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Functional cookies help to perform certain functionalities like sharing the content of the website on social media platforms, collect feedbacks, and other third-party features. The onset of dropout can be more accurately recognized and countered, while eliminating switching when there is little likelihood for improvement.
It consists of two complete receiver sections, each with its own associated antenna, and circuitry that selects the audio from the receiver that has the better signal. Switching noise is possible but when properly designed these systems can have very good dropout protection with little chance of other audible effects due to incorrect selection.
This is because the system compares the signal condition at each receiver output before audio switching occurs. Range is the same as with single antenna systems. Cost is higher, but setup is convenient. This design takes advantage of the fact that, most of the time, the signal at both antennas is useable. The diversity circuitry combines the outputs of the two receiver sections by proportionally mixing them rather than switching between them. At any given moment, the combination is proportional to the signal quality of each receiver.
The output will usually consist of a mix of the two audio sections. In the case of loss of reception at one antenna, the output is chosen from the other section. Excellent dropout protection is obtained with no possibility of switching noise since the diversity circuit is essentially an intelligent panpot, not a switch.
Signal-to-noise is improved by up to 3 dB. Range can be greater than with single antenna systems. Cost is somewhat higher, setup is convenient. A properly implemented diversity system can yield measurable improvements in reliability, range, and signal-to-noise ratio. Although a comparable non-diversity system will perform adequately most of the time in typical setups, the extra insurance of a diversity system is worthwhile.
This is particularly true if the RF environment is severe multipath , troubleshooting time is minimal no rehearsal , or dropout-free performance is required ideally always. The price difference is small enough that diversity receivers are typically chosen in all but the most budget-conscious applications. An additional method for improving signal reliability in the presence of interference is called "Frequency Diversity".
This technique relies on the low likelihood of simultaneous interference on two different radio frequencies. To set up a frequency diversity system requires two transmitters, each set to a different frequency, and two matching receiver channels.
The two received signals are connected to an audio mixer on two separate channels. If the signal from either transmitter is interrupted, the audio engineer can continue with the remaining signal. Presently, this is practical only by using two bodypack transmitters on a single individual, typically with lavaliere or headworn microphones.
They may be connected to a single microphone or possibly two closely-spaced microphones. Frequency diversity is generally reserved for the primary user in critical situations where the cost of "double-packing" is justified. However, handheld transmitters are now available that can transmit simultaneously on two different frequencies.
In addition, the matching receivers can automatically transition between the two signals when interference occurs so that only a single mixer channel is required and no manual intervention is necessary to maintain signal continuity.
Find An Answer Browse our vast Answer database for answers to many common technical questions. Search the Knowledge Base Fields Title. For example, the received signals are combined at the receiver using MRC to maximize the SNR and give the following expression:. But since we are equalizing the channel with h H , with N receive antennas, the effective SNR is given by:. In this section we present simulation results to evaluate the performance of our system.
We discuss the reliability and robustness of a cluster based WSN system by using smart antennas at the receiver. The proposed model has been simulated for a microcell environment. The focus of the model is to consider the scenario of local scattering giving rise to multipaths. These multipaths and the resulting fading are modeled as stochastic processes and channel characteristics like time-variation, amplitude, and angular spread are modeled using GBSBEM. We consider a cluster-based model with N sensor nodes randomly scattered over a large area.
These nodes collect a common message and transmit it towards the cluster head. The information received at the cluster head is filtered and modulated and transmitted to the receiving station. The cluster head is located within a range of 2 meters from this receiving station. In this case both the cluster head and the receiver are surrounded by scatterers and the receiving antenna array is not well above the surrounding objects.
The model parameters were chosen to fit the scenario. Table 1 shows the set of parameters used for simulations to develop the channel and the system model. The transmitted sequence is a BPSK modulated signal and the sequence length is 10 7. The whole sequence is divided into frames of length symbols and the total number of frames are 10 5. The channel considered here is a quasi-static channel; i. We have carried out the simulations where we have different combining schemes at the receiver.
We have compared the performance of these schemes with different number of antennas at the receiver. We further analyze the performance of the system by varying the system parameters like receiver height, maximum multipath delay, and transmit power and compare the performance with: i no diversity, and ii MRC at the receiver.
We present the performance analyses when we have multiple antennas at the receiver. Figure 3 shows the performance of the system with receive diversity techniques employed at the receiver with 2, 3, and 4 antenna elements. The transmission power is 10 W and all other parameters kept same as in Table 1.
The three graphs shows that the performance of the system increase as the number of antenna elements increases. SNR with SC. Table 2 compares the performance of the three receive diversity techniques. The table demonstrates that the BER of the system increases by increasing the antenna elements and decreases with the increase in SNR. The implementation complexity for EGC is significantly less than the MRC because of the requirement of correct weighing factors.
Hence, the basic idea of diversity reception is that, if two or more independent samples of a signal are taken, then these samples will fade in an uncorrelated manner. This means that the probability of all the samples being simultaneously below a given level is much less than the probability of any individual sample being below that level. Thus, a signal composed of a suitable combination of various samples will have much less severe fading properties than any individual sample alone.
In this section we analyze the performance when there is a single antenna in the receive array. The simulations were carried with different varying parameters. First, we perform the simulations based on varying receiver height. If the receiver height is low, there is a possibility that it may suffer from deep fades due to dense environment surrounding the receiver hence degrading the performance of the system.
On the other hand, if the receiver is mounted on a higher ground, it will be less susceptible to fading and hence will collect the signal more efficiently. Figure 4 a shows the variations in the BER as the height of the receiver is increased from 2 meters to 10 meters. It can be seen that the receivers closer to ground have higher BER whereas as the height of the receiver is raised from the ground, the BER improves.
SNR with varying receiver height, H R m. Figure 4 b shows the BER when the maximum multipath delay is varied. It can be explained in terms of the geometry of the ellipse. Larger ellipse means increase in the propagation delays, hence poorer performance. Smaller ellipse means lesser propagation delays, hence better performance.
Figure 4 c shows the BER performance of the model as a function of SNR under different values of transmission power based on numerical simulation. However, the performance of the system increases with increase in transmission power. It is evident that the performance of the system varies with variation in transmission power. As seen from the table, MRC gives the best performance, thus, for our further simulations we have focused on the system model with MRC at the receiver only and the implementation of EGC and SC is straight forward.
Figure 5 a shows that the performance of the system increase with receiver height irrespective of the number of the receive antenna elements. The simulations have been performed with number of receive antennas up to four but it is not limited and can be extended for higher numbers of receive antennas. The BER values for multiple receive antennas at different receiver height with different maximum multipath delay have been summarized in Table 3.
We analyze the problem from the overall performance of the system. The model presented in this paper has been developed for a microcell environment which has a quasi-static channel. A cluster based WSN architecture has been assumed at the transmission side. The cluster head is assumed to be surrounded by local scatterers giving rise to multipath and fading. At the receiver, receiving arrays are used to collect all the multipath components of the signal effectively.
The advantage of using smart antennas in a cluster based WSN model has been demonstrated where performance improvements can be realized in terms of received SNR. The numerical simulations based on the variations in receiver height reveal that the performance of the system increases if the receiver height is increased above ground level. Also the numerical simulations based on maximum multipath delay shows that the semi-major and semi-minor axis of the ellipse changes with variations in the maximum multipath delay, hence affecting the performance of the overall system.
The performance of the system is also improved as the transmission power increases. Since the cluster head is located very near to the sensor nodes, the sensor nodes do not require high transmission powers so they do not face the reachback problem.
The paper justifies the use of receive diversity at the receiver for reliable communication between the cluster head and the receiving arrays and proves that MRC provides the best performance when applying receive diversity. We also quantify the fact that with the increase in the number of antenna elements, we are able to increase the reliability and robustness of the system.
The number of antenna elements has been kept low while solving our problem. However, they can be extended to higher number of receive antennas for a large receiving array. National Center for Biotechnology Information , U. Journal List Sensors Basel v. Sensors Basel.
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