3,031 research outputs found
Basis expansion adaptive filters for time-varying system identification
No full textElectrical Engineering, Mathematics and Computer Scienc
Symbol Error Probability of Hexagonal QAM
No full textThis letter studies the symbol error probability (SEP) of quadrature-amplitude modulation (QAM) signals constructed from the hexagonal lattice, known as hexagonal QAM or triangular QAM. In particular, we propose a simple and accurate approximation for the SEP of hexagonal QAM in additive white Gaussian noise. Simulation results show that the proposed approximation is very accurate for all the best-known QAM constellations constructed from the hexagonal lattice, including triangular QAM, for both high and low signal-to-noise ratio. In addition, the proposed approximation is suitable for the accurate estimation of the SEP of hexagonal QAM in slow-fading channels, such as Rayleigh fading channels
Joint Impact of Frequency Synchronization Errors and Intermodulation Distortion on the Performance of Multicarrier DS-CDMA Systems
No full text The performance of multicarrier systems is highly impaired by intercarrier interference (ICI) due to frequency synchronization errors at the receiver and by intermodulation distortion (IMD) introduced by a nonlinear amplifier (NLA) at the transmitter. In this paper, we evaluate the bit-error rate (BER) of multicarrier direct-sequence code-division multiple-access (MC-DS-CDMA) downlink systems subject to these impairments in frequency-selective Rayleigh fading channels, assuming quadrature amplitude modulation (QAM). The analytical findings allow to establish the sensitivity of MC-DS-CDMA systems to carrier frequency offset (CFO) and NLA distortions, to identify the maximum CFO that is tolerable at the receiver side in different scenarios, and to find out the optimum value of the NLA output power backoff for a given CFO. Simulation results show that the approximated analysis is quite accurate in several conditions.</p
Pilot-aided estimation of carrier frequency offsets and channel impulse responses for OFDM cooperative communications
No full textWe consider a cooperative communication system where the
destination node receives an orthogonal frequency-division
multiplexing (OFDM) signal transmitted from two relay nodes. We propose and compare two pilot-aided algorithms for the estimation of the carrier frequency offsets (CFOs) and the channel impulse responses (CIRs) associated with the two relay-destination links. The first algorithm uses a basis expansion model (BEM) to estimate a time-varying (TV) multiple-input single-output (MISO) channel that incorporates both CFOs and CIRs effects. The CFOs are then extracted from the estimated TV-MISO channel by applying estimation of signal parameters via rotational invariance techniques (ESPRIT). The second algorithm exploits the structure
of a specific pilot sequence and estimates the CFOs by directly
applying ESPRIT on the observed signal. Simulation results show the effectiveness of the proposed algorithm
Soft-Output Demapper with Approximated LLR for DVB-T2 Systems
No full textBit-interleaved coded modulation (BICM) is at the heart of the second generation digital terrestrial television systems (DVB-T2), which achieves a large spectral efficiency by means of high-order quadrature amplitude modulation (QAM) and low-density parity-check (LDPC) codes. This paper proposes a simple but effective approximation for the log-likelihood ratio (LLR) of the bits estimated by the soft-output QAM demapper. The proposed approximation, which keeps few dominant terms of the LLR expression, needs low additional complexity with respect to the conventional Max-Log approximation. Simulation results for DVB-T2 in multipath channels show a performance gain with respect to the Max-Log approach, especially for QAM with large modulation order
BER Performance Degradation of MC-DS-CDMA Systems Jointly Affected by Transmitter HPA and Receiver CFO in Frequency Selective Fading Channels
No full textMulticarrier systems are highly sensitive to the intermodulation distortion (IMD) introduced by high-power amplifiers (HPA) at the transmitter and to the intercarrier interference (ICI) due to a carrier frequency offset (CFO) at the receiver. We analyze the bit-error rate (BER) degradation induced by these impairments in the downlink of a multi-carrier direct-sequence code-division multiple-access (MC-DS-CDMA) systems in frequency-selective Rayleigh fading channels
BER of MC-DS-CDMA Systems with CFO and Nonlinear Distortions
No full textMulticarrier systems are highly sensitive to the intercarrier interference (ICI) caused by a carrier frequency offset (CFO) at the receiver and to the intermodulation distortion (IMD) introduced by the nonlinear amplifier (NLA) at the transmitter. We analyze how these impairments degrade the bit-error rate (BER) of multicarrier direct-sequence code-division multiple-access (MC-DS-CDMA) downlink systems in frequency-selective Rayleigh fading channels
Performance of nonorthogonal FSK for the Internet of Things
No full textIEEE 802.15.4 is a popular standard for low-rate wireless communications used for the Internet of Things (IoT). This IEEE standard contains a variety of physical layers (such as SUN, TVWS, RCC LMR, and LECIM) that make use of different modulations, such as nonorthogonal frequency-shift keying (FSK) and position-based FSK. This paper proposes simple closed-form expressions to evaluate the bit-error rate (BER) performance of nonorthogonal FSK schemes used for the IoT. Both coherent and noncoherent detection cases are investigated in additive white Gaussian noise (AWGN) and frequency-nonselective fading channels. In case of AWGN channels, the proposed BER expressions are obtained by selecting and modifying two terms of a union bound on the error probability. In case of fading channels, the proposed BER expressions are obtained by integration of the conditional BER over the fading statistics. Simulation results confirm the good accuracy of the proposed analytical BER expressions for different channel models (such as AWGN, Nakagami-m, Rice, lognormal) and for different detection techniques (such as noncoherent, coherent, and coherent with a residual phase error). Experimental results with wireless transmission and reception confirm the accuracy of the proposed approach. In addition, this paper also presents a BER expression for coherent detection of position-based FSK. Simulation results demonstrate that the presented BER expression for position-based FSK is more accurate than the BER expressions proposed in the literature
Low-complexity frequency-domain turbo equalization for single-carrier transmissions over doubly-selective channels
No full textSingle-carrier transmissions with frequency-domain equalization have gained much interest due to their comparable complexity and performance to OFDM, which conversely suffers from a high peak-to-average power ratio. In this paper, we develop a new frequency-domain block turbo equalizer for single-carrier (SC) transmissions over doubly-selective channels. The main feature of the proposed equalizer is its low complexity, which is only linear in the block length. A comparison between SC and OFDM systems with channel coding in doubly-selective channels is also given
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