Telecommunications sector has undergone a paradigm shift in its customer profile extending from urban to rural areas owing to a stupendous growth of mobile technology, following upgrade path from 2G systems to 3G systems. Eventually, 3G technology has evolved through a different path involving Time Division Multiplexing (TDMA) and Code Division Multiplexing (CDMA)-based digital communication technology into W-CDMA and CDMA 2000 standards. Multimedia demand and IP-based network architecture with reliable high throughput air interface makes hybrid CDMA and Orthogonal Frequency Division Multiplexing Access (OFDMA)-based mobile worldwide interoperability for microwave access (mobile WiMax), a viable technology and opens new challenges to researchers to explore engineering methodology and technology to achieve quality of service. Developing a sustainable communication system, with the help of network resources in the best possible way to ensure acceptable information quality to the consumers is the need of the hour. Modern communication network accommodates wired, wireless and even optical links for long haul coverage and these hybrid networks need a careful attention for sustainable design of interfacing subsystems and network components to support heterogeneous traffic. This issue addresses some of the aspects of modern communication covering multiuser detection and channel estimation in wireless communications, receiver positioning in global positioning systems and virtual topology in optical WDM systems.

The CDMA communication system satisfies the mundane usage of information transmission utilizing network resources in an optimum way. The CDMA system capacity is limited by call processing algorithms and resource management strategies. In the first paper, “Optimization and Performance Enhancement of Multiuser Detection in DS-CDMA System“, the authors, Manoj Dewangan and Ajay Somkuwar have reported a superior detection performance in a multiuser DS-CDMA system using a subspace blind linear MMSE detector. They proposed the use of Gold sequence for Bit Error Rate improvement and subspace linear MMSE multiuser detection algorithms to yield a better detection performance with lower computational complexity as compared to DMI blind linear MMSE detector algorithms. Their claim is supported with simulation.

The authors K Jayanthi and P Dananjayan in the second paper of this issue, “Channel Estimation for Multiuser MIMO-OFDM System”, have proposed the Link Adaptation (LA) technique to protect the transmitted data against random channel impairments in a Multi-Input Multi-Output (MIMO) systems involving Orthogonal Frequency Division Multiplexing (OFDM) scheme. The authors used channel quality indicators such as instantaneous SNR, Shannon capacity and Log Likelihood Ratio (LLR) values, for efficient link adaptation. The paper reports channel information using LS and QRD algorithms to achieve better link performance of the multiuser MIMO-OFDM system in terms of quality and capacity.

In the third paper, “Receiver Position Error Analysis Using Point Solution Approach Algorithm”, the authors V Venkata Rao, G Sasibhushana Rao and M Madhavi Latha have used a non-recursive point solution approach algorithm to estimate the receiver position of a Global Positioning System (GPS) ignoring satellite clock bias, atmospheric delay, multipath error and receiver tracking error. The position error analysis reported may be helpful to the surveyors and the GPS Aided Geo Augmented Navigation (GAGAN) users over the Indian subcontinent in determining the obtained position.

In the fourth paper, “Simulation, Design and Development of Complementary-Symmetry Microstrip Antenna for Compactness, Enhanced Gain, Bandwidth and Low Cross-Polarization”, the authors, N M Sameena, G P Maddani, R B Konda, S K Satnoor and S N Mulgi, have presented a novel design of complementary-symmetry rectangular microstrip antenna with modified ground plane for compactness, enhanced gain, bandwidth and low cross-polarization operation. The complementary-symmetry geometry and modified ground plane effects have been considered to show an improvement in the antenna performance and its suitability for wireless communication systems.

The fifth paper, “A Study on the Performance of Wideband Bandpass Filter Designed Using Multimode Resonator with Etched Rectangular Lattice”, by P K Singhal, Suman Mathur and R N Baral, reports a design of compact microstrip wideband band pass filter using a multiple mode resonator with etched rectangular lattice suitable for pass band of 0.9 GHz-2.1 GHz.

The sixth paper, “Fuzzy Set Optimization Technique for Virtual Topology Reconfiguration for IP-over-WDM Networks with QoS Parameters”, by Ramasamy Mariappan, T Ravi and R S D Wahida Banu proposes a fuzzy set optimization techniques for the reconfiguration of optical internets using IP-over-WDM technology to show a better performance in terms of computational accuracy and average weighted hop count for dynamic traffic.

-- V K Chaubey
Consulting Editor