Hao Guan

Measurement-Based Characterizations of Indoor Massive MIMO Channels at 2 GHz, 4 GHz, and 6 GHz Frequency Bands

Massive MIMO has been chosen as one of the candidate technologies of the fifth-generation mobile communication system (5G), and channel modeling of massive MIMO is of great importance. The most direct and effective approach to investigate the propagation characteristics of massive MIMO channels is channel measurements. However, there are only few measurements of massive MIMO channels, and there still lacks deep investigations of massive MIMO channel characteristics. In this paper, we present a measurement campaign of indoor massive MIMO channels, by using a linear large-scale array with 64 elements. The measurements are conducted at 2 GHz, 4 GHz, and 6 GHz, respectively, with a bandwidth of 200 MHz. Both LOS and NLOS propagation scenarios are considered in the measurements. The basic channel parameters are extracted, including path loss, delay spread, and coherence bandwidth. The non-stationarity of radio channels, which is reflected by the variations of delay spread and coherence bandwidth over different array locations, is discussed. The impact of carrier frequency on the above channel parameters is further discussed. The results would be useful for the design of massive MIMO system in the indoor environments.

Study on Mobile Data Offloading in High Rise Building Scenario

In recent years, data traffic over cellular networks has experienced an exponential rise, primarily due to the explosion of smartphones, tablets and laptops. This increase in data traffic on cellular networks has caused an immediate need for offloading traffic for optimum performance of both voice and data services. The paper focuses on the coverage improvements of high floor users by offloading these users to picos. Four antenna patters with different vertical half power beam width are applied in both outband and inband pico scenarios. The simulation results indicate that both outband and inband picos can offload the same amount of high floor users but the outband picos can provide a much better coverage than macros while inband pico cannot significantly improve the coverage performance.

A modified poisson distribution for smartphone background traffic in cellular networks

Summary For the emerging applications such as Google Talk, Facebook, Skype and QQ, to mention a few, which run on smartphones, background traffic has become one of the significant issues in system design and optimization. Because of the complicated user behavior and interaction, the assumptions underlying the Poisson process model cannot be met; the Poisson distribution cannot approximate the distribution of background traffic arrivals accurately. In this paper, we propose a model, which can better fit the background traffic arrivals of smartphones than the Poisson distribution. The proposed model is a linear transformation of the Poisson distribution and is specified by three parameters, (a,b,λ), which can be estimated from the measured samples mean, variance, and third central moment. Simulation results have corroborated the fitness of the proposed model in both single and mixed applications scenarios. In addition, we have also observed that the normalized parameters, (a,b0,λ0), of each application is independent of the user number and completely characterized by the type of application. Hence, with the given trace cumulative distribution functions of all applications, the proposed modified Poisson distribution can be used as a tool for modeling and analyzing background traffic arrivals with arbitrary user numbers and mixed applications. Copyright

Study on the impact of pico site antenna pattern and tilt on TD-LTE networks in 3D scenario

With the rapid increase of traffic in cellular networks, low power nodes overlaid within a macro network is considered to be a cost-effective way to significantly enhance the capacity of cellular networks. In this paper, the impact of the pico cell antenna pattern and tilt on the performance of TD-LTE networks is analyzed in 3D Scenario. The optimal values of antenna tilts and the choice of antenna pattern are given under certain restriction. Besides, the simulation results show that the pico antenna pattern and tilt can significantly affect the key performance indices of the network, namely, the SINR, the capacity, the pico connected user ratio and others. In addition, the simulation results show that picos equipped with uptilt antennas can provide good coverage for high floor users.

Deterministic Modeling and Stochastic Analysis for Channel in Composite High-Speed Railway Scenario

The rapidly time-varying channel in high-speed railway poses tough design challenges, which necessitates the research of accurate channel models. Existing researches focus on the isolated high-speed railway scenarios, and mainly deal with path loss, shadowing fading, Ricean K-factor and delay spread. However, few studies have been done in Doppler domain. In this paper, a deterministic channel model that employs ray- tracing algorithm is presented. The proposed deterministic modeling approach is applied in composite high-speed railway scenario rather than isolated one. The scenario is flexibly reconstructed through SketchUp. The simulation results are validated by the data measured in the same scenario. The channel characteristics in Doppler domain and the effect of Doppler shift are statistically analyzed based on the deterministic channel model. The transition regions in the composite scenario are emphatically investigated, and the results are compared with those of prior studies.

Channel measurements and modeling for 5G communication systems at 3.5 GHz band

The fifth generation (5G) communication has recently attracted much interest. In this paper we present radio channel measurements on campus at 3.5 GHz, which is the candidate frequency band for the 5G communications. The measurement setup is based on software radio units with a bandwidth of 30 MHz, and the measurements were conducted on campus of Beijing Jiaotong University, China. We discuss the power delay profile, path loss, shadowing, and delay spread. It is found that the path loss exponent is up to 6.16 due to high carrier frequency. A lognormal distribution is used to model the shadowing effect, and the standard deviation is 4.21 dB. Furthermore, the root-mean-square delay spread is around 45 ns in the measured campus environments. The results can be applied to the 5G communication system design.

Quasi-stationarity regions analysis for channel in composite high-speed railway scenario

The channel nonstationarity caused by the train mobility is measured for the composite high-speed railway (HSR) scenario. The time-varying quasi-stationarity region analysis is based on spectral divergence (SD) metric carried on different frequencies. An obvious transition region is found in composite HSR. Moreover, based on the comparison of different frequencies, we found the apparent discrepancy of the quasi-stationarity region size estimated by the same threshold.

Network Upgrade with LTE-Advanced Small Cells

Complementing macro-only cellular networks with low-powered base stations is a promising deployment solution to cope with exploding data traffic in the coming years. In Long Term Evolution (LTE)-Advanced, interference mitigation technologies, like the linear interference rejection combining (IRC) receiver and Enhanced Inter-Cell Interference Coordination (eICIC), are introduced to address the co-channel interference between macro and small cells in downlink. These advanced techniques will boost the performance of small cells, and impact the network deployment upgrade. In this paper, LTE-A small cell deployments are evaluated through a network upgrade case study. A network upgrade with small cell deployments is simulated in a realistic metropolitan scenario to satisfy the traffic growth forecast over a period of ten years. A dynamic system level simulator is used to model the network behavior of IRC receiver and eICIC. The deployment time, scale and cost of the small cells improved by interference mitigation solutions are presented. The simulation results show that small cell deployments are the fundamental way to increase the system capacity as well as that eICIC is a promised solution to improve the system capacity. An increase of 56% in system capacity, which corresponds to a ~19 month network upgrade delay and 34% cost savings , can be achieved by eICIC in the case where small cells deployments become very dense.