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Wireless Research Group
The design of innovative air interface technologies which fulfill the demands on future wireless communications is the key objective of the Wireless Research Group. Flexible and adaptive solutions with high capacity and robustness for LTE-Advanced and future radio access are targeted. The research areas covered by the group are detailed in the following.
Radio Access
One of the major challenges for future mobile communication systems beyond LTE-Advanced is to elaborate new radio access schemes achieving high spectrum efficiency as well as reducing the power consumption of the user terminal. Especially in uplink, there are many aspects that need to be further optimized to achieve these targets such as orthogonal/non-orthogonal multiple access schemes, inter-cell interference rejection/exploitation schemes, transmission power control and resource allocation schemes. At the same time, there is a need for the development of efficient L1/L2 control signaling schemes that can convey more control information compared to the currently standardized LTE-Advanced systems.
Green Radio
The goal of the green radio research is to address the global environmental challenge by investigating and proposing effective mechanisms to drastically reduce energy wastage and improve energy efficiency of mobile broadband communication systems, without compromising user’s perceived quality of service and system capacity. Today’s mobile networks have a vast potential for energy savings. The design of mobile networks has until now been focused on reducing of the energy consumption of terminals, whose battery power imposes stringent requirements on energy consumption. This has led to a situation where terminal energy consumption is only a fraction of the energy consumption of the mobile network. Consequently, we focus in this project on optimizing the energy consumption of radio base stations. A holistic system view will be employed, ensuring that any proposed radio energy efficiency improvements do not degrade energy efficiency or performance on the terminal side or any other part of the system.
Heterogeneous Networks
A significant portion of the traffic load of a cellular network is generated indoors. However due to wall penetration losses and large distances between transmitter and receiver, broadband user experience is difficult to achieve, even by MIMO-OFDM based standards such as LTE and LTE-Advanced. Small, low power, low cost home base stations known as femto-cells, are the key enabler for indoor broadband user experience. Moreover, femto-cells effectively offload indoor user traffic from the macro-cells, so that the scarce frequency resources can be utilized more efficiently. Traditional frequency planning of cellular networks is no longer feasible, so that new means for interference management and coordination need to be identified.
Multicell MIMO
Cooperative/coordinated MIMO-based wireless access methods (coordinated multipoint, CoMP) can be categorized into four different techniques depending on the amount of information which has to be exchanged between the cooperating base stations:
• inter-cell interference coordination (ICIC, no exchange of data and channel state information, CSI),
• diversity techniques (exchange of data only),
• coordinated beamforming (exchange of CSI only), and
• joint processing (exchange of data and CSI).
The goal of multicell MIMO transmission techniques is to achieve high data rates for cell-edge users while keeping the signaling overhead in the system acceptable. The required precoding strategies can be either distributed or central, meaning that the algorithm is performed distributed in the network or performed at a central unit.
Relaying and Network Coding
A major challenge for future mobile communication systems beyond LTE-Advanced is to provide a wide coverage area of high data rate services as well as to increase the system capacity. An approach to achieve wide coverage area is to increase the user throughput especially at the cell boundary by introducing intermediate nodes that act as relays. One of our main targets is to develop the advanced MIMO relaying schemes focusing on space-time coding and/or precoding schemes as well as resource allocation schemes to combat and/or suppress the interference between direct link and relayed link. Another target is to elaborate more sophisticated HARQ relay schemes by exploiting additional signaling for cooperation between relay node and donor base station.
Advanced Receivers
In current systems channel estimation is exclusively carried out by reference signals (pilots). However, advanced MIMO schemes require high pilot overheads to achieve the required channel estimation accuracy, which may significantly compromise the spectral efficiency. Advanced receivers that are able to generate high accuracy channel estimates at substantially lower pilot overheads are therefore a key enabler for highly spectral efficient advanced MIMO and coordinated multi-point (CoMP) schemes. One major aspect of this project is to consider the effects of cellular interference on the proposed pilot design. In particular, schemes to mitigate cellular interference by means of spatial processing and/or soft interference cancellation require accurate CSI of the interfering source.
EU Projects
ARTIST4G – Advanced Radio Interface Technologies for 4G Systems
www.ict-artist4g.eu
The main objective of the ARTIST4G project is to improve the ubiquitous user experience of cellular mobile radio communications through innovations in interference management and exploitation of new relay concepts. A key performance indicator is the ratio of the cell-average over the cell-edge spectrum efficiency. The target is on building consensus to foster the development of future standards.
EARTH – Energy Aware Radio and Network Technologies
www.ict-earth.eu
The goal of the EARTH project is to address the global environmental challenge by investigating and proposing effective mechanisms to drastically reduce energy wastage and improve energy efficiency of mobile broadband communication systems, without compromising users’ perceived quality of service and system capacity.
BeFEMTO - Broadband Evolved FEMTO Networks
www.ict-befemto.eu
The aim of the BeFEMTO project is to develop evolved femto-cell technologies based on LTE-A that enable a cost-efficient provisioning of ubiquitous broadband services and support novel usage scenarios like networked, relay and mobile femto-cells.
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