Yuan Qi

Adaptive Channel Searching Scheme for Cooperative Spectrum Sensing in Cognitive Radio Networks

The MAC-layer sensing, as a key component of spectrum sensing in cognitive radio, concerns the sensing mechanism design to determine when to sense and access which channel. An important issue of MAC-layer sensing is to find an available channel with a minimized searching delay for the cognitive transmission without any harmful interference. In this paper, we focus on this issue and propose adaptive searching scheme and cluster-based searching scheme to reduce the searching time when channel conditions are various and the cooperative sensing is applied. Moreover, the optimization of these two schemes are also developed in this paper. By adaptive selecting the searching parameters according to the current environment, the average consumed time of channel searching can be minimized, while the searching quality is also satisfied. The simulation results verify the confidence of proposed schemes and show a better searching performance when combining these two schemes.

On the scale effects oriented MIMO detector: Diversity order, worst-case unit complexity and scale effects

In this paper, the insight into the scale effects oriented MIMO detector (SEOD) which is developed for the MIMO system that has to detect signals of multiple users, e.g., the multiple-antenna base-station (BS) system, is presented. The diversity order, complexity and scale effects of SEOD are investigated. The main contributions of this work can be listed as follows: (1) applying the concept of scale effects in microeconomics to MIMO detection and establishing the corresponding model for the analysis of scale effects; (2) presenting the complete proof of the existence of scale effects in our proposed SEOD scheme; (3) demonstrating that the scale effects can be utilized to realize MIMO detection that has the optimal performance in the sense of diversity order while keeping the worst-case unit complexity be polynomial in multiple-user system. Through the computer simulation, we obtain the numerical results which support the theoretical analysis.

Scale effects oriented MIMO detector

In this paper, a novel scheme of multiple-input multiple-output (MIMO) detector is proposed for base-station (BS) system that has to detect signals of multiple users, which is capable of exploiting the scale effects and thus named as the scale effects oriented MIMO detector. The scale effects is the feature that, the unit complexity of MIMO detector decreases as the number of users increases under certain condition while maintaining the full diversity. Through theoretic analysis of error probability, diversity order and complexity, as well as works of computer simulation, we demonstrate that the proposed MIMO detector has the scale effects.

Exploiting scalar effects of MIMO detection in could base-station: Feasible scheme and universal significance

In this paper, the problem of exploiting potential benefit from centralized processing nature of cloud base-station is addressed. We propose to exploit one kind of benefit available in cloud base-station, called scale effects, for MIMO detection by employing the scale effects oriented MIMO detector (SEOD). From this study, it can be found that SEOD is a feasible scheme being able to exploit two types of scale effects. The first type, called scale effect on diversity order, denotes the feature that the worst-case complexity per user of MIMO detection could decrease as the number of users increases while bringing no loss of diversity order; the second one, called scale effect on detecting outage, is the feature that the probability of detecting outage owing to the run-time limit is equal to or is asymptotic to a monotonic decreasing function of the number of users when fixing the worst-case complexity per user for MIMO detection. By using the large deviation principle (LDP), this work presents the proof of the existence of scale effect on detecting outage in SEOD which has not been obtained in literatures. Provided SEOD as a representative case, we also state the universal significance of exploiting scale effects for cloud base-station.

Asymptotic analysis of random lattices in high dimensions

This paper presents the asymptotic analysis of random lattices in high dimensions to clarify the distance properties of the considered lattices. These properties not only indicate the asymptotic value for the distance between any pair of lattice points (with and without noise corruption) in high-dimension random lattices, but also describe the convergence behavior of how the asymptotic value approaches the exact distance. Besides, we provide a discussion on further extensions and potential applications of the derived results regarding the lattice theory and multiple-input multiple-output (MIMO) technology.

Scale effect analysis of early-termination fixed-complexity sphere detector

In this paper, we show that the early-termination fixed-complexity sphere detector (ET-FSD) has a scale effect when being employed in multi-antenna systems that have to detect signals of multiple users under the constraint of sum complexity. The so-called scale effect stands for a kind of effect in which the complexity per user can be reduced as the number of users increases without loss of diversity order. The main contributions of this study are as follows: (1) we establish a mathematical model based on the large deviation principle to apply the concept of scale effect to ET-FSD; (2) we prove the existence of the scale effect of ET-FSD in a multi-user scenario; and (3) we demonstrate that within multi-user systems, the scale effect can be exploited to realize ET-FSD that has the optimal performance in the point view of diversity order under polynomial complexity constraint per user.

ET-FSD: A feasible scheme of MIMO detection to exploit scalar effects

In this paper, the early-termination fixed-complexity sphere detector (ET-FSD) that is a channel-adaptive version of FSD, is developed to exploit scale effects for the multiple-antenna system which has to detect signals of multiple users under the constraint of sum complexity (e.g., the base-station systems always encounter the run-time limit of signal detection of all the users). In order to apply the concept of scale effects in microeconomics to the study of ET-FSD, the corresponding mathematic model primarily based on the large deviation principle is established. The key evidence that tells the existence of scale effects in ET-FSD is presented instead of the complete proof due to the space limitation. We also argue that within multiple-user systems the scale effects can be utilized to realize ET-FSD that has both the optimal performance in the point view of diversity order and the polynomial time unit complexity in the worst-case sense (one can think of unit complexity as the complexity per user in multiple-user scenario). Finally, we provide the numerical results to support the theoretical analysis.

Closed-form approximations for secrecy capacity in Rayleigh-fading multi-antenna systems

In this paper a framework of analyzing the secrecy capacity of Raleigh fading multi-antenna system in presence of multiple eavesdroppers is presented. The multi-antenna system we concern adopts the transmit antenna selection with maximal-ratio combining (TAS/MRC) diversity scheme. We propose to make use of the closed-form approximations to analyze the secrecy capacity. The simulations validate the analytical results derived by the proposed framework.

On the capacity of ergodic channels: A large deviation analysis

The convergence behavior of capacity of ergodic channels is of great importance for the performance analysis of communication systems. This paper presents a fundamental study on the convergence rate of capacity of ergodic channels on the basis of large deviation theory. It can be revealed that both the probability that the information capacity differs from the ergodic capacity by more than δ(δ > 0) and the outage probability of information capacity decrease at a rate which is asymptotic to that of an exponential decaying function in the number of times of channel use N which are proposed in Theorem 1, Property 1 and 2. To verify the theoretical results, a case study of investigating the rate function for a Rayleigh fading channel is presented. The simulations show that the convergence rate of capacity of ergodic channel coincides with the Theorem and Properties. The achievability of capacity under the assumption of finite channel use is discussed as well.

Approximate distribution of log 2 (A + x 2 )

This study concerns the approximate distribution of the random variable log2(A + χ 2) and its applications in the performance analysis of communication systems where A is 0 or 1 and χ 2 a chi-square distributed random variable. The authors prove that log2(A + χ 2) is approximately Gaussian distributed and derive the expressions of the mean and variance of the approximate distribution. The approximate Gaussian distribution provides a new way to simplify the derivation of performance metrics and obtain analytical results. Then the authors utilise the approximate results in two applications, which are the approximation of the Gaussian Q-function and capacity analysis, respectively. For one thing, the approximate distribution can be explored to deduce a new approximate equivalent expression of the Q-function on the basis of which an accurate approximation of the Gaussian Q-function can be developed. For another, the approximate Gaussian distribution provides an intuitive approach to analyse the channel capacity of Rayleigh-fading multiple antenna systems. The approximate statistical distributions of the channel capacities of orthogonal space-time block codes, single-input multiple-output, multiple-input single-output, transmit antenna selection with maximal-ratio combining and multiple-input multiple-output systems are presented. The applicability of the approximate distribution can be demonstrated through simulation results in both applications.