In this letter, we investigate enhanced spatial modulation (ESM) aided orthogonal frequency division multiplexing (OFDM) systems. ESM extends the conventional SM by introducing a series of signal constellations. Existing research shows that ESM displays performance superiority over SM in flat-fading channels. For frequency-selective fading channels, we design a practical implementation of an ESM&SM aided OFDM hybrid system to characterize the bit error rate (BER) performance of ESM and conventional SM with an experimental wireless testbed. Form the experimental results, it is found that ESM achieves better BER performance than SM on frequency-selective channels, which are consistent with the Monte Carlo simulation results. Index Terms-Bit error rate (BER), enhanced spatial modulation (ESM), multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM), wireless testbed. I. INTRODUCTION M ULTIPLE-INPUT multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) [1] is a key enabling technique for modern high-rate communications. However, due to the use of multiple-antenna and multiplecarrier, current MIMO-OFDM suffers from several problems, such as the inter-channel interference (ICI), the inter-antenna interference (IAI), the need for multiple radio frequency (RF) chains [2], and the high peak-to-average power ratio (PAPR) of the transmitted signals. These problems result in extra complexity or power burden to MIMO-OFDM system design. Recently, spatial modulation-OFDM (SM-OFDM) has been proposed to address some of the above mentioned problems pertinent to MIMO-OFDM. The main idea of SM-OFDM is that at each channel use only one single transmit antenna (TA) activates its subcarrier for data transmission. The sparsity of the transmit vectors in frequency domain helps lower the PAPR, reduce the ICI, and allow a low-complexity receiver [2]-[4]. To date, some intensive studies have been conducted on SM-OFDM [5]-[7]. To be specific, [5] studied the average bit error rate (BER) performance of SM-OFDM with the socalled N-continuous (NC) precoder under perfect and imperfect channel estimations. [6] proposed a detection scheme for SM-OFDM which can effectively mitigate the effect of
This paper aims to improve the error rate performance of the enhanced spatial modulation based orthogonal frequency division multiplexing (ESM-OFDM) systems by jointly optimizing the signal constellation and the antenna power allocation (PA). We derive the closed form of the optimal PA of ESM-OFDM for some practical antenna setups and then implement and verify the system over Universal Software Radio Peripheral (USRP) platform. Both of our Monte Carlo simulation and experimental results show the superiority of ESM-OFDM with the derived optimal PA over the equal-gain case.
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