## 5 Characteristics of the Applied Communication Technologies for the Underground Mine Stope  
### Wi-Fi6  
Wi-Fi has evolved drastically over the years. Wi-Fi initially introduced Direct Sequence Spread Spectrum (DSSS) modulation [26], which spread a signal over a wider bandwidth as compared to its original size. This approach of spreading data reduced the effects of interference from other signals or noise, making the communication more robust. Wi-Fi uses Orthogonal Frequency Division Multiplexing (OFDM) [27], which enabled multi-user capabilities by allocating subcarriers to individual clients. For OFDM, the entire subcarrier could only be allocated to a single client. Wi-Fi3 uses the concept of channel bonding [28], which allows adjacent 20 MHz channels to be combined to create wider 40 MHz channels. This can effectively double the data throughput under optimal conditions. Wi-Fi4 applies Multiple-Input Multiple-Output (MIMO) technology [27], which allows for multiple streams of data to be transmitted simultaneously via multiple antennas. This improved spectral efficiency and greatly improved throughput. Wi-Fi5 introduced Multi-User MIMO (MU-MIMO) [29] for simultaneous data transmission to multiple clients. For MIMO, each antenna pair served a single client, whilst MU-MIMO serves multiple clients concurrently by spatially multiplexing the data streams. Whilst MIMO focused primarily on improving the performance of a single client, MU-MIMO enables simultaneous communication with multiple clients, thereby increasing overall network performance. Wi-Fi6 uses Orthogonal Frequency Division Multiple Access (OFDMA) [30] for improved efficiency in high-density environments. Wi-Fi6 also introduced BSS colouring [31], which is used to address co-channel interference. This helps devices make better decisions regarding channel access, hence reducing collisions and improving overall network efficiency in high-density environments. Due to the low-powered nature of Wi-Fi6, the devices can be installed in certain allocated points in slopes without being a burden to the miners. All these properties make Wi-Fi6 a good candidate for slopes. Wi-Fi6 implements several technologies to address the concerns of multipath interference. Wi-Fi6 uses OFDMA, which allows for a single channel to be divided into smaller sub-channels known as Resource Units (RUs) [32]. These RUs can be transmitted to different users simultaneously, thus allowing for the increased utilization of the available spectrum, hence reducing the impact of multipath interference. Wi-Fi6 also introduced techniques such as BSS colouring with spatial frequency reuse [33] which enables multiple devices within close proximity to communicate simultaneously whilst limiting interference. This spatial reuse capability helps mitigate the effects of multipath interference by allowing the more efficient use of the available spectrum. Although MU-MIMO was introduced in Wi-Fi5, Wi-Fi6 expanded its capabilities by supporting MU-MIMO in both uplink and downlink transmissions. This functionality enables multiple devices to simultaneously receive and transmit data, even in environments with excessive multipath interference, by using multiple antennas to spatially separate the signals [34]. Wi-Fi6 also utilizes an improved beamforming technique, which enhances the reliability and efficiency of transmissions by directing signals towards the intended recipients [35]. For these reasons, Wi-Fi6 has become the perfect low-cost candidate for mine stope communications. Previous research [5] has shown that COFDM offers slightly better signal robustness as compared to Wi-Fi6, which would have made COFDM the ideal choice for a stope. However, the cost of a COFDM device is much greater than that of a Wi-Fi6 device. Wi-Fi6 devices are substantially cheaper than COFDM devices whilst offering similar signal robustness. Wi-Fi6 devices also had substantially greater throughput than COFDM devices.