Measurement-Adaptive Cellular Random Access Protocols

This work considers a single-cell random access channel (RACH) in cellular wireless networks. Communications over RACH take place when users try to connect to a base station during a handover or when establishing a new connection. Within the framework of Self-Organizing Networks (SONs), the system should self- adapt to dynamically changing environments (channel fading, mobility, etc.) without human intervention. For the performance improvement of the RACH procedure, we aim here at maximizing throughput or alternatively minimizing the user dropping rate. In the context of SON, we propose protocols which exploit information from measurements and user reports in order to estimate current values of the system unknowns and broadcast global action-related values to all users. The protocols suggest an optimal pair of user actions (transmission power and back-off probability) found by minimizing the drift of a certain function. Numerical results illustrate considerable benefits of the dropping rate, at a very low or even zero cost in power expenditure and delay, as well as the fast adaptability of the protocols to environment changes. Although the proposed protocol is designed to minimize primarily the amount of discarded users per cell, our framework allows for other variations (power or delay minimization) as well.Comment: 31 pages, 13 figures, 3 tables. Springer Wireless Networks 201

Optimal control of transmission errors with power allocation and stability in ARQ downlink

In the current work a downlink scenario is studied where packets for each user are buffered at the base station waiting for service. The service rates are considered constant and determined by QoS requirements. Errors due to outages occur and are reported to the base station via a reliable binary feedback link. Erroneous packets are held in the queues and an Automatic Retransmission Request protocol that can be powercontrolled repeats transmission until success. Having a total power budget P(ind tot) available per slot to divide among users, the question which is the stability region of such a system is investigated and a power allocation that stabilizes the queues for all vectors within the aforementioned region is introduced. The optimal power allocation is the solution of a nonconcave maximization problem, the properties of which are analyzed. Algorithms based on the Lagrange dual problem are proposed that provide the actual or a relatively good approximation of the solution. Entnommen aus <a href="http://www.fiz-technik.de/db/b_tema.htm" target="_blank">TEMA</a