In this study, the problem of <alternatives>${\cal H}_\infty $<mml:math overflow="scroll"><mml:msub><mml:mrow><mml:mi mathvariant="script">H</mml:mi></mml:mrow><mml:mi mathvariant="normal">∞</mml:mi></mml:msub></mml:math><inline-graphic xlink:href="IET-SPR.2016.0469.IM2.gif" /></alternatives> filtering for sampled-data systems under unreliable communication links is investigated. The phenomena of data packet dropouts and signal transmission delays are addressed in a unified framework. The objective is to design an admissible filter to guarantee the asymptotic stability of the filtering error system and minimise the <alternatives>${\cal H}_\infty $<mml:math overflow="scroll"><mml:msub><mml:mrow><mml:mi mathvariant="script">H</mml:mi></mml:mrow><mml:mi mathvariant="normal">∞</mml:mi></mml:msub></mml:math><inline-graphic xlink:href="IET-SPR.2016.0469.IM3.gif" /></alternatives> disturbance attenuation level. Thanks to the proposed novel Lyapunov–Krasovskii functional together with the improved Wirtinger's inequality and the reciprocally convex approach, novel sufficient linear-matrix-inequality-based conditions are obtained for the existence and design of admissible filters. Finally, two simulation examples are provided to illustrate the efficiency and less conservativeness of the proposed <alternatives>${\cal H}_\infty $<mml:math overflow="scroll"><mml:msub><mml:mrow><mml:mi mathvariant="script">H</mml:mi></mml:mrow><mml:mi mathvariant="normal">∞</mml:mi></mml:msub></mml:math><inline-graphic xlink:href="IET-SPR.2016.0469.IM4.gif" /></alternatives> filter design methods.