Optimized constellations for two-way wireless relaying with physical network coding
01 Jun 2009-IEEE Journal on Selected Areas in Communications (Institute of Electrical and Electronics Engineers)-Vol. 27, Iss: 5, pp 773-787
TL;DR: The proposed modulation scheme can significantly improve end-to-end throughput for two-way relaying systems and is applicable to a relaying system using higher-level modulations of 16QAM in the MA stage.
Abstract: We investigate modulation schemes optimized for two-way wireless relaying systems, for which network coding is employed at the physical layer. We consider network coding based on denoise-and-forward (DNF) protocol, which consists of two stages: multiple access (MA) stage, where two terminals transmit simultaneously towards a relay, and broadcast (BC) stage, where the relay transmits towards the both terminals. We introduce a design principle of modulation and network coding, considering the superposed constellations during the MA stage. For the case of QPSK modulations at the MA stage, we show that QPSK constellations with an exclusive-or (XOR) network coding do not always offer the best transmission for the BC stage, and that there are several channel conditions in which unconventional 5-ary constellations lead to a better throughput performance. Through the use of sphere packing, we optimize the constellation for such an irregular network coding. We further discuss the design issue of the modulation in the case when the relay exploits diversity receptions such as multiple-antenna diversity and path diversity in frequency-selective fading. In addition, we apply our design strategy to a relaying system using higher-level modulations of 16QAM in the MA stage. Performance evaluations confirm that the proposed scheme can significantly improve end-to-end throughput for two-way relaying systems.
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TL;DR: Physical layer network coding (PNC) as mentioned in this paper exploits the network coding operation that occurs naturally when electromagnetic (EM) waves are superimposed on one another, which has profound and fundamental ramifications.
Abstract: The concept of physical-layer network coding (PNC) was proposed in 2006 for application in wireless networks. Since then it has developed into a subfield of network coding with wide followings. The basic idea of PNC is to exploit the network coding operation that occurs naturally when electromagnetic (EM) waves are superimposed on one another. This simple idea turns out to have profound and fundamental ramifications. Subsequent works by various researchers have led to many new results in the domains of 1) wireless communication; 2) wireless information theory; and 3) wireless networking. The purpose of this paper is fourfold. First, we give a brief tutorial on the basic concept of PNC. Second, we survey and discuss recent key results in the three aforementioned areas. Third, we examine a critical issue in PNC: synchronization. It has been a common belief that PNC requires tight synchronization. Our recent results suggest, however, that PNC may actually benefit from asynchrony. Fourth, we propose that PNC is not just for wireless networks; it can also be useful in optical networks. We provide an example showing that the throughput of a passive optical network (PON) could potentially be raised by 100% with PNC.
309 citations
TL;DR: It is proposed that PNC is not just for wireless networks; it can also be useful in optical networks, and an example is provided showing that the throughput of a passive optical network could potentially be raised by 100% with PNC.
297 citations
24 Jan 2011
TL;DR: Reliable physical layer network coding takes this idea one step further: using judiciously chosen linear error-correcting codes, intermediate nodes in a wireless network can directly recover linear combinations of the packets from the observed noisy superpositions of transmitted signals.
Abstract: When two or more users in a wireless network transmit simultaneously, their electromagnetic signals are linearly superimposed on the channel. As a result, a receiver that is interested in one of these signals sees the others as unwanted interference. This property of the wireless medium is typically viewed as a hindrance to reliable communication over a network. However, using a recently developed coding strategy, interference can in fact be harnessed for network coding. In a wired network, (linear) network coding refers to each intermediate node taking its received packets, computing a linear combination over a finite field, and forwarding the outcome towards the destinations. Then, given an appropriate set of linear combinations, a destination can solve for its desired packets. For certain topologies, this strategy can attain significantly higher throughputs over routing-based strategies. Reliable physical layer network coding takes this idea one step further: using judiciously chosen linear error-correcting codes, intermediate nodes in a wireless network can directly recover linear combinations of the packets from the observed noisy superpositions of transmitted signals. Starting with some simple examples, this paper explores the core ideas behind this new technique and the possibilities it offers for communication over interference-limited wireless networks.
284 citations
Posted Content•
TL;DR: In this paper, the authors explore the core ideas behind linear network coding and the possibilities it offers for communication over interference-limited wireless networks, and present some simple examples of such a technique.
Abstract: When two or more users in a wireless network transmit simultaneously, their electromagnetic signals are linearly superimposed on the channel. As a result, a receiver that is interested in one of these signals sees the others as unwanted interference. This property of the wireless medium is typically viewed as a hindrance to reliable communication over a network. However, using a recently developed coding strategy, interference can in fact be harnessed for network coding. In a wired network, (linear) network coding refers to each intermediate node taking its received packets, computing a linear combination over a finite field, and forwarding the outcome towards the destinations. Then, given an appropriate set of linear combinations, a destination can solve for its desired packets. For certain topologies, this strategy can attain significantly higher throughputs over routing-based strategies. Reliable physical layer network coding takes this idea one step further: using judiciously chosen linear error-correcting codes, intermediate nodes in a wireless network can directly recover linear combinations of the packets from the observed noisy superpositions of transmitted signals. Starting with some simple examples, this survey explores the core ideas behind this new technique and the possibilities it offers for communication over interference-limited wireless networks.
275 citations
References
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1,584 citations
"Optimized constellations for two-wa..." refers methods in this paper
...The major contributions of this paper are summarized as follows: • we develop a closest–neighbor clustering method to design network coding for reliable two–way relaying, • we present well–designed network coding rules for QPSK relaying scenario, some of which require 5–ary cardinality to improve system throughput, • we optimize a signal constellation for 5–ary network coding by means of sphere packing [17], • we demonstrate the constellation design for two–way relaying that uses 16QAM at the MA stage, • we introduce a way to optimize network coding when we exploit diversity reception techniques....
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...We use sphere packing approach [17] to design the modulation MR for such an irregular constellation....
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...At last, we optimize the constellationMR for the irregular 5– ary denoising through the use of sphere packing [17]....
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29 Sep 2006
TL;DR: This paper proposes a physical-layer network coding (PNC) scheme to coordinate transmissions among nodes that makes use of the additive nature of simultaneously arriving electromagnetic (EM) waves for equivalent coding operation and demonstrates its potential for boosting network capacity.
Abstract: A main distinguishing feature of a wireless network compared with a wired network is its broadcast nature, in which the signal transmitted by a node may reach several other nodes, and a node may receive signals from several other nodes simultaneously. Rather than a blessing, this feature is treated more as an interference-inducing nuisance in most wireless networks today (e.g., IEEE 802.11). The goal of this paper is to show how the concept of network coding can be applied at the physical layer to turn the broadcast property into a capacity-boosting advantage in wireless ad hoc networks. Specifically, we propose a physical-layer network coding (PNC) scheme to coordinate transmissions among nodes. In contrast to "straightforward" network coding which performs coding arithmetic on digital bit streams after they have been received, PNC makes use of the additive nature of simultaneously arriving electromagnetic (EM) waves for equivalent coding operation. PNC can yield higher capacity than straight-forward network coding when applied to wireless networks. We believe this is a first paper that ventures into EM-wave-based network coding at the physical layer and demonstrates its potential for boosting network capacity. PNC opens up a whole new research area because of its implications and new design requirements for the physical, MAC, and network layers of ad hoc wireless stations. The resolution of the many outstanding but interesting issues in PNC may lead to a revolutionary new paradigm for wireless ad hoc networking.
1,576 citations
27 Aug 2007
TL;DR: This paper adopts the opposite approach; it encourages strategically picked senders to interfere, and achieves significantly higher throughput than both traditional wireless routing and prior work on wireless network coding.
Abstract: Traditionally, interference is considered harmful. Wireless networks strive to avoid scheduling multiple transmissions at the same time in order to prevent interference. This paper adopts the opposite approach; it encourages strategically picked senders to interfere. Instead of forwarding packets, routers forward the interfering signals. The destination leverages network-level information to cancel the interference and recover the signal destined to it. The result is analog network coding because it mixes signals not bits.So, what if wireless routers forward signals instead of packets? Theoretically, such an approach doubles the capacity of the canonical 2-way relay network. Surprisingly, it is also practical. We implement our design using software radios and show that it achieves significantly higher throughput than both traditional wireless routing and prior work on wireless network coding.
1,440 citations
16 Sep 2005
1,362 citations
"Optimized constellations for two-wa..." refers background in this paper
...Since Shannon firstly considered a two–way channel in [10], some theoretical investigations on the bidirectional relaying have emerged so far [11]....
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Proceedings Article•
01 Aug 2004TL;DR: It is shown that mutual exchange of independent information between two nodes in a wireless network can be performed by exploiting network coding and the physical-layer broadcast property offered by the wireless medium.
Abstract: —We show that mutual exchange of independentinformation between two nodes in a wireless network can be effi-ciently performed by exploiting network coding and the physical-layer broadcast property offered by the wireless medium. Theproposed approach improves upon conventional solutions thatseparate the processing of the two unicast sessions, correspondingto information transfer along one direction and the oppositedirection. We propose a distributed scheme that obviates theneed for synchronization and is robust to random packet lossand delay, and so on. The scheme is simple and incurs minoroverhead. I. I NTRODUCTION In this paper, we investigate the mutual exchange of inde-pendent information between two nodes in a wireless network.Let us name the two nodes in consideration a and b, respec-tively. Consider a packet-based communication network withall packets of equal size. The basic problem is very simple: awants to transmit a sequence of packets {X 1 (n)} to b andb wants to transmit a sequence of packets {X
807 citations
"Optimized constellations for two-wa..." refers background in this paper
...Related Works Bidirectional (and multi–directional) wireless relaying systems that use network coding have been introduced in [3, 4]....
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