# LoRa Resource Allocation Algorithm for Higher Data Rates
## 3 LRA Algorithm Framework
### Resource Allocation Algorithm
#### 4.1.2 Different Bandwidths

In this experiment, one transmitter was configured to transmit 240 bytes of data using the 915 MHz radio channel with BW = 250 kHz and SF = 7. Another transmitter was configured to transfer a 240-byte packet using the same radio channel with SF = 7 and the BWs 125 kHz, 250 kHz, and 500 kHz. The receiver was configured using the 915 MHz radio

Figure 5:5 Different LoRa bandwidth and channel interference: The reflected radio channel (916 MHz) monitored for inter-channel interference. Data loss for LoRa parallel data transmission using two different BWs (BW 250 kHz and 500 kHz) with same SF = 7 and radio channel 915 MHz. Figure 5:6 LoRa parallel data transfer experimental setup. channel with SF = 7. Figure 8 shows the parallel transmission of different BWs with the same SF and radio channel. The receiver received the data from the transmitter of a similar configuration (915 MHz, BW = 250 kHz, and SF = 7). However, the transmitted data with a BW of 500 kHz causes noise that affects the physical channel with a 250 kHz BW, resulting in an SNR decrease from 10 to 1.25. We also observed a few bits of data loss in 20% of the overlapped data packets, denoted by green boxes in Figure 5:7 Therefore, LCs of different BW could not be used for parallel transmission. #### 4.1.3 Different Spreading Factors

In this experiment, the two transmitters were configured with the same parameters, except for SFs transmitting 240 bytes over the 915 MHz radio channel. As expected, due to the quasi-orthogonality of the SFs, no significant data loss was observed during parallel transmission when using SF = 7 in conjunction with SFs ranging from 8 to 10. However, in small SF combinations with higher SF values such as 7 and 12, the SNR value experienced a meaningful decrease. As different SFs are not perfectly orthogonal, this issue stems from inter-SF interference caused by the extended overlapping duration of the two transmission chirps. To mitigate this, long-duration overlaps should be avoided during parallel transmission using different SFs. ### Phase II

In this section, the parallel transmission of image data using different SFs is examined in terms of \(T_{tx}\), BR, BER, energy consumption, and received image quality. To do this, small sized images (around 20 to 30 kB) are transformed into strings of bytes and stored in an SD RAM, connected to the processor. The communications were conducted in an open field spanning approximately 200 m, with both the transmitter and receiver positioned 3 m above the ground, ensuring a LoS link. On the transmitter and receiver, one LoRa radio is set to operate on SF = \(i\) and the other on SF = \(j\), where \(i\), \(j\) = [7, 8, 9, 10] and \(i\
eq j\), to maximize the utilization of the LC, as discussed earlier in Section 3.3. CR and BW are the other parameters that contribute to the ToA (transmission time of one packet) and thus \(T_{tx}\). While a larger CR improves the robustness of the transmission against interference, it takes up packet capacity due to the added redundancy, thus diminishing the throughput of the LC and increasing the ToA. Therefore, CR in all experiments is fixed at 1 for all LoRa modules. We have repeated the experiment for every BW and measured the impact on \(T_{tx}\). The payload size of all LoRa modules is set to the highest value, 255 bytes. The image bytes are treated as a pool of information from which packets are formed and sent. To send an image over the LC, the LRA algorithm extracts the corresponding image bytes from the pool and segments them based on the SFs used by the LoRa modules at the transmitter (Section 3.3). In the first trial, the SFs on the transmitter and receiver are set to 7 and 8. According to Figure 5, to minimize synchronization loss in this parallel setup, a delay should be introduced to allow the reception of 2 packets over SF = 8 and 3 packets over SF = 7. This results in a total of 5 packets being received in a single round of parallel transmission, with 2 of them delivered using SF = 8.