Zoltan Vincze

Enhanced Mobility Load Balancing Optimisation in LTE

Self-Organising Network (SON) use cases are seen as key enablers of efficient Long Term Evolution (LTE) system operation. Mobility Load Balancing Optimisation (LB) is a prominent SON use case defined by 3GPP with the scope of balancing the load in a given coverage area by reconfiguring the handover thresholds. When overload is detected at a given cell, the LB reduces the handover thresholds of those user equipments that can be redirected to the underutilised neighbouring cells. This mechanism improves the user plane performance in the overloaded cell. Despite the potential benefits, the available LB mechanisms have two major deficiencies, both of them causing user experience degradation: on the one hand, they tend to overestimate the load on the air interface, resulting in unnecessary handovers; on the other hand, they are either transport agnostic or have limited capability to consider the transport load during their decision process. This paper provides an overview of the LB related problems and proposes an improved solution including accurate evaluation of the radio load and a transport aware mechanism for end-to-end optimisation. The performance of the solution was evaluated by simulations.

Integrated Mobility Load Balancing and Traffic Steering mechanism in LTE

Mobility Load Balancing (MLB) is a Self-Organising Networks (SON) use case with the scope of detecting and resolving radio overload. In case of overload, the MLB triggers the handover of cell edge users towards less loaded neighbour cells to better align the traffic demand with the capacity available on the air interface. This, however, also increases the load on the transport links of these cells; therefore, MLB should consider the transport status in order not to cause transport congestion while resolving air interface overload. This paper proposes a general MLB framework that, unlike existing mechanisms, has efficient means to properly consider the transport load and congestion in addition to the radio load. The solution is not limited to any particular transport network topology and it also acts as a Traffic Steering (TS) mechanism as it resolves transport overload by redirecting users to neighbour cells with spare transport resources. The performance of the proposed framework was evaluated with simulations. Results indicate that the solution improves the overall system performance by balancing both radio and transport load.

TCP performance improvement in mobile networks with coverage problems

Due to the evolution of mobile technology and the emergence of terminals like smart phones, Internet based applications mostly accessed over the Transmission Control Protocol (TCP) have become dominant on mobile platforms. However, since the TCP flow control mechanisms were designed for wired environments, short-term degradations on the air interface of radio access systems may lead to unnecessary performance drops. TCP freeze is a possible solution to improve such situations by triggering the persist mode of the TCP sender, preventing TCP timeouts and rate reductions during poor radio conditions. This paper investigates a network element based implementation of the TCP freeze mechanism, which has the advantage that it can accurately follow the radio conditions of the User Equipments (UE) while being completely transparent to the TCP sender and receiver. The possible performance gain of the solution was investigated by simulating a network with coverage holes. Results indicate that the network side freeze can considerably reduce the time the TCP connections spend in outage and thus it can increase the responsivity and data throughput provided by the system.

Bundling and multiplexing in packet based mobile backhaul

This paper investigates the bandwidth efficiency of packet based mobile backhaul in case of low rate, delay sensitive voice service. Evolved HSPA is a fully packet based mobile technology where the voice service is VoIP based. VoIP sources generate small packets periodically. The overhead on these packets is significant; it even exceeds the useful payload, causing efficiency problems on the mobile backhaul where bandwidth is still a scarce resource. A possible way to improve the efficiency of the voice service is to aggregate multiple voice packets into a single transport frame, a technique that reduces the relative overhead. This paper provides an overview of the available aggregation methods referred to as bundling and multiplexing. The performance of these solutions and their impact on the QoS of the voice service is investigated with simulations. Results show that if the backhaul is the bottleneck, the maximum number of VoIP connections that can be served jumps by up to 60%.

Adaptive VoIP Multiplexing in LTE Backhaul

LTE has a distributed system architecture optimized for IP connectivity. Circuit switched technology is not supported by LTE at all; therefore it provides VoIP based voice service only. In LTE, VoIP packets are carried with significant protocol overhead, thus transporting each voice packet separately is a waste of bandwidth. A possible way to improve the bandwidth efficiency of voice service over LTE is to multiplex the packets of parallel VoIP connections into a single transport frame. On the downside, multiplexing requires that some VoIP packets are retained which in turn will increase their end-to- end delay. This paper proposes a multiplexing method, which provides a good balance between bandwidth gain and quality of service by adapting its operation to the actual traffic mix. Three alternative solutions are proposed and investigated with simulations. The results show that VoIP multiplexing significantly improves the bandwidth efficiency of the voice service over LTE with only minor impact on the quality of service.

Handover friendly TCP proxy integrated in the LTE eNodeB

Serving online applications and commercial web sites with low latency is business critical. As content requests originate from geographically distant locations and increasingly from mobile devices, globally ensuring service quality is challenging. The content is delivered to the clients predominantly via the Transmission Control Protocol (TCP), therefore optimal TCP operation over radio access is highly relevant. The split connection TCP Proxy is an optimization mechanism by itself and also a basic component of solutions such as transparent caching aiming at improved interactivity and reduced access latency. In Long Term Evolution (LTE) systems, the Evolved Node B (eNB) is the best location for the TCP Proxy. However, the eNB side TCP Proxy may inherently cause the collapse of TCP connections after handover, a problem this paper is first to analyze. Due to how user plane connectivity is switched over during LTE handovers, the TCP Proxy uniquely creates the possibility for losing data that cannot be recovered through TCP retransmissions. As a solution, the paper presents a TCP Proxy integrated with the eNB Packet Data Convergence Protocol (PDCP) layer. Simulation results indicate that the PDCP integration complemented with X2 prioritization efficiently prevents unrecoverable losses and enables to safely leverage the benefits of an eNB side TCP Proxy.