Adaptive Receiver Research Articles

Spatial and temporal adaptive receiver for DS-CDMA systems

The objective of this paper is to propose a reception scheme to improve the performance of DS-CDMA (Direct Sequence Code Division Multiple Access) systems, compared to conventional direct channel receivers. The technique employs a spatial and temporal adaptive receiver composed of N spatial processors (associated with M antennas) and N Decision Feedback Equalizers (DFE), both of which are trained using a TMDP (Time Multiplexed Dedicated Pilot) sequence. The spatial and temporal receiver associated with TMDP offers considerable benefits when compared to the conventional Rake-Finger receiver. Performance results and details of the functioning of the proposed reception scheme are presented.

Design and Analysis of Adaptive Receiver Transmission Protocols for Receiver Blocking Problem in Wireless Ad Hoc Networks

Due to the lack of a centralized coordinator for wireless resource allocation, the design of medium access control (MAC) protocols is considered crucial for throughput enhancement in the wireless ad hoc networks. The receiver blocking problem, which has not been studied in most of the MAC protocol design, can lead to severe degradation on the throughput performance. In this paper, the multiple receiver transmission (MRT) and the fast NAV truncation (FNT) mechanisms are proposed to alleviate the receiver blocking problem without the adoption of additional control channels. The adaptive receiver transmission (ART) scheme is proposed to further enhance the throughput performance with dynamic adjustment of the selected receivers. Analytical model is also derived to validate the effectiveness of the proposed ART protocol. Simulations are performed to evaluate and compare the proposed three protocols with existing MAC schemes. It can be observed that the proposed ART protocol outperforms the other schemes by both alleviating the receiver blocking problem and enhancing the throughput performance for the wireless multihop ad hoc networks.

Low Complexity Selective Adaptive Multicarrier DS-CDMA Receiver

In this paper, selective adaptive (SA) receiver for Multicarrier Direct Sequence Code Division Multiple Access (MC DS-CDMA) system is presented. This receiver has high performance and at the same time reduces the multiple access interference (MAI) of the MC DS-CDMA) system with low computational complexity. The performance of SA receiver is measured in terms of the bit error rate (BER). An upper bound expression of the BER for the SA receiver under Rayleigh fading channel condition is derived and validated by computer simulations. Moreover, the implementation complexities of the SA receiver is compared with the Adaptive Parallel Interference Cancellation (APIC) receiver.

Scheduling schemes with adaptive blind detection for code reuse in multiuser MIMO systems

To improve spectrum efficiency in wireless multiple‐input, multiple‐output (MIMO) systems, it is essential to mitigate channel interference. Opportunistic scheduling of multiusers and interference cancellation, such as adaptive multiuser detection, are two commonly used techniques. In this paper, we study the performance improvement of using jointly these techniques to enable the use of the same set of spreading codes to transmit two data streams in closed‐loop multiuser MIMO systems. We show that with the proposed scheduling schemes, the performance of an adaptive blind receiver is not degraded when the scheduled users share the same spreading code.

Cell-Edge Multi-User Relaying with Overhearing

Carefully designed protocols can turn overheard interference into useful side information to allow simultaneous transmission of multiple communication flows and increase the spectral efficiency in interference-limited regime. We propose a novel scheme in a typical cell-edge scenario. By exploiting the overhearing link through proper relay precoding and adaptive receiver processing, rate performance can be significantly improved compared to the conventional transmission which does not utilize overhearing.

Novel Adaptive Nonlinear Receivers for UWB Multiple Access Communications

Ultra-wide bandwidth communication systems are known to suffer from non-Gaussian interference. In general, wireless ad-hoc networks, due to the lack of perfect power control and the random placement of nodes, are very likely to experience non-Gaussian multiple access interference. In systems with additive non-Gaussian noise, non-Gaussian signal detection and nonlinear signal processing can play important roles, especially in suppressing the multiple access interference. Practical ultra-wide bandwidth receiver designs based on the α-stable non-Gaussian additive impairment model are proposed and evaluated. It is demonstrated that the α-stable model together with a fractile based parameter estimation technique constitute a robust technique for adaptive receiver designs. The proposed receivers based on the α-stable model suppress multiple access interference, adapt to the noise and the interference in the environment, and are robust to estimation errors in the receiver parameters. The proposed receivers provide much better bit error rates than linear detectors and previously known nonlinear detectors.

Reconstructing parameters of sediment layers of a shallow sea bottom using broadband seismoacoustic sources

We study the possibilities of reconstructings the parameters of the sediment layers of a shallow sea bottom from interference patterns appearing during sounding of the bottom by broadband seismoacoustic sources with a bistatic sea-bottom sounding scheme, adaptive signal reception with a horizontal array, and matched filtration of low-frequency seismoacoustic pulses excited with an air gun and interacting with the sea bottom, as well as seismoacoustic noise from a vessel in a shallow sea. The parameters of sediment layers of the sea bottom are reconstructed by statistical checking of hypotheses on the parameters of dynamic spectra obtained by parametric models. Comparative possibilities of reconstructing sea bottom parameters with bistatic and monostatic observation schemes are discussed.

Research On BD2/GPS Dual-mode Adaptive Anti-jamming Receiver

The robust of satellite navigation receiver in complex electromagnetic environment is very important in military application, so the key technology of BD2/GPS Dual-mode Adaptive Antijamming Receiver is proposed. Space-time nulling and digital beam-forming anti-jamming methods were analyzed, if the wave direction is known, digital beam-forming can get a stronger anti-jamming ability than space-time nulling. Receiver cannot get the direction of arrival wave in cold start mode, so a method use navigation satellite almanac and inertial navigation module to estimate the direction of arrival wave which can make receiver get stronger anti-jamming ability at initial start time. Simulation tests show that: the method let receiver using digital beam-forming at the start time increase the anti-jamming capability than the original receiver witch only starts with nulling technology.

An Adaptive Receiver Design for OFDM Systems Using Conjugate Transmission

In this paper, we propose an adaptive receiver for efficient intercarrier interference (ICI) cancellation in orthogonal frequency division multiplexing (OFDM) systems using two-path conjugate transmission. This receiver design is based on the phase rotated conjugate cancellation (PRCC) concept presented recently, where two individual phase rotations are employed on the two receive paths, rather than only one phase rotation is adopted for the two transmit paths in the PRCC scheme. We derive the optimal phase rotations using the criterion of maximizing the carrier-to-interference ratio, and then develop an adaptive normalized block least mean-squared algorithm to approach the optimal solutions. With such adaptive phase rotations in the receiver, the carrier frequency offset (CFO) variations due to the channel effect and the mismatch between oscillators at the transmitter and receiver can effectively be tracked without feeding back the CFO estimate to the transmitter as required in PRCC. Simulation results demonstrate that the proposed approach has better bit error rate performance than the PRCC and the conventional CC scheme for various time-varying channels, even when the CFO/channel estimation error is considered.

Rf field mapping inside a large passenger-aircraft cabin using a refined ray-tracing algorithm

Radio-frequency (RF) field mapping and its analysis inside a large passenger aircraft is a complex EM analysis problem, owing to its inherent concavity. The further hybrid surface modeling required for such concave enclosures leads to ray proliferation, thereby making the problem computationally intractable. In this paper, a large passenger-aircraft cabin is modeled as a single curved elliptical cylindrical cavity having a floorboard and windows. Unlike the available ray-tracing packages that use extensive numerical search methods, a quasi-analytical ray-propagation model is proposed here. This involves uniform ray launching, an intelligent scheme for ray bunching, and an adaptive reception algorithm to obtain the ray-path details inside the concave cabin. Although the image method yields precise point-to-point solutions, it cannot be used for curved concave environments. The developed method is therefore validated with respect to the RF field inside a cuboid. The RF field at the receiver within the cabin is determined using the ray-path descriptions and the constitutive EM parameters of the aircraft's cabin materials. The convergence analysis of the RF field buildup is carried out with respect to the propagation time and the number of bounces.

RF Field Build-Up inside a Manned Space Vehicle Using Novel Ray-Tracing Algorithm

The radio-frequency (RF) field mapping and its analysis inside a space vehicle cabin, although of immense importance, represent a complex problem due to their inherent concavity. Further hybrid surface modeling required for such concave enclosures leads to ray proliferation, thereby making the problem computationally intractable. In this paper, space vehicle is modeled as a double-curvatured general paraboloid of revolution (GPOR) frustum, whose aft section is matched to an end-capped right circular cylinder. A 3D ray-tracing package is developed which involves a uniform ray-launching scheme, an intelligent scheme for ray bunching, and an adaptive reception algorithm for obtaining ray-path details inside the concave space vehicle. Due to nonavailability of image method for concave curvatured surfaces, the proposed ray-tracing method is validated with respect to the RF field build-up inside a closed lossy cuboid using image method. The RF field build-up within the space vehicle is determined using the details of ray paths and the material parameters. The results for RF field build-up inside a metal-backed dielectric space vehicle are compared with those of highly metallic one for parallel and perpendicular polarizations. The convergence of RF field within the vehicle is analyzed with respect to the propagation time and the number of bounces a ray undergoes before reaching the receiving point.

A Fast Adaptive Receive Antenna Selection Method in MIMO System

Antenna selection has been regarded as an effective method to acquire the diversity benefits of multiple antennas while potentially reduce hardware costs. This paper focuses on receive antenna selection. According to the proportion between the numbers of total receive antennas and selected antennas and the influence of each antenna on system capacity, we propose a fast adaptive antenna selection algorithm for wireless multiple-input multiple-output (MIMO) systems. Mathematical analysis and numerical results show that our algorithm significantly reduces the computational complexity and memory requirement and achieves considerable system capacity gain compared with the optimal selection technique in the same time.

Blind Adaptive Receiver for Uplink STBC MC-CDMA Systems in Multi-Cell Environments

Blind Adaptive Receiver for Uplink STBC MC-CDMA Systems in Multi-Cell Environments

Stochastic MIMO channel modelling using FMLP-based inference engine

A fuzzy-neural FN estimator of stochastic multi-input-multi-output MIMO wireless channels shows dependence on the membership and inference rule generation norms adopted. These two factors decide the ability of the fuzzy-estimator to capture the subtle variations in the input signal patterns and provide corresponding responses with optimum performance. They also determine the precision and processing speed of the FN-estimator while tackling stochastic behaviour of the MIMO channels. The membership and inference rule generation norms must not only capture the subtle variations but also should contribute towards lower bit error rate BER, reduced design and time complexity. Here, we propose the design of a fuzzy multilayer perceptron FMLP-based inference engine design for a FN-based MIMO modelling using multiple membership and inference rule generation norms. Experimental results derived show that a set formulated with seven linguistic hedges and six inference states helps in designing a FN MIMO estimator which can be an important element in the design of adaptive receivers for high data rate wireless communication.

Smart UWB System Based on STC and TR Techniques for BER Performance Enhancement and Interference Rejection

In this research, a novel smart UWB system is introduced. The proposed system is based on using an adaptive maximum ratio combining (MRC) Rake receiver. The proposed adaptive Rake receiver uses Genetic algorithm (GA) to adaptively select the delays of the fingers of the Rake receiver depending on the channel impulse response. It adaptively selects the delays that will allow the Rake receiver to capture most of the energy in the multipath components with minimum complexity. This adaptive Rake receiver is referred to as a GA Rake. The adaptive GA Rake is applied to a single-input single-output and space time coding (STC) multi-input single-output UWB systems. The performance of those systems using a GA Rake is compared to their performance when using a conventional MRC-Rake receiver and showed a great enhancement in performance with less receiver complexity. Also, in this paper, the smart UWB system using STC is modified by using the time reversal (TR) pre-coding technique. The modified system is referred to as a TR smart UWB system. This modification leads to more enhancements in performance and more reduction in receiver complexity over the smart UWB system. Moreover, this paper also shows the ability a TR smart UWB system in combating interference from other UWB systems.

Adaptive blind receivers for MC-CDMA communication systems

In this paper, we propose three adaptive blind algorithms for multiuser multicarrier code division multiple-access systems in multipath fading channels. The proposed adaptive blind receivers are based on the property of the discreteness of the input data symbol and are updated in every symbol interval. We also use the concept that the variance of the output signal approaches to the variance of the desired signal to get the cost function. The three proposed receiver structures are the traditional finite impulse response FIR structure, the despreading DES filter structure and the generalized sidelobe canceller GSC structure. The advantage of the FIR filter is that the length of the filter weights does not have to be the same length as the spreading code. For the DES filter, the combination of the adaptive weight and the despreading code has the simplest structure than the other two proposed receiver structures. The constrained GSC filter is superior to the other two proposed receiver structures in the environments dominated by multiple-access interference. By this constraint, the blind GSC filter can guarantee to converge to the desired solution. Simulation results are given to show the effectiveness and comparison of the proposed adaptive blind receivers. Copyright ©2012 John Wiley & Sons, Ltd.

Quantum Memetic Evolutionary Algorithm-Based Low-Complexity Signal Detection for Underwater Acoustic Sensor Networks

Modern communication engineering has brought forward impractical requirements on powerful computation engines as well as simple implementations. Apparently, the two aspects are contradicted in most realistic applications. Because of the dispersive multipath propagation in underwater acoustic channels, traditional coherent and adaptive receivers are computationally intensive and, hence, inapplicable to the large-scale underwater sensor networks. Inspired by quantum computing and nature intelligence that are incorporated with the concept of culture evolution, in this paper, we suggest a novel quantum memetic algorithm (QMA) built with more qualified problem-solving ability. Instead of classical gene representations, the quantum bit structure is employed by chromosomes to enhance the population diversity of genetic searching. The quantum gate rotating is then explored to update chromosomes in an efficiently parallel way. As a hybridization strategy, quantum-rotation-based local search is integrated in the lifetime learning to further refine individuals' performance and accelerate their convergence toward the global optimality. As a significant real-world application, we develop a noncoherent underwater signal receiver that is based on a QMA framework. From a pattern recognition aspect, the suggested detection scheme includes two sequential phases: Features extraction and pattern classification. Finally, the highly computational optimization problem is elegantly addressed by QMA. Providing favorable robustness to various parameter configurations, QMA can considerably reinforce the search performance and improve the underwater signal detection. It is demonstrated from numerical experiments that QMA is much superior to genetic algorithm (GA) in this high-dimensional optimization. Meanwhile, QMA shows remarkable advantages in search performance, even to the current state-of-the-art quantum-inspired GA and memetic algorithm.

Modification of the Watterson model of the ionospheric HF radio communication channel for adaptive spaced reception

We propose a model for the formation of signals from spaced antennas to be used as simulated ionospheric high-frequency radio channels for testing of algorithms and devices with spatiotemporal signal processing. Adequacy of the proposed model is demonstrated by its comparison with the experimental results. The model is used to determine potential capabilities of the spatial compensators of interference in a channel with scattering.

Optimum Power Allocation for Average Power Constrained Jammers in the Presence of Non-Gaussian Noise

We study the problem of determining the optimum power allocation policy for an average power constrained jammer operating over an arbitrary additive noise channel, where the aim is to minimize the detection probability of an instantaneously and fully adaptive receiver employing the Neyman-Pearson (NP) criterion. We show that the optimum jamming performance can be achieved via power randomization between at most two different power levels. We also provide sufficient conditions for the improvability and nonimprovability of the jamming performance via power randomization in comparison to a fixed power jamming scheme. Numerical examples are presented to illustrate theoretical results.

Complexity adaptive iterative receiver performing TBICM-ID-SSD

Flexible and iterative baseband receivers with advanced channel codes like turbo codes are widely adopted nowadays, ensuring promising error rate performances. Extension of this principle with an additional iterative feedback loop to the demapping function has proven to provide substantial error performance gain at the cost of increased complexity. However, this complexity overhead constitutes commonly an obstacle for its consideration in real implementations. This article illustrates the opposite of what is commonly assumed and proposes a complexity adaptive iterative receiver performing iterative demapping with turbo decoding (TBICM-ID-SSD). Targeting identical error rate, the article shows that for certain system configurations TBICM-ID-SSD presents lower complexity than TBICM-SSD (without iterative demapping). This original result is obtained when considering the equivalent number of iterations through detailed analysis of the corresponding computational and memory access complexity. The analysis is conducted for different parameters in terms of modulation orders and code rates and independently from the architecture for a fair comparison. Considering the proposed adaptive receiver which is able to perform both TBICM-ID-SSD and TBICM-SSD modes, results demonstrate a reduced complexity with TBICM-SSD for high modulation orders. However, for low modulation orders as for QPSK, results show a reduction in arithmetic operations and read access memory up to 45.9% and 47%, respectively for using the TBICM-ID-SSD mode rather than TBICM-SSD performing six turbo decoding iterations over Rayleigh fading channel with erasures.