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8/8/2019 Slide UMTS.08std

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Trng i hc Bch Khoa H Ni

Khoa in t Vin thng

Thng tin di ngMobile Communications

TS. Trng TunB mn K thut thng tin

H Ni, 10-2010


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2

Mng thng tin di ng 3G

UMTS / W-CDMA

(Universal Mobile Telecommunications System)

2. Nguyn l tri ph v s dng m trong UMTS2. Nguyn l tri ph v s dng m trong UMTS


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Multiple Access Schemes

Frequency Division Multiple Access (FDMA), different frequencies for differentusers

example Nordic Mobile Terminal (NMT) systems

Time Division Multiple Access (TDMA), same frequency but different timeslotsfor different users,

example Global System for Mobile Communication (GSM)

GSM also uses FDMA

Code Division Multiple Access (CDMA), same frequency and time but users areseparated from each other with orthogonal codes

Cod

e

Frequenc

yTim

e

1

2

N

TDMAFDMA CDMA


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Shannon Equation

C= Blog2 (1 + SNR)

B= Bandwidth

C= Channel

SNR = Signal-to-noise ratio


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CDMACDMA

Multiple users occupying the same band simultaneously by

having different codes is known as Code Division Multiple

Access or CDMA.

This leads to universal frequency reuse.

CDMA is a Spread Spectrum technique.

Direct Sequence - CDMA is used in mobile communication.

Data X Spread Data CarrierModulation

Code


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Spread Spectrum

Where does spread spectrum come from

First publications, late 40s

First applications: Military from the 50s

Rake receiver patent 1956 Cellular applications proposed late 70s

Investigations for cellular use 80s

IS-95 standard 1993 (2G)

1997/1998 3G technology choice

2001/2002 Commercial launch of WCDMAtechnology


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Direct Sequence

In direct sequence (DS) user bits are coded with unique binarysequence i.e. with spreading/channelization code

The bits of the channelization code are called chips

Chip rate (W) is typically much higher than bit rate (R)

Codes need to be in some respect orthogonal to each

other. Length of a channelization code

defines how many chips are used to spread a singleinformation bit and thus determines the end bit rate

Shorter code equals to higher bit rate but better Signalto Interference and Noise Ratio (SINR) is required Also the shorter the code, the fewer number of codes are available

Different bit rates have different geographical areascovered based on the interference levels


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Direct Sequence

Transmission (Tx) side with DS

Information signal is multiplied withchannelization code => spread signal

Receiving (Rx) side with DS

Spread signal is multiplied with channelizationcode

Multiplied signal (spread signal x code) is thenintegrated (i.e. summed together) If the integration results in adequately high (or low) values, the

signal is meant for the receiver


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Direct Sequence


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Direct Sequence

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