Physical Layer Network Coding for Mobile Communications

该项目的目的是研究一种无线多跳传输的新方法，该方法是Ahlswede等人提出的网络编码方案的扩展。在项目的过程中，各种均衡技术，使这种物理层网络编码（PNC）中继系统在传输受频率选择性衰落影响的环境中运行已经被开发出来。针对中继节点设计了三种序列估计方案。其中两种算法在全状态网格上运行，因此它们的性能代表了所有随后研究的方法的性能上限。由于随着信道脉冲响应长度的增加，基于全状态网格的方案的计算复杂性和内存消耗变得非常快，因此我们还设计了一种降低复杂性的方法。然而，复杂性的降低带来了相当大的性能损失。此外，我们设计了最优的传输滤波方法，允许中继节点使用线性均衡（LE）或决策反馈均衡（DFE）。通过在源节点使用这些滤波器，从两个节点到中继的传输受到相同的整体通道脉冲响应的影响，并且相对于所选择的均衡方法（LE或DFE）的信噪比（SNR）被最大化。一种基于最优Tomlinson-Harashima预编码（THP）的方法补充了上述算法。在源节点上使用适当的反馈（预编码）和前馈滤波器的组合，可以在两个通信节点上实现无码间干扰（ISI）的传输。对于该项目的更新，将PNC扩展到单载波频分多址（SC-FDMA）传输将是研究课题之一。SC-FDMA由于其具有吸引人的特性，已经被标准化用于长期演进（LTE）的上行链路。新的频域均衡器将研究与SC-FDMA的PNC方案。此外，我们将考虑更现实的网络拓扑。到目前为止，我们的重点主要放在双向中继信道（TWRC）上。在项目的最后一年，我们将把我们的研究扩展到多址中继信道（MARC）。此外，在进行项目时，我们注意到有几个有待进一步研究的开放点。基于THP的中继系统目前在广播阶段的目的节点上使用DFE。我们将在此阶段开发一种使用THP的方案，以部分补偿由两个无线电信道引起的ISI，并通过LE消除每个目标节点的残留ISI。最后，将开发一种最优的传输滤波方案，该方案便于在中继节点上使用低复杂度的基于网格的均衡器，如减少状态序列估计（RSSE）。

The objective of this project is to investigate a novel approach to wireless multi-hop transmission, which is an extension of the network coding scheme as presented by Ahlswede et al. In the course of the project, a variety of equalization techniques that enable such a physical layer network coding (PNC) relaying system to operate in an environment where transmissions are subject to frequency-selective fading have been developed.We have designed three sequence estimation schemes for the relay nodes. Two of these algorithms operate on a full-state trellis and therefore their performance represents an upper bound for the performance of all subsequently investigated approaches. Since the computational complexity and memory consumption of full-state trellis-based schemes becomes prohibitively large very fast as the length of the channel impulse response increases, we also devised a complexity-reduced approach. However, the reduction in complexity comes with a considerable performance penalty. Furthermore, we devised optimal transmit filtering approaches that allow the relay node to either use linear equalization (LE) or decision-feedback equalization (DFE). By employing those filters at the source nodes, the transmissions from both nodes to the relay are influenced by the same overall channel impulse response, and the signal-to-noise ratio (SNR) with respect to the chosen equalization approach (LE or DFE) is maximized. An optimal Tomlinson-Harashima precoding (THP) based approach complements the above mentioned algorithms. Using a combination of suitable feedback (precoding) and feedforward filters at the source nodes, a transmission that is free of intersymbol interference (ISI) can be achieved for both communicating nodes.For the renewal of the project, the extension of PNC to single-carrier frequency-division multiple access (SC-FDMA) transmission will be one of the research topics. SC-FDMA has been already standardized for the uplink of Long Term Evolution (LTE) due to its appealing features. New frequency domain equalizers will be investigated for a PNC scheme with SC-FDMA. Furthermore, we will consider more realistic network topologies. To date, our focus was mainly on the two-way relay channel (TWRC). In the last year of the project, we will expand our investigations to the multiple access relay channel (MARC).Additionally, there are several open points for further research that came to our attention while working on the project. The THP based relaying system currently uses DFE at the destination nodes in the broadcast phase. We will develop a scheme that uses THP instead also in this phase in order to partly compensate for the ISI caused by both radio channels and removes the residual ISI at each destination node with LE. Finally, an optimal transmit filtering scheme that facilitates the use of low complexity trellis-based equalizers like reduced-state sequence estimation (RSSE) at the relay node will be developed.