Instantaneous Symbol Error Outage Probability over Fading Channels with Imperfect Channel State Information

We propose to use the probability of instantaneous symbol error outage (ISEO) as a performance measure for digital communication over wireless channels. It is defined as the probability that the instantaneous symbol error probability (ISEP) exceeds an ISEP threshold. We analyze the impact of imperfect channel state information (CSI) on the ISEO probability over Rayleigh fading channels. A simple, but tight, closed-form upper bound on the ISEO probability is obtained as a function of the channel estimation mean square error (MSE). It is shown that the ISEO performance improves rapidly with decreasing MSE, when MSE drops below a certain value, which is determined partly by the ISEP threshold chosen. As CSI is commonly obtained by pilot-symbol-assisted channel estimation in packet transmission, we obtain the optimum allocation of pilot and data energy in a frame that minimizes the ISEO probability, which also minimizes the instantaneous packet error outage probability.