IMPACT OF DIVERSITY TECHNIQUES IN WIRELE

IMPACT OF DIVERSITY TECHNIQUES IN WIRELESS COMMUNICATION SYSTEMS : 

IMPACT OF DIVERSITY TECHNIQUES IN WIRELESS COMMUNICATION SYSTEMS

Created by Md. Abu Ayub Ansari : 

Created by Md. Abu Ayub Ansari

INTRODUCTION : 

INTRODUCTION Purpose Objectives Expected Benefits

PURPOSE : 

PURPOSE An overview of diversity techniques. How diversity technique can be utilized for performance improvement. Provide MATLAB computing to understand the performance improvement using diversity technique.

OBJECTIVES : 

OBJECTIVES To acquire an update on the development of mobile phone technologies with potential for supporting our own future carrier. To learn about the present wireless communication condition in our country. To demonstrate some latest technologies in communication field How diversity techniques are used to improve the performance of the radio channel without any increase in the transmitted power. To evaluate the system performance degradation due to fading. To undergo mathematical analysis and MATLAB simulation for analyzing the performance of Raleigh fading channels. To study Uniqueness of Mobile Radio Environment. To overall basic knowledge about telecommunication.

EXPECTED BENEFITS : 

EXPECTED BENEFITS To know about the recent status of telecommunication sector To work on the improvement of the communication services Diversity is now being considered as one of the most solution to mitigate the fading problem in wireless communication.

Communication : : 

Communication : Communication signifies transmission, reception and processing of information by electric means.

COMMUNICATION SYSTEM : 

COMMUNICATION SYSTEM

THE PROCESS OF COMMUNICATION BROKEN DOWN INTO DISCRETE COMPONENTS : 

THE PROCESS OF COMMUNICATION BROKEN DOWN INTO DISCRETE COMPONENTS An information source, presumably a person who creates a message. The message, which is both sent by the information source and received by the destination. A transmitter, a telephone instrument that captures an audio signal, converts it into an electronic signal, and amplifies it for transmission through the telephone network. A carrier or channel, which acts as a bridge between the transmitter and receiver. As the signal propagates through the channel, it gets attenuated due to transmission loss and distorted due to various nonlinear effects and interference. Channel can consist of a pair of wires, a coaxial cable or a radio link through free space Noise, in the form of secondary signals that obscure or confuse the signal carried Receiver It extracts the weakened and distorted signal from the channel, amplifies it and restores it to its original form and then passes it into the message destination.

BRANCHES OF COMMUNICATION : 

BRANCHES OF COMMUNICATION OPTICAL COMMUNICATION SYSTEM RADIO COMMUNICATION POWER LINE COMMUNICATIONS SYSTEMS DUPLEX COMMUNICATION SYSTEM TACTICAL COMMUNICATIONS SYSTEM WIRELESS COMMUNICATION

WIRELESS COMMUNICATION : 

WIRELESS COMMUNICATION The transfer of information over a distance without the use of electrical conductors or "wires“ An electromagnetic signal is created, modulated, amplified, and broadcast to one or more receivers that can be fixed or mobile.

BASICS OF A WIRELESS SYSTEMS : 

BASICS OF A WIRELESS SYSTEMS Every wireless system must have the basics of a transmitter (modulation), receiver (demodulation) and a channel (frequency) to transmit the signal from a stationary or mobile reference.

Slide 13: 

A TYPICAL GSM BASE STATION

KEY FREQUENCY BANDS FOR WIRELESS COMMUNICATION : 

KEY FREQUENCY BANDS FOR WIRELESS COMMUNICATION

APPLICATIONS OF WIRELESS TECHNOLOGY : 

APPLICATIONS OF WIRELESS TECHNOLOGY SECURITY SYSTEMS TELEVISION REMOTE CONTROL CELLULAR TELEPHONY (PHONES AND MODEMS) Wi–Fi WIRELESS ENERGY TRANSFER COMMUNICATIONS SATELLITE

MODULATION : 

MODULATION In telecommunications, modulation is the process of conveying a message signal inside another signal that can be physically transmitted.

AIM OF MODULATION : 

AIM OF MODULATION The aim of digital modulation is to transfer a digital bit stream over an analog passband channel The aim of analog modulation is to transfer an analog baseband (or lowpass) signal The aim of pulse modulation methods is to transfer a narrowband analog signal

CLASSIFICATION OF MODULATION : 

CLASSIFICATION OF MODULATION

ANALOG MODULATION METHODS : 

ANALOG MODULATION METHODS The modulation is applied continuously in response to the analog information signal. Amplitude Modulation The amplitude of the carrier signal is varied in accordance to the instantaneous amplitude of the modulating signal. Frequency Modulation The frequency of the carrier signal is varied in accordance to the instantaneous frequency of the modulating signal. Phase Modulation The phase shift of the carrier signal is varied in accordance to the instantaneous phase shift of the modulating signal.

DIGITAL MODULATION : 

DIGITAL MODULATION An analog carrier signal is modulated by a digital bit stream Considered as digital-to-analog conversion

Slide 21: 

AMPLITUDE-SHIFT KEYING (ASK) FREQUENCY-SHIFT KEYING (FSK) PHASE-SHIFT KEYING (PSK)

PULSE MODULATION : 

PULSE MODULATION Pulse modulation schemes aim at transferring a narrowband analog signal over an analog baseband channel as a two-level signal by modulating a pulse wave.

ORTHOGONAL FREQUENCY-DIVISION MULTIPLEXING : 

ORTHOGONAL FREQUENCY-DIVISION MULTIPLEXING Essentially identical to coded OFDM (COFDM) and discrete multi-tone modulation (DMT), is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. Orthogonal Frequency-Division Multiple Access (OFDMA) is a multi-user version of the popular Orthogonal frequency-division multiplexing (OFDM) digital modulation scheme.

Slide 24: 

AN OFDM (A) MODULATOR AND (B) DEMODULATOR

Slide 25: 

OFDM SIMULATION FLOWCHART

CLAIMED OFDMA ADVANTAGES : 

CLAIMED OFDMA ADVANTAGES Flexibility of deployment across various frequency bands with little needed modification to the air interface. Averaging interferences from neighboring cells, by using different basic carrier permutations between users in different cells. Interferences within the cell are averaged by using allocation with cyclic permutations. Enables orthogonality in the uplink by synchronizing users in time and frequency. Enables Single Frequency Network coverage, where coverage problem exists and gives excellent coverage. Offers Frequency diversity by spreading the carriers all over the used spectrum. Offers Time diversity by optional interleaving of carrier groups in time.

LIMITATION OF WIRELESS COMMUNICATION : 

LIMITATION OF WIRELESS COMMUNICATION FADING INTERFERENCE ERROR BURST FREQUENCY REUSES NOISE LEVEL IN CELLULAR FREQUENCY BAND PATH LOSS

FADING : 

FADING The fading is deviation of the attenuation that a carrier-modulated telecommunication signal experiences over certain propagation media. The fading may vary with time, geographical position and/or radio frequency, and is often modeled as a random process. In wireless systems, fading may either be due to multipath propagation or due to shadowing from obstacles affecting the wave propagation.

PARAMETERS OF FADING CHANNELS : 

PARAMETERS OF FADING CHANNELS Multipath Spread Tm It tells us the maximum delay between paths of significant power in the channel Coherence Bandwidth (Δ)c Gives an idea of how far apart –in frequency- for signals to undergo different degrees of fading Coherence Time (t)c Gives a measure of the time duration over which the channel impulse response is essentially invariant (highly correlated) Doppler Spread Bd It gives the maximum range of Doppler shifts

Slide 30: 

A MOBILE RADIO ENVIRONMENT (a) PROPAGATION LOSS (b) MULTIPATH FADING

Slide 31: 

FAST FADING vs. SLOW FADING

INTERFERENCE : 

INTERFERENCE CO-CHANNEL INTERFERENCE - Co-channel interference or CCI is crosstalk from two different radio transmitters using the same frequency. ADJACENT-CHANNEL INTERFERENCE - Adjacent-channel interference or ACI is interference caused by extraneous power from a signal in an adjacent channel.

FREQUENCY REUSE : 

FREQUENCY REUSE The core concept of the cellular mobile radio system. Users in different geographic locations may simultaneously use the same frequency . The frequency reuse concept can be used in the time domain and the space domain.

Slide 34: 

N-CELL REUSE PATTERN

Slide 35: 

Tow-ray models for mobile radio environments PATH loss

DIVERSITY SCHEME : 

DIVERSITY SCHEME TIME DIVERSITY FREQUENCY DIVERSITY SPACE DIVERSITY SPATIAL DIVERSITY PATTERN DIVERSITY POLARIZATION DIVERSITY MULTIUSER DIVERSITY COOPERATIVE DIVERSITY

TIME DIVERSITY : 

TIME DIVERSITY Time Diversity is used in digital communication systems to combat that the transmissions channel may suffer from error bursts due to time-varying channel conditions.

FREQUENCY DIVERSITY : 

FREQUENCY DIVERSITY The signal is transferred using several frequency channels or spread over a wide spectrum that is affected by frequency-selective fading.

SPACE DIVERSITY : 

SPACE DIVERSITY Antenna diversity, also known as space diversity, is any one of several wireless diversity schemes that use two or more antennas to improve the quality and reliability of a wireless link. Often, especially in urban and indoor environments, there is not a clear line-of-sight (LOS) between transmitter and receiver. Instead the signal is reflected along multiple paths before finally being received

SPATIAL DIVERSITY : 

SPATIAL DIVERSITY Spatial diversity employs multiple antennas, usually with the same characteristics, that are physically separated from one another. Depending upon the expected incidence of the incoming signal, sometimes a space on the order of a wavelength is sufficient.

PATTERN DIVERSITY : 

PATTERN DIVERSITY Pattern diversity consists of two or more co-located antennas with different radiation patterns. This type of diversity makes use of directive antennas that are usually physically separated by some (often short) distance. Collectively they are capable of discriminating a large portion of angle space and can provide a higher gain versus a single omni directional radiator.

POLARIZATION DIVERSITY : 

POLARIZATION DIVERSITY Multiple versions of a signal are transmitted and received via antennas with different polarization. LINEAR CIRCULAR ELLIPTICAL

COOPERATIVE DIVERSITY : 

COOPERATIVE DIVERSITY Achieves antenna diversity gain by using the cooperation of distributed antennas belonging to each node. Cooperative diversity is a cooperative multiple antenna technique for improving or maximizing total network channel capacities for any given set of bandwidths .

DIVERSITY COMBINING METHODS : 

DIVERSITY COMBINING METHODS SELECTION COMBINING SWITCHING COMBINING EQUAL GAIN COMBINING MAXIMAL-RATIO COMBINING

SELECTION COMBINING : 

SELECTION COMBINING Of the N received signals, the strongest signal is selected. Any additional gain diminishes rapidly with the increasing number of channels.

SWITCHING COMBINING : 

SWITCHING COMBINING The receiver switches to another signal when current signal drops below a predefined threshold. This is a less efficient technique than selection combining.

EQUAL GAIN COMBINING : 

EQUAL GAIN COMBINING All the received signals are summed coherently.

MAXIMAL-RATIO COMBINING : 

MAXIMAL-RATIO COMBINING The received signals are weighted with respect to their SNR and then summed.

MULTIPLE-INPUT AND MULTIPLE-OUTPUT : 

MULTIPLE-INPUT AND MULTIPLE-OUTPUT Use of multiple antennas at both the transmitter and receiver to improve quality (BER) or data rate (bits/sec). One of several forms of smart antenna technology. Core scheme of MIMO: space-time coding (STC) Two main functions of STC: diversity & multiplexing

Two popular techniques in wireless MIMO systems : 

Two popular techniques in wireless MIMO systems Spatial Diversity: Increased SNR Spatial Multiplexing: Increased rate Receive and transmit diversity mitigates fading and significantly improves link quality Spatial multiplexing yields substantial increase in spectral efficiency

Slide 52: 

DIFFERENT MIMO SCHEMES

RESULT : 

RESULT Diversity plays an important role in combating fading and co-channel interference and avoiding error bursts. It is based on the fact that individual channels experience different levels of fading and interference. Multiple versions of the same signal may be transmitted and/or received and combined in the receiver. Alternatively, a redundant forward error correction code may be added and different parts of the message transmitted over different channels. Diversity techniques may exploit the multipath propagation, resulting in a diversity gain, often measured in decibels.

Slide 55: 

Comparison of the Performance of a wireless Communication System using Antenna Diversity

Slide 56: 

The improvement of performance of a Wireless System using Multiple Antenna (Diversity) System

Slide 57: 

Comparison of Performance between one (L=1) and six receiving (L=6) Antenna of wireless Communication System using Maximum Ratio Combining Diversity Method

Slide 58: 

Comparison of Performance between one (L=1) and six receiving (L=6) Antenna of wireless Communication System

Slide 59: 

Comparison of Performance between one (L=1) and eight receiving (L=8) Antenna of wireless Communication System using Maximum Ratio Combining Diversity Method

Slide 60: 

Comparison of Performance between one (L=1) and eight receiving (L=8) Antenna of wireless Communication System

Slide 61: 

Comparison of Performance for different diversity schemes of a Wireless Communication System using Maximum Ratio Combining (MRC).

Slide 62: 

Comparison of Performance for different diversity schemes of a Wireless Communication System.

CONCLUSION : 

CONCLUSION The diversity is used to provide the receiver with several replicas of the same signal. Diversity techniques are used to improve the performance of the radio channel without any increase in the transmitted power. As higher as the received signal replicas are de correlated, as much as the diversity gain Among different combining techniques MRC has the best performance and the highest complexity, SC has the lowest performance and the least complexity. BER performance of a Multi-antenna system for both Coded and Un-coded system considering several number of Receiving Antenna. From the both figures it is noticed that there is remarkable improvement in the achievable probability of bit error as number of receiving antenna increase. The BER is measured as 10-5 , 10-7 , 10-8 ,10-10 , and 10-12 for Receiving Antenna Numbers 2, 3, 4, 5 and 6 respectively. Also it is revealed that Bit-Error-Rate of a Multi-Antenna System is 10-23, 10-30 , 10-38 , 10-47 and 10-56 for Receiving Antenna Numbers 2, 3, 4, 5 and 6 respectively.