Link Interference Research Articles

Context-aware Greedy Scheduling Algorithm in Wireless Network

In order to measure the link’s interference in static heterogeneous wireless networks, we need to know its context information, but the context information can not be informed before the link allocates the time slot. Because of the highly inadequate collection and the use of traditional scheduling algorithms for link interference information, which severely limits their performance, this paper proposes the context-aware greedy scheduling algorithm. This paper analyses the cumulative effect of interference and the sequence detection feature of the serial interference cancellation (SIC, successive interference cancellation). The algorithm researches the strategy of choosing time slot, defines tolerance to measure the saturation of the link set and gives two kinds of new heuristic time slot selection mechanism. Finally, network simulator (NS 2) conducts simulation experiments which adopt performance evaluation as throughput to assess the performance of scheduling algorithm of this paper in the case of a single multi-hop. The experiments show that: the scheduling performance of context-aware greedy scheduling algorithm in heterogeneous static wireless network has been improved.

Interference aware routing for mobile ad hoc networks based on node's sending and receiving capabilities

How to efficiently build routes among nodes is increasing important for mobile ad hoc networks (MANETs). This paper puts forward an interference aware routing protocol called Interference aware cross layer routing protocol (IA-CLR) for MANETs based on the IEEE 802.11 medium access layer (MAC). By defining the node's sending and receiving capabilities, IA-CLR can indicate the interference strength of the link in a real and comprehensive way. Further more, in order to choose the route with minimum bottleneck link interference, a new routing metric is proposed by combining the MAC layer and the network layer for cross layer design. Simulation results show that IA-CLR can significantly improve the performances of network such as the average end-to-end delay, the packets loss ratio and the throughput.

A Channel Allocation Algorithm Based on Minimum Interference in Wireless Mesh Network

Channel allocation based on multi-interface is a very important and difficult problem. Network throughput needs to be maximized while full consideration should be given to interference reduction and network connectivity. To solve this problem, the extended conflict graph was utilized to establish the link interference matrix; the frequency assignment technique in spectrum management based on greedy algorithm was introduced for channel allocation, and a channel assignment algorithm based on minimum interference was proposed. The algorithm fully considered link interference situation, and selected the link which currently suffers the minimum interference. For the selected link, select the idle channels when there are sufficient channels; select the channels with least potential interference when there are no idle channels. Based on this strategy, the link interference is effectively reduced, the number of links that can work simultaneously is increased, which fully maintained the connectivity of the network and effectively improved network throughput. Simulation results show that this scheme can effectively improve the performance of overall network.

A Survey of Cooperative MAC Protocols for Mobile Communication Networks

Cooperative communication is a promising and practical technique for realizing spatial diversity through a virtual antenna array formed by multiple antennas of different nodes. There has been a growing interest in designing and evaluating efficient cooperative medium access control (MAC) protocols in recent years. With the objective of translating a cooperative diversity gain at the physical layer to cooperative advantages at the MAC layer, an efficient cooperative MAC protocol should be able to accurately identify a beneficial cooperation opportunity, efficiently select the best relay(s), and coordinate the cooperative transmission at low cost and complexity. However, due to the randomness of channel dynamics, node mobility, and link interference, the design of an efficient cooperative MAC protocol is of great challenge, especially in a wireless multi-hop mobile network. In this article, we aim to provide a comprehensive overview of the existing cooperative MAC protocols according to their specific network scenarios and associated research problems. Three critical issues (i.e., when to cooperate, whom to cooperate with, and how to cooperate) are discussed in details, which should be addressed in designing an efficient cooperative MAC protocol. Open research issues are identified for further research.

Outage Performance of Statistical CSI Assisted Cognitive Relay with Interference from Primary User

This work has studied the outage performance of amplify-and-forward (AF) relaying in underlay spectrum sharing systems with interference from primary user (PU). To reduce the complexity and improve the feasibility, two schemes using statistical channel state information (CSI) of interference links are proposed. For each scheme, the closed-form expressions for outage probability of secondary user (SU) and PU are derived, as well as the asymptotic expressions and diversity order. The impact of using statistical CSI instead of instantaneous CSI has been evaluated through the comparison with existing scheme. The analytical results and the simulation results are in excellent agrement confirming the effectiveness of the analysis in this work.

Orientation-singularity analysis and orientationability evaluation of a special class of the Stewart–Gough parallel manipulators

SUMMARYThis paper addresses the orientation-singularity analysis and the orientationability evaluation of a special class of the Stewart–Gough parallel manipulators in which the moving and base platforms are two similar semi-symmetrical hexagons. Based on the half-angle transformation, an analytical polynomial of degree 13 that represents the orientation-singularity locus of this special class of parallel manipulators at a given position is derived. Graphical representations of the orientation-singularity locus of this class of manipulators are illustrated with examples to demonstrate the results. Based on the description of the orientation-singularity and nonsingular orientation region of this class of parallel manipulators, a performance index, referred to as orientationability, which describes the orientation capability of this class of manipulators at a given position, is introduced. A discretization algorithm is proposed for computing the orientationability of the special class of parallel manipulators at a given position in the workspace. Moreover, the effects of the design parameters and position parameters on the orientationability are also investigated in detail. Based on the orientationability performance index, another performance index, referred to as practical orientationability, representing the practical orientation capability of the manipulators at a given position, is introduced. In this performance index, singularities, the limitations of active and passive joints and link interferences are all taken into consideration. Furthermore, the practical orientationability of the special class of parallel manipulators studied here is also analyzed over several plane sections of the position-workspace in detail.

Incremental Relaying for the Gaussian Interference Channel With a Degraded Broadcasting Relay

This paper studies incremental relay strategies for a two-user Gaussian relay-interference channel with an in-band-reception and out-of-band-transmission relay, where the link between the relay and the two receivers is modelled as a degraded broadcast channel. It is shown that generalized hash-and-forward (GHF) can achieve the capacity region of this channel to within a constant number of bits in a certain weak-relay regime, where the transmitter-to-relay link gains are not unboundedly stronger than the interference links between the transmitters and the receivers. The GHF relaying strategy is ideally suited for the broadcasting relay because it can be implemented in an incremental fashion, i.e., the relay message to one receiver is a degraded version of the message to the other receiver. A generalized-degree-of-freedom (GDoF) analysis in the high signal-to-noise ratio (SNR) regime reveals that in the symmetric channel setting, each common relay bit can improve the sum rate roughly by either one bit or two bits asymptotically depending on the operating regime, and the rate gain can be interpreted as coming solely from the improvement of the common messages rate, or alternatively in the very weak interference regime as solely coming from the rate improvement of the private messages. Further, this paper studies an asymmetric case in which the relay has only a single link to one of the destinations. It is shown that with only one relay-destination link, the approximate capacity region can be established for a larger regime of channel parameters. Further, from a GDoF point of view, the sum-capacity gain due to the relay can now be thought as coming from either signal relaying only or interference forwarding only.

Spectrum Sharing with Limited Channel Feedback

In this paper, an underlay spectrum sharing scheme is proposed where both primary and secondary users are discrete power-rate adaptive systems with limited feedback from receivers. By receiving secondary and overhearing primary quantized channel quality information from the secondary receiver and primary receiver, respectively, the secondary transmitter adapts its resource allocation to the current channel quality by selecting a proper power-rate pair from a pre-designed secondary quantization codebook. The secondary quantization codebook is designed to maximize the secondary average rate subject to the primary rate loss constraint and the average secondary transmit power constraint, which is discussed in three cases when different amount of side information of the primary codebook and the cross interference link are available at the secondary receiver side. Differential Evolution algorithm is employed to provide the global optimal solutions to the proposed secondary quantization codebook optimization problems. Numerical results show that, by introducing the secondary feedback, the secondary throughput is greatly improved. Furthermore, more secondary feedback bits or more primary side information result in better secondary performance.

Channel allocation and relay selection scheme in relay-based networks

It has been demonstrated that either Channel Allocation (CA) or Relay Selection (RS) can improve the performance in relaying networks separately. However, there is little work concerning their combination in multi-cell uplink scenarios. In this paper, we investigate the issue which considers the CA and RS to optimize the system transmission rate in an uplink scenario, while maintaining the resource distribution fairness among users. This is first formulated as an optimization problem for a linear cellular system, where the same frequency channels can be reused in different cells. Based on the link and co-channel interference conditions, two low-complexity CA and RS schemes are then proposed with different decomposition sequences. Finally, numerical results are conducted to verify the effectiveness of the proposed CA and RS methods. Simulations results show that the proposed methods can yield significant improvements in system performance in terms of average sum rate.

Comparative study of classifiers to mitigate intersymbol interference in diffuse indoor optical wireless communication links

The maximum data rate that can be achieved in diffuse indoor optical wireless communication (OWC) is limited due to the effect of intersymbol interference (ISI). The adverse effect of ISI on the system performance can be minimised using a channel equaliser at the receiver. In this study, digital signal detection is formulated as a classification problem and hence a classifier is adopted at the receiver. The bit error performance of classifiers with non-linear decision boundary including a multilayer perceptron (MLP), a support vector machine (SVM), the radial basis function (RBF), and the Bayesian classifier is studied along with traditional equaliser and reported here. The MLP offers the best performance; however there is trade-off between the performance and complexity especially at highly diffuse channel.

New design of 6-RSS parallel manipulator with large rotation workspace

In this paper, we present a new design of 6-RSS parallel manipulator with large rotation workspace. The RSS chains of manipulator are divided into two groups and the length of the chains between two groups are different. By locating them at two different circles on the moving platform and the base platform respectively, the interference between the links is reduced substantially. Therefore, a large rotation workspace can be achieved. In addition, our new design can be presented as two different structures. The inverse kinematics and the workspaces of the two structures are provided. At the end of the paper, we compare the two structures with the consideration of kinematic constraints, including mechanical limits on passive joints and interference of links.

Hypergraph Modeling and Approximation Algorithms for the Minimum Length Link Scheduling in Multiuser MIMO Networks

This paper investigates the problem of the minimum length link scheduling (MLLS) in multiuser MIMO (MU-MIMO) networks. Generally, in the networks with MU-MIMO capability, the number of concurrent transmissions can be as large as that of antenna elements at the receiver. As a result, link interference is no longer binary but demonstrates a strong correlation among multiple links, which cannot be captured by the conventional conflict graph interference model. Hence, we propose a novel hypergraph interference model, which can accurately and efficiently characterize the relationship of multiple interferences induced by concurrent transmissions, and provide a tractable formalization of the minimum length link scheduling in MU-MIMO networks (MU-MIMO MLLS). Afterwards, we prove that the MU-MIMO MLLS problem is NP-hard and introduce two approximation algorithms to find the near-optimal feasible schedule. Finally, extensive simulation experiments are presented.

Outage Performance Study of Cognitive Relay Networks with Imperfect Channel Knowledge

This letter presents the outage performance analysis for a cognitive relay network (CRN) with imperfect channel knowledge estimations. Under the condition of imperfect channel state information (CSI) estimations of interference links between primary and secondary systems, especially the links from both secondary transmitter and secondary relays to primary users, the exact outage probability is derived over Rayleigh fading channels and is verified through simulations. The simulation results show that: 1) increasing the number of relays is an effective approach to mitigate the outage performance degradation caused by the imperfect CSI; 2) the imperfect CSI of the secondary transmitter-primary user (PU) link has a greater impact on the outage performance than that of the secondary relay-PU link.

도심 환경에서 보호대역과 단말밀도를 이용한 주파수 공유성능 분석

TV 방송 대역(white space) 내의 인접채널 간 WLAN과 WiBro 단말의 공존 가능성 파악을 위한 핵심 지표들을 얻기 위해 간섭분석을 수행하였다. 이를 위해 두 시스템의 각각에 해당하는 방사 및 블로킹 마스크, 안테나 높이 및 이득, 전송 전력 및 대역폭, 송수신 링크에 대한 채널모델 등 다양한 전송 파라미터를 적용하였다. 또한 이를 기반으로 인접채널에서 동작 가능한 사용자의 허용가능 전송 전력 및 서비스 단말 개수, 보호대역 변화에 따른 성능에 대해 분석을 수행하였다. 도심 환경을 고려하기 위하여 간섭원인 WLAN과 피간섭원인 WiBro 단말 부분에 각각 Extended Hata SRD, Extended Hata 모델을 적용하였다. 이를 통해 인접채널에서 각 단말이 어떻게 공존할 수 있는지를 확인할 수 있었다. We make an interference analysis to obtain a critical ctiteria for coexisting availability of WLAN and WiBro between adjacent channels can be used in TVWS(TV White Space). To meet this analysis, we set the various transmission parameters including the emission and blocking mask, antenna height and gain, transmission power and bandwidth, channel model etc. And, based on these parameters, we analyze on performances according to a variation of guard band, a number of service user and allowable transmit power of the user operating in the adjacent channels. In this paper, we consider a urban environment and apply a Extended Hata-SRD for WLAN and an interference link and Extended Hata model for WiBro, respectively. With these results, we can see how each system can be shared in an adjacent channel.

Power Adaptation for Joint Switched Diversity and Adaptive Modulation Schemes in Spectrum Sharing Systems

Under the scenario of an underlay cognitive radio network, we propose in this paper an adaptive scheme using transmit power adaptation, switched transmit diversity, and adaptive modulation in order to improve the performance of existing switching efficient schemes (SES) and bandwidth efficient schemes (BES). Taking advantage of the channel reciprocity principle, we assume that the channel state information (CSI) of the interference link is available to the secondary transmitter. This information is then used by the secondary transmitter to adapt its transmit power, modulation constellation size, and used transmit branch. The goal of this joint adaptation is to minimize the average number of switched branches and the average system delay given the fading channel conditions, the required error rate performance, and a peak interference constraint to the primary receiver. We analyze the proposed scheme in terms of the average number of branch switching, average delay, and we provide a closed-form expression of the average bit error rate (BER). We demonstrate through numerical examples that the proposed scheme provides a compromise between the SES and the BES schemes.

Mirror mirror on the ceiling

Modern data centers are massive, and support a range of distributed applications across potentially hundreds of server racks. As their utilization and bandwidth needs continue to grow, traditional methods of augmenting bandwidth have proven complex and costly in time and resources. Recent measurements show that data center traffic is often limited by congestion loss caused by short traffic bursts. Thus an attractive alternative to adding physical bandwidth is to augment wired links with wireless links in the 60 GHz band. We address two limitations with current 60 GHz wireless proposals. First, 60 GHz wireless links are limited by line-of-sight, and can be blocked by even small obstacles. Second, even beamforming links leak power, and potential interference will severely limit concurrent transmissions in dense data centers. We propose and evaluate a new wireless primitive for data centers, 3D beamforming , where 60 GHz signals bounce off data center ceilings, thus establishing indirect line-of-sight between any two racks in a data center. We build a small 3D beamforming testbed to demonstrate its ability to address both link blockage and link interference, thus improving link range and number of concurrent transmissions in the data center. In addition, we propose a simple link scheduler and use traffic simulations to show that these 3D links significantly expand wireless capacity compared to their 2D counterparts.

Symmetric Capacity of the Gaussian Interference Channel With an Out-of-Band Relay to Within 1.15 Bits

This paper studies the Gaussian interference channel (IC) with a relay, which transmits and receives in a band that is orthogonal to the IC. The channel associated with the relay is thus an out-of-band relay channel (OBRC). The focus is on a symmetric channel model, in order to assess the fundamental impact of the OBRC on the signal interaction of the IC, in the simplest possible setting. First, the linear deterministic model is investigated and the sum capacity of this channel is established for all possible channel parameters. In particular, it is observed that the impact of OBRC, as its links get stronger, is similar to that of output feedback for the IC. The insights obtained from the deterministic model are then used to design achievable schemes for the Gaussian model. The interference links are classified as extremely strong, very strong, strong, moderate, weak, and very weak. For strong and moderate interference, separate encoding is near optimal. For very strong and extremely strong interference, the interference links provide side information to the destinations, which can help the transmission through the OBRC. For weak or very weak interference, an extension of the Han-Kobayashi scheme for the IC is utilized, where the messages are split into common and private. To achieve higher rates, it is beneficial to further split the common message into two parts, and the OBRC plays an important role in decoding the common message. It is shown that our strategy achieves the symmetric capacity to within 1.14625 bits per channel use with duplexing factor 0.5, and 1.27125 bits per channel use for arbitrary duplexing factors, for all channel parameters. An important observation from the constant gap result is that strong interference can be beneficial with the presence of an OBR.

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.

On the Generalized Degrees of Freedom of the Gaussian Interference Relay Channel

The symmetric two-user Gaussian interference relay channel (IRC) is studied from a generalized degrees of freedom (GDoF) perspective. While it is known that the relay does not in crease the DoF of the IRC, such a characterization has not been reported for the GDoF yet. The focus of this paper is on all cases where the interference link is stronger than the link from the source to the relay. This regime basically covers half the space of all possible parameters of the IRC. By using genie-aided approaches, new sum-capacity upper bounds are derived. These bounds are then compared with rates achieved with a novel transmission scheme, which is based on a functional decode-and-forward (FDF) strategy. It is shown that the GDoF of the IRC is achieved by FDF in the given regime, and that a relay can indeed increase the GDoF of IRC. Finally, the FDF scheme is compared with other schemes like decode-and-forward as well as compress-and-forward at low, moderate, and high signal-to-noise ratios.

On the Performance of Spectrum Sharing Cognitive Relay Networks with Imperfect CSI

In a spectrum sharing scenario, when the channel state information (CSI) of interference links is imperfect, the transmission of the secondary user (SU) may cause a harmful interference on the primary user (PU). To quantify the impact of imperfect CSI on the PU, we present a performance metric termed as interference probability and derive the exact closed-form expression for interference probability of the PU. It is shown that the PU's interference probability is always equal to 0.75 when the CSI of interference links is imperfect. In order to guarantee the PU's interference probability below an acceptable value, a back-off power control mechanism is adopted. Then, under the PU's interference probability constraints, the exact outage probability of partial amplify-and-forward (AF) relay selection scheme in the cognitive relay networks is derived. Finally, numerical results are provided to validate our analysis.