Optimizing Joint Erasure- and Error-Correction Coding for Wireless Packet Transmissions

In this thesis, we cope with the fundamental mathematical and physical problems of the space-time-Doppler UWB system design for fading channels: multi-input multi-output (MIMO) wireless communication with adaptive filtering. The estimation algorithm from equalizer providing an accurate parameters estimate is investigated. UWB radio is a fast emerging technology with uniquely attractively features inviting major advances in wireless communications, networking, radar, imaging, and positioning systems. By its rule-making proposal in 2002, the Federal Communications Commission (FCC) in the United States essentially unleashed huge new bandwidth (3.6-10.6 GHz) at the noise floor, where UWB radios overlaying coexistence RF systems cerate using low-power ultra-short information bearing pulses. Right now, there are three basic types of UWB: multiband OFDM UWB (MB-OFDM UWB), impulse-UWB (I-UWB), and direct sequence UWB (DS-UWB). We focus on I-UWB and MB-OFDM-UWB, and compare their performance. A simple means for spreading the spectrum of low duty cycle pulse trains is time hopping (TH), with pulse position modulation (PPM) for data modulation at the rate of many pulses per data bit. The main contribution of this thesis for I-UWB is the design of leading edge detectors, coherent correlation detector (CCD), and pilot performance enhancement compared with different Rayleigh and Ricean fading conditions. For MB-OFDM UWB, we have considered the performance analysis and design criteria of MIMO OFDM UWB systems for high data-rate wireless transmission. The signal processing of frame detection, time synchronization, frequency synchronization, channel estimation, synchronization tracking using pilot subcarriers and 2-D MIMO detection algorithms is discussed. The main contributions of this thesis are 1) Compared with receiver employing the Maximum Likelihood (ML) detector, the receiver employing a low-complexity linear Minimum Mean Square Error (MMSE) demodulator can perform a limited performance loss in spatially uncorrelated channels. 2) Due to the operations of spreading and dispreading combined with MMSE-based frequency domain equalization, the adverse effects of the low-SNR subcarriers on the average BER performance are potentially improved. This is a direct consequence of spreading, because even if the signal corresponding to a specific chip is obliterated by a deep frequency domain channel fade, after dispreading these effects are spread over the Walsh-Hadamard Transform (WHT) length. Hence there is a high chance of still recovering all the partially affected subcarrier symbols without errors. 3) As a test case, the OFDM-based 200 Mb/s MB-UWB network (IEEE 802.15.3a) are considered, but the simulation results are shown above section. 4) The simulation channel can be easily applied to NOS and NLOS situation with WHT transformation from Simulink model. The fading channels of UWB with low/high signal to noise ratio (SNR), multipath effects, and multiuser interference may introduce large errors in location. The location engine performs the following tasks: █ Data fusion techniques: Different data fusion techniques are implemented using Time Of Arrival (TOA), Angle Of Arrival (AOA), or a combination of both. █ Channel modeling: A multipath, multiuser channel environment is created that models path loss, shadowing, Rayleigh fading, and Doppler frequency effects. █ Parameter estimation: TOA and AOA estimation algorithms are implemented as part of the location finding engine. Different variations of algorithms are implemented for performance and comparison purposes. █ Configuring the physical layer for different wireless networks. Among the programmable parameters are spreading factor, packet size, training length, constellation type, modulation technique, carrier frequency, level of transmitted signal power, and the number of antennas at the transmitter for both sides. █ Configuring the mobile user conditions. The wireless channel models depend on the Doppler frequencies present in the environment. The Doppler frequency depends on the mobile speed and carrier frequencies as input and generates a Rayleigh fading channel with the U-shape Doppler spectrum. █ Configuring the environmental parameters and network geographical structure. One of the factors affecting the performance of the wireless location system is the environment type (e.g., bad urban, urban, suburban, or rural area). For example, in a bad urban area with many blocking objects and buildings, non-line of sight (NLOS) effects plays an important role in the estimation accuracy.

We show that an $L$ -branch maximal ratio combining (MRC) receiver with an average signal-to-noise ratio (SNR) $\bar{\gamma}$ in Nakagami- $m$ fading channels is equivalent to an $mL$ -branch MRC receiver with average SNR $\bar{\gamma}/m$ in Rayleigh fading channels in terms of symbol error probability (SEP) when $mL$ is an integer. Moreover, the orthogonal space–time block code (OSTBC) employing $M_\mathrm{t}$ transmit antennas and $M_\mathrm{r}$ receive antennas with the average SNR $\bar{\gamma}$ in Nakagami- $m$ fading channels is shown to be equivalent to an $mM_\mathrm{t}M_\mathrm{r}$ -branch MRC single-input–multiple-output (SIMO) receiver with the average SNR $\bar{\gamma}/mM_\mathrm{t}$ in Rayleigh fading channels.

We propose a novel joint source and channel coding (JSCC) scheme for wireless image transmission that departs from the conventional use of explicit source and channel codes for compression and error correction, and directly maps the image pixel values to the complex-valued channel input signal. Our encoder-decoder pair form an autoencoder with a non-trainable layer in the middle, which represents the noisy communication channel. Our results show that the proposed deep JSCC scheme outperforms separation-based digital transmission at low signal-to-noise ratio (SNR) and low channel bandwidth regimes in the presence of additive white Gaussian noise (AWGN). More strikingly, deep JSCC does not suffer from the cliff effect as the channel SNR varies with respect to the SNR value assumed during training. In the case of a slow Rayleigh fading channel, deep JSCC can learn to communicate without explicit pilot signals or channel estimation, and significantly outperforms separation-based digital communication at all SNR and channel bandwidth values.

In this paper, we concentrate on opportunistic scheduling for multicast information. We pose the problem as a multicast throughput optimization problem. As a solution we present how one can jointly utilize fixed-rate and rateless erasure coding along with simple rate adaptation techniques in order to achieve the optimal multicast throughput per user. We first investigate the performance of the proposed system under i.i.d. channel conditions. Our analysis shows a linear gain for the multicast capacity over i.i.d. Rayleigh fading channels with respect to the number of users. Since the established results require coding over large number of blocks and hence induce large decoding delays, we extend our analysis to the cases where we code over shorter block lengths and thus quantify the delay-capacity tradeoffs under a simple setting. We further look into non-i.i.d. channel conditions and show achievable gains by modifying a scheduling heuristic whose fairness is well- established for opportunistic scheduling of unicast flows. Our overall evaluations demonstrate that under both i.i.d. and non-i.i.d. channel conditions, opportunistic multicasting with erasure coding can significantly improve the performance over the traditional techniques used in today's communication systems.

Using Moment Generating Function for Performance Analysis in Non-Regenerative Cooperative Relay Networks with Max-Min Relay Selection

We consider monitoring applications in multihop wireless sensor networks (WSNs), where nodes rely on limited batteries so that energy efficiency and reliability are of paramount importance. Typically, lossy compression is aimed at saving transmission energy, yet affects the quality of transmitted data over lossy channels. Accordingly, using error correction coding (ECC) along with compression is required to guarantee both energy efficiency and high-fidelity reconstruction. In this paper, we analyze the energy efficiency of the joint use of lossy compression along with ECC, with the twofold objective of extending the network lifetime and assuring reliability. Specifically, we consider an adaptive joint lossy source-channel coding (JLSCC) system, where the energy efficiency and reliability performances depend on both the compression and the coding rates. Therein, we first carry out a performance analysis of JLSCC, considering realistic models of communication and computational energies, when the communication is performed over a Rayleigh fading channel. Then, we evaluate the performance of the JLSCC system compared to lossy compression and ECC systems in both end-to-end and multihop communications. Our results reveal that an adaptive JLSCC results in substantial energy saving while guaranteeing the required reliability performance, compared to both lossy compression and channel coding systems, that cannot be efficient for both energy and reliability. Instead, the JLSCC system is proved to be energy efficient for small distance end-to-end communication and large-scale multihop network, while leading to satisfactory reliability performance.

The progressive growth in the volume of digital data has become a technological challenge of great interest in the field of computer science. That comes because, with the spread of personal computers and networks worldwide, content generation is taking larger proportions and very different formats from what had been usual until then. To analyze and extract relevant knowledge from these masses of complex and large volume data is particularly interesting, but before that, it is necessary to develop techniques to encourage their resilient storage. Very often, storage systems use a replication scheme for preserving the integrity of stored data. This involves generating copies of all information that, if lost by individual hardware failures inherent in any massive storage infrastructure, do not compromise access to what was stored. However, it was realized that accommodate such copies requires a real storage space often much greater than the information would originally occupy. Because of that, there is error correction codes, or erasure codes, which has been used with a mathematical approach considerably more refined than the simple replication, generating a smaller storage overhead than their predecessors techniques. The contribution of this work is a fully decentralized storage strategy that, on average, presents performance improvements of over 80% in access latency for both replicated and encoded data, while minimizing by 55% the overhead for a terabyte-sized dataset when encoded and compared to related works of the literature.

This paper is concerned with the soft-decision decoding of error-correcting codes in the context of h.f. data transmission. The use of soft-decision information from the data modem results in an improvement in the performance of a forward-error-correction scheme, when compared with hard-decision decoding, without any further redundancy penalty. In the paper, we estimate the theoretical improvements that can be expected from soft-decision decoding of block and convolutional codes, in terms of both random and burst error-correcting power. Also, this is related to expected coding gains for the Gaussian and Rayleigh fading channels. In addition, we investigate the performance of soft-decision decoding on two types of h.f. modem: a multisubcarrier parallel transmission format (p.t.f.) type modem, and an experimental serial transmission s.m.i.d.d. type modem. We conclude that significant improvements in the performance of coded systems are obtainable through the use of soft-decision decoding.

Network coding (NC) and erasure coding (EC) share a common principle of encoding incoming data packets at network intermediate nodes so that destination nodes can reconstruct the original data packets using a sufficient number of encoded data packets collected at the destinations. While NC in general reduces the number of packets sent through the network, EC introduces redundancy into the packet streams to recover from lost packets. Many research papers in NC assume loss-free packet transmission, and to address this issue, end-to-end packet loss recovery through EC has been proposed. In this paper, we investigate hop-by-hop packet loss recovery through EC so as to avoid the accumulation of lost packets throughout the network using flow oriented EC. Specifically, we explore combined NC and EC at intermediate nodes in the networks to allow for improved packet loss recovery compared to end-to-end EC. Different implementations trading the packet processing complexity at the intermediate and destination nodes are considered. This paper first examines the effects of data loss in NC and then the improvements achievable with the proposed method are presented.

Emerging very high-data-rate wireless communications requires that traditional diversity systems be adapted so that some performance is sacrificed for complexity reduction. With this goal in mind, we investigate the recently-developed absolute threshold generalized selection combining (AT-GSC). We show that AT-GSC has poor bit-error rate (BER) performance when the average branch signal-to-noise ratio (SNR) is comparably lower than the preset threshold. This paper therefore develops a new diversity combining scheme, referred to as switching GSC (S- GSC). This scheme combines all branches whose SNR's exceed a preset threshold and if all the branches drop below the threshold, the output is the single branch with the maximum SNR. We prove that for any two-dimensional amplitude/phase linear modulation schemes, the symbol error rate (SER) of S-GSC lies between those of maximal ratio combining (MRC) and selection combing (SC). Importantly, the complexity of S-GSC is only slightly above that of AT-GSC. We derive the moment generating function (mgf) of the S-GSC output SNR over independent fading channels. For identically and independently distributed (i.i.d.) Rayleigh fading channels, we also derive the output probability density function (pdf) and cumulative distribution function (cdf) and analyze the error rate and the outage probability performance of S-GSC. Higher order moments of the S-GSC output SNR are also derived. These theoretical results are sufficient to completely characterize the performance of S-GSC and enable one to compare S-GSC with conventional diversity schemes.

This paper presents bit error rate (BER) analysis of wireless sensor networks (WSNs) consisting of sensor nodes based on an IEEE 802.15.4 RF transceiver. Closed-form expressions for BER are obtained for WSNs operating over AWGN, Rayleigh and Nakagami-m fading channels. For the purpose of analysis, we consider an IEEE 802.15.4 RF transceiver using direct sequence spread spectrum-offset quadrature phase shift keying (DSSS-OQPSK) modulation under 2.4 GHz frequency band in a WSN. Analytical expressions for BER are derived for a wireless link between sensor nodes that act as a transmitter unit and a base station without considering the effect of interferers in the wireless environment. Numerical results for BER are obtained by varying the IEEE 802.15.4 standard specific physical layer parameters, such as number of bits used to represent a Zigbee symbol, number of modulation levels used in an OQPSK modulator, and various values of Rayleigh and Nakagami-m fading parameters, denoted as $$\alpha $$ ? and $$m$$ m , respectively. Moreover, optimum values of physical layer parameters are identified for improved system performance. It is found that error performance analysis of WSN shows improvement when lower number of bits is used to represent a Zigbee symbol. Specifically, under a Rayleigh fading channel which reflects a real-time WSN environment, the network exhibits better performance only when it is operated at high SNR values, i.e., BER of order $$10^{-2}$$ 10 - 2 is achieved when SNR lies in the range 5---15 dB. Also, the effect of fading parameters on network performance shows that better results are obtained for higher values of $$\alpha $$ ? and $$m$$ m for Rayleigh and Nakagami-m fading channels, respectively.

One challenge in applying erasure codes (or error-correcting codes) to distributed storage systems is to maintain consistency between data and redundancy blocks in the face of crashing servers. We present two access protocols that provide sequential consistency and maximum distance separable fault tolerance at the same time. The protocols use sequence numbers to recover a consistent version in the presence of failures or partial writes. The first (pessimistic) PSW protocol uses a master per stripe to execute updates in sequence. The second (optimistic) OCW protocol allows concurrent writes to blocks in the same stripe to happen in parallel at the cost of additional buffer space.We present empirical performance results for PSW and OCW and compare them to other protocols. Our results show that OCW is as fast as simple replication while providing better fault tolerance and/or reduced storage overhead. This demonstrates that erasure coding can be used as a space-efficient alternative to replication in distributed storage systems.

A new method for compact storage and transmission of medical images with concealed patient information in noisy environment is evinced. Digital watermarking is the technique adapted here for interleaving patient information with medical images. The patient information, which comprises of text data and signal graph, is encrypted to prevent unauthorized access of data. The latest encryption algorithm (Rijndael) is used for encrypting the text information. Signal graphs (ECG, EEG EMG etc.) are compressed using DPCM technique. To enhance the robustness of the embedded information, the patient information is coded by error correcting codes (ECC) such as (7,4) Hamming, Bose-Chaudhuri-Hocquenghem (BCH) and Reed Solomon (RS) codes .The noisy scenario is simulated by adding salt and pepper (S&P) noise to the embedded image. For different signal to noise ratio (SNR) of the image, bit error rate (BER) and number of character altered (NOCA) for text data and percentage distortion (PDIST) for the signal graph are evaluated. The performance comparison based on the above parameters is conducted for three types of ECC. It is elicited that coded systems can perform better than the uncoded systems.

It is known that Bluetooth systems employ a Hamming (15, 10) code for error correction. In this paper, we propose different error correction coding schemes for this purpose. A comparison study between the Hamming (7, 4), the cyclic (15, 11) and the BCH (15, 7) codes is held in the paper to choose an alternative to the Hamming (15, 10) code. The simulation experiments are held over both an Additive White Gaussian Noise (AWGN) channel and a Rayleigh fading channel. The experimental results reveal the superiority of the BCH (15, 7) code to all other coding schemes if a large redundancy is accepted. If the issue of redundancy is of major concern, the Hamming (7,4) code is the best.

We consider layered transmission of a successively refinable source over a quasi-static fading channel, where the goal is to minimize the expected end-to-end distortion of the received signal. The existing literature on this problem has been limited to either Gaussian sources or design metrics that are valid only for asymptotically high signal to noise ratios (SNR). In this paper, we explicitly solve the rate allocation problem for an arbitrary source and a finite SNR. We establish a duality relationship between this problem and that of packet transmission over erasure channels. The optimal rate allocation problem is then solved using the dual solution for the erasure channel. Numerical results for a MIMO Rayleigh fading channel and a practical image coder are presented.