Cognitive and Energy Harvesting-Based D2D Communication in Cellular Networks: Stochastic Geometry Modeling and Analysis

While cognitive radio enables spectrum-efficient wireless communication, radio frequency (RF) energy harvesting from ambient interference is an enabler for energy-efficient wireless communication. In this paper, we model and analyze cognitive and energy harvesting-based D2D communication in cellular networks. The cognitive D2D transmitters harvest energy from ambient interference and use one of the channels allocated to cellular users (in uplink or downlink), which is referred to as the D2D channel, to communicate with the corresponding receivers. We investigate two spectrum access policies for cellular communication in the uplink or downlink, namely, random spectrum access (RSA) policy and prioritized spectrum access (PSA) policy. In RSA, any of the available channels including the channel used by the D2D transmitters can be selected randomly for cellular communication, while in PSA the D2D channel is used only when all of the other channels are occupied. A D2D transmitter can communicate successfully with its receiver only when it harvests enough energy to perform channel inversion toward the receiver, the D2D channel is free, and the $\mathsf{SINR}$ at the receiver is above the required threshold; otherwise, an outage occurs for the D2D communication. We use tools from stochastic geometry to evaluate the performance of the proposed communication system model with general path-loss exponent in terms of outage probability for D2D and cellular users. We show that energy harvesting can be a reliable alternative to power cognitive D2D transmitters while achieving acceptable performance. Under the same $\mathsf{SINR}$ outage requirements as for the non-cognitive case, cognitive channel access improves the outage probability for D2D users for both the spectrum access policies.Comment: IEEE Transactions on Communications, to appea

Exchange Rate Policy under Floating Regime in Bangladesh: An Assessment and Strategic Policy Options

This paper examines the exchange rate policy in Bangladesh for the period 2000-08. Regime classification of the paper suggests that Bangladesh maintained a de facto managed floating regime by intervening in the foreign exchange market on a regular basis. This is at odds with the Bangladesh Bank's claim of maintaining de jure floating regimesince end-May 2003. A high exchange rate pass-through is observed along with high market pressure during the period of expansionary monetary policy. Given the thin foreign exchange market and high pass-through effects, it appears difficult for Bangladesh to mainatin a freely floating regime. Although Bangladesh maintained average competitiveness, the currency remained somewhat overvalued. Based on the findings, some pragmatic policies in managing the exchange rate in Bnagladesh have been suggested.Exchange Rate, Floating Regime, Bangladesh

Effect of diazinon 60 EC on Anabas testudineus, Channa punctatus and Barbodes gonionotus

Anabas testudineus, Channa punctatus and Barbodes gonionotus were exposed to 5.62, 6.25, 6.87, 7.50, 8.12 and 8.75 ppm; 1.13, 2.26, 3.39, 4.52, 5.65 and 6.78 ppm; and 2.00, 2.50, 3.00, 3.50, 4.00 and 4.50 ppm of Diazinon 60 EC, respectively. The median lethal concentration (LC50) values of Diazinon 60 EC on A. testudineus, C. punctatus and B. gonionotus were 6.55, 3.09 and 2.72 ppm for 96 hrs of exposure. The fish species showed several abnormal behaviors which included restlessness, arena movements, loss of equilibrium, increased opercular activities, strong spasm, paralysis and sudden quick movements during the exposure. For histopathological studies, A. testudineus, C. punctatus and B. gonionotus were exposed for 7 days to sublethal concentrations of 1.13 and 3.75 ppm; 1.13 and 2.26 ppm; and 1.13 and 2.26 ppm of Diazinon 60 EC, respectively. Hypertrophy, necrosis and pyknosis of hepatocytes, pyknosis and degenerative changes such as necrosis of tubular and haematopoietic cells of kidney were the major histopathological effects