RESEARCH 

Performance Evaluation of IEEE 802.16 for Fixed Broadband Wireless 

Access Systems (Current Research) 

The IEEE 802.16 task group recently published its WirelessMAN^TM air interface standard that standardizes the MAC and PHY layers for fixed BWA systems. A significant aspect of this standard is that it tries to retain much of what is already in use in the market and only tries to streamline the development process by recommending practices based on already widespread technology.

Many proprietary BWA systems adapt the DOCSIS v. 1.1 MAC to operate in a wireless environment using QPSK and QAM based PHY schemes. The WirelessMAN^TM air interface is also based on similar lines. It has been designed to address systems operating from 10 to 66 GHz. It standardizes a common DOCSIS-based MAC over a wide range of PHY options. The PHY supports various modulation and coding schemes in order to operate over this wide spectrum. In addition, IEEE 802.16 also defines a radio link control (RLC) layer enabling dynamic switching between PHY configurations. This allows the system to adapt to various physical channel impairments such as rain fades and multipath.

My research focuses on evaluating the performance of IEEE 802.16’s adaptive PHY capabilities. My interest is to study the performance of the various PHY options provided by IEEE 802.16 under various channel conditions. Based on this work I intend to propose an algorithm to implement adaptive modulation and coding in such systems. I have developed a model to simulate an IEEE 802.16 system, using OPNET Modeler.

:: Frequency sharing with Radio Determination (RD) Services

:: Frequency sharing with Fixed Service (FS) services

:: Propagation effects on AMSS signals received at the Earth's surface.          

:: Especially the 4/3 Earth radius effect.

:: Atmospheric and ground reflection multipath effects

:: Rain Effects

WORK EXPERIENCE

Product Engineer, Wipro Infotech Ltd., India (Summer 2000) 

Worked with Wipro’s Home and Desktop PC - Product Engineering Team. Was involved in testing hardware compatibility issues on the Windows/Windows NT platforms. Was also involved in network testing of Wipro products on the Windows NT platform. 

Radio Engineer, RPG Cellular Services Ltd., India (Nov 1999 - Mar 2000)

Worked on CME20, Ericsson's solution for GSM 900. Was involved in Cell Parameter Planning, Frequency Planning and Network Optimization. Have experience in using optimization packages such as Ericsson TEMS, Aircom Neptune etc. Am also familiar with planning tools like Aircom Asset.  Primary responsibilities included strict control over rxqual, call drops rate and handoff success rate. Was actively involved in Network Implementation. Have experience in BTS and repeater implementation.

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SELECTED PROJECTS

MAI and Capacity Issues in a Multirate CDMA System  [Report] [Presentation]

Third generation mobile communication standards such as WCDMA are aiming to provide multimedia services and support a number of different classes of users with different data rates and QoS requirements. These characteristics affect multiple access interference and hence capacity. In order to support higher and variable data rates WCDMA proposes using Orthogonal Variable Spreading Factor (OVSF) codes. Shorter codes with lower spreading length are assigned as the data rate increases. In this way variable data rate is achieved while keeping the chip rate constant.

This project analysis the effect on the system capacity when calls with different data rates are made. Extensive simulations were run on Matlab to determine how users of the same and different user-class affect each other. How exactly high data rate users limit the capacity is clearly shown in the results.

RAKE Receiver in Asynchronous CDMA System - Implementation on a DSP  [Report] [Presentation]

RAKE receivers capitalize on that fact that multipath components are phase-shifted versions of the desired signal. Instead of eliminating multipath it uses techniques to effectively use multipath to provide some gain in the output. This project ia an implementation of a RAKE receiver on TMS320C30 DSP processor. The performance of the RAKE is studied and the performance of various combination schemes is compared. The project also demonstrates performance improvement in BER when Parallel Interference Cancellation (PIC) is used.

DSP Implementation of Communication Subsystems

The following subsystems were implemented on a Texas Instruments TMS320C30 floating point DSP.

:: BPSK Transmitter
:: IIR and FIR Filters
:: Costas Loop Detector
:: Symbol Synch Subsystem
:: Code Synch Subsystem

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PUBLICATIONS AND TALKS

Conference Papers 

:: S. Ramachandran, C. W. Bostian and S. F. Midkiff, “Performance Evaluation of IEEE 802.16 for Broadband Wireless Access,” Proceedings of OPNETWORK 2002, Aug 2002.

Posters

:: S. Ramachandran, C. W. Bostian and S. F. Midkiff, “Performance Evaluation of IEEE 802.16,” Wireless Opportunities Workshop, CWT, Fall 2002.

:: S. Ramachandran, C. W. Bostian and S. F. Midkiff, “Performance Evaluation of IEEE 802.16,” 12th Wireless Personal Communications Symposium, MPRG, June 2002.

:: S. Ramachandran, C. W. Bostian and L. Sung, “Interference Analysis and Propagation Study for Connexion^TM by Boeing,” Wireless Opportunities Workshop, CWT, Fall 2001.

Talks

:: “Modeling Adaptive PHY Profiles in IEEE 802.16,” Cross-Layer Design Optimization Group, Virginia Tech, July 10^th, 2002.

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SOFTWARE SKILLS

 

Programming Languages	C, C++, VC++ ( MFC ), Visual Basic, Java
Databases	MS Access
Operating Systems	Windows 95/98/NT, UNIX
Simulation Tools	Matlab, OPNET
Processors	Texas Instruments TMS320C30, Intel 8085
Other Tools (GSM Optimization)	Aircom Neptune, Ericsson TEMS, Aircom Planet

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