After seeing some people create their own discrete (well, OP-AMPs are discrete nowadays, right?) RFID readers, I wanted to give it a try.
I first started by creating a simple, non-filtered, non-processed reader. I’ve used a coil of about 1mH for both sides. Since my chosen frequency was 125 KHz, my capacitor should be 1.62nF according to the following equation; I picked 1n5 standard value.
Equation 1.
So this configuration is probably one of the simplest forms of an RFID reader-tag pair:
Figure 1
L1 is driven via a low-impedance 125 KHz oscillator, can be a sine or a square wave since the LC circuit will filter out the unwanted harmonics that are presented in a square wave. If the Q of the inductor is high, then a voltage that is greater than the oscillator’s output is going to be present in the “Out”. I’ve seen 100 Vpp when I fed the LC circuit with 5Vpp!
So, the “Out” waveform at the top of the C1 is a sine wave of a 125 KHz frequency. Now, the fun thing begins when we put the tag near the reader. L2, C2 pair picks up the 125KHz waveform via L2. So, if you scope C2, you will see 125 KHz sine wave. Now, if you scope “Out”, you will see that Vpp at C1 will drop when we close the switch SW1. That is because we load L1′s magnetic field via L2. Now, push the button like you are sending a Morse code and watch the “Output” waveform on the scope. Aha, modulation!
Simple! That is how real RFID passive tags work. However, instead of sending Morse code, they modulate the signal with their specific modulation scheme. I am going to work with EM4100 protocol since it is widely used.
Okay, let’s bring some real circuitry here.
Figure 2
Ignore those jumpers (JP1 and JP2) since they are PCB jumpers that I needed when making a single-sided PCB.
OK, L1 and C6 are our main guys. They are the components that are mentioned before as “L1″ and “C1″ in Figure 1. The circuitry on the left side of L1 is used to drive this LC circuit, and right side of C6 is used to read the changes in the signal.
C1 AC couples the clock signal of 125KHz to the circuit. R1 and R2 biases the transistor Q1. R4 limits its base current. Q1 drives the input of push-pull follower formed by Q2 and Q3. A push-pull follower will drive the signal at low output impedance. D2 and D3 prevents distortions at the cross-overs from zero level.
Now, our signal at “TP1″ is something like this, with no processing and modulation:
Scope Shot 1
We are going to use an “envelope detector” formed by D4, C8 and R13. After the recovery, this is how our “modulated” signal looks like:
Scope Shot 2
Of course, these measurements are made with the tag almost touching the reader. If we move the tag away about 5 cm from the reader, we may not be able to see the signal even with the oscilloscope. So, we have to filter and amplify this signal and make it ready to be processed by a microcontroller later on.
As you can see above, the signal we are dealing with is an AC signal. To deal with AC signals with the OP-AMPs, you need either a dual supply which goes to negative (for example -12V, +12V), or you need a virtual ground. We are going to assume that half point of our supply voltage is ground. So, if we are using a 5V single supply, our half point is +2.5V. If +2.5V is ground, then +5V is our new +2.5V and 0V is our new -2.5V. There you have it, a dual supply. We need the output impedance of this supply low, so we use an OP-AMP to buffer the +2.5V point which is high impedance due to R15 and R16, and we get a low impedance output as shown:
Figure 3
OK, now that we have solved that problem, let’s go back to our filter design. We have a square wave at certain frequency that we want to boost. While boosting the desired frequency we want to kill the other frequencies. But we see a bump there; square wave. A square wave is a signal that includes lots of harmonics (theoretically; infinity) of its actual frequency. These harmonics are hidden in the rise and fall waves, sharper the rise and fall, more the harmonics count. So, that means, if you low pass filter a square wave -that is not letting higher frequencies to pass a filter, you delete those harmonics and remember, those harmonics are in rise and fall times. Thus, you end up with a sine wave. We do not want that, that’s why we are going to let these frequencies pass as the way they are, however we are going to boost the original frequency. To do this, we have a filter design like follows:
Figure 4
“SignalOut” is our input coming from the envelope detector. C2 and R3 form a high pass filter to AC couple the input, and D1 protects the non-inverting input of the U1:A from over-voltage. You may say that it is not needed as the capacitor C2 will not allow any DC voltage through, you are correct. But only in steady state, if the capacitor is discharged, then it will let DC until it is charged. By the way, think +2.5V point as a “ground” point, since it is a virtual ground. C5 and R10 AC couples the output from U1:A in case of any DC offset. Then, this signal is filtered again, resulting in more amplification. Here is a graph showing the transfer characteristics of these filters:
Graph 1
Here is the waveform at the output node, pin 7 of U1:
Scope Shot 3
Yay! We have a filtered, clean output! But not so fast, because we need logic output. This is done easily by a comparator. Normally, OP-AMP comparators compare the input with a reference voltage, generally half the supply voltage. However, this may not work well if the rise and fall times of the input waveform is not in symmetry or close enough. Let’s demonstrate that with a reference voltage of half the supply:
Graph 2
The input signal has a loooong fall time. It should fall down at 3ms point ideally, since this is a recovered, however badly distorted ~43% duty cycle square wave -well at least let’s assume. See how the output waveform is a ~56% duty cycle square wave. We do not want that.
What you have to do is simple, compare the input signal with its average. How do you find a signals average? That is simple too -put it into a low pass filter, and here is the output:
Graph 3
Now let’s look at our case and apply:
Figure 5
Again, ignore the jumper JP4, that is for PCB. Let’s look at R14 and C10, we have selected them so that we have a good averaging (should I say weighted?) level for both 1KHz and 2KHz outputs we will have. This is the final output, isn’t it great:
Scope Shot 4
Finished PCB:
Finished PCB
Front Side
Back Side
I have used KiCad to draw the schematics and PCB, and I am fascinated by the usability of it. Before, I was using Proteus from Labcenter Electronics UK, however, KiCad is cheap and more usable. I will use ISIS as my circuit simulator (not spice), though. Here are the design files:
1. Interfacing of graphical LCD to LPC2148 ARM Based 32-bit microcontroller
2. H-Bridge based DC Motor speed & Direction control using PWM using ARM 7 TDMI processor based LPC2148 Controller
3. Advanced mobile phone signal jammer for GSM, CDMA and 3G networks with prescheduled time duration using ARM 7 TDMI processor based LPC2148 Controller
4. Petrochemical Level Indicator and controller for automation of Cotton Purification industries using ARM 7 TDMI processor based LPC2148 Controller
5. Implementing character LCD Device Driverdevelopment on LPC2148 ARM Based 32-bit microcontroller
6. Biometric finger print based bank locker system using ARM 7 TDMI processor based LPC2148 Controller
7. Implementation of Data Encryption Standard on ARM(ARM7TDMI) processor based microcontroller(LPC2148)
8. Implementation of ZigBee based multipoint secured PC messaging system ARM 7 TDMI processor based LPC2148 Controller
9. GSM based automatic vehicle accident detection with GPS based location identification and messaging system using ARM 7 TDMI processor based LPC2148 Controller
10. Implementation of EEPROM Interfacing with I2C protocol using ARM 7 TDMI
11. Industrial Temperature Monitoring and controlling using ARM 7 TDMI processor based LPC2148 Controller
12. Automatic photovoltaic panel direction control for maximum power tracking using ARM 7 TDMI processor based LPC2148 Controller
13. GSM based Remote Industrial appliances control system using ARM 7 TDMI processor based LPC2148 Controller
14. Real time data acquisition using ARM 7 TDMI processor based LPC2148 Controller
15. GSM based advanced transformer load sharing system using ARM 7 TDMI processor based LPC2148 Controller
16. Implementation of Serial port device driver using ARM 7 TDMI processor based LPC2148 Controller
17. Biometric finger print based electronic voting system for rigging free governance using ARM 7 TDMI processor based LPC2148 Controller
18. Intelligent LPG / Smoke Detector with Auto dialer using ARM 7 TDMI processor based LPC2148 Controller
19. Auto turn off for water pump with four different time slots using ARM 7 TDMI processor based LPC2148 Controller
20. A smart ZigBee based wireless weather stationmonitoring system using ARM 7 TDMI processor based LPC2148 Controller....
We are witnessing a huge interest for wireless devices (phones and PDAs) and services especially from professionals and people “on the move”. The Short Message Service (SMS), or paging, can be considered as a significant market success either for business or entertainment purposes. The ability to exchange SMS messages provides the convenience of being able to reach anyone anytime and anywhere in urgent situations. Unfortunately, SMS has fundamental limitations that make it an unsuitable technology above which to layer collaborative services. On the other hand, as wireless networks are bringing the idea of the “unplugged Internet”, a new standard, called Wireless Application Protocol (WAP), is emerging and making a significant impact in the mobile market.
2. System Description:
In recent times, chat rooms and instant messaging have proved enormously popular services. The predecessor to these services is Internet Relay Chat (IRC), which is an IP based service with sophisticated support for distributed collaboration. IRC provides a variety of mechanisms for users to collaborate across the internet with friends, colleagues and others both publicly and privately by creating and subscribing to various “channels”, or chat rooms, to exchange text message and file transfers.
2.1User Scenario:
From an end user point of view, the scenario we consider enables mobile users to chat by sending to each other instant messages. They can interact according to the instant responses of their friends/colleagues (“bodies”). In terms of functionality, the users interact with our WAP Chat application that supports a Wireless Markup Language (WML) interface enabling them to:
• Select and connect to a given chat server: users can choose among a list of available servers, the closest server to his/her current location (for best performance).
• Once connected to the chat server, the user can choose from a list of open channels provided by the server the discussion room (channel) that they wish to join.
• Scroll through the messages sent by other users on a channel.
• Type and send messages to the channel.
• Join another channel.
• Disconnect from the chat server.
At the start of a session, users are asked to input their contact information [optional]: name, email, photo, WML home page, etc. (figure 1A). When the user joins a channel, a hyperlinked list of the current subscribers to the channel is presented. The user can follow any of these links to view the contact information [optionally] entered by each subscriber. Once the user has joined a channel, he or she will be able to view the messages that have been sent to this channel. Accompanying each message is the name of the person that sent that message, with the name of the person hyperlinked back to their contact information (figure 1B).The user also receives a notification message indicating when others users join and leave the channel (figure 1C)
The system is based on a three tier architecture, but not in the traditional sense. A WAP client (tier 1) connects, via a WAP gateway, to the WWW server hosting the WAP Chat service (tier 2) which manages collaborators on a per-user-session basis. The WWW server hosting the WAP-Chat service then connects to the IRC server (tier 3) as specified by the user at the start of the session. The WAP-Chat WWW hosted application server manages user chat sessions which, in turn, can interact with multiple IRC servers. The WAP-Chat application server is also responsible for dynamically generating a rich WML interface for the WAP clients.
Figure 2. WAP Collaboration Model
3.Security Hole At The WAP Gateway:
In general, the mobile customer and the e-merchant involved in an m-commerce transaction want (or should want) to ensure:
Confidentiality: Those messages are kept secret.
Authentication: That each party knows whom the other party is.
Message integrity: Those messages are passed unaltered from sender to receiver.
Replay attack prevention: That any unauthorized resending of messages is detected and rejected.
Non-repudiation: That neither party can later reject that the exchange took place.
All these issues must be addressed in a secure system. Indeed, it is the ambition of the WAP Forum to develop WAP into a standard that covers all relevant aspects of security, and some steps have been taking already with version 1.2.1 while version 2.0 goes a little bit further. For security, WAP provides a secure protocol for data transport: WTLS, Wireless Transport Layer Security. WTLS also contains features for authentication of both parties, as well as for non repudiation using message digests and digital signatures. Authentication of the user of a GSM phone may utilize the phone’s SIM card.
Finally, the definition of WML-Script includes a specification of a function library called a “crypto package”. This library contains a signing function, which can be used by a user to digitally sign a message, in the conventional manner in a Public Key Infrastructure. Thus WAP supports nonrepudiation of messages (such as a placement of an order) sent by a mobile WAP user. In the sequel, we merely discuss to what extent WAP achieves message confidentiality.
WAP’s two-stage security model: The basic security feature of WAP provides secrecy in the two half parts of the path that connects the WAP client and the web server: the (presumed) wireless path between the WAP client and WAP gateway, and the (presumed) wired path between the gateway and the web server (Figure 4). In the middle point constituted by the gateway, incoming data is decrypted; then while the data is in its original, un-encrypted form, it is subjected to some processing; and finally it is encrypted again before it is sent off along the other path. For encryption over the wired path, WAP simply relies on the Transport Layer Security (TLS) protocol, a widely used Internet standard. For encryption over the wireless path, WAP uses WTLS, which is in essence an adoption for wireless communication of the TLS protocol.
Figure 4. Security zones using standard security services (WTLS and TLS)
Thus prompted by the WAP client, the WSP layer at the gateway will initiate a TLS connection to the web server, in a way completely similar to setting up a connection between an ordinary web client and the server. This combination of WTLS and TLS provides secrecy (indeed, also integrity) over both halves of the WAP client / web server connection.
The crucial weakness is, of course, that all data transferred between the WAP client and the web server is decrypted at the WAP gateway, i.e., all data such as credit card numbers, etc. exists as free text in the memory of the gateway. Technical solutions, such as various programming techniques applied to the software that implements the WAP gateway, can make it somewhat difficult to get access to the data, but not impossible. Organizational solutions, such as tightening the security policy of the organization that hosts the WAP gateway, may limit access to the gateway and it’s data; but from the point of view of the two “end users” it is unsatisfactory that the privacy of their data is not under their own direct control.
4. Solutions For The WAP Security Problem:
4.1 Putting the gateway inside the “vault”:
The WAP gateway can be placed at the web server end of the connection, that is, inside the same security zone. When residing inside the local network of the merchant the gateway is protected against the outside world in a similar fashion to the way the web server is protected. A closer look at the business potential for the three stakeholders reveals that this solution does introduce further problems as well. Whether these will be solved is hard to say at the moment.
1. The Mobile Service Provider
For the Mobile Service Provider the main problem is a possible loss of business opportunities, e.g. “locking in” the customer to the provider’s m-portal. There are a number of possible WAP services that the MSP can offer only if it hosts the gateway, this being the MSP’s only way of ensuring that all data used in those services stays within the mobile network that the MSP is in control of. For instance, location dependent services utilize the MSP’s access to information from its own network about the exact location (cell) of the mobile phone. There may be strong business and security reasons for the MSP to not want such data to be available outside of the network. In the case of location information, the data is clearly sensitive, at the same time; the data may have a high business value, exactly because it is a prerequisite for certain services.
Moreover, this solution challenges the MSP to open its network to outsiders like the merchants running their own gateway. Each limitation on the MSP’s full control over the usage of its networks may introduce further traffic management problems.
2. The User
The user of the WAP client may witness degraded performance: The WAP protocols, which are tailored for the characteristics of wireless networks, are now used for the entire transport of the web content to the WAP client, instead of merely for the wireless part as intended. This may incur increased delays if there is congestion in the wired network. The end-user interface becomes less friendly, because the user of the WAP client will be forced to swap between gateways during Internet browsing. For example, the user that wants to buy from two distinct websites needs to use the WAP gateways of those sites. Swapping gateways raises two problems when changing the gateway profile of the phone. The gateway profile includes a dial-up phone number, the IP number of the gateway, etc.
3. The Merchant
The e-merchant is burdened with a complex piece of additional software (the gateway) that must be acquired and maintained. For a WAP gateway, maintenance work includes, for example, ensuring that the security-related software in the gateway is up-to-date, and updating the gateway to new versions of the WAP protocols. It is, however, not clear, whether the merchant will be further “burdened with handset provisioning and activation issues”.
4.2 Solution 2: Application level security on top of WAP:
This amounts to introducing security at a software layer above WAP, and considering WAP merely as a potentially insecure communication means (figure 5). Instead of using WAP’s protocol for secure transport (WTLS), security is taken care of by means of dedicated software running at the two “ends”, the mobile phone and the e-merchant’s web server. Such software could perform encryption in a way that eliminated the security hole at the gateway. In general, the approach would be in line with the conjecture about protocol design made in an end-to-end function, must be placed at a level where end-to-end control is available, i.e., at the application level.
While technically possible, above said solution would add a burden of extra complexity in the mobile phone. Indeed, the implementation of application-level security on top of WAP requires that sophisticated cryptographic functionality is made available to applications on the mobile WAP phone, either in the form of future enhancements of the WML Script Crypto Library or in other ways. It should be noted that the single function for digitally signing a message, which is presently the only function contained in the library is insufficient. Specifically, the Crypto Library’s signing function is not useful for encryption of data, because in principle, everyone in possession of the WAP user’s public key can read a message that she has signed digitally.
Moreover, this approach would partly neutralize most of the optimization provided by the WAP gateway: there will be a loss of the benefits of the data conversion and compression taking place in the gateway to accommodate the limited bandwidth of the wireless network. To minimize this, a balanced approach may be to encrypt only small fragments of the data, not the data as a whole. This would allow the WAP gateway to perform compression, decompression, and compilation by providing access to the WML tags and WSP/HTTP commands in their original, unencrypted form.
Figure 5. Security zones using application level encryption
4.3 Solution 3: Enabling internet on the mobile device:
The third and last approach is to re-design the WAP protocol to not use a gateway, and employ the existing Internet standards, including the transport protocol (TCP), for the entire wired and wire-less part of a connection. By definition, this solves the security problem introduced by the gateway. This change of design has been proposed by the WAP Forum for version 2.0 of the WAP protocol. The standard now allows a range of different gateways, corresponding to having the conversion between the two protocol stacks anywhere from the top to the bottom of the stack.
At the top layers, the gateway works like the traditional WAP gateway taking care of the functions mentioned, and at the bottom layer it works like a traditional bridge/router. Whereas a TCP level gateway allows for two versions of TCP, one for the wired and another for the wireless network, on the top of which a TLS channel can be established all the way from the mobile device to the server.
The move away from top level conversion constitutes a fundamental change of design, which does away not only with security problem, but also the optimization for the wireless network, made possible by the gateway. Discarding the WAP gateway makes it possible to attain the same high level of security for an m-commerce transaction as that of an e-commerce transaction on the ordinary web using full end-to-end encryption. Indeed, for WAP to discard the WAP gateway would turn the (fully) WAP enabled mobile phone into an ordinary Internet device.
Besides the cost of deploying a full Internet protocol stack in the mobile phone, this solution enforces additional messages to be send between the device and the Internet. A simple request for a WML document must – in contrast to the gateway-based WAP solution – wait for a DNS-lookup to derive the appropriate IP-number from the symbolic name in the original request. The gateway based solution only has this cost over the wired Internet, when the gateway converts the WAP request to an HTTP-request. A minor optimization would be to utilize a caching DNS server at the border between the wired and the wireless network.
5.Conclusion:
Mobile SMS messaging (or paging) can be considered as a significant market success. The ability to send text messages has proved enormously popular across many sectors of the market, in particular among younger people. A tremendous improvement over SMS, WAP-Chat is a novel service to be offered by operators for exchanging messages between mobile users. As we move forward to ubiquitous information access, the convergence of WAP and collaboration services will yield a range of new and exciting approaches for supporting mobile groups that may be potentially distributed around the world.
Although the security hole associated with the gateway is commonly recognized, the WAP Forum did not release its previous deliberations as to why it felt the gateway’s advantages would outweigh its disadvantages. The introduction and subsequent de-route of the WAP gateway – whether preconceived or not – has increased the complexity of the WAP standard, comprising variations both with and without the gateway. We foresee a future where all the communication oriented WAP standards are replaced by Internet standards, leaving only the application level protocols in WAE as WAP specifications. It is also interesting to observe how the old and open Internet technology is able to outperform a vendor provided network solution like WAP. One may hope that the significance of a fully open discussion and standardization process will be learned also by the vendors behind the semi-opened WAP Forum
WiMAX is an acronym that stands for Worldwide Interoperability for Microwave Access. WiMAX is a wireless metropolitan area network (MAN) technology that can connect IEEE 802.11 (Wi-Fi) hotspots with each other and to other parts of the Internet. It can provide a wireless alternative to cable and DSL for last mile (last km) broadband access. WiMAX is the wireless solution for the next step up in scale, the metropolitan area network (MAN). WiMax does not conflict with Wi-Fi but actually complements it. A WiMax system consists of two parts: A WiMax tower & A WiMax receiver. WiMAX has the potential to do to broadband Internet access what cell phones have done to phone access. Some cellular companies are also evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications. The purpose of this Paper is to highlight and assess the value of WiMAX as the right solution to:
offers cheap voice calls and high speed internet
ensures a boost for government security
extend the currently limited coverage of public LAN (hotspots) to citywide coverage (hot zones) the same technology being usable at home and on the move,
blanket metropolitan areas for mobile data-centric service delivery,
offer fixed broadband access in urban and suburban areas where copper quality is poor or unbundling difficult,
bridge the digital divide in low-density areas where technical and economic factors make broadband deployment very challenging.
In addition to these uses, this paper will highlight other potential applications, such as telephony or an effective point-to-multipoint backhauling solution for operators or enterprises
1. INTRODUCTION
WiMAX is an acronym that stands for Worldwide Interoperability for Microwave Access, a certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards. Products that pass the conformity tests for WiMAX are capable of forming wireless connections between them to permit the carrying of internet packet data. It is similar to Wi-Fi in concept, but has certain improvements that are aimed at improving performance and should permit usage over much greater distances. the WiMAX forum, backed by industry leaders, will encourage the widespread adoption of broadband wireless access by establishing a brand for the technology and pushing.
2. TECHNICAL ADVANTAGES OVER WIFI
Because IEEE 802.16 networks use the same Logical Link Controller (standardized by IEEE 802.2) as other LANs and WANs, it can be both bridged and routed to them.
An important aspect of the IEEE 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings. This is also an important aspect of why WiMAX can be described as a “framework for the evolution of wireless broadband” rather than a static implementation of wireless technologies. Enhancements to current and new technologies and potentially new basic technologies incorporated into the PHY (physical layer) can be used. A converging trend is the use of multi-mode and multi-radio SoCs and system designs that are harmonized through the use of common MAC, system management, roaming, IMS and other levels of the system. WiMAX may be described as a bold attempt at forging many technologies to serve many needs across many spectrums.
The MAC is significantly different from that of Wi-Fi (and ethernet from which Wi-Fi is derived). In Wi-Fi, the MAC uses contention access—all subscriber stations wishing to pass data through an access point are competing for the AP’s attention on random basis. This can cause distant nodes from the AP to be repeatedly interrupted by less sensitive, closer nodes, greatly reducing their throughput. By contrast, the 802.16 MAC is a scheduling MAC where the subscriber station only has to compete once (for initial entry into the network). After that it is allocated a time slot by the base station. The time slot can enlarge and constrict, but it remains assigned to the subscriber station meaning that other subscribers are not supposed to use it but take their turn. This scheduling algorithm is stable under overload and oversubscription (unlike 802.11). It is also much more bandwidth efficient. The scheduling algorithm also allows the base station to control Quality of Service by balancing the assignments among the needs of the subscriber stations. A recent addition to the WiMAX standard is underway which will add full capability by enabling WiMAX nodes to simultaneously operate in “subscriber station” and “base station” mode. This will blur that initial distinction and allow for widespread adoption of WiMAX based mesh networks and promises widespread WiMAX adoption. The original WiMAX standard, IEEE 802.16, specifies WiMAX in the 10 to 66 GHz range. 802.16a added support for the 2 to 11 GHz range, of which most parts are already unlicensed internationally and only very few still require domestic licenses. Most business interest will probably be in the 802.16a standard, as opposed to licensed frequencies. The WiMAX specification improves upon many of the limitations of the Wi-Fi standard by providing increased bandwidth and stronger encryption. It also aims to provide connectivity between network endpoints without direct line of sight in some circumstances. The details of performance under non-line of sight (NLOS) circumstances are unclear as they have yet to be demonstrated. It is commonly considered that spectrum under 5-6 GHz is needed to provide reasonable NLOS performance and cost effectiveness for PtM (point to multi-point) deployments.
3. HOW WIMAX WORKS
WIMAX Transmitter Tower
In practical terms, WiMAX would operate similar to WiFi but at higher speeds, over greater distances and for a greater number of users. WiMAX could potentially erase the suburban and rural blackout areas that currently have no broadband Internet access because phone and cable companies have not yet run the necessary wires to those remote locations.
A WiMAX system consists of two parts:
A WiMAX tower, similar in concept to a cell-phone tower – A single WiMAX tower can provide coverage to a very large area — as big as 3,000 square miles (~8,000 square km). A WiMAX receiver – The receiver and antenna could be a small box or PCMCIA card, or they could be built into a laptop the way WiFi access is today.
A WiMAX tower station can connect directly to the Internet using a high-bandwidth, wired connection (for example, a T3 line). It can also connect to another WiMAX tower using a line-of-sight, microwave link. This connection to a second tower (often referred to as a backhaul), along with the ability of a single tower to cover up to 3,000 square miles, is what allows WiMAX to provide coverage to remote rural areas. What this points out is that WiMAX actually can provide two forms of wireless service:
There is the non-line-of-sight, WiFi sort of service, where a small antenna on your computer connects to the tower. In this mode, WiMAX uses a lower frequency range — 2 GHz to 11 GHz (similar to WiFi). Lower-wavelength transmissions are not as easily disrupted by physical obstructions — they are better able to diffract, or bend, around obstacles
Working of WIMAX - Photo by howstuffworks
There is line-of-sight service, where a fixed dish antenna points straight at the WiMAX tower from a rooftop or pole. The line-of-sight connection is stronger and more stable, so it’s able to send a lot of data with fewer errors. Line-of-sight transmissions use higher frequencies, with ranges reaching a possible 66 GHz. At higher frequencies, there is less interference and lots more bandwidth. WiFi-style access will be limited to a 4-to-6 mile radius (perhaps 25 square miles or 65 square km of coverage, which is similar in range to a cell-phone zone). Through the stronger line-of-sight antennas, the WiMAX transmitting station would send data to WiMAX-enabled computers or routers set up within the transmitter’s 30-mile radius (2,800 square miles or 9,300 square km of coverage.
4. GLOBAL AREA NETWORK
The final step in the area network scale is the global area network (GAN). The proposal for GAN is IEEE 802.20. A true GAN would work a lot like today’s cell phone networks, with users able to travel across the country and still have access to the network the whole time. This network would have enough bandwidth to offer Internet access comparable to cable modem service, but it would be accessible to mobile, always-connected devices like laptops or next-generation cell phones). This is what allows WiMAX to achieve its maximum range.
5. USES FOR WIMAX
WiMAX is a wireless metropolitan area network (MAN) technology that can connect IEEE 802.11 (Wi-Fi) hotspots with each other and to other parts of the Internet and provide a wireless alternative to cable and DSL for last mile (last km) broadband access. IEEE 802.16 provides up to 50 km (31 miles) of linear service area range and allows connectivity between users without a direct line of sight. Note that this should not be taken to mean that users 50 km (31 miles) away without line of sight will have connectivity. Practical limits on real world tests seem to be around “3 to 5 miles” (5 to 8 kilometers). The technology has been claimed to provide shared data rates up to 70 Mbit/s, which, according to WiMAX proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and well over a thousand homes at 1Mbit/s DSL-level connectivity. Real world tests, however, show practical maximum data rates between 500kbit/s and 2 Mbit/s, depending on conditions at a given site.
WIMAX Uses
It is also anticipated that WiMAX will allow interpenetration for broadband service provision of VoIP, video, and Internet access—simultaneously. Most cable and traditional telephone companies are closely examining or actively trial-testing the potential of WiMAX for “last mile” connectivity. This should result in better price points for both home and business customers as competition results from the elimination of the “captive” customer bases both telephone and cable networks traditionally enjoyed. Even in areas without preexisting physical cable or telephone networks, WiMAX could allow access between anyone within range of each other. Home units the size of a paperback book that provide both phone and network connection points are already available and easy to install.
There is also interesting potential for interoperability of WiMAX with legacy cellular networks. WiMAX antennas can “share” a cell tower without compromising the function of cellular arrays already in place. Companies that already lease cell sites in widespread service areas have a unique opportunity to diversify, and often already have the necessary spectrum available to them (i.e. they own the licenses for radio frequencies important to increased speed and/or range of a WiMAX connection). WiMAX antennae may be even connected to an Internet backbone via either a light fiber optics cable or a directional microwave link. Some cellular companies are evaluating WiMAX as a means of increasing bandwidth for a variety of data-intensive applications. In line with these possible applications is the technology’s ability to serve as a very high bandwidth “backhaul” for Internet or cellular phone traffic from remote areas back to a backbone. Although the cost-effectiveness of WiMAX in a remote application will be higher, it is definitely not limited to such applications, and may in fact be an answer to expensive urban deployments of T1 backhauls as well. Given developing countries’ (such as in Africa) limited wired infrastructure, the costs to install a WiMAX station in conjunction with an existing cellular tower or even as a solitary hub will be diminutive in comparison to developing a wired solution. The wide, flat expanses and low population density of such an area lends itself well to WiMAX and its current diametrical range of 30 miles. For countries that have skipped wired infrastructure as a result of inhibitive costs and unsympathetic geography, WiMAX can enhance wireless infrastructure in an inexpensive, decentralized, deployment-friendly and effective manner.
Another application under consideration is gaming. Sony and Microsoft are closely considering the addition of WiMAX as a feature in their next generation game console. This will allow gamers to create ad hoc networks with other players. This may prove to be one of the “killer apps” driving WiMAX adoption: WiFi-like functionality with vastly improved range and greatly reduced network latency and the capability to create ad hoc mesh networks.
Think about how you access the Internet today. There are basically three different options:
Broadband access – In your home, you have either a DSL or cable modem. At the office, your company may be using a T1 or a T3 line.
WiFi access – In your home, you may have set up a WiFi router that lets you surf the Web while you lounge with your laptop. On the road, you can find WiFi hot spots in restaurants, hotels, coffee shops and libraries.
Dial-up access – If you are still using dial-up, chances are that either broadband access is not available, or you think that broadband access is too expensive.
The main problems with broadband access are that it is pretty expensive and it doesn’t reach all areas. The main problem with WiFi access is that hot spots are very small, so coverage is sparse. What if there were a new technology that solved all of these problems? This new technology would provide:
The high speed of broadband service
Wireless rather than wired access, so it would be a lot less expensive than cable or DSL and much easier to extend to suburban and rural areas
Broad coverage like the cell phone network instead of small WiFi hotspots
This system is actually coming into being right now, and it is called WiMAX. WiMAX is short for Worldwide Interoperability for Microwave Access, and it also goes by the IEEE name 802.16.
WiMAX has the potential to do to broadband Internet access what cell phones have done to phone access. In the same way that many people have given up their “land lines” in favor of cell phones, WiMAX could replace cable and DSL services, providing universal Internet access just about anywhere you go. WiMAX will also be as painless as WiFi — turning your computer on will automatically connect you to the closest available WiMAX antenna.
6. WHAT CAN WIMAX DO?
WiMAX operates on the same general principles as WiFi — it sends data from one computer to another via radio signals. A computer (either a desktop or a laptop) equipped with WiMAX would receive data from the WiMAX transmitting station, probably using encrypted data keys to prevent unauthorized users from stealing access.
The fastest WiFi connection can transmit up to 54 megabits per second under optimal conditions. WiMAX should be able to handle up to 70 megabits per second. Even once that 70 megabits is split up between several dozen businesses or a few hundred home users, it will provide at least the equivalent of cable-modem transfer rates to each user. The biggest difference isn’t speed; it’s distance. WiMAX outdistances WiFi by miles. WiFi’s range is about 100 feet (30 m). WiMAX will blanket a radius of 30 miles (50 km) with wireless access. The increased range is due to the frequencies used and the power of the transmitter. Of course, at that distance, terrain, weather and large buildings will act to reduce the maximum range in some circumstances, but the potential is there to cover huge tracts of land.
7. IEEE 802.16 SPECIFICATIONS
Range – 30-mile (50-km) radius from base station
Speed – 70 megabits per second
Line-of-sight not needed between user and base station
Frequency bands – 2 to 11 GHz and 10 to 66 GHz (licensed and unlicensed bands)
8. WIMAX COULD BOOST GOVERNMENT SECURITY
In an emergency, communication is crucial for government officials as they try to determine the cause of the problem, find out who may be injured and coordinate rescue efforts or cleanup operations. A gas-line explosion or terrorist attack could sever the cables that connect leaders and officials with their vital information networks.
WiMAX could be used to set up a back-up (or even primary) communications system that would be difficult to destroy with a single, pinpoint attack. A cluster of WiMAX transmitters would be set up in range of a key command center but as far from each other as possible. Each transmitter would be in a bunker hardened against bombs and other attacks. No single attack could destroy all of the transmitters, so the officials in the command center would remain in communication at all timesHere’s what would happen if you got WiMAX. An Internet service provider sets up a WiMAX base station 10 miles from your home. You would buy a WiMAX-enabled computer (some of them should be on store shelves in 2005) or upgrade your old computer to add WiMAX capability. You would receive a special encryption code that would give you access to the base station. The base station would beam data from the Internet to your computer (at speeds potentially higher than today’s cable modems), for which you would pay the provider a monthly fee. The cost for this service could be much lower than current high-speed Internet-subscription fees because the provider never had to run cables.
Network scale: The smallest-scale network is a personal area network (PAN). A PAN allows devices to communicate with each other over short distances. Bluetooth is the best example of a PAN.
The next step up is a local area network (LAN). A LAN allows devices to share information, but is limited to a fairly small central area, such as a company’s headquarters, a coffee shop or your house. Many LANs use WiFi to connect the network wirelessly.
WiMAX is the wireless solution for the next step up in scale, the metropolitan area network (MAN). A MAN allows areas the size of cities to be connected. If you have a home network, things wouldn’t change much. The WiMAX base station would send data to a WiMAX-enabled router, which would then send the data to the different computers on your network. You could even combine WiFi with WiMAX by having the router send the data to the computers via WiFi.
WiMAX doesn’t just pose a threat to providers of DSL and cable-modem service. The WiMAX protocol is designed to accommodate several different methods of data transmission, one of which is Voice over Internet Protocol (VoIP). VoIP allows people to make local, long-distance and even international calls through a broadband Internet connection, bypassing phone companies entirely. If WiMAX-compatible computers become very common, the use of VoIP could increase dramatically. Almost anyone with a laptop could make VoIP calls.
9. TECHNICAL ADVANTAGES
WiMax does not conflict with WiFi but actually complements it. WiMAX is a wireless metropolitan area network (MAN) technology that will connect 802.11(WiFi) hotspots to the Internet and provide a wireless extension to cable and DSL for last mile (last km) broadband access. 802.16 provides up to 50 km (31 miles) of linear service area range andallows users connectivity without a direct line of sight to a base station. The technology also provides shared data rates up to 70 Mbit/s, which, according to WiMax proponents, is enough bandwidth to simultaneously support more than 60 businesses with T1-type connectivity and hundreds of homes at DSL-type connectivity.
An important aspect of the 802.16 is that it defines a MAC layer that supports multiple physical layer (PHY) specifications. This is crucial to allow equipment makers to differentiate their offerings.
10. CONCLUSION
The WiMAX forum, backed by industry leaders, helps the widespread adoption of broadband wireless access by establishing a brand forth technology. Initially, WiMAX will bridge the digital divide, the scope of WiMAX deployment will broaden to cover markets where the low POTS penetration, high DSL unbundling costs, or poor copper quality have acted as a brake on extensive high-speed Internet and voice over broadband. WiMAX will reach its peak by making Portable Internet a reality. When WiMAX chipsets are integrated into laptops and other portable devices, it will provide high-speed data services on the move, extending today’s limited coverage of public WLAN to metropolitan areas. Integrated into new generation networks with seamless roaming between various accesses, it will enable endorsers to enjoy an “Always Best Connected” experience. The combination of these capabilities makes WiMAX attractive for a wide diversity of people: fixed operators, mobile operators and wireless ISPs, but also for many vertical markets and local authorities.
11. GLOSSARY CPE: Customer Premise Equipment DSL: Digital Subscriber Line FDD: Frequency Division Duplex MAC: Media Access Control MIMO: Multiple-Input-Multiple-Output NLOS: Non-Line-Of-Sight OFDMA: Orthogonal Frequency Division Multiplex Access PLC: Power Line Communications POTS: Plain Ordinary Telephone System STC: Space Time Coding TDD: Time Division Duplex WLAN: Wireless Local Area Network WLL: Wireless Local Loop
12. REFERENCES [1].WiMAX: The Critical Wireless Standard, Blueprint WiFi Report, October 2003 [2].WiMAX/802.16 and 802.20, ABI Research, Q4 2003 Last Mile Wireless High Speed Market, Skylight Research, March 2004 [3].Providing Always-on Broadband Access to Underserved Areas, Alcatel Telecommunication Review (p. 127-132), Q4 2003 [4].WiMAX forum web site: www.wimaxforum.org [5]. IEEE SPECTRUM. [6].howstaffworks.com
Equation 1.
