Whenever there is a collision involving several transmitted packets, the traditional approach for MAC (Medium Access Control) protocols is to discard all packets involved and request their retransmission, with a consequent loss in the overall throughput. Based on conventional Multiple Input Multiple Output (MIMO) techniques, in this paper we propose a multipacket detector for OFDM schemes (Orthogonal Frequency Division Multiplexing) that allows an efficient packet separation in the presence of collisions and can achieve high throughputs. We show that reliable detection is possible as long as different interleavers are used for different retransmissions. We also include a method to estimate the users involved in the collision, as well as well as the corresponding channel characteristics.