A Credit-Based Approach for Overcoming Free-Riding Behaviour in Peer-to-Peer Networks

The underlying premise of peer-to-peer(P2P)systems is the trading of digital resources among individual peers to facilitate file sharing,distributed computing,storage,collaborative applications and multimedia streaming.So-called free-riders challenge the foundations of this system by consuming resources from other peers without offering any resources in return,hindering resource exchange among peers.Therefore,immense effort has been invested in discouraging free-riding and overcoming the ill effects of such unfair use of the system.However,previous efforts have all fallen short of effectively addressing free-riding behaviour in P2P networks.This paper proposes a novel approach based on utilising a credit incentive for P2P networks,wherein a grace period is introduced during which free-riders must reimburse resources.In contrast to previous approaches,the proposed system takes into consideration the upload rate of peers and a grace period.The system has been thoroughly tested in a simulated environment,and the results show that the proposed approach effectively mitigates free-riding behaviour.Compared to previous systems,the number of downloads from free-riders decreased while downloads by contributing peers increased.The results also show that under longer grace periods,the number of downloads by fast peers(those reimbursing the system within the grace period)was greater than the number of downloads by slow peers.

Stability Analysis of Cross-Channel Excavation for Existing Anchor Removal Project in Subway Construction

The cutter head will be stuck when the shield machine pass through the area existing anchor left by foundation construction of surrounding high-rise building.Subsurface excavation method is an efficient way to remove the existed anchor.In this paper,a three-dimensional finite element model is developed to study stability of cross-channel excavation.The time-spatial effects of arch crown settlement,intrados uplift and side wall horizontal convergence are analyzed according to different excavation size,lining thickness and lining order.The results show that the excavation size is the main factor to control the deformation of the surrounding soil,especially in arch crown settlement;The influence of lining thickness on the spatial effect of surrounding soil deformation is obvious when the excavation size is large,but little on the time effect;The influence of the lining order on the deformation of the surrounding soil is obvious,in particular,the larger the excavation size,the more obvious advantages of the lining order.Finally,based on the time-spatial effects comparison of nine excavation schemes of the cross-channel,an optimum excavation scheme is adopted in the actual project.

Wideband Signal Detection Based on MWC Discrete Compressed Sampling Structure

In order to solve the cross-channel signal problem caused by the uniform channelized wideband digital receiver when processing wideband signal and the problem that the sensitivity of the system greatly decreases when the bandwidth of wideband digital receiver increases,which both decrease the wideband radar signal detection performance,a new wideband digital receiver based on the modulated wideband converter(MWC)discrete compressed sampling structure and an energy detection method based on the new receiver are proposed.Firstly,the proposed receiver utilizes periodic pseudo-random sequences to mix wideband signals with baseband and other sub-bands.Then the mixed signals are low-pass filtered and downsampled to obtain the baseband compressed sampling data,which can increase the sensitivity of the system.Meanwhile,the cross-channel signal will all appear in any subbands,so the cross-channel signal problem can be solved easily by processing the baseband compressed sampling data.Secondly,we establish the signal detection model and formulate the criterion of the energy detection method.And we directly utilize the baseband compressed sampling data to carry out signal detection without signal reconstruction,which decreases the complexity of the algorithm and reduces the computational burden.Finally,simulation experiments demonstrate the effectiveness of the proposed receiver and show that the proposed signal detection method is effective in low signal-to-noise ratio(SNR)compared with the conventional energy detection and the probability of detection increases significantly when SNR increases.

Design and optimization of electrolyte flow fields in electrochemical machining of cross-channel array with tool vibration

A metallic interconnect plate with a flow channel array is one of the most important elements in a solid oxide fuel cell(SOFC). Electrochemical machining(ECM) is considered to be an adoptable technology for fabricating flow channels in an interconnect plate on account of its efficiency and low cost. With respect to the traditional electrolyte flow mode in ECM cross-channel array, the electrolyte usually flows from one side to the opposite side of the rectangular processing area. However, obvious flow marks are typically formed at the bottom of channels perpendicular to the flow. According to multiphysical simulation analysis, the low electrolyte velocity in the channels perpendicular to the flow leads to uneven distribution of electrolyte products. To improve the uniformity of the flow field, two new electrolyte flow modes, “two-in and two-out” and “three-in and one-out”, are proposed. By adding one or two additional electrolyte inlets to the sides of the traditional flow field, the electrolyte flow velocity in the channels perpendicular to the traditional flow will be increased. Corresponding simulations and experiments were performed and the results showed that the “three-in and one-out” flow mode can produce a flatter bottom surface for the cross-channel array. Parameter optimization experiments for the preferred flow mode were undertaken and the optimal flow field parameters were determined.

A GAME THEORETICAL STUDY OF COOPERATIVE ADVERTISING WITH MULTIPLE RETAILERS IN A DISTRIBUTION CHANNEL

Extant studies of cooperative advertising mainly consider a single-manufacturer-single-retailer channel structure. This can provide limited insights, because a manufacturer, in real practices, usually deals with multiple retailers simultaneously. In order to examine the impact of the retailer＇s multiplicity on channel members＇ decisions and on total channel efficiencies, this paper develops a multiple-retailer model. In this model, the manufacturer and the retailers play a Stackelberg game to make the optimal advertising decisions. Based on the quantitative results, it is observed that： 1） When there are multiple symmetric retailers, as the number of retailers scales up, the manufacturer＇s national advertising investment contributes increasingly to add to channel members＇ profits in equilibrium, but the total channel efficiency deteriorates quickly and converges down to a certain value; 2） When there are multiple asymmetric retailers, the distribution channel suffers from the manufacturer＇s uniform participation strategy due to the retailer＇s free-riding, and benefits with the manufacturer＇s retailer-specific participation strategy. This study derives equilibrium solutions in closed form for all games considered and measures explicitly the gains/losses of channel efficiencies under different game settings.

Improving Performance of LDPC-Coded Links via Partial Superposition Retransmission

In this paper,we propose a transmission scheme for uplink and downlink transmissions,where the fifth generation(5G)low-density parity-check(LDPC)codes are implemented for error correction.In the proposed scheme,the acknowledgment(ACK)or negative acknowledgment(NACK)feedback information is transmitted along with the payload data by cyclically shifting coded sequence,while the re-transmitted codewords are superimposed(XORed)partially on the current codewords.The distinguished feature of the proposed transmission scheme is that it requires neither extra transmission bandwidth nor extra transmission power.We also propose to truncate the error patterns for the purpose of reducing the implementation complexity and reducing the error propagation.Numerical results show that the proposed scheme significantly outperforms conventional LDPC-coded transmission.For the 5G LDPC code with length 1920 at the signal-to-noise ratio(SNR)of 1.3 dB,the word error rate(WER)of the data transmitted by the proposed scheme is about 10^(−4),while that of the conventional LDPC-coded transmission is about 10^(−2).