For various reasons, there may be a desire to know the position or location of a terminal, a mobile station, or other user equipment (UE) such as a cellular phone or Internet of Things (IoT) device. For example, a location services (LCS) client may desire to know the position or location of the UE to support an emergency services call or to provide some other location-based or location-dependent service such as navigation assistance, direction finding, asset tracking, smart metering, and so on. In general, the position or location associated with the UE may be estimated based on information gathered from various systems. One such system may include the Global Positioning System (GPS), which is one example Global Navigation Satellite System (GNSS) or Satellite positioning system (SPS) that typically includes various space vehicles (SVs) orbiting the Earth. Another example system that may be used to estimate the position or location of a UE is a cellular communication system with aerial and/or terrestrial base stations to support communications for various UEs.
A position estimate for a particular UE, which may alternatively be referred to as a position “fix”, may be obtained based at least in part on distances or ranges from the UE to one or more transmitters, and also based at least in part on known locations of the one or more transmitters. Ranges to the transmitters may be estimated based on signals transmitted by the transmitters and received at the UE. The location of the transmitters may be ascertained, in at least some cases, based on the identities of the transmitters, and the identities of the transmitters may be ascertained from signals received from the transmitters. In general, the transmitters may comprise SVs in the case of an SPS and/or terrestrial base stations in the case of a cellular communications system where Observed Time Difference of Arrival (OTDOA) positioning techniques may be used.
For example, in OTDOA based positioning, the UE may measure time differences in received signals from multiple base stations that have known positions. Accordingly, the observed time differences in the signals received from the multiple base stations may be used to calculate the location of the UE. To further help location determination, a base station (BS) such as an eNodeB (eNB) may transmit Positioning Reference Signals (PRS) to improve OTDOA positioning performance. The measured time difference of arrival of the PRS from a reference cell (e.g., the serving cell) and one or more neighbor cells is known as a Reference Signal Time Difference (RSTD). The position associated with the UE may then be calculated using the RSTD measurements, the absolute or relative transmission timing of each cell, and the known position(s) of physical transmitting antenna(s) for the reference and neighbor cells. As such, OTDOA positioning techniques are a viable alternative positioning method that can be applied in many use cases, especially in harsh environmental conditions where GNSS signals are unavailable (e.g., indoors, in parking garages, tunnels, etc.).
Indeed, some carriers in the United States have mandated inter-frequency (IF) OTDOA to cover locations where eNBs have been isolated on one frequency but many more eNBs are present on other frequencies. Nevertheless, OTDOA-based positioning techniques present certain challenges. For example, in order to be able to measure the PRS from the reference cell and neighbor cells, the UE may send an assistance data request to an OTDOA system server, which may be referred to as a Location Server (LS) or Position Determining Entity (PDE). The server will then send cell information (e.g., cell configuration and timing info) to the UE. The server can also “push” the cell information to the UE without the UE affirmatively requesting the information. The cell information provided to the UE, by way of the generated assistance data, helps the UE to search for the PRS (Positioning Reference Signals). However, in a UE with limited hardware capabilities (e.g., a device that has a single radio frequency (RF) chain, low processing power, low memory, etc.), power optimization is an area of focus because the UE may need to survive on battery power for a substantial time period, sometimes as long as many years. One way to optimize power consumption is to use a Discontinuous Reception (DRx) or Connected Mode DRx (CDRx) cycle, as described in various public technical specifications available from the 3rd Generation Partnership Project (3GPP). As such, when IF-PRS signals used to perform IF-OTDOA measurements collide with a DRx/CDRx ON duration, the UE may need measurement gaps to define time periods when no uplink or downlink transmissions will be scheduled in order to perform the IF-OTDOA measurements (e.g., because the UE needs to monitor a downlink channel during the DRx/CDRx ON state such that the IF-PRS signals may not be received).
Among other problems, measurement gaps may therefore extend the time before which the UE is able to get a position fix and/or may limit the accuracy of the fix because time/resource constraints within the UE limit the number of PRS signals that can be received and thus used for OTDOA positioning. Furthermore, a network node (e.g., at an eNB) typically configures the gap pattern for the UE, which can be a substantial burden on the eNB/network, especially as IoT devices and other UEs contemplated to use OTDOA positioning are expected to be deployed in substantial numbers. Moreover, because measurement gaps define time periods when no uplink or downlink transmissions will be scheduled, measurement gaps may lead to underutilization and/or potentially limit network throughput. Accordingly, improved OTDOA positioning methods that can also reduce power consumption are desired.