Broadcast Aspects for Cellular Mobile Systems (Physical Layer)
Currently deployed mobile systems like GSM and UMTS exclusively use point-to-point (p-t-p) links, i.e. each link connects the base station with exactly one mobile, as required by services like voice and SMS/eMail. However, one can imagine many scenarios where several users want to receive the same data, for instance TV broadcasts, news tickers or firmware updates.
Instead of serving each user via a dedicated p-t-p link, it is more economical to broadcast the data to all users simultaneously over a point-to-multipoint (p-t-m) link. Therefore the latest version of the GSM/UMTS standard defines the so called Multimedia Broadcast/Multicast Service (MBMS).
The problem that arises in p-t-m links is, however, that the quality of the transmission channels is not constant for all users but varies significantly. Users close to the base station, for instance, will receive a strong signal, while users at the cell edge will receive a heavily attenuated signal, which is furthermore distorted due to multipath propagation. In p-t-p transmissions it is possible to adapt the transmission power and the channel coding scheme to the current link quality in order to ensure a virtually error-free reception while maximizing the data rate. In p-t-m links, this possibility does not apply.
In this project, we examine physical layer aspects of MBMS for the successor of UMTS, which is currently being specified under the working title "Long Term Evolution" (LTE).
Meik Dörpinghaus, Markus Jordan, Martin Senst