Fasil Berhanu Tesema

Mobility Modeling and Performance Evaluation of Multi-Connectivity in 5G Intra-Frequency Networks

Ultra-high reliable communication and improved capacity are some of the major requirements of the 5th generation (5G) mobile and wireless networks. Achieving the aforementioned requirements necessitates avoiding radio link failures and the service interruption that occurs during the failures and their re-establishment procedures. Moreover, the latency associated with packet forwarding in classical handover procedures should be resolved. This paper proposes a multi-connectivity concept for a cloud radio access network as a solution for mobility related link failures and throughput degradation of cell-edge users. The concept relies on the fact that the transmissions from co-operating cells are co-ordinated for both data and control signals. Latency incurred due to classical handover procedures will be inherently resolved in the proposed multi-connectivity scheme. Simulation results are shown for a stand alone ultra dense small cells that use the same carrier frequency. It is shown that the number of mobility failures can considerably be decreased without a loss in the throughput performance gain of cell-edge users.

Multiconnectivity for Mobility Robustness in Standalone 5G Ultra Dense Networks with Intrafrequency Cloud Radio Access

Capacity and ultra-reliable communication are some of the requirements for 5th generation (5G) networks. One of the candidate technologies to satisfy capacity requirement is standalone Ultra Dense Network (UDN). However, UDNs are characterized by fast change of received signal strength that creates mobility challenges in terms of increased handovers and connection failures. In this paper, a low layer multiconnectivity scheme is presented for standalone UDN aiming at ultra-reliable communication that is free of interruptions from handover procedures and connection failures. Furthermore, the problem in managing of the set of serving cells, that are involved in multiconnectivity for each user, is formulated. By using numerical method, feasible scheme for management of the set of serving cells is derived. Performance of the proposed multiconnectivity scheme is evaluated and compared against single connectivity. It is shown that the proposed multiconnectivity scheme outperforms single connectivity considerably in terms of connection failures and cell-edge throughput.

Fast cell select for mobility robustness in intra-frequency 5G ultra dense networks

5th Generation (5G) mobile networks are required to support transmission of capacity demanding services such as real-time remote computing without any interruption. One of the candidate solution for high capacity is Ultra Dense Networks (UDNs). However, UDNs are characterized by fast change of the received signal by a user. The fast change of the signal and high speed of users create too many handovers and connection failures such as handover failures and Radio Link Failures (RLFs). Consequently, conventional handovers and connection failures are the major sources of service interruption. To achieve ultra-reliable communication by tackling the service interruptions, this paper proposes a novel multi-connectivity scheme that uses fast selection of serving cell from a set of prepared cells. A similar feature in Long Term Evolution — Advanced (LTE-A) that is defined under Coordinated Multi-Point (CoMP) transmission is Dynamic Point Selection (DPS). However, in DPS a cell is selected dynamically for transmission of only data signals. Transmission of mobility related control signals is performed through one primary cell which is changed through a conventional handover. Unlike DPS, this paper proposes that the selected cell, from the set of prepared cells, is used for transmission of both data and control signals. Simulation results show that the connection failures due to RLFs are considerably resolved by the proposed scheme.

Evaluation of adaptive active set management for multi-connectivity in intra-frequency 5G networks

Improved throughput and reliable communication that is free of mobility failures are some of the requirements for 5th Generation (5G) mobile networks. One of the cost-effective solutions to meet capacity requirement is standalone ultra dense network that use the same spectrum and a cloud radio access. However, stand alone ultra dense networks are prone to mobility challenges. Previous work proposed and evaluated multi-connectivity that co-ordinates transmission on both the user plane and control plane; this enables improvement not only in throughput but also in mobility robustness. One of the major component of multi-connectivity is managing the “active set” which is the set of co-ordinating cells. Proper procedures for managing user-specific active set was defined for 3G Soft Handover. This paper revisits prior art schemes for active set management and proposes new adaptive one for 5G Networks. Performance evaluation is provided with the help of elaborated models for simulation. Among other things, it is shown that the adaptive active set management scheme reduces the signaling overhead associated to active set updates by around 19% compared to static active set management.

Evaluation of Context-Aware Mobility Robustness Optimization and Multi-Connectivity in Intra-Frequency 5G Ultra Dense Networks

Practical implementation of context-aware mobility robustness technique and a multi-connectivity scheme are investigated based on the requirements of 5th generation networks. Results show that context-aware mobility robustness considerably reduces connection failures and lowers the signaling overhead from handovers, but it has limitations in supporting ultra high reliability applications. On the other hand, multi-connectivity supports ultra high reliability applications at the expense of signaling overhead.

Enhancing Vertical Sectorization Performance with eICIC in AAS Based LTE-A Deployment

Cell densification is a typical means for capacity enhancement in a certain area. A flexible and dynamic way of cell densification can be provided via sectorization by Active Antenna Systems (AAS). By means of flexible beam forming capabilities, sectorization employs new sub-sector(s) reusing the same frequency band. The higher resource gain has to be paid off with more cell borders and cell edge users suffering from inter-sector interference. In this paper work, enhanced Intercell Interference Coordination (eICIC) technique is applied to coordinate the intra-site co-channel interference between the inner/outer sector in Vertical Sectorization (VS). Simulation results have shown that, eICIC brings significant system performance gain by improving the Signal to Interference plus Noise Ratio (SINR) experience of the users close to the inner/outer sector border regions; mainly, the severely affected regions of the outer sector.

Co-existence of enhanced inter cell interference co-ordination and mobility robustness optimization

Enhanced Inter-Cell Interference Co-ordination (eICIC) enables expanding the range of small cells (and thereby better Macro cell offloading) by protecting users in the expanded area through blanking subframes in the Macro cells. Range expansion is achieved by modifying the handover parameters. However, those handover parameters are already modified by the existing feature Mobility Robustness Optimization (MRO). The interaction between MRO and eICIC is particularly challenging since real deployments face a mixture of Rel. 10/11 users (which are able to perfectly exploit eICIC) and legacy Rel. 8/9 users. Furthermore, the details of the eICIC impact on mobility (failures) is not very well explored, in particular due to the lack of simulation tools capable of investigating both eICIC and MRO at the same time. In Release 11, there was a proposal for a new feature which enables proper interaction between MRO and eICIC in the presence of both Rel. 8/9 and Rel. 10/11 users. The feature allows setting up separate MRO statistics for Rel. 8/9 users and for Rel. 10/11 users. The paper presents comparison of this new feature with simpler workarounds. The results were created with a system level simulator which has elaborated mobility and eICIC model. The main conclusions are that mobility problems also exist for Rel. 10/11 users, and simple workaround solutions cannot solve the interaction problem.

Comparison of Abstract Resource Management Model for SON Algorithm of eICIC with Real Radio Resource Management

Mobility load balancing alone does not improve the performance of intra-frequency heterogeneous networks because at higher offloading, users in the range extended region suffer from low throughput and radio link failures. Enhanced Inter-Cell Interference Coordination (eICIC) improves mobility load balancing by protecting users in the range extended region. However, setting optimal blanking pattern configuration and range extension is not an easy task since the algorithm needs to take into account among other things user measurement capabilities, traffic variation due to mobility, mobility-associated characteristics such as radio link failures, etc. Moreover, eICIC is used in HetNets along with other SON features such as mobility robustness optimization and carrier aggregation. Coexistence studies cannot be undertaken by using a radio resource management model that have simulation step equivalent to a transmission time interval because of unfeasible computation time. Thus, an abstract radio resource management model is needed. This paper contributes the comparison of an abstract radio resource management with a real radio resource management based on proportional-fair scheduler. The abstract model uses ideal proportional fair scheduler based on utility maximization whereas the real radio resource management model use metric based proportional fair in the presence of link adaptation, packet error and retransmission. Despite the differences between the two models due to approximations and resource sharing behavior, the comparison shows that both models result in the same trend and order of gain in terms of 5-% user throughput.

Impact of cyclic prefix configuration on mobility performance of multi-connectivity in 5G networks

Service interruptions from mobility events, such as handovers and connection failures, are some of the major impairments for fulfilling the ultra-reliability requirements in fifth Generation (5G) mobile networks. One of the solutions to tackle the aforementioned challenges is multi-connectivity with Single Frequency Network (SFN) transmission, which refers to noncoherent joint transmission of a signal on the same radio resource in frequency and time. This paper investigates the impact of cyclic prefix configuration on user mobility performance using multiconnectivity with SFN transmission. The performance evaluation is carried out with respect to the number of connection failures, 5-%ile and average throughput. Simulation results have shown that, for a sufficiently long cyclic prefix duration, the multiconnectivity scheme can fully resolve connection failures, and improve 5-%ile and average throughput by around 33% and 9%, respectively, compared to single connectivity.