Krati Mittal

Bio: Krati Mittal is an academic researcher. The author has contributed to research in topics: MIMO & Channel state information. The author has an hindex of 1, co-authored 3 publications receiving 5 citations.

Channel State Information feedback overhead reduction using Arithmetic coding in massive MIMO systems

Abstract: By the virtue of the large number of antennas, the massive Multiple Input Multiple Output (MIMO) systems grant high spectral efficiency along with the promising gain in capacity. For the optimal detection of system parameters, generally perfect Channel State Information (CSI) is assumed to be known at both transmitter and receiver. However, in practice, due to mobility of communication environment, the impulse response of the channel varies, thus inducing the need of channel estimation. In addition, a permanent feedback signalling is required to notify the estimated CSI at the transmitter. Large number of time slots are engaged during the feedback, thus reducing the bandwidth efficiency of the system. This paper deals with reduction of feedback overhead by using Arithmetic coding for the estimated channel in the massive MIMO systems. Block type pilot estimation technique has been considered for the channel estimation.

Improved signal detection for multiuser MIMO system using BD QR-LRL

Abstract: QR-Least reliable layer (QR-LRL) technique in fusion with the channel block diagonalization (BD) is proposed for signal detection in the multiuser multiple input and multiple output (MU-MIMO) system. Literature survey shows various precoding techniques like BD-ZF, BD-MMSE, dirty paper coding (DPC) to overcome multiuser interference. However, they suffer in the terms of either noise enhancement or complexity or sum rate capacity. It is also shown in the literature that QR-LRL, an ordered successive interference cancellation (OSIC) detector achieves hard/soft ML performance with low complexity for SM-MIMO systems. In this paper, BD and QR-LRL are associated together in order to enhance the signal detection for MU-MIMO system. Simulation results showed that the proposed technique confirms improved detection compared to the conventional methods for multiuser scenario.

EVD-LRL based joint channel estimation and detection for very large MIMO systems

Abstract: This paper introduces a novel joint channel estimation and detection method for very large MIMO system. Conventionally, orthogonal pilot sequences are used to determine correct CSI(channel state information). It falls behind due to pilot contamination and spectral inefficiency in large MIMO systems. Many authors suggested promising approaches of blind and semi blind channel estimation[2][3], which work well with a trade-off for complexity. Author[1] suggested EVD-ILSP based estimation, which results in high spectral efficiency compared to conventional method, However, suffers from high complexity due to ILSP method. Here, the proposed method uses enlarged QR-LRL[5] based ordered Detection jointly with the EVD based estimated channel, which not only results in less complexity but also provides better BER performance compared to conventional EVD-ILSP method. Thus the throughput of large MIMO system is increased with reduced complexity. Simulation results demonstrate remarkable improvement in the performance of proposed method over conventional method.

Investigation of Future 5G-IoT Millimeter-Wave Network Performance at 38 GHz for Urban Microcell Outdoor Environment

Abstract: The advent of fifth-generation (5G) systems and their mechanics have introduced an unconventional frequency spectrum of high bandwidth with most falling under the millimeter wave (mmWave) spectrum. The benefit of adopting these bands of the frequency spectrum is two-fold. First, most of these bands appear to be unutilized and they are free, thus suggesting the absence of interference from other technologies. Second, the availability of a larger bandwidth offers higher data rates for all users, as there are higher numbers of users who are connected in a small geographical area, which is also stated as the Internet of Things (IoT). Nevertheless, high-frequency band poses several challenges in terms of coverage area limitations, signal attenuation, path and penetration losses, as well as scattering. Additionally, mmWave signal bands are susceptible to blockage from buildings and other structures, particularly in higher-density urban areas. Identifying the channel performance at a given frequency is indeed necessary to optimize communication efficiency between the transmitter and receiver. Therefore, this paper investigated the potential ability of mmWave path loss models, such as floating intercept (FI) and close-in (CI), based on real measurements gathered from urban microcell outdoor environments at 38 GHz conducted at the Universiti Teknologi Malaysia (UTM), Kuala Lumpur campus. The measurement data were obtained by using a narrow band mmWave channel sounder equipped with a steerable direction horn antenna. It investigated the potential of the network for outdoor scenarios of line-of-sight (LOS) and non-line-of-sight (NLOS) with both schemes of co- (vertical-vertical) and cross (vertical-horizontal) polarization. The parameters were selected to reflect the performance and the variances with other schemes, such as average users cell throughput, throughput of users that are at cell-edges, fairness index, and spectral efficiency. The outcomes were examined for various antenna configurations as well as at different channel bandwidths to prove the enhancement of overall network performance. This work showed that the CI path loss model predicted greater network performance for the LOS condition, and also estimated significant outcomes for the NLOS environment. The outputs proved that the FI path loss model, particularly for V-V antenna polarization, gave system simulation results that were unsuitable for the NLOS scenario.

On the Efficiency of MIMO Transmission with Channel State Information Feedback

Abstract: A channel state information (CSI) feedback algorithm based on scalar quantization is proposed for a multiple-input multiple-output (MIMO) transmission. The performance of the proposed algorithm is evaluated using the effective transmission rate, which incorporates the effect of the CSI feedback overhead on transmission time. Besides that, the power consumed due to the computational complexity of the CSI feedback algorithm is taken into account together with the transmit power when evaluating the energy efficiency. We compare our proposed algorithm to other typical CSI feedback algorithms under correlated channel conditions. Simulation results show that the proposed algorithm enables practical MIMO transmission to achieve an relative transmission rate at 95% of the ideal rate.

Efficient Lossless Feedback Compression for FDD Massive MIMO

Abstract: Massive MIMO is a promising technique for providing good spectral efficiency. However, the excessive feedback overhead is a major handicap in FDD Massive MIMO system. This paper presents an efficient lossless feedback overhead compression wich can achieve a compression ratio greater than 90% in Massive MIMO. The proposed method is based on the Lempel-ZivWelch (LZW) lossless compression algorithm and its performances are evaluated in several Massive MIMO configurations.

Ergodic Rate Performance in Nonlinear Omnidirectional Coding MIMO-OFDM Systems

Abstract: Omnidirectional coding (OC) is established to improve the spectral efficiency of pilot-assisted multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. But OC also improves the signal peak to average power ratio (PAPR) at the same time. This paper targets on the ergodic rate performance in OC based MIMO-OFDM systems when nonlinear power amplifier (PA) is considered. Using an inter-modulation product (IMP) analysis, the close-form expressions of ergodic rate in OC based nonlinear MIMO-OFDM system are presented. The ergodic rate performance with/without OC in linear and nonlinear systems is investigated as well. The PA behavioural model is extracted based on measurement of a LDMOS PA.

BER and Capacity Improvement for Multiuser MIMO System by MRT Precoding Technique

Abstract: In recent years several of endeavors have been conducted in various papers to improve capacity and bit error rate performance of multiuser MIMO system. Every effort tried to increase gain of the individual stream between base station and users’ antennas while reducing the interference among multiple users and interference between streams of single user itself. All these papers adopted precoding techniques for beam forming of individual stream. Various papers have compared precoding techniques such as DPC, BD-ZF, BD-MMSE, BD-QR-MRL, and BD-QR-LRL. Block diagonalization technique is capable to reduce multiuser interference, but not able to combat interference between antennas of single user itself. BD combines with other techniques to overcome this problem. This paper also proposes a precoding technique called modified maximum ratio transmission, which is able to deal with the problem without much complexity. Simulation is done to compare all precoding technique with MRT. The paper tests the precoding techniques on the parameters of BER and capacity, to achieve optimum receiver performance. BER curve and capacity curve are plotted to conclude the paper.