Cellular: What It Is, 4G and 5G Generations and How It Works

What Is Cellular Communication?

Cellular communication — a mobile radio communication standard based on dividing the territory into cells, each served by a base station (BS). When the device moves, a handover occurs — automatic switching between cells without connection interruption. Cells vary in size: macrocells (10–50 km) for rural areas, microcells (200–2000 m) for cities, femtocells (up to 50 m) for indoors.

The cellular network architecture includes three main components: User Equipment (UE) — a smartphone or modem; Radio Access Network (RAN) — a set of base stations with antennas; Core Network — routing, authentication, billing, and internet connection. Different generations differ in Core Network structure and radio signal modulation methods.

Unlike Wi-Fi, cellular networks use licensed frequencies — each operator receives exclusive bands at auctions. This guarantees no interference between operators but limits the speed of new standard deployment due to the need for frequency reallocation.

Cellular Generations: From 2G to 5G

Each cellular generation (N-G) brought exponential speed growth and new use cases. 2G (GSM) first digitized voice and introduced SMS. 3G (UMTS, HSDPA) opened mobile internet to the mass user. 4G LTE fully switched to IP packets, abandoning circuit switching. 5G NR focused on ultra-low latency and network division into virtual segments.

Mobile OSes determine the current network generation through the radio interface. On Android, TelephonyManager.getDataNetworkType() is available, returning NETWORK_TYPE_LTE or NETWORK_TYPE_NR constants. iOS provides CTTelephonyNetworkInfo with the serviceCurrentRadioAccessTechnology property.

4G LTE Architecture: EPC, eNB and Overlay Networks

4G LTE is based on a flat all-IP architecture divided into Evolved Packet Core (EPC) and Evolved Node B (eNB). eNB is a base station combining radio communication and basic routing functions. EPC consists of MME (Mobility Management Entity), SGW (Serving Gateway for data exchange with eNB), and PGW (Packet Gateway to the internet).

OFDMA (Orthogonal Frequency Division Multiple Access) — the key LTE technology: frequency resources are divided into subcarriers, each assigned to a specific user. 4×4 MIMO allows sending up to 4 independent data streams on one frequency. Carrier Aggregation combines up to 5 carrier frequencies, increasing bandwidth by 5 times.

Overlay networks — LTE-Advanced and LTE-Advanced Pro — added CoMP (coordinated transmission from multiple eNBs) and LAA (LTE in the unlicensed 5 GHz band). For developers, these improvements are transparent: the modem driver automatically uses available technologies without changing application code.

Example of Getting Network Type in Kotlin (Android)

fun getCellularType(context: Context): String {
    val tm = context.getSystemService(Context.TELEPHONY_SERVICE)
        as TelephonyManager
    return when (tm.dataNetworkType) {
        TelephonyManager.NETWORK_TYPE_NR -> "5G"
        TelephonyManager.NETWORK_TYPE_LTE -> "4G LTE"
        TelephonyManager.NETWORK_TYPE_HSPAP -> "3G HSPA+"
        else -> "2G/Unknown: ${tm.dataNetworkType}"
    }
}

The function obtains TelephonyManager and determines the active network type. On Android 10+, accessing dataNetworkType requires the READ_PHONE_STATE permission, and starting from Android 11 — only for apps installed as a call or SMS handler.

5G NR: Sub-6 and mmWave, Network Slicing, SA vs NSA

5G NR (New Radio) — a radical physical layer upgrade compared to LTE. The standard operates in two frequency ranges: FR1 (Sub-6, 1–6 GHz) for mass coverage and FR2 (mmWave, 24–52 GHz) for ultra-high speeds over short distances. mmWave requires a direct line of sight to the antenna — even tree foliage causes attenuation of up to 30 dB.

Two deployment modes: NSA (Non-Standalone) — 5G NR works with an LTE Core to accelerate launch, and SA (Standalone) — a fully autonomous 5G Core Network with Network Slicing support. Network Slicing divides physical infrastructure into virtual segments: one slice for IoT (low speed, ultra-low power consumption), another for autonomous vehicles (latency < 1 ms).

For mobile applications, 5G means not only speed but also new power consumption behavior: mmWave modules consume up to 2 W in active mode (versus 0.5 W for LTE). When developing for 5G, it is recommended to consider that frequent data transmission in mmWave quickly drains the battery — it is optimal to buffer data and send it in batches in the Sub-6 range.

Example of 5G NSA/SA Check in Swift (iOS)

import CoreTelephony

func check5GStatus() -> String {
    let info = CTTelephonyNetworkInfo()
    guard let tech = info.serviceCurrentRadioAccessTechnology
        ?.values.first else { return "No cellular" }

    if tech == CTRadioAccessTechnologyNRNSA {
        return "5G NSA"
    } else if tech == CTRadioAccessTechnologyNR {
        return "5G SA"
    } else {
        return "LTE or 3G: \(tech)"
    }
}

iOS via CoreTelephony reports the active connection type: CTRadioAccessTechnologyNR for SA (pure 5G) and CTRadioAccessTechnologyNRNSA for NSA (5G with LTE core). This information helps adapt app behavior — for example, loading heavy content only in SA mode with low latency.

Cellular in Mobile Apps: Network Type Detection and Signal Loss Handling

A mobile app can adapt its behavior based on the type and quality of the cellular connection. ConnectivityManager (Android) and NWPathMonitor (iOS) notify the app about network changes — switching from Wi-Fi to Cellular, signal loss, or 5G availability.

Key handling scenarios:

• Content downloading — when switching to cellular, limit the size of downloaded files (Android NetworkCapabilities.NET_CAPABILITY_NOT_METERED)
• Streaming — adapt video bitrate based on speed determined through bandwidth estimation (Android bandwidth estimate)
• Background sync — postpone synchronization on weak signal (RSSI < -110 dBm) to save battery and data
• Emergency fallback — on cellular signal loss, switch to the last cached data version and schedule a retry with exponential backoff

RSSI (Received Signal Strength Indicator) — the main cellular signal quality metric. Values range from -50 dBm (excellent signal) to -120 dBm (almost no network). Android provides RSSI access via SignalStrength.getLevel(), iOS — via CTCarrier (limited access).

Example of Cellular Network Monitoring in Swift (iOS)

import Network

let monitor = NWPathMonitor()
monitor.pathUpdateHandler = { path in
    if path.usesInterfaceType(.cellular) {
        print("Cellular network active")
        if path.isExpensive {
            print("Metered connection — limit traffic")
        }
    }
}
monitor.start(queue: .main)

NWPathMonitor from the Network framework monitors the connection type (cellular, wi-fi, wired) and the isExpensive flag, indicating a metered connection. On iOS, this is the primary way to adapt app behavior to the current network type without direct access to the radio interface.

Choosing a Plan and Carrier: Impact on App Performance

Although the app does not control carrier selection, understanding different plan characteristics helps the developer make decisions. APN (Access Point Name) — a gateway between the cellular network and the internet. Different APNs (internet, ims, mms) provide different QoS — the voice APN (IMS) has priority over internet traffic.

Modern operators are introducing DNN (Data Network Name) in 5G SA — an APN analog with the ability to segment by requirements: ultra-reliable low-latency (URLLC), enhanced mobile broadband (eMBB), massive IoT (mMTC). The developer does not choose the slice directly, but the app can request a specific QoS through 5G QoS Identifier (5QI) when using Network Slicing.

Recommendations for the developer: check connection availability via NetworkInfo.isConnectedOrConnecting before sending data; set request timeouts to at least 30 seconds for cellular networks (TCP session establishes more slowly under weak signal); use background tasks (WorkManager, BGTaskScheduler) for synchronization only when connected to Wi-Fi or an unlimited plan.