Rake Detector Research Articles

Spatial‐Doppler domain precoding for orthogonal time frequency space modulation with rake detector

Spatial‐Doppler domain precoding for orthogonal time frequency space modulation with rake detector

Low Complexity Iterative Rake Decision Feedback Equalizer for Zero-Padded OTFS Systems

This paper presents a linear complexity iterative rake detector for the recently proposed orthogonal time frequency space (OTFS) modulation scheme. The basic idea is to extract and coherently combine the received multipath components of the transmitted symbols in the delay-Doppler grid using maximal ratio combining (MRC) to improve the SNR of the combined signal. We reformulate the OTFS input-output relation in simple vector form by placing guard null symbols or zero padding (ZP) in the delay-Doppler grid and exploiting the resulting circulant property of the blocks of the channel matrix. Using this vector input-output relation we propose a low complexity iterative decision feedback equalizer (DFE) based on MRC. The performance and complexity of the proposed detector favorably compares with the state of the art message passing detector. An alternative time domain MRC based detector is also proposed for even faster detection. We further propose a Gauss-Seidel based over-relaxation parameter in the rake detector to improve the performance and the convergence speed of the iterative detection. We also show how the MRC detector can be combined with outer error-correcting codes to operate as a turbo DFE scheme to further improve the error performance. All results are compared with a baseline orthogonal frequency division multiplexing (OFDM) scheme employing a single tap minimum mean square error (MMSE) equalizer.

Performance Analysis of Multistage Interference Cancellation in THUWB Systems Using Adaptive Differential Evolution Algorithm with Novel Mutation and Crossover Strategies

We study the application of differential evolution optimization algorithm to the problem of multiuser detection (MUD) and the suppression of multiple-access interference (MAI) in time-hopping UWB (TH-UWB) system is carried out considering the performance-complexity trade-off. The importance of MUD for achieving high data or low bit error rates in these systems has already been established in several studies. However, the optimum MUD can be characterized as a nondeterministic polynomial-time hard combinatorial optimization problem such that the computational complexity increases exponentially with number of user. In this paper, we proposed modified differential evolution (MDE) optimization algorithm with novel mutation and crossover strategy based MUD is investigated by simulations, when communicating over Saleh---Valenzuela (S---V) channel model. The RAKE detector is used as the first stage to initialize the MDE-based MUD. Then, the MDE algorithm is applied to detect the received data bit by optimizing an objective function incorporating the system of the RAKE detector. The performance evaluation with extensive simulations show that our proposed MDE based MUD can go to convergence rapidly under TH-UWB channel model, the bit error ratio performance is better than of the traditional MUD.

A joint timing synchronization, channel estimation, and SFD detection for IR-UWB systems

This paper proposes a joint timing synchronization, channel estimation, and data detection for the impulse radio ultrawideband systems. The proposed timing synchronizer consists of coarse and fine timing estimation. The synchronizer discovers synchronization points in two stages and performs adaptive threshold based on the maximum pulse averaging and maximum (MAX-PA) method for more precise synchronization. Then, iterative channel estimation is performed based on the discovered synchronization points, and data are detected using the selective rake (S-RAKE) detector employing maximal ratio combining. The proposed synchronizer produces two signals-the start signal for channel estimation and the start signal for start frame delimiter (SFD) detection that detects the packet synchronization signal. With the proposed synchronization, channel estimation, and SFD detection, an S-RAKE receiver with binary pulse position modulation binary phase-shift keying modulation was constructed. In addition, an IEEE 802.15.4a channel model was used for performance comparison. The comparison results show that the constructed receiver yields high performance close to perfect synchronization.

Performance Evaluation of Space-Time and Harq Diversity in MIMO HSDPA

Multi-antenna techniques can be used to achieve improved system performance, including improved system capacity (more users per cell) and improved coverage (possibility for larger cells), as well as improved service provisioning, for example, higher per-user data rates. This study provides an overview of space-time diversity technique using Alamouti codes applied to the 3G evolution. The delays introduced by HARQ retransmission decrease the performance of the HSDPA system. Multi-antenna techniques are specifically applied to HSDPA to avoid HARQ retransmissions. The authors demonstrate that space-time Rake detector in MIMO 2x2 based on Alamouti code without HARQ process could give better performances than MIMO 2x1 taking into account the HARQ context. In the case of MIMO 2x2,they also observed that the limit of retransmissions affects the system performance and efficiency. Using the generalized Alamouti coding technique in MIMO 4x4 with Multipath Parallel Interference Canceller (MPIC) detector, we achieve notable improvement of performance under the same channel and signal to-Noise Ratio (SNR) conditions.

A Turbo Decoder Included in a Multi-User Detector: A Solution to be Retained

This paper deals with the presentation of different multi-user detectors in the Universal Mobile Telecommunications System (UMTS) context. The challenge is always to optimize the compromise between performance and complexity. Compared with the solution commonly used today, the rake detector, successive interference cancellation (SIC) detector has better performance despite its higher complexity. Our innovative solution proposes joining detector and channel turbo decoder to get a significant gain in terms of performance. Furthermore, when detection and decoding are implemented in a single function, complexity does not increase much.

New-User Detection in Time Hopping Multi-User Environment for UWB Impulse Radio Systems

This paper addresses the problem of detecting a new user in time-hopping multiple access communication environment targeted for ultra wideband impulse radio (IR) systems. The proposed detector is based on exploiting the orthogonality between the new user and the other active user(s) in frequency domain. This is because the time-domain orthogonality is destroyed due to the long delay spread of a dense multipath channel experienced by IR transmission. This results in the presence of inter-frame, inter-path as well as inter-symbol interferences. To ensure the frequency-domain orthogonality, we propose a TH code design as a means of encoding a unique spectrum that is orthogonal to each user. Simulation results highlight the note-worthy improvement in frequency-domain detection performance that utilizes our proposed design algorithm. This gain is obtained without any significant increase in computational complexity or hardware costs. Unlike the rake detector, the frequency-domain detector does not require the time-of-arrival information of the multipath components.

Multiuser Detection In Dualrate DS-CDMA Systems Using ICA

This article proposes an ICA-based blind multiuser detection technique to detect the signal of the desired user in a dual rate DS-CDMA system. In the present competitive scenario, communication is the most important tool in business and it has become a necessity to remain connected. Depending on the nature of data and quality of service requirements, users transmit signals at different rates. DS-CDMA systems provide straightforward implementation of multi rate signals and have been proposed as a promising system to support multi rate signals. It is desired to have spectrum efficient detection techniques for multi rate DS-CDMA systems. Keeping this requirement in mind, an ICA-based detection technique has been proposed for dual rate DS-CDMA systems. The BER performance of the proposed detection technique has been compared with the conventional matched filter and rake detector. The simulation results illustrate the effectiveness of the proposed approach.

Quasi-orthogonal chaotic CDMA multi-user detection using optimal chaos synchronization

In this paper, a novel optimal chaos synchronization (CS)-based method is proposed to realize multi-user detection of quasi-orthogonal chaotic code-division multiple access (CDMA) system. Theoretical analysis and computer simulations show that the multi-user quasi-orthogonal chaotic signal used in the CDMA system can be detected successfully by using the optimal CS. . Computer simulations show that the proposed method achieves a lower bit-error-rate performance than the conventional decorrelating detector and the minimum mean-square-error detector, and its performance is closer to that of the single-user Rake detector.

Turbo multiuser detection for turbo-coded CDMA in multipath fading channels

Multiuser detection and turbo coding are two of the most powerful techniques for enhancing the performance of next-generation wide-band code-division multiple-access (CDMA) systems. We develop an iterative multiuser receiver for turbo-coded CDMA systems with aperiodic spreading sequences operating in multipath fading, which exploits the power of both techniques. The key innovation in the proposed receiver is a low-complexity soft multiuser detector which uses the same decision statistic as the conventional RAKE receiver (i.e., the outputs of the maximum ratio combiners for all the users), and performs soft-interference cancellation and instantaneous minimum mean-square error (MMSE) filtering. The soft multiuser detector has a complexity of O(K/sup 2/) per bit per iteration, where K is the number of users. A single-user receiver which employs a soft RAKE detector followed by a turbo decoder is also considered. Simulation results demonstrate that the proposed multiuser receiver offers more than 0.5-dB gain over the single-user RAKE receiver at a bit-error rate (BER) of 10/sup -3/ and even outperforms the single-user RAKE receiver operating in a single-user environment.

Advanced ICA-based receivers for block fading DS-CDMA channels

In this paper we propose two types of receivers, which perform blind interference suppression. The receivers are suitable for the third generation mobile communications systems, which are based on direct-sequence code division multiple access (DS-CDMA). We especially consider the statistical technique called independent component analysis (ICA) as a tuning element attached to an existing single-user or blind multiuser detector. By doing this, the statistical independence of the users’ signals can be exploited. In addition, it makes it possible to alleviate the performance drop due to the erroneous parameters estimation in the receiver. From the ICA point of view, the receiver observes a mixture of users’ original signals, determined by the user-specific spreading codes, the data symbols, and the state of the propagation channel. Since all of them might be complex valued by nature, complex ICA is needed. In the paper, a proof of global convergence is given for the kurtosis-based FastICA algorithm in the case of complex valued source signals with circular distribution, and considered as the ICA component of the advanced receivers. Two types of receivers, RAKE-ICA and MMSE-ICA, are proposed and studied in a Rayleigh block fading channel. Extensive numerical simulations indicate that the performance of RAKE and subspace MMSE detector, respectively, can be greatly improved. Quite significantly, their performance is close to the theoretical bound of an equal length MMSE detector.