Keerti Tiwari

On the Capacity of MIMO Weibull-Gamma Fading Channels in Low SNR Regime

We present capacity analysis for multiple-input multiple-output MIMO system under a low signal-to-noise ratio SNR regime. We have selected a composite fading channel that considers Weibull fading for multipath and gamma fading for shadowing. We have presented the analysis in a detailed form for three different techniques, namely, spatial multiplexing SM with optimal detection, SM with minimum mean square error MMSE detection, and orthogonal space-time block codes OSTBC. Because capacity analysis at arbitrary signal-to-noise SNR is stringent, a low SNR regime is considered to achieve a positive rate and wideband slope. The improvement is the result of minimizing energy per information bit Eb. For the first time, closed-form expressions are evaluated for the capacity of MIMO systems at low SNR under WG fading channels which facilitate the performance comparison for proposed techniques.

ASEP of MIMO System with MMSE-OSIC Detection over Weibull-Gamma Fading Channel Subject to AWGGN

Ordered successive interference cancellation OSIC is adopted with minimum mean square error MMSE detection to enhance the multiple-input multiple-output MIMO system performance. The optimum detection technique improves the error rate performance but increases system complexity. Therefore, MMSE-OSIC detection is used which reduces error rate compared to traditional MMSE with low complexity. The system performance is analyzed in composite fading environment that includes multipath and shadowing effects known as Weibull-Gamma WG fading. Along with the composite fading, a generalized noise that is additive white generalized Gaussian noise AWGGN is considered to show the impact of wireless scenario. This noise model includes various forms of noise as special cases such as impulsive, Gamma, Laplacian, Gaussian, and uniform. Consequently, generalized Q-function is used to model noise. The average symbol error probability ASEP of MIMO system is computed for 16-quadrature amplitude modulation 16-QAM using MMSE-OSIC detection in WG fading perturbed by AWGGN. Analytical expressions are given in terms of Fox-H function FHF. These expressions demonstrate the best fit to simulation results.

Performance Improvement in Spatially Multiplexed MIMO Systems over Weibull-Gamma Fading Channel

Abstract In multiple-input multiple-output (MIMO) systems, spatial demultiplexing at the receiver has its own significance. Thus, several detection techniques have been investigated. There is a tradeoff between computational complexity and optimal performance in most of the detection techniques. One of the detection techniques which gives improved performance and acceptable level of complexity is ordered successive interference cancellation (OSIC) with minimum mean square error (MMSE). However, optimal performance can be achieved by maximum likelihood (ML) detection but at a higher complexity level. Therefore, MMSE-OSIC with candidates (OSIC2) detection is recommended as a solution. In this paper, spatial multiplexed (SM) MIMO systems are considered to evaluate error performance with different detection techniques such as MMSE-OSIC, ML and MMSE-OSIC2 in a composite fading i. e. Weibull-gamma (WG) fading environment. In WG distribution, Weibull and gamma distribution represent multipath and shadowing effects, respectively. Simulation results illustrate that MMSE-OSIC2 detection technique gives the improved symbol error rate (SER) performance which is similar to ML performance and its complexity level approaches to MMSE-OSIC.

BER performance comparison of MIMO system with STBC and MRC over different fading channels

In the present wireless scenario, multiple-input and multiple-output (MIMO) is an emerging technique in wireless communication to achieve reliability and high throughput. Transmit diversity i.e. Alamouti space time block codes (STBC) and receiver diversity i.e. maximal ratio combining (MRC), are used to improve the link performance. In this paper, bit error rate (BER) performance is evaluated using distinct modulation schemes like BPSK, QPSK, and 16-QAM with STBC and MRC diversity techniques over Rayleigh, Rician and Nakagami-m fading channels. It is shown by simulated results that improved BER is achieved using MRC. Signal-to-noise ratio (SNR) is considered from 0 to 20 dB.

Efficient Detection for Improving ASEP Performance of MIMO Composite Fading Channel with Generalized Noise

Multiple-input multiple-output (MIMO) system has achieved significant benefits by applying optimum detection techniques. Maximum likelihood (ML) detection technique improves the error rate performance of MIMO system at optimum level but with enhanced complexity. Therefore, we have considered minimum mean square error-ordered successive interference cancellation with candidate detection to approach the performance of ML with reduced complexity. The proposed system performance is analyzed in composite Weibull–gamma fading and additive white generalized Gaussian noise (AWGGN) scenario. Some special cases of WG fading and AWGGN yield the simplified results.

Error Rate Analysis of Precoded-OSTBC MIMO System Over Generalized-K Fading Channel

The orthogonal space–time block codes (OSTBCs) increase the diversity order of a multiple-input multiple-output (MIMO) system at a reasonable cost of complexity. However, the precoding technique in which complete channel knowledge is available at the base transceiver station has come into existence with OSTBC for improving the system performance. Moreover, a composite generalized-K channel model has become the key for analyzing both the effects of multipath fading and shadowing. Therefore, this chapter has exploited the precoded OSTBC to improve the bit error rate (BER) performance of MIMO system over a generalized-K fading channel.

SER Performance Improvement in OFDM System Over Generalized K-fading Channel

In this paper, performance metric of orthogonal frequency division multiplexing (OFDM) system is analyzed over a composite fading channel, i.e., generalized K-fading channel. Here, OFDM system is considered which includes repetition code to enhance the wireless link performance with simplicity. Symbol error rate (SER) performance is evaluated using binary phase shift keying (BPSK) and 16-quadrature amplitude modulation (16-QAM) over generalized K-fading channel. This channel model considers Nakagami-m distribution to define multipath and gamma distribution to represent shadowing effects. Simulation results demonstrate that improved system performance can be achieved by using repetition code in severely faded environment. A comparative study of coded and uncoded system is also given in this paper. Consequently, SER performance is improved with the increase of shape parameters.

Downlink Spectral Efficiency of ZF Precoding Based Multi-user MIMO System Over Weibull Fading Channel

Frequency division duplex (FDD) and time-division duplex (TDD) are two different ways of executing the downlink and uplink transmission over a given frequency band. In which, TDD is the superior mode due to less pilots’ requirement than FDD and its highly scalable quality, where the pilot length is independent of the number of base station (BS) antennas. The linear precoding scheme i.e., zero forcing (ZF) is simple and easy to implement. Therefore, this paper uses ZF for the performance comparison of multi-user multiple-input multiple-output (MU MIMO) system on the basis of downlink spectral efficiency (SE) obtained with perfect channel state information (CSI) and with CSI estimated through pilot sequences of a specified length. The SE is illustrated as a function of the number of BS antennas using TDD and FDD mode over a Weibull fading channel which considers favorable propagation case. The SE increases even after decreasing the signal to noise ratio (SNR). It is practically viable to organize FDD systems with many antennas, mainly for slow-varying channels where we can take a large pilot overhead, but TDD is preferable in this situation.