Farid Ghani

Enhanced performance of new family Modified Double Weight codes spectral amplitude coding optical CDMA system network

A new family of spectral/spatial spectral amplitude-coding (SAC) optical code division multiple access (OCDMA) scheme using Modified Double Weight (MDW) code is developed. The new codes are derived from Modified Double Weight codes with good cross correlation. This proposed system can suppress the phase-induced intensity noise (PIIN) by using multiuser interference (MUI) cancellation property. The proposed 2-D OCDMA MDW can offer a much larger capacity compare to the 1-D OCDMA MDW Code.

Performance bounds for block transmission system

The paper presents an analysis of the Block Transmission System (BTS) that has recently been proposed for mobile channels. Decision boundaries and decision regions have been obtained for the block linear equalizer and the optimum detector for the system. These provide the lower and upper bounds to the performance of the BTS in the presence of additive white Gaussian noise. It is shown that despite of the reduced transmission efficiency the performance of the block linear equalizer is comparable with that of the transversal equalizer and makes it suitable for use in mobile systems

Reduced complexity optimum detector for Block Data Transmission Systems

Block Data Transmission Systems (BDTS) are used in high-speed wireless communication systems with time dispersive channel characteristics. In such systems, blocks of data are separated by zeros to mitigate the effect of Inter-Symbol-Interference (ISI) between the blocks. An optimal detection process employs the Maximum Likelihood Block Detection (MLBD) technique on each block individually in the presence of ISI and Gaussian noise based on the Euclidean distance as an objective function. The detection process is computationally expensive therefore Genetic Algorithms have been used to reduce the overall design complexity. In this work, three types of Genetic Algorithms have been incorporated in the detection process i.e. the conventional GA, Micro GA(µGA), and Hybrid µGA to reduce computational load. In particular, a novel training method for Hybrid µGA has been proposed. Simulation results at 10dB channel SNR for the BDTS with Hybrid µGA executes as low as 3,750 number of objective functions evaluation for a block size of 20. The Bit Error Rate (BER) performance of this system is relatively good i.e. around 1dB inferior to the BDTS using the Exhaustive Search method that requires as many as 220 number of objective functions evaluation.

Memory efficient set partitioning in hierarchical tree (MESH) for wavelet image compression

This paper presents a memory efficient version of set partitioning in hierarchical tree (SPIHT). The proposed coder termed as memory efficient SPIHT (MESH), uses a single re-usable list instead of three continuously growing linked lists as in conventional SPIHT. The list is re-initialized at the beginning of each bit-plane (coding pass) and is exhausted within that bit-plane itself. Another feature of the proposed coder is that it uses a single pass for each bit-plane by merging the sorting and refinement passes of conventional SPIHT together. The reinitialization of the list in each bit-plane makes the proposed coder inherently error resilient. The performance of the proposed coder is measured in terms of coding efficiency and the worst case memory requirements for list entries in each bit-plane. The performance comparison with SPIHT shows that the proposed algorithm results in 50-70% memory saving while retaining a coding efficiency comparable to SPIHT.

Block data communication system for fading time dispersive channels

For reliable digital communication over fading channels such as mobile radio and HF channels, block data communication system has been proposed. The system is a synchronous serial data transmission system and employs transmission of alternating blocks of data and training symbols. In contrast to the recursive symbol-by-symbol detection approach, each data block is here detected as a unit. The scheme requires the estimate of the channel impulse response and assumes that it remains unchanged during the transmission of a block of data symbols. This paper presents an optimum linear and a decision directed detector for the block transmission system. The detection of a block of data symbols is here carried out iteratively through a sequence of similar operations using a simple piece of equipment. The same equipment that is used for signal detection is used for channel estimation. The noise performance of the two detectors is compared with that of the conventional linear transversal equalizer.

Phase-induced intensity noise suppression wavelength-time modified double weight codes optical code division multiple access systems

The wavelength-time modified double weight (MDW) optical division multiple access (OCDMA) scheme to reduce multiple access interference (MAI) and compensate bit error rate (BER) and phase-induced intensity noise (PIIN) in incoherent OCDMA systems is proposed. The analysis permits thorough understanding of PIIN, shot and thermal noises effect on 2-Dimensional (2-D) MDW OCDMA system performance. PIIN is the dominant noise factor in the OCDMA time-spreading scheme. The 2-D MDW code shows better tolerance to PIIN in comparison to others with enhanced system performance. We prove by numerical analysis that the PIIN is maximally suppressed by the proposed code through minimizing property of cross-correlation in comparison to the 2-D PDC and 2-D MQC OCDMA code.

Memory efficient image coding with embedded zero block-tree coder

The work presents an embedded and memory efficient image compression algorithm which exploits both inter- and intra-band correlation of wavelet coefficients. Set partitioning in hierarchical tree (SPIHT) is a zero-tree based coder which exploits inter-band correlation among bands of the same orientation, while the set-partitioning embedded block coder (SPECK) is a zero-block based coder which exploits intra-band correlation. However, they have extensively large memory requirements due to the use of three/two linked lists whose entries increase from one-bit-plane to the next. We propose an algorithm that is based on block-set partitioning and quad-splitting using two re-usable lists. The main list is initialized at the beginning of each bit-plane and is exhausted within the same bit-plane. This makes our proposed algorithm highly memory efficient. Experimental results show that the compression efficiency of the proposed method is comparable to any state-of-the-art image coder while reducing the memory requirement by 50-60% in comparison to the SPIHT algorithm.

Waveform Design for Improved Range and Doppler Resolution in Radar

The choice of a suitable transmit waveform is an important problem in radar design. This is so because the waveform controls resolution and clutter performance and also bears heavily on the system cost. Theoretical studies which provide the basis for technical advances have not, so far, solved the general signal design problem. The knowledge of the properties of the pulse trains, a class of signals particularly well suited to digital processing is therefore, of increasing practical importance. This paper presents a method for generating finite length sequences that have high energy ratio and low side lobe energy in their autocorrelation function. The multilevel sequences with spike like autocorrelation function are generated iteratively, starting with a sequence that has relatively low side lobes in its autocorrelation function. The method can be used to generate sequences of any desired length. It is shown that energy ratio of polyphase sequences that have low side lobe energy, is improved through the process of clipping. Such sequences then can be effectively used to improve the range and Doppler resolution of radars.

Alleviation Noise Effect Using Flexible Cross Correlation Code in Spectral Amplitude Coding Optical Code Division Multiple Access Systems

A new code for Spectral Amplitude Coding - Optical Code Division Multiple Access (SAC-OCDMA) is proposed and is called Flexible Cross-correlation (FCC) code. The FCC code possesses various advantages; including easy code construction using Tridiagonal matrix compared to other SAC-OCDMA codes such as MDW, MQC and MFH, shorter code length and the important properties of this code is the flexible cross-correlation. Our results reveal that FCC code can effectively alleviated Phase Induced Intensity Noise (PIIN) and allows large cardinality and improve the bit error rate performance.

New code with non-zero cross correlation for spectral amplitude coding optical code-division multiple-access systems

This paper presented the novel of a new class of code with Non-Zero Cross-Correlation for Spectral-Amplitude Coding in Optical Code Division Multiple Access (OCDMA) systems. A new code namely Modified Non-Zero Cross Correlation Code (MNZCC). MNZCC code can be constructed easily for a given number of users K, weights and for a given cross correlation (λmax). The proposed code was demonstrated in simulation using OptiSys. 6.0 to observe the system performance. The results shown, that, the proposed code has superior performance in term of spectrum efficiency and reducing the effect of MAI and suppressing the effects of PIIN, with better bit error probability. The results are obtained for the MNZCC were compared with others existing optical codes such as DW code.