Village 4G Coverage: Repeater, Band 28 or Small Cell
A village 12 km from a 4G site in Rajasthan receives Band 3 (1800 MHz) service. Outdoors, RSRP is −108 to −112 dBm and SINR 3–6 dB; indoors, RSRP falls to −118 to −122 dBm, and many calls drop. The site uses a 20 MHz carrier, 2×2 MIMO, and a 30 m tower with electrical downtilt. A local dealer proposes fitting a customer-side multi-band repeater with a 12 dBi outdoor Yagi and an 8 dBi indoor antenna, claiming it will give 'full bars'. The operator's RF team has not been consulted, and the repeater would be installed without a licence. The village council wants a written comparison of the repeater, a Band 28 (700 MHz) upgrade and a small cell, including likely gain, licensing and capacity effects.
1. Evaluate the dealer's repeater proposal technically and regulatorily. Explain why 'full bars' is not a sufficient acceptance criterion.
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A repeater is not a neutral fix. It amplifies the donor signal and the noise, and unless the donor–server antenna isolation exceeds the repeater gain by an adequate margin (typically 10–15 dB), it oscillates and desensitises the donor cell. At the quoted outdoor RSRP of −108 to −112 dBm and SINR of 3–6 dB, the input is usable but not strong; a high-gain Yagi helps the donor link, but the indoor retransmission raises the noise floor seen by the cell and can reduce capacity for all users. In India, customer repeaters and boosters require type approval and operator authorisation; installing one without the operator's consent can breach the licence and cause harmful interference. 'Full bars' only reflects received power, not quality: a strong but noisy signal can show full bars with poor SINR, dropped calls and low throughput. Acceptance must be based on RSRP, RSRQ, SINR, drop-call rate and throughput, measured before and after.
2. Compare the expected coverage benefit of 700 MHz against 1800 MHz for this village, using free-space path loss and building penetration. State assumptions and limitations.
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The free-space path loss difference is 20 log10(1800/700) = 20 log10(2.571) = 8.2 dB, so at the same EIRP and antenna gains 700 MHz arrives about 8 dB stronger; diffraction around buildings and building penetration are also generally lower at 700 MHz, so indoor coverage can improve by more than 8 dB. Limitations: a 700 MHz antenna is physically larger, the operator may have only 10 MHz of Band 28, which reduces capacity compared with 20 MHz at 1800, and the existing RRU/antenna may need replacement. The 12 km distance and clutter mean free-space loss alone is not a design; a link budget with clutter and penetration losses is needed. If capacity demand is low and coverage is the problem, Band 28 is attractive; if capacity is the issue, a small cell is better.
3. Recommend a phased solution and define measurable acceptance tests (RSRP, SINR, drop-call rate) before and after.
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Phase 1: optimise the existing site - check electrical tilt, azimuth, antenna gain and feeder loss, and verify that the site is not overshooting the village. Phase 2: deploy an operator-owned small cell or low-power RRU in the village with fibre or microwave backhaul; this adds capacity and shortens the path. Phase 3: consider Band 28 if spectrum and a business case exist. Use a repeater only if the operator supplies and commissions it. Acceptance tests: outdoor RSRP at least −100 dBm and SINR at least 5 dB on the main streets; indoor RSRP at least −110 dBm and SINR at least 0 dB in sampled homes; drop-call rate below 2%; downlink throughput above an agreed threshold at busy hour; 24 h monitoring and a before/after drive test. These thresholds should be agreed with the operator before work starts.