Complexity evaluation for the implementation of a pre-FFT equalizer in an OFDM receiver

A pre-FFT equalizer (PFE) has been shown to offer a significant throughput efficiency improvement when applied to an OFDM receiver. Alternatively, the PFE can be used to increase the maximum delay spread conditions under which the OFDM system can operate effectively. Due to the manner of its operation, the PFE requires the use of modified adaptation algorithms if iterative, decision directed, adaptation is required. The computational complexity required to implement a PFE and a suitable adaptation strategy is evaluated. Initially, an LMS adaptation algorithm is investigated and evaluated in terms of its suitability for application in conjunction with the PFE to standards such as ETSI DVB-T and HIPERLAN/2 and IEEE 802.11a. The complexity requirements are found to be high, particularly in the case of DVB-T. The demand for a lower complexity adaptation algorithm is thus identified. As a result, a CSI-based adaptation method is subsequently considered. The complexity requirement of this algorithm is also analyzed and evaluated and is shown to be much lower than that of the LMS algorithm. Thus, it is shown that if the CSI-based adaptation method is used, the dominant complexity requirement is due to the implementation of the equalizing filter and not the adaptation method. Reduced filter complexity requirement is thus shown to be the key to enabling effective application of the PFE. The ATSC 8-VSB standard is identified as a possible source of techniques to reduce or facilitate the high complexity demands for implementation of the PFE filter

Reducing feedback requirements of the multiple weight opportunistic beamforming scheme via selective multiuser diversity

Opportunistic beamforming (OB) relies on the transmission of Channel State Information (CSI) in the form of instantaneous Signal to Noise Ratio (SNR) from Mobile Stations (MSs) back to the Base Station (BS) for scheduling purposes that increase throughput and/or maintain resource allocation fairness. OB is employed in environments of low mobility and low scatter, artificially inducing channel fluctuations that can better exploit Multiuser diversity (MUD). Multiple antennas at the BS are randomly alter the channel’s response and generate peaks in gain where users can be scheduled on, maximising system throughput. Additional gains are achieved by transmitting multiple weighting vectors from the BS, but their use can significantly increase the load of the feedback channel and mitigate MUD gains. Selective Multiuser diversity (SMUD) has been proposed for the original beamforming scheme as a technique that reduces feedback requirements substantially without any significant throughput degradations. This paper considers the joined use of multiple weights and SMUD in opportunistic beamforming, aiming to increase capacity while reducing feedback overhead. Results show that with an appropriate use of threshold levels, not only average throughput can be increased through the use of multiple weighting vectors but also a notable decrease in feedback load requirements compared to the conventional OB with SMUD design is achieved. The terms Mobile Station (MS) and User are used interchangeably in this paper, with the same meaning.Opportunistic beamforming (OB) relies on the transmission of Channel State Information (CSI) in the form of instantaneous Signal to Noise Ratio (SNR) from Mobile Stations (MSs) back to the Base Station (BS) for scheduling purposes that increase throughput and/or maintain resource allocation fairness. OB is employed in environments of low mobility and low scatter, artificially inducing channel fluctuations that can better exploit Multiuser diversity (MUD). Multiple antennas at the BS are randomly alter the channel’s response and generate peaks in gain where users can be scheduled on, maximising system throughput. Additional gains are achieved by transmitting multiple weighting vectors from the BS, but their use can significantly increase the load of the feedback channel and mitigate MUD gains. Selective Multiuser diversity (SMUD) has been proposed for the original beamforming scheme as a technique that reduces feedback requirements substantially without any significant throughput degradations. This paper considers the joined use of multiple weights and SMUD in opportunistic beamforming, aiming to increase capacity while reducing feedback overhead. Results show that with an appropriate use of threshold levels, not only average throughput can be increased through the use of multiple weighting vectors but also a notable decrease in feedback load requirements compared to the conventional OB with SMUD design is achieved. The terms Mobile Station (MS) and User are used interchangeably in this paper, with the same meanin

SMD-based numerical stochastic perturbation theory

The viability of a variant of numerical stochastic perturbation theory, where the Langevin equation is replaced by the SMD algorithm, is examined. In particular, the convergence of the process to a unique stationary state is rigorously established and the use of higher-order symplectic integration schemes is shown to be highly profitable in this context. For illustration, the gradient-flow coupling in finite volume with Schr\"odinger functional boundary conditions is computed to two-loop (i.e. NNL) order in the SU(3) gauge theory. The scaling behaviour of the algorithm turns out to be rather favourable in this case, which allows the computations to be driven close to the continuum limit.Comment: 35 pages, 4 figures; v2: corrected typos, coincides with published versio

GaAs-based Self-Aligned Stripe Superluminescent Diodes Processed Normal to the Cleaved Facet

We demonstrate GaAs-based superluminescent diodes (SLDs) incorporating a window-like back facet in a self-aligned stripe. SLDs are realised with low spectral modulation depth (SMD) at high power spectral density, without application of anti-reflection coatings. Such application of a window-like facet reduces effective facet reflectivity in a broadband manner. We demonstrate 30mW output power in a narrow bandwidth with only 5% SMD, outline the design criteria for high power and low SMD, and describe the deviation from a linear dependence of SMD on output power as a result of Joule heating in SLDs under continuous wave current injection. Furthermore, SLDs processed normal to the facet demonstrate output powers as high as 20mW, offering improvements in beam quality, ease of packaging and use of real estate. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Parasympathetic functions in children with sensory processing disorder.

The overall goal of this study was to determine if parasympathetic nervous system (PsNS) activity is a significant biomarker of sensory processing difficulties in children. Several studies have demonstrated that PsNS activity is an important regulator of reactivity in children, and thus, it is of interest to study whether PsNS activity is related to sensory reactivity in children who have a type of condition associated with sensory processing disorders termed sensory modulation dysfunction (SMD). If so, this will have important implications for understanding the mechanisms underlying sensory processing problems of children and for developing intervention strategies to address them. The primary aims of this project were: (1) to evaluate PsNS activity in children with SMD compared to typically developing (TYP) children, and (2) to determine if PsNS activity is a significant predictor of sensory behaviors and adaptive functions among children with SMD. We examine PsNS activity during the Sensory Challenge Protocol; which includes baseline, the administration of eight sequential stimuli in five sensory domains, recovery, and also evaluate response to a prolonged auditory stimulus. As a secondary aim we examined whether subgroups of children with specific physiological and behavioral sensory reactivity profiles can be identified. Results indicate that as a total group the children with severe SMD demonstrated a trend for low baseline PsNS activity, compared to TYP children, suggesting this may be a biomarker for SMD. In addition, children with SMD as a total group demonstrated significantly poorer adaptive behavior in the communication and daily living subdomains and in the overall Adaptive Behavior Composite of the Vineland than TYP children. Using latent class analysis, the subjects were grouped by severity and the severe SMD group had significantly lower PsNS activity at baseline, tones and prolonged auditory. These results provide preliminary evidence that children who demonstrate severe SMD may have physiological activity that is different from children without SMD, and that these physiological and behavioral manifestations of SMD may affect a child\u27s ability to engage in everyday social, communication, and daily living skills

Decision feedback equalization in SC-FDMA

SC-FDMA (Single-Carrier Frequency Division Multiple Access) is employed in the 3GPP LTE (Long-Term Evolution) standard as the uplink transmission scheme. The SC-FDMA signal has a low PAPR. This makes it well-suited to power efficient transmission at the mobile terminal. Although it is a common assumption to use frequency-domain linear equalization in SC-FDMA, a decision feedback equalizer (DFE) composed of a frequency-domain feedforward filter and a time-domain feedback filter can provide enhanced performance. Even when error propagation is taken into account, results show that a DFE still offers a significant performance gain over the conventional LE for uncoded SC-FDMA. This paper demonstrates that SC-FDMA with DFE is capable of increasing the throughput in a power limited channel by up to 41% compared to LE. Alternatively, for a given peak transmit power, the use of a DFE can achieve a 14% coverage extension in NLOS and 19% in LOS.SC-FDMA (Single-Carrier Frequency Division Multiple Access) is employed in the 3GPP LTE (Long-Term Evolution) standard as the uplink transmission scheme. The SC-FDMA signal has a low PAPR. This makes it well-suited to power efficient transmission at the mobile terminal. Although it is a common assumption to use frequency-domain linear equalization in SC-FDMA, a decision feedback equalizer (DFE) composed of a frequency-domain feedforward filter and a time-domain feedback filter can provide enhanced performance. Even when error propagation is taken into account, results show that a DFE still offers a significant performance gain over the conventional LE for uncoded SC-FDMA. This paper demonstrates that SC-FDMA with DFE is capable of increasing the throughput in a power limited channel by up to 41% compared to LE. Alternatively, for a given peak transmit power, the use of a DFE can achieve a 14% coverage extension in NLOS and 19% in LOS

Performance evaluation of hybrid ARQ schemes of 3GPP LTE OFDMA system

Expectations and requirements for future wireless communication systems continue to grow and evolve. Thus, recently, the Third Generation Partnership Project (3GPP) has considered the Long Term Evolution (LTE) of 3G - also known as Super 3G - to ensure its competitiveness in the future. It is generally assumed that the downlink of the new air interface would be OFDMA based and that some form of Hybrid ARQ (HARQ) might be employed. This paper aims to evaluate the performance of various HARQ schemes over the OFDMA downlink of the currently proposed 3GPP LTE specification. Schemes are compared in terms of throughput and PER in the context their differing memory requirements for implementation. Simulation results show that Type II Incremental Redundancy offers the best throughput performance but at the cost of higher memory requirement. However, when the schemes are enhanced with subcarrier and constellation rearrangement techniques, the performance gap between the different HARQ types is reduced significantly

Performance evaluation of channel estimation techniques for MIMO-OFDM systems with adaptive sub-carrier allocation

Dynamic Sub-Carrier Allocation (DSA) strategies have been shown previously to achieve significant performance benefits when applied to OFDMA systems and further benefits for MIMOOFDMA systems. Analysis thus far has focussed on the assumption of ideal Channel State Information (CSI). In this paper, the impact of non-ideal CSI is investigated. Various channel estimation techniques are evaluated for application to MIMO-OFDMA systems. They are based on Least Squares (LS) Estimation with training pilots. ‘Conventional’ (as for MIMO-OFDM) CTP (combining training pilots and ‘improved’ (optimised for MIMO-OFDMA) STP (Separate training pilots) versions of both Frequency Domain Least Square (FDLS) and Time Domain Least Square (TDLS) channel estimation are considered, as are the options of both Space- Time Block coding (STBC) and Spatial Multiplexing (SM) as MIMO strategies. The STP-TDLS strategy is shown to significantly outperform other channel estimation options, achieving performance within 1dB of the ideal case. Subsequently, the use of the STP-TDLS channel estimation method in conjunction with the DSA algorithm is considered in order to determine the impact of non-ideal channel knowledge on the gain achieved by DSA. The performance for the cases of ideal CSI and CSI derived via STP-TDLS channel estimation are compared and evaluated for both the STBC and SM cases. The effects of non-ideal channel estimation in both the DSA mechanism and channel equalisation separately and together are evaluated. It is shown that STP-TDLS channel estimation works better in SM (only 1dB worse than ideal CSI case) than in STBC. Furthermore, it is shown that DSA is less sensitive than channel equalisation to nonideal CSI. The degradation of system performance in the realistic case of non-ideal CSI for both DSA and channel equalisation is a compound of the effects of the separate effects of non-ideal CSI error. It is shown here that in both STBC and SM cases, the effect is almost a linear addition of the two parts. Given the substantial benefits of DSA and its relative insensitivity to channel estimation errors, it is concluded that DSA remains a highly promising technique

Overcoming self-interference in SM-OFDMA with ESINR and dynamic subcarrier allocation

For a single user with multiple receive antennas, co-antenna interference can be the dominant source of impairment in a Spatial Multiplex Orthogonal Frequency Division Multiple Access (SM-OFDMA) system, particularly when correlation exists between spatial sub-channels. By exploiting knowledge of the channel response and combining it with Dynamic Sub- Carrier Allocation (DSA), the algorithm proposed in this paper aims to reduce the effect of interference, while providing fair gain and maximizing the SINR across all users. Simulation results reveal that the proposed algorithm considers self-interference that exists between multiple antennas and is capable of achieving a capacity gain for every user with improved BER performance compared to previous work.For a single user with multiple receive antennas, co-antenna interference can be the dominant source of impairment in a Spatial Multiplex Orthogonal Frequency Division Multiple Access (SM-OFDMA) system, particularly when correlation exists between spatial sub-channels. By exploiting knowledge of the channel response and combining it with Dynamic Sub- Carrier Allocation (DSA), the algorithm proposed in this paper aims to reduce the effect of interference, while providing fair gain and maximizing the SINR across all users. Simulation results reveal that the proposed algorithm considers self-interference that exists between multiple antennas and is capable of achieving a capacity gain for every user with improved BER performance compared to previous work