Repeater Station Research Articles

Surpassing the repeaterless bound with a photon-number encoded measurement-device-independent quantum key distribution protocol

Decoherence is detrimental to quantum key distribution (QKD) over large distances. One of the proposed solutions is to use quantum repeaters, which divide the total distance between the users into smaller segments to minimise the effects of the losses in the channel. Here we introduce a measurement-device-independent protocol which uses high-dimensional states prepared by two distant trusted parties and a coherent total photon number detection for the entanglement swapping measurement at the repeater station. We present an experimentally feasible protocol that can be implemented with current technology as the required states reduce down to the single-photon level over large distances. This protocol outperforms the existing measurement-device-independent and twin-field QKD protocols by achieving better key rates in general and higher transmission distance in total when experimental imperfections are considered. It also surpasses the fundamental limit of the repeaterless bound at a much shorter transmission distance in comparison to the existing TF-QKD protocols.

Optimal unambiguous discrimination of Bell-like states with linear optics

Quantum information processing using linear optics is challenging due to the limited set of deterministic operations achievable without using complicated resource-intensive methods. While techniques such as the use of ancillary photons can enhance the information processing capabilities of linear optical systems, they are technologically demanding. Therefore, determining the constraints posed by linear optics and optimizing linear optical operations for specific tasks under those constraints, without the use of ancillae, can facilitate their potential implementation. Here, we consider the task of unambiguously discriminating between Bell-like states using linear optics and without the use of ancillary photons. This is a basic problem relevant in diverse settings, for example, in the measurement of the output of an entangling quantum circuit or for entanglement swapping at a quantum repeater station. While it is known that exact Bell states of two qubits can be discriminated with an optimal success probability of 50%, we find, surprisingly, that for Bell-like states the optimal probability can be only 25%. We analyze a set of Bell-like states in terms of their distinguishability, entanglement as measured by concurrence, and parameters of the beam-splitter network used for unambiguous discrimination. Further, we provide the linear optical configuration comprising single-photon detectors and beam splitters with input-state-dependent parameters that achieves optimal discrimination in the Bell-like case.

Multiple-access relay stations for long-haul fiber-optic radio frequency transfer.

We report on the realization of a long-haul radio frequency (RF) transfer scheme by using multiple-access relay stations (MARSs). The proposed scheme with independent link noise compensation for each fiber sub-link effectively solves the limitation of compensation bandwidth for long-haul transfer. The MARS can have the capability to share the same modulated optical signal for the front and rear fiber sub-links, simplifying the configuration at the repeater station and enabling the transfer system to have the multiple-access capability. At the same time, we for the first time theoretically model the effect of the MARS position on the fractional frequency instability of the fiber-optic RF transfer, demonstrating that the MARS position has little effect on system's performance when the ratio of the front and rear fiber sub-links is around 1:1. We experimentally demonstrate a 1 GHz signal transfer by using one MARS connecting 260 and 280 km fiber links with the fractional frequency instabilities of less than 5.9 × 10-14 at 1 s and 8.5 × 10-17 at 10,000 s at the remote site and of 5.6 × 10-14 and 6.6 × 10-17 at the integration times of 1 s and 10,000 s at the MARS. The proposed scalable technique can arbitrarily add the same MARSs in the fiber link, which has great potential in realizing ultra-long-haul RF transfer.

All-Passive Cascaded Optical Frequency Transfer

We for the first time present an all-passive cascaded optical frequency transfer technique over a fiber link, in which the phase noise of the each fiber link introduced by environmental perturbation and the laser repeater station are simultaneously compensated by using passive phase noise cancellation. The laser repeater station consisting of a cavity-stabilized laser is employed as a regenerative amplifier with a 45 dB optical gain. We demonstrate a cascaded optical frequency transfer with two 100 km spooled fiber links and one laser repeater station, illustrating an instability of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.8\times 10^{-15}$ </tex-math></inline-formula> at the integration of 1 s and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.9\times 10^{-19}$ </tex-math></inline-formula> at 10,000 s improved by a factor of 2 compared to the single-span 200 km fiber link. Dividing the whole fiber link into sub-sections could significantly improve the bandwidth of the phase noise compensation. Additionally, all-passive phase noise cancellation has the advantage of avoiding the servo bumps in the transferred light relative to the conventional active technique. The proposed technique provides a promising solution for high-performance and robust long-distance optical frequency transfer.

Fishermen Rescue Mission

Abstract: The basic idea of this project is to save the life of fishermen at sea. We do this by installing a module in the fisherman’s life jacket. This module will be a transmitter which can transmit its current location. This module is made to be a floating module. Which is also waterproof. The person in the dangerous situation can press the button and the transmitter starts transmitting the location. The data is then transferred to the receiver via a network built by WLAN module which is also made by us. The WLAN module consists of the transmitter and the receiver and acts as repeater stations. These transmitters and receivers also contain the LoRa module. The LoRa module is Incorporated because of its long range communication specifications. The repeater station is placed buoy the help of buoys. Buoys are floating objects which are then anchored to make them stationary. The receiver is a portable one and dynamically we can get the location of the transmitter. Hence we can locate the person and then rescue them Keywords: LoRa, WLAN, GPS module,

Airborne Distributed Coherent Aperture Radar Synchronization Error Calibration Method Based on Prominent Points

Airborne Distributed Coherent Aperture Radar (DCAR) has the advantages of wide observation range, high maneuverability and flexible deployment. However, airborne DCAR is confronted with more stringent time, space and phase synchronization requirements. Therefore, an airborne DCAR signal model and its matrix representation based on Slow-Time Code Division Multiple Access (ST-CDMA) waveform are established successively. Moreover, the influence on target coherence synthesis resulted from time, space and phase synchronization errors is analyzed in detail, and a novel airborne DCAR synchronization error calibration method based on prominent points is proposed. This method utilizes the target parameter search strategy to eliminate the grid mismatch filtering firstly. Then, with the utilization of estimation approaches based on target model or repeater station model, the unit platform position error is calibrated. Finally, equivalent amplitude and phase errors are calibrated by Eigen structure methods. The validity of the proposed method to calibrate the airborne DCAR synchronization error is demonstrated by simulation experiments.

Limitations for private randomness repeaters

Cryptographic protocols are often based on the two main resources: private randomness and private key. In this paper, we develop a relationship between these two resources. First, we show that any state containing perfect, directly accessible, private key (a private state) is a particular case of the state containing perfect, directly accessible, private randomness (an independent state). We then demonstrate a fundamental limitation on the possibility of transferring the privacy of random bits in quantum networks with an intermediate repeater station. More precisely, we provide an upper bound on the rate of repeated randomness in this scenario, similar to the one derived for private key repeaters. This bound holds for states with positive partial transposition. We further demonstrate the power of this upper bound by showing a gap between the localisable and the repeated private randomness for separable Werner states. In the case of restricted class of operations, we provide also a bound on repeated randomness which holds for arbitrary states.

One-Way Quantum Repeater Based on Near-Deterministic Photon-Emitter Interfaces

We propose a novel one-way quantum repeater architecture based on photonic tree-cluster states. Encoding a qubit in a photonic tree-cluster protects the information from transmission loss and enables long-range quantum communication through a chain of repeater stations. As opposed to conventional approaches that are limited by the two-way communication time, the overall transmission rate of the current quantum repeater protocol is determined by the local processing time enabling very high communication rates. We further show that such a repeater can be constructed with as little as two stationary qubits and one quantum emitter per repeater station, which significantly increases the experimental feasibility. We discuss potential implementations with diamond defect centers and semiconductor quantum dots efficiently coupled to photonic nanostructures and outline how such systems may be integrated into repeater stations.

Optimization of Standalone Photovoltaic System Considering Loss of Power Supply Probability for Repeater Station of Nepal Telecom

Telecommunication plays the vital role in the human life and has become an integrated part of the society. The rapidly growing information and communications technology and increasing competition in telecommunication markets triggers the telecom operators to extend their networks and services to their potential customers in different geographical locations. It necessitates them to install repeaters and communication towers powered by standalone Photovoltaic system in remote rural areas. This paper presents optimization of standalone photovoltaic system maximizing reliability in one of such remotely located Palethar Repeater Station of Nepal Telecom situated in Dadeldhura district of Far-western region. The optimization is carried out using Genetic Algorithm in MATLAB software for given load profile enhancing reliability of the system with maximum reduction of overall system cost. The loss of power supply probability (LPSP) is considered for reflecting the reliability of the system. The paper discusses different optimal configuration of standalone PV system under various values of LPSP after optimization.

Design of Reconfigurable Digital IF Filter With Low Complexity

Due to limited frequency resources, new services are being applied to the existing frequencies, and service providers are allocating some of the existing frequencies for newly enhanced mobile communications. Because of this frequency environment, repeater and base station systems for mobile communications are becoming more complicated, and frequency interference caused by multiple bands and services is getting worse. Therefore, a heterodyne receiver using intermediate frequency (IF) filters with high selectivity has been used to minimize the interference between frequencies. However, repeater and base station systems in mobile communications employing fixed IF filters cannot actively cope with the usage of multiple frequency bands, the application of various services, and frequency recycling. Therefore, this brief proposes a reconfigurable digital IF filter with variable center frequency and bandwidth while achieving high selectivity as existing IF filters. The center frequency of a filter can vary from 10 MHz to 62.5 MHz, and the filter bandwidth can be selective to one of 10 MHz, 15 MHz, and 20 MHz. The proposed digital filter also reduces the complexity of adders and multipliers by 38.81% and 41.57%, respectively, compared to an existing digital filter by using a filter bank and a multi stage structure. This digital IF filter is fabricated on a 130-nm CMOS process and occupies 5.90 mm2.

A Detection Method of Time Slot Power Based on ARM Platform

In order to effectively detect the time slot power of the repeater station and the base station which the mobile communication system of time division multiple access (TDMA) communication systems, In this paper, a signal acquisition hardware circuit based on ARM platform is designed, and a method of synthetically calculating time slot power is proposed. The signal acquisition circuit used an 8 channel ADC108 chip connected to ARM through the SPI bus, the time slot power detection method is composed of signal timing acquisition module, data acquisition module and data processing module to calculate the time slot power. And the validity of the method in detecting the time slot power under the condition of system boot and normal operation is tested, the system CPU resource consumption, the error value of the tested time slot power are tested also. The results show that the proposed method can effectively detect and control time slot power of TDMA system, and it has important significance to the repeater station and the base station system network signal coverage and optimization.

Long-Range Big Quantum-Data Transmission.

We introduce an alternative type of quantum repeater for long-range quantum communication with improved scaling with the distance. We show that by employing hashing, a deterministic entanglement distillation protocol with one-way communication, one obtains a scalable scheme that allows one to reach arbitrary distances, with constant overhead in resources per repeater station, and ultrahigh rates. In practical terms, we show that, also with moderate resources of a few hundred qubits at each repeater station, one can reach intercontinental distances. At the same time, a measurement-based implementation allows one to tolerate high loss but also operational and memory errors of the order of several percent per qubit. This opens the way for long-distance communication of big quantum data.

Development of Water-Surface Robotic Vehicle to Assist Communication Between Remotely Operated Vehicle Underwater Robot and Control Station

This paper developed a water-surface robotic vehicle that act as repeater station to assist the communication between ROV (Remotely Operated Vehicle) underwater robot and control station. The key issue here is how the robot can relay the data communication between the ROV and the control station. The communication between repeater Station and control station is based on wireless, whereas the communication between repeater Station and ROV is based on wire. Data that have transmit from control station is received by Repeater Station and continued to the ROV through wire. The Power needed is suplied by photovoltaic (PV) to the Repeater Station and the ROV. The position of Repeater Station is controlled, so the position of Repeater Station and ROV always in parallel. In practices, there are two way directly communication between control station with ROV, that are based on wireless and through wire. Nevertheless, wireless communication system never used to observed on the ocean or the deep waters because there is a high attenuation of a signal when cross the air-water boundary. Based on these problems, we make a Repeater Station that used a buoyant communication system models. Communication from control station to Repeater Station in the form of motion control and data. Whereas, communication from Repeater Station to ROV in the form of motion control, data, and power supply. Communication frequency is at 5,8 GHz for audio video and 433 MHz for motion control and telemetry. The connection wire between Repeater Station and ROV can go along and shorten with automatically roll as feature. Electricity from PV is strorage to a battery in the Repeater Station. Charging of the battery occur when battery power is not full and will cease if battery power is being full. Power of the battery must be full if want to operated the Repeater Station. The availability of the Repeater Station is expected to assist the communication between ROV underwater robot with control station, so ROV can be controlled remotely and can increase range of the reach.

Coherence transfer of subhertz-linewidth laser light via an 82-km fiber link

We demonstrate optical coherence transfer of subhertz-linewidth laser light through fiber links by actively compensating random fiber phase noise induced by environmental perturbations. The relative linewidth of laser light after transferring through a 32-km urban fiber link is suppressed within 1 mHz (resolution bandwidth limited), and the absolute linewidth of the transferred laser light is less than 0.36 Hz. For an 82-km fiber link, a repeater station is constructed between a 32-km urban fiber and a 50-km spooled fiber to recover the spectral purity. A relative linewidth of 1 mHz is also demonstrated for light transferring through the 82-km cascaded fiber. Such an optical signal distribution network based on repeater stations allows optical coherence and synchronization available over spatially separated places.

Novel off-air repeater station in Hong Kong for government departments

The unified digital communications platform (UDCP) is a shared system for critical radio communication among government departments in Hong Kong for public safety. With a view to the increasing demand on maritime safety and law enforcement, there is an imminent need to improve the sea coverage of UDCP. The Electrical and Mechanical Services Department has been engaged for design and administration of the improvement project. With the support of various stakeholders, an innovative and cost-effective idea for an outdoor off-air repeater station is suggested. Despite the technical constraints in system design and installation, the off-air repeater station is successfully installed and its benefit is well demonstrated and appreciated by government departments.

Performance Measures of Tele-Protection System Based on Networked Microwave Radio Link

The purpose of paper is to compute reliability of Digital Tele-Protection System employing Digital Microwave Radio Link. In this paper, the whole Tele- Protection system is divided into six subsystems. The first subsystem is digital relaying equipment. Second subsystem is the tale-protection signaling equipment where the timing to sample line power currents is synchronized. Both relaying and Tele-Protection signaling equipments, are now assemble three-phase current data, sampled at 600 Hz for 50 Hz EHV systems and some control data into a 90 bit frame format at a transmission rate of 54 Kb/s. A frame consists of a frame synchronization field and some information fields including a cycle's redundancy check field. The third subsystem, Tele-Protection signed multiplexing equipment generates a super frame by multiplexing the seven, 54 Kb/s Tele-Protection signals into a 1.544 Mb/s stage using multi-point sampling technique to minimize the delay time variation and send them to the subsystem four, which is radio equipment, from here the data is transmitted with the help of the channel (subsystem 5) to the repeater station (subsystem 6). The subsystem six is used to remove the noise and to improve the power of the data. In this paper, we have taken standby digital relaying equipment and that can be online through an imperfect switching device. Also parallel redundant Tele-Protection signaling equipment is taken to improve system's overall performance.

Assisted entanglement distillation

Motivated by the problem of designing quantum repeaters, we study entanglement distillation between two parties, Alice and Bob, starting from a mixed state and with the help of ``repeater'' stations. To treat the case of a single repeater, we extend the notion of entanglement of assistance to arbitrary mixed tripartite states and exhibit a protocol, based on a random coding strategy, for extracting pure entanglement. The rates achievable by this protocol formally resemble those achievable if the repeater station could merge its state to one of Alice and Bob even when such merging is impossible. This rate is provably better than the hashing bound for sufficiently pure tripartite states. We also compare our assisted distillation protocol to a hierarchical strategy consisting of entanglement distillation followed by entanglement swapping. We demonstrate by the use of a simple example that our random measurement strategy outperforms hierarchical distillation strategies when the individual helper stations' states fail to individually factorize into portions associated specifically with Alice and Bob. Finally, we use these results to find achievable rates for the more general scenario, where many spatially separated repeaters help two recipients distill entanglement.

Performance Evaluation of Two-Hop Wireless Link under Rayleigh and Nakagami-m Fading Channel for 8-PSK and 16-QAM

One of the major challenges in wireless communications, especially in urban area, is to detect the digital data under different fading environment and additive white Gaussian noise (AWGN). In a two-hop wireless links, each link is affected by fading and noise which degrades the overall performance of the communication system. In this paper performance of two-hop link is analyzed under Rayleigh and Nakagami-m fading environments separately for 8-PSK and 16-QAM modulation schemes. The objective of the paper is to observe the relative impact of two fading environments on the two above mentioned modulation schemes if no combining scheme or error correction measure is taken on the repeater station.

Cascaded multiplexed optical link on a telecommunication network for frequency dissemination

We demonstrate a cascaded optical link for ultrastable frequency dissemination comprised of two compensated links of 150 km and a repeater station. Each link includes 114 km of Internet fiber simultaneously carrying data traffic through a dense wavelength division multiplexing technology, and passes through two routing centers of the telecommunication network. The optical reference signal is inserted in and extracted from the communication network using bidirectional optical add-drop multiplexers. The repeater station operates autonomously ensuring noise compensation on the two links and the ultra-stable signal optical regeneration. The compensated link shows a fractional frequency instability of 3 x 10(-15) at one second measurement time and 5 x 10(-20) at 20 hours. This work paves the way to a wide dissemination of ultra-stable optical clock signals between distant laboratories via the Internet network.

Near-unit-fidelity entanglement distribution scheme using Gaussian communication

We show how to distribute with percentage success probabilities almost perfectly entangled qubit memory pairs over repeater channel segments of the order of the optical attenuation distance. In addition to some weak, dispersive light-matter interactions, only Gaussian state transmissions and measurements are needed for this scheme, which even beats the coherent-state-benchmark for entanglement distribution based on error-free non-Gaussian measurements. This is achieved through two innovations: first, optical squeezed states are utilized instead of coherent states. Secondly, the amplitudes of the bright signal pulses are reamplified at each repeater station. This latter variation is a strategy reminiscent of classical repeaters and would be impossible in single-photon-based schemes.