Due to its large bandwidth and the complexity of indoor environment, the ultra-wideband(UWB) channel is frequency selective, which affects the data rate and reliability of UWB communication. This paper investigates amplify-and-forward(AF) relay scheme to mitigate this reliability problem for orthogonal frequency division multiplexing(OFDM)-UWB communication. The relay can be used to acquire capacity gain and diversity gain just like multiple-input and multiple-output(MIMO) system. The first investigation focuses on the relay-node selection criterion and combination ratio for capacity gain. Capacity gain depends on the correlation of frequency responses between direct link and relay link in addition to signal-to-noise ratio(SNR) of relay link. Increased similarity of the two frequency responses increases capacity gain. Capacity gain’s best relay and combination ratio are found by taking the derivative of the capacity equation. Solution of the quadratic derivative equation of ratio finds the optimal ratios for every potential relay node. The second investigation focuses on relay-node selection criterion and combination ratio for diversity gain. Higher diversity gain corresponds to less deep-faded sub-channels of combined signal. Reduced computation divides the problem into two steps: the first step selects the relay node according to the criterion that is dependent on the expectation value and variance of S(f)—the function of SNR of f; the second step solves the optimization problem for optimal combination ratio. Numerical simulation shows that our scheme is effective in pursuit of capacity gain and of diversity gain. Due to its large bandwidth and the complexity of indoor environment, the ultra-wideband (UWB) channel is frequency selective, which affects the data rate and reliability of UWB communication. This paper investigates amplify-and-forward (AF) relay scheme to mitigate The reliability problem for orthogonal frequency division multiplexing (OFDM) -UWB communication. The relay can be used to acquire capacity gain and diversity gain just like multiple-input and multiple-output (MIMO) system. The first investigation focuses on the relay-node selection criterion and combination ratio for capacity gain. Capacity of depends on the correlation of frequency responses between direct link and relay link in addition to signal-to-noise ratio (SNR) of relay link. Increased similarity of the two frequency responses increases capacity gain Capacity gain’s best relay and combination ratio are found by taking the derivative of the capacity equation. Solution of the quadratic derivative equation of ratio finds the second investigation focuses on relay-node selection criterion and combination ratio for diversity gain. Reduced computation divides the problem into two steps : the first step selects the relay node according to the criterion that is dependent on the expectation value and variance of S (f) -the function of SNR of f; the second step solves the optimization problem for optimal combination ratio. our scheme is effective in pursuit of capacity gain and of diversity gain.