Holger Degenhardt

Self-interference aware MIMO filter design for non-regenerative multi-pair two-way relaying

A multi-pair two-way relaying scenario with multi-antenna mobile stations is considered. The bidirectional communications between the mobile stations are supported by an intermediate non-regenerative multi-antenna relay station. It is assumed that the mobile stations can subtract the back-propagated self-interference. Different relay transceive filter design approaches which utilize the fact that the mobile stations can perform self-interference cancellation are introduced. First, a self-interference aware MMSE transceive filter is derived. Second, a multi-antenna MMSE extension of the zero-forcing block-diagonalization based approaches is proposed and an upper bound for these approaches is given. The proposed transceive filters require less antennas at the relay station and achieve higher sum rates compared to conventional relay transceive filter approaches which do not exploit the capability of the mobile stations to perform self-interference cancellation.

Non-Regenerative Multi-Way Relaying: Combining the Gains of Network Coding and Joint Processing

In this paper, we consider a non-regenerative multi-group multi-way relaying scenario in which each group consists of multiple half-duplex nodes. Each node wants to share its data with all other nodes within its group. The transmissions are performed via an intermediate non-regenerative half-duplex multi-antenna relay station, termed RS, which spatially separates the different groups. In our proposal, all nodes simultaneously transmit to RS during a common multiple access phase and RS retransmits linearly processed versions of the received signals back to the nodes during multiple broadcast (BC) phases. We propose a novel transmit strategy which exploits analog network coding (ANC) and efficiently combines spatial transceive processing at RS with joint receive processing at each node over multiple BC phases. A closed-form solution for an ANC aware relay transceive filter is introduced and closed-form solutions for the joint receive processing filters at the nodes are presented. Furthermore, self-interference cancellation and successive interference cancellation are exploited at the nodes to improve the joint receive processing. By numerical results, it is shown that the proposed transmit strategy significantly outperforms existing multi-way strategies.

Self-interference aware MMSE filter design for a cellular multi-antenna two-way relaying scenario

A single cell scenario with different multi-antenna nodes, i.e., a base station and several mobile stations, is considered. An intermediate multi-antenna relay station is used to support the bidirectional communications. In such a scenario, the required data rates for up - and downlink are typically different which is considered by introducing asymmetric rate requirements. Non-regenerative two-way relaying is applied and the nodes can subtract the back-propagated self-interference. To fully utilize this capability of the nodes for the transceive filter design at the relay station, an MMSE based transceive filter is derived which does not suppress self-interference. Thus, the required number of antennas at the relay station is reduced. Additionally, the transceive filter is optimized for asymmetric rate requirements by introducing a weighting parameter. Furthermore, an alternating optimization between the transceive filter at the relay station and the transmit and receive filters at the nodes is introduced to fulfill the asymmetric rate requirements and to increase the achievable sum rates. Simulation results show that the proposed filter design at the nodes and at the relay station requires less antennas and achieves higher sum rates compared to conventional approaches.

Pilot transmission scheme and robust filter design for non-regenerative multi-pair two-way relaying

In this paper, a pilot transmission scheme and a robust self-interference aware relay transceive filter for multipair two-way relaying are introduced. The bidirectional pairwise communications of multiple single-antenna nodes are simultaneously performed via an intermediate non-regenerative multi-antenna relay station and a pilot transmission scheme is proposed to obtain channel state information at the relay station and at the nodes. It is assumed that the nodes can use the available channel state information to subtract the back-propagated self-interference and the cases of perfect and imperfect self-interference cancellation are investigated. The relay station performs linear signal processing based on the estimated channels and a robust relay transceive filter approach is introduced which utilizes the fact that the nodes can perform self-interference cancellation. The proposed pilot transmission scheme requires less resources for channel estimation than conventional schemes and the proposed robust filter design increases the achievable sum rate in case of imperfect channel state information.

Non-regenerative multi-antenna two-hop relaying under an asymmetric rate constraint

In this work, the combination of one-way and two-way relaying is examined in a scenario where two multi-antenna nodes exchange information under an asymmetric rate constraint via a half-duplex non-regenerative multi-antenna relay. Two-way relaying overcomes the multiplexing loss of one-way relaying, but additional optimizations are required to fulfill the asymmetric rate constraint. To enable the consideration of suboptimal low-complexity approaches, a hybrid one-way / two-way scheme is suggested which ensures that the asymmetric rate constraint can always be fulfilled. The optimization problem of maximizing the overall sum rate for the considered scenario is formulated and an approach for transceive filter and power optimization considering the asymmetric rate constraint is derived. Simulation results for different link qualities and rate constraints confirm the theoretical considerations and show that the proposed algorithm performs close to the upper bound in case of high asymmetric rate constraints or highly asymmetric channels.

Filter design with optimized numbers of data streams for multi-pair two-way relaying under asymmetric rate requirements

A multi-pair two-way relaying scenario with multi-antenna nodes is considered. The bidirectional communications between the nodes are supported by an intermediate non-regenerative multi-antenna relay station. It is assumed that the nodes can subtract the back-propagated self-interference. In such a scenario, the required data rates for each direction of transmission are typically different which is considered by introducing asymmetric rate requirements. To maximize the achievable sum rate under asymmetric rate requirements, a strategy to optimize the number of simultaneously transmitted data streams of each node is presented. Furthermore, a weighted self-interference aware relay transceive filter as well as transmit and receive filters at the nodes are proposed. Additionally, the transmit powers of the nodes are optimized with respect to the transceive filter at the relay station and the asymmetric rate requirements. The aforementioned approach achieves higher sum rates compared to conventional approaches which do not optimize the number of simultaneously transmitted data streams of each node.

Bi-directional differential beamforming for multi-antenna relaying

In this work, we propose a differential beamforming (DBF) scheme for bi-directional communication between two single-antenna terminals via a multi-antenna relay station (RS). The proposed scheme utilizes differential phase-shift keying modulation to enable beamforming at the RS without knowledge of the instantaneous channel state information (CSI) at any entity in the network. In our differential scheme, receive and transmit beamforming at the RS is performed based on the implicit CSI contained in the received signals in the preceding time slots. Thus, the DBF scheme is applicable even if the communication channels are time-variant. For time-invariant channels, we show that our DBF scheme is associated with a performance penalty of 3 dB as compared to the ideal amplify-and-forward relaying scheme, which requires perfect CSI. Our simulation results confirm the analytical results for time-invariant channels. For time-variant channels, the simulation demonstrate a high performance gain of the DBF scheme compared to schemes of the literature.

Local array calibration using parametric modeling of position errors and a sparse calibration grid

We propose a new method for offline calibration of a sensor array with respect to position, gain and phase errors of the sensor elements. We model the effect of position errors explicitly, such that they can be corrected parametrically using a least-squares formulation. This is equivalent to the already existing Maximum-Likelihood position estimator, but does not require a minimal number of calibration sources. While this is crucial, especially for large (e.g. 2D) arrays, it also reduces costs by using a sparse calibration grid for smaller arrays. The effectiveness of the method is demonstrated by simulations and based on a real data experiment.

A resource requirement aware transmit strategy for non-regenerative multi-way relaying

Non-regenerative multi-antenna multi-way relaying is considered. The scenario consists of a group of single-antenna nodes that want to communicate using multiple subcarriers. Each node has a message which every other node in the group should receive. The communications between the nodes are performed via a half-duplex multi-antenna relay station. It is assumed that the nodes have individual resource requirements. A new transmit strategy, in which the individual resources requirements of the nodes are considered, is proposed. To ensure that the relay station has enough spatial dimensions to separate the incoming signals, it is proposed that the number of transmitting nodes per subcarrier is equal to the number of antennas at the relay station. Moreover, it is proposed that the required numbers of subcarriers are calculated according to the buffer level of the nodes, reflecting the amount of data a node has to transmit. To allocate the required number of subcarriers to each node, the proposed transmit strategy performs an efficient subcarrier allocation. Numerical results show that the proposed strategy outperforms existing transmit strategies especially when the number of antennas at the relay station is smaller than the number of nodes.

Known-interference aware iterative MMSE filter design for non-regenerative multi-way relaying

A multi-way relaying scenario is considered. Each node has to transmit an individual message and has to receive the messages of all other nodes. These multi-way communications between the multi-antenna nodes are performed via an intermediate non-regenerative multi-antenna relay station. An iterative MMSE approach is proposed to jointly design the transceive filter at the relay station and the receive filters at the nodes. For this approach, self- as well as known-interference cancellation are exploited at the nodes and are considered for the derivation of the relay transceive filter. The proposed iterative MMSE approach achieves significantly higher sum rates compared to conventional approaches.