As a promising technique, OFDM has been widely used in emerging broadband communication systems, such as digital audio broadcasting (DAB), high-definition television (HDTV), wireless local area network (IEEE 802.11a and HIPERLAN/2). However, as the OFDM signals are the sum of signals with random amplitude and phase, they are likely to have large PAPR that requires a linear high-power- amplifier (HPA) with an extremely high dynamic range, which is expensive and inefficient. Furthermore, any amplifier nonlinearity causes intermodulation products resulting in unwanted out-of-band power. A number of approaches have been proposed to deal with the PAPR problem, including clipping, clipping-and-filtering (CF), coding, companding transform, active constellation extension (ACE), selected mapping (SLM), partial transmit sequence (PTS), and so on.
This thesis proposes an improvement in Selected Mapping technique and Simulation results are compared to existing techniques namely Exponential Companding Transform, Repeated Clipping and Filtering and Adaptive Active Constellation Extension. The improvements which are proposed in classical Selective Mapping technique satisfies the PAPR Reduction criteria with reducing the computational complexity. Also this new scheme has an important advantage of avoiding the extra bits along with the transmitted OFDM signal .This scheme can also be applied to the multiple transmitting antenna cases.
Table of Contents
I Introduction
1.1 Introduction to LTE
1.2 Technologies Involved
1.2.1 OFDM (Orthogonal Frequency Division Multiplexing)
1.2.2 OFDMA (Orthogonal Frequency Division Multiplexing Access)
1.2.3 MIMO (Multiple Input Multiple Output)
1.2.4 SC-FDMA (Single Carrier Frequency Division Multiple Access)
1.3 Brief History of OFDM
1.3.1 Multipath Channels
1.4 Basic Concepts
1.4.1 Frequency Division Multiplexing (FDM)
1.4.2 Time Division Multiplexing (TDM)
1.4.3 Orthogonal Frequency Division Multiplexing (OFDM)
1.5 Introduction to OFDM
1.5.1 Orthogonal Frequency Division Multiplexing (OFDM)
1.5.2 OFDM is a special case of FDM
1.6 SC-FDMA and OFDMA Tx-Rx Structure
1.7 Inter-Symbol Interference
1.8 Inter Carrier Interference
1.9 Understanding concept of Cyclic Prefix
1.10 OFDM using Inverse DFT
1.11 Advantages of OFDM
1.12 Disadvantages of OFDM
1.13 Peak to Average Power Ratio
1.14 PAPR Reduction Techniques
II Literature Review
2.1 Different methods for Peak-to-Average Power (PAPR) Reduction in Orthogonal Frequency Division Multiplexing (OFDM)
III Problem Identification
3.1 Clipping & Filtering
3.2 Coding
3.3 Interleaving
3.4 Companding
3.5 Peak Windowing
3.6 Addictive Corrective Function
3.7 Selected Mapping (SLM)
3.8 Tone Reservation
3.9 Tone Injection
3.10 Selective Scrambling (Interleaving)
IV Methodology
4.1 Objectives
4.2 Hardware& Software Required
4.2.1 Hardware Required
4.2.2 Software Required
4.3 Simulation model of OFDM System
4.3.1 Random Data Generator
4.3.2 Serial to Parallel Conversion
4.3.3 Modulation of Data
4.3.4 Inverse Fourier Transform
4.3.5 Guard Period
4.3.6 Parallel to Serial Converter
4.3.7 Channel
4.3.8 Receiver
4.4 Calculation of PAPR & CCDF of Original OFDM Signal
4.5 Complimentary Cumulative Distribution Function (CCDF)
4.6 Calculation of SNR & BNR of Original OFDM Signal
4.6.1 Additive White Gaussian Noise (AWGN) Channel
4.6.2 Signal to Noise Ratio (SNR)
4.6.3 Bit Error Rate (BER)
4.7 Criteria for Selection of PAPR Reduction Techniques
4.8 Definition of Efficient PAPR
V PAPR Reduction Techniques
5.1 Selective Mapping
5.2 Clipping - Based Active Constellation Extension Algorithm
5.2.1 Limitations of CB-ACE Algorithm
5.3 Exponential Companding Transform
5.3.1 Companding of original OFDM Signal by using Exponential Companding Transform
5.3.2 Advantages of Exponential Companding Transform
5.3.3 Limitation of Exponential Companding Transform
5.4 Adaptive Active Constellation extension Algorithm
VI Proposed Method
6.1 Selected Mapping with Riemann Matrix
6.2 Concept of Riemann matrices
VII Results and Discussion
7.1 PAPR vs CCDF of Original OFDM Signal
7.2 BER of Original OFDM Signal
7.3 PAPR vs CCDF of Original OFDM signal using Selective Mapping (SLM) Technique
7.4 CCDF plot for Clipping-based Active Constellation Extension (CB-ACE) Technique
7.5 BER plot for Clipping-based Active Constellation Extension (CB-ACE) Technique
7.6 CCDF plot for Adaptive Active Constellation Extension (Adaptive-ACE) Technique
7.7 BER plot for Adaptive Active Constellation Extension (Adaptive-ACE) Technique
7.8 CCDF plot for Exponential Companding Technique
7.9 BER plot for Exponential Companding Technique
7.10 CCDF plot for proposed technique- SLM with Riemann Matrix
7.11 BER plot for proposed technique- SLM with Riemann Matrix
VII Conclusion and Future Scope
Research Objectives and Topics
This thesis investigates the problem of high Peak-to-Average Power Ratio (PAPR) in OFDM-based wireless communication systems, specifically within the context of LTE. The primary objective is to evaluate existing PAPR reduction techniques and propose an improved Selective Mapping (SLM) method using Riemann matrices to achieve better PAPR performance without the overhead of side information transmission.
- Analysis of PAPR characteristics in OFDM and OFDMA signals.
- Evaluation of existing reduction techniques: Clipping, Coding, Interleaving, Companding, and Active Constellation Extension (ACE).
- Development of an improved SLM technique utilizing normalized Riemann matrices for phase rotation.
- Performance comparison based on PAPR, bit error rate (BER), and computational complexity.
Excerpt from the Book
3.7 Selected Mapping (SLM)
Bäuml, Fischer and Huber (1996) [26] proposed this method to reduce PAPR for a wide range of applications. Because of the statistical independence of the carriers, the corresponding time domain samples in the equivalent complex valued lowpass domains are approximately Gaussian distributed. This results in a high peak to average power ratio.
Because of varying assignment of data to the transmit signal, this method is called “Selected Mapping”. The core concept is to choose one particular signal, which exhibits some desired properties out of N signal representing the same information. Then all N frames are transformed into the time domain and the one with the lowest PAPR is selected for transmission. To recover data, the receiver has to know which vector has actually used and the number n of the vector is transmitted to the receiver as side in formation. This method can be used for arbitrary number of carriers and any signal constellation. It provides significant gain against moderate additional complexity.[26]
Summary of Chapters
Introduction: Provides an overview of LTE, OFDM/OFDMA technologies, basic concepts like FDM and TDM, and the inherent PAPR challenge.
Literature Review: Discusses various historical and contemporary research papers and proposed methods for PAPR reduction in OFDM systems.
Problem Identification: Explains the impact of nonlinear power amplifiers on OFDM signals, highlighting the need for efficient PAPR reduction to maintain performance.
Methodology: Details the simulation model used for the OFDM system, including hardware/software requirements and evaluation criteria.
PAPR Reduction Techniques: Classifies and describes various PAPR reduction approaches, including clipping, coding, and scrambling techniques.
Proposed Method: Introduces the novel SLM technique using Riemann matrices to reduce PAPR without requiring the transmission of side information.
Results and Discussion: Presents comparative simulation results for various PAPR reduction techniques, analyzing metrics like CCDF, BER, and SNR.
Conclusion and Future Scope: Summarizes the findings and provides a comparative overview of the efficiency of the implemented techniques.
Keywords
OFDM, LTE, PAPR, Peak-to-Average Power Ratio, Selective Mapping, SLM, Riemann Matrix, BER, SNR, CCDF, Clipping, Active Constellation Extension, Companding, Wireless Communication, Signal Processing.
Frequently Asked Questions
What is the core problem addressed in this thesis?
The work focuses on the high Peak-to-Average Power Ratio (PAPR) inherent in OFDM signals, which leads to inefficient power amplifier usage, increased hardware complexity, and poor signal quality.
What are the primary PAPR reduction techniques evaluated?
The thesis evaluates techniques such as clipping and filtering, coding, interleaving, companding, and various forms of active constellation extension (ACE).
What is the ultimate goal of the proposed research?
The goal is to improve PAPR reduction performance while maintaining system efficiency, specifically by eliminating the need for side information in Selective Mapping (SLM).
Which scientific methodology is utilized?
The research employs numerical simulations using MATLAB, evaluating techniques based on performance metrics like the Complementary Cumulative Distribution Function (CCDF) and Bit Error Rate (BER).
What does the main body of the work cover?
The main body covers the analysis of PAPR causes, detailed literature reviews, simulation modeling of OFDM systems, implementation of specific reduction algorithms, and the comparative analysis of results.
How is the thesis characterized by its keywords?
The thesis is characterized by keywords related to multi-carrier modulation (OFDM), standards (LTE), performance metrics (PAPR, BER), and the proposed mathematical approach (Riemann Matrix).
What is the specific advantage of the proposed SLM method with Riemann matrices?
The proposed method achieves significant PAPR reduction without the need to send side information (SI) to the receiver, thus avoiding data rate loss and increased complexity.
How does the Riemann matrix structure aid the receiver?
The Riemann matrix possesses a specific, structured format that allows the receiver to generate it independently, eliminating the requirement to transmit phase sequence metadata.
- Quote paper
- Neelam Dewangan (Author), 2012, Selective Mapping technique for PAPR reduction in LTE-OFDM Systems, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/204995
