Analyzing the Impact of Structural Change in Iranian Agricultural Credit System

Replacement of the traditional interest based credit system with an Islamic credit system was one of the fundamental changes in Iran since 1979. The Islamic credit system, offers the prospect of risk sharing between the borrower and the lender. Small farmers are likely to be risk averse and they are reluctant to go heavily into debt in order to finance investments in new technology and capital intensive methods of production which they perceive to be risky. Farmer's decision making behaviour with regard to risk under the Islamic and interest based credit systems are explored with the aid of a simple conceptual model. Analysis of attitudinal data suggests that the majority of small farmers prefer credit provided under the Islamic credit system. Farmers' preferences for taking out loans from an Islamic credit system were found to be related to a number of factors. Risk sharing and religious acceptability of the profit and loss sharing loans over the interest based loans were two significant reasons.Islamic credit System, Iran, Agriculture, risk sharing, Agricultural Finance, Risk and Uncertainty,

Efficient LLR Calculation for Non-Binary Modulations over Fading Channels

Log-likelihood ratio (LLR) computation for non-binary modulations over fading channels is complicated. A measure of LLR accuracy on asymmetric binary channels is introduced to facilitate good LLR approximations for non-binary modulations. Considering piecewise linear LLR approximations, we prove convexity of optimizing the coefficients according to this measure. For the optimized approximate LLRs, we report negligible performance losses compared to true LLRs.Comment: Submitted to IEEE Transactions on Communication

On the Combined Effect of Directional Antennas and Imperfect Spectrum Sensing upon Ergodic Capacity of Cognitive Radio Systems

We consider a cognitive radio system, consisting of a primary transmitter (PUtx), a primary receiver (PUrx), a secondary transmitter (SUtx), and a secondary receiver (SUrx). The secondary users (SUs) are equipped with steerable directional antennas. We assume the SUs and primary users (PUs) coexist and the SUtx knows the geometry of network. We find the ergodic capacity of the channel between SUtx and SUrx , and study how spectrum sensing errors affect the capacity. In our system, the SUtx first senses the spectrum and then transmits data at two power levels, according to the result of sensing. The optimal SUtx transmit power levels and the optimal directions of SUtx transmit antenna and SUrx receive antenna are obtained by maximizing the ergodic capacity, subject to average transmit power and average interference power constraints. To study the effect of fading channel, we considered three scenarios: 1) when SUtx knows fading channels between SUtx and PUrx, PUtx and SUrx, SUtx and SUrx, 2) when SUtx knows only the channel between SUtx and SUrx, and statistics of the other two channels, and, 3) when SUtx only knows the statistics of these three fading channels. For each scenario, we explore the optimal SUtx transmit power levels and the optimal directions of SUtx and SUrx antennas, such that the ergodic capacity is maximized, while the power constraints are satisfied

Optimum Linear LLR Calculation for Iterative Decoding on Fading Channels

On a fading channel with no channel state information at the receiver, calculating true log-likelihood ratios (LLR) is complicated. Existing work assume that the power of the additive noise is known and use the expected value of the fading gain in a linear function of the channel output to find approximate LLRs. In this work, we first assume that the power of the additive noise is known and we find the optimum linear approximation of LLRs in the sense of maximum achievable transmission rate on the channel. The maximum achievable rate under this linear LLR calculation is almost equal to the maximum achievable rate under true LLR calculation. We also observe that this method appears to be the optimum in the sense of bit error rate performance too. These results are then extended to the case that the noise power is unknown at the receiver and a performance almost identical to the case that the noise power is perfectly known is obtained.Comment: This paper will be presented in IEEE International Symposium on Information Theory (ISIT) 2007 in Nice, Franc