Wenhao Xiong

MIMO cognitive radio user selection with and without primary channel state information

In this paper, we study user selection (US) strategies for a multiple-input-multiple-output (MIMO) cognitive radio (CR) downlink network, where the r-antenna underlay CR secondary users (SUs) coexist with a primary user (PU), and all terminals are equipped with multiple antennas. Two main scenarios are considered: 1) The t-antenna cognitive base station (CBS) has perfect or partial channel state information at the transmitter (CSIT) from the CBS to the PU receiver (RX), and 2) the CBS has absolutely no PU CSIT. For these scenarios, we propose and evaluate multiple SU selection schemes that are applicable to both best-effort PU interference mitigation and hard interference temperature (IT) constraints. The computational complexity of the proposed schemes can be significantly smaller than that of an exhaustive search with negligible performance degradation. For the selection of C SUs out of K candidates, our proposed sliding window scheme, for example, is of complexity O(Krt2), whereas an exhaustive search is on the order of O((CK)C4r3). When t and r are C of the same order, the computational complexity of the proposed scheme can be (CK)C4/K times smaller. Mathematical complexity analysis and C numerical simulations are provided to show the advantage of our schemes.

Underlay MIMO Cognitive Radio Downlink Scheduling with Multiple Primary Users and No CSI

In this work, we proposed user selection strategies for downlink of multiple input and multiple output (MIMO) cognitive radio (CR) network. Underlay CR secondary users (SUs) are selected by cognitive base station (CBS) to share subchannel with primary users (PUs). It is assumed that the cross interference channel from cognitive radio base station to PUs is not known. CBS selects underlay SUs based on the knowledge of SUs transmission channels in order to reduce the interference from base station to PUs. We propose and evaluate user selection schemes with low computational complexity and best-effort interference mitigation to PUs.

Effects of node geometry on cooperative distributed AF wireless relay network

This paper presents the effects of relay-node geometry on bit error rate (BER) performance of an amplifying and forward (AF) relay cooperative distributed wireless network. This paper considers one-source-one-destination pair and N relay nodes. In addition, this paper assumes that all relay nodes share their received signals from the source node and the channel coefficients for cooperation. Then, an optimal relay-amplifying matrix is derived using the minimum mean square error (MMSE) criterion under a total power constraint at the relay nodes. Simulation results are presented using the analytically derived amplifying matrix.

Two-level MMSE relay strategy for an AF wireless relay network

This paper presents optimal amplify-and-forward (AF) relay amplifying matrices based on the minimum mean square error (MMSE) criterion for a cooperative AF wireless relay network consisting of a one-source-one-destination node pair and two-level N relay nodes. During data transmission, power is constrained at the source node, at the relay nodes in the first and the second levels, and at the destination node. In addition, this paper considers the case that power is intentionally not constrained. Hence, for the no-power constraint example, a positive scaling factor is employed to meet the target signal-to-noise ratio (SNRTGT) at the destination node. With the derived optimal relay amplifying matrices, bit error rate (BER) of the wireless relay network under both power and no-power constraint is simulated.

Amplifying matrix design for noncooperative SIMO relay networks under channel uncertainty

This paper presents an optimum diagonal amplifying relay matrix based on minimum mean square error (MMSE) criterion for noncooperative distributed wireless relay networks under channel uncertainty. A single-input multiple-output (SIMO) system with one-source M-destination N-relay nodes is considered. Bit error rate (BER) of the wireless relay network under both certain and uncertain channel conditions is simulated using the derived optimum diagonal amplifying relay matrices. For comparisons, the case of both perfect and imperfect channel conditions for single-input single-output (SISO) system with N relay nodes is also considered.

Relay selection for AF SISO wireless relay networks under jamming environment with relay power constraint

A noncooperative amplify-and-forward (AF) wireless relay network consisting of a one-source-one-destination pair and N relays is investigated. The objective of this paper is to analytically derive the explicit optimal noncooperative relay amplifying matrices (or vector) under both jamming and no-jamming environments, with the relay power constraint based on the minimum mean square error (MMSE) criterion. The MMSE cost function behaviors will be analytically and numerically investigated using the relay amplifying vectors derived. Finally, the relay selection scheme for the noncooperative AF wireless relay network is presented using the maximum signal-to-noise ratio (SNR) criterion under both jamming and no-jamming environments.

CSI-unaware scheduling for coexistence of MIMO-OFDMA device-to-device links and cellular mobile terminals

In this paper, we examine scheduling methods for non-orthogonal resource sharing between device-to-device user equipments (D2D-UEs) and cellular user equipments (C-UEs) in a multi-carrier multi-antenna network. The cellular eNodeB (eNB) allocates a pool of frequency subchannels that may be used autonomously by D2D-UEs for D2D discovery and communication. We then propose to schedule C-UE uplink (UL) transmissions in the same subchannel pool based on a best-effort C-UE-to-D2D-UE interference mitigation method, which does not require knowledge of C-UE-to-D2D-UE cross-channels. The selection criterion is a combination of the number of spatial streams and subchannels as well as transmit power needed by C-UEs to achieve their target data rate. Simulation results show that the proposed scheduling methods allow a larger fraction of C-UEs to achieve their data rate targets without major degradation in the D2D network performance.

Mobile Relay Amplifying Matrix Design of the Cooperative Distributed MMSE Relaying for AF Wireless Mobile Networks

This paper presents an optimal amplify-and-forward (AF) relay scheme for a multiple-input-multiple-output (MIMO) system consisting of M-mobile sources, M-mobile destinations, and N-cooperative distributed mobile relay nodes. A wireless mobile relaying network with channel state information is investigated. The received signals from the mobile sources are ex- changed between mobile relays to achieve optimal performance. The main contribution in this paper is the derivation of mobile relaying amplifying matrices (MARMs) designed for cooperative MIMO networks based on the minimum mean square error (MMSE) criterion. By adopting the new proposed MRAMs, the bite error rate (BER) performance of the system is evaluated using Monte-Carlo simulations.

Agile MU-MIMO in congested environments with robust channel estimation

This paper proposes a novel multi-user multiple-input and multiple-output (MU-MIMO) selection and beamforming technique for a geosynchronous orbit (GSO) satellite communication (SATCOM) system. The MU-MIMO technique employs beam-forming and adaptive power allocation schemes in order to support a large numbers of users. Additionally, this paper provides a solution for the scenario where satellite ground terminals and cellular users are sharing the same spectrum band. The proposed MU-MIMO Selection And Beamforming (SAB) method makes it possible to constrain the interference created by a high powered satellite transponder, in order to maintain normal transceiving activity for commercial cellular users. Meanwhile the quality of service (QoS) is also satisfied for ground terminals. If the options of selectively serving certain users is available, the performance can be improved further in terms of constraining the interference level. The other novelty of this work is a robust channel estimation design to support the proposed MU-MIMO schemes with specifies the pilot structure design, such as the determination of proper pilot length and transmission power. Extensive simulation and numerical results illustrate and validate the theoretical development.

Relay Selection Scheme for AF Relay Network based on Cost Function Criterion

An amplify-and-forward (AF) wireless relay network consisting of a one-source-one-destination node pair and cooperative multiple N relay nodes is proposed in three adverse wireless communication environments, i.e., jamming, node geometry, and channel uncertainty. Based on the minimum mean square error (MMSE) criterion, the optimal amplifying relay matrix in three adverse wireless environments with the relay power constraint is derived. In addition, the MMSE cost function behavior in three adverse environments is analytically investigated using the proposed optimal relay amplifying matrix. Finally, using the cost function value, the relay selection scheme in adverse wireless communication environments is presented, which is the main contribution of this paper