In this article, we introduce MATLAB-based link and system level simulation environments for UMTS Long-Term Evolution (LTE). The source codes of both simulators are available under an academic non-commercial use license, allowing researchers full access to standard-compliant simulation environments. Owing to the open source availability, the simulators enable reproducible research in wireless communications and comparison of novel algorithms. In this study, we explain how link and system level simulations are connected and show how the link level simulator serves as a reference to design the system level simulator. We compare the accuracy of the PHY modeling at system level by means of simulations performed both with bit-accurate link level simulations and PHY-model-based system level simulations. We highlight some of the currently most interesting research questions for LTE, and explain by some research examples how our simulators can be applied.

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While the field of MIMO transmission has been explored over the past decade mainly theoretically, relatively few results exist on how these transmissions perform over realistic, imperfect channels. The reason for this is that measurement equipment is expensive, difficult to obtain, and often inflexible when a multitude of transmission parameters are of interest. This paper presents a flexible testbed developed to examine MIMO algorithms and channel models described in literature by transmitting data at 2.45 GHz through real, physical channels, supporting simultaneously four transmit and four receive antennas. Operation is performed directly from Matlab allowing for a cornucopia of real-world experiments with minimum effort. Examples measuring bit error rates on space-time block codes are provided in the paper.

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We evaluate the throughput performance of an OFDM WiMAX (IEEE 802.16-2004, Section 8.3) transmission system with adaptive modulation and coding (AMC) by outdoor measurements. The standard compliant AMC utilizes a 3-bit feedback for SISO and Alamouti coded MIMO transmissions. By applying a 6-bit feedback and spatial multiplexing with individual AMC on the two transmit antennas, the data throughput can be increased significantly for large SNR values. Our measurements show that at small SNR values, a single antenna transmission often outperforms an Alamouti transmission. We found that this effect is caused by the asymmetric behavior of the wireless channel and by poor channel knowledge in the two-transmit-antenna case. Our performance evaluation is based on a measurement campaign employing the Vienna MIMO testbed. The measurement scenarios include typical outdoor-to-indoor NLOS, outdoor-to-outdoor NLOS, as well as outdoor-to-indoor LOS connections. We found that in all these scenarios, the measured throughput is far from its achievable maximum; the loss is mainly caused by a too simple convolutional coding.

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