Different WLAN technologies
Wireless connectivity is well established with the with WLAN solutions available from IEEE 802.11 standard. This provides flexibility in performance of the systems, as it enables to connect different devices wirelessly. IEEE 802.11 standard is widely used in WLAN for setting up both temporary and permanent solution. The different IEEE 802.11 standards include 802.11 a, b, e, f, g, h, I, j, k, n, s, ac, ad, af and ah. Out of these standards, 802.11a, 802.11g, 802.11n and 802.11ac are discussed in the following section.
IEEE 802.11a was approved in July 1999. The maximum data rate speed offered by this standard is 54mbps (theoretical speed). It is based on OFMD modulation with a channel width of 20MHZ. The usage of orthogonal frequency divisional multiplexing is prominent in this standard and does not use FHSS or DSSS (Chakraborty eta al., 2014). However, the cost of implementation of IEEE 802.11a is higher than that of IEEE 802.11b although the specification of both the standard is somewhat similar. Each channel of IEEE 802.11a is subdivided into 52 subcarriers, out of which 48 are used for data.
The strength of IEEE 802.11a is that it provides a very high speed, where physical layer bit can rate up to 54mbps theoretically. The application throughput is however 20Mbps. This standard is suitable for real-time video and other multimedia applications. The OFMD modulation followed in this scheme is highly robust even in dispersive environment.
The weaknesses of this standard includes, high cost and tedious protocol specification.
IEEE 802.11g was launched in year 2003 with an attempt to combine the best of IEEE 802.11a and IEEE 802.11b. It supports bandwidth up to 54mbps, similar to that of IEEE 802.11a. This standard makes use of 2.4 GHZ frequency and is backward compatible with IEEE 802.11b (Baldi et al., 2013).
The strength of this standard is that it is capable of achieving maximum speed very fast with a good signal range. It has less interference issues.
One of the major weaknesses of this standard is that, the cost of implementation is higher than 802.11b (Yuan et al., 2013).
This standard was launched in the 2009 with an aim f improving the reliability and speed of wireless transmissions. The maximum achievable speed of this standard is 600Mbps and makes use of antenna technology. It introduces the MIMO technology that facilitates the is of multiple source transmitter and receiver. This in turn reduces the communication error considerably and reduces the communication time as well (Lim, Kim & Suh, 2012).
The major strength of this standard is its speed and its increasing resistance to interference.
The cost of implementation of this standard is considerably high and use of multiple signals from IEEE 802.11n might interfere with IEEE 802.11g/b networks.
IEEE 802.11ac is one of the newest generations of WI-Fi technology. It makes use of dual band that is capable of supporting simultaneous connection in both 2.4 GHz and 5 GHz bands. The theoretical speed of this standard is up to 1300MBps in 5 GHz band (Abdelrahman, Mustafa and Osman, 2015).
IEEE 802.11a
The major strength of this standard is the improved high speed and has considerably wider bandwidth.
The weakness the deployment of 5 GHz WIFI is considerably less, as there are fewer devices, which operate in this range.
However, considering the evaluation of wireless technology standards, evaluating on speed and reliability, it can be predicted that IEEE 802.11ac will be a dominant network in future. In the coming years, there will be a complete shift to IEEE 802.11ac in the organizations that are still using IEEE 802.11n, considering its speed and ease of usage.
In FHSS, the radio frequency carrier frequency differs according to the Pseudo-random sequence that is known to both transmitter and receiver. This method involves transmission of radio signals by switching carrier among the many frequency channels. This transmission technology finds its usage in LAWN transmission, where the carrier signal hops in a predictable sequence and hence the name. One of the striking feature of this technology is that, the signal is spread in time domain rather than dividing it into frequency domain. This furthermore reduces the interference between the signals (Torrieri, 2015).
A hopping code is responsible for determining the transmission frequencies. FHSS is a very robust technology as it is less affected by the noises, reflection and other environmental factors. FHSS is mostly used in designs that need to cover a large area, where use of DSSS is impossible practically. FHSS operates in GHz band and over 79 frequencies that ranges from 2.402 GHz to 2.480 GHz. Every frequency is GFSK modulated and the channel width is 1MHz. The rate of data transfer is 2Mbps (Zeng et al., 2012). It defines a total 79 different types of hops for carrier frequency. FHSS is practically chosen for installations that require a large coverage and multiple collocated cells. In FHSS, the system is capable of generating a wideband signal, which is controlled by commanding carrier frequency. It is less sensitive to Bluetooth interference and operates with a signal to noise ratio of 18 dB. The data security in FHSS is good.
One of the challenges in FHSS is the synchronization of the transmitter and the receiver. The data of the transmitter is identified with a special data sequence that might include checksum for checking the integrity of the data.
DSSS is a transmission technology that is mainly used in case of local area wireless networks. The data signal is generally combined with a high data bit rate sequence in DSSS that is responsible for dividing the user data in accordance to a spreading ratio. DSSS technology is resistance to jamming even through it uses single channels sharing to multiple users. The background noise and relative timing between the transmitter and the receiver less affect it. It is basically a modulation technique used for digital signal transmission over airwaves (Swamy et al., 2013). The entire data or information in DSSS is divided into small pieces that are associated with a specific frequency channels across the spectrum.
The differences between FHSS and DSSS are as follows (Quyen, Yem & Hoang, 2013).-
- Frequency change is observed in FHSS, whereas in DSSS the change in phase is observed.
- FHSS is considerably easier to synchronize in comparison to DSSS
- DSSS finds its usage in positioning system, which is not observed in case of FHSS.
- In DSSS, the carrier remains fixed to a specific frequency band, whereas in FHSS it hops from frequency to frequency.
- Frequency remains constant in DSSS, which is not the case for FHSS.
- FHSS is more resistant to noise in comparison to FHSS.
- FHSS however, offers a limited throughput, which is 2-3 Mbps, whereas DSSS offers a considerably higher throughput that is 11Mbps.
- DSSS is more reliable as it has an increasing integrity and security increase.
- DSSS has a considerably shorter latency time in comparison to FHSS.
- FHSS has short indoor and long outdoor range, whereas in DSSS, it has short indoor and outdoor range.
References
Abdelrahman, R. B. M., Mustafa, A. B. A., & Osman, A. A. (2015). A Comparison between IEEE 802.11 n and ac Standards.
Baldi, M., Bianchi, M., Maturo, N., & Chiaraluce, F. (2013). A physical layer secured key distribution technique for IEEE 802.11 g wireless networks. IEEE wireless communications letters, 2(2), 183-186.).
Chakraborty, U., Kundu, A., Chowdhury, S. K., & Bhattacharjee, A. K. (2014). Compact dual-band microstrip antenna for IEEE 802.11 a WLAN application. IEEE Antennas and Wireless Propagation Letters, 13, 407-410
Khanduri, R. and Rattan, S.S., 2013. Performance comparison analysis between IEEE 802. 11a/b/g/n standards. International Journal of Computer Applications, 78(1).
Lim, W. S., Kim, D. W., & Suh, Y. J. (2012). Design of efficient multicast protocol for IEEE 802.11 n WLANs and cross-layer optimization for scalable video streaming. IEEE Transactions on Mobile Computing, 11(5), 780-792
Quyen, N. X., Yem, V. V., & Hoang, T. M. (2013). A chaos-based direct-sequence/spread-spectrum communication scheme.).
Swamy, M.K., Deepthi, M., Mounika, V. and Saranya, R.N., 2013. Performance analysis of DSSS and FHSS techniques over AWGN channel. Development (IJECIERD), 3(2), pp.7-14.
Torrieri, D. (2015). Principles of spread-spectrum communication systems. Springer.
Yuan, W., Wang, X., Linnartz, J. P. M., & Niemegeers, I. G. (2013). Coexistence performance of IEEE 802.15. 4 wireless sensor networks under IEEE 802.11 b/g interference. Wireless Personal Communications, 1-22.
Zeng, X., Cai, H., Tang, X. and Yang, Y., 2012. A class of optimal frequency hopping sequences with new parameters. IEEE Transactions on Information Theory, 58(7), pp.4899-4907.
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