LTE Radio Load versus User Throughput Jari Salo A frequently asked question among LTE radio planners is that of how to determine the maximum acceptable LTE radio interface load that should not be exceeded in order to maintain some targeted user data throughput. This white paper summarizes some simple formulas for calculation of downlink user throughput as a function Physical Resource Block (PRB) utilization. The formulas are expressed in terms of standardized 3GPP KPIs and are hence computable from network performance counters. Examples from live LTE networks are given to illustrate the usefulness. 1. INTRODUCTION A frequently asked question in radio planning community is that of "what is the maximum LTE radio load so that user throughput is still ac- ceptable". A simple answer to the question is available by exploiting results from IP network- ing literature and basic queuing theory. In or- der to make those results practically useful for radio planners, the goal of this white paper is to state the existing theoretical results in terms of LTE radio utilization metrics that can be easily computed from network performance statistics available in commercial LTE base station prod- ucts. User throughput for elastic traffic transmit- ted over fixed bandwidth non-wireless links has been thoroughly investigated in engineer- ing literature, an overview and references can be found in [1]. Wireless network user throughput has been analyzed already in [2] and in other works of the authors thereof. The general idea has been to assume that the underlying trans- port protocol (usually TCP) realizes fair sharing of the link bandwidth between users, and there- fore the instantaneous user throughput is sim- ply the total link bandwidth divided by the in- stantaneous number of users. As the number of active users sharing the link varies over time the main challenge is how to find the average user throughput over time. In this paper the focus is on the average user throughput over LTE radio interface. In par- ticular the so-called M/G/1 Processor Sharing (PS) approach is used to express user through- put in terms of Physical Resource Block (PRB) utilization. Importantly, the formulas are pre- sented using the 3GPP standardized Key Perfor- mance Indicators (KPI) and measurement exam- ples from three live LTE networks are shown to illustrate their utility. The results can be used for both FDD and TDD variants of LTE. Although in principle the general approach is applicable to both downlink and uplink, the uplink case is dependent on power control and link adapta- tion, which leaves more degrees of freedom to be considered. For this reason, throughout the paper ’throughput’ refers to the downlink case, with the uplink applicability left for the reader to consider case-by-case. No new science that cannot be found some- where in the depths of engineering literature is developed in this white paper. The target audience are radio planning and optimization engineers with a working knowledge of LTE. Principles of LTE, as detailed in 3GPP specifica- tions, will not be repeated in this paper. Instead the reader is referred to the 3GPP standards or the latest editions of well-known literature ref- erences, e.g. [3–5] and many others. In Section 2 the average user throughput is formulated as a function of the number of active data flows sharing radio scheduler resources. In Section 3 these results are related to physical re- 1