Meaning
Redundant transmission of the same data block across consecutive subframes improves receiver sensitivity in narrow-band cellular networks. These redundant transmissions, known as nb-iot repetitions, allow low-power devices to communicate through high building losses and deep underground environments. The receiver uses chase combining to integrate the energy of the repeated signals, raising the effective signal-to-noise ratio.
Coverage Extension
A base station can configure up to one hundred and twenty-eight duplicate transmissions for a single uplink or downlink channel. Utilizing nb-iot repetitions extends the maximum coupling loss of the system to over one hundred and sixty-four decibels. This mechanism allows smart water meters and soil sensors to send alerts even when buried under concrete or soil.
Energy Cost
Every additional transmission increases the duration of the active radio state, leading to a proportional rise in energy consumption. A sensor that requires only a single transmission under good conditions will experience a major drop in battery life when repetitions are active. This trade-off requires system architects to balance reporting frequency against signal depth.
Link Budget
Network operators optimize these repetition levels to prevent channel congestion. High repetition counts limit the total number of devices that can share the available narrow-band spectrum simultaneously.
