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A detailed analysis is presented of noise and input impedance in noise thermometer preamplifiers. The analysis highlights the advantages of cascode amplifiers and the disadvantages of amplifiers employing global feedback. Feedback gives rise to two significant errors, one arising from an increase in the input-noise current, the other from the modification of the amplifier input impedance. With care, the errors arising from thermal-noise sources associated with the preamplifiers can be kept below 1 mK. However the largest error associated with the preamplifiers, typically 10 mK to 30 mK and previously unnoticed, arises from the interaction of the input capacitance and the transmission line inductance. This effect negates the common practice of matching the time constants in noise thermometers.

SUMMARYCooperative relaying recently emerged as a viable option for future wireless networks. By simultaneously exploiting path loss savings known from relaying scenarios and the diversity inherent to any scheme involving spatially separated transmitters, this technique is able to leverage gains from both relaying and spatial diversity techniques. In this paper, we study different cooperative relaying protocols and compare their performance with that of direct transmission and conventional relaying. We investigate under which conditions the developed techniques provide gains over other approaches. Our results confirm that cooperative relaying is an effective means of enhancing the performance of wireless systems whenever temporal and frequency diversity is scarce.

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