Venugopalachary Kotha

Bio: Venugopalachary Kotha is an academic researcher from Shiv Nadar University. The author has contributed to research in topics: Telecommunications link & MIMO. The author has an hindex of 1, co-authored 3 publications receiving 2 citations.

Performance of Downlink SISO NR System using MMSE-IRC Receiver

Abstract: In this work, we investigated the performance of single input single output (SISO) downlink channel considering 5G new radio (NR). A number of parameters such as different modulation schemes, channel coding with varying code rates, scalable numerology μ and 3GPP channel models have been considered for evaluation. In addition, the minimum mean square error-interference rejection combining (MMSE-IRC) technique for interference mitigation and bit error rate (BER) performance is analyzed and presented. We also compared the sum-rate performance of LTE and 5G NR. It is observed that MMSE-IRC receiver successfully mitigates the interferences compared to only MMSE based receiver. Simulation results also show performance improvement over various parameters like sum-rate, interference mitigation and BER compared to prior technologies i.e. 4G-LTE, WiMAX, etc.

Low Complexity Based QR-LRL OSIC Detector for Downlink NOMA-MIMO Systems

Abstract: Power domain NOMA SISO system achieve more capacity compared to OMA system for a given power. To enhance the overall system capacity, NOMA-MIMO based downlink system with superposition coding (SC) coding is considered in this work. With the incorporation of MIMO, the detector subject to interuser as well as interantenna interference. Conventionally, after receiving the signal from the base station (BS), each user eliminates the interantenna interference using zero-forcing (ZF) based linear detector. This paper proposes low-complexity based QR-LRL detector to overcome jointly the interuser interference and interantenna interference. The performance of the proposed detector under BER and capacity metrics compared with ZFSIC and ML detectors. Simulation results show that the proposed receiver guarantees near ML performance with lower complexity for NOMA-MIMO downlink systems. It presents the sumrate improvement for various MIMO configurations with different modulation orders. It also provides optimal power allocation factor $(\alpha)$ to experience the same BER at both the near user (NU) and the far user (FU) using ZF and QR-LRL detector.

Power Allocation and Relay Placement for Secrecy Outage Minimization over DF Relayed System

Abstract: This paper presents a novel joint transmit power sharing and relay placement scheme for decode-and-forward relay assisted secure communication to a legitimate user in presence of external eavesdropper. Observing that secrecy outage minimization problem for the trusted user is non-convex, key insights on optimal power sharing between source and relay are first presented to derive an equivalent single variable problem. Next, tight analytical bounds for optimal relay placement are discoursed to ultimately come up with a computationally-efficient jointly global optimization algorithm. Finally, selected numerical results validate analysis, present key insights, and demonstrate performance gains of around 30dB over benchmark schemes.

Performance Analysis of OSTBC in NOMA Assisted Downlink System with SIC Errors

Abstract: This paper investigates the error performance of the orthogonal space-time block coding (OSTBC) in non-orthogonal multiple access (NOMA) assisted downlink system in the presence of successive interference cancellation (SIC) errors. In the proposed system model, the base station communicates with multiple users to exploit the benefits of OSTBC in NOMA, like transmit diversity gain and low complexity. The system performance of the proposed OSTBC-NOMA system is analyzed in terms of the average symbol error rate (ASER) over the Rayleigh fading channel model. Further, in order to get a better insight to the system performance, the analysis is conducted over a high SNR regime to obtain diversity order and asymptotic ASER. The analytical results corroborated with Monte-Carlo simulations illustrate that the proposed OSTBC-NOMA system outperforms the conventional NOMA system over different combinations of the modulation scheme. Also, the power allocation coefficient’s impact on the system performance is numerically analyzed.

Performance analysis of least reliable symbol based ordered successive interference cancelation detection method for uplink NOMA

Abstract: Nonorthogonal multiple access (NOMA) is one of the key techniques to improve the spectral efficiency required for fifth‐generation (5G) mobile networks. A severe interuser interference is encountered during the detection process in the uplink NOMA scenario, leading to the imperfect successive interference cancelation (SIC), thereby resulting in extreme SIC error propagation. In this work, we propose a novel least‐reliable symbol‐based ordered‐successive interference cancelation (LRS‐OSIC) detection method for uplink NOMA to mitigate the severe effects of SIC error propagation. The bit error rate (BER) performance is presented for different phase‐shift keying (PSK) modulation schemes to better understand the proposed LRS‐OSIC algorithm. Further, detailed comparative analysis with the existing detection techniques for uplink NOMA is illustrated in terms of error rate and computation complexity. The obtained results prove that the proposed LRS‐OSIC detection method for uplink NOMA outperforms other existing techniques and closely matches the best achievable error performance as accomplished by the maximum likelihood (ML) decoder. Moreover, the simulation results are extended for three user scenarios to validate the benefits of the proposed LRS‐OSIC algorithm for more than two user scenarios.

Performance of NOMA‐assisted MRC receivers in presence of imperfect SIC and CSI errors

Abstract: In this paper, we analyze the performance of maximum‐ratio combining (MRC) receivers for single‐input multiple‐output (SIMO) non‐orthogonal multiple access (NOMA) system. We explore the aforesaid system performance in presence of impairments like imperfect channel state information (CSI) and successive interference cancellation (SIC) errors. In general, receive diversity provides diversity gain and helps to maintain quality of service (QoS), while the NOMA system achieves higher spectral efficiency compared to orthogonal multiple access (OMA). Power‐domain NOMA system transmits superimposed‐coded signal, which utilize SIC detection method at the receiving users. Here, we derive the closed‐form expression of the average bit error rate (BER) for the MRC‐based NOMA system. We also analyze the performance of the system in high signal‐to‐noise ratio (SNR) regime through derived asymptotic expression. Furthermore, the outage probability, diversity order, and sum rate comparison between NOMA and OMA system are also presented. Simulation results also validate the derived theoretical expressions and confirm the diversity gain achieved for the considered system.

An Energy-Efficient Internet of Things Relaying System for Delay-Constrained Applications

Abstract: The emerging Internet-of-things (IoT) systems contain a large number of small wireless devices with limited energy, communication, and computational capabilities. In such systems, a helping station located between the IoT devices and backhaul servers can be deployed to broadcast the IoT devices to the backhaul networks. This paper investigates a hybrid energy-efficient framework using multiple energy harvested relays with data buffering capabilities. The relays are powered by a hybrid energy supply consisting of a traditional electric grid and renewable energy grid. We propose an energy efficient novel approach aiming to support the wireless uplink transmission from IoT devices to backhaul servers with an acceptable delay threshold or transmission deadline. A mathematical mixed-integer linear programming (MILP) optimization problem is formulated to optimize the relays’ placement and energy consumption considering the association between relays and devices, instantaneous relays’ battery level, and transmit power budget. Due to the non-convex nature of the formulated optimization problem, we propose two heuristic low-complexity solutions to solve this problem. Finally, we compare the performance of the proposed algorithms with exhaustive search solutions as a benchmark.

Fixed-Point MIMO Detector for 5G New Radio

Abstract: Fixed-point simulation of multiple-input and multiple-output (MIMO) with ordered successive interference cancellation (OSIC) detector for 5G new radio (NR) is presented. 5G NR is in demand to provide high data rate (in Gbps) and the massive multiple devices connectivity. The above requirements are fulfilled with the incorporation of multiple antenna based transceiver in 5G NR. The spatial multiplexed MIMO system resulted from aforesaid incorporation effectively increases the data rate using MIMO detectors. The performance of various optimal and sub-optimal MIMO detectors used for MIMO channel matrix inversion is limited to the singularity of the channel matrix. While triangularization and orthogonalization are prerequisites for solving the singularity of the channel matrix in MIMO systems, QR decomposition using Gram-Schmidt (GS) method is one of the stable technique. Also, using the QROSIC detection, the system succeeds to achieve near maximum likelihood (ML) performance. In this work, we investigated the fixed-point implementation of QR-OSIC MIMO detector over 5G NR. The simulation results also validate the proposed fixed-point detector succeed to achieve near ML performance while maintaining the word precision low compared to floating-point implementation.

An Energy-Efficient Internet of Things Relaying System for Delay-Constrained Applications

Abstract: The emerging Internet-of-things (IoT) systems contain a large number of small wireless devices with limited energy, communication, and computational capabilities. In such systems, a helping station located between the IoT devices and backhaul servers can be deployed to broadcast the IoT devices to the backhaul networks. This paper investigates a hybrid energy-efficient framework using multiple energy harvested relays with data buffering capabilities. The relays are powered by a hybrid energy supply consisting of a traditional electric grid and renewable energy grid. We propose an energy efficient novel approach aiming to support the wireless uplink transmission from IoT devices to backhaul servers with an acceptable delay threshold or transmission deadline. A mathematical mixed-integer linear programming (MILP) optimization problem is formulated to optimize the relays’ placement and energy consumption considering the association between relays and devices, instantaneous relays’ battery level, and transmit power budget. Due to the non-convex nature of the formulated optimization problem, we propose two heuristic low-complexity solutions to solve this problem. Finally, we compare the performance of the proposed algorithms with exhaustive search solutions as a benchmark.