In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered. The degradation of the bit error rate (BER), caused by the presence of carrier frequency offset and carrier phase noise is analytically evaluated. It is shown that for a given BER degradation, the values of the frequency offset and the linewidth of the carrier generator that are allowed for OFDM are orders of magnitude smaller than for single carrier systems carrying the same bit rate. >

BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise

A fractional delay filter is a device for bandlimited interpolation between samples. It finds applications in numerous fields of signal processing, including communications, array processing, speech processing, and music technology. We present a comprehensive review of FIR and allpass filter design techniques for bandlimited approximation of a fractional digital delay. Emphasis is on simple and efficient methods that are well suited for fast coefficient update or continuous control of the delay value. Various new approaches are proposed and several examples are provided to illustrate the performance of the methods. We also discuss the implementation complexity of the algorithms. We focus on four applications where fractional delay filters are needed: synchronization of digital modems, incommensurate sampling rate conversion, high-resolution pitch prediction, and sound synthesis of musical instruments.

Splitting the unit delay [FIR/all pass filters design]

The latest research works on the synchronization scheme for either continuous transmission mode or burst packet transmission mode for the wireless OFDM communications are overviewed in this paper. The typical algorithms dealing with the symbol timing synchronization, the carrier frequency synchronization as well as the sampling clock synchronization are briefly introduced and analyzed. Three improved methods for the fine symbol timing synchronization in frequency domain are also proposed, with several key issues on the synchronization for the OFDM systems discussed.

On the synchronization techniques for wireless OFDM systems

https://www.dtc.umn.edu/s/resources/bib05eurasip.pdf

Bibliography on cyclostationarity

A digital information receiver (100) having a single oscillator (118) providing a clock signal to the receiver circuitry. The receiver (100) contains, in addition to the oscillator (118), an input signal processor (102), a symbol time loop, a demodulator (106), a transport decoder (108), a transport timing loop, one or more applications decoders (102) and a presentation device (116). The input signal processor (102) digitizes an input signal and resamples the input signal using an interpolator (204) such that the input signal is optimally sampled. The resampling is controlled by a symbol timing loop. In a first embodiment, the transport timing loop controls the frequency of the oscillator (118) using transmitter timing information contained in the received signal. In the second embodiment, the oscillator (1202) is a free running oscillator and the transport timing loop controls a numerically controlled counter (1002) that, in turn, controls presentation timing of the information carried by the information in the input signal. After the input signal is decoded, an output interpolator (1204) generates continuous signals from somewhat bursty signals for utilization by the presentation device.

Single oscillator compressed digital information receiver

This paper deals with the bit error rate (BER) performance of a fully digitally implemented receiver performing coherent detection on a narrowband BPSK or (O)QPSK signal, transmitted over a slow non-frequency selective Rician fading channel. The considered digital receiver operates on samples of the received signal, taken by a fixed clock which is not synchronized to the transmitter clock. Signal samples needed for detection of the information sequence are obtained from interpolation between the available samples. In the case of nonideal interpolation a BER degradation occurs. By means of theoretical analysis, we demonstrate that even simple interpolators, operating at only a few samples per symbol, yield BER degradations that are limited to a small fraction of a dB. This paper is an extension of the work of Erup, Gardner and Harris (see ibid., vol.41, no.6, p.998-1008, 1993) where only the AWGN channel was considered and results were obtained by computer simulations. >

The effect of interpolation on the BER performance of narrowband BPSK and (O)QPSK on Rician-fading channels

Fully digital receivers operate on samples of the received signal, taken by a fixed clock. Signal samples at instants of maximum eye opening are obtained by interpolating between available samples. In the Letter, a second-order (quadratic) interpolator is optimised for minimum bit error rate (BER) degradation, when operating on a bandlimited direct-sequence spread-spectrum (DS/SS) signal.

Optimisation of second-order interpolator for bandlimited direct-sequence spread-spectrum communication

Presents a simple approximate expression for the BER degradation, caused by random carrier phase and timing errors, of the maximum-likelihood (ML) receivers operating on narrowband M-PSK and bandlimited direct-sequence/spread-spectrum (DS/SS) M-PSK signals; this expression is very accurate for (small) degradations of practical interest, and reveals that the BER degradation (in dB) is essentially proportional with the tracking error variance. In the absence of ISI at the optimum decision instants, carrier phase errors yield exactly the same degradation for narrowband M-PSK as for bandlimited DS/SS M-PSK. When the product of the r.m.s. timing error and the minimum signal bandwidth is held constant, the degradation for bandlimited DS/SS M-PSK is considerably smaller than for narrowband M-PSK, especially for large values of M and small values of the rolloff. >

Effect of random carrier phase and timing errors on the detection of narrowband M-PSK and bandlimited DS/SS M-PSK signals

Deals with the symbol synchronization performance of a fully digitally implemented receiver, operating on a narrowband M-PSK signal (one-sided bandwidth not exceeding the symbol rate). The considered digital receiver operates on samples of the complex envelope r(t) of the received signal, taken by a fixed clock which is not synchronized to the transmitter clock. The synchronized samples required for the symbol synchronization algorithm are computed by interpolating between the available non-synchronized samples. In the case of non-ideal interpolation, some amount of distortion is introduced, which affects the performance of the symbol synchronizer. By means of theoretical analysis, the authors investigate the tracking performance of a specific decision-directed feedback synchronizer, assuming interpolation of orders zero and one. They show that non-ideal interpolation gives rise to a loop noise spectrum containing spectral lines, that mainly occur near f=0. Hence, a sufficiently small loop bandwidth is required to suppress these spectral lines.

The effect of non-ideal interpolation on symbol synchronization performance

Discusses the symbol synchronizer performance of a fully digitally implemented receiver, operating on a narrowband M-PSK signal (one-sided bandwidth not exceeding the symbol rate). The considered digital receiver operates on samples of the complex envelope r(t) of the received signal, taken by a fixed clock which is not synchronized to the transmitter clock. The synchronized samples required for the symbol synchronization algorithm are computed by interpolating between the available non-synchronized samples. Because of finite memory, interpolation is non-ideal; hence, some amount of distortion is introduced, which affects the performance of the symbol synchronizer. By means of theoretical analysis, the authors investigate the tracking performance of a specific decision-directed feedback synchronizer, assuming interpolation of orders zero, one and two. They show that non-ideal interpolation gives rise to a loop noise spectrum containing spectral lines, that mainly occur near f=0 when the number of samples per symbol is close to an integer. Unless a sufficiently small loop bandwidth is chosen, the contribution of these spectral lines could dominate the timing error variance, which then becomes much larger than for synchronized sampling. >

K. Bucket

Papers

The effect of interpolation on the BER performance of narrowband BPSK and (O)QPSK on Rician-fading channels

Optimisation of second-order interpolator for bandlimited direct-sequence spread-spectrum communication

Effect of random carrier phase and timing errors on the detection of narrowband M-PSK and bandlimited DS/SS M-PSK signals

The effect of non-ideal interpolation on symbol synchronization performance

Symbol synchronizer performance affected by non-ideal interpolation in digital modems