Jochen Giese

Centralized scheduling for joint transmission coordinated multi-point in LTE-Advanced

Coordinated multi-point transmission/reception is considered for LTE-Advanced as a tool to improve the coverage of high data rates, the cell-edge throughput and/or to increase the system throughput [1]. Joint transmission schemes are mentioned in [1] as an example of coordinated transmission between cells for the downlink. Here, data are transmitted simultaneously either coherently or non-coherently from multiple cells to a single mobile station. In this paper, a centralized MAC scheduling approach for joint transmission coordinated multi-point (JT CoMP) is proposed. Since several base stations transmit jointly to a single mobile station, the base stations are grouped together in so-called clusters. Several cluster strategies are investigated as well. The focus is on schemes that add only low complexity to the existing 3GPP LTE Release 8 system. Simulation results are provided for non-coherent transmission for full buffer and bursty traffic models with various system loads for different static cell clustering approaches.

Performance upper bounds for coordinated beam selection in LTE-Advanced

Coordinated Multipoint (CoMP) transmission techniques have been considered as tools to improve cell-edge and average data throughput for LTE-Advanced. First investigations of CoMP techniques in homogeneous hexagonal macro layouts have shown that interference coordination needs to involve dominant interferers to allow significant gain. Therefore, in the present paper the application of CoMP in a heterogeneous network is considered where a planned macro deployment coexists with randomly placed femtocells resulting in a scenario where dominant interference can potentially be mitigated more effectively. The impacts of a heterogeneous layout on the interference characteristics in the downlink are evaluated by simulation and an assessment of gains achieved through coordination is provided.

Application of coordinated beam selection in heterogeneous LTE-advanced networks

Coordinated Multipoint (CoMP) techniques and heterogeneous wireless networks are two enablers to achieve improvements in data rate both for average as well as cell-edge users. We present a general CoMP technique based on coordinated beam selection and apply this technique in a heterogeneous wireless network where a hexagonal layout of macro base stations is overlaid with clusters of femto cells with closed subscriber group functionality. Without coordination, this scenario can be extremely challenging to mobile users that are located in the vicinity of the femto cells but are not allowed to connect to them. We show that the proposed CoMP technique leads to significant improvements for these users.

On MAC Layer Throughput Enhancements in LTE-A by Downlink Macro Diversity

Coordinated transmission between base stations is one of the techniques under investigation to further improve the system performance of E-UTRA. In general, such a coordination, sometimes also called network MIMO, requires a large amount of signaling between cells. A relatively simple scheme for cell coordination is macro diversity. In this paper we consider macro diversity for the downlink direction of LTE-Advanced as a means to improve cell edge user throughput. We investigate the frequency-selectivity gains offered by over the air combining for different radio channels at link level. The impact on cell throughput as well as on user throughput for mobiles operated in macro diversity mode and for legacy mobile stations is investigated by means of system level simulations. Additionally, open issues related to network coordination are identified for future work.

On the SINR distribution of codebook-based precoding in LTE in case of inter-cell interference

Interference is an important performance limiting factor in cell-based mobile communication scenarios. Especially entities located at cell edges significantly suffer from inter-cell interference caused by base stations serving users in neighboring cells. The standard of LTE considers a frequency reuse factor of one, which makes inter-cell interference coordination a widely discussed topic. However, most of these techniques lead to a reduction of inter-cell interference instead of a full suppression. Hence, inter-cell interference remains an unpredictable random effect that has to be classified statistically. Within this paper, we derive the probability density function of the inter-cell interference and the resulting SINR PDF, which is given as a non-linear transformation of the interference. Unitary matrix precoding as applied in LTE Rel. 8 is taken into regard. The results are verified by simulative investigations.