Yueming Cai

Subcarrier and power allocation in uplink multi-cell OFDMA systems based on Game Theory

Subcarrier and power allocation plays an important part in optimizing the performance of OFDMA systems. However, inter-cellular interference is often neglected in resource allocation. In this paper, with the inter-cell interference taken into account, we propose a subcarrier and power allocation framework based on Game Theory in uplink OFDMA multi-cellular systems. In this algorithm, the subcarrier allocation is based on the normalized channel gain, and the power allocation is achieved by the pricing function. The existence of Nash Equilibrium is proved, and the effect of the algorithm in this paper is discussed about its iterative property and cost factors. Simulation results demonstrate that the inter-cell interference can virtually affect the system performance, and the proposed algorithm could achieve better fairness in users.

A High Efficiency Algorithm of Power and Bit Allocation for OFDMA Systems

In this paper, we propose a high efficiency algorithm of power and bit allocation for orthogonal frequency division multiple access (OFDMA) system, in which the allocation procedure is divided into three parts: linear water-filling power allocation, bit allocation and power and bit adjustment. It can quickly achieve the power and bit allocation on the users sub-carrier level with a good fairness performance. Simulation results show that the proposed algorithm can obviously decrease the operation complexity and slightly descended system throughput contrast to other algorithms. It is a promising algorithm to be used in a practical system for radio resource allocation.

Exploiting primary retransmission to improve secondary throughput by cognitive relaying with best-relay selection

In this paper, the authors propose two cognitive relaying schemes based on overlay and underlay, which exploit the cooperation opportunities inherent in primary retransmission to improve secondary throughput. If a primary signal is not decoded by the primary receiver (PR), a secondary user (SU) can be selected to relay it invisibly along with the primary retransmission. For overlay cognitive relaying, SUs intend to reduce primary retransmission time by relaying primary message, so that more access opportunities are available. While in underlay cognitive relaying, SU allocates part of its power to help primary user (PU) and the remaining power is used to transmit secondary message simultaneously. By controlling the phase of the relay signal, signals retransmitted from primary transmitter (PT) and SU can constructively combine at the PR. In both relaying schemes, we consider the best-relay selection as well. We define some novel metrics to evaluate the performance of PU and SU. For PU, we study the improvements in outage performance and average transmitting time per packet, while for SU, we consider the cooperation gain and cooperation efficiency, respectively. Theoretical analysis and numerical results verify the validity of both schemes, and a comparison is made between them.

Throughput Analysis of Slotted ALOHA with Cooperative Transmission

Cooperative transmission is widely applied to many fields for its high performance in overcoming wireless fading impairments. Aiming at traditional slotted ALOHA (S-ALOHA) with cooperative diversity, this paper proposes an effective theoretic analytical model and obtains the expression of its throughput. Results derived from our analytical model are mostly the same as that of the existed theoretic analysis model. And our model with distinct physical sense is simple and understandable. Numerical results show S-ALOHA with cooperative transmission (C-ALOHA) protocol can improve the throughput by 25.5% over a Rayleigh fading channel than traditional slotted ALOHA.

Modelling energy consumption for CoopMAC protocol

A focus of recent research activities in cooperative communication is the medium access control (MAC). However, few are from the perspective of energy consumption. In this paper, a novel and generalized energy model for cooperative MAC protocol called CoopMAC, which is a representation of MAC protocols in cooperative transmission, is proposed and its efficacy has been shown. Compared with the previous research, this paper gives a more comprehensive analysis of different operations in cooperation transmission. A formula of total energy consumption is derived. Simulation results reveal that cooperative MAC protocol is more energy-saved than the IEEE 802.11 protocol in transmission process.

Distributed beamforming for two-way amplify-and-forward relay in cooperative networks

Distributed beamforming is a promising technology in wireless communication. In this paper, we consider its application in the context of AF-based two-way relay. With a full CSI assumption, we make effort to maximize the sum-rate of source nodes S1 and S2 by optimizing the design of beamforming weight vector. However, an optimal closed form solution can not be derived for such a problem. Alternatively, we study two sub-optimal algorithms in the criterion of minimization of sum inverse-SNR and maximization of the minimum SNR. A discussion about their performance was presented at last, as well as their advantages and disadvantages.

Channel estimation for an OFDM-based amplify-and-forward relay system in the presence of co-channel interference

In this paper, we consider an OFDM-based amplify-and-forward forward (AF) relay system with multiple co-channel interferences (CCIs). On the premise of severe synchronous CCIs in both the data and pilot subcarriers, we propose an iterative method for pilot-aided channel estimation. Simulation results show that when multiple CCIs are in existence, our proposed method can effectively estimate the channel state information (CSI) of the equivalent channel and interference channel and the equivalent noise variance, and its mean square error (MSE) performance is as good as the traditional linear minimum mean square error (LMMSE) estimation, with the advantage of the lower complexity.

A MAC-PHY Cross-layer Scheduling Algorithm for Multiuser OFDM System

This paper investigate the cross-layer design for the packet scheduling and adaptive resource allocation for multiuser orthogonal frequency division multiplexing (OFDM) systems. The proposed algorithm executes fair scheduling at MAC layer and makes efficient use of wireless resource at PHY layer. Our objective is to develop a MAC-PHY layer scheduling mechanism in a more practical environment that users receive signal with different SNR level in a cell. The simulation results show that our proposed scheme satisfy most users in various SNR and have better average performance in packet drop rate, packet delay and total throughput.