We introduce a generalized two-way relay channel where two sources exchange information (not necessarily of the same rate) with help from a relay, and each source additionally sends private information to the relay. We consider the Gaussian setting where all point-to-point links are Gaussian channels. For this channel, we consider a two-phase protocol consisting of a multiple access channel (MAC) phase and a broadcast channel (BC) phase. We propose a general decode-and-forward (DF) scheme where the MAC phase is related to computation over MAC, while the BC phase is related to BC with receiver side information. In the MAC phase, we time share a capacity-achieving code for the MAC and a superposition code with a lattice code as its component code. We show that the proposed DF scheme is near optimal for any channel conditions, in that it achieves rates within half bit of the capacity region of the two-phase protocol.

Motivated by the femtocell networks where cross-tier interference management is crucial to achieve higher system throughput, we consider a basic interference model consisting of a MIMO two-way relay communication network in presence of a one-way point-to-point MIMO communication link. We propose an upper-bound on the maximum degrees of freedom of this channel. Precoders using signal-space alignment strategies at the transmitter and zero-forcing (ZF) receivers are shown to achieve the maximum degrees-of-freedom. The proposed solution is particularly interesting since it allows the macro transmitter to be oblivious to the interfering two-way link, which is an important feature for obtaining distributed solutions.

In the conventional two-way relay channel, two sources exchange information with help from a relay. We introduce a generalized two-way relay channel where each source additionally sends private information to the relay. For this channel, we consider a protocol that consists of a multiple- access (MA) phase and a broadcast (BC) phase and obtain achievable rate regions for both phases. The MA phase is related to computation over the multiple-access channel (MAC). We show that our scheme achieves rates that always lie within half bit of the capacity region for computation over MAC, and is capacity achieving in the BC phase. This near optimality in the MA phase can be achieved by time sharing a capacity-achieving code for the MAC and a superposition code that uses a lattice code as its component code.

This paper presents a systematic technique for constructing STBC-schemes (space-time block code schemes) with non-vanishing determinant, based on cyclic division algebras. Prior constructions of STBC-schemes with non-vanishing determinant are available only for 2,3,4 and 6 transmit antennas. In this paper, by using an appropriate representation of a cyclic division algebra over a maximal subfield, we construct STBC-schemes with non-vanishing determinant for the number of transmit antennas of the form 2kor 3middot2kor 2middot3kor qk(q - 1)/2, where q is a prime of the form 4s + 3 and s is any arbitrary integer. In a recent work, Elia et. al. have proved that non-vanishing determinant is a sufficient condition for STBC-schemes from cyclic division algebra to achieve the optimal diversity-multiplexing gain (D-MG) tradeoff; thus proving that the STBC-schemes constructed in this paper achieve the optimal D-MG tradeoff

This paper presents a systematic construction of high-rate and full-diversity space-frequency block codes for MIMO-OFDM systems. While all prior constructions offer only a maximum rate of one complex symbol per channel use, our construction yields rate equal to the number of transmit antennas and simultaneously achieves full-diversity. The proposed construction works for arbitrary number of transmit antennas and arbitrary channel power delay profile. A key step in this construction is the generalization of the stacked matrix code design criteria given by Bolcskei et al., (IEEE WCNC 2000). Explicit equivalence of our generalized code design criteria with the Hadamard-product based criteria of W. Su et al., (IEEE Trans. Sig. Proc. Nov 2003) is established and new high-rate codes are constructed using our criteria

A new transform is denned for the class of cocyclic group ring codes over a Galois ring, where the underlying group is Abelian and the cocycle is the Vandermonde-cocycle on the Abelian group. The class of Vandermonde-cocyclic (VC) group ring codes are characterized using this new transform by means of a structure theorem for VC group rings.