## 5 Frequency Manipulation and Communication Feasibility  
### Feasibility of Frequency Manipulation  
The communication parameters such as frequency, bandwidth, and sample rate as well as internal SDR transmitter and receiver gains are controlled using the GNU Radio software (v3.8.2.0). To manipulate these parameters during runtime, there is a need to access the inphase and quadrature (IQ) data stream inside GNU Radio Python and/or C ++ blocks. Various frequency reconfiguration techniques are used in satellite communications to optimize performance, increase measurement accuracy, and ensure reliable communication under different conditions. Frequency reconfiguration algorithms used in satellite communications include dynamic spectrum access (DSA) [53], cognitive radio-based frequency reconfiguration [54], frequency-hopping spread spectrum (FHSS) [55], adaptive beamforming and frequency steering [56], and adaptive modulation and coding (AMC) [57]. DSA algorithms allow satellites to adjust their frequency utilization dynamically depending on the availability of spectra in their operational environment. They are nevertheless quite sophisticated in terms of real-time spectrum detection, frequency reconfiguration procedures, and decision making. This complexity augments the likelihood of algorithmic errors. Utilizing cognitive radio approaches, it is possible to identify underutilized or unused frequency bands and opportunistically switch to them. Nonetheless, their spectrum detection, decision making, and reconfiguration impose delays, rendering them unsuitable for real-time applications or crucial communication scenarios.  
Moreover, FHSS frequency reconfiguration algorithms provide benefits in terms of security, interference avoidance, and fading resilience, they also present issues in terms of complexity, synchronization, latency, and possible constraints in data rates and bandwidth efficiency. The advantages of adaptive beamforming and frequency-steering frequency reconfiguration algorithms include improved signal quality, reduced interference, and dynamic adaptation; however, maintaining the accurate calibration and alignment of antenna rays are essential for efficient beamforming and steering. Any misalignment significantly degrades performance. AMC frequency reconfiguration methods enhance communication efficiency by dynamically altering the modulation scheme and error-correction coding dependent on the effectiveness of the communication channel. On the other hand, certain AMC algorithms rely on feedback from the receiver to precisely determine the optimal modulation and coding parameters, and this potentially adds communication overhead.  
In order to improve performance and reconfiguration speed in real time, ensure reliability, reduce complexity, ensure interoperability in systems and programming languages, and to lower network overhead two algorithms based on server and client architecture were proposed and implemented. These techniques are robust and they achieve the software-based manipulation of SDR and communication parameters in a remote setup of satellites in the ISL network. The first technique is a modified extensible markup language-remote procedure call (modified XMLRPC) and the second one is the TCP/IP method as shown in Figure 15.  
In previous versions of the GNU Radio software from 3.7 and below, the XMLRPC algorithm has been implemented to support this function in a server and client setup [44; 58]. However, the latest version of GNU Radio from 3.8 and above are incompatible with the traditional XMLRPC client blocks. This study demonstrated an innovation of two techniques that were implemented to grant access to interact with the IQ data stream of GNU Radio Python and C++ modules upon starting, in the middle or at the end of mission execution.