Connectivity

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Body sensor networks and wireless sensor networks in general will only fulfill their promise when the loop from the individual to the knowledge centre (physician, monitoring centre etc) and back again to the individual is closed. This requires that the sensed physical data can be reliably, securely, and with the individuals privacy respected, sent to a knowledge centre. Then, if required, action can be taken to assist the individual. This is a closed loop system and promises tremendous advantages in terms of wellbeing if it can be achieved. Key component of this loop are the communications mechanisms both on-body communications and body to back-end systems communications. As an example, there is little point in having a very good and accurate sensor system monitoring say on-body ECG if the data that arrives at the physician or monitoring centre is 'old' i.e. if the communications channels are either too slow or congested - the individual may have had a heart attack before the warning data even arrives! Of course the ideal scenario also is that this loop is closed in as near to real time as possible and this will be a goal of sensor networks as we move towards the so called 'Internet of Things'

Technologies for Connectivity

The success of the body sensor network will only be as good as the communications mechanism that is adopted, both the on body system and the person to monitoring centre/system link. Unreliable communications, packet loss, latency etc all detract from a successful system and should be avoided. The Connectivity aspect therefore for assisted living and body sensor network technologies can be divided into categories:

Inter-Network Connectivity

These can be wired or wireless connections between sensors, devices and aggregators providing local connectivity within the home environment or the personal area network. An example would be a body sensor network with two or three sensor nodes monitoring say ECG, respiration and Pulse oxidation and sending the data to an on-body control unit. This sensor to sensor and sensor to control unit communication can take various forms including

Bluetooth

Bluetooth wireless technology ^[1] is a short-range communications technology intended to replace the cables connecting portable and/or fixed devices while maintaining high levels of security. The key features of Bluetooth technology are robustness, low power, and low cost. The Bluetooth specification defines a uniform structure for a wide range of devices to connect and communicate with each other.

Bluetooth technology has achieved global acceptance such that any Bluetooth enabled device, almost everywhere in the world, can connect to other Bluetooth enabled devices in proximity. Bluetooth enabled electronic devices connect and communicate wirelessly through short-range, ad hoc networks known as piconets. Each device can simultaneously communicate with up to seven other devices within a single piconet. Each device can also belong to several piconets simultaneously. Piconets are established dynamically and automatically as Bluetooth enabled devices enter and leave radio proximity.

Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHz, using a spread spectrum, frequency hopping, full-duplex signal at a nominal rate of 1600 hops/sec. The 2.4 GHz ISM band is available and unlicensed in most countries. More information on Bluetooth is available at (1) or here

802.15.4 (Zigbee)

ZigBee ^[2] technology is a low data rate, low power consumption, low cost, wireless networking protocol targeted towards automation and remote control applications. IEEE 802.15.4 committee started working on a low data rate standard a short while later. Then the ZigBee Alliance and the IEEE decided to join forces and ZigBee is the commercial name for this technology. There is a lot of information on 802.15.4 available at ^[3] or via the Wikipedia entry Zigbee.

Bluetooth vs Zigbee

• ZigBee looks rather like Bluetooth but is simpler, has a lower data rate and spends most of its time snoozing. This characteristic means that a node on a ZigBee network should be able to run for six months to two years on just two AA batteries.
• The operational range of ZigBee is 10-75m compared to 10m for Bluetooth (without a power amplifier).
• ZigBee sits below Bluetooth in terms of data rate. The data rate of ZigBee is 250kbps at 2.4GHz, 40kbps at 915MHz and 20kbps at 868MHz whereas that of Bluetooth is 1Mbps.
• ZigBee uses a basic master-slave configuration suited to static star networks of many infrequently used devices that talk via small data packets. It allows up to 254 nodes. * Bluetooth’s protocol is more complex since it is geared towards handling voice, images and file transfers in ad hoc networks.
• Bluetooth devices can support scatternets of multiple smaller non-synchronized networks(piconets). It only allows up to 8 slave nodes in a basic master-slave piconet set-up.
• When ZigBee node is powered down, it can wake up and get a packet in around 15 msec whereas a Bluetooth device would take around 3sec to wake up and respond.

IEEE 802.11 (WiFi)

IEEE 802.11 is an evolving family of specifications for wireless local area networks (WLANs) developed by a working group of the Institute of Electrical and Electronics Engineers (IEEE). There are several specifications in the family and new ones are occasionally added. All the 802.11 specifications use the Ethernet protocol and Carrier Sense Multiple Access with collision avoidance (CSMA/CA) for path sharing. The original modulation used in 802.11 was phase-shift keying phase shift keying (PSK). However, other schemes, such as complementary code keying (CCK), are used in some of the newer specifications. The newer modulation methods provide higher data speed and reduced vulnerability to interference. There many versions of 802.11 including the .a, .b, .g and .n versions with the variances mainly referring to data rate and throughput differences. There is much information on 802.11 available here ^[4].

Ultra Wide Band (UWB)

UWB is defined as any radio technology having a spectrum that occupies a bandwidth greater than 20 percent of the center frequency, or a bandwidth of at least 500 MHz (hence the term Ultra-Wide). Ultra Wide Band communications allows for high data throughput with low power consumption for distances of less than 10 meters, or about 30 feet, which is very applicable to digital home requirements. It is touted as the next big thing for personal area networking where many devices are involved, low power is a must and high data rates are important (medical monitoring). It operates at 3-10GHz for medical applications and data rates of between 850 kbps to 20 Mbps. Since UWB operates at very high frequencies it has very high penetration loss which will significantly affect the performance and size of the implantable nodes in a Body sensor network application. Thus any wide body area network standard will most likely incorporate a narrow band together with the UWB technology to cover many environments in future. The standard is still accepting proposals for the development of the body area networks, the UWB wireless chips are not available commercially to apply WBAN at the moment. Although UWB was claimed very low power initially in the literature, the attempts of such technology in the integrated circuits have exhibited power consumption more than that of the conventional narrowband short range wireless chips. UWB technology is very promising for real time location systems though (RTLS) where accurate location whereabouts is important. Much work is being done in this area with the use of RFID devices for medical asset tracking within hospitals.

A major drawback to date with UWB has been the standards issue. In January 2006 the Institute of Electrical and Electronic Engineers (IEE) abandoned its efforts for standardisation or the 802.15.3a Task Group (TG3a). The two groups developing UWB technology failed to come to agreement on a single solution: As a result, the IEEE group responsible for finalizing the standard didn’t get the votes required to move onto the next stage of the standardization process. The IEEE task group TG3a reduced the number of competing standards from 23 to two: MultiBand Orthogonal Frequency Division Multiplexing UWB, supported by the WiMedia Alliance and including members Intel and Microsoft, and the UWB forum which favors Direct Sequence-UWB and includes members Motorola, Samsung and Sony. Unfortunately, the two technologies differ significantly and cannot interoperate and so a classic standards dilemma exists.

Comparison of the Technologies

A good visual comparison of the internetworking technologies is given here.

Backhaul Network Access Technologies

These can be wired or wireless connections providing connectivity with remote services, central processing units or data aggregation facilities. Examples would include body sensor networks connected back to healthcare information servers located in a hospital monitoring centre. Often this link is referred to as 'backhaul' and it is the data pipe that brings the sensed healthcare data back to a centre where it can be actioned. Although narrowband solutions (such as 56k modem type) can be used if the data rates are low and network latency is permissible, the key breakthrough here is the availability of Broadband technologies such as ADSL, WiMAX, 3G and satellite communications.

Broadband Proliferation

Since December 2004, broadband subscribers in the OECD have increased by 187%, reaching 221 million in June 2007 and 380 million in September 2008. Broadband is available to the majority of inhabitants even within the largest OECD countries. A number of countries have reached 100% coverage with at least one wired broadband technology and up to 60% with coverage by two.

Infrastructure

• Digital Subscriber Line (DSL) Access - Digital Subscriber Line access is a popular method of delivering broadband connectivity due to the fact that it is transmitted over the standard telephone lines (POTs). This fact ensures that it has wide coverage and deployment to the home is relatively inexpensive. The common DSL technology is called ADSL i.e. Asymmetric Digital Subscriber Line so called because the data rate downstream (uploading from the internet) is higher than the upstream (pushing data out to the internet) data rate. Data rates can vary depending on the version of DSL being deployed, however typical downstream rates can be around 8Mbits/sec with upstream rates around 1 Mbits/sec. A DSL line can carry both data and voice signals and the data part of the line is continuously connected i.e. 'Always On'. In the OECD area, DSL networks have the most extensive broadband coverage overall. DSL coverage is particularly high in Belgium, Korea, Luxembourg, the Netherlands, and the United Kingdom. In 2005, 22 OECD countries had at least 90% coverage measured by lines, households or population. Greece had the lowest DSL coverage in the OECD area with only 9% of the population able to obtain a DSL line in 2005.

• Cable Access- Cable providers have made impressive gains upgrading networks and offering broadband services to the majority of homes previously without cable television. Broadband coverage by cable networks is very high in countries such as the United States, Canada, Korea, Belgium and the Netherlands. In some areas it is even more extensive than DSL. A good source of information on Cable access is located here

• Fiber to The Home Networks (FTTH) - These networks bring high speed optical fiber links directly into the home where traditionally copper based POTs or Cable would reside. The obvious advantage is high speed and high data rates. Fiber optic cables are made of glass fiber that can carry data at speeds exceeding 2.5 gigabits per second (gbps). FTTH services commonly offer a fleet of plans with differing speeds that are price dependent. At the lower end of the scale, a service plan might offer speeds of 10 megabits per second (mbps), while typical ADSL service running on existing copper lines is 1.5 mbps. A more expensive FTTH plan might offer data transfer speeds of over 100 mbps (that's about 66 times faster than typical DSL). Many of these networks have been in metropolitan areas since the density reduces infrastructure costs on a per subscriber basis. The cities of Amsterdam, Vienna, Reykjavik and Paris all have FTTH networks in the planning or rollout stages. NTT of Japan has the largest FTTH network rollout in the world in terms of total homes connected. Verizon in the United States is upgrading users to fiber connections and they plan on passing 9 million homes with fiber by year-end 2008 and 18-20 million homes by 2010.

• WiMAX (Worldwide Interoperability for Microwave Access) - This wireless broadband technology provides up to 75 Mb/s symmetric broadband speed without the need for cables. The technology is based on the IEEE 802.16 standard (also called Broadband Wireless Access). The name "WiMAX" was created by the WiMAX Forum, which was formed in June 2001 to promote conformity and interoperability of the standard. The forum describes WiMAX as "a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSLFixed wireless access. WiMAX has become available in some rural areas but these networks serve only a small percentage of subscribers. Wireless Internet access depends on available spectrum and OECD countries have taken steps to improve the efficiency of spectrum use. The United States Federal Communications Commission (FCC) has been working to make a significant amount of spectrum available for wireless broadband services. In September 2006, the FCC completed its auction of 90 megahertz of Advanced Wireless Services spectrum. Then in January 2008, the FCC began auctioning an additional 62 megahertz of spectrum in the 700 MHz band, which is particularly well suited for wireless broadband

• 3G Access- 3G is the third generation of standards and technology for mobile networking, superseding 2.5G. 3G networks are wide-area (as opposed to 802.11 or other Local Area Network technology) cellular telephone networks that evolved to incorporate high-speed Internet access. Because of their reach, wireless Internet connections using 3G or emerging wireless networks will be an increasingly important but largely complementary access technology to wired broadband. OECD countries already have extensive 2G coverage and many of these networks are likely to be upgraded to 3G in the near future. All OECD countries have 2G mobile coverage of more than 90% of their populations. Even large countries with extensive rural areas typically have excellent coverage of places where people live. Data shows that subscribers are switching to 3G networks nearly as rapidly as they originally took up cellular/mobile phones. Third-generation mobile data coverage is very high in a number of countries including Sweden, Korea, Luxembourg, Italy, the United Kingdom and the United States.

• Satellite Access- The broadband technology with the broadest geographic coverage is satellite. Geo-stationary satellites can supply broadband over very large geographic areas. Early satellite broadband connections required a fixed-line return path (upstream data) but current terminals can now transmit and receive data. Satellite has a large coverage area but only accounts for a small fraction of OECD broadband connections – largely due to its relatively high price compared with other connectivity options. Satellite connections are used for backhaul and end-user connections in rural and remote areas and play a vital role connecting areas that have no other means of access. Good technical detail on satellite access can be found here

• Broadband over Power Lines (BPL)- The least deployed technology involves the use of electrical power lines to transmit broadband. Broadband over power lines (BPL), also known as power-line Internet or power band, is the use of Power Line Communications technology to provide broadband Internet access through ordinary power lines. A computer (or any other device) would need only to plug a BPL "modem" into any outlet in an equipped building to have high-speed Internet access. International Broadband Electric Communications or IBEC and other companies currently offer BPL service to several electric cooperatives. BPL may offer benefits over regular cable or DSL connections: the extensive infrastructure already available appears to allow people in remote locations to access the Internet with relatively little equipment investment by the utility. Also, such ubiquitous availability would make it much easier for other electronics, such as televisions or sound systems, to hook up. Unfortunately proliferation has been almost non existent. Denmark had 98 PLC subscribers at the end of 2006, while the United States had just over 5,000 in June of the same year. BPL technology suffers from a number of issues. The primary one is that power lines are inherently a very noisy environment. Every time a device turns on or off, it introduces a pop or click into the line. Energy-saving devices often introduce noisy harmonics into the line. The system must be designed to deal with these natural signaling disruptions and work around them. The second major issue is signal strength and operating frequency. The system is expected to use frequencies of 10 to 30 MHz, which has been used for many decades by amateur radio operators, as well as international shortwave broadcasters and a variety of communications systems (military, aeronautical, etc.). Power lines are unshielded and will act as antennas for the signals they carry, and have the potential to interfere with shortwave radio communications. A recent judgment ^[5] against BPL from the US District of Columbia Circuit Court looks set to retard significantly the further development of this technology, based on the excessive interference problem

Speed

Competition is a key to lowering prices but it also has a significant effect on the services and speeds available to businesses and consumers. Broadband quality tends to increase over time even as prices decline. This is a common feature in the ICT sector but broadband changes have been particularly rapid. At the end of 2004 the average DSL speed across the OECD was less than 2 Mbit/s. The average advertised broadband speed had more than quadrupled to nearly 9 Mbit/s over a period of less than three years. The average speed of advertised connections increased from 2 Mbit/s in 2004 to almost 9 Mbit/s in 2007. However the actual speed delivered to the customer can vary greatly form the 'advertised' speed and this has been an issue of some contention and has led to a lack of trust by consumers. A report from the United Kingdom regulator OFCOM found that only 20% of customers live close enough to a telephone exchange (3.2 kilometers) to receive the advertised 8 Mbit/s internet connection. If a user lives even further from the exchange, say 8 kilometers away, users may only receive between 0.5 and 2 Mbit/s. There is also a significant difference between connection speeds between rural and urban areas. The European Commission finds that download speeds between 144 kbit/s and 512 kbit/s have been the most common in rural areas in the past two years. In contrast, the most common speeds in urban areas are closer to 1 Mbit/s. The fastest advertised broadband connections offered by incumbent telecommunication operators were (2007) in Japan, Korea, Sweden, France and Finland. NTT in Japan offers 1 Gbit/s connections to apartment buildings while the other operators offer Fiber to the home (FTTH) at 100 Mbit/s to individual apartments or houses.

Cost

Price per Mbit per Second. Source: Broadband Growth and Policies in OECD Countries – OECD 2008

Prices have an impact in areas with wired coverage as well and can be a strong determinant of broadband take-up. According to a recent OECD report ^[6], between 2005 and 2006 the average price for a DSL connection fell by 19% and by 16% for cable Internet connections. Broadband is also affordable in most OECD countries. The price of a broadband subscription in 20 of the 30 OECD countries was less than 2% of monthly GDP per capita in October 2007. The introduction of entry-level broadband plans has helped broadband operators increase the number of total subscribers while still offering the possibility for customers to pay more for faster speeds. Unbundling of copper telephone lines itself seems to be a factor in reducing the price of broadband subscriptions, as they introduce more competition at the telecommunication exchange.

Coverage

Broadband Coverage - Source: Broadband Growth and Policies in OECD Countries – © OECD 2008

Coverage statistics and penetration rate data show that operators and governments have made great strides extending broadband to rural and remote areas. Satellite services are available in even the most remote areas of many OECD countries, although these tend to be more expensive relative to other access technologies. Many governments have also implemented broadband demand aggregation policies to bring connectivity to rural areas. High-speed wireless/mobile Internet connections are increasingly available as an important option for users.

Government Policy

In February 2004, the OECD Council adopted the Recommendation of the Council on Broadband Development. The Recommendation calls on Member countries to implement a set of policy principles to assist the expansion of broadband markets, promote efficient and innovative supply arrangements, and encourage effective use of broadband services. The Council instructed the OECD Committee for Information, Computer and Communications Policy (ICCP) to monitor the development of broadband in the context of this Recommendation within three years of its adoption and regularly thereafter.

Promoting the general ICT business and policy environment, fostering innovation in ICT (including R&D) as well as ICT diffusion and use (including e-government) have been priorities. Likewise, ICT skills and employment, digital content and promoting trust have been key concerns. In particular, OECD governments have implemented demand-based approaches for spreading broadband access. Policy makers have made particular efforts connecting schools, libraries and other public institutions. Overall, these policies have led to increased use of broadband across the board. Governments have also fostered broadband content and applications, for example, by acting as model users, by promoting e-government services and broadband-related standards, by putting content online and by supporting the development and distribution of digital content by other players. Governments and industry have also put into place regulatory measures to promote a culture of security. On the consumer protection side there has been focus on developing awareness campaigns to educate consumers about risks to Internet security; they have also instructed consumers on how to protect themselves against fraudulent practices.

References

1. ↑ http://www.bluetooth.org
2. ↑ http://www.zigbee.org
3. ↑ http://www.zigbee.org
4. ↑ http://standards.ieee.org/getieee802/802.11.html
5. ↑ http://news.cnet.com/8301-10784_3-9930223-7.html
6. ↑ BROADBAND GROWTH AND POLICIES IN OECD COUNTRIES – ISBN-978-92-64-04668-9 © OECD 2008. http://www.oecd.org/dataoecd/32/57/40629067.pdf

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