In this paper, we propose a direct mapping (DM) orthogonal frequency division multiplexing (OFDM) based transmission scheme for underwater acoustic multimedia (UAM). We adopt DM multi-input multi-output (MIMO), power assignment mechanism, OFDM, adaptive modulation, and unequal error protection in the UAM system. The proposed underwater acoustic multimedia system employs high power, low speed modulation, and schemes providing significant error protection for the transmission of sensor data messages requiring a stringent bit-error rate (BER). In contrast, low power, high speed modulation, and less capable error protection schemes are provided for messages that can tolerate a high BER. Simulation results show that the proposed scheme can not only fulfill the quality of services (QoS) required by a UAM system, but also achieve the mission of maximum transmission bit rates or minimum transmission power.

Although Max's algorithm is frequently thought of as a simple and adequate method for the design of scalar minimum mean squared error quantizers, there are two tactical problems associated with this iterative scheme: the initialization and the updating of the algorithm. This paper proposes easy and efficient solutions to these problems. A straightforward method for obtaining good initial conditions for three common input densities is presented. Also, an efficient technique for updating the algorithm for a wide class of input densities is given.

In the context of minimum mean-square error symmetric uniform quantization, we show that for several different distributions on the input signals, log-log plots of step size versus number of output levels and mean-square error versus number of output levels both exhibit nearly linear behavior. This observation results in a straightforward design procedure for symmetric uniform quantization.