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A new practical multiple-input multiple-output (MIMO) transceiver technique called spatially modulated integer-forcing (SM-IF) is proposed for hybrid beamforming array systems, which combines generalized spatial modulation (GSM) with integer-forcing (IF) MIMO multiplexing transmission to achieve improved spectral efficiency with low system complexity. In the proposed scheme, the transmitter first activates a subset of antennas using analog beamforming and delivers an SM information stream via the index of the activated antenna group. Then MIMO digital multiplexing is applied to send multiple MIMO information streams via multilevel coding (MLC) with binary channel codes through the activated antennas. At the receiver side, the receiver first estimates the index of the activated antenna group to recover the SM stream and then recovers the MIMO streams by IF sum decoding in conjunction with multi-stage decoding. The proposed scheme provides a unified coding framework to achieve a synergistic gain by integrating off-the-shelf practical binary codes and low complexity IF decoding into hybrid beamforming array systems. By extensive link-level numerical simulations, the proposed scheme is shown to outperform both the conventional plain IF MIMO and plain SM approaches. The results demonstrate that the proposed SM-IF can be a promising transceiver technique implementable in practical hybrid beamforming array systems. [ABSTRACT FROM AUTHOR]

In this paper, we study the achievable degrees of freedom (DoFs) for $K$ -user multiple-input single-output broadcast channel (BC) in the absence of channel state information at the transmitter under the finite channel coherent time. For the considered $K$ -user BC, a transmitter is equipped with multiple conventional antennas, and receivers are equipped with a reconfigurable antenna that is capable of dynamically modifying the receiving beam radiation pattern. In this system, we propose a blind interference alignment scheme that is able to allocate an asymmetric number of information symbols to each user, which is essentially required to improve DoFs under limited symbol extension. A generalized systematic construction method of transmit beamforming vectors and receiving mode selection patterns to deal with such asymmetric allocation is established. As a consequence, for a broad class of network configurations and symbol extension constraints, the proposed scheme attains an improved sum DoF compared to the previous works, allowing only for the same number of information symbols for all users. [ABSTRACT FROM AUTHOR]

We study Please be advised that per instructions from the Communications Society this proof was formatted in Times Roman font and therefore some of the fonts will appear different from the fonts in your originally submitted manuscript. For instance, the math calligraphy font may appear different due to usage of the usepackage[mathcal]euscript. The Communications Society has decided not to use Computer Modern fonts in their publications. the degrees of freedom (DoF) of cellular networks in which a full duplex (FD) base station (BS) equipped with multiple transmit and receive antennas communicates with multiple mobile users. We consider two different scenarios. In the first scenario, we study the case when half duplex (HD) users, partitioned to either the uplink (UL) set or the downlink (DL) set, simultaneously communicate with the FD BS. In the second scenario, we study the case when FD users simultaneously communicate UL and DL data with the FD BS. Unlike conventional HD only systems, inter-user interference (within the cell) may severely limit the DoF, and must be carefully taken into account. With the goal of providing theoretical guidelines for designing such FD systems, we completely characterize the sum DoFs for both FD cellular networks. The key idea of the proposed scheme is to carefully allocate UL and DL streams using interference alignment and beam forming techniques. By comparing the DoFs of the FD systems with those of the conventional HD systems, we show that the DoF can approach the two-fold gain over the HD systems, when the number of users becomes large enough compared with the number of antennas at the BS. [ABSTRACT FROM PUBLISHER]

The sum degrees of freedom (DoFs) of L -cell multiantenna cellular downlink systems are studied. Each base station (BS) equipped with M_{t} transmit antennas sends independent messages to its K serving users equipped with Mr reconfigurable antennas, each of which can choose its receiving mode from N preset modes at each time. It is assumed that each BS and user only knows channel state information (CSI) of its own cell. A novel two-stage interference management scheme is proposed in which intra-cell interference is first nulled out by zero-forcing outer beamforming based on intra-cell CSI and inter-cell interference is then aligned by inner beamforming in a blind manner without inter-cell CSI. It is proved that, for Mt>KMr and $N>1$ , the proposed scheme achieves an improved sum DoF compared with the conventional time division multiple access among cells. We further demonstrate that such DoF improvement yields an improved sum rate at the finite signal-to-noise ratio regime. [ABSTRACT FROM PUBLISHER]

The feasibility conditions of interference alignment (IA) are analyzed for interfering broadcast-multiple-access channels in which one cell operates as downlink but the other cell operates as uplink. Under a general multiple-input and multiple-output antenna configuration, a necessary condition and a sufficient condition for one-shot linear IA are established, i.e., linear IA without symbol or time extension. In various example networks of interest, the optimal sum degrees of freedom (DoFs) are characterized by the derived necessary condition and sufficient condition. For symmetric DoF within each cell, a sufficient condition is established in a more compact expression, which yields the necessary and sufficient condition for a class of symmetric DoFs. An iterative construction of transmit and receive beamforming vectors is further proposed, which provides a specific beamforming design satisfying one-shot IA. Simulation results demonstrate that the proposed IA not only achieves larger DoF, but also significantly improves the sum rate over the single-cell operation in the practical signal-to-noise ratio regime. [ABSTRACT FROM PUBLISHER]

This paper studies the degrees of freedom (DoFs) of full-duplex (FD) multicell networks that share the spectrum among multiple cells. In the considered network, we assume that FD base stations (BSs) with multiple transmit and receive antennas communicate with multiple single-antenna uplink (UL) and downlink (DL) mobile users. By spectrum sharing among multiple cells, and with FD radio, the network can utilize the spectrum more efficiently. However, since spectrum sharing and FD induce additional inter-cell and intra-cell interferences, interference management is crucial to take advantage of these features. In this paper, we propose novel interference management strategies which take into account the new sources of interferences caused by spectrum sharing and FD to establish a general achievability result on the sum DoFs. The key ideas in our proposed scheme are to minimize the dimension of UL inter-cell and user-to-user interferences using interference alignment at the UL users. On the BS side, we propose an interference management strategy to align or null out DL intra-cell and inter-cell interferences, and BS-to-BS interferences. We further establish an upper bound on the sum DoFs and show that our lower and upper bounds match under certain conditions. Several numerical evaluations are shown which demonstrate that spectrum sharing and FD can significantly improve the throughput over conventional cellular networks, especially for a network with large number of users and/or cells. [ABSTRACT FROM PUBLISHER]

The degrees of freedom (DoF) of $L$-path poor scattering full-duplex (FD) systems is studied in which a FD base station having M$ transmit antennas and M$ receive antennas supports a set of half-duplex mobile stations (MSs). Assuming no self-interference, a hybrid scheduling is proposed achieving the optimal sum DoF with partial channel state information at the transmitter side as the number of MSs increases. In particular, the proposed scheme combines a zero-forcing beamforming for uplink and a random transmit beamforming for downlink with opportunistic scheduling. It is shown that the optimal sum DoF of 2M, where {\sf{snr}} denotes the signal-to-noise ratio. [ABSTRACT FROM PUBLISHER]

An interference management problem among multiple overlapped random access networks (RANs) is investigated, each of which operates with a slotted ALOHA protocol. Assuming that access points and users have multiple antennas, a novel opportunistic interference alignment (OIA) is proposed to mitigate interference among overlapped RANs. The proposed technique intelligently combines the transmit beamforming technique at the physical layer and the opportunistic packet transmission at the medium access control layer. Transmit beamforming is based on interference alignment, and opportunistic packet transmission is based on the generating interference of users to other RANs, which can be regarded as a joint optimization of the physical layer and the medium access control layer. It is shown that the proposed OIA protocol significantly outperforms the conventional schemes such as multipacket reception and interference nulling. [ABSTRACT FROM PUBLISHER]

We consider a wireless network in which a single-source node having m antennas transmits independent messages to n destination nodes, where each destination node has a single antenna. We assume that the source is located at the center of a unit area and the destinations are located uniformly at random in the same area. By applying transmit beamforming at the source, an achievable sum rate can scale as \min \m,n\, which is defined by the aggregate rate of all messages. For transmit beamforming, however, channel state information (CSI) is essentially required at the transmitter (CSIT), which is hard to acquire in practice because of the time-varying nature of wireless channels and feedback overhead. We show that, even without CSIT, almost the same sum rate scaling law assuming CSIT is achievable by inducing cooperation between destinations. Specifically, we study the sum rate scaling law when both the number m of the source antennas and the number n of destinations increase such that n=m^\beta for \beta >0. If \beta >1 the optimal sum rate scales as m\log m and if 0< \beta \leq 1 the optimal sum rate scales between m^\beta (1-\epsilon) and m^\beta\log m, where \epsilon >0 is an arbitrarily small constant, which shows significant improvement compared to the case of no cooperation between destinations. Our result is of particular interest because we did not assume any additional bandwidth for cooperation. [ABSTRACT FROM PUBLISHER]

We show that the 2\,\times \,2\,\times \,2 interference network, i.e., the multihop interference network formed by concatenation of two two-user interference channels achieves the min-cut outer bound value of 2 DoF, for almost all values of channel coefficients, for both time-varying or fixed-channel coefficients. The key to this result is a new idea, called aligned interference neutralization, that provides a way to align interference terms over each hop in a manner that allows them to be canceled over the air at the last hop. [ABSTRACT FROM PUBLISHER]