k; maximising spectral efficiency to get more data bits into each hertz of RF spectrum maximising MAC efficiency SO that most of the transmitted bits are upper layer data rather than Link Control and MAC layer overhead ensuring security through strong encryption algorithms, with fast computation on low-cost hardware. In addressing these challenges, the WIGWAM consortium is considering broadly similar approaches to those under discussion by 802.11 TGn, for example, MIMO radio and OFDM with higher efficiency coding (LDPC and Turbo Codes - see next section) are under consideration to achieve high spectral efficiency. One additional technology being considered by WIGWAM is OFDMA with multi-carrier code division multiple access (OFDMA/MC-CDMA), described in the Section "Multi-Channel Code Division Multiple Access (MC-CDMA), p. 353". WIGWAM is initially targeting operation at 5 GHz but extensions in the 17, 24, 38 and 60 GHz RF bands are also under consideration. This would Chapter Fourteen bring wireless networking into the millimetre wave bands, with wavelengths of 8 mm at 38 GHz to 5 mm at 60 GHz. LDPC and Turbo Codes Low density parity check codes are error correction codes that are computationally efficient and perform close to the theoretical limit in enabling error recovery in noisy communication channels. Unlike a standard parity check, which simply flags bit errors during transmission, these codes also allow errors to be probabilistically recovered i.e. from a set of possible transmitted data blocks it is possible to compute which is most likely to have resulted in the received data block and check code. A check code is computed from a data block by sparsely sampling bits in the block using a random sampling matrix. Figure 14-3 illustrates a sampling matrix and the 4-bit check code resulting from the example 8-bit input work. The "low density" in LDPC refers to the fact that there are few 1's in the matrix. In this example, if the input word is incorrectly received as 00100101, the check code word can be used 