Mobile or Portable Communications Systems, 4G and Beyond

q       Wavelet Packet Transmission Systems

 

As proven by the success of OFDM, multi-carrier modulation has been recognized as an efficient solution for wireless communications. Waveform bases other than sine functions could similarly be used for multi-carrier systems in order to provide an alternative to OFDM. For example, wavelet packet modulation (WPM) for transmission over wireless channels, is shown to be overall quite similar to OFDM, but with some interesting additional features and improved characteristics.

 

Though the principle of multi-carrier modulation is not recent, its actual use in commercial systems had been delayed until the technology required to implement it became available at reasonable costs. Similarly, the idea of using more advanced transform than Fourier’s as the core of a multi-carrier system has been introduced more than a decade ago. However, such alternative methods have not been viewed with major interest and therefore have received little attention. With the current demand for high performance in wireless communication systems, one is entitled to wonder about the possible improvement that wavelet-based modulation could exhibit compared to OFDM systems.

 

Several objectives motivate the current research on WPM. First, the characteristics of a multi-carrier modulated signal are directly dependent on the set of waveforms of which it makes use. Hence, the sensitivity to multi-path channel distortion, synchronization error or non-linear amplifiers might present better values than a corresponding OFDM signal. Little attention has been given to the evaluation of those system level characteristics in the case of WPM. Moreover, the major advantage of WPM is its flexibility. This feature makes it eminently suitable for future generation of communication systems. With the ever-increasing need for enhanced performance, communication systems can no longer be designed for average performance while assuming channel conditions. Instead, new generation systems have to be designed to dynamically take advantage of the instantaneous propagation conditions. This situation has led to the study of flexible and reconfigurable systems capable of optimizing performance according to the current channel response. A tremendous amount of work has been done recently to fulfill this requirement at the physical layer of communication systems: complex equalization schemes, dynamic bit-loading and power control that can be used to dynamically improve system performance. While WPM can take advantage of all those advanced functionalities designed for multi-carrier systems, it benefits also from an inherent flexibility. This feature together with a modular implementation complexity makes WPM potential candidate for building highly flexible modulation schemes. Wavelet theory has been foreseen by many investigators as a good platform on which to build multi-carrier waveform bases.

 

q       Next-Generation Military Networks:

  Network-Enabled RF/Optical Wireless Communications

 

   Needless to say, where line-of-sight is available (see the figure below), using ultra-short laser pulses, one may achieve the ultimate wideband over unregulated optical frequency bands, using Free-Space-Optical (FSO) or a hybrid of RF/FSO links. Then one is able to beam optical band to distant points. This approach could help bring optical bandwidth, capable of carrying huge amounts of information, to applications ranging from wireless communications between air and ground vehicles on the battlefield, to short links between college campus buildings or to metropolitan area networks that connect all the buildings in a city.

 

 

The papers below are based on a recently devised new methodology to pack the data into rapid-fire bursts of light that can blast through fog and clouds. This new system uses ultra-short pulses of laser light that provide greater bandwidth and improved reliability over conventional optical wireless links. The approach uses a technique called "Fractal Modulation", which is a form of Wavelet Packet Modulation (WPM), to produce wavelets that can co-exist in a signal channel without interference, and provide frequency and time diversity, concurrently. By sending the same message at several different rates (multi-rate), one can get through adverse weather conditions.

 

Using Fractal modulation, each receiver has a menu to choose the best received signal transmission rate, thus adaptation is feed-forward.  At the same time, wavelets have the desirable properties of being both time and frequency limited, thus are able to pack a large amount of power in very short pulses, in addition to providing inherent diversity:

 

o     A 100 fs pulse at 100 mJ would produce a peak power of 1 Terawatt. At 2 Giga pulse per second, this is 200 Mega Watts of average power.  With today’s nano-second technology, a Terawatt of peak power would require laser energies of 1000 J.

 

 

 

Ultra-short Pulse Shaping Experimental Set-up

(CICTR LABS)

 

 

 

A Real-Time 460 Femto-second Meyer Wavelet Shaped Pulse at a 3 Giga Pulse per Second Rate

(Intensity Correlation Image at CICTR LABS)

 

 

Spatial and temporal matched filtering can then be applied through Spectral Encoding and Decoding of frequency components of the broadband ultra-short light pulses. The encoding/decoding may be realized all-optically through photolithographic masks or other types of spatial light modulators. 

 

The space-time focusing properties of this approach can lead to a new class of wireless “Opportunistic Communications” systems with significant advantages over current RF approaches. Using this approach, one is liberated from the many constraints of spectrum allocation and regulation. The spatial focusing potential of this approach is an appealing quality, in power saving and would allow accommodating as many users as possible within it. Interference issues of shared RF bands are non-existent here.

 

Potential applications include commercial wireless as well as specialized systems, such as secure communication systems that demand a low probability of intercept.

 

More information is available on: http://cictr.ee.psu.edu/research/ni/index.html. See also: Laser Transformation and DARPA ORCLE.

 

                Penn State Engineering, June 2007: Fiber in the sky

            

                     Penn-State Research News, November 10, 2006:  Cloudy day won't rain on laser communications

    

• S. Lee and M. Kavehrad,”Airborne Laser Communications with Impulse Response Shortening and Viterbi Decoding,” Proceedings of the IEEE MILCOM, Washington, D.C., October 2006.

 

                                            Defense Advanced Research Projects Agency News: US_ Politics Today

                                             Laser Focus: FREE-SPACE OPTICS: Laser link offers fiber quality through cloud cover

                                             Physic-Org : Cloudy day won't rain on ...........

                                             Innovation Germany :Cloudy.............

                                             PHOTONICS: Cloudy.....................

                                             Centauri Dreams: A Boost for Optical Communications

                                             Space Mart: Cloudy .....................

                                             Science Daily: Cloudy.......................

                                  

                                Penn-State Research News, October 27, 2004: Multi-Rate Laser Pulses Could Boost Outdoor Optical Wireless Performance

o                                                           Penn-State Board of Trustees meets, November 19, 2004: President Spanier's remarks

 

• M. Kavehrad, “Through clouds fractal ultra-short pulse laser communications,” SPIE Great Lakes Photonics Symposium, Dayton, Ohio, June 12-16, 2006.

• B. Hamzeh, “Multi-rate wireless optical communications in cloud obscured channels,” Ph.D. Thesis, Advisor: Kavehrad, Mohsen, THE PENNSYLVANIA STATE UNIVERSITY, ISBN: 0-542-47552-9, Publish Date: Jun 2006.

• B. Hamzeh, M. Kavehrad, “Laser Communications to Beam Optical Band to Distant Points,” Proceedings of NASA ICNS’06, Baltimore, MD, May 1, 2006.

• Haiping Wu; Belal Hamzeh; Mohsen Kavehrad, “Availability of airborne hybrid FSO/RF links,” Proceed. of the SPIE, Volume 5819, pp. 89-100, 2005.

• B. Hamzeh, S. Jivkova, and M. Kavehrad, "Arbitrary Waveform Synthesis for Communication Applications," Journal of Optical Networking, Vol. 4, No. 10, pp. 647-656, September 2005, OSA Journal of Optical Networking.

• M. Kavehrad, B. Hamzeh ”Laser Communication System Using Wavelet-Based Multi-Rate Signaling,” Proceedings of IEEE MILCOM, Monterey-California, November 2004.

• SCI-TECH TODAY: Digital Dolphins May Improve Telecom.

• Government Technology: Optical Wireless Signals

• Laser Focus World: Multi-rate laser pulses could boost outdoor optical wireless performance.

• Laser Focus World: CONFERENCE REVIEW: Optics East features nanotechnology and ITCom.

• M. Kavehrad, D. Zaccarin, "Optical Code-Division-Multi-plexed Systems Based on Spectral Encoding of Non-coherent Sources," Jour. of Lightwave Tech., Vol. 13, No. 3, March 1995.

• M. Kavehrad, “A Countermeasure to Improve Outage Performance of Interference-Limited Microwave Radio Links,” Canadian Journal of Electrical & Computer Engineering, Vol. 16, No. 1, January 1991.

• M. Kavehrad, "Design and Performance Considerations for the Hybrid Atmospheric Optical/Digital Microwave Network Systems," Technical Memorandum, AT&T Bell Laboratories, December 1987.

 

Acknowledgments

A DARPA Grant sponsored by the U.S. Air Force Research Laboratory/Wright-Patterson AFB Contract-FA8650-04-C-7114 and The Pennsylvania State University CICTR has supported this research.

 

q       Robust and Error-Resilient Multi-media Transmission over Wireless Channels

 

Starting with H.263+ and H.323 standards software code for packet-video encoding, appropriate measures are being added to this software, in order to make associated compression algorithms more error-resilient on fading multi-path channels.

 

Agoren, M. Kavehrad, “Robust Mobile Multi-media Conferencing,” Proceedings of the Third IEEE Workshop on Wireless Local Area Networks, Boston-Mass., September 2001.

 

Return to top of page

Related Patents / Papers:

 

B. Hamzeh, M. Kavehrad, “Laser Communications to Beam Optical Band to Distant Points,”   Proceedings of NASA ICNS’06, Baltimore, MD, May 1, 2006.

 

M. Kavehrad, B. Hamzeh, ”Ultra-short Pulsed FSO Communications System with Wavelet Fractal Modulation,” Proceedings of Optics East, Philadelphia Pennsylvania, October 2004.

 

M. Kavehrad, B. Hamzeh ”Laser Communication System Using Wavelet-Based Multi-Rate Signaling,” Proceedings of IEEE MILCOM, Monterey-California, November 2004.

 

H. Liu, A. Ravindran, D.J. Miller, M. Kavehrad, J.F. Doherty, I. Agoren, A. Lackpour, “Error-Resilient H.263 Video Coding for Wideband CDMA Systems,” Proceedings of the Thirty-Fifth Asilomar Conference on   Signals, Systems and Computers, Pacific Grove, CA., November 2001.

 

Ravindran, H. Liu, I. Agoren, A. Lackpour, D. Miller, M. Kavehrad, J. Doherty, “Mobile Multi-media Services for Third Generation Communications Systems,” Proceedings of the IEEE Vehicular Technology Conference, Atlantic City, October 2001.

 

Agoren, M. Kavehrad, “Robust Mobile Multi-media Conferencing,” Proceedings of the Third IEEE Workshop on Wireless Local Area Networks, Boston-Mass., September 2001.

 

US patent # 4,672,658, Spread Spectrum Wireless PBX (W-CDMA).

 

M. Kavehrad, B. Ramamurthi, "Direct-Sequence Spread Spectrum with DPSK Modulation and Diversity for Indoor, Wireless Communications," IEEE Trans. on Communications, February 1987, pp. 224-236.

 

M. Kavehrad, G.E. Bodeep, "Design and Experimental Results for a Direct-Sequence Spread-Spectrum Radio using Differential Phase Shift Keying Modulation for Indoor, Wireless Communications," IEEE Journal on Selected Areas in Communications, June 1987, pp. 815- 823.

 

M. Kavehrad, P.J. McLane, "Performance of Low-Complexity Channel-Coding and Diversity for Spread-Spectrum in Indoor, Wireless Communication," AT&T Technical Journal, Vol. 64, No. 8, October 1985, pp. 1927-1966.

 

M. Kavehrad, "Performance of Non-diversity Receivers for Spread Spectrum in Indoor Wireless Communications," AT&T Technical Journal, Vol. 64, No. 6, Part-1, July-August 1985, pp. 1181-1210.

 

M. Kavehrad, P.J. McLane, "Spread Spectrum for Indoor Digital Radio," IEEE Communications Magazine, June 1987, pp. 32-40.

 

M. Kavehrad, "An Accessing Technique for Information Packet Networks," Proceedings of EASCON, Washington, D.C., Nov. 1981.

 

Chung, J., J. Metzner. October 1992. Packet Synchronization and Identification for Incremental Redundancy Transmission in FH-CDMA Systems. Proceedings of Third International Symposium on Personal, Indoor, and Mobile Communications. pp. 961-964.

 

A. Higashi, T. Matsumoto, M. Kavehrad, "Effect of Noise-Only-Paths on the Performance Improvement of Post-Demodulation Selection Diversity in DS/SS Mobile Radio, "IEICE Trans. on Communications (Japan), Vol. E76-B, No. 4, April 1993.

 

Return to top of page

 

Return To CICTR Current Research Page