Jinkang Zhu

Traffic-aware relay sleep control for joint macro-relay network energy efficiency

With the ever growing demand of data applications, the joint macro-relay networks are emerging as a promising heterogeneous deployment to provide coverage extension and throughput enhancement. However, the current cellular networks are usually designed to be performance-oriented without enough considerations on the traffic variation, causing substantial energy waste. In this paper, we consider a joint macro-relay network with densely deployed relay stations (RSs), where the traffic load varies in both time and spatial domains. An energy-efficient scheme is proposed to dynamically adjust the RS working modes (active or sleeping) according to the traffic variations, which is called traffic-aware relay sleep control (TRSC). To evaluate the performance of TRSC, we establish an analytical model using stochastic geometry theory and derive explicit expressions of coverage probability, mean achievable rate and network energy efficiency (NEE). Simulation results demonstrate that the derived analytic results are reasonable and the proposed TRSC can significantly improve the NEE when the network traffic varies dynamically.

A novel decoding algorithm of STBC for CDMA receiver in multipath fading environments

We propose a new algorithm to realize STBC (space-time block coding) decoding with multipath components in a CDMA receiver. We construct a symbol-by-symbol detector directly utilizing multipath components to achieve better performance. Our proposed algorithm equivalently extends the number of receive antennas. We deduce the BER expression of our proposed algorithm, and we perform numerical results of BER performance.

Improved coarse frequency synchronization algorithm with extended differential detection

OFDM (orthogonal frequency division modulation) is a very promising technique for future communication system. However, frequency offset is well known as one of the main factors that influence the performance of OFDM communication systems. Various coarse frequency synchronization algorithms based on differential detection have been proposed to cope with the oscillation in frequency response in dispersive channel. This paper extends the concept of differential detection and improves existing coarse frequency offset synchronization algorithm. In this modified algorithm, parameter can be adjusted to obtain different performance tradeoff. In addition, compared with the conventional algorithm, the computation complexity of this proposed algorithm only increases a little and remains the same order. Simulations are carried out to verify the improvement of performance of our proposed algorithm.

Maximizing energy efficiency in analog network coding based two-way relay-assisted system

In this paper, we investigate the energy efficiency maximization problem of analog network coding (ANC) based two-way relay (TWR) assisted cellular network under quality of service (QoS) constraints through transmit power optimization. Circuit power cannot be ignored since it influences energy efficiency greatly. However, the difficulty is that maximizing energy efficiency is shown to be non-convex in TWR-assisted network, and cannot be equivalent to the convex minimizing transmit power because of the effect of circuit power. A two-stage maximum energy efficiency (MEE) method is proposed to tackle this problem effectively. Closed form expressions of both the optimal transmit power and energy efficiency are derived. We prove the optimality of MEE method through both analytical and simulation results, and show that it can increase energy efficiency significantly. Furthermore, it is theoretically proved that the optimal relay selection (RS) criterion is the Max-Harmonic-Mean (MHM) criterion in multiple relay scenarios.

Energy efficiency optimization in relay-assisted networks with energy harvesting relay constraints

In this paper we consider data transmission in a decode-and-forward (DF) relay-assisted network in which the relay is energy harvesting (EH) powered while the base station (BS) is power-grid powered. Our purpose is to maximize the BSs energy efficiency (EE) while making full use of the relays renewable energy and satisfying the specific average throughput requirements. In contrast to existing literature on energy harvesting system which only considers the radio transmission power, we take the static circuit power into account as well. We formulate the EE optimization problem and prove that the EE of the BS and relay are both quasiconvex in the instantaneous transmission rate. Then we divide the complex optimization problem into two point-to-point link level optimization parts and propose an energy-efficient resource allocation (EERA) scheme in which power control and sleep mode management are jointly used. The simulation results demonstrate that EERA may achieve good energy saving effects. We also compare the EE of an energy harvesting relay system with a power-grid powered one and provide more insight into the EE problem of energy harvesting relay system.

User Selection and Resource Allocation for Multi-User MIMO-OFDM Systems with Downlink Beamforming

In this paper, a multi-user MIMO-OFDM system with downlink beamforming technique is considered. We aim at minimizing the total transmission power while fulfilling each users data rate and bit error rate (BER) requirement. This problem is formulated as a linear optimization problem in our paper. Since the optimal solution obtained from integer programming (IP) approach can hardly be implemented due to its high computational complexity, we present a heuristic user selection and resource allocation algorithm. Simulation results show that compared with existing SDMA-OFDM systems with or without resource allocation, our algorithm achieves significant performance improvement. The performance of the proposed heuristic algorithm is very close to that of the optimal solution.

Performance analysis of multiple reject ARQ theme at RLC layer in 3G

In this paper, we analyze the ARQ mechanism at RLC (radio link control) layer in a UMTS WCDMA system in detail and get good throughput and waiting time approximations. The ARQ method proposed in WCDMA belongs to multiple reject (MR) ARQ methods that outperforms the normal Go-back-N and selective repeat methods especially under inferior conditions of wireless communications. According to 3GPP specifications, the traffic rate varies from 3.4 kbit/s to 2 Mbit/s, and may be asymmetrical between uplink and downlink. To reach the peak or near-peak throughput, different parameters should be used with different traffic types and different directions. The main purpose of this paper is to analyze the performance of MR and study how the parameters affect the performance. We have also implemented the whole protocol stack on a hardware platform and done many experiments under different SNR channels. Based on the analysis and experiments, we can give good advice on timer control and buffer control of RLC layer in 3G.

Study on wideband CDMA modulation, power control and wireless access for CDMA multimedia systems

In this paper, we present our researches on wideband code division multiple access (W-CDMA) multimedia wireless system which is sponsored by Communication Subjects of High Technology R&D Programme of China. We propose a W-CDMA modulation scheme of variable transmission rate, partial-balance power control algorithm, and wireless access method for variable access rate. The proposed algorithm integrates traffic priority ranking and transmit power control and access information rate control. Our simulation results show that the partial-balance power control algorithm can render the special QoS requirements of traffic with higher priority orders guaranteed and maximize the CIR of the traffic with lower priority orders. Access rate adaption provides higher channel usage and more successful access probability than the fixed access rate algorithm. Based on the above techniques, we also develop a experimental system which consists of base station and multimedia terminals.

Spectral and energy efficiencies of a hybrid cellular network structure

In this paper, we propose a hybrid cellular network structure where co-frequency vertical coverage embedded on the cell edge, to improve the performance in the cell edge, using the cell interference depth as the interference threshold. Based on this proposed structure, three key performance metrics, i.e., the spectral efficiency, the cell throughput and the energy efficiency, are analyzed. The results demonstrate that the proposed hybrid cellular structure can significantly improve the spectral and energy efficiencies without modifying the current cellular infrastructures, making the operation and implementation of cellular networks simple and feasible.

Energy-efficient scheduling of delay constrained traffic under practical power model

In this paper, we focus on the delay constrained scheduling problem for wireless link communication under the practical concerns, such as the practical power consumption of transmitter and energy used for channel estimation. In particular, we target to design an energy-efficient scheduling policy that minimizes the total energy expenditure while satisfying the deadline constraint based on knowledge about the unserved bits, channel state/statistics, practical power model and the remaining time slots to the deadline. We formulate the scheduling problem as a stochastic programming problem and propose a suboptimal policy by analyzing the structure of the solution. In addition, we study a special case that the whole packet is served in a single slot and propose an optimal channel-threshold policy based on the stopping theory. Numerical results illustrate that the proposed policies provide great energy efficiency especially when the data amount is relatively small and the transmission independent power consumption is large.