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Worldwide Interoperability for Microwave Access (WiMAX) digital communications technology is based on wireless transmission methods defined by the IEEE-802.16 air interface standard. Intended for wireless metropolitan area networks, it provides broadband wireless access up to 30 miles for fixed stations, and 3 to 10 miles for mobile stations. WiMAX has a range of potential uses, including providing high-speed mobile data and telecommunications services (such as 4G), as a wireless alternative to cable and DSL for last mile broadband access, and to connect Wi-Fi hotspots with each other and to other parts of the Internet.
The 802.16 air interface standard supports fixed, nomadic, portable and mobile access (Table 1). To meet the requirements of different types of access, two versions of WiMAX have been defined. The first, IEEE 802.16-2004 (fixed WiMAX), is optimized for fixed and nomadic broadband wireless access to homes and businesses. This point-to-multipoint version specifies WiMAX for systems in the 10 to 66 GHz and sub 11-GHz frequency ranges. The second version, IEEE 802.16e (mobile WiMAX), is designed to support portability and mobility and offers the full mobility of cellular networks at true broadband speeds. Both fixed and mobile applications of WiMAX are engineered to help deliver ubiquitous, high-throughput broadband wireless services at a low cost.
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Table 1. Types of Access to a WiMAX network.
This How To article focuses on the measurement procedures for fixed WiMAX networks. Its objective is to present practical field measurement tips and procedures which will help a field-based network technician or RF engineer conduct measurements on WiMAX networks.
Understanding WiMAX Technology
The 802.16 broadband wireless access (BWA) standard is designed to provide increased bandwidth and range, efficient bandwidth interference avoidance, and stronger encryption. Conformance and interoperability of the standard is overseen by the WiMAX Forum . In favorable circumstances, wireless connectivity is possible between network endpoints without the need for direct line of sight. Non-line-of-sight propagation (NLOS) performance is also possible and relies on a clever use of multi-path signals.
Some of the main advantages of WiMAX networks include:
- Higher data rates over a longer distance. Thanks to good antenna technology, the WiMAX transmitting station can send data to WiMAX-enabled computers or routers set up within the transmitter's 30-mile radius.
- Operates on both licensed and non-licensed frequencies. Consequently, WiMAX provides a regulated environment and viable economic model for wireless carriers.
- The lower frequencies of 802.16-2004 and 802.16e suffer less from signal attenuation and therefore give improved range and in-building penetration.
- WiMAX offers better coverage, easier self installation, reduced power consumption, frequency re-use and bandwidth efficiency. The mobile version also adds a capability for full mobility support.
Because 802.16 was designed to cover application to diverse markets it contains allowances for a number of physical layers to accommodate different frequency bands and region-by-region frequency regulatory rules. These options may leave implementers facing some tough decisions. To address this issue and help speed WiMAX adoption in real-world networks, the WiMAX Forum has created a limited number of system profiles. These profiles specify which features are mandatory or optional for the various MAC or PHY scenarios that are most likely to arise in the deployment of real WiMAX systems. As a result, vendors addressing the same market can build systems for that market which are interoperable but that do not require the implementation of absolutely every feature.
The choice of profiles is driven by market demand, spectrum availability, regulatory constraints, the services to be offered, and vendor interest. For example, the availability of spectrum for BWA services in several countries motivated the creation of profiles in the 3.5-GHz band. By the same token, the availability of license-exempt spectrum and demand for fixed services drove the creation of a profile in the 2.4-MHz and 5.8-GHz bands.
A list of fixed WiMAX system profiles is specified in Table 2. Here, the most globally harmonized band is the licensed 3.5 GHz band (3400 - 3600 MHz).
Table 2. Fixed WiMAX Initial Profiles (source: WiMAX Forum).
A list of Release-1 mobile WiMAX profiles is provided in Table 3. These profiles cover a range of channel bandwidths for licensed worldwide spectrum allocations in the 2.3, 2.5, 3.3 and 3.5 GHz frequency bands. Selection of frequency for mobile WiMAX deployment directly affects the quality and cost of the network. Lower frequency bands are generally preferred as they offer lower attenuation and longer reach which, in turn, leads to a smaller number of required cells to provide mobility coverage. The most preferred bands of many would-be mobile WiMAX operators today are between 1.9 GHz and 2.1 GHz. These bands, though, have already been assigned to 3G operators. There is also a growing interest in the 700 - 800 MHz bands traditionally used by analog TV broadcast, but it is unclear when these bands will be completely vacated.
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Table 3. Release-1 Mobile WiMAX System Profiles (source: WiMAX Forum). For 7 and 8.75 MHz channel bandwidths, sampling factor (instead of FFT size) is made variable.
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