There are different types of WLAN technologies. Four technologies are discussed in the following paragraph. They are 802.11a, 802.11b, 802.11g and 802.11n.
802.11a is the first type of standard in 802.11. 802.11a operate in 5GHz Industrial, Scientific and Medical (ISM) band which means that it gives much higher speed and data transfer rate. However, the chips are expensive. It produces high level of performance (Siddiqui, Zeadally & Salah, 2015). 802.11a has a good range but not when the speed is at its full data rate which is a limit for this standard. It is used worldwide in a band which is license free. 802.11a has subcarriers and they are BPSK, QPSK, 16-QAM and 64-QAM. Orthogonal Frequency Division Multiplex (OFDM) is complex to use in 802.11a but offers advantage of reducing interference issues caused by effect of multipath. 802.11b was widely used and adopted in laptop and other equipments and operates at 2.4 GHz (Dalal et al., 2014). It provides much higher data rate than 802.11b and it has data rates up to 11 Mbps. 802.11b uses CSMA/CA technique to transmit data. It transmits clear channels and retransmits the channel if not get an acknowledgement from receiver. 802.11b uses Complementary Code Keying (CCK). This signal is easier to upgrade the chipset and therefore readily available in the market. It has disadvantage which is if signal falls in between or interference is higher therefore the system adopt slower data rate with some errors. 802.11g is predecessor of 802.11b and operates in 2.4 GHz ISM band (Ermakov et al., 2014). Maximum data rate is 54 Mbps. It has compatibility issue with 802.11b due to which there is reduction in speed. 802.11g has four layers which are used and they are ERP-DSSS-CCK, ERP-OFDM, ERP-DSSS/PBCC and DSSS-OFDM. Usually it has no issue of interference in signal. It has two main parts and they are Preamble/Header and Payload. Payload is the actual data which has size and it is then transmitted by Preamble. It has limitation that is overall decoding process is not able to complete in a given time as 16 µs still required (Clerckx & Oestges, 2013). However a signal extension of 6 µs is used to achieve this performance. 802.11n is the latest standard in 802.11 which offers very high speed than the previous standards. It is compatible to work with 802.11b and 802.11g. Its performance is able to keep pace with fluctuating speed. It has some innovations which add complexity to the system and these innovations are implemented to provide high performance. 802.11n offers advantage when operated in a single mode that are Legacy mode, mixed mode ad Greenfield mode. It is suitable for large networks and not for small networks.
802.11n is going to be a dominant player as it has features which are regularly updating. It provides much higher data rate than 802.1a, 802.11b and 802.11g. It has four spatial streams which give significant improvement to data flow and it has the capability of up to 4*4*4. It has advantages and they are power saving, increased bandwidth and antenna technology. It has only disadvantage that is preferable for large networks and not suitable for small networks.
Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS). Frequency hopping Spread Spectrum uses frequency hopping which is achieved by division of large bandwidth to fit the data and the division is in small channels (Alatabani & Abdalla, 2015). However, Direct Sequence Spread Spectrum uses pseudo noise to introduce in signal and the phase is changed due to this at any time. FHSS is useful for big coverage installation and multiple collocated cells installation. DSSS is not useful as collocated cells are overlapped. DSSS can be used if collocated cells are non-overlapped and DSSS will require directional antennas to be useful for collocate cells. FHSS operates with Signal to Noise Ratio (SNR) at 18 dB while DSSS operates with Phase-shift keying (PSK) at 12dB. DSSS is able to operate for larger distances than FHSS DSSS has operations with lower SNR (Hasan, Thakur & Podder, 2014). Interference level is higher in DSSS than FHSS as because spectrum is 83.5 MHz while DSSS has spectrum of 22 MHz. Foreign transmitters issue is in DSSS and FHSS both but the difference is that in DSSS the signals will not be heard while in FHSS the signal will be at least operable despite some issues. Throughput is greater in DSSS than FHSS. Multipath issue is highly sensitive in DSSS as compared to FHSS. Overall DSSS has higher capacity than FHSS however FHSS is more robust.
Antennas in wireless network are of two types and they are Omni-directional and directional. Omni-directional is in 360 degree pattern while directional antenna is only in one direction. Directional antennas are of four types and they are Yagi, Dish, Sector and Grid (Khan, Riaz & Bilal, 2016). Omni-directional antennas are of four types and they are Rubber duck antenna, Spider Omni-directional antenna, ceiling mount Omni-directional antennas and outdoor Omni-directional antennas. The directional antennas are described in the following paragraphs.
Yagi is most commonly used antenna and its applications are in old television sets. It has multiple parallel lines. It is used for high range of frequencies (Bandyopadhyay, Roy & Ueda, 2016). It is suitable for short to medium distance and point-to-point communication. It is situated outdoors. It is mostly used for long distance applications and has strength of reaching multiple frequencies. Dish is another type of directional antennas. It is widely known as dish network and used as a parabolic reflector. It is highly directive. The parabolic antenna is used to direct the radio waves in narrowest form and radio wave is received from one direction only. It is widely used for high frequencies, television and sound. It has ability to collect a bunch of signals due to large surface area. Sector antenna is a type of directional antenna which focuses its beam pattern in a shape which is elongated. It ranges from 30 degrees to 120 degrees which allows it to operate in hemisphere structure (Rumsey, 2014). It is largely used for station sites which has base operations as cell phone. Grid antennas are a type of directional antenna which has similar structure to dish antenna. Grid antenna has reflector in the form of grid which can withstand extreme wind conditions. The spaces in grid are frequency dependent. It is used for long distance transmissions through wifi.
Omni-directional antenna has 360 degrees coverage range. They are used mostly inside the office premises. They have applications in mobile devices and walki-talkies because of 360 degree range coverage. Rubber Duck Antenna is used as routers. Spider Omni-directional Antenna is simple in design and contains a standard N-type connector (Rusch & Potter, 2013). Ceiling Mount Omni-directional Antennas is mounted on the ceiling which is an advantage of this antenna. Outdoor Omni-directional Antennas are also known as GP and available in weatherproof option and waterproof option if used in outdoor.
The directional antenna is best used for certain indoor applications. Directional antennas are suitable for point-to-point and point-to-multipoint links in long ranges. It reduces interferences from multiple unwanted signals. Directional antennas provide better quality of link to any network. Directional antennas are going to dominate in future as they operate in single direction. Different types of directional antenna are used for different purposes. Connection between two buildings will require Yagi or Grid. However, inside an office, Omni-directional antennas are used as they provide more frequency range in small network and they have 360 degree wireless coverage in small network. Directional antennas are going to be used only for internal environment of any office or industrial purpose.
References
Alatabani, L. E., & Abdalla, A. G. E. (2015). FHSS, DSSS, And Hybrid DS/FH Performance Evaluation For VSAT. INTERNATIONAL JOURNAL OF SCIENTIFIC and TECHNOLOGY RESEARCH, 4(09).
Bandyopadhyay, S., Roy, S., & Ueda, T. (2016). Enhancing the performance of ad hoc wireless networks with smart antennas. CRC Press.
Clerckx, B., & Oestges, C. (2013). MIMO wireless networks: Channels, techniques and standards for multi-antenna, multi-user and multi-cell systems. Academic Press.
Dalal, P., Sarkar, M., Dasgupta, K., & Kothari, N. (2014). Link Layer Correction Techniques and Impact on TCP’s Performance in IEEE 802.11 Wireless Networks. Communications and Network, 6(02), 49.
Ermakov, S. A., Zavorykin, A. S., Kolenbet, N. S., Ostapenko, A. G., & Kalashnikov, A. O. (2014). Optimization of expert methods used to analyze information security risk in modern wireless networks. Life Sciences Journal, 23, 1239.
Hasan, M. M., Thakur, J. M., & Podder, P. (2014). Design & Implementation of FHSS and DSSS for Secure Data Transmission. International Journal of Signal Processing Systems.
Khan, A. Q., Riaz, M., & Bilal, A. (2016). Various Types of Antenna with Respect to Their Applications: A Review. International Journal of Multidisciplinary sciences and Engineering, 7(3).
Rumsey, V. H. (2014). Frequency independent antennas. Academic Press.
Rusch, W. V. T., & Potter, P. D. (2013). Analysis of reflector antennas. Academic Press.
Siddiqui, F., Zeadally, S., & Salah, K. (2015). Gigabit Wireless Networking with IEEE 802.11 ac: Technical Overview and Challenges. JNW, 10(3), 164-171.
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