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Image Processing
Quasicoherent Reception
Multipath Reception
Smart Antenna Forward Link or Smart Antenna Reverse Link
Multi Antenna Reception and Transmission
Optimal balance of info & pilot signal components
Power and Data Rate Transmission Control
Multi-User Detection
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Smart Antenna Forward Channel | Smart Antenna Reverse Channel

Smart Antenna Forward Channel

There are developed smart antenna operation algorithms in the forward channel of cellular communication system that are efficient both in the absence and presence of power-ful interferences. The first algorithm is intended for relatively small (less 300) values of angle spread of user signals, the second algorithm – at arbitrary including great values (more 90°) of a signal angle spread. Moreover the second algorithm is developed for the case when a general pilot signal is transmitted from one of antenna array elements, and the information signal is transmitted to each user from all antenna array elements. In this case propagation channels for informational and pilot signals are different.

The algorithms operate just by MS signals and include the original estimation of the angel of arrival, and for the second algorithm they include the signal angle spread. Here it is impossible to use conventional methods of estimating the angle of arrival as it can result in substantial errors due to the presence of powerful interferences (high-rate mobile users). In this case the estimation of the direction of arrival can be mistakenly in favor of the direction to interferences.

There is performed an imitation simulation of the developed and alternative algo-rithms. From the simulation results follows that the developed algorithms operate quite effi-cient in the absence and presence of powerful interferences both at small and great values of angle spread of a desired signal. Errors of the proposed algorithm of estimating angle of arri-val are not great. From the simulation results of different interference-signal configurations follows that energetically losses of the first algorithm are small (less 0.4dB). Besides no blunder is found
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Figure. 1, Figure. 2 show the computer simulation results of the described procedure of forming AAA beam for the second algorithm. Figure. 1, a and Figure. 2, a present beams of the forward channel at different values of angle of arrival, , and signal angle spread, . It is evident that the beam width necessary to provide phase coherence between pilot signal and information signal considerably narrower than an angle spread of rereflectors.

Figure. 1, b and Figure. 2, b illustrate dependences of bit error rate probabilities versus SNR. Two other methods of information signal transmission are simulated in order to compare. In the first method the information signal is transmitted from one antenna array element (from which pi-lot signal is transmitted) –. . For the second method the information signal is transmitted from all antenna array elements, moreover amplitude coefficients are equal to each other - .

The analysis of characteristics confirms that in the proposed AAA beam forming algo-rithm a sufficient degree of phase coherence is provided between information and pilot sig-nals. The proposed algorithm has shown a high efficiency and in general case provided a considerable gain as compared with alternative transmission methods due to the flexible con-trol of the beam width.



 

Smart Antenna (Reverse Channel)


The use of the adaptive antenna array (AAA) at base stations of contemporary cellular communication systems is a promising method of improving communication systems parameters, in particular, increasing its capacity, increasing service zone, and so forth. In this connection 3G and 4G cellular communication systems provides the utilization of AAA at base stations.
For some cellular communication systems (for example, 3GPP2) the contribution of different user signals to multi-user interference is different. Besides a great number of low-rate voice users can contain users performing a high-rate data transmission. Signal power of the latter at a base station can be in tens times higher than signal powers of low-rate users. Therefore signals of high-rate users are powerful interferences for signals of low-rate users.
There is developed a smart antenna operation algorithm in the reverse channel of cellular communication system taking into account the possibility of interference presence. The proposed algorithm includes the generation of cost function and maximization of this function in space of weight vectors using the iterative method. In this case the values of weight coefficients is set so that to provide the best reception conditions of a desired signal under changeable interference-signal conditions. The maximum position of used cost function coincides with the maximum position of a signal-(interference+noise) ratio. The adaptation of weight coefficients by the cost function maximum is performed successively at arbitrary low level of noises and interferences.
There are researched different methods of weight coefficients adaptation: a simplex method, coordinatewise descent method, gradient method, and the fastest descent method while using the modified cost function.
Computer simulation results of the developed (Max SINR) and alternative algorithms (MRC, Switching beam, LMS, MMSE, and so on) for a great number of interfere-signal configurations indicates that the proposed algorithm practically always provides the gain in characteristics as compared with alternative algorithms, except for MMSE algorithm. Figure. 1,b and Figure. 2,b show, as an example, dependences of bit error rate probability versus SNR for developed and several alternative algorithms of smart antenna operation for two interference-signal configurations presented in Figure. 1,a and Figure. 2,а.
This gain substantially depends on a number and position of high-rate interferences and can reach considerable values. For separate configurations all alternative algorithms (except MMSE) become non-operable, whereas the proposed algorithm operates satisfactorily, flexibly controlling the beam of the antenna array depending on the interference position and performing their efficient canceling. As for the comparison with a bit faster and more complicated in implementation MMSE algorithm, then in some interference-signal configurations the proposed algorithm is bit more efficient, in other configurations - MMSE algorithm.

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| About Us | Image Processing | Quasicoherent Reception |
| Multipath Reception | Smart Antenna Forward Link |
| Smart Antenna Reverse Link | Multi Antenna Reception and Transmission |
| Optimal balance of info & pilot signal components |
| Power and Data Rate Transmission Control | Multi-User Detection | Contact |