## 1 Introduction
However, they still struggle to meet performance requirements in scenarios with a large number of IoT terminals [12; 13; 14]. CRDSA introduces SIC on the basis of the DSA protocol to recover collided packets. In CRDSA, two copies of a packet contain identical valid data information and corresponding slot position information for each copy selected. After successfully receiving one copy of a packet, its copy slot position can be located and eliminated. CSA protocol introduces linear coding modules that divide packets into several fields for linear encoding before transmission. Receivers use linear decoding and SIC techniques to resolve collisions. Under the condition of dual copies, CRDSA protocol can achieve a throughput of 0.612. On the basis of CRDSA, IRSA adjusts the number of copies when a terminal sends a packet. It changes the mechanism in CRDSA, where terminals send a fixed number of copies to select the number of copies based on probability distribution. In addition, some protocols adopt spread spectrum technology to improve the system throughput, such as spread spectrum ALOHA (SSA) and enhanced spread spectrum ALOHA (E-SSA) [15; 16]. Since the spreading code has a time-delay capture characteristic, as long as the arrival times of two packets are not absolutely identical, these packets can be considered quasi-orthogonal. If the structure of the uplink receivers in the base station is reasonably set up, its collided packets can be demodulated. However, collision resolution with spread spectrum technology largely depends on packet arrival times and also lacks the utilization of spatial resources. The asynchronous contention resolution diversity ALOHA (ACRDA) protocol introduces the concept of virtual time slots in a data frame based on the CRDSA, changing the protocol from synchronous to asynchronous [17]. Similar to CRDSA, ACRDA solves the problem of packet collision through time and/or power/carrier frequency diversity. Overall, the above-mentioned improvements are limited to the processing of a single receiver and have weak capabilities in handling packet collision. Therefore, some improved solutions have begun to study the diversity of resources in the space domain of IoT, using LEO as distributed beamforming nodes for collaboration to improve performance or reduce system power consumption [18; 19]. The authors of [20] proposed a novel multi-satellite cooperative random access (MSC-RA) scheme, which utilized multi-satellite overlapping coverage conditions for the IoT terminals. An asynchronous cooperative ALOHA (ACA) scheme is proposed in the literature [21], where packets generated by IoT terminals are received by multiple receiving satellites to form spatial copies of the packet. The un-collided packets on one satellite are then used to resolve collisions, which exist on other satellites using SIC technology, thus improving the system channel utilization. This scheme does not require the terminal to send additional packets compared to traditional schemes that transmit time-domain or frequency-domain copies classes, which not only saves power but also reduces the overall load on the network. However, the ACA scheme resolves packet collision only if at least one of the spatial copies of packets from multiple satellites has not collided before the SIC technique can be used to iteratively recover more collided packets. If all the satellite's spatial copies of packets collided, the \"deadlock\" phenomenon will occur in the processing of the gateway station. ACA solution will not be able to resolve the \"deadlock\" packets, thus reducing the benefits of spatial diversity. A scheme based on packet signal strength indicator and geographic location information is proposed in the literature [22] to solve packet preamble collisions in grant-free random access (GFRA). This scheme is based on the characteristic that the adjacent access points of the IoT terminals have stronger channel gain.