Orthogonal Frequency Division Multiplexing (OFDM) is a communications technique that transmits a signal over multiple, evenly spaced, discrete frequency bands. OFDM offers some advantages over traditional, single-carrier modulation techniques, such as increased immunity to inter-symbol interference. For this reason OFDM is an attractive candidate for sensor network application; it has already been included in several standards, including Digital Audio Broadcast (DAB); digital television standards in Europe, Japan and Australia; asymmetric digital subscriber line (ASDL); and wireless local area networks (WLAN), specifically IEEE 802.11a. Many of these applications currently make use of a standard convolutional code with Viterbi decoding to perform forward error correction (FEC). Replacing such convolutional codes with advanced coding techniques using iterative decoding, such as Turbo codes, can substantially improve the performance of the OFDM communications link. This paper demonstrates such improvements using the 802.11a wireless LAN standard.
The objective of this paper is to discuss research being conducted at Rome Laboratory in the area of mobile wireless communications. We have developed a differentially coherent spread spectrum communications modem with noise-like transmission properties that would make it difficult to detect and exploit. This modem has been simulated with excellent performance in additive white Gaussian noise (AWGN). We are now developing a detection process that will have good performance in the harsh mobile multipath environment inherent in most law enforcement and military operations.