Baofeng Ji

Performance Analysis of Antenna Selection in Two-Way Relay Networks

We investigate the performance of multi-antenna two-way relay networks, where both amplify-and-forward (AF) and decode-and-forward (DF) relaying strategies are considered. First an antenna selection scheme among all nodes is proposed based on maximizing the worse received signal-to-noise ratio (SNR) of two end users. Then, we derive the probability density function (PDF) and cumulative distribution function (CDF) of the received SNRs of both users. We also obtain the closed-form expressions of average bit error rates (BER) and the outage probability of our system. Furthermore, we study the asymptotic behavior of our system when transmitting SNR or the number of antennas is large. The results show that the proposed antenna selection scheme achieves full diversity, and the simulation results closely match to our theoretical analysis. To further improve the spectrum efficiency of the system, a hybrid selection antenna scheme is proposed. Finally, the numerical results show that our scheme outperforms the state of art.

A Cooperative Relay Selection for Two-Way Cooperative Relay Networks in Nakagami Channels

We investigate the performance of the best-worse relay selection strategy in a two way cooperative non-regenerative relay network, where the relay is selected to maximize the worst Signal to Noise Ratio (SNR) of two links. In contrast to existing work, we aim to provide a theoretical performance analysis for this scheme under the more practical Nakagami channel. Closed-form expression of the probability density function for the SNRs of both two links is derived, based on which the outage probability of the best-worse relay selection is obtained. It is shown that the best-worse relay selection scheme achieves full diversity gain. Furthermore, the asymptotic packet error ratio with SNR increasing is also analyzed through rigorous derivations. The accuracy of our derivation is validated by computer simulations.

Energy-efficiency resource allocation of very large multi-user MIMO systems

With increasing demand in multimedia applications and high data rate services, energy consumption of wireless devices has become a problem. At the user equipment side, high-level energy consumption brings much inconvenience, especially for mobile terminals that cannot connect an external charger, due to an exponentially increasing gap between the available and required battery capacity. Motivated by this, in this paper we consider uplink energy-efficient resource allocation in very large multi-user MIMO systems. Specifically, both the number of antenna arrays at BS and the transmit data rate at the user are adjusted to maximize the energy efficiency, in which the power consumption accounts for both transmit power and circuit power. We proposed two algorithms. Algorithm1, we demonstrate the existence of a unique globally optimal data rate and the number of antenna arrays by exploiting the properties of objective function, then we develop an iterative algorithm to obtain this optimal solution. Algorithm2, we transform the considered nonconvex optimization problem into a convex optimization problem by exploiting the properties of fractional programming, then we develop an efficient iterative resource allocation algorithm to obtain this optimal solution. Our simulation results did not only show that the the proposed two algorithms converge to the solution within a small number of iterations, but demonstrated also the performances of the proposed two algorithms are close to the optimum. Meanwhile, it also shows that with a given number iterations the performance of proposed algorithm1 is superior to proposed algorithm2 under small pC. On the contrary, the performance of proposed algorithm2 is superior to proposed algorithm1 under large pC.

Cooperative Transmission Mechanisms in Next Generation WiFi: IEEE 802.11ac

Very high throughput (VHT) WLAN, known as IEEE 802.11ac, can provide compelling performance and has attracted extensive attention for achieving transmission rate over 1u2009G bps for 5u2009GHz band owing to involving the MU-MIMO and maximum 160u2009MHz bandwidth transmission. Despite extensive studies and dramatic performance, the conventional carrier sensing mechanism emerges some drawbacks especially in the overlapping BSS scenario responsible for employment of MU-MIMO and bandwidth expansion. In order to address the issue of conventional carrier sensing mechanism, namely, redundant or useless network allocation vector (NAV) setting, this paper proposes an enhanced NAV transmission mechanism, which not only needs little modifications to current standard draft but also can achieve performance improvement significantly. On this basis, in order to solve the SINR inaccuracy calculated based on null data packet (NDP) in the actual MU-MIMO transmission, the SINR feedback mechanism is proposed and the frame structure modifications are displayed in detail. Furthermore, theoretical analysis is also performed on the proposed mechanism and the formulas of the achieved gains are also derived. Numerical results confirm the validation of our theoretical analysis and further substantiate that the proposed scheme obtains obvious throughput gain over the conventional mechanism.

Energy-Efficient Resource Allocation in Uplink Multiuser Massive MIMO Systems

Energy-efficient communications, namely, green communications, has attracted increasing attention due to energy shortage nand greenhouse effect. Motivated by this, we consider the uplink energy-efficient resource allocation in multiuser massive nmultiple-input multiple-output (MIMO) systems. Specifically, we consider that both the number of antenna arrays at the base station n(BS) and the transmit data rate at UE are adjusted adaptively to maximize the energy efficiency. Firstly, we demonstrate the existence nof a unique resource allocation solution that is globally optimal by exploiting the properties of objective function. Then we develop an niterative algorithm to solve it. By transforming the originally fractional optimization problem into an equivalent subtractive form using nthe properties of fractional programming, we develop another efficient iterative resource allocation algorithm. Simulation results have nvalidated the effectiveness of the proposed two algorithms and have shown that both algorithms can fast converge to a near-optimal nsolution in a small number of iterations.

Throughput enhancement for VHT WLANs based on two-level network allocation vector

Very high throughput (VHT) WLAN, known as IEEE 802.11ac, has attracted extensive attentions for achieving transmission rate over 1G bps. Due to the introduction of MU-MIMO and maximum 160MHz bandwidth transmission, the conventional carrier sensing mechanism emerges some drawbacks especially in the overlapping BSS scenario. In order to address the issue of redundant or useless network allocation vector (NAV) setting, this paper proposes a two-level NAV mechanism which only needs small modification to current standard draft. Theoretical analysis is also performed on the proposed mechanism and the formulas of the achieved gain is derived. Numerical results confirm the validation of our theoretical analysis and show that the proposed scheme obtains obvious throughput gain over the conventional mechanism.

Performance analysis of two-way relaying satellite mobile communication

In this paper, a two-way relaying GEO satellite communication scheme is proposed, which significantly reduces the transmission delay as compared to conventional satellite communication strategy. The outage probability of this scheme under Ricean channel model is further analyzed, and a theoretical expression is found. Simulation results show that the derived expression of outage probability is consistent with the numerical results. The BER performances of the proposed scheme under different Ricean factors are also investigated.

Performance Analysis of Heterogeneous Networks With Interference Cancellation

The performance of heterogeneous networks (HetNets) is investigated with both direct and relay-aided transmission strategies in a macrocell. We first propose an interference cancelation scheme at the macro base station on the basis of canceling cross-tier interferences from the macro base station to small-cell users. Then, expressions of the probability density function (PDF) and cumulative distribution function (CDF) of all receivers in both macro and small cells are derived, and the closed-form overall outage probability, average bit error rate (BER), and spectral efficiency of the network are obtained. Based on the derivations, we propose two adaptive relay-aided transmission schemes with instantaneous and statistical channel state information (CSI) to further improve the spectral efficiency. We show that the SNR boost at the small-cell mobile station comes from the cancelation of the cross-layer interference by the macro base station. Therefore, the performance of the small cell is improved greatly with interference cancelation, while the overall performance of the HetNet is also ameliorated. The numerical results finally show the validity of our analysis.

Performance analysis of antenna selection in two-way decode-and-forward relay networks

This paper investigates the performance of a two-way decode-and-forward (DF) multi-antenna relay network. A joint antenna selection scheme for all nodes is first proposed based on the maximizing the worse received signal to noise ratio (SNR) of two end users. Then, we derive the probability density function (PDF) and cumulative distribution function (CDF) of the received SNRs of both users. We also achieve the closed-form expressions of average bit error rate (BER) and outage probability of the relay system. Furthermore, we reveal the asymptotic behavior of our system when transmitting SNR or the number of antennas is large. Our analysis shows that the proposed DF antenna selection scheme achieves full diversity. The numerical results finally verify the accuracy of our analysis.

Efficient MAC protocol design and performance analysis for dense WLANs

AbstractIn this paper, we analytically study the dense basic service set network transmission problems in very high throughput (VHT, namely IEEE 802.11ac) wireless local area networks (WLANs) due to nervous bandwidth resources. Our contributions are threefold as follows. Firstly, we derive the closed-form expressions of throughput gains for primary channel establishment from multi-band selection using the optimal skipping rule, which balances the throughput gain from finding a good quality band with the overhead of measuring multiple bands. Secondly, in order to satisfy the quality of service of overlapping BSS users, we design a space interference avoidance mechanism, which can improve the system throughput for the whole dense WLANs. Thirdly, in order to further improve the transmission performance of dense BSS networks, we propose an unequal bandwidth transmission mechanism based on the VHT WLANs, which can not only clear the redundant network allocation vector duration timely but also use the limited bandwidth efficiently. The proposed protocols and mechanisms exploit both time and frequency diversity sufficiently, and are shown to result in typical throughput gains compared with the traditional IEEE 802.11 MAC protocol.n