A Category M1 (Cat-M1) Long Term Evolution (LTE) user equipment (UE) category was created to support Internet of Things (IoT) use cases with lower data rate, higher coverage and capacity. IoT includes both fixed and mobile use cases, which is one of the major differences between Cat-M1 and narrowband IoT (NB-IoT). Both Cat-M1 and NB-IoT UEs may be categorized as “narrowband UEs,” as they use only a portion or subset of a total radio frequency (RF) bandwidth offered by a cell, and use a significantly narrower RF bandwidth than traditional UEs, such as LTE Cat-1+ UEs. For example, a cell may be operated with a 10 MHz or 20 MHz total bandwidth, much or all of which (for example, 10 MHz or 20 MHz) may be used by an LTE Cat-1+ UE for communications. However, a Cat-M1 UE instead only makes use of 1.4 MHz of that total bandwidth at any given time. In many implementations, a narrowband radio transceiver included in a narrowband UE is limited to operating with this narrower RF bandwidth, and cannot operate using the full bandwidth offered by a cell.
For narrowband UEs that change locations or require mobility, lack of connected mode mobility support will cause dragging; produce interference to non-narrowband UEs, which may be running critical applications such as Voice Over LTE (VoLTE) in neighboring cells; and longer interruptions to narrowband devices. Due to only being able to use a subset or portion of a total RF bandwidth offered by a cell, narrowband UEs generally cannot use the same techniques for connected mode mobility that are used by traditional UEs. For example, a Cat-M1 UE needs to tune away from its allocated PDSCH physical resource blocks (PRBs) to a center six PRBs (located at different subcarrier frequencies than the allocated PDSCH) to receive and process primary synchronization signals (PSS) and secondary synchronization signals (SSS), and perform reference signal received power (RSRP) measurement on a cell-specific reference signal (CRS) transmitted by a neighbor cell. A period of time that a UE must tune away from its current connection with a serving cell to measure signals from neighboring cells is referred to as a “measurement gap.” For Cat-1+ UEs, only inter-frequency handover (HO) requires use of a measurement gap. However, according to the Cat-M1 standard, a measurement gap is required for all HOs, including intra-frequency HOs. Measurement gap requires UEs to tune away from their assigned PRBs, thereby interrupting communications.
In some networks or network architectures, serving cells are expected to schedule measurement gaps for, and communicate such schedules to, their connected UEs. However, as narrowband UEs providing connected mode mobility are further deployed, the scheduling demands for serving cells continue to grow. For example, a single base station could be required to perform measurement gap scheduling activities for thousands of connected narrowband UEs. These scheduling activities are burdensome computationally and interrupt other communication activities.