SBAA682 April   2025 AFE7728D , AFE7768D , AFE7769D

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Acronyms Used in This Document
  5. 2Distributive Antenna System
  6. 3Repeater System
  7. 4Goals of DAS and Repeater Design
  8. 5RF Repeater System Without FPGA/ASIC
  9.   10
  10. 6Overcoming Bandpass Filter Effects From Cable Dispersions and Multi-Path
  11. 7Summary

2 Distributive Antenna System

An example of a typical wireless communications system environment using DAS is described in this section.

Typical Environment for DAS Setup Figure 2-1 Typical Environment for DAS Setup

Figure 2-1 shows a typical service environment for DAS. Many private office buildings and public service buildings have many mobile users in a crowded and enclosed environment. The enclosed nature of the building environment does not allow external wireless signals from a base station (BTS) to reach inside the buildings. Therefore, without additional remedies to the wireless signal path, these buildings have coverage and capacity issues for the mobile users.

Principle of DAS Operation to Improve Indoor Coverage and Capacity Figure 2-2 Principle of DAS Operation to Improve Indoor Coverage and Capacity

The building owners or manager can introduce DAS to simply redistribute the wireless signal path from outside the building to inside the building. Per Figure 2-2, a DAS typically consists of two principle elements: a master unit (MU) and one or more remote units (RU). The simplified operating principle is based on the master unit interface with an outside BTS or donor antenna that redistributes the outside signal indoors through indoor remote units. The indoor remote units can be placed throughout the building to improve coverage and capacity of the service. The key constraint is that the DAS is transparent to the mobile user and the BTS as the DAS is simply redistributing the signal.

The following summarizes the functionalities of each key component of the DAS:

  • MU: this is the master unit of the DAS. The MU interfaces primarily with an outside BTS or donor antenna, and it bridges the outside signal with indoor RUs.
  • RU: the building owner or manager can install various RUs throughout the building to increase coverage and capacity of the interface with the mobile users. The RUs interface with the MU to bridge the mobile users with the MU.
  • BTS: this unit is responsible for the air interface between the mobile service provider and the mobile user. Since the air interface has difficulty penetrating through the buildings, DAS are installed to bridge the BTS with the mobile user and service provider.
  • Donor Antenna: in case the air interface signal is sufficiently strong without significant fading effect, the MU can interface directly with a donor antenna to reach a more remote BTS as opposed to installing a BTS outside the building. Installing the BTS directly outside the building to interface with the MU directly requires RF cell planning from the service provider to assess potential interference to other cells. The use of a donor antenna can possibly save the building manager the cost of BTS cell planning and installation and also reduces DAS installation time. If a BTS is indeed installed near the building, the MU can connect to the BTS with fiber cable directly without the use of a donor antenna.

New trend of the DAS design includes power distribution over Ethernet or over fiber. This approach allows the entire MU and RU to be powered over Ethernet or fiber line directly. The idea of power over cable is to allow the entire DAS system to be powered directly and independently from the main building power distribution service. The power utility bill can be separated between the DAS system and building owners.