Abstract
In this paper, we propose an optimum transmit structure for spatial modulation (SM), a unique single-stream multiple-input multiple-output (MIMO) transmission technique. As a three-dimensional modulation scheme, SM enables a trade-off between the size of the spatial constellation diagram and the size of the signal constellation diagram. Based on this fact, the novel method, named transmission optimized spatial modulation (TOSM), selects the best transmit structure that minimizes the average bit error probability (ABEP). Unlike the traditional antenna selection methods, the proposed method relies on statistical channel state information (CSI) instead of instant CSI, and feedback is only needed for the optimal number of transmit antennas. The overhead for this, however, is negligible. In addition, TOSM has low computational complexity as the optimization problem is solved through a simple closed-form objective function with a single variable. Simulation results show that TOSM significantly improves the performance of SM at various channel correlations. Assuming Rayleigh fading channels, TOSM outperforms the original SM by up to 9 dB. Moreover, we propose a single radio-frequency (RF) chain base station (BS) based on TOSM, which achieves low hardware complexity and high energy efficiency. In comparison with multi-stream MIMO schemes, TOSM offers an energy saving of at least 56% in the continuous transmission mode, and 62% in the discontinuous transmission mode.
Highlights
T HE need to curtail the carbon footprint and the operation cost of wireless networks requires an overall energy reduction of base stations (BSs) in the region of two to three orders of magnitude [3]
The context is arranged in four portions: i) an average bit error probability (ABEP) upper bound is introduced for spatial modulation (SM) over generalized fading channels; ii) the ABEP upper bound is simplified to suit the minimization on the subject of either M or N ; iii) the optimum (M, N ) is obtained by solving the minimization problem; and iv) the required number of transmit antennas are selected from the antenna array
The reason for choosing the second case is threefold: i) multipath fading is typically modeled by a Rayleigh distribution; ii) by fixing the parameter m, the main trends of transmission optimized spatial modulation (TOSM) in relation to the channel correlation can be studied; and iii) a look-up table is formed within this scenario to exhibit the optimum transmit structure
Summary
T HE need to curtail the carbon footprint and the operation cost of wireless networks requires an overall energy reduction of base stations (BSs) in the region of two to three orders of magnitude [3]. Compared with our preceding studies in [1] and [2], the contributions in this paper are four-fold: i) a two-stage optimization method is proposed to balance the spatial modulation order with the signal modulation order in SM systems; ii) a complete derivation of a simplified ABEP bound for SM over generalized fading channels is presented; iii) a direct antenna selection method based on circle packing is proposed; and iv) the energy efficiency of TOSM in terms of the BS energy consumption is evaluated for both the continuous mode and the DTX mode.
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