Physical Layer Network Research Articles

Exploiting Interference for Intelligent Relaying in Integrated Space and Terrestrial Networks Based on PNC and SIC

The integrated space and terrestrial networks which incorporate various satellite systems and ground networks could provide a wide variety of services and global seamless network access. The integrated network is composed of multiple heterogeneous nodes and sub-networks which requires intelligent and efficient physical layer transmission techniques to maintain high-speed links between these subsystems. As a traditional technology in satellite communications, relay could still work as an important part in these heterogeneous and complex networks. In this paper, two interference exploitation schemes, i.e., physical-layer network coding (PNC) and successive interference cancellation (SIC) which can efficiently increase data exchange rate for relay systems are studied, and an intelligent relaying scheme combining both the advantages of these two schemes is proposed. Simulation results show the proposed adaptive transmission scheme achieves a smoother sum-rate gain while being more robust to dynamic topologies.

Globally Synchronized Time via Datacenter Networks

Synchronized time is critical to distributed systems and network applications in a datacenter network. Unfortunately, many clock synchronization protocols in datacenter networks such as NTP and PTP are fundamentally limited by the characteristics of packet-switched networks. In particular, network jitter, packet buffering and scheduling in switches, and network stack overheads add non-deterministic variances to the round trip time, which must be accurately measured to synchronize clocks precisely. We present the Datacenter Time Protocol (DTP), a clock synchronization protocol that does not use packets at all, but is able to achieve nanosecond precision. In essence, the DTP uses the physical layer of network devices to implement a decentralized clock synchronization protocol. By doing so, the DTP eliminates most non-deterministic elements in clock synchronization protocols and has virtually zero protocol overhead since it does not add load at layer-2 or higher at all. It does require replacing network devices, which can be done incrementally and with very small amount of hardware resource consumption. We demonstrate that the precision provided by DTP in hardware is bounded by 4TD where D is the longest distance between any two nodes in a network in terms of number of hops and T is the period of the fastest clock. The precision can be further improved by combining DTP with frequency synchronization. By contrast, the precision of the state-of-the-art protocol (PTP) is not bounded: The precision is hundreds of nanoseconds in an idle network and can decrease to hundreds of microseconds in a heavily congested network.

Investigation of error performance in network coded MIMO-VBLAST wireless communication systems

Abstract Paper aims to enhance the performance of bit error rate (BER) in wireless communication based on the multiple-input multiple-output (MIMO) system of vertical Bell laboratories layered space-time (VBLAST) algorithm. The VBLAST algorithm uses zero-forcing (ZF) and the minimum mean square error (MMSE) to evaluate the BER of wireless communication. MIMO VBLAST techniques function as an adaptive filter and can minimize the interference and multipath fading in the received signal of the channel. Physical layer network coding (PNC) is a new technique used to exploit the spatial diversity of the MIMO VBLAST system to improve the throughput and performance of wireless communication. The bit-error-rate (BER) of proposed VBLAST MIMO with PNC with binary phase-shift keying (BPSK) and quadrature phase-shift keying (QPSK) modulation over the additive white Gaussian noise and Rayleigh fading channel are analyzed. The performance of both BPSK and QPSK modulation in two and four antennas are compared. From the simulation results, it was found that the proposed scheme MIMO VBLAST PNC has a 45.2 % higher BER performance compared to the traditional MIMO scheme with an increase in the BER using MMSE and ZF respectively in both two and four antennas.

Outage probability bound of decode and forward two‐way relay employing optical spatial modulation over gamma‐gamma channels

In this study, free space optical communication has been studied for different atmospheric conditions. Spatial modulation (SM) has been used to improve the performance of two-way relay cooperative communication. The proposed system employs decode and forward (DF) relaying technique along with physical layer network coding, hence it has been named as optical SM based DF two-way relay. It enables full-duplex communication thereby enhancing the system efficiency. The transmit optical source index as well as the information are exchanged between the two bidirectional nodes. Performance analysis of the system has been carried out in terms of lower and upper bounds of outage probability and average data rate for N -γ cascaded fading channels. The analytical results have been validated by means of Monte Carlo simulations. The variation of the performance due to change in different parameters has also been reported in this study.

Buffer-Aided Max-Link Relay Selection for Multi-Way Cooperative Multi-Antenna Systems

In this letter, we present a relay-selection strategy for multi-way cooperative multi-antenna systems that are aided by a central processor node, where a cluster formed by two users is selected to simultaneously transmit to each other with the help of relays. In particular, we present a novel multi-way relay selection strategy based on the selection of the best link, exploiting the use of buffers and physical-layer network coding, that is called multi-way buffer-aided max-link (MW-Max-Link). We compare the proposed MW-Max-Link to existing techniques in terms of bit error rate, pairwise error probability, sum rate, and computational complexity. Simulations are then employed to evaluate the performance of the proposed and existing techniques.

Protocol Sequences for Asynchronous Multiple Access With Physical-Layer Network Coding

This letter proposes a new feedback-free solution that can put collisions to good use for decoding among asynchronous transmitters. Our key idea is to jointly exploit physical-layer network coding that allows a receiver to extract the bitwise XOR information out of time-overlapping signals, and a protocol-sequence-based scheme that allows each transmitter to deterministically determine which and when source packets contribute to the transmitted signal. In the application of group-based event detection, our design enables all source packets from asynchronous transmitters to be decoded within a quite short time duration. Simulation results show that our design, with low energy consumption, outperforms both conventional and state-of-the-art schemes in terms of the worst-case detecting delay.

Modeling and topology design for free-space optical networks

To date, free-space optical (FSO) networks play an important role in current network construction to support large-capacity transmission, where randomly distributed FSO terminals desire to exchange a tremendous amount of information over atmospheric turbulence channels. However, in the presence of atmospheric turbulence and misalignment fading channels, FSO network topology can be dynamic and disconnected. To mitigate the impact of dynamic network environments, appropriate higher-layer protocols should be designed. We explore a practical terrestrial mobile ad-hoc FSO network based on the bundle protocol of disruption-tolerant network, and the theoretical cross-layer system model between physical layer and network layer is derived. To design the topology, at the bundle layer, the distributed routing scheme centrality and probability (CAP) is proposed, where contact probability, sociocentric measure, and message replication strategy are considered simultaneously, and the joint forwarding decision rule is given. Simulation results on the opportunistic networking environment simulator are presented, which show that CAP can be better compared with the conventional end-to-end protocol-based routing scheme.

Decode-and-forward cooperative transmission in wireless sensor networks based on physical-layer network coding

In order to tackle the problem of reducing the transmission delay of multi-data acquisition source nodes in wireless sensor networks, we propose a cooperative method based on decode-and-forward (DF) and physical-layer network coding. In this proposed method, the two source nodes simultaneously transmit the respective information to the relay node and the data sink node using the orthogonal carriers. The relay node demodulates the received information separately from two source nodes and employs quadrature phase shift keying to modulate these information before forwarding them. The data sink node decodes the information of two source nodes using log likelihood ratio based on the signals received from the direct link and the relay link. Simulation results of bit error rate and system throughput show that the cooperative method can effectively improve the performance of the cooperative system compared with the traditional DF.

Fiber ring architecture implementation by using survivability techniques

In Communication Network(s) Physical Layer provides the path connectivity in a given network topology. In this protectioni.e. fault finding with respect to Link Failure and refurbishment in order to obtain Protection and Refurbishment Survivability Factor(PRSF). In optical network the switching capacity is controlled by Central Office(CO) or Manually, In order to be cost effective among different fiber network architecture such as 1:1, R:N. In the first category it applies theoretically, where as in R:N level the Fiber Cable (FC) is well protected in the form of Passive Active Optical Ring Network(PAORN) to its central switched architecture. In this Optical Elements(OE), Optical Devices(OD) are well used for Protection Refurbishment Triggering Mode(PRTM). In passive ring network is designed and implemented by using Optical Signal Protection Scheme (OSPS). In this paper further the feasibility of Fiber Loop Network Architecture (FLNA) is well compared by using Point-to-Point Passive Active Signal Transportation Mechanism (PPPASTM).

Physical Layer Performance of a Cooperative Amplify and Forward Scheme for MIMO WLANs

This paper proposes a novel cooperative amplify and forward (CAF) architecture for MIMO WLANs to improve their coverage and transmission rates, without requiring any modifications in the IEEE 802.11 standards at the clients. System models are used for analyzing the physical layer of CAF networks, and compared with the conventional amplify-and-forward (AF) and decode-and-forward (DF) networks. Numerical results demonstrate that the CAF network clearly outperforms conventional 802.11 networks, and AF and DF networks in terms of coverage and throughput.

A WDM Network Controller With Real-Time Updates of the Physical Layer Abstraction

This paper describes the implementation of a wavelength division multiplexing network controller that accounts for the varying conditions of the network physical layer in real time. A newly added software module is used to estimate the physical layer quality of transmission (QoT-E) in the form of a single transmission figure of merit for every line span in the network, i.e., the optical signal-to-noise ratio (OSNR) degradation. The estimated OSNR degradation is used to verify lightpath feasibility in the network, and produce optimal routing and wavelength assignment solutions in real time, without the need for a separate network planning tool. The OSNR degradation is estimated without requiring detailed knowledge of the optical components deployed in the network, and consequently the approach is vendor agnostic. The accuracy of the estimated OSNR degradation is assessed experimentally, and its impact on two network-wide performance indicators is studied through simulation.

When analog meets digital: Source-Encoded Physical-Layer Network Coding

We revisit Physical-Layer Network Coding (PLNC) in order to integrate this interference management technique in multi-hop wireless networks. We identify its strong coupling to the Two-Way Relay Channel (TWRC) as a main reason preventing it from becoming a staple in large networks. We introduce SE-PLNC (Source-Encoded PLNC), a new PLNC scheme that is traffic pattern independent and involves coordination only among one-hop neighbors, making PLNC significantly more practical to adopt in multi-hop wireless networks. To accomplish this, SE-PLNC introduces three innovations: it combines bit-level with physical-level network coding, it shifts most of the coding burden from the relay to the source of the PLNC scheme, and it leverages multi-path relaying opportunities available to a particular traffic flow. We evaluate SE-PLNC using proof-of-concept implementation on a Universal Software Radio Peripherals (USRP) testbed, theoretical analysis, and simulations. Testbed experiments show its real-life feasibility over a wide range of different channel conditions. The theoretical analysis highlight the scalability of SE-PLNC and its efficiency in large ad-hoc networks while large-scale simulations show that SE-PLNC improves network throughput by over 30% compared to state-of-the-art PLNC schemes.

Multi User-Multiple Input Multiple Output Detector Capacity Enhancement by Resource Allocation in Transmission of Physical Layer Network

Multi User-Multiple Input Multiple Output Detector Capacity Enhancement by Resource Allocation in Transmission of Physical Layer Network

Ultra-Dense LEO: Integration of Satellite Access Networks into 5G and Beyond

To support the explosive growth of wireless devices and applications, various access techniques need to be developed for future wireless systems to provide reliable data services in vast areas. With recent significant advances in ultra-dense low Earth orbit (LEO) satellite constellations, satellite access networks (SANs) have shown their significant potential to integrate with 5G and beyond to support ubiquitous global wireless access. In this article, we propose an enabling network architecture for dense LEO-SANs in which the terrestrial and satellite communications are integrated to offer more reliable and flexible access. Through various physical-layer techniques such as effective interference management, diversity techniques, and cognitive radio schemes, the proposed SAN architecture can provide seamless and high-rate wireless links for wireless devices with different quality of service requirements. Three extensive applications and some future research directions in both the physical layer and network layer are then discussed.

An Adaptive Optimal Mapping Selection Algorithm for PNC Using Variable QAM Modulation

Fifth generation wireless networks will need to serve much higher user densities than existing 4G networks, and will therefore require an enhanced radio access network (RAN) infrastructure. Physical layer network coding (PNC) has been shown to enable such high densities with much lower backhaul load than approaches, such as Cloud-RAN and coordinated multipoint. In this letter, we present an engineering applicable PNC scheme which allows different cooperating users to use different modulation schemes, according to the relative strength of their channels to a given access point. This is in contrast with compute-and-forward and previous PNC schemes which are designed for the two-way relay channel. A two-stage search algorithm to identify the optimum PNC mappings for given channel state information and modulation is proposed in this letter. Numerical results show that the proposed scheme achieves low bit error rate with reduced backhaul load.

Physical-Layer Network Coding Based Decoding Scheme for Random Access

In this paper, we propose an enhanced low-complexity binary physical-layer network coding (PNC) based decoding scheme for random access systems with binary phase-shift keying modulation to improve the system throughput. In the proposed scheme, the linear combinations of collided users’ messages in each time slot are first obtained by exploiting a low-complexity PNC decoding scheme. Based on the decoded linear combinations within a MAC frame, we then propose an enhanced message-level successive interference cancellation algorithm to recover more users’ messages. We propose an analytical framework for the PNC-based decoding scheme and derive a tight approximation of the system throughput for the proposed scheme. Subsequently, the number of repeated transmissions of a message, i.e., the number of replicas transmitted by each user, is optimized to further improve the system throughput and energy efficiency. Interestingly, the optimization results show that the optimal number of replicas for maximizing the energy efficiency is a constant for all offered loads. On the other hand, the optimal number of replicas that maximizes the system throughput decreases as the offered load increases. Numerical results show that the derived analytical results closely match with the simulation results. Furthermore, the proposed scheme achieves a considerable throughput improvement, compared to the CRDSA++ scheme.

Phase-Aligned Physical-Layer Network Coding in Visible Light Communications

Deploying relay nodes in visible light communication (VLC) relieves the requirement of line-of-sight transmission and thus extends the service coverage of VLC systems. In this paper, we propose to employ physical-layer network coding (PNC) in the VLC system to increase its throughput by boosting the data transmission at the relay node. We design a unified PNC–VLC framework that includes both the physical-layer signal processing algorithm and the medium access control method. To further improve the feasibility, we propose a novel phase-aligning method to counter the phase offset among nodes in practical VLC systems. Experimental results show a throughput improvement of 88.23% by employing the PNC–VLC framework, and the link budget is reduced by 4 dB at a bit error rate of 3.8 × 10−3 by using the phase-aligning method.

Optimizing Transmission Power and Energy Efficient Routing Protocol in MANETs

Energy is the important criterion for a decentralized network. By the cooperative physical layer network coding scheme, the requirement of energy transmission can be reduced. This could be implemented using two routing algorithms namely CCSPR and COSPNCR. An algorithm is constructed for reducing power consumption and rate control. In contradiction of the conventional power aware algorithms, an efficient power aware routing (EPAR) method is proposed which distinguishes the capability of nodes by its residual battery power, and through the expected energy that spent in reliably data packets forwarding on a specific link. To evaluate this, the data routing is performed with high mobility in dynamic environment. By using this algorithm, less cost path can be chosen and data rate can also be controlled. Thus energy consumption can be decreased and hence lifetime of a node can be improved. This approach first identifies the path having high lifetime and through that path, the communication will take place. This work consumes a lesser amount of energy for the routing, thus makes power efficient routing. Hence the throughput is increased and the power consumption is reduced. The conventional shortest path routing method on regular line and the grid line networks attains the gain of energy savings up to 45–75% correspondingly. By using EPAR algorithm, the energy consumption rate is minimized, so the network life time and the performance are improved. The energy consumption rate can be decreased to 80% by using EPAR approach in Mobile Ad hoc Networks.

Channel-aware cooperative routing in underwater acoustic sensor networks

This paper proposes cooperative routing algorithms to improve the performance of underwater acoustic sensor networks (UW-ASNs). With the consideration of the poor acoustic link quality, a cross-layer design of physical layer and network layer is described for selecting simultaneously routing relays (RR) for forwarding data on routing paths and cooperative relays (CR) for one-hop cooperative communications. In the networks, sources that have data to transmit independently selects their own relays (i.e., both RR and CR) among their neighbors based on their link quality indicators (i.e., signal-to-noise ratio (SNR), time of arrival (ToA)) and their physical distances represented by hop count (HC) to the destination. Exploiting packet receiving or overhearing in the networks, these parameters are averaged and updated frequently to adapt to the unreliable and varying characteristics of acoustic channel over the time. By this way, the “best” relays with the “best” estimated measurements are selected reliably. Our simulation results show that the proposed algorithms improve the network performance in terms of end-to-end delay, energy consumption and packet delivery ratio.

Design and Simulation of Bit-interleaved SCCPM with Physical-layer Network Coding

Serially concatenated continuous phase modulation (SCCPM) is bandwidth and power efficient in point-to-point communication systems. The physical-layer network coding (PNC) protocol propsed in 2006 can boost the throughput of a two-way relay channel (TWRC). In this paper, we integrate SCCPM with bit interleavers into PNC, i.e., SCCPM-PNC, which inherits the advantages of the both, in wireless TWRC. The decoding structure of the relay for the superimposed SCCPM signals is designed. Furthermore, the influences of various parameters such as the constraint length of convolutional code (CC), the interleaver size and the number of iterations, on the performance of SCCPM-PNC are simulated and discussed.