Measured Channel Hardening in an Indoor Multiband Scenario

A study of channel hardening in a large-scale antenna system has been carried out by means of indoor channel measurements over four frequency bands, namely 1.472 GHz, 2.6 GHz, 3.82 GHz and 4.16 GHz. NTNU's Reconfigurable Radio Network Platform has been used to record the channel estimates for 40 single user non-line of sight radio links to a 64 element wide-band antenna array. By examining the rms delay spread and the ratio of the normalized subcarrier to average SISO link power of the radio channel received by a single user after combination, the hardening of this equivalent channel is analyzed for various numbers of nodes. The channel hardening merits show consistent behaviour throughout the frequency bands. By combining 16 antennas the rms delay spread of the equivalent channel is reduced from above 100 ns to below 35 ns with significantly reduced variation in the channel power.Comment: 6 pages, 7 figures, presented at IEEE PIMRC 201

A Hardware-in-the-Loop Evaluation of the Impact of the V2X Channel on the Traffic-Safety Versus Efficiency Trade-offs

Vehicles are increasingly becoming connected and short-range wireless communications promise to introduce a radical change in the drivers' behaviors. Among the main use cases, the intersection management is surely one of those that could mostly impact on both traffic safety and efficiency. In this work, we consider an intersection collision warning application and exploit an hardware-in-the-loop (HIL) platform to verify the impact on the risk of accidents as well as the average time to travel a given distance. Besides including real ITS-G5 compliant message exchanges, the platform also includes a channel emulator with real signals. Results show that the risk of collisions can be drastically reduced, with an overall trade-off between safety and traffic efficiency. At the same time, it is shown that the presence of real channel conditions cannot guarantee the same condition of zero-risk as with ideal channel propagation, remarking the importance of channel conditions and signal processing

Persistent homology approach for human presence detection from 60 GHz OTFS transmissions

Orthogonal Time Frequency Space (OTFS) is a new, promising modulation waveform candidate for the next generation integrated sensing and communication (ISAC) systems, providing the environment-awareness capabilities together with high speed wireless data communications. This paper presents original results of OTFS-based person monitoring measurements in the 60 GHz millimeter-wave frequency band under realistic conditions, without the assumption of an integer ratio between the actual delays and Doppler shifts of the reflected components and the corresponding resolution of the OTFS grid. As the main contribution of the paper, we propose the use of the persistent homology technique as a method for processing of gathered delay-Doppler responses. We highlight the advantages of persistence homology approach over the standard constant false alarm rate target detector for selected scenarios

Effective Channel Hardening in an Indoor Multiband Scenario

We evaluate channel hardening for a large scale antenna system by means of indoor channel measurements over four frequency bands, 1.472 GHz, 2.6 GHz, 3.82 GHz and 4.16 GHz. NTNU’s Reconfgurable Radio Network Platform has been used to record the channel estimates for 40 radio links to a 64 element array with wideband antennas in a rich scattering environment. We examine metrics for channel hardening, namely, the coherence bandwidth, the rms delay spread and the normalized efective subcarrier power, for the efective channel perceived by a single user after precoding and superposition in the downlink. We describe these metrics analytically and demonstrate them with measured data in order to characterize the rate of hardening of the efective channel as the number of antenna elements at the base station increases. The metrics allow for direct insight into the benefts of channel hardening with respect to radio system requirements

Real-Time Emulation of Nonstationary Channels in Safety-Relevant Vehicular Scenarios

This paper proposes and discusses the architecture for a real-time vehicular channel emulator capable of reproducing the input/output behavior of nonstationary time-variant radio propagation channels in safety-relevant vehicular scenarios. The vehicular channel emulator architecture aims at a hardware implementation which requires minimal hardware complexity for emulating channels with the varying delay-Doppler characteristics of safety-relevant vehicular scenarios. The varying delay-Doppler characteristics require real-time updates to the multipath propagation model for each local stationarity region. The vehicular channel emulator is used for benchmarking the packet error performance of commercial off-the-shelf (COTS) vehicular IEEE 802.11p modems and a fully software-defined radio-based IEEE 802.11p modem stack. The packet error ratio (PER) estimated from temporal averaging over a single virtual drive and the packet error probability (PEP) estimated from ensemble averaging over repeated virtual drives are evaluated and compared for the same vehicular scenario. The proposed architecture is realized as a virtual instrument on National Instruments™ LabVIEW. The National Instrument universal software radio peripheral with reconfigurable input-output (USRP-Rio) 2953R is used as the software-defined radio platform for implementation; however, the results and considerations reported are of general purpose and can be applied to other platforms. Finally, we discuss the PER performance of the modem for two categories of vehicular channel models: a vehicular nonstationary channel model derived for urban single lane street crossing scenario of the DRIVEWAY’09 measurement campaign and the stationary ETSI models

Real-Time Vehicular Channel Emulator for Future Conformance Tests of Wireless ITS Modems

In the vehicular communication channels, the mobility of the receiver (RX) and the transmitter (TX) along with the movements of interacting objects in the propagation environment result in significant non-stationary channel fading. The channel impulse response exhibits not just significant delay- and Doppler spreads, but also the delay- and Doppler spreads themselves are changing over the time- and frequency axes. In other words: the channel statistics change as the geometry of RX, TX, and interacting objects evolve over time. To account for this, the local stationary regions in time and frequency are specified and each one is modeled by a distinct local scattering function. We present an architecture for a real-time emulator capable of reproducing the input/output behavior of a non-stationary n-tap wireless vehicular propagation channel. The architecture is implemented as a virtual instrument on LabView and we benchmark the packet error ratio (PER) of a commercial off the shelf (COTS) vehicular IEEE 802.11p modem. The emulator architecture aims at a hardware implementation which features optimised hardware complexity while providing the required flexibility for calculating the non-stationary channel responses by reconfiguring the scattering model for each local stationary region. The National Instrument USRP-Rio 2953R is used as the Software-Defined Radio platform for implementation, however the results and considerations reported are general-purpose and can be applied to other platforms. Finally, we discuss the PER performance of a COTS modem for a vehicular non-stationary channel model derived for highway obstructed line of sight (LOS) scenario in the DRIVEWAY'09 measurement campaign