Broadband Access Networks Research Articles

Toward enabling broadband for a billion plus population with TV white spaces

One of the major impediments to providing broadband connectivity in semi-urban and rural India is the lack of robust and affordable backhaul. Fiber connectivity in terms of backhaul that is being planned (or provided) by the Government of India would reach only till rural offices (named Gram Panchayat) in the Indian rural areas. In this exposition, we articulate how TV white space can address the challenge in providing broadband connectivity to a billion plus population within India. The villages can form local Wi-Fi clusters. The problem of connecting the Wi-Fi clusters to the optical fiber points can be addressed using a TV white space based backhaul (middle-mile) network. The amount of TV white space present in India is very large when compared with the developed world. Therefore, we discuss a backhaul architecture for rural India, which utilizes TV white spaces. We also showcase results from our TV white space testbed, which support the effectiveness of backhaul by using TV white spaces. Our testbed provides a broadband access network to rural population in thirteen villages. The testbed is deployed over an area of $25$km$^2$, and extends seamless broadband connectivity from optical fiber locations or Internet gateways to remote (difficult to connect) rural regions. We also discuss standards and TV white space regulations, which are pertinent to the backhaul architecture mentioned above.

Design and development of a portable bit-error rate tester with low cost for any rate between 10 Mb/s and 11.3 Gb/s

The bit-error rate (BER) is an important specification for characterizing the reliability of a communication network link. Aiming at the passive optical access network and wireless broadband access network with the multi-rate levels and the high cost of operation and maintenance, a low cost and portable bit-error rate tester (BERT) with both optical and electrical ports, and operational rates between 10Mb/s and 11.3Gb/s, is designed and developed in this paper, which consists of a pseudo random binary sequence (PRBS) generator, an error detector (ED), a microcontroller unit (MCU) and a small form-factor pluggable optical transceiver. The test results reveals the generated PRBS has the characteristics of high stability and low jitter and the error counter is accurate for a variety of communication protocols.

Provisioning 1 Gb/s symmetrical services with next-generation passive optical network technologies

Service providers spend billions upgrading their broadband access networks to the latest access standards. Fiber has become the technology of choice in the medium and long term, thanks to its speed, reach, and future-proofness. A differential advantage of fiber over other broadband access technologies is that it makes it possible for operators to deliver symmetric-rate services. Most of today’s commercial offers based on regular PON range from 10 to 100 Mb/s of committed information rate, and higher rates are advertised as peak rates with unspecified guarantees. In this article we focus on delivering symmetrical 1 Gb/s access to residential users with a target temporal guarantee at the least cost using next-generation PON technologies. We compare four NG-PON standard access technologies, GPON, XGPON, WDM-PON, and the emerging TWDM-PON, from technical and economic perspectives. The study shows that if a service provider wants to keep up with the growing user traffic pattern in the long run, only TWDM-PON can provide 1 Gb/s nearly guaranteed at a moderate cost with respect to the fully dedicated 1 Gb/s point-to-point connection available in WDM-PON technologies.

A Femtocell Cross-Tier Interference Mitigation Technique in OFDMA-LTE System: A Cuckoo Search based Approach

Background/Objectives: In wireless broadband access networks, most indoor environments encounter serious coverage problem. Femtocells have been introduced as an efficient solution to improve cell coverage, enhance area spectral-efficiency and provide better Quality-of-Service (QoS) to mobile users. However, cross-tier interference issues continue to be the major technical challenge associated with femtocell deployment. Methods/Statistical analysis: This study introduce a resource allocation technique-based cuckoo search algorithm RACSA for cross-tier interference mitigation in Orthogonal Frequency Division Multiple Access based Long Term Evolution (OFDMA-LTE) system. The innovative RACSA technique takes upon itself the task of maximizing the throughput of network according to a specified threshold for the interference. Cuckoo search Algorithm is extensively employed to successfully address the problem of resource optimization by finding and allocating the suitable power and bandwidth for all the users and this ultimately, leads to mitigating the cross-tier interference for OFDMA macro-femtocell networks. Results/Conclusions: The simulation results reveal that RACSA mitigate the cross-tier interference and improve the system performance. In addition, an assessment is carried out and it confirmed that RACSA gives (38%) and (21%) higher system throughput and (14%) and (35%) higher in spectral efficiency and (55%) and (33%) lower in the outage probability when comparing with results of genetic algorithm and auction algorithm respectively.

Co-investment in ultra-fast broadband access networks: Is there a role for content providers?

In many countries, Next Generation Access networks (NGA) deployment and penetration rate proceed at a slower pace than expected. It is argued that an ex ante contractual arrangement among residential-access Internet Service Providers (ISPs) and Content Providers (CPs), which builds on the complementarity between infrastructure and content, can promote the roll out of NGA. Indeed, one such contract brings down the portion of the investment cost borne by the ISPs (for a given cost of investment), increases end users׳ demand for improved connectivity and internalizes investment externalities. It is studied how a departure from network neutrality (NN) regulation of the Internet, allowing the ISP to negotiate with the CP a fee for (priority) delivery of content, affects firms׳ investment incentives. Using a simple model, it is shown that the ISP may invest more with than without NN, since the CP may have high bargaining power ex post (after NGA investment is sunk). Instead, the CP may be more willing to co-invest when NN is abandoned, either to evade high ex post fees (if the investment cost is low), or to foster NGA deployment (if the investment cost is high and the ISP has low bargaining power ex post).

N∶1 Protection Design for Minimizing OLTs in Resilient Dual-Homed Long-Reach Passive Optical Network

Long-reach passive optical networks (LR-PONs) prove to be a suitable candidate for future broadband access networks. The longer reach of the feeder fiber in a LR-PON enables us to consolidate a large number of end users. The longer reach also eliminates a degree of electronic processing by eliminating the metro network and connecting the local exchanges (or the central offices) directly to a consolidated metro/core (MC) node. However, longer reach makes the feeder fiber more vulnerable to failures, and therefore, for resiliency purposes, a dual-homed architecture is proposed. For the usual case of 1 + 1 protection, the dual-homed secondary MC node would contain duplicate resources that would take over in the event of the failure of any of the individual working optical line terminals (OLTs) or the entire primary MC node in the case of a catastrophe. In this work we propose an Nl1 protection mechanism to reduce backup OLTs in a resilient dual-homed LR-PON deployment. We model the problem as an integer linear program and solve it for Irish and UK network deployments. Our results show that the percentage of backup OLTs can be reduced by 6 times for Ireland and by 4 times for the UK compared to a 1 + 1 protection deployment scenario.

Determining the feasibility of Free Space Optical Communication in Namibia

Namibia has a great potential for Free Space Optical Communication (FSOC) because of its clear skies. This paper determines the feasibility of FSOC in Namibia by using theoretical models. Visibility, wind speed, and altitude data for several locations are used to compute atmospheric losses under average and worst case atmospheric conditions. Optimal FSOC link distances for all the locations are determined under both conditions by evaluating each location's atmospheric loss against the power link margin. Results show that under average conditions, an FSOC optimal link distance of up to 7500m can be achieved for inland locations. On the other hand, Grootfontein and Katima Mulilo, at 6900m, have the longest distance under worst case atmospheric conditions. Walvis Bay has the shortest FSOC link distances of 3224m and 2500m under average and worst case conditions respectively. This study shows that FSOC in Namibia is feasible for last mile broadband access networks, where link distances are generally less than 10km. These results are based on theoretical models, which have taken into account reasonable realistic assumptions. Practical field tests using FSOC equipment will be conducted as part of future work. Comparisons will be made with theoretical results obtained in this study.

Computation of Various QoS Parameters for FiWi Access Network

Fiber wireless (FiWi) access network is one of the broad band access networks used to support multimedia applications and interactive services. However minimum QoS needs to be maintained by the network. In this paper a method has been proposed to compute the various network parameters such as packet delivery ratio (PDR), average delay and network throughput for a FiWi network, to ensure minimum QoS. This approach may be proved very useful in computing these parameters comprehensively for any algorithm related with research issues of FiWi network like ONU placement, survivability, energy efficient algorithms etc.

Maximizing Power Saving for VoIP over WiMAX Systems

The voice-over-Internet protocol (VoIP) service is expected to be widely supported in wireless mobile networks. Mobile Broadband Wireless networks VoIP service to users with high mobility requirements, connecting via portable devices which rely on the use of batteries by necessity. Energy consumption significantly affects mobile subscriber stations in wireless broadband access networks. Efficient energy saving is an important and challenging issue because all mobile stations are powered by limited battery lifetimes. Therefore, the authors propose an adaptive mechanism suitable for VoIP service with silence suppression. The proposed mechanism was examined with a computer simulation. The simulation results demonstrate that the proposed mechanism reduces energy consumption.

Wavelength division multiplexing passive optical networks (WDM PONs) With Downstream DPSK and Upstream Remodulated OOK using Injection-Locked Fabry-Perot Laser Diodes (FP-LDs)

Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) system based on the injection locked Fabry-Perot laser diode (FP-LD) has been investigated. The system has been demonstrated without dispersion compensation for both 10Gbps Differential phase-shift keying (DPSK) downstream signal and 2.5Gbps On-off keying (OOK) upstream signal respectively. Error free transmission over 50-km is achieved by tailoring the parameters of the FP-LD. The BER performance of our system shows that the injection locked FP-LD is a low cost effective colourless transmitter for high-speed WDM-PONs. Full Text: PDF References E. Wong, "Next-Generation Broadband Access Networks and Technologies", J. Lightwave Technol. 30(4), 597 (2012). CrossRef F.T. An, D. Gutierrez, K.S. Kim, J.W. Lee, L.G. Kazovsky, "SUCCESS-HPON: A next-generation optical access architecture for smooth migration from TDM-PON to WDM-PON", IEEE Commun. Mag. 43(11), S40 (2005). CrossRef S.-J. Park, C.-H. Lee, K.-T. Jeong, H.-J. Park, J.-G. Ahn, K.-H. Song, "Fiber-to-the-home services based on wavelength-division-multiplexing passive optical network", J. Lightwave Technol. 22, 2582 (2004). CrossRef C.W. Chow, C.H. Yeh, "Using Downstream DPSK and Upstream Wavelength-Shifted ASK for Rayleigh Backscattering Mitigation in TDM-PON to WDM-PON Migration Scheme", IEEE Photon. J. 5(2), 7900407 (2013). CrossRef J. He, D. Yang, L. Chen, "A full-duplex radio-over-fiber system with differential phase-shift keying signals", J. Phys. Conf. 276, 012062 (2011). CrossRef L.Y. Chan, C.K. Chan, D.T.K Tong, E Tong, L.K. Chen, "Upstream traffic transmitter using injection-locked Fabry-Perot laser diode as modulator for WDM access networks", Electron. Lett. 38(I), 43 (2002). CrossRef Z. Xu, Y. J. Wen, C. J. Chae, Y. Wang, C. Lu, Proc. Opt. Fiber Commun. Conf. (OFC06), JThB72 (2006). C.H. Yeh, C.W. Chow, H.Y. Chen, J.Y. Sung, Y.L. Liu, "Demonstration of using injection-locked Fabry-Pe?rot laser diode for 10?Gbit/s 16-QAM OFDM WDM-PON", Electron. Lett. 48(15), 940 (2012). CrossRef J. H. Lee et al., "Single, Depolarized, CW Supercontinuum-Based Wavelength-Division-Multiplexed Passive Optical Network Architecture With C-Band OLT, L-Band ONU, and U-Band Monitoring", IEEE J. Light. Tech. 25(10), 2891 (2007). CrossRef Q.T. Nguyen et al., "Bidirectional Transmission in Colourless WDM-PON based on Injection-Locked Fabry-Perot Laser at 2.5 Gbit/s using Low-Cost Seeding Source", in: Proc. Eur. Conf. Opt. Commun. (ECOC), Vienna, Austria, Paper 6.5.1, (2009). DirectLink T. Yoshida, S. Kimura, H. Kimura, K. Kumozaki, T. Imai, "A new single-fiber 10-gb/s optical loopback method using phase Modulation for WDM optical access networks", J. Lightw. Technol. 24,786 (2006) CrossRef W. Hung, C.-K. Chan, L.-K. Chen, F. Tong, "An optical network unit for WDM access networks with downstream DPSK and upstream remodulated OOK data using injection-locked FP laser", IEEE Phot. Techn. Lett. 15(10), 1476 (2003). CrossRef OptiSystem Package from Optiwave.

Performance analysis of bidirectional hybrid orthogonal frequency division multiplexing-Ethernet passive optical access network

For the bottleneck problem of broadband access networks, the Ethernet passive optical network comes out as a striking and promising solution. Even though, Ethernet passive optical network nodes necessitate a cost-effective up-gradation. Accordingly, we propose and demonstrate a hybrid orthogonal frequency division multiplexing-Ethernet passive optical network employing an optical single side band modulation scheme. Case A demonstrates a contrast between a symmetric bidirectional single channel orthogonal frequency division multiplexing-Ethernet passive optical network at a data rate of 10 and 5 Gbps after a fiber link of 20 km. Case B targets the transmission of a symmetric bidirectional single channel orthogonal frequency division multiplexing-optical single side band-Ethernet passive optical network system and achieves a fiber link of 20 km with a split ratio of 8. Afterwards, eight upstream channels are transmitted simultaneously and successfully obtained at the optical linear terminal side to make a bidirectional Ethernet passive optical network system. Further, a contrast between transmission at a data rate of 10 and 5 Gbps is carried out that achieves a fiber link of 20 km with a split ratio of 8.

Increasing the Capacity of SAC-OCDMA by Using OFDM Modulation

Optical CDMA (OCDMA) systems have received more attention because CDMA allows many users share the same transmission medium asynchronously and simultaneously with a high level of transmission security. In this paper, we describe the improved performance of the spectrum amplitude coding (SAC) OCDMA system using OFDM technique compare to SCM/SAC-OCDMA system. The theoretical results of proposed system shows that, the new SAC/OCDMA system with OFDM technique provides better performance compare to SCM/OCDMA system based on Random Diagonal Code (RD), the results evaluated based on BER, number of users and weight of code. Thus this system could be one promising solution to the symmetric high capacity access network with high spectral efficiency, reducing the required power and cost effective of broadband access network

Cooperative security management for broadband network environments

AbstractFrom an internet service provider's (ISP) perspective, modern broadband access networks pose significant and ever increasing challenges in terms of security management. The growing number of permanently connected home networks, with a myriad of poorly managed devices, imposes significant security risks not only to the domestic customers, unable to defend themselves from security attacks, but also to the ISP and third‐parties potentially targeted by large‐scale distributed botnet attacks fed by swarms of zombie domestic personal computers. In this context, the traditional delimitation of customer and ISP perimeters is no longer effective. Home networks became too complex and vulnerable to be autonomously managed by the average customer, and the scale and sophistication of distributed security attacks make it more and more difficult for the ISP to properly manage security without intervening outside the boundaries of its own network. Considering this state of affairs, we propose an alternative architecture for security management. This architecture increases the level of integration and cooperation between the domains of the ISP infrastructure and the home network. At the same time, it potentially improves the scalability and granularity of traditional intrusion detection and prevention mechanisms. Copyright © 2015 John Wiley & Sons, Ltd.

Green Wireless-Optical Broadband Access Network: Energy and Quality-of-Service Considerations

Growing energy demands in the information and communication technology (ICT) sector have been recognized as a major challenge worldwide. Researchers have been actively working to address this challenge, and the major focus centers around improving the energy efficiency of access networks, which are known for consuming about three-quarters of the total network power. Among various access networks, the hybrid wireless–optical broadband access network (WOBAN), which combines a passive optical network (PON) with broadband wireless technology, is highly regarded for its enormous capacity, cost efficiency, and ease of deployment. To develop a green WOBAN, it is important to focus on reducing its power consumption, and in this work, we present an efficient resource management technique for WOBAN that reduces the power consumption of the optical line terminal (OLT) and optical network unit (ONU) by introducing sleep modes for the OLT and ONU, based on the service class and traffic load. Moreover, it considers the quality-of-service requirement of each service class. Simulation results confirm that our proposed solution can save a significant amount of power in the WOBAN network without sacrificing the quality of service of end applications.

An Adaptive DBA Scheme Using Bi-Partition Scheduling Based on Prioritized Traffics to Support Multiple Services over GPON

With the emerging broadband demand of diversified services, the gigabit-capable PON (GPON) has emerged as one of the most promising broadband access network solutions due to the increasing demand for residential bandwidth. In this paper, a novel bi-partition group based on prioritized traffics dynamic bandwidth allocation (BDBA) scheme is proposed to deliver the differentiated services over GPON. The proposed BDBA scheme divides the transmission cycle time into two groups with prioritized traffics and adjusts the bandwidth dynamically between the first group for high priorities T-CONT 1, and T-CONT 2 and the second group for low priorities T-CONT 3, and T-CONT 4. Moreover, the T-CONT 2 traffic has prediction mechanism and recycles the remaining unused bandwidth for the low priority T-CONTs. Simulation result shows that the proposed BDBA scheme can improve the system performance in terms of the throughput, blocking probability, end-to-end packet delay, jitter and fairness for 16 ONUs and 32 ONUs, and also can enhance Quality of Service (QoS) services without sacrificing the low priority traffic except before the system is half-loaded.

System performance analysis of time-division-multiplexing passive optical network using directly modulated lasers or colorless optical network units

As a promising technology for broadband communication, passive optical network (PON) has been deployed to support the last-mile broadband access network. In particular, time-division-multiplexing PON (TDM-PON) has been widely used owing to its mature technology and low cost. To practically implement TDM-PONs, the combination of intensity modulation and direct detection is a very promising technique because it achieves cost reduction in system installation and maintenance. However, the current intensity-modulation and direct-detection TDM-PON still suffers from some problems, which mainly include a high-power penalty, detrimental Brillouin backscattering (BB), and so on. Thus, using directly modulated lasers (DMLs) and colorless optical network units (ONUs), respectively, two intensity-modulation and direct-detection TDM-PON architectures are proposed. Using VPI (an optical simulation software developed by VPIphotonics company) simulators, we first analyze the influences on DML-based intensity-modulation and direct-detection TDM-PON (system 1) performances, which mainly include bit error rate (BER) and power penalty. Next, the BB effect on the BER of the intensity-modulation and direct-detection TDM-PON that uses colorless ONUs (system 2) is also investigated. The simulation results show that: (1) a low-power penalty is achieved without degrading the BER of system 1, and (2) the BB can be effectively reduced using phase modulation of the optical carrier in system 2.

Increasing the efficiency of real-time content delivery by improving the technology of priority assignment and processing of IP traffic

The method of dynamic prioritization of real-time multimedia flows is proposed. This method stabilizes the delay of packet processing when transmitting real-time flows in cases of network devices overload. As the result, the jitter of the flow can be significantly decreased. Moreover, decreasing the delay of packets processing allows to use the preserved time for more intelligent encryption algorithms that are usually very time-consuming. Based on the proposed prioritization method the algorithm of processing of high priority real-time flows that suffer from high delay has been developed in this paper. The algorithm is able to establish how long the specific packet has been transmitting through the network and determine the way to process it as fast as possible if the packets delay has exceeded a critical value. The proposed method and algorithm form a basis for ensuring quality of service in transport networks of long-distance class that require high level scalability and quality of service. This features are especially important when organizing networks of civil and military purposes including wireless broadband access networks. The proposed method becomes especially effective under the conditions of high incoming load on the communication core of the network since even small reduction of real time packets delay significantly increases quality of service. In case of special purpose networks, the developed algorithm allows to stabilize the delay and significantly decrease jitter which are a crucial factor when ensuring promptness of network reaction on the crisis situation.

Short-term fairness in slotted WDM rings

Single-hop WDM ring networks are promising architectures for future broadband access and metro networks. However, ring networks exhibit significant fairness issues, which must be handled by a fairness enforcing protocol. Fairness is usually ensured over a time window of several network propagation delays. Thus, data flows might experience large access delays which might be not compatible to support time-sensitive applications. We solve this issue proposing the Multi-Fasnet protocol, which is able to enforce fairness in a relative short time scale, in the order of few propagation delays, without trading off the aggregated throughput network performance. We discuss Multi-Fasnet limitations and propose several novel strategies that achieve high and fair network throughput as well as low, bounded and fair access delays.

The Road to an Open Internet is Paved with Pragmatic Disclosure & Transparency Policies

Ensuring a healthy ecosystem for broadband services is critical to securing the future of a healthy and open Internet. From the perspective of social welfare maximization, this means collective management of the decision-making regarding how we design, operate, provide access to, use, and pay for our broadband access networks. Realizing this collective goal requires balancing the interests of multiple market participants that are often in conflict and evolve in light of changing technical, business, and policy conditions. The efficiency of markets and regulatory interventions depends on whether decision-makers at all market levels are appropriately informed. This requires the selective sharing of information. Consumers need information about their broadband access options in order to make informed decisions about which (if any) broadband services to subscribe to, how to use those services, and what investments to make in complementary assets (devices, content, applications). Providers of content, applications, and other complementary goods and services need to know about broadband access options to appropriately position their offerings in the market. And, regulators need information about broadband access options to design and enforce policies that will promote competition and ensure appropriate market choices exist. All of these stakeholders need information about broadband service availability, pricing, performance, and to the extent discernible, about trends and plans that will shape future options. Furthermore, broadband access service providers either already possess or may more easily obtain a great deal of the information needed by market participants. However, the information sharing challenges are far from simple. Different stakeholders need different information, information is costly to collect and share, and to the extent it impacts market outcomes, has strategic value. For example, better informed consumers might be more inclined to switch providers, thereby intensifying price competition; while better informed regulators may be better able to limit supra-competitive profit opportunities. Additionally, sharing of too much information about the performance of specific broadband connections might threaten subscriber privacy or render broadband networks more vulnerable to attack. Disclosure and Transparency (D&T) policies comprise a toolset of rules, processes, and mechanisms that are used by market participants to help structure and manage the flow of information that is needed for informed decision-making. D&T policies comprise a significant component of the regulatory provisions in the FCC's 2015 OIO, which sets forth the FCC's approach for regulating providers of broadband access services. The focus of this paper is on providing a framework with which to interpret the OIO's D&T provisions within the larger market context. The OIO's specific D&T provisions are just one component of the tools and mechanisms that shape how broadband management relevant information is discovered, shared, and interpreted. Other regulatory provisions in the OIO and other market mechanisms such as performance testing platforms interact with the explicit D&T provisions that mandate specific obligations and responsibilities. As we shall explain, the richness of D&T tools is desirable in order to address the complex and diverse questions that arise in the context of broadband management requiring information sharing. Moreover, understanding how these D&T policy tools interact and complement (or substitute) for each other is helpful if these tools are to be appropriately applied and appreciated. Application of these tools should be nuanced and evolvable to incentivize cooperation and voluntary disclosure by the ISPs while also safeguarding the interests of end users and intermediaries in the broadband Internet ecosystem.In Section 2, we review the specific D&T provisions in the FCC's 2015 OIO and situate these within the larger D&T policy framework. We introduce a meta-tool, the D&T Coordinator, to assist in better understanding the landscape of potential interventions and with which to contrast the relative merits of different interventions in different contexts. In Section 3, we apply our framework to divergent prototypical examples of the sorts of questions that confront the challenge of how to best manage broadband networks. At one end, we have what appears to be the narrow and specific question of crafting an appropriate set of D&T policies to ensure adequate reporting of packet loss by ISPs. At the other extreme, we consider open-ended questions that relate to society's aspirations or goals for what the Internet and broadband services should be. We argue that an assortment of D&T tools are needed for the array of questions confronting broadband stakeholders, but with different emphasis, because the contexts within which they arise engage both specific and general, closed and open-ended details to be addressed appropriately. Section 4 offers our concluding summary and directions for future work.

QoE-Driven Cross-Layer Optimization for Wireless Dynamic Adaptive Streaming of Scalable Videos Over HTTP

Recently, Dynamic Adaptive Streaming over HTTP (DASH) has attracted significant attention. In this paper, we consider DASH-based transmission of scalable videos in wireless broadband access networks (e.g., long-term evolution and WiMAX), and propose three methods to enhance the quality of experience of wireless DASH users. First, we design an improved mapping scheme from scalable video coding layers to DASH layers that can provide the desired bitrates, enhance the video end-to-end throughput, and reduce the HTTP communication overhead. Second, we develop a DASH-friendly scheduling and resource allocation algorithm by integrating the DASH-based media delivery and the radio-level adaptation via a cross-layer approach. It utilizes the characteristics of video content and scalable video coding, and greatly reduces the possibility of video playback interruption by considering the client buffer status. The optimization problem is formulated as a mixed binary integer programming problem, and is solved by a subgradient method. Finally, a DASH proxy-based bitrate stabilization algorithm is proposed to improve the video playback smoothness that can achieve the desired tradeoff between playback quality and stability. Simulations with the Qualnet tool demonstrate that our schemes achieve better performances than other methods in the literature.