RFWiMAX Network Architecture Explained
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WiMAX stands for Worldwide Interoperability for Microwave Access. It’s used to provide broadband internet wirelessly, primarily at 2.5GHz, 3.5GHz, and 5.8GHz radio frequencies.
It’s also known as a 4G technology. It delivers internet speeds about 4 times faster compared to its 3G counterpart. This speed increase is largely due to OFDM (Orthogonal Frequency-Division Multiplexing), which carries multiple carriers, each transmitting multiple data bits based on modulation techniques like QPSK and 16QAM. These carriers are tightly packed together to save bandwidth. Intel played a key role in the development and proliferation of WiMAX worldwide.
In this tutorial, we’ll explore the WiMAX architecture and its role as a wireless network communication technology. WiMAX is considered a metropolitan area network (MAN). It can replace DSL technologies, providing wireless internet at around 70 Mbps up to a distance of 35 Km. There are two main versions of WiMAX: fixed WiMAX and mobile WiMAX.
In fixed WiMAX, the terminal or subscriber is fixed to a location, while in mobile WiMAX, subscribers can move at various speeds. Fixed WiMAX is often referred to as 802.16d or 16d, and mobile WiMAX as 802.16e or 16e. The IEEE 802.16 standard defines several physical layers, with the most commonly used being Single Carrier, OFDM, and OFDMA. Single Carrier is used for the 10-66 GHz frequency range, while OFDM/OFDMA is used for the 2-11 GHz frequency band. OFDM is employed in fixed WiMAX, and OFDMA in mobile WiMAX.
WiMAX Architecture Explained with a Block Diagram
The WiMAX system consists of various network elements working together to deliver wireless connectivity. The block diagram includes: SS (Subscriber Station) or CPE, BS (Base Station) or AP, Access Service Network (ASN), ASN Gateway, Connectivity Service Network (CSN), AAA server, Home Agent (HA), Foreign Agent (FA), Mobile IP Home Agent (MIHA), Mobile IP Foreign Agent (MIFA), and the backhaul network.
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Subscriber Station (SS): The end-user device that communicates with the WiMAX Base Station. The SS can be a fixed or mobile device. It’s also known as CPE (Customer Premises Equipment).
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Base Station (BS): The central component of WiMAX, serving multiple subscriber stations and connecting to the core network (CN). It communicates with SSs using an air interface.
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ASN: Responsible for managing radio resources and providing connectivity to SSs. It includes BS(s) and ASN-GW.
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ASN-GW: Serves as an aggregation point for multiple BSs and provides connectivity between the ASN and CN. It handles functions such as IP address assignment and security.
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CSN: Responsible for high-level functions such as authentication, authorization, accounting (AAA), and IP connectivity with external networks.
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AAA server: Responsible for verifying subscriber identities, authorizing their access to the network, and tracking their usage for billing and accounting purposes.
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Home Agent (HA): Used in mobile WiMAX. It manages the mobility of subscriber stations as they move between different BSs. It tracks the location of mobile subscribers and helps maintain their connections.
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Foreign Agent (FA): Like the Home Agent, it assists with subscriber mobility in different networks. It communicates with the Home Agent to manage seamless handoffs when subscribers move between different service areas.
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MIHA: Used in mobile WiMAX networks. It manages the mobility of SSs that use Mobile IP for seamless handoffs.
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MIFA: Similar to the Mobile IP Home Agent, it assists with mobility management for SSs moving between different networks.
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Backhaul Network: Connects BSs to the CN (Core Network). It carries data traffic between the WiMAX access network and the rest of the internet.
Fixed WiMAX System Features
The following table outlines the features of a Fixed WiMAX System.
| Feature | Fixed WiMAX Support |
|---|---|
| IEEE Standard | 802.16-2004 OFDM PHY/MAC, 16d |
| Symbol Parameters | Cyclic Prefix (1/4,1/8,1/16,1/32), FFT size(256), Channel Bandwidth(1.75/2.5/3/3.5/5/5.5/7/10MHz) |
| Preamble | Long Preamble for Downlink sub frame and Short Preamble for Uplink Bursts |
| Frame Duration | 2.5, 4, 5, 8, 10, 12.5, 20 ms |
| Modulation | DL BPSK, DL QPSK, DL 16 QAM, DL 64 QAM, UL BPSK, UL QPSK, UL 16 QAM, UL 64 QAM |
| Channel Models | SUI channel models |
| Channel Coding | Randomization, Concatenated RS-CC, Interleaving |
Mobile WiMAX System Specifications
The table below details the specifications of a Mobile WiMAX system.
| Feature | Mobile WiMAX Support |
|---|---|
| IEEE Standard | 802.16-2005 OFDMA PHY/MAC, 16e |
| FFT Size | 2048/1024/512/128 |
| Sampling Factor | If channel bandwidth is a multiple of 1.75MHz then n=8/7 else if channel bandwidth is a multiple of any of 1.25, 1.5, 2 or 2.75 MHz then n=28/25 else if not otherwise specified then n=8/7. |
| Cyclic Prefix | 1/8 |
| Frame Size | 5 ms |
| DL Subcarrier Allocation | PUSC, FUSC, AMC2x3 |
| UL Subcarrier Allocation | PUSC, AMC2x3 |
| DL Modulation | QPSK, 16QAM, 64QAM |
| UL Modulation | QPSK, 16QAM |
| Convolutional Coding | Tail biting/CTC |
| MAP Type | Normal/Compressed |
| DL MIMO | 2-antenna, matrix A, 2-antenna, matrix B vertical encoding |
| UL MIMO | Collaborative SM for two MS with single transmit antenna |
WiMAX OFDM PHY and MAC Layer
wimax physical layer transmitter
Summary
Overall, the WiMAX architecture is designed to provide wireless broadband connectivity over a large coverage area. It plays a pivotal role in enhancing modern network infrastructures by providing robust and efficient wireless communication. It relies on a combination of network elements to deliver seamless communication, mobility management, and data transmission/reception for both fixed and mobile WiMAX deployments. Understanding these elements is crucial for leveraging WiMAX in optimizing wireless networks and ensuring seamless connectivity across various applications.
