Changming Zhang

Double-link beam tracking against human blockage and device mobility for 60-GHz WLAN

Due to human blockage and device mobility, 60GHz wireless local-area network (WLAN) faces the challenge of communication-link outage. To cope with this problem, a double-link beam tracking scheme is proposed in this paper. This scheme includes a search strategy of transmission and alternative links, and an in-packet double-link tracking and switching method. The transmission and alternative links are simultaneously tracked against device mobility, through probing neighboring beams; once the human blockage is detected in transmission link, the system can thus switch to the alternative link directly. Besides, the proposed scheme finds the finish of human blockage quickly through in-packet double-link tracking, and enables the system to communication in the maximal received-power link. The comparison between the proposed scheme and the IEEE 802.11ad scheme is conducted. The comparison shows that the proposed scheme significantly reduces the probability of outage, and achieves an improved throughput.

Three-Stage Treatment of TX/RX IQ Imbalance and Channel with CFO for SC-FDE Systems

Direct-conversion transceiver obtains increasing attentions due to its low power consumption, but it confronts with serious IQ imbalance. In this paper, a three-stage treatment of transmitter/receiver (TX/RX) IQ imbalance and channel, in the presence of carrier frequency offset (CFO), is proposed for single-carrier-frequency-domain-equalization (SC-FDE) systems. First, RX IQ imbalance and CFO are handled with a repetitive preamble. Second, joint responses of TX IQ imbalance and channel are estimated by designing another preamble via complementary Golay codes. Third, joint compensation of TX IQ imbalance and time-varying channel is conducted using the minimal-mean-square-error criterion. Simulations are presented to verify the proposed method, in terms of normalized mean square error for the estimation and bit error rate for the overall system.

Performance comparison of channel coding for 60GHz SC-PHY and a multigigabit Viterbi decoder

In this paper, we make a performance comparison between convolutional(171,133) codes (CC), concatenated RS(255,239)-convolutional(171,133) codes (RS-CC) and LDPC(672,336) based on 60GHz single carrier physical layer (SC-PHY). With the effect of phase noise and non-linear distortion of power amplifier (NLPA) taken into account, RS-CC reveals higher robustness against the effect over LDPC, and it has the better bit-error rate performance than LDPC. Over and above, a forward independent sliding-block architecture for Viterbi decoders (FISB-VD) is proposed to achieve multigigabit inner-CC decoding of the RS-CC. A 16-parallel FISB-VD has been implemented in a Xilinx Virtex-6 FPGA device, of which the maximum decoding rate can be up to 3.2 Gbps.

GLRT Approach for Robust Burst Packet Acquisition in Wireless Communications

Rapid detection of the arrival of a packet is challenging in burst wireless communications, where many parameters are unknown, such as signal power, noise power and carrier phase offset. Due to the unknown noise power, it is hard to set appropriate thresholds for the existing common detectors under the Neyman-Pearson criterion, which results in vulnerable acquisition and poor performance. In order to solve this problem, we propose the generalized likelihood-ratio test (GLRT) approach for sequence-aided packet acquisition in this paper. GLRT detection is formulated under multipath channel. Moreover, false alarm probability and detection probability of GLRT are derived and confirmed via simulations. Comparisons are conducted between GLRT and the common detectors, as well as GLRT under different channels. Results show that GLRT basically reveals more competitive and robust performance than the common detectors in practice, with only a little extra hardware cost by using the provided recursive computation structure. Additionally, it is shown that fading results in significant deterioration for GLRT; whereas GLRT has ability to exploit multipath diversity to reduce fading effect and improve acquisition performance.

Sparse/dense channel estimation with non-zero tapdetection for 60-GHz beam training

Estimation of the multipath channel in 60-GHz communications is challenging, because the channel may be sparse or dense during beam training. Specifically, because of the variation of the number of non-zero taps, it is hard for common estimators to obtain robust and prominent performance. In order to address this problem, the authors propose a sparse/dense channel estimation with non-zero tap detection (SDCE-NTD). The estimation is conducted in a three-stage fashion, including initial estimation with the unstructured least-square (LS) algorithm, non-zero-tap detection with the generalised likelihood ratio test approach, and posterior estimation with the structured LS algorithm. The false-alarm and detection probability of the tap detector, as well as the mean square error (MSE) of SDCE-NTD, are derived and confirmed via simulations. Comparisons are conducted between SDCE-NTD and the common estimators in the beam training scenarios, where both dense and sparse channels exist. Results show that SDCE-NTD reveals a significant gain in terms of MSE over both the conventional LS algorithm, which does not exploit the sparse nature of the channel, and the matching pursuit algorithm, which endeavours to exploit the sparsity. In addition, it is also demonstrated that the proposed estimator can approach the lower bound with high signal-to-noise ratio.

Performance analysis on the OFDM PHY of IEEE 802.11ad standard

In order to analyze the performance on the Orthogonal Frequency Division Multiplex (OFDM) physical layer (PHY) of IEEE 802.11ad, a transceiver is designed based on the draft. The impacts of hardware impairments on the Bit Error Rate (BER) performance are studied, including phase noise and power amplifier (PA) nonlinear distortion. Simulation results indicate that phase noise makes a smaller effect on performance than PA nonlinear distortion. Additionally, 16-QAM and 64-QAM are more sensitive to hardware impairments than SQPSK and QPSK. To guarantee a good performance and get a high data rate, QPSK is a good choice in general, and 16-QAM is better when the backoff power of PA is relative large.

Delay-Based Weighted Proportional Fair Algorithm for LTE Downlink Packet Scheduling

This paper proposes an algorithm of delay-based weighted proportional fair (DBWPF) for downlink packet scheduling in the long term evolution cellular networks. Besides the tradeoff between throughput and throughput fairness, which is the target of the traditional PF scheduling, DBWPF also considers the weighted average delay of each user, where the user with larger delay is more likely to obtain resources. With this treatment, the DBWPF scheduling is conducive to achieve delay fairness and implementation rate fairness between different users, which is significant in the case that users in a cell have different traffic volumes. Simulation results indicate that the proposed method has an approximate throughput and throughput fairness compared with the PF scheduling. Moreover, in the aspects of delay fairness and implementation rate fairness, DBWPF is competitively superior to the traditional algorithms.

Iterative channel estimation and phase noise compensation for SC-FDE based mmWave systems

In the future super dense wireless networks, millimeter-wave (mmWave) communications systems have great prospects, mainly due to the huge bandwidths and the directional transmissions. However, phase noise is significant due to the high oscillation frequency, which affects channel estimation and deteriorates the bit-error-rate (BER) performance. This paper emphasizes that phase noise may be estimated in the frequency domain, and a scheme with iterative channel estimation and phase noise compensation is proposed for single-carrier frequency-domain equalization (SC-FDE) based mmWave systems. We achieve channel estimation by calculating small perturbations iteratively with the first-order approximation. For signal demodulation, we adopt an iterative receiver to compensate phase noise with the decision feedback result. Comprehensive simulations demonstrate that our scheme achieves competitive performance and outperforms the traditional methods, in terms of both mean square error (MSE) in channel estimation and BER in signal demodulation.

Joint SNR and channel estimation for 60 GHz systems using compressed sensing

60 GHz communication supporting multigigabit data rate is a popular choice of industry for next generation short distance wireless communications. However, multi-Gsps ADC becomes a challenge in 60 GHz systems which have ultra wide Nyquist bandwidth. To reduce sampling rate of ADC in the estimation stage, we propose a joint signal-to-noise ratio (SNR) and channel estimation algorithm using compressed sensing (CS) theory. In 60 GHz systems, CS encoding and decoding strategies are optimized to maximize benefits from the design of pilots and estimators. For pilot design, m-sequence rather than conventional Bernoulli random sequence is selected owning to a better average restricted isometry property; for estimator design, a quasi-optimal channel and noise power estimation is put forward underlying signal subspace provided by CS algorithm. Simulation results show that the proposed algorithm reduces the sampling rate of ADC to 9.1% Nyquist bandwidth of 60 GHz communication. Moreover, the algorithm with this compressed sampling efficiently outperforms classical least square algorithm with Nyquist sampling as SNR exceeds 7 dB.

Iterative Tx and Rx phase noise compensation for 60 GHz systems with SC-FDE transmission

Due to the extremely high oscillation frequency of 60 GHz systems, phase noise (PN) imported at both transmitter (Tx) and receiver (Rx) is significant, which degrades the transmission performance. This paper proposes an architecture employing iterative Tx and Rx PN compensation (ITR-PNC) for 60 GHz systems with single-carrier frequency-domain equalization (SC-FDE) transmission. The ITR-PNC iteratively performs PNC before equalization (PNC-BE) and PNC after equalization (PNC-AE), which are mainly set to manage Rx PN (RPN) and Tx PN (TPN), respectively. The PNC-BE and PNC-AE both exploit the one-tap least mean square (LMS) algorithm for PN extraction (PNE). In PNC-AE, the decision feedback result is used as the reference signal for PNE. And in PNC-BE, the reference signal is the signal replica, which is generated via the decision result and the estimated TPN of last iteration, and the estimated channel response. Comprehensive simulations indicate that the proposed architecture employing the proposed ITR-PNC achieves competitive bit-error-rate (BER) performance with only two iterations, for the cases whether only RPN or both TPN and RPN are taken into consideration.