MBMS in Release 6, can combine signals from different cells and this can be used to boost the reliability of the received signal. Though this concept is good, the other neighbouring cells are still causing interference since the adjacent cells are not orthogonal due to different scrambling codes. If the same scrambling code were to be used in all cells and the cells were to be synchronised, the other cells’ interference would turn into multipath
propagation. The received signal looks as if there is only a single base station transmitting, but with more multipath components. Therefore, this approach is called an SFN (Single Frequency Network).
propagation. The received signal looks as if there is only a single base station transmitting, but with more multipath components. Therefore, this approach is called an SFN (Single Frequency Network).
Similar approach is also used in other Mobile-TV technologies like DVB-H.
The SFN approach is available in Release 7 and can be implemented with relatively minor modifications to the radio network while providing a major gain in the broadcast data rates. On the other hand, SFN transmission requires that the whole 5 MHz carrier is allocated for MBMS usage only, which requires that the total amount of spectrum for the operator is large enough.
Source: WCDMA for UMTS – HSPA Evolution and LTE, fourth edition. Edited by Harri Holma and Antti Toskala, John Wiley & Sons, Ltd.
No comments:
Post a Comment