Analysis Explaination Of What A Femtocell Is Computer Science Essay

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The purpose of this report is to analyse and explain what a Femtocell is, how they can be used by CompHelp Ltd and what benefits they will bring, finally, what will be the difficulties (if any) in deploying them within the employees home. The company has recently upgraded all its employees' mobile phones but some of the employees are complaining that in their area the 3G signal is very weak or nonexistent.

In the report, the findings discuss the advantages and disadvantages of Femtocells, any security issues and the benefits to the company if adopted. Following these findings, a conclusion is drawn and recommendations will be made as to whether CompHelp would benefit from investing in Femtocell technology.

What are Femtocells?

A Femtocell is a small cellular base station designed for use in residential or small business environments. It connects to the service provider's network via broadband (such as DSL or cable) and typically supports 2 to 5 mobile phones in a residential setting. A Femtocell allows service providers to extend service coverage inside of your home - especially where access would otherwise be limited or unavailable - without the need for expensive cellular towers. It also decreases backhaul costs since it routes your mobile phone traffic through the IP network.

Early Femtocell products look very much like WiFi broadband modems, needing only two cables - one for power and one internet connection. Several vendors such as Thomson, Netgear, Pirelli, Cisco and others have integrated the Femtocell with other features such as DSL modem, WiFi and even IPTV into a single box. It is expected that in the longer term, most Femtocells will be sold in this form. Unlike WiFi, these devices use licensed radio spectrum, so must be operated and controlled by a mobile phone company. Thus it will work with only one mobile phone operator, and thus encourages all users in a household to switch to the same network operator.

When in range of the Femtocell at home, the mobile phone will automatically detect it and use it in preference to the outdoor mobile network radio masts. Calls are made and received in exactly the same way as before, except that the signals are sent encrypted from the Femtocell via the broadband IP network to one of the mobile operators' main switching centres. Making and receiving calls uses the same procedures and telephone numbers, and all the standard features (call divert, text messaging, web browsing) are available in the same way - indeed data services should operate more quickly and efficiently due to the short range involved.

Femtocells operate at very low radio power levels - less than cordless phones, WiFi or many other household equipment. This substantially increases the battery life, both on standby and talktime. Since they are so much closer to the handset or mobile device, call quality is excellent and data devices can operate at full speed. Standard units can handle up to 3 or 4 simultaneous calls from different users depending on the model. Larger Femtocell designs intended for business (enterprise) use can handle 8, 16 or even 32 concurrent calls.

Finally, they are compatible with existing standard mobile phones, although in future some minor enhancements would allow clear indication of when the phone is using the local Femtocell (and thus using a free call charge) - currently this can be provided by tones at the start of each call.

The benefits of Femtocells

The key benefit is of course that they get coverage where perhaps there was previously none. We have all heard stories from people that cannot get a signal without stepping outside, or those who get coverage from different carriers in different parts of the house. However, for the consumer the technology does not really matter as long as it is relatively seamless in use. Products already exist using the so-called UMA (Unlicensed Mobile Access) technology, for example Unik from Orange France, T-Mobile USA's [email protected] and BT's Fusion. The radio link in this case is not 3G but Bluetooth or WiFi, (or perhaps even DECT), and this requires a dual-mode handset, for example the Nokia N95 with integral WiFi, so that the handset can be "captured" by the UMA base station when you enter the house. With dual-mode handsets it's also possible to use VoIP-over-WiFi services such as Truphone, Fring or Skype.

The issues around security

From a security Femtocell technologies can create a secure tunnel to the carrier's gateway and interact with exchange to switch the call to the desired circuit. UMA capable mobile handsets use EAP/SIM [RFC4186] to create IPSec VPN tunnels to the UMA Network Controllers [UNCs] in the carrier network. UNC's don't distinguish a authenticated connection from a phone vs. a laptop as long the EAP/SIM authentication succeeds the device is attached to the providers network giving attackers a nifty way to attach to the carriers core network. EAP-SIM uses a secret key stored in the SM as the starting material (among others) for the key-derivation process for the VPN tunnel.

This key can be copied from the SIM using SIM card reading tools. Armed with the secret key and a EAP/SIM supplicant an attacker can authenticate her workstation to the UNC and create a successful VPN tunnel. EAP/SIM does not provide session independence i.e. the cipher key produces remains the same as long the initial SIM secret key is the same. Knowledge of the cipher key allows an attacker to eavesdrop on the the communications. Dual-mode phones can also be targeted by localized DoS attacks/resource starvation to prevent a user's phone from handing off to the UMA network.

It is essential for carriers to place IDS and network segregation devices to monitor network intrusion from UMA/Femtocell mobile devices. Femtocells have certain provisioning parameters that carriers can remotely set to make sure only the subscriber's phones are able to use the particular Femtocell, this ensures your next door neighbour doesn't talk on your Femtocell.

3G interference

Interference is a key issue associated with Femtocell development. There are a number of issues associated with interference all of which have needed to be investigated and solutions found to ensure that the deployment of any Femtocells will take place successfully.

The issue arises from the fact that Femtocells will utilise the spectrum already allocated for cellular telecommunications. The Femtocells will be deployed in what may be termed an ad-hoc fashion, without the network planning that is normally undertaken for the deployment of cellular telecommunications base stations. As a result there is very real the possibility that interference will arise. This could cause problems to the main network resulting in poor levels of performance being achieved, not only by those using the Femtocell, but other users who may be communicating via the main cellular network.

Even though Femtocell interference is a problem that needs to be addressed and kept in mind, there are strategies that have been developed to overcome it. The Femtocells being developed and deployed have several methods of reducing and overcoming the Femtocell interference problems that are likely to occur. As a result it is anticipated that it is unlikely to be the problem many thought it could be.


It would be a recommendation that HelpComp Ltd adopt the use of Femtocells for their home-based workers as they would help these workers benefit from all the functionality of a "high speed" 3G network. However, it has been advised that there are a few security concerns with the use of Femtocells but any such concerns would be discussed and investigated with the mobile provider as to their steps in reducing the risk and how they are tackling the so said security flaws before any contract was struck.


Femtocell use has a big future to play within the public/commercial domain and the benefits are plain to see. The relatively low cost solution to poor 3G network coverage can aid users and company employees alike to the benefits of 3G technology. In a high paced world, users want more and more data as quick as they can get it and will not accept anything less. This was once part of everyday life in the big cities where the 3G coverage is vast but now, also rural areas can benefit at a low cost to the user and the mobile network of 3G technologies.

It has been concluded that the use of Femtocell technology should be used and budgeted for not only in CompHelp Ltd but to any home user or company that suffers from poor 3G coverage.

[1427 words]


Question 2

Cognitive Radio Web Site Pages

How will the pages fit together?

The 6 pages for the website will link together like a tutorial each following on from the previous page. For example, the first page would be the overview and at the bottom of that page there would be a link to the next, "please click here to see how CR works". I have provided pictures for each page so the website is a little more visually appealing and kept the word count to each page under the required 250 words.

The last page would be the quiz for the website containing some multiple choice questions on the topics covered in the previous pages. I have supplied a sample question with the correct and incorrect responses for that question.

Although I have supplied sample pages for the material it is only meant as a guide as to what material could be used in each page and how they could be set out.

[157 words]

Page 1 - Overview of Cognitive Radio

Cognitive radio (CR) is a form of wireless communication in which a transceiver can intelligently detect which communication channels are being used and which are not, and instantly move into channels which are free thus, avoiding occupied ones. This optimizes the use of available radio-frequency (RF) spectrum while minimizing interference to other users.

In its most basic form, CR is a hybrid technology involving software defined radio (SDR) as applied to spread spectrum communications. Possible functions of cognitive radio include the ability of a transceiver to determine its geographic location, identify and authorize its user, encrypt or decrypt signals, sense neighbouring wireless devices in operation, and adjust output power and modulation characteristics.

There are two main types of cognitive radio, full cognitive radio and spectrum-sensing cognitive radio. Full cognitive radio takes into account all parameters that a wireless node or network can be aware of. Spectrum-sensing cognitive radio is used to detect channels in the radio frequency spectrum.

The Federal Communications Commission (FCC) ruled in November 2008 that unused portions of the RF spectrum (known as white spaces) are made available for public use. White space devices must include technologies to prevent interference, such as spectrum sensing and geo-location capabilities.

The idea for CR was developed by Joseph Mitola at the Defence Advanced Research Projects Agency (DARPA) in the United States. Full cognitive radio is sometimes known as "Mitola radio."

[236 words]

Page 2 - How Cognitive Radio Works

CR (Cognitive Radio) technology works within a standard radio-based wireless network consisting of transmitters, receivers, and antennas. CR systems use an RF sensor, which is part of the receiver, for awareness of radio-spectrum usage. These sensors detect where spectrum is being used and find available frequencies suitable for communications. CR works with a cognitive engine to recognize if a wireless channel isn't being used. And they frequently use a policy engine to determine if the radio is allowed to use that channel.

CR augments RF awareness via a database of licensed users of the slices of spectrum being analyzed, as well as their geographic coordinates. This would detect spectrum users that aren't working via RF, such as TV broadcasters. To enable dynamic spectrum access and create the best link while minimizing interference with other radios, CR uses a set of decision-making algorithms running on a processor within the system to change RF frequencies, protocols, or modulation techniques.

To improve a link, CR systems must understand user needs, such as quality of service requirements for various types of transmissions, whether battery life is more important than high throughput, and what protocol and frequency the intended recipient is using. The systems also must recognize the RF environment's physical properties such as signal interference and attenuation. CR uses these capabilities to adjust factors such as signal power, communications protocol, and spectrum.

[234 words]

Page 3 - Cognitive Radio Femtocells

Femtocell is envisioned as a highly promising solution to tackle the communications in the indoor environments, which has been a very challenging problem for mobile network operators. Currently, the spectrum allocated to Femtocells is from the same licensed spectrum of Macrocells, and the same mobile network operator. In this case, the capacity of Femtocell networks may be largely limited due to the finite number of licensed spectrum bands and also the interference with other Femtocells and Macrocells.

Cognitive radio enabled Femtocells are able to access licensed spectrum bands not only from Macrocells but also from other licensed systems (e.g. TV systems). Thus, the co-channel interference in Femtocells can be greatly reduced and the network capacity can be significantly improved. Results indicate that Cognitive radio enabled Femtocells are able to achieve much higher capacity than the Femtocell networks which does not employ agile spectrum access.

[149 words]

Page 4 - Advantages of Cognitive Radio

Cognitive radio is a powerful concept on its own. However under some circumstances it is possible to build a network of radios - nodes by linking several cognitive radio nodes. In this way several elements of the performance can be considerably enhanced.

In many instances a single cognitive radio will communicate with several non-cognitive radio stations as in the case of a Femtocell which requires cognitive functionality to set itself up, and then communicate with non-cognitive cell-phones. In other cases, several cognitive radios will be able to form a network and act as an overall cognitive radio network. This scenario has many advantages in terms of improving the performance of the overall network well beyond that of the individual elements.

Cognitive radio network advantages

The use of a cognitive radio network provides a number of advantages when compared to cognitive radios operating purely autonomously:

•Improved spectrum sensing: By using cognitive radio networks, it is possible to gain significant advantages in terms of spectrum sensing.

•Improved coverage: By setting up cognitive radio network, it is possible to relay data from one node to the next. In this way power levels can be reduced and performance maintained.

[201 words]

Page 5 - Software-defined Radio

Software-defined radio (SDR), sometimes shortened to software radio (SR), refers to wireless communication in which the transmitter modulation is generated or defined by a computer, and the receiver uses a computer to recover the signal intelligence. To select the desired modulation type, the proper programs must be run by microcomputers that control the transmitter and receiver.

The most significant asset of SDR is versatility. Wireless systems employ protocols that vary from one service to another. Even in the same type of service, for example wireless fax, the protocol often differs from country to country. A single SDR set with an all-inclusive software repertoire can be used in any mode, anywhere in the world. Changing the service type, the mode, and/or the modulation protocol involves simply selecting and launching the requisite computer program, and making sure the batteries are adequately charged if portable operation is contemplated.

The ultimate goal of SDR is to provide a single radio transceiver capable of playing the roles of cordless telephone, cell phone, wireless fax, wireless e-mail system, pager, wireless videoconferencing unit, wireless Web browser, Global Positioning System (GPS) unit, and other functions still in the realm of science fiction, operable from any location on the surface of the earth, and perhaps in space as well.

[210 words]

Page 6 - Test your knowledge of CR

Sample Multiple Choice Question

What do the acronyms CR, RF and SDR stand for? Is it:

Cognitive Radio, Relative Frequency, Standard Ratio

Incorrect option, one out of the three is correct, please review page 2 and page 5

Complicated Radio, Radio Frequency, Software-Defined Radio

b) Incorrect option, two out of the three is correct, please review page 5

Cognitive Radio, Radio Frequency, Software-Defined Radio

c) Correct option

Cognitive Radio, Radio Frequency, Standard Ratio

d) Incorrect option, two out of the three is correct, please review page 5

Complicated Radio, Radio Frequency, Standard Ratio

e) Incorrect option, one out of the three is correct, please review page 1 and page 5