To increase channel capacity in tunnels, MIMO seems to be a promising technique despite the low angular spread of the rays. Indeed, for transmitting frequencies on the order or larger than 1 GHz, the tunnel behaves as an oversized waveguide and the concept of spatial diversity can be replaced by the concept of modal diversity. Nevertheless if the maximum capacity which can be reached is an interesting criterion, it is also important to study the performance of a MIMO link in terms of bit error rate or symbol error rate. Furthermore, these performances must be compared to those which would be obtained by using simple diversity receiving systems as selection combining or maximum ratio combining. In this presentation, a 2-element array will be considered, both at the transmitter and at the receiver, the element spacing varying between 0.5 to 3 wavelengths. From channel matrices measured in a tunnel at 2.8 GHz, error rates for different diversity schemes are deduced from simulation tools to draw conclusions on their efficiency.