In this paper, the bit error rate (BER) and the outage probability are presented for a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver operating in a correlated frequency-selective Nakagami-m fading environment with multiple access interference. A simple approximated probability distribution function of the signal-to-interference-plus-noise ratio (SINR) is derived for the receiver with multiple correlated antennas and RAKE branches in arbitrary fading environments. The combined effects of spatial and temporal diversity order, average received signal-to-noise ratio, the number of multiple access interference, angular spread, antennae spacing and multi-path Nakagami-m fading environment on the system performance are illustrated. Numerical results indicate that the performance of the 2D-RAKE receiver depends highly on the operating environment and antenna array configuration. The performance can be improved by increasing the spatio-temporal diversity gains and antenna spacing.

In this paper, Pre-Rake scheme for pulse based Ultra Wideband impulse radio (UWB-IR) communications system is proposed considering a standardized UWB channel model from IEEE 802.15 SG3a, which is based on an extensive set of short-range indoor channel measurements. Two kinds of pulse waveforms are taken in account here, namely, Gaussian mono-pulse and newly designed Prolate Spheroidal Wave Functions (PSWF) pulses corresponding to FCC Spectrum Mask. The Pre-Rake scheme is shown to contribute to the low-power, cost-efficient UWB system designing as well as Rake combining gain. Instead of building a Rake receiver at the receiving side (e.g. portable unit), the transmitter (e.g. access point) can pre-combine the UWB signal before transmission in the forward link by estimating the channel impulse response from the reverse link. While the Pre-Raked signal is convolved with the estimated channel impulse response, the function of Rake combination at the receiver is automatically performed. Meanwhile, in order to defeat inter-pulse-interferences (IPI) caused by severe multipath fading conditions, adaptive guard-time scheme for consecutive pulses is proposed as well. Monte-Carlo simulations are carried out to compare the Pre-Rake with Rake results and show that Pre-Rake scheme is as good as Rake combining for both types of pulse waveforms. Then the mobile or portable unit with a conventional receiver can still achieve the diversity gain of Rake combination. Moreover, the effects of placing guard-time between pulses are also verified.

Performance of selective Rake (SRake) receiver is evaluated for direct sequence ultra wideband (DS-UWB) communications considering an independent Rayleigh channel having exponentially decaying power delay profile (PDP). BEP performances are shown. The results obtained are compared with similar results in a channel having flat PDP. Assumption of a flat PDP is found to predict the optimum spreading bandwidth to be lower and sub-optimum operating performance beyond optimum spreading bandwidth to be severely worse than that is achievable in a channel having exponentially decaying PDP by employing an SRake receiver having fixed number of combined paths. Optimum spreading bandwidth for SRake in a channel having exponentially decaying PDP is shown to be much larger than the one in a channel having flat PDP; that is specifically a good-news for UWB communications. Effects of partial band interference are also investigated. Interference is found to be less effective in exponentially decaying PDP.

In this paper, we study DS-CDMA delay transmit diversity that transmits the weighted and time-delayed versions of the same signal from multiple antennas in a frequency non-selective fading environment. At a receiver, one receive antenna is used and the received delayed signals are coherently combined by Rake receiver. The set of optimum antenna weights for maximizing the received signal-to-noise power ratio (SNR) is theoretically derived to reveal that the optimum solution is to transmit only from the best antenna that has the maximum channel gain. The bit error rate (BER) performance improvement over conventional delay transmit diversity is theoretically analyzed and confirmed by computer simulations. The combined effect of transmit diversity and transmit power control (TPC) is also evaluated. Furthermore, the impact of fading decorrelation between the transmit and receive channels is also investigated for both the time division duplex (TDD) and frequency division duplex (FDD) schemes.

The new frequency bands that will be allocated to W-CDMA cellular networks might open the possibility to use higher bandwidths than the 5 MHz specified in 3GPP. In this paper the temporal channel properties, i.e., power delay profile, in terms of number of Rake receiver fingers and their characteristics, are analyzed for 5, 10, 20, and 30 MHz bandwidths. The lower bandwidth impulse responses are obtained by filtering measurement results obtained with a channel sounder having a bandwidth of 30 MHz.

Frequency-domain representation of the well-known time-domain rake combining for the antenna diversity reception of DS-CDMA signals is derived. Two receiver structures using frequency-domain rake combining are presented. Frequency-domain rake combining can alleviate the complexity problem of the time-domain rake arising from too many paths in a severe frequency selective fading channel at the cost of guard interval insertion. The results shown in this paper show a possibility that a DS-CDMA approach still remain to be promising for broadband wireless access technique.

In this paper, we study a delay transmit diversity system combined with antenna diversity reception that transmits the time-delayed and weighted versions of the same signal from multiple antennas. At a receiver, multiple receive antennas are used and all delayed signals received on multiple antennas are coherently combined by a Rake receiver. The set of optimum antenna weights for maximizing the received signal-to-noise power ratio (SNR) after Rake combining is theoretically analyzed to show that the optimum solution is to transmit only from the best antenna that has the maximum equivalent channel gain seen after Rake combining. The bit error rate (BER) performance is theoretically analyzed and evaluated by computer simulation. The combined effect of transmit diversity and transmit power control (TPC) is also investigated.

Without transmit power control (TPC) and Rake combining, the uplink capacity of a direct sequence code division multiple access (DS-CDMA) packet mobile communication system significantly degrades due to the near-far problem and multipath fading. In this letter, assuming a single cell system with an interference-limited channel, the impact of the joint use of Rake combining and TPC on the uplink capacity is evaluated by computer simulation. Slow TPC is found to give a link capacity larger than fast TPC. This is because, with slow TPC, the received signal power variations due to fading remain intact and this results in a larger capture effect.

This paper proposes an ROF ubiquitous antenna architecture for the wireless CDMA system. The proposed system separates each component of independent signals passing through the multipath in radio and optical links, which are gathered at passive double star link, by using RAKE reception and the macrodiversity effect is obtained. Theoretical analysis shows that the proposed system improves BER performance by 22 dB and reduces the transmission power and its control range by 19 dB.

In this paper, we propose a new transmitter diversity. We propose a combined system with path diversity gain of the distributed antennas and frequency diversity gain of the multi-carrier. The proposed system transmits different data using several sub-carriers which are correlated, while, transmitting the same data using several sub-carriers which are decorrelated. It can achieve combined path and frequency diversity in a variable frequency selective fading channel. It provides high data rate services by transmitting the different data using each correlated carrier, and supports good quality by transmitting the same data on decorrelated carriers using multiple antennas. The proposed system is applicable to multimedia service and can achieve high quality according to channel condition. Thus, the proposed system is sufficiently flexible enough to very support a variety of video, image, voice and data services at a high level of quality.

We describe a DS-CDMA adaptive modulation system in which high-rate-data for moving pictures and LANs is transmitted to a high-speed traveling mobile terminal in the down-link. The transmission data rate is constant by changing the data-modulation level and the number of multiplex channels. We use computer simulation to evaluate the performance of the system using a RAKE receiver in a multipath-channel environment. For fdTslot 0.08, which is fading maximum Doppler frequency fd normalized by slot time Tslot, the following results are obtained. The average bit error rate (BER) of BER 1 10-3 necessary to ensure quality of high-rate-data transmission for moving pictures and LANs without error correction is attainable at low symbol-to-noise power ratio of ES/N0 14 dB and channel-use rate lower than 65%. The cell capacity of 17.2% is about 1.4 times that of the conventional system. Also, fdTslot=0.08 corresponds to the traveling speed of about 250 km/h at a carrier frequency of 8 GHz. Thus, the system enables high-rate-data and high-quality transmission needed for the moving pictures and LANs at mobile terminals with a traveling speed higher than 100 km/h at high carrier frequencies of the microwave band.

In this paper, the closed-form expressions of signal-to-interference-plus-noise ratio (SINR) and the outage probability are derived for a maximal ratio combining (MRC) two-dimensional (2-D)-RAKE receiver with imperfect power control in a frequency-selective Nakagami fading channel. The impact of power control error (PCE) on the performance of the receiver is analyzed for all kinds of fading environments. The results of numerical derivation and simulation indicate that the performance of 2-D-RAKE receivers degrades due to imperfect power control. But when PCE is not serious, increasing the number of antennae and temporal diversity order can compensate for the performance loss. The exact performance improvement due to space-time processing varies with the PCE and the fading environment.

This paper presents architecture design, FPGA implementation, and measurement results of a real-time signal processing circuit for WCDMA uplink baseband receiver. To enhance uplink signal-to-interference-plus-noise ratio (SINR) performance, a four-element antenna array and a four-finger Rake combiner are integrated in the proposed receiver. Moreover, a low-complexity beamforming architecture using a correlator-based beam searcher, a decision-directed carrier synchronization loop, and a matched-filter based channel estimator is also designed. Simulations are based on the standard Doppler-fading scalar channel models provided by 3GPP and an extension to vector channel models that specify angle of arrival for each path is also made for beamformer simulation. Simulation and hardware emulation results show that the proposed architecture meets the specified requirements. In addition, this architecture, with its correlator-based beamformer weights, achieves such performance improvement with relatively low hardware complexity.

It is well known that some of urban man-made noises can be characterized by a wideband impulsive noise (pure impulsive noise). The presence of this pure impulsive noise may significantly degrade the wireless digital transmission performance. As the data rate becomes higher and the radio bandwidth becomes wider, the performance degradation due to pure impulsive interference may become larger. In this paper, the DS-CDMA transmission performance in the presence of pure impulsive interference is theoretically analyzed. First, the BER expressions are derived for DS-CDMA with antenna diversity and Rake combining in a frequency selective fading channel. Then, the numerical computation based on Monte-Carlo method is performed to evaluate the BER performance. Two types of error floor are observed: one is due to impulsive interference and the other due to the multi access interference (MAI). It is found that the error floor due to impulsive interference becomes larger as the area of impulse and the error floor is linearly proportional to the impulse occurrence rate. Furthermore, it is found that the antenna diversity and Rake combining do not help to reduce the error floor caused by impulsive interference and that the influence of impulsive interference can be negligible when the channel is limited by the MAI (i.e., large number of users are in communication).

The pre-Rake system is known as a technique in TDD DS/CDMA system to reduce the mobile complexity and achieve the same BER performance like Rake receiver. The pre-Rake system itself is not optimum, since the channel impulse responses of uplink and downlink are slightly different in TDD system, so the signal- to-noise ratio (SNR) can be maximized with a matched filter based Rake receiver, which has not been considered in the conventional pre-Rake system. Furthermore pre-Rake system is sensitive to the Doppler frequency. Even though the pre-Rake system has the ability to suppress other user interference, it is not efficient to maximize the received signal in high Doppler frequency. However, Rake combiner is utilized for the detection method in our proposed system. So the maximized signal can keep the orthogonality better than the pre-Rake system and our proposed system can compensate the Doppler frequency effect. From these reasons, our system achieves better BER performance than that of the pre-Rake system with increasing the number of users in high Doppler frequency.

A unified view of RAKE reception is proposed which models a RAKE receiver as an antenna array. This unified view provides valuable insight to the signal environment under RAKE reception. Based on this view, an optimum combining scheme for RAKE receivers is proposed for the downlink of multi-code W-CDMA systems. In multi-code scenarios, the presence of inter-code interference causes severe performance degradation. The antenna array model suggests that enhancement can be achieved by increasing the receiver's degrees of freedom which is defined as the number of RAKE fingers and employs an appropriate combining scheme. The conventional maximum-ratio combining scheme is excluded since it is not capable of exploiting the increased degrees of freedom. In contrast, the proposed combining scheme provides better interference suppression when the degrees of freedom are increased. Numerical results obtained show that the proposed scheme provides very promising performance.

A DS-CDMA mobile communication system accommodating multi-class users is considered. The number of supportable users depends on the distributions of data rate and required communication quality among users. Simple expressions for the reverse link capacity with transmit power control, antenna diversity, and rake combining, are derived for a single-cell system and a multi-cell system.

A space-time (ST) receiver is proposed for multiple access interference (MAI) and narrowband interference (NBI) suppression, and multipath diversity reception in wireless multi-carrier CDMA communications incorporating antenna arrays. The scheme involves three stages. First, an adaptive matched filter is attached to each finger at each antenna to combat the MAI. Second, an adaptive beamformer is constructed for each finger which provides effective reception of the signal of interest (SOI) and suppression of time-varying NBI. Finally, beamformer output data from different fingers are combined to capture the signal multipath components coherently. The proposed ST receiver is shown to perform reliably under strong interference, and outperform the ST MMSE receiver with pilot symbols aided channel estimation.

We propose a new receiver structure to mitigate interpath interference (IPI) in W-CDMA systems. We model IPI in RAKE combining as intersymbol interference (ISI) and use a two-stage receiver structure. The first stage is a RAKE receiver and the second stage is an equalizer. In cases of multi-code transmission, interference among code channels causes extra impairments which can not be modelled as ISI. Under these circumstances, they are estimated by using decisions from the first stage and then subtracted from the input of the equalizer. The residual interference is equivalent to ISI and can be mitigated by the equalizer. Simulation results show that the proposed receiver provides very promising performance in low spreading factor W-CDMA.

The frequency- and time-domain expressions are derived for the signal-to-noise power ratio (SNR) of an ideal Rake combiner output in a direct sequence spread spectrum (DS-SS) mobile communication system. The derived SNR expressions make it possible to estimate the SNR statistics after Rake combining for an arbitrary spreading chip rate in the frequency-selective multipath channel.