Timing estimation consists of two main tasks: packet synchronization and symbol synchronization.
The IEEE 802.11 MAC protocol is essentially a random access network, so the receiver does not know exactly when a packet starts. The first task of the receiver is to detect the start of an incoming packet. HiperLAN/2 medium access architecture is a hybrid of both random access and time scheduled networks. Thus HiperLAN/2 receivers also have to be able to reliably detect the start of incoming packets, without prior knowledge.
Broadcast systems naturally do not require packet detection algorithms, because transmission is always on. However, for a packet oriented network architecture, finding the packets is obviously of central importance ...