Statistical properties of out-of-frame detection schemes fordigital transmission systems

The importance of the misframe times for DS1 frame synchronization has often been addressed in designing and using network elements and mediation units. By extending the work of J. H. Eu and W. W. Rollins (1991), Markov chain first passage time analysis is used to derive higher moments of the misframe times in both random and burst error environments. This methodology is of great value in evaluating frame synchronization techniques for digital transmission systems. By experimenting with several out-of-frame detection schemes and reasonable values for bit error ratio (BER), it is shown that misframe times are always approximately exponentially distributed for all schemes     

Frame alignment in a digital carrier system-a tutorial

Four key timing parameters that are used as performance measures are defined; reframe time, false in-frame time, out-of-frame detection time, and misframe time. Several strategies that improve frame alignment performance are considered for the case of a burst frame alignment word (FAW). With a little modification, the same strategies could also be applied to the case of a distributed FAW. The probability generating function is introduced, and its derivation from a state transition diagram is presented. The probability generating function is used in the timing parameters estimation. As an example, the frame alignment of a SONET (synchronized optical network) STS-3 signal is discussed     

An evaluation of error performance estimation schemes for DS1transmission systems carrying live traffic

Under the memoryless binary symmetric channel assumption, the author evaluates performance estimation schemes for DS1 transmission systems carrying live traffic. Bipolar violations, framing bit errors, and code-detected errors are commonly used to estimate bit error ratios and the respective numbers of errored seconds and severely errored seconds that are fundamental parameters in characterizing the performance of DS1 transmission systems. A basic framework based on the coefficient of variation is proposed to evaluate several estimation schemes. Serious drawbacks of the existing estimation schemes based on the superframe (D4) format are identified. A new method for estimating the number of errored seconds is proposed. A computer simulation shows that this proposed method performs much better than the conventional counting method. The performance of the cyclic redundancy check (CRC) code of the extended superframe (ESF) format is also evaluated through the use of a computer simulation model. The simulation results show that all the errored seconds are detected by the CRC code. This is a welcome feature of the code for real-time performance monitoring. Furthermore, the results suggest a new threshold of 326 CRC errors per second for determining severely errored seconds     

多带UWB优先级竞争接入饱和吞吐量优化方法

采用二维马尔可夫链模型,计入了超帧中的标记期和硬预留,对系统中的同一优先级竞争接入站点在差错信道下的饱和吞吐量进行研究。分析表明,信道质量较差时短帧比长帧的系统饱和吞吐量大。理论计算结果与NS2软件仿真结果在误差范围内相一致。差错信道条件下存在最优传输帧长,为优化链路控制,提高系统吞吐量提供了理论依据。     

Energy efficiency analysis of IEEE 802.15.6 based wireless body area networks in scheduled access mode

This paper investigates the energy efficiency of IEEE 802.15.6 based wireless body area networks in the scheduled access mode. We assume that the hub operates in beacon mode with superframes and the nodes obtain scheduled allocation intervals consisting of finite number of allocation slots from the hub. In this paper, first of all, we present analytical models to compute the energy efficiency of the network for various scheduled allocation and acknowledgement policies assuming ideal channel conditions. The numerical and simulation results show that energy efficiency can be improved by (1) increasing the number of uploads in an active superframe, (2) increasing the payload size, (3) adopting block acknowledgement policy instead of immediate acknowledgement policy or (4) by decreasing the periodicity of allocations. We then present an analytical model to evaluate the energy efficiency in the presence of channel error. An approximate analytical solution for optimal frame size that maximize the energy efficiency of the network in error prone channel is obtained. For each node, we also provide analytical expression for the optimal allocation interval per superframe that maximize the energy efficiency of the network. Through extensive simulation studies, we establish that, in an error prone channel, the energy efficiency can be improved if the nodes make use of computed optimal frame size and optimal allocation interval for the uplink data transfer.     

Throughput performance of memory ARQ schemes

We present a throughput analysis for the memory automatic repeat request (ARQ) schemes with self-decodable frame retransmissions, taking into account frame header and frame acknowledgment failure probability. A lower bound on the throughput is obtained for a very general class of schemes which encompasses many of those proposed in the literature. Numerical results are given for several example systems, and suitable header and acknowledgment forward error correction (FEC) encodings are determined     

MIMO iterative receiver SNR estimation strategies for link to system interfacing

This paper presents link to system (L2S) interfacing technique for multiple input and multiple output (MIMO) iterative receivers. In L2S interfacing, usually the post detection signal to noise ratio (SNR)‐based frame error rate lookup tables (LUT) are used to predict the link level performance of receivers. While L2S interfacing for linear MIMO receivers can be conveniently implemented, it is more challenging for MIMO iterative receivers due to unavailability of the closed form SNR expressions. In this paper, we propose three methods for post detection SNR estimation for MIMO iterative receivers. The first is based on the QR decomposition of the channel matrix, the second relies on the residual noise calculation based on the soft symbols, and the third exploits the closed form SNR expressions for linear receivers. A link to system interface model for iterative receivers is developed for evaluating the reference curves for different modulation and coding schemes, and results are validated by comparing the simulated and predicted frame error rates. It is shown that linear and residual noise‐based SNR approximations result in a very good prediction performance whereas the performance of QR decomposition‐based method degrades for higher order modulations and coding schemes. This paper presents link to system interfacing technique for MIMO iterative receivers. A link to system interface model for iterative receivers is developed for evaluating the reference curves for different modulation and coding schemes, and results are validated by comparing the simulated and predicted frame error rates. Three post detection SNR evaluation schemes have been proposed for link to system interfacing all of which give good prediction performance especially at lower order modulation.     

A Simple Time Shift Scheme for Beacon Broadcasting Based on Cluster-Tree IEEE 802.15.4 Low-Rate WPANs

Wireless sensor networks based on the IEEE 802.15.4 standard is able to carry out short-distance transmissions in low-rate and low-power wireless personal area networks. To access the channel, it uses the slotted carrier sense multiple access with collision avoidance (CSMA/CA) in the contention access period (CAP) under superframe structure with beacon frame broadcast to bound the duration of superframe. However, the beacon frame is transmitted periodically without CSMA/CA so that it could be collided continuously. This type of collision causes node lost synchronization and unable to join a network because the beacon frame cannot be normally received. This paper proposes a simple time shift scheme based on IEEE 802.15.4 to keep original superframe structure and distribute transmission of beacon frame over active period to avoid beacon frame collisions. We use a simple function to allocate beacon frame transmission in the active period. The simulation results show that the proposed scheme significantly reduces the beacon collision and lost synchronization rate, and it also improves the throughput.     

Frame-theoretic analysis of DFT codes with erasures

Discrete Fourier transform (DFT) codes have been used as joint source-channel codes in order to provide robustness against channel errors and erasures. This paper presents a frame-theoretic analysis of lowpass DFT codes with erasures. First, it is shown that such codes make a special class of frames. Then, the message reconstructions by the frame-theoretic signal space projection and coding-theoretic syndrome decoding of erasures are analyzed, and their equivalence is proved. The error performance of lowpass DFT codes is analyzed using the frame theory. The analysis helps in classifying the subframes of a DFT frame into several classes. This classification leads to the development of packetization criteria in order to guarantee minimum mean square reconstruction error and, thus, to minimize the effect of the quantization error. Simulation results substantiate the presented theory and the proposed packetization schemes.     

Design and comparison of turbo codes under frame‐length and code‐rate constraints

When the performances of error‐correcting codes for space communications are investigated, with the aim to translate them into practical recommendations, comparison among different schemes is usually a very difficult task. As a matter of fact, these comparisons rarely yield general conclusions. On the other hand, most practical space applications impose strong constraints on the code parameters, which have important effects on code selection. In this paper, we show a methodology and several examples of design and comparison, derived under fixed constraints imposed by the system application on the frame‐length and the code‐rate. CCSDS Earth observation missions requiring both large coding gains and high spectral efficiency are considered as a case study. Though referred to this specific space mission framework, the presented study is quite general and applies to many other digital communication systems; e.g. for wireless or wired applications where similar constraints exist but are often not taken in due consideration by the designer of the error‐correcting schemes. Copyright © 2006 John Wiley & Sons, Ltd.     

On the Statistical Analysis of Queue Lengths and Waiting Times for Statistical Multiplexers with ARQ Retransmission Schemes

The stop-and-wait and continuous error detection retransmission schemes are widely used to control errors in many computercommunication systems. In this paper a model is developed which describes the statistical behavior of the multiplexer using these error detection and retransmission schemes. The model is applied to the case where errors are independent and can occur during data and/or acknowledgment transmission. Numerical results for the mean waiting time and mean queue occupancy are presented for the case of independent errors.     

MMSE interference suppression for direct-sequence spread-spectrumCDMA

We consider interference suppression for direct-sequence spread-spectrum code-division multiple-access (CDMA) systems using the minimum mean squared error (MMSE) performance criterion. The conventional matched filter receiver suffers from the near-far problem, and requires strict power control (typically involving feedback from receiver to transmitter) for acceptable performance. Multiuser detection schemes previously proposed mitigate the near-far problem, but are complex and require explicit knowledge or estimates of the interference parameters. In this paper, we present and analyze several new MMSE interference suppression schemes, which have the advantage of being near-far resistant (to varying degrees, depending on their complexity), and can be implemented adaptively when interference parameters are unknown and/or time-varying, Numerical results are provided that show that these schemes offer significant performance gains relative to the matched filter receiver. We conclude that MMSE detectors can alleviate the need for stringent power control. In CDMA systems, and may be a practical alternative to the matched filter receiver     

Analysis of diversity schemes employing antenna selection in the presence of channel estimation errors and feedback delay

The main objective of this paper is to provide an extensive and complete examination on the effect of practical impairments such as channel estimation errors (CEEs) and feedback delay (FD) on the performance of diversity schemes over Nakagami‐m fading channels. Under erroneous channel estimation and outdated feedback cases, statistical expressions and several performance metrics related to the post‐processing signal‐to‐noise ratio (SNR) are derived for four different diversity schemes: transmit antenna selection (TAS)/orthogonal space–time block coding, TAS/maximal‐ratio transmission (MRT), MRT/receive antenna selection (RAS), and joint transmit and RAS. Exact analytical expressions for outage probability and average error rates of M‐ary modulations are derived in order to provide insightful perspectives on the capacity and error performance of diversity schemes that experience both CEE and FD. The asymptotic diversity order of the investigated diversity schemes are derived via a high‐SNR approximation approach. In order to assess the real‐world performance of the investigated diversity schemes and to observe their robustness or sensitivities in practical imperfections, various configurations are considered together with several performance comparisons. Also, Monte Carlo simulations are performed in order to validate the theoretical results. Copyright © 2014 John Wiley & Sons, Ltd.     

Carrier synchronization for 3- and 4-bit-per-symbol optical transmission

We investigate carrier synchronization for coherent detection of optical signals encoding 3 and 4 bits/symbol. We consider the effects of laser phase noise and of additive white Gaussian noise (AWGN), which can arise from local oscillator (LO) shot noise or LO-spontaneous beat noise. We identify 8- and 16-ary quadrature amplitude modulation (QAM) schemes that perform well when the receiver phase-locked loop (PLL) tracks the instantaneous signal phase with moderate phase error. We propose implementations of 8- and 16-QAM transmitters using Mach-Zehnder (MZ) modulators. We outline a numerical method for computing the bit error rate (BER) of 8- and 16-QAM in the presence of AWGN and phase error. It is found that these schemes can tolerate phase-error standard deviations of 2.48/spl deg/ and 1.24/spl deg/, respectively, for a power penalty of 0.5 dB at a BER of 10/sup -9/. We propose a suitable PLL design and analyze its performance, taking account of laser phase noise, AWGN, and propagation delay within the PLL. Our analysis shows that the phase error depends on the constellation penalty, which is the mean power of constellation symbols times the mean inverse power. We establish a procedure for finding the optimal PLL natural frequency, and determine tolerable laser linewidths and PLL propagation delays. For zero propagation delay, 8- and 16-QAM can tolerate linewidth-to-bit-rate ratios of 1.8/spl times/10/sup -5/ and 1.4/spl times/10/sup -6/, respectively, assuming a total penalty of 1.0 dB.     

Communication FSK a voies diversite non identiques — comparaison avec un codage correcteur d'erreur

An FSK communication system using 2nd or 3rd order diversity schemes is investigated in presence of Rayleigh fading. Special attention is devoted to the case of non equal signal and noise powers in the diversity paths and the effects of the single path fading is discussed. Some numerical and graphical comparisons are given.The second part of this paper compares the performance of such a diversity system to error correcting code schemes in terms of mean error probability and channel capacity. Several figures illustrate the results.     

Decision feedback detection with error compensation for hybrid space-time block codes

Spatial division multiplexing (SDM) techniques increase the total throughput by transmitting independent information streams through multiple transmit antennas whereas space time coding (STC) techniques utilize diversity gain. Hybrid space-time block code (STBC) schemes proposed combine the above two techniques to maximize the link performance. We propose a decision feedback detection method to improve the performance of the hybrid STBC scheme for orthogonal frequency division multiplexing (OFDM). In this scheme, we take the error propagation effect into account to enhance the detection performance. Simulation results show that the proposed method outperforms the conventional hybrid STBC detection algorithm by more than 3dB at 1% frame error rate for frequency selective fading channels.     

Hybrid ARQ schemes for point-to-multipoint communication overnonstationary broadcast channels

Hybrid automatic-repeat-request (ARQ) error control schemes make use of both error detection and error correction in order to achieve high throughput and low undetected error probabilities on two way channels. Two hybrid ARQ schemes, termed hybrid go-back-N (HGB- N) and hybrid selective-repeat (HSR), are proposed for point-to-multipoint communications over broadcast channels. Both schemes incorporate a concatenated code for error correction and error detection. The performance study of the hybrid schemes is based on a two-state Markov model of a burst noise channel. An analytic solution is derived for the throughput efficiency of the HSR scheme, while approximations and computer simulation are used to evaluate the throughput efficiency of the HGB-N scheme. It is shown that the schemes perform considerably better than the corresponding pure ARQ schemes in which a block code is used for error detection only, especially in environments with a large number of receivers and large channel roundtrip delays, such as satellite broadcast links     

Design and evaluation of multicast GFR for supporting TCP/IP over hybrid wired/wireless ATM

The major challenges of designing multicast traffic control protocols for a combined wired/wireless network are the varying transmission characteristics (bandwidth, error, and propagation delay) of the wireless and wired media, and the different, possibly conflicting frame rate requests from multiple sources. To address these issues, in this paper we design and evaluate new unicast and multicast guaranteed frame rate (GFR) schemes for supporting TCP/IP traffic over a combined wired/wireless ATM network. We first propose a new, flexible weighted buffer management, and a frame‐based virtual spacing (VS) mechanism implementing weighted fair queueing. The unicast GFR scheme is based on the integration of the new weighted buffer management, and either cell‐based or frame‐based VS. It is then extended to support multicast GFR flows. The multicast scheme presented in this paper is the first multicast GFR scheme appeared in the literature. These schemes are carefully evaluated over several network configuration, supporting heterogeneous TCP/IP traffic with various frame rates. Simulation results show that the new schemes guarantee the minimum rates requested, provide excellent fairness, and achieve reasonably high efficiency. The new schemes may be extended to provide differentiated service in both IP and mobile IP frame work. This revised version was published online in July 2006 with corrections to the Cover Date.     

Iterative packet combining schemes for intersymbol interferencechannels

We study packet combining techniques for retransmission schemes over intersymbol interference (ISI) channels. Two types of combining schemes are investigated, namely, maximum-likelihood combining (MLC) and iterative combining (IC). By first employing a precoding technique and then by interpreting the ISI channel as a trellis code, the transmissions of the same data packet at different times through the channel can be treated as the parallel concatenation of recursive trellis codes. If interleavers are used in between retransmissions, "turbo" coding gains can be achieved by iterative equalization. It is shown that IC provides excellent performance and outperforms other forms of combining in terms of frame error rate performance both analytically and through simulations     

Word error rate for group codes detected by correlation and other means

General expressions for the probability of word error for several encoding/detection schemes using group codes are derived. Correlation detection, digital decoding, straight Wagner codes, "Wagnerized" codes, and direct transmission are covered. Specific results are given for each in the case where the additive channel noise is white and Gaussian. A good indication of the relative amounts of power required by two schemes operating at the same error rate is available from an asymptotic relationship as the signal-to-noise ratio approaches infinity. Numerical results are presented for three easily implemented codes.