Telecommunication industry continues to implement new technologies to provide high bandwidth efficiency and high speed multimedia data transmission capabilities through sophisticated wire line, optical cables or wireless technologies. Today’s telecommunication networks extended from wired to wireless interfaces connect more than half of the world’s population to exchange voice, text and images to implement transformational effects on social life, national economies, education, healthcare and industrial growth. Obviously to meet the challenges of ubiquitous transmission of multimedia traffic through heterogeneous networks attracted researchers and technology developers to explore the opportunities and do research and development in the telecommunication and related industries. The research and innovation in these areas provide better and cheaper products for telecommunication standards, wireless extensions to IEEE 802.xx data networks and wireless connectivity to Internet compatible with GSM, CDMA and 3G-based cellular systems. New research trends are to support high speed data with QoS allowing roaming throughout different service providers even using different delivery technologies. Multimedia demand and IP-based network architecture with reliable high throughput air interface utilize the potentials of Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO) system to support Gigabit Ethernet and wireless routers. Mobile IP allows both universal mobility and high data access either in a fixed location or in motion and thus needs efficient interfaces and protocols for medium access. The present issue addresses some of these subjects to improve the wireless network performance and presents five papers covering MIMO and OFDM techniques to improve wireless link, packet and IP switching in data networks, Medium Access Control (MAC) protocols for Ad Hoc networks, resonator antenna and antenna design optimization techniques.

Wireless system link performance is usually limited by multifading and interference from other users. The OFDM is really a form of multicarrier transmission technique exploiting orthogonal property of carrier to avoid interference and provides an enhanced data transfer rate over fixed FDM transmission system. The first paper of this issue,“A Survey of Intercarrier Interference Cancellation Schemes in MIMO-OFDM System“ authored by Alka Kalra and Rajesh Khanna is a review paper presenting a useful survey of OFDM-MIMO system applicable for wireless system. The paper reports the reduction in computational effort by implementing flat-fading MIMO algorithms on a carrier-by-carrier basis in OFDM system. The Intercarrier Interference (ICI) cancellation techniques have also been presented.

The authors, V S Tripathi and S Tiwari in the second paper, “Design and Analysis of a Modified-Cyclic-Banyan-Based ATM/IP Switching Fabric Using JENQ’s Model” have analyzed a N ´ N switch fabric applicable for packet routing, mixed ATM and IP traffic. Deflection-routing algorithm in each switching element of the generic Banyan network has been applied. The paper presents scalable switch architecture based on the topological properties of Banyan networks and claims a better performance.

In the third paper, “A TDMA-Based MAC-Protocol for Ad Hoc Networks” the author Jorma Jormakka proposes a MAC protocol for medium-sized Ad Hoc networks which supports quality-of-service over several hops by reservation of time slots. As a new feature, the protocol avoids the hidden and exposed terminal problem by a two-hop reservation, not by the RTS/CTS protocol. The proposed protocol ISMA/RA supports constant bit rate voice communication and shows a TDMA solution.

The authors, R G Madhuri, P M Hadalgi and S L Mallikarjun in the fourth paper entitled “A Simple Slot-Fed Cylindrical Dielectric Resonator Antenna” have presented a simple slot-fed Cylindrical Dielectric Resonator Antenna (CDRA) fed by a microstrip line through a coupling slot. The paper reports an improved impedance bandwidth for a thicker Dielectric Resonator showing better bandwidth for dual modes and also presents return loss, radiation patterns of the proposed antennas.

The final fifth paper, “Optimization of Five-Element Nu-Dipole Yagi-Uda Antenna Using Genetic Algorithms” authored by Dauda and Umar Suleiman reports the analysis of radiation characteristics of an optimized five-element nu-dipole Yagi-Uda antenna array. Current distributions on the antenna array, maximum directive gain and input have been computed using spacing Integro-differential equation for the antenna array. A combination of MOM and Genetic Algorithm (GA) was used to maximize directive gain as a single objective function for the five-element array.

-- V K Chaubey
Consulting Editor