Structure of an OFDM Packet

Home Signal Processing (DSP) 📘 Wireless Communication Modulation Techniques BER vs SNR Constellation Diagrams Channel Impulse Response MIMO Technology OFDM MATLAB Projects Online Simulator Software/AI/ML More... Contact

Structure of an OFDM Packet

📘 What does an OFDM signal look like?
📘 What are the roles of cyclic prefixes in an OFDM packet?
📘 The process of sending an OFDM packet practically
📘 MATLAB Codes
📚 Further Reading

What does an OFDM signal look like?

An OFDM signal contains a header (that is called a cyclic prefix). That message bits are placed. Then again, a cyclic prefix and other message bits are located. The length of the cyclic prefix is a fraction of the length of the message bits. The structure is called a packet containing cyclic prefixes and message bits.

Let's assume I need to transmit 16 bits as an OFDM symbol. If the length of the cyclic prefix is 4, then the original OFDM symbol, for example, is 1001100101010110. The OFDM symbol with the cyclic prefix will be 01101001100101010110, where the last 4 bits of the OFDM symbol are copied to the front of the original symbol.

Fig: OFDM Modulation and Demodulation

What are the roles of cyclic prefixes in an OFDM packet?

It mitigates the inter-symbol interference (ISI)
It works as training bits
It helps in equalization

The process of sending an OFDM packet practically

Firstly, we apply inverse fast Fourier transform (IFFT) on the OFDM packet's bits to define it in the time domain. Oppositely, on the receiver side, we apply a fast Fourier transform (FFT) to recover the original OFDM packet.

For example, if you are transmitting 100 OFDM symbols, each symbol contains 64 bits, and the number of subcarriers is 64, then there will be 64 subchannels in parallel.

📘 Overview 🧮 Simulator for constellation diagram of FSK 🧮 Theory 🧮 MATLAB Code 📚 Further Reading 📚 BER vs SNR from Constellation Binary bits '0' and '1' can be mapped to 'j' and '1' to '1', respectively, for Baseband Binary Frequency Shift Keying (BFSK) . Signals are in phase here. These bits can be mapped into baseband representation for a number of uses, including power spectral density (PSD) calculations. For passband BFSK transmission, we can modulate signal 'j' with a lower carrier frequency and signal '1' with a higher carrier frequency while transmitting over a wireless channel. Let's assume we are transmitting carrier signal fc1 for the transmission of binary bit '1' and carrier signal fc2 for the transmission of binary bit '0'. Simulator for 2-FSK Constellation Diagram Simulator for 2-FSK Constellation Diagram ...

UGC NET Electronic Science Previous Year Question Papers with Solutions

Home / Engineering & Other Exams / UGC NET 2026 PYQ ⬇️ Download Papers and Solutions 📋 Exam Pattern 💡 Preparation Tips ❓ FAQs 📊 Exam Highlights: Electronic Science (88) Feature Details Junior Research Fellowship (JRF) ₹37,000 + HRA per month Eligibility M.Sc/M.Tech in Electronics (55%) Validity of Certificate JRF (3 Years) | Lectureship (Lifetime) 📥 Download UGC NET Electronics PDFs Complete collection of previous year question papers, answer keys and explanations for Subject Code 88. Start Downloading 📂 View All Question Papers June 2025 - Question Paper Download PDF June 2025 - Solved Paper + Explanation ...

FM Bandwidth and FM Band Explained

FM radio uses the frequency band from 88 MHz to 108 MHz , which is a 20 MHz-wide spectrum . This is the range of carrier frequencies available to stations. 108 MHz − 88 MHz = 20 MHz However, a single FM station occupies only about 200 kHz . This is the bandwidth of the modulated FM signal. 1. Why One FM Station Needs ~200 kHz FM uses frequency modulation . The bandwidth depends on how far the carrier swings. Carson's Rule gives the approximate FM bandwidth: B = 2 ( Δf + f m ) ...

What is Frequency Resolution?

Formula for Frequency Resolution (in general) The frequency resolution is the smallest frequency difference between two adjacent frequency points in your sampling range. It is determined by the total frequency range and the number of frequency samples N . The formula for the frequency resolution (or step size) Δf is: Δf = (f max - f min ) / (N - 1) Where: f min is the minimum frequency in the range (in this case, -50 Hz). f max is the maximum frequency in the range (in this case, 50 Hz). N is the number of frequency points / frequency bins. Using the Given Values: From the function: f min = -50 Hz f max = 50 Hz N = 1000 The frequency resolution is: Δf = (50 - (-50)) / (1000 - 1) = 100 / 999 ≈ 0.1001 Hz Understanding Frequency Resolution in Signal Processing Alternative Formula Using Time Duration Another common way to define frequency resolution, especially in time-domain signal processing, is: Δf = 1 / T W...

Ph.D. admissions in IITs without a GATE score

PhD Admission in IITs With Low CGPA approximately 6.5 – 7.0 / 10 No valid GATE score Willing to strengthen research proposal, contact faculty, apply to multiple institutes Expanded List of IITs: Eligibility & Links IIT Eligibility & Notes PhD Info Link IIT Gandhinagar Minimum: 60% marks or 6.0 CGPA (General) or 55%/5.5 (SC/ST/PD) in qualifying degree. GATE/NET may be waived in certain cases; but short‑listing criteria likely higher. iitgn.ac.in/admissions/phd IIT Kharagpur Minimum eligibility: 60% marks or 6.5 CGPA in qualifying exam for many branches. However brochure notes “for test & interview this minimum must be met and higher cut‑offs may apply”. iitkgp.ac.in/phd_brochure.pdf IIT Bhubaneswar Minimum: Engineering Schools – M.Tech/ME with minimum 60% marks or 6.5 CGPA....

BER performance of QPSK with BPSK, 4-QAM, 16-QAM, 64-QAM, 256-QAM, etc (MATLAB + Simulator)

📘 Overview 📚 QPSK vs BPSK and QAM: A Comparison of Modulation Schemes in Wireless Communication 📚 Real-World Example 🧮 MATLAB Code 📚 Further Reading QPSK provides twice the data rate compared to BPSK. However, the bit error rate (BER) is approximately the same as BPSK at low SNR values when gray coding is used. On the other hand, QPSK exhibits similar spectral efficiency to 4-QAM and 16-QAM under low SNR conditions. In very noisy channels, QPSK can sometimes achieve better spectral efficiency than 4-QAM or 16-QAM. In practical wireless communication scenarios, QPSK is commonly used along with QAM techniques, especially where adaptive modulation is applied. Modulation Bits/Symbol Points in Constellation Usage Notes BPSK 1 2 Very robust, used in weak signals QPSK 2 4 Balanced speed & reliability 4-QAM ...

Coherence Bandwidth and Coherence Time (with MATLAB + Simulator)

🧮 Coherence Bandwidth 🧮 Coherence Time 🧮 MATLAB Code s 📚 Further Reading For Doppler Delay or Multi-path Delay Coherence time T coh ∝ 1 / v max (For slow fading, coherence time T coh is greater than the signaling interval.) Coherence bandwidth W coh ∝ 1 / τ max (For frequency-flat fading, coherence bandwidth W coh is greater than the signaling bandwidth.) Where: T coh = coherence time W coh = coherence bandwidth v max = maximum Doppler frequency (or maximum Doppler shift) τ max = maximum excess delay (maximum time delay spread) Notes: The notation v max −1 and τ max −1 indicate inverse proportionality. Doppler spread refers to the range of frequency shifts caused by relative motion, determining T coh . Delay spread (or multipath delay spread) determines W coh . Frequency-flat fading occurs when W coh is greater than the signaling bandwidth. Coherence Bandwidth Coherence bandwidth is...

Search This Blog