WIRELESS NETWORKS AND MOBILE COMMUNICATIONS (WNMC)

Contents

• 1. Introduction to Digital Modulation
• 2. Amplitude Shift Keying
• 3. Frequency Shift Keying
• 4. Phase Shift Keying
• 5. Advanced Digital Modulation Schemes
• 6. Limitations of Digital Modulation Schemes

Carrier Wave 

(Drag the buttons to appreciate the parameters)

Amplitude (A): 1.0

Frequency (f): 1.00

Phase ($\phi$): 0.00

Period (T): 1.00

1. Introduction to String Manipulation

Digital modulation is the process of encoding digital information onto an analog carrier wave by varying one or more of the three fundamental parameters of Amplitude (A), Frequency (f), or Phase. Digital modulation is essential for long-distance transmission because baseband digital signals cannot propagate efficiently.

The career wave is defined as:

s(t)=A(t)cos(2πfct+ϕ(t)). 

Modulation is of A(t), fc, or ϕ(t) at discrete time intervals.

This modulation offers improved noise immunity, simplified signal regeneration, and efficient spectral utilization.

Performance Metrics

Bit Rate (Rb)

Bit rate is the rate of information transfer, measured in bits per second (bps). Rb​ is directly proportional to the amount of data transmitted.

Symbol Rate (Rs)

Symbol rate defines the rate at which the signal's electrical characteristics (amplitude/phase/frequency) change. Rs (Baud rate) is measured in symbols per second. It is limited by the channel bandwidth (B), and is given by the Nyquist relationship, also called the Nyquist criterion, below.

Rs≤2B 

Data Rate 

The maximum theoretical data rate or channel capacity (C) in bits/s is a function of the channel bandwidth (B) channel in Hz and the signal-to-noise ratio (SNR):

C = B log2(1 + SNR) - Shannon-Hartley law

Baud Rate

Baud rate, is the number of modulation symbols transmitted per second. A modulation symbol refers to a specific state of a sine carrier signal. It can be an amplitude, a frequency, a phase, or some combination of them. Basic binary transmission uses one bit per symbol.

Bit Error Rate (BER) 

The ratio of erroneous bits to the total bits transmitted. BER must be kept low (10−6 for data), higher transmit power, and lower-order modulation, and strong error correction coding.

Spectral Efficiency (η)

Data rate per unit bandwidth. The higher the spectral efficiency, the more the number of users or data fitted in a limited spectrum. QAM schemes are more spectral efficient than PSK.

Power Efficiency 

The ability of a scheme to maintain a low BER at a low Signal-to-Noise Ratio (SNR). This is especially necessary for mobile devices to maximize battery life and coverage area. PSK and GMSK are more power-efficient than high-order QAM.

M-ary Modulation

M-ary Modulation is a modulation scheme where the number of distinct signal elements (symbols) is M. Each symbol encodes k=log2M bits.

Rb=Rs⋅log2M. Higher M increases Rb for the same Rs.

Constellation Diagram

A constellation diagram is a plot (in the I-Q plane) showing the possible complex values (amplitude and phase) a transmitted symbol can take. I (In-phase) is on the x-axis, Q (Quadrature) is on the y-axis.

Digital Modulation Schemes

2. Amplitude Shift Keying

Amplitude Shift Keying (ASK): Amplitude is varied. OOK (On-Off Keying): M=2. For example, 1 maps to a high amplitude, while 0 maps to zero or a lower amplitude. The key advantages of ASK is its simple implementation. On the other hand, its limitation is the highly susceptibility to noise and fading. Low spectral efficiency.

Figure 1: Amplitude Shift Keying

3. Frequency Shift Keyng

Frequency Shift Keying (FSK): Frequency is varied. BFSK (Binary FSK): M=2.Good noise immunity (constant amplitude), but generally requires more bandwidth than PSK/QAM. Used in low-rate systems like the early cordless phone.

Figure 2: Frequency Shift Keying (FSK)

4. Phase Shift Keying

Phase Shift Keying (PSK): Phase is varied. BPSK (M=2): ϕ∈{0∘,180∘}. QPSK (M=4): ϕ∈{45∘,135∘,...}.Excellent noise immunity (constant envelope helps with power efficiency). Widely used in cellular (e.g., 3G) and Wi-Fi. QPSK is spectral efficient (k=2 bits/symbol).

Figure 3: Binary Phase Shift Keying

Figure 4: Quadrature Phase Shift Keying

Differential PSK (DPSK): Phase shift is determined by the difference between the current and previous symbol. DQPSK (Differential QPSK) avoids the need for a coherent phase reference at the receiver, simplifying demodulator design, though at a slight BER penalty.

Multiple Phase Shift Keying (M-PSK): M-ary Phase Shift Keying (M-PSK) is a digital modulation method that enhances data transmission efficiency by representing multiple bits in a single symbol through variations in the phase of the carrier signal. M, which represents the number of levels is given by:

M = 2N, where N indicates the number of bits encoded per symbol. 

For instance, a QPSK has M=4, with N=2 bits corresponds to the four different phases of 0°, 90°, 180°, and 270°). Likewise, for 8-PSK (M=8) encodes N=3 bits into eight unique phases. The M phase points are generally arranged equally around a circle on a constellation diagram. An increase in M leads to enhanced spectral efficiency (more bits per Hertz of bandwidth), but comes with the drawback of diminished robustness. As M rises, the spacing between neighboring phase points becomes smaller, which makes the system more vulnerable to noise and interference, resulting in a higher Bit Error Rate (BER) at the same signal power. 

5. Advanced Digital Modulation Schemes

a) Quadrature Amplitude Modulation (QAM): Quadrature Amplitude Modulation (QAM) is an advanced digital modulation method that conveys data by altering both the amplitude and phase of a carrier wave simultaneously. This approach combines aspects of Amplitude Shift Keying (ASK) and Phase Shift Keying (PSK). At the heart of QAM are two carrier waves that have the same frequency but are 90 degrees out of phase with one another, referred to as the In-phase (I) and Quadrature (Q) components. Digital information is encoded by adjusting specific amplitude levels for the I carrier and the Q carrier. When these two amplitude-modulated signals are combined, they produce a signal characterized by a distinctive combination of amplitude and phase, representing a unique symbol. The modulation order, M, indicates the number of unique symbols (for instance, 16-QAM has M=16 symbols, which encodes log216=4 bits per symbol). By encoding several bits within each symbol, QAM achieves exceptional spectral efficiency, which is vital for contemporary communication networks such as Wi-Fi, 4G/5G cellular, and cable modems. Nevertheless, higher-order QAM schemes face increased susceptibility to noise due to the proximity of constellation points (symbols), necessitating a greater Signal-to-Noise Ratio (SNR) for dependable transmission.

b) Gaussian Minimum Shift Keying (GMSK): Gaussian Minimum Shift Keying (GMSK) is a variant of Continuous Phase Frequency Shift Keying (CPFSK) in which the binary information (M=2) is initially filtered through a Gaussian low-pass filter prior to modulation of the frequency. This pre-modulation pulse shaping facilitates smoother transitions between frequency shifts, which is essential for its advantages. The Gaussian filter mitigates sudden phase transitions, leading to a reduced spectral bandwidth and significantly lower out-of-band emissions. This vital characteristic permits the use of simpler and more efficient non-linear power amplifiers in mobile devices, enhancing power efficiency These features established GMSK as the requisite option for the GSM (2G) cellular standard.

c) Orthogonal Frequency-Division Multiplexing (OFDM): OFDM is an effective multi-carrier modulation method that enables high data rates by transforming a single high-speed data stream into multiple parallel low-rate streams. Each of these low-rate streams modulates its own closely-spaced orthogonal subcarrier. The orthogonality of the subcarriers helps them to overlap spectrally without causing interference, which enhances spectral efficiency. 

One of the main benefits is its robustness against channel impairments. By significantly extending the symbol duration for each low-rate subcarrier, OFDM ensures the symbol time is considerably longer than the channel's delay spread. This effectively reduces Inter-Symbol Interference (ISI). Techniques like QAM (such as 64-QAM and 256-QAM) are employed on each subcarrier to maximize throughput. This approach is vital for wideband technologies such as 4G LTE, 5G New Radio, and various Wi-Fi standards (802.11 a/g/n/ac/ax).

6. Limitations of Digital Modulation Schemes

Limitations of Digital Modulation Techniques

The primary challenge in designing digital communication systems revolves around the ongoing, opposing balance between efficiency and robustness, influenced by both the modulation technique and the quality of the channel.

Efficient schemes, such as 64-QAM (Quadrature Amplitude Modulation), optimize the data rate (bits per symbol) by densely packing information into the signal’s amplitude and phase. This enables extremely fast transmission, making these schemes suitable for high-SNR (Signal-to-Noise Ratio) environments like short-range Wi-Fi or fixed fiber-optic broadband. However, the close arrangement of symbol constellations makes them vulnerable to even minor noise or interference; a small change in amplitude or phase can easily shift a received symbol into the decision region of an adjacent symbol, resulting in a high Bit Error Rate (BER) when channel conditions worsen. 

On the other hand, using basic modulation techniques like BPSK (Binary Phase Shift Keying) or FSK (Frequency Shift Keying) achieves greater robustness. These methods rely on fewer, widely spaced constellation points (or frequencies), which allow for fewer bits to be transmitted per symbol and consequently lower data speeds. The ample distance between symbols provides them with enhanced noise immunity, enabling them to maintain a very low BER, even in low-SNR, poor-quality channels such as those used long-range IoT devices that operate under stringent power and interference limitations. Therefore, there is need to select a scheme that effectively balances the necessary speed (efficiency) with the anticipated channel impairments (robustness) for the specific application.

Conclusion

Digital modulation techniques are continually advancing to meet the growing needs of communication systems. And digital modulation is expected to witness further advancements in sophisticated methods that can achieve higher data rates and enhanced resistance to interference. Moreover, the adoption of machine learning approaches for optimizing modulation schemes is anticipated to expand.

These techniques will remain grounded in the concept of modulating a digital signal onto a carrier wave. And the approach facilitates more efficient bandwidth utilization and leads to a more resilient signal. As technology progresses, it is very probable that innovative and enhanced modulation schemes will emerge, offering even superior performance.

End of Module Activity

Question 1 of X

WIRELESS NETWORKS AND MOBILE COMMUNICATIONS

ANALOG DIGITAL MODULATION

Modulation is the process of embedding information onto a high-frequency carrier wave for transmission over long distances. It involves changing a characteristic of the carrier wave—its amplitude, frequency, or phase—in a way that corresponds to the information signal. 

Modulation can be either analog or digital as illustrated on Figure 1 below

Figure 1: Categorization of Modulation techniques

ANALOG MODULATION

Analog modulation is a technique used to encode information from a low-frequency analog signal onto a high-frequency carrier wave. The goal of modulation is to modify a specific characteristic of the carrier wave (frequency, amplitude, phase) in proportion to changes in the modulating signal. Modulation is essential for efficient transmission over long distances. It also allows multiple signals to share the same transmission medium without interfering with each other (Compare with notes on Multi-Access). There are three major categories of analog modulation techniques: Amplitude, frequency, and phase modulation techniques

1.Amplitude Modulation (AM)

In Amplitude Modulation (AM) is the varying of carrier wave in accordance with the changes in amplitude of the modulating signal. The frequency and phase of the carrier wave remain constant. AM is one of the oldest and simplest forms of analog modulation and was widely used for radio broadcasting.

When one speaks into a microphone, the voice signal/modulating signal causes peaks and troughs of the carrier wave to change.

Figure 2: Amplitude modulation (AM)

The mathematical representation of an AM signal is given by:

Modulation Index is the ratio of the modulating signal amplitude to the carrier amplitude. It indicates the depth of modulation. If it is greater than 1, it results in over-modulation, which causes distortion.

The main drawbacks of AM are that it is a highly susceptibly to noise and interference because most noise sources (e.g., lightning and electrical sparks) are amplitude-based and can easily to mistaken for part of the signal.

2. Frequency Modulation (FM)

Frequency Modulation (FM) varies the instantaneous frequency of the carrier wave in proportion to the change in amplitude of the modulating signal. The amplitude of the carrier remains constant. FM is known for its high fidelity and resistance to noise.

Figure 3: Frequency Modulation

FM has the advantage of being much more immune to noise than AM. Since most noise affects the amplitude of a signal, this is the reason why FM radio stations are preferred for broadcasting music.

FM signal also has a wider bandwidth than an AM signal. The required bandwidth is approximated by Carson's Rule:

 

 

 

WIRELESS NETWORKS AND MOBILE COMMUNICATIONS

Fundamentals of Wireless Networks

Unlike wired connections that utilize guided media, wireless communication uses the

air as its channel, which is relatively unpredictable. This module will discuss the fundamental concepts that control signal transmission using air as the medium. It covers the electromagnetic spectrum, the physical features of radio frequencies, and the different impairments that reduce signal quality, such as path loss, interference, and fading. And at the end of it, it discusses Shannon's Theorem, which specifies the theoretical limits of wireless data transmission.

The Electro-Magnetic Spectrum

Wireless communication relies on radio waves, which are a form of electromagnetic (EM) radiation. The entire range of this radiation, from radio waves to gamma rays, is called the electromagnetic spectrum. Wireless technologies like Wi-Fi, Bluetooth, and cellular networks operate in specific, regulated parts of this spectrum to avoid interference.

The Electromagnetic (EM) spectrum is the complete range of all types of radiation that have both electric and magnetic fields and travel in waves.  A wave's frequency is the number of cycles it completes in one second and is measured in Hertz (Hz). Different frequencies have different properties, and the different frequencies are divided into different frequency bands.

Figure 1: The Electromagnetic Spectrum - [https://en.wikipedia.org/wiki/Electromagnetic_spectrum - accessed 26 August 2025]

Radio Frequency (RF)

Radio frequency (RF) is the electromagnetic spectrum that is most commonly used for wireless communication. This range is the band from about 3 kilohertz (kHz) to 300 gigahertz (GHz), and the different wireless technologies operate at the different RF bands as follows:

• Bluetooth and Wi-Fi typically operate in the 2.4 GHz and 5 GHz bands.
• Cellular networks use a variety of bands, including 700 MHz, 1.9 GHz, and 2.1 GHz.
• Understanding the specific frequency is critical because it dictates how a signal propagates, its range, and its resistance to obstacles.

The Wireless Channel
In wired networks, the channel is a physical medium like a fiber optic, twisted pair, coaxial cable or Ethernet cable. In wireless communication, the wireless channel is the air or space between the transmitter and the receiver. Unlike a cable, the wireless channel is unpredictable and introduces significant challenges as follows;

•          Path Loss: Path loss is the natural decrease in signal's power as it travels from source to destination. The farther a signal travels, the weaker it gets.
•          Interference: Interference refers to the disturbances of data as it is transmitted from source to destination.
•          Fading: This is caused by multipath propagation, where signals bounce off objects and arrive at the receiver at different times, causing rapid fluctuations in signal strength. 

Shannon's Theorem and Data Transmission
 Shannon's Theorem, (Shannon-Hartley theorem), is a fundamental principle that defines the theoretical maximum data rate of a channel with a given amount of noise. It provides an absolute limit on how fast we can send data over a wireless link.

It is expressed by the following formula:

C=Blog2​(1+S/N)

•      C is the channel capacity, the maximum achievable data rate in bits per second (bps). 
•      B is the bandwidth of the channel in Hertz (Hz). This is the width of the frequency band being used. 
•      S/N is the Signal-to-Noise Ratio (SNR), a measure of the signal's strength relative to the background noise. A higher SNR means a clearer signal.

The theorem shows that to increase the data rate (C), you must either increase the bandwidth (B) or improve the signal quality by increasing the SNR. It explains techniques to improve SNR, to achieve higher speeds.

CS_Document Management - I

A Word document is a digital file created using a word processing application, typically Microsoft Word. For example, text, tables, etc. They are used in composing letters, reports and possess features that are used in grammar checks and text formatting. Like any other types of files, Word documents have the extensions: .doc, .docx. .rtf, and PDF.

 
On the other hand, Google Docs is a complimentary online word processing tool that enables individuals to create, modify, and collaborate on documents over the internet, even in real-time, with changes automatically stored in the cloud. Google Docs is included in the Google Workspace (Formally Google Drive).
 
Microsoft Word and Google Docs are both proper word processing tools designed for crafting and modifying a variety of documents. Although their functionalities are comparable, their user interfaces vary slightly. While Microsoft Word is a stand-alone program included in the Microsoft Office Suite, Google Docs operates in the cloud and is accessed through a web browser.

Figure 1: The Microsoft Word Working Environment (Interface)

Microsoft Word has a main Ribbon at the top of the window that acts as the main control center. The Ribbon is sectioned into tabs that include Home, Insert, and Page Layout, etc. Each of these contain groups of commands relating to the associated tasks. For example, the Review tab includes Spelling & proofing, accessibility, etc.  

Below the Ribbon, is the Ruler for managing indents and tabs, and the main Document Pane that has the content of the document.

The bottom of the window has the Status Bar, which provides information like page and word count.

Figure 2: Google Docs Working Environment (Interface)

Unlike Microsoft Word, Google Docs has only a minimum number of features reflected on top of the window. There is a Menu Toolbar with dropdown menus that have commands like File, Edit, and View, among others.

Right below the toolbar is the Shortcuts Toolbar, for quick access to frequently used formatting options.

The main document is where content is populated, and the Ruler is also available for adjustments. Unlike Word, Google Docs automatically works, and the "Saved changes" notification appears to confirm that this has happened.

CLASS ACTIVITY

Margins & Orientation

1.     To change page Margins: Go to the Layout tab, click Margins, and select a preset or create a custom margin. Whereas in Google Docs, go to File, choose page setup, and adjust the margin values.

2.     Change orientation: Navigate to the layout tab, click Orientation, and select the orientation. In Google docs, go to file, and select page setup.

Fonts & Paragraphs

1.     To modify font: Select a block of text of interest. Form the ribbon, select the Home tab and choose font. For Google Docs, use the Shortcuts Toolbar to modify the font type and size.

2.  Working with the font family: Select text and click the font color icon to choose a new color. To change the font to bold, Italic, or underline: Highlight the text and click the B, I, or U to bold, italicize, or underline, respectively.    

3.     Paragraph alignment: Select the paragraph and use the alignment buttons to left align, right align or justify. in the Paragraph group or on the Shortcuts Toolbar.

4.     Adjust Line Spacing: From the Home tab, select paragraph, and then use the line and paragraph spacing tool to change it to a desired spacing.

Headers and Footers

1.     Insert a Header/Footer: Double-click the top or bottom of a page to activate the header/footer area. In Google Docs, go to Insert > Headers & footers.

2.     To add a Page Number: While in the header or footer area, go to Insert, choose page Number. And for Google Docs choose to insert, page elements, page numbers and choose a format.

3.     To have a unique header/footer on the first page, select the page option.

Lists

Lists organize information. The commonly used are: bulleted and numbered lists.

1.     Bulleted List: Select the typed items and click the Bulleted List icon in the toolbar and choose the style. 

2.     Numbered List: elect the items and click the Numbered List icon. and choose the numbering methods from Arabic numerals, Roman numerals, or letters.

3.     Multi-Level List: Indent the next line. This will create a nested list, with a new bullet or numbering style. To return to the previous level, press Shift + Tab.

CS_Operating Systems & File Management

An operating system (OS) is software that acts as an intermediary ("broker role") between the user and the hardware. The OS is responsible for managing all the computer's resources, including its memory, processes, software, and hardware. 

1. File Management

The Operating System (OS) provides a structured way of storing, organizing, and retrieving data on storage devices. The different operating systems structure data in different ways. The file-related activities include creating, deleting, and modifying files. A file is the smallest unit of logical secondary storage. It keeps track of file attributes, which may include name, size, and permissions, among other details. 

File: A file is a collection of related information stored on a secondary storage medium. These can be images, text, or executables.

File Attributes / Metadata: This is information associated with a file, such as name, size, or date of creation. Information about data may help when controlling file access and usage. 

Directory/Folder: Depending on the type of OS, they have been referred to as a directory or folder. It is a collection of files of the same type. A hierarchical structure has been employed by several OSs because it makes it easier to navigate and locate files. 

File Operations

The OS provides operations for handling files. These operations include: 

Creation: File creation is the process of using a computer program to set up a new file. File creation can be carried out by the user using the help of the OS or automatically by the OS, or by an unauthorized program. 

Open: To open a file is the process of making a file available to the user or program for any of the operations of reading from, writing to.

Read: Reading a file is the process of accessing and retrieving data that has been stored in a file on a storage medium and bringing that data into the program's memory.  

Write: Writing is to store data in a file. Data obtained from the OS is saved in a persistent storage such as the hard disk.

Delete: To remove a file from storage and free up space. The process removes the file from the file system.

Rename: To change a file's name.

2. File Allocation and Access Control

The operating system also manages how files are physically stored and accessed from a storage medium. 

a) File Allocation: 

File allocation is how the OS assigns and manages disk space for files. The primary methods of file allocation are contiguous and linked allocation methods. 

i) Contiguous Allocation: A file is assigned a single, continuous block of storage. The method is fast because of the sequential nature of access. It is, however, susceptible to fragmentation, where free space is broken into small, unusable chunks. 

ii) Linked Allocation: Each block of a file contains a pointer to the next block.  

iii) Indexed Allocation: In indexed allocation, an index block is used to store pointers to all the blocks that make up a file. One strength is its support for fast random access, but it has overhead because an entire block is needed to store the indices. 

Many modern file systems use hybrid approaches to leverage the benefits of these methods.

b) Access Control: 

The OS ensures data security by controlling who can access a file and what they can do with it. It is typically managed through file permissions (read, write, and execute) or access control lists. 

CLASS ACTIVITY

Navigating the Desktop

A desktop refers to the main screen seen when a computer starts up. It typically includes the taskbar or dock in case of macOS at the bottom, to simplify its use. The desktop provides an environment that allows users to place frequently used files and program shortcuts. 

How to create a folder

As defined above, a folder is a collection of multiple files (both similar and dissimilar). To create a folder in windows OS, follow the following steps:

·         Right-click the area where you want to place the folder

·         Select New from the menu, and choose Folder.

·         Type a name for the folder next to the new folder that appears, and press Enter.

Good Practices in File Naming  ️

• Be Specific and descriptive: E.g., Lecture_Notes, Semester_exams, etc
• Avoid Special Characters because they have special meanings to the system: E.g., ?, /, \, *, <, >, and |, 
• Be Consistent: Use a consistent naming structure. For example, if your folder contains lecture notes (e.g., Computer_skills_Module_1, 2025, Development_studies_Module_1, 2025).

Finding Files 

Most OSs provide tools to allow searching for files. To search for a file, do the following.

For windows: 

Click the Start button or the search icon on the taskbar and type the file's name.

For macOS: 

Click the search (Spotlight) and type the file's name.

Shortcuts 

A shortcut is a small file that points to another file, folder, or application. shortcuts save time to navigate to the original files whenever we want to access them.

To create a shortcut, follow the following steps: 

For Windows: 

Right-click on a file or program, select Create shortcut, and then drag the new shortcut to your desired location. 

For macOS: 

Right-click a file or program, select Make Alias, and then drag the alias to your desired location