Multicast Channel Research Articles

Precoder Design for Physical Layer Multicasting

This paper studies the instantaneous rate maximization and the weighted sum delay minimization problems over a K-user multicast channel, where multiple antennas are available at the transmitter as well as at all the receivers. Motivated by the degree of freedom optimality and the simplicity offered by linear precoding schemes, we consider the design of linear precoders using the aforementioned two criteria. We first consider the scenario wherein the linear precoder can be any complex-valued matrix subject to rank and power constraints. We propose cyclic alternating ascent based precoder design algorithms and establish their convergence to respective stationary points. Simulation results reveal that our proposed algorithms considerably outperform known competing solutions. We then consider a scenario in which the linear precoder can be formed by selecting and concatenating precoders from a given finite codebook of precoding matrices, subject to rank and power constraints. We show that under this scenario, the instantaneous rate maximization problem is equivalent to a robust submodular maximization problem which is strongly NP hard. We propose a deterministic approximation algorithm and show that it yields a bicriteria approximation. For the weighted sum delay minimization problem we propose a simple deterministic greedy algorithm, which at each step entails approximately maximizing a submodular set function subject to multiple knapsack constraints, and establish its performance guarantee.

Downlink and Uplink Physical Channels in Long Term Evolution

Long Term Evolution (LTE) defines a number of physical channels to carry information blocks received from the MAC and higher layers. This paper presents two types of Physical channels: the first type is downlink physical channels which consist of Physical Broadcast Channel (PBCH), Physical Downlink Shared Channel (PDSCH), Physical Multicast Channel (PMCH), Physical Downlink Control Channel (PDCCH), Physical Control Format Indicator Channel (PCFICH) and Physical Hybrid ARQ Indicator Channel (PHICH). The second type of Physical channels is uplink physical channels which consist of Physical Uplink Shared Channel (PUSCH), Physical Uplink Control Channel (PUCCH) and Physical Random Access Channel (PRACH). This paper also highlights the structure of PDSCH and PUSCH, discuss the algorithms of the two types of physical channel and each of its features. The aim of this paper is to discuss the well-designed PHY Channels which provide high cell-edge performance with specific features, such as dynamic bandwidth allocation to users, the design of reference signals and control channels. These channels take into account a more challenging path loss and interference environment at the cell edge.

A novel optical picosecond-duration NRZ-to-RZ format converter with simultaneous wavelength multicasting using a single-stage Mach–Zehnder modulator

We propose a novel and simple scheme to achieve NRZ-to-RZ format conversion and simultaneous wavelength multicasting based on a single-stage dual-arm electro-optic Mach–Zehnder modulator (MZM) and a short single mode fiber (SMF). The format conversion and wavelength multicast process are achieved by chirp compensation under the condition of generation of optical flat frequency comb. 40Gb/s NRZ-to-RZ conversion with one-to-five multiple-wavelength channel multicasting and transmission of the NRZ and the converted signals over 200km dispersion-managed fiber-link are successfully demonstrated by numerical simulation. Research results show that 40Gb/s 2ps RZ signal with wavelength-preserving can be obtained after format conversion. The converted RZ signal presents good transmission performance and can easily be multiplexed to 160Gb/s using optical time division multiplexing (OTDM) technology. All the multicast channels can be error free after 50km transmission. Besides, the conversion operation can also greatly reduce the timing jitter of the degraded NRZ signal due to the retiming function of the proposed scheme.

Yi등이 제안한 그룹 키 교환 프로토콜의 보안 취약성 및 개선 방법

그룹 키 교환 프로토콜은 일련의 그룹을 형성하는 다수의 통신 참여자들이 공개된 통신망을 통해 그룹의 공통 비밀키를 설정하기 위한 목적으로 설계된다. 그룹 지향적인 응용분야들이 인터넷상에서 인기를 더해감에 따라서 이들 응용분야에 안전한 멀티캐스트 채널을 제공하기 위해 많은 그룹 키 교환 프로토콜이 제안되었다. 그동안 제안된 그룹 키 교환 프로토콜 중에 최근 Yi 등이 발표한 패스워드 기반 프로토콜이 있다. 이 프로토콜에서는 각 프로토콜 참가자가 자신의 패스워드를 가지고 있으며 이 패스워드는 신뢰할 수 있는 서버에 등록되어 있다고 가정된다. 패스워드 기반 키 교환에서 가장 근본적인 보안 요구사항은 오프라인 사전 공격에 대한 안전성이라 할 수 있다. 그러나 Yi 등이 제안한 프로토콜은 패스워드에 기반한 프로토콜임에도 불구하고 이 요구사항을 만족하지 못하는 것으로 드러났다. 본 논문에서는 Yi 등의 프로토콜에서 발견되는 이러한 보안 문제점을 지적하고 그 해결책을 제시한다. A group key exchange (GKE) protocol is designed to allow a group of parties communicating over a public network to establish a common secret key. As group-oriented applications gain popularity over the Internet, a number of GKE protocols have been suggested to provide those applications with a secure multicast channel. Among the many protocols is Yi et al.'s password-based GKE protocol in which each participant is assumed to hold their individual password registered with a trusted server. A fundamental requirement for password-based key exchange is security against off-line dictionary attacks. However, Yi et al.'s protocol fails to meet the requirement. In this paper, we report this security problem with Yi et al.'s protocol and show how to solve it.

Polarization insensitive wavelength multicasting of DPSK signal using four-wave mixing in a birefringent photonic crystal fiber

We demonstrate polarization-insensitive wavelength multicasting of differential phase-shift keying (DPSK) signal based on four-wave mixing (FWM) in a highly nonlinear, birefringent photonic crystal fiber (PCF). The 10-Gbit/s RZ-DPSK input signal is copied to 8 wavelength channels through FWM with three optical pumps. The pump wavelengths are unequally spaced to avoid undesirable crosstalk from pump-to-pump beatings. The dependence of conversion efficiency on input signal polarization is suppressed by exploiting the PCF birefringence together with control of the pump polarizations. All pump polarizations are aligned at 45 degrees to the principal axes of the PCF. Open eyes and error-free results are obtained in all the 8 multicast channels for polarization-scrambled RZ-DPSK input signal.

QoS Supported IPTV Service Architecture over Hybrid-Tree-Based Explicit Routed Multicast Network

With the rapid advance in multimedia streaming and multicast transport technology, current IP multicast protocols, especially PIM-SM, become the major channel delivery mechanism for IPTV system over Internet. The goals for IPTV service are to provide two-way interactive services for viewers to select popular program channel with high quality for watching during fast channel surfing period. However, existing IP multicast protocol cannot meet above QoS requirements for IPTV applications between media server and subscribers. Therefore, we propose a cooperative scheme of hybrid-tree based on explicit routed multicast, called as HT-ERM to combine the advantages of shared tree and source tree for QoS-supported IPTV service. To increase network utilization, the constrained shortest path first (CSPF) routing algorithm is designed for construction of hybrid tree to deliver the high-quality video stream over watching channel and standard quality over surfing channel. Furthermore, the Resource Reservation Protocol- Traffic Engineering (RSVP-TE) is used as signaling mechanism to set up QoS path for multicast channel admission control. Our simulation results demonstrated that the proposed HT-ERM scheme outperforms other multicast QoS-based delivery scheme in terms of channel switching delay, resource utilization, and blocking ratio for IPTV service.

Optimal Layered Video IPTV Multicast Streaming Over Mobile WiMAX Systems

A WiMAX radio resource allocation (WRA) problem is investigated in the context of IPTV broadcasting over mobile WiMAX multicast, broadcast services (MBS) channels. The goal is to maximize quality of services, in terms of number of subscribers served, number of IPTV channels carried, and perceived video qualities of individual viewers, subject to constraints on multicast channel capacities and space-time channel quality variations. We present an efficient heuristic algorithm based on the Pareto principle that achieves near-optimal results in polynomial time complexity. Extensive simulations are conducted to compare this new approach against state-of-the-art heuristic algorithms and consistent superior performance has been observed.

All-optical UWB signal generation and multicasting using a nonlinear optical loop mirror

An all-optical scheme for ultra-wideband (UWB) signal generation (positive and negative monocycle and doublet pulses) and multicasting using a nonlinear optical loop mirror (NOLM) is proposed and demonstrated. Five UWB signals (1 monocycle and 4 doublet pulses) are generated simultaneously from a single Gaussian optical pulse. The fractional bandwidths of the monocycle pulses are approximately 100% while those of the doublet pulses range from 100% to 133%. The UWB signals are then modulated using a 2(15)-1 pseudorandom bit sequence (PRBS) and error-free performance for each multicast channel is obtained.

Wavelength multicasting of DPSK signal with NRZ-to-RZ format conversion

10 Gbit/s 1×4 wavelength multicasting of a DPSK signal with NRZ-to-RZ format conversion is demonstrated. The operation is achieved by four-wave mixing of the input DPSK signal with a time- and wavelength-interleaved pulsed source. Four multicast channels have been achieved with error-free operation.

Efficient Use of Multicast and Unicast Channels for Multicast Service Transmission

To overcome the problem that the transmission rate of a multicast channel is limited by the user with the worst channel quality, which causes the total system throughput to be low, the use of both multicast and unicast channels for multicast service is considered in this letter. Unicast channels, in addition to a multicast channel, are allocated to users with signal-to-noise ratios (SNRs) lower than a predefined threshold in order to enable the increase of the transmission rate of the multicast channel. The used unicast channels consume additional radio resource. It is examined whether use of such unicast channels can raise the spectral efficiency defined as the total system throughput normalized by the total consumed bandwidth. The optimal value of the threshold SNR is derived by maximizing the spectral efficiency. When a unicast channel is additionally allocated for multicast service, two decoding schemes are considered: one is to use only the signal of a unicast channel, and the other is to use and combine both the signals of multicast and unicast channels. Numerical examples are presented to show the performance gains obtained by using unicast channels in addition to a multicast channel.

Distributed Power Allocation for Parallel Broadcast Channels with Only Common Information in Cognitive Tactical Radio Networks

A tactical radio network is a radio network in which a transmitter broadcasts the same information to its receivers. In this paper, dynamic spectrum management is studied for multiple cognitive tactical radio networks coexisting in the same area. First, we consider the problem of common rate maximization subject to a total power constraint for a single tactical radio network having multiple receivers and using parallel subchannels (parallel multicast channels). Mathematical derivations show that the optimal power allocation can be found in closed form under multiple hypothesis testing. An outer loop can be used tominimize the power subject to a common rate constraint. Then, we extend the iterative water-filling algorithm to the coexistence of multiple cognitive tactical radio networks without requiring any cooperation between the different networks. The power allocation is performed autonomously at the transmit side assuming knowledge of the noise variances and channel variations of the network. Simulation results show that the proposed algorithm is very robust in satisfying these constraints while minimizing the overall power in various scenarios.

An adaptive harmonic broadcasting scheme with download and playback synchronisation for video on demand

Harmonic broadcasting is a broadcasting scheme to reduce the bandwidth requirement in video-on-demand service where a video is divided into segments of equal size and each segment is repeatedly transmitted over a number of channels having bandwidth that follows a harmonic series. As the bandwidth of channels differ from each other and a user can join at any time to these multicast channels, a synchronisation problem between download and playback is created. To deal with this issue, some schemes have been proposed, however, at the cost of additional or wastage of bandwidth. In this paper, we propose an adaptive harmonic broadcasting scheme that deals with the synchronisation problem at the same average bandwidth consumption as traditional harmonic broadcasting scheme. We present several analytical results to exhibit the efficiency of the proposed scheme over the existing ones.

Security Improvement on Wu and Zhu's Protocol for Password-Authenticated Group Key Exchange

A group key exchange (GKE) protocol allows a group of parties communicating over a public network to establish a common secret key. As group-oriented applications gain popularity over the Internet, a number of GKE protocols have been suggested to provide those applications with a secure multicast channel. In this work, we investigate the security of Wu and Zhu's password-authenticated GKE protocol presented recently in FC'08. Wu and Zhu's protocol is efficient, supports dynamic groups, and can be constructed generically from any password-authenticated 2-party key exchange protocol. However, despite its attractive features, the Wu-Zhu protocol should not be adopted in its present form. Due to a flaw in its design, the Wu-Zhu protocol fails to achieve authenticated key exchange. We here report this security problem with the Wu-Zhu protocol and show how to solve it.

Adaptive Forward Error Correction Scheme for Real-Time Communication in Satellite IP Networks

In this paper, a new forward error correction (FEC) protocol is proposed for point-to-multipoint satellite links. Link-layer error control protocols in point-to-multipoint satellite links impose several problems such as unreliability and receiver-heterogeneity. To resolve the problem of heterogeneous error rates at different receivers, the proposed scheme exploits multiple multicast channels to which each receiver tunes. The more channels a receiver tunes to, the more powerful error correcting capability it achieves. Based on its own channel condition, each receiver tunes to as many channels as it needs, which prevents from receiving unwanted parities. Furthermore, each receiver saves the decoding time, processing overhead, and processing energy. Performance evaluation shows that the proposed scheme guarantees the target PER while saving energy. The proposed technique is highly adaptive to the channel variation with respect to the throughput efficiency, and provides scalable PER and throughput efficiency.

Performance Comparison of Using SOA and HNLF as FWM Medium in a Wavelength Multicasting Scheme With Reduced Polarization Sensitivity

In this paper, we propose and demonstrate the practical all-optical wavelength multicasting scheme based on the four-wave mixing (FWM) effect in both a highly nonlinear fiber (HNLF) and a semiconductor optical amplifier (SOA). Then we carry out comprehensive comparisons of the performance differences between using the HNLF and SOA for this proposed multicasting scheme. Seven multicast channels are experimentally demonstrated by using three co-polarized probes and a modulated signal. The merit of the proposed scheme is that the polarization sensitivity is significantly reduced from more than 20 dB to approximately 5 dB using the HNFL and 2.5 dB using the SOA. The low polarization sensitivity leads to a difference of less than 1 dB in the power penalty of the multicast channels at bit error rate . In addition, we compare the multicasting performance of the OOK and differential phase-shift keying (DPSK) signals using the proposed scheme and found that the power penalties of the DPSK multicast channels in the HNLF and the SOA are less than 1.25 and 1.1 dB respectively, and the power penalties of the OOK multicast channels are less than 1.5 dB and 3.1 dB in the HNLF and the SOA, respectively.

MBS zone configuration schemes for wireless multicast and broadcast service

AbstractThe Multicast Broadcast Service (MBS) zone technology is proposed to provide MBS with high QoS on Mobile Communications Networks (MCNs). An MBS zone consists of a group of Base Stations (BSs) synchronized to transmit the same MBS content using the same multicasting channel, which potentially reduces the time delay for Mobile Stations (MSs) to handoff between different BSs in the same MBS zone. However, significant time delay still incurs while MSs handoff between different BSs belonging to different MBS zones (i.e., the inter‐MBS zone handoff). To reduce the possibility for the inter‐MBS zone handoff, we may increase the size of an MBS zone (i.e., more BSs contained in an MBS zone), which may result in poor multicasting channel utilization. This paper proposes the OverLapping Scheme (OLS) and the Enhanced OverLapping Scheme (EOLS) for more flexible MBS zone configuration to get better performance for MBS in terms of QoS and radio resource utilization. We propose the analytical models for the original MBS zone technology (namely the Basic scheme), and the OLS scheme, which are validated against the simulation experiments. Based on the simulation results, we investigate the performance for the Basic scheme, the OLS scheme, and the EOLS scheme. Copyright © 2010 John Wiley & Sons, Ltd.

Designing an effective P2P system for a VoD system to exploit the multicast communication

A distributed video-on-demand system (DVoD) with multiple server-nodes is a cost-effective and fault-tolerant solution for a high scalable enterprise video-on-demand (VoD) system. However, such a server-oriented design is highly vulnerable to workload variations given that the service capacity is limited. Peer-to-Peer (P2P) has been introduced as an architectural solution with self-growing capacity. However, the characteristics of a pure P2P system such as the peer transient nature and high network overhead make this kind of architecture unsuitable for a fully interactive VoD system. In this paper, we propose a new efficient integrated VoD architecture, called D P n 2 P m , that combines DVoD with a P2P system and multicast communications. The DVoD’s server-nodes provide a minimum required quality of service (QoS) and the P2P system is able to offer the mechanism to increase the system service capacity according to client demands. Multicast communication, wherever it is possible, is effectively exploited by our P2P system. In our design, each client is able to send video information to a set of m clients using only one multicast channel. Furthermore, the collaboration mechanism is able to coordinate a set of clients to create one collaboration group to replace the server, providing an extensive, efficient and low network-overhead collaboration mechanism from n -peers to m -peers. Regardless of the video the client is watching, our P2P scheme allows every active client to collaborate with the server. The P2P scheme is complemented with recovery mechanisms that are able to replace the failed client before affecting the QoS, offering continuous playback. The proposed approach has been broadly evaluated, firstly using a mathematical model to derive the theoretical performance and secondly using a simulation environment to analyze the system’s dynamic behavior, the VCR interaction impact and the client failures. Comparing D P n 2 P m with other DVoD architectures and the most relevant P2P delivery policies, we show that our design is an improvement on previous solutions, providing a higher scalability.

All-optical modulation-transparent wavelength multicasting in a highly nonlinear fiber Sagnac loop mirror

An all-optical wavelength multicasting scheme using four-wave mixing (FWM) in a highly nonlinear fiber (HNLF) Sagnac loop mirror has been demonstrated. This proposed scheme has the advantage that even when the wavelength of a multicast channel overlaps with the pump-pump generated idler, clear eye diagram can still be observed. Six and ten 10-Gb/s multicast channels, compliant with the ITU grid, are successfully obtained by using two- and three-pump lasers, respectively. Multicasting of on-off shift keying (OOK) and differential phase-shift keying (DPSK) signals are both successfully demonstrated. The maximum power penalty of the multicast channels is less than 3.5 dB. Furthermore, compared with the non-loop configuration, up to 1.2 dB power penalty improvement can be achieved in this proposed Sagnac loop configuration.

An efficient causal ordering algorithm for multicast communication channels

In this paper, we present an efficient causal algorithm that can be used in multicast communication environments, in particular the overlapping multi-channel case, where a participant can belong to and communicate through more than one multicast channel. The causal algorithm is built on the paradigm of group communication. The groups are established according to the participant channel subscription. In order to reduce the amount of control information (CI), we propose an extension of the immediate dependency relation (IDR), which was introduced by Peterson in the context of one group. This IDR extension allows us to define necessary and sufficient CI to ensure causal delivery in a multi-group environment. We show that through the use of the IDR extension, we reduce the amount of CI sent per message without imposing restrictions on interaction or execution (e.g. network topology, rediffusion servers, execution models, etc.). These characteristics allow our algorithm to be suitable for use in large distributed decentralised systems. We show the efficiency of our causal algorithm in terms of the overhead timestamped per message.

Time-dependent multi-scheduling of multicast

Many network applications that need to distribute content and data to a large number of clients use a hybrid scheme in which one (or more) multicast channel is used in parallel to a unicast dissemination. This way the application can distribute data using one of its available multicast channels or by sending one or more unicast transmissions. In such a model the utilization of the multicast channels is critical for the overall performance of the system. We study the scheduling algorithm of the sender in such a model. We describe this scheduling problem as an optimization problem where the objective is to maximize the utilization of the multicast channel. Our model captures the fact that it may be beneficial to multicast an object more than once (e.g., page update). Thus, the benefit depends, among other things, on the last time the object was sent, which makes the problem much more complex than previous related scheduling problems. We show that our problem is NP-hard. Then, using the local ratio technique we obtain a 4-approximation algorithm for the case where the objects are of fixed size and a 10-approximation algorithm for the general case. We also consider a special case which may be of practical interest, and prove that a simple greedy algorithm is a 3-approximation algorithm in this case.