Review Paper Int. J. on Recent Trends in Engineering and Technology, Vol. 6, No. 1, Nov 2011
A Survey on Wireless Technologies Shakti.R.Chopra Lovely Professional University Phagwara,Punjab INDIA Email:
[email protected]
modulation technique. Other standards in the family (c–f, h, j) are service amendments and extensions or corrections to the previous specifications. 802.11b and 802.11g use the 2.4 GHz ISM band , Because of this choice of frequency band, 802.11b and g equipment may occasionally suffer interference from microwave ovens, cordless telephones and Blue tooth devices. 802.11b and 802.11g control their interference and susceptibility to interference by using direct-sequence spread spectrum (DSSS) and orthogonal frequency-division multiplexing (OFDM) signaling methods, respectively. 802.11a uses the 5 GHz U-NII band, which, for much of the world, offers at least 19 non-overlapping channels rather than the 3 offered in the 2.4 GHz ISM frequency band. Better or worse performance with higher or lower frequencies (channels) may be realized, depending on the environment. Fig.1 shows The IEEE 802.11 MAC sublayer provides a fairly controlled access to the shared wireless medium through two different access mechanisms: the basic access mechanism, called the distributed coordination function (DCF), and a centrally controlled access mechanism, called the point coordination function (PCF)[3].
Abstract- The demand for broadband communications is rapidly increasing now a days, three major standardization bodies are currently working towards a standards LANs: IEEE802.11, Wimax:IEEE 802.16 and Bluetooth:IEEE 802.15. This paper describes an overview on Wireless Technologies viz WLAN, WiMAX and Bluetooth etc. finally comparison in tabular form has been done on these technologies.
I. INTRODUCTION Wireless networks are one of the most growing segments of information technology. Because of the flexibility of wireless networks, businesses, educational establishments and households are adapting this technology which makes it an integral part of modern life. Over recent years, the market for wireless communications has enjoyed tremendous growth. Wireless technology now reaches or is capable of reaching virtually every location on the face of the earth. Hundreds of millions of people exchange information every day using pagers, cellular telephones, and other wireless communication products. With tremendous success of wireless telephony and messaging services, it is hardly surprising that wireless communication is beginning to be applied to the realm of personal and business computing. No longer bound by the harnesses of wired networks, people will be able to access and share information on a global scale nearly anywhere they venture. The paper is out lined as follows: In section II 802.11 outlines are provided. Bluetooth and its protocol architecture in section III. WiMax overview and its architecture is defined in section IV. Finally paper concluded with comparison of all topologies. II. LEGACY IEEE 802.11 IEEE 802.11 is a set of standards carrying out wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the LAN/MAN IEEE Standards Committee (IEEE 802.11). The 802.11 family includes over-the-air modulation techniques that use the same basic protocol. The most popular are those defined by the 802.11b and 802.11g protocols, which are amendments to the original standard. 802.11-1997 was the first wireless networking standard, but 802.11b was the first widely accepted one, followed by 802.11g and 802.11n. Security was originally purposefully weak due to export requirements of some governments, and was later enhanced via the 802.11i amendment after governmental and legislative changes. 802.11n is a new multi-streaming © 2011 ACEEE DOI: 01.IJRTET.06.01.550
Fig 1. Mac layer in IEEE 80.11
A. DISTRIBUTED COORDINATION FUNCTION DCF requires a station wishing to transmit to listen for the channel status for a DIFS interval. If the channel is found busy during the DIFS interval, the station defers its transmission. In a network where a number of stations contend for the wireless medium. If multiple stations sense the channel busy and defer their access, they will also virtually simultaneously find that the channel is released and then try to seize the channel. As a result, collisions may occur. In order to avoid such collisions, DCF also specifies random back off, which forces a station to defer its access to the 153
Review Paper Int. J. on Recent Trends in Engineering and Technology, Vol. 6, No. 1, Nov 2011 The IEEE 802.11 standard also defines an optional access method using a Point Coordination Function (PCF). PCF allows the Access Point acting as the network coordinator to manage channel access. The IEEE 802.11e enhances the DCF and the PCF, through a new coordination function called Hybrid Coordination Function (HCF)
channel for an extra period. The length of the back off period is determined by the following equation: Back off Time = random() × a Slot Time DCF also has an optional virtual carrier sense mechanism that exchanges short Request-to-send (RTS) and Clear-tosend (CTS) frames between source and destination stations during the intervals between the data frame transmissions. DCF includes a positive acknowledge scheme, which means that if a frame is successfully received by the destination it is addressed to, the destination needs to send an ACK frame to notify the source of the successful reception..DCF relies on CSMA/CA and optional 802.11 RTS/ CTS to share the medium between stations as in Fig.3. RTS/ CTS scheme reducing the hidden station problem inherent in CSMA. Before transmitting data frames, a station has the option to transmit a short RTS frame, followed by the CTS transmission by the receiving station. The RTS and CTS frames include the information of how long it does take to transmit the next data frame, i.e., the first fragment, and the corresponding ACK response. Thus, other stations close to the transmitting station and hidden stations close to the receiving station will not start any transmissions; their timer called Network Allocation Vector, NAV, is set. RTS/CTS helps to protect long data frames against hidden stations. With fragmentation, multiple ACKs are transmitted, whereas with RTS/CTS the MSDU can be efficiently transmitted in a single data frame. Between two consecutive frames in the sequence of RTS, CTS, data, and ACK frames, a Short Interframe Space (SIFS), which is 16 us for 802.11a, gives transceivers time to turn around. It is important to note that SIFS is shorter than DIFS, which gives CTS responds and ACKs always the highest priority for access to the wireless medium[6].
B. POINT COORDINATION FUNCTION Point coordination function is a Media Access Control (MAC) technique used in IEEE 802.11 based WLANs. It resides in a point coordinator also known as Access Point (AP), to coordinate the communication within the network. The AP wait for PIFS duration rather than DIFS duration to grasp the channel. PIFS is less than DIFS duration and hence the point coordinator has higher priority than the DCF, because it may start transmissions after a shorter duration than DIFS; this time space is called PCF Interframe Space (PIFS), which is 25 us for 802.11a and longer than SIFS, i.e., the shortest inter-frame-space. Time is always divided into repeated periods, called superframes. With PCF, a Contention Free Period (CFP) and a Contention Period (CP) alternate over time, in which a CFP and the following CP form a superframe. During the CFP, the PCF is used for accessing the medium, while the DCF is used during the CP. It is mandatory that a superframe includes a CP of a minimum length that allows at least one MSDU delivery under DCF[6].
Fig 3. Timing of PCF
The PCF is located directly above the Distributed Coordination Function (DCF), in the IEEE 802.11 MAC Architecture. Channel access in PCF mode is centralized and hence the point coordinator sends CF-Poll frame to the PCF capable station to permit it to transmit a frame. In case the polled stations does not have any frames to send, then it must transmit null frame. Since most APs have logical bus topologies (they are shared circuits) only one message can be processed at one time (it is a contention based system), and thus a media access control technique is required.Wireless networks may suffer from a hidden node problem where some regular nodes (which communicate only with the AP) cannot see other nodes on the extreme edge of the geographical radius of the network because the wireless signal attenuates before it can reach that far. Thus having an AP in the middle allows the distance to be halved, allowing all nodes to see the AP, and consequentially, halving the maximum distance between two nodes on the extreme edges of a circle-star topology seems to be implemented only in very few hardware devices as it is not part of the WI-Fi Alliance’s interoperability standard.
Fig 2. Timing of DCF with RTS/CTS.
But DCF has several limitations: If many stations attempt to communicate at the same time, many collisions will occur which will lower the available bandwidth and possibly lead to congestive collapse. There are no Quality of Service (QoS) guarantees. In particular, there is no notion of high or low priority traffic. Once a station “wins” access to the medium, it may keep the medium for as long as it chooses. If a station has a low bit rate (1 Mbit/s, for example), then it will take a long time to send its packet, and transmission from all other stations will be held off. © 2011 ACEEE DOI: 01.IJRTET.06.01. 550
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Review Paper Int. J. on Recent Trends in Engineering and Technology, Vol. 6, No. 1, Nov 2011 III. BLUETOOTH Blue tooth is a specification for the use of low-power radio communications to wirelessly link phones, computers and other network devices over short distances. The name Blue tooth is borrowed from Harald Blue tooth, a king in Denmark more than 1,000 years ago. Bluetooth is a highspeed, low-power microwave wireless link technology, designed to connect phones, laptops and other portable devices together,Operates at 2.4 GHz the effective range is 10m(30feet) and have a Point to point connecting device. The Bluetooth specifications are developed and licensed by the bluetooth special interest group(SIG) Average data transfer rate:1Mbps known as the IEEE 802.15 standards[6]. A. PROTOCOL ARCHITECTURE Fig.4 shows protocol architecture of Blue tooth having layered protocol architecture, Core protocols, Cable replacement and telephony control protocols and adopted protocols. In Core protocols Radio , Baseband ,Link manager protocol (LMP) ,Logical link control and adaptation protocol (L2CAP) ,Service discovery protocol (SDP). In Cable replacement protocol RFCOMM, In Telephony control protocol Telephony control specification – binary (TCS BIN) and in Adopted protocols PPP,TCP/UDP/IP,OBEX,WAE/ WAP. Link Manager Protocol (LMP) used for link management between the endpoints, a Logical Link Control and Adaptation Protocol (L2CAP) for the data link, a Radio Frequency Communication (RFCOMM) protocol to provide emulation of serial ports over L2CAP, and a Service Discovery Protocol (SDP) for the dynamic discovery of services— because the set of services changes dynamically based on the RF proximity of the devices. In addition, the Host Controller Interface (HCI) provides a uniform command interface to the baseband controller and the link manager to have access to the hardware registers. LMP is required for authentication encryption, switching of roles between master and slave, power control , and so on. L2CAP provides both connection-oriented and connectionless data services functions, including protocol multiplexing, segmentation and reassembly, and piconetbased group abstraction. As part of the multiplexing function, L2CAP uses the concept of channels, with a channel ID representing a logical channel endpoint on a BT device. L2CAP offers services to the higher layers for connection setup, disconnect, data reading and writing, pinging the endpoint, and so on. RFCOMM, which provides emulation of serial ports on the BT link, can support up to 60 simultaneous connections between two BT devices. The most common emulation is of the RS-232 interface, which includes emulation of the various signals of this interface such as Request To Send (RTS), Clear To Send (CTS), Data Terminal Ready (DTR), and so on.
© 2011 ACEEE DOI: 01.IJRTET.06.01. 550
Fig 4. Protocol Architecture
RFCOMM is used with two types of BT devicesendpoints such as printers and computers and intermediate devices such as modems. In Figure 3, the IP stack over Pointto-Point Protocol (PPP) over RFCOMM emulates the mode of operation over a dialup or dedicated serial link. Because the various BT devices in a piconet may offer or require a different set of services, the Service Discovery Protocol (SDP) is used to determine the nature of the services available on the other nodes. SDP uses a request-response packet scheme for its operation.. BT Radio(2.4 GHZ Freq.Band) Modulation: Gaussian Frequency Shift Keying. Baseband: FH-SS (79 carriers), CDMA (hopping sequence from the node MAC address) Audio: interfaces directly with the baseband. Each voice connection is over a 64Kbps SCO link. The voice coding scheme is the Continuous Variable Slope Delta(CVSD) Link Manager Protocol (LMP): link setup and control, authentication and encryption. Host Controller Interface: provides a uniform method of access to the baseband, control registers, etc through USB,PCI and UART. Logical Link Control and Adaptation Layer (L2CAP): higher protocols multiplexing, packet segmentation/ reassembly,QOS. Service Discover Protocol (SDP): protocol of locating services provided by Bluetooth device. Telephony Control Specification (TCS): defines the call control signaling for the establishment of speech and data calls between Blue tooth devices. RFCOMM: provides emulation of serial links (RS232),Upto 60 connections[7]
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Review Paper Int. J. on Recent Trends in Engineering and Technology, Vol. 6, No. 1, Nov 2011 B. PICONETS AND SCATTERNETS PICONET: Piconet is the basic unit of Bluetooth networking.It is a set of Bluetooth nodes synchronized to a master node as shown in Fig.5.Each piconet has one master and up to 7 slaves in which master determines hopping sequence and slaves have to synchronize to communication between piconets ,devices jumping back and forth between the piconets.
A. IEEE 802.16 PROTOCOL ARCHITECTURE The IEEE 802.16 protocol architecture is structured into two main layers: the Medium Access Control (MAC) layer and the Physical (PHY) layer.
Fig 7. IEEE 802.16 Protocol Architecture
MAC layer consists of three sub-layers. The first sublayer is the Service Specific Convergence Sub-layer (CS), which maps higher level data services to MAC layer service flow and connections. The second sub-layer is Common Part Sub- layer (CPS), which is the core of the standard and is tightly integrated with the security sub-layer. This layer defines the rules and mechanisms for system access, bandwidth allocation and connection management. The MAC protocol data units are constructed in this sub-layer. The last sub-layer of MAC layer is the Security Sub-layer which lies between the MAC CPS and the PHY layer, Mobile WiMAX is the WiMAX incarnation that has the most commercial interest to date and is being actively deployed in many countries. Mobile WiMAX is also the basis of future revisions of WiMAX. As such, references to and comparisons with “WiMAX” in this Wikipedia article mean “Mobile WiMAX”. WiMax equipment exists in two forms. WiMax base stations are installed by service providers to deploy the technology in a coverage addressing the authentication, key establishment and exchange, encryption and decryption of data exchanged between MAC and PHY layers. The PHY layer provides a two-way mapping between MAC protocol data units and the PHY layer frames received and transmitted through coding and modulation of radio frequency signals. WiMAX refers to interoperable implementations of the IEEE 802.16 wireless-networks standard (ratified by the WiMAX Forum), in similarity with Wi-Fi, which refers to interoperable implementations of the IEEE 802.11 Wireless LAN standard (ratified by the Wi-Fi Alliance). The WiMAX Forum certification allows vendors to sell their equipment as WiMAX (Fixed or Mobile) certified, thus ensuring a level of interoperability with other certified products, as long as they fit the same profile. WiMax antennas must be installed at the home or other receiving location. As WiMax evolves, these antennas will change from being mounted outdoors, to smaller varieties set up indoors, and then finally to built-in versions integrated inside mobile computers. Similar to other types of Internet access, consumers will subscribe and pay a recurring fee to connect to the Internet via WiMax.
Fig 5. Set of Bluetooth devices forms Piconet
SCATTERNET: Scatternet is a set of piconet as in Fig.5.Device in one piconet may exist as master or slave in another piconet. It allows many devices to share same area which makes efficient use of bandwidth.
Fig 6. Set of Piconets forms Scatternet.
IV. WIMAX Worldwide Interoperability for Microwave Access is the industry term for a long-range wireless networking standard. WiMax technology has the potential to deliver high-speed Internet access to rural areas and other locations not serviced by cable or DSL technology. WiMax also offers an alternative to satellite Internet services. .WiMAX is a telecommunications protocol that provides fixed and fully mobile Internet access. The current WiMAX revision provides up to 40 Mbit/s with the IEEE 802.16m update expected to offer up to 1 Gbit/s fixed speeds. 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 DSL”. © 2011 ACEEE DOI: 01.IJRTET.06.01. 550
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Review Paper Int. J. on Recent Trends in Engineering and Technology, Vol. 6, No. 1, Nov 2011 peak data speeds of about 70mbps, with average user data rates between 1mbps and 10mbps.For all wireless technologies different standards are compared ,Table.1 shows different technologies with their standards.This paper mainly emphasizes only the WiFi, Bluetooth and WiMax, we can further go beyond this to include other technologies related to wireless like Zigbee, EnOcean; Personal area networks, TransUltra, wide band and others.
TABLE I. COMPARISION OF BLUETOOTH,WIFI AND WIMAX
REFERENCES [1] H. Berghel, “Wireless Infidelity II: Air Jacking,”Communications of ACM on Digital Village, 47(12), pp.15-21, December [2] W. Conklin, D. Williams, G. White, R. Davis, and C.Cothern, “Principles of Computer Security,” McGraw Hill Technology Education, 2004. [3] Wireless LAN - Wikipedia, the free encyclopedia.htm [4] Behrouz A. Forouzan, Data communications and networking McGrawHill,fourth edition, ISBN-13 978-0-07-296775-3 ISBNto 0-07-296775-7 [5] Jochen H. Schiller, Mobile CommunicationsAddison-Wesley, 2003 ISBN0321123816, 9780321123817 [6] Stefan Mangold, Sunghyun Choi, Peter May, Ole Klein1, Guido Hiertz1, Lothar Stibor, “IEEE 802.11e Wireless LAN for Quality of Service” [7] IEEE 802.11 LAN/MAN Wireless LANS MAC Protocols with Fast Collision Resolution forWireless Local Area Networks,” IEEE Trans. on Wireless Communications, May 2004 [8] IEEE 802.1 1 WG, Purt 11: Wireless LAN Mediutn Access Control (MAC)und Physical Layer (PHY) specificuriotis, Standard, IEEE, Aug 1999. [9] IEEE 802.11 LAN/MAN Wireless LANS MAC Protocols with Fast Collision Resolution forWireless Local Area Networks,” IEEE Trans. on Wireless Communications, May 2004. [10] Encyclopedia of Networking and Tele communication ISBN 0-07-212005-3N. [11] 802.11 Medium Access Methods on wi fiplanet.com J. Deng, P. K. Varshney, and Z. J. Haas, “A New Backoff Algorithm for the IEEE 802.11 Distributed Coordination Function,” Proc. of Communication Networks and Distributed Systems Modeling and Simulation (CNDS), January 2004. [12] P. Lettieri and M. B. Srivastava, “Adaptive Frame Length Control for Improving Wireless Link Throughput, Range, and Energy Efficiency,” inPrnc. IEEE INFOCOM’98, San Francisco, California, Mar 1998. [13] Mangold, S. and Choi, S. and Esseling, N., “An Error Model for Radio Transmissions of Wireless LANs at 5GHz,” in Proc. Aachen Symposium’2001, Aachen, Germany, pp. 209-214, Sept. 2001
CONCLUSION Originally a second-class citizen in terms of transfer speeds, wi-fi is a wireless technology that can support a wireless local area network and provides high-speed access to the internet with data transmission rates approaching 54mbps. bluetooth is a wireless networking standard that provides short-range (about 10 meters) connectivity to electrical devices such as cell phones, computers and their peripherals, notebooks, and pda’s. WiMax is an emerging technology that provides high-throughput broadband connections to a large geographic area. Considered the successor to Wi-Fi, WiMAX provides improved performance and usage over much greater distances. WiMax supports
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