Visible Light Positioning (VLP) is an exciting new technology that has the potential to provide indoor positioning in a myriad of applications. Typically, VLP uses LED luminaires for positioning beacons and, like other positioning technologies, there is a requirement that sufficient beacons are available in the field of view (FOV) for triangulation. This can be challenging in many environments due to the luminaire placement and size. In this paper we investigate the use of luminaire reference points (LRPs) and hybrid imaging-photodiode (HIP) receivers to improve the reliability and robustness of VLP. LRPs are precisely defined points on a luminaire that can be recognised by the imaging sensor in a HIP receiver. We show that, by associating multiple LRPs with a single luminaire, it is possible to achieve positioning when only one luminaire is in the FOV of the receiver. We demonstrate, using the geometric dilution of precision, that low positioning errors can be achieved even when luminaire geometry and spacing is non-ideal.

In this paper, we introduce a new two-stage receiver structure for visible light positioning (VLP) and a particular implementation of the new structure called the QADA-PLUS receiver. By using two sensors, one a photodiode (PD) based sensor and the other an image-based sensor, the new structure exploits the strengths of both technologies while avoiding their weaknesses. The QADA-PLUS uses a quadrant angular diversity aperture receiver (QADA) for the PD-based stage. The QADA has a very compact, planar structure suitable for incorporation in a smartphone or other small device and has been shown to provide good angular diversity in a proof-of-concept laboratory experiment. The QADA is also, unlike typical image sensors, able to reliably demodulate high frequency visible light signals. In this paper extensive simulation results for a range of typical indoor scenarios and realistic parameters show that the QADA has the potential to accurately estimate the polar and incident angle of light transmitted by LED luminaires. The average absolute error in estimation of incident angle was 0.0006° and for polar angle estimation was 0.005°. A limitation of these simulations is that it is assumed that the luminaires can be modelled as point sources and that the dimensions of the QADA are very precisely known. Incorporation of the QADA in the new two-stage QADA-PLUS receiver removes these limitations in two ways - the image-based receiver provides very accurate angle-of-arrival estimates and the use of visible reference points means that the QADA-PLUS is compatible with luminaires of any shape.

Visible light positioning (VLP) for indoor applications has recently received considerable attention. In this paper, an aperture based receiver is considered and the position is estimated based on the angle-of-arrival (AOA), because the AOA can be determined by comparing the relative differences in the received signal strengths (RSS) in the different photodiodes (PDs) of the receiver. Hence, in contrast to RSS based positioning solutions, knowledge of the transmitted signal strengths is not required. The performance of the proposed approach depends on the transmitted signal strength only through the dependency on the signal-to-noise ratio. To evaluate the accuracy of the estimates of the AOA, we derive the Cramer-Rao lower bound, and show that the expected error on the AOA is very small. Applying triangulation to determine the position of the receiver, it follows that centimetre accuracy can be obtained with the aperture-based receiver.

In this paper, we present a detailed comparison of the performance of asymmetrically clipped optical OFDM (ACO-OFDM), ACO-OFDM with diversity combining, and DC-biased optical OFDM (DCO-OFDM) using a range of different bias levels. Comparisons are made for both an additive white Gaussian noise (AWGN) channel and for a typical frequency selective visible light communication channel. Adaptive bit loading is used to maximize the bit rate for the frequency selective channel using a target bit error rate of 10-3. Clipping noise in DCO-OFDM, unlike AWGN, is added at the transmitter, not the receiver. New analytical results are derived which include this effect in the bit-loading calculations. It is shown that diversity-combining alters the spectral distribution of the noise after equalization. The effect of this in bit loading is also analyzed. It is shown that for both the AWGN and the frequency selective channel ACO-OFDM with diversity combining is the most energy efficient at lower bit rates/normalized bandwidths but for higher data rates DCO-OFDM requires the smallest transmit power. For example, for the frequency selective channel for bit rates/normalized bandwidths up to 6, ACO-OFDM with diversity combining is the most power efficient. For higher data rates DCO-OFDM requires the smallest transmit power, but these data rates require very large constellation sizes, for example, the constellation size of 128 for DCO-OFDM for some subcarriers and 2048 for ACO-OFDM with diversity-combining.

Spatial multiplexing (SMP) and optical spatial modulation (OSM) are two important technologies for indoor multiple-input multiple-output (MIMO) visible light communications (VLC). In this paper, we compare the performance of SMP and OSM systems which are operated with typical configurations in an indoor scenario. Both systems transmit data using asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) as the modulation scheme. It is shown that in order to achieve the same data rate with the SMP, the OSM has to employ large constellations which become impractical when either the number of luminaires or the constellation size of the SMP is greater than four. Simulation results are presented for both MIMO systems using four luminaires as transmitters and a receiver configured with three different front-ends. These receivers include a conventional non-imaging receiver, a prism-based receiver and an aperture-based receiver. The BER results demonstrate that SMP outperforms OSM in terms of both the size of the region in which a receiver can achieve low BER and the BER at typical receiver positions.

In this paper, we investigate the problem of indoor positioning using visible light systems. The directional detector array we use is comprised of a number of receiving elements, each consisting of an aperture and a photo diode, which are arranged to offer good angular diversity, and can be implemented within a compact receiver structure [1]. The receiving elements receive the light from a number of white LEDs, which are typically attached to the ceiling, and which act as anchors. In order to get an indication of the received signal strengths of the different LEDs, we average the received signals over time. The relative signal strengths in the different receiving elements do not only provide information on the distance between the LEDs and the detector array, but also about the angle-of-arrival of the light. By combining the information of the receiving elements, the position of the detector can be estimated. In order to assess the accuracy of positioning algorithms based on this approach, we derive the Cramer-Rao lower bound on the position accuracy. Assuming the white LEDs transmit an optical power of 1 W, and the time averaging is done over 1 millisecond, an accuracy of the order of a centimetre can be achieved.

Machine type communications (MTC) could play a significant role in fifth generation (5G) wireless communications systems. In terms of reducing the side-lobes of orthogonal frequency-division multiplexing (OFDM) to support large numbers of asynchronous MTC devices, several waveform designs could be used. This paper provides closed form signal-to-interference-plus-noise ratio (SINR) and capacity results for this asynchronous scenario. We compare three candidate multi-carrier waveforms, which are OFDM, universal filtered multi-carrier (UFMC) and polynomial cancellation coded (PCC-OFDM). Our results indicate that both PCC and UFMC can provide better frequency roll-off than OFDM. PCC is more easier to implement and performs strongly against inter carrier interference (ICI) with cost of losing spectral efficiency and a higher peak-to-average power ratio (PAPR). UFMC is more robust to very dispersive multipath channels but with cost of increasing computational complexity.

In this paper, we present a new type of receiver for MIMO optical wireless communications. The new receiver consists of multiple receiving elements (REs), each made up of a photodetector (PD) placed under an aperture. The directionality of each RE is shown to depend on the relative position of the PD and the aperture. Receiving patterns are calculated for various MIMO receiver designs, demonstrating that significant angular diversity can be achieved within a compact receiver structure. Simulation results are presented for a number of typical indoor scenarios when the transmitted signals are modulated using asymmetrically clipped optical OFDM (ACO-OFDM). For the scenarios considered, the bit error rate is lowest in the middle of the room and highest in the corners. The results indicate that for typical parameter values, reliable communication can be achieved throughout the room.

This paper describes a new form of receiver for multiple-input multiple-output (MIMO) optical wireless communications. The new receiver uses a number of photodetectors (PDs), all facing in the same direction but with different fields of view (FOVs). This enables a compact planar receiver structure. The performance of the receiver is analyzed for an indoor visible light communications system where LED lights are used as data transmitters. It is shown that the MIMO channel matrix has full rank for typical receiver positions and that for a given number of PDs, the new receiver provides much greater diversity than a conventional receiver of the same overall dimensions in which all of the PDs have the same FOV. Finally the overall bit error rate (BER) is presented for systems using asymmetrically clipped optical OFDM (ACO-OFDM) as the modulation scheme. Results are presented for both zero forcing (ZF) and minimum mean square error (MMSE) equalization in the receiver. It is shown that the BER varies with receiver position, with relatively high values in the center and the corners of the room.

In this paper, we analyze the performance of a prism-array receiver in a multiple-input multiple-output (MIMO) intensity-modulated direct-detection optical wireless communication system. The elements of the MIMO channel matrix depend on the geometry of each prism and the orientation of the prism relative to the optical transmitter. An expression is derived for each channel gain as a function of the angle of the prism, the aspect ratio and area of the receiving surface of the prism, and the orientation and distance between the transmitter and receiver. Results are presented for the directionality and overall field of view (FOV) of a receiver comprising six prisms, showing that compact receivers can be designed, which combine well-conditioned channel matrices with wide FOVs. Simulation results are presented for a typical indoor visible light communication system where four light-emitting diode lights transmit information using asymmetrically clipped optical orthogonal frequency division multiplexing and linear equalizers are used in the receiver. It is shown that the overall bit error rate depends very strongly on the angle of the prisms and on the position of the receiver, but that a simple six-prism receiver can successfully decouple the four transmitted signals at typical receiver positions within the room.

This paper investigates the effect of fractional linear misalignment between the transmitter and the receiver for a pixelated MIMO optical wireless system using spatial orthogonal frequency division multiplexing (OFDM). The novelty of this work is in the modeling and analysis of fractional misalignment for spatial OFDM. It is shown that when the receiver is perfectly focused and when fractional misalignment is the only impairment, the received constellation points are phase shifted and attenuated. MATLAB simulations show that the impact of misalignment is the greatest when the fractional offset is equal to half of a pixel. Unlike integral misalignment, the use of equalizers cannot fully compensate the effect of fractional misalignment. It is revealed that when the fractional offset is half of a pixel, the offset causes bit error rate (BER) floor and the degradation is greater for a system with lower number of subcarriers than a system with larger number of subcarriers. We show that the BER degradation caused by fractional offset can be mitigated when a number of higher spatial frequency subcarriers are not used for data transmission.

In this paper we derive information theoretic results for asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) in an intensity modulated direct detection (IM/DD) optical communication system subject to a range of constraints. ACO-OFDM is a form of OFDM designed for IM/DD systems. It is an effective solution to intersymbol interference (ISI) caused by a dispersive channel and also requires less optical power than conventional optical modulation formats. Although the classical Shannon capacity formula cannot be applied directly to an IM/DD system, we show that when ACO-OFDM is used in an IM/DD system, it can be adapted to calculate the information rate of the data-carrying odd frequency subcarriers. As a result conventional water filling techniques can be used for a frequency selective channel. These results are applied to indoor wireless systems using realistic parameters for the transmitter, receiver and channel. The maximum rate at which data can be transmitted depends on the channel, the electrical bandwidth and the transmitted optical power. Even when there is no line of sight (LOS) path, when the electrical bandwidth is limited to 50 MHz and the average optical power is limited to 0.4 W, data rates of approximately 80 Mbit/s can theoretically be achieved.

Wireless access in vehicular environment (WAVE) is a technology developed for high data rate vehicle-to-vehicle and vehicle-to-infrastructure communications. Accurate estimation of speed of a vehicular node is essential in applications of WAVE such as collision avoidance systems and intersection safety applications. A novel speed estimation technique in WAVE is presented in this paper. The method estimates the relative speed of a vehicle using the Doppler shift which causes frequency offset in the received orthogonal frequency division multiplexed subcarriers. The frequency offset in the received subcarriers is calculated using a cross correlation metric between the transmitted pilot subcarriers and the received pilot subcarriers. The method gives good estimates of relative speed even at low signal to noise ratios and the simulations demonstrate that wide range of speeds (0 to 360 km/h) can be accurately estimated.

Timing jitter is emerging as an important factor in determining the performance of high-speed Orthogonal Frequency Division Multiplexing (OFDM) systems, particularly in optical OFDM systems where bit rates reach 100 Gbit/s and beyond. In OFDM timing jitter causes intercarrier interference (ICI). For a given subcarrier power, high frequency subcarriers in the sampled signal cause more ICI than lower frequency subcarriers, although the resulting ICI is equally distributed across all subcarriers. In this paper we show that by using this property and allocating more power to lower frequency subcarriers the overall capacity is greater than for a uniform power allocation. For systems where timing jitter is the main impairment, significant capacity increases can be achieved by applying this technique.

In this paper we propose an improved multiple-input multiple-output (MIMO) polynomial cancellation coding (PCC) orthogonal frequency division multiplexing (OFDM) system. In this improved system, PCC OFDM symbols are transmitted from different antennae with different time offsets. At the receiver these symbols are demodulated using each of those time offsets. Time offsets substantially reduce the power of the interfering signal relative to the wanted signal at the PCC OFDM demodulation stage. The improved system has significantly reduced sensitivity to imperfect channel state information (CSI) and also retains the insensitivity of normal PCC OFDM to frequency offsets. Results are presented for the improved system with (2, 2) MIMO in flat Rayleigh fading channels. It shows that the improved system has a lower bit error rate (BER).

In this paper, we investigate a radio resource allocation scheme for orthogonal frequency-division multiple-access (OFDMA)-based multiple-input multiple-output (MIMO) multihop networks. The half-duplex orthogonal relay channel construction method and related multihop transmission mechanism are designed to avoid the inter-hop interference. We propose a multistage resource allocation scheme for throughput maximization. And, the fairness consideration on sharing subcarriers among relay nodes is also discussed. Simulation results show that the spatial diversity gain offered by relay antenna array can effectively balance the tradeoff between the fairness performance and the system throughput. Results also show the proposed scheme is efficient with channel impairment when relay nodes are subject to severe shadowing effects.

This paper introduces a new constellation mapping scheme for asymmetrically-clipped optical OFDM (ACO-OFDM) that puts more bits on the low-frequency subcarriers. The lowpass nature of the wireless optical channel motivates the use of this generic bit-loading scheme. This scheme has no knowledge of the channel at the receiver; it performs significantly better than the traditional constant constellation mapping on all subcarriers in a variety of channels. The average bit-error rate (BER) curves for the new modulation scheme have up to a 5 dB improvement for signal-to-noise ratios (SNRs) where the BER is in the order of 10-3. In addition to the generic low-frequency bit-loading, this paper also proposes clipping the ACO-OFDM signal at the receiver to mitigate the additive electronic noise.

We present a new modulation scheme for asymmetrically-clipped optical OFDM (ACO-OFDM). We show that a generic bit-loading scheme that puts more bits on the low-frequency subcarriers is more efficient for wireless optical channels than the constant modulation scheme typically used in radio frequency (RF) OFDM schemes. We discuss the low- pass nature of the wireless optical channel that motivates the use of this generic bit-loading scheme. This scheme performs significantly better than the traditional constant modulation on all tones in a variety of channels. The average Bit-error rate (BER) curves for the new modulation scheme have up to a 5 dB improvement for Signal-to-Noise Ratios where the BER is in the order of 10-3.

In this paper, new timing synchronization methods for optical wireless systems using asymmetrically clipped optical orthogonal frequency division multiplexing(ACO-OFDM) are described. It is well known that OFDM systems are sensitive to timing synchronization errors. Existing synchronization methods cannot be used directly or do not perform well in ACO-OFDM systems because ACO-OFDM signals are unipolar. Therefore, new synchronization methods using a novel training symbol designed for the characteristics of ACO-OFDM are presented. The sensitivity of the new methods to the phase of the receiver sampling clock is considered and it is shown that if only the lower frequency subcarriers in the training symbol are non zero, the sensitivity can be reduced. Analysis and simulation results show that the new timing synchronization methods are effective in ACO-OFDM systems.

In this paper we investigate the channel capacity of intensity modulated direct detection (IM/DD) wireless optical communication systems for an AWGN channel with a limit on the average transmitted optical power. It has recently been shown that asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) is more efficient in terms of optical power than conventional optical modulation techniques such as pulse position modulation (PPM). When ACO-OFDM is used, the transmitted signal has a clipped Gaussian probability distribution. We calculate the channel capacity for systems using transmitted signals with exponential and clipped Gaussian distributions, and for an ACO-OFDM system. For practical signal to noise ratios, ACO-OFDM has a slightly lower capacity than the other distributions, due to the correlation between samples caused by the ACO-OFDM modulation process. ACO-OFDM has many practical advantages including its tolerance to multipath distortion. This paper shows that it also makes efficient use of the available power and bandwidth.

Orthogonal frequency division multiplexing (OFDM) is used in many wired and wireless broadband communication systems because of its resilience in the presence of signal dispersion or multipath distortion. OFDM has not been used in practical optical communication systems because the bipolar waveform cannot be used in intensity-modulated direct detection (IM/DD) systems. A new unipolar form of OFDM, asymmetrically clipped optical OFDM (ACO-OFDM), has recently been developed. For the case of an AWGN channel, we compare ACO- OFDM and other modulation schemes. It is shown that ACO- OFDM with 4-QAVI subcarrier modulation has the same bandwidth efficiency but requires 2 dB less energy per bit than on-off keying. ACO-OFDM with larger constellation sizes gives higher bandwidth efficiencies and lower optical power than other modulation schemes. Unlike existing methods, the performance of ACO-OFDM is limited by the bandwidth of the transmitter and receiver not the dispersion of the channel.

In this paper we investigate the error probability for OFDM with carrier frequency offset (CFO) in additive white Gaussian noise (AWGN) and Rayleigh fading channels. The statistical nature of the intercarrier interference (ICI) due to CFO and the validity of the usual Gaussian distributed ICI assumption are studied. In AWGN channels, our simulations indicate that the theoretical symbol error rate (SER) obtained by assuming Gaussian characteristics for the ICI is not accurate. The effect of adjacent channel ICI coefficients must be considered. However in a fading channel provided that the channel correlation effects on the useful OFDM signal and the ICI are considered, the theoretical BER results due to Gaussian ICI approach and simulations closely agree. The theoretical SER for MQAM signaling in fading channels is also derived in closed form.

OFDM has a very high peak-to-average power ratio. This imposes stringent dynamic range requirements on the analog front-ends of the transmitter and receiver and, if a fixed-point processor is used, on the digital sections of the system, particularly the FFT/IFFT. OFDM systems often use digital peak reduction techniques such as clipping and filtering but these require several FFT/IFFT operations. In this paper results are presented for the combination of a novel FFT algorithm which allows numeric overflow to occur with low probability, and several computationally efficient clipping techniques. Results are presented for the mean-square error of the clipped and filtered OFDM signal and for the computational complexity of the system in terms of cycle counts. These show that the technique causes negligible signal degradation and can be very efficiently implemented on low cost processors

Oscillator phase noise (PN) in orthogonal frequency division multiplexing (OFDM) systems can cause severe performance degradation. In contrary to the assumptions made previously, recent work has discovered that the intercarrier interference (ICI) distribution due to a wide range of PN strengths in fact deviates from Gaussian characteristics. Hence we have compared the accuracy of a theoretical Gaussian symbol error rate (SER) analysis to that of the simulated SER in additive white Gaussian noise (AWGN), frequency flat and frequency selective Rayleigh fading channels. In multipath channels the SER is evaluated jointly considering the fading effects on the OFDM signal and ICI. Our results indicate that modeling ICI due to PN as Gaussian in the AWGN channel can lead to pessimistic theoretical predictions. However in fading channels, the difference between the simulated and the theoretical results is marginal.

Distributed MIMO technology is an effective way of dealing with the inter-cell interference problem in single frequency wireless communication networks. This paper studies the generic channel capacity formula for a distributed MIMO-OFDM system. A practical two-ring STBC distributed MIMO-OFDM transmission scheme is introduced. The cell throughput formula for this distributed scheme is derived. The impact of inner cell radius on cell throughput performance is analyzed for a multi-cell simulation model. From simulation results, we show that the two-ring distributed scheme can effectively mitigate inter-cell interference and provide good radio propagation channel quality, particularly for users at cells boundary. Moreover, we show that, with proper inner cell radius, the two-ring distributed MIMO-OFDM scheme can achieve significant cell throughput gain compared with that of conventional centralized MIMO-OFDM scheme.

It is well known that orthogonal frequency division multiplexing (OFDM) systems are sensitive to carrier frequency offset (CFO). In this paper we present the effects of CFO for OFDM systems where the Alamouti code is used to map adjacent subcarriers (space-frequency) or symbols (space-time) across the space-frequency grid. Simulation results show that space-time-frequency coded OFDM systems are more sensitive to CFO effects than conventional OFDM. We have also presented an analytical error performance analysis for the case of STC-OFDM over frequency flat Rayleigh fading channels. The theoretical results have been validated from the simulations. However the usually assumed signal independent Gaussian ICI analysis provides pessimistic results

This paper investigates the capacity behavior of spatially semi-correlated orthogonal frequency division multiplexing (OFDM) based multiple input multiple output (MIMO) systems. We extend the previous analysis on capacity by considering realistic scattering distributions such as Laplacian and von Mises distributions. Receiver angle spread, antenna spacing and nonuniform antenna configuration are also considered in this paper. Furthermore, we also investigate the accuracy of a Gaussian approximation of the outage capacity of MIMO-OFDM systems. Simulation results indicate that for both the i.i.d and semicorrelated fading cases considered, a Gaussian approximation is very accurate. We also demonstrate that both the delay spread and antenna configuration can increase the capacity of not-so-rich scattering MIMO-OFDM system.

Impulse noise is a significant problem in some OFDM applications, including digital television broadcasting. In this paper, we study a novel decision directed impulse mitigation algorithm, both analytically and with simulations for the DVB-T parameters. In this algorithm, the noise component in each received input sample is estimated based on preliminary decisions on the transmitted data. When the estimate is large enough to indicate that impulse noise is present in the sample, the estimated noise component is subtracted from the input sample before final demodulation. This technique has been shown to be extremely effective in flat fading channels. In this paper, its application in frequency selective fading channels is analyzed. The optimum weighting factors for combining noise estimates from subcarriers subject to different fading are calculated. Simulation results are presented for Rayleigh and Ricean channels which show that the technique can reduce the error rates due to impulsive noise by an order of magnitude.

Previous studies on the effect of the clipping noise on the error performance of orthogonal frequency-division multiplexing (OFDM) systems in frequency selective fading channels provide pessimistic results. They do not consider the effect of channel fading on the clipping noise. The clipping noise is added at the transmitter and hence fades with the signal. Here, the authors show that the "bad" subcarriers that dominate the error performance of the OFDM system are least affected by the clipping noise and, as a result, the degradation in the error performance of OFDM system in fading channels is very small.

Polynomial cancellation coded orthogonal frequency division multiplexing (PCC-OFDM) with overlapping symbol periods is a modulation technique which overcomes many of the disadvantages of OFDM. Overlap PCC-OFDM is much less sensitive to frequency offset and Doppler spread and has better performance in channels with long delay spread than OFDM. This paper analyzes the equalizers that are required. Results are presented for linear and decision feedback equalizers of varying length in the presence of additive white Gaussian noise. The performance is degraded by two effects: the nonorthogonality of the basis functions, and the limited span of the equalizers. Despite these effects, for the same bandwidth efficiency overlap PCC-OFDM systems can be designed to have similar performance to OFDM with a cyclic prefix even when the only channel impairment is noise.

Polynomial cancellation coded orthogonal frequency division multiplexing (PCC-OFDM) with overlapping symbol periods is a modulation technique which overcomes many of the disadvantages of OFDM. PCC-OFDM is much less sensitive to frequency offset and Doppler spread than OFDM. Only the length of the equalizer used limits the delay spread that can be tolerated in a PCC-OFDM system. In this paper expressions are calculated for the intercarrier interference (ICI) and intersymbol interference (ISI) caused by timing errors in PCC-OFDM. Results are presented for simulations of PCC-OFDM in channels subject to frequency error and multipath. It is shown that good performance can be achieved using equalizers of only moderate complexity.

We give a mathematical context for polynomial cancellation coding, proposed previously to reduce intercarrier interference in orthogonal frequency division multiplexing (OFDM). In particular, we analyze polynomial cancellation coding (PCC) in terms of finite differences.

Orthogonal frequency division multiplexing (OFDM) is very sensitive to frequency errors caused by frequency differences between transmitter and receiver local oscillators. This sensitivity is analyzed in terms of the complex weighting coefficients which give the contribution of each transmitter subcarrier to each demodulated subcarrier. Previously described windowing and self intercarrier interference (ICI) cancellation methods are analyzed in terms of these weighting coefficients. New ICI cancellation schemes with very much improved performance are described. A condition for orthogonality of windowing schemes is derived in terms of the discrete Fourier transform (DFT) of the windowing function.

A method for symbol synchronization using two unsynchronized signal samples per symbol is presented. Signal values between the sample points are calculated by interpolation and then processed digitally to find a suitable strobe point. The interpolated value at the strobe point is used for data detection or input to an equalizer. Simulations show that low variance timing estimates can be made for pulses with raised-cosine spectra degraded by quadratic delay distortion.>

An algorithm for symbol timing recovery using baud-rate sampling is presented. Using this algorithm, the decoded data sequence is scanned for particular data patterns that yield samples which need only to be added or subtracted to give an estimate of the required timing function. The statistics of occurrence of these data patterns are calculated for random binary data. The variance of the timing function estimates is calculated for pulses with raised-cosine spectra that have been degraded by quadratic delay distortion and is shown to be lower, in most cases, than for other synchronizers using baud-rate sampling.>