Upgrade to Pro
— share decks privately, control downloads, hide ads and more …
Speaker Deck
Features
Speaker Deck
PRO
Sign in
Sign up for free
Search
Search
E716_lec08
Search
Ahmad El-Banna
December 02, 2014
Education
0
380
E716_lec08
7th Year, Integrated Technical Education Cluster AlAmeeria
lec#7, Mobile Communication Systems
Ahmad El-Banna
December 02, 2014
Tweet
Share
More Decks by Ahmad El-Banna
See All by Ahmad El-Banna
E716_lec12
ahmad_elbanna
0
1.4k
J601_lec12
ahmad_elbanna
1
830
E716_lec11
ahmad_elbanna
1
520
E716_lec10
ahmad_elbanna
0
460
J601_lec11
ahmad_elbanna
0
860
J601_lec10
ahmad_elbanna
1
860
E716_lec09
ahmad_elbanna
0
580
J601_lec09
ahmad_elbanna
0
460
J601_lec08.pdf
ahmad_elbanna
1
940
Other Decks in Education
See All in Education
Requirements Analysis and Prototyping - Lecture 3 - Human-Computer Interaction (1023841ANR)
signer
PRO
0
770
小学生にスクラムを試してみた件~中学受検までの100週間の舞台裏~
ukky86
0
320
不登校予防・再登校支援プログラムを提供するToCo (トーコ) の会社紹介資料 toco.mom
toco3week
0
330
Flinga
matleenalaakso
2
13k
Introduction - Lecture 1 - Web Technologies (1019888BNR)
signer
PRO
0
4.8k
オープンソース防災教育ARアプリの開発と地域防災での活用
nro2daisuke
0
150
Zoom-ohjeet
matleenalaakso
7
7.2k
1030
cbtlibrary
0
290
cbt2324
cbtlibrary
0
110
"数学" をプログラミングしてもらう際に気をつけていること / Key Considerations When Programming "Mathematics"
guvalif
0
540
寺沢拓敬 2024. 09. 「言語政策研究と教育政策研究の狭間で英語教育政策を考える」
terasawat
0
200
RSJ2024学術ランチョンセミナー「若手・中堅による国際化リーダーシップに向けて」資料 (河原塚)
haraduka
0
210
Featured
See All Featured
KATA
mclloyd
29
13k
Stop Working from a Prison Cell
hatefulcrawdad
267
20k
A Modern Web Designer's Workflow
chriscoyier
692
190k
BBQ
matthewcrist
85
9.3k
The Power of CSS Pseudo Elements
geoffreycrofte
72
5.3k
Into the Great Unknown - MozCon
thekraken
31
1.5k
Java REST API Framework Comparison - PWX 2021
mraible
PRO
28
7.9k
Templates, Plugins, & Blocks: Oh My! Creating the theme that thinks of everything
marktimemedia
26
2.1k
Building Better People: How to give real-time feedback that sticks.
wjessup
363
19k
Why You Should Never Use an ORM
jnunemaker
PRO
53
9k
How GitHub (no longer) Works
holman
311
140k
Understanding Cognitive Biases in Performance Measurement
bluesmoon
26
1.4k
Transcript
Lecture #8 2G CDMA Mobile Systems Instructor: Dr. Ahmad El-Banna
December 2014 E-716-A Mobile Communications Systems Integrated Technical Education Cluster At AlAmeeria © Ahmad El-Banna
Agenda 2G in Egypt Second Generation CDMA • Introduction to
CDMA • IS-95 system 2 E-716-A, Lec#8 , Dec 2014 © Ahmad El-Banna
2G IN EGYPT 3 © Ahmad El-Banna E-716-A, Lec#8 ,
Dec 2014
2G in Egypt • Mobinil • 1998, Buy the 1st
mobile license in Egypt from Telecom Egypt. • Contributors: Orascom Telecom Egypt &France Telecom Orange . • First announcement of EDGE Technology. • First usage of Micro BTS to cover El-Azhar tunnels and Metro/Subway stations. • Vodafone • 1998, got the 2nd mobile license in Egypt. • Known as (misr phone/ Click GSM) • Contributors: Vodafone, air touch and some local & International partners. • 2002, Vodafone Egypt instead of Click GSM. • 2007, 54.93% for Vodafone & 44.94% Telecom Egypt & 0.13 % free • Etisalat • In 2007, got the 3rd mobile license in Egypt. • Contributors: Etisalat Emirates , Egypt Post, NBE bank & others. • The first 3G (3.5 G) services (video call, mobile TV, .. ) in Egypt. • 1 million subscriber in 50 days ! • Currently provide 2G & 3G services. 4 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
2G CDMA 5 © Ahmad El-Banna E-716-A, Lec#8 , Dec
2014
2G CDMA • Higher quality signals • Higher data rates
• Support of digital services • Greater capacity • Digital traffic channels • Support digital data • Voice traffic digitized • User traffic (data or digitized voice) converted to analog signal for transmission • Encryption • Simple to encrypt digital traffic • Error detection and correction • Very clear voice reception • Channel access • Channel dynamically shared by users via Time division multiple access (TDMA) or code division multiple access (CDMA) • Each cell allocated frequency bandwidth • Split in two • Half for reverse, half for forward • Direct-sequence spread spectrum (DSSS) 6 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
CDMA Advantages • Frequency diversity • Frequency-dependent transmission impairments (noise
bursts, selective fading) have less effect • Multipath resistance • DSSS overcomes multipath fading by frequency diversity • Also, chipping codes used only exhibit low cross correlation and low autocorrelation • Version of signal delayed more than one chip interval does not interfere with the dominant signal as much • Privacy • From spread spectrum (see chapter 9) • Graceful degradation • With FDMA or TDMA, fixed number of users can access system simultaneously • With CDMA, as more users access the system simultaneously, noise level and hence error rate increases • Gradually system degrades 7 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
CDMA Disadvantages • Self-jamming • Unless all mobile users are
perfectly synchronized, arriving transmissions from multiple users will not be perfectly aligned on chip boundaries • Spreading sequences of different users not orthogonal • Some cross correlation • Distinct from either TDMA or FDMA • In which, for reasonable time or frequency guardbands, respectively, received signals are orthogonal or nearly so • Near-far problem • Signals closer to receiver are received with less attenuation than signals farther away • Given lack of complete orthogonality, transmissions from more remote mobile units may be more difficult to recover 8 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
CDMA Design Consideration (RAKE Receiver) • If multiple versions of
signal arrive more than one chip interval apart, receiver can recover signal by correlating chip sequence with dominant incoming signal • Remaining signals treated as noise • Better performance if receiver attempts to recover signals from multiple paths and combine them, with suitable delays • Original binary signal is spread by XOR operation with chipping code • Spread sequence modulated for transmission over wireless channel • Multipath effects generate multiple copies of signal • Each with a different amount of time delay (1, 2, etc.) • Each with a different attenuation factors (a1, a2, etc.) • Receiver demodulates combined signal • Demodulated chip stream fed into multiple correlators, each delayed by different amount • Signals combined using weighting factors estimated from the channel 9 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
Principal of RAKE Receiver 10 © Ahmad El-Banna E-716-A, Lec#8
, Dec 2014
IS-95 Channel Structure 11 © Ahmad El-Banna E-716-A, Lec#8 ,
Dec 2014 • IS-95 • Second generation CDMA scheme • Primarily deployed in North America • Transmission structures different on forward and reverse links
IS-95 Forward Link • Up to 64 logical CDMA channels
each occupying the same 1228- kHz bandwidth • Four types of channels: • Pilot (channel 0) • Continuous signal on a single channel • Allows mobile unit to acquire timing information • Provides phase reference for demodulation process • Provides signal strength comparison for handoff determination • Consists of all zeros • Synchronization (channel 32) • 1200-bps channel used by mobile station to obtain identification information about the cellular system • System time, long code state, protocol revision, etc. 12 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
IS-95 Forward Link.. • Paging (channels 1 to 7) •
Contain messages for one or more mobile stations • Traffic (channels 8 to 31 and 33 to 63) • 55 traffic channels • Original specification supported data rates of up to 9600 bps • Revision added rates up to 14,400 bps • All channels use same bandwidth • Chipping code distinguishes among channels • Chipping codes are the 64 orthogonal 64-bit codes derived from 64 64 Walsh matrix 13 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
Forward Link Processing • Voice traffic encoded at 8550 bps
• Additional bits added for error detection • Rate now 9600 bps • Full capacity not used when user not speaking • Quiet period data rate as low as 1200 bps • 2400 bps rate used to transmit transients in background noise • 4800 bps rate to mix digitized speech and signaling data • Data transmitted in 20 ms blocks • Forward error correction • Convolutional encoder with rate ½ • Doubling effective data rate to 19.2 kbps • For lower data rates encoder output bits (called code symbols) replicated to yield 19.2-kbps • Data interleaved in blocks to reduce effects of errors by spreading them 14 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
Scrambling • After interleaver, data scrambled • Privacy mask •
Prevent sending of repetitive patterns • Reduces probability of users sending at peak power at same time • Scrambling done by long code • Pseudorandom number generated from 42-bit-long shift register • Shift register initialized with user's electronic serial number • Output of long code generator is at a rate of 1.2288 Mbps • 64 times 19.2 kbps • One bit in 64 selected (by the decimator function) • Resulting stream XORed with output of block interleaver 15 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
Power Control & DSSS • Next step inserts power control
information in traffic channel • To control the power output of antenna • Robs traffic channel of bits at rate of 800 bps by stealing code bits • 800-bps channel carries information directing mobile unit to change output level • Power control stream multiplexed into 19.2 kbps • Replace some code bits, using long code generator to encode bits 16 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014 DSSS: • Spreads 19.2 kbps to 1.2288 Mbps • Using one row of Walsh matrix • Assigned to mobile station during call setup • If 0 presented to XOR, 64 bits of assigned row sent • If 1 presented, bitwise XOR of row sent • Final bit rate 1.2288 Mbps • Bit stream modulated onto carrier using QPSK • Data split into I and Q (in-phase and quadrature) channels • Data in each channel XORed with unique short code • Pseudorandom numbers from 15-bit-long shift register
Forward Link Transmission 17 © Ahmad El-Banna E-716-A, Lec#8 ,
Dec 2014
Reverse Link • Up to 94 logical CDMA channels •
Each occupying same 1228-kHz bandwidth • Supports up to 32 access channels and 62 traffic channels • Traffic channels mobile unique • Each station has unique long code mask based on serial number • 42-bit number, 242 – 1 different masks • Access channel used by mobile to initiate call, respond to paging channel message, and for location update 18 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
Reverse Link Processing and Spreading • First steps same as
forward channel • Convolutional encoder rate 1/3 • Tripling effective data rate to max. 28.8 kbps • Data block interleaved • Spreading using Walsh matrix • Use and purpose different from forward channel • Data from block interleaver grouped in units of 6 bits • Each 6-bit unit serves as index to select row of matrix (26 = 64) • Row is substituted for input • Data rate expanded by factor of 64/6 to 307.2 kbps • Done to improve reception at BS • Because possible codings orthogonal, block coding enhances decision- making algorithm at receiver • Also computationally efficient • Walsh modulation form of block error-correcting code • (n, k) = (64, 6) and dmin = 32 • In fact, all distances 32 19 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
Data Burst Randomizer & DSSS • Reduce interference from other
mobile stations • Using long code mask to smooth data out over 20 ms frame DSSS: • Long code unique to mobile XORed with output of randomizer • 1.2288-Mbps final data stream • Modulated using orthogonal QPSK modulation scheme • Differs from forward channel in use of delay element in modulator to produce orthogonality • Forward channel, spreading codes orthogonal • Coming from Walsh matrix • Reverse channel orthogonality of spreading codes not guaranteed 20 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
21 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014 Reverse
Link Transmission
22 © Ahmad El-Banna E-716-A, Lec#8 , Dec 2014
• For more details, refer to: • Chapter 4, J.
Chiller, Mobile Communications, 2003. • Chapter 10, W. Stallings, Wireless Communications and Networks, 2005. • The lecture is available online at: • https://speakerdeck.com/ahmad_elbanna • For inquires, send to: •
[email protected]
23 E-716-A, Lec#7 , Nov 2014 © Ahmad El-Banna