Mobile Backhaul Networks Research Articles

Fiber-wireless integrated mobile backhaul network based on a hybrid millimeter-wave and free-space-optics architecture with an adaptive diversity combining technique.

We propose and experimentally demonstrate a novel fiber-wireless integrated mobile backhaul network based on a hybrid millimeter-wave (MMW) and free-space-optics (FSO) architecture using an adaptive combining technique. Both 60 GHz MMW and FSO links are demonstrated and fully integrated with optical fibers in a scalable and cost-effective backhaul system setup. Joint signal processing with an adaptive diversity combining technique (ADCT) is utilized at the receiver side based on a maximum ratio combining algorithm. Mobile backhaul transportation of 4-Gb/s 16 quadrature amplitude modulation frequency-division multiplexing (QAM-OFDM) data is experimentally demonstrated and tested under various weather conditions synthesized in the lab. Performance improvement in terms of reduced error vector magnitude (EVM) and enhanced link reliability are validated under fog, rain, and turbulence conditions.

Transport Mechanisms for Mobility Support in Optical Slot Switching-Based Next-Generation Mobile Backhaul Networks

In order to implement the next-generation (e.g., LTE-A) mobile backhaul networking segment, an optical slot switching solution called packet optical add/drop multiplexer (POADM) was previously proposed. Optical slot switching is at the same time a high capacity, energy-efficient, and low-latency optical transport network technology that relies on the direct transmission of data from base station to base station without resorting to time-consuming electronic processing and energy-hungry optoelectronic conversions. Low latency is an important requirement of mobile backhaul networks for real-time traffic such as Coordinated MultiPoint (CoMP) and POADM was shown to be compatible with the strict latency requirement of CoMP—1 ms end-to-end—even for very high network loads of 80% and above. However, user mobility was not taken into account. The traffic of users moving from one cell to another cell during handovers should also meet this strict requirement. In this paper, we propose and evaluate several transport mechanisms to support User Element mobility at the optical layer in a next-generation mobile backhaul network implemented using our previously proposed optical slot switching technology. We show with simulations that with smart introduction of additional electronic processing for handover traffic only (traffic of user elements that have moved from one cell to another), very strict latency constraints (sub-ms) can be met even for the time-sensitive mobile traffic.

Mixed mmWave RF/FSO Relaying Systems over Generalized Fading Channels with Pointing Errors

This paper studies the performance of mixed millimeter-wave radio-frequency (mmWave RF), free-space optics (FSO) systems in a highly scalable and cost-effective solution for fifth-generation (5G) mobile backhaul networks. The mmWave RF and FSO fading channels are, respectively, modeled by the Rician and the generalized Malaga ( $\mathcal {M}$ ) distributions. The effect of pointing errors due to the misalignment between the transmitter and the receiver in the FSO link is also included. Novel accurate closed-form expressions for the cumulative distribution function, the probability density function, and the moment generating function (MGF) in terms of Meijer's G functions are derived. Capitalizing on these new results, we analytically derive precise closed-form expressions for various performance metrics of the proposed system, including the outage probability, the average bit error rate (ABER), and the average capacity. Additionally, new asymptotic results are provided for the outage probability, the MGF, and the ABER in terms of simple elementary functions by applying the asymptotic expansion of the Meijer's G function at high signal-to-noise ratios (SNRs). Numerical results further validate the mathematical analysis by Monte-Carlo simulations.

Cost-Effective Mobile Backhaul Network Using Existing ODN of PONs for the 5G Wireless Systems

An optical distribution network (ODN) sharing scheme to integrate mobile backhaul networks with the existing passive optical network (PON) systems is proposed and demonstrated. With the ODN sharing scheme, the expense of building new fibers for the next-generation fifth-generation (5G) mobile backhaul networks can be reduced. As many wavelengths are allocated to the already deployed PON systems, there remain limited wavelengths for the mobile backhaul systems. Hence, to efficiently increase the serving cell sites of the 5G systems, spectral-efficient orthogonal frequency-division multiplexing (OFDM) is adopted in the mobile backhaul systems. In order to reduce the latency of the system, adaptive adjustment of the OFDM signals for different transmission distances is averted. The OFDM signals are transmitted only using specific available bandwidth. The available bandwidth for each wavelength is studied according to the power fading relationship between the transmission distances and the chirp induced from signal modulation. A proof-of-concept demonstration experiment has been performed. In our results, 20.17 Gb/s with a bit error rate (BER) lower than $3.8\times 10^{-3}$ was realized with a split ratio of 256 and a 40-km transmission distance of the PON ODN. Hence, each wavelength can support about 20, six, and two nodes for the IMT-advanced, current Long-Term Evolution-Advanced (LTE-A) systems, and the expected 5G systems, respectively.

Minimax Optimum Estimators for Phase Synchronization in IEEE 1588

The IEEE 1588 protocol has received recent interest as a means of delivering sub-microsecond level clock phase synchronization over packet-switched mobile backhaul networks. Due to the randomness of the end-to-end delays in packet networks, the recovery of clock phase from packet timestamps in IEEE 1588 must be treated as a statistical estimation problem. A number of estimators for this problem have been suggested in the literature, but little is known about the best achievable performance. In this paper, we describe new minimax estimators for this problem, that are optimum in terms of minimizing the maximum mean squared error over all possible values of the unknown parameters. Minimax estimators that utilize information from past timestamps to improve accuracy are also introduced. Simulation results indicate that significant performance gains over conventional estimators can be obtained via such optimum processing techniques. These minimax estimators also provide fundamental limits on the performance of phase offset estimation schemes.

Options for future mobile backhaul and fronthaul

This paper describes the options for constructing mobile backhaul (MBH) and mobile fronthaul (MFH) networks that can support mobile broadband services beyond LTE Advanced. It first reviews the current architecture of Radio Access Network (RAN) which comprises MBH and MFH as well as the wireless section to reach the user equipment (UE). Then, it describes technologies for future MBH/MFH networks that are capable to the drastic increase of wireless bandwidth as well as the massive deployment of small cells.

Backhaul-Aware User Association in FiWi Enhanced LTE-A Heterogeneous Networks

In this paper, we shed some light on the latency and reliability issues of mobile backhaul networks, which have been largely ignored in the past, and examine their impact on LTE-A heterogeneous networks (HetNets). Specifically, we propose a backhaul-aware user association algorithm for fiber-wireless (FiWi) enhanced LTE-A HetNets. The performance limiting factors of state-of-the-art fiber backhaul infrastructures are highlighted and a variety of solutions are described. To mitigate the vulnerability of the backhaul against fiber cuts, we introduce different advanced protection techniques. Accounting for the given conditions of the backhaul in terms of delay and reliability, we present a distributed load-balancing algorithm for user association in FiWi-LTE HetNets. The proposed algorithm is analyzed and evaluated numerically by comparing its performance with state-of-the-art alternative approaches in terms of average delay, blocking probability, average achievable throughput, and service interruption percentage. The obtained results demonstrate that our algorithm outperform its counterparts in terms of delay and service interruption percentage, while its average achievable throughput is the same as that of a backhaul-unaware alternative solution. In addition, the blocking probability of the proposed backhaul-aware load-balancing method is shown to be higher than that of backhaul-unaware ones.

Proposal and analysis of integrated PTN architecture in the mobile backhaul to improve the QoS of HetNets

The rapid progress made in mobile device technologies has implied that the access network must evolute and develop new strategies to satisfy the requirements of the users. Heterogeneous network (HetNet) allows for a flexible deployment strategy and offers economically viable solutions to improve network scalability and indoor coverage. This emerging topic has caught the attention of the research community and the industry because of the importance of these networks to satisfy the demand of data services. To provide this demand, different parameters of quality of service (QoS) must be satisfied. In this paper, we present a study on recent advances and open research issues on Mobility Protocols in conjunction with Multi-Protocol Label Switching (MPLS)-based packet transport networks (PTN) to provide QoS in wireless heterogeneous networks. Various mobile management protocols and their interaction with the mobile backhaul and packet core network are briefly introduced. A new architecture called Integrated Proxy Mobile MPLS-TP (IPM-TP) is also outlined to reduce the signalling cost and improve the QoS in HetNets with high rates of mobility.

In-service communication channel sensing based on reflectometry for dynamic wavelength assigned wavelength- and time-division multiplexed passive optical network systems

In future radio access systems, base stations will be mainly accommodated in wavelength- and time-division multiplexing passive optical network (PON) based mobile backhaul and fronthaul networks, and in such networks, failed connections in an optical network unit (ONU) wavelength channel will severely degrade mobile system performance. A cost-effective in-service ONU wavelength channel monitor is essential to ensure proper system operation without failed connections. To address this issue, we propose a reflectometry-based remote sensing method that provides ONU wavelength channel information with the optical line terminal-ONU distance. The proposed method enables real-time monitoring of ONU wavelength channels without data signal quality degradation and is also able to determine if the ONUs are connected to the PON. Experimental results show that it achieves wavelength channel distinction with a high distance resolution (∼ 10 m ). Additionally, with the method, the distance resolution for distinguishing the ONUs after the PON splitter is determined by the received signal bandwidth or the test light modulation speed rather than by the pulse width as in conventional optical time-domain reflectometry.

Optical Slot Switching Latency in Mobile Backhaul Networks

Next generation mobile networks such as LTE-Advanced will offer high data rates to users utilizing new radio access technologies. In addition, new applications as well as devices such as smartphones and tablets will result in a rapid mobile traffic growth. Consequently, a rapid increase of the load in the mobile backhaul segment is expected, resulting in turn into a substantial increase of the energy consumption. Moreover, by allowing the possibility of direct communications between base stations for instance to support interference cancellation mechanisms such as “CoMP” and expedite handovers, the traffic pattern turns into any-to-any node communication in the next generation mobile networks. In previous papers, we proposed an optical mobile backhaul network to transport the mobile user data in an energy-efficient fashion while supporting any-to-any traffic exchanges. In this paper, we evaluate, analytically and by simulation, the latency in such next-generation optical mobile backhaul networks for realistic scenarios. We also study the impact of the support of several classes of service.

Performance Lower Bounds for Phase Offset Estimation in IEEE 1588 Synchronization

In this paper, we describe new lower bounds on error variance of phase offset estimation schemes used in IEEE 1588 based synchronization. The motivation for this study is to determine the feasibility of providing microsecond-level time synchronization over mobile backhaul networks for the backend in 4G cellular systems. Many packet filtering/selection techniques for phase offset estimation have been proposed in synchronization literature, however, lower limits on the performance of such estimators have not yet been described. In this paper, we re-derive two Bayesian estimation bounds, namely the Ziv-Zakai and Weiss-Weinstien bounds, for use under a non-Bayesian formulation. This enables us to apply these bounds to the problem of phase offset estimation. Simulation results compare the performance of existing estimation schemes against these lower bounds under a variety of different network scenarios.

Тестування floodlight-контролеру з mininet в sdn топології

The Software Defined Networking (SDN) is currently one of the most promising technologies in mobile backhaul networks based on the OpenFlow protocol. OpenFlow provides a specification to migrate the control logic from a switch into the controller. In this paper we apply Mininet software with Floodlight controller to verify the OpenFlow controller to perform its function.

Forecasting changes of frame alignment loss probability in convergent networks

The paper provides a developed method that allows to predict a change in the frame alignment loss probability when using the unstructured circuit emulation services in mobile backhaul networks based on the bit-error monitoring. This method allows to determine the moments of exceeding the threshold value by frame alignment loss probability for any technically possible number of TDM cycles, encapsulated in an Ethernet frame. The fragments of dependences of the frame alignment loss probability on the bit error value with different values of the number of TDM cycles, encapsulated in an Ethernet frame, produced using the developed model were shown. It was shown that large threshold values of frame alignment loss probability correspond to the large values of the number of TDM cycles, encapsulated in an Ethernet frame. With the increase in the number of TDM cycles, encapsulated in an Ethernet frame, the probability that frame alignment loss probability exceeds its threshold value grows, which is undesirable. The developed method allows to decide on the possibility to increase the communication channel utilization by increasing the number of TDM cycles, encapsulated in an Ethernet frame, based on data of forecasting changes in the frame alignment loss probability.

Тестування та аналіз SDN-технології

The Software Defined Networking (SDN) is currently one of the most promising technologies in mobile backhaul networks based on the OpenFlow protocol. OpenFlow provides a specification to migrate the control logic from a switch into the controller. In this paper we apply Mininet software to verify the OpenFlow protocol messages.

New Unified PON-RAN Access Architecture for 4G LTE Networks

This work presents a new converged access architecture for LTE mobile backhaul networks. In the proposed architecture, evolved NodeBs (eNBs) are interconnected with local ring-based wavelength-division-multiplexed (WDM) passive optical networks (PONs), which aggregate and efficiently transport traffic to the evolved packet core (EPC). The proposed WDM-PON ring design supports a dynamic setup of virtual circuits for inter-base-station communication, over a dedicated Alan channel. It also supports load balancing, by dynamically reallocating and sharing the capacity of the downstream wavelengths. The reservation mechanism is arbitrated by the optical line terminal, which monitors the traffic imbalances of downstream channels and orchestrates the setup of subwavelength ?transient flows.?

Standard-compliant QoS provisioning scheme for LTE/EPON integrated networks

Passive optical networking has been recognized as a solution for next generation mobile backhaul network. Such technology allows service providers to reduce costs by using already deployed fiber to the x systems while simultaneously supporting increasing demands for mobile broadband Internet access. In this article, we describe a QoS provisioning scheme for LTE/ EPON integrated networks. With this approach, the radio resource management functions of an integrated device, known as ONU-eNB, can take advantage of the information available from the LTE and EPON networks to improve performance. Furthermore, as an example, we show how the implementation of the proposed approach can improve network utilization and users' QoS in an integrated network even under variation of the available bandwidth in the mobile backhaul network.

이동 백홀 네트워크에서 QoS 기능

This paper addresses QoS functions in mobile backhaul network to accommodate the diverse traffics in cell site. The traffics assigned to the switching function in RAN system, such as Ethernet frame, IP packet, and ATM cell, are segmented, and then encapsulated to transfer then to the mobile backhaul network. ISP can converge all generation traffics, such as voice, HSPA, over all-IP RAN through standard pseudowire encapsulation. These can be enhanced with diverse QoS methods as well as comprehensive monitoring and diagnostic capabilities. Therefore in this paper, QoS functions under theses operations is simulated according to the encapsulation functions.

Mobile backhaul for small cells [Guest Editorial

Mobile broadband services have expanded considerably in recent years, driving operators to improve and densify their radio access network (RAN). It has become clear that small cells as well as macrocells must be included in a heterogeneous network, due to the scale of densification required. In order to maximize the end user experience, some level of radio coordination between these small and macrocells is needed - this coordination will be signaled across a mobile backhaul network. Mobile backhaul typically refers to the network between the base station site and the network controller site, but can also include interconnection between base station sites. Mobile backhaul includes a spectrum of networks and network technologies, including the RAN and core networks. There is considerable market interest on the development of small cell backhaul solutions that are an evolution of existing backhaul networks. Packet synchronisation mechanisms that are being developed are key to support the mobile backhaul application. Various standards bodies such as the Next Generation Mobile Networks Alliance (NGMN), Small Cell Forum (SCF), Metro Ethernet Forum (MEF), and Broadband Forum (BBF) are also studying what the implications would be on their defined mobile backhaul network architectures.

Advanced wireless and optical technologies for small-cell mobile backhaul with dynamic software-defined management

This article discusses novel wireless and optical technologies to address the radical new challenges of small cell mobile backhaul (MBH). Specifically, we examine 60 GHz and 70-80 GHz millimeter-wave technologies for high-capacity last mile and pre-aggregation backhaul, and orthogonal frequency-division multiple access passive optical networks as the optical technology complement for enabling flexible cost-efficient hybrid backhaul coverage. Flexible high-capacity hybrid millimeter wave/optical MBH network operation is next verified via network simulations in the context of a demanding, urban small-cell backhaul application. Finally, a novel software defined networking tool called the backhaul resource manager is introduced for automated dynamic resource provisioning and capacity-aware path computation that improves fairness, network utilization and end-to-end user quality of experience. The introduction of the novel wireless, optical, and software-defined technologies thus has the potential to truly revolutionize the future MBH network.

Synchronization aspects in LTE small cells

This article addresses the synchronization needs for mobile backhaul networks when deploying LTE small cells. Existing synchronization solutions for both FDD and TDD macro networks are discussed as well as the applicability of those solutions to small cells deployed in LTE TDD and LTE FDD networks. The benefits of using radio coordination features in a small cell environment and the corresponding demands placed on synchronization solutions are highlighted. Potential issues relating to synchronization of small cells are also discussed, and some additional synchronization solutions are proposed to address those issues.