Femtocell Tutorial: A Comprehensive Guide to Enhanced Indoor Coverage

Femtocells are compact, low-power cellular base stations that enhance indoor coverage and connectivity by providing localized signal support. With their ability to extend cellular network services into homes, offices, and remote areas, femtocells play a crucial role in modern telecommunications.

This tutorial delves into the fundamentals of femtocell technology, including its network architecture, handover mechanisms, security considerations, and interference management. Additionally, it covers femtocell testing techniques and introduces some of the leading manufacturers in this domain.

As we know, wireless signals become weak when they travel from their point of origin to the receiver. This happens due to signal path loss as well as interference. Hence, it’s required to be boosted or amplified to obtain better coverage.

The other option is to have smaller internal base stations within the home or office premises, which will take care of providing boosted cellular signals to extend the coverage. This small base station is known as a femtocell.

The femtocell will interact with a femtocell gateway which interfaces with the cellular mobile operator infrastructure. This backbone infrastructure will be connected to the internet. For different technologies, different femtocells have been developed to provide the respective boosted signal to users or subscribers or CPEs. Hence, WiMAX femtocells, 3G femtocells, and LTE femtocells are available as per WiMAX, UMTS, and LTE standards respectively.

Femtocells provide benefits to both users and operators. They offer improved performance to users and extra revenue to operators due to the addition of extra services.

Femtocell standards 3GPP release 8 specifies 3G femtocells (UMTS femtocells), and 3GPP release 9 specifies LTE femtocell specifications. Please note that UMTS femtocells are known as HNBs and LTE femtocells are known as HeNBs. HNB refers to Home NodeB and HeNB refers to Home eNodeB or Home eNB.

ITU-R IMT family have defined femtocell standards, as follows:

• 3GPP standard for HNB for WCDMA and TD-SCDMA. Both TDD and FDD topologies are defined in the specifications.
• 3GPP standard for Home eNode-B (HeNB) for LTE, both TDD and FDD are specified.
• 3GPP program for femtocells as per CDMA2000 1X, 1X EV-DO, CDMA2000.
• WiMAX Forum program for femtocells compliant to IEEE WiMAX standard.

Femtocell Network Architecture

Figure 1: Femtocell Architecture

Figure 1 depicts a high-level femtocell architecture, irrespective of any standard-based technology. As shown, the femtocell system consists of the following elements:

• Femtocell device
• Router (DSL or Cable)
• ISP link
• Mobile operator network
• Cellular tower

Based on the technologies, different femtocell network architectures exist viz. WiMAX, UMTS(3G), CDMA2000, LTE, etc.

The architecture consists of various femtocell interfaces with the other network system elements. Basically, there will be two main elements: the femtocell and the gateway. The femtocell provides connectivity with various subscribers/users. The gateway is the interface between the femtocell and the network.

For example, a UMTS network consists of Home NodeB (HNB) i.e. femtocell and Home NodeB Gateway. The femtocell architectures of 3GPP and 3GPP2 are different. 3GPP is the standardization body behind UMTS which is 3G upgradation to GSM. 3GPP2 is the body behind CDMA2000 which is 3G upgradation to cdmaOne network. This is the difference between 3GPP and 3GPP2.

Femtocell Architecture.

Figure 2: Femtocell Network

Femtocell Handover

As shown in Figure 2, the femtocell network consists of femtocells in the office, home, or apartment premises, and macro cells outside. Based on this, there are various types of femtocell handovers. A macrocell refers to the region usually covered by a standard cellular network.

• From macrocell to the femtocell
• From femtocell to the macrocell
• Between femtocells in the region

Femtocells provide hard handovers which are automatic as well as seamless between home networks (such as Wi-Fi) and cellular networks (such as UMTS or LTE) in use.

Femtocell Interference

As we know, interference is usually caused due to the high power of a nearby channel interfering with the proper functioning of the desired channel. To overcome this, there are many solutions. One such solution is limiting the transmitter power enough to keep the transmission within the coverage as designed.

Femtocell Security

Though wireless systems provide better security compared to wired networks, the security of femtocells is threatened due to various probable security aspects such as intrusion, hacking, and so on.

In femtocells, security lies with the protection provided to the IP packets traveling between network elements. IPsec protocol provides security in femtocell-based networks.

Femtocell Testing

Based on the various stages of femtocell development, there are various tests which are essential to be performed. The tests are related to verification, conformance, regulatory, manufacturing, and interoperability of femtocell devices. In all the tests, transmitter and receiver modules are required to be tested. All the protocol stack layers are required to be tested based on the test type. The protocol stack layers are different based on technologies.

Femtocell testing helps avoid any functional and performance related issues.

Femtocell Manufacturers

Following are the femtocell developers or manufacturers:

• Gemtek, Taiwan
• SagemComm
• Tecom, Taiwan (ODM of Ubiquisys)
• Zyxel, Taiwan
• Foxconn
• C & S microwave
• Askey
• Comba

Conclusion

Femtocell technology addresses the challenges of indoor coverage and network capacity, making it a valuable addition to cellular networks.

As femtocell technology continues to evolve, it will remain instrumental in shaping the future of wireless communication by providing innovative solutions for enhanced indoor coverage and network efficiency.