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Photodetectors and Receiver Architectures
Published in Hamid Hemmati, Near-Earth Laser Communications, 2020
Peter Winzer, Klaus Kudielka, Werner Klaus
These effects ask for an additional effort in the receiver development. While a coherent receiver in combination with a homodyne PSK modulation format is known to have the highest receiver sensitivity, it is likely that many advances in terms of intradyne detection, DSP, and space division multiplexing owing to the rapid development of fiber optic transmission systems in recent years will also find practical applications in future space systems. Furthermore, signal routing inside the receiver terminal through optical fibers allows for a flexible and low-weight receiver design, enables optical pre-amplification, and thus ensures close to quantum-limited detection. As such, multimode fiber optics in combination with digital coherent combining seems to be a very promising means to increase receiver sensitivity for Earth-to-Space communications, while keeping down both cost and complexity.
The Calculation of System Temperature for a Microwave Receiver
Published in Jerry D. Gibson, The Communications Handbook, 2018
An Earth station antenna typically exchanges energy with the sky in the vicinity of the satellite at which it is pointed, the ground via its side lobes, and the sun, usually in the antenna side lobe structure but occasionally in the main beam. A satellite antenna exchanges energy, principally with the ground, but also with the sky and occasionally with the moon and sun. Obviously, the satellite orbit and antenna coverage determine the situation. Antenna temperature is much affected by atmospheric losses and especially by rain attenuation. By way of example, a narrow beam antenna pointed at the clear sky might have a temperature of 20 K, but this will increase to more than 180 K with 4.0 dB of rain loss, as is easily calculated from the hot pad formula (61.9). With a receiver excess temperature of 50 K, the system temperature will increase from 70 to 230 K or 5.0 dB. Note that this is a greater loss than that due to the signal attenuation by the rain. This is a frequently overlooked effect of rain attenuation. The implication for system design, at those frequencies where rain loss is anything other than negligible, is significant. The margin achieved using high-performance, low-noise receivers, is something of an illusion. The margin disappears quickly just when one needs it the most. The performance improvement achieved with a larger antenna is better than that achieved with a low-noise receiver because the deterioration of the former because of rain attenuation is only that due to the signal loss, whereas the latter suffers the signal loss and the increase in antenna temperature.
Continuous-Time Circuits
Published in Tertulien Ndjountche, CMOS Analog Integrated Circuits, 2017
In the low-IF receiver of Figure 7.6, the RF signal is first translated to a low IF, before being down-converted to baseband frequency in the digital domain. Conversely, the low-IF transmitter, as depicted in Figure 7.7, uses both digital and analog steps to perform the up-conversion from the baseband frequency to RF. The image rejection is achieved by summing the output signals provided by a pair of quadrature mixers such that image-band signals ideally cancel out while the desired signals add together coherently. The use of harmonic rejection mixers excludes the need for discrete IF filters, thus making low-IF architectures well suited for single-chip integration than superheterodyne structures. In contrast to direct-conversion architectures, low-IF structures use local oscillators operating at frequencies that are lower than that of the incoming RF signal, to reduce the LO re-transmission, thereby attenuating the dc offset level. It should be noted that the static errors associated with the baseband section can generally be canceled by suitable calibration techniques.
A reconfigurable wireless superheterodyne receiver for multi-standard communication systems
Published in International Journal of Electronics, 2023
Qing Wang, Yongle Wu, Yue Qi, Weimin Wang
At present, there are many mainstream wireless receiver architectures for communication equipment. Such as superheterodyne receiver architecture (Dan et al., 2019), zero intermediate frequency (zero-IF) receiver architecture (T. Wang et al., 2019), and low intermediate frequency (low-IF) receiver architecture (Zhang et al., 2018). Among them, the superheterodyne receiver architecture is widely used in wireless communication systems. The superheterodyne receiver has many advantages, such as excellent frequency selection characteristics, good interference suppression, and a large dynamic range. The zero-IF receiver is simple and easily integrated, but noise and linearity are not as good as the superheterodyne receiver. The cost of the low-IF receiver is high because it needs a high-performance Analog-to-Digital Converter. According to our design requirements, we finally choose the superheterodyne structure to form the proposed receiver.