Academia.eduAcademia.edu

Mobility State Estimation in LTE

Abstract

—Estimating mobile user speed is a problematic issue which has significant impacts to radio resource management and also to the mobility management of Long Term Evolution (LTE) networks. This paper introduces two algorithms that can estimate the speed of mobile user equipments (UE), with low computational requirement, and without modification of neither current user equipment nor 3GPP standard protocol. The proposed methods rely on uplink (UL) sounding reference signal (SRS) power measurements performed at the eNodeB (eNB) and remain efficient with large sampling period (e.g., 40 ms or beyond). We evaluate the effectiveness of our algorithms using realistic LTE system data provided by the eNB Layer1 team of Alcatel-Lucent. Results show that the classification of UE's speed required by LTE can be achieved with high accuracy. In addition, they have minimal impact to the central processing unit (CPU) and the memory of eNB modem. We see that they are very practical to today's LTE networks and would allow a continuous and real-time UE speed estimation.

Key takeaways

  • Clearly, the more frequently the UE sends SRS, the higher will be the speed estimation accuracy.
  • In practice, due to large sampling period of SRS, the Nyquist frequency for avoiding spectrum aliasing is reduced, which limits the maximum observable Doppler frequency and thus decreases the maximum observable UE speed.
  • The UE speed is thus deduced, in considering the speed corresponding to the computed metric, which is obtained during 1).
  • With low speed UE, the SRS measurements vary slowly since they are often highly correlated for a long duration, whereas with high speed UE, the period of high correlation is relatively short.
  • While computing the probability of speed classification, we further consider errors on the shadowing decorrelation distance D. The term "no error on D" stands for the case where the algorithm has chosen the right mapping (among the possible Ds) for the UE metric computed online and the metric computed offline in the database.