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In this paper, receiver design and performance analysis for coded asynchronous code-division multiple access (CDMA) systems is considered. The receiver front-end consists of the near-far resistant multiuser detector known as the projection receiver (PR). The PR performs multiple-access interference resolution and is followed by error-control decodi...
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... number of chips per symbol) is assumed identical for all users and equal to , and each user transmits a sequence of symbols. For simplicity, we further assume that the delays in (2) are integer multiples of the chip duration , i.e., the system is chip synchronous. Note that the symbol synchronous case is simply a special case of (2) with . Fig. 2 shows the basic (baseband) system block diagram of a CDMA multiuser system using error-control coding. The samples after the chip matched filter are spaced by multiples of , i.e., we are considering a single-sample per chip system. Each user's data stream drives an encoder of rate , whose outputs are spread by , the spreading sequence ...
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Citations
... These multi-user detection techniques give acceptable BERs even with low SNRs. Some detection techniques incorporating channel decoding are presented in [18], [19], [20], [21], [22]. Other detection solutions developed for multibeam communications, which are detailed and evaluated, can be found in [23], [24]. ...
This paper deals with multi-user detection techniques in asynchronous
multibeam satellite communications. The proposed solutions are based on
successive interference cancellation architecture (SIC) and channel decoding
algorithms. The aim of these detection methods is to reduce the effect of
cochannel interference due to co-frequency access, and consequently, improves
the capacity of the mulitbeam communications systems, by improving frequency
reuse. Channel estimation allows the determination of interference
coefficients, which helps their effects compensation. The developed multiuser
detections techniques are iterative. Therefore, detection quality is improved
from a stage to another. Moreover, a signals combining method, which is
integrated into these detection solutions, enhances their capability. The
proposed solutions are evaluated through computer simulations, where an
asynchronous multibeam satellite link is considered over an AWGN channel. The
obtained simulation results showed the robustness of these multi-user detection
techniques.
... 66-A, no. 5, pp. [20][21][22][23][24][25][26][27][28][29]1983. A disadvantage of such decorrelators is that they cause noise enhancement. ...
... A receiver according to claim 24, wherein the receiver modules are arranged in hierarchical order according to Signal power and each lower power receiver module uses a constraint matrix formed from constraints-sets Supplied by each of the higher power receiver modules. 27. A receiver according to claim 23, wherein each of the receiver modules in one of Said sets is different from the receiver modules in the other Sets. ...
A receiver of the present invention addresses the need for improved interference suppression without the number of transmissions by the power control system being increased, and, to this end, provides a receiver for a CDMA communications system which employs interference subspace rejection to tune a substantially null response to interference components from selected signals of other user stations. Preferably, the receiver also tunes a substantially unity response for a propagation channel via which a corresponding user's signal was received. The receiver may be used in a base station or in a user/mobile station.
... As noted in the beginning of this section, most of the channel coding and decoding procedures are designed for single-user AWGN channels or fading channels. In the presence of multiaccess interference, joint multiuser detection and decoding [142][143][144][145][146] can lead to lower error performance at the expense of increased receiver complexity. ...
Wireless cellular systems have grown dramatically in the last two decades, thanks to several key innovations in communication algorithms and high speed silicon technology. We review fundamental physical layer techniques for the future high speed wireless networks.
... where is an diagonal matrix of positive weights and an additional weighting factor. One can show that the above general weighted ISR solution reduces to MMSE combining with respect to the ISR signal decomposition selected by setting , the noise variance estimate, and in the TR mode in the R mode in the D mode times in the H mode (51) The instantaneous parameter estimates in the equation above can be further averaged or smoothed in time. The columns of the constraint matrix estimate are reconstructed without normalization. ...
... At the high end in complexity, the decorrelator [6]- [8] and the ZF-DF partial decorrelator [14] can be regarded as a combination of the H and D modes of ISR with one antenna. This hybrid of ISR is also similar to the projection receiver (PR) [50], [51], which implements a ZF-type detector through exploitation of a projector orthogonal to the interference subspace. In the general case, however, ISR characterizes interference from different interference subspace decompositions and accordingly suppresses it along modes (i.e., TR, R, D, H, etc ) that require reduced complexity. ...
We present a unifying framework for a new class of receivers that
employ linearly-constrained interference cancellation (IC). The
associated multiuser detectors operate in various modes and options
ranging in performance from that of IC detectors to that of linear
receivers, yet provide more attractive performance/complexity tradeoffs.
They exploit both space and time diversities as well as the
array-processing capabilities of multiple antennas and carry out
simultaneous channel and timing estimation, signal combining and
interference rejection. Additionally, they can operate on both links and
in multiple mixed-rate traffic scenarios. The improved performance can
be translated to increased utilization of wideband code division
multiple access networks, particularly at high data rates
... In a situation of slowly changing array responses, the correlation matrix itself can be updated as R gg n = 1 , R gg n , 1 + gng H n: 26 where the forgetting factor is chosen for appropriate tracking of R gg and we h a ve 0 ...
Amultiple receiveantenna #MRA# system is studied for code division multiple access #CDMA# using pseudo-random spreading codes. The core component, the receiver, jointly processes the multiple antenna array signals, despreading and error control code metric generation. Interference from joint users is cancelled by the projection method, where the signals are projected away from the interfering signal space. This method requires knowledge of the array response vectors, whichis acquired via blind subspace estimation techniques. It is shown that the increase in system capacity is linear to the number of receiveantennas. Performance analysis and simulation results are given to substantiate these #ndings. 1 Introduction Mobile wireless communication systems are rapidly evolving from second generation to third generation #3G#. Code division multiple access technology has been adopted by the major 3G standards, such as cdma2000 #1# and WCDMA #Wideband CDMA# #2, 3#. An important advantage of 3...
... Linear receivers typically use linear matrix filters (such as the decorrelator and LMMSE see [4] for a textbook treatment ), followed by independent decoding of each user. Indeed, linear filters may be specifically designed to assist in this process [5] . Such schemes are however fundamentally limited in the spectral efficiency that they can offer [6, 7]. ...
We investigate a sub-optimal reduced-complexity iterative
technique for joint detection and estimation for sets of constrained
sequences and derive analytical results concerning convergence regions
and fixed points. We apply this theory to the problem of multiple-user
decoding
... In the sequel we assume st arrives at a 90 incident angle. In this case the received sampled signal vectors y 1 Using the de nitions, y = y 1 ; y 2 T , A = A;A T , A I = f I A I e j ; f I A I e j+ T , and n = n 1 ; n 2 T , equation 1 can be written as y = Ad + A I d I + n: 2 The rst term on the right hand is the desired constrained data. The second term is the co-channel interference CCI. ...
A narrowband mobile communication system is proposed in this
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... In [1] below, an efficient algorithm for adaptive metric generation for the receiver for a coded, asynchronous CDMA was reported. Extensive simulations were performed to study the performance of this receiver with fixed, bit-length spreading sequences as well as long pseudo-random spreading sequences. ...
The next generation of personal communications networks are expected to provide support for multimedia traffic (integrated transport of voice/video/data) accordingly, new spectrum allocations with larger bandwidth (broadband access) are being explored. Support of higher rates and heterogeneous traffic will require breakthroughs at level of network design. In this work, we focus on several signal processing aspects of advanced digital wireless transceivers for Code Division Multiple Access (CDMA) systems for next generation broadband applications. Specifically, progress is reported on the design of efficient Multi-User (MU) detectors for CDMA that possess acceptable complexity performance trade off.
Species in the class Myxomycetes (or Myxogastrea) are essential components of biodiversity and play important ecological roles in terrestrial ecosystems, especially in forests. Studies on the taxonomy and diversity of these organisms started late in China. However, significant progress in China has been made in modern taxonomic studies on myxomycetes based on long-term species surveying and specimen collecting. The existing achievements have shown that comprehensive and continuous studies on the taxonomy and diversity of myxomycetes in China have the potential to enhance global biodiversity and improve the geographic distribution pattern of myxomycetes. Therefore, building on the current research foundation and expanding myxomycete research in a wider and more in-depth approach is imperative.
A clockless, continuous-time (CT) analog correlator circuit realization is presented based on time-encoded analog signal processing. Voltage-controlled oscillators (VCOs) transform the analog voltage signals into time-encoded analog signals and, in the process, perform signal integration; CT, digital-style delay cells combined with phase-frequency detectors followed by capacitive summers implement a CT matched filter. The correlator prototype designed in 65-nm CMOS-LP technology consumes 37 nW from 0.54 V and is used in the baseband of a wake-up receiver to despread asynchronous code-division multiple access (CDMA) codes and demonstrate code-domain filtering for an 11-bit Barker code. The wake-up receiver's sensitivity is enhanced by 2 dB to -80.9 dBm for a missed detection ratio of 10
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, and its selectivity is improved by 5 dB, thanks to the use of the correlator. Simultaneous wake-up using CDMA is demonstrated with selective responses of the receiver to different desired codes in the presence of an undesired code.
