Simple Mini FM Receiver / Radio Receiver

This is a very simple and mini fm radio receiver with good performances that works great even if the sensitivity is not too high. The working principle of this fm receiver may seem a little unusual. It is made of an oscillator (T2 and T3) that is synchronized with the received frequency of T1. This transistor works as a broadband preamplifier in VHF range.  The oscillator is adjusted between 87 … 108 MHz with C5. Because of the synchronization, the oscillator output will have the same frequency deviation as the received signal from the fm antenna. This deviations are caused by the broadcasted audio informations. The frequency modulated signal show up on P1 + R5. Low pass filter R6/C6 extracts the audio signal and then is amplifier by T4 … T6 and transmitted at the output through C9 capacitor.

The coil details are presented in the fm receiver circuit diagram. The radio receiver is adjusted on different stations with the help of C5. P1 potentiometer is adjusted untill the best reception is obtained. If we attach an audio amplifier and a speaker then this fm receiver can be made very compact as a pocket radio.

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Nonlinear MIMO

Affordable MIMO Technology for Wireless Sensor Networks
     

Abstract—

We consider a sensor network, where an access point (AP) communicates with many sensor nodes (SN), which are simple, cheap, low-complexity and low-power communication nodes. Such systems typically use nonlinear modulation and detection, due to their low power consumption. Increasing their performance by means of multiple antennas at the AP and the SNs has not been considered, since this would violate the
stringent power and cost constraints at the SN. We consider SNs with MIMO receivers that perform a nonlinear operation on the complex-valued received signal (amplitude or phase detection). These receivers enjoy the low-cost, low-power, low-complexity characteristics that are crucial for a sensor network. Such
nonlinear MIMO systems are first introduced and studied here. They bring the high-rate, high-performance world of MIMO systems and the low-cost, low-complexity world of sensor networks together. We only consider the single-user MIMO system between the AP and one SN, and study the fundamental limits
of such systems. We compute achievable rates under perfect and noisy CSI at the SN, and observe that these systems also achieve spatial multiplexing gain, albeit different to legacy linear MIMO systems. We quantify and analyze these gains using numerical means, and give insight into the effect of the nonlinearity on the information theoretic limits of nonlinear MIMO systems.

Ref :- IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 9, NO. 2, FEBRUARY 2010

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Multiple Antenna Spectrum Sensing in Cognitive Radios

Abstract—

In this paper, we consider the problem of spectrum sensing by using multiple antenna in cognitive radios when the noise and the primary user signal are assumed as independent complex zero-mean Gaussian random signals. The optimal multiple antenna spectrum sensing detector needs to know the channel gains, noise variance, and primary user signal variance. In practice some or all of these parameters may be unknown, so we derive the Generalized Likelihood Ratio (GLR) detectors under these circumstances. The proposed GLR detector, in which all the parameters are unknown, is a blind and invariant detector with a

low computational complexity. We also analytically compute the missed detection and false alarm probabilities for the proposed GLR detectors. The simulation results provide the available traded-off in using multiple antenna techniques for spectrum sensing and illustrates the robustness of the proposed GLR detectors compared to the traditional energy detector when there is some uncertainty in the given noise variance.

Ref : IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS, VOL. 9, NO. 2, FEBRUARY 2010

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