The invention provides a mulch film that may be sprayed over soil or existing mulch in a plant bed or in crop rows. The lead-free Au\u2014Sn\u2014Ag-based solder alloy contains 27. Therefore, interference between cells is reduced, and system capacity and efficiency are improved. If QAM constellation includes less than 64 QAM plant points, the passband mode is selected, and if QAM constellation includes more than 64 QAM plant points, the baseband mode is selected.