Athanasios Stavridis

Energy Evaluation of Spatial Modulation at a Multi-Antenna Base Station

In this paper, we aim to study the Energy Efficiency (EE) of Spatial Modulation (SM) at different Base Stations (BSs) taking into account the total power consumption. Compared to conventional Multiple-Input Multiple-Output (MIMO) schemes, SM benefits from a single Radio Frequency (RF) chain which results in decreased power supply (W), higher EE (Mbits/J), and reduced complexity. Using the fundamental limits of Shannon capacity, we show that SM achieves a range of average data rates with only a fraction, which can be as low as 24% for four transmit antennas, of the total power supply of conventional MIMO. In addition, we demonstrate that the EE of the studied schemes is maximized for a certain average data rate and that SM achieves the highest EE among them. Finally, we note that a BS employing SM can be up to 67% more energy efficient compared to a BS under a conventional MIMO transmission scheme, for four transmit antennas.

An energy saving base station employing spatial modulation

In this paper, we evaluate the energy efficiency of a multi-antenna Base Station (BS) employing Spatial Modulation (SM). Taking advantage of the single Radio Frequency (RF) chain configuration of SM, we show that SM offers a significant total power reduction compared to other multi-RF chain Multiple-Input Multiple-Output (MIMO) architectures. For the same RF transmit power, we demonstrate that the total power saving of SM scales linearly with the number of RF chains required by other MIMO schemes. Furthermore, we clarify that for the same ergodic capacity, SM has a significant advantage in energy efficiency compared to the studied multi-RF chain MIMO configurations. In addition, for a number of transmit antennas larger than two, we establish that SM results in higher ergodic capacity than Space-Time Block-Coding (STBC), combined with significant power saving. For a BS with 8 transmit antenna, the achieved power saving of SM can reach up to almost 90%. Finally, based on simulation results, we demonstrate that the energy efficiency (bits/J) of the studied MIMO schemes exhibits a maximum as function of ergodic capacity, and it is further shown that this maximum is several times higher in SM compared to the studied state-of-the-art MIMO schemes.

Transmit Precoding for Receive Spatial Modulation Using Imperfect Channel Knowledge

In this paper, motivated by the relatively new concept of Spatial Modulation (SM), we are addressing the problem of Receive-Spatial Modulation (R-SM) under two cases of imperfect channel knowledge at the transmitter side. In the first case, we adopt a statistical model for the channel uncertainties, whereas in the second one a worst-case approach is followed and the channel uncertainties are expressed as a bounded set. Based on Zero-Forcing (ZF) precoding and using standard tools from optimization theory, we derive closed form solutions that turn out to be robust. Simulation results show that the proposed schemes have a performance close to the perfect channel knowledge scenario in low and mid-low SNRs. Furthermore, these designs can be applied to wide range of channels with different correlation states combined with a transmit power gain.

A Virtual MIMO Dual-Hop Architecture Based on Hybrid Spatial Modulation

In this paper, we propose a novel Virtual Multiple-Input-Multiple-Output (VMIMO) architecture based on the concept of Spatial Modulation (SM). Using a dual-hop and Decode-and-Forward protocol, we form a distributed system, called Dual-Hop Hybrid SM (DH-HSM). DH-HSM conveys information from a Source Node (SN) to a Destination Node (DN) via multiple Relay Nodes (RNs). The spatial position of the RNs is exploited for transferring information in addition to, or even without, a conventional symbol. In order to increase the performance of our architecture, while keeping the complexity of the RNs and DN low, we employ linear precoding using Channel State Information (CSI) at the SN. In this way, we form a Receive-Spatial Modulation (R-SM) pattern from the SN to the RNs, which is able to employ a centralized coordinated or a distributed uncoordinated detection algorithm at the RNs. In addition, we focus on the SN and propose two regularized linear precoding methods that employ realistic Imperfect Channel State Information at the Transmitter. The power of each precoder is analyzed theoretically. Using the Bit Error Rate (BER) metric, we evaluate our architecture against the following benchmark systems: 1) single relay; 2) best relay selection; 3) distributed Space Time Block Coding (STBC) VMIMO scheme; and 4) the direct communication link. We show that DH-HSM is able to achieve significant Signal-to-Noise Ratio (SNR) gains, which can be as high as 10.5 dB for a very large scale system setup. In order to verify our simulation results, we provide an analytical framework for the evaluation of the Average Bit Error Probability (ABEP).

Performance Analysis of Multistream Receive Spatial Modulation in the MIMO Broadcast Channel

In this paper, Multi-Stream Receive-Spatial Modulation (MSR-SM) for application to the Multiple-Input Multiple-Output (MIMO) broadcast channel is introduced and studied. MSR-SM is a closed-loop transmission scheme, which applies the concept of multistream space modulation at the receiver side. An accurate mathematical framework for the evaluation of the Bit Error Rate (BER) is proposed. In addition, the diversity order and coding gain of the new architecture are derived. Note that the proposed analytical framework takes into account both the small-scale fading and the system topology, and is directly applicable to the conventional MIMO broadcast channel. Compared with the state-of-the-art MIMO transmission in the broadcast channel, it is mathematically shown that MSR-SM achieves the same diversity order and a better coding gain, in the high Signal-to-Noise Ratio (SNR) regime. Finally, the proposed mathematical framework and the new findings are validated via Monte Carlo simulation results.

Multi-user spatial modulation MIMO

Spatial Modulation (SM) is a recently proposed single-RF multiple-input-multiple-output (MIMO) technique, which is capable of outperforming many conventional MIMO transmission schemes with low implementation and computational complexity. Recently, there have been some attempts in understanding the performance of SM in multi-user environments. However, most of the work has been oriented towards uplink multi-access scenarios. Also, conventional downlink/broadcast MIMO precoding techniques such as Zero Forcing (ZF) or Minimum Mean Square Error (MMSE) cannot be used in Multi-User SM (MU-SM), as part of the data in SM is also encoded into the Channel Impulse Responses (CIRs). In this paper, a novel precoding scheme for single-cell downlink MU-SM systems is proposed with a two-fold objective: i) the precoder needs to be able to completely eliminate the Multi-User Interference (MUI) by taking advantage of the Channel State Information (CSI) at the transmitter and ii) it needs to allow the users to use a single-user Maximum Likelihood (ML) optimum detector while achieving the same performance as interference-free point-to-point SM transmission. Finally, we also develop an interference-aware multi-user detection scheme, which does not require any CSI at the transmitter, and compare its performance with that of single-user detection schemes based on precoding.

A power saving dual-hop architecture based on hybrid spatial modulation

In this paper, we propose a novel Dual-Hop Decode-and-Forward (DF) architecture based on Multiple-Input Multiple-Output (MIMO) Zero Forcing (ZF) precoding and Spatial Modulation (SM) that employs a centralized or a distributed detection algorithm at the Relay Nodes (RNs). Using Tikhonov Regularization (TR) we form a precoding technique that turns out to reduce significantly the transmitted power at the Source Node (SN) under certain scenarios. Moreover, the use of TR enables our scheme to communicate in channels with low and medium correlation at the first hop without a Bit Error Rate (BER) penalty. Finally, we extend our scheme in order to take into account realistic Channel State Information (CSI) at the the Source Node (SN).

Distributed Spatially-Modulated Space-Time-Block-Codes

In this paper, a novel energy-efficient protocol, intended for wireless networks with large number of relay nodes, is proposed. The main distinguishable feature of the proposed protocol is that it offers throughput enhancement, by having the same diversity-gain and having to activate the same number of relay nodes at any given time-instance, as the the conventional distributed space-time-block-codes (D-STBC). The proposed protocol applies the recently introduced idea of Spatially-Modulated Space-Time-Block-Codes (SM-STBC) devised for multiple-input-multiple-output (MIMO) systems to cooperative relay networks. The specific contributions of this paper are: i) an error-aware Maximum-Likelihood (ML) demodulator, which is robust to demodulation errors at the relays is developed; ii) a low-complexity error-aware demodulator is also developed; and iii) it is shown, with the help of Monte Carlo simulations, that the proposed protocol outperforms state-of-the-art relaying protocols.

Performance evaluation of space modulation techniques in VLC systems

In this paper, the Bit Error Rate (BER) performance of three major space modulation techniques in a Multiple-Input Multiple-Output (MIMO) Visible Light Communication (VLC) system is studied. The considered space modulation techniques are Optical Spatial Modulation (OSM); Optical Generalized Spatial Modulation (OGeSM); and Optical Multi-Stream Spatial Modulation (OMS-SM). The space modulation techniques are evaluated against two benchmark systems: Optical Spatial MultipleXing (OSMX) and Optical Repetition Coding (ORC). The performance assessment, for both the space modulation schemes and the benchmark systems, is undertaken using simulation and analytical results. For the considered system setup, it is concluded that, in relative low Signal-to-Noise Ratio (SNR), OSM offers the best performance. Whereas, in relative high SNR and for high spectral efficiency, OMS-SM is the most efficient scheme in terms of BER.

On the Asymptotic Performance of Receive Space Modulation in the Shadowing Broadcast Channel

In this letter, the diversity order and the coding gain of Receive Space Modulation (RSM) in the Multiple-Input Multiple-Output (MIMO) broadcast channel are derived by taking into account both small and large scale fading. The considered linear precoding method is Zero Forcing (ZF). Note that the proposed framework is directly applicable to the conventional spatially multiplexed broadcast channel. Based on the derived mathematical framework, a theoretical criterion is provided, which determines the superiority between the deployment of RSM and Spatial MultipleXing (SMX) in the shadowing MIMO broadcast channel. Finally, the provided theoretical results are validated via Monte Carlo simulation results.