---
title: "Hybrid multiple access techniques"
subject: "Wireless Communication"
chapter: 7
key: "semester_7/wireless_communication:hybrid-multiple-access"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/hybrid-multiple-access
site: BCT Engineering
---

# Hybrid multiple access techniques

Wireless Communication · Chapter 7: Multiple Access in Wireless Communication

- Asked in: 2080 Bhadra, 4 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/wireless_communication/hybrid-multiple-access
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-7

## Question

Explain any two hybrid multiple access techniques.

## Short answer

Hybrid FDMA/CDMA splits the spectrum into sub-bands, each carrying an independent CDMA system, giving flexibility but lower processing gain. Hybrid DS/FHMA direct-sequence spreads the signal and then hops its center frequency pseudo-randomly, avoiding the near-far problem but requiring fast synthesizers and tight synchronization.

## Answer

**Hybrid multiple access** techniques combine two basic schemes (FDMA, TDMA, CDMA, FHMA) to get the benefits of both. Two common ones:

#### 1. Hybrid FDMA/CDMA (FCDMA)

```text
 |<------------ total spectrum ------------>|
 | CDMA band 1 | CDMA band 2 | CDMA band 3 |
   (users by code inside each sub-band)
```

- The wide spectrum is split into narrower sub-bands; each sub-band carries an independent CDMA system.
- Sub-bands need not be adjacent, so spectrum can be used flexibly; hardware works at lower chip rate.
- Drawback: lower processing gain per sub-band. IS-95 carriers of 1.25 MHz are an example.

#### 2. Hybrid Direct Sequence / Frequency Hopped Multiple Access (DS/FHMA)

```text
 data->(×PN code)->[modulator]->(×)-> hopping DS signal
                                 ^
               [PN]->[frequency synthesizer]
```

- The signal is direct-sequence spread, and the centre frequency of the spread signal hops pseudo-randomly.
- **Advantage:** avoids the near–far problem, since a strong nearby user seldom occupies the same hop frequency.
- **Disadvantage:** complex, needs fast synthesizers and tight synchronisation.

(Others: **Time Division CDMA** – different codes per cell, one user per time slot within a cell; **Time Division Frequency Hopping** – the user hops to a new frequency each TDMA frame, as in GSM.)

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is a hybrid multiple access technique?
   A. A combination of two basic schemes to get the benefits of both
   B. A scheme without any code
   C. Another name for TDMA
   D. A single-user method
   Answer: A. Hybrid schemes combine FDMA, TDMA, CDMA or FHMA. (Key point: Hybrid concept)

2. How does FCDMA work?
   A. Spectrum is split into sub-bands, each carrying an independent CDMA system
   B. One time slot per user
   C. Users hop each frame
   D. All users on one carrier with no codes
   Answer: A. Each sub-band is its own CDMA system, which need not be adjacent. (Key point: FCDMA structure)

3. Why does DS/FHMA avoid the near-far problem?
   A. A strong nearby user seldom occupies the same hop frequency
   B. It uses lower power
   C. It has no PN code
   D. It uses time slots
   Answer: A. Frequency hopping spreads users in frequency over time. (Key point: DS/FHMA advantage)

4. What is the disadvantage of DS/FHMA?
   A. Complexity: fast synthesizers and tight synchronisation
   B. Low bandwidth
   C. No jamming resistance
   D. Lower processing gain per sub-band
   Answer: A. It needs both code and hop synchronisation with fast synthesizers. (Key point: DS/FHMA drawback)

## Related in Wireless Communication

- [SDMA and hybrid SS techniques against near-far](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Asdma-hybrid-near-far) — Wireless Communication, chapter 7
- [FHMA principle and hybrid techniques for near-far](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afhma-hybrid-near-far) — Wireless Communication, chapter 7
- [Self jamming, FHMA and hybrid SS techniques](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aself-jamming-fhma-hybrid) — Wireless Communication, chapter 7
- [Multiple access and near-far effect mitigation](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Amultiple-access-near-far) — Wireless Communication, chapter 7
- [Spread spectrum multiple access; FDMA vs CDMA](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Aspread-spectrum-ma-fdma-cdma) — Wireless Communication, chapter 7
- [Frequency hopped multiple access (FHMA)](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Afhma-operation) — Wireless Communication, chapter 7, asked 5×

## Related in other subjects

- [Multiple access protocols](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Amultiple-access-protocols) — Computer Networks and Security, chapter 3, asked 2×
- [Multiple access in IEEE 802.5](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aieee-802-5-access) — Computer Networks and Security, chapter 3
- [Multiplexing vs multiple access](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Amux-vs-multiple-access) — Data Communication, chapter 6
- [Soil improvement techniques; explain two](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asoil-improvement-explain-two) — Foundation Engineering, chapter 10, asked 2×