
Maxim > App Notes > Wireless, RF, and Cable
Keywords: femto, basestation, 3G, 3GPP, WCDMA, WiFi, 802.11, WiMAX, WiBRO, 802.16, cellular, handset, node-b,
macrocell, transceiver, ts25.104, gsm, edge, sensitivity, evm, broadband, transmitter, receiver
Jun 29, 2007
APPLICATION NOTE 4063
Notes on Femto Base Station Application and a Radio Approach
Abstract: This application note discusses the development and deployment of 3G cellular femto base stations. The
market position and the technical challenges for last-mile residential connectivity are discussed, and 3G femto
base stations are proposed as a very good solution. Maxim's 3GPP TS25.104-compliant radio solution is presented.
Introduction to Deploying Femto Base Stations
The third-generation cellular phone system under 3GPP was designed to offer a fully mobile multimedia experience.
In many cases, widespread adoption has been limited by the available reception, especially in remote areas and in
residences.
One solution is the home base station, which provides in-home mobility with maximum user data rates, without
loading the macro node-B cell sites. They are classified as "femto" power.
● +45dBm: macro base station covers an outdoor cell site of ~5km
● +30dBm: pico base station covers a campus of ~0.5km
● +15dBm: femto base station covers an indoor residence of ~50m
Femto home base stations access the network through the publicly-switched telephone network, which is typically
available through a residential DSL line. The handset only communicates to the femto station in the home, and this
completely offloads that user from the macrocell.
In the following paragraphs, we review the basis for femto home base-station deployment and show how Maxim's
radio solution offers key advantages for this technology.
General Case for Improving Cellular Coverage Compared to Other
Solutions
Cellular systems are deliberately designed to trade off handset battery life, handset computing power, and cell site
user loading. In addition, cellular standards are continually evolving to take advantage of the constantly increasing
mobile-DSP performance. Cellular carriers leverage this trend to provide more and better multimedia content so that
they can increase revenue and attract new customers. The user ultimately benefits from "anywhere" mobility. For
example, because the cellular adoption rates are in the 100 millions per year, a very streamlined and well-
understood competitive supply chain exists to keep pricing low and performance high.
Broadband Wireless Compared to Cellular RF Service
In parallel with this cellular development effort, wide-area broadband wireless systems are in the works. Initially, so-
called "coffee-house" Wi-Fi gave users 802.11 Internet access when they parked near or sat in certain enabled
restaurants. Later, some cities built experimental metro-Wi-Fi access points to serve the downtown cores. The
models were so successful that, in 2004, a better wireless system, 802.16 WiMAX™ (and Korean WiBro™) was
launched, with a view to "metro area broadband wireless access" service.
Using OFDM instead of single-carrier modulation permits these broadband wireless systems to overcome urban
multipaths, but they require four times the transmit power. This is because OFDM 802.16d peak-to-average ratio