Mobile phones have become widely popular, as we find difficult nowadays to imagine a time when people were not always connected, at least by the phone, when not even through PDAs, smart phones and advanced tools like these. With an ever increasing number of subscribers worldwide, mobile phones are relevant sector of the information markets in continuous evolution. The first success story in this field has been the GSM system for Europe and many Asian countries. At the same time, CDMA2000 was spreading in USA. More recently, 3GPP solutions have reached the market, with UMTS devices in Europe and 1xEVDO solutions in the USA. But more is to come, as the new long term evolution (LTE) of 3GPP has been already standardized, promising even higher bit rates and new services. Behind all this there is cutting edge technology and advanced solutions, on which our group at d.g.t. has been actively involved in these years.
A number of issues have been addressed, from the equalization to channel estimation, from planning of resources to optimization of transmission techniques when multiple antennas are available. Among the most recent research activity, we mention the study of use of multiple antennas to focus the transmission from the base station to each terminal and vice versa. Resource allocation plays in this case an important role: if the transmitter is able to transmit to a user that is now in a good channel condition, while delaying transmission to users that are in a fade, the network throughput can be increased significantly.
Another relevant area of research for our group is the access techniques, i.e. how to share the resources among the different users. Relevant results have been achieved in the study of code division multiple access (CDMA) systems, where the common spectrum is shared among users by suitable coding applied on the information. The interference among users is mitigated by the coding, and further advanced signal processing techniques can be applied to remove the residual interference. Another possibility is to use frequency division multiple access (FDMA), possibly in combination with single carrier transmission (see also the single/multicarrier transmission section).
For further information, please contact dr. Stefano Tomasin.