In the scalar dirty multiple-access channel, in addition to Gaussian noise, two additive interference signals are present, each known non-causally to a single transmitter. It was shown by Philosof et al. that for stro...
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In the scalar dirty multiple-access channel, in addition to Gaussian noise, two additive interference signals are present, each known non-causally to a single transmitter. It was shown by Philosof et al. that for strong interferences, an independent identically distributed ensemble of codes does not achieve the capacity region. Rather, a structured-codes approach was presented that was shown to be optimal in the limit of high signal-to-noise ratios, where the sum capacity is dictated by the minimal ("bottleneck") channel gain. In this paper, we consider the multiple-input multiple-output (MIMO) variant of this setting. In order to incorporate structured codes in this case, one can utilize matrix decompositions that transform the channel into effective parallel scalar dirty multiple-access channels. This approach, however, suffers from a "bottleneck" effect for each effective scalar channel and, therefore, the achievable rates strongly depend on the chosen decomposition. It is shown that a recently proposed decomposition, where the diagonals of the effective channel matrices are equal up to a scaling factor, is optimal at high signal-to-noise ratios, under an equal rank assumption. This approach is then extended to any number of transmitters. Finally, an application to physical-layer network coding for the MIMO two-way relay channel is presented.
Relay-based cooperative communication has become a research focus in recent years because it can achieve diversity gain in wireless networks. In existing works, networkcoding and the two-path relay scheme is exploite...
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Relay-based cooperative communication has become a research focus in recent years because it can achieve diversity gain in wireless networks. In existing works, networkcoding and the two-path relay scheme is exploited to deal with the increase in network size and the half-duplex nature of relay, respectively. To further improve bandwidth efficiency, we propose a novel cooperative transmission scheme which combines networkcoding and the two-path relay scheme together in the multi-source system. Due to the utilization of two-path relay, our proposed scheme achieves full-rate transmission. Adopting complex field networkcoding (CFNC) at both the sources and the relays ensures that symbols from different sources are allowed to be broadcasted in the same time slot. We also adopt physical-layer network coding (PNC) at the relay nodes to deal with the inter-relay interference caused by the two-path relay. With careful process design, our scheme can achieve the ideal throughput up to 1 symbol per source per time slot (sym/S/TS). Furthermore, the theoretical analysis provides a method to estimate the symbol error probability (SEP) and throughput in complex additive white Gaussian noise (AWGN) and Rayleigh fading channels. The simulation results verify the improvements achieved by the proposed scheme.
This paper studies and analyzes a multi-pair MIMO two-way relay (TWR) system from a principal-angle perspective. In this system, users are grouped into pairs and two users in each pair exchange information through a c...
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This paper studies and analyzes a multi-pair MIMO two-way relay (TWR) system from a principal-angle perspective. In this system, users are grouped into pairs and two users in each pair exchange information through a common relay. The transmission scheme consists of two phases. In the uplink phase, the relay's receive signal space is divided into two subspaces for each pair: in one subspace, the signals of the two users are near-parallel, and physical-layer network coding (PNC) decoding is applied to retrieve network-coded messages;in the other subspace, the two user signals are near-orthogonal, and complete decoding (CD) is applied to retrieve individual user messages. In the downlink phase, the relay's transmit signal space is split into orthogonal subspaces for each pair, and in each subspace a common message is broadcasted to the two users. Our main contribution is to establish a critical link between the transmission scheme and the concept of principal angle in linear algebra. In particular, principal angle quantizes the degree of orthogonality between the user signals and helps determining how to partition the relay's receive signal space into PNC decoding subspace and CD decoding subspace. Building on that, we discuss the optimal design of user/relay precoders for both uplink and downlink phases to maximize the asymptotic sum-rate of the proposed scheme at high signal-to-noise ratio (SNR). The analysis and numerical results indicate that our scheme performs close to the cut-set outer bound and significantly outperforms the existing schemes in the literature.
We consider secret key agreement based on radio propagation characteristics in a two-way relaying system where two legitimate parties named Alice and Bob communicate with each other via a trusted relay. In this system...
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We consider secret key agreement based on radio propagation characteristics in a two-way relaying system where two legitimate parties named Alice and Bob communicate with each other via a trusted relay. In this system, Alice and Bob share secret keys generated from measured radio propagation characteristics with the help of the relay in the presence of an eavesdropper. We present four secret key agreement schemes: an amplify-and-forward (AF) scheme, a signal-combining amplify-and-forward (SC-AF) scheme, a multiple-access amplify-and-forward (MA-AF) scheme, and an amplify-and-forward with artificial noise (AF with AN) scheme. In these schemes, the basic idea is to share the effective fading coefficients between Alice and Bob and use them as the source of the secret keys. The AF scheme is based on a conventional amplify-and-forward two-way relaying method, whereas in the SC-AF scheme and the MA-AF scheme, we apply the idea of physical-layer network coding to the secret key agreement. In the AF with AN scheme, the relay transmits artificially generated noise, as well as channel information signal, in order to conceal the latter. Simulation results show that the MA-AF scheme outperforms the other schemes in Rayleigh fading channels, whereas the AF with AN scheme is suitable for Rician fading channels.
This paper presents a first real-time network-coded multiple access (NCMA) system that jointly exploits physical (PHY)-layernetworkcoding (PNC) and multiuser decoding (MUD) to boost the throughput of a wireless loca...
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This paper presents a first real-time network-coded multiple access (NCMA) system that jointly exploits physical (PHY)-layernetworkcoding (PNC) and multiuser decoding (MUD) to boost the throughput of a wireless local area network (WLAN). NCMA is a new design paradigm for multipacket reception wireless networks, in which the access point can receive and decode several packets simultaneously transmitted by multiple users. Conventionally, multipacket reception is realized using MUD only, whereas the key idea of NCMA is to use PNC together with MUD to realize multipacket reception. Although the feasibility of NCMA has previously been studied by the authors, our previous NCMA prototype was a version with offline signal processing. In addition, our previous investigation left open a number of theoretical and implementation issues, the resolution of which is critical to the adoption of NCMA in real practice. The current investigation makes the following state-of-the-art contributions toward NCMA: 1) we demonstrate a first NCMA system with integrated real-time PHY- and MAC-layer decoding;2) we construct a new unified framework for MAC-layer decoding that yields higher throughput with faster decoding-the faster decoding is one of the key enablers of our real-time implementation;and 3) we design new PHY-layer decoding techniques that overcome the poor performance of the first-generation NCMA prototype at low SNR. Experimental results show that, compared with the previous NCMA prototype, our new NCMA prototype improves real-time throughput by more than 100% at medium-high SNR (>= 8 dB).
The integrated space and terrestrial networks which incorporate various satellite systems and ground networks could provide a wide variety of services and global seamless network access. The integrated network is comp...
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The integrated space and terrestrial networks which incorporate various satellite systems and ground networks could provide a wide variety of services and global seamless network access. The integrated network is composed of multiple heterogeneous nodes and sub-networks which requires intelligent and efficient physicallayer transmission techniques to maintain high-speed links between these subsystems. As a traditional technology in satellite communications, relay could still work as an important part in these heterogeneous and complex networks. In this paper, two interference exploitation schemes, i.e., physical-layer network coding (PNC) and successive interference cancellation (SIC) which can efficiently increase data exchange rate for relay systems are studied, and an intelligent relaying scheme combining both the advantages of these two schemes is proposed. Simulation results show the proposed adaptive transmission scheme achieves a smoother sum-rate gain while being more robust to dynamic topologies.
Increasing the density of base stations deployment is regarded as a means to satisfy the growing demand of wireless connectivity over a shared bandwidth, however, increasing the disparity in the service received by ea...
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Increasing the density of base stations deployment is regarded as a means to satisfy the growing demand of wireless connectivity over a shared bandwidth, however, increasing the disparity in the service received by each user. Fairness can be realized by dynamically allocating resources to users using detailed channel state information at the transmitter (CSIT), which constitutes an expensive overhead, especially, for dense networks. One solution to improve the fairness without CSIT is to introduce spatial diversity through the use of relays in combination with physical-layer network coding (PNC). Most relaying-PNC solutions focus on the particular case of the two-way relay channel or they require additional relays and a large transmission time. In this paper, we propose a multiple-relay communication protocol (MRCP) for achieving fairness in dense networks. It exploits spatial diversity without requiring additional relays since it uses the base stations as relays. Furthermore, MRCP is applicable to an arbitrary number of base stations and users, while keeping a small transmission time. We show that our approach achieves the highest max-min fairness among users and almost full diversity with asymmetric transmissions.
This article presents a cross-layer design of backbone-assisted wireless local area network (WLAN) for dense WLAN deployment. The popularity of 802.11-based WLANs leads to dense WLAN deployment in geographically limit...
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This article presents a cross-layer design of backbone-assisted wireless local area network (WLAN) for dense WLAN deployment. The popularity of 802.11-based WLANs leads to dense WLAN deployment in geographically limited space, including dense access points (AP) and dense users. With dense APs, an AP could overhear packets destined for other APs. Backbone-assisted WLAN is a new system architecture where cooperative APs share the overheard packets through a backbone network, thereby reducing packet retransmission and improving system throughput. Conventional WLAN, such as Wi-Fi, uses Stop-and-Wait ARQ. This article argues that Stop-and-Wait does not work well with backbone-assisted WLAN because of large backbone delays. We first show that with a variant of Selective Repeat ARQ tailored for backbone-assisted WLAN, a single-user backbone-assisted WLAN system can achieve substantial throughput improvement over that with Stop-and-Wait ARQ. Then, we put forth a new system architecture targeted for dense users, referred to as network-coded backbone-assisted WLAN, in which multiple users are allowed to transmit simultaneously. A distinguishing feature of this system is the joint use of physical-layernetwork-coding (PNC) decoding and multiuser decoding (MUD) in multipacket reception. This article is the first attempt to design an ARQ for multiuser backbone-assisted WLAN. Our overall system design solves a PNC sequence obfuscation problem and addresses long packet latency in Selective Repeat ARQ. Experiments on our software-defined radio prototype indicate that network-coded Ethernet-backbone-assisted WLAN can achieve high system throughput and low packet latency. Specifically, the system throughput can outperform an MUD-only multiuser WLAN and a single-user WLAN by 60 and 100 percent, respectively. Overall, we believe that network-coded backbone-assisted WLAN is a viable solution for boosting throughput and reducing latency in dense WLAN environments.
Compute-and-forward (CF) harnesses interference in a wireless network by allowing relays to compute combinations of source messages. The computed message combinations at relays are correlated, and so directly forwardi...
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Compute-and-forward (CF) harnesses interference in a wireless network by allowing relays to compute combinations of source messages. The computed message combinations at relays are correlated, and so directly forwarding these combinations to a destination generally incurs information redundancy and spectrum inefficiency. To address this issue, we propose a novel relay strategy, termed compute-compress-and-forward (CCF). In CCF, source messages are encoded using nested lattice codes constructed on a chain of nested coding and shaping lattices. A key difference of CCF from CF is an extra compressing stage inserted in between the computing and forwarding stages of a relay, so as to reduce the forwarding information rate of the relay. The compressing stage at each relay consists of two operations: first to quantize the computed message combination on an appropriately chosen lattice (referred to as a quantization lattice), and then to take modulo on another lattice (referred to as a modulo lattice). We study the design of the quantization and modulo lattices and propose successive recovering algorithms to ensure the recoverability of source messages at destination. Based on that, we formulate a sum-rate maximization problem that is in general an NP-hard mixed integer program. A low-complexity algorithm is proposed to give a suboptimal solution. Numerical results are presented to demonstrate the superiority of CCF over the existing CF schemes.
It is understood that the performance of networkcoding (NC) is largely dependent on link scheduling schemes, and greedy NC may in fact reduce network throughput due to the reduction of spectrum spatial reuse. In this...
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ISBN:
(纸本)9781479913510
It is understood that the performance of networkcoding (NC) is largely dependent on link scheduling schemes, and greedy NC may in fact reduce network throughput due to the reduction of spectrum spatial reuse. In this paper, we study the interplay between NC and spatial reuse, and present a NC-aware link scheduling scheme to increase network throughput. Then, we propose an adaptive power control scheme to decrease interference so that NC and spatial reuse can be complementary in throughput improvement. Simulation results demonstrate that NC and spatial reuse are suitable for different network environments, and our proposed schemes can optimize network throughput by taking full advantage of the superiorities of both NC and spatial reuse in different network topologies.
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