In wireless communication, the sender needs to select an optimal wireless channel from several available ones. However, the instantaneous channel state is time-varying with unknown statistics. Therefore, the channel selection must be based on channel observation. Before the packet arrives, the sender needs to observe the channel state in the observation period. And then the sender transmits packets through the best channel. Observation needs cost time. We investigate the trade-off between the observation period and transmission period. A short observation period usually leads to wrong selection while long observation might waste time. Our simulation results show that there is an optimal length of observation period. The total transmission time experience a sharp decrease before the optimal point. The longer observation does not cause an obvious increase in transmission time. We analyze how the observation time affects the transmission time to explain the simulation results.

在无线通信中，发送方需要从几个可用的无线信道中选择一个最优的无线信道。然而，瞬时信道状态随时间变化，统计数据未知。因此，信道选择必须基于信道观察。在数据包到达之前，发送方需要在观察期内观察信道状态。然后发送方通过最佳通道传输数据包。观察需要花费时间。我们研究了观察期和传输期之间的权衡。观察时间短通常会导致错误选择，而长时间观察可能会浪费时间。我们的模拟结果表明存在最佳的观察期长度。总传输时间在最佳点之前急剧减少。更长的观察时间不会导致传输时间的明显增加。我们分析观察时间如何影响传输时间来解释模拟结果。