«2.1 Time Synchronization The actual need for time synchronization within an underwater acoustic network is not always present. It can be argued that ...»
In terrestrial wireless communication systems, ACM has been in widespread use for some time. But as is pointed out in , the key difference between a terrestrial radio-based communications system and an underwater acoustic communication system is the large propagation delay, low bandwidth and high bit-error-rate. Their conclusion is that a direct adaptation of a terrestrial radio protocol may not provide acceptable results, and that protocols for this purpose need to be developed from the ground up.
The research into adaptive data rates in underwater communication systems seems to be in its infancy, and in order to move this research forward and in the end create a successful system employing ACM the following factors needs to be
The special requirements for an underwater acoustic communication system need to be taken into account already at the design stage. There are currently no existing solutions that can directly be applied.
Measures for estimating the (strongly time varying) channel impulse response needs to be built into the burst structure in order to reduce measurement latency and overhead in the communication link.
In order to have maximum ﬂexibility in the selection of possible signalling waveforms to use at any given time, a software deﬁned radio (SDR) approach is necessary. In any case, lessons learnt in the SDR arena should be taken into consideration in a new design.
In order to be able to realize a fully software deﬁned radio, the hardware platform need to be as ﬂexible as possible, and that means that all the necessary functions must be realized in digital domain. Especially important in this respect is to ensure that the digital-to-analog (DAC) and analog-to-digital (ADC) conversion subsystems have the speed and precision needed.
Fortunately, the latter is steadily improving with the advances in ADCs, DACs, ﬁeld-programmable-gate-arrays (FPGA) and microcontrollers (uC), and in the end the transducers and the required signal conditioning circuitry will be the limiting factors.
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