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Performance of multi-rate DS-CDMA system with multi-stage partial parallel interference cancellation
Abstract
A multi-stage partial parallel interference cancellation receiver
is proposed for the multi-rate DS-CDMA system which adopts the multiple
processing gain scheme. In each stage of the proposed receiver, partial
cancellation is performed with an adaptive decision threshold which is
computed from the matched filter outputs of the previous stage. The BER
performance of the proposed receiver is obtained by simulation in a
Rayleigh fading channel. It is shown that the proposed receiver achieves
smaller BER than the multi-stage parallel interference cancellation
receiver and extended group-wise successive interference cancellation
receiver in the multi-rate DS-CDMA system
... Figure 2 shows the BER of the 1-and 2-stage GSIC receiver with gradient descent search (GSIC-GDS) for the dual-rate DS-CDMA system in a Rayleigh fading channel. BER of the MF receiver, 2-stage GSIC receiver, 3-stage parallel interference cancellation (PIC) receiver [6], 3-stage partial PIC (PPIC) receiver [9]- [11], and 1-and 2-stage GSIC receiver with PIC (GSIC-PIC) [2]- [4] is also shown in Fig. 2 for comparison. Partial cancellation factors for the 1st, 2nd, and 3rd stage of the 3-stage PPIC receiver are set as 0.4, 0.8, Fig. 2 BER of the GSIC receiver with gradient descent search for the dual-rate DS-CDMA system with the MPG scheme in a Rayleigh fading channel for 8 LR and 4 HR users. ...
... Partial cancellation factors for the 1st, 2nd, and 3rd stage of the 3-stage PPIC receiver are set as 0.4, 0.8, Fig. 2 BER of the GSIC receiver with gradient descent search for the dual-rate DS-CDMA system with the MPG scheme in a Rayleigh fading channel for 8 LR and 4 HR users. and 1.0, respectively [9]- [11] and the number of PIC stages in the GSIC-PIC receiver, S p , is set as 1. Figure 2(a) and Fig. 2(b) show the BER of various receivers for each of the LR and HR users. It is shown that the MF receiver suffers from MAI and achieves poor BER performance. ...
In this letter, we propose a groupwise successive interference cancellation (GSIC) receiver with gradient descent search for multirate DS-CDMA system. Proposed receiver incorporates iterative gradient descent search algorithm into conventional GSIC receiver for multi-rate DS-CDMA system. It is shown that the receiver achieves significant performance improvement over the matched filter (MF) receiver, GSIC receiver, multi-stage parallel interference cacnellation (PIC) receiver, multi-stage partial PIC receiver, and GSIC receiver with PIC in a Rayleigh fading channel.
... Under assumption of perfect channel estimation, the non Linear PIC outperforms the LPIC. An extension to PIC, called partial parallel interference cancellation (PPIC), has been proposed in [7]. In this scheme, it has been shown that if interference is removed partially at each stage, the performance of the system would be significantly better than complete cancellation. ...
In this paper, selective adaptive (SA) receiver for Multicarrier Direct Sequence Code Division Multiple Access (MC DS-CDMA) system is presented. This receiver has high performance and at the same time reduces the multiple access interference (MAI) of the MC DS-CDMA) system with low computational complexity. The performance of SA receiver is measured in terms of the bit error rate (BER). An upper bound expression of the BER for the SA receiver under Rayleigh fading channel condition is derived and validated by computer simulations. Moreover, the implementation complexities of the SA receiver is compared with the Adaptive Parallel Interference Cancellation (APIC) receiver.
... Since the WCDMA codes are fixed for the duration of a data block, it becomes practical to use multiuser detection, because the filter coefficients can be re-used across several symbol intervals. Also, because of the relatively large MAI, MUD becomes essential for proper interference mitigation.For most of the experiments, the spreading factor is fixed at Q = 16, however the receiver structures and grouping algorithms can also be used in multirate systems as well.This can be achieved by considering each symbol transmitted as originating from a different "virtual user" (see e.g.:[HL00]).6.1.1 Space-time channel modelIn the space-time model used in this work, each user has up to W time-differentiable paths arriving at the base station multi-antennas receiver. ...
... The adaptive weights are set taking the reliability of each sub-bit estimate into consideration. With λ (s−1) k,n [i] = 1, the adaptive multi-stage PIC receiver is the same as the conventional multi-stage PIC receiver for the multi-rate DS- CDMA system [9]–[11]. To obtain the adaptive weights, the received signal is sampled at the chip-rate. ...
An adaptive multi-stage parallel interference cancellation (PIC)
receiver is considered for a multi-rate DS-CDMA system. In each stage of
the adaptive multi-stage PIC receiver, multiple access interference
(MAI) estimates are obtained using the sub-bit estimates from the
previous stage and the adaptive weights for the sub-bit estimates. The
adaptive weights are obtained by minimizing the mean squared error
between the received signal and its estimate through a least mean square
(LMS) algorithm. It is shown that the adaptive multi-stage PIC receiver
achieves smaller BER than the matched filter receiver, multi-stage PIC
receiver, and multi-stage partial PIC receiver for the multi-rate
DS-CDMA system in a Rayleigh fading channel
We propose a block-based multi-rate parallel interference
canceller (PIC) for the International Mobile Telecommunications-2000
(IMT-2000) 3rd-Generation Partnership Project (3GPP) system. It removes
effectively multiple access interference (MAI) due to multiple users
with different rates through block-based cancellation. For an
asynchronous channel, we propose an advance removal scheme that removes
in advance MAI due to the next block of other users with shorter delays.
We also propose a pipeline structure that can remove MAI due to the next
block without invoking extra hardware and/or computations. Computer
simulations are performed to assess the performance of the proposed
structure in terms of the bit error rate (BER) and the capacity
Different modulation schemes supporting multiple data rates in a Direct Sequence Code Division Multiple Access (DS-CDMA) system are studied. Both AWGN and multipath Rayleigh fading channels are considered. It is shown that the multi processing-gain scheme and the multi-channel scheme have almost the same performance. However, the multi-channel scheme may have some advantages due to easier code design and multiuser receiver construction. The drawback though, is the need for linear amplifiers also in mobile terminals. A multi-modulation scheme is also possible, but the performance for the users with the high data rates are significantly worse than for the other schemes. Furthermore multi chip-rate, parallel combinatory spread spectrum (PC/SS), pulse position modulation (PPM) and variable duty cycle schemes are discussed briefly.
A multiuser detection strategy for coherent demodulation in an
asynchronous code-division multiple-access system is proposed and
analyzed. The resulting detectors process the sufficient statistics by
means of a multistage algorithm based on a scheme for annihilating
successive multiple-access interference. An efficient real-time
implementation of the multistage algorithm with a fixed decoding delay
is obtained and shown to require a computational complexity per symbol
which is linear in the number of users K . Hence, the multistage
detector contrasts with the optimum demodulator, which is based on a
dynamic programming algorithm, has a variable decoding delay, and has a
software complexity per symbol that is exponential in K . An
exact expression is obtained and used to compute the probability of
error is obtained for the two-stage detector, showing that the two-stage
receiver is particularly well suited for near-far situations,
approaching performance of single-user communications as the interfering
signals become stronger. The near-far problem is therefore alleviated.
Significant performance gains over the conventional receiver are
obtained even for relatively high-bandwidth-efficiency situations
This paper presents the performance of groupwise successive
interference cancellation (GSIC) in a DS-CDMA system with multiple data
rates (multirate). The performance is evaluated both in AWGN and
Rayleigh fading channels. In the GSIC scheme users with the same data
rate are grouped and detected, using either a matched filter or a
parallel interference cancellation (PIC) receiver, interference between
the groups is cancelled in a successive order. The results show that in
a multirate system the GSIC yields a better performance than the PIC
receiver. Further a delay error of 0.1 Tc is found to be
tolerable
This report considers a general parallel interference cancellation scheme that significantly reduces the degradation effect of user interference but with a lesser implementation complexity than the maximum-likelihood technique. The scheme operates on the fact that parallel processing simultaneously removes from each user the interference produced by the remaining users accessing the channel in an amount proportional to their reliability. The parallel processing can be done in multiple stages. The proposed scheme uses tentative decision devices with different optimum thresholds at the multiple stages to produce the most reliably received data for generation and cancellation of user interference. The 1-stage interference cancellation is analyzed for three types of tentative decision devices, namely, hard, null zone, and soft decision, and two types of user power distribution, namely, equal and unequal powers. Simulation results are given for a multitude of different situations, in particular, those cases for which the analysis is too complex.
Consider the reverse link of an asynchronous DS-CDMA system in
which each user's signal is transmitted over a channel with Rayleigh
fading and AWGN. For the CDMA system a new parallel interference
cancellation (PIC) receiver with an adaptive decision threshold is
proposed which is complete with the method to adjust the decision
threshold. The decision threshold for partial cancellation is adjusted
according to the statistics of its matched filter (MF) outputs. The BER
of the proposed PIC receiver is obtained by simulation and compared with
those of the conventional PIC and other PIC receivers in a Rayleigh
fading channel. It is shown that the proposed PIC receiver achieves
better performance than the conventional PIC receiver and the PIC
receiver using null zone hard decision in a Rayleigh fading
channel
This work is an extension of the multi-rate LMMSE detectors (Ge
1997) for asynchronous multi-rate CDMA systems. The proposed LMMSE
detectors can work on dual-rate mode according to different
quality-of-service (QoS) requirements and computational constraints. In
using the proposed multirate LMMSE detectors, only the signature and
timing information of the desired user are required. The proposed
detectors can achieve better detection performance with less computation
than the dual-rate decorrelating detectors. Adaptive schemes of
implementing the proposed detectors can handle both synchronous and
asynchronous channels as long as the signature and timing information on
the desired user is available
This paper addresses the use of decorrelating detectors for a dual rate DS/CDMA system that serves both low bit rate and high bit rate users. We assume that in an interval of duration T
0, a low rate user transmits one bit while a high rate user transmits M bits. Applying a standard decorrelator to the interval of duration T
0 yields an M bit processing delay for high rate users and a computational complexity that grows with M. In this paper, we propose a decorrelator that generates bit decisions for each high rate user in every subinterval of duration T0/M. To decode a low rate user, a soft decoding rule applies maximal ratio combining on M separate decorrelated outputs of each low rate user. The soft decoding dual rate decorrelator eliminates the bit processing delay for high rate users and also reduces the computational complexity of a standard decorrelator. Further, it is shown that the asymptotic efficiency of the standard decorrelator is greater than or equal to the proposed decorrelator. By evaluation, it is observed that when the signature sequences have good correlation properties, the proposed soft decoding decorrelator is found to perform nearly as well as the standard decorrelator. However, when the signature sequences have high cross-correlation, then the proposed decorrelator suffers in terms of bit error rate while retaining the near-far resistance property.
This paper focuses on a CDMA design study for future
third-generation mobile and personal communication systems such as
FPLMTS and UMTS. In the design study, a rigorous top down approach is
adopted starting from the most essential objectives and requirements of
universal third-generation mobile systems. Emphasis is laid on high
flexibility with respect to the implementation of a wide range of
services and service bit rates including variable rate and packet
services. Flexibility in frequency and radio resource management, system
and service deployment, and easy operation in mixed-cell and
multioperator scenarios are further important design goals. The system
concept under investigation is centered around an open and flexible
radio interface architecture based on asynchronous direct-sequence CDMA
with three different chip rates of approximately 1, 5, and 20 Mchip/s.
The presented CDMA system concept forms the basis for an experimental
test system (testbed) which is currently under development. This
experimental system concept has been jointly established by the partners
in the European RACE project R2020 (CODIT). The paper describes the
radio transmission scheme and appropriate receiver principles and
presents first performance results based on simulations
The basis for any air interface design is how the common
transmission medium is shared between users (i.e., multiple access
scheme). The underlying multiple access method for all mobile radio
systems is FDMA. The performance of TDMA and CDMA has been subject to
vigorous debate, without any definitive conclusions. This article gives
an overview of worldwide research and standardization activities related
to the multiple access schemes for third-generation mobile
communications systems IMT-2000 and UMTS
Direct-sequence code-division multiple access (DS-CDMA) is a
popular wireless technology. In DS-CDMA communications, all of the
users' signals overlap in time and frequency and cause mutual
interference. The conventional DS-CDMA detector follows a single-user
detection strategy in which each user is detected separately without
regard for the other users. A better strategy is multi-user detection,
where information about multiple users is used to improve detection of
each individual user. This article describes a number of important
multiuser DS-CDMA detectors that have been proposed