multiple_access_schemes_for_two_way_relaying_using_multiple_antennas_in_multi_user_scenarios

Non-Regenerative Multi-Antenna Two-Way and Multi-Way Relaying

Relaying techniques are highly beneficial in wireless communication systems to overcome shadowing effects, to increase the communication range, to improve the energy efficiency and to increase the achievable throughput. To further  increase the achievable throughput, multi-antenna techniques can be exploited. In this project, transmit strategies and filter designs for three different non-regenerative multi-antenna relaying scenarios are proposed. To investigate relaying in future cellular networks, a cellular multi-user relaying scenario is considered where a multi-antenna base station wants to bidirectionally communicate with several multi-antenna mobile stations. To investigate relaying in future ad-hoc and sensor networks, a multi-pair relaying scenario and a multi-group multi-way relaying scenario are considered. In the multi-pair relaying scenario, several pairs of multi-antenna nodes want to perform bidirectional pairwise communications. In the multi-group multi-way relaying scenario, each group consists of several multi-antenna nodes and each node wants to share its data with all other nodes within its group. In all scenarios, the nodes simultaneously transmit to the relay station during one multiple access phase. Afterwards, the relay station retransmits linearly processed versions of the received signals during several broadcast (BC) phases to the nodes. In the cellular multi-user and in the multi-pair relaying scenario, one BC phase is required due to considering bidirectional communications. In the multi-group multi-way relaying scenario, several BC phases are required because each node has to receive the messages of all other nodes within its group.

To consider that each node typically requires different data rates for transmission and reception, e.g., the required data rates in downlink are typically higher than the required data rates in uplink, asymmetric data rate (ADR)  requirements are introduced. However, the problem of maximizing the sum rate with and without considering the introduced ADR requirements is non-convex for the considered scenarios and searching for an optimal solution has a very high computational complexity. Thus, in this project, a decomposition of the sum rate maximization problem is proposed for each considered scenario. Based on the proposed decompositions, the following low-complexity approaches are introduced.

In the cellular multi-user relaying scenario, joint spatial processing over all antennas at the base station can be performed for transmission and reception. For this scenario, a relay transceive filter design is proposed which exploits that the signals transmitted by the mobile stations can be jointly processed at the base station. For the proposed filter design, the self-interference and successive interference cancellation capabilities of the nodes are exploited and an analytical solution based on minimizing the weighted mean square error is derived. Furthermore, a successive interference cancellation aware transmit filter design at the base station is proposed. Additionally, an approach to enable a joint design of the filters at the nodes and at the relay station is introduced. Moreover, two low-complexity transmit strategies are proposed which adjust the transmit powers of the mobile stations and the transmit power distributions at the base station and at relay station to tackle the considered ADR requirements. Additionally, one of the proposed transmit strategies performs a low-complexity subcarrier allocation to adjust the numbers of simultaneously transmitted data streams with respect to the considered ADR requirements. By numerical results, it is shown that the proposed transmit strategies combined with the proposed filter designs at the nodes and at the relay station significantly outperform conventional approaches. For instance, for the considered configurations, the proposed approaches require up to three antennas less at the relay station than conventional approaches to achieve the same sum rate.

In the multi-pair relaying scenario, neither the transmit signals nor the receive signals of nodes which belong to different pairs can be jointly processed at one node. For this scenario, a relay transceive filter design is proposed which suppresses the interferences between nodes of different pairs and thus, enables the simultaneous communication of all pairs. Furthermore, the proposed filter design exploits the capability of the nodes to perform self-interference and successive interference cancellation. The proposed relay transceive filter design is based on minimizing the weighted mean square error and an analytical solution is derived. Furthermore, two approaches for designing the transmit and receive filters at the multi-antenna nodes are introduced. Moreover, two low-complexity transmit strategies are proposed which adjust the transmit powers of the nodes and the transmit power distribution at the relay station to tackle the considered ADR requirements. Additionally, one of the proposed transmit strategies performs an exhaustive search to optimize the numbers of simultaneously transmitted data streams with respect to the considered ADR requirements. By numerical results, it is shown that the proposed transmit strategy which additionally optimizes the numbers of simultaneously transmitted data streams combined with the proposed filter designs at the nodes and at the relay station significantly outperforms conventional approaches. For instance, for the considered configurations, the proposed approach requires up to three antennas less at the relay station than conventional approaches to achieve the same sum rate.

In the multi-group multi-way relaying scenario, the selection of the signals which are retransmitted in each BC phase can be optimized which is an additional challenge compared to the other two relaying scenarios. Furthermore, the nodes can additionally perform joint temporal receive processing over the received signals of the different BC phases. For this scenario, two low-complexity transmit strategies are proposed which utilize analog network coding to exploit the spatial processing capabilities of the nodes and of the relay station as well as the capability of the nodes to perform temporal receive processing over the received signals of the different BC phases. Additionally, the proposed transmit strategies exploit the capability of the nodes to perform selfinterference and successive interference cancellation. To enable an efficient application of the proposed transmit strategies, an analog network coding aware relay transceive filter design is proposed. The relay transceive filter design is based on minimizing the weighted mean square error and an analytical solution is derived which can be adjusted via the considered weighting parameters. Additionally, a joint approach for designing the receive filters at the nodes together with the proposed analog network coding aware relay transceive filter is introduced. By numerical results, it is shown that the proposed transmit strategies combined with the proposed joint filter design at the nodes and at the relay station significantly outperform conventional approaches. For instance, if a single group with ten nodes is considered, the proposed approaches require up to six antennas less at the relay station than conventional approaches to achieve the same sum rate.