Davinder S. Saini

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.

Flexible fixed set portioning and performance improvement in OVSF based networks

The limited codes in orthogonal variable spreading factor (OVSF) based CDMA networks need efficient code assignment. With the continuous progress in code assignment research, the efficiency reaches close to 100 percent. However, the cost and complexity in these schemes increases significantly. For real time calls there is an additional requirement of minimizing call establishment delay which is directly proportional to the number of code searches before assignment. Therefore to design a good code assignment scheme the system has to sacrifice some performance measure. Fixed set partitioning (FSP) is known to be the best method for real time calls handling. This paper describes a flexible fixed set partitioning (FFSP) scheme which is the extension of FSP scheme. The scheme is suited for real time applications as the code searches (which reduces to call establishment delay) in the proposed scheme are fewer than most of the proposed schemes. The code searches are higher in FFSP schemes as compared to FSP scheme, and also the code blocking probability is significantly reduced due to flexibility of controlled region overlapping. The simulation results verify the reduction in number of code searches.

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.

GA-PTS Using Novel Mapping Scheme for PAPR Reduction of OFDM Signals Without SI

In recent time orthogonal frequency division multiplexing (OFDM) has proved its mettle as a preferred choice for high speed transmission in wireless applications due its efficient mechanism to combat the inter symbol interference. However sudden high peaks in OFDM signal envelope lead to high peak to average power ratio (PAPR). Enhanced values of PAPR result into complex RF amplifier circuit with reduced efficiency. There are various methods available for PAPR reduction, out of them partial transmit sequence (PTS) is most effective proven choice for PAPR reduction. However PTS technique requires cumbersome searching of all possible phase factors to find optimal phase factor which produces lowest PAPR, the information regarding optimal phase set used at the transmitter need to be sent to the receiver as side information (SI) for decoding purpose, however transmitting SI requires additional transmission bandwidth thus reducing overall bandwidth efficiency. To reduce the exhaustive searching genetic algorithm (GA) could be used with PTS leading to GA-PTS system. In this paper a GA-PTS system is proposed which uses novel octagonal geometry for constellation extension purpose. This scheme does not require transmission of any side information for decoding purpose at receiver and at the same time GA-PTS system reduces the required number of searches. Simulations are presented to show that proposed scheme provides similar PAPR performance as conventional PTS but without need of SI transmission at reduced number of searches.

Signal generation employing Chebyshev polynomial for pulse compression with small relative side-lobe level

The theme of this paper is to present the improvement in the peak side-lobe levels (PSL) and time-bandwidth product with Chebyshev polynomial. This PSL behavior is observed by the matched filter (MF) response, which contains main-lobe width as well as side-lobes. Here to get a better reduction in the side-lobes, Chebyshev polynomials are modified by using zero-crossing there by getting the positive and negative pulse. Here two cases have been considered, in first ordinary Chebyshev polynomial are analyzed, second is a modification in the cycles of Chebyshev polynomial is incorporated. After this the smallest duration of the pulse has been used in determining the optimal duration which has the smallest mean square error (MSE) between the number of pulses incorporated and original signal. This is giving a much larger signal with less PSL by reducing the search domain considerably. This new method tries to implement a side lobe level reduction technique. All of the mentioned procedure is carried out by mathematical equations and simulation verification.

Fast OVSF Code Assignment Scheme for WCDMA Wireless Networks

In 3G and beyond wireless networks orthogonal variable spreading factor (OVSF) codes are used to handle multimedia rates. These codes suffer from code blocking limitation which reduces the throughput and spectral efficiency of the system. Also, real time calls suffer from call processing delay. We propose a single OVSF code assignment design which utilizes offline optimum code selection algorithm so that the optimum code is available at the arrival of new call. The design finds the optimum code using a variable code index for all the parents of the available vacant codes. If a tie occurs for two or more parents for code index, the parent with the higher code index is chosen. The procedure repeats till a unique solution is reached. If still tie is not resolved the average elapse time of busy children of these parents can be used to choose single optimum code option.