Sihai Zhang

Spray and wait routing based on position prediction in opportunistic networks

For opportunistic networks, we propose a new routing protocol named PPSW, which exploits the benefit of the polynomial interpolation prediction of mobile nodes positions. This scheme can deliver the message faster with appropriate opportunities. Specifically, in wait phase, relay can forward message to another one moving closer to destination, instead of waiting to encounter the destination itself. Simulation results show that PPSW achieves about 20% improvement compared with Spray and Wait protocol in delivery rate and delay performance.

Proportional-fair downlink resource allocation in OFDMA-based relay networks

In this paper, we consider resource allocation with proportional fairness in the downlink orthogonal frequency division multiple access relay networks, in which relay nodes operate in decode-and-forward mode. A joint optimization problem is formulated for relay selection, subcarrier assignment and power allocation. Since the formulated primal problem is nondeterministic polynomial time-complete, we make continuous relaxation and solve the dual problem by Lagrangian dual decomposition method. A near-optimal solution is obtained using Karush-Kuhn-Tucker conditions. Simulation results show that the proposed algorithm provides superior system throughput and much better fairness among users comparing with a heuristic algorithm.

Energy-Friendly Network Selection in Heterogeneous Wireless Networks

Mobile terminals in heterogeneous wireless networks continuously undergo network selection within the initial access process and handover process. In order for a mobile terminal to be connected to a network in the best possible way in terms of QoS performance and energy consumption, this paper presents a novel method that takes into account user preferences, network conditions, QoS and energy consumption requirements in order to select the optimal network which achieves the best balance between performance and energy consumption. The proposed network selection method incorporates the use of fuzzy logic because of the available sources of information from different radio access technology (RAT) are qualitatively interpreted and heterogeneous in nature, and adopts different energy consumption metrics for real-time and non-real-time applications. Finally, simulations confirm our schemes suitability and effectiveness.

Outage Analysis of Distributed Scheme on Opportunistic Relaying with Limited CSI

In this letter, we propose a distributed scheme on opportunistic amplify-and-forward (AF) relaying to minimize the system outage probability with low feedback overhead. Only the subset of relays report the calculated outage probability information to the source based on the outage probability threshold with the limited channel state information (CSI). We present the approximate expressions for the system outage probability under two scenarios, the statistical CSI and the statistical quantized CSI of the relay-destination links, respectively. Numerical results indicate that the derived analytic results are reasonable and the outage performance is better for the statistical quantized CSI case with acceptable feedback cost.

Bound Analysis of Physical Layer Network Coding in Interference-Limited Two-Way Relaying System

In this paper, performance of three-time slot (3TS) physical layer network coding (PNC) is investigated in interference-limited two-way relaying system. Effective lower and upper bounds are derived for important performance metrics like outage probability and average bit error rate (BER) with different modulation modes. Asymptotic behavior is also proposed to intuitively exhibit the trend of performance in high signal-to-interference and noise ratio (SINR) regime. We differentiate practical applications with different relay power for the bounds. A particular scenario with positional grid structure of sources, relay and co-channel interferers is established for numerical analysis, and the effects of some critical parameters, such as relays location, forwarding capability and power allocation factor, are compared and discussed. The theoretic solutions are finally verified by simulation results.

Computing on Base Station Behavior Using Erlang Measurement and Call Detail Record

With the impressive development of wireless devices and growth of mobile users, telecommunication operators are thirsty for understanding the characteristics of mobile network behavior. Based on the big data generated in the telecommunication networks, telecommunication operators are able to obtain substantial insights using big data analysis and computing techniques. This paper introduces the important aspects in this topic, including data set information, data analysis techniques, and two case studies. We categorize the data set in the telecommunication networks into two types, user-oriented and network-oriented, and discuss the potential application. Then, several important data analysis techniques are summarized and reviewed, from temporal and spatial analysis to data mining and statistical test. Finally, we present two case studies, using Erlang measurement and call detail record, respectively, to understand the base station behavior. Interestingly, the night burst phenomenon of college students is revealed by comparing the base stations location and real-world map, and we conclude that it is not proper to model the voice call arrivals as Poisson process.

Utility-based resource allocation in OFDMA relay networks with service differentiation

In this paper, we investigate the utility-based resource allocation problem in OFDMA relay networks with service differentiation, where Rate Constraint (RC) and Best Effort (BE) services are supported. Our objective of resource allocation is to maximize the sum utility of BE service users, while guaranteeing that the utility of each RC service user is equal to one. A joint optimization problem for relay selection, subcarrier assignment and power allocation is formulated. Since the problem cannot be solved directly, we make continuous relaxation and solve it by La-grangian dual method. The optimal allocation strategy is obtained using Karush-Kuhn-Tucker (KKT) conditions. As it is difficult to converge to the optimal solution, thus we further present a heuristic resource allocation algorithm with low complexity. Simulation results show that our proposed algorithm achieves higher utility of BE users and lower outage probability of RC users, and also yields a good tradeoff between system throughput and user fairness.

Weighted message passing algorithm for SCMA

Sparse code multiple access (SCMA) is a new frequency domain non-orthogonal multiple-access technique which can make full use of limited spectrum resources in wireless communication system. In SCMA, multiple users share the same time-frequency resources of orthogonal frequency division multiple access (OFDMA). However, message passing algorithm (MPA) is used in the process of SCMA decoding. And when the iteration number of MPA is large, the decoding complexity of SCMA is very high. In this paper, we propose an algorithm to decrease the decoding complexity of SCMA by introducing weight factors to replace MPA algorithm iterative process. We give each codeword in the codebook an original probability value which is related to the distance between received signal and the codeword. We set a corresponding weight factor for each probability value to change the original probability distribution of each codeword in the codebook. Simulation shows that this algorithm can greatly decrease the decoding complexity of SCMA while suffering only a bit of performance loss.

Performance Analysis on Two-Way Relay System with Co-Channel Interference

In this paper, we investigate the performance of two-way relay system with co-channel interference in a Rayleigh fading environment. Due to the mathematical intractability of original expression of signal-to-interference and noise ratio (SINR) induced by the bi-directional forwarding, a couple of effective bounds are derived for important performance metrics such as outage probability and average bit error rate of modulation, with application of diverse physical layer network coding (PNC) schemes of two time slot (2TS) and three time slot (3TS). Some asymptotic solutions are also proposed to intuitively exhibit the trends of performance in high SINR regime. We demonstrate that the performance bounds have practical meaning corresponding to different forwarding capability of the relay. Numeric simulations validate our analysis by showing that the theoretic bounds match well with simulation results. Additionally, the effect of distance between relay and sources is discussed in our interference scenario, as well as the impact of relay’s power allocation factor in 3TS PNC scheme.

Performance Analysis of Two-Way Relay Selection Scheme Based on ARDT Protocol

Adaptive Relay-Assisted/ Direct Transmission (ARDT) proposed in [13] is a simple and efficient protocol which adaptively utilizes the direct link between two sources with only channel state information at receiver (CSIR), and it validly enhances the spectrum efficiency of time division broadcast (TDBC) system. In this paper, we combine ARDT with joint power allocation and relay selection for multi-relay scenario. Each relay optimize its own forwarding power to maximize the minimum end to end signal to noise ratio (SNR) towards two sources, and the optimal relay is then selected to cooperate. System outage probability, average throughput and average bit error rate (BER) are analyzed with theoretical upper and lower bounds. Numerical simulations validate the rationality of bounds, and show that whether maximal ratio combining (MRC) is adopted for receiving makes little difference. The proposed relay selection scheme is verified to outperform that based on original TDBC in reference work.