Stability Region of a Slotted Aloha Network with K-Exponential Backoff

Stability region of random access wireless networks is known for only simple network scenarios. The main problem in this respect is due to interaction among queues. When transmission probabilities during successive transmissions change, e.g., when exponential backoff mechanism is exploited, the interactions in the network are stimulated. In this paper, we derive the stability region of a buffered slotted Aloha network with K-exponential backoff mechanism, approximately, when a finite number of nodes exist. To this end, we propose a new approach in modeling the interaction among wireless nodes. In this approach, we model the network with inter-related quasi-birth-death (QBD) processes such that at each QBD corresponding to each node, a finite number of phases consider the status of the other nodes. Then, by exploiting the available theorems on stability of QBDs, we find the stability region. We show that exponential backoff mechanism is able to increase the area of the stability region of a simple slotted Aloha network with two nodes, more than 40\%. We also show that a slotted Aloha network with exponential backoff may perform very near to ideal scheduling. The accuracy of our modeling approach is verified by simulation in different conditions.Comment: 30 pages, 6 figure

Ricci cubic gravity in d dimensions, gravitons and SAdS/Lifshitz black holes

A special class of higher curvature theories of gravity, Ricci Cubic Gravity (RCG), in general d dimensional space-time has been investigated in this paper. We have used two different approaches, the linearized equations of motion and auxiliary field formalism to study the massive and massless graviton propagating modes of the AdS background. Using the auxiliary field formalism, we have found the renormalized boundary stress tensor to compute the mass of Schwarzschild AdS and Lifshitz black holes in RCG theory.Comment: 35 pages. Published versio

Urban morphology and transformation the pattern of housing in the historical cities of Iran

Regardless of the historical and cultural collapse of today's contemporary architecture that arose in the aftermath of the advent of modernity, if we look at the process of the emergence of architecture before this era, we see that most architectural monuments in different periods have been able, due to modeling, to possess A distinct and defined style. The study of urban morphology and architectural typology on different scales show that the formation of ancient cities in the Middle East has always been subject to various conditions, including political, social, economic, geographical and cultural conditions. Cultural conditions are the most important and the first parameter in the formation of urban structure in Iranian cities. The city of Shiraz is one of the sample cities. By studying the historical context of Shiraz from the past and reviewing its morphology, it can be understood that the city's structure is based on cultural conditions. The modern city structure in Shiraz is very different from the historical structure that continued to Qajar period that is the finalist historical period of Iranian urbanism.In this paper, by analyzing different parts of the historical texture of Shiraz, the concept and dimensions of changing the pattern of housing based on urban morphology have been analyzed and analyzed. The results of this descriptive-analytic study show that the concept of housing in this city has been changed and the main factor of development has been derived from the inside. Therefore, it can be argued that the core of the forces forming the Islamic cities, based on the concept of housing in the present age, has lost its meaning