Abbreviations

of the proposed MIMO systems with APM is equivalent to that of the conventional 2 � 1 MIMO system. Hence, diversity gain cannot be obtained even if the number of

Ergodic capacity of MIMO systems with APM technique for various number of orthogonal antenna patterns.

Then we consider the case that the average SNR per antenna pattern or virtual antenna is given as γ. In this case, the coefficients in the matrix D are random variables shown as exp ð Þ jΘ where Θ is a uniform random variable in the interval ½ Þ 0, 2π . The ergodic capacities of the proposed MIMO systems with APM are shown for N<sup>a</sup> ¼ 1, 2, 4, and 8 for N<sup>p</sup> ¼ 16 in Figure 5. In the figure, we also illustrate the capacities of the conventional MIMO systems for 2 � 1, 2 � 2, 2 � 4, and 2 � 8 in terms of the numbers of transmit and receive antennas. As we can see from the figure, the capacities are equivalent to each other between N<sup>a</sup> for APM and the same number of receive antennas for the conventional MIMO. For example, when N<sup>a</sup> ¼ 8, the capacity is the same as that of 2 � 8 MIMO systems. Therefore, when the average SNR per antenna pattern is same as the average SNR per the number of receive antennas, the proposed APM-based MIMO systems with N<sup>a</sup> antenna patterns achieve almost equivalent capacity to the conventional N<sup>t</sup> � N<sup>a</sup> MIMO

In this chapter we propose a concept of APM for MIMO receiver to reduce the antenna size and hardware cost with keeping the availability of diversity gain. We discuss the types of antennas which achieve the APM, i.e., generating time-varying antenna pattern. Also, we discuss the benefits of the antennas, in particular, for ESPAR antenna-based structure. The number of virtual antennas or antenna patterns can be increased with the number of multiplexed orthogonal signals used to change the antenna patterns. A model of receiving process is proposed for analysing the capacity of systems using APM. We derive a model of received signals to analyse the system performance. The received signal in matrix form includes an equivalent channel matrix, which is a product of antenna pattern matrix, the channel coeffi-

When the number of arrival paths and the number of antenna pattern are sufficiently large, the ergodic capacity approaches to that of 2 � 2 MIMO systems.

arrival paths is sufficiently large.

Advances in Array Optimization

Average SNR per antenna pattern is a constant (Nt ¼ 2, Np ¼ 16).

systems.

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Figure 5.

5. Conclusions

cient vector for each output.


Advances in Array Optimization
