# A Multiple Access Protocol Based on Gray Forecast for Satellite Network
## 6 Simulation Analysis  
In this paper, OPNET Modeler is used for experimental simulation and comparison analysis to verify the validity of the proposed access protocol. The simulation parameters are shown in Table 3. The satellite communication channel model used in this paper is the OPNET Transceiver Pipeline model. The comparison and analysis of the packet stacking numbers of the user queues under the different access protocols and the average communication delay are based on the conditions of different channel loads and numbers of users. The multiple access protocols for the comparison of experimental simulations are the CFDAMA-GF algorithm in this paper, the combined free/demand assignment multiple access-piggy back (CFDAMA-PB) algorithm and the pure demand assignment multiple access (PURE-DAMA) algorithm. \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Parameter** & **Value** \\ \hline Synchronous satellite height (km) & 37,500 \\ Ground station number & 50 \\ Channel rate (Mbit/s) & 2 \\ Number of slots per frame & 128 \\ Frame duration (s) & 0.027136 \\ Channel load & 0.1–0.9 \\ Source model & ON-OFF model \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The settings of the simulation parameters. Figure 2: Flowchart of CFDAMA-GF. The CFDAMA-PB protocol is also an improvement over the CFDAMA protocol by piggy backing the time slot application information of each user in the uplink frame and calculating the number of time slot subscriptions that the user needs to send in the uplink according to Equation (12). \[RS=(RQ-1)-NRS \tag{12}\]  
where \(RS\) is the timeslot reservation number that needs to be sent, \(NRS\) is the number of packets that have sent the reservation request, but have not been allocated by the timeslot, and \(RQ\) is the actual number of packets in the user sending queue. The pure algorithm is called the pure demand assignment method. After the satellite completes the demand assignment, it does not consider continuing to process the possible remaining timeslots related to the CFDAMA protocol. In order to verify the user time slot occupancy of CFDAMA-FP under the burst source, assume that the current number of users as five and the channel load as 0.1. The time slot occupancy distribution of users under the burst source is shown in Figure 3. In Figure 3, the x-label represents the current simulation time, and the y-label is the transmitter busy state, radio transmitter.busy. If the current user has time slot requests or data packets sent, the transmitter is busy with a value of one. At the initial stage of the simulation, the user calculated the number of time slots needed to send the data and added the calculated results to the access control packet to send out through the access slot. As illustrated in Figure 3, five users occupy five different time slot points, respectively. The interval of each time slot point is about 0.0002 s, which meets the slot slot length in the simulation parameters table. The trend of changes in the stacking number of queue packets and the average communication delay can be obtained for the channel load within the range of 0.1-0.9, as shown in Figures 4 and 5, where the number of access user is constant at 50. Figure 4 shows the relationship between the number of packets in the user queue and the channel load. The channel load is the average throughput of the system, indicating the burst level of the packets sent by the ON/OFF source model, and the unit is bits per timeslot. The queue packet count refers to the number of queued packets in the user's send queue. The higher the channel load is, the more obvious the trend of group queues in the user's queue will be because the total amount of data packets for all current users has exceeded the range of the capacity of the entire satellite system. Figure 3: The time slot occupancy of five users. Thus, it should be queued for transmission at the next moment.