Publié le 14 août 2013
The wireless soup
The Heterogeneous Network, which has been dubbed the HetNet, is a mix and match of several wireless technologies, including both long range and short range, indoor and outdoor, private or public, residential or commercial, and so on. Unfortunately, it’s quite easy for newbies in the wireless world to get tangled up in all the details. Hopefully, the following paragraphs will clear up some of the confusion.
Until now, small cells have had a limited, yet growing presence in wireless networks. Whether customers were using femtocells in their homes, picocells at a hotel, or micro cells on a broader level, small cells were sparsely sprinkled across the landscape. As their names imply, a femtocell is a cell site that is smaller than a picocell, which is in turn smaller than a microcell, which is a step down from the macrocell. The larger the cell site, the more connections it is able to carry and the greater a range it can cover.
- Femtocells are designed for residential use.
- Picocells can typically handle anywhere from 10 to 60 simultaneous callers, and can be deployed both indoors and outdoors.
- A step up from picocells, microcells are base stations that are often used to support cellular service in large buildings, conference centers, or shopping areas. In high-rise buildings, the microcell is typically connected to a distributed antenna system (DAS) to ensure that coverage can be provided on multiple floors. Microcells are utilized in situations where a macrocell would be excessive.
A remote radio head (RRH) is a single outdoor unit in which only the radio frequency (RF) front‑end functionalities are implemented. The RRH is connected to the remaining baseband processing portion of the base station by way of analog or digital interconnection links. The usual choice of optical fiber for the interconnection cable is based on the requirement of high-linearity.
The typical RRH interconnection is a simple bidirectional point-to-point link, although other more complex solutions can be implemented (star, ring, or daisy chain).
Active Distributed Antenna System (DAS) equipment is, for the most part, composed of headend and remote units, which are used to distribute cellular signals throughout a given building. In particular, DAS utilizes and takes advantage of the expensive part of the system, i.e., the base station, to spread coverage throughout the building.
The DAS is defined as a multi-airlink/multifrequency/multi-wireless service provider (WSP), fiber-optics-based (but sometimes coax) distributed antenna system. Its main objective, which also constitutes its main difference from the RRH concept, is greater flexibility and capacity that can be dynamically allocated and optimized for varying traffic needs.
The DAS enables independent operation of multiple frequency bands and multiple protocols across a single access network. Consequently, multiple-operator network sharing can be supported by a DAS system.
Today, DAS has experienced significant commercial success in the United States, which enjoys a strong presence of cellular operators utilizing several different standards (GSM, IS-136, AMPS, SMR, FDD W-CDMA, among others) and various RF frequency bands.
EXFO is a proud member of the HetNet Forum, which is dedicated to the development of the Heterogeneous Network. For more information on this subject, visit the FTTA, RRH and DAS webpage, or see the Wireless Network Service Providers section of our website.