---
title: "Near-far effect and a hybrid SS technique"
subject: "Wireless Communication"
chapter: 7
key: "semester_7/wireless_communication:near-far-hybrid-technique"
source: https://www.bctengineer.com/q/semester_7/wireless_communication/near-far-hybrid-technique
site: BCT Engineering
---

# Near-far effect and a hybrid SS technique

Wireless Communication · Chapter 7: Multiple Access in Wireless Communication

- Asked in: 2071 Magh, 2+2 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/wireless_communication/near-far-hybrid-technique
- Whole chapter: https://www.bctengineer.com/md/semester_7/wireless_communication/chapter-7

## Question

Define near-far effect. Briefly describe any one hybrid spread spectrum multiple access technique which can mitigate the near-far problem.

## Short answer

The near-far effect in CDMA occurs when a nearby mobile's strong signal drowns out a distant user's signal because all share the same band and are treated as noise. Time Division CDMA (TCDMA) mitigates it by giving each cell a unique spreading code and assigning different time slots to users in the same cell, so near and far users never transmit simultaneously, eliminating in-cell near-far interference.

## Answer

#### Near-far effect
The near-far effect occurs in the CDMA uplink when a mobile **close to the base station** is received with much higher power than a mobile **far away**. Since all users share the same band and other users act as noise, the strong near signal drowns the weak far signal, which then cannot be despread correctly. It is controlled mainly by power control.

#### Hybrid technique: Time Division CDMA (TCDMA)
- Each cell is given a different spreading code.
- Inside a cell, users are assigned different **time slots**, so only **one user per cell** transmits at any time.
- A near user and a far user of the same cell are therefore never received together, and the near-far problem is avoided. On handoff the user's code is changed to the new cell's code.

```text
 Cell code C1: |U1|U2|U3|U1|U2|U3|
```

(Hybrid DS/FHMA is another option: a DS signal whose carrier hops, so near and far users rarely share the same frequency at the same time.)

## Check yourself

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

1. Which describes the near-far effect?
   A. A far mobile transmits too much power
   B. A mobile close to the base station is received with much higher power and drowns a far mobile's signal
   C. Two users use the same code
   D. The base station is too far from the PSTN
   Answer: B. Since users share the band and act as noise to each other, the strong near signal swamps the weak far one. (Key point: Near-far definition)

2. What mainly controls the near-far effect?
   A. Larger guard bands
   B. Time slots in FDMA
   C. Power control
   D. Higher modulation order
   Answer: C. Power control equalises received powers. (Key point: Control of near-far)

3. In TCDMA how many users per cell transmit at any time?
   A. One
   B. All of them
   C. Half of them
   D. Two per slot
   Answer: A. Users take different time slots, so only one per cell transmits at once. (Key point: TCDMA structure)

4. How does DS/FHMA also help against near-far?
   A. It cancels interference
   B. Near and far users rarely share the same hop frequency at the same time
   C. It removes spreading
   D. It increases power of far user
   Answer: B. The DS signal's carrier hops, so near and far users seldom coincide. (Key point: DS/FHMA alternative)

## 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
- [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
- [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
- [Spread spectrum multiple access variants](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Assma-variants-applications) — 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
- [Hybrid spread spectrum and FHMA types](https://www.bctengineer.com/question.md?key=semester_7%2Fwireless_communication%3Ahybrid-ss-fhma-types) — Wireless Communication, chapter 7

## Related in other subjects

- [Near-far problem in CDMA](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Acdma-near-far) — Data Communication, chapter 6
- [RF safety practices and reactive/near/far fields](https://www.bctengineer.com/question.md?key=semester_7%2Frf_and_microwave_engineering%3Arf-safety-practices-near-far-field) — RF and Microwave Engineering, chapter 7
- [Spread spectrum security; pros and cons](https://www.bctengineer.com/question.md?key=semester_5%2Fdata_communication%3Ass-security-jamming) — Data Communication, chapter 6