These notes surveys wireless links and mobility, the cellular paradigm from coverage to resource reuse, and the evolution from 1G to 5G. They detail GSM architecture and channels, LTE/E-UTRAN and EPC functions, bearer concepts, and mobility procedures including roaming and handover. They also introduce 5G objectives, Service-Based Architecture (SBA), Multi-access Edge Computing (MEC), and New Radio (NR) features such as massive MIMO and beamforming. The closing section reviews IEEE 802.11 WLAN architecture, association, CSMA/CA, and frame structure.
Learning objectives:
Wireless/mobile subscriptions and mobile-broadband devices outnumber fixed counterparts. Modern 4G/5G stacks embrace Internet protocols and Software-Defined Networking (SDN). Two distinct challenges arise: the wireless link itself and mobility as a user changes point of attachment.
A wireless network comprises:
Infrastructure mode attaches mobiles to the wired network via base stations with handoff; ad hoc mode has nodes self-organize and route without base stations.
Compared with wired links, wireless suffers decreased signal strength (path loss), interference from other devices (e.g., 2.4 GHz band), and multipath propagation causing time-dispersed replicas. Signal-to-noise ratio (SNR) governs bit error rate (BER) and throughput: higher power raises SNR and reduces BER for a fixed physical layer; for a given SNR one selects a physical layer (e.g., BPSK, QAM16, QAM256) meeting BER with maximal throughput. Mobility drives dynamic adaptation of modulation and rate.
Hidden terminals and attenuation create collisions unseen by some senders, complicating multiple access.
A cellular network tessellates geography into adjacent or overlapping cells, allowing terminals to move with handover. Idealized models place isotropic antennas at cell centers with hexagonal cells, or three 120° sectors per site; practical deployments exhibit irregular shapes and sizes determined by power, height, gain, morphology, fading, and propagation.