Unicast Signal Research Articles

NOMA-Aided Joint Radar and Multicast-Unicast Communication Systems

The novel concept of non-orthogonal multiple access (NOMA) aided joint radar and multicast-unicast communication (Rad-MU-Com) is investigated. Employing the same spectrum resource, a multi-input-multi-output (MIMO) dual-functional radar-communication (DFRC) base station detects the radar-centric users (R-user), while transmitting mixed multicast-unicast messages both to the R-user and to the communication-centric user (C-user). In particular, the multicast information is intended for both the R- and C-users, whereas the unicast information is only intended for the C-user. More explicitly, NOMA is employed to facilitate this <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">double spectrum sharing</i> , where the multicast and unicast signals are superimposed in the power domain and the superimposed communication signals are also exploited as radar probing waveforms. First, a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">beamformer-based</i> NOMA-aided joint Rad-MU-Com framework is proposed for the system having a single R-user and a single C-user. Based on this framework, the unicast rate maximization problem is formulated by optimizing the beamformers employed, while satisfying the rate requirement of multicast and the predefined accuracy of the radar beam pattern. The resultant non-convex optimization problem is solved by a penalty-based iterative algorithm to find a high-quality near-optimal solution. Next, the system is extended to the scenario of multiple pairs of R- and C-users, where a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cluster-based</i> NOMA-aided joint Rad-MU-Com framework is proposed. A joint beamformer design and power allocation optimization problem is formulated for the maximization of the sum of the unicast rate at each C-user, subject to the constraints on both the minimum multicast rate for each R&C pair and on accuracy of the radar beam pattern for detecting multiple R-users. The resultant joint optimization problem is efficiently solved by another penalty-based iterative algorithm developed. Finally, our numerical results reveal that significant performance gains can be achieved by the proposed schemes over the benchmark schemes employing conventional transmission strategies.

Performance analysis of nyquist superchannel with multicast overlay system

We demonstrate the performance of Nyquist superchannel system along with multicast overlay system which employs Nyquist dual polarization quadrature amplitude modulation (DP-16QAM) and polarization shift keying (POLSK) modulation to transmit 640 GB/s as unicast and differential phase shift keying (DPSK) modulation for 40Gb/s as multicast. The performance of multicast overlay system transmits total 5.1Tb/s data rate using 8*640 GB/s unicast signal and 40Gb/s multicast signals. From the simulation results, best BER, input power, and Q-factor have been analyzed for multicast overlay system. In addition, the proposed design Nyquist DP-16QAM modulation offers efficient utilization of bandwidth for transmission of each channel at the high data rate.

Fronthaul Compression and Precoding Optimization for NOMA-Based Joint Transmission of Broadcast and Unicast Services in C-RAN

This paper tackles a non-orthogonal multiplexing (NOM)-based realization of broadcast-unicast overlay transmission in cloud-radio access networks (C-RANs). In particular, fronthaul compression and precoding are jointly optimized to maximize the throughput in the considered network. The problem further optimizing the power allocation between broadcast and unicast signals is addressed as well. The algorithmic solutions are obtained by means of majorization minimization (MM)-type difference-of-convex (DC) programming. Moreover, the proposed solutions are further extended to cope with the uncertainty of channel state information (CSI) to enable robust transmission. Computer simulations are performed to verify that the proposed scheme attains substantial achievable rate gain over the conventional decentralized precoding in entire parameter regions considered.

Two-Layered Superposition of Broadcast/Multicast and Unicast Signals in Multiuser OFDMA Systems

We study optimal delivery strategies of one common and ${K}$ independent messages from a source to multiple users in wireless environments. In particular, two-layered superposition of broadcast/multicast and unicast signals is considered in a downlink multiuser OFDMA system. In the literature and industry, the two-layer superposition is often considered as a pragmatic approach to make a compromise between the simple but suboptimal orthogonal multiplexing (OM) and the optimal but complex fully-layered non-orthogonal multiplexing. In this work, we show that only two-layers are necessary to achieve the maximum sum-rate when the common message has higher priority than the ${K}$ individual unicast messages, and OM cannot be sum-rate optimal in general. We develop an algorithm that finds the optimal power allocation over the two-layers and across the OFDMA radio resources in static channels and a class of fading channels. Two main use-cases are considered: i) Multicast and unicast multiplexing when ${K}$ users with uplink capabilities request both common and independent messages, and ii) broadcast and unicast multiplexing when the common message targets receive-only devices and ${K}$ users with uplink capabilities additionally request independent messages. Finally, we develop a transceiver design for broadcast/multicast and unicast superposition transmission based on LTE-A-Pro physical layer and show with numerical evaluations in mobile environments with multipath propagation that the capacity improvements can be translated into significant practical performance gains compared to the orthogonal schemes in the 3GPP specifications. The impact of real channel estimation is also analyzed and it is shown that significant gains in terms of spectral efficiency or increased coverage area are still available even in the presence of estimation errors and imperfect interference cancellation for the two-layered superposition system.

New Security Improvements in Next-Generation Passive Optical Networks Stage 2

Passive optical networks are currently the most promising solution for access networks. These networks rely on broadcast signal distribution in the downstream direction and unicast signal transmission in the upstream direction. The upstream direction is controlled by optical line termination (OLT). The broadcast transmission method increases security vulnerability because the attacker is able to connect his/her modified optical network unit (ONU) to the free port of the splitter (commonly in the basement). We present the concept for the activation process of ONUs based on physical unclonable function (PUF) for next-generation passive optical networks stage 2 (NG-PON2). The use of PUF increases security in the NG-PON2. Furthermore, the registration identifier (ID) is not stored in a nonvolatile memory, in comparison with the common solution defined by the International Telecommunication Union (ITU) recommendation G.989.3. An attacker cannot perform a reverse engineering attack to obtain the registration ID. For this reason, the attacker cannot clone an ONU. We proposed security improvements that involve authentication, encryption, integrity protection, and data origin verification methods in the NG-PON2. Our model uses the standard implementation of the transmission convergence layer of NG-PON2 with the new physical layer operations, administration, and maintenance (PLOAM) messages. The recommendation G.989.3 allows specifying own PLOAM messages since not all IDs are used in the current specification.

Minimum shift keying based protection mode capable wavelength division multiplexed passive optical network optical overlay system

We explored the functioning of an optical overlay of multicast and unicast data streams on a survival wavelength division multiplexed passive optical network using intensity and minimum shift keying modulation for both single and multiuser. In optical line terminal, using a sinusoidal clock, optical subcarriers are generated not only to carry the multicast and unicast data streams simultaneously but also in case of fiber failure, protection mode is enabled to carry the data streams smoothly. Here, 10 Gbps downstream multicast in normal mode and unicast signals both in normal and protection mode are transmitted error-free through 30 km dispersion shifted fiber. In both the cases 10 Gbps upstream signal is modulated and sent back to the optical line terminal. For single user nearly similar power penalty is witnessed for downstream unicast as well as re-modulated upstream data in both the conditions and also when multicast data is disabled. The power penalties between single and multiuser for both the modes are found to be approximately 0.06, 0.42 and 0.7 dB for unicast MSK, multicast and upstream respectively.

Limitations on Hybrid WDM/OTDM Multicast Overlay System Imposed by Nonlinear Polarization Effect and its Mitigation

This paper investigates the nonlinear polarization effect of 120-Gbps polarization and subcarrier multiplexed unicast signal and 40-Gbps multicast signal on transmission performance of hybrid WDM/OTDM multicast overlay system. The interaction between Kerr nonlinearity and polarization mode dispersion (PMD) induced nonlinear cross polarization modulation (XPolM) effect can significant limits the transmission performance of hybrid WDM/OTDM multicast overlay system. The effect of signal input power, extinction ratio, PMD, and differential group delay is studied in multicast enable and disable mode. Also, a mitigation technique of nonlinear polarization effect is introduced by use of group delay compensator, judicious addition of some PMD, and inline pre-DCF in the transmission channel. It is also found that the amplitude to phase interaction between multicast and unicast signal transmission can be suppressed by controlling the loss of orthogonality.

Performance analysis of hybrid WDM-OTDM optical multicast overlay system employing 120 Gbps polarization and subcarrier multiplexed unicast signal with 40 Gbps multicast signal

In this paper, we have propose and investigated the performance of hybrid WDM-OTDM optical multicast overlay system which employs 120Gbps unicast and 40Gbps multicast data operating over SMF+DCF and amplifier link in C-band. The polarization and subcarrier multiplexed modulation formats are used to obtain 120Gbps unicast data and DPSK (differential phase shift keying) modulation format for 40Gbps multicast data transmission. In multicast operation, DPSK data is superimposed on to multiplexed unicast data channels. The impact of extinction ratio, input power and transmission distance on the performance of proposed system in terms of output optical power, BER and Q-factor has been investigated for both unicast and multicast data. We have also concluded that polarization and subcarrier multiplexed modulation formats are promising option to increase per channel capacity and less vulnerable to CD and PMD. In addition, the proposed system using hybrid modulation techniques offers higher bandwidth utilization efficiency at higher per channel data rate than conventional modulation formats.

Performance analysis of long reach colorless wavelength division multiplexed-orthogonal frequency division multiplexing-passive optical network with broadcast capability

A colorless wavelength division multiplexed-orthogonal frequency division multiplexing-passive optical network (WDM-OFDM-PON) is presented, which is capable of supporting symmetric 10 Gbps downlink direct detection (DD) OFDM unicast signal, broadcast signal, and uplink on–off keying (OOK) signal up to 60 km that includes both single mode and dispersion compensation fiber. At each optical network unit (ONU), DD has been used to receive downlink unicast and broadcast OFDM data. A delay interferometer (DI) has been used at a central office to achieve 10 Gbps uplink signal transmission over 60 km distance utilizing a reflective semiconductor optical amplifier (bandwidth=1.5 GHz) at the ONU because DI works as a vestigial sideband filter and an optical equalizer. Broadcast channel does not affect the system performance because it generates a limited interference of the order of 0.1 to 0.28 dB to downlink and uplink channels, and this interference is distributed to every ONU. For bit error rate of 10−9, the receiver sensitivity of −24, −23.1, and −20.14 dBm is achieved by simulating downlink OFDM unicast channels, OFDM broadcast channel, and uplink OOK unicast channels, respectively, for a symmetric data rate of 10 Gbps over 60 km.

Dynamic λ-OFDMA with selective multicast overlaid

This paper experimentally demonstrates a novel dynamic λ-OFDMA architecture with selective differential phase shift keying (DPSK) overlaid and colorless optical network unit (ONU). The wavelength can be dynamically assigned to the splitter node in demand through a group of optical switches. Multicast control is realized through an alternative local oscillator at the optical line terminal (OLT). The 10-Gb/s × 4-channel 16QAM-OFDM unicast signal with 2.5-Gb/s DPSK overlaid and 1.25-Gb/s upstream signal have been transmitted over 25-km fiber successfully.

An optical multicast overlay scheme using optical sub-carriers for WDM passive optical networks

We propose to make use of optical sub-carriers to realize optical multicast overlay on a WDM passive optical network. By employing optical carrier suppression technique at each downstream optical transmitter at the OLT, two coherent optical sub-carriers are generated to carry the 10-Gb/s downstream unicast DPSK signal and the 10-Gb/s downstream multicast ASK signal, separately without any additional light sources. At the ONU, the 10-Gb/s upstream data is superimposed on the received downstream unicast DPSK signal, to form the upstream ASK signal. System characterization is performed to optimize the performance. In addition, we further demonstrate simultaneous optical overlay of two streams of multicast data in the network.

Transmission Schemes for Multicarrier Broadcast and Unicast Hybrid Systems

Wireless infrastructures can be conveniently categorized into two types: those that provide point-to-point dasiaunicastpsila connectivity (e.g., cellular) and others that are dasiabroadcastpsila in nature (such as TV and radio) and are inherently point-to-multipoint. This paper introduces a transmission scheme for multicarrier hybrid system that supports both broadcasting and unicasting on a single-frequency platform. In particular, we present a dirty-paper coding (DPC) based overlay architecture to enable interference-free reception of unicast signals. The fundamental limits of hybrid communications are investigated, along with power allocation algorithms that approach the hybrid capacity. Our results show that OFDMA for unicast offers the best hybrid performance and considerable gains over orthogonal multiplexing (e.g., TDM/FDM) can be achieved through interference-free overlay. In addition, we describe approaches to further improve the spectral efficiency and the broadcast coverage through multicell collaboration.

A WDM passive optical network enabling multicasting with color-free ONUs

We propose a wavelength-division-multiplexed (WDM) passive optical network (PON) to provide conventional unicast data and downstream multicast function. At the optical line terminal (OLT), for each WDM channel, a dual-drive Mach-Zehnder modulator (DDMZM) is used to generate a sub-carrier double-sideband differential-phase-shift-keying (DPSK) signal. All the central carriers are separated and subsequently modulated to deliver the multicast data, while the remaining sub-carrier DPSK signals carry the downstream unicast traffic. In the optical network units (ONUs), part of the downstream unicast signal power is re-modulated for upstream transmission, which enables source-free ONUs. The proposed scheme is experimentally demonstrated with 1.25-Gb/s downstream unicast, multicast and upstream data.

A hybrid satellite/terrestrial network linking Europe and North America

This short paper will document a demonstration given at the Third Ka-band Conference, Sorrento, Italy, September 1997. The principal objective was to illustrate interoperability over a complex hybrid satellite and terrestrial Asynchronous Transport Mode (ATM) network. The network linked Ka-band satellites in Europe and in North America, via the European JAMES Research and Development (R + D) Network, and the CANTAT-3 trans-Atlantic submarine fibre. The ISABEL application facilitated Computer Supported Collaborative Workspace (CSCW) among locations in Canada, Italy and the U.S.A. The demonstration consisted of the presentation of one full conference session from Italy to observers in Canada and the U.S.A., with the opportunity for the remote, as well as the local audiences, to interact with presenters during the 'Question and Answer' periods. There were also short presentations from the Communications Research Centre (Canada), and NASA Lewis Research Centre (U.S.A.). The ISABEL application required two virtual networks, one to handle unicast signals for control and monitoring, etc., the other to distribute multicast traffic. They shared a common star topology over point to point symmetrical Virtual Paths (VPs) through the interconnected ATM networks. The three participating locations were connected to a Network Node at the Communications Research Centre (CRC), Ottawa, Canada over full duplex El (2.048 Mbps) circuits. The application traffic from each ISABEL workstation was directed to the Network Node, where it was combined. The Control Workstation, at the Conference Centre, Sorrento, Italy, allocated window sizes in the combined image, selected local inputs, and switched presentation material as required. The combined image was multicast from the Network Node to the three networked locations. The overall network included the Italsat-2 satellite and the U.S. Advanced Communications Technology Satellite (ACTS), the Canadian and Italian national test networks, the European R + D network, and the CANTAT-3 submarine fibre.