Can One Achieve Multiuser Diversity in Uplink Multi-Cell Networks?

We introduce a distributed opportunistic scheduling (DOS) strategy, based on two pre-determined thresholds, for uplink $K$-cell networks with time-invariant channel coefficients. Each base station (BS) opportunistically selects a mobile station (MS) who has a large signal strength of the desired channel link among a set of MSs generating a sufficiently small interference to other BSs. Then, performance on the achievable throughput scaling law is analyzed. As our main result, it is shown that the achievable sum-rate scales as $K\log(\text{SNR}\log N)$ in a high signal-to-noise ratio (SNR) regime, if the total number of users in a cell, $N$, scales faster than $\text{SNR}^{\frac{K-1}{1-\epsilon}}$ for a constant $\epsilon\in(0,1)$. This result indicates that the proposed scheme achieves the multiuser diversity gain as well as the degrees-of-freedom gain even under multi-cell environments. Simulation results show that the DOS provides a better sum-rate throughput over conventional schemes.Comment: 11 pages, 3 figures, 2 tables, to appear in IEEE Transactions on Communication

Vandermonde-subspace Frequency Division Multiplexing for Two-Tiered Cognitive Radio Networks

Vandermonde-subspace frequency division multiplexing (VFDM) is an overlay spectrum sharing technique for cognitive radio. VFDM makes use of a precoder based on a Vandermonde structure to transmit information over a secondary system, while keeping an orthogonal frequency division multiplexing (OFDM)-based primary system interference-free. To do so, VFDM exploits frequency selectivity and the use of cyclic prefixes by the primary system. Herein, a global view of VFDM is presented, including also practical aspects such as linear receivers and the impact of channel estimation. We show that VFDM provides a spectral efficiency increase of up to 1 bps/Hz over cognitive radio systems based on unused band detection. We also present some key design parameters for its future implementation and a feasible channel estimation protocol. Finally we show that, even when some of the theoretical assumptions are relaxed, VFDM provides non-negligible rates while protecting the primary system.Comment: 9 pages, accepted for publication in IEEE Transactions on Communication

Wireless information and energy transfer in multi-cluster MIMO uplink networks through opportunistic interference alignment

In this paper, we consider a K-cluster (K >= 2) simultaneous wireless information and power transfer (SWIPT) network, where S nodes (S >= 2) are selected from N nodes within each cluster for the uplink information transmission (IT) and the remaining N - S idle nodes are dedicated to energy harvesting (EH). Based on the intra-cluster performance aware (ICPA) philosophy, a pair of opportunistic interference alignment (OIA) schemes, namely the coarse ICPA-OIA (C-ICPA-OIA) and the refined ICPA-OIA (R-ICPA-OIA), are proposed for balancing the sum rate performance achieved and the energy harvested. Specifically, the C-ICPA-OIA treats the overall signal strength within the reference signal subspace (RSS) as a coarse description of the node’s effective signal strength. By comparison, to take full advantage of zero-forcing (ZF) based reception, the R-ICPA-OIA considers the projected signal strength with respect to the orthonormal basis of RSS as a substantially refined description of the node’s effective signal strength. Furthermore, we analyzed the harvested power and the working time of the system. Extensive simulation results validate our theoretical analyses, demonstrating that our schemes outperform the existing OIA schemes