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Smart Antenna Reverse 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
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
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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