Clemens Schnurr

Broadcast Capacity Region of Two-Phase Bidirectional Relaying

In a three-node network bidirectional communication between two nodes can be enabled by a half-duplex relay node with a decode-and-forward protocol. In the first phase, the messages of two nodes are transmitted to the relay node. In the second phase a re-encoded composition is broadcasted by the relay node. In this work the capacity region of the broadcast phase in terms of the maximal probability of error is determined. It is characterized by the mutual informations of the separate channels coupled by the common input.

Achievable Rates for the Restricted Half-Duplex Two-Way Relay Channel

The main result of the paper is a new achievable rate region for the two-phase two-way relay channel with half duplex nodes. The new region is obtained using a compress- and-forward like protocol. Even though all information passes the relay, there are channels where decoding at the relay is suboptimal. The proposed protocol establishes a virtual two-way channel by forwarding a good enough version of the MAC output at the relay to both the receivers. In effect, the side information at the receivers can be used for the decoding of the transmission in the first phase.

Achievable Rate Region of a Two Phase Bidirectional Relay Channel

In this work, the capacity region of the broadcast channel in a two phase bidirectional relay communication scenario is proved. Thereby, each receiving node has perfect knowledge about the message intended for the other node. The capacity region can be achieved using an auxiliary random variable taking two values, i.e., by the principle of time-sharing. The resulting achievable rate region of the two-phase bidirectional relaying includes the region which can be achieved by network coding applying XOR on the decoded messages at the relay node.

Achievable rates for the restricted half-duplex two-way relay channel under a partial-decode-and-forward protocol

In this paper, we state a new achievable rate region for the two-phase two-way relay channel with a half-duplex relay node. The new region is obtained using a partial-decode-and-forward protocol, which is a superposition of both, decode-and-forward and compress-and-forward. It contains the achievable rate regions according to Oechtering et al. (2008) and Schmurr et al. (2007) as special cases.

On Coding for the Broadcast Phase in the Two-Way Relay Channel

In this paper, we address the problem of designing practical codes for the broadcast phase in the two-way relay channel. The paper provides guidelines for the use of well-developed single-user codes in the bidirectional broadcast channel, with the goal of achieving or closely approaching the performance bounds. In case of finite alphabet channels with the channel distortion being independent of the channel input, the performance of our coding scheme only depends on the performance of the base codes on the corresponding single-user channels. If the involved single-user codes provides the best possible performance, so also does the proposed coding scheme for the bidirectional broadcast channel.

Coding theorems for the restricted half-duplex two-way relay channel with joint decoding

In this paper, we prove a new achievable rate region for the two-phase two-way relay channel under half-duplex constraints. The points in the region are achieved by a combination of a compress-and-forward strategy at the relay node (potentially including partial decoding) with a kind of joint decoding at the receivers. For some channels, the achievable rate region presented in this paper is shown to be a proper superset of a rate region proven in some recent papers where a separate decoding was assumed.

On the Strong Converse for the Broadcast Capacity Region of Two-Pase Bidirectional Relaying

In our previous work we determined the weak capacity region for the broadcast phase of two-phase bidirectional relay channel. It turned out that the set of achievable rates obtained by optimizing over the two communication phases exceeds that obtained by using the network coding principle, i.e. by applying XOR to the decoded messages. In this paper we supplement our result by a proof of the strong converse with respect to the maximum error probability to the coding theorem for the broadcast phase. This result implies that the capacity region of that phase remains constant for a certain range of values of average error parameters [epsiv1,epsiv2].

Energy efficiency of a two-stage relaying scheme in wireless sensor networks

This paper deals with a wireless relay system consisting of one source node, a number of relay nodes and one destination node. The relay nodes amplify and then encode their received signals using a distributed space-time code. Under a non-restrictive asymptotic assumption, we prove some upper bounds on the pairwise error probability for different transmission scenarios. These bounds suggest that significant diversity gains can be achieved in such cooperative systems. Moreover, they can be used to optimize the allocation of transmit powers to the nodes. In wireless sensor networks, however, the energy consumption associated with the hardware cannot be neglected. Therefore, we introduce a simple but realistic hardware model to numerically evaluate the overall energy-efficiency of the analyzed space-time coded cooperative relaying scheme. The numerical results show that, for a large range of path losses between the source and destination, direct transmission provides the best performance in terms of the overall energy consumption.