A method includes receiving an optical signal through an optical link and determining a receiving power for the optical link. The method further includes comparing the receiving power for the optical link to a first receiving power threshold and transitioning a clock and data recovery circuit form a normal mode to a holdover mode when the receiving power is less than the first receiving power threshold. The clock and data recovery circuit, when operating in the holdover mode, configured to hold a recovered clock to a known-good clock frequency. When the receiving power for the optical link is greater than a second receiving power threshold, the method initiates a transition of the clock and data recovery circuit from the holdover mode to the normal mode and reacquires synchronization between the recovered clock and a current rate of the incoming data stream using the known-good clock frequency.

In accordance with embodiments disclosed herein, there is provided systems and methods for link training between a host device and a device. The host device includes a clock source, front-end circuitry, a duty cycle monitor (DCM), link training logic, and a duty cycle adjustor (DCA). The front-end circuitry is to transmit a training sequence and a forward clock signal to the device and is to receive a strobe signal from the device over a physical transmission media. The DCM is to monitor duty cycle of the strobe signal and duty cycle of the clock signal. The link training logic is to determine a adjustment to the clock signal and is to generate a control signal. The DCA is to receive the clock signal and the control signal and is to adjust the clock signal to generate an adjusted forward clock signal in view of the control signal.

A circuit arrangement for clock and data recovery comprises a control unit, a phase-locked loop circuit and a sampling unit. The control unit is configured to derive a first reference signal and a second reference signal from an input signal. Furthermore, the control unit is configured to derive a common reference signal from one of the first reference signal and the second reference signal, selected depending on a mode of operation of the circuit arrangement. The phase-locked loop circuit is configured to generate an oscillator signal based on the common reference signal. The sampling unit is configured to extract a recovered data signal from the input signal.

A method for synchronizing time in an Ethernet-based network having a master network subscriber and a slave network subscriber includes sending out a first telegram via the master network subscriber, where the slave subscriber receives the first telegram at a first receipt time value of a local system time and stores the first receipt time value. The method can also include reading out the first receipt time value via the master subscriber, sending out a second telegram by the master subscriber, where the slave subscriber receives the second telegram at a second receipt time value of the local system time and stores the second receipt time value, and reading out the second receipt time value via the master network subscriber. A speed parameter of the local system time can be calculated from the receipt time values via the master network subscriber, and transmitted to the slave subscriber.

A method for synchronizing time in an Ethernet-based network having a master network subscriber and a slave network subscriber includes sending out a first telegram via the master network subscriber, where the slave subscriber receives the first telegram at a first receipt time value of a local system time and stores the first receipt time value. The method can also include reading out the first receipt time value via the master subscriber, sending out a second telegram by the master subscriber, where the slave subscriber receives the second telegram at a second receipt time value of the local system time and stores the second receipt time value, and reading out the second receipt time value via the master network subscriber. A speed parameter of the local system time can be calculated from the receipt time values via the master network subscriber, and transmitted to the slave subscriber.

A method is provided for sending an acknowledgement frame by a receiving entity. The method includes: subsequent to reception of a data frame sent by a sending entity and including a synchronization field containing an invariant item of information known to the entities and an identification field containing information identifying the sending entity and the receiving entity, sending an acknowledgment frame including a synchronization field; and calculating a signature of a transmission channel between the sending entity and the receiving entity, the synchronization field of the acknowledgment frame being obtained on the basis of the synchronization field of the data frame, by using the signature.

A method is provided for sending an acknowledgement frame by a receiving entity. The method includes: subsequent to reception of a data frame sent by a sending entity and including a synchronization field containing an invariant item of information known to the entities and an identification field containing information identifying the sending entity and the receiving entity, sending an acknowledgment frame including a synchronization field; and calculating a signature of a transmission channel between the sending entity and the receiving entity, the synchronization field of the acknowledgment frame being obtained on the basis of the synchronization field of the data frame, by using the signature.

Embodiments of this disclosure provide an apparatus and method for generating a transmitting sequence, a training sequence synchronization apparatus and method, an apparatus and method for estimating channel spacing and a system. The training sequence synchronization apparatus includes: a delay correlation processing unit configured to parallelly perform autocorrelation operations of different delay amounts on a receiving sequence containing a periodic training sequence to obtain multiple parallel correlation sequences; a superimposition processing unit configured to perform a superimposition operation on the multiple parallel correlation sequences to obtain a synchronization correlation sequence; and a synchronization extracting unit configured to perform a synchronization position extraction on the synchronization correlation sequence to obtain a synchronization position of the training sequence. With the embodiments of this disclosure, anti-noise performance of the training sequence may be enhanced.

A method of configuring a preamble of a downlink frame for synchronization in data frame transmission of a 60 GHz a wireless local area network system, the method comprising arranging a short preamble having a plurality of repetitive S symbols, and an IS symbol, and arranging a long preamble having a long cyclic prefix (CP) and a plurality of L symbols for frame synchronization and symbol timing by performing auto-correlation according to the length of window of the auto-correlation.

A method of configuring a preamble of a downlink frame for synchronization in data frame transmission of a 60 GHz a wireless local area network system, the method comprising arranging a short preamble having a plurality of repetitive S symbols, and an IS symbol, and arranging a long preamble having a long cyclic prefix (CP) and a plurality of L symbols for frame synchronization and symbol timing by performing auto-correlation according to the length of window of the auto-correlation.