# A New Resource Allocation Protocol for the Backhaul of Underwater Cellular Wireless Networks
###### Abstract
The studies to design the topology of a UCWN was done in [11; 13; 14]; a cell radius, spatial frequency reuse pattern, the available number of UTs per cell, and the capacity per cell are mathematically derived by considering the given bandwidth and signal-to-interference ratio (SIR). A few guidelines targeted for planning a UCWN are also suggested via extensive simulation works. In [15], a collision-free medium access control (MAC) protocol was proposed for a UCWN to completely avoid collisions among UTs located in a cell; a UBS sets UTs' tier according to their distance from the UBS, and manages UTs' transmission scheduling corresponding to the tier. In addition, a resource allocation protocol, which determines the backhaul capacity of UBSs being applied to its backhaul link, was primarily proposed for a UCWN in [16] by considering following remarkable differences between the backhaul link of a UCWN and that of a TCWN. * Traffic volume. The amount of the uplink traffic (i.e., from a base station to a base station controller) is much larger than that of the downlink traffic (i.e., from a base station controller to a base station) in a UCWN, which is completely contrary to a TCWN. * Performance. The transmission rate of a backhaul link of a UCWN is much lower than that of a TCWN. Besides, the latency of a backhaul link of a UCWN is much higher than that of a TCWN. The differences mentioned above and asymmetrically increasing traffic of UBSs due to applying various underwater applications result in the traffic congestion in backhaul links of a UCWN. The protocol in [16] helps a UCWN deal with this bottleneck occurred at the backhaul link; a UBSC adaptively allocates the backhaul capacity of a UBS being proportional to its input traffic (i.e., the data collected from UTs in its cell), and thus improves backhaul transmission efficiency and fairness. To do this, a UBSC allocates several time slots per frame to UBSs for their backhaul capacity based on time division multiple access (TDMA). Three input traffic values are considered: current traffic, accumulated mean traffic, and the maximum traffic. Also, two methods that a UBS sends its input traffic to a UBSC are employed according to whether the transmission period is fixed or not: fixed period and adaptive period. It was shown via simulations that sending accumulated mean traffic with adaptive period mostly guarantees the best performance [16]. In spite of its novelty, the resource allocation technique described in [16] still needs to be enhanced considering the following aspects. * The ability to manage drastic change of uplink traffic. As the protocol in [16] was designed under the assumption that the UBSC capacity is enough to manage the input traffic from all the UBSs, it can be partially efficient when the uplink traffic of all the UBSs does not change quickly or does not show any bursty nature (which can be caused by mobile UTs such as autonomous underwater vehicles (AUVs)). However, in practice, it is possible that the uplink traffic of a UBS may abruptly increase due to burst traffic caused by mobile UTs or the rise of traffic gathered from (fixed) UTs in its cell. This can make a UBSC experience a shortage of backhaul capacity, and consequently it suffers from long latency and packet drops by queue-overflow. Thus, a more responsive resource reallocation reflecting traffic condition, that the uplink traffic of each UBS changes fast or the outbreak of burst uplink traffic occurs frequently, is strongly required. * The way to readjust the backhaul capacity of a UBS. In [16], a UBSC collects traffic information from all the UBSs, calculates their backhaul capacity, and periodically reassigns their backhaul capacity by informing them of their new backhaul capacity. In other words, all the UBSs must communicate with a UBSC for the readjustment of their backhaul capacity at the same time.