Two-way Network Research Articles

Effects of Channel Estimation Error on Full-Duplex Two-Way Networks

Bidirectional communication systems based on full-duplex transmission have been proposed as a way to increase the ergodic capacity of multiantenna two-way networks. This type of system enables simultaneous exchange of data between two nodes via bidirectional use of spatial resources. However, when channel estimation error is present, each node experiences both desired-channel interference (DI) and echo-channel interference (EI). This paper investigates the effect of channel estimation errors on the ergodic capacities for bidirectional full-duplex transmission (BFD) using one of two combining schemes: maximal-ratio combining (MRC) or optimum combining (OC). We derive the ergodic capacities as closed-form expressions and quantify the effect of channel estimation errors on ergodic capacities for BFD with MRC (BFD-MRC) or OC (BFD-OC). Numerical results demonstrate that full-duplex transmission in two-way networks is an attractive option when channel estimation error is present.

Impact of Correlated Log-Normal Shadowing on Two-Way Network Coded Cooperative Wireless Networks

In this letter, we provide a novel theoretical framework for studying the effects of correlated shadowing, in the number of relays that are capable of helping two nodes (sources) to exchange their messages. The relays use network coding to simultaneously transmit the received messages to the sources. We prove theoretically and verify by means of simulations that the average number of relays that are capable of forwarding the network coded message, is independent from any correlation between the links from one source to the relays. Finally, we apply this framework, to compute the network outage probability. The presented results are essential for the theoretical study of medium access control and relay selection protocols designed for network coded cooperative communications.

Two-Way Networks: When Adaptation is Useless

Most wireless communication networks are two-way, where nodes act as both sources and destinations of messages. This allows for adaptation at or interaction between the nodes-a node's channel inputs may be functions of its message(s) and previously received signals allowing for potentially larger rates than those achievable in feedback-free one-way channels where inputs are functions of messages only. However, examples exist of channels where adaptation is not beneficial from a capacity perspective. We ask whether analogous results hold for several multiuser two-way networks. We first consider deterministic two-way channel models: the binary modulo-2 addition channel and a generalization of this, and the linear deterministic channel, which models Gaussian channels at high SNR. For these deterministic models, we obtain the capacity region for the two-way multiple access/broadcast channel (MAC/BC), the two-way Z channel, and the two-way interference channel (under certain partial adaptation constraints in some regimes). We permit all nodes to adapt their channel inputs to past outputs (except for portions of the linear high-SNR two-way interference channel where we only permit two of the four nodes to fully adapt). However, we show that the two-way fully or partially adaptive capacity region consists of two parallel one-way regions operating simultaneously in opposite directions, i.e., adaptation is useless. We next consider two noisy channel models: 1) the Gaussian two-way MAC/BC, where we show that adaptation can at most increase the sum-rate by (1/2) bit in each direction and 2) the two-way interference channel, where partial adaptation is shown to be useless when the interference is very strong. In the strong and weak interference regimes, we show that the nonadaptive Han and Kobayashi scheme utilized in parallel in both directions achieves to within a constant gap for the symmetric rate of the fully (for some regimes) or partially (for the remaining regimes) adaptive models. The central technical contribution is the derivation of new, computable outer bounds which allow for adaptation.

An Efficient Relay Node Placement Scheme for Two-Way MIMO Multi-Hop Networks in Practical Indoor Environments

Relay deployment has been gaining attention for network designers. Recently, MIMO Two-way Multi-hop Network (M2WMN) where all links share the same frequency is introduced as a relaying scheme which achieves higher spectral efficiency than other conventional multi-hop schemes. A power control strategy for M2WMN has been proposed to alleviate the frequency-sharing interference problem which degrades the scheme's performance. However, for ease of analysis, the past studies on M2WMN just theoretically assumed Rayleigh fading model for all links of the network. This assumption is far from reality where the channels of different links might experience different pathloss conditions including shadowing. This paper conducts 3D ray-tracing simulation in a U-shaped corridor environment to attain practical propagation channels. Based on the channel data, this paper studies the performance of different multi-hop schemes and investigates an open problem of choosing optimal relay placement which can maximize the performance of M2WMN in real environments. Our results show that without power control, the optimal locations are where adjacent nodes are both in Line-of-Sight (LOS). Interestingly, the optimal locations are no more LOS environments when power control is applied. In addition, this paper also proposes a sub-optimal relay placement search algorithm relaxing the complexity of exhaustive search.

Relay Selection Schemes and Performance Analysis Approximations for Two-Way Networks

This paper studies relay selection schemes for two-way amplify-and-forward (AF) relay networks. For a network with two users that exchange information via multiple AF relays, we first consider a single-relay selection (SRS) scheme based on the maximization of the worse signal-to-noise ratio (SNR) of the two end users. The cumulative distribution function (CDF) of the worse SNR of the two users and its approximations are obtained, based on which the block error rate (BLER), the diversity order, the outage probability, and the sum-rate of the two-way network are derived. Then, with the help of a relay ordering, a multiple-relay selection (MRS) scheme is developed. The training overhead and feedback requirement for the implementation of the relay selection schemes are discussed. Numerical and simulation results are provided to corroborate the analytical results.

Lifetime maximization routing with network coding in wireless multihop networks

In this paper, we consider the lifetime maximization routing with network coding in wireless multihop networks. We first show that lifetime maximization with network coding is different from pure routing, throughput maximization with network coding and energy minimization with network coding. Then we formulate lifetime maximization problems in three different cases of (i) no network coding, (ii) two-way network coding, and (iii) overhearing network coding. To solve these problems, we use flow augmenting routing (FA) for the first case, and then extend the FA with network coding (FANC) by using energy minimized one-hop network coding. After that, we investigate the influence of parameters of FANC, evaluate the performance of FANC with two-way and overhearing network coding schemes and compare it with that without network coding under two different power control models, namely, protocol and physical ones. The results show that the lifetime can be improved significantly by using network coding, and the performance gain of network coding decreases with the increase of flow asymmetry and the power control ability.

Interference management strategy for multiuser two-way relay networks

We investigate the interference management strategy for multiuser two-way transmission network where multiple pairs of users communicate with their pre-assigned partners, with assistance of an amplify-and-forward relay. The design objective is that the tradeoff between the efficiency and reliability could be achieved as much as possible. By taking advantage of the signal space alignment technique to cancel the multi-user interference, all users can transmit massages to the relay simultaneously over the same channel resource. And a new multiple-input multiple-output (MIMO) precoding matrix is designed to reduce the decoding complexity. Simulation result shows the average sum rate performance of the proposed system, and the achievable degrees of freedom can outperform MU-MIMO scheme and TDMA scheme.

Max-Min Optimal Joint Power Control and Distributed Beamforming for Two-Way Relay Networks Under Per-Node Power Constraints

This paper deals with optimal joint user power control and relay distributed beamforming for two-way relay networks, where two end-users exchange information through multiple relays, each of which is assumed to have its own power constraint. The problem includes the design of the distributed beamformer at the relays and the power control scheme for the two end-users to optimize the network performance. Considering the overall two-way network performance, we maximize the lower signal-to-noise ratio (SNR) of the two communication links. For single-relay networks, this maximization problem is solved analytically. For multi-relay networks, we propose an iterative numerical algorithm to find the optimal solution. While the complexity of the optimal algorithm is too high for large networks, two sub-optimal algorithms with low complexity are also proposed, which are numerically shown to perform close to the optimal technique. It is also shown via simulation that for two-way networks with both single relay and multiple relays, proper user power control and relay distributed beamforming can significantly improve the network performance, especially when the power constraints of the two end-users in the networks are unbalanced. Our approach also improves the power efficiency of the network largely.

Research on Digital TV Anonymous Authentication

Now many television operators are providing subscribers with more and more value-added service. When people use these services they will have the risk of leaking personal information, such as the watching habit, the privacy problem has become a hot topic to the public. This paper proposes a scheme of CAS anonymous authentication in two-way network, and the scheme uses group signatures based on the elliptic curve. It meets both efficient authentication and transaction tracking needs, and can also protect user's privacy in a certain extent.

Achievable Rate Region under Joint Distributed Beamforming and Power Allocation for Two-Way Relay Networks

We obtain the achievable beamforming rate region for a two-way cooperative network consisting of two transceivers and multiple relays, all single-antenna nodes. Assuming that the relay beamforming weights as well as the transceiver transmit powers are the design parameters, this region is characterized under a constraint on the total (network) transmit power consumption. Using the shape of the rate region, we then use a sum-rate maximization approach to obtain the jointly optimal relay beamforming weights and transceiver transmit powers. Interestingly, we show that the sum-rate maximization approach yields the same solution as the max-min fair design approach does. Using this relationship, we further present a semi-closed-form solution to the underlying distributed beamforming problem. We then prove that the transmit power of any of the two transceivers can be obtained as the solution to a one-dimensional optimization problem using a simple bisection method which enjoys a low computational complexity. Furthermore, we extend these results to obtain the relay beamforming weights and transceiver transmit powers corresponding to any point on the boundary of the rate region, through a weighted sum-rate maximization approach.

Relay Beamforming in Cognitive Two-Way Networks with Imperfect Channel State Information

A cooperative bidirectional relaying scheme based on relay beamforming is proposed for an underlay cognitive relay network (CRN) which consists of two secondary transceivers and K cognitive relay nodes and a primary network (PN) with a transmitter and receiver, all equipped with single antenna. The result of incoordination between PN and SN is that the instantaneous channel gains of interference links between two networks are unavailable. So, it is reasonable to assume the availability of second-order statistics (SOS) of the channel coefficients between the relays and PN. Also the perfect channel state information (CSI) is assumed for SN itself. In this paper we find the beamforming coefficients based on requirements of PN or SN. To do so we propose signal-to-interference-plus-noise ratio (SINR) balancing and interference minimization approaches. Our simulation results show that the performance of the network can be degraded considerably by uncertainty about the channel coefficients.

Performance Tradeoffs in Amplify-and-Forward Bidirectional Network Beamforming

We study and compare the performance of two bidirectional network beamforming schemes, namely the multiple access broadcast channel (MABC) strategy and the time division broadcast channel (TDBC) protocol, using joint optimal power control and beamforming design. To do so, we first design two TDBC-based bidirectional network beamformers, through minimization of the total power consumed in the whole network subject to quality of service (QoS) constraints, for the two cases with and without a direct link between the two transceivers. The corresponding power minimization problems are carried out over the transceiver transmit powers as well as relay beamforming weights, thus resulting in a jointly optimal power allocation and beamforming criterion. We devise optimal second-order cone programming based solutions as well as fast gradient-based solutions to these problems. We then use these solutions to compare the performance of the underlying TDBC-based approach to that of the MABC-based technique. This comparison is important because the TDBC approach appears to have certain advantages which can be exploited towards improving the performance of two-way network beamforming. These advantages include the additional degrees of freedom as well as the possibility of benefitting from the availability of a direct link between the two transceivers. Interestingly, in the absence of a direct link between the two transceivers, we show that when the QoS constraints are imposed to meet certain given probabilities of uncoded error [or, equivalently, to meet certain signal-to-noise ratio (SNR) constraints], these two schemes perform closely in terms of the minimum total transmit power. However, when the QoS constraints are used to guarantee certain given rates, the MABC-based scheme outperforms the TDBC counterpart. In the case when a direct link exists between the two transceivers, the TDBC-based approach can outperform the MABC-based method, even for rate satisfying QoS constraints, provided that the direct link is strong enough.

The Smart Grid Isn't All That Smart — Yet: Conflicting Standards, Differing Upgrade Cycles Stifle Two-Way Power Networks

Market and policy realities are compelling utilities worldwide to upgrade their communications capabilities to implement the smart grid. Although much of the grid communications overlay won't be on the public Internet, the IP suite will form its foundation However, the complex lattice of technical, policy, and regulatory jurisdictions inherent in creating the smart grid contribute to confusion surrounding how to harmonize its foundational documentation, which elements will be updated to include two-way capabilities first, and what and who will be able to communicate and how soon.

A Semi-Closed-Form Solution to Optimal Distributed Beamforming for Two-Way Relay Networks

In this correspondence, we present a computationally simple semi-closed-form solution to the problem of designing distributed beamformer for two-way (bi-directional) multi-relay networks. In such a network, the relay nodes use amplify-and-forward relaying protocol to help two transceivers exchange information in a bidirectional manner. We consider a total power minimization approach to optimally find the relay beamforming weights and the transceiver transmit powers. This approach is based on the minimization of the total transmit power, consumed in the whole network, subject to SNR constraints at the two transceivers. We show that as far as the relay beamforming weight vector is concerned, this minimization problem is equivalent to the minimization of the total transmit power for a one-way relay network where the target SNR of the receiving transceiver is equal to the sum of the target SNRs of the two transceivers in the original two-way relay network. Based on this observation, we show that the relay beamforming weight vector can be obtained in a closed from given that an intermediate parameter, namely the transmit power of the transmitter in the equivalent one-way relay network, is available. This intermediate parameter is shown to be the solution to a one-dimensional optimization problem, and thus, it can be obtained using a simple bisection method. Our semi-closed-form solution not only reveals the structure of the optimal beamforming weight vector, but also leads to a one-dimensional search regardless of the number of relays. This provides the computational advantage over the gradient based numerical method of Havary-Nassab , where the gradient dimension reflects the number of relays.

Analytical Capacity Comparison of One-Way and Two-Way Signalized Street Networks

Recently cities have been converting traditional one-way downtown street networks to two-way operation partly because one-way networks are seen as confusing and as less conducive to economic activity and a livable environment and they require vehicles to travel longer distances on average. However, one of the main disadvantages of such conversions is thought to be a reduction in the network's ability to serve vehicles. Intersections in two-way networks can serve fewer vehicles per unit time than their one-way counterparts. Several studies have assessed the differences between these two types of networks, but most studies are site specific and do not consider the best possible two-way networks. This paper presents an analytical model that uses macroscopic analysis techniques to compare various one-way and two-way networks using their trip-serving capacities. This metric is a key indicator of network performance. Two-way networks can serve more trips per unit time than one-way networks when average trip lengths are short. This study also found that two-way networks in which left-turn movements were banned at intersections could always serve trips at a higher rate than one-way networks could, even long trips. Thus, the trip-serving capacity of a one-way network can actually be increased when it is converted to two-way operation if left turns are banned. In this way, livability and efficiency objectives can be achieved simultaneously. This framework can be used by planners and engineers to determine how much a network's capacity changes after a conversion, and also to unveil superior conversion options.

Transmission Power Minimization with Network Coding for Mobile Terminals in Cellular Relay Networks

This paper jointly investigates the bandwidth allocation, transmission strategy and relay positions for two-way transmission aware cellular networks with network coding (NC). Our goal is to minimize the transmission power of mobile terminals (MTs). Consider a cellular system, where multiple MTs exchange information with their common base station, firstly, we propose an efficient bandwidth allocation method and then give a transmission strategy for each MT to determine whether to use relay stations (RSs) for its two-way transmission with the BS or not. To further improve the system performance, the optimal positions of RSs are also jointly discussed. A GA-based algorithm is presented to obtain the optimum positions for RSs. Besides, the impacts of frequency reuse on MT’s transmission power and system spectral efficiency (SE) under different number of relays are also discussed in our work. Numerical results show that the proposed NC aware scheme can extend MTs’ battery life at least 6% more than traditional method.

Distributed Relay Beamforming in Cognitive Two-Way Networks: SINR Balancing Approach

In this paper, we study the problem of distributed relay beamforming for a bidirectional cognitive relay network which consists of two secondary transceivers and K cognitive relay nodes and a primary network with a transmitter and receiver, using underlay model. For effective use of spectrum, we propose a Multiple Access Broadcasting (MABC) two-way relaying scheme for cognitive networks. The two transceivers transmit their data towards the relays and then relays retransmit the processed form of signal towards the receiver. Our aim is to design the beamforming coefficients to maximize quality of service (QoS) for the secondary network while satisfying tolerable interference constraint for the primary network. We show that this approach yields a closed-form solution. Our simulation results show that the maximum achievable SINR improved while the tolerable interference temperature becomes not strict for primary receiver.

Tight performance bounds for two-way opportunistic amplify-and-forward wireless relaying networks with TDBC protocols

Abstract Based on amplify-and-forward network coding (AFNC) protocol, the outage probability and ergodic capacity of two-way network coding opportunistic relaying (TWOR-AFNC) systems are investigated as well as the corresponding closed-form solutions. For the TWOR-AFNC systems, it is investigated under two scenarios, namely, the TWOR-AFNC systems without direct link (TWOR-AFNC-Nodir) and the TWOR-AFNC systems with direct link (TWOR-AFNC-Dir). First, we investigate TWOR-AFNC-Nodir systems by employing the approximate analysis in high SNR, and obtain closed-form solutions to the cumulative distribution function (CDF) and the probability density function (PDF) of the instantaneous end-to-end signal-to-noise ratio (SNR) with very simple expressions. The derived simple expressions are given by defining an equivalent variable ω eq-k (θ), 2 ≤ θ ≤ 3. When θ = 2, the derived results are the tight lower bounds to CDF and PDF. The sequent simulation demonstrates that the derived tight lower bounds are also very effective over the entire SNR region though which the results are derived in high SNR approximation. Then, with the derived tight closed-form lower bound solutions (θ = 2) in TWOR-AFNC-Nodir systems, we investigate TWOR-AFNC-Dir systems as well as the overall comparison of the outage probability and the ergodic capacity between the two system models. The comparison analysis performed over path loss model basis shows that, in urban environment, due to utilizing the direct link the TWOR-AFNC-Dir outperform considerably the TWOR-AF-Nodir systems. However, when the value of path loss exponent is relatively large, the achievable gain is very small and the direct link can be omitted. In this case, the TWOR-AFNC-Dir model can be displaced by TWOR-AFNC-Nodir model having lower implementation complexity.

Design of flexible and reconfigurable optical add/drop multiplexer

We present a two-way hitless reconfigurable optical add/drop multiplexer (ROADM) and an Optical Cross Connect (OXC) structures based on microring resonators (MRRs). The OXC is simulated by the transfer matrix compound with Finite-Different Time-Domain method, and the results show that optical signals can be carried out to any destination in this structure. The two-way hitless ROADM is suit for two-way network and the OXC can be used as core node in mesh network. It is shown the port number can be reduced when use the structures presented as the node module in optical networks.

The First Fibers to Homes

Thirty-five years ago this month, Japan’s Ministry for International Trade and Industry announced plans to build the world’s first fibered city. A two-way fiber-optic network called the Highly Interactive Optical Visual Information (Hi-OVIS) was far ahead of its time.