Performance Of RAKE Receiver Research Articles

Channel Estimation for DS-CDMA Rake Receiver using Sparse Recovery Approach

In the literature of direct-sequence code-division multiple-access (DS-CDMA), for issues related to channel estimation, some exclusive architectures have been proposed, which are characterized by known channel noise statistics and noise observation. But in reality, the channel parameters are frequently assessed utilizing training sequences that lead to difficulty in obtaining the channel noise statistics. Channel estimation quality has been proved to play an important role in the performance of rake receiver. This paper addresses the issues of optimizing DS–CDMA rake receiver channel estimation equipped with an Iterative least square sparse recovery (IL2SR) channel estimator. Moreover, the ambient noises corrupt the signal received and multiple-access interference further aggravates it. Because of this observation noises become hard to acquire. Hence this paper proposes as an iterative least square structure for channel estimation algorithm in rake receiver employed in DS-CDMA communication systems. Further, examination of blind channel estimation problem for rake-based DS-CDMA communication framework having multi-path fading channels with time variation is also attempted. The validity of the proposed techniques has been verified through results obtained from simulation for different channel parameters and spreading codes. Further exploration has been carried out with execution of the IL2SR with Rake receiver in DS-CDMA framework for multi-path fading channels. It is found that better performance is obtained with this framework under various channels with different spreading codes. The proposed system is compared with Kalman based techniques and it was found that DS-CDMA framework under additive white gaussian noise (AWGN)channel with IL2SR receiver reveals better outcomes in terms of bit error rate (BER). Also, there has been improvement in video quality while using the proposed IL2SR receiver with increase in the values of ratio of signal to noise ratio.

A Bayesian Approach to Adaptive RAKE Receiver

The RAKE receivers are widely used in code division multiple access communication systems to achieve anti-multipath fading. However, a traditional RAKE receiver requires pilot data stream inserted into the sequence, which occupies channel resources and limits its applications. In this paper, a new adaptive RAKE receiver based on Bayesian theory is reported that only uses received signals to estimate its channel parameters. Observed data are used to obtain the information of the channel impulse response. Next, the prior information is used. In the iterative process, a priori information is accumulated to improve the receiver performance. Thus, the mean and covariance of the channel impulse response that is modeled as a complex and uncertain Gaussian random vector are recursively estimated using Bayesian theory. Finally, the RAKE weights are obtained using the mean and covariance. As shown in the simulation results, the bit error rate (BER) decreases as the number of fingers increases. The performance of the new RAKE receiver has been greatly improved compared with the all-RAKE receiver with maximal ratio combining, RAKE receiver with singular value decomposition, and RAKE receiver with fast approximated power iteration. Under medium to high SNR conditions (i.e., ≥−5 dB), the BER performance of the new RAKE receiver provides at least $3\times 10^{-4}$ less than that of the other receiver tested.

Impact of Self-Interference on the Performance of Joint Partial RAKE Receiver and Adaptive Modulation

In this paper, we investigate the impact of self-interference on the performance of a joint partial RAKE (PRAKE) receiver and adaptive modulation over both independent and identically distributed and independent but non-identically distributed Rayleigh fading channels. To better observe the impact of self-interference, our approach starts from considering the signal to interference plus noise ratio. Specifically, we accurately analyze the outage probability, the average spectral efficiency, and the average bit error rate as performance measures in the presence of self-interference. Several numerical and simulation results are selected to present the performance of the joint PRAKE receiver and adaptive modulation subject to self-interference.

The Simulation of DS-UWB RAKE Receiver over the Multipath Channel

Ultra-Wideband (UWB) wireless communication is a new potential communication technology currently in its field. It becomes very popular in the world since it’s high performance, low radicalization and low cost. Currently UWB wireless system, we can call it Impulse Radio technology too, be invented in 20 century 1960s. But it was only used in military affairs field, bailout searching, radar location and so on. After civil using, it usually is used in indoor wireless LAN .In this paper, the development and application of UWB are introduced, the characteristic and limitation of UWB are simply analyzed. According to the simulating depending on Multipath channel, it shows increasing SNR about 1.5dB to the base of primary power district or increasing SNR about 1dB to primary power district and minor power district, we can get whole performance of RAKE receiver in perfect channel.

A NEW PARALLEL INTERFERENCE CANCELLATION ALGORITHM FOR RAKE SYSTEMS

In order to suppres the multi-path interference (MPI) in the DS CDMA system, a new RAKE receiver based on parallel interference elimination is first proposed in this paper data symbol tentative decision is obtained by linear decision; the multi-path interference are evaluated by tentative decision and known user information. Then the performance over Rayleigh fading channel are analyzed and compared to conventional parallel interference cancellation (PIC) and RAKE receiver. It is shown that RAKE receiver performance can be improved greatly by using this method with simple structure and easy implementation.

Joint Statistics of Partial Sums of Ordered Exponential Variates and Performance of GSC RAKE Receivers over Rayleigh Fading Channel

Spread spectrum receivers with generalized selection combining (GSC) RAKE reception were proposed and have been studied as alternatives to the classical two fundamental schemes: maximal ratio combining and selection combining because the number of diversity paths increases with the transmission bandwidth. Previous work on performance analyses of GSC RAKE receivers based on the signal to noise ratio focused on the development of methodologies to derive exact closed-form expressions for various performance measures. However, some open problems related to the performance evaluation of GSC RAKE receivers still remain to be solved such as the exact performance analysis of the capture probability and an exact assessment of the impact of self-interference on GSC RAKE receivers. The major difficulty in these problems is to derive some joint statistics of ordered exponential variates. With this motivation in mind, we capitalize in this paper on some new order statistics results to derive exact closed-form expressions for the capture probability and outage probability of GSC RAKE receivers subject to self-interference over independent and identically distributed Rayleigh fading channels, and compare it to that of partial RAKE receivers.

Performance Evaluation of Binary Modulations through Wireless Body Area Network Channel

The error rate link performance has been evaluated and compared for efficient Rake receiver structures in low data rate WBAN (Wireless Body Area Network) channel. Rayleigh and Weibull distributions have been used for generating fading power profiles. This model is based on extensive measurements inside or on the surface of human body. The power profiles for WBAN channel have been generated. The bit error rate has been obtained by using different modulation schemes i.e. BPSK (Binary Phase Shift Keying), 2-PAM (Pulse Amplitude Modulation) and 2-BOK (Bi-orthogonal Keying). With the aid of these graphs, bit error rate performance evaluation of Rake receivers has been done. Through simulative investigations of Bit Error Rate (BER), it has been found from these three binary modulations; 2-PAM is suitable for WBAN channel. It has been observed that the performance of selective rake receiver (for optimum number of fingers) is better than partial rake receiver for all modulation schemes. General Terms WBAN channel Model, BPSK, 802.15.6.

Suboptimal Rake Finger Allocation: Performance and Complexity Tradeoffs

Suboptimal Rake Finger Allocation: Performance and Complexity TradeoffsOptimal finger placement improves significantly the performance of RAKE receivers. However, due to its high complexity, it is rarely applied in mobile systems with large channel spread. In this paper, we evaluate the merits of suboptimal finger allocation in terms of performance and complexity. A subset of the RAKE fingers is optimally positioned based on the received signal correlation properties while the rest of them are uniformly distributed within the channel spread. The tradeoffs between performance and complexity of the method are discussed. Results show that optimizing half finger positions lead to similar performance with the full optimization scheme. Finally, comparisons with conventional and optimal receivers exhibit the advantages of the method.

Performance Comparison of RAKE Receivers in SC-UWB Systems and DS-UWB Systems

RAKE receivers are generally employed to collect multipath energy in single-carrier ultra-wideband (SC-UWB) systems and direct-sequence ultra-wideband (DS-UWB) systems. Performance of RAKE receivers in these two kinds of systems is studied and compared with each other in this letter. Both theoretical analysis and simulation results over IEEE 802.15.3a UWB channels are presented. Our results show that, with the same signal to noise ratio (SNR) per bit, the same occupied bandwidth and the same number of RAKE fingers, RAKE receivers with maximum ratio combination (MRC) in SC-UWB systems can achieve exactly the same performance as that in DS-UWB systems.

MRC in the Presence of Asynchronous Cochannel Interference Over Frequency-Selective Rayleigh Fading Channels

This paper studies the performance of Rake receivers with maximal ratio combining (MRC) in the presence of cochannel interference over slowly varying frequency-selective fading channels with combined spatial receive antenna diversity and temporal multipath diversity. Two models for the instantaneous powers of the residual multipath components and the resolved cochannel interfering signals, which represent the overall interfering signals, are employed. The first model considers the phase asynchronism between the desired signal replicas and interfering signals, whereas the second model assumes that the instantaneous powers of interfering signals incoherently add up. The desired signal replicas and interfering signals are assumed to experience statistically independent Rayleigh fading processes with arbitrary statistics. For the system model previously described, new closed-form expressions for the probability density function (pdf) of the combined signal-to-interference-plus-noise ratio (SINR) are derived. These expressions are then used to obtain formulas for various performance measures. The case study under consideration and the corresponding derived expressions for the statistical measures generalize many previous results and can usefully be employed to investigate the impact of various system and channel parameters on the performance of Rake receivers with MRC in the presence of cochannel interference.

Cyclic Prefix Signaling for Pulse Shape Modulation UWB RAKE Receivers

Combining transmission of ultra wideband pulses, organized in blocks, with the inclusion of cyclic prefixing pulses yields a pulsewidth periodic signal at the receiver. Although unknown, this signal fits perfectly the diversity exploitive architecture of a RAKE receiver. Aiming to profit from this signal arrangement, we propose a pulse shape modulation system employing a RAKE receiver that estimates this periodic signal during a training interval and uses the estimated values for detection of data symbols. Our proposal relies on the invariability of the multipath propagation channel during the transmission of a UWB packet, the adequate application of the cyclic prefix, and the fact that different transmitted pulses result in different periodic signals at the receiver. This system is equivalent to transforming the multipath nature of the UWB propagation channel into a multichannel digital communications affected solely by additive noise. Our proposal is important because it ameliorates the performance of a pulse shape modulation RAKE receiver. On the other hand, the cost of our proposed system resides in the inefficiencies product of the cyclic prefix inclusion.

Performance of Rake Receivers in IR-UWB Networks Using Energy-Efficient Power Control

This paper studies the performance of partial-Rake (PRake) receivers in impulse-radio ultrawideband wireless networks when an energy-efficient power control scheme is adopted. Due to the large bandwidth of the system, the multipath channel is assumed to be frequency-selective. By making use of noncooperative game-theoretic models and large-system analysis tools, explicit expressions are derived in terms of network parameters to measure the effects of self-interference and multiple-access interference at a receiving access point. Performance of the PRake receivers is thus compared in terms of achieved utilities and loss to that of the all-Rake receiver. Simulation results are provided to validate the analysis.

Cross-Modulation Interference and Mitigation Technique for Ultrawideband PPM Signaling

The detection issues of ultrawideband (UWB) signals depend on the type of modulation scheme that is used during the transmission. Cross-modulation interference (CMI) is a problem that is specific to UWB pulse-position-modulation (PPM) signaling. In this paper, the effects of CMI on the performance of noncoherent UWB receivers are analyzed. The probabilities of error for transmitted-reference (TR) and energy detector (ED) receivers in the presence and absence of CMI are derived. Optimal and suboptimal CMI avoidance algorithms, which are based on novel acquisition techniques, are proposed for Rake receivers. The results show that the performance degradation in both receivers, which is due to the CMI effects, can be significant, depending on the modulation index. TR receivers still can be functional in the presence of CMI, and the target performance level determines the modulation index to be used. It is unlikely that effects of CMI on the performance of ED receivers in the presence of CMI are more severe relative to TR receivers, and the performance level is not acceptable. As a result, PPM signaling is not an appropriate modulation technique for ED receivers that are operating in the CMI region, unless CMI mitigation algorithms can be developed. Furthermore, the proposed optimal and suboptimal algorithms are two promising schemes for avoiding the CMI effects and, consequently, for improving the performance of Rake receivers operating in the CMI region.

Practical Chip-level Equalizers in HSDPA

High-speed downlink packet access (HSDPA) has been developed to upgrade the current WCDMA system in yerms of providing a higher data rate for mobile users. To ensure a downlink speed of up to 14Mbps, the HSDPA system has three main features: adaptive modulation and coding, a hybrid automatic repeat request, and fast scheduling. Because standard documents describe only the specifications of Node B, various kinds of HSDPA receivers cen be used with different architectures. An ordinary receiver generally has a rake architecture, though a rake receiver is not good at reducing multiple access interference (MAI). The performance of rake receiver is indispensably deteriorated when the number of mobile users in the system increases. Conversely, an equalizer can alleviate the MAI significantly at the expense of complexity and can therefore be an alternative solution for a rake receiver in a HSDPA system. In this paper, the performance of several equalizers of a HSDPA system is compared in terms of several implementation issues. The simulation results provide useful information about proper equalizers for different design purposes with respect to the performance and complexity trade-off.

Energy Efficient Power Control in Impulse Radio UWB Wireless Networks

In this paper, a game-theoretic model for studying power control for wireless data networks in frequency-selective multipath environments is analyzed. The uplink of an impulse-radio ultrawideband system is considered. The effects of self-interference and multiple-access interference on the performance of generic Rake receivers are investigated for synchronous systems. Focusing on energy efficiency, a noncooperative game is proposed in which users in the network are allowed to choose their transmit powers to maximize their own utilities, and the Nash equilibrium for the proposed game is derived. It is shown that, due to the frequency selective multipath, the noncooperative solution is achieved at different signal-to-interference-plus-noise ratios, depending on the channel realization and the type of Rake receiver employed. A large-system analysis is performed to derive explicit expressions for the achieved utilities. The Pareto-optimal (cooperative) solution is also discussed and compared with the noncooperative approach.

A Comparative Analysis of Optimum and Suboptimum Rake Receivers in Impulsive UWB Environment

In this paper, the performance of rake receivers in the presence of fading and impulsive noise is addressed. The optimum maximum likelihood (ML) rake receiver for impulsive fading channel is derived, and a suboptimum rake receiver with a reduced complexity is obtained for practical purposes. Numerical results show that the suboptimum rake receiver exhibits almost the same performance as the optimum rake receiver. It is also observed that, as the number of fingers of a rake receiver increases, the performance of the rake receiver designed for impulsive environment improves, while the rake receiver optimized for Gaussian environment experiences performance degradation in an impulsive environment

Effects of Dominant Other-Sector Interference on Dual Rx-Antenna HSDPA Performance

Link level SINR simulation results and network level sector throughput simulation results that quantify the benefit of dual antenna MMSE reception in a macrocellular WCDMA/HSDPA system are provided. Dual antenna RAKE receiver performance serves as baseline reference. Link-level simulation results are accompanied by a novel analytical expression that in flat Rayleigh fading and for uncorrelated rx-antenna branches describes spatial interference suppression mean SINR gain as function of a dominant other-sector interference ratio (DIR). It is shown that the MMSE receiver's spatial interference suppression gain heavily depends on the amount of experienced DIR. The higher the DIR the higher the SINR gain. Nevertheless, seen on network level the SINR gain turns into moderate sector throughput gain, well below 50%. This is due to the fact that high DIR situations are rare in the investigated macrocellular scenario. Moreover, the logarithmic relation between SINR and capacity hinders translation of the full SINR gain into HSDPA sector throughput.

Channel Estimation Method with Improved Performance for the UMTS-TDD Mode

Channel estimation is an essential building block for UTRA-TDD high performance receivers. Once the performance of the channel estimator algorithm proposed by 3GPP is highly dependent on the time spreading between consecutive multi-path components, a Successive Multi-path channel Estimation Technique (SMET) that improves the time resolution is proposed in this paper. A SMET based maximum likelihood approach for vectorial channel estimation, to include the estimation of the direction-of-arrival, is also proposed. This algorithm solves efficiently the complex problem of DOA estimation of multiple users in a multi path propagation environment even when the number of required DOA's exceeds the number of antenna array elements. Another property of the proposed algorithm is its ability to resolve signals from different users arriving from the same direction. This is due to processing in both time and space dimensions. The performance of these algorithms is assessed by resorting to simulations in multi-path environments using the UMTS-TDD specifications, and also by comparing the rms estimation errors against the Cramer-Rao Bound. The effect of imperfect channel estimation on the performance of RAKE and Hard-Decision Parallel Interference Canceller receivers is also analysed. The results show that a good performance can be achieved with SMET, from low to high values of Eb/n0.

Optimal Sampling and Processing of an Impulse Radio Signal Subjected to Narrow Band Interference

In this paper the sampling, quantization and processing of an ultra-wideband (UWB) impulse radio (IR) receiver signal is considered when the propagation link is subjected to additive white Gaussian noise (AWGN) and narrow band interference (NBI) which may be non-Gaussian. The Neyman Pearson log likelihood ratio formulation results in receiver processing that consists of a Generalized Matched Filter (GMF) and linear sampling which exploits the correlation of the NBI noise to effectively suppress it. However, the processing requirements to implement the GMF are prohibitive in the context of an UWB IR. Hence an alternate highly efficient processing scheme based on crude 2 and 3 level quantization with maximum ratio combining (MRC) Rake processing is considered and analyzed. As demonstrated in this paper, the 3 level quantizer is an excellent compromise between receiver performance and computational efficiency and can in some cases exceed the performance of a comparable Rake receiver using linear sampling. This happens in some practical instances when the noise is non-gaussian as will be demonstrated.

Adaptive Chip-Level Channel Estimation for IMT-DS System: DL and UL

In this paper, chip-level adaptive channel estimation has been explored by using LMS algorithm for wideband CDMA channel estimation. The expression for the optimum step-size is modified for fading channel estimation problem. In addition, a new method is proposed to obtain channel estimates with known pilot symbols which is found to give better results than other methods. For slow fading channels, like pedestrian channel, LMS estimator with no update mode is found to give satisfactory results. For fast fading channels, like vehicular channel, a common decision directed technique of channel estimation is modified to be used at chip-level in the downlink (DL). A novel despreader-respreader based channel estimator has been proposed to obtain uplink channel estimates at chip level which resolves the deficiencies of conventional methods. The performance of Rake receiver with proposed channel estimation schemes for IMT-DS system --- a 3G mobile communication standard --- is evaluated in terms of BER.