NR Positioning Reference Signals (PRS)
Introduction:
NR (New Radio) is a new wireless communication standard that has been introduced by the 3rd Generation Partnership Project (3GPP) to provide higher data rates, lower latency, better energy efficiency, and improved coverage compared to previous cellular standards. One of the key features of NR is the use of a new type of reference signal known as the NR Positioning Reference Signal (PRS). The PRS is used to assist with the positioning of mobile devices in a cellular network, which is important for a range of applications including emergency services, public safety, and location-based services. In this article, we will discuss the technical aspects of the NR PRS and its role in the NR network.
Overview of NR PRS:
The NR PRS is a type of reference signal that is transmitted by the base station (i.e., the cell tower) and received by the mobile device. The PRS is used to assist with the positioning of the mobile device by providing accurate timing and location information. The PRS is based on a repeating pattern of signals that are transmitted at a specific time interval. The PRS is transmitted on specific resource blocks (RBs) within the frequency domain, which are reserved for this purpose.
The NR PRS consists of two main types of signals: the primary PRS and the secondary PRS. The primary PRS is transmitted continuously and is used for initial synchronization and cell search. The secondary PRS is transmitted periodically and is used for positioning and measurement purposes.
Technical Details:
The NR PRS is based on a complex modulation scheme known as Zadoff-Chu (ZC) sequences. ZC sequences are a family of complex sequences that are used in various wireless communication systems due to their desirable properties, such as low peak-to-average power ratio (PAPR), good correlation properties, and low cross-correlation between sequences.
The ZC sequences used in the NR PRS are specifically designed to have good correlation properties, which is important for accurate positioning. The sequences are selected from a pre-defined set of sequences, which are based on a specific root index (u) and a cyclic shift (n). The root index determines the length and properties of the sequence, while the cyclic shift determines the timing of the sequence.
The NR PRS is transmitted in the time domain by mapping the ZC sequences onto specific symbols within a subframe. The subframe is a fixed length of time that is used to transmit data and control information in the NR system. The PRS symbols are mapped onto specific time slots within the subframe, which allows for accurate timing and synchronization.
The NR PRS is transmitted in the frequency domain by mapping the PRS symbols onto specific RBs within a carrier. The carrier is a frequency band that is used to transmit data and control information in the NR system. The PRS symbols are mapped onto specific RBs within the carrier, which allows for accurate frequency information and channel estimation.
The primary PRS is transmitted continuously on specific RBs within the carrier. The primary PRS is used for initial synchronization and cell search, which is the process of identifying and selecting the strongest available cell for communication. The primary PRS is also used for handover, which is the process of transferring a mobile device from one cell to another as it moves through the network.
The secondary PRS is transmitted periodically on specific RBs within the carrier. The secondary PRS is used for positioning and measurement purposes, which allows for accurate determination of the location of the mobile device. The secondary PRS is also used for beamforming, which is the process of directing the transmission and reception of the wireless signal towards a specific direction.
Conclusion:
The NR PRS is an important feature of the NR system that is used to assist with the positioning of mobile devices. The PRS is based on a complex modulation scheme known as Zadoff-Chu sequences, which are designed to have good correlation properties for accurate positioning. The PRS is transmitted in the time and frequency domains by mapping the ZC sequences onto specific symbols within a subframe and specific RBs within a carrier.
The primary PRS is transmitted continuously and used for initial synchronization and cell search, while the secondary PRS is transmitted periodically and used for positioning and measurement purposes. The NR PRS plays a vital role in various applications, including emergency services, public safety, and location-based services, by providing accurate timing and location information for mobile devices.
Overall, the NR PRS is a key technology that enhances the performance of the NR system by providing accurate positioning capabilities. Its use can enable a range of new applications and services that depend on location-based information, making it an important area of research and development for future wireless communication systems.