## 1 Introduction and Motivation
The neighboring sensor nodes use a random access technique to reply to the AUV-transmitted probe signal during the probe interval. It is highly probable that some reply packets transmitted by sensor nodes may be lost owing to collisions or an adverse channel. This could lead to the failure of a network to detect crucial events that may be catastrophic in certain applications. In addition, the AUV has to wait for all information to be retrieved from the neighborhood before it moves to the next neighborhood. Thus, this approach increases the AUV's touring time which has an adverse effect on AUV operational costs. Moreover, owing to the probabilistic nature of the neighborhood, it is very difficult to achieve uniform energy consumption over the entire neighborhood. Similarly, in [10] the authors considered a polling scheme for an AUV to communicate neighboring sensor nodes at a tour point. In such a data-gathering approach, the probabilistic neighborhood, where the probability of successful communication is low, may result in many retransmissions. These retransmission overheads cause additional costs in term of excessive resource consumption in addition to AUV operational costs. In [11], the authors analyzed a heterogeneous underwater network scenario, where sensor nodes are categorized based on their functionalities. In such an approach, a special fixed node called a head node takes the responsibility of gathering data from a neighborhood. In this scheme, head nodes, which are distributed over the network, collect data from respective neighborhoods and forward the data to an AUV that is taking a data-gathering tour. However, the authors have not discussed how these head nodes may be placed or selected in a network to form a number of data gathering neighborhoods that deal with issues such as non-uniform energy consumption at ordinary nodes during transmission to head nodes or the rapid depletion of energy at head nodes during an AUV data-gathering tour. As a result, the approach of using fixed relaying nodes may be highly prone to failure owing to uneven depletion of the nodes' energy in certain coverage areas, which may directly affect overall network performance. It is evident that the prior information on the probabilistic neighborhood results in deterministic neighborhood, which may increase the efficiency of the AUV probing interval. Therefore, a framework is to be developed that may result in deterministic neighborhoods for the AUV at the tour path, which is still an open issue that needs to be addressed. In addition, the framework should also be able to handle the selection of each relay-node for a neighborhood in such a way that uniform energy consumption may take place over the network. The designing of such a framework that achieves a deterministic neighborhood for AUV data gathering and which may also meet the requirement of uniform energy consumption is a challenging task owing to adverse channel conditions and absence of global information on energy consumption. In the proposed scheme, a node clustering technique is employed, which has been known [4,5] as a way to design a more deterministic neighborhood for AUV data collection on a tour point. The proposed scheme uses the hybrid multiple access protocol of time division multiple access (TDMA) and code division multiple access (CDMA). In the proposed scheme, an AUV visits some identified locations that act as a temporary sink. To do this, the AUV travels the network deployment region in a predefined lawn-mower pattern to deliver network-partitioning information to sensor nodes. Based on the partitioning information, the entire network is organized into a number of clusters so that each contains a cluster head (CH). Then, the CH further divides the cluster into several subclusters and nominates a sensor node called a path-node (PN) for each subcluster to collect local data from the member-nodes (MN) and reduce the impact of unequal inter-nodal transmission distances.