Digital Communications Research Laboratory

Some Pieces of Equipment

 

 

Research Team Members

Students at Work

 

 

 

Sponsored Research Projects

 

1.      “Programmable, variable rate and multi-mode MODEM/CODEC at Ka Band for Advanced Communications Technology Satellite (Hardware design and implementation)”, NASA Lewis Research Center, Oct. 1, 1991- Jan. 31, 1994.

2.      “Modem/Codec techniques in satellite communications”, NASA Lewis Research Center, Aug. 26, 1991-Mar. 31, 1992.

3.      “Intersatellite Link Techniques”, NASA Lewis Research Center,  Jun. 15, 1992-Mar. 31, 1993.

4.      “Power Efficient Reflectarray System Modulation Study”, NASA Glenn Research Center, Jan. 16-Sept. 21, 2001.

5.      “Synchronization Study in Mobile Aeronautical Communication Systems,” NASA Glenn Research Center, May 2001-May 2002.

6.      “Self-modulation Reflectarray”, NASA Glenn Research Center, Jan. 2004-Dec, 2005.

 

Other Research Projects

 

1.     “Carrier synchronization in coherent ASK-OFDM systems,”  since 2000.

2.     “ICI due to multipath effect and its estimation and correction in multipath fading channels for ASK-OFDM,”, since 2001.

3.     “Coding for coherent ASK-OFSM systems,” since 2002.

4.     “Robust symbol timing for Mobile Aeronautical Satellite Communication Systems,” since 2001.

5.     “MASK-OFDM modem design for the 5 GHz Microwave Landing System, since 2004.

6.     “Channel estimation and equalization of the MASK-OFDM modem for the 5 GHz MLS Extension Band,” since 2004.

7.     “Carrier synchronization of the MASK-OFDM modem for the 5 GHz MLS Extension Band,” since 2004.

8.     “Symbol synchronization of the MASK-OFDM modem for the 5 GHz MLS Extension Band,” since 2004.

 

Descriptions of Research Projects

 

M-ary ASK OFDM System


Research and development are taking place all over the world to define the next generation of wireless broadband multimedia communications systems (WBMCS). For such large data rates with sufficient robustness to radio channel impairments, OFDM seems to be the most suitable modulation choice. It has already been deployed in the IEEE802.11, HIPERLAN and also in the Digital Video Broadcasting (DVB), Digital Audio Broadcasting (DAB) (in Europe).


Our project investigates the feasibility of using M-ary ASK in contrary to QAM and QPSK that are conventional modulation techniques used in OFDM systems. M-ary ASK OFDM also facilitates use of FCT/IFCT for sub-carrier modulation, a transform that operates on real numbers and requires fewer computations than the DFT/IDFT (used in QAM-OFDM and QPSK-OFDM systems). (A patent is pending on MASK-OFDM using FCT/IFCT).


Other than a simplified VLSI implementation of the OFDM modem, this scheme also offers comparable performance in terms of power-efficiency and bit error performance.
In our lab, we are investigating some important aspects of this system such as:


* Synchronization techniques
* Complexities of post-transform detection
* Channel estimation techniques
* Coding techniques to be used to improve bit-error performance

Lab members working on this project:


Dr. F. Xiong, Yan Ma, Vishu Suvarna, Mukul Gandhi

 

NASA/CSU Modulation Study of Reflectarray Antenna Systems (completed, 2003)

 

With the wider application of the Reflectarray Antenna, people begin to concern the intersymbol interference (ISI) problem that comes with the way the Reflectarray antenna operates. This problem has ultimately limited the size and the gain of the antenna. Therefore our research focuses on the ISI analysis as well as finding the best modulation schemes for high date rate links.

 

This project is under the supervision of Dr. Fuqin Xiong in Electrical and Computer Engineering Department at Cleveland State University and supported by NASA Glenn Research Center, RA branch. The research assistants are Yan Ma and Stanley Pinchak at Digital Communication Research Lab at CSU.

 

NASA/CSU Self-modulation Reflectarray Antenna (in progress as of March 2005)

 

The objective of this project is to study the feasibility and performance of using inherent phase shifters on a reflectarry antenna to realize BPSK so that no separate modulator is needed.

 

Lab members working on this project:


Dr. F. Xiong, Huaihai Guo.

 

 

NASA/CSU Robust Synchronization Project (completed 2004)

 

The objective of the robust synchronization project is to research advanced synchronization techniques applicable to NASA’s satellite to mobile vehicle communication link, and to perform detailed analysis and simulation on the most suitable technique.  This synchronization technique will be recommended to NASA for use in its upcoming satellite to mobile modems.  The project began in May 2001 and will continue until September 2003.  Currently, a symbol synchronization scheme called sliding window synchronizer is being analyzed and simulated as potential candidate. 

 

Communication lab members working on this project are Dr. Xiong and Stanley Pinchak

 

Waveform Study of 5-GHz MLS Extension Band Project (in progress as of March 2005)

 

As a part of the research effort of NASA’s ACAST project, we are studying the waveforms for transmission in the extension frequency band (5.091- 5.150 GHz) of FutureCom microwave landing system (MLS). In particular, we are studying the use of DCT-MASK-OFDM (Discrete Cosine Transform-based M-ary Amplitude Shift Keying Orthogonal Frequency Division Multiplexing) for the MLS channel. DCT-MASK-OFDM was recently invented by Dr. Fuqin Xiong and is getting popularity among the communication researchers. Based on the preliminary studies at CSU's Digital Communication Research Laboratory, in comparison with the conventional QAM-OFDM, DCT-MASK-OFDM uses the same bandwidth and can offer the same BER performance in AWGN channel while it has the advantages of less system complexity and more robustness against carrier frequency offset. We also will combine DCT-MASK-OFDM with CDMA to form DCT-MC-CDMA. We will design the blocks in a DCT-MASK-OFDM transceiver and a DCT-MC-CDMA transceiver and evaluate their performances in the MLS extension channel. Various channel conditions will be considered: fading, carrier frequency offset, Doppler frequency shift, etc. A set of evaluation criteria will be developed to form a “waveforms vs. criteria matrix” which can be used for performance evaluations. Computer simulations via Matlab-Simulink will be carried out to verify the analytical results and to aid the analysis. Results will be compared with the conventional OFDM systems.

 

Lab members working on this project:


Dr. F. Xiong, Huaihai Guo, Vijay Normula, Ying Yang, Sai Mantripragada.