Wireless Network Concepts

This article discusses the concept of spread spectrum transmission and the different methods used for multiple access. It also covers the components of a radio system and explains the different types of mixers with diagrams. The article is relevant for students studying wireless network concepts and related courses.

Running head: WIRELESS NETWORK CONCEPTS
Wireless Network Concepts
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Q1. Why is spread spectrum transmission used? Comparison between two common methods
used for spread spectrum transmission.
Ans. Spread spectrum refers to the form of wireless communication where the transmitted
signal’s frequency is varied deliberately, which ultimately results in the formation of a
bandwidth which is much greater than the bandwidth which the signal would be having when the
frequency was not varied. The signal transmitted occupies a much higher bandwidth than the
systems which are used in the conventional modulation methods (Torrieri, 2015). The spreading
of the band is achieved my selecting waveforms of appropriate bandwidth which generally
consists of waveforms with wide bandwidth. One of the most popular way is by multiplying the
data signals of the user with a fast code sequence and this is mostly independent of the data
message which has been already transmitted (Rappaport et al., 2013). For this case the radio
portion that is shared by the users is same but the code used is different so as to distinguish the
transmissions made by them.
There exists mainly methods for implementation of multiple access and they are namely
FDMA or Frequency Division Multiple access, TDMA or Time Division Multiple Access and
lastly CDMA or Code Division Multiple Access.
Time Division Multiple Access is the method which generally comes under the process
of modulation. This method is associated with providing of users at a larger rate so as to access
the single radio frequency channel or RF channel without the involvement of any type of
interference and is associated with allocating each user with an independent time slot (Sha, Qiu
& Mei, 2012). In this method different types of users communicate with each other which means
listening and speaking in accordance to the time slots that has been allocate to them. It is mainly
used in the digital cellular telephones and is associated with dividing each and every cellular

channels into three time slots for the purpose of increase the data that is to be carried. TDMA
was firstly identified as the standard in the EIA/TIA Interim Standard 54 or IS-54. This later
evolved to Interim Standard-136 or IS-136 and is used by US standards for the TDMA for
cellular as well as the personal communication services spectrum which is having an frequency
of around 850MHz and 1.9GHz.the TDMA is also used for the DECT or Digital Enhances
Cordless Telecommunication. The mobile stations radio components are allowed to listen and
broadcast by the TDMA only in the time slot assigned to them. Along with this during rest of the
time the mobile stations might apply the network measurements by the detection of the different
transmitters that surrounds it having different frequencies.
Code Division Multiple Access generally refers to the different types of protocols which
are generally used in the second generation or 2G and the third generation or 3G wireless
communication. According to the term it can be stated that is one of the form of multiplexing and
is generally associated with allowing several signals to occupy a single channel responsible for
transmission. This also optimizes the use of the bandwidth which is available. This technology is
generally used in the ultrahigh frequencies cellular telephone system which has a frequency
range of around 899MHz and 1.9 GHz. Conversion of the analog to digital signal is also
employed by the CDMA (Kaddoum, Richardson & Gagnon, 2013). This is associated with
sharing of the channels for the purpose of transmitting information of different type which is
generally having a definite RF bandwidth which is mainly associated with the other users
instantaneously and also with the interference of each other. This is initially responsible for
providing flexibility at larger amounts and overall system capacity which is high with respect to
the Cellular systems. Each digital packet in the CDMA is sent along with a unique key and the
responsible receiver which possess the key to that code is capable of picking up those signals

quickly and then demodulate that for this reason a special type of coding scheme is followed in
order to allow numerous users to be multiplexed over same channels.
Fig 1: CDMA Spread Spectrum Generation
Fig 2: CDMA Spread Spectrum Decoding
Q2. Different components of a radio system. What are different mixers? Explain different types
of Mixers with diagram?
Ans: Different types of radio components are available for appropriate platform installation
(Sadegh Amiri et al., 2013). The different components of a radio spectrum are listed below:
 Filter and Multi-coupler
 Power amplifiers
 Antenna tuning units
 Remote control units
 Power suppliers

 Audio units
 System racks
Fig 3: Components of a radio system
In a radio system a mixer or a frequency mixer can be considered as a non-liner electrical
circuit that is associated with the creation of new frequencies by making use of two different
signals which are applied to the mixer. Two signals are applied to the mixers so as to produce a
new signal with respect to the sum and difference of the two original frequencies. A frequency
mixer or a mixer can produce other frequency components as well. There are two types of mixers
and this includes the Diode mixers and switching mixers (Hotokezaka & Piran, 2015). Mixers
are also widely used for the purpose of shifting signals from one range to the other, this process
is also known as heterodyning. This is done for the transmissions convenience or for further
processing of the signals. The devices which are having a non-liner characteristic can be
considered as a mixer.

Fig 4: An Ideal Mixer
Passive mixers are those mixers which generally makes use of a single diode ora numver
of diode and along with this the passive mixers mainly depends on the non-liner relation that
exists between the voltage and the current so as to supply an element having a multiplying
nature. The passive mixers produces an output which is at all times lower in value than the value
of the input signals.
Active mixers are something which makes use of an amplifying device so as to increase
the strength of the signal product. This type of mixers are having an improved isolation which
exists between the different ports. Along with this this there might also exist high noise and more
consumption of power (Hotokezaka & Piran, 2015). The active mixers might also be less tolerant
to the overload.
Mixers can also be classified according to their topology and they are listed below:
Unbalance mixers: This type of mixers are associated with allowing both of the input
signals to pass through and appear as component in the output.

Single balanced mixers: This type of mixers are arranged with on eof the inputs and are
applied to a balanced circuit in order to suppress either the local oscillator or the signal input at
the output but in both.
Fig 5: Single balanced mixer
Double balanced mixer: This type of mixer consists of both the inputs which are applied
to the differential circuits so as to make sure that at the output there is no appearance of the input
signals. Only the product signal should appear at the output (Lin, Mak & Martins, 2014). This
type of mixers are more complex and generally requires higher drive levels tan the unbalanced
and the signal balanced designs.

Fig 6: Double balanced Mixer
A diode is generally used for the purpose of creating a simple unbalanced mixture. And
this type of mixtures are associated with producing the original frequency along with the sum
and difference of the frequency. One of the significant feature of the diode is its non-linearity
which means the response of this not proportional to the input. Along with this the diode is also
not associated with the reproducing of the frequencies responsible for its driving voltage in the
current which is passing through the diode. For this reason the manipulation is possible as
desired by the user.

Fig 7: A diode mixer
Switching is one of another way in which the mixer operates. This operation is associated
with a smaller amount of input signal which is generally passed in inverted or non-inverted form
and this happens according the phase of the local oscillator (Lin, Mak & Martins, 2014).
According to the mathematical term the switching mixer is almost similar to the multiplying
mixer and this is because in the switching mixer signal function is used instead of the LO sine
wave. Switching is considered to be the typical form of the normal operations that is done by the
double balanced mixer which is having a local oscillator so as to drive at a considerable higher
speed than the amplitude of the signal. The most essential advantage of the switching mixer is
that it is capable of achieving a noise figure of lower range and conversion gain of higher range.
This happens because of the reason that the switching diode or the transistors generally act as a
small resistor or like a large resistor (Myslivets et al., 2012). For both the cases a minimal
amount of noise is added. From the perspective of a circuit it can be stated that many of the

multiplying mixers can be used as a switching mixer and this can be done by only increasing the
LO amplitude.
Fig 8: A switching type Mixer
There is another type of mixer known as the harmonic mixer and the subharmonic mixer
which is considered to be a circuit associated with charging one signal frequency to the other.
The harmonic and subharmonic mixers is associated with the formation of the sum and
difference frequencies which is the harmonic multiple of any one of the inputs. Whereas the
normal mixers consists of two input signals and one output signal.

References:
Hotokezaka, K., & Piran, T. (2015). Mass ejection from neutron star mergers: different
components and expected radio signals. Monthly Notices of the Royal Astronomical
Society, 450(2), 1430-1440.
Kaddoum, G., Richardson, F. D., & Gagnon, F. (2013). Design and analysis of a multi-carrier
differential chaos shift keying communication system. IEEE Transactions on
Communications, 61(8), 3281-3291.
Lin, F., Mak, P. I., & Martins, R. (2014, February). 3.9 An RF-to-BB current-reuse wideband
receiver with parallel N-path active/passive mixers and a single-MOS pole-zero LPF.
In Solid-State Circuits Conference Digest of Technical Papers (ISSCC), 2014 IEEE
International (pp. 74-75). IEEE.
Myslivets, E., Kuo, B. P., Alic, N., & Radic, S. (2012). Generation of wideband frequency
combs by continuous-wave seeding of multistage mixers with synthesized
dispersion. Optics express, 20(3), 3331-3344.
Rappaport, T. S., Sun, S., Mayzus, R., Zhao, H., Azar, Y., Wang, K., ... & Gutierrez, F. (2013).
Millimeter wave mobile communications for 5G cellular: It will work!. IEEE access, 1,
335-349.
Sadegh Amiri, I., Nikmaram, M., Shahidinejad, A., & Ali, J. (2013). Generation of potential
wells used for quantum codes transmission via a TDMA network communication
system. Security and Communication Networks, 6(11), 1301-1309.

Sha, X. J., Qiu, X., & Mei, L. (2012). Hybrid carrier CDMA communication system based on
weighted-type fractional Fourier transform. IEEE Communications Letters, 16(4), 432-
435.
Torrieri, D. (2015). Principles of spread-spectrum communication systems. Springer.

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