“…Frequency Reference T1 11 articles [46], [106], [51], [97], [109], [27], [54], [110], [82], [55], [114] T2 25 articles [32], [29], [62], [24], [34], [73], [48], [50], [39], [94], [40], [95], [42], [78], [67], [31], [101], [37], [103], [85], [38], [111], [112], [113], [115] T3 18 articles [86], [87], [88], [90], [71], [64], [93], [35], [72], [74], [36], [96], [98], [69], …”