Hello, everyone!
Today, I would like to continue with the article on WiMAX System Components.
Base station equipment and Customer premise equipment are the two main components of WiMAX architecture for the access network. The CPE enables a user in the customer’s network to access Wide Area Network (WAN). The BS controls the CPEs within a coverage area, and consists of many access points or wireless hubs, each of which control the CPE in one sector. The following figure shows the basic components of a radio communication system.
Fig. a. Components of a radio communication system
1. Customer Premise Equipment – CPE:
Residential CPEs are expected to be available in a fully integrated indoor self-installable unit as well as indoor/outdoor configuration with a high-gain antenna for use on customer sites with lower signal strength. In most cases, a simple plug and play terminal, similar to a DSL modem, provides connectivity. For customers located several kilometers away from the WiMAX base station, an outdoor antenna may be required to improve transmission quality. To serve isolated customers, a directive antenna pointing to the WiMAX base station may be required.
Fig. b. FWA Subscriber Configuration (Outdoor CPE)
CPE or terminals are expected to be available in a number of configurations for customer specific applications and for different types of customers. Households in multi-tenant buildings can be served by installing a high throughput WiMAX outdoor unit with a low to medium capacity DSLAM (Digital Subscriber Line Access Multiplexer) as an in-building access device utilising the in-building telephone wiring to reach individual apartments or by installing an individual WiMAX terminal in each household. These units are priced higher for the business case, consistent with the added performance.
FWA CPE is often divided into three main components parts (Above Fig. b):
The modem
The radio
The antenna
The modem device provides an interface between the customer’s network and the fixed broadband wireless access network, while the radio provides an interface between the modem and the antenna. As a matter of fact, some vendors integrate these two components to form a compact CPE, while others have the three units as standalone systems. The CPE antenna type depends on the Non-Line-of-Sight capabilities of the system. In a Line-of-Sight FWA network, the CPE antennas are highly directional and installed outdoors by a professional technician. In Non-Line-of-Sight systems, the beamwidth of the CPE antenna is typically larger, and in the case of user-installable CPE’s the antenna should be omnidirectional.
2. Base Station Equipment
The capacity of a single FWA base station sector depends on the channel bandwidth and the spectral efficiency of the utilised modulation and coding scheme. WiMAX systems take advantage of adaptive modulation and coding, meaning that inside one BS sector each CPE may use the most suitable modulation and coding type irrespective of the others.
Fig. c. Base Station components
The base station equipment, like CPE, consists of two main building blocks:
The antenna unit
The modulator/demodulator equipment
(see Above Fig. c and Below Fig. d).
The antenna unit represents the outdoor part of the base station, and is composed of an antenna, a duplexer, a radio frequency (RF), a low noise amplifier and a down/up converter. The choice of antennas has a great impact on the capacity and coverage of fixed wireless systems.
The BS consists of one or more radio transceivers, each of which connects to several CPEs inside a sectorised area. In the BS one directional sector antenna is required for each sector.
Sector antennas are directional antennas and the beamwidth depends both on the service area and capacity requirements of the system. A BS with one sector using an omnidirectional antenna has a quarter of the capacity of a four-sector system. The modem equipment modulates and mixes together each flow over the IF cable which is connected to the antenna unit.
Fig. d. Base Station components
As we can see in the Above Fig. d, each FWA base station consists of a number of sectors. The traffic capacities of these sectors depend most importantly on the modulation and coding methods, as well as on the bandwidth of the radio channel in use. The sector capacity is divided between all the subscribers in the sector’s coverage area.
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