A Simulation Study on LTE Handover and the Impact of Cell Size

Abstract

In this paper we address the impact of cell size on the handover procedure in a Long Term Evolution (LTE) network. In particular, we highlight the potential problems that may occur when small cell densification is applied. In addition, the impact of the User Equipment (UE) speed is also analyzed. System level simulations are provided using a detailed LTE network simulator accounting for multiple points-of-failure and channel modeling compliant with LTE standards. We conclude that a certain cell size can be found around which any increase or decrease of the cell size brings performance degradations due to different limitations in the uplink. The performance is also degraded as UE speed increases, especially for small cell sizes. And for large cell sizes, we note that low speed UEs handover failures may rise due to the inability to "escape" from a poor radio condition area.

Uplink Reference Signals for Energy-Efficient Handover

“…The second cause is linked to especially the low ISDs. In our previous work [19], we found that the failures due to timer T310 expiry before HOcmd reception are very frequent when ISD is small and low when the ISD increases. We argued that for small cell sizes, the UEs that are able to transmit the measurement report subsequently move out of the serving cell coverage, and thus the HO command, sent by the serving cell, cannot reach the UE.…”

“…The lowest power consumption is attained for ISD 500m, which constitutes an "optimum" ISD under the simulated assumptions. An ISD of 500m turns to be optimal since we are able to avoid the UL impairment problems arising for small ISDs (due to high interference from neighboring UEs) and large ISDs (due to low UE transmitted power at the cell edge), see also [19]. The other trend of the graph shows that increasing UE speed, increases power consumption, especially at low ISDs, due to the high signaling rate observed in Fig.…”

“…It may also happen, that the UE failed to HO to a neighboring cell and subsequent efforts to reconnect to the same cell, resulting in a high PP rate and thus to high HO rates. It is to be noted that the ping pong events can also appear as the consequence of failed HOs to neighboring cells, and the subsequent efforts to reconnect the UE to neighboring cells even if not the most adequate at that time [19].…”

“…In the case where the HO request is rejected by the target cell, the proposed system fallbacks to the existing gNB assisted HO which further increases the HO delay. In our previous work [19], we found that increasing/decreasing the inter-site distance (ISD), after a certain limit, degrades the HO performance mainly due to limitations in the UL. In [20], we included a power consumption model for the transmitted signaling messages during handover.…”

“…Similar to the signaling rate case, increasing the TTT and the offset enforce a reduction of the signaling which significantly reduces the power consumption. However, this signaling and power reduction comes at the cost of increased HOFs as noted in [19].…”