ADAPTIVE MODULATION TECHNIQUES FOR CAPACITY IMPROVEMENT OF BER IN WCDMA

ADAPTIVE MODULATION TECHNIQUES FOR

CAPACITY IMPROVEMENT OF BER IN WCDMA

Presented By:

Mirza Asif HaiderID No. 1308023

Department of Electronics And Telecommunication EngineeringChittagong University of Engineering And Technology

Contents:

1. Introduction2. WCDMA3. Adaptive Modulation4. BER in QPSK and QAM5. Improvement of Traditional QAM

INTRODUCTION:

The specific objectives of the research are: (1) To evaluate the effects of noise on the bit error rate and throughputs on a W- CDMA network.

(2) Evaluation of Bit Error rate of QAM and QPSK system versus signal to noise ratio (SNR) are used to evaluate system for adaptive modulation for capacity improvement.

OBJECTIVES OF THIS PRESENTATION:

Introduction :

W-CDMA (Wide- band Code Division Multiple Access )

that allows a large number of users to share access to a single communication channel by encoding their data with a special pseudo noise (PN) code for each channel

spread spectrum technique

Introduction :

W-CDMA (Wide- band Code Division Multiple Access )

W- CDMA offers many advantages which includes :

W- CDMA

jam resistance

privacy

flexibility

a greater cellular spectral efficiency than

2G systems

3,84 Mcps chipping rate

5 MHz bandwidth for

one user CDMA has been considered and recognized as a viable alternative to both FDMA and TDMA

WCDMA used by Universal Mobile Telecommunication System (UMTS) as platform of the 3rd generation cellular communication system.

W-CDMA uses noise-like broadband frequency spectrum where it has high resistance to multipath fading where as this was not present in conventional narrowband signal of 2nd generation (2G) communication system.

Adaptive Modulationan Adaptive modulation in cognitive radio as: ―an intelligent wireless communication system that is aware of its environment― uses the understanding-by-building methodology to learn from the environment and adapt to statistical variations in the input stimuli.

Adapting Modulation provides many parameters that can be adjusted relative to the :• Channel Fading • Including data rate • Transfer Power• Instantaneous BER

-spectral efficiency -probability of bit error

USE of Adaptive Modulation :

transmit simultaneously at equal powersthe receiver will receive more power from the nearest transmitter

One‘s transmitted signal is the other‘s noise, the signal-to-noise ratio (SNR) for the farther transmitter is much lower

the nearest transmitter transmits a signal of magnitude higherthe SNR for the Further may be below detect ability

higher magnitude

lowerMagnitude

and SNR

Below detect ability

the nearest transmitter ---uses less power---higher order modulation techniques so that the SNR for all transmitters at the receiver is roughly the same.

Why We Use Adapting Modulation in WCDMA:

SourceModulatio

nselector

Modulator Power

Fading

Demodulator

Channel StateAnd

QualityEstimato

r

Sink

Feedback

Fig::Block Diagram of Link Adaption Mechanism

Block Diagram of Adapting Modulation in WCDMA:

The received SNR and path loss exponent is used as the channel metric to decide on the modulation type .

Channel State And Quality Estimator

path loss exponent is small choose QPSK and when it is large Choose QAM.

There also exists a SNR target for satisfying the target BER

Performance of WCDMA system using 16-QAM:

Performance of WCDMA System using QPSK:

Curve is more striper than !6-QAM

. Comparison between QPSK and 16-QAM modulation schemes shows that

--the new simple 4-state trellis-coded adaptive MQAM achieves 3-dB effective coding gain relative to un-coded adaptive M-QAM

--3.6 dB for 8-state trellis. Compared with traditional trellis codes and fixed-rate modulation, the new scheme showed more than 20 dB power savings.

16-QAM performs very poorly in both AWGN and AWGN with multipath fading channel

IMPROVEMENT of M-QAM:

Conclusions:

• WCDMA technique• Adaptive Modulation• BER of QPSK and MQAM• Improvement of MQAM

THANK YOU

QUESTIONS:1. W- CDMA cellular systems2. BASIC difference between WCDMA and CDMA3. jam resistance:4. Mcps5. Throughputs6. Trellis Coded Modulation7. Quadrature Phase Shift Keying (QPSK)8. M-ARY QUADRATURE AMPLITUDE MODULATION (QAM)

W-CDMA (Wide- band Code Division Multiple Access )

W- CDMA cellular systems use a form of direct sequence CDMA (DS- CDMA). Third generation systems use W-CDMA as the carrier modulation scheme ; this is because of the many advantages that it offers.

jam resistance:

Anti-jamming is the process of applying certain techniques to a signal to make effective jamming impractical. Techniques for anti-jamming involve spreading the frequency spectrum to be very wide band or hopping the frequency unpredictably to avoid any basic blocking.

The basic difference between the CDMA and WCDMA is bandwidth ,CDMA uses 1.25 MHz frequency bandwidth while WCDMA uses 5 MHz bandwidth.

Again CDMA is 2g telecommunication standard and provide very less data rates compared to WCDMA which is third generation technology.

CDMA being 2g standard provide mainly circuit switched services while WCDMA being used in UMTS system is used in both circuit switched and packet switched networks.

BASIC difference between WCDMA and CDMA

Megachips per second (Mcps) is a measure of the speed with chips are generated in Direct Sequence Spread Spectrum (DSSS) signals. This speed is also known as the chipping rate. A speed of 1 Mcps is equivalent to 1,000,000, or 106, chips per second

The chip rate of a code is the number of pulses per second (chips per second) at which the code is transmitted (or received).

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwijqv_E2NnPAhXBso8KHZt5BQcQFgg2MAQ&url=https%3A%2F%2Fwww.clear.rice.edu%2Felec301%2FProjects01%2Fcdma%2Fcompare.html&usg=AFQjCNGSU1Cf4Zwi9Pj2COtUx6t4491FDA

Trellis Coded ModulationIn simplest terms it is a combination of coding and modulationwhere the word trellis Stand for the use of trellis (also called convolutional) codes. Whereas we normally talk about coding and modulation as two independent Aspects of the communications link, in TCM they are combined.

The throughputs defined as the number of bits per second correctly received

4-state trellis-coded adaptive MQAM achieves 3-dB effective coding gain relative to un-coded adaptive M-QAM

8-state trellis-coded adaptive MQAM achieves 3.6-dB effective coding gain relative to un-coded adaptive M-QAM

V. MODULATION SCHEMES IN WIRELESS SYSTEMS

Quadrature Phase Shift Keying (QPSK) is a digital modulation technique. Quadrature Phase Shift Keying (QPSK) is a form of Phase Shift Keying in which two bits are modulated at once, selecting one of four possible carrier phase shifts (0, Π/2, Π, and 3Π/2).

QPSK perform by changing the phase of the In-phase (I) carrier from 0° to 180° and the Quadrature-phase (Q) carrier between 90° and 270°. Which indicate the four states of a 2-bit binary code. Each state of these carriers is referred to as a Symbol [4]

Quadrature Phase-shift Keying (QPSK) is a widely used method of transferring digital data by changing or modulating the phase of a carrier signal.

In PSK all points lie on a circle so the I and Q values are related to each other.PSK signals are constant envelops because of this; all points have the same amplitude. If we allow the phase and amplitude to change from symbol to symbol, then we get a modulation called quadrature amplitude modulation (QAM).

VI. M-ARY QUADRATURE AMPLITUDE MODULATION (QAM)

It can be considered a linear combination of two DSB-SC.so it is an AM and a PM modulation at same time.

used to create an hybrid type of modulation that varies both in amplitude and the phase. When M=16,we have 16 symbols, each representing a four bit word. We can lay these out in a circle but they would be too close an error rate is likely to be high.