Showing papers by "Susmita Das published in 2011"

Neural network based multiuser detection techniques in SDMA-OFDM system

Abstract: The multiuser detection (MUD) process followed by the prominent channel estimation at the receiver end of the SDMA-OFDM (Space Division Multiple Access - Orthogonal Frequency Division Multiplexing) system plays a vital role to retrieve data appropriately. This paper examines the neural network (NN) model based MUD schemes as a possible alternative to Genetic Algorithm (GA) based Minimum Bit Error Rate (MBER) MUD schemes. In this paper, both Widrow-Hoff (WH) learning in single layer structured NN and Back Propagation (BP) learning in a Multi layer perceptron (MLP) structured NN models are described. These techniques offer low complexity and the need for channel estimation can be eliminated. Simulation based performance study is carried out to prove the efficiency of the proposed techniques. The bit Error Rate (BER) and complexity plots show improvement over the previous techniques.

Performance Study of Discrete Wavelet Packet Based MB-OFDM System for Short Range Indoor Wireless Environment

Abstract: Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) approach using UWB signals with short duration of pulses provide unique advantages in short-range high data rate wireless applications which include easy penetration through obstacles, high precision ranging and low processing power. A perfect reconstruction using discrete wavelet packet transmultiplexer in MB-OFDM transceiver counters the degrading effect of ISI, and also conserves bandwidth. In comparison to conventional FFT MB-OFDM, Discrete Wavelet Packet Modulation (DWPM) offers much lower side lobes in the transmitted signal, which reduces inter carrier interference (ICI) and narrowband interference (NBI). In this paper a detail study on conventional MB-OFDM and Discrete Wavelet Packet Transform (DWPT) MB-OFDM is attempted for high data rate ultra wideband (UWB) WPAN physical layer standard. Different multipath components in the UWB channels are characterized by different delays and attenuation. BER performances of MB-OFDM UWB on IEEE 802.15.3a channel models are investigated through simulation study. We show that, at low data rate (55 Mbps) the DWPT MB-OFDM system performs better in the CM4 channel environment than in the CM3 channel due to its inherent frequency diversity. In high data rate (480 Mbps), the BER performance in CM3 channel model is found to be better than in CM4 channel model. DWPT MB-OFDM outperforms than the conventional FFT MB-OFDM for high data rate applications.

Low Complexity Near Optimal Multiuser Detection Scheme for SDMA-OFDM System

Abstract: SDMA (Space-Division Multiple Access) is a MIMO (Multiple-Input and Multiple-Output) based wireless communication network architecture which has the potential to significantly increase the spectral efficiency and system performance. So far several multiuser detection (MUD) schemes like Zero Forcing (ZF), Minimum Mean Square Error estimation (MMSE), ordered successive interference cancellation (OSIC) and maximum likelihood (ML) detection have been proposed by various researchers. Among them, maximum likelihood (ML) detection scheme provides the minimum bit error rate (BER). However, the complexity of ML detection increases exponentially with the constellation size of modulation and number of users. The M-algorithm combined with QR decomposition (QRD-M) can be substitute to ML detection due its low complexity and it's near optimal performance. In this paper the complexity of QRD-M scheme is compared with ML by means of number of foundational operations and the elapsed time.

Suppression of Narrowband Interference in Impulse Radio Based High Data Rate UWB WPAN Communication System Using NLOS Channel Model

Abstract: Study on suppression of interference in time domain equalizers is attempted for high data rate impulse radio (IR) ultra wideband communication system. The narrow band systems may cause interference with UWB devices as it is having very low transmission power and the large bandwidth. SRAKE receiver improves system performance by equalizing signals from different paths. This enables the use of SRAKE receiver techniques in IRUWB systems. But Rake receiver alone fails to suppress narrowband interference (NBI). A hybrid SRake-MMSE time domain equalizer is proposed to overcome this by taking into account both the effect of the number of rake fingers and equalizer taps. It also combats intersymbol interference. A semi analytical approach and Monte-Carlo simulation are used to investigate the BER performance of SRAKEMMSE receiver on IEEE 802.15.3a UWB channel models. Study on non-line of sight indoor channel models (both CM3 and CM4) illustrates that bit error rate performance of SRake-MMSE receiver with NBI performs better than that of Rake receiver without NBI. We show that for a MMSE equalizer operating at high SNR’s the number of equalizer taps plays a more significant role in suppressing interference. Keywords—IR-UWB, UWB, IEEE 802.15.3a, NBI, Data rate, Bit Error Rate

Effect of Erodent on Erosion Wear of Fly Ash-Illmenite

Abstract: In the present piece of research work, plasma sprayed coatings of fly ashillmenite is deposited on mild steel substrate using a 40 kW atmospheric plasma spray system. Solid particle erosion tests are conducted at three different impact angles (i.e. at 30°, 60°and at 90°) using dry silica sand and silicon carbide as erodent. It is observed that, erosion rate is mainly dependant on angle of attack. The rate of erosion is also affected by the type of erodent. Microstructural observations reveal that the coating removal is mainly by chipping/plowing type mechanism at low impact angles. At higher impact angles (i.e. at 60° & 90°) the erosion wear behavior is as of the brittle material.

Comparative Analysis of Various Multiuser Detection Techniques in SDMA-OFDM System Over the Correlated MIMO Channel Model for IEEE 802.16n

Abstract: S pace-Division Multiple Access-OFDM based wireless communication has the potential to significantly increase the spectral efficiency, system performance and number of users. Research in the development of efficient Multiuser Detection (MUD) algorithms for such systems has generated much interest in recent years. The linear Minimum Mean S quare Error (MMS E) MUD processes with low complexity but it is limited by its poor performance. The maximum likelihood (ML) detection provides the optimal performance, but its complexity increases exponentially with the number of users. The S uccessive Interference Cancellation (S IC) and QR decomposition (QRD) MUD can be a substitute to ML detection due its low complexity and near optimal performance. Howe ver, all these techniques are incapable to detect users in rank deficient scenario, where number of users is more than that of number of receiving antennas. Hence, the Minimum Bit Error Rate (MBER) MUD by minimizing probability of error directly has become a possible alternative to all aforementioned MUDs in rank deficient scenario and also its BER performance is close to ML detector. This research proposes a comparative analysis of all these MUD schemes. In this paper the performance of various MUD techniques is verified for the correlated MIMO channel models based on IEEE 802.16n standard.

Performance evaluation of MB-OFDM UWB WPAN system based on channel estimation technique using realistic channel models

Abstract: Under the condition of indoor short-range wireless transmission, the UWB systems can provide very high data rate whereas the power consumption is very low, which makes it a promising candidate for wireless personal area networks (WPAN) where the data rate is greater than 110Mbps and the range is shorter than 10 meters in general. Moreover, UWB is also introduced into the underlying transport mechanism of wireless USB and wireless 1394 for even higher throughput up to 480Mbps within 2 meters [1]. The UWB systems based on MB-OFDM divide the whole assigned spectrum into several smaller sub-bands and each sub-band into a few subcarriers to transmit the information, which leads to lower design complexity as well as better spectral efficiency and fl exibility than the DS-UWB systems [1–3].

Comparative Analysis of Various Multiuser Detection Techniques in SDMA-OFDM System Over the Correlated MIMO Channel Model for

Abstract: SDMA (Space-Division Multiple Access) is a MIMO (Multiple-Input and Multiple-Output) based wireless communication network architecture which has the potential to significantly increase the spectral efficiency and the system performance. The maximum likelihood (ML) detection provides the optimal performance, but its complexity increases exponentially with the constellation size of modulation and number of users. The QR decomposition (QRD) MUD can be a substitute to ML detection due its low complexity and near optimal performance. The minimum mean-squared-error (MMSE) multiuser detection (MUD) minimises the mean square error (MSE), which may not give guarantee that the BER of the system is also minimum. But the minimum bit error rate (MBER) MUD performs better than the classic MMSE MUD in term of minimum probability of error by directly minimising the BER cost function. Also the MBER MUD is able to support more users than the number of receiving antennas, whereas the rest of MUDs fail in this scenario. In this paper the performance of various MUD techniques is verified for the correlated MIMO channel models based on IEEE 802.16n standard.