Wu Weiling

Bio: Wu Weiling is an academic researcher from Beijing University of Posts and Telecommunications. The author has contributed to research in topics: Communication channel & Fading. The author has an hindex of 5, co-authored 42 publications receiving 132 citations.

A comparative study of robust channel estimators for OFDM systems

Abstract: In this paper, we investigate robust channel estimation methods for OFDM systems. Three pilot-symbol-aided channel estimation schemes are discussed, i.e., the maximum likelihood estimator (MLE), the estimator based on parametric channel modeling, and the least square (LS) estimation with low-pass interpolation. We analyze the complexities of the estimators and compare the mean square error (MSE) and symbol error rate (SER) over frequency-selective fading channels. It is shown that the low-pass interpolation-based estimation gives the lowest complexity among the three estimators, but its performance is not so good as the other two. The estimator based on parametric channel modeling is simpler than MLE with slightly better performance.

A Hierarchical Resource Allocation for OFDMA Distributed Wireless Communication Systems

Abstract: In this paper, a fair and simple resource allocation scheme is proposed for orthogonal frequency-division multiple-access distributed wireless communication systems (OFDMA-DWCS). Instead of finding global optimal solution, we hierarchically decouple the subcarrier and power allocation problem into two subproblems. A distributed scheduling is employed on two levels: access-point-level (AP-level) and user-level. In AP-level scheduling, the subcarriers are roughly allocated by the central unit (CU) to different APs. In user-level scheduling, a further subcarrier and power allocation is performed by each AP for its underlying users. We adopt Nash bargain solution fairness criterion in our scheme, which ensures a good tradeoff between fairness and efficiency on both the AP-level and the user-level. Simulation results demonstrate that the distributed scheme can achieve comparable overall system rate to that of centralized algorithms with much reduced complexity.

A steady source model for VBR video conferences

Abstract: In this paper, we proposed a new approach to model video traffic H263 encoded By introducing marginal matching technique and a variable of uniform distribution in different manners, we get two modified models, called MMB-DAR (Marginal Matching Based-DAR) and MMB-DAR, respectively The simulation results show that two MMB-DAR models can simulate the video traffic more steadily and accurately than GBAR and DAR models Especially, the MMB-DAR model is simple to realize, which can save our time to study source controlling algorithms At the same time, we corrected one unilateral standpoint brought forward by Heyman

Performance analysis for CDMA distributed antenna systems in an imperfect multipath environment

Abstract: Most of the previous studies in CDMA distributed antenna (DA) systems only provide a performance analysis based on the ideal channel estimation assumption in a flat fading environment. In this paper, the impact of imperfect channel estimation on the forward-link outage performance of CDMA DA systems in a multipath fading environment is investigated. A detailed analytical model based on a hybrid signal combining method is presented and the exact outage probability expression is derived. Our investigation shows that the effect of imperfect channel estimates varies with system load. Furthermore, we find that for the forward-link of DA systems, if simulcasting is employed, macrodiversity can decrease both the sensitivity of performance to channel estimation errors and the outage probability, which is contrary to the conclusion drawn based on the ideal channel estimation assumption.

QoS-guaranteed downlink transmission optimization for multi-service distributed antenna system

Abstract: To utilize wireless resources more efficiently and fulfill the requirements of future wireless communications, the scheme of quality-of-service (QoS) guaranteed downlink transmission optimization for multi-service distributed antenna system (DAS) is investigated. The design of the scheme involves balancing a number of conflicting requirements, including QoS provision, throughput maximization, and low system cost. A novel uni-access scheme combined with transmit beamforming algorithm is proposed to maximize DAS downlink throughput while guaranteeing the QoS requirements of multi-service. The optimization of the scheme is proved analytically. Furthermore, by taking system cost into account, the cost-effective solution of our scheme is proposed through simulation efforts. Simulation results also demonstrate effectiveness of our beamforming scheme, in comparison with previously proposed equal power per antenna transmission combined with MRC combining

On the capacity of a cellular CDMA system

Abstract: It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

Blind channel identification based on second-order statistics: a frequency-domain approach

Abstract: In this communication, necessary and sufficient conditions are presented for the unique blind identification of possibly nonminimum phase channels driven by cyclostationary processes. Using a frequencydomain formulation, it is first shown that a channel can be identified by the second-order statistics of the observation if and only if the channel transfer function does not have special uniformly spaced zeros. This condition leads to several necessary and sufficient conditions on the observation spectra and the channel impulse response. Based on the frequency-domain formulation, a new identification algorithm is proposed

Channel Estimation in OFDM Systems

Abstract: 1 OFDM Background 2 2 Baseband Model 2 3 Block-Type Pilot Channel Estimation 4 4 Comb-Type Pilot Channel Estimation 7 5 Other Pilot-Aided Channel Estimations 9 6 Performance Evaluation 10 7 Conclusions 14 8 References 15 This application note gives an overview of the channel estimation strategies used in orthogonal frequency division multiplexing (OFDM) systems. Section 1 describes the protocols associated with OFDM systems and the problems posed by such systems. Section 2 through Section 5 describe the various types of channel estimation methods for use in such systems. The implementation complexity and system performance of the methods are studied and compared in Section 6, measuring performance in terms of symbol error rate (SER).

A Survey on Handoffs — Lessons for 60 GHz Based Wireless Systems

Abstract: Wireless communication is playing an important role in our daily life since it offers flexibility and mobility. New multimedia services demand data-rates of up to hundreds of Mbps and thus higher frequency bands are being explored to support these new high data rate services. However, to support mobility, handoff is a must in many of these networks and systems. In the mean time the 60 GHz band has received much attention due to its 5 GHz of the available spectrum globally. However, the 60 GHz channels face many challenges such as high attenuation and NLOS propagation. The high reduction in signal strength as a function of distance results in a small coverage area, thereby causing frequent handoffs for mobile terminals. In this paper, we discuss and compare handoff algorithms intended for WLAN, GSM, UMTS, etc. We study these algorithms from the point of view of their usability in 60 GHz networks and make recommendations for handoff algorithms in such networks.