Single-input Single-output Interference Channel Research Articles

General precoder interference alignment design with achievable higher multiplexing gain and reduced channel extension cases

In a K-user single input-single output interference channel, it is proved that the upper bound for multiplexing gain (MG) is K / 2 . Based on interference alignment technique, Cadambe and Jafar introduced a scheme known as Original Interference Alignment (IA). This scheme is improved by Choi–Jafar–Chung (CJC) in which for reduced channel extension, higher MG is achievable. These designs requirean infinite number of channel extension to achieve the upper bound. In this study, as a common generalisation of Original IA and CJC, the authors focus on designing new precoding matrices. With the same conditions as in Original IA and CJC, by changing the values of defined variables (t and s), different cases could be generated so that different MGs with different channel extensions become possible. Broadly speaking, setting appropriate values to the assigned variables, the proposed scheme yields the same results as Original IA and CJC schemes. For all other values of t and s parameters better results than Original IA are obtained but for some special t and s parameters better results than CJC scheme are achieved. Thus, it is possible to simultaneously achieve a higher MG with lower channel extension (i.e. the reduction of computational complexity) in comparison with previously designed schemes.

The Degrees of Freedom of the Interference Channel With a Cognitive Relay Under Delayed Feedback

This paper studies the interference channel with a cognitive relay under delayed feedback. Three types of delayed feedback are studied: delayed channel state information at the transmitter, delayed output feedback, and delayed Shannon feedback. Outer bounds are derived for the degrees of freedom (DoF) region of the two-user multiple-input multiple-output interference channel with a cognitive relay with delayed feedback as well as without feedback. For the single-input single-output scenario, optimal schemes are proposed based on retrospective interference alignment. It is shown that while a cognitive relay without feedback cannot improve the sum-DoF in the two-user single-input single-output interference channel, delayed feedback in the same scenario can increase the sum-DoF to $4/3$ . For the multiple-input multiple-output case, achievable schemes are obtained via extensions of retrospective interference alignment, leading to the DoF regions that meet the respective upper bounds.

Achievable Degrees of Freedom of the <inline-formula> <tex-math notation="LaTeX">$K$</tex-math> </inline-formula>-User SISO Interference Channel With Blind Interference Alignment Using Staggered Antenna Switching

In this paper, we characterize the achievable (linear) degrees of freedom (DoFs) of the $K$ -user single-input single-output (SISO) interference channel with blind interference alignment (BIA) using staggered antenna switching. In this scheme, each transmitter is equipped with one conventional antenna, and each receiver is equipped with one reconfigurable (multimode) antenna. Assuming that the channel is known to the receivers only, we show that by using linear BIA with staggered antenna switching at the receiver, a sum DoF of $\text{2}K/(K+\text{2})$ is achievable. This result implies that in using BIA, we can double the DoF achieved by orthogonal multiple-access schemes for a large number of users. Moreover, we propose a systematic algorithm to generate the transmit beamforming vectors and the reconfigurable antenna switching patterns, showing that it can achieve the $\text{2}K/(K+\text{2})$ sum DoF for any $K$ . Finally, we apply this algorithm to the four-user SISO interference channel and demonstrate that $\text{4}/\text{3}$ sum DoF is indeed achievable.

Retrospective Interference Alignment: Degrees of Freedom Scaling With Distributed Transmitters

In this paper, we consider the $K$ -user single-input single-output interference channel with delayed channel state information at the transmitters (CSIT). Our main contribution is to show that even with delayed CSIT and distributed transmitters, the achievable degrees of freedom (DoFs) still scale with the number of users. More specifically, we propose a method that achieves $K/(2\sqrt {K} - 1) \geq \sqrt {K}/2$ DoF. The main idea behind the proposed method is to use interference alignment (IA) at the receiver side in conjunction with repetition coding at the transmitters. Repetition coding repeats the data $R$ times while IA makes the interference generated by a given transmitter identical: 1) at all non-intended receivers and 2) all transmission repetitions. Therefore, one retransmission per transmitter is sufficient to cancel all the interference. This reduces significantly the overhead required for interference removal since the number of interference terms is reduced from $RK(K-1)$ to $K$ .

Achievable Sum DoF of the K-User MIMO Interference Channel with Delayed CSIT

This paper considers a $K$-user multiple-input-multiple-output (MIMO) interference channel (IC) where 1) the channel state information obtained by the transmitters (CSIT) is completely outdated, and 2) the number of transmit antennas at each transmitter, i.e., $M$, is greater than the number of receive antennas at each user, i.e., $N$. The usefulness of the delayed CSIT was firstly identified in a $K$-phase Retrospective Interference Alignment (RIA) scheme proposed by Maddah-Ali et al for the Multiple-Input-Single-Output Broadcast Channel, but the extension to the MIMO IC is a non-trivial step as each transmitter only has the message intended for the corresponding user. Recently, Abdoli et al focused on a Single-Input-Single-Output IC and solved such bottleneck by inventing a $K$-phase RIA with distributed overheard interference retransmission. In this paper, we propose two $K$-phase RIA schemes suitable for the MIMO IC by generalizing and integrating some key features of both Abdoli's and Maddah-Ali's works. The two schemes jointly yield the best known sum Degrees-of-Freedom (DoF) performance so far. For the case $\frac{M}{N}{\geq}K$, the achieved sum DoF is asymptotically given by $\frac{64}{15}N$ when $K{\to}\infty$.

Pre‐coder design over two‐symbol extension for K ‐user cyclic interference channels

The authors consider K -user cyclic single-input–single-output (SISO) interference channel (IC) where each receiver is interfered with from only one neighbouring transmitter. In the K -user cyclic SISO IC, K /2 sum degrees of freedom can be achieved when two-symbol extension is applied even without channel state information at the transmitter. They derive an approximation of the ergodic sum rate as a function of pre-coders and propose designs of pre-coders to maximise the ergodic sum rate.

Interference alignment for a multi-user SISO interference channel

Our work addresses the single-input single-output interference channel. The goal is to show that although interference alignment is suboptimal in the finite power region, it is able to achieve a significant overall throughput. We investigate the interference alignment scheme proposed by Choi et al. (IEEE Commun. Lett. 13(11): 847-849, 2009), which achieves a higher multiplexing gain at any given signal dimension than the scheme proposed by Cadambe and Jafar (IEEE Trans. Inform. Theory 54(8), 2008). Then, we try to modify the IA design in order to achieve enhanced sum-rate performance in the practical signal-to-noise ratio (SNR) region. Firstly, we introduce a way to optimize the precoding subspaces at all transmitters, exploiting the fact that channel matrices in the interference model of a single-input single-output channel are diagonal. Secondly, we propose to optimize jointly the set of precoder bases within their associated precoding subspaces. To this end, we combine each precoder with a new combination precoder, and this latter seeks the optimal basis that maximizes the network sum rate. We also introduce an improved closed-form interference alignment scheme that performs close to the other proposed schemes.

Transmit Optimization With Improper Gaussian Signaling for Interference Channels

This paper studies the achievable rates of Gaussian interference channels with additive white Gaussian noise (AWGN), when improper or circularly asymmetric complex Gaussian signaling is applied. For the Gaussian multiple-input multiple-output interference channel (MIMO-IC) with the interference treated as Gaussian noise, we show that the user's achievable rate can be expressed as a summation of the rate achievable by the conventional proper or circularly symmetric complex Gaussian signaling in terms of the users' transmit covariance matrices, and an additional term, which is a function of both the users' transmit covariance and pseudo-covariance matrices. The additional degrees of freedom in the pseudo-covariance matrix, which is conventionally set to be zero for the case of proper Gaussian signaling, provide an opportunity to further improve the achievable rates of Gaussian MIMO-ICs by employing improper Gaussian signaling. To this end, this paper proposes widely linear precoding, which efficiently maps proper information-bearing signals to improper transmitted signals at each transmitter for any given pair of transmit covariance and pseudo-covariance matrices. In particular, for the case of two-user Gaussian single-input single-output interference channel (SISO-IC), we propose a joint covariance and pseudo-covariance optimization algorithm with improper Gaussian signaling to achieve the Pareto-optimal rates. By utilizing the separable structure of the achievable rate expression, an alternative algorithm with separate covariance and pseudo-covariance optimization is also proposed, which guarantees the rate improvement over conventional proper Gaussian signaling.

An Iterative Interference Alignment Scheme for the SISO Interference Channel

In this paper, we propose a novel iterative interference alignment (IA) scheme for the single-input single-output (SISO) interference channel system using minimum total mean square error criterion under the individual transmitter power constraints. We show that interference alignment under such criterion could be realized through an iterative algorithm. The convergence of the proposed algorithm is discussed. We also proposed a robust MMSE-based iterative design with imperfect channel state information. Simulation results, compared with several existing IA schemes, have shown that the proposed method could effectively improve the BER performance of the SISO interference channel system while maintaining the same degree of freedom as Cadambe–Jafar scheme. The proposed robust MMSE-based iterative interference alignment scheme is shown to be less sensitive to channel estimation error.