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A physical layer implementation on reconfigurable underwater acoustic modem
Abstract
Underwater acoustic (UWA) multi-user network algorithms can only be fully tested through experimental studies where communication signals are transmitted through a real underwater channel. Reconfigurable UWA modem provides a flexible environment for the testing of different communication algorithms including networking protocols. In this paper we present design, implementation, and testing of a physical layer algorithm on reconfigurable acoustic modem. This physical layer is very flexible; therefore it can easily be modified in order to be employed for the testing of different UWA networking algorithms.
... rModem is also a reconfigurable modem, which is designed to simplify cross-layer optimization-based experimentation studies [9,104]. Its field programmable gate array enables researchers to choose carrier frequency from the [1−100]kHz range. ...
... Its field programmable gate array enables researchers to choose carrier frequency from the [1−100]kHz range. With Simulink toolbox [104], researchers can reach modem hardware to handle data transmission or events recording related activities [9]. rModem can work with an omnidirectional Teledyne transducer (e.g., AT-408) and allows multiple-input-multiple-output transmissions by using its four configurable input and output channels [9]. ...
... With Simulink toolbox [104], researchers can reach modem hardware to handle data transmission or events recording related activities [9]. rModem can work with an omnidirectional Teledyne transducer (e.g., AT-408) and allows multiple-input-multiple-output transmissions by using its four configurable input and output channels [9]. Although rModem is reconfigurable, the protocol stacks and its Simulink tool need to be run on a personal computer (PC), which may impair its performance. ...
Ocean and water basically cover the major parts of our planet. To obtain the best utilization of the underlying resources on these parts of the Earth, people have made some research advancements. Specifically, the research on underwater wireless acoustic sensor networks (UWA-SNs) has made great progress. However, wide deployment of UWA-SNs is far from a reality due to several reasons. One important reason is that offshore deployment and field-level experiments of ocean-centric applications are both expensive and labor intensive. Other alternatives to attain this objective are to conduct simulation or experimentation that can reduce cost and accelerate the research activities and their outcomes. However, designing efficient and reliable simulation and experimentation platforms have proven to be more challenging beyond the expectation. In this article, we explore the main techniques (including their pros and cons) and components to develop simulation and experimentation platforms and provide a comprehensive survey report in this area. We classify simulation and experimentation platforms based on some typical criteria and then provide useful guidelines for researchers on choosing suitable platforms in accordance with their requirements. Finally, we address some open and un-resolved issues in this context and provide some suggestions on future research.
... A data rate of 100 bps -1000 bps was achieved. In [12], a flexible physical layer on r-MODEM platform was designed and implemented. The r-MODEM used recursive least square (RLS) equalizer with phase locked loop to recover the transmitted symbols, a bit rate of 550 bps was achieved. ...
... The MODEMs mentioned above in [1]- [12] are based on single carrier, multi-carrier such as orthogonal frequency division multiplexing (OFDM) technology has already been widely applied to point-to-point communication and network. OFDM technology has many advantages such as robustness to large multipath delay spread, high spectral efficiency, and the ability to exploit the multiuser and/or multipath diversity, but limited literatures report the design and implementation for underwater acoustic OFDM MODEM. ...
Orthogonal frequency division multiplexing (OFDM) provides an effective approach to combat multipath with high bandwidth efficiency for underwater acoustic communication, thus design and implementation of acoustic OFDM MODEMs draw more and more attention. Extensive work has been performed to mitigate multipath, Doppler shift, and peak average power ratio from the viewpoint of theoretical analysis. Meanwhile, design and implementation of a parameter-configurable OFDM to adapt to highly diverse underwater channels and various missions become more and more important. Traditional MODEM with fixed parameters will not achieve the best tradeoff between data rate and bit error rate. In order to obtain the best communication performance under long time delay channels, Doppler channels, and frequency-selective channels, in this paper, we provide the design and implementation of a parameter-configurable underwater acoustic OFDM MODEM with the purpose to achieve flexibility. Specifically, the reconfigurable parameters of the OFDM MODEM include the number of receivers, the number of null subcarriers, the number of pilot subcarriers, as well as the type of channel estimation algorithms. The number of pilot subcarriers and type of channel estimation methods are determined based on channel characteristics, the number of null subcarriers is determined based on the Doppler shift, and the number of the received channels is based on fading channel. Moreover, in this paper, the Doppler estimation performance under different number of null subcarriers, and the channel estimation performance under different number of pilot subcarriers and under different channel estimation algorithms, are analyzed in terms of bit error rate. Finally, the effectiveness for the proposed highly configurable OFDM MODEM is demonstrated by two sea trials corresponding to different communication scenarios.
... The modem was embedded to the DSP board memory, but still in a laboratory scale implementation. The development of acoustic modem test bed has been done on a commercial scale such as Hermes, and T-mote base as in [40] [41] and [42]. The reliability of the system has been tested on the field scale testing in the sea for a various distance of transmitter and receiver [41] and [42]. ...
... The reliability of the system has been tested on the field scale testing in the sea for a various distance of transmitter and receiver [41] and [42]. The low cost test bed has been developed by Benson [40], but the coverage is relatively close and low data rate. This model is intended for environmental monitoring with small coverage. ...
Acoustic propagation in the underwater channel influenced by three factors: signal attenuation, multipath propagation, and low speed of sound propagation. Understanding of underwater acoustic channel is the basis in the design of a reliable communication system, and until now there is no standard fading model for underwater acoustic channel. Experimental method supported with measurement data is a commonly method used as a first step in modeling of channel properties for underwater sensor network applications. In this study, we will begin a discussion about research development of underwater acoustic communications. In the next section will be presented about experimental planning for underwater propagation characteristics. The characterization results are used to evaluate the performance of communication system through software simulation. At the end of this paper, a PC-based soft acoustic modem test bed will be presented.
... ITACA reached 1 kbps with 1 kHz bandwidth (84.5 kHz frequency is used for symbol ‘0’ and 85.5 kHz for symbol ‘1’), which is clearly higher than other FSK solutions such as [17,21,22] or [33]. Moreover, 1 kHz bandwidth is not far from more complex modulation techniques, such as [34] (QPSK, 550 bps), [19] (PSK, 300–5 kbps), although ITACA has a lower power consumption than rModem and WHOI. Finally, there are high consumption modems that reach 16 kbps [18] or 75 kbps [35] and are very suitable for image transmission. ...
... Piezoelectric transducer excitation has been previously carried out mainly using three power amplifier types: class-B [34]; class-D [19,21,33]; and class-AB [37]. Although the class-B amplifier architecture uses just one power transistor, it is clearly inefficient because only positive voltages are used (50% of the input signal) and this leads to low efficiency. ...
This paper is focused on the description of the physical layer of a new acoustic modem called ITACA. The modem architecture includes as a major novelty an ultra-low power asynchronous wake-up system implementation for underwater acoustic transmission that is based on a low-cost off-the-shelf RFID peripheral integrated circuit. This feature enables a reduced power dissipation of 10 μW in stand-by mode and registers very low power values during reception and transmission. The modem also incorporates clear channel assessment (CCA) to support CSMA-based medium access control (MAC) layer protocols. The design is part of a compact platform for a long-life short/medium range underwater wireless sensor network.
... In general, acoustic communications are a good solution for long range transmissions (>1000 m), but having several robots sharing the same acoustic channel might degrade the performance of the communication link. Therefore, alternative solutions based on radio frequency (RF) [1][2][3] are also considered for short range communications between ROVs. The problem with RF is the strong attenuation of electromagnetic signals in marine water, which limits the communication range to 15 m [4]. ...
... The system is configured with four different wavebands, which will activate FH-FSK mode at low communication rate and PSK mode at high speed [6]. Mehmet Aydinlik, A.Turan Ozdemir [7] have developed and verified a variety of communication algorithms in the physical layer, including QPSK modulation, convolutional coding and channel equalization by using Texas Instruments TMS320C6713 DSP. The above modems are all based on the traditional modulation and demodulation technology. ...
Underwater acoustic communication plays an important role in underwater wireless sensor network. Different from terrestrial radio channel, modeling of underwater acoustic channel is very challenging due to its unique and dynamic characteristics. In order to verify the proposed acoustic communication algorithms, a general emulation platform which can reduce the verification cost has a wide application prospect. In this paper, we design a general hardware in the loop underwater communication emulation system based on the LabVIEW and MATLAB software and real acoustic transducer. In the emulation system, LabVIEW calls MATLAB script to achieve algorithm implementation, and then uses DAQmx to send and receive data through the acquisition card. The proposed system supports a variety of modulation and demodulation methods, such as multiple frequency-shift-keying(MFSK), multi-carrier frequency-shift-keying( MCFSK), orthogonal frequency division multiplexing(OFDM), etc. In addition, in order to detect frame efficiently, we propose a light-weight frame synchronous algorithm. To verify the function of the systems, lake test and sea test are conducted for different algorithms.
... In a multipath environment, multi-carrier modulation becomes the first choice over the single-carrier, becuase it is able to overcome the multipath's influence. OFDM is a multi-carrier modulation technique that can be utilized on SDR systems [5], [6]. ...
A radio system design providing various data service needs becomes one of the Software Defined Radio (SDR) system advantages. SDR technology applies software functions further to be run in hardware platforms. The need for services with greater data rates can be resolved by using multi-carrier transmission techniques, one of which is the Orthogonal Frequency Division Multiplexing (OFDM) technique. This paper discusses the detection of OFDM signals and their parameters. Multi-carrier transmission can prevent Inter-Symbol Interference (ISI) occurrence due to multi-path fading effect. The recognition can classify the correctly received signals, including the signal conditions mixed with AWGN noise. The autocorrelation method was used to estimate the OFDM parameters, namely the one symbol duration and the cyclic prefix duration. The detected cyclic prefix durations were 1/2, 1/4, 1/8, and 1/16. This method is very simple, because with the cyclic prefix presence, a different signal peak will be detected to further estimate the cyclic prefix duration. The results show the correlation method performance can detect one symbol duration with 100%, accuracy, starting at SNR 0 dB, whereas the cyclic prefix duration accuracy rate is getting more accurate by using a less cyclic prefix duration, which is 1/16 of the total symbol duration.
... Among the selected modems, UNET-2, SeaNet and NILUS are the first endeavors to design real-time reconfigurable and programmable cognitive modems. a) rModem: rModem is a rapid prototyping research tool [107], [119]. Its programmability feature focuses on physical layer, and it provides a JAVA-based graphical user interface (GUI) to program its hardware. ...
The ocean covers nearly two-thirds of the surface on the Earth, and there has been great interest in developing underwater wireless sensor networks (UWSNs) to help us explore the ocean realm. A great deal of efforts have been devoted to it, and significant progress has been made since the beginning of 2000s. However, most of the networks are isolatedly developed currently, inherently hardware-based and application-oriented with inflexible closed-form architectures, which are difficult to reconfigure, reprogram and evolve. They also lack the capability in sharing resources, and are far from service-oriented networks. These limitations impair their capacity for wide range of applications. To further propel the development of UWSNs, next-generation UWSNs have been proposed recently, which are robust, flexible, adaptive, programmable, support resource-sharing feature and are easy to manage and evolve. Moreover, a number of novel software-defined techniques and paradigms, such as software-defined radio (SDR), cognitive acoustic radio (CAR), network function virtualization (NFV), software-defined networking (SDN), Internet of underwater things (IoUTs) and sensor-cloud, have been emerging. These software-defined technologies have the capability of softwarizing network resources, and then redefining them to satisfy diverse application requirements, improve resource utilization efficiency and simplify network management. Consequently, these evolving technologies are envisioned as critical building blocks and major driving forces, which will transform conventional UWSNs towards software-based, programmable, user-customizable and service-oriented next-generation UWSNs. In this paper, we provide a comprehensive review of existing works on implementing these techniques, and also present discussions for future research. We hope to inspire more active research on these areas and take a step further towards realizing next-generation UWSNs.
... Yan, H. demonstrated the real-time capabilities with both a floating point and a fixed-point DSP with QPSK modulation and described its detailed implementation in [7]. Aydinlik, M. presented the implementation of the physical layer of a reconfigurable underwater acoustic modem using QPSK modulation [8]. Blueprint Subsea developed the SeaTrac modem with QPSK modulation based on front-end specifications by Newcastle University in [9]. ...
A novel portable underwater acoustic modem is proposed in this paper for covert communication between divers or underwater unmanned vehicles (UUVs) and divers at a short distance. For the first time, real dolphin calls are used in the modem to realize biologically inspired Covert Underwater Acoustic Communication (CUAC). A variety of dolphin whistles and clicks stored in an SD card inside the modem helps to realize different biomimetic CUAC algorithms based on the specified covert scenario. In this paper, the information is conveyed during the time interval between dolphin clicks. TMS320C6748 and TLV320AIC3106 are the core processors used in our unique modem for fast digital processing and interconnection with other terminals or sensors. Simulation results show that the bit error rate (BER) of the CUAC algorithm is less than 10‒5 when the signal to noise ratio is over –5 dB. The modem was tested in an underwater pool, and a data rate of 27.1 bits per second at a distance of 10 m was achieved.
... Though commercial acoustic modems are available, there are not many to choose from and their proprietary nature makes customization of these products expensive or simply infeasible [3]. Researchers need a better option to prototype their algorithms and further develop the field of UWA communication. ...
We describe how the Universal Software Radio Peripheral (USRP) coupled with GNU Radio can be adapted for use as a configurable underwater acoustic (UWA) modem. The USRP contains an Altera Cyclone EP1C12 FPGA and typically acts as the baseband and IF section of a radio communication system. Our work is the first time that the USRP/GNU Radio is applied to an UWA channel and represents an exciting branch into a field that has a need for cost-effective and configurable modems. The USRP facilitates such needs through its low cost, ability to be used to rapidly prototype, and synergistic open platform. We outline how to set up a USRP for receiving acoustic signals and passing the received information to a host PC so that the reception and processing are done in a mix of hardware and software. UWA communication research will benefit greatly from the adaption of the USRP as an underwater acoustic modem. First and foremost, the development of a modem using the USRP has applications in oceanographic monitoring and communication. Quantitative information such as pollution and military surveillance data can be monitored in a more cost-effective way and relayed in underwater networks. Also, improved acoustic networking would allow more efficient transfer of information between oceanographic equipment such as autonomous vehicles, piloted vehicles, and underwater profilers [1].
... Thus, underwater sensor networks must rely on acoustic signals that feature large latency, low bandwidth, and long end-to-end delay; and 2) sensor nodes move with water currents and dispersion, which results in dynamic network configurations that need to be monitored. All these unique features cause grand challenges to the networking issues at almost every layer of the protocol stack [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]. Localization of mobile sensor nodes is indispensable for underwater sensor networks. ...
Due to adverse aqueous environments, non-negligible node mobility and large network scale, localization for large-scale mobile underwater sensor networks is very challenging. In this paper, by utilizing the predictable mobility patterns of underwater objects, we propose a scheme, called Scalable Localization scheme with mobility prediction (SLMP), for underwater sensor networks. In SLMP, localization is performed in a hierarchical way, and the whole localization process is divided into two parts: anchor node localization and ordinary node localization. During the localization process, every node predicts its future mobility pattern according to its past known location information, and it can estimate its future location based on its predicted mobility pattern. Anchor nodes with known locations in the network will control the whole localization process in order to balance the tradeoff between localization accuracy, localization coverage and communication cost. We conduct extensive simulations, and our results show that SLMP can greatly reduce localization communication cost while maintaining relatively high localization coverage and localization accuracy.
... Thus, underwater sensor networks must rely on acoustic signals that feature large latency, low bandwidth, and long end-to-end delay; and 2) sensor nodes move with water currents and dispersion, which results in dynamic network configurations that need to be monitored. All these unique features cause grand challenges to the networking issues at almost every layer of the protocol stack [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]. ...
Due to harsh aqueous environments, non-negligible node mobility and large network scale, localization for large-scale mobile underwater sensor networks is very challenging. In this paper, by utilizing the predictable mobility patterns of underwater objects, we propose a scheme, called Scalable Localization scheme with Mobility Prediction (SLMP), for underwater sensor networks. In SLMP, localization is performed in a hierarchical way, and the whole localization process is divided into two parts: anchor node localization and ordinary node localization. During the localization process, every node predicts its future mobility pattern according to its past known location information, and it can estimate its future location based on the predicted mobility pattern. Anchor nodes with known locations in the network will control the localization process in order to balance the trade-off between localization accuracy, localization coverage, and communication cost. We conduct extensive simulations, and our results show that SLMP can greatly reduce localization communication cost while maintaining relatively high localization coverage and localization accuracy.
Recently the orthogonal frequency division multiplexing (OFDM) technique has attracted increasing interests in underwater acoustic (UA) communications. In this paper, we present an OFDM-based UA communication system, which is designed based on the National Instruments LabVIEW software and the CompactDAQ device. Details on both the transmitter and receiver system design are discussed. The performance of this UA OFDM system is verified through recent UA communication experiments performed in a tank, in the Canning River, and in the estuary of the Swan River, Western Australia. Experimental results show that the system achieves a reliable bit error rate performance even with high-order modulation schemes. Compared with conventional field-programmable gate array and digital signal processor based designs, the proposed implementation simplifies the prototype design process and reduces the software development time. The proposed system provides a flexible and reconfigurable prototype for researchers to test and validate the performance of UA communication algorithms in real UA channels.
Driven by the huge demand to explore oceans, underwater wireless communications have been rapidly developed in the past few decades. Due to the complex physical characteristics of water, acoustic wave is the only media available for underwater wireless communication at any distance. As a result, underwater acoustic communication (UAC) is the major research field in underwater wireless communication. In this paper, characteristics of underwater acoustic channels are first introduced and compared with terrestrial communication to demonstrate the difficulties in UAC research. To give a general impression of the UAC, current important research areas are mentioned. Furthermore, different principal modulation-based schemes for short- and medium-range communications with high data rates are investigated and summarized. To evaluate the performance of UAC systems in general, three criteria are presented based on the research publications and our years of experience in high-rate short- to medium-range communications. These three criteria provide useful tools to generally guide the design and evaluate the performance of underwater acoustic communication systems.
Flexible/adaptive acoustic modems that are reprogrammable/reconfigurable at all layers of the communication stack, either by a user or by means of autonomous decisions, are considered as an important enabler for interoperability and cognitive networking in the underwater domain. In this paper, we review the existing literature on software-defined acoustic modems (SDAMs) for underwater communications and networking, considering past and ongoing academic efforts, as well as industrial developments and European collaborations centered on software-defined modem structures and functionalities. We then zoom in on relevant R&D efforts currently taking place in a defense cooperation between The Netherlands and Norway, targeting the design of a software-defined modem for the NILUS MK 2 sensor node. This modem is built using general-purpose (GP) computing architectures running open-source operating system and tools, thereby making a further step toward software-defined open-architecture underwater acoustic modems. The first field tests of the NILUS MK 2 node in multihop underwater acoustic networks are presented, showing satisfactory performance in shallow and open waters.
In recent years, orthogonal frequency division multiplexing (OFDM) technology has been widely investigated for both point-to-point underwater acoustic communications and for networks. In this paper, we implement the OFDM underwater acoustic communication algorithm on an OMAP-L138 platform, which possesses characteristics of low-power, rich peripheral and dual-core cooperation. The real-time processing capacity and good expansibility of this system have been verified. An error-free communication result has been achieved in a quasi-stationary pool experiment.
In view of the requirements for the applications of ocean development, environmental monitoring, disaster prevention etc., the HEU OFDM-modem for underwater acoustic communication and networking is presented in this paper. Orthogonal frequency division multiplexing (OFDM) technology is utilized in the physical layer, and protocols of ALOHA, MACAW are adopted in the data link layer. We conducted a mobile point-to-point communication experiment in May 2014, in the South Sea, China, where the bit error rate was less than 1.8×10-5, with bandwidth of 4 kHz, data rate of 3.03 kbps, and horizontal communication distance of 5 km. A small-scale underwater networking experiment was also carried out in the South Sea during the period from June 2nd to July 15th, 2014, where each node's depth and the water temperature around the node measured by TD (Temperature and Depth) profiling instruments were sent back to the gateway every 25 minutes through underwater acoustic channel.
In this paper, we focus on the need for remote and robust underwater acoustic(UWA) communication in shallow sea. A set of OFDM underwater acoustic communication algorithm is designed including the techniques of Doppler estimation and compensation, channel equalization and frequency diversity. This algorithm is realized in the DSP and successfully applied on the OFDM-Modem platform. In Da- Lian shallow sea trial, the horizontal communication distance is 36 kilometers under the condition of QPSK modulation, 1/2 rate convolution code, bandwidth between 4 and 8kHz. The communication rate of the OFDM-Modem can reach 426bps and the ultimate BER is less than 10-3.
Underwater acoustic communication systems are of increasing importance to all nations and organization performing maritime/littoral activities. Currently, few standards exist for underwater communications, and modems from different vendors are in general incompatible. This leads to a lack in interoperability. This paper points out a possible roadmap to standardization and flexible modems and protocols, arguing that in order to be successful in standardization of underwater communications, it is essential that standardized simulation models and methods are agreed upon first. The paper also discusses various efforts known to the authors, and their relation to the proposed roadmap.
In this paper we discuss issues related to the design of underwater acoustic network protocols which are tailored around, and leverage on, the differences between underwater acoustics and terrestrial radio. These differences span physical propagation and energy consumption, and influence the design of medium access control, routing and topology management.By first reviewing a simple model for underwater sound propagation and hardware energy consumption, we introduce a set of solutions which explicitly account for, or make use of, the longer propagation delays of acoustic waves in the water with respect to radio waves in the air, and the different ratio between transmit and receive energy consumption offered by underwater transducers. These protocols deal with the problems of efficiently scheduling transmissions in a fixed 3D deployment, of optimizing the use of energy by choosing the best mechanisms for topology management, and of choosing the best hop length over a multihop path.We then review some more realistic underwater sound propagation behaviors, and detail their consequences on the simulation of MAC protocols for underwater networks. Finally, we briefly discuss the currently available underwater communications hardware (including both commercial and research modems) and comment on which paradigms are currently realizable, with special regard to those requiring the adaptability of transmit power and frequency.
The micro-modem is a compact, low-power, underwater acoustic communications and navigation subsystem. It has the capability to perform low-rate frequency-hopping frequency-shift keying (FH-FSK), variable rate phase-coherent keying (PSK), and two different types of long base line navigation, narrow-band and broadband. The system can be configured to transmit in four different bands from 3 to 30 kHz, with a larger board required for the lowest frequency. The user interface is based on the NMEA standard, which is a serial port specification. The modem also includes a simple built-in networking capability which supports up to 16 units in a polled or random-access mode and has an acknowledgement capability which supports guaranteed delivery transactions. The paper contains a detailed system description and results from several tests are also presented
With the advances in acoustic modem technology that enabled
high-rate reliable communications, current research focuses on
communication between various remote instruments within a network
environment. Underwater acoustic (UWA) networks are generally formed by
acoustically connected ocean-bottom sensors, autonomous underwater
vehicles, and a surface station, which provides a link to an on-shore
control center. While many applications require long-term monitoring of
the deployment area, the battery-powered network nodes limit the
lifetime of UWA networks. In addition, shallow-water acoustic channel
characteristics, such as low available bandwidth, highly varying
multipath, and large propagation delays, restrict the efficiency of UWA
networks. Within such an environment, designing an UWA network that
maximizes throughput and reliability while minimizing the power
consumption becomes a very difficult task. The goal of this paper is to
survey the existing network technology and its applicability to
underwater acoustic channels. In addition, we present a shallow-water
acoustic network example and outline some future research directions
We propose a distributed, scalable, energy-efficient MAC protocol that works despite long, unknown propagation delays of the underwater acoustic medium. This protocol can be used for delay-tolerant applications such as underwater ecological sensor networks between energy-limited nodes. Our protocol differs significantly from ALOHA, MACA, and MACAW protocols in that energy is the main performance metric in our case rather than bandwidth utilization. It is shown that under a realistic underwater sensor network scenario, our proposed MAC protocol wastes only 3 percent of the transmit energy due to collisions, when an average number of 1-hop neighbors is 5, and the duty cycle is 0.004. This distributed, scalable MAC protocol has the potential to serve as a primer for the development of energy-efficient MAC protocols for future underwater sensor networks
There is a growing interest for underwater sensor networks where long term monitoring of water masses around the world for scientific, environmental, commercial, and military reasons is desired. In this paper we will present the concept of a highly flexible acoustic modem called the Reconfigurable Modem (rModem) that can be used for rapid testing and development of such networks.
The performance of networked undersea acoustic communications is
improved through implementation of handshaking between each pair of
adjacent modems along the network route. The handshake begins with the
sending modem transmitting a short request to send (RTS) packet to the
receiving modem. On successful receipt of the RTS, the receiving modem
replies with a short clear to send (CTS) packet. In the event of failure
to complete the handshake, a timer in the transmitting modem triggers
additional RTS transmissions. On successful completion of the RTS/CTS
handshake, the sending modem transmits the data packet. Large data
packets can require acoustic transmission times on the order of tens of
seconds. During these long transmissions, there is increased potential
for dropped packets as a result of unrecoverable bit errors. The
automatic repeat request (ARQ) is a means of accomplishing a successful,
error-free data transfer in the event of such dropped data. The
receiving modem, upon receipt of a corrupted data packet, issues a short
ARQ packet to the sending modem that acts as a request to re-send the
data packet or portions thereof. Statistics from an actual undersea
acoustic network demonstrate the advantages of using RTS/CTS handshaking
and ARQ retransmissions
performance of undersea acoustic networking using rts/cts handshaking and arq retransmission
- boxley
Performance of undersea acoustic networking using rts/cts handshaking and arq retransmission
- P A Boxley
- C L Fletcher
- R K Creber
- J A Rice