An implementation of nonlinear multiuser detection in Rayleigh fading channel

A blind nonlinear interference cancellation receiver for code-division multiple-access- (CDMA-) based communication systems operating over Rayleigh flat-fading channels is proposed. The receiver which assumes knowledge of the signature waveforms of all the users is implemented in an asynchronous CDMA environment. Unlike the conventional MMSE receiver, the proposed blind ICA multiuser detector is shown to be robust without training sequences and with only knowledge of the signature waveforms. It has achieved nearly the same performance of the conventional training-based MMSE receiver. Several comparisons and experiments are performed based on examining BER performance in AWGN and Rayleigh fading in order to verify the validity of the proposed blind ICA multiuser detector.

Implementing ICA in blind multiuser detection

This paper introduces a blind multiuser detection algorithm for MIMO channels. The receiver is required to separate and recover the information signal of the desired user(s) based on independent component analysis (ICA) of the received sequence. The received sequence is assumed to be independent identically distributed. Experimental results show that the proposed blind ICA multiuser detection works well with a short symbol sequence, even if the channel time span is not accurately estimated. It is concluded that the proposed blind multiuser detection performs better than the conventional matched filters in a noisy environment.

Performance comparisons between greedy and lagrange algorithms in adaptive MIMO MC-CDMA systems

This paper describes two algorithms for adaptive power and bit allocations in a multiple input multiple output multiple-carrier code division multiple access (MIMO MC-CDMA) system. The first is the greedy algorithm, which has already been presented in the literature. The other one, which is proposed by the authors, is based on the use of the Lagrange multiplier method. The performances of the two algorithms are compared via Monte Carlo simulations. At present stage, the simulations are restricted to a single user MIMO MC-CDMA system, which is equivalent to a MIMO OFDM system. It is assumed that the system operates in a frequency selective fading environment. The transmitter has a partial knowledge of the channel whose properties are measured at the receiver. The use of the two algorithms results in similar system performances. The advantage of the Lagrange algorithm is that is much faster than the greedy algorithm. ©2005 IEEE

Hop selection in peer-to-peer WPAN networks

Currently, wireless technology is revolutionizing the way we share information and communicate. The demands for mobility have made wireless technology the primary source for voice communication. Code-division multiple-access (CDMA) is a very popular spread spectrum application due to its claims of low transmission power, higher system capacity, ability to mitigate multipath fading and user interference. In that case, frequency-hopping code-division multiple access (FH-CDMA) has received considerable attention over the past few years. This technique will allow a better performance over a fading channel, message privacy, and immunity to narrowband interference. This paper addresses the characteristics of FH-CDMA in WPAN networks, with an emphasis on frequency-hopped Bluetooth systems. A performance evaluation of FH-CDMA is discussed and simulated. The analysis shows the interaction between the designed parameters and their effect on the network system. Most specifically, the FH-CDMA scheme provides frequency and temporal diversity to combat the effects of interference.

Effect of mutual coupling on the interference rejection capabilities of linear and circular arrays in CDMA systems

This paper is concerned with assessing the interference rejection capabilities of linear and circular array of dipoles that can be part of a base station of a code-division multiple-access cellular communication system. The performance criteria for signal-to-interference ratio (SIR) improvement employed in this paper is the spatial interference suppression coefficient. We first derive an expression for this figure of merit and then analyze and compare the SIR performance of the two types of arrays. For a linear array, we quantitatively assess the degradation in SIR performance, as we move from array broadside to array end-fire direction. In addition, the effect of mutual coupling is taken into account.

Assessment of arginine 97 and lysine 72 as determinants of substrate specificity in cytochrome P450 2C9 (CYP2C9)

CYP2C9 is distinguished by a preference for substrates bearing a negative charge at physiological pH. Previous studies have suggested that CYP2C9 residues R97 and K72 may play roles in determining preference for anionic substrates by interaction at the active site or in the access channel. The aim of the present study was to assess the role of these two residues in determining substrate selectivity. R97 and K72 were substituted with negative, uncharged polar and hydrophobic residues using a degenerate polymerase chain reaction-directed strategy. Wild-type and mutant enzymes were expressed in bicistronic format with human cytochrome P450 reductase in Escherichia coli. Mutation of R97 led to a loss of holoenzyme expression for R97A, R97V, R97L, R97T, and R97E mutants. Low levels of hemoprotein were detected for R97Q, R97K, R97I, and R97P mutants. Significant apoenzyme was observed, suggesting that heme insertion or protein stability was compromised in R97 mutants. These observations are consistent with a structural role for R97 in addition to any role in substrate binding. By contrast, all K72 mutants examined (K72E, K72Q, K72V, and K72L) could be expressed as hemoprotein at levels comparable to wild-type. Type I binding spectra were obtained with wildtype and K72 mutants using diclofenac and ibuprofen. Mutation of K72 had little or no effect on the interaction with these substrates, arguing against a critical role in determining substrate specificity. Thus, neither residue appears to play a role in determining substrate specificity, but a structural role for R97 can be proposed consistent with recently published crystallographic data for CYP2C9 and CYP2C5.

Analysis of the error performance of adaptive array antennas for CDMA with noncoherent M-ary orthogonal modulation in Nakagami fading

This letter presents an analytical model for evaluating the Bit Error Rate (BER) of a Direct Sequence Code Division Multiple Access (DS-CDMA) system, with M-ary orthogonal modulation and noncoherent detection, employing an array antenna operating in a Nakagami fading environment. An expression of the Signal to Interference plus Noise Ratio (SINR) at the output of the receiver is derived, which allows the BER to be evaluated using a closed form expression. The analytical model is validated by comparing the obtained results with simulation results.

Blind multiuser receiver for DS-CDMA wireless system

We consider blind signal detection in an asynchronous code-division multiple-access (CDMA) system employing short spreading sequences in the presence of unknown multipath fading. This approach is capable of countering the presence of multiple-access interference (MAI) in CDMA fading channels. The proposed blind multiuser detector is based on an independent component analysis (ICA) to mitigate both MAI and noise. This algorithm has been utilised in blind source separation (BSS) of unknown sources from their mixtures. It can also be used for estimating the basis vectors of BSS. The aim is to include an ICA algorithm within a wireless receiver in order to reduce the level of interference in wideband systems. This blind multiuser detector requires no training sequence compared with the conventional multiuser detection receiver. The proposed ICA blind multiuser detector is made robust with respect to knowledge of signature waveforms and the timing of the user of interest. Several experiments are performed in order to verify the validity of the proposed ICA algorithm.

Novel ultra-wideband pulse spectrum modulation scheme

Current ultra-wideband communication systems use short narrow timed pulse sequences to transmit information. Some disadvantages of UWB communication systems are its interference of other conventional wireless systems and its reliance on time hopping schemes for multiple access. This paper presents a novel UWB data modulation scheme based on pulse shaping. This modulation scheme adds more flexibility for data modulation in UWB communication systems. The modulation scheme encodes data in both the timing and frequency spectrum of the transmitted pulse. This has the potential to improve data throughput rates and to lower interference between UWB and narrowband systems.

CIC-5: A chloride channel with multiple roles in renal tubular albumin uptake

CIC-5 is a chloride (Cl-) channel expressed in renal tubules and is critical for normal tubular function. Loss of function nonsense or missense mutations in CIC-5 are associated with Dent's disease, a condition in which patients present with low molecular weight (LMW) proteinuria (including albuminuria), hypercalciuria and nephrolithiasis. Several key studies in CIC-5 knockout mice have shown that the proteinuria results from defective tubular reabsorption of proteins. CIC-5 is typically regarded as an intracellular Cl- channel and thus the defect in this receptor-mediated uptake pathway was initially attributed to the failure of the early endosomes to acidify correctly. CIC-5 was postulated to play a key role in transporting the Cl- ions required to compensate for the movement of H+ during endosomal acidification. However, more recent studies suggest additional roles for CIC-5 in the endocytosis of albumin. CIC-5 is now known to be expressed at low levels at the cell surface and appears to be a key component in the assembly of the macromolecular complex involved in protein endocytosis. Furthermore, mutations in CIC-5 affect the trafficking of v-H+-ATPase and result in decreased expression of the albumin receptor megalin/cubulin. Thus, the expression of CIC-5 at the cell surface as well as its presence in endosomes appears to be essential for normal protein uptake by the renal proximal tubule. (c) 2005 Elsevier Ltd. All rights reserved.