Showing papers in "IEEE Communications Letters in 1997"
TL;DR: This letter describes the SISO APP module that updates the APP corresponding to the input and the output bits, of a code, and shows how to embed it into an iterative decoder for a new hybrid concatenation of three codes, to fully exploit the benefits of the proposed S ISO APP module.
Abstract: Concatenated coding schemes consist of the combination of two or more simple constituent encoders and interleavers. The parallel concatenation known as "turbo code" has been shown to yield remarkable coding gains close to theoretical limits, yet admitting a relatively simple iterative decoding technique. The recently proposed serial concatenation of interleaved codes may offer superior performance to that of turbo codes. In both coding schemes, the core of the iterative decoding structure is a soft-input soft-output (SISO) a posteriori probability (APP) module. In this letter, we describe the SISO APP module that updates the APP's corresponding to the input and the output bits, of a code, and show how to embed it into an iterative decoder for a new hybrid concatenation of three codes, to fully exploit the benefits of the proposed SISO APP module.
609 citations
TL;DR: A simple iterative decoding technique using hard-decision feedback is presented for bit-interleaved coded modulation (BICM), making BICM with iterative decode suitable for both types of channels.
Abstract: A simple iterative decoding technique using hard-decision feedback is presented for bit-interleaved coded modulation (BICM). With an 8-state, rate-2/3 convolutional code, and 8-PSK modulation, the improvement over the conventional BICM scheme exceeds 1 dB for a fully-interleaved Rayleigh flat-fading channel and exceeds 1.5 dB for a channel with additive white Gaussian noise. This robust performance makes BICM with iterative decoding suitable for both types of channels.
562 citations
TL;DR: This work proposes a novel subspace approach to estimate the AOA and delays of multipath signals from digitally modulated sources arriving at an antenna array using a collection of estimates of a space-time vector channel.
Abstract: In wireless communications, mobiles emit signals that arrive at a base station via multiple paths. Estimating each path's angle-of-arrival (AOA) and propagation delay is necessary for several applications, such as mobile localization for emergency services. We propose a novel subspace approach to estimate the AOA and delays of multipath signals from digitally modulated sources arriving at an antenna array. Our method uses a collection of estimates of a space-time vector channel. The Cramer-Rao bound (CRB) and simulations are provided.
237 citations
TL;DR: A novel automatic repeat request (ARQ) technique based on the turbo coding principle that uses the log-likelihood ratios generated by the decoder during a previous transmission as a priori information when decoding retransmissions is presented.
Abstract: A novel automatic repeat request (ARQ) technique based on the turbo coding principle is presented. The technique uses the log-likelihood ratios generated by the decoder during a previous transmission as a priori information when decoding retransmissions. Simulation results show a significant decrease in frame error rate, especially at low-to-moderate E/sub b//N/sub 0/.
216 citations
TL;DR: An algorithm is presented that finds a feasible joint base assignment and transmission power vector in the downlink and shows that under some conditions the algorithm also minimizes the sum of downlink powers.
Abstract: The joint power control and base station assignment for the downlink is considered in this paper. Based on the results and observations of previous work we present an algorithm that finds a feasible joint base assignment and transmission power vector in the downlink. We show that under some conditions the algorithm also minimizes the sum of downlink powers. Interestingly, there is not always a Pareto optimal power vector for the joint problem in the downlink as is the case in the uplink. This fact is demonstrated through a counterexample.
106 citations
TL;DR: The optimum linear time-invariant filter that maximizes the signal-to-noise ratio (SNR) is the solution to an integral equation and the full form of the complex integral equation using the complex baseband representation of signals is presented.
Abstract: The optimum linear time-invariant (LTI) filter that maximizes the signal-to-noise ratio (SNR) is, in general, the solution to an integral equation. This is the well-known matched filter. With regards to the detection of bandpass signals, we present the full form of the integral equation using the complex baseband representation of signals. The correct form of the complex integral equation includes, in addition to the autocorrelation function, a pseudoautocorrelation function which vanishes for most applications. However, in the presence of improper complex noise, overlooking the pseudoautocorrelation leads to a "nonoptimal" filter. To illustrate the concept, we apply the theory to a direct-sequence code-division multi-access (DS-CDMA) system in which improper complex noise arises. In the application, we derive the SNR maximizing filter and the nonoptimal filter and compare their near-far resistances.
96 citations
TL;DR: A burst frequency synchronization procedure which is based on the usage of single-carrier training data and orthogonal frequency division multiplexing (OFDM) payload modulation is proposed, which is suitable for burst transmission and single-burst demodulation.
Abstract: We propose a burst frequency synchronization procedure which is based on the usage of single-carrier training data and orthogonal frequency division multiplexing (OFDM) payload modulation. The payload modulation format is similar to the one that is used in the DAB standard, whereas training data are chosen as simple CAZAC sequences. It is shown that the resulting modulation and transmission scheme is suitable for burst transmission and single-burst demodulation. Performance degradation due to synchronization errors is shown to be small.
77 citations
TL;DR: An eigenvector solution is derived for the joint optimization of the weight vector and the modified channel vector by a space-time filter designed to maximize signal-to-interference-plus-noise ratio (SINR) by jointly optimizing the weight vectors and themodified channel vector.
Abstract: We present a hybrid approach for separate cochannel interference (CCI) reduction and intersymbol interference (ISI) equalization in a slow Rayleigh fading channel. In this hybrid approach, a space-time filter is designed to maximize signal-to-interference-plus-noise ratio (SINR) by jointly optimizing the weight vector and the modified channel vector. A Viterbi equalizer then follows to equalize ISI and demodulate data symbols without noise enhancement. We derive an eigenvector solution for the joint optimization of the weight vector and the modified channel vector. Simulation results show good performance even at low carrier-to-interference-ratio (CIR).
76 citations
TL;DR: A new nondata-aided clock recovery scheme for phase-shift keying (PSK) modulated signals is proposed that is based on maximum-likelihood methods and leads to a feedforward structure that can be easily implemented in digital form.
Abstract: We propose a new nondata-aided clock recovery scheme for phase-shift keying (PSK) modulated signals. Its derivation is based on maximum-likelihood (ML) methods and leads to a feedforward structure that can be easily implemented in digital form. The algorithm exhibits improvements with respect to other existing circuits, especially with small excess bandwidth factors. Its performance is assessed by simulation for quaternary PSK (QPSK) and 8PSK formats.
70 citations
TL;DR: The effect of directional antennas at the base station on the Doppler spectrum is analyzed and the probability density function of the angle-of-arrival of the multipath components at the mobile unit and the direction of the motion of the mobile is analyzed.
Abstract: We analyze the effect of directional antennas at the base station on the Doppler spectrum. It is well known that the Doppler spectrum is dependent on the probability density function (pdf) of the angle-of-arrival (AOA) of the multipath components at the mobile unit and the direction of the motion of the mobile. The Doppler spectrum is U-shaped, when the pdf of the AOA of the multipath components at the mobile is uniform. Here, however, we study the Doppler fading at the base station and assume that the scatterers are uniformly located around the mobile within a circle and derive the pdf of the AOA of the multipath components at the mobile when directional antennas are used at the base station.
62 citations
TL;DR: A simple model for future data traffic in wireless radio networks intended for design and performance analysis of radio resource allocation algorithms in future wireless systems is proposed.
Abstract: Based on an analysis of Internet protocols for data communication, we propose a simple model for future data traffic in wireless radio networks. Model parameters are selected so as to resemble traffic from the Worldwide Web (WWW) access and from distributed file systems. By changing a single parameter, the model can be switched between resembling up- or down-link traffic. The model is intended for design and performance analysis of radio resource allocation algorithms in future wireless systems.
TL;DR: A framework for modifying a decoder for parallel concatenated codes to incorporate a general hidden Markov source model is presented, which allows the receiver to utilize the statistical characteristics of the source during the decoding process, and leads to significantly improved performance relative to systems in which source statistics are not exploited.
Abstract: We present here a framework for modifying a decoder for parallel concatenated codes to incorporate a general hidden Markov source model. This allows the receiver to utilize the statistical characteristics of the source during the decoding process, and leads to significantly improved performance relative to systems in which source statistics are not exploited. One of the constituent decoders makes use of a modified trellis which jointly describes the source and the encoder. The number of states in this modified trellis is the product of the number of states in the hidden Markov source and the number of states in the encoder.
TL;DR: The authors show that the Shannon capacity limit for the additive white Gaussian noise (AWGN) channel can be approached within 0.27 dB at a bit error rate (BER) of 10/sup -5/ by applying long but simple Hamming codes as component codes to an iterative turbo-decoding scheme.
Abstract: The authors show that the Shannon capacity limit for the additive white Gaussian noise (AWGN) channel can be approached within 0.27 dB at a bit error rate (BER) of 10/sup -5/ by applying long but simple Hamming codes as component codes to an iterative turbo-decoding scheme. In general, the complexity of soft-in/soft-out decoding of binary block codes is rather high. However, the application of a neurocomputer in combination with a parallelization of the decoding rule facilitates an implementation of the decoding algorithm in the logarithmic domain which requires only matrix additions and multiplications. But the storage requirement might still be quite high depending on the interleavers used.
TL;DR: A structured linear channel model is developed that is linearly parametrized by an unknown vector and used in a multisensor and oversampled maximum-likelihood sequence estimation (MLSE) receiver.
Abstract: This letter describes a channel estimator using known prior information about the transmit and receive filters. It is shown that the composite channel lies in the subspace of the transmit and receive filter impulse responses. A structured linear channel model is then developed that is linearly parametrized by an unknown vector. To illustrate the potential usefulness of such an approach, the estimated structured channel is used in a multisensor and oversampled maximum-likelihood sequence estimation (MLSE) receiver.
TL;DR: In this letter, the average maximum-likelihood performance of the three ways of co-decoding turbo codes is defined and evaluated.
Abstract: In this letter we define and evaluate the average maximum-likelihood performance of the three ways of co-decoding turbo codes. In all cases the information sequence is split into blocks of N bits (N being the length of the interleaver used by the turbo code), that are encoded by the first constituent encoder and, after interleaving, by the second encoder. In the first operation mode, both constituent encoders work in a continuous fashion, whereas in the second, at the end of each block, a suitably chosen sequence of bits is appended to the information block in order to terminate the trellises of both constituent codes. In the third mode, the operation is similar to the second, but, instead of trellis termination, both constituent encoders are simply reset.
TL;DR: The effect of error correlations on the throughput of a single transport control protocol (TCP) Tahoe connection is studied and it is found that TCP Tahoe performs better in the presence of clustered errors.
Abstract: Wireless channels are known to introduce correlated bursts of errors at the physical layer. Although these errors affect the performance at all layers of a protocol stack, their precise impact, especially at the higher layers, is not completely understood. We study the effect of error correlations on the throughput of a single transport control protocol (TCP) Tahoe connection. We find that TCP Tahoe performs better in the presence of clustered errors. This suggests that techniques that reduce channel memory may be undesirable.
TL;DR: Simulation results for an additive white Gaussian noise channel show that the bit-error rate (BER) floor of the turbo code can be lowered by using this serial concatenation scheme.
Abstract: A serial concatenation scheme consisting of a Bose-Chaudhuri-Hocquenghem (BCH) outer code and a turbo inner code is proposed. We first establish that only a small number of bit positions at the turbo decoder output are likely to be in error at high signal-to-noise ratios. A double-error correcting BCH outer code is used to protect these particular error prone bits. Simulation results for an additive white Gaussian noise (AWGN) channel show that the bit-error rate (BER) floor of the turbo code can be lowered by using this serial concatenation scheme. The proposed technique offers higher throughput efficiency and lower complexity than other serial concatenation schemes.
TL;DR: It is shown that there exists an optimum diversity level under certain channel conditions and the derived characteristic function is used to obtain a compact bit error rate (BER) expression for different diversity levels.
Abstract: An exact closed-form expression of the characteristic function is derived for a fast frequency-hopping (FFH) binary orthogonal frequency-shift-keying (FSK) spread-spectrum (SS) communication system. The FFH system employs a product combining receiver over a Rayleigh-fading channel with partial-band jamming and additive white Gaussian noise (AWGN). The derived characteristic function is then used to obtain a compact bit error rate (BER) expression for different diversity levels. Our study shows that there exists an optimum diversity level under certain channel conditions.
TL;DR: This letter provides a downlink power control algorithm and its convergence for adjusting as well as allocating appropriate power levels according to the need of mobiles.
Abstract: This letter provides a downlink power control algorithm and its convergence for adjusting as well as allocating appropriate power levels according to the need of mobiles. The adjustment process and its property provide a distinct view for understanding existing CDMA downlink power control algorithms.
TL;DR: A new technique for joint channel estimation and symbol detection in the Rayleigh flat-fading channels with impulsive noise is developed and it is seen that the proposed detector outperforms the detector based on the Kalman filter.
Abstract: A new technique for joint channel estimation and symbol detection in the Rayleigh flat-fading channels with impulsive noise is developed. This technique involves an approximation to the likelihood statistics for such channels, which in turn is based on the Masreliez approximation of nonlinear filtering. It is seen that the proposed detector outperforms the detector based on the Kalman filter.
TL;DR: A polynomial-time algorithm is proposed that computes a table that maps all intervals for r to the corresponding paths that minimize the end-to-end delay.
Abstract: We consider the transmission of a message of size r from a source to a destination with the minimum end-to-end delay over a computer network where bandwidth can be reserved and guaranteed on the links. Different paths will be required for different intervals of values for r. We propose a polynomial-time algorithm that computes a table that maps all intervals for r to the corresponding paths that minimize the end-to-end delay.
TL;DR: This work defines and then simulate a specific implementation of the TRSP scheme for an integrated voice and broadband data system and shows that this scheme provides good performance for both voice and data.
Abstract: We propose a time slot reuse partitioning (TRSP) scheme for resource assignment in packet-switched fixed TDMA wireless networks. The TSRP scheme is based upon two key ideas. The first one is for the system to have more than one coexisting reuse pattern in the time domain. The second is to match a terminal or application to an appropriate reuse pattern, so as to guarantee the required quality of service (QoS). We define and then simulate a specific implementation of the TRSP scheme for an integrated voice and broadband data system. The results show that this scheme provides good performance for both voice and data.
TL;DR: A secure authentication protocol which supports both the privacy of messages and the authenticity of communicating parties is proposed and can be achieved with two messages merely between two parties involved.
Abstract: A secure authentication protocol which supports both the privacy of messages and the authenticity of communicating parties is proposed. The trusted third party (key information center) is not needed once the secure network system is set up. Mutual authentication and key distribution can be achieved with two messages merely between two parties involved.
TL;DR: Simulation results are presented to demonstrate the effectiveness of the proposed reservation with Preemption and Acknowledgment approach to ATM switches.
Abstract: Reservation with Preemption and Acknowledgment (RPA) is a simple, efficient, and flexible queuing discipline and scheduling algorithm for input buffered asynchronous transfer-mode (ATM) switches. This letter describes the RPA algorithms, and presents simulation results to demonstrate the effectiveness of the proposed approach.
TL;DR: The bit error rate performance for both external modulation and modulation of the injection current is examined and only a moderate penalty is found associated with the limited phase excursion.
Abstract: We examine the bit error rate (BER) of the conventional matched-filter detector for an optical code division multiple access (CDMA) system employing coherent homodyne detection. We assume a phase shift keying (PSK) modulation format where the phase is modulated by one of two methods: (1) an external phase modulator or (2) injection locking. Phase excursion is limited to /spl plusmn/0.42 /spl pi/ when using injection locking. We examine the bit error rate performance for both external modulation and modulation of the injection current and find only a moderate penalty (0.55 dB) associated with the limited phase excursion.
TL;DR: It is demonstrated that the classical receiver used for coherent detection of differentially encoded M-ary phase-shift keying (M-PSK) can be arrived at by a suitable approximation of the likelihood function used to derive the true optimum receiver whose structure is also given.
Abstract: This paper demonstrates that the classical receiver used for coherent detection of differentially encoded M-ary phase-shift keying (M-PSK), namely, the one that makes optimum coherent decisions on two successive symbol phases and then differences these to arrive at a decision on the information phase is suboptimum when M>2. However, this receiver structure can be arrived at by a suitable approximation of the likelihood function used to derive the true optimum receiver whose structure is also given.
TL;DR: This work extends the DR algorithm to not only exploit the knowledge of the PN code but also to preserve the constant modulus property of the signal to create a new algorithm called LS-DRMTCMA.
Abstract: We apply the concept of the despread-respread (DR) algorithm to multi-target arrays for code-division multiple-access (CDMA) signals, the despread-respread algorithm exploits the knowledge of the pseudo-noise (PN) code used to generate the transmitted CDMA signal. We extend the DR algorithm to not only exploit the knowledge of the PN code but also to preserve the constant modulus property of the signal. This new algorithm is called the least squares despread respread multi-target constant modulus array (LS-DRMTCMA). LS-DRMTCMA performs better than the least squares despread respread multi-target array (LS-DTMTA), least squares multi-target constant modulus array (LS-MTCMA), and steepest descent multi-target decision directed array (SD-MTDDA).
TL;DR: A combined probability density function approach for the forward link and a mean-method technique for the reverse link are proposed to significantly reduce the computational complexity of the bit error rate analysis of a direct-sequence code-division multiple-access cellular system.
Abstract: The bit error rate (BER) analysis of a direct-sequence code-division multiple-access (DS-CDMA) cellular system over a Rayleigh-fading channel often results in complicated expressions even though the Gaussian approximation is applied. A combined probability density function (pdf) approach for the forward link and a mean-method technique for the reverse link are proposed to significantly reduce the computational complexity. The simplified BER expressions are derived and yield accurate results.
TL;DR: A bifurcated queueing approach to breaking the well-known 0.586 barrier for the throughput of input queued switches with head-of-line blocking and shows that as k increases, the throughput approaches one.
Abstract: We propose a bifurcated queueing approach to breaking the well-known 0.586 barrier for the throughput of input queued switches with head-of-line blocking. Each input line maintains a small number k of parallel queues, one for each of a set of k mutually exclusive subsets of the set of output-port addresses. We generalize the analysis of Karol et al. (1987) and show that the upper bound on throughput is (1+k)-/spl radic/1+k/sup 2/, k=1, 2, 3, .... We point out that even for k=2, there is a significant improvement in throughput and that as k increases, the throughput approaches one.
TL;DR: Simulation results under bursty and imbalanced traffic conditions show that quasi-pushout cell discarding can achieve comparable cell loss performance as pushout at a much lower complexity.
Abstract: In asynchronous transfer mode (ATM) switching networks, buffers are required to accommodate traffic fluctuations due to statistical multiplexing. However, cell discarding takes place when the buffer space of a network node is used up during a traffic surge. Though pushout cell discarding was found to achieve fair buffer utilization and good cell loss performance, it is difficult to implement because of the large number of queue length comparisons. We propose quasi-pushout cell discarding which reduces the number of queue length comparisons by employing the concept of quasi-longest queue. Simulation results under bursty and imbalanced traffic conditions show that quasi-pushout can achieve comparable cell loss performance as pushout at a much lower complexity.