Mobile computing is computing that moves with the user: phones, tablets, wearables and vehicles, connected by wireless networks. The subject covers how mobile networks actually work (cells, handovers, radio sharing), how Internet protocols cope with a moving device, and how mobile software is built. For a cloud engineer it explains why mobile clients behave differently from desktops: variable latency, dropped connections, battery limits. This article revisits the five units of the JNTUK course.
Unit 1: Introduction and wireless fundamentals
What makes mobility hard
| Challenge | Effect |
|---|---|
| Wireless channel | Lower and varying bandwidth, higher error rates, interference |
| Mobility | Changing location and network attachment |
| Portability | Limited battery, small screen, limited CPU and storage |
| Security | Open radio medium, lost devices |
| Heterogeneity | Many devices, platforms and networks |
Applications can be location-aware, context-aware and often disconnected for periods, so apps must cache data and synchronise later.
Radio propagation
Signals suffer attenuation (path loss grows with distance), reflection, diffraction, scattering, shadowing and multipath fading (copies of the signal arrive at slightly different times and combine badly). The Doppler effect shifts frequency when moving. Techniques to cope: diversity (several antennas), equalisation, spread spectrum, error-correcting codes and MIMO (multiple antennas for higher rate or reliability).
Modulation and multiplexing
Digital modulation (BPSK, QPSK, QAM) carries data on the radio signal. Sharing the channel among many users uses multiplexing:
| Method | Splits by | Used in |
|---|---|---|
| FDMA | Frequency | Early analog cellular |
| TDMA | Time slots | GSM |
| CDMA | Spreading codes | 3G (UMTS, CDMA2000) |
| OFDMA | Many orthogonal subcarriers across users | 4G LTE and 5G, Wi-Fi 6 |
Spread spectrum (frequency hopping, direct sequence) resists interference and is used in CDMA and Bluetooth.
Today: an app that works well on office Wi-Fi may stall on a moving train: the wireless channel’s variability is the reason mobile apps use retries, caching, compression and offline modes. OFDM and MIMO are in every modern phone and router.
Unit 2: Cellular networks and mobile generations
The cellular idea
The service area is divided into cells, each with a base station. Because the same frequencies are reused in cells far enough apart (the reuse distance), the system serves many more users than a single large transmitter could. Cells can be split (cell splitting) and sectored to add capacity. Interference between cells using the same frequency is co-channel interference.
Mobility management
| Function | Meaning |
|---|---|
| Location management | The network tracks which area a phone is in (location area updates, paging to reach it) |
| Handover (handoff) | Switching a call or session from one cell to another as the user moves: hard (break before make) or soft (make before break, in CDMA) |
| Roaming | Service in another operator’s network, using home and visitor registers |
| Authentication and billing | SIM-based identity |
GSM architecture
The classic second-generation system:
| Part | Role |
|---|---|
| MS (mobile station) | The phone, with a SIM card |
| BTS and BSC | Base transceiver station and controller (radio side) |
| MSC | Mobile switching centre: connects calls |
| HLR / VLR | Home and visitor location registers |
| AuC / EIR | Authentication centre; equipment identity register |
GSM uses TDMA and FDMA, encrypts the radio link and supports SMS. GPRS and EDGE added packet data.
Generations
| Generation | Technology | Key feature |
|---|---|---|
| 1G | Analog | Voice only |
| 2G | GSM, CDMA | Digital voice, SMS |
| 3G | UMTS, HSPA | Mobile Internet |
| 4G | LTE | All-IP, OFDMA, high-speed broadband |
| 5G | New Radio (NR) | Very high speed, low latency, huge numbers of devices; network slicing and edge computing; uses sub-6 GHz and millimetre-wave bands |
In LTE and 5G the core network is IP-based (the EPC and the 5G core), and many functions are virtualised and run as software on cloud infrastructure.
Today: the 5G core is a set of cloud-native microservices running on Kubernetes, so telecom operators run the same platform tools. Latency-sensitive applications (gaming, industrial control) are why edge computing and multi-access edge computing (MEC) exist.
Unit 3: Wireless LANs and medium access
MAC problems in wireless
Wireless nodes cannot hear collisions while they transmit, and the hidden terminal problem (two nodes cannot hear each other but both reach a third) and the exposed terminal problem make plain CSMA unreliable. CSMA/CA (collision avoidance) with a random backoff and optional RTS/CTS handshake is used.
IEEE 802.11 (Wi-Fi)
| Standard | Name | Band | Notes |
|---|---|---|---|
| 802.11b | 2.4 GHz | 11 Mbit/s | |
| 802.11a / g | 5 / 2.4 GHz | 54 Mbit/s, OFDM | |
| 802.11n | Wi-Fi 4 | 2.4 / 5 GHz | MIMO |
| 802.11ac | Wi-Fi 5 | 5 GHz | Wider channels, MU-MIMO |
| 802.11ax | Wi-Fi 6 / 6E | 2.4, 5, 6 GHz | OFDMA, better in crowds |
| 802.11be | Wi-Fi 7 | 2.4, 5, 6 GHz | Multi-link operation, very high rates |
A network has access points (APs) and stations, in infrastructure mode (through an AP) or ad hoc mode. A BSS is one AP and its clients, an ESS links several. Security has progressed from the broken WEP to WPA2 (AES-CCMP) and WPA3.
Other short-range technologies
| Technology | Range and use |
|---|---|
| Bluetooth / BLE | Personal area, low power: headphones, wearables, beacons |
| Zigbee, Thread | Low-power mesh for smart homes |
| NFC | A few centimetres: payments |
| UWB | Precise location |
| WiMAX | Older wireless metropolitan access (superseded by LTE) |
Today: Wi-Fi roaming between access points, channel planning and “5 GHz is faster but shorter range” are everyday wireless topics. Office and data-centre access networks use controllers and cloud-managed APs, and a congested 2.4 GHz band is a frequent cause of “slow Wi-Fi”.
Unit 4: Mobile network and transport layers, ad hoc networks
Mobile IP
When a device moves to a new network, its IP address would normally change and break connections. Mobile IP keeps a fixed address:
| Term | Role |
|---|---|
| Home agent (HA) | A router on the home network that receives packets for the mobile node |
| Foreign agent (FA) | A router on the visited network |
| Home address | The permanent address used by others |
| Care-of address (CoA) | The temporary address in the visited network |
| Tunnelling | The HA encapsulates packets and forwards them to the CoA |
Triangular routing (traffic goes via the home agent) is inefficient and is improved by route optimisation. IPv6 has built-in support for mobility.
Mobile TCP
TCP treats packet loss as congestion and slows down, but in wireless networks loss is often due to a bad radio link or handover. This wrongly cuts throughput. Solutions:
| Approach | Idea |
|---|---|
| Indirect TCP (I-TCP) | Split the connection at the base station |
| Snooping TCP | The base station caches and retransmits locally, hiding wireless loss |
| Mobile TCP (M-TCP) | Freezes the sender during disconnection |
| Selective retransmission, fast retransmit | Recover from loss without a long timeout |
| QUIC / HTTP/3 | Connection migration across networks, better loss handling |
Ad hoc and sensor networks
A mobile ad hoc network (MANET) has no fixed infrastructure: nodes move and forward packets for each other (multi-hop). Routing is hard because the topology changes:
| Type | Protocols |
|---|---|
| Proactive (table-driven) | DSDV, OLSR: maintain routes all the time |
| Reactive (on-demand) | AODV, DSR: discover a route only when needed |
| Hybrid | ZRP |
Wireless sensor networks (many tiny, battery-powered nodes) stress energy-efficient routing and data aggregation. Vehicular networks (VANET) and delay-tolerant networks are related areas.
Today: a phone switching from Wi-Fi to mobile data keeps its apps working because modern protocols (QUIC, long-lived sessions with reconnect logic, push notification services) tolerate address changes, not because of Mobile IP itself. Mesh Wi-Fi and Bluetooth mesh use multi-hop forwarding.
Unit 5: Mobile platforms, data management and applications
Mobile operating systems and architecture
| OS | Notes |
|---|---|
| Android | Linux-based; apps in Kotlin or Java; APK/AAB packages; Google Play |
| iOS | Apps in Swift or Objective-C; sandboxed; App Store review |
| Cross-platform | Flutter (Dart), React Native, Kotlin Multiplatform, progressive web apps |
An Android app’s main components are Activities (screens), Services (background work), Broadcast receivers (system events) and Content providers (shared data); the manifest declares them and the permissions needed. The activity life cycle (created, started, resumed, paused, stopped, destroyed) matters because the OS can kill apps to save memory. Permissions (location, camera, contacts) are requested at run time.
Design constraints
| Constraint | Response |
|---|---|
| Battery | Batch network calls, avoid wake-locks, use push instead of polling |
| Intermittent connectivity | Offline-first design, local database (SQLite, Room), sync queues and conflict resolution |
| Small screen and touch | Responsive layout, large targets |
| Variable network | Compression, caching, retries with back-off, pagination |
| Fragmentation | Many devices and OS versions; test matrices |
Data management
Data synchronisation between device and server, caching and replication, conflict resolution (last-write-wins, merge), data broadcasting and mobile database issues (location-dependent queries, limited storage). Context- and location-aware services use GPS, Wi-Fi and cell data.
Mobile security and services
Device loss and theft (remote wipe, encryption), app permissions and malicious apps, secure storage (keychain/keystore), certificate pinning, mobile device management (MDM) for companies, and biometric authentication. Push notifications (FCM, APNs) deliver messages without polling. Mobile payments (UPI, NFC wallets) tie into the E-Commerce subject.
The back end of a mobile app
A mobile app is typically a thin client over REST/JSON or GraphQL APIs, with authentication by tokens (OAuth 2.0), a CDN for media, push and analytics services, and crash reporting. Releases go through app stores and staged rollouts; an old app version may be in use for months, so the API must stay backward compatible.
Today: DevOps for mobile includes CI builds (Fastlane, GitHub Actions, Bitrise), signing keys, store releases, feature flags, remote config and crash analytics (Firebase Crashlytics, Sentry). Server-side, API versioning and backward compatibility, rate limiting and efficient pagination are shaped by the mobile constraints described here.
One-minute recap
| Unit | Key idea | You meet it in |
|---|---|---|
| 1. Wireless fundamentals | Fading, multipath, FDMA/TDMA/CDMA/OFDMA, MIMO | Retries, caching, variable mobile latency |
| 2. Cellular networks | Cells, frequency reuse, handover, GSM to 5G | 5G core on Kubernetes, edge computing |
| 3. WLANs and MAC | CSMA/CA, hidden terminal, Wi-Fi 4 to 7, Bluetooth | Wi-Fi roaming, channel planning |
| 4. Mobile IP, TCP, ad hoc | Home and foreign agents, snooping TCP, AODV | QUIC, connection migration, mesh networks |
| 5. Mobile platforms and apps | Android components, offline-first, sync, push | Mobile CI/CD, API versioning, crash analytics |
Next in Engineering Revisited: Multimedia & Application Development.
Written by Claude, Anthropic’s AI assistant, as part of Engineering Revisited, a quick refresher of the B.Tech subjects one at a time.