- 2078 Chaitra · 4 marks
Feedback vs maximum ratio combining diversity
Short answer
Feedback diversity scans branches in order, selects the first above a threshold, and uses one receiver—simple but lower performance. MRC co-phases all branches, weights each by its SNR, and sums them; output SNR equals the sum of branch SNRs, yielding best performance but requiring a receiver per branch.
Compare between feedback and maximum ratio combining technique used in antenna diversity.
Feedback (scanning) diversity scans the antenna branches in a fixed order and stays with the first branch whose signal is above a threshold. When that signal falls below the threshold, it scans again. Maximal ratio combining (MRC) uses all branches at once: it co-phases each branch, weights it in proportion to its SNR, and adds them.
Feedback/scanning MRC
Ant1 -+ Ant1 ->(xG1)-+
Ant2 -+-[Switch]->Rx Ant2 ->(xG2)-(Σ)->Rx
AntM -+ ^ AntM ->(xGM)-+
[Compare with threshold]
| Point | Feedback (scanning) | Maximal ratio combining |
|---|---|---|
| Branches used | One at a time | All at the same time |
| Selection rule | First branch above threshold | Weighted sum, weight ∝ SNR |
| Receivers needed | Only one | One per branch |
| Co-phasing | Not needed | Needed |
| Output SNR | That of the chosen branch | Sum of all branch SNRs (Σγ_i) |
| Performance | Poorer than other methods | Best of all linear combiners |
| Complexity / cost | Very simple, cheap | Complex, costly |
| Works when all branches are weak | No | Yes, can still give usable SNR |
✓ Answer checked by Claude Opus 5.5 (high effort)
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