This paper proposes a generalized sequential slotted amplify and forward (GSSAF) strategy for single-antenna wireless cooperative networks. The diversity and multiplexing tradeoff (DMT) is analyzed. Applications to cooperative multiple relay channels, cooperative broadcast channels (CBC) and cooperative multiple access channels are considered and the DMT upper bound is proven to be achievable for each case. Other than proposing the best known near-optimal strategy for CBC, another important contribution is to show that GSSAF can be used as a unified strategy to achieve DMT optimality in wireless cooperative networks with unit multiplexing gains.

This paper studies the diversity benefit of different interference alignment solutions. While most research about interference alignment was aiming at deriving or realizing the maximum achievable multiplexing gain, the symbol error rate performance, which can be characterized by the diversity gain is of equal importance. Different interference alignment solutions are classified into two categories called diversity interference alignment and zero-forcing interference alignment. Although these two types of solutions are not distinguishable in terms of the multiplexing gain, this paper will show their difference lies in the fact that they have different diversity gains. In this paper, a K-user (M × N) interference channel is used, with each user sending 1 degree of freedom of information by using interference alignment precoding and receiving filters but without space-time codes. The feasibility conditions for diversity interference alignment to be achieved are analyzed and the diversity orders different solutions can provide are compared. The results imply that diversity interference alignment solutions offer both multiplexing and diversity gains simultaneously. It also tells us two important rules about the interference alignment precoding filters design: an optimal design has to take both desired and interference channel matrices into consideration and the separation of interference alignment precoding filters design and space-time codes design may not be optimal in general.

Consider a (1 × 1, ½)Ksymmetric wireless interference network where K single-antenna user-pairs want to achieve ½ degrees of freedom each. It has been proved that it is almost surely infeasible to achieve interference alignment without symbol extension. While it was proved relays can not increase the degree of freedom of wireless interference networks, we show this does not preclude the usefulness of using relays to construct practical solutions to approach interference alignment with finite symbol extensions. Feasibility conditions for relay-aided interference alignment are analyzed and an example about how to design the relaying functions to approach interference alignment is given. Simulation results also justify the use of relays as a practical means to do interference alignment with finite symbol extensions.

We propose a near-optimal relaying strategy for cooperative broadcast channels (CBC), CBC-SSAF, based on the class of sequential slotted amplify and forward (SSAF) strategies. Our strategy allows each destination to act in turn as a relay and forward its previously received signal to other destinations. While CBC-SSAF is not a full multiplexing gain strategy, the loss is negligible when the number of destinations is large. Moreover, CBC-SSAF allows each destination to be protected by the maximum number of extra paths in order to achieve the near-optimal diversity gain in the high multiplexing gain regime. A diversity and multiplexing tradeoff (DMT) lower bound for CBC-SSAF is derived which suggests that our proposed relaying strategy approaches the multiple-input multiple-output (MIMO) DMT upper bound and is therefore asymptotically optimal.