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Receiver Front Ends with Robustness to Process Variations
Published in Reza Mahmoudi, Krzysztof Iniewski, Low Power Emerging Wireless Technologies, 2017
Pooyan Sakian Dezfuli, Reza Mahmoudi, Arthur van Roermund
The NPD can also be affected by IQ mismatch (only in receivers with I and Q paths) and phase noise. IQ phase or amplitude imbalance results in some cross talk between I and Q channels. This cross talk appears as a distortion and affects the NPD. Block-level budgeting of the noise, gain, and nonlinearity does not have a significant (if any) impact on the IQ mismatch. Therefore, if the amount of the IQ cross talk is known, its impact can be treated as a constant distortion added to the NPD and in this way it can be incorporated in the analysis. Extensive research has been done on IQ mismatch cancelation methods over the past years. Digital IQ imbalance compensation methods are widely used to suppress the impact of IQ mismatch. Details of these methods are beyond the scope of this chapter.
Distortion and Modulation Effects in RF Power Amplifiers
Published in Abdullah Eroglu, Linear and Switch-Mode RF Power Amplifiers, 2017
Quadrature modulation is a convenient and flexible way to produce nearly any type of waveform and has been in use for decades. As such, quadrature modulators are ubiquitous in communication systems as shown in Figure 8.1, and the performance of this device is important to the overall system [1]. Ideal quadrature modulators generate single continuous wave (CW) tone that can be used in radio frequency (RF) systems. The ideal system assumes no gain or phase changes in either the phase (I) or quadrature (Q) paths as shown in Figure 8.1. However, with real components, there will be losses, phase changes, and DC offsets that need to be taken into account to have a balanced system. IQ imbalance reduces the dynamic range and as a result degrades the performance of the system [2].
Wavelet Transform for OFDM-IM under Hardware Impairments Performance Enhancement
Published in Mangesh M. Ghonge, Ramchandra Sharad Mangrulkar, Pradip M. Jawandhiya, Nitin Goje, Future Trends in 5G and 6G, 2021
Asma Bouhlel, Anis Sakly, Salama Said Ikki
The hardware effects are usually modeled as ideal. Thereby, for a wireless transmission over high frequencies and with dynamic ranges, hardware imperfections extremely affect the system performance. Accordingly, it is imperative to take into account the influence of these impairments in performance analysis. However, hardware impairments are a result of many RF components imperfections such as:Phase noise: In communication systems, the phase noise is a result of local oscillator's imperfections. Theoretically, the local oscillator frequency is fos. But in practice, this frequency is perturbed laterally by fluctuations, thus forming the phase noise. The phase noise is generally expressed in dB/Hz at the frequency fel. This corresponds to the attenuation in decibels per Hz of the oscillator spectrum, distant from the carrier frequency fos with fel [28]. The phase noise negatively affects OFDM subcarriers orthogonality and leads to system performance degradation, [29] and [30].Nonlinearities: The evaluation of the peak factor is important in the dimensioning of nonlinear components in a communication system. Indeed, before conveying the signal over the channel, a power amplifier is necessary. However, in practice, radio amplifiers have a nonlinear characteristic. To eliminate signal distortion in the amplifier, it is necessary for the signal to remain in the linear operating range and hence its maximum power is less than that corresponding to the compression point. But since OFDM modulation becomes advantageous with high number of subcarriers, a significant level of peak average power ratio is obtained and leads to OFDM performance deterioration, [31] and [32].IQI: The IQ imbalance is defined as the quadrature loss between I and Q channels of a transmitter or receiver. This loss due to the inevitable RF components imperfections is the principal cause of performance degradation [33,34].
Analysis of energy harvesting in SWIPT using bio-inspired algorithms
Published in International Journal of Electronics, 2023
Simultaneous wireless information and power transfer (SWIPT) is capable of simultaneously transferring information and energy. SWIPT have gained significant attention among researchers in wireless communication systems were first introduced in (Varshney,2008). The practical implementation of SWIPT involves two major architectures: power-splitting (PS) and time-switching (TS). Most of the investigations in SWIPT are based on the trade-off between energy harvesting and achievable information rates (Kang et al., 2017; Li et al., 2019; H.-S. Nguyen et al., 2018) that considers ideal information transmission models with no hardware impairments. Above mentioned research works have not considered the practical SWIPT system that contains low-quality hardware transceiver components. The actual SWIPT system is exposed to numerous hardware impairments such as in-phase and quadrature-phase (IQ) imbalances, high-power amplifier non-linearity and oscillator phase noise, which will significantly degrade the performance of various wireless systems as mentioned in (Perera et al., 2017). The low-cost hardware solutions with compact analog IQ modulators and demodulators mentioned in (Kirthiga & Jayakumar, 2014; Kumar & Jayakumar, 2010; R. Zhang et al., 2015; Zhou et al., 2013) are commonly preferred over the direct digitalization of RF in multi gigahertz bandwidth (above 60 GHz) such as IEEE 802.11ad. But to perform IQ modulation and IQ demodulation, I and Q takes different paths in both transmitter and receiver sections. Theoretically, the I and Q branches assume perfect orthogonal in transmitter and receiver as mentioned in (Schenk,2008). But here we have considered the practical scenario as indicated in (Zekkari et al., 2019), where the IQ imbalance becomes significant on the receiver side rather than on the transmitter side. During the decoding operation, the IQ imbalance will induce offsets in the signal constellation, and this affects symbol detection rate. Also, the results in (Tsou, 1998) show that 0.2 dB of amplitude imbalance and phase imbalance will induce above 25 dB of carrier suppression leading to overall performance degradation of 1 dB at the receiver side.