Which other 802.11 PHY specifications must VHT capable devices be backward compatible with?

The correct answer is that VHT (Very High Throughput) capable devices must be backward compatible with HT (High Throughput) and OFDM (Orthogonal Frequency Division Multiplexing). This is critical for maintaining interoperability within wireless networks that utilize multiple generations of Wi-Fi technology.

HT is part of the IEEE 802.11n standard, which introduced enhancements that allow for higher data rates, improved range, and increased capacity. OFDM is a modulation scheme used in several 802.11 standards, including both HT and VHT, that helps in maintaining a robust connection with higher data rates over mult-path propagation environments typical in Wi-Fi scenarios.

Backward compatibility ensures that newer devices using the VHT standard can still communicate effectively with older devices that utilize the HT standard and the underlying OFDM modulation technique. This capability is essential for network support and transition, allowing for a gradual upgrade path and promoting a seamless user experience across different generations of wireless communication technologies.