Performance analysis of uncoordinated medium access control in low data rate UWB networks

Power efficient ultra-wideband based wireless communication for wireless body area network applications

This paper investigates the parameters of time-hopping impulse radio ultra wide band (TH-IR-UWB). At a given spreading factor and a given system load, a trade-off has to be done in the choice of the frame length and the repetition factor. This trade-off lays on the condition of validity of the standard Gaussian approximation for multi user interferences (MUI). This study concerns both pulse amplitude modulation and pulse position modulation and may be applied to UWB networks with high density of users and low data rates like ad-hoc sensor networks, as well as networks with higher data rate and small number of users

In-car wireless data communications systems require a short-range unlicensed radio communications technology that causes a very low level of interference in the other, already deployed radio links and networks, offers low and medium data rate, can reuse the already occupied radio-frequency (RF) bands, and assures low probability of message collisions. Ultrawide band (UWB) impulse radio employs RF pulses with very short duration to carry the information; consequently, it is an optimal candidate for the in-car wireless communications and intravehicular wireless sensor networks. Data rate and shape of RF carrier pulse determine the performance of a UWB radio link. To limit the interference caused, the maximum power radiated by an UWB device is restricted by the Federal Communications Commission (FCC) in the U.S. Introducing a new mathematical model and starting from the FCC regulations, analytical expressions for the calculation of FCC power limits are derived here. It is shown that the low- and high-rate UWB impulse radio systems are peak and average power limited, respectively. The relationship between the mathematical model and the parameters of an UWB carrier pulse used in a built UWB radio is established. The performances of RF carrier pulses known from the literature are evaluated and compared. All expressions derived are verified by measurements.

1.1 Impulse Radio (IR) Ultra Wideband (UWB) Communications Ultra wideband (UWB) communication is a fast emerging technology that offers new opportunities such as high data rates, low equipment cost, low power, precise positioning capability and extremely low interference Ghawami (2005). A wide range of possible UWB communication system applications includes radars due to UWB ultra high precision ranging at the centimeter level, wireless personal area networks (WPAN), sensor networks, imaging systems, UWB positioning systems, etc. Yang (2004), Kshetrimayum (2009). From a commercial point of view, the high data rates are the most attractive feature of UWB systems for which speeds of over 100Mb/s have been demonstrated Ghawami (2005). There exist three main types of UWB technologies: impulse radio (IR UWB), direct sequence (DS UWB), and multi-band orthogonal frequency division multiplexing (MB OFDM) Ran (2009). IR UWB communication technique is essentially different from all other communication techniques because it is carrier free and uses for communication between transmitters and receivers very narrow radio frequency (RF) pulses generated from the UWB pulse generator, while traditional transmission systems transmit information by varying the power, frequency, and/or phase of a sinusoidal wave in a modulation process Kshetrimayum (2009), Yao (2007). Consequently, complicated frequency mixers and local oscillators for carrier frequency up and down conversion are not necessary Yao (2007). IR UWB modulation techniques are especially important because the UWB spectrum has been made available by the Federal Communication Commission (FCC) and it can be used with IRs developed to date Lin (2005). Waveforms for IR UWB are designed to obtain a flat frequency response over the bandwidth of the pulse and to avoid a DC component. The large spectrum of a UWB signal may interfere with existing users. In order to keep this interference to the minimum, FCC specifies spectral masks for different applications, i.e. the allowed power output for specific frequencies Ghawami (2005). A contiguous bandwidth of 7.5GHz is available in the frequency interval of (3.1− 10.6)GHz at a maximum power output of −41.3dBm/MHz which is considered as extremely low Ghawami (2005). The power spectral density (PSD) of UWB systems defined as a ratio of the transmitted power P in watts and a signal bandwidth B in hertz is extremely low as compared to other communication systems due to the very wide bandwidth B of short pulses that are typically of nanosecond or picosecond order Ghawami (2005). The selection of the impulse signal type for IR UWB communication system is essential since it determines

The ranging and positioning systems for the LR WPAN (low-rate wireless personal area network) have been one of the attracting issues for indoor location applications. In order to support the ranging functions in WPAN, IEEE 802.15.4a Task Group has released new standard of alternative PHY (Physical layer) and amendment of MAC (medium access control) with IR-UWB (impulse radio ultra wide band) signals for high ranging resolution. This paper shows the implementation of IEEE 802.15.4a PHY and MAC protocol for ranging and data communications, and the positioning system including data acquisition, display, and positioning algorithm.

GTS size adaptation algorithm for IEEE 802.15.4 wireless networks

Pulse-based communication systems are a promising candidate in the deployment of future wireless networks, thanks to the potential robustness and capacity guaranteed by the transmission of pulses of very short duration. In the framework of pulse-based communication systems, the Impulse Radio-Ultra Wide Band (IR-UWB) technique recently received particular attention. In the past, most of the UWB research focused on hardware and physical layer aspects in order to solve the technological challenges posed by IR-UWB. UWB peculiar characteristics may, however, also stimulate innovative higher layers' design. This work addresses Medium Access Control (MAC) issues for IR-UWB communication systems and extends the discussion to wireless optical communication systems. Typical characteristics of an IR-UWB system are presented, and solutions proposed for such systems at the MAC layer are reviewed. The applicability of such solutions to an optical wireless communications system is then discussed, highlighting analogies and differences between IR-UWB and wireless optical systems.

The 5G prospect of seamlessly connected global devices with delay-tolerant communication, millisecond latency and gigabits per second data rate suggests the need for location-aware devices, systems and networks. This requires new methods for high resolution positioning services. It is however believed that Impulse Radio (IR) Ultrawideband (UWB) promises better positioning methods for accuracy-critical situations expected in 5G setting. This paper discusses the IR UWB D2D-based localization for ultra-dense networks. It proposes an IR-UWB D2D WWAN along with its cluster formation scheme. This is followed with performance evaluation of the cluster lifetime and system throughput. Also proposed is an IR UWB D2D-propagation-based combined localization and communication scheme (UD-CLOCS). Results of related UD-CLOCS performance assessment experiments have been impressive while some highlights are presented in this paper. It is believed that the proposed solutions have potential for robust and cost efficient localization in 5G setting as well as prospect to decongest licensed spectrums in 5G wireless environment.

This paper deals with the positioning performance of the 3-Way ranging protocol (3-WR) in a wireless body area network (WBAN). The purpose is to propose a new cooperative algorithm to improve the number of estimated positions with a conditional permutation of the on-body anchors. To do so, we first evaluate and analyze the positioning success rate under a realistic mobility scenario and using two scheduling strategies: Broadcast single node localization (P2P-B) and aggregated and broadcast (A\&B)) with a medium access control (MAC) layer based on time division multiple access (TDMA). The 3-WR estimates the distance between two nodes placed on the body with the transmission of three packets. The wireless transmission is based on impulse radio ultra wideband (IR-UWB). However, these transactions can be lost through the WBAN channel leading into a ``bad positioning service.'' We consider a physical layer based on IR-UWB with three different channels: (1) an empirical theoretical model based on the on-body CM3 path loss channel (Anechoic chamber), (2) a simulated channel calculated by ray-tracing with the PyLayers simulator, and (3) an experimental channel model obtained by measurements. Our results show that the channel affects the positioning success rate that decreases as a function of the sensitivity threshold at the receiver. This can be solved with long and short term analysis for the choice of virtual anchors to increase the positioning performance.

Ultra wideband (UWB) radio is a promising technology for short range wireless communications. It can be used for both high rate and low rate transmissions. High data rate can be achieved by using multiband (MB)-UWB approach whereas low data rate with robust system performance can be obtained by employing time hopping (TH)-UWB radio systems Majhi et al. (2006); Win & Scholtz (1998a). Nowadays, applications of UWB are spreading to various fields such as vehicle communications, wireless sensor networks, ad hoc wireless networks, and controller area networks. The most of the systems require low to moderate (1 kbs-100 mbs) data rates with an acceptable implementation cost. However, due to the presence of fast Fourier transform (FFT) and inverse FFT (IFFT), MB-UWB may not be a cost effective procedure for low data rate systems. Therefore, one needs an efficient system which adaptively changes the data rate from low to moderate with robust system performance. TH-UWB with OOK-PSM modulation provides low data rate with robust system performance Majhi, Madhukumar, Premkumar & Richardson (2008). However, it is possible to scale the TH-UWB radio system for low to moderate data rates by incorporating higher level modulation schemes with an adaptive method. For TH-UWB systems, various M-ary modulation schemes such as pulse positionmodulation (PPM), pulse amplitude modulation (PAM), pulse shape modulation (PSM), and their combined forms have been proposed to improve data rates and system performance with low complexities Bin et al. (2003); Durisi & Benedetto (2003); Ghavami et al. (2002); Michell et al. (2003); Usuda et al. (2004). However, due to the increase of inter symbol interference (ISI) in the presence of multipath channel, M-ary PPM or M-ary orthogonal PPM (OPPM) are not effective for TH-UWB systems with RAKE reception when M is high Foerster (2003); Win & Scholtz (1998b). High-level M-ary PAM is rarely used in short range and low power consumption communications systems Guvenc & Arslan (2003). This is because that the Euclidian distances between constellations become small with increase in M. Due to its robustness against ISI and multiple access interference (MAI), pulse-based modulation such as PSM has become an interesting research topic in TH-UWB, direct sequence UWB (DS-UWB) and transmitted referenceUWB (TR-UWB) radio systemsChu M de Abrue et al. (2003); Gezici et al. (2006); Hwang et al. (2007); Kim & Womack (2007); Parr et al. (2003). However, high-level M-ary PSM cannot be used due to the limited auto correlation properties 2

As discussed in the previous chapter, Low Power Communication is the key to realization of a low power sensor node. Since sensor nodes require only low data rate communication, it might sound intuitively clear that they should also naturally be low power. After all, if a node does less work, it should also consume lesser power. But somehow this doesn’t seem to fit the behavior for low data rate communication, short range radios. If we look at existing radio designs at various data rates and ranges, we see that the design space occupied is very wide. There are designs that operate at very high (~100 Mbps) data rates and designs that operate at low data rates (~100 Kbps). There are designs that take wall supply, consuming a few watts of power, while some work on batteries. If one looks at energy per bit requirements of these designs, while some designs operate at hundreds of nJ/bit, some other designs exist consuming only 0.1 nJ/bit (Fig. 2.1). Now if we plot the range over these designs and examine how they should scale according to the energy/bit requirements we should see radios working at low data rates while consuming few microwatts of power, as required by sensor networks. These designs do not exist. The reasons there aren’t any designs in this space requires us to consider the consequences of scaling traditional design as we go for lower and lower data rate. Since Shannon’s law governs the limit on the energy efficiency of radio communication and link margin vis-à-vis the channel capacity, it makes sense to have a closer look at it and then see what constraints typical radio architectures have that prevent power from scaling in low data rate applications.KeywordsSensor NodeSpectral EfficiencyLeakage PowerGain StageImpulse RadioThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Wireless Local Area Networks (WLANs) and Wireless Metropolitan Area Networks (WMANs) are two of the main technologies in wireless data networks. WLANs have a short range and aim at providing connectivity to end users. On the other hand, WMANs have a long range and aim at serving as a backbone network and also at serving end users. In this dissertation, we consider the problem of Medium Access Control (MAC) in WLANs and the placement of Relay Stations (RSs) in WMANs. We propose a MAC scheme for WLANs in which stations contend by using jams on the channel. We present analytic and simulation results to find the optimal parameters of the scheme and measure its performance. Our scheme has a low collision rate and delay and a high throughput and fairness performance. Secondly, we present a MAC scheme for the latest generation of WLANs which have very high data rates. In this scheme, we divide the stations into groups and only one station from each group contends to the channel. We also use frame aggregation to reduce the overhead. We present analytic and simulation results which show that our scheme provides a small collision rate and, hence, achieves a high throughput. The results also show that our scheme provides a delay performance that is suitable for real-time applications and also has a high level of fairness. Finally, we consider the problem of placing Relay Stations (RSs) in WMANs. We consider the Worldwide Interoperability for Microwave Access (WIMAX) technology. The RSs are used to increase the capacity of the network and to extend its range. We present an optimization formulation that places RSs in the WiMAX network to serve a number of customers with a pre-defined bit rate. Our solution also provides fault-tolerance by allowing one RS to fail at a given time so that the performance to the users remains at a predictable level. The goal of our solution is to meet the demands of the users, provide fault-tolerance and minimize the number of RSs used.

Traditional algorithms for Media Access Control (MAC) in Mobile Ad Hoc Networks (MANET) such as CSMA-CA allow only a single user to transmit at a given time. This means that the sum throughput in a MANET cannot increase to service additional users. Such MAC protocols disregard the possibility that by utilizing multiple antenna processing to handle interference intelligently at the Physical layer (PHY), many concurrent user transmissions can co-exist. Previous works have proposed altered versions of CSMA-CA that allow multi user operation but may not necessarily be able to coexist with an existing IEEE 802:11 based network. This paper proposes a Concurrent CSMA MAC protocol that is completely compatible with traditional CSMA based MAC and follows the same timing structure allowing co-existence of both protocols. Specifically, in Concurrent CSMA after a primary user has captured the channel, secondary users listen to the RTS/CTS handshake and form a beamnull towards the primary receiver. Hence secondary users can communicate concurrently with minimal increase in interference to the primary receiver. Simulations show that the proposed PHY and MAC scheme is able to achieve 2 to 3 times the network spectral efficiency of CSMA with a single antenna and this improvement factor is sustained as the network scales in size. Further the proposed scheme allows the network spectral efficiency (sum throughput per unit bandwidth) to scale with users and improves upon a previous promising approach which uses Interference Alignment.

An egress Network Access Control (NAC) is widely deployed to control users in a wireless network. However, Medium Access Control (MAC) address spoofing is a technique that can easily bypass the egress NAC. So, this vulnerability is a big problem in almost all NAC systems around the world. To solve this problem, we proposeaVisa mechanism to enhance the egress NAC authentication. The mechanism needs only a JAVA applet to run without manually installing any agent-program. To evaluate our new mechanism, we have built a prototyped program, and experiment on a wireless test-bed. The performance evaluation has demonstrated favorable features of our new Visa mechanism.

This paper details the medium access control (MAC) layer designed in the PULSERS project for low data rate (LDR) systems, whose main features are low power consumption, low complexity location and relaying capabilities. The MAC developed in PULSERS is based on the IEEE 802.15.4 standard, which, in spite of many virtues, is not the ideal solution for the targeted UWB applications. Thus, the MAC implemented in the project deviates from the standard in a few areas such as the support to peer-to-peer communications, the systematic usage of guaranteed time slots for data transmissions (TDMA), dedicated time slots for ranging or allocation requests, specification of a new ranging procedure, and finally, the definition of a relaying functionality in layer 2. Furthermore, as recent application studies have revealed that mesh networking is necessary for most of the targeted applications, mesh algorithms have also been specified and will be implemented in the next release of the PULSERS MAC layer. The paper first presents the applications targeted in the project. Then, it describes the MAC layer proposal, putting the emphasis on its major specificities in comparison with the IEEE 802.15.4 standard. The expected performances are also provided through OPNET simulation results. Finally, the paper focuses on the localization procedures implemented in the MAC layer, and proposes some enhancements of the current implementation with respect to localization.