Bandwidth efficiency

Due to the high peak to average power ratio (PAPR) of modern modulated signals, power amplifiers (PAs) have been forced to operate at the back-off (BO) region of their saturation power in order to avoid signal clipping and distortion. However, classical PAs suffer from low efficiency in the BO region operation. Therefore, efficiency has to be enhanced in that region. Many techniques have been proposed. Among them, the Doherty power amplifier (DPA) is considered as the most suitable technique due to its simple structure and high performance. However, its conventional design is limited to a 6 dB BO level, which does not satisfy the requirements of modern communication systems. In this paper, a brief review of the most significant techniques of high-efficiency DPA is presented. First, DPA topology and its operation principles are briefly discussed. Second, efficiency enhancement techniques such as an asymmetrical DPA, output combiner modification, gate bias adaption, offset line optimization, and multi-way DPA were discussed. The study shows that the most suitable, simple, and effective solution is an asymmetrical approach. However, it needs to be investigated in terms of bandwidth in order to meet the efficiency-bandwidth requirements of modern wireless communication systems such as 5G.

The concept of modulation is a key factor in communication, because without an appropriate modulation method or scheme, getting an expected throughput in such a communication effort would be impossible to achieve. Communication engineers and researchers have not relented in trying to find the best modulation methods aimed at achieving an expected throughput, bandwidth/power efficiency, low error performance, etc in digital communication networks. Digital modulation is preferred to the analogue modulation due to their error-free capability.Moreso, this choice of digital modulation is dependent on the type of communication network that is to be established. However, trade-offs must be made between the bandwidth efficiency, power efficiency and the cost of implementation of such a network. This paper focuses onsome methods usually employed in the process of modulation in digital communication networks. Specifically, binary phase shift keying, quadrature phase shift keying, eight phase ...

IEEE 802.15.4 Medium Access Control (MAC) layer does not include the Request-To-Send/Clear-To-Send (RTS/CTS)handshake mechanism, in order to overcome the hidden node problem that affects Wireless Sensor Networks (WSNs). In this paper we propose and analyse the use of RTS/CTS in IEEE 802.15.4 for the nonbeacon-enable mode. The proposed solution shows that by considering the RTS/CTS mechanism combined with packet aggregation we improve the network performance in terms of maximum throughput, minimum delay and bandwidth efficiency. In IEEE 802.15.4 with RTS/CTS, the backoff procedure process is not repeated for each data packet sent unl ike the basic access mode of IEEE 802.15.4, but only for each RTS/CTS set. Therefore, the channel utilization is maximized by decreasing the deferral time period before transmitting a data packet. Our work introduces an analytical model capable of accounting the retransmission delay and the maximum number of backoff stages. The successful validation of our analytical model is carried out by comparison against simulation results by using the OMNeT++ simulator.

This paper considers semiblind channel estimation and data detection for orthogonal frequency-division multiplexing (OFDM) over frequency-selective fading channels. We show that the samples of an OFDM symbol are jointly complex Gaussian distributed, where the mean and covariance are determined by the locations and values of fixed pilot symbols. We exploit this distribution to derive a novel maximum-likelihood (ML) semiblind gradient-descent channel estimator. By exploiting the channel impulse response (CIR) statistics, we also derive a semiblind data detector for both Rayleigh and Ricean fading channels. Furthermore, we develop an enhanced data detector, which uses the estimator error statistics to mitigate the effect of channel estimation errors. Efficient implementation of both the semiblind and the improved data detectors is provided via sphere decoding and nulling-canceling detection. We also derive the Cramér-Rao bound (CRB) and design optimal pilots by minimizing the CRB. Our proposed channel estimator and data detector exhibit high bandwidth efficiency (requiring only a few pilot symbols), achieve the CRB, and also nearly reach the performance of an ideal reference receiver.

This paper analyses preemptive and non preemptive opportunistic spectrum access of secondary user in cognitive radio network (CRN) using M/D/1 analytical queuing model. Secondary users opportunistically access the spectrum of primary user if the channel is free. For preemptive priority high priority packet preempt a low priority packet and for non preemptive a high priority packet does not preempt a low priority packet instead it waits at head of line (HOL) until channel becomes free. Preempting a Secondary packet and not preempting a secondary packet has effect on packet waiting time and revenue collected from SUs for spectrum sharing. Through spectrum sharing spectrum owner tries to generate more revenue whereas SUs tries to maximize their satisfaction. Numerical illustration is presented using utility function to determine upper and lower boundary of primary arrivals for both preemptive and non preemptive. By using boundaries Optimal secondary packet arrival rates are derived .Analytical results demonstrate that the preemptive priority allow many Secondary packets to be transmitted in short time and in case of non preemptive priority the transmitting secondary packet uses short time but transmitting probability of secondary packet waiting in queue to get a channel becomes very low.

A scheme for delivery of variable bit-rate (VBR) video over asynchronous transfer mode (ATM) networks where bandwidth can be renegotiated during the duration of a call between the video source and the network is considered. Renegotiation can be initiated by either the video source or the network. The video bandwidth requirement is characterized by a usage parameter control (UPC) consisting, in general, of peak rate, burst length, and sustained rate. A baseline design is outlined where rate-control adjusts the source's rate while a new UPC is requested from the network. When granted, the new UPC allows the source to maintain its target quantization and delay requirements. Rate control epochs may be extended when the network blocks UPC requests or sets a lower UPC value to temporally deal with congestion. Simulation results are presented for VBR MPEG video. The results show that with a moderate renegotiation rate the scheme tracks the bandwidth requirements of the source. As a result, video quality and bandwidth efficiency can be maintained.

Thanks to the research on Vehicular Ad Hoc Networks (VANETs), we will be able to deploy applications on roadways that will contribute to energy efficiency through a better planning of long trips. With this goal in mind, we have designed a gas/charging station advertising system, which takes advantage of the broadcast nature of the network. We have found that reducing the number of total sent packets is important, as it allows for a better use of the available bandwidth. We have designed improvements for a distance-based flooding scheme, so that it can support the advertising application with good results in sparse to dense roadway scenarios.

It has been known that adaptive modulation and coding (AMC) at the physical layer can be combined with a truncated automatic repeat request (ARQ) at the data link layer so as to maximize the spectral efficiency under prescribed delay and error performance constraint. In this paper, we consider the same joint design approach when incremental redundancy-based hybrid ARQ (IR-HARQ) is associated with an AMC design at the physical layer. The extensive simulation studies for predicting the progressive combining gain with each retransmission enables to evaluate the bandwidth efficiency that can be achieved by selecting a more aggressive modulation and coding rate set (MCS) at the expense of packet error rate in earlier transmissions. It has been demonstrated that the aggressive AMC design approach in association with IR-based truncated HARQ can improve bandwidth efficiency by 5.8 and 3.3 dB, as compared to the conservative AMC design approach with truncated HARQ and aggressive AMC design approach with truncated ARQ (i.e., without taking the progressive combining gain in HARQ into account), respectively.

The performance of high-speed digital fiber-optic transmission using subcarrier multiplexing (SCM) is investigated both analytically and numerically. In order to reduce the impact of fiber chromatic dispersion and increase bandwidth efficiency, optical single-sideband (OSSB) modulation was used. Because frequency spacing between adjacent subcarriers can be much narrower than in a conventional DWDM system, nonlinear crosstalk must be considered. Although chromatic dispersion is not a limiting factor in SCM systems because the data rate at each subcarrier is low, polarization mode dispersion (PMD) has a big impact on the system performance if radiofrequency (RF) phase detection is used in the receiver. In order to optimize the system performance, tradeoffs must be made between data rate per subcarrier, levels of modulation, channel spacing between subcarriers, optical power, and modulation indexes. A 10-Gb/s SCM test bed has been set up in which 4 2.5 Gb/s data streams are combined into one wavelength that occupies a 20-GHz optical bandwidth. OSSB modulation is used in the experiment. The measured results agree well with the analytical prediction.

The IEEE 802.15.6 was established in Feb 2012 due to emergency of wireless body area networks (WBANs). In order to improve the performance of WBANs, the physical (PHY) layer, medium access control (MAC) layer and network layer have been discussed in a number of literatures. Although there are also many previous works on performance analysis for WBANs, a noise free was frequently assumed when contention error is taken into account in MAC layer. It means that in these works bit error rates (BERs) were not taken into consideration adequately. In this paper, we propose the Markov chain Monte Carlo (MCMC) method to analyze performance in the PHY and MAC layers for WBANs, in which BERs are taken into consideration. The BERs are theoretically analyzed depending on different Bose-Chaudhuri-Hocquenghem (BCH) code rates, and then the BCH code rate for every sensor node is optimized in sense of the highest throughput while assuming the signal to noise ratio (SNR) of every sensor node is different. Furthermore, the dependence of throughput on the BER is clearly explained by calculating the access probability for every sensor node in large SNR region. The BCH code was adopted as an example and then adaptive BCH code rates for WBANs were proposed. The application of proposal method to other error correcting codes is straightforward. Keywords Wireless body area networks Á Discrete time Markov chain method Á BCH code Á Bit error rate Á IEEE 802.15.6

Due to the gathering of sickrooms and consultation rooms in almost all hospitals, the performance of wireless devices system is deteriorated by the increase of collision probability and waiting time. In order to improve the performance of wireless devices system, relay is added to control the access point and then the access of devices is distributed. The concentration of access point is avoided and then the performance of system is expected to be improved. The discrete time Markov chain (DTMC) is proposed to calculate the access probability of devices in a duration time slot. The collision probability, throughput, delay, bandwidth and so on are theoretically calculated based on the standard IEEE802.15.6 and the performance of the system with and without relay is compared. The numerical result indicates that the performance of the system with control access point is higher than that of the system without control access point when the number of devices and/or packet arrive rate are high. However, the system with control access point is more complicated. It is the trade-off between the performance and the complication.

Hierarchical quadrature amplitude modulation (HQAM) enables unequal priority transmission through the use of non-uniformly spaced constellations. In this paper, we propose an adaptive HQAM (A-HQAM) scheme where the ratios between the constellation distances are regularly adjusted based on the channel condition with the objective of maximizing the transmission efficiency. The source bit stream is divided into multiple substreams which are simultaneously transmitted, each on a different priority level. When using A-HQAM, the high priority substream maintains an acceptable bit error rate performance over all channel conditions. As the channel condition improves, the required protection for the high priority sub-stream is reduced allowing for increasing the protection level of lower priority sub-streams. Hence, the number of sub-streams with acceptable BER performances is incrementally increased as the channel condition improves. Analysis and simulation results show that the proposed A-HQAM not only enhances the transmission efficiency but also provides reduced peak to average power ratio (PAPR). The proposed scheme offers reduced complexity by using one constellation size, unlike conventional adaptive schemes which require the use of several constellation sizes. Moreover, a practical A-HQAM implementation is presented which enables the receiver to successfully demodulate the received signal without knowing the varying transmission parameters.

In this paper, a new multicarrier based DCSK system that is combined a wavelet packet modulation (WPM) with differential chaos shift keying (DCSK) and named WPM-DCSK is proposed. WPM-DCSK system is an extension of orthogonal frequency division multiplexing OFDM-DCSK system that aims to replace the fast Fourier transform in OFDM system with wavelet packet transform and improves the spectral efficiency by removing the cyclic prefix and reduced the complexity by using real operation instead of complex operation. WPM-DCSK system has all the benefit of OFDM-DCSK and furthermore improves the limitations and drawbacks of it. The data rate improvement, the energy saving improvement and data-energy-to-bit-energy-ratio factors are derived and compared with DCSK and OFDM-DCSK systems. The validity of the derived analytic expression of the bit error rate of the proposed system is confirmed by the simulation under an additive white Gaussian noise channel.

Steiner Systems constitute an example of codes that achieve asymptotic error-free transmission for the Gaussian channel. In contrast to simplex and orthogonal codes which also have this property, these codes make more efficient use of the bandwidth by reducing the required dimensionality to generate the M signals. Tight upper bounds for the symbol error probability are derived for coherent and noncoherent detection that include previously reported results as special cases.

This paper deals with Single Carrier/Frequency Domain Equalization (SC/FDE) for uplink transmission within a Multi-User (MU) Multi-Input Multi-Output (MIMO) system where the number of Base Station (BS) antennas can be much larger than the number of transmitter antennas jointly using the same time/frequency resource at Mobile Terminals (MT). Selected Quadrature Amplitude Modulation (QAM) schemes are assumed for transmission, so that high bandwidth efficiencies are achievable. In this context, we consider either a linear detection or a reduced-complexity, iterative Decision Feedback (DF) detection, evaluate the achievable performances in both cases, and discuss them with the help of selected performance bounds and semi-analytically evaluated error floor levels. From our performance results, we conclude that simple linear detection techniques, designed to avoid the need of complex matrix inversions, can lead to unacceptably high error floor levels. However, by combining the use of such...

We present the first analytic study of stream tapping protocols, a family of protocols that provide the most efficient way to distribute videos on demand at low to medium request arrival rates, say, less than ten requests per hour for a two-hour video. The main results of this study are analytical solutions for the optimal operational points of stream tapping, stream tapping with small client buffers, stream tapping with partial preloading and stream tapping with proactive streams. In addition we introduce a new stream tapping protocol with batching that caps the bandwidth requirements of stream tapping at high to very high arrival rates.

This paper studies the use of a traffic optimization technique named TCM (Tunneling, Compressing and Multiplexing) to reduce the bandwidth of MMORPGs (Massively Multiplayer Online Role-Playing Games), which employ TCP to provide a soft real-time service. In order to optimize the traffic and to improve bandwidth efficiency, TCM can be applied when the packets of a number of players share the same link, which occurs in some scenarios, as e.g. the traffic between proxies and servers of game-supporting infrastructures. First, TCP/IP headers are compressed using standard algorithms that avoid sending repeated fields; next, a number of packets are blended into a bigger one and finally, they are sent using a tunnel. The expected compressed header size has been obtained using traffic traces of a real game. Next, simulations using a traffic model of a popular MMORPG have been performed in order to estimate the expected bandwidth savings and the reduction in packets per second. The obtained bandwidth saving is about 60 percent. Packets per second are also significantly reduced. In addition, the added delays are shown to be small enough so as not to impair players' experienced quality.

M-ary Frequency Shift Keying is a power efficient modulation scheme that is currently used by manufacturers of low power low data rate data transmission equipment. The power efficiency of this modulation increases as the signal alphabet increases at the expense of increased complexity and reduced bandwidth efficiency. There is, however, a gap between the performance of real world systems employing Frequency Shift Keying (FSK) and that of theoretical FSK systems. To investigate the nature of this gap, a comparison is needed between the performance of real world systems using FSK and that of theoretical FSK systems. This thesis investigates the nature of this gap by simulating 2, 4 and 8-level FSK systems in additive white Gaussian noise channel using MATLAB, measuring of the performance of commercially available data transmission equipment manufactured by RACOM s.r.o of the Czech Republic, and comparison of their performances. Some important results have been illustrated and also, it...

In this contribution we propose a robust H.264 coded wireless video transmission scheme using iteratively decoded self-concatenated convolutional coding (SECCC). The proposed SECCC scheme is composed of constituent recursive systematic convolutional (RSC) codes and an interleaver is used to randomise the extrinsic information exchanged between the constituent RSC codes. Additionally, a puncturer is used to increase the achievable bandwidth efficiency. At the receiver selfiterative decoding is invoked between the hypothetical decoder components. The performance of the system was evaluated using the H.264/AVC source codec for interactive video telephony. Furthermore, EXIT charts were utilised in order to analyse the convergence behaviour of the SECCC scheme advocated. We demonstrate the efficiency of this approach by showing that the video quality is significantly improved, when using the binary SECCC scheme. More explicitly, the proposed system exhibits an E b /N0 gain of 6 dB at the PSNR degradation point of 2 dB in comparison to the identical-rate benchmarker carrying out RSC coding and puncturing, while communicating over correlated Rayleigh fading channels.

Al 0.38 Ga 0.62 N/GaN heterojunction solar-blind Schottky photodetectors with low dark current, high responsivity, and fast pulse response were demonstrated. A five-step microwave compatible fabrication process was utilized to fabricate the devices. The solarblind detectors displayed extremely low dark current values: 30 lm diameter devices exhibited leakage current below 3 fA under reverse bias up to 12 V. True solar-blind operation was ensured with a sharp cutoff around 266 nm. Peak responsivity of 147 mA/W was measured at 256 nm under 20 V reverse bias. A visible rejection more than 4 orders of magnitude was achieved. The thermally-limited detectivity of the devices was calculated as 1.8 • 10 13 cm Hz 1/2 W À1. Temporal pulse response measurements of the solar-blind detectors resulted in fast pulses with high 3-dB bandwidths. The best devices had 53 ps pulse-width and 4.1 GHz bandwidth. A bandwidth-efficiency product of 2.9 GHz was achieved with the AlGaN Schottky photodiodes.

The key performance bottleneck for a video-on-demand (VOD) server is bandwidth, which controls the number of clients the server can simultaneously support. Previous work has shown that a strategy called stream tapping can make efficient use of bandwidth when clients are not allowed to interact (through VCR-like controls) with the video they are viewing. Here we present an interactive version of stream tapping and analyze its performance through the use of discrete event simulation. In particular, we show that stream tapping can use as little as 10% of the bandwidth required by dedicating a unique stream of data to each client request.

An efficient MAC protocol and flexible dynamic channel allocation (DCA) scheme for the UMTS-TDD mode is presented which exploits the characteristics of connectionless and connectionoriented services. The proposed protocol gives fast channel access and high bandwidth efficiency in any traffic scenario asymmetric between uplink and downlink channels, particularly in the presence of internet traffic.

Nowadays, the energy efficiency in wireless sensor networks (WSN) has become a challenging issue. Indeed, due to the sustainable development and deployment of such networks in our daily lives, energy efficiency is asked lto be significantly improved in order to achieve green networking. Greedy behaviours are one of the most malicious and insidious Denial of Service attacks, that threaten the green behaviour of wireless network. In such an attack, a greedy node attempts to improve its bandwidth at the expense of other nodes by not respecting its access network procedure, resulting in an overall increase of the energy consumption in the network. In this paper, we are interested in evaluating the energy efficiency of WSN in presence of a greedy behaviour. For this effect, we consider ZigBee networks using the non slotted IEEE 802.15.4 procedure. A time Petri net based modelling that characterizes the behaviour of both greedy and sane nodes, is first presented. Then, we simulate the model under TiNA platform by considering different scenarios in order to assess the energy efficiency of the network as well as other performance parameters. Hence, we confront the obtained values to discuss the impact of the greedy attack on the energy efficiency as well as a strategy to detect such a non green behaviour. Finally, we propose countermeasures to thwart the impact of the latter on the energy efficiency of the network.

In this contribution we propose a robust H.264 coded wireless video transmission scheme using iteratively decoded self-concatenated convolutional coding (SECCC). The proposed SECCC scheme is composed of constituent recursive systematic convolutional (RSC) codes and an interleaver is used to randomise the extrinsic information exchanged between the constituent RSC codes. Additionally, a puncturer is used to increase the achievable bandwidth efficiency. At the receiver selfiterative decoding is invoked between the hypothetical decoder components. The performance of the system was evaluated using the H.264/AVC source codec for interactive video telephony. Furthermore, EXIT charts were utilised in order to analyse the convergence behaviour of the SECCC scheme advocated. We demonstrate the efficiency of this approach by showing that the video quality is significantly improved, when using the binary SECCC scheme. More explicitly, the proposed system exhibits an E b /N0 gain of 6 dB at the PSNR degradation point of 2 dB in comparison to the identical-rate benchmarker carrying out RSC coding and puncturing, while communicating over correlated Rayleigh fading channels.

Preface 1. A one-term course in analog and digital communication: Selected review sections from Chapters 2 and 4, all of chapters 3, 5, 7, and 8, and selections from chapters 6, 9, and 10. 2. A one-term course in digital communication: Selected review sections from Chapters 2 and 4, and Chapters 6-10. A two-term course sequence on analog and digital communications: (a) Chapters 2-6 for the first course. (b) Chapters 7-10 for the second course. We wish to thank Gloria Doukakis for her assistance in the preparation of the manuscript.

A new quadrature-overlapped modulation (QOTRC modulation) with a quasi-constant , envelope is proposed in this paper. The new modulation possesses fast-decayed spectral side lobes. Bandwidth efficiency and detection efficiency of the new modulation under coherent detection over a band-limited non-linear satellite channel are studied and compared with those of MSK (a constant-envelope modulation) and SQORC (staggered quadrature-overlapped raised-cosine) modulations. The results obtained in this paper show that the new modulation can offer a satisfactory bit error rate (BER), which is comparable to or even better than that of MSK and much better than that of SQORC (a previously reported quadrature-overlapped modulation), depending on the signal-to-noise ratios (SNRs) and system bandwidth.

Nowadays, communication systems need to satisfy very demanding constraints in order to cope with users new necessities. One of the most promising techniques to improve the system capacity is multiple input multiple output (MIMO). However, the use of MIMO implies a huge complexity increase in the detection process. In this paper, a method to reduce the aforementioned complexity is presented. Although the proposed method is analyzed for digital video broadcasting next generation for handhelds, its implementation is useful for any MIMO system that requires the computation of log likelihood ratios (LLRs), used by the low density parity check codes. The presented technique consists of applying a simplification when calculating the Euclidean distances needed by the LLRs. The simplification avoids almost all the multiplications, very area demanding when translated into hardware, and presents a performance loss under 0.1 dB. Index Terms-Digital video broadcasting next generation for handhelds (DVB-NGH), multiple input multiple output (MIMO), decoder, orthogonal frequency division multiplexion (OFDM). I. INTRODUCTION N OWADAYS, wireless communication systems have a performance close to the theoretical limits exposed by Shannon. This is mainly due to the mature state of the technologies applied in them. Clear examples of this are the 802.11 family standards (a, b, g, n), 802.16 (WiMax) or the mobile telephone standards as Universal Mobile Telephone System (UMTS). Increasing the data rate in these types of systems (power, bandwidth and complexity limited) represents a very challenging task. In order to achieve this target, one of the most recent and widely used technologies is Multiple Input Multiple Output (MIMO). This technology is already applied in state-of-the-art communication standards as Long Term Evolution (LTE) and it is said to be one of the key features for incoming new ones as Digital Video Broadcasting Next Generation for Handhelds (DVB-NGH) [1]. MIMO consists in using several transmission and reception antennas. The use of MIMO schemes leads to an increase of the channel capacity. The first works on this area were carried out by Winters [2], Foschini and Gans [3], and Telatar [4] and Manuscript

M-ary Frequency Shift Keying is a power efficient modulation scheme that is currently used by manufacturers of low power low data rate data transmission equipment. The power efficiency of this modulation increases as the signal alphabet increases at the expense of increased complexity and reduced bandwidth efficiency. There is, however, a gap between the performance of real world systems employing Frequency Shift Keying (FSK) and that of theoretical FSK systems. To investigate the nature of this gap, a comparison is needed between the performance of real world systems using FSK and that of theoretical FSK systems. This thesis investigates the nature of this gap by simulating 2, 4 and 8-level FSK systems in additive white Gaussian noise channel using MATLAB, measuring of the performance of commercially available data transmission equipment manufactured by RACOM s.r.o of the Czech Republic, and comparison of their performances. Some important results have been illustrated and also, it...

The key performance bottleneck for a video-on-demand (VOD) server is bandwidth, which controls the number of clients the server can simultaneously support. Previous work has shown that a strategy called stream tapping can make efficient use of bandwidth when clients are not allowed to interact (through VCR-like controls) with the video they are viewing. Here we present an interactive version of stream tapping and analyze its performance through the use of discrete event simulation. In particular, we show that stream tapping can use as little as 10% of the bandwidth required by dedicating a unique stream of data to each client request.

Wireless technology has enabled the development of increasingly diverse applications and devices resulting in an exponential growth in usage and services. These advancements made the radio frequency spectrum a scarce resource, and consequently, its efficient use is of the ultimate importance. To cope with the growing demand, network design focused on increasing the spectral efficiency by making use of advancement in Cognitive Radio technology. Cognitive Radio can reduce the spectrum shortage problem by enabling unlicensed users equipped with Cognitive Radios to reuse and share the licensed spectrum bands. Using the fact that a Cognitive Radio is capable of sensing the environmental conditions and automatically adapting its operating parameters in order to enhance network performance, we would like to make use of its knowledge to predict the mobility of Cognitive Radio users to improve the overall performance of the Cognitive Radio network. This study makes novel use of mobility prediction techniques to enhance reliability, bandwidth efficiency and scalability of the cognitive radio networks. Firstly, prediction techniques are evaluated and compared for prediction accuracy. Secondly, routing protocol reliability, efficiency and scalability performances are evaluated under different prediction techniques. Simulation results verify the performance improvements even with moderate accuracy predictors. Results clearly show that hybrid Markov CDF prediction performs the best. When compared with no prediction it significantly improves average reliability and efficiency by 11% and 8%, respectively.