Saturday, July 26, 2008

WiBro vs. WiMAX

WiMAX, is an acronym of Worldwide Interoperability for Microwave Access, is a telecommunications technology provides wireless data over long distance. It is based on the IEEE 802.16 standard, also called WirelessMAN. According to WiMAX forum WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL.  

WiBro (Wireless Broadband) is a wireless broadband Internet technology being developed by the South Korean telecoms industry. WiBro is the South Korean service name for IEEE 802.16e (mobile WiMAX) international standard. Actually, WiBro was developed to overcome the data rate limitation of mobile phones (for example CDMA 1x) and to add mobility to broadband Internet access (e.g. ADSL or Wireless LAN). WiBro adapts TDD for duplexing, OFDMA for multiple access and 8.75 MHz as a channel bandwidth. WiBro base stations offer an aggregate data throughput of 30 to 50 Mbit/s and cover a radius of 1-5 km allowing for the use of portable internet usage. It provides mobility for moving devices up to 120 km/h.

Advantages of WiBro over WiMax:

WiBro provides mobility for moving devices up to 120 km/h compared to WLAN having mobility up to walking speed and Mobile Phone having mobility up to 250 km/h. It also offers QoS. The inclusion of QoS allows for WiBro to stream video content and other loss-sensitive data in a reliable manner. 

Friday, July 25, 2008

A sensor network which covers 2 Km x 2 Km to measure a temperature, humidity and CO2 levels every 10 seconds.

We design a sensor network that collects data monitoring temperature, humidity and CO2 levels. The sensors in 2x2 Km2 area relays collected data to its neighboring sensors and then to a base node. Base node is connected with computer that processes and analyzes data. We selected following factors to design the network

Sensor Nodes (Motes): Crossbow Berkeley Motes may be the most versatile wireless sensor network devices in the market commercially available. MICAz is the latest generation of Motes from Crossbow Technology. MICAz motes come with several sensors installed - Temperature, Humidity, Gas, Light, Acceleration/Seismic, Vibration etc. Different sensors can be installed if desired. The MPR2400 (2400 MHz to 2483.5 MHz band) uses the Chipcon CC2420, IEEE 802.15.4 compliant, ZigBee ready radio frequency transceiver integrated with an Atmega128L micro-controller. 51 pin I/O connector, and serial flash memory is used. Alternatively, USS 2400 marketed by a Korean Company HUINS (Human Intelligent System) can be used. USS 2400 is compatible with Berkeley Motes. 
These motes are low power and small physical size enable placement virtually anywhere. Since all sensor nodes in a network can act as base stations, the network can self configure and has multi-hop routing capabilities. 

Number of Nodes required: We can apply a grid structure to uniformly deploy sensors. MICAz’s maximum transmission range is 100m in open air. However it is always safe to use  N= Gx × Gy = X/r × Y/r

=(2000 m)/(50 m)×(2000 m)/(50 m)=1600

Where, Gx and Gy are the total number of grids in X and Y respectively. r is a transmission range of the node (transmission range is given as 50 m). Above calculation shows total number of nodes required is 1600. 

Base Stations: A base station allows the aggregation of sensor network data onto a PC or other computer platform. According to our network plan at least one Base Station is required. Any MICAz Mote can function as a base station by plugging the MPR2400CA Processor/Radio Board into an MIB510CA serial interface board. The MIB510CA provides an RS-232 serial interface for both programming and data communications. 

Computer (PC): We need at least one computer for data aggregation, processing and analysis. Any latest version of readily available computer can be used for this purpose. Better and dedicated server can be considered according to the significance of the data.

Routers: As we implement AODV (Ad Hoc on Demand Distance Vector) routing protocol we do not need dedicated router. It is an ad hoc structure i.e. any normal sensor node (MICAz mote) in the network can be a router. 

Battery Power : MICAz form factor is designed to match up with two AA batteries; however any battery combination (AAA, C, D, etc., cells) can be used provided that the output is between 2.7 VDC to 3.6 VDC.

OS: Freely available and open source, TinyOS has become the de facto industry-standard operating system for sensor network research and applications. A researcher’s group from UC Berkeley designed this sophisticated operating system to manage mote hardware. TinyOS is written in nesC. nesC supports the event-driven processing that is typical of motes, which remain "asleep" until sensors acquire data or receive messages. 

MAC: We use S-MAC as a MAC layer protocol. S-MAC protocol is designed for wireless sensor networks. S-MAC uses three novel techniques to reduce energy consumption and support self-configuration. To reduce energy consumption in listening to an idle channel, nodes periodically sleep. Neighboring nodes form virtual clusters to auto-synchronize on sleep schedules. S-MAC applies message passing to reduce contention latency for sensor-network applications that require store-and-forward processing as data move through the network. 

Routing: Our network design is static or barely dynamic in nature. AODV (Ad Hoc on Demand Distance Vector) routing protocol can be used. AODV routing algorithm is an on demand algorithm, it is loop-free, self-starting, and scales to large numbers of nodes. AODV builds routes using a route request / route reply query cycle. If any link is broken in the link it repairs using route error message.

Thursday, July 24, 2008

Future trends for Cell phones, PDAs and Mobile Internet Devices

These days, our cell phones can take and send pictures/video. We can text message, download ringtones, watch streaming music video and even download and play mobile games. Not only that we can watch DMB and surf internet as well. The services available now couldn't even be imagined by most of us 10 years ago. The rapid advancements in information and communication technology have made it possible to do all these things. Before lunching 2G in Finland for the first time in 1991, today’s revolutionary 3G/4G communication were out of imagination. 

PDA is a handheld computer having many uses: calculation, use as a clock and calendar, accessing the Internet, sending and receiving E-mails, word processing, use as an address book, making and writing on spreadsheets, playing computer games and Global Positioning System (GPS). PDAs can access the Internet, intranets or extranets via Wi-Fi, or Wireless Wide-Area Networks (WWANs). Many PDAs employ touch screen technology. 

Mobile Internet Device (MID) gives an internet experience in our pocket. MID represent a portable and mobile devices category that gives wireless connectivity and long battery life. Samsung Q1, is an example of Mobile Internet Device, comes with a 7" (18 cm) LCD and exists in several different versions.

However, people are beginning to appreciate the value of connecting to the internet from their portable mobile devices. Carrying multiple devices is not convenient, so they prefer single device having versatile capabilities. New generation cell phones (smart phones) are capable of performing PDA’s tasks. Today most smart phones sold worldwide incorporate at least one advanced feature. Competition among phone manufacturers is primarily based upon a race to add additional features within accepted price ranges. The smart phones (with 4G+ or future technological standard) in the near future will bring the complete solution for the user by providing all in one solution.

The iPhone is a one example of the media based mobile device. Mobile companies they are selling iPhones are generating revenue not only by selling a phone plan, but also charging on bandwidth for audio and video downloads. Also, they are making money through mobile marketing.

Technically, in my opinion, in the future cell phones will dominate the future internet. Because IEEE 802.11 is not channelized, so control packets, such as RTS, CTS, and ACK, use the same channel as data packets. This leads to complex arbitration schemes and potentially unfair bandwidth allocation due to hidden and exposed terminals. Cell phones use channelized media, which intrinsically share the wireless medium better and are immune to a variety of hidden terminal problems. Moreover, unlike a WiFi-based PDA, a cell phone cannot be blocked from accessing the channel because the data channel is hogged by another cell phone. For these reasons, it appears that a channelized cell phone may better use wireless spectrum than a WiFi-based laptop or PDA. Incidentally, cell phone spectrum is licensed, so it is also immune to interference from cordless phones and microwave ovens that occupy the unlicensed ISM bands.

Generally, these handheld devices will become powerful computing devices, comparable to desktop systems. But there will be no market for standalone, handheld devices like only PDA, MID or Cell phones. Growing popularity shows all portable devices including cell phones, PDA and Mobile Internet Devices will come in one device.

Wednesday, July 23, 2008

2G and 3G cell phones and Internet

2G cell Phones: 2G stands for Second Generation Wireless Telephone Technology. 2G networks were analog but its predecessor 1G networks were analog. 2G technology came with text messaging (SMS) capabilities.

3G cell Phones: 3G is the third generation of mobile phone technology provides a wider range of more advanced services while achieving greater network capacity through improved spectral efficiency. This technology also offers wide-area wireless voice telephony, video calls, and broadband wireless data, all in a mobile environment. Also includes HSPA data transmission capabilities able to deliver speeds up to 14.4Mbit/s on the downlink and 5.8Mbit/s on the uplink.

Internet: Internet is a "network of networks" that consists of millions networks, which together carry various information and services, such as electronic mail, online chat, file transfer, and the interlinked web pages and other resources of the World Wide Web. Internet can be accessed in both wired and wireless environment. IEEE 802.11 is a standard for WLAN. The term 802.11b and Wi-Fi are often used interchangeably. IEEE 802.11 (Wi-Fi or WLAN) networks are short range, high-bandwidth networks primarily developed for data communication.

In the following prospective 2G, 3G and Internet are same:

  • All are wireless technologies
  • Both offer broadband data service

In the following prospective 2G and 3G, and Internet are different:

  • From the users prospective 2G is for voice communication with some messaging service, 3G is mostly voice and then data service and Internet is mostly for data communication service with voice capability.
  • 2G/3G and Internet’s network structure is different.
  • Current business models/deployments are different. 3G services provided by Mobile operators where as WiFi provided by data communications industry or we can say it’s a byproduct of the internet industry.
  • Spectrum policy and management: (2G and 3G use licensed spectrum but Internet uses unlicensed shared spectrum. This has important implications for (1) cost of service; (2) quality of service (QoS) and congestion management; and (3) industry structure.)
  • 3G offers better support for secure/private communications than others.
  • 3G has a relatively small family of internationally sanctioned standards, collectively referred to as IMT-
  • 2000.36. In contrast, Wireless Internet is one of the families of continuously evolving 802.11x wireless Ethernet standards, which is itself one of many WLAN technologies that are under development.
  • Getting license for 3G is difficult than 2G.
  • 3G is more developed than WiFi as a business and service model.

All of them have some advantages and disadvantages. 2G requires lower powered radio signals and consumes less battery power, so phones last much longer. 2G (without GPRS) is not much capable for data service. 3G is very reliable in voice communication with a wide range of more advanced services with improved spectral efficiency. But data communication with 3G phones is expensive comparing to general internet service. It consumes more power than 2G cell phones and it is not fully IP-based integrated system. Internet is basically for data communication with some voice communication capabilities. Of course, it is less expensive than the general telephony but still internet is not preferred for the voice communication.