Wireless Network Analysis: VSAT, WLAN, WiMAX, GSM, and LTE

This article provides a foundational understanding of wireless network analysis, applicable to various technologies and standards like VSAT, WLAN, WiMAX, GSM, CDMA, and LTE. It highlights essential tools used by developers and network engineers for troubleshooting across the globe. This guide aims to offer solutions to problems or issues related to these wireless technologies.

VSAT Network Analysis

VSAT (Very Small Aperture Terminal) is a transmission system used to provide voice and data connectivity to remote areas where laying copper or fiber optic cables isn’t feasible.

A VSAT system typically comprises two main parts:

• Outdoor Part: Consisting of an antenna and RF subsystems (RF ODU, PA, LNA).
• Indoor Part: Includes a mux-demux, modem, and a small exchange (PBX).

There are two main VSAT topologies:

• Star: Features VSATs and a hub station.
• Mesh: Utilizes VSATs with larger antennas, without a central hub station.

VSAT operates across various RF bands, including C band, Ku band, and Ka band. Effective VSAT network analysis requires a strong understanding of the RF component following installation.

A VSAT network engineer needs a spectrum analyzer to monitor the RF frequencies assigned to different VSATs and the hub station. This helps determine if a VSAT station is powered on and transmitting a carrier. If the RF signal isn’t visible on the spectrum analyzer, the VSAT is either off or has an RF component issue (RF ODU or power amplifier).

The receiver part can be verified by checking the received RF signal strength in the modem or spectrum analyzer. Another critical parameter to monitor in the modem is the Eb/No (Energy per bit to Noise power spectral density ratio) or CNR (Carrier-to-Noise Ratio). Based on the BER (Bit Error Rate) and modulation type, a specific CNR (or Eb/No) is required for the VSAT system to function efficiently. Other necessary equipment includes a frequency counter for frequency stability testing and a power meter for measuring absolute power levels.

WiMAX Network Analysis

WiMAX is designed primarily as a replacement for existing wired internet technologies like ADSL.

The system consists of two subsystems:

• Subscriber Station (SS)
• Base Station (BS)

WiMAX operates based on TDD (Time Division Duplexing) frame concepts, where the base station’s downlink transmission and the subscriber station’s uplink transmission use the same frequency at different time intervals. WiMAX network analysis requires an over-the-air protocol analyzer. An RF spectrum analyzer helps in analyzing RF issues, if any.

WiMAX subsystems (SS and BS) consist of multiple layers in a protocol stack, including PHY (Physical), MAC (Media Access Control), and upper layers. For PHY layer analysis, various test and measurement applications have been developed that work with or without RF hardware. For MAC and upper layer protocol analysis, MAC sniffers and protocol analyzers compliant with the WiMAX standard have been developed. Real-time WiMAX signal analysis requires sophisticated real-time spectrum analyzers, such as the RSA 3408A from Tektronix.

WLAN Network Analysis

A WLAN (Wireless Local Area Network) network consists of access points (APs) and stations (STAs) that communicate wirelessly using dipole antennas. The AP is also known as a WiFi or WLAN router.

The WLAN protocol stack also consists of RF, PHY, MAC, and upper layers. RF and PHY layers are tested using test and measurement tools. For MAC and upper layers, a protocol analyzer and/or network analyzer is needed.

Various standards have been developed under the WLAN family, such as 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, and 802.11ad.

GSM Network Analysis

A GSM (Global System for Mobile Communications) network is composed of mobile subscribers, BTS (Base Transceiver Station), BSC (Base Station Controller), MSC (Mobile Switching Center), and backbone connectivity for voice and data transport.

GSM network analysis is divided into mobile (MS) analysis and base station analysis. A protocol analyzer, RF signal generator and analyzer, and network analyzer are needed for GSM signal analysis.

Companies working on GSM stack development usually develop their own debugging applications for mobile and network log analysis. BER (Bit Error Rate) analyzers are also used for performance benchmarking of these wireless systems end-to-end for short-term and long-term stability tests.

Application to Other Wireless Networks

The concepts described above can also be applied to CDMA (Code Division Multiple Access), LTE (Long-Term Evolution), LTE Advanced, TD-SCDMA (Time Division Synchronous Code Division Multiple Access), and other wireless networks.

Tools

• Spectrum Analyzer: Used to visualize the frequency spectrum of a signal.
• Spectrum vs. Network Analyzer: Spectrum analyzers display signal amplitude vs. frequency, while network analyzers measure network parameters like impedance and scattering parameters.
• Power Meter: Measures the absolute power level of a signal.
• VSG vs. VSA: VSG (Vector Signal Generator) generates complex modulated signals, while VSA (Vector Signal Analyzer) analyzes these signals.
• Protocol Analyzer: Captures and analyzes network protocol traffic.
• BER Testing Equipment: Measures the bit error rate to assess the quality of a digital communication system.