# Analysis of Grating Lobe Effects on GEO DSC Distributed Antennas
## 2 DSC Distributed Antenna Cooperative Transmission  
### Scenario Modelling  
The DSC consists of a set of lightweight satellites in GEO distributed in the same or adjacent orbit, as shown in Figure 1, with each node of the satellites in the DSC sharing a GEO position of less than \(1^{\circ}\). To prevent collisions and ensure safe communication, the minimum distance between the DSC satellites was maintained at 15 km or more, and a multi-satellite co-location strategy was employed. The type and aperture of the antennas carried on DSC satellites can vary and may include array antennas or reflective surface antennas. By integrating multiple DSC satellite antennas and ground antennas, a distributed MIMO system can be established, which utilizes spatial diversity and gain multiplexing to enhance the system capacity and antenna gain [7]. Each DSC satellite antenna can transmit and receive data independently, enabling the system to handle multiple data streams simultaneously. The distributed MIMO system can also boost channel capacity and antenna performance by combining the received signals from multiple antennas and facilitating cooperative transmission from DSC distributed antennas. With inter-satellite synchronization techniques, the antenna beams of \(N\) DSC satellites can be synthesized in-phase on-satellite and on the ground, resulting in a higher ratio of antenna gain \(G\) to the equivalent noise temperature \(T\) of the receiving system (\(G/T\) value) and equivalent omnidirectional radiated power (\(EIRP\)) in the satellite communication link. The DSC distributed antenna uses multiple antennas distributed on different DSC satellites to receive signals from the same source, the received signals are amplified by low noise amplifiers, and then the radio frequency (RF) signals are transformed into intermediate frequency (IF) signals by a down-converter, followed by a series of operations of signal alignment and synthesis, carrier tracking, subcarrier tracking, and symbol synchronization to achieve the synthesis of the signals received by each antenna; thus, the signal-to-noise ratio of the received signal is improved and a reliable and useful signal is obtained [14].  
For the uplink of the signal, a block diagram of the received signal synthesis scheme of the DSC distributed antenna system is given in Figure 2. Each satellite antenna that forms part of the DSC distributed antenna system can not only work individually, but can also perform DSC distributed antenna arraying to complete the received signal synthesis. During the DSC distributed antenna arraying, the antennas on each satellite receive signals from the same client, and the RF/IF converter module (RF/IF) in each antenna downconverts the received RF signal to an IF signal. Delay compensation is applied to the IF signal from each antenna and the amount of delay compensation is roughly calculated using the geometry of the DSC satellite in relation to the client. The delay-compensated IF signalsare further determined by inter-correlation operations between each other, and this is used to compensate the delay residuals for the IF signals, which are then synthesized. For the downlink of the signal, a block diagram of the transmit signal synthesis scheme for the DSC distributed antenna system is given in Figure 3. The transmitter compensates the IF signal for the delay and the amount of delay compensation is calculated by the geometrical relationship between the satellite and the user side. The delay-compensated IF signal is converted into an RF signal by the RF/IF converter module, which is then radiated by each antenna, resulting in signal synthesis on the same user side.  
Figure 1: DSC distributed antenna scenario modelling.  
Figure 2: Block diagram of received signal synthesis scheme for DSC distributed antenna system.