4G: LTE and WiMAX
Fourth generation mobile networks brought all-IP architecture, OFDMA modulation, and data rates up to 1 Gbps. LTE became the dominant global standard, enabling the smartphone app ecosystem.
The LTE Revolution
Long Term Evolution (LTE) was not merely an incremental improvement over 3G—it represented a complete architectural shift. Unlike its predecessors which carried both voice and data on circuit-switched networks, LTE was designed from the ground up as an all-IP (Internet Protocol) network. This "voice over LTE" (VoLTE) approach meant that all services, including voice calls, were treated as data packets.
The choice of OFDMA (Orthogonal Frequency Division Multiple Access) as the downlink modulation scheme was crucial. Unlike CDMA used in 3G, OFDMA allows multiple users to share the spectrum efficiently by assigning each user a subset of subcarriers. This provided better spectral efficiency, reduced interference, and enabled higher data rates.
Technical Specifications
- Peak Download: 100 Mbps (Release 8) to 1 Gbps (Release 10+)
- Peak Upload: 50 Mbps
- Latency: 10-30 ms (compared to 100-500 ms on 3G)
- Channel Bandwidth: 1.4 MHz to 20 MHz
- Frequency Bands: Numerous bands from 700 MHz to 2.6 GHz
- Multiple Antenna: 2x2 MIMO standard, up to 8x8 in Release 10
WiMAX: The Competing Standard
While LTE became the global standard, WiMAX (IEEE 802.16) was its primary competitor in the early 2000s. WiMAX offered similar capabilities and was deployed by providers like Clearwire in the United States. However, LTE's backing by virtually all major GSM carriers and its evolution path eventually made it the dominant technology. WiMAX was effectively phased out by 2015, though its influence on broadband wireless persists.
Carrier Aggregation
A key feature introduced in LTE-Advanced (Release 10) was carrier aggregation, allowing operators to combine multiple frequency bands for even higher data rates. By aggregating 5 carriers of 20 MHz each, theoretical peaks of 1 Gbps became possible. This technique is now standard in 4G networks worldwide.
Global Impact
By 2015, LTE had become the fastest-growing mobile technology in history, with over 1 billion subscribers. The smartphone ecosystem truly exploded with 4G—the iPhone 5 (2012) was the first to support LTE, and by the iPhone 6, LTE was standard. Apps requiring constant connectivity—video streaming (Netflix, YouTube), social media, real-time gaming—all flourished on 4G networks.
VoLTE and语音
The transition to all-IP networks required new solutions for voice. VoLTE (Voice over LTE) emerged as the standard, using AMR-WB (Adaptive Multi-Rate Wideband) codec for HD voice quality. Carriers initially deployed circuit- switched fallback (CSFB), temporarily switching to 3G for voice calls, before fully implementing VoLTE networks.