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A Survey on Jamming Attacks and Countermeasures in WSNs

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标签: JammingAttacksWSNs

A Survey on Jamming Attacks and Countermeasures in WSNs

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42 IEEE COMMUNICATIONS SURVEYS TUTORIALS VOL 11 NO 4 FOURTH QUARTER 2009 A Survey on Jamming Attacks and Countermeasures in WSNs Aristides Mpitziopoulos Damianos Gavalas Charalampos Konstantopoulos and Grammati Pantziou AbstractJamming represents the most serious security threat in the eld of Wireless Sensor Networks WSNs as it can easily put out of order even WSNs that utilize strong high layer security mechanisms simply because it is often ignored in the initial WSN design The objective of th......

42 IEEE COMMUNICATIONS SURVEYS & TUTORIALS, VOL. 11, NO. 4, FOURTH QUARTER 2009 A Survey on Jamming Attacks and Countermeasures in WSNs Aristides Mpitziopoulos, Damianos Gavalas, Charalampos Konstantopoulos, and Grammati Pantziou Abstract—Jamming represents the most serious security threat in the field of Wireless Sensor Networks (WSNs), as it can easily put out of order even WSNs that utilize strong high- layer security mechanisms, simply because it is often ignored in the initial WSN design. The objective of this article is to provide a general overview of the critical issue of jamming in WSNs and cover all the relevant work, providing the interested researcher pointers for open research issues in this field. We provide a brief overview of the communication protocols typically used in WSN deployments and highlight the characteristics of contemporary WSNs, that make them susceptible to jamming attacks, along with the various types of jamming which can be exercised against WSNs. Common jamming techniques and an overview of various types of jammers are reviewed and typical countermeasures against jamming are also analyzed. The key ideas of existing security mechanisms against jamming attacks in WSNs are presented and open research issues, with respect to the defense against jamming attacks are highlighted. Index Terms—Jamming, wireless sensor networks, ZigBee, FHSS, DSSS. I. INTRODUCTION W IRELESS Sensor Networks (WSNs) [1] are used in many applications which often include the monitoring and recording of sensitive information (e.g. battlefield aware- ness, secure area monitoring and target detection). Recently the high drop in the prices of CMOS cameras and microphones has given rise to the development of a special class of WSNs, that of Wireless Multimedia Sensor Networks (WMSNs) [2] [3] [4]. WMSNs allow the retrieval of video and audio streams, still images, and scalar sensor data from deployed nodes [4]. Hence, they can be efficiently used in various security applications such as surveillance systems for monitoring of secure areas, patients, children, etc. In these applications, QoS requirements rise, since in such systems even a temporal disruption of the proper data streaming may lead to disastrous results. It is therefore evident that the critical importance of WSNs raises major security concerns. Jamming is defined as the act of intentionally directing electromagnetic energy towards a communication system to disrupt or prevent signal transmission [5]. In the context of WSNs, jamming is the type of attack which interferes Manuscript received 31 December 2007; revised 13 May 2008 and 26 August 2008. Aristides Mpitziopoulos and Damianos Gavalas are with the Department of Cultural Technology and Communication, University of the Aegean, Lesvos, Greece (e-mail: crmaris,dgavalas@aegean.gr). Charalampos Konstantopoulos is with Department of Informatics, Univer- sity of Piraeus, Greece (e-mail: konstant@unipi.gr). Grammati Pantziou is with the Department of Informatics, Tech- Institution of Athens, Athens, Greece (e-mail: nological Educational pantziou@teiath.gr). Digital Object Identifier 10.1109/SURV.2009.090404. with the radio frequencies used by network nodes [6]. In the event that an attacker uses a rather powerful jamming source, disruptions of WSNs’ proper function are likely to occur. As a result, the use of countermeasures against jamming in WSN environments is of immense importance, especially taking into account that WSNs suffer from many constraints, including low computation capability, limited memory and energy resources, susceptibility to physical capture and the use of insecure wireless communication channels1. Jamming attacks may be viewed as a special case of Denial of Service (DoS) attacks. Wood and Stankovic define DoS attack as “any event that diminishes or eliminates a network’s capacity to perform its expected function” [7]. Typically, DoS prevents or inhibits the normal use or management of communications through flooding a network with ‘useless’ information. In a jamming attack the Radio Frequency (RF) signal emitted by the jammer corresponds to the ‘useless’ information received by all sensor nodes. This signal can be white noise or any signal that resembles network traffic. The main objective of this article is to provide a general overview of the critical issue of jamming in WSNs and cover all the relevant work, providing the interested researcher pointers for open research issues in this field. The remainder of this article is organized as follows: Section II comprises an introduction to the main concepts, issues and applications of WSNs while Section III briefly overviews the communication protocols typically used in WSN deployments. Section III also refers to the vulnerabilities of these protocols that make them susceptible to jamming attacks. Jamming definition, a brief reference to jamming history and jamming techniques are discussed in Section IV. Section V refers to several types of jammers that may be used against WSNs and Section VI analyzes typical countermeasures against jamming. The key ideas of existing security mechanisms against jam- ming attacks in WSNs are reviewed in Section VII. Section VIII summarizes the relevant advantages and shortcomings of the anti-jamming schemes, Section IX identifies open research issues and Section X concludes the paper. II. SENSOR NETWORKS HISTORY AND TODAY’S WSN APPLICATIONS Similarly to other technologies the evolution of sensor networks commenced targeting military applications. The first known sensor network application was the Sound Surveillance System (SOSUS) [8]. This network had been used in the early 1950s, during the Cold War, for the detection and 1A communication channel may be composed of a single frequency (e.g. 306.7 MHz) or a range of frequencies (e.g. 2403.5 − 2406.5 MHz). 1553-877X/09/$25.00 c(cid:2) 2009 IEEE MPITZIOPOULOS et al.: A SURVEY ON JAMMING ATTACKS AND COUNTERMEASURES IN WSNS 43 tracking of Soviet submarines with the help of acoustic sensors (hydrophones). SOSUS is still in operation and mainly used for monitoring various events, such as seismic and animal activity in the ocean [9]. The next sensor network application has also been devel- oped for military purposes. Around 1980, the Distributed Sen- sor Networks (DSNs) project was initiated by the Defence Ad- vanced Research Projects Agency (DARPA) [10]. The original name of DARPA was Advanced Research Projects Agency (ARPA). ARPANET was a network created in 1969 that led to the development of contemporary Internet. The possibility to extend ARPANET to sensor networks was considered by R. Kahn (co inventor of the TCP/IP protocols and actively enrolled in the development of the Internet) along with some research on supporting components such as operating system and knowledge-based signal processing techniques [10]. Recent advances in hardware and communications had a substantial impact on sensor network research. Small and in- expensive sensors based upon micro-electromechanical system (MEMS) [11] technology, wireless networking, and inexpen- sive low-power processors allowed the deployment of WSNs for various applications. A few examples of WSNs applications are the following: (cid:129) Security: WSNs can be used for security applications such as the surveillance of critical and sensitive areas and the detection of possible biological-chemical attacks [12]. Furthermore, the use of WMSNs can lead to improved coverage and easier detection of threats and false alarms. (cid:129) Environment and habitat monitoring: WSNs can offer improved flexibility in this field since they are able to monitor areas with no infrastructure and get more consistent data [13]. (cid:129) Medical monitoring: patients can be easily monitored with the use of proper WSNs by their doctors [14]. (cid:129) Object tracking: moving objects or persons can be tracked with the use of WSNs equipped with the appropriate sensors [15]. (cid:129) Assistive environments: such environments can use WSN technology to improve the functional capabilities of in- dividuals with disabilities. WSNs can enable a cost- effective self-care to users and provide them indepen- dence along with a better quality of life. Representative examples of assistive environments that utilize WSNs are [16] and [17]. III. COMMUNICATION IN WSNS AND THEIR VULNERABILITIES AGAINST JAMMING A WSN is usually composed of hundreds or even thousands of sensor nodes. These sensor nodes are often randomly deployed in the field and form an infrastructure-less network. Each node is capable of collecting data and routing it back to the Processing Element (PE) via ad hoc connections with neighbor sensor nodes. A sensor node consists of five basic parts: sensing unit, central processing unit (CPU), storage unit, transceiver unit, and power unit [1]. It may also have additional application-dependent components attached, such as location finding system (GPS), mobilizer and power generator. A. Communication Protocol Stack The protocol stack used in sensor nodes contains physical, data link, network, transport, and application layers defined as follows [1]: (cid:129) Physical layer: responsible for frequency selection, car- rier frequency generation, signal deflection, data encryp- tion2 and modulation. This is the layer that suffers the most damage from radio jamming attacks. (cid:129) Data link layer: responsible for the multiplexing of data streams, data frame detection, medium access control (MAC), data encryption and error control; as well as en- suring reliable point-to-point and point-to-multipoint con- nections. This layer and more specific MAC are heavily damaged by link-layer jamming. In link-layer jamming [18] [19], sophisticated jammers can take advantage of the data link layer to achieve energy efficient jamming. Compared to radio jamming, link-layer jamming offers better energy efficiency. (cid:129) Network layer: responsible for specifying the assignment of addresses and how packets are forwarded. (cid:129) Transport layer: responsible for the reliable transport of packets and data encryption. (cid:129) Application layer: responsible for specifying how the data are requested and provided for both individual sensor nodes and interactions with the end user. B. ZigBee Protocol and 802.15.4 Standard overview A considerable percentage of the nodes currently used in WSN environments comply with the ZigBee [20] commu- nications protocol. ZigBee protocol minimizes the time the radio functions so as to reduce power consumption. All ZigBee devices are required to comply with the IEEE 802.15.4-2003 [21] or IEEE 802.15.4-2006 [22] Low-Rate Wireless Personal Area Network (WPAN) standard. The standard only specifies the lower protocol layers, the physical layer (PHY), and the medium access control (MAC) portion of the data link layer (DLL). The standard’s specified operation is in the unlicensed 2.4 GHz, 902-928 MHz (North America) and 868 MHz (Europe) ISM (Industrial, Scientific and Medical) bands. In the 2.4 GHz band there are 16 ZigBee channels (for both 2003, 2006 version of IEEE 802.15.4), with each channel occupying 3 MHz of wireless spectrum and 5 MHZ channel spacing. The center frequency for each channel can be calculated as, F C = (2400 + 5 ∗ k) MHz, where k = 1, 2, . . . , 16. In 902- 928 MHz there are ten channels (extended to thirty in 2006) with 2 MHz channel spacing and in 868 MHz one channel (extended to two in 2006). The radios use Direct-Sequence Spread Spectrum (DSSS) [23] coding in which the transmitted signal takes up more bandwidth than the information signal that is being modulated. In IEEE 802.15.4-2003 [21] two physical layers are specified: BPSK [24] in the 868 MHz and 902-928 MHz, and orthogonal O-QPSK [24] that transmits two bits per-symbol in the 2.4 GHz band. The raw, over-the-air data rate is 250 kbit/s per channel in the 2.4 GHz band, 40 kbit/s per channel in 902-928 2Data encryption more commonly is done at the data link or transport layers. 44 IEEE COMMUNICATIONS SURVEYS & TUTORIALS, VOL. 11, NO. 4, FOURTH QUARTER 2009 MHz, and 20 kbit/s in the 868 MHz band. The 2006 revision [22] improves the maximum data rates of the 868/915 MHz bands, bringing them up to support 100 and 250 kbit/s as well. Moreover, it defines four physical layers depending on the modulation method used: BPSK and O-QPSK in 868/915 MHz band, O-QPSK in 2.4 GHz band and a combination of binary keying and amplitude shift keying for 868/915 MHz band. Transmission range for both versions is between 10 and 75 meters (33 and 246 feet), although it is heavily dependent on the particular environment where the nodes are deployed. The maximum output power of the radios is generally 0 dBm (1 mW). C. Vulnerabilities of today WSNs that make them susceptible to jamming The above discussion makes clear that a node that follows the IEEE 802.15.4 communications protocol [21] [22] (2003 or 2006 revision) may connect to the network via a limited number of communication channels:16 channels in 2.4 GHz band (2400-2483.5 MHz), 10 channels (30 for 2006) in 902- 928 MHz and 1 channel (3 for 2006) in 868.3 MHz. In addition, taking into account the maximum output power of the radio of a node (0 dBm), it becomes apparent that an attacker could easily jam a WSN (with the use of low power output) and disrupt sensor nodes communication . The main limitation of the above-mentioned protocols is that they have not been originally designed taking radio jamming into account. WSN nodes design also presents the same limitation. Other types of widely utilized motes such as Mica-2 [25] are even more susceptible to jamming since they use an even smaller number of communication channels (support of only lower 868/916 bands and not 2.4 GHz band). Thus with typical WSNs in use today is very difficult to take effective measures against jamming, which raises a major security issue. A significant number of research works suggest addressing jamming attacks utilizing hardware used in contemporary WSNs [26] [27] [28] [29] [30] [31], while other works suggest new design requirements of nodes that can effectively defend jamming attacks [32]. The main advantage of the former is that the implementation is much cheaper and straightforward and the compatibility with currently available hardware; yet, they cannot easily cope with heavy jamming attacks. On the other hand, suggesting new design requirements for nodes, jam- ming attacks can be addressed more efficiently. However the implementation of these nodes requires a significant amount of research, while the associated cost is highly increased. In addition, this approach offers no compatibility with existing hardware. IV. JAMMING DEFINITION, HISTORY AND TECHNIQUES Jamming is defined as the emission of radio signals aiming at disturbing the transceivers’ operation [5]. The main dif- ference between jamming and radio frequency interference (RFI) is that the former is intentional and against a specific target while the latter is unintentional, as a result of nearby transmitters that transmit in the same or very close frequencies (for instance, the coexistence of multiple WSNs on the same area using the same frequency channel may result in RFI). A. Brief History of Jamming The first occasions of jamming attacks were recorded back in the beginning of the 20th century against military radio telegraphs. Germany and Russia were the first to engage in jamming. The jamming signal most frequently consisted of co-channel characters. The first wartime jamming activities can be traced back to the World War II [33], when allied ground radio operators attempted to mislead pilots by giving false instructions in their own language (an example of deceptive jamming). These operators were known by the code name ‘Raven’ which soon became ‘Crow’. The crow represents the universal sign of jamming ever since. Also during World War II the first jamming operations against radars (a new invention at that time) have been reported. Jamming of foreign radio broadcast stations has been of- ten used during periods of tense international relations and wartime to prevent the listening of radio broadcasts from enemy countries [34]. This type of jamming could be relative easy addressed by the stations with the change of transmitting frequency, adding of additional frequencies and by increasing transmission power. B. Jamming Techniques The key point in successful jamming attacks is Signal-to- Noise Ratio (SNR), SNR= Psignal/Pnoise, where P is the average power. Noise simply represents the undesirable acci- dental fluctuation of electromagnetic spectrum, collected by the antenna. Jamming can be considered effective if SNR< 1. Existing jamming methods are described below. 1) Spot Jamming: The most popular jamming method is the spot jamming wherein the attacker directs all its transmitting power on a single frequency that the target uses with the same modulation and enough power to override the original signal. Spot jamming is usually very powerful, but since it jams a single frequency each time it may be easily avoided by changing to another frequency. 2) Sweep Jamming: In sweep jamming a jammer’s full power shifts rapidly from one frequency to another. While this method of jamming has the advantage of be- ing able to jam multiple frequencies in quick succession, it does not affect them all at the same time, and thus lim- its the effectiveness of this type of jamming. However, in a WSN environment, it is likely to cause considerable packet loss and retransmissions and, thereby, consume valuable energy resources. 3) Barrage Jamming: In barrage jamming a range of fre- quencies is jammed at the same time. Its main advantage is that it is able to jam multiple frequencies at once with enough power to decrease the SNR of the enemy receivers. However as the range of the jammed frequen- cies grows bigger the output power of the jamming is reduced proportionally. 4) Deceptive Jamming: Deceptive jamming can be applied in a single frequency or in a set of frequencies and is used when the adversary wishes not to reveal her existence. By flooding the WSN with fake data she can MPITZIOPOULOS et al.: A SURVEY ON JAMMING ATTACKS AND COUNTERMEASURES IN WSNS 45 Fig. 1. Constant and Deceptive jammers Fig. 2. Random and Reactive jammers deceive the network’s defensive mechanisms (if any) and complete her task without leaving any traces. Deceptive jamming is a very dangerous type of attack as it cannot be easily detected and has the potential to flood the PE with useless or fake data that will mislead the WSN’s operator and occupy the available bandwidth used by legitimate nodes. V. TYPES OF JAMMERS With the word ‘jammer’ we refer to the equipment and its capabilities that are exploited by the adversary to achieve her goal. A jammer may be anything from a simple transmitter to entire jamming stations equipped with special equipment. There are several types of jammers that may be used against WSNs. Xu et al. in [30] propose generic jammer models, namely (1) the constant jammer, (2) the deceptive jammer, (3) the random jammer and (4) the reactive jammer. The constant jammer emits continuous radio signals in the wireless medium (see Fig. 1). The signals that she emits are to- tally random. They don’t follow any underlying MAC protocol and are just random bits. This type of jammer aims at keeping the channel busy and disrupting nodes’ communication or causing interference to nodes that have already commenced data transfers and corrupt their packets. The deceptive jammer uses deceptive jamming techniques (see previous section) to attack the WSN (see Fig. 1). The random jammer sleeps for a random time ts and jams for a random time tj (see Fig. 2). The type of jamming used can be of any kind depending on the situation. Also by changing ts and tj we can achieve different levels of effectiveness and power saving. The reactive jammer (see Fig. 2) listens for activity on the channel, and in case of activity, immediately sends out a random signal to collide with the existing signal on the channel. As a result the transmitted packets of data will be corrupted. According to Xu et al. [30], the constant jammers, deceptive jammers and reactive jammers are effective jammers in that they can cause the packet delivery ratio to fall to zero or almost zero, if they are placed within a suitable distance from the victim nodes. However these jammers are also energy- inefficient, meaning they would exhaust their energy sooner than their victims would supposed they are energy-constrained. Although random jammers save energy by sleeping, they are less effective. With respect to energy-efficiency, DEEJAM [35] presents a reactive design that is relatively energy-efficient. VI. COUNTERMEASURES AGAINST JAMMING In this section we present countermeasures that deal with possible radio jamming scenarios aiming at informing and familiarizing the reader with the most effective countermea- sures against jamming; the latter will be referred to in the next section, while reviewing the proposed security schemes against jamming in WSNs. A. Regulated Transmitted Power The use of low transmission power decreases the discovery probability from an attacker (an attacker must locate first the target before transmitting jamming signal). Higher transmitted power implies higher resistance against jamming because a stronger jamming signal is needed to overcome the original signal. A considerable percentage of sensor nodes currently used in contemporary WSNs (e.g., Sunspots [36]) possess the capability to change the output power of their transmitter. B. Frequency-Hopping Spread Spectrum Frequency-Hopping Spread Spectrum (FHSS) [37] [38] is a spread-spectrum method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a shared algorithm known both to the transmitter and the receiver. FHSS brings forward many advantages in WSN environments: (cid:129) It minimizes unauthorized interception and jamming of radio transmission between the nodes. (cid:129) The SNR required for the carrier, relative to the back- ground, decreases as a wider range of frequencies is used for transmission. (cid:129) It deals effectively with the multipath effect3. (cid:129) Multiple WSNs can coexist in the same area without causing interference problems. One of the main drawbacks of frequency-hopping is that the overall bandwidth required is much wider than that required 3Multipath in wireless telecommunications is the propagation phenomenon that results in radio signals reaching the receiving antenna through two or more paths due to reflections of the original signal [39] [40]. FHSS eliminates the multipath effect for increased hop rates: when the receiver receives the original signal it immediately changes frequency, thus the ghost of the original signal (harmonic signal) isn’t received at all. 46 IEEE COMMUNICATIONS SURVEYS & TUTORIALS, VOL. 11, NO. 4, FOURTH QUARTER 2009 to transmit the same data using a single carrier frequency. However, transmission in each frequency lasts for a very limited period of time so the frequency is not occupied for long. C. Direct Sequence Spread Spectrum Direct Sequence Spread Spectrum (DSSS) [37] [23] trans- missions are performed by multiplying the data (RF carrier) being transmitted and a Pseudo-Noise (PN) digital signal. This PN digital signal is a pseudorandom sequence of 1 and −1 values, at a frequency (chip rate4) much higher than that of the original signal. This process causes the RF signal to be replaced with a very wide bandwidth signal with the spectral equivalent of a noise signal; however, this noise can be filtered out at the receiving end to recover the original data, through multiplying the incoming RF signal with the same PN modulated carrier. The first three of the above-mentioned FHSS advantages also apply to DSSS. Furthermore, the processing applied to the original signal by DSSS makes it difficult to the attacker to descramble the transmitted RF carrier and recover the original signal. Also since the transmitted signal of DSSS resembles white noise, radio direction finding of the transmitting source is a difficult task. We should note that although 802.15.4 standard [21] [22] uses DSSS modulation, that does not make it invulnerable to jamming. On the contrary due to the limited supported chip rate (2 Mchip/s) and the restricted transmission power of sensor nodes (typically 0 dBm) the network is very likely to collapse under a jamming attack. D. Hybrid FHSS/DSSS Hybrid FHSS/DSSS [37] communication between WSN nodes represents a promising anti-jamming measure. In gen- eral terms direct-sequence systems achieve their process- ing gains through interference attenuation using a wider bandwidth for signal transmission, while frequency hop- ping systems through interference avoidance. Consequently using both these two modulations, resistance to jam- ming may be highly increased. Also Hybrid FHSS/DSSS compared to standard FHSS or DSSS modulation pro- vides better Low-Probability-of-Detection/Low-Probability- of-Interception (LPD/LPI) properties. Fairly specialized in- terception equipment is required to mirror the frequency changes uninvited. It is stressed though that both the frequency sequence and the PN code of DSSS should be known to recover the original signal. Thus Hybrid FHSS/DSSS improves the ability to combat the near-far problem5 [41] which arises in DSSS communications schemes. Another welcome feature is the ability to adapt to a variety of channel problems. 4Chip represents a single bit of a pseudo-noise sequence while chip rate is the rate at which chips are sent. 5An example of near-far problem is the following: consider a receiver and two transmitters (one close to the receiver and the other far away). If both transmitters transmit simultaneously at equal powers, the receiver will receive more power from the nearby transmitter. This makes the signal from the distant transmitter more difficult to resolve. E. Ultra Wide Band Technology Ultra Wide Band (UWB) technology is a modulation tech- nique based on transmitting very short pulses [42] on a large spectrum of a frequency band simultaneously. This renders the transmitted signal very hard to be intercepted/jammed and also resistant to multipath effects. In the context of WSNs, UWB can provide many advantages. The research work of Oppermann et al. [43] promises low power and low- cost wide-deployment of sensor networks. In addition, UWB- based sensor networks guarantee more accurate localization and prolonged battery lifetime. The IEEE standard for UWB, 802.15.3.a, is under development. F. Antenna Polarization The polarization of an antenna [44] is the orientation of the electric field of the radio wave with respect to the earths’ surface and is determined by the physical structure of the antenna and its orientation. The antenna polarization of a nodes’ radio unit plays a significant role in jamming environments. For line-of-sight communications (mainly used in WSNs) for which polarization can be relied upon, it can make a significant difference in signal quality to have the transmitter and receiver using the same polarization. Thus, an antenna with right circular polarization is not able to receive left circularly polarized signals and vice-versa. Furthermore, there will be 3 dB loss from a linear polarized antenna that receives signals circular polarized; the same also stands vice-versa. Hence, if the nodes of a WSN are capable of changing the polarization of their antennas when they sense interference, they will be able to effectively defend in jamming environments. An uninvited side-effect of that the nodes must inform first each other about the change of their antenna’s polarization, otherwise communication among peers will be interrupted. A method to overcome this problem is to program the nodes when they sense interference or lack of network connectivity, to change to specific polarizations until they establish reliable links to the network. The change of nodes’ polarization of a WSN incommodes the jamming process because it makes necessary to use specialized jamming equipment with the capability to change its signal polarization rapidly during the jamming. is that G. Directional Transmission Today’s sensor nodes typically use omni-directional anten- nas [44]. The use of directional antennas [44] could dramati- cally improve jamming tolerance in WSNs. In general, direc- tional antennas/transmission provide better protection against eavesdropping, detection and jamming than omni-directional transmission [45] [46] [47]. A directional antenna transmits or receives radio waves only from one particular direction unlike the omni-directional antenna that transmits and receives radio waves from all directions in the same time. This feature allows increased transmission performance, more receiving sensitivity and reduced interference from unwanted sources (e.g. jammers) compared to omni-directional antennas. The main problems with directional transmission are: (a) the requirement of a more sophisticated MAC protocol [48]
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