Abstract
Signal space diversity (SSD) is a technique to obtain diversity without loss in spectral efficiency. Despite this, SSD has been minimally studied in multiuser scenarios. In this paper, SSD is operated in the uplink of orthogonal frequency division multiple access (OFDMA) cellular systems that exploit frequency diversity, use the optimum maximum-likelihood detector (MLD) and employ antenna arrays at the receivers. Thus, a multiuser multiple-input-multiple-output (MU-MIMO) system that works in presence of own-cell and co-cell interference (CCI) is taken into account. In order to diminish CCI, fractional frequency reuse (FFR) is used in the cellular system. For a feasible MLD implementation, a matrix structure of the received signals is obtained in order to use the sphere decoder algorithm. An exact closed-form expression to calculate the pairwise error probability between two multidimensional symbols is derived. From this, a bit error rate (BER) upper bound is found for single user scenarios. This BER expression is an accurate lower bound for high diversity orders in multiuser scenarios. The BER asymptotic analysis shows that our approach maintains the SSD multidimensional diversity, the spatial diversity of MIMO and the frequency diversity. This allows to overload the system by minimizing the BER and increasing the spectral efficiency, simultaneously.
Highlights
Signal space diversity (SSD) is a technique proposed in [1] to obtain diversity without loss in spectral efficiency
The results show that SSD yields a noteworthy improvement on the bit error rate (BER) with just a low increase in complexity
We focus on finding the matrix structure of the received samples for scenarios where U > 1 users are transmitting simultaneously in the same group of G subcarriers
Summary
Signal space diversity (SSD) is a technique proposed in [1] to obtain diversity without loss in spectral efficiency. As TAS is employed, it is not produced interference in the reception, as consequence, maximal ratio combining is employed in the receiver With this technique and by considering correlated receive antennas, the authors obtain an expression to evaluate the PEP. Perfect channel state information (CSI) at the receiver is assumed motivated by the fact that previous works have considered this scenario and have not been able to find exact expressions to evaluate the SSD performance. Another aim of this work is to find exact expressions to evaluate this kind of technique.
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