7.2. Physical layer
In this section, we describe NB-IoT physical layer design with an emphasis on how these channels are designed to fulfill the objectives that NB-IoT targets, namely, deployment flexibility, ubiquitous coverage, ultra-low device cost, long battery lifetime, and capacity sufficient for supporting a massive number of devices in a cell. NB-IoT was initially designed to support frequency division duplex (FDD) operation. In 3GPP Release 15, support for time division duplex (TDD) operation was introduced. We focus on FDD design in this section. Many of the FDD designs apply to TDD as well, although there are also a few differences. The most critical differences between the FDD and TDD designs will be described in Section 7.2.8.
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