Linzhen Xie

Self-Healing Optical Access Networks (SHOAN) Operated by Optical Switching Technologies

An optical access network should offer low-cost reliable services to its end users. To address this problem, an optimal solution is needed which can turn an optical access architecture into a self-healing system. Hence, we propose the Self-Healing Optical Access Network (SHOAN), in which two or more optical access architectures are partners of each other, and they are interconnected by elementary optical crossbar switches into a simple mesh network. In SHOAN, the crossbar switches can keep each access architecture as an independent and closed system for only serving its own end users in normal state. But the crossbars become open in fault scenarios. Whenever a failure occurs in the network, the fault can be monitored and affected services can be recovered by the partner of the access architecture that is affected. Such an interconnected optical access network can withstand failures in its transmission paths, and recover network services in a self-healing way. Compared to existing solutions (e.g., dual-home architecture), illustrative examples demonstrate that SHOAN has many desirable properties: (1) it is robust because risks are disjointed, (2) it is reliable because service recovery is given top priority, and (3) it has low cost because redundant backup components are not necessary since the partners resources act as backup resources. Analysis results show that SHOAN can minimize disruption duration and network cost for broadband access services.

Interference Self-Coordination: A Proposal to Enhance Reliability of System-Level Information in OFDM-Based Mobile Networks via PCI Planning

For system-level information in OFDM-based mobile networks, the full-cell coverage requirement raises the issue of Inter-Cell Interference (ICI) in physical control channels. Unfortunately, conventional approaches (e.g., scheduling, beamforming) cannot effectively deal with this kind of ICI because of configuration limitations in physical control channels. To solve this challenge, this study defines a new concept of `Interference Self-Coordination (ISC) for enhancing this system-level information delivery. Specifically, we apply ISC to relieve the ICI effect over the Physical Downlink Control Channel (PDCCH), the most important physical control channel in Long-Term Evolution (LTE/LTE-Advanced) networks, in which Physical Cell Identifier (PCI) planning naturally serves as a self-coordination mechanism. We prove that PCI planning is the most effective solution to relieve ICI over PDCCHs, under the constraint of non-orthogonal control regions between neighboring cells. Since PCI planning is an NP-Complete problem, heuristic-strategy algorithms are devised for implementation, which are self-adaptive to dynamic configurations of the network and system, and compatible with any applicable ICI solutions. The numerical analysis and system-level simulation experiment results demonstrate that this proposal can increase overall system throughput by up to 17%, and also improve cell-edge throughput by up to 42%. In the worst 5% of sectors, the proposal can still obtain 45% system throughput and 200% cell-edge throughput gain.

A Sensor-Based Seamless Handover Solution for Express Train Access Networks (ETANs)

Express train transportation is becoming a major tool for carrying approximately one million passengers daily in China today. To provide broadband information services for train passengers, the greatest challenge is achieving a seamless handover solution to guarantee wireless service continuity. This motivates us to incorporate sensor technology into Radio over Fiber architecture to construct an Express Train Access Network (ETAN), where the deployed sensor network captures the train movement status, which can indicate the wireless signal strength. Since the train moves on a fixed rail with fixed direction, it is possible to form an intelligent handover decision system, in which a critical movement state can exactly trigger an optical switch unit in the central station to carry out the handover procedure. Theory analyses and simulation results demonstrate that the proposed architecture can perform handover within 22 ms at a train speed of 350 km/h, providing wireless services for users without disruption, even for a cell radius as small as 100 m.

Power synergy to enhance DCI reliability for OFDM-based mobile system optimization

In Orthogonal Frequency Division Multiplexing (OFDM)-based mobile networks (e.g., Long Term Evolution Advanced), Downlink Control Information (DCI) in a Physical Downlink Control Channel (PDCCH) plays a unique role in carrying control signaling and scheduling information, which enables the flexibility and diversity of radio resource utilization. Due to system configuration limitations, power dimension is the only potential to enhance DCI reliability. Based on this motivation, we apply the synergy concept to power dimension: called Power Synergy, which can deal with negative effects caused by Cell-specific Reference Signal (CRS) power boosting, and also allow flexibly power lending between OFDM symbols in the physical control region. Under the constraints of the Block Error Rate (BLER) threshold 102 given for PDCCHs and the CRS full-cell coverage requirement, performance tests reveal there are significant profits (for example, 10-dB gain available for enhancing DCI reliability in the worst case) from the power headroom in the physical control region. This valuable gain is helpful to accommodate emerging mobile broadband services (e.g., mobile health) in LTE/LTE-A networks.

A novel solution to improve uplink synchronization control in OFDM-based mobile networks

In OFDM-based mobile networks, uplink synchronization is essential in order for an eNB (evolved Node Base station) to handle a variety of interference issues. To guarantee uplink synchronization control, the HARQ (Hybrid Automatic Repeat-reQuest) mechanism is applied into the process of its TAC (Timing Advance Command) transmission in current standards. But HARQ conflicts with the TAC scheduling mechanism in nature, because TAC control information is typically scheduled for transmission at the end of a synchronization period in order to save signaling overhead by reducing TAT (Time Alignment Timer) restart frequency. To handle the conflict between the extra HARQ retransmission delay and TAC scheduling mechanism, we propose a novel TO (Time Offset)-TAC solution that can remove the side effects from TAC information delivery caused by the extra delay of HARQ retransmission. We conduct system-level simulation experiments to evaluate our proposals performance gain. Results demonstrate that our solution can avoid losing synchronization due to its TAT expiration, at a slight penalty of signaling overhead. This study is the first effort at addressing how to guarantee uplink time alignment in the control layer, which is the basis for suppressing interference from “time-staggered symbols” among multiple paths.

A Service-oriented Self-adaptive CCE (S2-CCE) configuration mechanism to enhance time-sensitive mHealth applications

In Long Term Evolution-Advanced (LTE-A) networks, the quasi-static configuration of Control Channel Element (CCE) creates multiple challenges to real-time mobile health (mHealth) applications. To handle these challenges, we propose a novel solution, Service-oriented Self-adaptive CCE (S2-CCE) configuration mechanism. This proposal can dynamically configure the just-enough number of CCEs for mHealth users according to their scenarios, which can avoid the over-utilization of the limited CCE resources. Furthermore, this self-adaptive CCE configuration is also self-aware to service quality from an mHealth user, which can solve the time-sensitive concern in mHealth applications, for example, emergency call and Consultation Video for the point of care. Consequently, we conceive an algorithm to implement the S2-CCE mechanism, in which the initial CCE configuration is based on the Channel Quality Indicator (CQI) reported by an mHealth user from a real deployment, and then this initialized CCE configuration can be intelligently adjusted according to QoS (Quality of Service) requirements from the mHealth user by introducing a concept of Service-Aware Degree (SAD). Our LTE-A system-level simulation experiments demonstrate that the S2-CCE can reduce average delay remarkably for mHealth applications (including HL7, DICOM mHealth users achieving 50% lower delay in contrast with non-service-aware method when there are 50 mHealth users in the cell). And it achieves high user satisfaction (almost 100%) in multi-user scenarios given a milder relaxation to user fairness.

A hop-constraint timing assembly algorithm for facilitating iBUS in IP-over-WDM networks

The iBUS (inbuilt burstification urgency-driven scheduling) algorithm delivers packets in IP-over-WDM networks in an accurate and timely manner. It employs a flexible assembly process which can interact effectively with the urgency-driven process of the iBUS algorithm. In this letter, a hop-constraint timing assembly approach is proposed, where input packets are classified by their routing hops. Then, input packets whose routing hops are more than a threshold are assembled into multi-hop bursts. Multi-hop bursts have higher priority to be scheduled by their urgency degrees, and limitedhop packets (without assembly) can be filled in voids between multi-hop bursts. This approach gives freedom to the urgencydriven process to facilitate iBUS in IP-over-WDM networks.

Best-fit cell attachment for decoupling DL/UL to promote traffic offloading in HetNets

Heterogeneous Networks (HetNets), in which small cells are ultra-densely deployed within a macro cell, is widely regarded as a key solution to mobile traffic offloading. However, this kind of traffic offloading is confronted by two challenges. Firstly, the number of users in any small cell is really limited due to the larger power gap between macros and small cells in HetNets. In return, this phenomenon may degrade traffic offloading performance. Secondly, spectrum efficiency may be deteriorated since uplink channel states are not involved in the conventional cell attachment strategies. To address these challenges, we propose a best-fit cell attachment where downlink and uplink are decoupled and attached to cells independently. Specifically, in this paper, we conceive best-fit strategies for downlink and uplink cell attachment, for taking into account of both channel quality and cell load. And then, their implementation issues in different scenarios are discussed in detail. System-level simulation results demonstrated that our proposal can effectively offload traffic from macros to small cells, and improve data rates for cell-edge users significantly.

A novel distributed scheduling approach powered by central databases in optical burst networks

In terms of the growth rate, network capacity is slower than network traffic. To solve the mismatch between them, utilization of available capacity can be maximized to provide “best-fit” service for emerging applications (e.g., eBanking, Peer-to-Peer (P2P) file exchanges, etc.). To satisfy such a requirement, we propose a three-dimensional label scheduling algorithm (TD-LSA), which is a distributed scheduling approach powered by central databases. In the proposal, all connections are provisioned in three dimensions (i.e., space, time and wavelength) in a distributed way and uniquely identified by three-dimensional labels. And in this way a three-dimensional connection is more robust than a single-dimensional connection because the three-dimensional approach can avoid potential scheduling conflicts as much as possible by using central databases in a network. Thus, the central databases can reduce bandwidth consumption and offer “best-fit” service for three-dimensional connections. Furthermore, in order to further reduce bandwidth consumption and to match with a priority of traffic, K-least hop first path (K-LHPF) and a rescheduling mechanism are applied to our proposal. Simulation experiments demonstrate that our proposal achieves the expected performance gain against existing alternates.

Realizing of OADM using FP resonator as both dropping and bypass device

FP resonator has a very nice character which can be easily used as an OADM device. It can drop the selected channels and reflect the other channels which dont satisfy the resonance requirements. It can be sued as both channels drop and bypass device. In this paper, the design of good reflection spectrum is considered. The factors which affect the reflection spectrum of FP resonator are carefully studied. When using two FP resonators which have both nice reflection and transmission spectrum, it can be realized an OADM node without a circulator.