Dataset for Hybrid beamforming in mm-wave MIMO systems having a finite input alphabet

Recently, there has been significant research effort towards achieving high data rates in the millimeter wave bands by employing large antenna systems. These systems are considered to have only a fraction of the RF chains compared to the total number of antennas and employ analog phase shifters to steer the transmit and receive beams in addition to the conventional beamforming/combining invoked in the baseband domain. This scheme, which is popularly known as hybrid beamforming, has been extensively studied in the literature. To the best of our knowledge, all the existing schemes focus on obtaining the beamforming/combining matrices that maximize the system capacity computed using a Gaussian input alphabet. However, this choice of matrices may be suboptimal for practical systems, since they employ a finite input alphabet, such as QAM/PSK constellations. Hence, in this paper, we consider a hybrid beamforming/combining system operating with a finite input alphabet and optimize the analog as well as digital beamforming/combining matrices by maximizing the mutual information (MI). This is achieved by an iterative gradient ascent algorithm that exploits the relationship between the minimum mean-squared error and the MI. Furthermore, an iterative algorithm is proposed for designing a codebook for the analog and digital beamforming/combining matrices based on a vector quantization approach. Our simulation results demonstrate that the proposed gradient ascent algorithm achieves an ergodic rate improvement of up to 0.4 bits per channel use (bpcu) compared to the Gaussian input scenario. Furthermore, the gain in the ergodic rate achieved by employing the vector quantization based codebook is about 0.5 bpcu compared to the Gaussian input scenario.</span

Dataset for Iterative matrix decomposition aided block diagonalization for mm-Wave multiuser MIMO systems

Considering the dearth for spectrum in the congested microwave band, the next generation of cellular communication systems is envisaged to incorporate part of the millimeter wave (mm-wave) band. Hence recently, there has been a significant interest in beamforming aided mm-wave systems. We consider a downlink multiuser mm-wave system employing a large number of antennas combined with a fewer radio frequency (RF) chains both at the base station (BS) and at each of the user equipment (UE). The BS and each of the UE is assumed to have a hybrid beamforming architecture, where a set of analog phase shifters is followed by digital precoding/combining blocks. In this paper, 1) we propose an iterative matrix decomposition based hybrid beamforming (IMD-HBF) scheme for a singleuser scenario, which accurately approximates the unconstrained beamforming solution, 2) we show that the knowledge of the angle of departure (AoD) of the various channel paths is sufficient for the block diagonalization (BD) of the downlink mm-wave channel and hence for achieving interference free channels for each of the UEs, 3) we propose a novel subspace projection based AoD aided BD (SP-AoD-BD) that achieves significantly better performance than the conventional BD, while still only requiring the knowledge of the AoD of various channel paths, 4) we use IMD-HBF in order to employ SP-AoD-BD in the hybrid beamforming architecture and study its performance with respect to the unconstrained system. We demonstrate using simulation results that the proposed IMD-HBF gives the same spectral efficiency as that of the unconstrained system in the single user scenario. Furthermore, we study the achievable sum rate of the users, when employing SP-AoD-BD with the aid of IMD-HBF and show that the loss in the performance with respect to the unconstrained system as well as the existing schemes is negligible, provided that the number of users is not excessive. This dataset accompanies the publication: Rajashekar, Rakshith and Hanzo, Lajos (2016) Iterative matrix decomposition aided block diagonalization for mm-Wave multiuser MIMO systems. IEEE Transactions on Wireless Communications (doi:10.1109/TWC.2016.2628357).</span

Dataset for User Selection Algorithms for Block Diagonalization Aided Multiuser Downlink mm-Wave Communication

In order to meet the ever increasing datarate demands, the next generation of wireless communication systems is being designed for exploiting the large amounts of unused spectrum in the millimeter (mm) wave band. Since operating at mm-wave frequencies imposes several challenges, such as high path loss, as well as both spatial and temporal channel sparsity, there is a significant research interest focused on designing feasible solutions for establishing reliable and high-throughput links at mm-wave frequencies. In this paper, we consider a cellular system relying on hybrid beamforming aided basestation (BS) as well as user equipment and study the user selection problem, which has not been hitherto studied in the literature. More specifically, we study the problem of selecting $K^\prime$ users by the BS for communication out of $K$ users whilst ensuring that the sum rate is maximized. Specifically, we propose a user selection algorithm, which relies on the knowledge of both the channel gains and of the angle-of-departure (AoD) of the channel paths spanning to the various users, which is termed as the AoD aided user selection (AoD-US). Furthermore, we devise a pair of subspace metrics based on a) the angle between the subspaces spanned by the BS array response vectors; b) the ratio of interference and of the signal space dimensions of various users, in order to reduce the user search space in AoD-US. This modified user selection algorithm is termed as the AoD aided user selection with user set pruning (AoD-US-P). Furthermore, we study the attainable sum-rate performance of the block-diagonalization (BD) aided downlink and show that the proposed selection algorithms guarantee both multiuser diversity and multiplexing gains. Additionally, the proposed algorithms are studied in the round-robin (RR) scheduling scenario, where all the $K$ users are scheduled for achieving fairness. Our simulation results revealed that the AoD-US-P achieves nearly the same performance as that achieved by the AoD-US despite having a small user set, while both are observed to outperform the channel power based selection scheme.</span

Reduced-complexity ML detection and capacity-optimized training for spatial modulation systems

Spatial Modulation (SM) is a recently developed low-complexity Multiple-Input Multiple-Output scheme that jointly uses antenna indices and a conventional signal set to convey information. It has been shown that the Maximum-Likelihood (ML) detector of an SM system involves joint detection of the transmit antenna index and of the transmitted symbol, hence, the ML search complexity grows linearly with the number of transmit antennas and the size of the signal set. To circumvent the problem, we show that the ML search complexity of an SM system may be rendered independent of the constellation size, provided that the signal set employed is a square- or a rectangular-QAM. Furthermore, we derive bounds for the capacity of the SM system and derive the optimal power allocation between the data and the training sequences by maximizing the worst-case capacity bound of the SM system operating with imperfect channel state information. We show, with the aid of our simulation results, that the proposed detector is ML-optimal, despite its lowest complexity amongst the existing detectors. Furthermore, we show that employing the proposed optimal power allocation provides a substantial gain in terms of the SM system's capacity as well as signal-to-noise ratio compared to its equal-power-allocation counterpart. Finally, we compare the performance of the SM system to that of the conventional Multiple-Input Multiple-Output (MIMO) system and show that the SM system is capable of outperforming the conventional MIMO system by a significant margin, when both the systems are employing optimal power splitting

Transmit antenna subset selection for single and multiuser spatial modulation systems operating in frequency selective channels

Transmit antenna (TA) subset selection (TAS) is a well known multiple-input multiple-output technique that exploits the channel state information (CSI) at the transmitter in order to improve the attainable bit error rate (BER) performance. The extensive study of TAS in the context of spatial modulation (SM) has recently revealed that a significant performance gains are attainable compared to SM systems without TAS. However, the existing TAS techniques conceived for SM were studied by considering a frequency-flat channel, which does not represent the practical channels which are frequency-selective. In this paper, we address this hitherto-not-addressed problem by studying the TAS schemes for zero-padded single-carrier (ZP-SC) SM systems. Specifically, we employ the partial interference cancellation receiver with SIC in order to convert the frequency-selective channel into parallel sub-channels and invoke Euclidean distance based antenna subset selection (EDAS) over each of the sub-channels. This SIC aided TAS algorithm is termed as SIC-TAS. Furthermore, we show using theoretical analysis that the parallel sub-channels thus obtained are nearly identical, which enables us to employ a majority logic to obtain a single TA subset to be used in all the sub-channels. The majority logic based TAS scheme (MAJ-TAS) reduces the feedback overhead to that of frequency-flat scenario as it requires a single TA subset to be used over all the sub-channels. Furthermore, the computational burden of MAJ-TAS is further reduced by restricting the number of sub-channels over which the EDAS is invoked. This reduced complexity TAS scheme is termed as $L$-MAJ-TAS scheme, where $L$ represents the number of sub-channels over which the EDAS is invoked. Furthermore, the proposed TAS schemes are extended to the multi-user scenario. All the theoretical insights are validated using simulation results. Furthermore, it is observed through numerical simulations that the proposed TAS schemes provide a significant BER performance improvement when compared to the systems without TAS. Specifically, a signal-to-noise ratio (SNR) gain as high as 3dB is observed in single user scenario and of about 1dB in case of two-user scenario while employing TAS

Dateset for Transmit Antenna Subset Selection in Spatial Modulation Relying on a Realistic Error-Infested Feedback Channel

Dataset supports: Mysore Rajashekar, R., Hari, K. V. S., &amp; Hanzo, L. (2017). Transmit Antenna Subset Selection in Spatial Modulation Relying on a Realistic Error-Infested Feedback Channel. IEEE Access. In this paper, we study the performance of spatial modulation (SM) employing Euclidean distance based antenna selection (EDAS) operating in a realistic error-infested feedback channel, which has hitherto only been studied under ideal feedback channel conditions. Specifically, we model the feedback channel by a bit-flip probability $\delta$ and study its impact on the forward link employing EDAS. We show that the erroneous feedback channel severely degrades the performance of EDAS-aided SM (EDAS-SM) system by imposing an error floor in the forward link. Furthermore, we quantify the error floors associated both with the spatial and with the conventional symbols with the aid of asymptotic symbol error rate analysis. The expressions derived for the error floors in the forward link are utilised for optimizing the feedback signalling, which are shown to help reduce the error floor levels. Furthermore, a pilot-aided selection verification (PSV) algorithm is proposed for mitigating the effects of antenna-set mismatch between the transmitter and the receiver, which eliminates the error floor in the forward link. Simulations are conducted in order to validate the theoretical results presented in the paper. Furthermore, the bit-error ratio (BER) performance of the EDAS-SM is compared to that of the conventional antenna selection (C-AS) both in the PSV as well as in the no selection verification scenarios. It is observed that EDAS-SM outperforms C-AS in both the scenarios considered. Specifically, at a BER of $10^{-5}$, EDAS-SM is observed to give a 3dB signal-to-noise ratio gain compared to the C-AS, when operating at a spectral efficiency of 7 bits per channel use in the face of a feedback BER of $\delta=0.05$.</span

Data set for Transmit Antenna Subset Selection for Single and Multiuser Spatial Modulation Systems Operating in Frequency Selective Channels

Dataset supports: R. Rajashekar, K. V. S. Hari, &amp; L. Hanzo, (2018). Transmit Antenna Subset Selection for Single and Multiuser Spatial Modulation Systems Operating in Frequency Selective Channels. IEEE Transactions on Vehicular Technology. </span

Data set for Transmit Antenna Subset Selection in Generalised Spatial Modulation Systems

Dataset supports: Mysore Rajashekar, R. et al (2018). Transmit Antenna Subset Selection in Generalised Spatial Modulation Systems. IEEE Transactions on Vehicular Technology.The existing literature on transmit antenna selection (TAS) aided spatial modulation (SM) systems extensively deals with the Euclidean distance (ED) based TAS owing to its high transmit diversity gain. In this paper, we consider the ED-TAS aided generalized spatial modulation (GSM) system that transmits multiple symbols in each channel use and characterise its attainable diversity gain. Secondly, we show that the minimum ED of the receive constellation does not grow beyond a certain point when the size of the signal set is sufficiently large, which facilitates low-complexity implementations of the ED-TAS aided SM system. Our numerical studies revealed that a signal-to-noise gain of about 8 dB is achievable by employing ED-TAS in the GSM system compared to its counterpart dispensing with ED-TAS.</span

Transmit antenna subset selection in generalised spatial modulation systems

The existing literature on transmit antenna selection (TAS) aided spatial modulation (SM) systems extensively deals with the Euclidean distance (ED) based TAS owing to its high transmit diversity gain. In this paper, we consider the ED-TAS aided generalized spatial modulation (GSM) system that transmits multiple symbols in each channel use and characterise its attainable diversity gain. Secondly, we show that the minimum ED of the receive constellation does not grow beyond a certain point when the size of the signal set is sufficiently large, which facilitates low-complexity implementations of the ED-TAS aided SM system. Our numerical studies revealed that a signal-to-noise gain of about 8 dB is achievable by employing ED-TAS in the GSM system compared to its counterpart dispensing with ED-TAS

Data set for A Beamforming Aided Full-Diversity Scheme for Low-Altitude Air-to-Ground Communication Systems Operating with Limited Feedback

Unmanned aerial vehicles (UAV) have gained significant popularity in the recent past owing to their easy deployability and wide range of applications. In most of the short and medium range applications, WiFi is used as the access technology for establishing communication between the ground stations and the UAVs. Although WiFi is known to perform well in most of the scenarios, it is important to note that WiFi has been mainly designed for indoor communication in rich scattering environments, whereas the air-to-ground (A2G) channel is characterised by sparse scattering. Considering this important difference in the channel characteristics, we revisit some of the WiFi features and propose efficient design alternatives. Firstly, we provide a statistical model for the sparse A2G channel and design an optimal time-domain quantizer (TDQ) for its feedback. In contrast to the frequency-domain quantizer (FDQ) of 802.11n/ac standard, the proposed TDQ exploits the time-domain sparsity in the channel and requires about fifteen times lesser quantization bits than FDQ. Secondly, we propose a beamforming scheme with the aid of full-diversity rotation (FDR) matrices and analytically evaluate its symbol error probability in order to quantify the attainable diversity order. Our numerical simulations demonstrate that the proposed FDR beamforming (FDR-BF) scheme outperforms the relevant benchmark schemes in both coded as well as uncoded scenarios. Specifically, the proposed FDR-BF scheme was observed to attain a signal-to-noise ratio gain as high as 6dB compared to the popular geometric mean decomposition based beamforming scheme, when operating at an elevation angle of $7.5^o$.</span