Yidong Lang

Generalized Joint Channel Coding and Physical Network Coding for Two-Way Relay Systems

In this paper we present a generalized joint channel coding and physical layer network coding scheme for two-way relay systems, where the two sources A and B desire to exchange information from each other through the relay R simultaneously. Physical network coding scheme allows the relay to decode the network-coded information of both sources from the superimposed received signal. A novel iterative decoding approach is developed for arbitrary linear channel code, e.g. Low-Density Parity-Check (LDPC) code. Simulation results show that the proposed scheme outperforms other recently proposed network coding schemes with slightly increased complexity.

An improved physical layer network coding scheme for two-way relay systems

In this paper we consider a two-way relaying system with two sources A, B and one relay R, where the two sources desire to exchange information through the relay. The transmission consists of two states: multiple access (MAC) stage, where A and B transmit the channel-coded signals to R simultaneously, and broadcast (BC) stage, where R transmits towards both A and B. One critical process at R is to decode the superimposed signal from A and B in such a way that A and B could decode the information from each other reliably at the BC stage. Instead of decoding the individual information belonging to A and B separately, R aims to decode the superimposed signal to the network-coded combination of the two source information, i.e., the binary XOR of the two source information. We refer this decoding process as the joint channel decoding and physical network encoding (JCNC). In this paper, a novel iterative decoding algorithm is presented for the physical network coding scheme, which is applicable to any linear channel code, e.g. Low-Density Parity-Check (LDPC) code. Furthermore, the two-way relaying scheme is extended to distributed multiple input multiple output (MIMO) multi-hop networks. Based on an antenna selection criterion within each virtual antenna array (VAA), the end-to-end (e2e) BER of the multi-hop system can be further reduced. Simulation results show that the proposed scheme outperforms other recently proposed network coding schemes with slightly increased complexity.

Improved HARQ based on network coding and its application in LTE

In this paper, a novel HARQ transmission scheme based on network coding is proposed for wireless unicast scenarios. Instead of retransmitting erroneous packets individually, a network coded packet constructed by the XOR of two erroneous packets is transmitted similar to network coding. In order to fully exploit the network coded packet in combination with the previously received erroneous packets, soft combining methods with respect to Chase Combing (CC) and Incremental Redundancy (IR) are developed. The expected throughput gain of 33% for one retransmission for the proposed solution compared to common HARQ transmission is confirmed by LTE link-level simulations.

A closed power allocation solution for outage restricted distributed MIMO multi-hop networks

Power consumption and Quality-of-Service are the critical factors when developing resource allocation strategies for wireless networks. In order to minimize total transmission power while meeting the end-to-end outage probability requirement in a distributed MIMO multi-hop network, we will formulate the power allocation task as a convex optimization problem. By using some approximations to the optimization problem, we derive a novel near-optimal power allocation solution with lower complexity for distributed MIMO multi-hop networks. For the network with a large number of relaying nodes per virtual antenna array even a simple closed-form solution can be obtained. The simulation results show that our solution achieves a near-optimal performance.

Near-Optimum Power Allocation for Outage Restricted Distributed MIMO Multi-Hop Networks

The throughput of multi-hop communication systems can significantly be increased by the application of MIMO concepts. To utilize the physical resources in an efficient way while meeting the quality-of-service (QoS) constraints, appropriate power allocation strategies are desired. In this paper the total transmit power of a MIMO multi-hop system is minimized under the constraint of a given end-to-end outage probability. The optimum power allocation corresponds to a convex optimization problem. In order to achieve an analytical solution, the original task is relaxed by stringent approximations and a simple closed- form near-optimum solution is proposed. As this improved approximative power allocation (IAPA) achieves excellent performance results, this new approach is also very useful for investigating outage restricted multi-hop systems analytically.

Efficient power allocation for outage restricted asymmetric distributed MIMO multi-hop networks

Distributed MIMO multi-hop schemes can provide high data rates through spatially distributed relaying nodes. The relaying nodes allow the deployment of MIMO techniques to enhance the throughput by utilizing uncorrelated sub-channels. However, the spatial farness of geometrically separated relaying nodes results in different path losses from the nodes of one virtual antenna array (VAA) to the nodes of another VAA. In this paper we derive an approximative expression for the end-to-end (e2e) outage probability for such asymmetric networks, where orthogonal space-time block codes (OSTBC) are utilized for transmission. Based on this analytical expression a convex optimization problem that aims to reduce the total transmission power while meeting a given e2e outage level is formulated and an efficient near-optimal power allocation approach with low complexity is proposed. This near-optimum solution leads to the interesting result, that the same power is assigned to each node of one VAA. Thus, the power allocation turns out to be symmetric with respect to the nodes of one VAA also for networks with asymmetrically distributed nodes.

Power Allocations for Adaptive Distributed MIMO Multi-Hop Networks

Distributed MIMO multi-hop relaying is one of the most promising technologies that permits cost-effective improvement of coverage, data rate and end-to-end (e2e) user experience by utilizing distributed low-complexity space-time codes to overcome path losses and deep fades of wireless channels. However, an efficient transmission scheme and resource management are required to exploit these advantages. Specifically, low-complexity adaptive schemes and power control strategies should be designed, thereby achieving robust and cost-efficient e2e communications. In this paper an adaptive transmission scheme is presented, where one relay stops forwarding the message if it is in outage and other nodes adapt to a new space-time code. For this adaptive scheme, optimal as well as sub-optimal closed-form power allocation solutions are derived which minimize the total transmission power while satisfying a given e2e outage probability. The significant power savings due to the proposed approaches in comparison to a non-adaptive scheme is demonstrated by numerical results.

A novel resource allocation strategy for distributed MIMO multi-hop multi-commodity communications

In this paper, we present a near-optimum resource allocation strategy for distributed multiple-input-multiple-output multiple hops multiple commodities OFDMA wireless networks. The novel per-hop-optimization strategy aims to reduce the total transmission power of the network while meeting the individual end-to-end outage probability constraint of each commodity, i.e. for each link of the network. It utilizes the Greedy edge-coloring algorithm to determine reused orthogonal subbands for overlapping hops and allows a distributed implementation per hop. In comparison to other bandwidth allocation strategies like equal or dynamic bandwidth for each commodity, our per-hop-bandwidth-allocation (PHBA) approach uses the bandwidth in a near-optimum way and reduces the total transmission power significantly.

Optimal Power Routing for End-to-End Outage Restricted Distributed MIMO Multi-Hop Networks

This paper investigates the optimal power routing problem in relay-based cooperative networks, where the relays are arbitrarily positioned. We generalize the standard shortest path routing algorithm (GSPRA) to find an minimum-power distributed MIMO multi-hop route from a source to a destination while satisfying a given e2e outage probability demand. The task of the proposed approach includes how to group relays to virtual antenna array (VAA) and discover the optimal multi-hop path. Instead of using per hop (or link) constraint, which is assumed by most of the existing routing algorithm, an e2e outage probability constraint is assumed for more relevance and freedom in practical systems. Under the concept of virtual node and virtual link, an efficient power allocation solution for general distributed MIMO multi-hop networks is used to calculate link costs for the shortest path algorithm. The proposed routing approach can fully exploit the merits of both cooperative communications and multi-hop transmissions. The significant power savings due to the proposed approach in comparison to the existing algorithms is demonstrated by numerical results.

Joint Power and Time Allocation for Adaptive Distributed MIMO Multi-Hop Networks

Distributed MIMO multi-hop relaying can provide cooperative diversity and overcome path losses, hence, boost the end-to-end (e2e) performance. By using a low-complexity adaptive scheme, where one relay stops sending the message if it is in outage and other nodes adapt to a new space-time code, robust communication links can be further achieved. The contribution of this paper is the derivation of near-optimal closed-form solution for joint power and time allocation for such adaptive scheme that minimizes he transmission power while satisfying a given e2e non-ergodic outage probability.