Antennas, FDMA and CDMA
Q1: Different antenna, such as yagi, horn, and celluar antennas, etc. has different merits. Research these technologies in details and pay specific attention to how they are used as well their strengths and weakness. Provide an opinion regarding which antenna types will become the dominant players in the future of medium- and long-distance wireless links
An Antenna is a device which is used to send and receive the electromagnetic waves. This electromagnetic wave carries the information in the form of voice, data, video image etc. Antennas are the important part of any electrical signal which converts the electronic signal into the electromagnetic waves.
There are different types of antennas used in the wireless communication:
Yagi Antenna: Yagi antennas are the strong directional antennas, which needs to be set up pointing in the direction of the tower. As this is a directional antenna it picks up the signal only in one direction. It is measured in “gain.” Yagi Antennas are mostly used for TV reception.They are not compatible for wide frequency range.
Horn Antenna: To avoid the mismatch in the normal wave guide, flaring is done at the end of the waveguide to create the “HORN” antenna. More will be the flare more will be the matching.
Use: Horn antenna along with the parabolic antennas is used in Dish. Horn antenna can be operated on a wide range of frequencies.
Parabolic Reflector Antenna: The Parabolic antenna is used along with the Horn antenna. In the transmission process the EM waves fall on the wide dish and get into the air. And in the receiving process EM waves fall on the dish and get focused to horn antenna.
Log Periodic Antenna: Log Periodic antennas are formed by multiple length elements. The elements which are longest and shortest are of half wavelength. The signals are sent to different to have high directivity and maximum gain. It can be used in wide bandwidth applications.
The above antennas are the conventional antennas having the weakness of narrow bandwidth, large size and non circular polarization.
Cellular Antennas: Cellular Antennas are the most dominant antennas used in the future wireless communications. Cellular antennas are used in the cellular phones for mobile communication. It provides the wide bandwidth with small size having high data rate connectivity. The cellular antennas are widely used in Global Positioning system (GPS), Global Navigation satellite system (GNSS).
Q2: Compare and contrast the multiplexing techniques CDMA and FDMA in the area of wireless networking?
Frequency division multiple access (FDMA):
FDMA is a technology in which the available bandwidth of the system is assigned to a transmission channel between a sender and a receiver. In this the complete band of frequencies is divided into different RF (Radio Frequency) channels. In this technology the frequencies are pre-assigned to the users or calls. It is used for the analog Transmission. There is no overlapping of the frequencies. It is not an efficient method for digital transmission. In this technology there is a limitation of capacity. This technology works like an FM radio in which all radios have their own frequency bands and they have to send their signals carefully to their allocated unique frequency.
In this technology single frequency is used for one call only which can be illustrated from below figure:
Code Division Multiple Access (CDMA):
CDMA is a technology where in all the calls are attached to specific and unique codes. In this the data is divided into the small pieces and sent over multiple frequencies available at any point of time. It is used in a digital communication. In this technology multiple signals uses the transmission channel, which in turn optimizes the use of available bandwidth. Due to optimize use of bandwidth there is less limitation of capacity. In CDMA technology overlapping between multiple calls is possible within same channel.
In this technology single frequency is used for different calls which can be illustrated from below figure:
The difference between FDMA and CDMA can be summarized as:
- No.
Parameter
FDMA
CDMA
1
Transmission
Analog or Discontinuous
Digital or continuous
2
Channel
Divide the frequency bands
Spread the spectrum using the unique code.
3
Technology
Single frequency single call
Single frequency multiple calls
4
Speed
Each terminal has its own frequency at a specific time
Each terminal can be active at the same time
5
Application
TACS (Total Access Communication System)
Ultra-high frequency (UHF) cellular telephone systems
6
Limitation
Inflexible, Limited Frequency resources
Complex receivers, requires more complex senders
REFERENCE
[1] Theodore S. Rappaport, “Wireless Communication, principles and practice”, Prentice Hall, 2002.
[2] H.Eriksson, “Multiple Access Options for Cellular Based Personal Communications,” in Proc. Of IEEE Veh. Technol. Conf., pp.957-962, (1993)
[3] W.C.Y. Lee, “Spectrum Efficiency in Cellular,” IEEE Trans. Veh. Technol., vol. 38, pp 69-75, (1989)
[4] W.Heger, “Pro’s and Con’s of TDMA and CDMA for Digital Cellular Networks”, IEEE Proc., pp810-815
[5] K.V.Ravi, “Comparison of Multiple Accessing Schemes for Mobile Communication System”, , 1994., in Proc. Of IEEE International Conference on Personal Wireless Communications, pp. 152-156 (1994)
[6] D.D.Falconer,”Time Division Multiple Access Methods for wireless Personal Communication”, IEEE Communications Magazine, Volume: 33 Issue 1, pp50 -57, (1995)
[7] P.Jung,”Advantages of CDMA and Spread Spectrum Techniques over FDMA and TDMA in Cellular Mobile Radio Applications”, IEEE Trans. on Veh. Tech., Volume 42 Issue: 3, pp357-364, (1993)
[8] T.Ojanpera and R.Prasad, “an Overview of Air Interface Multilpe Access for IMT-2000/UMTS,” IEEE Commun. Mag., vol.36, no.9, pp 82-95, (1998)
[9] M.Zeng, A.Annamalai and V.Bhargava, “Recent Advances in Cellular Wireless Communications,” IEEE Commun. Mag., vol.37, no.9, pp 128-138, (1999)
[10] P.Chaudhury, W.Mohr and S.onoe, “The 3GPP proposal for IMT-2000,” IEEE Commun. Mag., vol.37, no.12, pp 72-81, (1998) [11] W.C.Y.Lee, “Overview of Cellular CDMA”, IEEE Trans. On Vehicular Tech, vol.40, pp 291-302. (1991)