Frequency Hopping Spread Spectrum (FHSS)
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Added on 2019-11-20
Frequency Hopping Spread Spectrum (FHSS)
Added on 2019-11-20
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Abstract— Wireless communication is by far the most used technology today, from wireless networks such as Wi-Ficonnections that transmit information using radio signals including their most notable application today where they are usedto connect to the worldwide web i.e. the internet. While wireless communication may offer many benefits and conveniences,its operation is limited due to the many setbacks of wireless connections such as interferences and congestions. To minimizethese limitations, operational techniques such as spread spectrum are used where the information transmitted using radiosignals is spread and augmented to improve its immunity. Now, Frequency hopping spread spectrum (FHSS) is a goodexample of these techniques where signals are moved from one frequency to another thus nullifying the limitations of wirelesscommunication. This report provides a critical analysis of this technique including the emerging trends and applications.Keywords: Spread spectrum, FHSS, QAM, BW, PNI.INTRODUCTIONWhile wired communication may have the benefit of solid mediums to perform its operations, wirelesscommunication uses a versatile and dynamic medium to transfer information. This medium is filled with many elementsand conditions that change abruptly which necessitates the need to improve the performance of the signals beingtransmitted. FHSS will improve the quality of the signals by minimizing signal interference and fading through hoppingtechnique that carries information from one signal band to another [ CITATION Bad141 \l 1033 ]. Now, to understandthe operation of this technique it’s important to highlight the entire concept of spread spectrum. In general, there are twomain types of spread spectrum; FHSS and DSSS (direct sequence spread spectrum). In both instances, thecommunication bandwidth i.e. the transmission signal is enlarged as compared to the bandwidth of the transmittedsignal (original message). This variation accommodates the limitations of wireless communication particularly in theshort range application improving the quality of the signals[ CITATION Bad142 \l 1033 ].FHSS as a component of spread spectrum will further its course by utilizing the frequencies of communication andrandomly selected chipping codes. In essence, unique codes are used to generate spread chips that assign the transmittedsignals carrier frequencies[ CITATION Bad141 \l 1033 ]. Through this operational procedure, the FHSS can becombined with modulation schemes to convert digital signals to analogue signals, an added advantage of the technique.However, while these operations take place, the communication process must ensure that the hops do not interfere witheach other as they would cancel the entire process. Again, this process is accomplished using adaptive FH techniquesthat avoid signal collision and congestion during the hopping sequences. II.LITERATUREREVIEWMany researchers and scholars who study spread spectrum techniques compare them to narrow band techniques,where the difference in the signal spectrum orientation is highlighted including the advantages of the methods. Now,while narrow band mobile communication may be efficient to use due to its operational structure that assigns users(subscribers) fractions of the communication channel, its allocation process is prone to many challenges. For one, theallocation process requires a well-coordinated process to assign the available frequencies to the different subscribers.Furthermore, having assigned the resources, the system must be aware of the drawbacks of jamming and interception ofdata more so, through eavesdropping techniques[ CITATION Mot14 \l 1033 ]. While there are many solutions to theseproblems, they can all be eliminated by the technique described above where the bandwidth is spread to fulfil the needsof the subscribers.FHSS like any other spread spectrum technique will increase the dimensional attributes of communication signalsthus minimize the incidences of eavesdropping and any other form of interference. Furthermore, through the chippingcodes that facilitate the hops of the carrier frequencies the transferred information is only distinguishable to the verifiedmembers. These operational conveniences have led to the application of the technique in modern wirelessinfrastructures such as WLAN (wireless local area networks) and Bluetooth communication. In all, when using FHSS,the following advantages are experienced:Minimal narrowband interferences.No signal interceptions, in fact, it’s very difficult to eavesdrop on a signal[ CITATION Vem16 \l 1033 ].Frequency Hopping Spread Spectrum (FHSS)[First A. Author], and [Second B. Author]
III.CRITICALANALYSISOF FHSSFHSS OperationTo understand the FHSS operation, we have to consider the Capacity formula as put forward by Shannon andHartley[ CITATION Dav12 \l 1033 ]. In their theorem; C = B Log 2(1+S/N). Here, the C is the data in bits per secondswhile the B highlights our required bandwidth. Therefore, for maximum information transmission, the value of B (BW)must be high to accommodate the data quota. Now, shifting back to FHSS, a carrier signal (encapsulates the message)moving from one frequency channel to another over a specific period of time. Moreover, the carrier frequency isaccorded a wide range of frequencies (band) which maximizes the operational bandwidth hence improving the qualityof the communication signals and also reduces the limitations (interferences and jamming)[ CITATION Dav12 \l1033 ]. Fig: FHSS block diagramNow, during the hop activity, the data session or signal will remain in a given frequency channel for a specific periodof time, which helps to maintain a consistent level of operation. According to the IEEE standards, this value should be300 ms and is set as so in order to synchronize the operations of both the transmitter and receiver. In addition to this, thepattern of operation is dictated by a spreading code that is developed by a pseudo-random generating program. Thisprogram or generator is again synchronized between the transmitter and receiver in order to demodulate the signal at thereception stage. Therefore, when all is said and done, the transmitter and receiver must have a one to onesynchronization for them to communicate[ CITATION Bad142 \l 1033 ].Fig: FHSS operationA common feature or attribute that distinguishes FHSS from DSSS is the signal output given by the technique,instead of the envelope shaped signal (Sin X)/X)2 a flat output is given over the different frequencies used.Furthermore, size of the hopping bandwidth is usually N-times the total number of slots (frequency bands) available,where N is the bandwidth of each slot[ CITATION Max17 \l 1033 ].FHSS Features:Identified by the IEEE 802.11 standardOperates within the 2.4 GHz band while having 79 frequencies (2.402 – 2.480GHz).Each of the frequencies outlined above is modulated (FSK) with a width of 1MHz[ CITATION Sch16 \l1033 ].
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