System-level performance of LTE-Advanced with joint transmission and dynamic point selection schemes
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System-level performance of LTE-Advanced with joint transmission and dynamic point selection schemes Helka-Liina M¨aa¨ tt¨anen1* , Kari H¨am¨al¨ainen1 , Juha Ven¨al¨ainen2 , Karol Schober3 , Mihai Enescu1 and Mikko Valkama2 Abstract In this article, we present a practical coordinated multipoint (CoMP) system for LTE-Advanced. In this CoMP system, cooperation is enabled for cell-edge users via dynamic switching between the normal single-cell operation and CoMP. We first formulate a general CoMP system model of several CoMP schemes. We then investigate a practical finite-rate feedback design that simultaneously supports interference coordination, joint transmission (JT), and dynamic point selection (DPS) with a varying number of cooperating transmission points while operating a single-cell transmission as a fallback mode. We provide both link-level and system-level results for the evaluation of different feedback options for general CoMP operation. The results show that there are substantial performance gains in cell-edge throughputs for both JT and DPS CoMP over the baseline Release 10 LTE-Advanced with practical feedback options. We also show that CoMP can enable improved mobility management in real networks. 1 Introduction Multiple-input multiple-output (MIMO) systems have the potential to provide the capacity needed for futuregeneration wireless systems, and for this reason they have been adopted by 3GPP Long-Term Evolution (LTE) and LTE-Advanced (LTE-A) [1,2]. MIMO operation was already defined in the early stage of LTE specification work. In the downlink, 2 × 2 and 4 × 4 MIMO operation have been defined in Release 8 [3], and these have been further extended to 8 × 8 MIMO in Release 10 [2]. The main scenario is single-user (SU)-MIMO, where spatial multiplexing within individual time-frequency resource blocks is performed for a single user equipment (UE) at a time. In addition, multi-user (MU)-MIMO operation, where a time-frequency resource block is shared by multiple users in the spatial domain, has been possible since Release 8. In LTE Release 8, MU-MIMO is allowed only in a standard non-transparent manner, but in LTE Release 9 and 10 it can be enabled in a standard transparent manner. In Release 10, certain features have been included to improve the MU-MIMO performance com*Correspondence: [email protected] 1 Renesas Mobile Europe Ltd., Porkkalankatu 24, 00180 Helsinki, Finland Full list of author information is available at the end of the article
pared to Release 8. One such feature is a user-specific reference signal (RS) that makes it possible to suppress MU interference with a linear receiver. With a frequency re-use factor of 1, single-cell SUand MU-MIMO network performance is highly interference limited, especially at the cell-edge. Therefore, the introduction of coordinated multipoint (CoMP) transmission/reception was already considered in Release 10. In downlink CoMP, the transmission points co-operate in scheduling and transmission in order to strengthen the desired signal
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