Wprowadzenie do WiMAX

Worldwide Interoperability for Microwave Access technology.

1. What is WiMAX? The Vision of Wireless Broadband for Everyone

WiMAX, which stands for Worldwide Interoperability for Microwave Access, is a wireless communications standard designed to provide high-speed broadband access over long distances. At its core, WiMAX was conceived as a technology to solve the "last mile" problem.

The refers to the final segment of a network that connects the main internet backbone, which runs between cities and countries, to individual homes and businesses. Historically, this last mile was dominated by physical cables: the copper telephone lines used for DSL and the coaxial cables used for cable internet. Laying these cables is an expensive and time-consuming process, especially in rural, remote, or geographically challenging areas.

WiMAX was developed to offer a wireless alternative. The vision was to create a technology that could deliver internet speeds comparable to DSL and cable, but without the need to dig trenches and lay physical wires to every building. It was designed to provide broadband access over an entire metropolitan area, blanketing a city with high-speed internet accessible from homes, businesses, and eventually, mobile devices.

2. WiMAX vs. Wi-Fi vs. Cellular (LTE): Understanding the Differences

To fully grasp the role WiMAX was intended to play, it is helpful to compare it to the two other major wireless technologies: Wi-Fi and Cellular (like LTE).

Wi-Fi (IEEE 802.11)

Purpose: Designed for Wireless Local Area Networks (WLANs). It is meant to provide high-speed internet access in a relatively small, localized area like your home, an office, or a coffee shop.

Range: Very short, typically tens of meters.
Spectrum: Operates in unlicensed frequency bands (like 2.4 GHz and 5 GHz), which means anyone can set up a Wi-Fi network without a government license, but it also means it is susceptible to interference from other Wi-Fi networks and devices.

WiMAX (IEEE 802.16)

Purpose: Designed for Wireless Metropolitan Area Networks (WMANs). It aims to provide broadband coverage over a much larger area, covering several square kilometers from a single base station.

Range: Much longer than Wi-Fi, typically several kilometers. In some fixed, line-of-sight configurations, it could reach tens of kilometers.
Spectrum: Designed to operate in licensed frequency bands, meaning an operator must purchase the rights to use that spectrum. This guarantees a higher quality of service with less interference.

Cellular LTE (4G)

Purpose: Designed for nationwide mobile communication, supporting seamless handovers between cells for users in high-speed motion (e.g., in cars and trains).

Range: Similar to WiMAX, covering several kilometers from a base station.
Spectrum: Also operates in licensed spectrum.
Key Differentiator: The primary design focus of cellular technology is robust mobility support and ubiquitous national and international coverage, something that was an evolutionary add-on for WiMAX rather than a day-one design goal.

3. The Standardization Behind WiMAX: IEEE 802.16

The technology behind WiMAX is formally defined by the in its 802.16 family of standards. The journey of this standard shows a clear evolution from a fixed wireless technology to a fully mobile broadband solution.

IEEE 802.16 (2001) - The Original Vision

The first version of the standard was designed for Fixed Wireless Access (FWA). It was intended as a wireless alternative to cable and DSL for stationary users, such as homes and businesses. This initial version had one significant limitation: it required a path between the subscriber's antenna and the provider's base station. This meant an installation technician had to carefully mount an outdoor antenna on a rooftop and aim it precisely at the tower, which limited its practical deployment. It operated in a very high frequency band from 10 to 66 GHz.

IEEE 802.16-2004 - The Breakthrough

This revised standard, which incorporated earlier amendments like 802.16a, was a game-changer. It introduced two critical improvements:

Lower Frequency Bands: It specified operation in lower frequency bands, between 2 and 11 GHz. Lower frequency signals are much better at penetrating obstacles and do not require a direct line of sight.
Non-Line-of-Sight (NLOS) Capability: Thanks to the lower frequencies and the introduction of advanced radio technologies like OFDMA, this version could provide a reliable connection even when obstacles blocked the direct path between the base station and the user. This made deployment dramatically easier and cheaper. A user could now potentially use a self-installed indoor modem, much like a cable or DSL modem. This standard is what most early "Fixed WiMAX" deployments were based on.

IEEE 802.16e-2005 - The Mobile Revolution (Mobile WiMAX)

This amendment was the most significant step in the evolution of WiMAX, as it added full mobility support. While previous versions were for stationary or nomadic users, IEEE 802.16e introduced mechanisms for seamless between base stations. This allowed users to maintain a connection while moving at high speeds, for example in a vehicle. It transformed WiMAX from purely a fixed wireless access technology into a true mobile broadband solution, placing it in direct competition with emerging 4G cellular technologies like LTE. This standard is often referred to as "Mobile WiMAX."

The WiMAX Forum

While the IEEE developed the technical standard, an industry alliance called the WiMAX Forum was created to promote the technology and ensure interoperability. The WiMAX Forum's role was to test and certify that equipment from different vendors complied with the standard and could work together. This certification process was crucial for building a healthy ecosystem of compatible devices and infrastructure, much like the role the Wi-Fi Alliance plays for Wi-Fi products.

4. The Core Technology: How WiMAX Works

The high performance and robustness of WiMAX are thanks to a set of advanced radio technologies that it shares with its contemporary, LTE. The core of the WiMAX radio interface is OFDMA.

OFDMA (Orthogonal Frequency-Division Multiple Access)

WiMAX was one of the first major wireless standards to be built from the ground up on OFDMA. As explained in the context of LTE, OFDMA is a highly efficient way to manage a wide frequency channel. Instead of transmitting a single high-speed stream of data, the data is split into thousands of slower streams, each transmitted on its own closely spaced .

Multipath Resilience: This parallel transmission structure makes OFDMA inherently robust against multipath fading and Inter-Symbol Interference (ISI), which is a major problem in urban environments.
Flexible Allocation: OFDMA allows the base station to dynamically allocate different groups of subcarriers to different users based on their needs, providing great flexibility in managing bandwidth.

Scalable OFDMA (SOFDMA)

Mobile WiMAX (IEEE 802.16e) uses a specific variant called SOFDMA. The "Scalable" part refers to its ability to adapt its parameters based on the available channel bandwidth. Operators might deploy WiMAX in different channel sizes, for example 5 MHz, 7 MHz, or 10 MHz. SOFDMA allows the system to scale its size, which in turn changes the number of subcarriers used. For example, a system could use a 512-point FFT for a 5 MHz channel or a 1024-point FFT for a 10 MHz channel. This scalability allows the standard to be efficiently adapted to various regulatory domains and spectrum allocations around the world.

MIMO (Multiple-Input Multiple-Output)

WiMAX was also an early adopter of MIMO technology. By using multiple antennas at the base station and the subscriber station, WiMAX could significantly improve its performance through spatial multiplexing (sending multiple data streams for higher speed) or transmit diversity (sending the same data over multiple paths for higher reliability).

5. The WiMAX Network Architecture

The overall WiMAX network is also designed with a clear, layered structure, comprising the user devices, the access network, and the core network.

Subscriber Station (SS/MS)

This is the user's device. For fixed WiMAX, this was typically an outdoor antenna or an indoor desktop modem. For Mobile WiMAX, this became a USB dongle, a PC card, or eventually, a chip integrated into a laptop or a mobile phone.

Access Service Network (ASN)

This is the WiMAX equivalent of the Radio Access Network. It consists of two main parts: the Base Stations (BS) that provide the radio coverage, and the ASN Gateway (ASN-GW), which acts as a control point, managing handovers and connecting the radio network to the core.

Connectivity Service Network (CSN)

This is the WiMAX core network. It is an All-IP network responsible for providing IP connectivity, authenticating users (via an AAA server), and connecting the WiMAX network to the internet or other networks. It is the brain that manages the user's internet session.

6. The Rise and Fall: Why WiMAX Lost to LTE

In the mid-2000s, there was a fierce battle to determine which technology would become the global standard for 4G. For a time, WiMAX was a major contender and even had a head start in deployments, with operators like Clearwire in the United States building out large networks. However, ultimately, LTE emerged as the dominant global standard.

The Battle of Ecosystems

The outcome was not decided purely on technical merit. Technologically, Mobile WiMAX and LTE are very similar; they are cousins built on the same foundational OFDMA and MIMO principles. The decisive factor was the business and industry ecosystem behind each technology.

LTE's Backing: LTE was developed by the 3GPP, a partnership of the world's most powerful and established cellular standards organizations (the GSMA). It had the full backing of the vast majority of existing mobile operators (like Verizon, AT&T, Vodafone) and equipment manufacturers (like Ericsson and Nokia). For these companies, LTE was the clear and natural evolutionary path from their massive existing 2G (GSM) and 3G (UMTS) networks.
WiMAX's Backing: WiMAX was championed more by the computing and data industries, with Intel being one of its strongest proponents. While it had support from some operators, it lacked the unified, global backing of the established cellular world.
Seamless Evolution and Roaming: The established cellular ecosystem gave LTE a crucial advantage. Operators could offer their customers a device that could seamlessly "fall back" to their vast 2G/3G networks in areas where 4G LTE was not yet available. This provided a much smoother transition path and guaranteed ubiquitous connectivity. WiMAX, being a newer technology without this deep legacy, could not offer the same seamless roaming experience.
Economies of Scale: Once the global cellular industry unified behind LTE, it created enormous economies of scale. The massive production volume of LTE chips and infrastructure equipment drove down costs rapidly. WiMAX could not compete with the sheer scale and momentum of the global LTE ecosystem.

The Legacy of WiMAX

Though it did not become the global standard for mobile broadband, WiMAX was far from a failure. Its technology was sound, and its influence is still felt. Many of the core concepts proven by WiMAX were adopted and refined in LTE and 5G. Furthermore, WiMAX found a lasting and successful niche in other markets, particularly for providing Fixed Wireless Access (FWA). Many Wireless Internet Service Providers (WISPs) around the world still use WiMAX-based technology to deliver reliable broadband internet to homes and businesses in rural areas where laying fiber or cable is not economically feasible.