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Complete comparison of all modulation techniques AM FM PM ASK FSK PSK QPSK QAM with performance metrics, bandwidth efficiency, power efficiency, BER, applications, and selection criteria for engineering students.
In this chapter, we will compare all modulation techniques together – analog (AM, FM, PM) and digital (ASK, FSK, PSK, QPSK, QAM). This comparison is very important for exams and interviews.
📻 Analog Modulation Comparison
| Parameter | AM | FM | PM |
|---|---|---|---|
| Varies | Amplitude | Frequency | Phase |
| Constant | Freq, Phase | Amplitude | Amplitude |
| Bandwidth | 2fm (narrow) | 2(Δf+fm) (wide) | 2(βp×fm+fm) |
| Noise immunity | Poor | Excellent | Good |
| Power efficiency | Low (33% max) | Better | Good |
| Complexity | Simple | Medium | Medium |
| Audio quality | Moderate | High fidelity | Good |
| Range | Long (ground wave) | Medium (LOS) | Medium |
| Application | AM Radio | FM Radio, TV audio | Digital systems base |
| Receiver | Envelope detector | Discriminator | Phase detector |
Key Insight:
| AM: Simple but poor quality | Legacy broadcasting |
| FM: Better quality, more BW | High-quality audio |
| PM: Foundation for digital PSK | Modern digital comms |
💻 Digital Modulation Comparison
Binary Schemes (1 bit/symbol):
| Parameter | ASK (OOK) | BFSK | BPSK |
|---|---|---|---|
| Varies | Amplitude | Frequency | Phase |
| BER (BER=10⁻⁶) | 13.5 dB Eb/N₀ | 13.5 dB (coh) | 10.5 dB ✅ |
| Bandwidth | Rb(1+r) | 2(Δf+Rb) | Rb(1+r) |
| Spectral eff. | 1 bps/Hz | <1 bps/Hz | 1 bps/Hz |
| Noise immunity | Poor ❌ | Good | Best ✅ |
| Fading resistance | Poor | Good | Good |
| Complexity | Very Low ✅ | Low | Medium |
| Power eff. | Low | Medium | High ✅ |
| Constant envelope | No | Yes ✅ | No |
| Application | RFID, fiber | Bluetooth, IoT | GPS, satellite |
Higher-Order Schemes:
| Parameter | QPSK | 16-QAM | 64-QAM | 256-QAM | 1024-QAM |
|---|---|---|---|---|---|
| Bits/symbol | 2 | 4 | 6 | 8 | 10 |
| Spectral eff. | 2 bps/Hz | 4 bps/Hz | 6 bps/Hz | 8 bps/Hz | 10 bps/Hz |
| SNR for 10⁻⁶ | 10.5 dB | 14.5 dB | 18.5 dB | 24 dB | 30 dB |
| Robustness | ✅✅✅ | ✅✅ | ✅ | Sensitive | Very sensitive |
| Linear amp? | No | Yes | Yes | Yes | Yes |
| Use case | Cell edge | Medium | Good channel | Close range | Very close |
⚡ Analog vs Digital Modulation
| Aspect | Analog | Digital |
|---|---|---|
| Signal type | Continuous | Discrete (bits) |
| Noise immunity | Poor (accumulates) | Good (regenerate) |
| Error correction | Not possible | FEC codes applied |
| Encryption | Difficult | Easy (bit-level) |
| Compression | Limited | Highly compressible |
| Multiplexing | FDM only | TDM, FDM, CDM, OFDM |
| Processing | Analog circuits | DSP (software) |
| Quality over distance | Degrades | Maintained (until threshold) |
| Modern relevance | Legacy only | Standard for all new systems |
| Example | AM/FM Radio | 4G, 5G, WiFi, DVB |
📊 Performance Metrics
BER Performance Ranking (Best to Worst):
┌─────────────────────────────────────────────────────────────────────┐
│ POWER EFFICIENCY (lower Eb/N₀ needed = better) │
│ │
│ Most efficient ─────────────────────────▶ Least efficient │
│ │
│ BPSK/QPSK > 8-PSK > 16-QAM > 64-QAM > 256-QAM > 1024-QAM │
│ 10.5 dB 14 dB 14.5dB 18.5dB 24 dB 30 dB │
│ │
│ BANDWIDTH EFFICIENCY (higher bps/Hz = better) │
│ │
│ Most efficient ─────────────────────────▶ Least efficient │
│ │
│ 1024-QAM > 256-QAM > 64-QAM > 16-QAM > QPSK > BPSK > BFSK │
│ 10 bps/Hz 8 bps/Hz 6 bps/Hz 4 bps/Hz 2 1 <1 │
│ │
│ ⚠️ FUNDAMENTAL TRADE-OFF: │
│ Power efficiency ←────────────────────▶ Bandwidth efficiency │
│ (cannot have both maximized simultaneously!) │
└─────────────────────────────────────────────────────────────────────┘
The Trade-off Diagram:
Bandwidth Higher QAM: More bps/Hz but needs more power
Efficiency
(bps/Hz) ↑
│ ● 1024-QAM
10 │ ● 256-QAM
│ ● 64-QAM
6 │ ● 16-QAM
│ ● 8-PSK
2 │ ● QPSK/4-QAM
│ ● BPSK
1 │● BFSK
┼────────────────────────────────▶ Eb/N₀ (dB)
5 10 15 20 25 30
Power Efficiency (lower = better)
🎯 Selection Criteria
When to use which modulation:
Choose based on:
| If you need... | Choose | Reason |
|---|---|---|
| Maximum robustness | BPSK/QPSK | Lowest SNR requirement |
| Highest speed | 1024/4096-QAM | Most bits per symbol |
| Power-limited channel | BPSK | Best Eb/N₀ performance |
| Bandwidth-limited | 256/1024-QAM | Most bps/Hz |
| Constant envelope (for PA) | FSK/GFSK/MSK | No amplitude variation |
| Simple low-cost device | ASK/OOK or GFSK | Minimal hardware |
| Fading channel | FSK or OFDM+QPSK | Amplitude-independent |
| Best overall balance | QPSK + adaptive QAM | Industry standard |
Decision Flowchart:
┌─────────────────────────────────────────────────────────────────────┐
│ START: What is your constraint? │
│ │
│ Power limited? ─── YES ──▶ BPSK/QPSK (satellite, deep space) │
│ │ │
│ NO │
│ │ │
│ Bandwidth limited? ─── YES ──▶ High-order QAM (64/256/1024) │
│ │ │
│ NO │
│ │ │
│ Need constant envelope? ─── YES ──▶ GFSK/MSK/GMSK │
│ │ │
│ NO │
│ │ │
│ Variable channel? ─── YES ──▶ Adaptive QAM (QPSK to 1024-QAM) │
│ │ │
│ NO │
│ │ │
│ Ultra-low cost? ─── YES ──▶ OOK/ASK │
└─────────────────────────────────────────────────────────────────────┘
📱 Modern Systems & Their Modulation
| System | Modulation Used | Why? |
|---|---|---|
| AM Radio | AM (DSB-FC) | Legacy, simple receivers |
| FM Radio | Wideband FM | Quality audio |
| GSM (2G) | GMSK | Constant envelope, spectral eff. |
| 3G (WCDMA) | QPSK + HPSK | Spread spectrum |
| 4G LTE | OFDM + QPSK/16/64/256-QAM | Adaptive, high speed |
| 5G NR | OFDM + QPSK to 1024-QAM | Maximum flexibility |
| WiFi 6 | OFDM + BPSK to 1024-QAM | Adaptive |
| WiFi 7 | OFDM + BPSK to 4096-QAM | Extreme speed |
| Bluetooth | GFSK / π/4-DQPSK / 8-DPSK | Low power, simple |
| LoRa | CSS (Chirp Spread Spectrum) | Long range, low power |
| GPS | BPSK | Maximum robustness |
| DVB-S (satellite TV) | QPSK/8PSK | Power limited |
| DVB-T (digital TV) | OFDM + QPSK/16/64-QAM | Terrestrial broadcast |
| Cable (DOCSIS 3.1) | OFDM + up to 4096-QAM | High SNR cable |
📝 Summary Table
Complete Comparison:
| Modulation | Type | Bits/Sym | BW Eff | Power Eff | Complexity | Best For |
|---|---|---|---|---|---|---|
| AM | Analog | – | Low | Very low | Very low | Legacy radio |
| FM | Analog | – | Low | Medium | Medium | Audio broadcast |
| OOK/ASK | Digital | 1 | 1 bps/Hz | Low | Very low | RFID, fiber |
| BFSK | Digital | 1 | <1 bps/Hz | Medium | Low | IoT, Bluetooth |
| GFSK | Digital | 1 | ~1 bps/Hz | Medium | Low | Bluetooth |
| BPSK | Digital | 1 | 1 bps/Hz | Best | Medium | GPS, satellite |
| QPSK | Digital | 2 | 2 bps/Hz | Very good | Medium | 4G/5G base |
| 16-QAM | Digital | 4 | 4 bps/Hz | Good | High | WiFi, 4G |
| 64-QAM | Digital | 6 | 6 bps/Hz | Moderate | High | WiFi, 4G, 5G |
| 256-QAM | Digital | 8 | 8 bps/Hz | Fair | Very high | WiFi 5/6, 5G |
| 1024-QAM | Digital | 10 | 10 bps/Hz | Low | Very high | WiFi 6, 5G |
| 4096-QAM | Digital | 12 | 12 bps/Hz | Very low | Extreme | WiFi 7, cable |
❓ FAQ
Q: Exam mein "best modulation technique" puchha toh kya likhein? A: There is no single "best" – it depends on constraints. Power-limited → BPSK. Bandwidth-limited → High QAM. Modern systems use adaptive modulation (QPSK to 1024-QAM dynamically).
Q: Which modulation is used in 5G? A: 5G NR uses OFDM with adaptive modulation: QPSK (cell edge, low SNR) → 16-QAM → 64-QAM → 256-QAM → 1024-QAM (close to tower, high SNR).
Q: OFDM kya hai? Yeh modulation hai? A: OFDM is not a modulation technique, it is a multiplexing technique. It divides the channel into many narrow subcarriers. Each subcarrier uses QAM/PSK modulation. OFDM + QAM is the winning combination in 5G.
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