Apparatus and methods are presented for synchronising a slave device signal to a reference timebase, in situations where the slave device lacks knowledge of the propagation delay for signals from the reference device, e.g. if the positions of one or both of the devices are unknown or classified, or the inter-device signal propagation distance is otherwise a-priori unknown. Reference signal propagation delay is determined using an exchange of signals between the devices, with each device using a differencing procedure for eliminating effects of receiver line bias and other hardware delays. In another aspect an exchange of signals between the devices is used to detect a time residual arising from an inaccurate propagation delay estimate. The synchronisation methods can be applied to a plurality of slave devices for providing a synchronised location network. In certain embodiments signals are transmitted wirelessly, while in other embodiments they are transmitted via a fixed line.

Disclosed is a method of operating a network, the network having one or more nodes which are in communication with a server, the server including or being in communication with a high precision time source, to estimate a time delay between the server and each node, comprising initiating a delay request from the server which is transported over a transport layer to the node, the server receiving a delay response from the node receiving the delay request, wherein a timestamp for the delay request and a timestamp for the delay response are times recorded from the high precision time source, wherein the time delay is estimated from half of a time difference between the timestamps.

A method and structure for a coherent optical receiver device. Timing recovery (TR) is implemented after channel dispersion (i.e., chromatic dispersion (CD) and polarization mode dispersion (PMD)) compensation blocks. This architecture provides both improves performance and reduces power consumption of the device. Also, a TR loop is provided, enabling computing, by an error evaluation module, a first sampling phase error (SPE) and computing, by a timing phase information (TPI) module coupled to the error evaluation module, a second SPE from a plurality of CD equalizer taps PMD equalizer taps. The first and second SPE are combined into a total phase error (TPE) in a combining module, and the resulting TPE is filtered by a timing recovery (TR) filter coupled to an interpolated timing recovery (ITR) module and the combining module. The ITR module then synchronizes an input signal of the coherent optical receiver according to the TPE.

A code acquisition module for a direct sequence spread spectrum (DSSS) receiver includes: a Sparse Discrete Fourier transform (SDFT) module configured to perform an SDFT on a finite number of non-uniformly distributed frequencies comprising a preamble of a received DSSS frame to calculate Fourier coefficients for the finite number of non-uniformly distributed frequencies; a multiplier configured to multiply the Fourier coefficients for the finite number of non-uniformly distributed frequencies of the received DSSS frame by complex conjugate Fourier coefficients for the finite number of non-uniformly distributed frequencies to generate a cross-correlation of the received DSSS frame and the complex conjugate Fourier coefficients; and a filter module configured to input the cross-correlation and output a delay estimation for the received DSSS frame.

Apparatus and methods are disclosed for communicating between distributed automotive sensors, including radar sensors, wherein sensors transmit a synchronization (SYNC) signal, each SYNC signal transmitted via a substantially equal-length fiber optic link corresponding with each sensor. A central node receives the SYNC signals via the fiber optic links corresponding with each of the sensors and determines a master SYNC signal based on the received SYNC signals. The central node then transmits the master SYNC signal via the fiber optic links to the sensors, which receive the master SYNC signal and transmit, via fiber optic link, sensor data synchronized in accordance with the master SYNC signal. The synchronized sensor data are received at the central node and coherently aggregated, and transmitted to a compute node for post-processing. For radar data, the post-processing may include determination of an angular position of an object within detection range of at least two radar sensors.

A configurable wide area distributed antenna system is provided. At least one remote master unit of the system is in communication with at least one base station. The remote master unit includes a remote switch function that provides at least multiplexing in a downlink direction, demultiplexing in an uplink direction and routing of digital samples. The local master unit is located remote from the remote master unit. The local master unit is in communication with at least one remote antenna unit used to provide communication coverage in a select coverage area. The local master unit includes a local switch function providing at least demultiplexing in a downlink direction, multiplexing in an uplink direction and routing of digital samples. At least one communication link communicatively couples the remote master unit to the local communication unit with transport media interfaces.

A method of time aligning signals transmitted from a plurality of access nodes to a distributor is disclosed. The signals are formed according to a cyclic structure of a predetermined number of segments, including content segments and control segments, each segment having two markers. A controller of the distributor allocates observation time slots for each access node corresponding to control segments. The controller detects, from a portion of a signal received from an access node during a respective observation time slot, a position of a particular marker and a segment index then determines a temporal displacement of the signal accordingly. If the temporal displacement exceeds a predefined value, a distributing mechanism of the distributor halts signal transfer from the access node to all other access nodes and instructs the access node to adjust transmission time according to the temporal displacement.

The satellite system for navigation and/or geodesy according to the invention is provided with a plurality of MEO satellites, each comprising a dedicated clock, which are arranged in a distributed manner on orbital planes and orbit the Earth, wherein a plurality of MEO satellites, particularly eight, are located in each orbital plane. The satellite system according to the invention is further provided with a plurality of LEO satellites and/or a plurality of ground stations. Each MEO satellite comprises two optical terminals for bidirectional transmission of optical free-beam signals by use of lasers with the respectively first and/or second MEO satellite orbiting ahead in the same orbital plane and with the first and/or second MEO satellite orbiting behind. By use of the optical free-beam signals, the clocks of the MEO satellites are synchronized with each other for each orbital plane at an orbital plane time applicable to this orbital plane.

Systems and methods for quantum clock synchronization are provided. Various embodiments can use time-energy and polarization entangled photons to securely extract the absolute time difference between two remote clocks. In some embodiments, two parties can each have a source of entangled photons. Each party can detect one member of the pair locally and time stamp the detection time, while the other photon gets sent over a common channel (single optical mode) to the other party where the transmitted photon is detected and time stamped. The time stamp values can be shared over an open authenticated channel and each receiver can run a cross-correlation of the detection times. The authenticity and non-spoofability of the timing signal are ensured if each party does not just perform a simple time of arrival measurement but also incorporate polarization measurements whose joint values constitute a Bell test.

An optical transceiver is configured to receive an optical signal on which a monitoring signal encoded by Manchester encoding is superimposed. The optical transceiver includes a decoding circuit configured to decode the monitoring signal from an electrical signal generated from the optical signal. The decoding circuit includes an interval measuring unit and a decoding unit. The interval measuring unit is configured to detect only a rising edge or a falling edge of a waveform of the electrical signal, to measure a first time interval between a detected first edge and a second edge detected immediately after detecting the first edge, and to measure a second time interval between the second edge and a third edge detected immediately after detecting the second edge. The decoding unit is configured to decode the monitoring signal encoded by the Manchester encoding based on a ratio between the first and second time intervals.