Chunhui Zhou

Antenna Array Design for LOS-MIMO and Gigabit Ethernet Switch-Based Gbps Radio System

The high spectrum efficiency of multiple-input multiple-output (MIMO) transmission traditionally depends on the high multiplexing gain in rich scattering environments, which will not always hold in the line-of-sight (LOS) environments, especially at higher microwave frequency band. In this paper, a novel antenna array design rule is proposed to guarantee full multiplexing gain for LOS-MIMO systems with one- or two-dimensional antenna arrays in LOS scenarios, and the strict perpendicular constraint is released in the two-dimensional case. The minimum antenna array area and the performance sensitivity to the area error are also obtained to guide the practical system design. Then, a demo MIMO-OFDM system with the designed square antenna array at 15 GHz carrier is implemented on a novel Gigabit Ethernet (GE) switch-based software defined radio (SDR) platform, which combines the hardware accelerating units (HAUs) with the general-purpose processors (GPPs). The field evaluation results show that the system throughput and spectrum efficiency are greater than 1 Gbps and 15 bps/Hz, respectively. To the best of our knowledge, it is the first time to demonstrate the Gbps LOS-MIMO-OFDM system at such microwave bands in the world, which can be a successful design example for the next generation wireless backhaul or fixed wireless access.

Accelerating the 3GPP LTE System Level Simulation with NVidia CUDA

With the rapid progress of standardization of 3GPP’s LTE (Long Term Evolution) and LTE-Advanced, many research attentions have been focused on the link level evaluations of the 3GPP LTE systems, so as to demonstrate the rationality of novel transmission techniques. Different from theoretical studies, incorporating novel transmission techniques in to the LTE communication systems may affect many parts of the systems, such as signaling process, reference signal design, feedback link design, and compatibility, etc. Link level studies might be too simple to evaluate the benefits of these novel techniques to the entire system. On the other hand, system level simulation concentrates on the performance of the entire network with tens of cells and hundreds to thousands of users. It is possible to illustrate the actual performance of a LTE system by simulations designed from a system standpoint. Since the simulated system is quite large, one can understand the speed of simulation is very important for system level simulation platform. In this paper, we propose a design of Matlab-based 3GPP LTE system level simulator, which makes use of parallel computing techniques supported by NVidia GeForce GTX 260 graphic card. Our simulation experience shows that the simulation time reduces by nearly 1/3 after employing parallel computing techniques.

A cooperative transmission strategy for uplink cellular systems

This paper presents a cooperative transmission strategy for uplink cellular systems, especially for the case that the base station (BS) is mounted with many antennas, but the mobile terminal (MT) and relays each has much fewer antennas. Single userpsilas maximal rate of the proposed strategy is derived. We consider power allocation and time slot scheduling to increase the data rate. The simulation results show that this strategy achieves a great increase of the userpsilas data rate than that in non-relay systems. Moreover, our cooperative transmission strategy can increase the spectral efficiency of half-duplex relay networks by allowing the hops for different users to reuse the same time slot. The simulation results show that our approach achieves a higher system throughput (multiple users) than the existing strategy from literatures.

Effect of nonlinearities in wireless communication with digital receiver

This paper discusses the effect of nonlinearities introduced by Radio Frequency (RF) amplifier in practical digital receivers. Taking downlink as an example, after considering several main limitations in engineering implementation and simplifying the model of the receiver, the effects of receiver nonlinearities on the performance both in A WGN and Rayleigh fading channel are obtained. In A WGN channel, the SNR at the input of Am converter has a limit, even though the transmitting SNR is very large with given input power of A/D converter. Combining with the characteristic of quantization, we find trade-off relationship between the SNR at the input and the output of A/D converter. Then, a method is proposed to maximize the SNR at the output of Am converter, and an upper bound of the SNR is also obtained. Considering nonlinearities and using the optimizing method in this paper, the SNR at the output of AID converter increase 4 dB at most, as the digital bit increases 1 bit. In Rayleigh fading channel, a threshold of transmitting rate is derived, which is affected by nonlinearities of the receiver.

A cross-band cooperation architecture for spectrum efficiency improvement

Limited spectrum resource restricts the concerned performance such as spectrum efficiency, data rate and system capacity in wireless communications. To address above issues and explore potential higher frequency spectrum together, we propose a cross-band cooperation architecture in this paper. Then, we apply this architecture to some typical user cooperation scenarios: intra-cell and inter-cell cooperation, aiming at peak data rate, multiuser capacity and interference mitigation respectively. Moreover, we set up a demo system which implements this architecture in the case that higher frequency band as a backhaul to assist lower frequency band. Finally, we verify this architecture through both field trials and system level simulation. Measured data and simulation results indicate that cross-band cooperation architecture can improve peak data rate and cell throughput significantly.