Non-Data-Aided Parameter Estimation in an Additive White Gaussian Noise Channel

Non-data-aided (NDA) parameter estimation is considered for binary-phase-shift-keying transmission in an additive white Gaussian noise channel. Cramer-Rao lower bounds (CRLBs) for signal amplitude, noise variance, channel reliability constant and bit-error rate are derived and it is shown how these parameters relate to the signal-to-noise ratio (SNR). An alternative derivation of the iterative maximum likelihood (ML) SNR estimator is presented together with a novel, low complexity NDA SNR estimator. The performance of the proposed estimator is compared to previously suggested estimators and the CRLB. The results show that the proposed estimator performs close to the iterative ML estimator at significantly lower computational complexity

Interactions between pre- and post-emergence weed harrowing in spring cereals

Pre- and post-emergence weed harrowing were studied in spring cereals in different environments and with two types of harrows in Norway during 2004–2006. The objectives were to investigate interactions between pre and post-emergence weed harrowing and the importance of harrow type. We hypothesised that pre- and post-emergence harrowing interact positively, that a combination gives more stable weed control effects than pre- and post-emergence weed harrowing used alone, and that a harrow type with bent tines is more aggressive and suitable on hard-packed soils than a harrow with strait tines. The results only supported the last of these hypotheses. Post-emergence weed harrowing controlled a certain percentage of the present weeds, and this percentage was not dependent on pre-emergence weed harrowing. On average, pre-emergence harrowing reduced weed density by 26% and weed biomass by 22%, while the average effect of postemergence harrowing was 47% on weed density and 41% on weed biomass. The combined effect of pre- and post-emergence weed harrowing was 61% on weed density and 54% on weed biomass. The combination did not give more stable weed control effects than preand post-emergence weed harrowing used alone. Preemergence harrowing increased the average crop yield by 6.2%, post-emergence harrowing by 4.0% and the combined effect was 10%. Crop yield was mainly increased on hard-packed soils. Weed and crop responses varied strongly among experiments, but the efficacy of pre- and post-emergence weed harrowing was positively correlated across experiments. Weed species composition was of minor importance regarding weed control. The study indicates that one aggressive postemergence cultivation may be as good as one preemergence and one less aggressive post-emergence cultivation. However, little is known about the interactions between cultivation at different crop and weed growth stage

Non-inverting Tillage: Early-Stage Effects on Soil Mechanical Behaviour

Organic farmers often claim positive effects of non-inverting and reduced tillage systems. There is a need of quantifying tilth characteristics in the former plough layer of soil converted to such tillage systems. A non-inverting tillage system (NINV) was tested in a field experiment conducted on a Danish sandy loam soil. It included deep loosening and shallow intensive cultivation and was compared to a conventional ploughing-harrowing tillage system (CONV). A hierarchical analytical procedure was applied in studies of soil fragmentation and soil strength characteristics for the 7-14 cm soil layer. A visual description was carried out and ease of fragmentation was evaluated in the field using a soil drop test. Soil strength was measured in the field with a cone penetrometer and a torsional shear box method, and in the laboratory using an annulus shear strength method. Tensile strength was determined in the laboratory on field-sampled aggregates. The CONV treated soil displayed a higher ease of fragmentation in the field in May as well as in September. In general, aggregates from the NINV treated soil were stronger than aggregates from the CONV treatment. The soils had similar friability indices in May. In September, however, a higher friability index was found for the CONV treated soil (k=0.22 and 0.16, respectively for CONV and NINV). The NINV treated soil also displayed the highest soil strength. The soil tilth was evaluated to be best in the CONV treated soil. Supposed meliorating actions during the growing season did not eliminate the differences between the treatments

A Tight Lower Bound to the Outage Probability of Discrete-Input Block-Fading Channels

In this correspondence, we propose a tight lower bound to the outage probability of discrete-input Nakagami-m block-fading channels. The approach permits an efficient method for numerical evaluation of the bound, providing an additional tool for system design. The optimal rate-diversity trade-off for the Nakagami-m block-fading channel is also derived and a tight upper bound is obtained for the optimal coding gain constant.Comment: 22 pages, 4 figures. This work has been accepted for IEEE Transactions on Information Theory and has been presented in part at the 2007 IEEE International Symposium on Information Theory, Nice, France, June 200