132 CHAPTER 6 Robust Wireless Infrastructure against Jamming Attacks against a jamming effort of 15% and 0.18 against 20% jamming effort. When using a cryptographically strong interleaver, the upper bound on throughput can be computed from Shannon channel capacity for a binary sym- metric channel 1 + log( ) + (1 - ) log(1 - ). Dividing a packet into l blocks encoded using best-known short codes leads to extremely poor performance when l increases. For binary mod- ulation schemes, a simple concatenated coding scheme (e.g., Preparata code and Reed-Solomon codes) achieves reasonable performance for rea- sonably long packets (e.g., throughput 15% against 14% jamming effort for packets of length 400 bits). The overall conclusion is that the most suitable codes for binary modulation would be the Low Density Parity Codes (LDPC) because in addition to being close to Shannons bound, they can be long enough for IP packets (thousands of bits) and still have reasonably low decoding com- mobility. Mobility expands the minimum connec- tivity achieved by sectored antennas. Although the combination of directivity and mobility increases the connectivity, existing routing and transport protocols are not designed to make use of it. The applications' assumptions have also to be reassessed to operate in such envi- ronments. Designing routing and transport pro- tocols that can exploit mobility under jamming using sectored antennas is an important open question. 6.3.2. Link Layer Resiliency As discussed earlier, increasing the jamming-to- signal ratio is not sufficient for a reliable com- munication; adequate coding and rate adaptation are necessary to counter smart jammers. Cryptographic Interleavers and Coding. Combining error correction codes and crypto-