Blind Interference Alignment Scheme Research Articles

On the Synergistic Benefits of Reconfigurable Antennas and Partial Channel Knowledge for the MIMO Interference Channel

Author(s): Yuan, Bofeng; Ismailoglu, Nilab; Jafar, Syed A | Abstract: Blind Interference Alignment (BIA) schemes create and exploit channel coherence patterns without the knowledge of channel realizations at transmitters, while beamforming schemes rely primarily on channel knowledge available to the transmit- ters without regard to channel coherence patterns. In order to explore the compatibility of these disparate ideas and the possibility of synergistic gains, this work studies the Degrees of Freedom (DoF) of the 2-user (?1 × ?1)(?2 × ?2) Multiple- Input Multiple-Output (MIMO) Interference Channel (IC) where Transmitter 1 is equipped with reconfigurable antennas and has no channel knowledge, while Transmitter 2 has partial channel knowledge but no reconfigurable antennas. Taking a fundamental dimensional analysis perspective, the main question is to identify which antenna configurations allow synergistic DoF gains. The main results of this work are two-fold. The first result identifies antenna configurations where both reconfigurable antennas and partial channel knowledge are individually beneficial, as those where ?1 l ?1 l min(?2,?2). The second result shows that synergistic gains exist in each of these settings, over the best known solutions that rely on either reconfigurable antennas or partial channel knowledge alone. Coding schemes that jointly exploit partial channel knowledge and reconfigurable antennas emerge as a byproduct of the analysis.

Balanced-Switching-Oriented Blind Interference-Alignment Scheme for 2-User MISO Interference Channel

This letter considers the number of mode-switching associated with reconfigurable-antenna-based blind interference alignment (BIA) scheme for a 2-user MISO interference channel (IC). It is assumed that each user is equipped with a single reconfigurable antenna, which can switch among multiple independent modes. The switching-oriented BIA (S-BIA) scheme was proposed to minimize the overall mode-switching operations of reconfigurable antennas at the receivers. However, in S-BIA, the receivers can have a significantly different number of mode-switching operations, thus some users may experience longer delays, resulting in unfairness on their QoS. In this letter, we consider a 2-user MISO interference channel and propose a balanced-switching-based BIA (BS-BIA) scheme, which balances the individual mode-switching operations of the two users while reserving the same number of overall mode-switching operations as that in systems with S-BIA. Mathematical proofs and simulations results concur and show that the proposed BS-BIA scheme can reduce the differences in the numbers of mode-switching operations between the 2 users while keeping the overall mode-switching operation numbers close to that of systems with S-BIA.

Blind Integer-Forcing Interference Alignment for Downlink Cellular Networks

A novel blind interference alignment (IA) scheme in conjunction with interference decoding by virtue of integer forcing is proposed for downlink cellular networks without channel state information at the base station. In the proposed scheme, inter-user interference at each mobile user is aligned in blind manner, and by employing the same lattice code for all users, each user directly decodes integer-linear combinations of interfering codewords from the aligned interference signals in contrast to the previous works that simply null out the aligned interference by zero forcing. Numerical simulations demonstrate that the proposed scheme significantly improves the sum rate compared with the previous blind IA schemes.

Degrees of Freedom of 2-Tier Networks Without Channel State Information at the Transmitter

We characterize the degrees of freedom (DoF) of the two-tier heterogeneous networks without channel state information at the transmitters or cooperation among transmitters. We consider conventional transmitters while the users are equipped with a multimode receiver. In contrast to previous works focused on two-tier networks, the derived DoF consider the management of the intracell, the intercell, and intertier interference. The derived bounds define the DoF region for any two-tier network. Furthermore, these bounds are achievable by combining blind interference alignment schemes properly.

User-Centric Blind Interference Alignment Design for Visible Light Communications

Visible light communications (VLC) are considered as a key technology for future wireless communications. In order to mitigate the interference, several transmit precoding (TPC) schemes have been proposed for VLC. However, beyond the need for channel state information and backhaul links, the TPC schemes are subject to additional constraints given by the features of the optical channel such as ensuring a real and non-negative transmitted signal or a low correlation among users. Besides, the traditional network-centric (NC) design, i.e., considering only the position of the transmitters, leads to rigid transmission schemes for VLC networks due to the small and confined coverage of the optical transmitters.In this paper, we consider blind interference alignment (BIA) schemes for VLC, which solve the aforementioned issues, based on the concept of reconfigurable photodetector. In this context, we propose a user-centric (UC) clustering strategy based on the K-means algorithm where the users are treated as an active element of the network instead of a mere endpoint. For the proposed UC design, we derive two BIA schemes based on the connectivity of the clusters; a straightforward scheme considering each cluster as a broadcast channel referred to as KM-sBIA and a scheme that is flexible to the connectivity of each user within the cluster referred to as KM-topBIA. The simulation results show that the proposed schemes outperform the use of classical TPC or other BIA-based schemes considering both NC and UC approach.

Blind Interference Alignment for the <inline-formula> <tex-math notation="LaTeX">$K$</tex-math> </inline-formula>-User MISO BC Under Limited Symbol Extension

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.

Cognitive Blind Interference Alignment for Macro-Femto Networks

We propose a cognitive blind interference alignment (BIA) scheme for macro-femto two-tier networks where the users are equipped with a single reconfigurable antenna. The proposed scheme fully cancels the intracell interference in both the upper and lower tiers. Moreover, it provides the optimal Degrees of Freedom (DoF) in the macro-tier while the lower tier subject to inter-tier interference achieves non-zero DoF. To do so, the proposed scheme relies on a topology management scheme where the users belong to the macro-tier if and only if they can optimally treat the interference caused by the transmission at the femto-tier as noise. The proposed scheme does not require any channel state information at the transmitter or data sharing between the macro- and femto-tiers. An outer bound of the DoF is derived for the considered macro-femto network. It is demonstrated that the proposed scheme can attain the outer bound subject to optimal sum DoF for the macro-tier. Furthermore, compared to previous approaches, cognitive BIA can achieve better sum rates for macro-femto networks for femtocells subject to different levels of inter-tier interference.

On the Mode Switching of Reconfigurable-Antenna-Based Blind Interference Alignment

This paper reconsiders the design of blind interference alignment (BIA) for $K$ -user MISO interference channel in which each receiver is equipped with a reconfigurable antenna of preset $M_k\geq 3$ modes. Beyond the degree of freedom (DoF)-oriented BIA (D-BIA) design proposed by Lu et al. , we further take into account the frequency of mode switching within one supersymbol frame. Even though every receiving antenna is reconfigurable with preset multiple modes, from an engineering perspective, it is of practical importance for each receiving antenna to make less number of mode switching in order to gain the benefits such as less switching power consumption and less signal distortion. To this end, we propose in this paper switching-oriented BIA (S-BIA) scheme, which preserves the same degree of freedom (DoF) gain as D-BIA while offering reduced mode switching frequency. Theoretical analysis and simulation results demonstrate that, compared to D-BIA, S-BIA can gain $100/(M-1)$ percent of switching saving when $M_k = M$ is odd for all transmitters. Remarkably, S-BIA offers 50% switching saving for multiuser $3\times 1$ interference channels.

Blind Interference Alignment for Multiuser MISO Indoor Visible Light Communications

A filter-pair-based blind interference alignment scheme is proposed to improve the achievable degree of freedom (DoF) in multiuser multiple-input single-output indoor visible light communications. In the proposed scheme, the transmitter does not need to know channel state information. Different transmit sub-channels employ different pulse-shaping filters, and each user is equipped with multiple receive filters. The transmitter sends signals according to the predesigned strategy, and each user sets the receive mode by choosing the corresponding receive filter. Optical orthogonal frequency division multiplexing is employed in the proposed scheme to combat the intersymbol interference in high-speed transmissions, and the maximum achievable spectrum efficiency (SE) of the proposed scheme is analyzed. Simulation results validate that the proposed scheme can achieve higher SE and more DoF than the orthogonal multiple access schemes.

Blind Interference Alignment in Two-Cell Z Interference MIMO Channel

This paper proposes a blind interference alignment (BIA) scheme in two-cell Z interference multiple-input multiple-output channel where the cell edge user equipment (UE) of the first cell is interfered by the base station of the second cell during downlink transmissions, while the UE of the second cell is free from inter-cell interference. By employing the reconfigurable antennas at receivers, the transmit strategy of the proposed scheme is designed. The achievable degree of freedom (DoF), the achievable rates, and the bit error rate performance of the proposed BIA scheme are analyzed. Simulation results show that the achievable DoF and the throughput of the proposed scheme are improved compared with conventional interference control scheme. Furthermore, in the proposed BIA scheme, all UEs can achieve a good diversity gain to combat fading.

Hierarchical Blind Interference Alignment Over Interference Networks With Finite Coherence Time

We investigate a blind interference alignment (BIA) scheme through staggered antenna switching over various interference networks (e.g., broadcast channel, interference channel, and cellular networks) with realistic channel assumptions. In existing BIA, the coherence time of channel is assumed to be long enough, but that may not always be true in realistic scenarios. Therefore, we propose a dynamic supersymbol design method which can construct a supersymbol with limited symbol extension that is determined by the coherence time of channel. It is demonstrated that the supersymbol block length can be reduced significantly by aligning interferences in a hierarchical manner, referred to as hierarchical BIA. The key idea of hierarchical BIA is to align interferences in groups and to use the same supersymbol structure between groups, producing aligned inter-group interferences without inner-group interference. Consequently, it is observed that with a given coherence time the proposed dynamic supersymbol design that exploits hierarchical BIA achieves higher degrees of freedom than the conventional method.

Blind Interference Alignment for Cellular Networks

We propose a blind interference alignment scheme for partially connected cellular networks. The scheme cancels both intracell and intercell interference by relying on receivers with one reconfigurable antenna and by allowing users at the cell edge to be served by all the base stations in their proximity. An outer bound for the degrees of freedom is derived for general partially connected networks with single-antenna receivers when knowledge of the channel state information at the transmitter is not available. It is demonstrated that for symmetric scenarios, this outer bound is achieved by the proposed scheme. On the other hand, for asymmetric scenarios, the achievable degrees of freedom are not always equal to the outer bound. However, the penalty is typically small, and the proposed scheme outperforms other blind interference alignment schemes. Moreover, significant reduction of the supersymbol length is achieved compared with a standard blind interference alignment strategy designed for fully connected networks.

Degrees of freedom for MIMO interference broadcast channels

Multiple-input multiple-output (MIMO) interference broadcast channel (IBC) plays an important role in the modern wireless communications. The upper bound of degrees of freedom (DoF) and its Corresponding achievable schemes was investigated. However, all the achievable schemes require perfect channel state information at transmitters (CSIT). In absence of CSIT, the DoF value is still unknown. This article mainly focuses on the G-cell K-user MIMO IBC, where there are M antennas at each transmitter and N antennas at each receiver. The transmitters only know channel coherence time internals rather than the values of channel coefficients. The users in the same cell are assumed to be able to share the channel information. Based on a heterogeneous semi-staggered block fading model, a blind interference alignment (IA) scheme was proposed for this scenario. It is shown that when R≥1/(G-1) and R = min(M,KN)/max(M,KN), a total of GKMN/(M + KN) DoF can be achieved. The inner bound is same with the decomposition DoF upper bound. Since the complexity is an important performance index to evaluate the achievable scheme, the quantitative analysis for the complexity is presented.

Semi-Blind Interference Alignment Techniques for Small Cell Networks

This paper investigates the application of blind and semi-blind interference alignment methods in clustered small cell networks. First, we examine two simple straightforward extensions of blind interference alignment and observe that neither of them is uniformly superior under all user distribution. Then, we exploit the location information of the users and base stations (BSs) in the cluster to define the semi-blind interference alignment problem, whose objective function is to minimize the supersymbol length by grouping the users that can be served in the same time slot. We show that this problem is NP-hard and propose two heuristic centralized algorithms that can provide effective solutions. The first scheme, top-level semi-blind supersymbol design, employs a grouping indicator matrix to determine the supersymbol while the second scheme, ordered semi-blind supersymbol design, constructs the supersymbol in an ordered and greedy fashion. Finally, we propose a more decentralized scheme which does not have the location information of all users and BSs in the cluster, but the BS utilizes the long-term SINR values, obtained via feedback, of each user it serves. By numerical simulations, we show that the proposed semi-blind algorithms perform uniformly better than pure blind interference alignment schemes for any possible user distribution scenario.

The Degrees of Freedom for MIMO Interference Broadcast Channels with no CSIT

Multiple-input multiple-output (MIMO) interference broadcast channel (IBC) plays an important role in the modern wireless communications. The upper bound of degree of freedom (DoF) and corresponding achievable schemes have been investigated. However, all the achievable schemes require perfect channel state information at transmitters (CSIT). In the absence of CSIT, the DoF value is still unknown. This paper mainly focuses on theG-cellK-user MIMO IBC, where there areMantennas at each transmitter andNantennas at each receiver. The transmitters only know channel coherent time internals rather than the values of channel coefficients. The users in the same cell are assumed to be able to share the channel information. Based on a heterogeneous block fading model, a blind interference alignment (IA) scheme is proposed for this scenario. We show that when and , then a total of degrees of freedom (DoF) can be achieved. The inner bound is same with the decomposition DoF upper bound.

Blind Interference Alignment With Diversity in <inline-formula> <tex-math notation="TeX">$K$</tex-math> </inline-formula>-User Interference Channels

In this paper, we propose blind interference alignment (BIA) schemes using reconfigurable antenna technology to achieve high degree of freedom (DoF) or diversity gain in K-user interference channels. First, two DoF-oriented BIA schemes are proposed that fully and partially align the inter-user interference, respectively. We compare the achievable DoF of the two schemes and show that the partial BIA scheme has higher DoF than the full BIA scheme under some conditions, and vice versa. Then, three diversity-oriented BIA schemes with space-time coding are proposed to achieve both spatial diversity gain and reconfigurable antenna pattern diversity gain. With different tradeoffs among the diversity gain, the rate and the decoding complexity, the BIA with threaded algebraic space-time (TAST) codes, the BIA with orthogonal space-time block codes (OSTBCs), and the BIA with multiplexing Alamouti codes are proposed, respectively. The BIA with TAST codes can achieve the full diversity and high rate with high decoding complexity. The BIA with OSTBCs can achieve the full diversity and the linear decoding complexity but has low rate. The BIA with multiplexing Alamouti codes can achieve high rate with low decoding complexity at the expense of full diversity loss.

Blind interference alignment tracking for two‐way interference channel

In this study, the authors propose a novel blind adaptive minor subspace tracking interference alignment (BAMST-IA) scheme for slowly fading two-way interference channel. In this scheme, a new frame structure is designed to exploit the dependency of the channels between consecutive fading blocks. Then, the IA problem is reformulated as a minor subspace tracking problem, and the low computational complexity fast data projection method algorithm is integrated with the BAMST-IA scheme to update the IA solutions. Moreover, the update uses only observed data without any channel state information, thus requires lower signalling overhead. Simulation results are presented to show that the proposed BAMST-IA scheme is fit for slowly fading channels.

Alamouti Coded Blind Interference Alignment with Partial Interference Cancellation Group Decoding

Interference alignment is a promising technique which suppresses interference in multiuser wireless networks. Most research on interference alignment aims at deriving or realizing the maximum achievable Degrees of Freedom (DoF), as well as the diversity gain is usually one. However, achieving better diversity performance is equally important. To improve the diversity gain, this paper presents an Alamouti coded Blind Interference Alignment (BIA) scheme, which combines interference alignment with Alamouti coding. First, the Alamouti coded BIA scheme for a two-user MIMO X channel is proposed. The proposed scheme results in 4/3 DoF with no channel state information at transmitters, and an equivalent channel matrix with partly orthogonal columns. The orthogonal structure can be exploited to obtain diversity gain. Therefore, we then explore the Partial Interference Cancellation (PIC) group decoding and ZF algorithm. Simulation results show that the proposed scheme achieves a higher diversity gain of 2, while keeps the same DoF as the original BIA scheme.

Blind Interference Alignment

The main contribution of this paper is the insight that the transmitters' knowledge of channel coherence intervals alone (without any knowledge of the values of channel coefficients) can be surprisingly useful in a multiuser setting, illustrated by the idea of blind interference alignment that is introduced in this work. Specifically, we explore five network communication problems where the possibility of interference alignment, and consequently the total number of degrees of freedom (DoF) with channel uncertainty at the transmitters, are unknown. These problems share the common property that in each case the best known outer bounds are essentially robust to channel uncertainty and represent the outcome with interference alignment, but the best inner bounds-in some cases conjectured to be optimal-predict a total collapse of DoF, thus indicating the infeasibility of interference alignment under channel uncertainty at transmitters. For each of these settings we show that even with no knowledge of channel coefficient values at the transmitters, under certain heterogeneous block fading models, i.e., when certain users experience smaller coherence time/bandwidth than others, blind interference alignment can be achieved. In each case we also establish the DoF optimality of the blind interference alignment scheme.

Aiming Perfectly in the Dark-Blind Interference Alignment Through Staggered Antenna Switching

We propose a blind interference alignment scheme for the vector broadcast channel where the transmitter is equipped with M antennas and there are K receivers, each equipped with a reconfigurable antenna capable of switching among M preset modes. Without any knowledge of the channel coefficient values at the transmitters and with only mild assumptions on the channel coherence structure we show that MK/M+K-1 degrees of freedom are achievable. The key to the blind interference alignment scheme is the ability of the receivers to switch between reconfigurable antenna modes to create short term channel fluctuation patterns that are exploited by the transmitter. The achievable scheme does not require cooperation between transmit antennas and is therefore applicable to the MxK X network as well. Only finite symbol extensions are used, and no channel knowledge at the receivers is required to null the interference.