Ratnam V. Raja Kumar

How green the LTE technology can be

Reducing Carbon emissions in general in ICT from the present 3 percent and in particular in Mobile communications has been of a serious concern. In the next generation cellular technologies like LTE, base stations are very energy hungry, as they need to provide high spectral efficiency and wide coverage. Given that there is no cooling required for modern systems, the transmit power in a typical link is the most important constituent in a base station. This is mainly due to its power amplifiers and also due to energy loss in the power supply. LTE uses OFDM in downlink, which requires huge complex computations, and the power consumption of the transceiver hardware. With the latest CMOS technology, a two-fold reduction in the operating voltage from 130 nm technology to 22 nm technology, results in a four-fold reductions in the transceiver power consumption. With the LTE technology poised to take off, it is interesting to see the energy consumption assessment of LTE considering the projection of technology and exploiting the different mode of operation and the methods of reducing energy consumption. This paper discusses about the various possibilities and makes a practical assessment of a possible green form of LTE.

Tracking of bandpass signals using center-frequency adaptive filters

A class of constrained adaptive filters, called recursive center-frequency adaptive filters, is applied to the tracking of bandpass signals. For this application, these filters form a class of completely digital tracking filters which are shown to have several advantages over existing analog and semidigital tracking filters. A procedure of analyzing the tracking behavior of these filters using the ordinary differential equation approach is presented. The tracking performance of two examples of these filters is analyzed for step, ramp, and sinusoidal variations of the input signal center frequency, and these are shown to track the signals very effectively. The dependency of the performance on the parameters of the algorithm, transfer function of the filter, and the input signal is studied. >

A gradient algorithm for center-frequency adaptive recursive bandpass filters

Mean-square output of a center-frequency variable bandpass filter is employed as the performance criterion to make the filter self-adjusting to the center frequency of the input signal. A gradient ascending algorithm is proposed to update the center-frequency-dependent coefficients of the filter to maximize the performance function.

An Efficient Frequency Offset Estimation Scheme for Multi-Band OFDM Ultra-Wideband Systems

A frequency offset estimation scheme is presented for coarse frequency offset estimation of Ultra-Wideband (UWB) Multi-Band Orthogonal Frequency Division Multiplexing (MB- OFDM) systems. Cramer Rao Lower Bound (CRLB) for variance of the estimated frequency offset is derived and compared with the simulated results of the proposed scheme. Performance of the MB-OFDM system in terms of the Bit Error Rate (BER) with suggested frequency offset estimator is also reported. The algorithm is tested by computer simulation over multiple UWB channel models (CM), CM1: 0-4m line-of-sight, CM2: 0-4m non-line-of-sight (NLOS), CM3: 4-10m NLOS, and CM4: 25 nsec. delay spread as suggested by IEEE 802.15 Channel Modeling sub-committee. With higher number of iteration the algorithm shows improvement of the system performance by 8.8 dB in both CM1 and CM2; 7.6 dB for CM3 and 8.3 dB for CM4 at BER=10-4.

Recursive center-frequency adaptive filters for the enhancement of bandpass signals

In some signal enhancement and tracking applications, where a priori information regarding the signal bandwidth and spectral shape is available, it is suggested to use a recursive center-frequency adaptive filter instead of a fully adaptive filter. A new adaptive algorithm, namely, the recursive maximum-mean-squares (RMXMS) algorithm, is developed based on the gradient ascent technique for the implementation of these filters. An adaptation mechanism based on the Gauss-Newton algorithm is also presented. This class of filters is found to have several advantages which include faster convergence and lesser computational complexity compared to the fully adaptive filters.

Symbol timing synchronization for ultra-wideband (UWB) multi-band OFDM (MB-OFDM) systems

A low-complexity correlation based symbol timing synchronization (CBTS) algorithm for UWB MB-OFDM systems is presented. The correlation based scheme attempts to locate the start of the FFT window during frame synchronization sequence (FS) of the received preamble by firstly correlating the received samples with known training samples and then identifying the first significant multi-path component by comparing the correlated samples of two consecutive OFDM symbols against a predefined threshold. Performance of the proposed algorithm is measured through mean-squared error (MSE) of timing estimation and probability of synchronization. Each of the 100 channel realizations for UWB channel model1 (CM1) (0-4 m LOS) and CM2 (0-4 m NLOS) are simulated for 1000 noisy channel realizations for 17 dB SNR. Synchronization probability and MSE for CM1 and CM2 are reported for 320 Mbps data rate.

Development of a CDMA system with RAKE receiver for the third generation wireless communication systems

The main constituent of the third generation (3G) digital cellular mobile communication systems is a CDMA transceiver. The transmitter includes complex scrambling code generation, channelization code generation, and the spreading operation with both. The receiver involves RAKE reception, code synchronization, descrambling code and channelization code generation and the despreading operations. The RAKE receiver is used to mitigate the fading introduced by the wireless channel by maximally combining the delayed replicas of the signal. Its output may be used for further baseband processing for detection. With the present state-of-art VLSI technology, an ASIC solution is essential for a miniaturized full specification 3G air interface development. Therefore, in this paper, we present the development of an ASIC solution, which has been fabricated using the 0.25 /spl mu/ CMOS technology, for a RAKE receiver based 3G CDMA system.

Fast communication: An efficient technique for the integer frequency offset estimation in OFDM systems

This communication proposes a novel null subcarrier based algorithm for the integer frequency offset (IFO) estimation in orthogonal frequency division multiplexing (OFDM) systems. Bandwidth overhead of the proposed algorithm is less than 5% of the bandwidth of first OFDM symbol in a frame. The IFO is estimated by computing the energy of subcarriers at the DFT output just once and by finding the shift in null subcarrier indices using a simple statistical approach. The proposed method is computationally very efficient as compared to the methods which use exhaustive search procedures. It also achieves advantages over a few recently published methods in terms of the number of real additions (RAs) and bandwidth overhead required for IFO estimation. Computer simulation studies show that the estimator is able to achieve an IFO estimation range equal to the OFDM bandwidth.

Least squares based optimal switched predictors for lossless compression of images

Gradient adjusted predictor (GAP), used in CALIC, consists of seven slope bins and one predictor each is associated with these bins. As the relationship between the predicted pixels and their contexts are complex, these predictors may not be appropriate for prediction of the pixels belonging to the respective slope bins. In this work, we present the least-squares (LS) based approach to find optimal predictors for pixels belonging to various slope bins of GAP. Our simulation results show that the proposed method results in similar performance as that of edge directed prediction (EDP) and Run-length and Adaptive Linear Predictive (RALP) coding. EDP and RALP use symmetrical encoder and decoder structure. On the other hand, we propose an unsymmetrical codec that has higher encoding complexity but decoder is very fast - as fast as a decoder based on GAP principle. However, our encoder is computationally much simpler than an EDP and RALP based encoders.

A GLRT detector in partially correlated texture based compound-Gaussian clutter

This paper addresses the problem of target detection in the presence of a non-Gaussian clutter modeled in compound-Gaussian form which realizes the clutter process as a product of two independent random processes ‘texture’ and ‘speckle’. The likelihood ratio test (LRT) detector applied to this detection problem reduces the detector to a matched filter (MF) when the texture is considered as completely correlated during a coherent processing interval (CPI). However, in practical applications, the textural component exhibits a correlation which is less than unity. The conventional form of MF based detectors existing in the literature yield a significant fall in the detection performance in such clutter scenarios. In this paper, we propose a generalized likelihood ratio test (GLRT) detector which can effectively detect a fluctuating target in the presence of a compound-Gaussian clutter with partially correlated texture. The results are presented to show the performance superiority of the proposed detector over the existing MF detector in such varying texture scenarios.