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This paper presents the throughput analysis of an M-group heterogeneous IEEE 802.11 DCF network where nodes in different groups have distinct input rates and initial backoff window sizes. An explicit expression of the network steady-state operating point is obtained based on the fixed-point equation of the limiting probability of successful transmission of Head-of-Line (HOL) packets given that the channel is idle, which is shown to be closely dependent on the backoff parameters of saturated groups and the input rates of unsaturated groups. Both the network throughput and the group throughput performance are further characterized, and the maximum network throughput is derived as an explicit function of the holding times of HOL packets in successful transmission and collision states. The analysis reveals that to achieve the maximum network throughput, the optimal set of input rates of unsaturated groups and initial backoff window sizes of saturated groups should satisfy a constraint that is determined by the group sizes of saturated groups. Given the input rates of unsaturated groups, for instance, the initial backoff window sizes of saturated groups should linearly increase with their group sizes, and those with higher increasing rates achieve lower group throughput.