Statistical Pruning for Near Maximum Likelihood Detection of MIMO Systems

We show a statistical pruning approach for maximum likelihood (ML) detection of multiple-input multiple-output (MIMO) systems. We present a general pruning strategy for sphere decoder (SD), which can also be applied to any tree search algorithms. Our pruning rules are effective especially for the case when SD has high complexity. Three specific pruning rules are given and discussed. From analyzing the union bound on the symbol error probability, we show that the diversity order of the deterministic pruning is only one by fixing the pruning probability. By choosing different pruning probability distribution functions, the statistical pruning can achieve arbitrary diversity orders and SNR gains. Our statistical pruning strategy thus achieves a flexible trade-off between complexity and performance

Long-Term Evaluation of the Influence of Mechanical Pruning on Olive Growing

In Portugal, olive (Olea europaea L.) groves with the traditional tree density of around 100 trees ha -1, necessitate increasing pruning costs every year. As a result farmers tend to lengthen pruning intervals. With the purpose of studying a mechanised alternative to the expensive, labor-intensive manual pruning practice, the authors established in 1997 field trials with the following three treatments: i) manual pruning with a chain saw; ii) mechanical pruning, performed by a tractor mounted cutting bar provided with 6 circular disc-saws; and iii) mechanical pruning, as in the mechanical pruning treatment, followed by a manual pruning complement. The effect of the above treatments on olive production and on harvesting efficiency was evaluated every year for 8 yr. The harvesting was performed by a trunk shaker, and the remaining non-detached fruits were collected manually. The pruning rate of mechanical pruning (487 trees hour-1man-1) was substantially higher than the values of manual pruning and mechanical+manual pruning, which were the same (20 trees hour-1man-1). Over the 8-yr period, mechanical pruning had an average yield of 36,4 kg tree-1 year-1 which was significantly higher than the 30,1 kg tree-1 year-1 of manual pruning and no significantly different from the 34,1 kg tree-1 year-1 of mechanical+manual pruning. The shaker efficiency was significantly influenced by the year, ranging from 72% to 96%; no significant differences were found between treatments in terms of harvesting efficiency. These tests indicate that after mechanized pruning (horizontal cut at the uppermost part of the canopy) trees can be kept for at least 8 years without any significant loss in olive yield per tree and no effect in harvesting efficiency, therefore reducing costs. Selective manual complement to the mechanized pruning, performed in the same year, does not provide any further advantages in olive yield nor in shaker performance and consequently increasing production costs

An ergonomics analysis of manual versus chainsaw high ladder pruning of Pinus radiata in New Zealand : a thesis in partial fulfilment of the requirements for the degree of Master of Philosophy at Massey University

Two methods of ladder pruning Pinus radiata from 4.5 - 6.0 metres were compared using a cost-benefit approach within a framework provided by ergonomics. Chainsaw pruning is practiced in areas of New Zealand where large branches occur. The objectives of the research were to compare the costs and benefits of the two pruning techniques and provide recommendations as to whether or not the practice of chainsaw pruning should continue. These objectives were achieved by comparing the risk of injury, the physiological costs, the musculoskeletal costs, the productivity and the quality associated with the use of the two techniques. The general methods used to assess the relative costs and benefits of the two techniques were: l. Numeric descriptions of the 'risk' involved with each method of pruning 2. The use of a relative heart rate index to compare the physiological cost of the two techniques 3. Using questionnaires focusing on musculoskeletal pain and discomfort to assess any relative differences between the two techniques 4. Using continuous time study to quantify any difference in labour productivity between the two techniques 5. Sampling pruned trees to assess differences in the quality of work between manual and chainsaw pruning The research concludes that although both methods of pruning are hazardous, chainsaw pruning is more hazardous than manual pruning. Chainsaw and manual pruning were found to have the same physiological costs. Findings of the research indicate that manual pruning is not associated with a higher prevalence of musculoskeletal discomfort than chainsaw pruning on a yearly basis, although it is associated with a greater relative increase in BPD on a day to day basis and that this may lead to the development of musculoskeletal disease. Chainsaw pruning was found to be significantly more productive than manual pruning, although this was at the cost of quality. The research concludes by recommending that the use of chainsaw pruning should be limited to areas where the branches are demonstrably large. Further research is called for to compare the physiological and musculoskeletal costs of manual pruning in plantation areas of both large and small branch sizes. Further research is called for to compare the safety of two methods of chainsaw pruning with the use of the technique of wrapping one leg around the tree as opposed to not wrapping the leg around the tree. Research to investigate new ladder designs which are safer to use in the New Zealand forest environment is also called for