Ruiming Zheng

Performance Evaluation on the Coexistence Scenario of Two 3GPP LTE Systems

The standardization of the Long Term Evolution (LTE) of 3G networks is currently carried through in 3GPP. With the deployment of frequency planning, the coexistence issue between TDD and FDD LTE systems is becoming urgent in certain frequency bands. In this paper, the detailed LTE system interference environment is investigated, including single system scenario and inter-system interference, network deployment, propagation models, power control scheme, Adjacent Channel Leakage power Ratio (ACLR) model and link level model. Typical coexistence scenarios with two LTE systems deployed in macro cellular networks are simulated and analyzed. The discussion includes the influence of several system parameters on network performance, such as power control sets, system bandwidths and occupied frequency bands. Meanwhile, the possible approach of adopting beam-forming technology or intercell interference coordination mechanism is also investigated in TDD-LTE systems of coexisting cases. The simulation results show that two LTE systems could coexist with proposed advanced techniques under current LTE Radio Frequency (RF) system parameters. Keywordscoexistence; interference; LTE; ACIR;

Interference Avoidance and Adaptive Fraction Frequency Reuse in a Hierarchical Cell Structure

Due to high data rate requirement for indoor radio coverage, femtocells have been proposed as a potential good solution in recent years. Under this configuration, a main design objective is to coordinate the mutual interference between macro and femto cells. In this paper, the flexible assignment of downlink resource in a hierarchical cell structure is investigated. A dynamic frequency assignment technique called adaptive fraction frequency reuse (AFFR) is proposed, by avoidance of severe interference between macro and femto cells. A network model and system level simulations for LTE macrocell/femtocell scenarios are presented. The results show that, AFFR has better average and cell- edge performance compared with co-channel frequency allocation (co-channel FA) and orthogonal frequency allocation (OFA) for both macro and femto cells.

Solution of Information Exchange for Cooperative Sensing in Cognitive Radios

Recently, cooperative sensing which can enhance the sensing performance becomes popular in the design of cognitive radio (CR) networks. CR networks need reliable information exchange to conduct cooperative sensing,but it is difficult to transmit information for CR networks without licensed band over the air interface. In this paper, we propose to use spread spectrum technology to transmit low rate exchange information through wide bandwidth. Simulation results show that the capacity loss of primary user is minor, while the exchange information can be demodulated and decoded at a high SNR level based on our proposed scheme. The tradeoff between detection performance and interference to primary user is also discussed.

Novel Cooperative Schemes on Spectrum Sensing in Multi-Primary-User Cognitive Radio Network

It is widely accepted that the emergence of cognitive radio (CR) will lead to a wireless communication revolution. Spectrum sensing is one key process of CR, which makes effective use of scarce spectrum. Two novel schemes, clustering and locating schemes, are presented for spectrum sensing based on energy detection on the condition that there are multiple primary users in the cognitive radio network. Clustering scheme is used for estimating the number of primary users and dividing the secondary users into several groups based on their geographical position as well as received energy by my proposed iterative max-min theory, and then locates the position of primary user by locating scheme based on the center of gravity algorithm. These schemes work well when only geographic information and the amount of energy can be obtained. Finally, numerical analysis and simulation results of these schemes are provided. It is proved that the proposed criteria are practical and efficient in the absence of the type of primary signal and the amount of noise which are necessary for previous methods.

A Novel Scheme with Adaptive Sampling for Better Spectrum Utilization in Cognitive Radios

In cognitive radio (CR) networks, cognitive users need continuously monitor spectrum to decrease or avoid interference to primary users, yet attain a reasonable throughput. In this paper, we exploit a scheme to dynamically change the detection time duration to gain maximum throughput. Meanwhile the average de-tection time is kept as small as possible. The advantages of our approaches are approved by the deductions. Also the simulation results enable us to recognize the improved performance of our scheme over those ones with fixed detection time assignment.

Coexistence Study in the 2500-2690 MHz Band between WiMAX and WCDMA Systems

WiMAX (802.16e) has been recognized as an official member of IMT-2000 by WRC-07, which permits its use of 3G systems bandwidth, including 2500 to 2690 MHz. The work of coexistence interference analysis between WiMAX and WCDMA systems in 2.5 GHz band is a potential research field. This paper presents several interference paths, investigates the methods of evaluating two coexisting systems in details, and analyzes necessary assumptions as well as simulation parameters. Some typical interference scenarios in which WiMAX and WCDMA systems are operated on the adjacent frequency bands are simulated and discussed from three different respects: separation distances for these two systems, uplink power control mechanisms of WiMAX system and frequency reuse schemes. It is shown that when uplink power control methods or frequency reuse scheme is implemented, the interference from WiMAX mobile stations to WCDMA system is not quite severe. At last, a few suggestions and mitigation technologies are introduced to better implement these two systems.

Theoretical Analysis of CDMA Reverse Link Capacity with Interference Cancellation

Interference cancellation (IC) is an effective and easy implemented technology in the multi-user system. Previous studies demonstrate the principles of IC and IC process which show a great improvement in the system capacity with IC. However, no research has focused on the IC systems capacity domain by giving an accurate formula. This article carries on the theoretical analysis of CDMA reverse link capacity with IC, presents the expressions as well as its optimal answer for synchronous frame and brings forward the formula as well as its suboptimal solution for asynchronous frame. Numerical result reveals that the commercial EV-DO reverse link capacity with IC will increase by at least 135% compared with the one without IC. Finally, the stability of the IC system is explored.