A 24-dimensional Leech lattice coding and modulation scheme is proposed to improve the physical layer performance of the IEEE 802.11 a wireless LAN standard. We present in this paper the construction of an IEEE 802.11 a compliant Leech lattice encoder and the implementation of a maximum-likelihood soft-decision decoder based on half Leech lattice set partitioning. Within the constraint of the current IEEE 802.11a standard, the proposed Leech lattice code supports flexible data rates of up to 96 Mbit/s. Substantial coding gain and better SNR performance are achieved at high data rate, in both bit error rate (BER) and packet error rate (PER). As a candidate for implementation of block-coded modulation in OFDM systems, the potential of the Leech lattice is evaluated by comparing with uncoded QAM and one trellis coded modulation (TCM) scheme. Simulation results on BER and PER in an AWGN channel are demonstrated at different data rates.