Light Fidelity (LiFi) allows wireless data transmission via Light Emitting Diode (LED) using the visible light spectrum between 400 THz and 800 THz, with high transmission rate of 10 Gbps achieved. In order to guarantee reliable data transmission, we propose a joint frame detection and channel estimation approach for DC biased Optical Orthogonal Frequency Division Multiplexing (DCO-OFDM) LiFi systems, with a single DCO-OFDM training block used. By designing a training structure, frame detection and channel estimation can be performed simultaneously. The proposed frame detection method is powerful and suitable for high-speed LiFi systems, as it is robust against the effect of Inter-Symbol Interference (ISI) caused by the response speed of the LED. Simulation results show that the proposed frame detection approach significantly outperforms existing Radio Frequency (RF) based frame detection methods in terms of probability of false detection. Using the frame detection method, the channel estimation scheme can provide a Mean Square Error (MSE) performance, better than the Least-Square (LS) channel estimation with perfect frame detection.