We present a study on the performance of TCP, in terms of both throughput and energy consumption by considering a Wideband CDMA radio interface. The results show that the relationship between throughput and average error rate is largely independent on the network load, making it possible to introduce a universal throughput curve, which gives throughput predictions for each value of the user error probability. Furthermore, the possibility to select an optimal power control threshold to maximize the tradeoff between throughput and energy, is discussed.