Signal Processing for Communications

Spread Spectrum (SS) techniques have raised a significant importance in mobile communications in recent years. A common form of SS is Direct-Sequence Spread-Spectrum (DS/SS) in which the transmitter multiplies a binary data sequence by a higher rate pseudo-random or pseudo-noise (PN) binary sequence. In particular, DS/SS Code-Division Multiple-Access (CDMA) has emerged as the incoming standard for third-generation radio-mobile transmission technology, since it offers significant advantages in terms of channel capacity, mobile power consumption, link quality and resilience to multi-path propagation. However, in order to exploit the advantages of a SS signal in a CDMA system, receivers must synchronize the local PN code with the incoming PN code. Thus, quickly achieving and then maintaining PN code synchronization is a critical issue to be satisfied because even a small misalignment can cause dramatic signal-to-noise ratio (SNR) degradation.

Another technique that an emerging trend has focused on is, Time Division Duplexing (TDD), in which the same carrier is used for both up- and downlink in different time slots. One of the main advantages of using TDD is that since the same frequency channel is used, reciprocity exists between the link channel characteristics and, hence, this helps knowledge of the channel impulse response. This statement can be used to implement a number of important functions to respond to unfriendly urban mobile channel conditions. In particular, it allows achieving multi-path diversity gain using signal processing at the transmitter, instead of employing a Rake receiver at the mobile station. The flexibility exhibited by the CDMA technique is strictly limited by the interference. To reduce the outage probability, adoption of blind 2D Rake receivers using multiple antennas to resolve different users has been proposed in a number of papers. The goal of a space-time Rake receiver is to optimally combine the contributions received through different paths for the desired user across both space and time. In principle, for each user, the equalizer should coherently combine different contributions arrived with different time delays from different directions. Blind (nondata- aided) adaptive multi-user detection based on the constant modulus algorithm (CMA) has received a lot of attention recently. New criteria for blind deconvolution, such as the Kurtosis maximization algorithm (KMA), develop a necessary and sufficient condition for solving the problem of blind equalization that requires the equalization of only a few higher moments of the corresponding probability distributions. Moreover, the importance of using objective function based on higher order statistics was widely underlined, for code acquisition purposes.

  1. E. Guzzon, F. Benedetto , G. Giunta - "A New Test for Initial Code Acquisition of Correlated Cells" - IEEE Trans. on Vehicular Technology , vol. 62, no. 5, pp. 2349-2358, 2013. DOI: 10.1109/TVT.2013.2240325 . Impact Factor: 1.921.
  2. F. Benedetto, G. Giunta - "On Efficient Code Acquisition of Optical Orthogonal Codes in Optical CDMA Systems" - IEEE Trans. on Communications , Vol. 58, no. 2, pp. 438-441, Feb. 2010. DOI: 10.1109/TCOMM.2010.02.080043
  3. F. Benedetto, G. Giunta - "Two-Dwell Synchronization Techniques and Mimo Systems for Performance Improvements of 3G Mobile Communications" - International Journal of Communications, Network and System Sciences (IJCNS) , vol.6, pp. 511-517, Sept. 2009. DOI: 10.4236/ijcns.2009.26056
  4. F. Benedetto, G. Giunta - "A Self-Synchronizing Method for Asynchronous Code Acquisition in Band-Limited Spread Spectrum Communications" - IEEE Trans. on Communications , vol. 57, no. 8, pp. 2410-2419, August 2009. DOI: 10.1109/TCOMM.2008.08.070030
  5. F. Benedetto, G. Giunta, L. Vandendorpe - "A Blind Equalization Algorithm Based on Minimization of Normalized Variance for DS/CDMA Communications" - IEEE Trans. on Vehicular Technology, in press (Jan. 2008).
  6. G. Giunta, F. Benedetto - “Spread-Spectrum Code Acquisition in the Presence of Cell Correlation” - IEEE Transactions on Communications, vol. 55, no. 2, pp. 257-261, Feb. 2007.
  7. F. Benedetto, G. Giunta - "Improving the Initial Code Acquisition in Asynchronous Band-Limited Spread-Spectrum Systems" - 10th IEEE International Symposium on Spread Spectrum Techniques and Applications, Creating New Dimensions in the Wireless World (ISSSTA 2008) , Bologna, Italy, 25-28 Aug. 2008
  8. G. Giunta, L. Vandendorpe, F. Benedetto - "All-Pass Pre-Filtering in Pre-Post-Rake Schemes for Spread-Spectrum Communications", IEEE Trans. on Signal Processing, vol. 55, no. 8, pp. 4330 - 4334, Aug. 2007
  9. G. Giunta, L. Vandendorpe, F. Benedetto - "Improving Pre-Post Rake Shemes for DS/CDMA Mobile Communications" - Mediterranean Journal of Electronics and Communications, vol. 1, no. 1, pp.16-24, December 2005