Physical Layer Network Research Articles

Three-Way Channels With Multiple Unicast Sessions: Capacity Approximation via Network Transformation

A network of 3 nodes mutually communicating with each other is studied. This multi-way network is a suitable model for 3-user device-to-device communications. The main goal of this paper is to characterize the capacity region of the underlying Gaussian 3-way channel (3WC) within a constant gap. To this end, a capacity outer bound is derived using cut-set bounds and genie-aided bounds. For achievability, the 3WC is first transformed into an equivalent star-channel. This latter is then decomposed into a set of `successive' sub-channels, leading to a sub-channel allocation problem. Using backward decoding, interference neutralization, and known results on the capacity of the star-channel relying of physical-layer network coding, an achievable rate region for the 3WC is obtained. It is then shown that the achievable rate region is within a constant gap of the developed outer bound, leading to the desired capacity approximation. Interestingly, in contrast to the Gaussian two-way channel (TWC), adaptation is necessary in the 3WC. Furthermore, message splitting is another ingredient of the developed scheme for the 3WC which is not required in the TWC. The two setups are, however, similar in terms of their sum-capacity pre-log which is equal to 2. Finally, some interesting networks and their approximate capacities are recovered as special cases of the 3WC, such as the cooperative BC and MAC.

Investigation on iterative multiuser detection physical layer network coding in two-way relay free-space optical links with turbulences and pointing errors.

Physical layer network coding (PNC) improves the throughput in wireless networks by enabling two nodes to exchange information using a minimum number of time slots. The PNC technique is proposed for two-way relay channel free space optical (TWR-FSO) communications with the aim of maximizing the utilization of network resources. The multipair TWR-FSO is considered in this paper, where a single antenna on each pair seeks to communicate via a common receiver aperture at the relay. Therefore, chip interleaving is adopted as a technique to separate the different transmitted signals at the relay node to perform PNC mapping. Accordingly, this scheme relies on the iterative multiuser technique for detection of users at the receiver. The bit error rate (BER) performance of the proposed system is examined under the combined influences of atmospheric loss, turbulence-induced channel fading, and pointing errors (PEs). By adopting the joint PNC mapping with interleaving and multiuser detection techniques, the BER results show that the proposed scheme can achieve a significant performance improvement against the degrading effects of turbulences and PEs. It is also demonstrated that a larger number of simultaneous users can be supported with this new scheme in establishing a communication link between multiple pairs of nodes in two time slots, thereby improving the channel capacity.

An overview of multi-antenna technologies for space-ground integrated networks

Multi-antenna technologies have already achieved a series of great successes in the development of information networks. For future space-ground integrated networks (SGINs), the traditional various kinds of separated information networks will converge to a whole fully connected information network to provide more flexible and reliable services on a world scale. Regarding their great successes in existing systems, multi-antenna technologies will be of critical importance for the realization of SGINs and multi-antenna technologies are definitely one of the most important enabling technologies for future converged SGINs. In this article, a comprehensive overview on multi-antenna technologies is given. We first investigate multi-antenna technologies from a theoretical viewpoint. It is shown that we can understand multi-antenna technologies in a general and unified point of view. This fact has two-fold meanings. First, the research on multi-antennas can help us understand the relationships between different technologies e.g., OFDMA, CDMA, etc. On the other hand, multi-antenna technologies are easy to integrate into various information systems. Following that, we discuss in depth the potentials and challenges of the multi-antenna technologies on different platforms and in different applications case by case. More specifically, we investigate spaceborne multi-antenna technologies, airborne multi-antenna technologies, shipborne multi-antenna technologies, etc. Moreover, the combinations of multi-antenna technologies with other advanced wireless technologies e.g., physical layer network coding, cooperative communication, etc., are also elaborated.

Wireless-powered cooperative energy aware anycast routing in wireless sensor networks

A wireless-powered cooperative energy aware anycast routing protocol is proposed in this work. In contrary to conventional cooperative networks, it is considered here that all the relays did not have embedded energy supply, rather equipped with rechargeable batteries and energy harvesting units. Hence, from source signals, they accumulate sufficient harvested energy before the information is forwarded to its destination. Each relay between two basic modes will switch adaptively, which are information forwarding and energy harvesting. The research is limited to decode-and-forward scheme and fixed ratio combining, which works at the relay node of the network and the receiver end, respectively. The physical layer cooperative diversity and network layer multi-hop routing lead us to devise a minimum energy routing protocol as the joint optimization of power required for transmission at physical layer and also at network layer for the process to select a link. Simulating our algorithm demonstrates that the suggested cooperative energy aware anycast routing scheme has a better end-to-end delay and better ratio of packet delivery. Results further reveal that our proposed algorithm has improved energy consumption in comparison to the non-cooperative energy aware anycast scheme and the cooperation-based robust cooperative routing protocol scheme. Sensed data are allocated between nearby nodes by cooperative energy aware anycast routing in a cost-effective way in order to achieve maximum network lifetime.

Cellular-Aided Device-to-Device Communication: The Benefit of Physical Layer Network Coding

We introduce a cellular-aided device-to-device (D2D) communication model in which two D2D transmitters (Txs) send independent messages $W_{1}$ and $W_{2}$ to their intended D2D receivers (Rxs) with the help of a base station (BS). Specifically, at the first phase, two Txs send their signals to both the BS and two Rxs and then at the second phase the BS sends its signal to the Rxs. We consider a feasible channel assumption that D2D channels are not always available at the BS and each Tx, thus resulting in an outage. For the proposed cellular-aided D2D scheme, the Txs send their messages via physical layer network coding , and thus, the BS is able to decode $W_{1}\oplus W_{2}$ and broadcasts it to the Rxs. In consequence, from the fact that an outage does not occur if each Rx can decode $W_{1}$ or $W_{2}$ from its D2D links, the outage probability is significantly reduced compared with the D2D only communication where each Rx needs to decode its own message

Physical-Layer Network Coding in Two-Way Heterogeneous Cellular Networks With Power Imbalance

The growing demand for high-speed data, quality of service (QoS) assurance and energy efficiency has triggered the evolution of 4G LTE-A networks to 5G and beyond. Interference is still a major performance bottleneck. This paper studies the application of physical-layer network coding (PNC), a technique that exploits interference, in heterogeneous cellular networks. In particular, we propose a rate-maximising relay selection algorithm for a single cell with multiple relays based on the decode-and-forward strategy. With nodes transmitting at different powers, the proposed algorithm adapts the resource allocation according to the differing link rates and we prove theoretically that the optimisation problem is log-concave. The proposed technique is shown to perform significantly better than the widely studied selection-cooperation technique. We then undertake an experimental study on a software radio platform of the decoding performance of PNC with unbalanced SNRs in the multiple-access transmissions. This problem is inherent in cellular networks and it is shown that with channel coding and decoders based on multiuser detection and successive interference cancellation, the performance is better with power imbalance. This paper paves the way for further research in multi-cell PNC, resource allocation, and the implementation of PNC with higher-order modulations and advanced coding techniques.

Non‐binary turbo‐coded physical‐layer network coding on impulsive noise channels

Non-binary turbo codes promise excellent performance for a wide range of applications and environments, but research in this area is sparse. The performance of a non-binary turbo code defined in GF(4) on a two-way wireless relay channel (TWRC) employing physical-layer network coding, which is affected by impulsive noise is investigated. Simulation results for binary and non-binary turbo codes are presented and validated with an error floor analysis at the relay of the TWRC and it is observed that non-binary turbo codes significantly outperform binary turbo codes at low signal-to-noise ratios.

Performance Analysis of Repeat Accumulate Channel Code in MIMO Two Way Relay Channel with Physical Layer Network Coding

This paper provides a performance analysis of channel coding in multiple antenna TWRC with physical layer network coding. Data is transmitted from two source nodes S1 and S2 to a relay node with multiple antennas. The best antenna for transmission is selected and the data is transmitted through a Rayleigh fading channel with AWGN Noise after channel coding and BPSK modulation. Then this relay performs channel decoding and network coding operations and retransmits the coded sequence to their respective destinations. The channel coding employed here is repeat accumulate code. The BER analysis at the relay with and without channel coding is done using Monte Carlo simulations. The results show that the BER of a Bidirectional relay with channel coding is less than that without channel coding for multiple antennas. Also the analysis of SIMO, MISO and MIMO has been made for TWRC with channel coding. The results show that the performance of TWRC with channel coding has increased with increase in the number of antennas.

Approaching Single-Hop Performance in Multihop Networks: End-to-End Known-Interference Cancelation (E2E-KIC)

To improve the efficiency of wireless data communications, new physical-layer transmission methods based on known-interference cancellation (KIC) have been developed. These methods share the common idea that the interference can be cancelled when the content of it is known. Existing work on KIC mainly focuses on single-hop or two-hop networks, with physical-layer network coding (PNC) and full-duplex (FD) communications as typical examples. This paper extends the idea of KIC to general multi-hop networks, and proposes an end-to-end KIC (E2E-KIC) transmission method together with its MAC design. With E2E-KIC, multiple nodes in a flow passing through a few nodes in an arbitrary topology can simultaneously transmit and receive on the same channel. We first present a theoretical analysis on the effectiveness of E2E-KIC in an idealized case. Then, to support E2E-KIC in multi-hop networks with arbitrary topology, we propose an E2E-KIC-supported MAC protocol (E2E-KIC MAC), which is based on an extension of the Request-to-Send/Clear-to-Send (RTS/CTS) mechanism in the IEEE 802.11 MAC. We also analytically analyze the performance of the proposed E2E-KIC MAC in the presence of hidden terminals. Simulation results illustrate that the proposed E2E-KIC MAC protocol can improve the network throughput and reduce the end-to-end delay.

양방향 중계채널에서 중계기 다중안테나가 물리계층네트워크 코딩의 성능에 미치는 영향

양방향 중계채널에서 중계기 다중안테나가 물리계층네트워크 코딩의 성능에 미치는 영향

Joint Relay and Antenna Selection in MIMO PLNC Inter-vehicular Communication Systems over Cascaded Fading Channels

We investigate the joint relay and antenna selection performance in a multiple input multiple output (MIMO) Vehicle-to-Vehicle (V2V) communication system employing physical layer network coding (PLNC) with amplify-and-forward (AF) scheme at the relay antenna. Analytic results are derived under the cascaded Nakagami-m fading channel model assumption, which covers cascaded Rayleigh and conventional cellular channel models as well. We evaluate the performance of the system in terms of joint outage probability of sources and derive closed-form expressions for lower and upper bounds while an exact expression is found as a single integral form. Besides, the asymptotic diversity order is analyzed and quantified as a function of number of relays and antennas installed on the source and relay vehicles, and channel parameters. Finally, we verify the analytic derivations by computer simulations. Our results show that the outage probability performance decreases with the increasing cascading degrees of the channels but joint relay and antenna selection enhances the performance of the system superbly with the increasing number of relays and antennas. Also it is shown throughout all the simulation results, the lower bound for the joint outage probability seems to consistently be well tight for large SNR. Therefore it can be used for practical design of inter-vehicular communication systems which contain multiple relays and antennas.

Physical layer security issues in interference- alignment-based wireless networks

IA is a promising solution for the interference management of future wireless networks. On the other hand, physical layer security is a critical issue of wireless communications in the presence of adversaries. Recently, these two important fields tend to be researched closely together. In this article, some of the key results are summarized, and two primary attacks at the physical layer of IA-based networks, adversarial jamming and eavesdropping, are further studied. We first propose an anti-jamming scheme by aligning the jamming signal together with interference among users cooperatively when an adversarial jammer exists. Then an AN scheme is proposed, in which the external eavesdropping is disrupted by AN without introducing any additional interference to the legitimate network. To further analyze the potential threat, a collusive eavesdropping scheme by some hostile IA users in the network is also proposed. Simulation results are presented to show the effectiveness of these schemes. Finally, some future challenges are also summarized.

Linear Physical-Layer Network Coding and Information Combining for the <inline-formula> <tex-math notation="LaTeX">$K$ </tex-math> </inline-formula>-User Fading Multiple-Access Relay Network

We propose a new linear physical-layer network coding (LPNC) and information combining scheme for the $K$ -user fading multiple-access relay network (MARN), which consists of $K$ users, one relay, and one destination. The relay and the destination are connected by a rate-constraint wired or wireless backhaul. In the proposed scheme, the $K$ users transmit signals simultaneously. The relay and the destination receive the superimposed signals distorted by fading and noise. The relay reconstructs $L$ linear combinations of the $K$ users’ messages, referred to as $L$ network-coded (NC) messages, and forwards them to the destination. The destination then attempts to recover all $K$ users’ messages by combining its received signals and the NC messages obtained from the relay. We develop an explicit expression on the selection of the coefficients of the NC messages at the relay that minimizes the end-to-end error probability at a high signal-to-noise ratio. We develop a channel-coded LPNC scheme by using an irregular repeat-accumulate modulation code over GF( $q$ ). An iterative belief-propagation algorithm is employed to compute the NC messages at the relay, while a new algorithm is proposed for the information combining decoding at the destination. We demonstrate that our proposed scheme outperforms benchmark schemes significantly in both un-channel-coded and channel-coded MARNs.

A Hybrid EF/DF Protocol With Rateless Coded Network Code for Two-Way Relay Channels

In this paper, we investigate a rateless code design for a two-time slot two-way relay channel (TWRC), where network coding operation is employed at the relay. Rateless codes are used at both users and the relay nodes as they can cope with various channel conditions. We consider a general TWRC framework, where the two users may use different rateless code generator matrices, thus, the relay cannot directly recover the physical-layer network coded (PNC) message of the two users. We propose a hybrid estimate and forward (EF)/decode and forward (DF) protocol with rateless codes for the TWRC. In the proposed scheme, the relay uses a joint belief propagation decoding process to decode the messages of two users. Depending on whether the relay recovers both users’ messages, only one user’s message or no users’ messages, the relay will generate three different types of signals, namely, NC, soft NC, and soft PNC, respectively. We design the degree distributions of the rateless codes for the three nodes of the TWRC, to make them suitable not only for decoding at two users at high signal-to-noise ratio (SNR), but also for decoding at the relay at low SNR. We show that the proposed hybrid EF/DF protocol with the designed rateless codes outperforms other schemes significantly in terms of bit error rate performance.

Perfect Secrecy in Physical-Layer Network Coding Systems From Structured Interference

Physical-layer network coding (PNC) has been proposed for next generation networks. In this paper, we investigate PNC schemes with embedded perfect secrecy by exploiting structured interference in relay networks with two users and a single relay. In a practical scenario where both users employ finite and uniform signal input distributions, we establish upper bounds (UBs) on the achievable perfect secrecy rates and make these explicit when pulse amplitude modulation modems are used. We then describe two simple, explicit encoders that can achieve perfect secrecy rates close to these UBs with respect to an untrustworthy relay in the single antenna and single relay setting. Last, we generalize our system to a multiple-input multiple-output relay channel, where the relay has more antennas than the users and study optimal precoding matrices, which maintain a required secrecy constraint. Our results establish that the design of PNC transmission schemes with enhanced throughput and guaranteed data confidentiality is feasible in next generation systems.

Improved Performance Robustness of DSP-Enabled Flexible ROADMs Free from Optical Filters and O-E-O Conversions

Utilizing Hilbert-pair-based digital filtering, intensity modulation, and passive optical coupling, digital signal processing (DSP) enabled flexible reconfigurable optical add/drop multiplexers (ROADMs) are reported, which are free from optical filters and optical-electrical-optical (O-E-O) conversions and offer excellent flexibility, colorlessness, gridlessness, contentionlessness, adaptability, and transparency to physical-layer network characteristics. In this paper, the ROADM performance robustness against variations in numerous network design aspects is, for the first time to the best of our knowledge, extensively explored in intensity-modulation- and direct-detection-based optical network nodes. Numerical results show that DSPs not only enable the ROADMs to dynamically and flexibly perform add/drop operations at wavelength, subwavelength, and spectrally overlapped orthogonal subband levels but also considerably improve the ROADM performance robustness against variations in modulation formats, transmission system characteristics/impairments, and terminal equipment configurations.

Optimised Joint Channel Network Coding for Sensor Network with Correlated Sources

In this paper, we consider a Generalized Joint Channel Network Coding (GJCNC) scheme applied to Physical Layer Network Coding (PLNC) for a sensor network. For this purpose, M correlated sources desire to send information to one receiver by the help of a relay. The main goal is to estimate the information being sent from the last source at the destination by using the informations from sources and relay. For this purpose, we propose firstly a classic joint channel network coding at the relay which consider each source signal separately. Then, an optimization of this scheme is done by grouping by pair the nodes in the sensor network. The GJCNC decoding algorithm for each pair of sources is performed at the relay to improve performance. So, an iterative decoding scheme is proposed at the destination to extract the information sent from the last source. Simulation results show that by exploiting the correlation between sources, a significant gain can be achieved.

Optical Physical-Layer Digital Network Coding for 2.5-Gb/s RoF-Based FiWi Networks

We demonstrate the first digital optical physical-layer network coding (OPNC) scheme for 2.5-Gb/s ON/OFF keyed (OOK) subcarrier modulated (SCM) signals suitable for the application in fiber-wireless networks. The proposed OPNC scheme employs all optical XOR logic gates that rely on cross-phase modulation-based Semiconductor Optical Amplifier (SOA) Mach–Zehnder interferometers to perform encoding and decoding operations. The proposed encoding and decoding scheme is targeting deployment at the central office and the clients site at the remote antenna units, respectively. Proof of concept verification is experimentally demonstrated for 2.5-Gb/s OOK-SCM data using a 10-GHz subcarrier. Both synchronous and asynchronous operations are evaluated, achieving error free operation.

ARQ for Physical-Layer Network Coding

This paper investigates Automatic Repeat request (ARQ) designs for Physical-layer Network Coding (PNC) systems. Most prior work related to PNC explores its use in Two-Way Relay Channel (TWRC). We have previously found that, besides TWRC, there are many other PNC building blocks-building blocks are simple small network structures that can be used to construct a large network. In some of these PNC building blocks, the receivers can obtain side information through overhearing. Although such overheard information is not the target information that the receivers desire, the receivers can exploit the overheard information together with a network-coded packet received to obtain a desired native packet. This can yield substantial throughput gain. Our previous study, however, assumed what is sent always gets received. In practice, that is not the case. Error control is needed to ensure reliable communication. This paper focuses on ARQ designs for ensuring reliable PNC communication. The availability of overheard Information and its potential exploitation make the ARQ design of a network-coded system different from that of a non-network-coded system. In this paper, we lay out the fundamental considerations for such ARQ designs: 1) we put forth a framework to track the stored coded packets and overheard packets to increase the chance of packet extraction, and derive the throughput gain achieved therefore; 2) we investigate two variations of PNC ARQ, coupled and non-coupled ARQs, and prove that non-coupled ARQ is more efficient; 3) we show how to optimize parameters in PNC ARQ - specifically the window size and the ACK frequency - to minimize the throughput degradation caused by ACK feedback overhead and wasteful retransmissions due to lost ACK.

An alternative for the implementation of 40-km reach Ethernet at 400 Gb/s using an 8×50 Gb/s PHY at 1310 nm with SOA pre-amplification

The proposal and technical feasibility of a wavelength-division multiplexed system consisting of eight optical channels, each transporting data at 50Gb/s in NRZ modulation format, are presented. It is numerically demonstrated that, aided by a semiconductor optical pre-amplifier with 23dB of gain and setting the laser output power of an electro-absorption-based transmitter to +7.9dBm, a propagation distance of 40km over conventional single-mode optical fiber can be achieved with a BER < 1×10−13. Despite its high sensitivity, dispersion power penalty is minimized by setting a 400GHz channel plan in O-band whose center is slightly red-shifted from the zero-dispersion wavelength of the fiber. Moreover, non-zero dispersion is found to be useful in reducing the deleterious amplifier nonlinear gain modulation at mid-range distances, whereas four-wave mixing is found to play a practically inconsequential role. In agreement with previous results derived for 25Gb/s multi-channel links, optical signal-to-noise ratio degradation becomes the prominent corrupting factor at long fiber span lengths. The proposed architecture thus represents an alternative for the implementation of the physical layer of next-generation Ethernet or similar metropolitan data networks.