Spread Spectrum Communication Systems

Advantages of Spread Spectrum Communication Systems

Discuss about the Spread Spectrum Communication Systems.

Before attempting to pinpoint the reason why spread spectrum transmission is used, there is a need to understand what is spread spectrum. A form of wireless communication, which is spread spectrum. In spread spectrum transmission, the frequency of signal to be transmitted is intentionally varied (Torrieri, 2015). It is done to increase the bandwidth of the signal. Following portion will talk about the reason for the usage of spread spectrum. 1) Cross talk interference is reduced. For systems utilizing spread spectrum, cross talk is greatly reduced because of the processing gain of spread spectrum. Additionally, by the help of digital processing effect of interference associated with suppressed crosstalk can be removed. 2) Voice quality is better for systems using spread spectrum technology. Spread spectrum system is immune towards noise and interferences because of the digital processing nature and processing gain of the spread spectrum. Analog wireless system often experience device induced noise that is static. Spread spectrum technology helps in reducing induced static noises. 3) Systems using spread spectrum technology are less susceptible to multi-path fading. In a spread spectrum system, frequency can be varied and this property leads to less susceptibility towards multi-path fading. 4) The fourth point will clarify about security. A PN sequence is used to modulate signal. Since the nature of PN sequence is pseudo random, the signal is randomized. For the receiver to de-modulate the signal to receive the original one, it needs to have the same pseudo random sequence. Therefore, it is established that systems using spread spectrum technology are more secure than other systems. 5) The fifth point will describe about co existence for spread spectrum. If pseudo random sequences are properly designed, then several spread spectrum systems can co-exist without the fear that it will create interference for other systems. 6) Operating distance is much longer. In the ISM band where a spread spectrum device is operated it is allowed to have transmission power, which is higher. Operating distance for devices using spread spectrum technology is much longer when compared to an analog device. 7) Spread spectrum signals are much harder to detect. Narrowband transmissions are much less wider than spread spectrum signals. Since the band is much more widespread, low power is required for its transmission. 8) Spread spectrum signals are hard to demodulate.  A specific code is required for demodulation of the signal. It is nearly impossible to decipher the signal without knowing the actual code that was used to modulate the signal. This is the reason why deciphering this signal is hard. 9) A spread spectrum signal is harder to jam. Most important property of spread spectrum systems is rejection of interference. Since the system rejects interference, it is harder to jam.

Comparison of Frequency Hopping and Direct Sequence Spread Spectrum

This portion will provide a comparison between two methods used for spread spectrum transmission. Frequency hopping and direct sequence of spread spectrum are two most used methods.  The way by which data is spread can tell which method was used for spreading the signal. DSSS uses pseudo noise and FHSS uses frequency hopping for modification of the phase of the signal. In frequency hopping, large bandwidth is divided into smaller channels is which data would be fitted in. After this, the signal is sent into a different channel pseudo randomly ("What is frequency-hopping spread spectrum? - Definition from WhatIs.com", 2018). However, there is a particular drawback on using this technique, since only a single channel is used at a given time. Because of this, bandwidth is wasted. DSSS manages to spread the signal by a different manner. Pseudo random noise is introduced to change the phase of the signal (Naden & Reiser, 2015). Output closely resembles static noise however during demodulation the original signal can be extracted if the pseudo random sequence used to modulate the signal is known. 

A radio system is made up of transmitters and receivers and therefore components will be listed under transmitters and for receivers. Radio transmitters are composed of- Power supply, Oscillator, Modulator, Amplifier and Antenna. Radio receivers are composed of- Antenna, RF amplifier, Tuner, Detector and Audio Amplifier.

This section will provide the basic concept of a mixer. Frequency mixer is a type of electrical circuit. Frequency mixers are generally used for creation of new frequencies that helps in the inter connection of two signals. The task of transmitting signal from one frequency range to the other is critical for radio systems (Wada, Sagawa, & Makimoto, 2016). Mixer’s main objective is for identification of difference level and sum at the end of the communication. A mixer is divided into two types- the first one is named active mixers and the second one is named passive mixers. Signal strength can be increased by the use of active mixers that is further composed of active devices. On the other hand, passive mixers are designed with the help of passive devices such as diodes. Output, which is generated by passive mixers, is much lower when compared to the input signal. However, for active mixers the story is little bit different. Because of the nature of active mixers, they are able to generate more power. When comparing it is seen that active mixers are less tolerant to overload. Passive mixers are used several cases since they have wider bandwidth.

Components of Radio Transmitters and Receivers

This section will provide the answer to different types of mixers. Generally, there are different types of mixers available. Based on functionalities and user requirements, mixers can be classified into two types. The first type is known as single balanced mixer and the second type is known as double balanced mixer.

Single balanced mixers- This mixer is a special type of mixture, which is able to handle any kind of radio frequency or noise. Single balanced mixture is able to manipulate the data when it passes between the LO and because of this it is able to eradicate the noise. Single balanced mixtures needs to provide isolation between RF and LO (Kimishima, 2009). Working of device mixers is based on connection of two single devices at ninety degree or at one eighty degree. Since the structure of single balanced mixer is simple, users are able to get a good grip of the structure at first glance. Simple structure helps to keep the linearity of signal in check and additionally isolation is generated in every port.

Double balanced mixer- Double balanced mixer is a type of passive mixer device. Four-diode ring forms the central part of double balanced mixer. LO signal is rejected when the rings does not match up to a level.  When compared to single balanced mixers it is seen that double balanced mixers have certain advantages. There is one major advantage for double balanced mixer which is it improves linearity in the system but it generates more noise when compared to the other type of mixer (Salameh, 2017).  It generates more noise since it does not support cancellation. For double balanced mixers, output is in the form of differential and this allows for easy removal of non-linearity in the signal.  Ring mixer and star mixer are examples of double balanced mixer. It is also seen that double balanced mixer suppresses both RF and LO but single balanced mixer does not do that. Advantages of using single balanced mixer is more but usage of double balanced mixer is more  because of its isolation and linearity properties.

Air is the medium for wireless communication. There are no wires or cables required. Information gets transmitted form one point to the other via electromagnetic waves. Some of the advanced wireless technologies are Li-Fi, Bluetooth and ZigBee. This paragraph will mention some key points about those advanced technologies. Li-Fi uses visible light communication system and it claims to be much faster than the standard Wi-Fi (Karthika & Balakrishnan, 2015). As simple as it may sound Li-Fi can use household LED bulbs for data transfer and speeds can be up to 224 Gigabytes per second. Since Li-Fi uses visible light communication systems, it means it include photo detector for receiving light signals. The light signals are then processed by a signal-processing element for conversion of data into another form for transmission. Zigbee communication is a product of Zigbee alliance. The system is specially built for sensor and control networks. It follows IEEE 802.15.4 standard. Data transfer rates are slower than standard Wi-Fi however cost incurred for a Zigbee system is much less than a Wi-Fi. Zigbee consists of a mesh network and it is used for controlling and monitoring purposes (Gomaa et al., 2014). Bluetooth is a wireless technology, which is used by hand held digital devices for connecting with one another.

Antenna are of various types but the dominant ones are horn antenna, parabolic reflector antenna, helical antenna, slot antenna, dielectric antenna, micro strip patch antenna, phased array antenna, dipole antenna and YAGI antenna. Horn antenna is used in satellite communication. It works efficiently with parabolic reflector as evident from dish antennas. Parabolic reflector antenna is coupled with horn antenna and used. It is made up of screen mesh or metal. The next portion will talk about some important points via a power point slide.

References:

Single balanced mixer vs double balanced mixer difference. (2018). Rfwireless-world.com. Retrieved 4 April 2018, from https://www.rfwireless-world.com/Terminology/single-balanced-mixer-vs-double-balanced-mixer-vs-triple-balanced-mixer.html

Double Balanced Mixer | Theory; Circuit; Operation | Tutorial - Radio-Electronics.Com. (2018). Radio-electronics.com. Retrieved 5 April 2018, from https://www.radio-electronics.com/info/rf-technology-design/mixers/double-balanced-mixer-tutorial.php

Torrieri, D. (2015). Principles of spread-spectrum communication systems. Springer.

Naden, G., & Reiser, D. (2015). U.S. Patent No. 9,225,383. Washington, DC: U.S. Patent and Trademark Office.

What is frequency-hopping spread spectrum? - Definition from WhatIs.com. (2018). SearchNetworking. Retrieved 5 April 2018, from https://searchnetworking.techtarget.com/definition/frequency-hopping-spread-spectrum

Wada, K., Sagawa, M., & Makimoto, M. (2016). U.S. Patent No. 9,270,008. Washington, DC: U.S. Patent and Trademark Office.

Kimishima, M. (2009). U.S. Patent No. 7,577,416. Washington, DC: U.S. Patent and Trademark Office.

Salameh, D. (2017). U.S. Patent No. 9,780,728. Washington, DC: U.S. Patent and Trademark Office.

Karthika, R., & Balakrishnan, S. (2015). Wireless communication using Li-Fi technology. SSRG International Journal of Electronics and Communication Engineering (SSRG-IJECE), 2(3), 32-40.

Gomaa, R. I., Shohdy, I. A., Sharshar, K. A., Al-Kabbani, A. S., & Ragai, H. F. (2014). Real-time radiological monitoring of nuclear facilities using ZigBee technology. IEEE Sensors Journal, 14(11), 4007-4013.