Hua Mu

MSE-Based Source and Relay Precoder Design for Cognitive Multiuser Multi-Way Relay Systems

We consider joint design of source and relay precoders in a cognitive multiuser multi-way relay system, which supports simultaneous transmission of multiple secondary users concurrently with primary network with the help of a relay station. The design criterion is minimum mean-square error (MMSE) of all secondary users under a transmit power constraint for each transmitting node and a constraint on the interference to primary network assuming complete knowledge of the channel state information is available. To solve this non-convex optimization problem, an iterative algorithm is proposed to iteratively solve the precoding matrices at secondary source nodes and relay node, and the decoding matrices at secondary nodes, where each subproblem is convex. To reduce the computational complexity, a matrix distance based non-iterative algorithm which can be implemented in a distributed manner is also proposed. Given the fact that perfect channel state information is usually non-realistic, a robust precoder design is also proposed to address this problem. Simulation results show the effectiveness of our proposed algorithms.

Achievable Degrees of Freedom for

We consider a K-user multiple input multiple output (MIMO) Y channel consisting of K(≥ 3) users and a relay. Each user has K-1 independent messages for all the other K-1 users. Degrees of freedom (DoF) of such channels is not known in general but it is known that the DoF of K(K-1)/2 is achievable for a network operating in a half-duplex mode by using signal space alignment for network coding during both the multiple access phase and the broadcast phase. In this paper, a novel signal group based alignment scheme is proposed, which divides all K(K-1) signals into l groups where l = K or K-1. Then, the signals in each group are aligned into a smaller subspace at the relay. If the i-th user is equipped with Mi antennas and the relay is equipped with N antennas where all antennas are used for both transmitting and receiving, we prove that when Mi = K-1, N = (K-1)2 for even K and Mi = K-1, N = K(K-2) for odd K, the optimal total DoF of this K-user MIMO Y channel is K(K-1)/2. As a consequence, to achieve the total DoF of K(K-1)/2, the requirements on Mi and N are Mi ≥ K-1 and N ≥ (K-1)2 for even K, and Mi ≥ K-1 and N ≥ K(K-2) for odd K. In our proposed approach, we significantly decrease the minimum Mi at the expense of higher N for a given number of users K and achievable DoF of K(K-1)/2, compared to an existing approach. This signal group alignment concept also motivates other signal grouping methods, which provide a tradeoff between number of antennas at end users and the relay. Also, for the K-user Y channel where all end users have a single antenna and the relay node has N antennas, it is shown that the DoF of min{K/2, (N + 1)/2} is achievable.

K

We consider joint design of source and relay pre-coders in a cognitive multiuser two-way relay system, which supports simultaneous transmission of multiple secondary users concurrently with primary network with the help of a relay node. The design criterion is to minimize the sum mean square error (MSE) of all users under a transmit power constraint for each transmitting node while causing no interference to the primary network. To solve this non-convex optimization problem, an iterative algorithm is proposed to iteratively solve for the precoding matrices at secondary source nodes and relay node, and then the decoding matrices at secondary nodes. To reduce the computational complexity, a matrix distance based non-iterative algorithm is also proposed. Simulation results show the effectiveness of our proposed algorithms.

-User MIMO Y Channels Using Signal Group Based Alignment

We study the secure degrees of freedom (DoF) in a cognitive radio system. A cognitive radio user helps to secure primary users transmission against an eavesdropper and in return, primary users allows secondary user to access its licensed spectrum. All users are equipped with multiple antennas. We investigate the secure DoF using interference alignment concept with partial channel state information (CSI). When eavesdropper is interested only in primary users data, it is shown that if all users, including primary transmitter-receiver pair, secondary transmitter-receiver pair and eavesdropper, have M antennas, achievable secure DoF dp and DoF ds of primary and secondary users, respectively, satisfy 2dp ≤ M and ds ≤ M - 2dp.

MSE-based source and relay precoder design for cognitive radio multiuser two-way relay systems

In this paper, we design relay precoder in a MIMO cognitive radio network where two-way transmission of multiple secondary user pairs occurs concurrently with primary networks transmission. We propose an interference alignment like precoder design which jointly aligns the direction of interference and the desired signal while interference to primary network is completely canceled. When the secondary transmitters and receivers are equipped with multiple antennas, sources, relay and receivers can all participate in aligning the interference and signal directions. It is shown that zero-forcing relay beamforming in which inter-pair interference is aligned to the null space of desired signal space is a special case of our algorithm. Our proposed algorithm can also work in the scenario where the number of antennas at relay node is not large enough and therefore zero-forcing is not possible. The effectiveness of the proposed algorithm is illustrated via simulations and compared with zero-forcing and MSE based designs.

Secure degrees of freedom in MIMO cognitive radio systems

We study the achievable secure degrees of freedom (DoF) in a cooperative MIMO cognitive radio system consisting of one primary source-destination pair, one or two secondary sourcedestination pairs, and one eavesdropper who is interested only in primary users data. The cognitive radio users help to secure primary users transmission against the eavesdropper and in return, the primary user allows the secondary users to access its licensed spectrum. All users are equipped with multiple antennas. We investigate the secure DoF using the interference alignment concept coupled with a zero inter-user interference constraint. We propose a beamforming design based only on the channel state information (CSI) between the primary and secondary user pairs which the legitimate users exchange among each other; no information data are exchanged and no eavesdropper CSI is needed. In the case of a single secondary user pair, we show that if all users have M antennas, secure DoF d_p and DoF d_s of primary and secondary users, respectively, are achievable if they satisfy 2d_p ≤ M and d_s ≤ M - 2d_p. In the case of two secondary user pairs, secure DoF d_p and DoFs d_s₁, d_s₂ of primary user and two secondary users, respectively, are achievable if they satisfy 2d_p <; M, d_p + d_i ≤ M, d_s₁ + d_s₂ ≤ M, i ∈ {s₁,s₂}, or 2d_p = M, d_p + d_i ≤ M, d_s₁ + d_s₂ <; M, i ∈ {s₁, s₂}. Simulation examples corroborating the theoretical results are presented.

Interference alignment-like precoder design in multi-pair two-way relay cognitive radio networks

In this paper, we consider a K-user MIMO (multiple input multiple output) Y channel consisting of K, K ≥3, users and a relay. Each user has K - 1 independent messages for all the other K-1 users. With the deployment of multiple antennas at both end users and the relay, K(K - 1) messages can be conveyed to their desired receivers within two time slots for a network operating in a half-duplex mode. A signal group based alignment scheme is proposed which divide all K(K - 1) signals into K groups when K is odd and K - 1 groups when K is even. Then the signals in each group are aligned into a smaller subspace at the relay. If each user is equipped with M antennas and the relay is equipped with N antennas, we show that in order to exchange K(K - 1) messages, the requirements on M and N are KM ≥ N +K - 1 and N ≥ (K - 1)2 for even K and (K - 1)M ≥ N +1 and N ≥ K(K - 2) for odd K. In our proposed approach we significantly decrease the minimum M at the expense of higher N for a given number of users K, compared to an existing approach.

Secure Degrees of Freedom in Cooperative MIMO Cognitive Radio Systems

Abstract We study the achievable secure degrees of freedom (DoF) in a cooperative MIMO cognitive radio system comprised of one primary source–destination pair, multiple secondary source–destination pairs and an eavesdropper against whom the primary user intends to secure its data. In this system, multiple secondary user pairs help to secure primary user’s data against eavesdropping. In return, these secondary users are allowed to access primary user’s spectrum. All users, including primary user pair, K ≥ 2 secondary user pairs and the eavesdropper are equipped with M antennas. We investigate the secure DoF without the knowledge of eavesdropper’s channel state information (CSI), using the interference alignment concept combined with a zero inter-user interference constraint. A beamforming design is proposed to achieve secure DoF d for the primary user and DoF d for all secondary users if K d ≤ M . The case of untrusted secondary users is also investigated where the secondary users may potentially eavesdrop. Simulation examples corroborating the theoretical results are presented.

Signal group based alignment in K-user MIMO Y channel

Secure degrees of freedom (DoF) in MIMO cognitive radio system is studied in this paper. We consider a cognitive radio system with one primary source-destination pair, multiple secondary source-destination pairs and an eavesdropper against whom the primary user intends to secure its data. In this system, multiple secondary user pairs help to secure primary users data against eavesdropping. In return, these secondary users are allowed to access primary users spectrum. All users, including primary user pair, K≥2 secondary user pairs and the eavesdropper are equipped with M antennas. We investigate the secure DoF without the knowledge of eavesdroppers channel state information (CSI). A beamforming design is proposed to achieve secure DoF d for primary user and DoF d for all secondary users if Kd≤M. Simulation examples corroborating the theoretical results are presented.