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Zhang Z.,NEC Laboratories China NLC | Zhang L.,Alcatel - Lucent | You M.,Alcatel - Lucent | Lei M.,NEC Laboratories China NLC
Eurasip Journal on Wireless Communications and Networking | Year: 2010

The bit error rate (BER) of multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems with carrier frequency offset and channel estimation errors is analyzed in this paper. Intercarrier interference (ICI) and interantenna interference (IAI) due to the residual frequency offsets are analyzed, and the average signal-to-interference-and-noise ratio (SINR) is derived. The BER of equal gain combining (EGC) and maximal ratio combining (MRC) with MIMO-OFDM is also derived. The simulation results demonstrate the accuracy of the theoretical analysis. Copyright © 2010 Zhongshan Zhang et al.


Cao J.,NEC Laboratories China NLC | Zhu D.,NEC Laboratories China NLC | Lei M.,NEC Laboratories China NLC
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC | Year: 2013

Considering the time duplex division (TDD)-based cellular network, this paper investigates the uplink/downlink interference under the framework of centralized-radio access network (C-RAN). According to different uplink/downlink configurations within three neighboring cells, two fundamental cases are discussed, which can be further classified into several scenarios. For the sake of tackling this kind of interference, the interference alignment (IA) transceivers are studied case-by-case. Specifically, by applying the concept of reference vectors, to which direction the interference is to be aligned, we propose a simply methodology to align the interference at the un-intended receivers. Then with respect to the antenna settings, the heuristic process of IA design is presented and discussed. Finally, simulations verify the proposed IA transceivers greatly outperform its benchmark, when there is strong uplink/downlink inter-cell interference. © 2013 IEEE.


Zhu D.,NEC Laboratories China NLC | Lei M.,NEC Laboratories China NLC
IEEE Vehicular Technology Conference | Year: 2011

In this paper, a novel two-stage coexistence detection scheme for 60-GHz millimeter-wave (mmW) WLAN/WPAN is proposed. Specifically, orthogonal frequency division multiplexing (OFDM) is employed as the transmission mode. The energy detector (ED) is used at the first stage to perform coarse scan. If required, the arithmetic mean to geometric mean detector (AGD) is invoked at the second stage to refine the overall detection performance. The second-stage AGD does not rely on any prior information of the channel gains, transmitted signal pattern or noise variance. Instead, it investigates the inherent correlation of the received data samples and is derived strictly following the generalized likelihood ratio test (GLRT) paradigm. © 2011 IEEE.


Zhu D.,NEC Laboratories China NLC | Lei M.,NEC Laboratories China NLC
IEEE Vehicular Technology Conference | Year: 2012

In closed-loop precoded multiple-input multiple-output (MIMO) systems, the representative quantized channel state information (CSI) usually becomes outdated before its actual use at the transmitter due to the delayed feedback. In this paper, by exploiting the differential geometric properties of the Grassmannian manifold, we invoke the use of Grassmannian subspace predictive coding (GSPC) to compensate for this feedback delay. More specifically, a novel limited feedback strategy is presented which consists of a two-stage optimization process at the receiver. The first-stage optimization is accomplished by the quantization, which is custom designed as a function of the optimally predicted CSI under the framework of GSPC; after the first-stage codeword selection, the second-stage optimization is performed by optimizing the prediction on the Grassmannian manifold. We show by simulations that, the proposed encoding/decoding algorithm exhibits promised system performance over the existing prediction methods, for both spatial multiplexing and transmit beamforming MIMO, under the same amount of feedback bits. © 2012 IEEE.


Zhu D.,Stanford University | Zhu D.,NEC Laboratories China NLC | Lei M.,Stanford University
2013 IEEE International Conference on Communications Workshops, ICC 2013 | Year: 2013

In this paper, we propose and evaluate a novel resource allocation scheme in C-RAN TDD by means of dynamic BBU-RRU mapping. Specifically, in our proposed scheme, the logical connections between BBUs and RRUs are dynamically adjusted according to the asymmetric DL/UL resource allocation and traffic condition. In addition, since the asynchronous DL/UL allocation results in significant cross-subframe co-channel interference (CCI), a novel interference coordination scheme, termed cross-subframe coordinated scheduling/beamforming (CCS/CCB) is developed for CCI management. The proposed BBU-RRU mapping scheme and the CCS/CCD algorithm are interacted with each other, which in turn improves the system performance. © 2013 IEEE.


Zhu D.,NEC Laboratories China NLC | Lei M.,NEC Laboratories China NLC
2013 8th International ICST Conference on Communications and Networking in China, CHINACOM 2013 - Proceedings | Year: 2013

In this paper, we investigate traffic adaptation and energy saving potential of centralized radio access networks (C-RAN) with coordinated resource allocation and consolidation (CoRAC). The proposed CoRAC scheme comprises dynamic base-band unit-remote radio unit (BBU-RRU) mapping and cooperative dynamic downlink/uplink (DL/UL) reconfiguration. Specifically, in our proposed scheme, the logical connections between BBUs and RRUs are adaptively adjusted according the the traffic condition and interference patterns. Cell clusters are correspondingly formed, on which the developed cooperative reconfiguration method is conducted. With this setup, the DL/UL configurations are no longer determined with respect to an individual cell, but are chosen in form of the cluster-specific configuration patterns (CPs) with optimized performance metrics. Our proposed CoRAC scheme is custom designed for time-division duplex (TDD) systems aiming at (1) asymmetric traffic adaptation with load balancing; and (2) cross-subframe co-channel interference (CCI) management. In addition to (1) and (2), the CoRAC is beneficial from the perspective of network energy savings. This is because by shutting down under-utilized BBUs and selecting appropriate DL/UL configurations for traffic adaptation, the power consumption of both BBUs and RRUs (in terms of per-subframe radiated transmission power) can be reduced. System level evaluation results are provided, which show that by employing our proposed scheme, remarkable performance improvements can be obtained relative to the existing methods, in terms of the packet throughput, traffic adaptation and power consumption. © 2013 IEEE.


Zhu D.,NEC Laboratories China NLC | Lei M.,NEC Laboratories China NLC
2011 IEEE Wireless Communications and Networking Conference, WCNC 2011 | Year: 2011

In this paper, we propose a novel two-stage detection framework to facilitate the coexistence detection for OFDM-based 60-GHz millimeter-wave (MMW) WLAN/WPAN. Either blind or non-blind detection scheme can be employed at both stages regarding practical concerns. Here, the "non-blind" only refers to the case that relies on the prior knowledge of the noise variance. On the other hand, the blind detection schemes do not require any prior information of the channel gains, transmitted signal pattern or noise level. They are therefore robust to the noise uncertainty. We show by simulation that by carefully designing the two stages (e.g., non-blind detectors for stage-one and blind detectors for stage-two at relatively low SNR), our proposed two-stage detection scheme exhibits promised overall detection performance in practical 60-GHz channels with reduced computational complexity. © 2011 IEEE.


Zhu D.,NEC Laboratories China NLC | Lei M.,NEC Laboratories China NLC
IEEE Vehicular Technology Conference | Year: 2011

Single-carrier frequency domain equalization (SC-FDE) has been standardized as an alternative of orthogonal frequency division multiplexing (OFDM) in IEEE 802.11ad and 802.15.3c. In addition, with the use of low density parity-check (LDPC) codes, multi-Giga bits transmission can be supported in 60-GHz millimeter-wave (mmW) WLAN/WPAN with desired decoding complexity. In this paper, we present and evaluate an enhanced log-likelihood ratio (LLR) calculation method to facilitate the LDPC decoding in SC-FDE. In contrast to the virtual channel (VC) based LLR calculation approach (i.e., the Unique Word (UW) tracking scheme), our proposed method exhibits better bit error rate (BER) performance, and is more spectrally efficient. © 2011 IEEE.


Zhu D.,Stanford University | Zhu D.,NEC Laboratories China NLC | Lei M.,NEC Laboratories China NLC
IEEE Wireless Communications and Networking Conference, WCNC | Year: 2013

In this paper, we propose and evaluate a novel cluster-based dynamic downlink/uplink reconfiguration method in centralized TDD networks with dense deployment of remote radio units. All cells of interest are first divided into disjoint cell clusters. Cells that are highly interfered with each other are grouped into the same cluster. The central control units of the network optimize and reconfigure the downlink/uplink allocations on the basis of cell cluster. The optimization/reconfiguration aims at maximizing the overall system throughput and adapting the traffic variations. In addition, we investigate the use of the trellis exploration algorithm to facilitate the optimization/ reconfiguration process with low complexity. System level simulations validate the effectiveness of our proposed approach. © 2013 IEEE.


Zhu D.,NEC Laboratories China NLC | Zhang Y.,NEC Laboratories China NLC | Wang G.,NEC Laboratories China NLC | Lei M.,NEC Laboratories China NLC
IEEE Signal Processing Letters | Year: 2011

In unitary precoded multi-antenna systems with delayed feedback, the quantized channel state information (CSI) may become outdated before its actual use at the transmitter. In this letter, by exploiting the geometric properties of the Grassmannian manifold, we invoke the use of Grassmannian subspace predictive coding (GSPC) to overcome this problem. Under the framework of GSPC, a novel limited feedback strategy is proposed which consists of a two-stage optimization process at the receiver. The first stage quantizes the estimated CSI by accounting for the feedback delay; while the second stage optimizes the prediction on the Grassmannian manifold. © 2011 IEEE.

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