Transactional Memories (TM) have attracted much interest as an alternative to lock-based synchronization in shared-memory multiprocessors. Considering the use of TM on an embedded, NoC-based MPSoC, this paper evaluates a LogTM implementation. It is shown that the time an aborted transaction waits before restarting its execution (the backoff delay) can seriously affect the overall performance and energy consumption of the system. This work also shows the difficulty to find a general and optimal solution to set this time and analyzes three backoff policies to handle it. A new solution to this issue is presented based on a handshake between transactions.