4G/5G COMMUNICATION NETWORKS OFDM ADVANCED (CYCLIC PREFIX)

5G

1. OFDM BASICS

2. DAY 6 TOPICS INTRODUCTION TO OFDM HISTORY OF OFDM OFDM BASICS ORTHOGONALITY IN OFDM OFDM SYMBOL STRUCTURE OFDM SUBCARRIERS FREQUENCY AND TIME DOMAIN REPRESENTATION

3. DAY 6 TOPICS OFDM TRANSMITTER AND RECEIVER OFDM MODULATION AND DEMODULATION GUARD INTERVAL CYCLIC PREFIX IN OFDM INTER-CARRIER INTERFERENCE (ICI) PEAK-TO-AVERAGE POWER RATIO (PAPR) OFDM IN WIRELESS COMMUNICATION

4. DAY 6 TOPICS OFDM IN 4G LTE OFDM IN 5G NR OFDM AND CHANNEL ESTIMATION OFDM AND MIMO OFDM AND BEAMFORMING PERFORMANCE ANALYSIS OF OFDM FUTURE TRENDS IN OFDM

5. INTRODUCTION TO OFDM Definition: Orthogonal Frequency Division Multiplexing (OFDM) is a digital modulation technique used to encode digital data on multiple carrier frequencies. Purpose of OFDM Efficient Spectrum Utilization : By splitting a high-speed data stream into multiple slower streams, each transmitted on a separate subcarrier, OFDM optimizes the use of the available spectrum.

6. INTRODUCTION TO OFDM Key Characteristics Orthogonality : Ensures that subcarriers are mathematically orthogonal, preventing interference. Multi-carrier Modulation : Breaks the data stream into parallel subcarriers for more reliable data transmission.

7. INTRODUCTION TO OFDM Why OFDM? Resilience to Multipath Fading : Handles delay spreads and multipath propagation efficiently. High Data Rates : Supports high-speed data transmission. Spectral Efficiency : Maximizes data throughput per unit bandwidth.

8. HISTORY OF OFDM Early Concepts and Theoretical Foundations: 1960s: Initial concepts of frequency division multiplexing (FDM). 1966: R.W. Chang proposes the first principles of OFDM in his paper "Synthesis of Band-Limited Orthogonal Signals for Multicarrier Data Transmission.“ Development in the 1970s and 1980s: 1971: Weinstein and Ebert introduce the use of discrete Fourier transform (DFT) for OFDM, reducing complexity.

9. HISTORY OF OFDM 1980s: Exploration of OFDM for high-speed modems and local area networks (LANs). Commercial Adoption and Standardization: 1990s: OFDM becomes a key technology for ADSL (Asymmetric Digital Subscriber Line) and DVB (Digital Video Broadcasting). 1999: OFDM adopted as the standard for IEEE 802.11a (Wi-Fi). 21st Century Innovations: 2000s: OFDM is utilized in 4G LTE (Long-Term Evolution) networks, enhancing mobile broadband.

10. HISTORY OF OFDM 2006: Introduction of WiMAX (Worldwide Interoperability for Microwave Access) utilizing OFDM. Ongoing: Development and implementation in 5G technology for improved connectivity and efficiency. Future Prospects: Continued evolution with 6G and beyond. Integration with emerging technologies such as IoT (Internet of Things) and AI (Artificial Intelligence).

11. OFDM BASICS Definition : OFDM is a digital multi-carrier modulation technique. Purpose : It improves spectral efficiency and robustness against interference. Applications : Used in Wi-Fi, LTE, ADSL, DVB-T, and more.

12. OFDM BASICS Key Concepts Subcarriers : Multiple closely spaced orthogonal subcarriers are used. Orthogonality : Subcarriers are mathematically orthogonal, reducing interference. FFT/IFFT : Fast Fourier Transform (FFT) and Inverse FFT (IFFT) are used for modulation and demodulation.

13. ORTHOGONALITY IN OFDM Definition : Orthogonality means that the subcarriers are mathematically independent of each other. Mathematical Orthogonality : The integral of the product of two orthogonal functions over one period is zero. Benefit : This property ensures that subcarriers do not interfere with each other despite overlapping in frequency.

14. ORTHOGONALITY IN OFDM Why Orthogonality Matters in OFDM Elimination of Interference : Subcarriers are orthogonal, preventing interference and allowing efficient spectrum use. Efficient Demodulation : Enables the use of Fast Fourier Transform (FFT) for efficient signal demodulation.

15. ORTHOGONALITY IN OFDM Achieving Orthogonality Frequency Spacing : Subcarriers are spaced such that the peak of one subcarrier coincides with the nulls of others. Time Domain Representation : By using IFFT/FFT operations, subcarriers maintain orthogonality in the time domain.

16. ORTHOGONALITY IN OFDM Impact of Orthogonality Enhanced Spectral Efficiency : Maximizes data throughput in a given bandwidth. Reduced Inter-Carrier Interference (ICI) : Ensures clean separation between subcarriers, minimizing the likelihood of cross-talk.

17. OFDM SYMBOL STRUCTURE Components of an OFDM Symbol Subcarriers : Multiple orthogonal subcarriers, each carrying a part of the overall data stream. Data Symbols : Modulated data (e.g., QAM symbols) assigned to each subcarrier. Cyclic Prefix (CP) : A copy of the end portion of the OFDM symbol, appended to the beginning to combat inter-symbol interference (ISI).

18. OFDM SYMBOL STRUCTURE Symbol Formation Process Data Mapping : Input data is mapped onto subcarriers using modulation schemes like QAM or PSK. IFFT Operation : Converts the frequency domain data into the time domain, forming the OFDM symbol. Cyclic Prefix Addition : A segment of the OFDM symbol is copied and added to the beginning to mitigate ISI and simplify equalization.

19. OFDM SYMBOL STRUCTURE

20. OFDM SYMBOL STRUCTURE Key Parameters Subcarrier Spacing : Determined by the system bandwidth and the number of subcarriers. Symbol Duration : Inversely proportional to the subcarrier spacing. Cyclic Prefix Duration : Typically a fraction of the symbol duration, chosen to cover the maximum expected delay spread in the channel.

21. OFDM SYMBOL STRUCTURE Example Calculation Given : 64 subcarriers, bandwidth of 20 MHz, cyclic prefix of 1/8th of the symbol duration. Subcarrier Spacing : Bandwidth / Number of subcarriers = 20 MHz / 64 = 312.5 kHz. Symbol Duration (without CP) : 1 / Subcarrier spacing = 1 / 312.5 kHz ≈ 3.2 µs. Cyclic Prefix Duration : Symbol duration / 8 ≈ 0.4 µs.

22. OFDM SUBCARRIERS Definition : Subcarriers are individual carrier frequencies that make up an OFDM signal, each carrying a portion of the overall data. Orthogonality : Subcarriers are orthogonally spaced to avoid interference with each other

23. OFDM SUBCARRIERS Characteristics of Subcarriers Frequency Spacing : Subcarriers are spaced at intervals of 1T\frac{1}{T}T1​, where TTT is the OFDM symbol duration. Modulation : Each subcarrier is modulated using schemes such as QAM (Quadrature Amplitude Modulation) or PSK (Phase Shift Keying). Bandwidth : The bandwidth of each subcarrier is inversely proportional to the symbol duration.

24. OFDM SUBCARRIERS Types of Subcarriers Data Subcarriers : Carry the actual data. Pilot Subcarriers : Used for synchronization and channel estimation. Guard Subcarriers : Provide a buffer to reduce interference from adjacent channels.

25. OFDM SUBCARRIERS

26. OFDM SUBCARRIERS Advantages of Using Subcarriers Increased Data Rate : By transmitting data simultaneously on multiple subcarriers, OFDM achieves higher data rates. Resilience to Multipath : Subcarriers are robust against multipath fading and delay spread. Efficient Use of Spectrum : Orthogonal subcarriers allow dense packing within the available bandwidth .

27. OFDM SUBCARRIERS Example Configuration Example : For a system with 128 subcarriers in a 10 MHz bandwidth: Subcarrier Spacing : 10 MHz / 128 ≈ 78.125 kHz. Symbol Duration : 1 / 78.125 kHz ≈ 12.8 µs. Guard Interval (Cyclic Prefix) : Typically, 1/4th of symbol duration ≈ 3.2 µs.

28. FREQUENCY & TIME REPRESENTATION . To analyze a signal, it has to be represented. This representation in communication systems is of two types − Frequency domain representation, and Time domain representation .

29. FREQUENCY & TIME REPRESENTATION . In the frequency domain, the signal is analyzed as a mathematical function with respect to the frequency. Frequency domain representation is needed where the signal processing such as filtering, amplifying and mixing are done. It Shows subcarriers overlapping yet orthogonal, where each subcarrier’s peak aligns with the nulls of neighboring subcarriers .

30. FREQUENCY & TIME REPRESENTATION . Time domain analysis, gives the signal behavior over a certain time period. 

31. FREQUENCY & TIME REPRESENTATION . .

32. . .

33. OFDM TRANSMITTER .

34. OFDM TRANSMITTER Input Data : Digital data stream is divided into multiple parallel streams. Modulation : Each stream is mapped to a modulation scheme (e.g., QAM). Serial to Parallel Conversion : Converts the serial data into parallel streams for each subcarrier. Inverse FFT (IFFT) : Transforms the frequency domain signals into the time domain, creating the OFDM symbol.

35. OFDM TRANSMITTER Cyclic Prefix Addition : A copy of the end part of the OFDM symbol is added to the beginning to mitigate ISI. Parallel to Serial Conversion : Converts parallel streams back to a single serial stream. Digital to Analog Conversion (DAC) : Converts the digital signal to an analog signal for transmission.

36. OFDM TRANSMITTER Transmission : The analog signal is transmitted over the communication channel. BPF: A band-pass filter (BPF) is a device that  allows frequencies within a specific range to pass while rejecting (attenuating) frequencies outside that range .

37. OFDM RECEIVER Reception : The analog signal is received from the communication channel. Analog to Digital Conversion (ADC) : Converts the received analog signal to a digital signal. Serial to Parallel Conversion : Converts the serial digital signal into parallel streams. Cyclic Prefix Removal : Removes the cyclic prefix to retrieve the original OFDM symbol.

38. OFDM RECEIVER FFT Operation : Transforms the time domain signal back into the frequency domain. Channel Equalization : Compensates for channel effects using pilot subcarriers. Demodulation : Extracts the data symbols from each subcarrier. Parallel to Serial Conversion : Converts parallel streams back to a single serial data stream. Output Data : The original digital data stream is reconstructed.

39. OFDM MOD & DEMOD .

40. OFDM MODULATION Input Data : Digital data is input as a serial bit stream. Serial to Parallel Conversion : The input bit stream is divided into multiple parallel streams. Symbol Mapping : Each parallel stream is mapped to modulation symbols (e.g., QAM, PSK). Inverse FFT (IFFT) : Converts the modulated symbols from the frequency domain to the time domain.

41. OFDM MODULATION Cyclic Prefix Addition : A copy of the end part of the OFDM symbol is added to the beginning to combat inter-symbol interference (ISI). Parallel to Serial Conversion : The parallel time-domain samples are converted back to a serial stream. Digital to Analog Conversion (DAC) : The digital signal is converted to an analog signal for transmission.

42. OFDM MODULATION Example Configuration Example Parameters : Number of Subcarriers: 64 Modulation Scheme: 16-QAM Bandwidth: 20 MHz Cyclic Prefix: 1/8th of the OFDM symbol duration

43. OFDM MODULATION Calculation : Subcarrier Spacing: 20 MHz / 64 = 312.5 kHz Symbol Duration (without CP): 1 / 312.5 kHz ≈ 3.2 µs Cyclic Prefix Duration: 3.2 µs / 8 ≈ 0.4 µs

44. OFDM DEMODULATION Reception : The analog signal is received from the communication channel. Analog to Digital Conversion (ADC) : Converts the received analog signal to a digital signal. Serial to Parallel Conversion : The serial digital signal is converted into multiple parallel streams. Cyclic Prefix Removal : The cyclic prefix is removed to retrieve the original OFDM symbol. Fast Fourier Transform (FFT) : Converts the time-domain signal back into the frequency domain.

45. OFDM DEMODULATION Channel Equalization : Compensates for channel effects using pilot subcarriers. Symbol Demapping : Extracts the data symbols from each subcarrier and maps them back to the bitstream. Parallel to Serial Conversion : The parallel streams are recombined into a single serial data stream. Output Data : The original digital data stream is reconstructed.

46. OFDM DEMODULATION Example Configuration Example Parameters : Number of Subcarriers: 64 Modulation Scheme: 16-QAM Bandwidth: 20 MHz Cyclic Prefix: 1/8th of the OFDM symbol duration

47. OFDM DEMODULATION Calculation : Subcarrier Spacing: 20 MHz / 64 = 312.5 kHz Symbol Duration (without CP): 1 / 312.5 kHz ≈ 3.2 µs Cyclic Prefix Duration: 3.2 µs / 8 ≈ 0.4 µs

48. Spectral Efficiency Robustness to Multipath Fading Scalability Ease of Equalization Interference Management Implementation Efficiency Support for High Data Rates ADVANTAGES OF OFDM

49. CHALLENGES OF OFDM High PAPR : OFDM signals have a high peak-to-average power ratio, requiring linear power amplifiers which can be inefficient. Timing and Frequency Synchronization : Accurate synchronization is critical in OFDM systems to maintain orthogonality and prevent inter-carrier interference. Cyclic Prefix Overhead : The addition of a cyclic prefix, while necessary for ISI mitigation, reduces spectral efficiency by consuming part of the bandwidth.

50. CHALLENGES OF OFDM Computational Complexity : The implementation of FFT/IFFT and the need for precise synchronization and equalization add to the computational complexity of OFDM systems. ICI Management : Although OFDM is designed to minimize ICI, imperfections in synchronization and channel conditions can still lead to interference. Cost and Power Consumption : The need for linear power amplifiers and precise signal processing can increase the cost and power consumption of OFDM systems.

51. GUARD INTERVAL Inter-Symbol Interference (ISI) Mitigation : Prevents overlap between consecutive OFDM symbols caused by multipath propagation. Channel Delay Spread Handling : Accommodates the delay spread of the channel, ensuring signal integrity.

52. GUARD INTERVAL Types of Guard Intervals Cyclic Prefix (CP) : A portion of the OFDM symbol is copied and added to the beginning. Zero Padding : Adding zeros at the beginning or end of the OFDM symbol (less common). .

53. GUARD INTERVAL Benefits of Guard Intervals ISI Prevention : Ensures that delayed versions of the OFDM symbol do not interfere with the next symbol. Simplified Equalization : Makes channel estimation and equalization easier.

54. GUARD INTERVAL Guard Interval Duration Duration : Typically a fraction of the OFDM symbol duration (e.g., 1/4, 1/8, 1/16). Trade-off : Longer guard intervals improve robustness but reduce spectral efficiency.

55. CYCLIC PREFIX IN OFDM Cyclic Prefix (CP) : A copy of the last part of the OFDM symbol, appended to the beginning.

56. CYCLIC PREFIX IN OFDM Purpose of Cyclic Prefix ISI Mitigation : Prevents inter-symbol interference by absorbing delayed signal paths. Orthogonality Preservation : Maintains subcarrier orthogonality even in the presence of multipath delays.

57. CYCLIC PREFIX IN OFDM Benefits Robustness to Multipath : Enhances the system’s resilience to multipath propagation. Simplified Equalization : Facilitates simpler equalization algorithms at the receiver.

58. CYCLIC PREFIX IN OFDM Cyclic Prefix Duration Duration : Chosen based on the maximum expected delay spread of the channel (e.g., 1/8th of the symbol duration). Trade-off : Balances ISI mitigation with spectral efficiency loss.

59. ICI Inter-Carrier Interference (ICI) : Interference between subcarriers in an OFDM system. Causes of ICI Frequency Offset : Caused by Doppler shifts or oscillator mismatches. Synchronization Errors : Imperfect timing and frequency synchronization.

60. ICI Effects of ICI Degraded Performance : Leads to signal distortion and reduced data throughput. Reduced SNR : Lowers the signal-to-noise ratio, impacting overall communication quality.

61. ICI Mitigation Techniques Accurate Synchronization : Ensuring precise timing and frequency synchronization. Frequency Offset Compensation : Techniques like pilot-based estimation and correction. Advanced Modulation Schemes : Using robust modulation schemes less sensitive to ICI.

62. ICI

63. Peak-to-Average Power Ratio (PAPR) in OFDM The ratio of the peak power to the average power of an OFDM signal. Causes of High PAPR Multi-Carrier Nature : The superposition of multiple subcarriers can result in high peaks. Modulation Scheme : Higher-order modulation schemes can contribute to higher PAPR. PAPR

64. Effects of High PAPR Power Amplifier Requirements : Requires highly linear power amplifiers to avoid distortion. Efficiency Loss : Reduces the efficiency of the power amplifier, leading to higher power consumption. PAPR

65. Mitigation Techniques Clipping and Filtering : Clipping the peaks and filtering the signal to reduce out-of-band radiation. Selective Mapping (SLM) : Using different signal representations to find one with lower PAPR. Partial Transmit Sequence (PTS) : Dividing the OFDM signal into sub-blocks and optimizing their phases to reduce PAPR. PAPR

66. Role of OFDM in Wireless Communication Efficient Spectrum Utilization : OFDM allows for the efficient use of available spectrum, crucial for wireless communication. Robustness to Multipath Fading : OFDM's resilience to multipath propagation makes it ideal for wireless environments. OFDM IN WC

67. Applications in Wireless Communication Wi-Fi : Widely used in IEEE 802.11 standards (e.g., 802.11a/g/n/ac/ ax ). WiMAX : Used in IEEE 802.16 standards for wireless metropolitan area networks. Digital Broadcasting : Employed in standards like DVB-T and ISDB-T for digital TV broadcasting. OFDM IN WC

68. Implementation in LTE Downlink (DL) : OFDMA (Orthogonal Frequency Division Multiple Access) is used, allowing multiple users to access the network simultaneously. Uplink (UL) : SC-FDMA (Single Carrier Frequency Division Multiple Access) is used to reduce PAPR. OFDM IN 4G LTE

69. Benefits in LTE High Data Rates : Supports high data rates necessary for 4G applications. Flexibility : Allows dynamic allocation of subcarriers to users based on demand and channel conditions. Improved Efficiency : Enhances spectral efficiency and network capacity. OFDM IN 4G LTE

70. OFDM IN 4G LTE

71. Numerologies : Multiple subcarrier spacings (e.g., 15 kHz, 30 kHz, 60 kHz) to support diverse use cases. Scalability : Supports both low and high-frequency bands, including mmWave . OFDM IN 5G NR

72. OFDM IN 5G NR

73. Enhanced Features Dynamic TDD : Time-division duplexing adapts dynamically to traffic conditions. Massive MIMO : Supports massive MIMO for increased capacity and coverage. Beamforming : Advanced beamforming techniques for improved signal strength and quality. OFDM IN 5G NR

74. Importance of Channel Estimation Accurate Equalization : Essential for compensating for channel impairments and ensuring reliable data transmission. Performance Optimization : Enhances overall system performance by adapting to varying channel conditions. OFDM AND CHANNEL ESTIMATION

75. Techniques for Channel Estimation Pilot-Based Estimation : Known pilot symbols are transmitted to estimate the channel response. Interpolation : Channel estimates at pilot positions are interpolated to estimate the entire channel. Advanced Algorithms : Techniques like Least Squares (LS) and Minimum Mean Square Error (MMSE) are used for improved accuracy. OFDM AND CHANNEL ESTIMATION

76. Combining OFDM and MIMO Increased Capacity : MIMO (Multiple Input Multiple Output) uses multiple antennas to increase data throughput. Robustness : Enhances robustness to fading and improves signal quality. OFDM AND MIMO

77. Techniques in MIMO-OFDM Spatial Multiplexing : Transmits independent data streams simultaneously, increasing data rates. Diversity Schemes : Uses multiple antennas to improve reliability (e.g., Alamouti scheme). Beamforming : Directs the transmission power towards the receiver, improving signal strength. OFDM AND MIMO

78. Concept of Beamforming Directional Transmission : Focuses the transmission power in specific directions to improve signal quality and coverage. Adaptive Beamforming : Dynamically adjusts the beam direction based on the receiver’s location. OFDM AND BEAMFORMING

79. Benefits in OFDM Systems Improved SNR : Enhances signal-to-noise ratio by directing power towards the intended receiver. Interference Reduction : Minimizes interference by steering beams away from other users. Capacity Enhancement : Increases network capacity by allowing spatial reuse of frequencies. OFDM AND BEAMFORMING

80. Performance Metrics Bit Error Rate (BER) : Measures the rate of errors in the received data. Spectral Efficiency : Evaluates how efficiently the bandwidth is used. PAPR : Assesses the peak-to-average power ratio and its impact on power efficiency. Latency : Measures the delay in data transmission and reception. PERFORMANCE ANALYSIS OF OFDM

81. Factors Influencing Performance Channel Conditions : Multipath fading, Doppler shifts, and interference. System Configuration : Number of subcarriers, modulation scheme, and cyclic prefix length. Synchronization : Accuracy of timing and frequency synchronization. PERFORMANCE ANALYSIS OF OFDM

82. Emerging Technologies OFDM in Beyond 5G (B5G) : Exploring new frequency bands and higher subcarrier spacings. OFDM in IoT : Optimizing OFDM for low-power, wide-area networks (LPWAN) for Internet of Things applications. FUTURE TRENDS IN OFDM

83. Advancements in Modulation Non-Orthogonal Multiple Access (NOMA) : Integrating NOMA with OFDM for improved spectral efficiency and capacity. Adaptive Modulation and Coding (AMC) : Dynamic adjustment of modulation and coding schemes based on channel conditions . FUTURE TRENDS IN OFDM

84. Integration with Other Technologies Machine Learning (ML) and AI : Utilizing ML and AI for adaptive OFDM system optimization and resource allocation. Quantum OFDM : Exploring the potential of quantum computing in enhancing OFDM performance. FUTURE TRENDS IN OFDM