  While cooperative communication has many benefits and is expected to play an
important role in future wireless networks, many challenges are still unsolved.
Previous research has developed different relaying strategies for cooperative
multiple access channels (CMA), cooperative multiple relay channels (CMR) and
cooperative broadcast channels (CBC). However, there lacks a unifying strategy
that is universally optimal for these three classical channel models.
Sequential slotted amplify and forward (SSAF) strategy was previously proposed
to achieve the optimal diversity and multiplexing tradeoff (DMT) for CMR. In
this paper, the use of SSAF strategy is extended to CBC and CMA, and its
optimality for both of them is shown. For CBC, a CBC-SSAF strategy is proposed
which can asymptotically achieve the DMT upper bound when the number of
cooperative users is large. For CMA, a CMA-SSAF strategy is proposed which even
can exactly achieve the DMT upper bound with any number of cooperative users.
In this way, SSAF strategy is shown to be universally optimal for all these
three classical channel models and has great potential to provide universal
optimality for wireless cooperative networks.
