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In conventional communication systems, the random access (RA) is a necessary procedure for a user equipment (UE) to establish wireless connection to the network before actual data transmission.Focusing on the massive IoT with large number of nodes, the fundamental characteristics and limitations of conventional grant-based RA were firstly discussed.Then, the grant-free RA, semi-grant-free RA and unsourced RA for massive IoT were addressed in details from multiple perspectives, including their system models, protocol frameworks, algorithm procedures, system performance, related pros and cons, as well as critical challenges and potential opportunities.Finally, some highlights on the related key techniques and common issues in random access for massive IoT were concluded.

Objective To observe the effect of different doses of ε-aminocaproic acid （EACA） on wound bleeding in infants undergoing cleft palate repair. Methods One hundred and twenty infants scheduled to undergo cleft palate repair， aged from 6 to 36 months， ASA status Ⅰ or Ⅱ， were randomly divided into the control （group C）， conventional-dose EACA （group E1） and low-dose EACA groups （group E2）， 40 cases in each group. Infants in groups E1 and E2 were administrated with a loading dose of EACA （40 mg/kg） for 20 min before incision， followed by continuous infusion of 30 mg/（kg·h） and 10 mg/（kg·h） in two groups， respectively. In group C， continuous infusion of normal saline was applied. Same anesthesia regimen was delivered for all patients among three groups. Wound bleeding scores during operation， before extubation and 24 h after operation， intraoperative blood loss， anesthesia time， operation time， and fibrinogen concentration before and 24 h after surgery， and the incidence of delayed haemorrhage， deep vein thrombosis and epilepsy were recorded. Results Compared with group C， the wound bleeding scores during operation and before extubation in group E1 and E2 were significantly lower， the amount of intraoperative blood loss was significantly less， and the fibrinogen concentration at postoperative 24 h was significantly increased （all P < 0.05）， while no significant statistical difference was observed between groups E1 and E2 （all P > 0.05）. There were no statistically significant differences in operation time， anesthesia time and the incidence of delayed hemorrhage among three groups （all P > 0.05）. No deep vein thrombosis or epilepsy occurred among three groups. Conclusion The application of EACA in infants with cleft palate repair can mitigate perioperative wound bleeding and lower the incidence of delayed hemorrhage. Low-dose EACA yields favorable hemostatic effect. These findings provide reference for drug use in clinical practice.