Why Did GSM Use GMSK Instead of BPSK? Understanding the Engineering Behind 2G Networks One of the most common questions in digital communication is: Why did GSM choose GMSK modulation instead of BPSK? At first glance, both Binary Phase Shift Keying (BPSK) and Minimum Shift Keying (MSK) appear to have constant-amplitude RF waveforms. So why did engineers developing second-generation (2G) GSM networks select Gaussian Minimum Shift Keying (GMSK) as the standard modulation technique? The answer lies in spectral efficiency, phase continuity, amplifier performance, and battery life . In this article, we'll explore the technical reasons behind GSM's choice of GMSK and compare it with BPSK. What Is BPSK Modulation? Binary Phase Shift Keying (BPSK) is one of the simplest digital modulation schemes. The transmitted passband signal is represented as: s(t) = A cos(2πf₍c₎t + φ(t)) Where: A is the carrier amplitude f c is the carrier frequency φ(t) take...

4x4 MIMO in LTE 4×4 MIMO in LTE (Signal Processing Perspective) This explains how a 4×4 MIMO system works in LTE, extending the 2×2 case to a more realistic scenario. 1. System Setup 4 transmitted signals (streams/users) 4 receive antennas at base station 2. Signal Model y = Hx + n x = [ x1 x2 x3 x4 ] y = [ y1 y2 y3 y4 ] 3. Channel Matrix H = [ h11 h12 h13 h14 h21 h22 h23 h24 h31 h32 h33 h34 h41 h42 h43 h44 ] Each receive antenna gets a mixture of all transmitted signals. 4. Received Signal Expansion y1 = h11x1 + h12x2 + h13x3 + h14x4 y2 = h21x1 + h22x2 + h23x3 + h24x4 y3 = h31x1 + h32x2 + h33x3 + h34x4 y4 = h41x1 + h42x2 + h43x3 + h44x4 All received signals are mixtures — no antenna gets a clean signal. 5. Detection Techniques (A) Zero Forcing (ZF) x̂ = H⁻¹ y Removes interference Sensitive to noise (B) MMSE (Used in LTE) x̂ = (HᴴH + N₀...

LTE 2-User MIMO (Uplink) – Step-by-Step Example This example shows how two mobile users transmit simultaneously and how the base station separates their signals using linear algebra. 1. Transmission x = [ x1 x2 ] x1: Signal from User 1 x2: Signal from User 2 2. Channel Matrix H = [ 1 0.5 0.3 1 ] Signals from both users mix across both receive antennas. 3. Received Signal y = Hx y1 = x1 + 0.5x2 y2 = 0.3x1 + x2 The base station receives only mixed signals — no clean separation exists. 4. Detection Using Zero Forcing (ZF) x̂ = H⁻¹ y Inverse of H det(H) = 1 - (0.5 × 0.3) = 0.85 H⁻¹ = (1 / 0.85) × [ 1 -0.5 -0.3 1 ] H⁻¹ = [ 1.176 -0.588 -0.353 1.176 ] 5. Recover Signals x̂1 = 1.176y1 - 0.588y2 x̂2 = -0.353y1 + 1.176y2 6. Substitution For x̂1: x̂1 = 1.176(x1 + 0.5x2) - 0.588(0.3x1 + x2) = x1 For x̂2: x̂2 = -0.353(x1 + 0.5x2) + 1.176(0.3x1 + x2) = x2 Final Result...

T-Carrier Systems (T1, T2, T3, T4) T-Carrier Systems (T1, T2, T3, T4) T-carrier systems are digital transmission systems used to send multiple voice or data channels over a single physical line. They are commonly used in North America for telephone and data networks. The “T” stands for Trunk . Each level (T1, T2, T3, T4) represents increasing numbers of multiplexed channels and higher data rates. T1 System Channels: 24 voice channels Data rate: 1.544 Mbps Multiplexing: Each channel = 64 Kbps → 24 × 64 Kbps + framing bits Purpose: Small to medium scale digital voice/data transmission T2 System Channels: 96 voice channels Data rate: 6.312 Mbps Multiplexing: 4 T1 streams combined Purpose: Medium scale transmission T3 System Channels: 672 voice channels Data rate: 44.736 Mbps Multiplexing: 7 T2 streams combined Purpose: Large scale trunking T4 System ...

Erlangs in Telecommunications Erlangs are a unit used in telecommunications to measure traffic load or how busy a system is. Named after Danish mathematician and engineer Agner Krarup Erlang . Simple Meaning 1 Erlang = one communication channel fully used for 1 hour 1 call lasting 1 hour → 1 Erlang 2 calls lasting 30 minutes each → 1 Erlang 60 calls lasting 1 minute each → 1 Erlang Formula Traffic (Erlangs) = (Number of calls × Average call duration) / Time period Why It’s Important Design telephone networks Avoid congestion Determine number of channels needed Real Example If 120 calls happen in 1 hour and each call lasts 3 minutes: Traffic = (120 × 3) / 60 = 6 Erlangs Erlang B (Blocking Probability) Used when blocked calls are cleared (no waiting). Common in traditional telephone systems. B(A, N) = (A^N / N!) / Σ (k=0 to N) (A^k / k!) A = traffic in Erlangs N = number of channels Gives probabi...

Advanced Cellular System Simulator Advanced Cellular System Simulator Cluster Size Calculator i: j: Calculate Formula: N = i² + j² + ij Workflow: 1. Enter i and j values 2. Square both values 3. Multiply i × j 4. Add all → gives cluster size (N) Frequency Reuse Calculator Total Channels: Cell Radius (R): Calculate Channels per Cell = Total Channels / N Reuse Distance: D = √(3N) × R Workflow: 1. Compute cluster size (N) 2. Divide total channels by N 3. Calculate reuse distance using √(3N) × R Co-channel Reuse Ratio (Q) Calculate Q Q = √(3N) Workflow: 1. Find N 2. Multiply 3 × N 3. Take square root → gives Q Signal-to-Interference Ratio (S/I) Path Loss Exponent (n): Interfering Cells (i₀): Calculate S/I S/I = (Qⁿ) / i₀ Workflow: 1. Calculate Q = √(3N) 2. Raise Q to power n 3. Divide by number of interfering cells (i₀)

DSSS-CDMA  This explanation builds intuition step by step for DSSS-CDMA , chip rate , processing gain , and how multiple users share the same analog carrier . What DSSS-CDMA Really Is All users transmit at the same time Over the same frequency band Using the same RF carrier Separated using codes FDMA → Different frequencies TDMA → Different time slots CDMA → Same time + same frequency, different codes Role of the Carrier Signal There is one common carrier frequency for all users. Carrier frequency: 900 MHz Bandwidth: 1.25 MHz (IS-95) The carrier is NOT assigned per user. s k (t) = b k (t) · c k (t) · cos(2πf c t) b k (t): user data (low rate) ...

Time Division Multiple Access (TDMA) Overview Time Division Multiple Access (TDMA) is a channel access method used in communication systems to allow multiple users to share the same frequency channel. Each user is allocated a specific time slot during which they can transmit or receive data. TDMA is used in cellular networks (e.g., GSM), satellite communications, and other wireless systems. Key Concepts of TDMA Time Slots: TDMA divides the available bandwidth into discrete time slots, each allocated to a user. Each user transmits during their allocated time slot. Frame Structure: The total available time is organized into frames, where each frame consists of several time slots. A frame has slots for each user. Channel Sharing: Multiple users share the same frequency by transmitting in different time slots. Mathematical Representation of TDMA ...

  Code Division Multiplexing Access (CDMA) is the technique used to enable multiple signals from multiple users to share a single communication channel when CDM is utilized. Individual talks are encoded in a digital sequence, and each group of users is given a shared code. The users connected with a specific code can only access the data that is available on the shared channel. Walsh-Hadamard codes are designed to provide efficient and orthogonal coding sequences, which allow multiple signals or users to share the same frequency band without interfering with each other Example: H2  = [1, 1 ; 1, −1)] ;                  H4  = [1, 1, 1, 1; 1, −1, 1, −1; 1, 1, −1, −1 ; 1, −1, −1, 1 ] Each row in the above matrices represents a codeword The dot product of any two distinct codewords is 0 Consider that there are four stations, w, x, y, and z, that have been assigned the codes cw, cx, cy, and cz and need to transmit data dw, dx, dy, a...

  2G connectivity was introduced in the mid-1990s. It exposed us to data networks, or PSDNs, and voice communication through phone calls. In the case of 2G GSM, each communication channel had a frequency of 200 KHz and could connect up to eight users at once. FDM (frequency division multiplexing) and TDM (time division multiplexing) were two popular modulation techniques for 2G. (time division multiplexing). But why are we talking about 2G here? G's have evolved primarily in operating frequency, bandwidth, and modulation techniques. Similarly, the bandwidth of each channel in 3G is about 1.25 MHz. The frequency range for 4G will be between 5 and 20 MHz. FDMA (frequency division multiplexing access), TDMA (time division multiplexing access), and CDMA (code division multiplexing access) were the most prevalent modulation techniques for 3G. (code division multiplexing access). For 3G, CDMA was a common modulation technique. 3G was launched in 2001, while 4G was launched around 20...

  Yeah. Telecom experience can help you indirectly to pursue a career in networking filed. It can assist you, but computer networking is a separate domain. Some telecommunication concepts, such as routing and switching, modem, switch, router, TCP/IP, and so on, are shared by both fields. In telecommunications, we primarily concentrate on modulation techniques, uplink-downlink frequencies, base stations, user equipment, transmitting antennas, switching, power supply, fibre optic maintenance, billing, and so on. The networking field differs slightly from the telecommunications field. We will primarily focus on computer connections, DHCP, TCP/IP, routing and switching, proper and sequential transmission of data packets from one computer to another, server-to-client computer communication, network security, and so on. Most important individual networking devices are -- Bridge, Hub, Switch, Router, Modem, Repeater, Gateway, etc. 

  To get a job in the electronics and telecommunications industry, you must have a solid understanding of basic communication systems, such as how signals are modulated, the concept of wireless or wired channels, random variables, basic trigonometry used in wireless communication, and so on. You should also be familiar with mobile wireless generations in telecommunications. Routing and switching, TCP/IP suite, operating system fundamentals, and so on are required to work in telecommunications. In addition to the above requirements, candidates with strong knowledge of any programming language, such as C or C++, or Python, are preferred nowadays. You are welcome to apply for a telecommunications job if you are only interested in communication systems; otherwise, it is not for you. Our blog/website focuses on basic wireless communication systems, telecommunication, and modern wireless communication technologies such as 5G technology, Massive MIMO systems, IoTs, etc. You can learn more...

  Significance of Network ID in data transmission Last Updated: 7/1/22 To transfer data packets from one computer to another, some protocol is used. The procedure is analogous to postal mail delivery. If you want to send a letter to a friend who lives 500 miles away, the corresponding office will handle the backend process of getting your letter to your friend. TCP/IP is a popular internet transmission protocol for transferring data packets from one computer to another. The network ID is the destination network's address as well as the host's address. TCP/IP transports the following data: Source address  Destination address (network address + host address) Checksum Data, etc When two computers are connected to the same network, there is no need for routing. However, it is less likely. When you send a from your computer, it is routed through several intermediate networks / routers. The number of intermediate routers is referred to as the 'number of hops.' Computer networ...

Doppler Shift Formula When either the transmitter or the receiver is in motion, or when both are in motion, Doppler Shift is an essential parameter in wireless communication. We notice variations in reception frequencies in vehicles, trains, or other similar environments. In plain language, the received signal frequency increases as the receiver moves toward the transmitter and drops as the receiver moves in the opposite direction. This phenomenon is called the Doppler shift or Doppler spread. Doppler Shift Formula The relationship between the transmitted and received frequency is defined as: fR = fT ± fD fR = Receiving frequency fT = Transmitted frequency fD = Doppler frequency (shift) The Doppler frequency is determined by the speed of the vehicle and the angle of the arriving wave: Doppler shift (LOS path): ν1 = fc * v / c ...

📘 Overview 📘 LARGE SCALE FADING 📘 SMALL SCALE FADING 📘 SLOW FADING 📘 FAST FADING 🧮 MATLAB Codes 📚 Further Reading LARGE SCALE FADING The term 'Large scale fading' is used to describe variations in received signal power over a long distance, usually just considering shadowing.  Assume that a transmitter (say, a cell tower) and a receiver  (say, your smartphone) are in constant communication. Take into account the fact that you are in a moving vehicle. An obstacle, such as a tall building, comes between your cell tower and your vehicle's line of sight (LOS) path. Then you'll notice a decline in the power of your received signal on the spectrogram. Large-scale fading is the term for this type of phenomenon. SMALL SCALE FADING  Small scale fading is a term that describes rapid fluctuations in the received signal power on a small time scale. This includes multipath propagation effects as well as movement-induced Doppler fr...

  By typing in our browser, we can find any content, video, or other information on the internet. Our smartphones, laptops, and PDAs then transmit an electrical signal to a nearby cell tower or Wi-Fi router. In plain language we call it a "http request". The DNS server is then contacted. The IP addresses of the websites are stored on the DNS server. For example, in your browser's search box, you type "http://www.example.com." Your smartphone then generates an electrical signal containing the data you've searched for. The data is then transferred to the DNS server via your cell tower and fibre optic connections. The DNS server then looks for "http://www.example.com"'s IP address.  The specific request (together with the IP address) is then forwarded to the webserver. The Webserver then sends HTML files (request files of a particular website) to the computer that generated the request. HTML, CSS, and JavaScript files are all transmitted to the ...

It is quite simple: you'll need a modem to connect your device to the internet. Modem  performs proper modulation and demodulation. Actually, you could think of it this way: whatever data you're browsing, the search results comes from a web server or data server. That portion of internet is referred to as the core network. In most cases, your laptop generates digital data. However, communication mediums include wireless channels, coaxial cables, and fiber optics etc., are analogue in nature. A modem is required to convert analogue to digital data and vice versa. You just need a modem if you simply need to connect one device to the internet. A router is required if you want to connect several devices.  Even then, a modem is necessary. Now we'll talk about how a router works. A modem and a router serve different purposes. As an interference between your computer and the core network, a modem is required. Because internet data signals are analog, and your computer can only ...

  'Modem' is the abbreviation of modulation and demodulation . The importance of modulation and demodulation in a communication system has already been discussed. We usually use a modem when we need to connect our laptops to cellular networks. If you think this is the only modem application, you are wrong. Almost all devices require a modem or router to connect to the internet. Even your cell phone contains a modem. We usually use a telecommunication line, cable, or fiber optics to connect one cell tower to another. Copper wires were commonly used in the past. Fiber optics has since taken its place. The only wireless connection is between your device and the cell tower. Now we'll talk about what modems do. As we know, communication mediums like — wireless channels, cables, telecommunication lines, fiber optics, etc. - are all analog in nature.   Digital data cannot be sent directly to analog mediums. We convert digital data / quantized digital into analog waveforms via mo...

Cellular wireless evolution Generation Frequency band PHY features Data rate Spectral Eff. (bps/Hz) 1G 850 MHz FDMA, FM N/A N/A 2G 900 MHz, 1.8 GHz TDMA/CDMA, GMSK/QPSK, FEC, PC 10 Kbps < 1 3G 1.8–2.5 GHz CDMA, QAM 1–40 Mbps 1–8 4G 2–8 GHz OFDMA, SC-FDMA, QAM, MIMO-OFDM 100–600 Mbps 15 5G 1–6 GHz mm wave (26–28 GHz) < 1 GHz (massive IoT) visible light? massive MIMO, beamforming D2D, Full duplex, NOMA LDPC and Polar codes OFDM & variants (adapted to extremes?) multi-Gbps several tens Waveform design is the major change between the generations Mobile Wireless Generations Specifications  1G  Voice, Analog traffic, FDMA  2G  Voice, SMS, CS data ...