Archives October 2023

What is WIMAX

WiMAX, short for Worldwide Interoperability for Microwave Access, is a wireless communication standard that provides high-speed broadband connectivity over long distances. It is based on the IEEE 802.16 family of standards and is designed to deliver wireless metropolitan area network (MAN) and wide-area network (WAN) connectivity.

Here are key features and aspects of the standard:

1. Broadband Wireless Access:

  • WiMAX is designed to provide broadband wireless access, delivering high-speed internet connectivity to both fixed and mobile users.

2. Frequency Bands:

  • It operates in various frequency bands, including the 2.3 GHz, 2.5 GHz, 3.5 GHz, and 5.8 GHz bands. The specific frequency bands used can vary depending on regulatory considerations in different regions.

3. Point-to-Multipoint Communication:

  • It supports point-to-multipoint communication, allowing a base station (access point) to communicate with multiple subscriber stations simultaneously.

4. Last Mile Connectivity:

  • One of the applications of WiMAX is providing last-mile connectivity, especially in areas where traditional wired broadband infrastructure is not readily available.

5. Mobility Support:

  • While WiMAX was initially designed as a fixed wireless access technology, the standard was later extended to support mobile applications, allowing users to connect to the network while on the move.

6. IEEE 802.16 Standards:

  • The IEEE 802.16 family includes multiple standards. The original standard was IEEE 802.16-2004, followed by amendments such as IEEE 802.16e-2005 for mobile WiMAX and IEEE 802.16m for advanced mobile WiMAX.

7. WiMAX Forum:

  • The WiMAX Forum is an industry association that promotes the adoption of WiMAX technology and ensures interoperability between different vendors’ equipment.

8. Coverage and Range:

  • WiMAX can provide coverage over long distances, making it suitable for serving both urban and rural areas. The range can extend to several kilometers from a base station.

9. Competition and Evolution:

  • While it was initially considered a competitor to other broadband technologies like DSL and cable, its adoption faced challenges. Long-Term Evolution (LTE), a competing 4G technology, gained broader acceptance, and many mobile operators shifted their focus to LTE and later 5G technologies.

Today, while it is still in use in some regions and specific applications, it is not as widely deployed as LTE and 5G for mobile broadband. The industry has moved toward the adoption of these newer technologies for enhanced performance and capabilities.

What is WIFI

What is WIFI

Wi-Fi, short for Wireless Fidelity, is a technology that enables wireless local area networking (WLAN) based on the IEEE 802.11 family of standards. Wi-Fi allows devices such as computers, smartphones, tablets, and other wireless-enabled devices to connect to the internet and communicate with one another within a local network without the need for physical cables.

Here are some key aspects of Wi-Fi:

1. Wireless Standards:

  • Wi-Fi operates based on IEEE 802.11 standards, with different letters and numbers denoting various iterations of the technology. For example, Wi-Fi 6 is based on the IEEE 802.11ax standard.

2. Frequency Bands:

  • Wi-Fi devices can operate in the 2.4 GHz and 5 GHz frequency bands. The 2.4 GHz band has a longer range but is more susceptible to interference, while the 5 GHz band offers higher data rates and is less congested.

3. Wireless Access Points (APs):

  • Wi-Fi networks consist of one or more access points, which are devices that transmit and receive Wi-Fi signals. Access points are often integrated into routers.

4. Security:

  • Wi-Fi networks use various security protocols, such as WPA3 (Wi-Fi Protected Access 3), to encrypt data and protect against unauthorized access.

5. SSID (Service Set Identifier):

  • Wi-Fi networks are identified by their SSID, which is a name that users can see when searching for available networks. It is essential to secure Wi-Fi networks with a strong password to prevent unauthorized access.

6. Modes and Bands:

  • Wi-Fi devices can operate in different modes, including Infrastructure mode (connecting to a network through an access point) and Ad-hoc mode (direct device-to-device connection). Dual-band and tri-band Wi-Fi routers support multiple frequency bands.

7. Evolution:

  • Wi-Fi technology has evolved over the years, with each new generation offering improved speed, capacity, and performance. Wi-Fi 6 and Wi-Fi 6E are the latest standards, providing faster data rates and better performance in crowded environments.

8. Hotspots:

  • Wi-Fi hotspots are locations where Wi-Fi access is available to the public, such as in coffee shops, airports, and libraries.

So to conclude, what is WIFI..

Wi-Fi is a ubiquitous technology, providing wireless connectivity in homes, businesses, public spaces, and educational institutions. It has become an integral part of modern life, enabling seamless internet access and connectivity for a wide range of devices.

ptt over cellular mast

Cellular networks

Cellular networks, including GSM (Global System for Mobile Communications) and UMTS (Universal Mobile Telecommunications System), are mobile communication technologies that enable wireless communication between mobile devices and provide voice and data services.

1. GSM (Global System for Mobile Communications):

  • Introduction: GSM is a 2G (second-generation) cellular network standard that was developed to replace analog cellular networks. It is a digital technology that uses time-division multiple access (TDMA) for channel access.
  • Architecture: GSM networks are divided into cells, each served by a base station. Multiple cells together form a cellular network, and each cell has a corresponding base transceiver station (BTS).
  • Frequency Bands: GSM operates in various frequency bands, including the 900 MHz and 1800 MHz bands in Europe and the 850 MHz and 1900 MHz bands in North America.
  • Services: GSM provides voice services, Short Message Service (SMS), and data services (GPRS – General Packet Radio Service).

2. UMTS (Universal Mobile Telecommunications System):

  • Introduction: UMTS is a 3G (third-generation) cellular technology that evolved from GSM. It provides higher data rates and additional services compared to GSM.
  • Architecture: UMTS employs a wider band of frequencies and uses a different air interface based on wideband code division multiple access (WCDMA). The network architecture includes Node-B (base station), Radio Network Controller (RNC), and a core network.
  • Frequency Bands: UMTS operates in various frequency bands, including the 2100 MHz band.
  • Services: UMTS supports higher data rates, enabling services like mobile internet, video calling, and multimedia messaging. It is also backward-compatible with GSM, allowing for seamless handovers between GSM and UMTS networks.

Key Features Common to Both GSM and UMTS:

  1. Cellular Architecture: Both GSM and UMTS networks are divided into cells, allowing for efficient use of the available frequency spectrum.
  2. Handover Capability: Mobile devices can seamlessly switch from one cell to another as they move, ensuring continuous connectivity.
  3. Global Standards: GSM and UMTS are global standards, facilitating international roaming and interoperability.
  4. Subscriber Identity Module (SIM): Both technologies use a SIM card that stores subscriber information, allowing users to easily switch devices while retaining their identity and services.
  5. Security: Both GSM and UMTS incorporate security features to protect communication, including encryption and authentication.

UMTS, being a 3G technology, provides higher data rates and more advanced services compared to GSM, which is a 2G technology. However, with the evolution of technology, both GSM and UMTS have been succeeded by 4G LTE (Long-Term Evolution) and 5G for even higher data rates and enhanced capabilities.


CSMA/CA stands for Carrier Sense Multiple Access with Collision Avoidance. It is a network protocol used in wireless communication to avoid collisions in the transmission of data.

Here’s a breakdown of how CSMA/CA works:

  1. Carrier Sense (CS): Before transmitting data, a device using CSMA/CA listens to the wireless channel to check for the presence of other signals. If the channel is clear, the device proceeds with transmission.
  2. Multiple Access (MA): Multiple devices share the same communication channel. CSMA/CA allows multiple devices to access the channel, but they must follow certain rules to avoid collisions.
  3. Collision Avoidance (CA): Unlike CSMA/CD (Carrier Sense Multiple Access with Collision Detection), which is used in wired Ethernet networks, CSMA/CA focuses on collision avoidance rather than detection. In a wireless environment, it’s challenging to detect collisions reliably, so the emphasis is on avoiding collisions in the first place.

In CSMA/CA, a device wishing to transmit data follows a procedure:

  • Request to Send (RTS): The device sends a short RTS frame to the intended recipient, indicating its intention to transmit.
  • Clear to Send (CTS): If the intended recipient is ready to receive, it replies with a CTS frame.
  • Data Transmission: The sender then transmits the actual data.
  • Acknowledgment (ACK): The recipient sends an acknowledgment to confirm successful reception.

This process helps in avoiding collisions by ensuring that the channel is clear before transmission and by coordinating communication between devices.

CSMA/CA is commonly used in wireless LANs, such as Wi-Fi networks, where multiple devices share the same frequency spectrum. It helps manage the shared medium to avoid interference and collisions, promoting more efficient and reliable communication.

What is CDMA

Code Division Multiple Access (CDMA) is a digital cellular technology that allows multiple users to share the same frequency band simultaneously. Unlike Time Division Multiple Access (TDMA) or Frequency Division Multiple Access (FDMA), which divide the frequency band into time slots or channels, CDMA uses a spread spectrum technique.

In CDMA, each user is assigned a unique code, known as a spreading code. These codes are used to modulate the user’s signal before transmission. All users in the system share the same frequency band, but their signals are distinguished by the unique codes.

Key characteristics include:

  1. Spread Spectrum: CDMA uses spread spectrum technology, which spreads the signal across a wider frequency band. This provides advantages in terms of resistance to interference and improved security.
  2. Soft Capacity: the systems exhibit a concept called “soft capacity,” meaning that the system can support a higher number of users than the number of available orthogonal codes. This is because users can be distinguished not only by their unique codes but also by the strength of their received signals.
  3. Interference Rejection: it is known for its ability to handle interference well. Users can share the same frequency band, and the receiver can separate and recover the individual signals based on their unique spreading codes.

CDMA has been widely used in 2G (second generation) and 3G (third generation) cellular networks. CDMA2000 and WCDMA (Wideband CDMA) are examples of CDMA-based 3G technologies. However, in recent years, many mobile networks have transitioned to LTE (Long-Term Evolution) and 5G technologies, which use different modulation schemes.

Quadrature Phase Shift Keying

Quadrature Phase Shift Keying (QPSK) is a digital modulation scheme that represents two bits of data per symbol. In QPSK, four different phase shifts of the carrier signal are used to encode the binary data. Each phase shift corresponds to a specific combination of two bits (00, 01, 10, and 11).

The term “quadrature” refers to the use of two carriers that are 90 degrees out of phase with each other. The QPSK modulation constellation diagram typically illustrates the four different phase positions.

Here’s a basic breakdown of how QPSK works:

  1. Mapping Bits to Phase Shifts:
    • 00 is represented by a 0-degree phase shift.
    • 01 is represented by a 90-degree phase shift.
    • 10 is represented by a 180-degree phase shift.
    • 11 is represented by a 270-degree phase shift.
  2. Transmission:
    • Each symbol represents two bits of information.
    • The carrier signal is modulated with the appropriate phase shift based on the two-bit data.

QPSK is used in various communication systems, including satellite communication, digital television, and some wireless communication standards. While Quadrature Phase Shift Keying provides a higher data rate compared to Binary Phase Shift Keying (BPSK), it is more susceptible to noise and interference than higher-order modulations like 16-QAM or 64-QAM.

Quadrature Amplitude Modulation

Quadrature Amplitude Modulation (QAM) is a modulation scheme used in digital communication to transmit data by varying both the amplitude and phase of a carrier signal. QAM allows for the transmission of multiple bits of information per symbol, making it a more bandwidth-efficient modulation scheme.

In QAM, the amplitude and phase of the carrier signal are simultaneously modulated to represent different combinations of amplitude and phase levels. The most common form is Quadrature Amplitude Modulation, where both amplitude and phase are modulated. The term “quadrature” refers to the use of two carriers that are 90 degrees out of phase with each other.

The number of amplitude and phase combinations determines the order of the QAM modulation. For example, in 16-QAM, there are 16 different possible combinations, allowing the transmission of 4 bits per symbol. Higher-order QAM, such as 64-QAM or 256-QAM, can transmit even more bits per symbol, but they are more susceptible to noise and interference.

QAM is widely used in digital communication systems, including cable modems, digital television broadcasting, and some wireless communication standards like Wi-Fi and 4G LTE. It strikes a balance between spectral efficiency and susceptibility to noise, making it suitable for various applications.

What is PSK

Phase Shift Keying (PSK) is a digital modulation technique used in communication systems to encode information in the phase of a carrier wave. In PSK, the phase of the carrier signal is varied to represent different symbols or bits. The most common forms include Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), and higher-order variants like 8-PSK or 16-PSK.

In BPSK, for example, two different phases are used to represent binary 0 and 1. The carrier signal undergoes a 180-degree phase shift for each bit, allowing for the transmission of binary data.

QPSK extends this concept by using four different phase shifts, allowing each symbol to represent two bits of information. This allows for higher data rates compared to BPSK.

Phase Shift Keying is widely used in various communication systems, including satellite communication, digital television broadcasting, and some wireless communication standards. The advantage of PSK lies in its ability to transmit data efficiently by varying the phase of the carrier signal, making it resilient to certain types of noise and interference.

What is FSK

Frequency Shift Keying is a modulation technique used in digital signal processing and communication systems. In FSK, the digital information is encoded by varying the frequency of the carrier signal between two distinct frequencies. Typically, one frequency represents a binary “0,” and the other frequency represents a binary “1.”

For example, in binary FSK, if a digital signal is transmitting a stream of 0s and 1s, the carrier frequency might switch between two specific frequencies for each bit. The receiver can then detect these frequency changes to demodulate and decode the original digital signal.

FSK is commonly used in various communication systems, including radio frequency identification (RFID), data modems, and some types of analog modems. It’s a straightforward and efficient way to encode digital information for transmission over analog channels.

What is FDMA

FDMA stands for Frequency Division Multiple Access. It’s a channel access method used in telecommunications to divide the available bandwidth into frequency channels. Each channel is then assigned to a different user or communication stream, allowing multiple users to transmit simultaneously without interference. FDMA is commonly used in analog systems like traditional radio and television broadcasting. It’s one of the multiple access methods, with others including TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access).