Hosseinali Jamal

Comparison of L-DACS and FBMC performance in over-water air-ground channels

The demand for air transportation is continuously growing. Likewise, unmanned aircraft systems (UAS) are proliferating at a tremendous pace. Both current and future air-to-ground (AG) communications systems will be deployed in the L-band (960-1164 MHz), and possibly in other bands. Aiming toward modernization, Eurocontrol recently defined two L-Band Digital Aeronautical Communication Systems (L-DACS). Primary goals of LDACS are high data rate transmission and high reliability. There are two L-DACS technology candidates, LDACS1 and LDACS2. The LDACS1 scheme employs a fairly broadband (0.5 MHz) transmission using Orthogonal Frequency-Division Multiplexing (OFDM) together with adaptive coding and modulation. The LDACS2 scheme follows a more traditional approach which is based on GSM (Global System for Mobile Communications), i.e., on second generation cellular mobile radio technology. In this paper, we investigate and compare the physical layer characteristics of L-DACS1 and L-DACS2 and then via simulations we illustrate the performance of these two communication systems in an air-to-ground channel. The air-to-ground channel we employ is one based upon a recent extensive measurement campaign. Results for error probability vs. signal to noise ratio are the focus. We also propose a new filterbank multicarrier (FBMC) based air-ground communication air interface which is consistent with previous requirements of L-DACS. We compare the FBMC performance with that of the LDACS schemes and show that FBMC has higher spectral efficiency via better time-frequency localized prototype subcarrier filters. This enables use of some guard subcarriers as data carrying subcarriers, increasing throughput. The BER results of our FBMC based L-DACS system are equivalent to those of L-DACS1 and better than those of L-DACS2. The simulation results also show the sensitivity of L-DACS2 systems to channel phase shifts and show the necessity of channel equalization for L-DACS2 receivers.

Channel estimation in an over-water air-ground channel using low complexity OFDM-OQAM modulations

Demands for very reliable and robust communications systems are becoming commonplace, and this is true for air-to-ground (AG) systems, which are seeing increased usage, particularly for unmanned aircraft. Available spectrum exists for AG communications systems in the L-band (960-1164 MHz). Two robust L-Band Digital Aeronautical Communication Systems (L-DACS) were recently defined, LDACS1 and LDACS2. The L-DACS1 scheme employs a fairly broadband (0.5 MHz) transmission using Cyclic-Prefix Orthogonal Frequency-Division Multiplexing (CP-OFDM) together with adaptive coding and modulation. In this paper we propose a new AG communication system based on OFDM-OQAM filter bank modulation, using features similar to those of the L-DACS1 physical layer, and show how better subcarrier filtering can improve spectrum efficiency in AG channels. Channel estimation (CE) in OFDM-OQAM systems must employ a pilot method completely different from classical pilot-based CP-OFDM systems, since in OFDM-OQAM the pilots should remove pilot subcarrier interference from neighboring subcarriers. We employ a low complexity pilot-based CE on the OFDM-OQAM signal, and show BER results for L-DACS1 and for comparable OFDM-OQAM based systems in an example AG channel. The AG channel we employ is one based upon a recent extensive measurement campaign. We also estimate channel throughput and mean square error (MSE) for these two systems, and show that for similar BER performance, both channel estimation and throughput of the new system are better than that for L-DACS1.

Performance of L-band aeronautical communication system candidates in the presence of multiple DME interferers

Aeronautical vehicle use, and consequently, air-to-ground communication systems, are growing rapidly. A growing portion of these vehicles are unmanned aerial vehicles (UAVs) or unmanned aerial systems (UAS) operating in civil aviation systems. As a consequence of this growth, air traffic volume for these vehicles is increasing dramatically, and it is estimated that traffic density will at least double by 2025. This traffic growth has led civil aviation authorities to explore development of future communication infrastructures (FCI). The L-band digital aeronautical communication system one (L-DACS1) is one of the air-ground (AG) communication systems proposed by Eurocontrol. L-DACS1 is a multicarrier communication system whose channels will be deployed in between Distance Measurement Equipment (DME) channels in frequency. DME is a transponder-based radio navigation technology, and its channels are distributed in 1 MHz frequency increments in the L-band spectrum from 960 to 1164 MHz. In this paper we investigate the effect of DME as the main interference signal to AG FCI systems. Recently we proposed a new multicarrier L-band communication system based on filterbank multicarrier (FBMC), which has some significant advantages over L-DACS1. In this paper we briefly describe these systems and compare the performance of L-DACS1 and FBMC communication systems in the coverage volume of one cell of an L-band communication cellular network working in the area of multiple DME stations. We will show the advantage and robustness of the L-band FBMC system in suppressing the DME interference from several DME ground stations across a range of geometries. In our simulations we use a channel model proposed for hilly/suburban environments based on the channel measurement results obtained by NASA Glenn Research Center. We compare bit error ratio (BER) results, power spectral densities for L-DACS1 and FBMC communication systems, and show the advantages of FBMC as a promising candidate for FCI systems.

Enhanced airport surface multi-carrier communication systems: Filterbank advantages over AeroMACS OFDM

Civil aviation is continuing to grow, and along with growth in numbers of flights and passengers comes growth in communications. In particular airport surface environments are one of the areas in which rapid development of communication systems is taking place. Several years ago the Federal Aviation Administration, EUROCONTROL, and the International Civil Aviation Organization proposed a communication system based on WiMAX technology for airport surface areas: AeroMACS. The AeroMACS communication system is designed for civil aircraft but could also be applied to military airports as well. In this paper we investigate a new communication system for the unique airport surface environment. Our system has physical layer specifications similar to the orthogonal frequency division multiplexing (OFDM) approach used in AeroMACS, but is instead based on the filterbank multicarrier (FBMC) technique. Via computer simulations, using channel models based on measured data collected by NASA Glenn Research Center, we illustrate the FBMC advantages over AeroMACS. Our results show that using zero-forcing or least-square (LS) channel estimation techniques, FBMC and AeroMACS have similar performance, but FBMC affords a significant gain in throughput. Although FBMC has slightly worse bit error ratio (BER) performance than AeroMACS at high signal-to-noise ratios (SNRs) the throughput advantage of the proposed FBMC design is approximately 23 percent.

Spatial and frequency correlations in two-ray air-ground SIMO channels

The correlation between signals received on multiple antennas is a function of the channel(s) between them, and analysis of this is useful for spatial diversity and spatial multiplexing. In this paper we compute the correlations in both the spatial and frequency domains for a classical two-ray channel in a SIMO setting for an air-ground setting. We analyze this for the “pure” (deterministic) two-ray case, and also include results for the case where the two-ray channel incurs Ricean fading. After describing the setting and basic analysis, we show corroborating NASA measurement results for an air-ground over-sea channel. We show that both the spatial and frequency domain correlations are numerically computable, oscillatory functions, dependent upon link geometric parameters (antenna heights and link distance), surface electrical parameters, and frequency. With knowledge of these parameters, one can in principle select antenna separation and/or frequency separation to achieve diversity in settings where this classical channel model applies. This can be beneficial when narrowbeam (tracking) antennas that suppress the surface reflection are impractical to deploy.

A geometrical-statistical model for the air-ground channel

We present a geometrical-statistical architecture to model the air-ground channel. In this paper we focus on the modeling elements influencing line-of-sight path: ground multi-path propagation, antenna effects, and ground shadowing. We validate the channel model against channel sounding data from flight experiments collected in 2013.

Spectrally shaped filter bank multicarrier systems for L-band aeronautical communication systems

Aeronautical communication systems will play an increasingly important role in the future. Due to increasing flight traffic, which is estimated to double by 2025, and the inadequacy of current aeronautical communication systems to support such an increase, the demand for new and state of the art communication systems is increasing. In this paper we investigate a new spectrally shaped Filter Bank Multicarrier (SS-FBMC) based communication system for air to ground communication. We study a 0.5 MHz spectrally shaped communication system as an inlay system between the 1 MHz separated distance measurement equipment (DME) channels in the L-band. The idea of using the gap in the spectrum that exists between DME channels was first proposed by EUROCONTROL in their L-DACS1 communication system. In the L-DACS1 communication system, which is based on CP-OFDM, the transmitting power is equally distributed among all subcarriers. In this paper we deviate from this convention by using FBMC and assigning different power levels to the subcarriers to mitigate DME interference. We propose a method to find the required guard subcarriers and optimize the amount of allocated power for each remaining subcarrier in order to obtain the best bit error ratio (BER) performance, without any error floor, for different QAM modulation orders and communication links. In so doing we increase the communication systems efficiency and performance. In prior work we have shown that our original FBMC system has higher spectral efficiency and better resilience to DME interference than L-DACS1, but in some cases still incurs a BER floor (as does L-DACS1). Via our spectral shaping approach we remove these BER floors.