# US 2020/0404607 A1 · Synchronizing a cloud radio access network to a network time protocol reference clock > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2020/0404607 A1 - Document ID: US20200404607A1 - Status: Published application - Kind: A1 - Application number: 16/884,916 - Filed: 2020-05-27 - Published: 2020-12-24 - Earliest claimed: 2019-06-18 - Assignees: CommScope Technologies LLC - Applicants: CommScope Technologies LLC - Inventors: Gopikrishna Charipadi - Web page: https://patentgrep.com/patent/US20200404607A1 ## CPC - H04W 56/0055: {determining timing error of reception due to propagation delay} - H04W 56/0015: {one node acting as a reference for the others} - H04W 56/0035: {detecting errors in frequency or phase} - H04J 3/0667: {Bidirectional timestamps, e.g. NTP or PTP for compensation of clock drift and for compensation of propagation delays (arrangements for monitoring round trip delays in packet switching networks H04L43/0864)} - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) ## Abstract A cloud radio access network (C-RAN) includes a baseband controller communicatively coupled to a plurality of radio points (RP) via a fronthaul network. Each of the plurality of RPs are configured to exchange radio frequency (RF) signals with at least one user equipment (UE). At least one of the RPs is configured to determine a timing difference while synchronizing to the baseband controller; and determine a frequency error, between the RP and a neighboring base station, based on a radio environment monitoring (REM) procedure. A phase error is determined, between the baseband controller and the neighboring base station, phase error is determined based on the timing difference for the RP and baseband controller, and the frequency error for the RP and the neighboring base station. ## Claims ### Claim 1 A cloud radio access network (C-RAN), comprising: a baseband controller communicatively coupled to a plurality of radio points (RP) via a fronthaul network; the plurality of RPs, each configured to exchange radio frequency (RF) signals with at least one user equipment (UE), one of the RPs being configured to: determine a timing difference while synchronizing to the baseband controller; determine a frequency error, between the RP and a neighboring base station, based on a radio environment monitoring (REM) procedure; and wherein a phase error is determined based on the timing difference for the RP and the frequency error for the RP and the neighboring base station. ### Claim 2 (depends on 1) The C-RAN of claim 1, wherein the baseband controller is configured to synchronize to a Network Timing Protocol (NTP) grandmaster clock using the phase error as an initial phase error. ### Claim 3 (depends on 2) The C-RAN of claim 2, wherein the timing difference is determined before the baseband controller synchronizes to the NTP grandmaster clock. ### Claim 4 (depends on 1) The C-RAN of claim 1, wherein the timing difference is a timing difference between an oscillator in the RP and an oscillator in the baseband controller. ### Claim 5 (depends on 1) The C-RAN of claim 1, wherein the RP is further configured to determine the timing difference using a time-stamping protocol, implemented over the User Datagram Protocol (UDP)/Internet Protocol (IP), between the baseband controller acting as a master clock and the RP acting as a slave clock. ### Claim 6 (depends on 5) The C-RAN of claim 5, wherein the time-stamping protocol is Institute of Electrical and Electronics Engineers 1588 standard (IEEE 1588); wherein the timing difference is determined using one of the following: only the estimation phase of 1588 IEEE synchronization between baseband controller and the RP; and the estimation phase, coasting phase, and lock phase of IEEE 1588 synchronization. ### Claim 7 (depends on 1) The C-RAN of claim 1, wherein the REM procedure comprises the RP monitoring downlink signals transmitted by the neighboring base station. ### Claim 8 (depends on 7) The C-RAN of claim 7, wherein the downlink signals monitored during REM comprise at least a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) transmitted by the neighboring base station. ### Claim 9 (depends on 8) The C-RAN of claim 8, wherein the downlink signals monitored during REM further comprise a Cell Specific Reference Signal (CS-RS) transmitted by the neighboring base station. ### Claim 10 (depends on 8) The C-RAN of claim 8, wherein monitoring the PSS comprises iteratively performing PSS correlation-based frequency-error estimation; and wherein symbol derotation is performed for frequency correction, following each iteration of PSS correlation-based frequency-error estimation, using circuitry in the RP configured to perform physical uplink Fast Fourier Transform (PUFFT). ### Claim 11 (depends on 1) The C-RAN of claim 1, wherein each of the plurality of RPs determines a respective timing difference between a respective oscillator in the respective RP and an oscillator in the baseband controller; and wherein the baseband controller selects the timing difference from a plurality of timing differences. ### Claim 12 (depends on 1) The C-RAN of claim 1, wherein each of the plurality of RPs determines, based on a respective REM procedure, a respective frequency error for each of at least one neighboring base station monitored during the respective REM procedure; and wherein the baseband controller selects the frequency error from a plurality of frequency errors. ### Claim 13 (depends on 12) The C-RAN of claim 12, wherein the baseband controller is configured to select the frequency error by: identifying a physical cell identifier (PCI) belonging to a neighboring base station that is a macro base station that is detected, at the RP, with a strongest reference signal received power (RSRP); and selecting a frequency error, associated with the neighboring base station having the identified PCI, as the initial phase error. ### Claim 14 (depends on 1) The C-RAN of claim 1, wherein the phase error is determined by: converting the frequency error to a timing error; and summing the timing difference and the frequency error. ### Claim 15 A method, comprising: determining, at a radio point (RP) in a cloud radio access network (C-RAN), a timing difference while synchronizing to a baseband controller in the C-RAN; determining a frequency error, between the RP and a neighboring base station, based on a radio environment monitoring (REM) procedure performed at the RP; and determining a phase error based on the timing difference for the RP and the frequency error for the RP and the neighboring base station. ### Claim 16 (depends on 15) The method of claim 15, further comprising synchronizing the baseband controller to a Network Timing Protocol (NTP) grandmaster clock using the phase error as an initial phase error. ### Claim 17 (depends on 16) The method of claim 16, wherein the timing difference is determined before the baseband controller synchronizes to the NTP grandmaster clock. ### Claim 18 (depends on 15) The method of claim 15, wherein the timing difference is a timing difference between an oscillator in the RP and an oscillator in the baseband controller. ### Claim 19 (depends on 15) The method of claim 15, wherein determining the timing difference comprises determining the timing difference using a time-stamping protocol, implemented over the User Datagram Protocol (UDP)/Internet Protocol (IP), between the baseband controller acting as a master clock and the RP acting as a slave clock. ### Claim 20 (depends on 19) The method of claim 19, wherein the time-stamping protocol is Institute of Electrical and Electronics Engineers 1588 standard (IEEE 1588); wherein the timing difference is determined using one of the following: only the estimation phase of 1588 IEEE synchronization between baseband controller and the RP; and the estimation phase, coasting phase, and lock phase of IEEE 1588 synchronization. ### Claim 21 (depends on 15) The method of claim 15, wherein the REM procedure comprises the RP monitoring downlink signals transmitted by the neighboring base station. ### Claim 22 (depends on 21) The method of claim 21, wherein the downlink signals monitored during REM comprise at least a Primary Synchronization Signal (PSS) and a Secondary Synchronization Signal (SSS) transmitted by the neighboring base station. ### Claim 23 (depends on 22) The method of claim 22, wherein the downlink signals monitored during REM further comprise a Cell Specific Reference Signal (CS-RS) transmitted by the neighboring base station. ### Claim 24 (depends on 22) The method of claim 22, wherein monitoring the PSS comprises iteratively performing PSS correlation-based frequency-error estimation; and wherein symbol derotation is performed for frequency correction, following each iteration of PSS correlation-based frequency-error estimation, using circuitry in the RP configured to perform physical uplink Fast Fourier Transform (PUFFT). ### Claim 25 (depends on 15) The method of claim 15, wherein each of a plurality of RPs determines a respective timing difference between a respective oscillator in the respective RP and an oscillator in the baseband controller; and wherein the baseband controller selects the timing difference from a plurality of timing differences. ### Claim 26 (depends on 15) The method of claim 15, wherein each of a plurality of RPs determines, based on a respective REM procedure, a respective frequency error for each of at least one neighboring base station monitored during the respective REM procedure; and wherein the baseband controller selects the frequency error from a plurality of frequency errors. ### Claim 27 (depends on 26) The method of claim 26, wherein the frequency error is selected by: identifying a physical cell identifier (PCI) belonging to a neighboring base station that is a macro base station that is detected, at the RP, with a strongest reference signal received power (RSRP); and selecting a frequency error, associated with the neighboring base station having the identified PCI, as the initial phase error. ### Claim 28 (depends on 15) The method of claim 15, wherein the phase error is determined by: converting the frequency error to a timing error; and summing the timing difference and the frequency error.