ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Mon, 12 Apr 2021 01:43:36 GMT2021-04-12T01:43:36Z50571- Systematic study of channel non-symmetry for differentially coherent detection in general Rician fading channelshttps://scholarbank.nus.edu.sg/handle/10635/112299Title: Systematic study of channel non-symmetry for differentially coherent detection in general Rician fading channels
Authors: Ma, Y.; Lim, T.J.; Chai, C.C.
Abstract: A study is presented into the phenomenon of differing BEPs for different symbols transmitted (termed channel non-symmetry) for binary and quaternary differential phase shift keying (2/4-DPSK) in arbitrarily correlated multipath Rician fading channels. The systematic study is facilitated by the moment generating function (MGF) of the decision statistic of 2/4-DPSK. The work unifies many of the previously published results for channel non-symmetry and gives new insight into the problem.
Thu, 03 Feb 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122992000-02-03T00:00:00Z
- Bit-error probabilities for 2- and 4-DPSK in general Nakagami fading channels with correlated Gaussian noisehttps://scholarbank.nus.edu.sg/handle/10635/112221Title: Bit-error probabilities for 2- and 4-DPSK in general Nakagami fading channels with correlated Gaussian noise
Authors: Ma, Y.; Chai, C.C.; Lim, T.J.
Abstract: Exact bit-error probability (BEP) expressions are derived for 2- and 4-ary differential phase shift keying (2- and 4-DPSK) with post-detection equal gain combining (EGC) in arbitrarily correlated slow Nakagami fading channels. Unlike previous work, the effect of noise correlation between adjacent symbol intervals is considered and shown explicitly in the BEP expressions. The characteristic function method is used to give a BEP expression in a general form for 2- and 4-DPSK. Furthermore, closed-form BEP expressions are derived for 2-DPSK with coloured noise, and for 4-DPSK with white noise and integer fading parameter m. The theoretical result is demonstrated by analysing two antenna configurations, giving some interesting findings. © IEE, 2000.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122212000-01-01T00:00:00Z
- Breadth-first maximum likelihood detection in multiuser CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112223Title: Breadth-first maximum likelihood detection in multiuser CDMA
Authors: Rasmussen, L.K.; Lim, T.J.; Aulin, T.M.
Abstract: In this letter, we derive a recursive, additive metric for complexity-constrained maximum likelihood detection for multiuser CDMA using breadth-first detection algorithms. The metric requires linear filtering of the matched-filtered received signal vector. It is shown that a class of filters fulfilling certain requirements lead to identical performance. © 1997 IEEE.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122231997-01-01T00:00:00Z
- Aspects on linear parallel interference cancellation in CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112314Title: Aspects on linear parallel interference cancellation in CDMA
Authors: Rasmussen, L.K.; Guo, D.; Lim, T.J.; Ma, Y.
Abstract: In this paper we devise a matrix-algebraic approach to analysing linear parallel interference cancellation. We show that linear parallel interference cancellation schemes correspond to linear matrix filtering. © 1998 IEEE.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123141998-01-01T00:00:00Z
- A matrix-algebraic approach to successive interference cancellation in CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112208Title: A matrix-algebraic approach to successive interference cancellation in CDMA
Authors: Rasmussen, L.K.; Lim, T.J.; Johansson, A.-L.
Abstract: In this paper, we describe linear successive interference cancellation (SIC) based on matrix-algebra. We show that linear SIC schemes (single-stage and multistage) correspond to linear matrix filtering that can be performed directly on the received chip-matched filtered signal vector without explicitly performing the interference cancellation. This leads to an analytical expression for calculating the resulting bit-error rate which is of particular use for short-code systems. Convergence issues are discussed, and the concept of ∈-convergence is introduced to determine the number of stages required for practical convergence for both short and long codes. © 2000 IEEE.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122082000-01-01T00:00:00Z
- Optimal power and range adaptation for green broadcastinghttps://scholarbank.nus.edu.sg/handle/10635/56941Title: Optimal power and range adaptation for green broadcasting
Authors: Luo, S.; Zhang, R.; Lim, T.J.
Abstract: Improving energy efficiency is key to network providers maintaining profit levels and an acceptable carbon footprint in the face of rapidly increasing data traffic in cellular networks in the coming years. The energy-saving concept studied in this paper is the adaptation of a base station's (BS's) transmit power levels and coverage area according to channel conditions and traffic load. Cell coverage is usually pre-designed based on the estimated static (e.g. peak) traffic load. However, traffic load in cellular networks exhibits significant fluctuations in both space and time, which can be exploited, through cell range adaptation, for energy saving. In this paper, we design short-and long-term BS power control (STPC and LTPC respectively) policies for the OFDMA-based downlink of a single-cell system, where bandwidth is dynamically and equally shared among a random number of mobile users (MUs). STPC is a function of all MUs' channel gains that maintains the required user-level quality of service (QoS), while LTPC (including BS on-off control) is a function of traffic density that minimizes the long-term energy consumption at the BS under a minimum throughput constraint. We first develop a power scaling law that relates the (short-term) average transmit power at BS with the given cell range and MU density. Based on this result, we derive the optimal (long-term) transmit adaptation policy by considering a joint range adaptation and LTPC problem. By identifying the fact that energy saving at BS essentially comes from two major energy saving mechanisms (ESMs), i.e. range adaptation and BS on-off power control, we propose low-complexity suboptimal schemes with various combinations of the two ESMs to investigate their impacts on system energy consumption. It is shown that when the network throughput is low, BS on-off power control is the most effective ESM, while when the network throughput is higher, range adaptation becomes more effective. © 2013 IEEE.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/569412013-01-01T00:00:00Z
- Maximum-likelihood receiver of FFH/BFSK systems with multitone jamming and AWGN over Rayleigh-fading channelshttps://scholarbank.nus.edu.sg/handle/10635/112265Title: Maximum-likelihood receiver of FFH/BFSK systems with multitone jamming and AWGN over Rayleigh-fading channels
Authors: Teh, K.C.; Lim, T.J.
Abstract: A maximum-likelihood receiver for fast frequency-hopped binary frequency-shift-keying (FFH/BFSK) systems which operates in an additive white Gaussian noise (AWGN) environment and is subjected to multitone jamming over Rayleigh-fading channels is derived. Simulation results show that the proposed maximum-likelihood receiver outperforms existing receivers with the same channel and jamming conditions.
Thu, 01 Apr 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122651999-04-01T00:00:00Z
- Bit error probability for MDPSK and NCFSK over arbitrary Rician fading channelshttps://scholarbank.nus.edu.sg/handle/10635/112220Title: Bit error probability for MDPSK and NCFSK over arbitrary Rician fading channels
Authors: Ma, Y.; Lim, T.J.
Abstract: In this paper, we analyze the bit error probability (BEP) of binary and quaternary differential phase shift keying (2/4 DPSK) and noncoherent frequency shift keying (NCFSK) with postdetection diversity combining in arbitrary Rician fading channels. The model is quite general in that it accommodates fading correlation and noise correlation between different diversity branches as well as between adjacent symbol intervals. We show that the relevant decision statistic can be expressed in a noncentral Gaussian quadratic form, and its moment generating function (MGF) is derived. Using the MGF and the saddle point technique, we give an efficient numerical quadrature scheme to compute the BEP. The most significant contribution of the paper, however, lies in the derivation of a closed-form cumulative distribution function (cdf) for the decision statistic. As a result, a closed-form BEP expression in the form of an infinite series of elementary functions is developed, which is general and unifies previous published BEP results for 2/4 DPSK and NCFSK for multichannel reception in Rician fading. Specialization to some important cases are discussed and, as a byproduct, a new and general finite-series expression for the BEP in arbitrarily correlated Rayleigh fading is obtained. The theory is applied to study 2/4 DPSK and NCFSK performance for independent and correlated Rician fading channels; and some interesting findings are presented.
Wed, 01 Nov 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122202000-11-01T00:00:00Z
- Constrained surplus energy adaptive blind CDMA detectionhttps://scholarbank.nus.edu.sg/handle/10635/112236Title: Constrained surplus energy adaptive blind CDMA detection
Authors: Lim, T.J.; Gong, Y.; Farhang-Boroujeny, B.
Abstract: The blind minimum output energy (MOE) adaptive detector for code division multiple access (CDMA) signals requires exact knowledge of the received spreading code of the desired user. This requirement can be relaxed by constraining the so-called surplus energy of the adaptive tap-weight vector, but the ideal constraint value is not easily obtained in practice. An algorithm is proposed to adaptively track this value and hence to approach the best possible performance for this class of CDMA detector.
Thu, 07 Dec 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122362000-12-07T00:00:00Z
- Linear parallel interference cancellation in long-code CDMA multiuser detectionhttps://scholarbank.nus.edu.sg/handle/10635/112261Title: Linear parallel interference cancellation in long-code CDMA multiuser detection
Authors: Guo, D.; Rasmussen, L.K.; Lim, T.J.
Abstract: Parallel interference cancellation (PIC) is a promising detection technique for code division multiple access (CDMA) systems. It has previously been shown that the weighted multistage PIC can be seen as an implementation of the steepest descent algorithm used to minimize the mean squared error (MSE). Following this interpretation, a unique set of weights, based on the eigenvalues of the correlation matrix, was found to lead to the minimum achievable MSE for a given number of stages in a short-code system. In this paper, we introduce a method for finding an appropriate set of time-invariant weights for systems using long codes. The weights are dependent on moments of the eigenvalues of the correlation matrix, exact expressions of which can be derived. This set of weights is optimal in the sense that it minimizes the ensemble averaged MSE over all code-sets. The loss incurred by averaging rather than using the optimal, time-varying weights is practically negligible, since the eigenvalues of sample correlation matrices are tightly clustered in most cases of interest. The complexity required for computing the weights increases linearly with the number of users but is independent of the processing gain, hence on-line weight updating is possible in a dynamic system. Simulation results show that a few stages is usually sufficient for near-MMSE performance.
Wed, 01 Dec 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122611999-12-01T00:00:00Z
- On-line interpolation using spline functionshttps://scholarbank.nus.edu.sg/handle/10635/112280Title: On-line interpolation using spline functions
Authors: Lim, T.J.; Macleod, M.D.
Abstract: In this letter, an off-line or block B-spline interpolation algorithm is modified to an on-line or running form which handles growing data sequences more efficiently. Some loss of interpolation accuracy is suffered with lowpass signals but when the signal is broadband, the increase in interpolation error is negligible while a significant saving in computational effort is obtained.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122801996-01-01T00:00:00Z
- Optimal save-then-transmit protocol for energy harvesting wireless transmittershttps://scholarbank.nus.edu.sg/handle/10635/56943Title: Optimal save-then-transmit protocol for energy harvesting wireless transmitters
Authors: Luo, S.; Zhang, R.; Lim, T.J.
Abstract: In this paper, the design of a wireless communication device relying exclusively on energy harvesting is considered. Due to the inability of rechargeable energy sources to charge and discharge at the same time, a constraint we term the energy half-duplex constraint, two rechargeable energy storage devices (ESDs) are assumed so that at any given time, there is always one ESD being recharged. The energy harvesting rate is assumed to be a random variable that is constant over the time interval of interest. A save-then-transmit (ST) protocol is introduced, in which a fraction of time ρ (dubbed the save-ratio) is devoted exclusively to energy harvesting, with the remaining fraction 1-ρ used for data transmission. The ratio of the energy obtainable from an ESD to the energy harvested is termed the energy storage efficiency, η. We address the practical case of the secondary ESD being a battery with η < 1, and the main ESD being a super-capacitor with η = 1. Important properties of the optimal save-ratio that minimizes outage probability are derived, from which useful design guidelines are drawn. In addition, we compare the outage performance of random power supply to that of constant power supply over the Rayleigh fading channel. The diversity order with random power is shown to be the same as that of constant power, but the performance gap can be large. Finally, we extend the proposed ST protocol to wireless networks with multiple transmitters. It is shown that the system-level outage performance is critically dependent on the number of transmitters and the optimal save-ratio for single-channel outage minimization. © 2002-2012 IEEE.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/569432013-01-01T00:00:00Z
- Linear and nonlinear chip-rate minimum mean-squared-error multiuser CDMA detectionhttps://scholarbank.nus.edu.sg/handle/10635/112260Title: Linear and nonlinear chip-rate minimum mean-squared-error multiuser CDMA detection
Authors: Ma, Y.; Lim, T.J.
Abstract: In this paper, a linear Kalman filter detector for code-division multiple access proposed earlier in the literature is extended to a structure that can handle arbitrary detection delays, through the mechanism of state augmentation. Because pre-detection RAKE combining is used in the detector, it is optimal for multipath channels, unlike the previous structure that performed post-detection combining. We also derive nonlinear Kalman detectors, which approximate the highly complex nonlinear minimum mean-squared-error detector, using the concept of "additional observations". Both linear and nonlinear detectors require processing at one or more times the chip rate, and knowledge of the spreading codes of interfering users. They have the advantage over many other multiuser detection algorithms of not requiring the spreading codes to be periodic at the symbol rate, or matrix inversion. In addition, two of the detectors are able to generate and update a posteriori probabilities of the transmitted symbols, making them interesting for iterative multiuser detection.
Thu, 01 Mar 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122602001-03-01T00:00:00Z
- Soft handoffs in CDMA mobile systemshttps://scholarbank.nus.edu.sg/handle/10635/112294Title: Soft handoffs in CDMA mobile systems
Authors: Wong, D.; Lim, T.J.
Abstract: This article presents an overview of soft handoff, an idea which is becoming quite important because of its use in the IS-95 code-division multiple access (CDMA) cellular phone standard. The benefits and disadvantages of using soft handoff over hard handoff are discussed, with most results drawn from the available literature. The two most well-known benefits are fade margin improvement and higher uplink capacity, while disadvantages include increased downlink interference and more complex implementation. Handoff parameter optimization is extremely important, so various studies on the trade-offs to be considered when selecting these parameters are surveyed, from both the link quality and resource allocation perspectives. Finally, research directions and future trends are discussed.
Mon, 01 Dec 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122941997-12-01T00:00:00Z
- Performance analysis of SC-FDMA in the presence of receiver phase Noisehttps://scholarbank.nus.edu.sg/handle/10635/112283Title: Performance analysis of SC-FDMA in the presence of receiver phase Noise
Authors: Sridharan, G.; Lim, T.J.
Abstract: In this paper we study the effect of receiver phase noise on single carrier frequency division multiple access (SC-FDMA). We show that common phase error rotates all the symbols by a certain angle and that the higher order frequency components of phase noise result in inter-carrier interference, or ICI and draw parallels to orthogonal frequency division multiple access (OFDMA). We then study the effect of phase noise on the performance of linear receivers that are often used in practice. In particular, we show that the amount of ICI affecting the sub-carriers depends closely on the allocation of sub-carriers among different users and prove that the performance of linear receivers in the presence of receiver phase noise deteriorates much more in the case of interleaved SC-FDMA than in the case of localized SC-FDMA. We identify the association of the significant phase noise components with the components of multi-user interference to be the fundamental reason behind the performance gap between interleaved and localized SC-FDMA. © 2012 IEEE.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122832012-01-01T00:00:00Z
- Relative performance of BPSK and QPSK in the presence of complex multiuser CDMA interferencehttps://scholarbank.nus.edu.sg/handle/10635/112289Title: Relative performance of BPSK and QPSK in the presence of complex multiuser CDMA interference
Authors: Lim, T.J.; Rasmussen, L.K.; Sugimoto, H.
Abstract: In a typical mobile communications channel, the multiple access interference (MAI) experienced by any user in a multiuser CDMA system will be complex-valued due to independent phase offsets between signals received from different users. In addition, complex spreading codes may also be employed, in which case MAI is complex-valued even without phase offsets. This paper shows that complex MAI substantially alters the single-user relationship between BPSK and QPSK modulation, in which QPSK offers twice the bandwidth efficiency of BPSK without sacrificing BER versus Eb/N0 performance. It is shown both analytically and through simulations that it is possible to adjust system parameters to achieve identical system bandwidth efficiency and BER performance in BPSK and QPSK systems using the conventional detector. The performance of the well-known successive interference canceller and decorrelating detector are also examined.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122892000-01-01T00:00:00Z
- Estimation of directions of arrival of multipath signals in CDMA systemshttps://scholarbank.nus.edu.sg/handle/10635/112245Title: Estimation of directions of arrival of multipath signals in CDMA systems
Authors: Lei, Z.; Lim, T.J.
Abstract: In this paper, an algorithm is proposed for estimating the directions of arrival (DOA's) of multipath signals received from multiple users on the uplink of a code-division multiple-access system. The correlation matrices of the received signal before and after code-matched filtering are used to provide unique estimates even when the number of required DOA's exceeds the number of antenna array elements. This scenario is well known to cause conventional direction-finding algorithms (such as MUSIC) to fail. Both intersymbol interference (ISI) and multiple-access interference (MAI) are modeled exactly, and so the algorithm performs much better than those which model ISI and MAI as Gaussian noise.
Thu, 01 Jun 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122452000-06-01T00:00:00Z
- Unified analysis of error probability for MRC in correlated fading channelshttps://scholarbank.nus.edu.sg/handle/10635/112306Title: Unified analysis of error probability for MRC in correlated fading channels
Authors: Ma, Y.; Chai, C.C.; Lim, T.J.
Abstract: Combining the characteristic function method and alternate forms of the Marcum Q and Gaussian probability functions, a unified approach is presented for obtaining the error probabilities of different modulation schemes employing maximum ratio combining (MRC) in correlated fading channels.
Thu, 05 Aug 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123061999-08-05T00:00:00Z
- Digital network coding aided two-way relaying: Energy minimization and queue analysishttps://scholarbank.nus.edu.sg/handle/10635/55640Title: Digital network coding aided two-way relaying: Energy minimization and queue analysis
Authors: Chen, Z.; Lim, T.J.; Motani, M.
Abstract: In this paper, we consider a three-node, two-way relay system with digital network coding. The aim is to minimize total energy consumption while ensuring queue stability at all nodes, for a given pair of random packet arrival rates. Specifically, we allow for a set of transmission modes and solve for the optimal fraction of resources allocated to each mode. First, we formulate and solve the static-channel problem, where all link gains are constant over the duration of transmission. Then, we solve the fading-channel problem, where link gains are random. We call the latter the ergodic energy efficiency problem and show that its solution has a water-filling structure. Finally, we provide a detailed analysis of the queues at each node when a random scheduling method that closely approximates the theoretical design is used. © 2002-2012 IEEE.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/556402013-01-01T00:00:00Z
- Energy minimization in two-way relay networks with digital network codinghttps://scholarbank.nus.edu.sg/handle/10635/70169Title: Energy minimization in two-way relay networks with digital network coding
Authors: Chen, Z.; Lim, T.J.; Motani, M.
Abstract: In a two-way wireless relay network, two nodes communicate with each other through a relay, and throughput is enhanced by the relay transmitting a linear combination of the messages received from the two sources either at the bit level (digital network coding) or the signal level (analog network coding). In this paper, we solve for the fraction of time resources allocated to each transmission mode in a DNC-based two-way relay network that minimizes total energy while ensuring queue stability at all nodes, for a given pair of random packet arrival rates. We also provide a queueing analysis of the relaying protocol designed. © 2012 IEEE.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/701692012-01-01T00:00:00Z
- Hybrid NOMA for an Energy Harvesting MAC with Non-Ideal Batteries and Circuit Powerhttps://scholarbank.nus.edu.sg/handle/10635/156444Title: Hybrid NOMA for an Energy Harvesting MAC with Non-Ideal Batteries and Circuit Power
Authors: Bhat, Rajshekhar Vishweshwar; MOTANI,MEHUL; LIM TENG JOON
Tue, 01 Jan 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1564442019-01-01T00:00:00Z
- A GLRT Based Mechanism for Detecting Relay Misbehavior in Clustered IoT Networkshttps://scholarbank.nus.edu.sg/handle/10635/156443Title: A GLRT Based Mechanism for Detecting Relay Misbehavior in Clustered IoT Networks
Authors: Abhishek, Nalam Venkata; ANSHOO TANDON; LIM TENG JOON; BIPLAB SIKDAR
Tue, 01 Jan 2019 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1564432019-01-01T00:00:00Z
- Optimal save-then-transmit protocol for energy harvesting wireless transmittershttps://scholarbank.nus.edu.sg/handle/10635/71301Title: Optimal save-then-transmit protocol for energy harvesting wireless transmitters
Authors: Luo, S.; Zhang, R.; Lim, T.J.
Abstract: In this paper, the design of a wireless communication device relying exclusively on energy harvesting is considered. Due to the inability of rechargeable energy sources to charge and discharge at the same time, a constraint we term the energy half-duplex constraint, two rechargeable energy storage devices (ESDs) are assumed so that at any given time, there is always one ESD being recharged. The energy harvesting rate is a random variable that is constant over the time interval of interest. A save-then-transmit (ST) protocol is introduced, in which a fraction of time ρ (dubbed the save ratio) is devoted exclusively to energy harvesting, with the remaining fraction 1 - ρ used for data transmission. The ratio of the energy obtainable from an ESD to the energy harvested is termed the ESD efficiency, η. We address the practical case of the secondary ESD being a battery with η < 1, and the main ESD being a super-capacitor with η = 1. The optimal save-ratio that minimizes outage probability is derived, from which some useful design guidelines are drawn. Numerical results are provided to validate our proposed study. © 2012 IEEE.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/713012012-01-01T00:00:00Z
- Optimal power and range adaptation for green broadcastinghttps://scholarbank.nus.edu.sg/handle/10635/71292Title: Optimal power and range adaptation for green broadcasting
Authors: Luo, S.; Zhang, R.; Lim, T.J.
Abstract: Improving energy efficiency is key to network providers maintaining profit levels and an acceptable carbon footprint in the face of rapidly increasing data traffic in cellular networks in the coming years. The energy-saving concept studied in this paper is the adaptation of a base station's (BS's) transmit power levels and coverage area according to channel conditions and traffic load. Cell coverage is usually pre-designed based on the estimated peak traffic load. However, traffic load in cellular networks exhibits significant fluctuations in both space and time. We design short- and long-term power control (STPC and LTPC respectively) policies for the OFDMA-based downlink of a single-cell system, where bandwidth is dynamically and equally shared among a random number of mobile users (MUs). STPC is a function of all MUs' channel gains that maintains the required user-level quality of service (QoS), while LTPC is a function of traffic density that minimizes the long-term energy consumption at the BS under a minimum throughput constraint. We first develop a power scaling law that relates the (short-term) average transmit power at BS with the given cell range and MU density. Based on this result, we derive the optimal (long-term) transmit adaptation policy by considering a joint range adaptation and LTPC problem. Finally, we compare our proposed adaptation scheme with suboptimal schemes of lower complexity to demonstrate the potential energy saving in broadcast channels. © 2013 IEEE.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/712922013-01-01T00:00:00Z
- Receiving device and channel estimator for use in a CDMA communication systemhttps://scholarbank.nus.edu.sg/handle/10635/32661Title: Receiving device and channel estimator for use in a CDMA communication system
Authors: SUGIMOTO, HIROKI; LIM, TENG JOON; RASMUSSEN, LARS; CHEAH, KOK LEONG; SUN, SUMEI; MATSUMOTO, YOSHIHIRO; OYAMA, TAKASHI
Abstract: At a base station 2, a CDMA received signal coming in through an antenna 4 is fed to a radio frequency unit (RFU) or high frequency unit 6. The RFU 6 demodulates a baseband signal BB from a signal RF and delivers the signal BB to an analog-to-digital converter (A/D) 8. The resulting digital signal output from the A/D 8 is input to a hybrid interference canceller (HIC) 12 as a received signal Rx Data 10. The HIC 12 divides users into two groups and assigns one combination of a parallel interference canceller and a serial interference canceller to each group. The HIC 12 cancels interference contained in the received signal Rx Data 10 for thereby estimating symbols particular to a plurality of users.
Tue, 09 Dec 2003 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/326612003-12-09T00:00:00Z
- Multi-user code division multiple access receiverhttps://scholarbank.nus.edu.sg/handle/10635/32591Title: Multi-user code division multiple access receiver
Authors: LIM, TENG JOON; RASMUSSEN, LARS; SUGIMOTO, HIROKI
Abstract: A receiver and method for receiving a code-division multiple-access (CDMA) signal combining symbol values spread by a plurality of spreading codes, which method comprises the steps of: (a) converting the CDMA signal to a baseband signal; (b) recognizing symbol boundaries in every multipath for every user in the baseband signal to produce a delay estimate; (c) estimating an attenuation and phase rotation impressed on the signal by each multipath to produce channel estimates; (d) generating new symbol estimates for every user at a sampling rate that is greater than a symbol rate of the signal; (e) generating an estimate of the received signal using said symbol estimates and channel estimates; (f) comparing the received signal with its estimate and feeding estimation error back to a means for estimating the transmitted symbols; (g) sampling the symbol estimates at the estimated symbol boundaries of each user to obtain final symbol estimates; and (h) repeating steps (b) through (g) with every new sample.
Tue, 29 May 2001 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/325912001-05-29T00:00:00Z
- Convergence analysis of chip- and fractionally spaced LMS adaptive multiuser CDMA detectorshttps://scholarbank.nus.edu.sg/handle/10635/61974Title: Convergence analysis of chip- and fractionally spaced LMS adaptive multiuser CDMA detectors
Authors: Lim, T.J.; Gong, Y.; Farhang-Boroujeny, B.
Abstract: This paper analyzes the convergence behavior of the least mean square (LMS) filter when used in an adaptive code division multiple access (CDMA) detector consisting of a tapped delay line with adjustable tap weights. The sampling rate may be equal to or higher than the chip rate, and these correspond to chip-spaced (CS) and fractionally spaced (FS) detection, respectively. It is shown that CS and FS detectors with the same time-span exhibit identical convergence behavior if the baseband received signal is strictly bandlimited to half the chip rate. Even in the practical case when this condition is not met, deviations from this observation are imperceptible unless the initial tap-weight vector gives an extremely large mean squared error (MSE). This phenomenon is carefully explained with reference to the eigenvalues of the correlation matrix when the input signal is not perfectly bandlimited. The inadequacy of the eigenvalue spread of the tap-input correlation matrix as an indicator of transient behavior and the influence of the initial tap weight vector on convergence speed are highlighted. Specifically, initialization within the signal subspace or to the origin leads to very much faster convergence compared with initialization in the noise subspace.
Tue, 01 Aug 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/619742000-08-01T00:00:00Z
- Simplified polynomial-expansion linear detectors for DS-CDMA systemshttps://scholarbank.nus.edu.sg/handle/10635/81171Title: Simplified polynomial-expansion linear detectors for DS-CDMA systems
Authors: Lei, Z.D.; Lim, T.J.
Abstract: The multistage linear receiver of Moshavi et al. was designed to approximate the decorrelating detector and the MMSE detector without calculating the inverse of the cross-correlation matrix R of the spreading codes directly. However, it is complicated by the need to calculate a set of weights using a procedure involving the inverting of a large matrix. A modified structure is proposed to accomplish the same task without the need for computationally-intensive procedures such as matrix inversion.
Thu, 06 Aug 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/811711998-08-06T00:00:00Z
- Performance analysis of the LMS blind minimum-output-energy CDMA detectorhttps://scholarbank.nus.edu.sg/handle/10635/81660Title: Performance analysis of the LMS blind minimum-output-energy CDMA detector
Authors: Gong, Yu; Lim, Teng Joon; Farhang-Boroujeny, B.
Abstract: Adaptive filters used in code division multiple access (CDMA) receivers to counter interference have been formulated both with and without the assumption of training symbols being transmitted. They are known as training-based and blind detectors respectively. We show in this letter that the convergence behaviour of the blind minimum output energy (MOE) detector can be quite easily derived, unlike what was implied by the procedure outlined in a previous paper. The simplification results from the observation that the correlation matrix determining convergence performance can be made symmetric, after which many standard results from the literature on least mean square (LMS) filters apply immediately.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/816602000-01-01T00:00:00Z
- Impact of estimation errors on multiuser detection in CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112337Title: Impact of estimation errors on multiuser detection in CDMA
Authors: Rasmussen, Lars K.; Sun, Sumei; Lim, Teng J.; Sugimoto, Hiroki
Abstract: A majority of multiuser detectors for CDMA are based on coherent detection where carrier frequency, carrier phase, transmission delays and channel characteristics are assumed known at the receiver. In a real system, these parameters must however be estimated based on the received signal. In this paper we investigate the impact of delay and channel estimation errors on the performance of multi-stage successive interference cancellation and limited tree-search detection. The estimation errors are modelled as zero-mean Gaussian random variables with the variance being a measure of the accuracy of the estimation.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123371998-01-01T00:00:00Z
- MMSE-based linear parallel interference cancellation in CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112348Title: MMSE-based linear parallel interference cancellation in CDMA
Authors: Guo, Dongning; Rasmussen, Lars K.; Sun, Sumei; Lim, Teng J.; Cheah, Christopher
Abstract: In this paper we mathematically describe the linear parallel interference canceller (PIC) using matrix algebra. It is shown that the linear PIC, whether conventional or weighted, can be seen as a linear matrix filter applied directly to the received chip-matched filtered signal vector. It is then possible to get an analytical expression for the exact bit error rate and to derive necessary conditions on the eigenvalues of the code correlation matrix and the weighting factors to ensure convergence. The close relationship between the steepest descent method for minimizing the mean squared error (MSE) and linear PIC is demonstrated and a modified PIC structure is suggested which converges to the MMSE detector rather than the decorrelator. Following the principles of the steepest descent method techniques are devised for optimizing the choice of weighting factors with respect to the mean squared error. It is shown that only K (the number of users) PIC stages are required for the equivalent matrix filter to be identical to the MMSE filter. For fewer stages, m
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123481998-01-01T00:00:00Z
- MIMO-OFDMA rate allocation and beamformer design using a multi-access channel frameworkhttps://scholarbank.nus.edu.sg/handle/10635/112347Title: MIMO-OFDMA rate allocation and beamformer design using a multi-access channel framework
Authors: Khanafer, A.; Lim, T.J.; Doostnejad, R.; Tang, T.
Abstract: This paper tackles the downlink user scheduling and transmit beamforming problems in MIMO-OFDMA by extending a recent algorithm that maximizes the weighted sum rate (WSR) to all users in MIMO flat fading channels. The proposed method has a complexity that is proportional to the number of OFDMA subcarriers, which makes it practically attractive. Having assigned users to each subcarrier and designed beamformers for each user in each subcarrier, it remains to find the best, in terms of rate maximization, adaptive modulation and coding (AMC) mode to use for each data stream. The latter problem is solved in the second half of the paper through viewing the channel from the base station to the k-th receiver as a multiple access channel (MAC) with Nk 'users', where Nk is the number of antennas at receiver k. The proposed method maps the available AMC modes to the space of allowed theoretical rates, using the signal-to-noise ratio (SNR) gap to capacity concept, and selects the operating point with the largest sum-rate. © 2012 IEEE.
Sun, 01 Jan 2012 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123472012-01-01T00:00:00Z
- Systematic approach to multistage linear successive interference cancellation for multiuser detection in dynamic asynchronous COMA systemshttps://scholarbank.nus.edu.sg/handle/10635/112298Title: Systematic approach to multistage linear successive interference cancellation for multiuser detection in dynamic asynchronous COMA systems
Authors: Ma, Y.; Tan, P.H.; Lim, T.J.
Abstract: A systematic approach is proposed for the implementation of multistage linear successive interference cancellation (SIC) in dynamic asynchronous CDMA systems. It is shown that the multistage linear SIC can asymptotically converge to the ideal decorrelating or LMMSE detector in the random code time-varying CDMA systems as well as in short-code time-invariant systems. Through simulations it is found that a moderate number of stages gives a performance close to that of an ideal detector.
Thu, 26 Nov 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122981998-11-26T00:00:00Z
- Adaptive narrowband interference cancellation in overlaid CDMA systems using prior knowledgehttps://scholarbank.nus.edu.sg/handle/10635/112311Title: Adaptive narrowband interference cancellation in overlaid CDMA systems using prior knowledge
Authors: Lim, Teng Joon; Rasmussen, Lars K.
Abstract: Narrowband interference cancellation techniques described in the literature often overlook the possibility of using prior information known to the receiver in a commercial radio environment to improve their performance. This paper examines an adaptive receiver which exploits knowledge about the narrowband interference which is readily available in commercial CDMA systems, namely its frequency and signal pulse shape, to remove it. The proposed algorithm uses only one adaptive weight per interferer, as opposed to a transversal filter interference canceller which would require many more. Attendant advantages include faster convergence, removal of the need for filter order selection and reduced distortion of the desired signal.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123111996-01-01T00:00:00Z
- Adaptive delay tracking in asynchronous multiuser CDMA systemshttps://scholarbank.nus.edu.sg/handle/10635/112310Title: Adaptive delay tracking in asynchronous multiuser CDMA systems
Authors: Lim, Teng Joon; Rasmussen, Lars K.
Abstract: Published work on multiuser code division multiple access (CDMA) receivers often assume knowledge of most system parameters. But in a mobile system, it is unreasonable to assume perfect knowledge of the propagation delays for each mobile user at all times since these delays change when mobile units move. Therefore a method for tracking propagation delays in a practical asynchronous CDMA system is needed. In this paper, we introduce a multiuser detector which is able to track time-varying delays directly, and converges in a stationary environment to the decorrelating detector. It has the advantage of being a blind algorithm, in the sense that it does not require the use of training sequences, and therefore represents a more practical approach than other adaptive multiuser detectors based on linear filtering.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123101996-01-01T00:00:00Z
- Complexity-constrained maximum-likelihood detection in multiuser CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112324Title: Complexity-constrained maximum-likelihood detection in multiuser CDMA
Authors: Rasmussen, Lars K.; Lim, Teng J.; Aulin, Tor M.
Abstract: In this paper we derive a general, recursive, additive metric for complexity-constrained maximum-likelihood detection for multiuser CDMA using breadth-first detection algorithms.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123241997-01-01T00:00:00Z
- Multipath searcher with the hybrid CDMA interference cancellerhttps://scholarbank.nus.edu.sg/handle/10635/112350Title: Multipath searcher with the hybrid CDMA interference canceller
Authors: Sun, S.; Sugimoto, H.; Rasmussen, L.K.; Lim, T.J.
Abstract: In this paper we consider the multipath searcher in a multiuser CDMA system. The conventional configuration where the searcher uses the received signal as its input is studied and a new configuration in which the searcher uses the hybrid interference canceller (HIC) output is proposed. Due to MAI reduction in the searcher's input signal, a much better performance is obtained in the new configuration. For a medium-loaded system, simulation results show that the new configuration increases the detection probability by about 8 - 40%, and the acquisition-based capacity by 260 - 360% when the targeted acquisition probability is set to 95%.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123502000-01-01T00:00:00Z
- Modified blind adaptive multiuser CDMA detectorhttps://scholarbank.nus.edu.sg/handle/10635/112349Title: Modified blind adaptive multiuser CDMA detector
Authors: You, Dunhua; Lim, Teng Joon
Abstract: In this paper, we propose a modified blind adaptive multiuser detector. It is designed to surmount the problems that the blind adaptive detector of [1] has in the multipath scenario. It needs to know the spreading code and timings of the significant multipath signals of the desired user, but is actually a `blinder' detector because it can still work when our timing knowledge is not accurate. Its performance in the case of wrong timing can be restored through signal subspace projection, assuming the estimation of the signal subspace using the received signal.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123491998-01-01T00:00:00Z
- New geometrical interpretation of the decorrelator in multiuser CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112352Title: New geometrical interpretation of the decorrelator in multiuser CDMA
Authors: Rasmussen, Lars K.; Lim, Teng J.; Alexander, Paul D.
Abstract: In this paper we present a new geometrical interpretation of the multiuser CDMA decorrelator. This interpretation relates the output of the decorrelator to the subspace spanned by the spreading codes. The interpretation makes it clear that a decision feedback detector based on the soft outputs from a decorrelator and a multistage detector with a soft output first stage decorrelator do not provide any performance improvement over the single stage decorrelator. These conclusions are confirmed by analytical results.
Mon, 01 Jan 1996 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123521996-01-01T00:00:00Z
- New soft handoff scheme using Signal Prediction Priority Queuing for the CDMA Dynamic Simulcast Systemhttps://scholarbank.nus.edu.sg/handle/10635/112354Title: New soft handoff scheme using Signal Prediction Priority Queuing for the CDMA Dynamic Simulcast System
Authors: Lu, Fan; Lim, Teng Joon
Abstract: In this paper, a new Signal Prediction Priority Queuing (SPPQ) handoff ordering scheme is proposed. A new idea of the Dynamic Simulcast System for CDMA microcell system is presented. The call performances comparison between the new SPPQ scheme and First In First Out (FIFO) queuing are obtained by the computer simulation. It is shown that the call blocking probability of the new SPRQ scheme is lower than that of FIFO queuing in the same case scenario. It is also shown that the outage probability of the new SPPQ is superior to that of FIFO.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123541997-01-01T00:00:00Z
- Online energy management strategies for base stations powered by the smart gridhttps://scholarbank.nus.edu.sg/handle/10635/112358Title: Online energy management strategies for base stations powered by the smart grid
Authors: Leithon, J.; Lim, T.J.; Sun, S.
Abstract: We consider the problem of minimizing the electricity bill for a cellular base station powered by the smart grid and locally harvested renewable energy. We consider hourly-varying electricity prices made known one day ahead to the base station. We assume that the base station is equipped with a finite-capacity battery. We ensure that the instantaneous energy demand of the base station is satisfied and the constraints imposed by the battery are observed at any point in time. We propose several online energy management strategies that require only causal knowledge of the renewable energy generation and the power consumption profiles. We benchmark our proposed strategies against the optimal energy management policy which assumes perfect knowledge of all system parameters, e.g., base station energy usage and renewable energy generation, both in the past and the future. Simulation results show that the performance of our proposed online strategy deviates from the optimal by 2% at most. © 2013 IEEE.
Tue, 01 Jan 2013 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123582013-01-01T00:00:00Z
- One-shot filtering equivalence for linear successive interference cancellation in CDMAhttps://scholarbank.nus.edu.sg/handle/10635/112357Title: One-shot filtering equivalence for linear successive interference cancellation in CDMA
Authors: Rasmussen, Lars K.; Lim, Teng J.; Johansson, Ann-Louise
Abstract: In this paper we consider a matrix-algebraic approach to linear successive interference cancellation (SIC). It is shown that both single- and multi-stage linear SIC schemes correspond to a one-shot linear matrix filtering that can be performed directly on the received chip-matched filtered received vector without explicitly performing the interference cancellation. This description allows for determining the bit error rate analytically. Also eigenvalue conditions for convergence of the multi-stage scheme are derived and the concept of ε-convergence introduced for determining the number of stages necessary for practical convergence.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123571997-01-01T00:00:00Z
- Adaptive filters in multiuser (MU) CDMA detectionhttps://scholarbank.nus.edu.sg/handle/10635/112212Title: Adaptive filters in multiuser (MU) CDMA detection
Authors: Lim, T.J.; Roy, S.
Abstract: The primary purpose of this work is to provide a perspective on adaptive code-division multiple-access (CDMA) MU receivers that have been proposed for future digital wireless systems. Adaptive receivers can potentially adapt to unknown and time-varying environmental parameters such as the number of users, their received powers, spreading codes and time-delays. Two adaptive receiver architectures are primarily considered - one in which the sampled received signal is filtered, and can be used in both the uplink (i.e., at the base station) and downlink (i.e., at the mobile handset), and another in which the spreading codes of users are filtered (assuming knowledge of users' codes and its timing at the receiver) for use in the uplink. Relevant issues such as training-based and blind implementations of the adaptive receiver are discussed, as well as (transient) convergence rates and estimation noise in steady-state. © J.C. Baltzer AG, Science Publishers.
Thu, 01 Jan 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122121998-01-01T00:00:00Z
- Adaptive symbol and parameter estimation in asynchronous multiuser CDMA detectorshttps://scholarbank.nus.edu.sg/handle/10635/112215Title: Adaptive symbol and parameter estimation in asynchronous multiuser CDMA detectors
Authors: Lim, T.J.; Rasmussen, L.K.
Abstract: Existing multiuser code-division multiple-access (CDMA) detectors either have to rely on strict power control or near-perfect parameter estimation for reliable operation. In this paper, a novel adaptive multiuser CDMA detector structure is introduced. Using either an extended Kaiman filter (EKF) or a recursive least squares (RLS) formulation, adaptive algorithms which jointly estimate the transmitted bits of each user and individual amplitudes and time delays may be derived. The proposed detectors work in a tracking mode after initial delay acquisition is accomplished using other techniques not discussed here. Through computer simulations, we show that the algorithms perform better than a bank of single-user (SU) receivers in terms of near-far resistance. Practical issues such as the selection of adaptation parameters are also discussed in some detail. © 1997 IEEE.
Wed, 01 Jan 1997 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122151997-01-01T00:00:00Z
- Adaptive IIR filtering for asynchronous multiuser CDMA detectionhttps://scholarbank.nus.edu.sg/handle/10635/112214Title: Adaptive IIR filtering for asynchronous multiuser CDMA detection
Authors: Lim, Teng Joon; Wong, Siew Ying
Abstract: The use of adaptive finite-impulse response (FIR) filters to suppress multiple access interference (MAI) in code division multiple access (CDMA) receivers has been well documented. But the linear minimum mean squared error (MMSE) detector is in fact the Kalman filter, which is a first-order recursive filter for asynchronous multiuser CDMA systems. Therefore in an adaptive implementation, the filter structure should be a first-order IIR filter. Of the host of adaptive IIR filtering algorithms, we choose to study the simplest of them, the recursive least mean square (LMS) method. Although mis-convergence has been reported for this algorithm when the system order is under-estimated, in our case this does not occur since the system order is unity at all times. Exact modelling is therefore possible, and convergence to the global minimum is seen in all our simulations using an algorithm that has a complexity linear in the number of adaptive parameters.
Fri, 01 Jan 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122141999-01-01T00:00:00Z
- An asynchronous multiuser CDMA detector based on the Kalman filterhttps://scholarbank.nus.edu.sg/handle/10635/112216Title: An asynchronous multiuser CDMA detector based on the Kalman filter
Authors: Lim, T.J.; Rasmussen, L.K.; Sugimoto, H.
Abstract: In this paper, we introduce a multiuser receiver based on the Kalman filter, which can be used for joint symbol detection and channel estimation. The proposed algorithm has the advantage of working even when the spreading codes used have a period larger than one symbol interval ("long codes"), unlike adaptive equalizer-type detectors. Simulation results which demonstrate the performance advantage of the proposed receiver over the conventional detector, the minimum mean squared error (MMSE) detector and a recursive least squares (RLS) multiuser detector are presented. A thorough comparison of the MMSE detector and the proposed detector is attempted because the Kalman filter also solves the MMSE parameter estimation problem, and it is concluded that, because the statespace model assumed by the Kalman filter fits the code division multiple access (CDMA) system exactly, a multiuser detector based on the Kalman filter must necessarily perform better than a nonrecursive, finite-length MMSE detector. The computational complexity of the detector and its use in channel estimation are also studied.
Tue, 01 Dec 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122161998-12-01T00:00:00Z
- Simplified polynomial-expansion linear detectors for DS-CDMA systemshttps://scholarbank.nus.edu.sg/handle/10635/50598Title: Simplified polynomial-expansion linear detectors for DS-CDMA systems
Authors: Lei, Z.D.; Lim, T.J.
Abstract: The multistage linear receiver of Moshavi et al. was designed to approximate the decorrelating detector and the MMSE detector without calculating the inverse of the cross-correlation matrix R of the spreading codes directly. However, it is complicated by the need to calculate a set of weights using a procedure involving the inverting of a large matrix. A modified structure is proposed to accomplish the same task without the need for computationally-intensive procedures such as matrix inversion.
Thu, 06 Aug 1998 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/505981998-08-06T00:00:00Z
- The kaiman filter as the optimal linear minimum mean-squared error multiuser cdma detectorhttps://scholarbank.nus.edu.sg/handle/10635/112301Title: The kaiman filter as the optimal linear minimum mean-squared error multiuser cdma detector
Authors: Lim, T.J.; Ma, Y.
Abstract: In this paper, it is shown that a first-order linear state-space model applies to the asynchronous code-division multiple-access (CDMA) channel, and thus the Kaiman filter produces symbol estimates with the minimum mean-squared error (MMSE) among all linear filters, in long- or short-code systems for a given detection delay. This result may be used as a benchmark against which to compare the performance of other linear detectors in asynchronous channels. It also reveals that a time-varying recursive filter with a fixed and finite complexity implements the fixed-lag linear MMSE (LMMSE) detector, which hitherto has been assumed to require a processing window (and hence complexity) that grows with time. © 2000 IEEE.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123012000-01-01T00:00:00Z
- Bias in CDMA channel estimates with the use of short spreading sequenceshttps://scholarbank.nus.edu.sg/handle/10635/112317Title: Bias in CDMA channel estimates with the use of short spreading sequences
Authors: Lim, Teng Joon
Abstract: When short spreading sequences are employed in CDMA systems, the channel estimates obtained using the correlation based approach are biased. A simple decorrelating estimator is proposed to remove the bias and hence improve parameter performance. Simulation results show that the proposed estimator reduces channel estimation error and improves bit error rate (BER) substantially.
Sat, 01 Jan 2000 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1123172000-01-01T00:00:00Z
- Systematic approach to multistage linear successive interference cancellation for multiuser detection in dynamic asynchronous CDMA systemshttps://scholarbank.nus.edu.sg/handle/10635/112297Title: Systematic approach to multistage linear successive interference cancellation for multiuser detection in dynamic asynchronous CDMA systems
Authors: Ma, Y.; Tan, P.H.; Lim, T.J.
Abstract: A systematic approach is proposed for the implementation of multistage linear successive interference cancellation (SIC) in dynamic asynchronous CDMA systems. It is shown that the multistage linear SIC can asymptotically converge to the ideal decorrelating or LMMSE detector in random code time-varying CDMA systems as well as in short-code time-invariant systems. Through simulations it is found that a moderate number of stages gives a performance close to that of an ideal detector.
Thu, 04 Feb 1999 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1122971999-02-04T00:00:00Z