CCDF -Optimized Wideband Predistortion for Frequency-Hopped Signals Using Multitone Training

A CMOS class-E outphasing RF power amplifier is presented with a new passive combining circuit that provides high efficiency and high output power. An efficiency enhancement circuit and a power enhancement circuit are proposed as part of the combiner that improve efficiency at power back-off and increase output power without violating reliability limits, respectively. The proposed power amplifier is designed in a 45nm CMOS technology. The power amplifier (PA) delivers 29.5 dBm peak output power at 2.4 GHz with 46.76% drain efficiency at peak output power, 32.96% drain efficiency at 3 dB power back-off, and 21.16% drain efficiency at 6 dB power back-off. The proposed power amplifier shows excellent linearity with digital pre-distortion. Better than -50 dBc adjacent channel power ratio (ACPR) is obtained with 64-QAM long-term evolution (LTE) signal with 10 MHz and 20 MHz bandwidth. For two-carrier 20 MHz LTE signal, -44 dBc ACPR is achieved. 21% average drain efficiency is obtained with LTE signal with a 6 dB peak-to-average power ratio. The PA is also tested with 802.11g WLAN signal and it satisfies the spectral mask requirement with high margin. 1.4% (-37.1 dB) error vector magnitude (EVM) is obtained with LTE signal (64-QAM) with a 10 MHz bandwidth.

Long-term evolution (LTE) signals are potential signals-of-opportunity for position and navigation, especially in challenging urban and indoor environments. A major challenge is that the LTE signal time-of-arrival (TOA) estimations are susceptible to the multipath propagation effects. In this paper, the multipath estimating delay lock loop (MEDLL), which is originally designed for global positioning system receivers, is applied to LTE signal TOA estimation in multipath environments. We derive the analytical expression of the correlation function for LTE signals and present the procedure for estimating parameters of the detected multipath components. Two initialization methods without and with super-resolution algorithm (SRA) are developed for the MEDLL. Our analyses show that the MEDLL with SRA-based initialization can achieve better multipath resolution, while the one without SRA has less complexity. Extensive simulations involving static multipath scenarios are conducted to examine the statistical TOA estimation performance of the proposed MEDLL with LTE cell-specific reference signal. The simulation results and computational complexity analysis indicate that the proposed MEDLL outperforms the conventional delay lock loop and SRA in term of multipath mitigation performance and computational complexity. Experimental results using real collected LTE signals in urban environments are also provided to demonstrate the effectiveness of the proposed technique for realistic scenarios.

The continuous growth in mobile data traffic and limited license wireless spectrum have led to dramatically increase the demand of the radio spectrum. It is widespread the concern about the coexistence of long term evolution (LTE) and Wi-Fi in the unlicensed band. There are several techniques have been proposed to enable the coexistence of LTE and Wi-Fi in the unlicensed band, but these works are targeted on the impact of the LTE to the Wi-Fi network performance. An experiment is carried out in this work to evaluate the impact of Wi-Fi signal on the video streaming in the LTE network. The experimental test comprised of the national instrument (NI) universal software radio peripheral (USRP) 2953R that is controlled by the LabVIEW Communication LTE application framework. Extensiveexperiments are carried out under two scenarios, i.e. (1) Coexistence of LTE and Wi-Fi signal, (2) LTE signal only. Performance evaluations are carried out with different Modulation and coding schemes (MCS) values and different mode of operations, i.e. frequency division duplex (FDD) and time division duplex (TDD) mode. The results illustrated that the interference from Wi-Fi signal caused the performance degradation of the LTE network in throughput and the power received by user equipment (UE).

This letter presents a dual-mode multi-band second harmonic controlled SOI LDMOS power amplifier (PA). A mode selection switch is designed to have better power handing capability than a conventional switch, which improves performance in low power mode (LPM). To improve the PA's linearity in high power mode (HPM), second harmonic is controlled with the aid of a path for LPM. The PA, implemented with a 0.13- $\mu$ m SOI LDMOS process, operates in triple bands (band 5, 8, and 20) with dual power modes. It is measured using a 16 QAM long-term evolution (LTE) signal with a 10 MHz bandwidth. At 850 MHz, the results show 27.7 dBm average output power (Pout), 31.4 dB gain, and 31.4% power-added efficiency (PAE) with 4% error-vector magnitude (EVM) in HPM and 10.4 dB gain, 15.5 dBm Pout, and 22.5% PAE with 4% EVM in LPM with the LTE signal.

Widespread availability of long-term evolution (LTE) signals makes them potential for use in passive bistatic radar (PBR) applications. However, their utility in such applications is yet to be fully explored. This research focuses on the key LTE signal attributes, such as modulation schemes and bandwidth, and their effect on PBR application. Space-time adaptive processing (STAP) concepts, both full-dimension (FD-STAP) and reduced-dimension (RD-STAP), were employed to evaluate and compare the effects of varying these signal attributes, in terms of signal to interference-plus-noise ratio (SINR) metrics. Simulation results indicate that decreasing LTE signal's bandwidth and increasing its bitrate will worsen both SINR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> and SINR <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L,o</sub> . This trend remained valid irrespective of the type of STAP algorithm used.

In this paper, a novel multi-band reduced sampling rate technique is proposed for power amplifier (PA) linearization system. It is used to enhance performance and reduce hardware costs in spectrum aggregation discontinuous broadband systems and compensate in-phase/quadrature (I/Q) imbalance in the multi-band case. During the feedback loop process of sampling rate, a band-limited filter is introduced, and the frequency band extrapolation is carried out so that the spectrum outside the limited band is compensated effectively. Theoretical analysis is performed to compare the proposed method and the conventional methods. To evaluate the performance of the proposed method, a broadband PA is excited by a tri-band signal composed of a 20 MHz long-term evolution (LTE) signal at 1.31 GHz, a 20 MHz 4-carrier wideband code division multiple access (WCDMA) signal at 2.49 GHz, and a 20 MHz 2-carrier WiMAX signal at 2.58 GHz respectively. The experimental results demonstrate that the normalized mean square error (NMSE) can get high accuracy less than −41 dB, with peak-to-average power ratio (PAPR) equaling 9 dB accompanied by a large reduction in sampling rate. Error vector magnitude (EVM) is 1% better than band-limited memory polynomial (MP) model and 2.3% better than conventional MP model.

We investigate the transmission performance of an optical signal composed by a custom orthogonal frequency-division multiplexing (OFDM) gigabit ethernet (GbE) signal, a long-term evolution (LTE) signal, and an OFDM ultrawideband (OFDM-UWB) signal, when chirp is introduced in the intensity modulation based on a dual electrode Mach-Zehnder modulator. The results show that, when the optical signal is generated with controlled negative chirp, it is possible to reduce the optical signal-to-noise (OSNR) penalty after transmission through a long reach fiber-to-the-home network by approximately 5, 1.5, and 0.5 dB, for the OFDM-UWB, LTE, and OFDM-GbE signals, respectively. Furthermore, the results show negative OSNR penalty for OFDM-UWB and LTE signals after transmission, for specific distances.

Low sampling rate technique based frequency-domain random demodulation for broadband digital predistortion

Satellite/Terrestrial Integrated mobile Communications System (STICS) employs the frequency sharing between the satellite and terrestrial components for efficient spectrum utilization. It is required to estimate the interference level between the satellite and terrestrial link to realize the frequency sharing because co-channel interference occurs between the satellite and terrestrial link outside the satellite beam. Measurement campaign of the cellular phone transmit power in 3G network operated in Japan has been carried out to obtain the reference data of estimating the interference level. On the other hand, recently, Long Term Evolution (LTE) is rapidly penetrated into terrestrial mobile network in Japan. Therefore, in future application of LTE to terrestrial component in STICS, we have conducted the measurement experiment of transmit power for LTE terminal to estimate the interference level in STICS satellite receiver. Measurement setup to measure LTE signal is studied and a realtime spectrum analyzer is applied to measure the time-and-frequency-based LTE signal. Measurement has been carried out at six to eight measurement sites per mobile communication carrier with population density of from 60 to 27,000 /km2 in Kansai district in Japan for the operational band of 1920–1980 MHz. The initial analysis of the measured data indicates that the correlation between transmit power and population density is not observed in LTE signal. This trend is different from the fact that the correlation between the measured EIRP of 3G voice transmission in LTE terminal and the population density is observed. From these observations we confirmed the trend of LTE terminal transmit power.

The signal conditioning treatment to achieve good relation of power with radio-frequency (RF) conversion in conventional transceiver systems require precise baseband models. A developed framework is built to provide a demonstration of the modeling figures of merit with orthogonal frequency division multiplexing (OFDM) support under signal conditioning and transmission restrictions to waveforms with high peak to average power ratio (PAPR) in practical applications. Therefore, peak and average power levels have to be limited to correct high PAPR for a better suited correction power from the amplifier that can lead to compression or clipping in the signal of interest. This work presents an alternative joint crest factor reduction (CFR) algorithm to correct the performance of PAPR. A real-time field-programmable gate array (FPGA) testbed is developed to characterize and measure the behavior of an amplifier using a single-carrier 64–QAM OFDM based on long-term evolution (LTE) downlink at GHz as stimulus, across wide modulation bandwidths. The results demonstrate that the CFR accuracy capabilities for the signal conditioning show a reliable clipping reduction to give a smooth version of the clipping signal and provide a factor of correction for the unwanted out-of-band emission validated according to the adjacent channel power ratio (ACPR), PAPR, peak power, complementary cumulative distribution function (CCDF), and error vector magnitude (EVM) figures of merit.

C-RAN is the next-generation clean wireless access network architecture, which is based on centralized processing, the Collaborative Radio and Real-time Cloud Infrastructure. In C-RAN architecture, different access technology (eg.GSM / TD-SCDMA / WCDMA / LTE) can be support on the same hardware platform in baseband pool system; C-RAN can be applied to reduce the consumption of operators. LTE (Long Term Evolution) and LTE-A, which are based on OFDM and MIMO technologies, are regarded as the main wireless access technology in the evolution from 3G to 4G. LTE introduces variety of novel technologies to improve the system performance, especially in C-RAN architecture, such as Multi antennas MIMO, Carrier Aggregation, CoMP. However, C -RAN architecture also brings about lager data transmission in the optical fiber. In this paper a low-latency baseband signal compression algorithm used in ALU is introduced to reduce the data rate. Based on the Characteristics of LTE signal data, the algorithm removal redundancies in the spectral domain firstly, and then the block scaling, which is combined with non-linear (nonuniform) quantizer, is designed to minimize quantization error. This algorithm can effectively reduce the amount of data transferred between BBU and RUU in LTE system, to facilitate the deployment of LTE in the CRan architecture. Simulation analysis is given out in the paper; meanwhile TD-LTE system demo verification is also implemented. The results indicate that the scheme introduced can get good performance under a certain compression rate in the real system. Further research is also in progress.

This paper presents a concept and an implementation of a linearized analog photonic link for wideband wireless communication that yields improved adjacent channel leakage ratio (ACLR). The link consists of two parallel Mach-Zehnder modulators (MZMs) driven by two lasers, and a modified uni-traveling-carrier photodetector capable of outputting high RF power when assisted by an erbium-doped fiber amplifier. The third-order intermodulation (IMD3) attributed to the MZM transfer function is suppressed by asymmetric RF and optical feeding that impose a π-phase difference between the signals in the two MZM channels. Long-Term Evolution (LTE) signals of various bandwidths are used to validate this broadband linearization approach experimentally. It is demonstrated that with this approach the first ACLR (ACLR1) can be improved by 19.2 dB for a 10-MHz LTE signal and 18.1 dB for a 20-MHz LTE signal at the cost of approximately 2-dB link gain penalty.

This paper presents a localization framework that consists of a combined code and carrier phase observation model and can be used to estimate the unknown position and clock states of a Long Term Evolution (LTE) transmitter for navigation. The LTE signals are tracked within a Global Navigation Satellite System (GNSS) type receiver architecture, using Multi Sensor Navigation Analysis Tool (MuSNAT) software receiver, for four dynamic receiver trajectories around a target base station. The low noise carrier phase observation enables estimation of the base station position up to sub-meter level accuracy for signal measurements having a sufficiently long duration of stable carrier tracking. The paper presents the localization results of a research-oriented Amarisoft base station pertaining to two receiver platforms - a ground vehicle and an airborne Unmanned Aerial Vehicle (UAV). For each platform, the received LTE signal quality is first analyzed using Code-Minus-Carrier (CMC) time series and then for time durations where the code and phase tracking is stable, the observations are fed into a Kalman filter which estimates the transmitter 3-dimensional position, clock bias and drift over time as well as the LTE carrier phase float ambiguity. The estimated position states results are then compared against a ground-truth measurement of the transmit antenna coordinates, which is obtained using GNSS Real Time Kinematic (RTK) and triangulation with a surveying multi-station device.

This paper presents a dual power-mode and multi-band power amplifier (PA) for handset applications that improves the efficiency in low-power regions. This PA operates in two modes through path control by a shunt switched capacitor. The proposed control method provides efficient mode control without any efficiency degrading and bandwidth (BW) limiting. The proposed PA, in conjunction with a boosted supply modulator for envelope tracking (ET) operation not only in the high-power mode, but also in the low-power mode, delivers good performance at all average output power levels. The linearity is improved by ET through a proper envelope-shaping method. For demonstrative purposes, the PA and supply modulator are implemented using an InGaP/GaAs heterojunction bipolar transistor and AIGaAs/InGaAs enhancement/depletion-mode pseudomorphic high electron-mobility transistor process and a 0.18- $\mu$ m CMOS process, respectively. The ET PA is tested across the range of 1.7–2.0 GHz using a long-term evolution signal with 16 quadrature amplitude modulation, a 7.5-dB peak-to-average power ratio, and 10-MHz BW. The proposed dual power-mode multi-band ET PA delivers good performance for high- and low-power modes, indicating that the architecture is promising for handset PA applications.

Alternative positioning techniques, such as those using ambient signals-of-opportunity, have been increasingly developed for global navigation satellite system (GNSS)-challenging urban and indoor environments. For instance, cellular long-term evolution (LTE) network supports a variety of positioning methods based on signal measurements such as received signal strength or time-of-arrival (TOA). Carrier phase measurement extracted from LTE signals has also received substantial attention due to its potential high ranging accuracy. This paper presents a closed-loop (CL) carrier phase tracking architecture for positioning in LTE networks with robustness to the channel fading effects. The pilot cell-specific reference signal (CRS) is exploited for generating the channel estimation results, which are inputs for the carrier phase discriminator to measure the carrier phase error. The undesired bias corrupting the phase discriminator output for multipath channels is analytically derived. Then, the state-space model of LTE carrier signal tracking in light of the specific CRS time-frequency domain pattern is established and the state estimator gain matrix is derived based on the proportional integral filter deign. Simulation assessment of the proposed carrier phase tracking architecture is performed in a single path Rician fading channel under different Rician factors and signal powers. The impact of loop parameters, e.g., loop bandwidth and updating interval, is investigated. Real collected LTE data in a multipath fading channel is also used to comparatively analyze the performances of the existing open-loop and proposed CL carrier tracking methods combined with three LTE signal TOA estimators. The proposed algorithm in conjunction with the multipath estimating delay lock loop is shown to provide accurate and robust carrier phase measurements against multipath fading effects compared to other considered tracking schemes.