 Dec 2010.


http://electronics.howstuffworks.com/cell-phone1.htm






Questions


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