K. Vinoth Babu

A reduced MIMO (R-MIMO) system using norm based approach (NBA) for transmit antenna selection (TAS)

For Multiple Input Multiple Output (MIMO) systems, antenna selection is a must since the Radio Frequency (RF) chains connected with antennas consumes a lot of power. This paper studies the effect of antenna selection at transmitter side since the base station power consumption is around 60-80% of the entire wireless system. The TAS is performed by a simple and computationally efficient NBA scheme. The NBA is employed at the receiver side, where channel estimation is performed, and the antenna indices corresponding to the selected transmit antennas are fed back to the transmitting side which in turn result in a considerable decrease in feedback data. It is seen that the reduced MIMO system provide with the same performance as the conventional full MIMO that uses all the antennas.

Fractionally spaced equalizer based on dynamically varying modulus algorithm for spectrally efficient channel compensation in SC-FDMA based systems

Abstract Orthogonal frequency division multiplexing (OFDM) based wireless communication systems are expected to satisfy the thirst for ever increasing demand on higher spectral efficiency. But, OFDM systems suffer from peak to average power ratio (PAPR) and inter carrier interference (ICI) problems. It is observed that when OFDM is used in the uplink, PAPR problem is more severe and the relative mobility of the user equipments with respect to the base station will cause Doppler spread which leads to ICI. One of the solutions to minimize PAPR and ICI is single carrier frequency division multiple access. But there is a tradeoff in spectral efficiency. The main objective of this paper is to evaluate the performance of fractionally spaced equalizer (FSE) for blind channel estimation based on higher order statistics and to identify any better alternative to improve its performance. Dynamically varying modulus algorithm (DVMA) based FSE is proposed in this paper which is a better alternative for supervised equalization. The simulation results prove that FSE blind equalizer based on DVMA outperform the conventional supervised and blind equalizers.Orthogonal frequency division multiplexing (OFDM) based wireless communication systems are expected to satisfy the thirst for ever increasing demand on higher spectral efficiency. But, OFDM systems suffer from peak to average power ratio (PAPR) and inter carrier interference (ICI) problems. It is observed that when OFDM is used in the uplink, PAPR problem is more severe and the relative mobility of the user equipments with respect to the base station will cause Doppler spread which leads to ICI. One of the solutions to minimize PAPR and ICI is single carrier frequency division multiple access. But there is a tradeoff in spectral efficiency. The main objective of this paper is to evaluate the performance of fractionally spaced equalizer (FSE) for blind channel estimation based on higher order statistics and to identify any better alternative to improve its performance. Dynamically varying modulus algorithm (DVMA) based FSE is proposed in this paper which is a better alternative for supervised equalization. The simulation results prove that FSE blind equalizer based on DVMA outperform the conventional supervised and blind equalizers.

Spectral efficiency improvement in OFDMA systems with modified adaptive subcarrier spacing based resource allocation algorithm

Future broadband wireless communication standards are expected to offer high-quality services under all mobility conditions. Achieving high-quality services in a wireless fading environment is a challenging task. To combat the effect of frequency selective fading, recent wireless standards prefer multicarrier modulation schemes such as orthogonal frequency division multiplexing (OFDM) instead of single carrier modulation. The high mobility of the users leads to a larger amount of inter-carrier interference (ICI) in orthogonal frequency division multiple access (OFDMA) systems and thus the spectral efficiency reduces. Achieving higher spectral efficiency by combating the effect of ICI with reasonable complexity is the essence of this paper. Considering carrier frequency offset (CFO) pre-correction schemes along with adaptive subcarrier spacing (ASS)–adaptive bit loading (ABL) algorithms, we present the modified adaptive subcarrier spacing (MASS) resource allocation algorithm to cancel ICI and to increase spectral efficiency. The simulation results show that the MASS algorithm is far better than the conventional ASS–ABL algorithm in terms of spectral efficiency.

An efficient Relay Station deployment scheme based on the coverage and budget constraints in Multi-hop Relay networks

Optimum deployment of Relay Station (RS) is considered as the most important issue especially for the users near cell boundary. The Multi hop Relay (MHR) network introduces the RS for the purpose of extended coverage and increased throughput. The main objective of this work is to provide a better Quality of Service (QoS) with a minimum deployment cost. In this paper, we identify the candidate positions of RS that will achieve maximum system capacity. Based on the relay location, we propose two algorithms based on coverage and budget constraints. The simulation results indicate that the proposed algorithms achieved a reasonable coverage ratio within the budget constraint.

Hybrid antenna selection at transmitter (HAST) scheme for future broadband wireless system

In this paper, a new adaptive HAST scheme is proposed for Space Frequency Block Coded (SFBC)-Orthogonal Frequency Division Multiplexing (OFDM) system. This HAST scheme uses subcarrier by subcarrier antenna selection. The performance of the proposed scheme is analyzed for different antenna configurations with average Signal to Noise Ratio (SNR) gain and Bit Error Rate (BER) parameters. The simulation results prove that the performance of conventional SFBC-OFDM system is greatly improved with the proposed scheme.

Signal detection for Spatially Multiplexed multi input multi output (MIMO) systems

High-data-rate transmission can be achieved by Spatially Multiplexed (SM) MIMO systems. Spatial demultiplexing at the receiver end is a difficult task. Thus, several research works has been developed for demultiplexing and decoding. In this paper three signal detection methods namely Zero-Forcing (ZF), Minimum Mean Squared Error (MMSE) and Maximum Likelihood (ML) are implemented. In Zero-Forcing method, noise enhancement is the problem. The complexity of implementing ZF and MMSE is much low but their performance is remarkably inferior to ML detection. Many active researchers are done to develop the signal detection methods based on the ML detection criterion while still aimed to achieve a near-optimal performance with low complexity. The comparative study of three methods is done in relevance to three digital modulation schemes namely Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK) and 16-Quadrature Amplitude Modulation (QAM). Simulation results also state that ML gives better performance as compared to ZF and MMSE detection methods.

Effective frequency offset correction in OFDM systems with extended Kalman filtering technique

Disaster Management System (DMS) is a key solution for humanitarian relief from natural disasters and manmade disasters. This paper discusses the use of Orthogonal Frequency Division Multiplexing (OFDM) in DMS. OFDM is a multicarrier modulation (MCM) in which single data stream is transmitted over a number of lower rate sub carriers. The main reason to use OFDM is to increase the robustness against frequency selective fading and narrow band interference. However an important issue like inter carrier interference (ICI) caused due to Doppler frequency offset and variations in local oscillators distorts the transmitted OFDM signal. In this letter a novel ICI mitigation method which uses Extended Kalman Filter (EKF) is proposed to mitigate the ICI effects. Final simulated results show that the proposed method in this paper outperforms the conventional ICI mitigation techniques.

SINR Improvement in OFDM Systems Using VSB-VBL Technique for High Mobility Applications

OFDM based wireless system provides high spectral efficiency but they are very sensitive to Doppler shift. High mobility causes the channel to be fast fading channel. The rapid variation of the channel can induce Inter Carrier Interference (ICI). ICI due to carrier frequency offset can be mitigated by accurate frequency synchronization but ICI due to fast fading channel is more difficult to handle. Thus ICI reduces the throughput and increases the BER. In this paper we proposed an OFDM system which will use Variable Sub carrier Bandwidth (VSB) with Variable Bit Loading (VBL) to minimize the effect of ICI due to high mobility. We investigate the performance of such VSB-VBL OFDM system with Fixed Sub carrier Bandwidth (FSB-OFDM) system based on Signal Interference to Noise Ratio (SINR).

Low -Complex ICI Reduction due to Channel Estimation Error in OFDM systems using VSB-VBL Technique for High Mobility Applications

OFDM based wireless systems are spectrally efficient but they are vulnerable to Inter carrier interference (ICI). The rapid variation of the channel can induce ICI. ICI will significantly increase the difficulty of OFDM channel estimation. ICI due to carrier frequency offset can be mitigated by accurate frequency synchronization but ICI due to fast fading channel is more difficult to handle. This kind of ICI can be easily reduced by increasing the sub carrier spacing. In this paper we proposed an OFDM system which will use Variable Sub carrier Bandwidth (VSB) with Variable Bit Loading (VBL) to minimize the effect of ICI due to channel estimation error. We investigate the performance of such VSB-VBL OFDM system with Fixed Subcarrier Bandwidth (FSB-OFDM) system based on Signal Interference to Noise Ratio (SINR) and Symbol Error Rate (SER).

Quality of Service Aware Inter Carrier Interference Mitigation and Antenna Selection Schemes for Beyond 4G Systems

Future broadband wireless communication systems demand high quality of service (QoS) for anytime anywhere multimedia applications. The standards which use orthogonal frequency division multiplexing (OFDM) coupled with multi input multi output (MIMO) are expected to rule the future wireless world. Time selective nature of the channel introduces inter carrier interference (ICI), which is the major performance limiting parameter in OFDM based systems. ICI causes loss in spectral efficiency and results in poor bit error rate (BER) performance, affecting the QoS of MIMO-OFDM systems. The conventional single input single output (SISO)-OFDM-flexible subcarrier spacing (FSS) system offers better performance than the fixed subcarrier spacing systems in terms of ICI mitigation. But BER and spectral efficiency performance of SISO-OFDM-FSS is not good enough to satisfy the requirements of future wireless broadband services. To improve the BER performance, SISO-OFDM system is replaced by space frequency block coded (SFBC)-OFDM system, which adds spatial and frequency diversity benefits to the conventional system. More number of antennas in the MIMO scheme increases the hardware cost, computational complexity and percentage of overhead. In the present study, to improve the spectral efficiency and to reduce the complexity and cost, optimal transmit antenna selection (OTAS) is combined with the SFBC-OFDM-FSS scheme. The simulation results prove that the proposed SFBC-OFDM-FSS-OTAS scheme offers better QoS than the conventional SISO-OFDM-FSS scheme.