A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Hardware Implementation of SM <s> In this paper, we seek to characterize the performance of spatial modulation (SM) and spatial multiplexing (SMX) with an experimental testbed. Two National Instruments (NI) PXIe devices are used for the system testing: one for the transmitter and one for the receiver. The digital signal processing (DSP) that formats the information data in preparation for transmission is described, along with the DSP that recovers the information data. In addition, the hardware limitations of the system are also analyzed. The average bit-error ratio (ABER) of the system is validated through both theoretical analysis and simulation results for SM and SMX under the line-of-sight (LoS) channel conditions. <s> BIB001 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Hardware Implementation of SM <s> In this paper, we research the multiuser detection (MUD) in a new Spatial Modulation Multiple-Input-Multiple-Output (SM-MIMO) system, whose Base Station (BS) is equipped with massive Radio-Frequency (RF) chains with low-resolution Analog-to-Digital Convertors (ADCs), and the User Equipments (UEs) have multiple Transmit Antennas (TAs) but single RF chain. In the uplink, UEs transmit their data by the Cyclic-Prefix Single-Carrier (CP-SC) SM technique. The key is how to design practical MU detectors to handle the severely quantized measurements and antenna correlations. Coherent detection is focused, so a Least-Square (LS) channel estimator is designed to acquire the the channel side information (CSI) at the Receiver (CSIR). Then, we firstly solve the MUD problem by the Sum-Product-Algorithm (SPA) on a clustered factor graph (FG) whose variable nodes correspond to the transmitted vectors from the UEs. Next, based on the Central Limit Theorem (CLT) and Taylor expansions, the SPA detector (SPAD) is simplified as a new low-complexity Message Passing De-Quantization Detector (MPDQD), which exploits both the structured sparsity and prior probability distribution of the transmitted signal. By utilizing the clustering technique, damping mechanism, and Analog Spatial Filtering (ASF), the robustness of MPDQD is improved significantly. Simulation results show that MPDQD outperforms the linear detectors, works steadily under strong channel correlations, and even performs similarly as its counterpart in the un-quantized SM-MIMO. <s> BIB002 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Hardware Implementation of SM <s> Spatial modulation (SM) is an emerging technology that reduces hardware complexity, power consumption, interchannel interference, and antenna synchronization problems of multiple-input multiple-output (MIMO) communications. However, SM depends on continuous antenna transitions that rely on RF antenna switches, which consume considerable time. Because of this, the data rates of SM schemes face a cap and are bound to certain limitations and the effective SM transmission is much less than the nominal value. In this letter, we study the impact of switching time on SM and develop expressions for the effective transmission rate, effective capacity, and spectral efficiency. An upper bound on the switching time is derived such that SM sustains capacity superiority in comparison with SIMO systems. <s> BIB003 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Hardware Implementation of SM <s> In this work, the performance of spatial modulation (SM) for multiple-input multiple output (MIMO) underlay cognitive radio systems is studied under the effect of channel and hardware impairments. Specifically, a closed-form expression of the average pairwise error probability (APEP), an asymptotic APEP, and a tight upper bound of the average bit error rate (ABER) are derived for Rayleigh fading channels. Useful remarks are highlighted on the system diversity and on the impact of channel and hardware impairments. Numerical results, which are corroborated through simulations, show that the ABER performance saturates to a constant value in the high power region due to the effects of channel and hardware impairments. <s> BIB004 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Hardware Implementation of SM <s> Space modulation techniques (SMTs), in which some or all of the data bits modulate a block of spatial constellation symbol, are promising candidates for future 5G wireless systems. They promise data rate enhancements while maintaining low energy consumption, hardware cost, and computational complexity. As such, they attracted significant research interest in the past few years. One of the major assets of SMTs is the assumption that they can operate with a single RF chain at the transmitter even though multiple antennas might be activated at one time instant. Thus far, this claim is anticipated in several research articles but the transmitter designs of the different SMTs with a single RF chain are not addressed yet in the literature. SMTs include different system configurations, such as spatial modulation, space shift keying, quadrature spatial modulation, and quadrature space shift keying. The required hardware components to implement a transmitter for each of these systems with the minimum number of RF-chains are discussed in this paper. In addition, hardware limitations and the impact of different hardware blocks on the overall system performance are discussed. Besides, a comparison among different schemes along with conventional spatial multiplexing algorithm in terms of power consumption, hardware cost, probability of error, and receiver computational complexity is presented. It is shown that some of these techniques can operate without any RF-chain while a single-RF chain is sufficient for other systems. Moreover, these schemes can be traded off in terms of energy savings, complexity, performance, and cost. <s> BIB005 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Hardware Implementation of SM <s> We analyze the bit error rate performance of spatial modulation (SM)-based direct-conversion transceivers under transmit in-phase/quadrature (I/Q) imbalance. To investigate the impact of transmit I/Q imbalance on SM, we derive the signal-to-noise ratio loss due to I/Q imbalance impact compared with an ideal direct-conversion transceiver with no I/Q imbalance. Our analysis unveils the robustness of SM to transmit I/Q imbalance compared with conventional single-input multi-output transmissions, by relying more on the spatial domain. <s> BIB006 </s> A Survey on Spatial Modulation in Emerging Wireless Systems: Research Progresses and Applications <s> C. Hardware Implementation of SM <s> This paper investigates the performance of spatial modulation for multiple-input multiple-output underlay spectrum-sharing systems in the presence of three practical deleterious effects: 1) transceiver hardware impairments, 2) outdated channel state information (CSI), and 3) imperfect CSI. In particular, for Rayleigh fading channels, a closed-form expression of the average pairwise error probability and a tight upper bound of the average bit error rate (ABER) are derived. In addition, asymptotic and yet simple approximate expressions are obtained, and consequently insightful discussions are manifested on the impacts of channel and hardware imperfections and on the diversity order. Moreover, explicit exact and approximate expressions for the Cramer–Rao bound are computed for assessing the channel estimation accuracy. Numerical results, which are validated through simulations, show that nonzero bounds of the ABER occur in the high power domain because of the effects of channel and hardware impairments. <s> BIB007
It is worth pointing out that most research works on SM make the impractical assumption of ideal hardware at the transceiver. Therefore, practical implementation of the SM family is an important and challenging research direction, since the channel estimation, transceiver movement, and hardware impairments due to phase noise, I/Q imbalance, and nonlinearity of the amplifier can have negative effects on the system performance. The first attempt on the hardware implementation and experimental assessment of the SM principle is reported in BIB001 , where the testbed platform with two National Instruments (NI) PXIe devices is designed to verify the experimental performance of SM under the indoor propagation environment characterized by LoS wireless channels. In particular, the implementation and applicability of SM has been first approved, which reveals the impact of various hardware impairments at the transceiver, e.g., imperfect channel estimation, spatial correlation, and I/Q imbalance. On the other hand, it is preferable to use low-resolution analog-to-digital converters (ADCs) with few-bits quantization at the user terminal to achieve a much lower power consumption and reduce hardware cost significantly. In BIB002 , the multiuser detection problem of the SM system is investigated for the large-scale MIMO implementation employing low-resolution ADCs. It is shown that the SM system developed in BIB002 is robust to quantization error and channel correlation, and the proposed low-complexity detector achieves better performance than its linear counterparts. Noted that the antenna-switcher incurs time delays and is not cost-free, BIB003 studies the impact and limitation of the antenna-switching time for SM, in which the spectral efficiency and achievable rate are analyzed under the practical hardware constraint of antenna-switching. In BIB004 and BIB007 , the performance of SM based cognitive radio communications is investigated under the consideration of channel estimation error and hardware imperfections, where some theoretical results are derived for Rayleigh fading channels. The hardware requirements and limitations of various SM members are discussed in BIB005 , which shows that hardware impairments have a significant influence on practical performance. After developing an analytical framework under the transmit I/Q imbalance for SM, the authors of BIB006 show the robustness of SM to the I/Q imbalance. In  , a practical hardware implementation of the SM detector is realized by using 87.4-K logic gates in the 0.18-μm CMOS technology, which adopts the signal-vector-based list detection and dualdata-path architecture to achieve low hardware complexity and near-optimal performance. Furthermore, hardware realization of the ML detection is implemented with 70.5-K gates under the TSMC 90-nm CMOS technology in  , where the Givens rotation is applied to achieve stable division operation and low-complexity implementation.