Advanced Satellite Communications Research
The impact on wireless communication system performance was investigated for five channel conditions, which included (1) additive white Gaussian noise, (2) flat Raleigh fading, (3) frequency selective Raleigh fading, (4) flat Rician fading, and (5) frequency selective Rician fading.
New algorithm strategies and diverse communication techniques are constantly emerging in the telecommunications realm that consumers, commercial, government, and military demand in order to push the boundaries of data throughput to receive information as quickly as possible. Currently, the Ku/Ka satellite band (20–30 GHz) becomes congested during peak service. There has been a strong demand for a wider bandwidth and higher data rate in both cellular and satellite communication service. As the carrier frequency increases, a wider bandwidth can be made available, and a higher data rate can be obtained with beamforming or precoding. Particularly, the V band (50–75 GHz) and W band (75–110 GHz) offer unprecedented broadband capabilities and extremely large contiguous allocations of bandwidth. This is the reason NASA and AFRL have been investigating these bands for civilian and military use.
At W/V-band, the wavelength is on the order of 3 to 4 millimeters. Thus, receivers can be implemented via very small devices. Further, a W/V-band system can have a very narrow beam angle-spread, which can significantly reduce the interference among beams and recover propagation loss.
When a new wireless terrestrial or satellite communication system is planned, the channel path attenuation data is typically collected first by transmitting a carrier frequency signal without modulation under a line-of-sight (LOS) and an Additive White Gaussian Noise (AWGN) environment. Since the transmit power, PT, and the distance, dTR, between a transmitter (TX) and a receiver (RX) are known, the free space path loss, P path = (λ /4 π dTR)2 , can be precalculated for a given wavelength λ = c/fc, i.e., a given carrier frequency fc where c is the speed of the light. Hence, the channel attenuation, Pattn due to the channel medium can be obtained as Pattn = PT – PR – Ppath by measuring the received power PR at the RX for a given transmitted power PT.
These channel attenuation data can be obtained more economically than by sending a modulated signal. Data enables an RF communication system engineer to determine the appropriate transmit power, antenna type, antenna size, modulation type, forward error correction coding type, code rate, and data rate.
The technical objective of this project was to investigate bandwidth efficiency of wireless communication waveforms under Rayleigh and Rician fading environments, in addition to additive white Gaussian noise, for satellite communication links. Initial research, simulations, and analyses are presented in this report, but the entire scope of work was not completed due to limitation of funds and premature termination of the program.
In this work, the same bandwidth efficiency (BWE) conversion methods were used to model the estimated BWE of a W/V-band channel under Rayleigh and Rician fading. Both flat fading and frequency selective fading were considered for both types of fading (i.e., Rayleigh and Rican). Measured data from the W/V-band Terrestrial Link Experiment were used to model the communications channel. Simulations were conducted using adaptive code modulation (ACM) methods included in the Digital Video Broadcasting – Second Generation (DVBS2) communications protocol. Simulations and analysis was accomplished using Matlab tools. The DVB-S2 satellite link protocol has been in existence since 2014 and includes 28 possible combinations of forward error correction (FEC) coding and modulations, depending on the channel conditions.
Models and simulations were developed to compare the performance for an additive white Gaussian noise (AWGN) channel, a Rayleigh fading channel, and a Rician fading channel. Both flat and frequency selective channels were considered for the later two models. Simulations were performed using channel attenuation data measured at 72 GHz from the W/V-band Terrestrial Link Experiment. Analysis was presented using the DVB-S2 protocol. Results suggest that multipath fading significantly deteriorates performance.
Models and simulations were developed that implemented orthogonal frequency division multiplexing (OFDM), similar to that used by 5G wireless commercial networks. Implementation of OFDM improved performance against severe multipath fading environments. However, the bit error rate performance was worse than under a no-fading, AWGN channel.
This work was performed by Hyuck M. Kwon and Richard T. Lahman for the Air Force Research Laboratory, Space Vehicles Directorate. For more information, download the Technical Support Package (free white paper) below. AFRL-007723
This Brief includes a Technical Support Package (TSP).
Advanced Satellite Communications Research
(reference AFRL-007723) is currently available for download from the TSP library.
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