Beam Pattern Optimization Method for Subarray-Based Hybrid Beamforming Systems

Massive multiple-input multiple-output (MIMO) systems operating at millimeter-wave (mmWave) frequencies promise to satisfy the demand for higher data rates in mobile communication networks. A practical challenge that arises is the calibration in amplitude and phase of these massive MIMO systems, as the antenna elements are too densely packed to provide a separate calibration branch for measuring them independently. Over-the-air (OTA) calibration methods are viable solutions to this problem. In contrast to previous works, the here presented OTA calibration method is investigated and optimized for subarray-based hybrid beamforming (SBHB) systems. SBHB systems represent an efficient architectural solution to realize massive MIMO systems. Moreover, based on OTA scattering parameter measurements, the ambiguities of the phase shifters are exploited and two criteria to optimize the beam pattern are formulated. Finally, the optimization criteria are examined in measurements utilizing a novel SBHB receiver system operating at 27.8 GHz

Functional Invertebrate Prey Groups Reflect Dietary Responses to Phenology and Farming Activity and Pest Control Services in Three Sympatric Species of Aerially Foraging Insectivorous Birds

<div><p>Farming activity severely impacts the invertebrate food resources of farmland birds, with direct mortality to populations of above-ground arthropods thorough mechanical damage during crop harvests. In this study we assessed the effects of phenological periods, including the timing of harvest, on the composition and biomass of prey consumed by three species of aerial insectivorous birds. Common Swifts <i>Apus apus</i>, Barn Swallows <i>Hirundo rustica</i> and House Martins <i>Delichon urbica</i> breed sympatrically and most of their diet is obtained from agricultural sources of invertebrate prey, especially from oil-seed rape crops. We categorized invertebrate prey into six functional groups, including oil-seed rape pests; pests of other arable crops; other crop-provisioned taxa; coprophilous taxa; and taxa living in non-crop and mixed crop/non-crop habitats. Seasonality impacted functional groups differently, but the general direction of change (increase/decrease) of all groups was consistent as indexed by prey composition of the three aerial insectivores studied here. After the oil-seed rape crop harvest (mid July), all three species exhibited a dietary shift from oil-seed rape insect pests to other aerial invertebrate prey groups. However, Common Switfts also consumed a relative large quantity of oil-seed rape insect pests in the late summer (August), suggesting that they could reduce pest insect emigration beyond the host plant/crop. Since these aerially foraging insectivorous birds operate in specific conditions and feed on specific pest resources unavailable to foliage/ground foraging avian predators, our results suggest that in some crops like oil-seed rape cultivations, the potential integration of the insectivory of aerial foraging birds into pest management schemes might provide economic benefits. We advise further research into the origin of airborne insects and the role of aerial insectivores as agents of the biological control of crop insect pests, especially the determination of depredation rates and the cascading effects of insectivory on crop damage and yield.</p></div

Percentage composition (average±SE) of the number of six functional aerial invertebrate prey groups identified in individual faecal sacs of nestlings of Common Swifts <i>Apus apus</i> (□), Barn Swallows <i>Hirundo rustica</i> (▴) and House Martins <i>Delichon urbica</i> (•) in various periods of the breeding season 2012; note different scales on y-axes; the harvest of oil-seed rape crops (15–20 July) is indicated by the vertical dotted grey line; for Common Swifts, Barn Swallows and House Martins the number of faecal sacs analysed in consecutive periods was: 25–30 May (0/0/4), 1–15 June (0/27/62), 16–30 June (10/76/33), 1–14 July (17/7/35), 15–20 July (66/35/27), 21–31 July (9/14/13), 1–15 August (10/65/45), 16–31 August (0/22/18), 1–7 September (0/0/35).

<p>Percentage composition (average±SE) of the number of six functional aerial invertebrate prey groups identified in individual faecal sacs of nestlings of Common Swifts <i>Apus apus</i> (□), Barn Swallows <i>Hirundo rustica</i> (▴) and House Martins <i>Delichon urbica</i> (•) in various periods of the breeding season 2012; note different scales on y-axes; the harvest of oil-seed rape crops (15–20 July) is indicated by the vertical dotted grey line; for Common Swifts, Barn Swallows and House Martins the number of faecal sacs analysed in consecutive periods was: 25–30 May (0/0/4), 1–15 June (0/27/62), 16–30 June (10/76/33), 1–14 July (17/7/35), 15–20 July (66/35/27), 21–31 July (9/14/13), 1–15 August (10/65/45), 16–31 August (0/22/18), 1–7 September (0/0/35).</p

Total number and biomass of six functional aerial invertebrate prey groups identified in the diet of nestlings of Common Swifts <i>Apus apus</i> (<i>n</i> = 112 faecal sacs), Barn Swallows <i>Hirundo rustica</i> (<i>n</i> = 246) and House Martins <i>Delichon urbica</i> (<i>n</i> = 272) during the entire breeding season in 2012; see S2 File for a complete list of prey.

<p>Total number and biomass of six functional aerial invertebrate prey groups identified in the diet of nestlings of Common Swifts <i>Apus apus</i> (<i>n</i> = 112 faecal sacs), Barn Swallows <i>Hirundo rustica</i> (<i>n</i> = 246) and House Martins <i>Delichon urbica</i> (<i>n</i> = 272) during the entire breeding season in 2012; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114906#pone.0114906.s002" target="_blank">S2 File</a> for a complete list of prey.</p

Effect of Brood Age on Nestling Diet and Prey Composition in a Hedgerow Specialist Bird, the Barred Warbler Sylvia nisoria.

The composition and quality of food provided to nestling birds influence their growth and development and offers key insight into the ecological requirements of birds. One bird species whose feeding ecology is poorly understood is the Barred Warbler (Sylvia nisoria), which utilizes semi-natural shrubby vegetation in agroecosystems. Because Barred Warbler nestlings vary greatly in body mass we hypothesised that diet and prey properties (size, diversity, taxonomic composition, and chitin content and resulting body hardness and digestibility) would differ as the nestlings aged. We quantified the diet based on faecal analysis, sampling faecal sacs from the nestlings pooled into three age classes: 2-3 days old, 4-6 d old, and 7-9 d old. Nestlings were provided a wide diversity of food and a strong relationship existed between food characteristics and nestling age. The youngest nestlings (2-3 d old) had the lowest values of each dietary characteristic (diversity, number and total biomass of prey, and individual prey weight), that were significantly lower than the oldest nestlings (7-9 d old). Nestlings aged 4-6 d exhibited intermediate dietary characteristics. Differences in dietary composition of the six major food types showed marked differences between the individual broods and age categories. Percentages of the number and biomass of soft-bodied prey were highest in the diet of 2-3 d and 4-6 d old nestlings, and decreased with increasing age, whereas the opposite trend was observed in the percentage of intermediately and heavily chitinised prey. Parent Barred Warblers probably preferentially select soft-bodied prey for the youngest nestlings, and satisfy the greater energy demands of the older ones by providing them with a greater variety of prey containing more chitin, as well as plant food. The provisioning of less-readily digestible prey to older nestlings suggests that as the quality of food decreases the quantity increases, implying that the youngest nestlings may be physiologically limited as regards their ability to digest more heavily chitinised prey

Results of MANOVA testing the effect of age and brood identity (nested within age) of nestlings on dietary composition expressed as four dietary variables (each representing the six major food types: Arachnida, Coleoptera, Hemiptera, Lepidoptera larvae, Diptera/Hymenoptera and other invertebrates) in Barred Warbler <i>Sylvia nisoria</i> nestlings.

<p>Results of MANOVA testing the effect of age and brood identity (nested within age) of nestlings on dietary composition expressed as four dietary variables (each representing the six major food types: Arachnida, Coleoptera, Hemiptera, Lepidoptera larvae, Diptera/Hymenoptera and other invertebrates) in Barred Warbler <i>Sylvia nisoria</i> nestlings.</p

The average (±SE) number and biomass of four dietary variables expressing the six major food types (class/orders of invertebrates) identified in individual faecal sacs (<i>N</i> = 101) of nestling Barred Warblers <i>Sylvia nisoria</i> in three age classes, 2–3 d old (<i>n</i> = 17 faecal sacs), 4–6 d old (<i>n</i> = 23) and 7–9 d old (<i>n</i> = 61); the various letters indicate statistically significant differences between various age classes obtained in the <i>post-hoc</i> comparison with MANOVA (see Table 3).

<p>The average (±SE) number and biomass of four dietary variables expressing the six major food types (class/orders of invertebrates) identified in individual faecal sacs (<i>N</i> = 101) of nestling Barred Warblers <i>Sylvia nisoria</i> in three age classes, 2–3 d old (<i>n</i> = 17 faecal sacs), 4–6 d old (<i>n</i> = 23) and 7–9 d old (<i>n</i> = 61); the various letters indicate statistically significant differences between various age classes obtained in the <i>post-hoc</i> comparison with MANOVA (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0131100#pone.0131100.t003" target="_blank">Table 3</a>).</p