The problem of information overload in business organisations: a review of the literature

In code-division multiple-access (CDMA) systems transmitting over time-varying multipath channels, both intersymbol interference (ISI) and multiple-access interference (MAI) arise. The conventional suboptimum receiver consisting of a bank of matched filters is often inefficient because interference is treated as noise. The optimum multiuser detector is too complex to be implemented at present. Four suboptimum detection techniques based on zero forcing (ZF) and minimum mean-square-error (MMSE) equalization with and without decision feedback (DF) are presented and compared. They combat both ISI and MAI. The computational complexity of all four equalizers is essentially the same. All four equalizers are independent of the size of the data symbol alphabet. It is shown that the performance of the MMSE equalizers is better than that of the corresponding ZF equalizers. Furthermore, the performance of the equalizers with DF is better than that of the corresponding equalizers without DF. The impairing effect of error propagation on the equalizers with DF is reduced by channel sorting.

Zero forcing and minimum mean-square-error equalization for multiuser detection in code-division multiple-access channels

Working towards agile manufacturing in the UK industry

The growth in wireless communications necessitates more efficient utilization of spectrum. The increased sharing of spectrum translates into a higher likelihood of users interfering with one another. Interference rejection techniques allow a high capacity of users within the available spectrum. This overview comprises a literature review of published papers pertaining to single-channel adaptive interference rejection in digital wireless dating primarily from 1980 to the present. Though previous overviews are referenced and summarized, the focus is on advances not covered by previous overviews (consequently, some papers are included that predate 1980 because they are not covered in previous overviews). An organizational chart (divided into spread spectrum and nonspread spectrum techniques) is shown which outlines the types of techniques covered. Interference rejection is important for several reasons. Cellular capacity is inherently interference limited, particularly by co-channel interference (CCI) and adjacent-channel interference (ACI). One solution to combat CCI and ACI is to split cells and decrease the power, but cell-splitting is expensive. Interference-rejection techniques often represent a less expensive alternative to cell-splitting. In addition, as newer communication technologies supersede older technologies, interference-rejection techniques are important in helping to facilitate compatibility during transitions between the old and new technologies.

Interference rejection in digital wireless communications

http://www.jim-stone.staff.shef.ac.uk/papers/neuroimage_stica_2002.pdf

Spatiotemporal independent component analysis of event-related fMRI data using skewed probability density functions.

Asynchronous code division multiple access (CDMA) systems using digital matched filtering (DMF) reception techniques suffer from poor multiple access spectral efficiency. This is due entirely to the lower bound on the mean square crosscorrelation levels which exist between the orthogonal codes allocated to each system subscriber. This interference can be estimated through channel measurement, and it is then possible to regenerate and subsequently cancel crosscorrelation components from individual interfering channels, thereafter increasing the effective signal-to-interference ratio on the desired channel for a given subscriber activity level. This paper suggests a technique to exploit this ability in order to gain an increase in the number of multiple access channels available within a particular bandwidth. Theoretical analysis of the proposed cancellation scheme shows an upper bound on the spectral efficiency approaching 130% or 1.3 normalised channels per hertz for successive cascaded cancellation stages. Simulation results for CDMA systems show that, for the traditional DMF receiver without dynamic cancellation, the CDMA efficiency is approximately 10% for a bit error rate of 10−4. Analysis is presented for single and two stage cancellation receivers showing 40% and 50% capacity, respectively, for the same error rates derived from a receiver whose complexity is linear in the number of supported active subscribers.

Increased CDMA system capacity through adaptive cochannel interference regeneration and cancellation

Increased CDMA System Capacity through Adaptive Co-channel Interference Regeneration and Cancellation

The operation of a decision-directed RAKE receiver is described that has the advantage of not requiring any bandwidth overhead for training bits. The performance is illustrated using bit error rate (BER) graphs and burst error length cumulative distribution functions (CDFs) obtained from Monte Carlo simulations. The receiver simulated operates over a fast-fading (100-Hz Doppler) mobile channel at a bit rate of 4.8 kbit/s using a 900-MHz carrier. It is shown that the receiver is not greatly affected by error propagation. However, the incurred lag on the channel impulse response estimate is the major limitation mechanism, and the resulting irreducible BER is quantified for various numbers of taps in our receiver design. The RAKE receiver performance is examined and compared using maximal-ratio, equal-gain, and differential phase combining techniques.

A decision-directed spread-spectrum RAKE receiver for fast-fading mobile channels

The operation of a decision-directed RAKE receiver is described which has the advantage of not requiring any overhead for training bits. The performance is illustrated using bit error rate (BER) graphs obtained from Monte Carlo simulations. The receiver is simulated using a fast fading (100 Hz Doppler) mobile channel at a bit rate of 4.8 kbit/s for a 900 MHz carrier. The receiver is not greatly affected by error propagation. However, the lag on the channel impulse response estimate is the major limitation on the system performance and it introduces an irreducible BER. Results are shown for the maximal ratio, equal gain, and differential phase combining schemes. >

R. D. Pringle

Papers

Increased CDMA system capacity through adaptive cochannel interference regeneration and cancellation

Increased CDMA System Capacity through Adaptive Co-channel Interference Regeneration and Cancellation

A decision-directed spread-spectrum RAKE receiver for fast-fading mobile channels

A decision-directed spread spectrum RAKE receiver for fast fading mobile channels

IEE Colloquium Digest