Abstract
System-level simulations have become an indispensable tool for predicting the behavior of wireless cellular systems. As exact link-level modeling is unfeasible due to its huge complexity, mathematical abstraction is required to obtain equivalent results by less complexity. A particular problem in such approaches is the modeling of multiple coherent transmissions. Those arise in multiple-input-multiple-output transmissions at every base station but nowadays so-called coordinated multipoint (CoMP) techniques have become very popular, allowing to allocate two or more spatially separated transmission points. Also, multimedia broadcast single frequency networks (MBSFNs) have been introduced recently in long-term evolution (LTE), which enables efficient broadcasting transmission suitable for spreading information that has a high user demand as well as simultaneously sending updates to a large number of devices. This paper introduces the concept of runtime-precoding, which allows to accurately abstract many coherent transmission schemes while keeping additional complexity at a minimum. We explain its implementation and advantages. For validation, we incorporate the runtime-precoding functionality into the Vienna LTE-A downlink system-level simulator, which is an open source tool, freely available under an academic noncommercial use license. We measure simulation run times and compare them against the legacy approach as well as link-level simulations. Furthermore, we present multiple application examples in the context of intrasite and intersite CoMP for train communications and MBSFN.
Highlights
We extend the User Equipment (UE) link quality model of the Vienna long-term evolution (LTE)-A simulator by the runtime-precoding functionality according to Algorithm 1
The price to pay for enabling coherent multi-point transmission turned out to be an additional upscaling of the simulation run time which is proportional to the product of the number of transmit- and receive antennas, respectively
The run times showed a linearrather than a quadratic growth with the bandwidth, the latter being observed in link level simulations
Summary
We provide a brief introduction to modeling concepts of the physical layer of LTE-A on system level. The Vienna LTE-A simulator employs a Mutual Information based exponential SNR Mapping (MIESM) for the SINR-to-BLER mapping [32], [33], which already proved beneficial in Release 5 of UMTS [34], and was shown to outperform all other approaches (e.g., Exponential effective SINR mapping (EESM) [35]) in both complexity and performance This method compresses the Signal-to-Interferenceplus-Noise Ratio (SINR) values of the assigned Resource Blocks (RBs) for each User Equipment (UE) and 1 ms-long subframe (subsequently denoted as Transmission Time Interval (TTI)) into an effective SINR, yielding an AWGN-equivalent representation in terms of mutual information.
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