Provided herein are various improvements to laser communication ranging. In one example, a method includes combining a ranging signal with data communications into an optical transmission for receipt by a communication node, and obtaining an additional optical transmission transferred by the communication node comprising additional data communications combined with a retransmitted version of the ranging signal. The method includes determining an indication of a range to the communication node based at least on a comparison between properties of the ranging signal and properties of the retransmitted version of the ranging signal after separation from the additional data communications.

A system for data transport in a Distributed Antenna System (DAS) includes a plurality of remote Digital Access Units (DAUs) located at a Remote location. The plurality of remote DAUs are coupled to each other and operable to transport digital signals between the plurality of remote DAUs. The system also includes a plurality of central hubs. Each of the plurality of central hubs is in communication with one of the remote DAUs using an electrical communications path. The system further includes a plurality of transmit/receive cells. Each of the plurality of transmit/receive cells includes a plurality of remote hubs. Each of the remote hubs in one of the plurality of transmit/receive cells is in communication with one of the plurality of central hubs using an optical communications path.

A passive optical network includes a central office providing subscriber signals; a fiber distribution hub including an optical power splitter and a termination field; and a drop terminal. Distribution fibers have first ends coupled to output ports of a drop terminal and second ends coupled to the termination field. A remote unit of a DAS is retrofitted to the network by routing a second feeder cable from a base station to the hub and coupling one the distribution fibers to the second feeder cable. The remote unit is plugged into the corresponding drop terminal port, for example, with a cable arrangement having a sealed wave division multiplexer.

A derivation method is a derivation method performed by a communication system, including: a transmission step of transmitting a first radio-wave signal according to an optical signal with a first wavelength and a second radio-wave signal according to an optical signal with a second wavelength; a communication start time information acquisition step of acquiring information on a first communication start time and information on a second communication start time; a reception time information acquisition step of acquiring information on a first reception time that is a reception time related to the first radio-wave signal, and information on a second reception time that is a reception time related to the second radio-wave signal; and an optical fiber length derivation step of deriving a length of the optical fiber, based on the first communication start time, the first reception time, the second communication start time, the second reception time, a group velocity or a group delay time of the optical signal with the first wavelength, and a group velocity or a group delay time of the optical signal with the second wavelength.

n wavelengths set such that delay differences between optical signals due to wavelength dispersion in an optical fiber between accommodation and base stations are at equal intervals are assigned to n antenna elements of the base station which are at predetermined intervals. The accommodation station adjusts the phases of optical signals of the wavelengths or modulated signals that modulate the optical signals such that the amounts of phase shift of their RF signals are at predetermined intervals. The accommodation station transmits beacon signals multiple times while varying a transmission phase shift interval α.sub.1 and the terminal transmits beacon number information of a beacon signal selected based on received power multiple times. The accommodation station varies a reception phase shift interval α.sub.2 for each piece of beacon number information to determine a reception phase shift interval α.sub.2 which maximizes the received power and determines the transmission phase shift interval α.sub.1 based on the beacon number information received from the terminal.

A derivation method includes: a transmission step of transmitting, to a wireless terminal, a first radio-wave signal according to an optical signal with a first wavelength and a second radio-wave signal according to an optical signal with a second wavelength; a communication start time information acquisition step of acquiring information on a first communication start time and information on a second communication start time; a reception time information acquisition step of acquiring information on a first reception time and information on a second reception time; a transmission time period derivation step of deriving a first round trip time and deriving a second round trip time; and an optical fiber length derivation step of deriving an optical fiber length, based on the first round trip time, the second round trip time, a group velocity or a group delay time of the optical signal with the first wavelength, and a group velocity or a group delay time of the optical signal with the second wavelength.

A method of distance synchronization of a series of remote optical receiver points with an optical transmission point, the method including the steps of: (a) sending an optical timing pulse from the optical transmission point to each of the series of remote optical receiver points and back; (b) determining a round trip time of the timing pulse; and (c) storing an indicative measure of the roundtrip time of the timing pulse and utilising the indicative measure to adjust the timing of signals at the remote optical receiver points to determine the relative reception time of signals received by the series of remote optical receiver points.

A network or system in which a hub or primary node may communicate with a plurality of leaf or secondary nodes. The hub node may operate or have a capacity greater than that of the leaf nodes. Accordingly, relatively inexpensive leaf nodes may be deployed to receive data carrying optical signals from, and supply data carrying optical signals to, the hub node. One or more connections may couple each leaf node to the hub node, whereby each connection may include one or more spans or segments of optical fibers, optical amplifiers, optical splitters/combiners, and optical add/drop multiplexer, for example. Optical subcarriers may be transmitted over such connections, each carrying a data stream. The subcarriers may be generated by a combination of a laser and a modulator, such that multiple lasers and modulators are not required, and costs may be reduced. As the bandwidth or capacity requirements of the leaf nodes change, the number of subcarriers, and thus the amount of data provided to each node, may be changed accordingly. Each subcarrier within a dedicated group of subcarriers may carry OAM or control channel information to a corresponding leaf node, and such information may be used by the leaf node to configure the leaf node to have a desired bandwidth or capacity.

Methods, systems, and devices for a decision directed multi-modulus searching algorithm are described. A receiver may receive a signal including a set of data symbols. The receiver may iteratively determine a set of centroids for demodulating the set of data symbols (e.g., as part of a training procedure). The centroids may be used to demodulate the set of data symbols according to a modulation constellation associated with the set of data symbols. The training procedure may include, for each data symbol of a subset of data symbols, assigning a centroid of the set of centroids to each data symbol and updating the set of centroids based on assigning the centroid to each data symbol. The receiver may demodulate the set of data symbols based on the updated set of centroids.

The present disclosure relates to an optical line terminal that can be used in an optical fiber access system based on passive optical networks. The present disclosure further relates to a PON system; in particular the optical line terminal can be configured such that colourless components can be employed in a PON system using the optical line terminal and such that wireless communication can be directly employed in a PON system. One embodiment relates to an optical line terminal for a passive optical network, comprising at least a first transmitter for generating a time division multiplexed (TDM) optical carrier signal, said first transmitter comprising a first time lens optical signal processor configured to convert the TDM optical carrier signal to an wavelength division multiplexed (WDM) optical carrier signal for distribution to a plurality of users/ONUs, at least a second transmitter for generating a wavelength division multiplexed (WDM) downstream optical data signal for distribution to said plurality of users/ONUs, and at least one receiver for receiving and processing an upstream signal from said users.