Environmental effects on the coevolution of pursuit and evasion strategies

The game of tag is frequently used in the study of pursuit and evasion strategies that are discovered through competitive coevolution. The aim of coevolution is to create an arms race where opposing populations cyclically evolve in incremental improvements, driving the system towards better strategies. A coevolutionary simulation of the game of tag involving two populations of agents; pursuers and evaders, is developed to investigate the effects of a boundary and two obstacles. The evolution of strategies through Chemical Genetic Programming optimizes the mapping of genotypic strings to phenotypic trees. Four experiments were conducted, distinguished by speed differentials and environmental conditions. Designing experiments to evaluate the efficacy of emergent strategies often reveal necessary steps needed for coevolutionary progress. The experiments that excluded obstacles and boundaries provided design pointers to ensure coevolutionary progress as well as a deeper understanding of strategies that emerged when obstacles and boundaries were added. In the latter, we found that an awareness of the environment and the pursuer was not critical in an evader’s strategy to survive, instead heading to the edge of the boundary or behind an obstacle in a bid to ‘throw-off or hide from the pursuer’ or simply turn in circles was often sufficient, thereby revealing possible suboptimal strategies that were environment specific. We also observed that a condition for coevolutionary progress was that the problem complexity must be surmountable by at least one population; that is, some pursuer must be able to tag an opponent. Due to the use of amino-acid building blocks in our Chemical Genetic Program, our simulations were able to achieve significant complexity in a short period of time.

Convergence analysis of the stop-and-go blind equalizationalgorithm

Unlike traditional trained channel equalizers, not much work has been done to theoretically characterize the convergence properties of blind channel equalizers due to their inherent nonlinearity. It is only recently that convergence properties of some well-known algorithms such as the generalised Sato algorithm (GSA) and the constant modulus algorithm (CMA) have been analytically derived. In this paper, the convergence properties of the stop-and-go algorithm proposed by Picchi and Prati (1987) are analyzed. The derived mean squared error and the coefficient trajectories are compared with simulation results to verify the validity of the analytical results     

Performance of the limiter-discriminator-integrator detector infrequency-hop spread-spectrum multiple-access networks

This paper evaluates the performance of the limiter-discriminator-integrator detector (LDID) in asynchronous frequency-hop spread-spectrum multiple-access (AFHSS-MA) networks using binary frequency shift-keying (BFSK) modulation via Monte Carlo simulations. Both additive white Gaussian noise (AWGN) and Rayleigh-fading channels are considered and we find that the LDID offers a performance that is slightly worse than or comparable to that of the matched filter detector for the nonfading and Rayleigh-fading cases respectively. Also, hard limiting of the integrator input is proposed which significantly improves the performance of the LDID in AFHSS-MA networks resulting in a higher throughput than that achievable with a matched filter detector     

A novel frequency-hopping spread-spectrum multiple-access network using M-ary orthogonal Walsh sequence keying

A novel frequency-hop spread-spectrum multiple-access network employing M-ary orthogonal Walsh sequence keying with noncoherent demodulation is proposed. The transmitted Walsh sequence is overlaid by a user-specific pseudonoise sequence to reduce the effect of multiple-access hits. Two Gaussian approximations for the multiple-access interference from both the dehopped slot and its neighboring slots are developed and are used to analyze the performance of the proposed network for synchronous and asynchronous hopping under nonfading and Rayleigh fading channels. The effect of imperfect hop timing synchronization at the receiver is also analyzed. It is shown that the proposed network offers significantly improved network throughput compared to networks based on traditional M-ary frequency-shift keying modulation.     

Design of concatenated space-time block codes using signal space diversity and the Alamouti scheme

New full-rate space-time block codes achieving full diversity for quadrature amplitude modulation (QAM) using an even number of transmit antennas over quasi-static Rayleigh fading channels are proposed. The proposed codes are constructed by serially concatenating unitary rotating precoders with the Alamouti code. The coding advantage of the proposed code for a codeword pair corresponding to any distinct input pair is shown to be greater than or equal to that of the ST-CR code.     

Improving the performance of SM-MIMO/BICM-ID systems with LLR distribution matching

In this paper, a distribution matching technique is proposed to process the extrinsic information produced by practical multiple-antenna detectors with iteratively demodulated, bit-interleaved coded modulation (BICM-ID). It is shown that significant gains may be achieved by appropriately processing the extrinsic information generated by practical multiple-antenna detectors before feeding it to the channel decoder. The validity of the proposed matching technique is shown via simulation results applied to Turbo-coded BICM-ID systems using (QRD)-M and list sphere detectors.     

Development of a new biomonitoring method to detect the abnormal activity of Daphnia magna using automated Grid Counter device

The aim of the present study was to develop a biological early warning system (BEWS), equipped with six monitoring channels to individually observe the activity of Daphnia magna, using a digital 'Grid Counter', which would trigger an alarm within an appropriate time, and examine the functional performance of the newly developed BEWS for detecting unusual water quality. In order to detect the changes in the activity of D. magna, six relative activity parameter values (Z(a)) were computed from the 6 individual monitoring channels; with the activity data for D. magna calculated every 5 min. The Student's t-test was used to verify the difference between the mean value of the system in a steady state, as a control, and the exposure values during a sudden pollution event. The test results illustrate that the threshold value for the alarm can be at p=0.0093 for 3 consecutive detections. The time period, defined as the average time taken from the detection of hyper to retarded activity of the organism, for Cu concentrations of 50, 100, 200 and 400 ppb were 7.17+/-1.75, 3.94+/-2.02, 1.85+/-0.49 and 1.00+/-0.18 h, respectively. Based on the results of this study, it is proposed that p values from the t-test, with Z(a), are more accurate, stable and predictable parameters for the detection of chemical exposures than the other values, such as the swimming speed and trajectory, etc. Consequently, it would be possible to reduce the number of false alarms and achieve confidence for a system, with the ability of highly accurate detection, such as with the six-channel monitoring system developed in this study.     

Influences of elevated pressures on soot formation in coaxial ethylene–air diffusion flames under different ventilation conditions

The effect of elevated pressures on the soot formation in coaxial ethylene-diffusion flame was investigated under different ventilation conditions, i.e. one with a chamber valve closed and the other with a chamber valve open. Experimental measurements include the soot volume fraction and macroscopic flame behaviors such as visible height and flame shape. The presence of ventilation-assisted flow around the flame was found to further increase the visible flame radius and height at elevated pressures. The maximum soot volume fraction measured within the flame was also increased with the ventilation-assisted flow as well as with the ambient pressure. Experimental results clearly indicate that changes in the physical appearance of the flames altered by ventilation-assisted flow are an important factor to affect the sooting behavior in coaxial diffusion flames.