Guangxin Yue

An Energy Detection Algorithm Based on Double-Threshold in Cognitive Radio Systems

Based on conventional single-threshold energy detection algorithm, we put forward a double-threshold version in cognitive radio system, and then, we analyze the detection probability, false alarm probability, miss probability and their relationships. For further research, we define two parameters for performance evaluation: the probability of collision between the cognitive user and the primary user, and the probability of spectrum unavailable to the cognitive user. Comparing to the single-threshold energy detection algorithm, both analysis and simulation results show that the proposed double-threshold energy detection algorithm can make a lower collision probability between the cognitive user and the primary user, despite a little increasing of the spectrum unavailable probability.

Delay-Bounded Power-Efficient Packet Scheduling for Uplink Systems of LTE

In this paper, we study minimal power transmission for uplink systems of LTE with constraints on mean queuing delay. Power consumption is important concern for multimedia services of mobile station of LTE .The power minimizing scheduler adapts power and rate of transmission based on the queue and channel state. Our extensive simulations show that small increases in average delay can lead to substantial savings in transmission power, thereby providing another avenue for mobile devices to save on battery power. We propose a low-complexity scheduler that has near-optimal performance.

Unified view of channel estimation in MIMO-OFDM systems

This paper provides a unified view of time-domain and frequency-domain least square (LS) channel estimation in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. Time-domain and frequency-domain LS channel estimation are formulated under the same framework and their average mean square error (MSE) lower bounds for arbitrary number of transmit antennas and arbitrary number of pilot symbols are derived. Moreover, general optimum pilot design rules are developed to achieve average MSE lower bounds for time-domain and frequency-domain LS channel estimation, respectively. Their applicable conditions and computational complexity are also investigated and compared. It can be shown by theory and simulation that time-domain LS channel estimation is equivalent to frequency-domain LS channel estimation with discrete-time Fourier transform (DFT) improvement, but time-domain LS channel estimation has boarder applicable condition.

Relay-Assisted MIMO Multiuser Precoding in Fixed Relay Networks

In this paper, downlink multiple input multiple output (MIMO) multiuser transmission using precoding in fixed relay networks is studied. We propose two relay-assisted MIMO multiuser precoding models. For the first model, multiuser precoding is performed at base station (BS). The fixed relay processes the received signal and forwards it, which is amplify- and-forward. While for the second model, the multiuser precoding is done at relay. Thus, detect-and-forward or decode- and-forward transmission can be used. Based on these models, some multiuser precoding algorithms are investigated. Our simulation results show that fixed relay offers significant gain. And our system architectures give the means on how to utilize fixed relay in MIMO multiuser system.

Pilot Aided LS Channel Estimation in MIMO-OFDM Systems

This paper presents the theoretical and simulation results for least square channel estimation in MlMO-OFDM systems based on two types of pilot structure, the block-type pilot and the comb-type pilot. We derive their estimation equations, average mean square error lower bounds and optimum pilot design rules. Simulation results verify the theoretical analysis and show that the comb-type pilot aided channel estimation has a better performance when the channel is time-variant

Performance comparison of two kinds of UWB Rake receiver

Compared with carrierless pulse shaping, carrier-based pulse shaping is flexible to fit the FCCs frequency allocation for UWB and enriches the transceiver schemes. With the assumption that BPSK is used, this paper analyzes and compares the BER performance of two kinds of UWB Rake receiver, named radio-frequency Rake (RF-Rake) and base-band Rake (BB-Rake). The theoretical analysis and simulation results show that BB-Rake performs worse than RF-Rake in multipath environments, which is due to random carrier phase deviation.

Channel Estimation and Space-Time Decoding under MIMO System

Recursive expectation-maximization (EM) algorithm along with stochastic approximation is employed in this paper to estimate unknown time-invariant/variant parameters. In addition, we modify the conventional Viterbi algorithm used in space-time encoder under the MIMO system, and give the recursive metric equation. The modified Viterbi algorithm can be used in the receiver when the MIMO channel information has been estimated. Compared with the conventional decoding algorithm, the improved algorithm can be used in the every receiver respectively. It is shown that the improved algorithm is also an optimal algorithm, however, its metric convergence speed is faster than the standard Viterbi algorithm.

Optimized Signal to Noise Ratio Threshold Based on Transmission Power and Complexity of Cognitive Detector

Scarcity of the spectrum is becoming a major issue based on traditional frequency planning scheme, cognitive radio (CR) has been proposed for better spectrum utilization efficiency by intelligently sensing and opportunistic access. In this paper, a novel method is proposed to determine signal to noise ratio threshold (SNRT) based on transmission power and complexity of cognitive detector under lognormal shadowing conditions. Since there is tradeoff between detection probability and false alarm probability, we can maximize spectrum utilization efficiency with pre-determined detection performance,meanwhile SNRT is adjusted to void unacceptable interference to primary receiver (PR) and minimize complexity of cognitive detector according to transmission power. Numerical results will show that cognitive radio can adjust SNRT adaptively in order to guarantee the PR decoding signal from primary transmitter (PT) without unacceptable interference.

Spectrum Detection Based Cyclostationarity in Spectrum Pooling System

Cognitive radios should have the capability to detect idle spectrum and share it without harmful interference with other users. This paper presents a strategy for extracting second-order cyclostationary characteristics of licensed system and rental system signals based on spectrum pooling system. According to cyclostationary characteristics of licensed users signals received at the nodes of CRs, predicting whether a signal from a primary transmitter is locally present or not and estimates the channel allocation information. In this paper, formulas for calculations of cyclostationary characteristics are derived and consistent conclusions are illustrated using simulation results.

A novel channel predictor based on constrained hidden Markov model

In order to realize the potential of link adaptation, reliable channel prediction is necessary. In this paper, we propose a novel channel predictor based on constrained hidden Markov model (CHMM), By partitioning the range of the received signal envelope into several intervals, a CHMM can be constructed with the high efficiency algorithm. Then an improved prediction method is presented, which is more accurate than the simple prediction method of the largest transition probability. Finally, simulation results are given to show the effectiveness of the CHMM channel predictor.