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We consider a single hop interference network with K transmitters and J receivers, all having M antennas. Each transmitter emits an independent message and each receiver requests an arbitrary subset of the messages. This generalizes the well-known K-user M -antenna interference channel, where each message is requested by a unique receiver. For our setup, we derive the degrees of freedom (DoF) region. The achievability scheme generalizes the interference alignment schemes proposed by Cadambe and Jafar. In particular, we achieve general points in the DoF region by using multiple base vectors and aligning all interferers at a given receiver to the interferer with the largest DoF. As a byproduct, we obtain the DoF region for the original interference channel. We also discuss extensions of our approach where the same region can be achieved by considering a reduced set of interference alignment constraints, thus reducing the time-expansion duration needed. The DoF region for the considered system depends only on a subset of receivers whose demands meet certain characteristics. The geometric shape of the DoF region is also discussed. Index TermsInterference alignment, degrees of freedom region, multicast, multiple-input multiple-output, interference network.L. Ke was with the

Wafer bonding techniques, which are very different from epitaxial growth techniques, can be used not only for the fabrication of micro-electromechanical systems (MEMS), silicon on insulator (SOI), and Si-based device integration, but have recently been applied to the achievement of high-quality homojunctions and heterojunctions in the photoelectric field. That is, carrier transport at the interface of the wafer-bonded junction should be unimpeded and carrier recombination at the bonded interface should be restrained. For Si/Si wafer bonding, although a high bonding strength and a bubble-free bonded interface are needed for the fabrication of the MEMS and SOI, a perfect Si/Si bonded interface which is expected to be bubble-free, oxide-layer-free, and dislocation-free is needed for the achievement of high-performance photoelectric devices, such as Ge/Si single-photon avalanche photodiodes. On the other hand, for Ge/Si heterogeneous hybrid integration (high lattice mismatch), threading dislocations (TDs) in the Ge film can be eliminated by low-temperature heterogeneous wafer bonding, due to the lower diffusion rate of misfit dislocations (MDs) at the Ge/Si bonded interface. This is very different from epitaxial growth, in which high-density TDs form in the integrated Ge layer due to the threading of MDs at high-temperature. In this paper, we review the wafer bonding of Si-based semiconductors based on different bonding methods. The advantages and disadvantages of different bonding methods are pointed out for comparison. We focus on the illustration of the fabrication of Si/Si and Ge/Si wafer pairs with TD-free, bubble-free, and oxide-layer-free bonded interfaces. Finally, the outlook for the development of Si/Si and Ge/Si wafer bonding and devices based on the wafer bonding technique is considered. We trust that this work may provide guidance for the low-temperature heterogeneous hybrid integration of different group materials with ultrahigh lattice mismatch, such as GeSn on Si and III-V materials on Si.

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