Signal-to-noise (SNR) compares the level of the received signal to the level of background noise and specifies the number of dBs a received signal is above the noise floor. Modern day WLANs should be designed to meet a minimum SNR of 25dB to help ensure successful RF operations.
Co-channel contention occurs when two access points (or their clients) on the same channel can hear and decode each others’ signals. In this scenario, the devices will share the capacity of a single channel. It is therefore desirable when designing Wi-Fi networks to ensure two access point configured for the same channel cannot receive and decode each others’ signals - we call this 'channel reuse'. While our goal in Wi-Fi design should be have no co-channel contention between APs, it is not always possible, especially in the 2.4GHz band where we only have three channels available. Therefore, as the designer, you have to decide what will be an acceptable level of co-channel contention.