21IEEE Network • May/June 2005 0890-8044/05/$20.00 © 2005 IEEE

he initial IEEE 802.11 standard [1] specifies data ratesof 1 Mb/s and 2 Mb/s for three different physical layersbased on direct sequence spread spectrum (DSSS), fre-quency hopping spread spectrum (FHSS), and infrared

(IR) techniques, respectively. The operation of both DSSSand FHSS is specified at the 2.4 GHz industrial, scientific, andmedical (ISM) band. From those three physical layers, theDSSS-based one is the most widely accepted as it is extend-able to provide higher data rates. The rapid evolvement ofwireless LAN (WLAN) technology brought to the foregroundthe IEEE 802.11b/a/g standards. IEEE 802.11b [2] providesdata rates up to 11 Mb/s at 2.4 GHz using DSSS with eithercomplementary code keying (CCK) modulation or the packetbinary convolutional coding (PBCC) algorithm (which hasbeen officially ratified by the IEEE as an alternative to CCK).IEEE 802.11a [3] specifies an OFDM (orthogonal frequency-division multiplexing) physical layer that splits an informationsignal across 52 separate subcarriers to provide transmissionof data rates from 6 Mb/s to 54 Mb/s at the 5 GHz unlicensednational information infrastructure (U-NII) band. While theIEEE 802.11a standard increases the available data rates from11 Mb/s to 54 Mb/s, its operation at the 5 GHz band cannotprovide interoperability with IEEE 802.11 and IEEE 802.11bdevices.

The convergence of the IEEE 802.11a and IEEE 802.11bstandards came with the publication of the IEEE 802.11gstandard [4]. The latter provides the data rates of IEEE802.11a at the 2.4 GHz band, thus allowing interoperabilitywith older IEEE 802.11 and IEEE 802.11b devices. For thisreason, this current last step of the IEEE seems to be themost widely accepted specification of the 802.11 standardsfamily. Complementing tutorials on IEEE 802.11 [5], IEEE802.11a [6], and IEEE 802.11b [7], this article deals withIEEE 802.11g. Specifically, it provides a detailed descrip-tion of the new features of the standard and evaluates itsperformance compared to the older IEEE 802.11 standardsversions.

The rest of the article is organized as follows. We elaborateon the new features of IEEE 802.11g. We evaluate the perfor-mance of these features using an open source C++-basedsimulation tool. Finally, we conclude the article.

New Features of the IEEE 802.11gStandardEpigrammatically, the new features of the IEEE 802.11g stan-dard are:• The provision of four different physical layers• The mandatory support of the short preamble type• The ERP network attribute• Newly defined protection mechanisms that deal with inter-

operability aspects• The CTS-to-self mechanismIn the next subsections, each of the above features is explainedextensively.

Four Different Physical LayersWhile IEEE 802.11b uses only DSSS technology, IEEE802.11g uses DSSS, OFDM, or both at the 2.4 GHz ISM bandto provide high data rates of up to 54 Mb/s. Combined use ofboth DSSS and OFDM is achieved through the provision offour different physical layers. These layers, defined in thestandard as extended rate physicals (ERPs), coexist during aframe exchange, so the sender and receiver have the option toselect and use one of the four layers as long as they both sup-port it. The four different physical layers defined in the IEEE82.11g standard are the following:• ERP-DSSS/CCK: This is the old physical layer used by

IEEE 802.11b. DSSS technology is used with CCK modula-tion. The data rates provided are those of IEEE 802.11b.

• ERP-OFDM: This is a new physical layer, introduced byIEEE 802.11g. OFDM is used to provide IEEE 802.11adata rates at the 2.4 GHz band.

• ERP-DSSS/PBCC: This physical layer was introduced inIEEE 802.11b and provides the same data rates as theDSSS/CCK physical layer. It uses DSSS technology with thePBCC coding algorithm. IEEE 802.11g extended the set ofdata rates by adding those of 22 and 33 Mb/s.

• DSSS-OFDM: This is a new physical layer that uses a hybridcombination of DSSS and OFDM. The packet physicalheader is transmitted using DSSS, while the packet payloadis transmitted using OFDM. The scope of this hybrid

TT

Dimitris Vassis, George Kormentzas, Angelos Rouskas, and Ilias MaglogiannisUniversity of the Aegean

AbstractContinuous WLAN public acceptance comes with increasing demand for provisionof higher data rates. Building on this context, the IEEE published the IEEE 802.11gstandard for providing data rates of up to 54 Mb/s at the 2.4 GHz band. Thisarticle presents the new features of IEEE 802.11g and, using an open source C++-based simulation tool, evaluates both the performance and effectiveness of thesefeatures compared to the older IEEE 802.11 standard versions.

The IEEE 802.11g Standard forHigh Data Rate WLANs

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IEEE Network • May/June 200522

approach is to cover interoperability aspects, as explainedlater.From the above four physical layers, the first two are

mandatory; every IEEE 802.11g device must support them.The other two are optional. Column 2 of Table 1 summarizesthe supported data rates for the different physical layers ofthe IEEE 802.11g specification. Columns 3 and 4 areexplained in the next subsection.

Mandatory Support of the Short PreambleThe physical layer packet overhead of an IEEE 802.11 packetconsists of two parts: the Physical Layer Convergence Proto-col (PLCP) preambleused for synchronization and the PLCPheader that holds packet information related to the physicallayer. The IEEE 802.11b group realized that the PLCPpreamble is too long and adds considerable overhead in aWLAN system. Hence, an option to support a shorter type ofpreamble (called short preamble in contrast to the old longpreamble) was introduced in order to reduce packet overheadand improve network performance. If both the sender andreceiver support this option, the communication is performedusing the short preamble. IEEE 802.11g recommends manda-tory use of the short preamble option.

Columns 3 and 4 of Table 1 summarize the delay andlength of the short and long preambles for the different physi-cal layers of the IEEE 802.11g standard. When the preambleand header are transmitted using DSSS (this happens at allphysical layers except the ERP-OFDM), short and long typesof preamble and header are defined. For the ERP-OFDMphysical layer there is only one type of preamble and header,the format of which is almost identical to that of the IEEE802.11a standard.

The ERP Network AttributeThe default values of the slot time and minimum contentionwindow for IEEE 802.11b are 20 µs and 31 slots, respectively.IEEE 802.11g, as it supports IEEE 802.11b stations, adoptedthese values in all its physical layers as well. These parametersare tuned in order to maximize the performance under DSSStransmission for data rates of up to 11 Mb/s with preambles of192 or 96 µs. However, when stations transmit at ERP-OFDMdata rates (6–54 Mb/s) with the significantly shorter preambleof 20 µs, the above values of slot time and minimum con-tention window degrade network performance. The mostappropriate values in this case would be those defined in the

IEEE 802.11a standard (which are 9 µs and 15slots, respectively), where stations transmit exclu-sively at OFDM data rates.

The IEEE 802.11g standard incorporatesdynamic adjustment of the values of the slot timeand minimum contention window by defining anERP network attribute, which is a flag publishedto the stations via a beacon frame (i.e., a controlframe that contains network information). TheERP attribute is enabled if all stations associatedto a WLAN are capable of supporting ERP-OFDM data rates. In such a case, the values ofthe slot time and minimum contention windowdepend on the WLAN mode of operation: basicservice set (BSS) or independent BSS (IBSS).

For BSS operation, if the ERP attribute isenabled, the value of the slot time parameter isset to 9 µs, the value of the minimum contentionwindow parameter is set to 15 slots, and all frameexchanges are performed using ERP-OFDM datarates. Under these settings, the operation of thenetwork is similar to that of an IEEE 802.11a

network. The value of the minimum contention window canbe set to 15 slots even if the ERP attribute is disabled, as longas the access point (AP) of the BSS setting supports ERP-OFDM data rates. For IBSS operation, if the ERP attribute isenabled, the value of the minimum contention window is setto 15 slots and all frame exchanges are performed using ERP-OFDM data rates. The value of the slot time is always set to20 µs.

Interoperability Aspects and Protection MechanismsIn an IEEE 802.11g network, the stations can choose between14 different data rates and four physical layers in order totransmit a packet in the most efficient manner. This plethoraof data rates and physical layers raises interoperability prob-lems.

Before proceeding any further, it is essential to sort out thedifferent types of stations that may exist in an IEEE 802.11gnetwork:• ERP stations: The stations that support the ERP-OFDM

physical layer. These stations are equipped with a pureIEEE 802.11g wireless interface.

• Non-ERP stations that support short preamble: These stationsare equipped with an IEEE 802.11b wireless interface of anewer release, which supports up to 11 Mb/s, but itsfirmware is upgraded in order to support the use of shortpreamble.

• Non-ERP stations that do not support short preamble: Thesestations are equipped with an IEEE 802.11b wireless inter-face of an older release or an IEEE 802.11 wireless inter-face that does not support the use of short preamble.Different communication combinations arise; Table 2 sum-

marizes the physical layer parameters for different pairs. Bynon-ERP/S or non-ERP/L, we denote non-ERP stations thatsupport or do not support short preamble, respectively.

Now, let us return to the interoperability problem. Consid-er a network consisting of ERP and non-ERP stations. ERPstations communicate among them using ERP-OFDM pack-ets, but non-ERP stations are not able to detect an OFDMtransmission. Hence, if an ERP station transmits, the mediumis sensed idle for non-ERP stations, and any attempt fromthem to transmit will result in a collision. The first solutionthe IEEE 802.11g standard proposes is the use of the DSSS-OFDM physical layer, where all stations will be able to detectthe DSSS-transmitted PLCP preamble and header and refrainfrom transmitting, even if they cannot detect the OFDM-

n Table 1. Parameters of the different IEEE 802.11g physical layers.

Physicallayer

Supportedrates (Mb/s)

PLCP preamble+ header delay

PLCP preamble+ header length

Long Short Long Short

ERP-DSSS(mandatory) 1, 2, 5.5, 11 192 µs 96 µs 192 bits 120 bits

ERP-OFDM(mandatory)

6, 9, 12, 18,24, 36, 48, 54

20 µs 40 bits1

ERP-PBCC(optional)

1, 2, 5.5, 11,22, 33

192 µs 96 µs 192 bits 120 bits

DSSS-OFDM(optional)

6, 9, 12, 18,24, 36, 48, 54

192 µs 96 µs 192 bits 120 bits

1 This is the length of the PLCP header only. The PLCP preamble, which is usedfor synchronization, is a pure time interval equal to 16 ms that does not con-tain any bits.

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IEEE Network • May/June 2005 23

transmitted payload. The second solution is the use of requestto send/clear to send (RTS/CTS) frames to protect the OFDM-transmitted packets. According to IEEE 802.11g, when non-ERP and ERP stations coexist, all RTS and CTS frames mustbe transmitted using the ERP-DSSS physical layer. Hence, allstations are informed about the incoming transmission, even ifthe data packet is transmitted using OFDM. Obviously, whenonly ERP stations exist in the network, there is no need to useRTS/CTS, as all stations are able to detect an OFDM trans-mission.

Besides RTS/CTS, IEEE 802.11g defines an alternative pro-tection mechanism called CTS-to-self to prevent collisionscaused by the DSSS/OFDM interoperability problem. TheCTS-to-self mechanism is discussed in the next subsection.

The CTS-to-Self MechanismThe IEEE 802.11g standard defines the CTS-to-self protec-tion mechanism as an alternative to RTS/CTS in order toreduce the overhead added in a WLAN system. UnlikeRTS/CTS, CTS-to-self cannot efficiently face the hidden ter-minal problem. Figure 1 depicts the frame exchange proce-dure for both RTS/CTS and CTS-to-self mechanisms before asender starts transmitting a data packet.

In Fig. 1a (RTS/CTS mechanism), when station A wishes tosend a packet to station C, it first sends an RTS frame (arrow1), which is received by stations B and C (arrows labeled 2)that are located within the coverage range of the sender. Sta-

tions B and C send CTS frames (arrows labeled 3) that arereceived by all stations (arrows labeled 4). Station D, which ishidden for the sender (out of the coverage range of stationA), although it is not able to receive the RTS frame of thesender, receives the CTS of station C, so it will refrain fromtransmitting. After the reception of a CTS frame, station Astarts transmitting its data packet.

On the other hand, in Fig. 1b (CTS-to-self mechanism),when station A wishes to send a packet to station C, it firstsends a CTS frame (arrow 1), which is received from both sta-tions B and C (arrows labeled 2). Both stations will defertransmission. However, station D, which is out of the sender’scoverage area, will not receive the CTS frame and will notdetect the transmission of A. Hence, if station D decides totransmit, a collision will occur. Consequently, the CTS-to-selfframe can only prevent accidental collisions (two or more sta-tions initiate a transmission at the same slot). Unfortunately,it cannot prevent collisions caused by the hidden terminalproblem. Hence, CTS-to-self should be used only when all sta-tions can detect the transmission of each other. In other casesRTS/CTS should be used.

IEEE 802.11g Performance EvaluationToward performance evaluation of the effectiveness of IEEE802.11g’s new features compared to the older IEEE 802.11standard versions, an open source C++-based simulatorcalled Pythagor [8] was developed. The simulator performs adetailed simulation of the IEEE 802.11 standard and its physi-cal layer extensions (i.e., 802.11a, 802.11b, and 802.11g).

As the performance evaluation concerned a variety of dif-ferent data rates, we selected as a reference metric the chan-nel capacity, which is independent of specific data rates. Bychannel capacity, we mean the maximum channel utilization(channel throughput/channel data rate) the network canreach. In order to achieve maximum channel capacity in allsimulation scenarios (all but the one that concerns the hid-den terminal problem), absence of hidden terminals andclear channel conditions were assumed. Regarding the net-work traffic load, in each scenario the network consists of 10stations that transmit in saturation conditions, meaning thateach station always has a packet to send in the transmitterqueue. Moreover, the packet payload was exponentially dis-tributed with a mean value of 1024 bytes. While the capacityincreases as the packet size increases, the value of 1024 bytes

n Figure 1. a) RTS/CTS vs. b) CTS-to-self.

Network

(a)

Network

(b)

B

22

3 34 4 4 41

RTSRTS

RTSCTS

CTSCTS CTS

CTS

CTS

Wireless medium Wireless medium

2 1

CTS

CTS

2

CTS

CA D DC

AB

n Table 2. Physical layer parameters for different communicationscenarios.

Communication Preamble SlotTime CwMin

ERP–ERP ERP-OFDM 20 µs 31

ERP–non-ERP/S Short 20 µs 31

ERP–non-ERP/L Long 20 µs 31

Non-ERP/S–non-ERP/S Short 20 µs 31

Non-ERP/S–non-ERP/L Long 20 µs 31

Non-ERP/L–non-ERP/L Long 20 µs 31

All ERP ERP-OFDM 9 µs 15

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IEEE Network • May/June 200524

was chosen as the size of a representative IP packet. Finally,regarding the RTS threshold, as noted in [9], its optimalvalue depends on a variety of different parameters (networksize, fixed or variable packet payload length, minimum con-tention window) and can only be defined empirically. Forour case, after performing different simulation scenarios, thevalue of 256 bytes, which is one fourth of the mean packetpayload size, was chosen as the optimal value of the RTSthreshold.

The following subsections present simulation results con-cerning the performance evaluation of the new features of theIEEE 802.11g standard. It is important to note that the adopt-ed simulation setting is representative of many simulationsperformed with different simulation parameters (number ofstations, packet payload size and distribution, optimal value ofRTS threshold). Focusing on the performance evaluation ofIEEE 802.11g, besides their quantitative numerical differ-ences, all different simulation settings sum up with the samequalitative results, discussed in the sequel.

Evaluation of the ERP-OFDM Physical LayerIn this subsection the ERP-OFDM physical layer is evaluated,along with the efficiency of the ERP network attribute. Threesimulation scenarios were performed for a variety of differentERP-OFDM data rates. In the first scenario, all stations sup-port ERP-OFDM data rates, so the ERP network attribute isenabled. In the second scenario, one of the stations does notsupport ERP-OFDM data rates, so the ERP attribute is dis-abled. The third scenario concerns the simulation of an IEEE802.11a network with parameters identical to those of theIEEE 802.11g network (defined at the beginning of this sec-tion). Figure 2 depicts the channel capacity for different datarates in all three scenarios.

As shown, when the ERP network attribute is enabled, thenetwork capacity is increased compared to that when at leastone non-ERP station exists. Particularl for the 6 Mb/s datarate, the capacity is 0.78 (4.7 Mb/s) in the absence of non-ERP stations, 24 percent more than the capacity when non-ERP stations exist (0.63 or 3.8 Mb/s). Especially for the 54Mb/s data rate, the capacity improvement reaches 72 percent(i.e., almost 9 Mb/s). This is due to the smaller slot time andminimum contention window values and also to the shorterpreamble durations IEEE 802.11g specifies in the absence ofnon-ERP stations. These values are the same as those ofIEEE 802.11a. As a matter of fact, as shown in Fig. 2, IEEE802.11g can almost reach the performance of IEEE 802.11a(i.e., about 5 percent more than that of IEEE 802.11g) whenthe ERP attribute is enabled.

Evaluation of the ERP-DSSS and DSSS-OFDMPhysical LayersIn this subsection the ERP-DSSS and DSSS-OFDM physicallayers are evaluated, along with the efficiency of using theshort preamble. Three simulation scenarios were performedfor a variety of different data rates. In the first scenario, allstations are assumed to be non-ERP stations and support theuse of short preamble. Hence, all transmissions are performedusing the short preamble at ERP-DSSS/PBCC data rates(1–33 Mb/s). PBCC was chosen; hence, rates of 22 Mb/s and33 Mb/s were supported. Still, similar results would be pro-duced if ERP-DSSS/CCK was used. In the second scenario,all stations are assumed to be non-ERP stations and do notsupport the use of short preamble. This scenario is the case ofan old IEEE 802.11b network (i.e., all stations transmit atdata rates up to 11 Mb/s). Hence, there are no results con-cerning rates higher than 11 Mb/s. The last scenario concernsthe evaluation of the DSSS-OFDM physical layer. Under thissetting, all stations are assumed to support the DSSS-OFDMphysical layer with short preamble. Packet transmission is per-formed at one of the OFDM data rates (6–54 Mb/s). Figure 3depicts channel capacity for a variety of data rates in the threesimulation scenarios.

It can be shown from Fig. 3 that the use of short preamblein the ERP-DSSS physical layer efficiently improves the net-work performance compared to the old IEEE 802.11b stan-dard. While the capacity with the long preamble is 0.36 (4Mb/s) at 11 Mb/s data rate, the use of short preamble raisescapacity to 0.44 (almost 5 Mb/s), 22 percent higher. On theother hand, the channel capacity under the DSSS-OFDMphysical layer is remarkably lower than that of ERP-OFDM(Fig. 2). Indeed, for a 6 Mb/s data rate, under the ERP-OFDM physical layer with non-ERP stations present, thechannel capacity is 9 percent (300 kb/s) higher than the DSSS-OFDM case. For a 54 Mb/s data rate, the increase in capacityreaches 57 percent (4.3 Mb/s). Obviously, due to the networkoverhead that the DSSS preamble adds to the system, theDSSS-OFDM physical layer is inefficient for transmission withOFDM data rates. Finally, a general conclusion, concerningall the physical layers is that the channel capacity is decreasedwith the increase of the data rate. This capacity degradation iscaused due to the small packet size, compared to the highdata rates that the protocol provides.

Evaluation of the CTS-to-Self MechanismIn this subsection the efficiency of the CTS-to-self mechanismis evaluated on two different aspects: the overhead it adds tothe system and the extent to which it can handle the hiddenterminal problem. In order to study each case separately thesimulation scenarios are grouped by line of sight (LOS) andnon-LOS (NLOS). First, let us consider a simulation configu-

n Figure 2. Channel capacity for ERP-OFDM data rates.

Channel data rate (Mb/s)54

0.1

Cha

nnel

cap

acit

y

0

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

3624126

ERP disabledERP enabledIEEE 802.11a

n Figure 3. Channel capacity for ERP-DSSS/DSSS-OFDM datarates.

Data rate (Mb/s)

221 2 5.5 6 11 12 24 33 36 54

0.2

Cha

nnel

cap

acit

y

0.10

0.3

0.4

0.5

0.6

0.7

0.8

0.9Short preambleLong preamble (802.11b)DSSS-OFDM

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IEEE Network • May/June 2005 25

ration with the parameters described at the beginning of thissection. The 10 ERP stations transmit in saturation, with theERP network parameter enabled. Stations are located withinLOS of each other; hence, no hidden terminals exist. More-over, as all stations are ERP, they can detect the transmissionof each other, so no protection mechanism is required. How-ever, similar results would arise if RTS/CTS and CTS-to-selfwere also used as protection mechanisms by assuming that aconsiderable number of stations are non-ERP. Under this set-ting, only accidental collisions may occur, where two or morestations may initiate transmissions at the same slot. Figure 4depicts the channel capacity for different data rates whenRTS/CTS and CTS-to-self are used, respectively.

As shown, CTS-to-self is more efficient than RTS/CTSwhen all stations are in LOS. The small overhead the singleCTS frame includes, compared to the overhead added by theRTS-CTS exchange, can significantly improve channel capaci-ty. In particular, for a 54 Mb/s data rate, with the use of CTS-to-self the channel capacity is 0.45 (24.3 Mb/s), 18 percenthigher that that when RTS/CTS is used (0.38 or 20.5 Mb/s).That means 3.8 Mb/s of throughput increase.

Now let us include the hidden terminal problem in oursimulation assuming that some stations are hidden. The simu-lation scenario is the same as the previous one, except thatthe position and coverage of each station are configured suchthat for each station, 22 percent of the remaining stations(i.e., 2 out of 9) are NLOS. Figure 4 depicts the channelcapacity for different data rates when RTS/CTS and CTS-to-self are used, respectively. The inefficiency of the CTS-to-selfmechanism in this case is obvious. The single broadcast of aCTS frame cannot prevent hidden terminals from transmis-sion. On the contrary, RTS/CTS guarantees that the majorityof hidden terminals will receive a CTS frame from one of thestations and refrain from transmission. A remarkable note isthe convergence in the difference of the channel capacitybetween the RTS/CTS and CTS-to-self cases as the data rateincreases. Indeed, the difference in capacity is 0.54 at a 6Mb/s data rate, while at a 54 Mb/s data rate it is only 0.03.Thos means 3.2 Mb/s of additional throughput in the firstcase and 1.6 Mb/s in the second. This is mainly explained byconsidering that a packet transmission is longer when thepacket is transmitted at 6 Mb/s than at 54 Mb/s. Hence, at 6Mb/s the probability of a hidden terminal transmitting duringan ongoing transmission is higher. In other words, more hid-den-terminal-caused collisions occur at 6 Mb/s than at 54Mb/s (and generally at low data rates than at high datarates). The problem of the CTS-to-self mechanism is that itcannot prevent these collisions. Obviously, as the data rateincreases and the number of such collisions decreases, CTS-to-self becomes more efficient.

Evaluation of the Stations’ Multirate CapabilityThe IEEE 802.11 standards family provides multirate supportwith data rate agility capabilities, which means that stationscan dynamically adjust their data rate according to their dis-tance from the receiver. In this subsection we examine viasimulation how stations that transmit at low data rates affectstations that transmit at high data rates and vice versa. Again,we consider 10 ERP stations that transmit in saturation. Thesimulation parameters are already described at the beginningof this section. Furthermore, from those 10 stations, sometransmit at 54 Mb/s (i.e., are near the receiving stations),while the rest of them transmit at 6 Mb/s (i.e., are far fromthe receiving stations). Figure 5 depicts each station’s through-put vs. the number of stations that transmit at 54 Mb/s. Thetotal channel throughput (sum of all stations’ throughput) isalso depicted.

As the number of stations transmitting at 54 Mb/s increas-es, so does the total channel throughput, considered as a sumof all stations’ throughput. The slope of the channel through-put curve changes significantly in the absence of low-data-ratestations. As noted in [10], the performance degradation of anIEEE 802.11 system by the existence of low-data-rate stationsis due to the nature of carrier sense multiple access with colli-sion avoidance (CSMA/CA) that guarantees equal long-termchannel access probability to all hosts. As the packet transmis-sion duration of low-data-rate stations is longer than that ofhigh-data-rate ones, a low-data-rate station captures the chan-nel for a longer time, and thus penalizes high-data-rate sta-tions, leading to throughput degradation.

ConclusionsThe presentation of IEEE 802.11g performed in this articleshows that this standard is undoubtedly the most complete ofthe IEEE 802.11 standards family. The major novelty of IEEE802.11g is support of four different physical layers that com-bine the provision of IEEE 802.11a data rates together withbackward compatibility to the old IEEE 802.11 and IEEE802.11b specifications. Simulation results prove that the newphysical layer features supported (ERP network attribute,short and long preambles) improve channel capacity, mostlywhen all stations have IEEE 802.11g wireless interfaces (sup-port of ERP data rates). Furthermore, the CTS-to-self mecha-nism is more efficient in clear channel conditions (no hiddenterminals) but less robust than the RTS/CTS mechanismagainst hidden terminals. Considering the above, it seems thatat least until the publication of the IEEE 802.11n standardthat is going to provide data rates of up to 320 Mb/s, theIEEE 802.11g standard will become the most widely acceptedone in high-data-rate WLAN settings.

n Figure 4. RTS/CTS vs. CTS-to-self.

Data rate (Mb/s)54

0.1

Cha

nnel

cap

acit

y

0

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

3624126

RTS/CTS - LOSCTS-to-self - LOSRTS/CTS - NLOSCTS-to-self - NLOS

n Figure 5. Stations’ throughput vs. the number of stations thattransmit at 54 Mb/s.

Number of stations that transmit with 54 Mb/s

8

5.00

Stat

ions

’ thr

ough

put

(Mb/

s)

0.00

10.00

15.00

20.00

25.00

6420 10

6 Mb/s stations54 Mb/s stationsChannel throughput

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References[1] IEEE Std. 802.11, “Wireless LAN Medium Access Control (MAC) and Physi-

cal Layer (PHY) Specification,” 1999.[2] IEEE Std. 802.11b, “Higher-Speed Physical Layer (PHY) Extension in the 2.4

GHz Band,” 2001.[3] IEEE Std. 802.11a, “High-Speed Physical Layer in the 5 GHz Band,” 2000.[4] IEEE Std. 802.11g, “Further Higher-Speed Physical Layer Extension in the 2.4

GHz Band,” 2003.[5] B. Crow et al., “IEEE 802.11 Wireless Local Area Networks,” IEEE Commun.

Mag., vol. 35, no. 9, Sept. 1997, pp. 116–26.[6] S. Simoens et al., “The Evolution of 5GHz WLAN Toward Higher Through-

puts,” IEEE Wireless Commun., vol. 10, no. 6, Dec. 2003, pp. 6–13.[7] C. Heegard et al., “High-Performance Wireless Ethernet,” IEEE Commun.

Mag., vol. 39, no. 11, Nov. 2001, pp. 64–73.[8] Pythagor Simulation Tool, http://www.icsd.aegean.gr/telecom/pythagor/

index.htm[9] G. Bianchi, “Performance Analysis of the IEEE 802.11 Distributed Coordina-

tion Function,” IEEE JSAC, vol. 18, no. 3, Mar. 2000, pp. 535–47.[10] M.Heusse et al., “Performance Anomaly of 802.11b,” Proc. IEEE INFO-

COM, San Francisco, CA, Apr. 2003.

BiographiesDIMITRIS VASSIS (divas@aegean.gr) received his Diploma in electrical and comput-ing engineering and M.B.A. in techno-economic systems from the National Tech-nical University of Athens (NTUA), Greece, in 2001 and 2004, respectively.Currently, he is a PhD student at the University of the Aegean (UoA), Departmentof Information and Communication Systems Engineering. His research interestsare in the fields of performance evaluation and performance analysis of wirelessaccess networks.

GEORGE KORMENTZAS (gkorm@aegean.gr) is currently a lecturer at the Universityof the Aegean, Department of Information and Communication Systems Engi-neering. He received his Diploma in electrical and computer engineering andPh.D. in computer science both from NTUA in 1995 and 2000, respectively.

From 2000 to 2002 he was a research associate with the Institute of Informatics& Telecommunications of the Greek National Center for Scientific Research“Demokritos.” His research interests are in the fields of traffic analysis, networkcontrol, resource management, and quality of service in broadband networks.He has published extensively in the fields above in international scientific jour-nals, and edited books and conference proceedings. He is a member of \ pro-fessional societies, an active reviewer and guest editor for several journals andconferences, and EU evaluator for Marie Curie Actions. He has participated in anumber of national and international research projects, serving in some instancesas the project’s technical representative for UoA and/or WP leader and/or tech-nical manager.

ANGELOS ROUSKAS [M] (arouskas@aegean.gr) received a five-year Diploma inelectrical engineering from NTUA, an M.Sc. in communications and signal pro-cessing from Imperial College, London, and a Ph.D. in electrical and computerengineering from NTUA. He is an assistant professor in the Department of Infor-mation and Communication Systems Engineering of UoA, and director of theComputer and Communication Systems Laboratory. Prior to joining UoA, heworked as a research associate at the Telecommunications Laboratory of NTUAin the framework of several European and Greek funded research projects, andat the Network Performance Group of the Greek cellular operator CosmOTE S.A.His current research interests are in the areas of resource management of mobilecommunication networks, mobile and ad hoc network security, and pricing andadmission control in wireless and mobile networks; he has several publications inthe above areas.

ILIAS MAGLOGIANNIS [M] (imaglo@aegean.gr) received his Diploma in electricaland computer engineering and Ph.D. in medical informatics from NTUA in 1996and 2000, respectively. From 1996 until 2000 he worked as a researcher in theBiomedical Engineering Laboratory in NTUA. Since February 2001 he has beena lecturer in the Department of Information and Communication Systems Engi-neering, UoA.His scientific activities include biomedical engineering, image pro-cessing, computer vision, and multimedia communications. He is the author ofover 40 publications in the above areas. He is a member of the ACM, SPIE, andHellenic Association of Biomedical Engineering.

26 IEEE Network • May/June 2005

IEEE NETWORK MAGAZINE — CALL FOR PAPERSSPECIAL ISSUE ON: MULTIMEDIA OVER BROADBAND WIRELESS NETWORKS

The goal of this special issue is to present a concise reference of state-of-the-art efforts in delivering multimedia over emergingpacket-based broadband wireless networks. Specifically, the special issue is intended to present tutorials, survey and originalresearch articles (in a tutorial manner readable by non-specialists) on emerging architectures, protocols and services for deliveringmultimedia over single-hop or mesh broadband wireless networks. It also focuses on the protocols needed to integrate the applica-tion layer requirements, such as QoS, security, etc., with the base functionality offered by the standardized 802.16/11 and otherWLAN and WMAN interfaces. Of particular interest is the inter-play between newer techniques of multimedia encoding and stream-ing and the network-layer features to exploit these techniques.

Following are the topics of interest for which we solicit contributions for this special issue:* IP-based multimedia delivery and services over WLANs and WMANs* QoS for real-time voice and video in broadband wireless networks* Media multicasting and broadcasting problems and solutions for wireless links* Caching and content management in WLANs, WMANs and 3G Networks* VoIP over wireless networks* Multimedia over single-hop and mesh-based wireless networks* Multimedia delivery for broadband vehicular networks* Multimedia services for ambient intelligent and pervasive environments* Broadband multimedia prototypes and system experiences* Broadcast and point-to-point multimedia in indoor & outdoor environments, e.g. homes, convention centers,

sports arenas

Manuscript Submission:Papers should be submitted in PDF format at http://colibri.iit.cnr.it. For any questions or clarification, please contact any of the guesteditors. With regard to both the content and formatting style of the submissions, prospective contributors should follow the IEEENetwork guidelines for authors that can be found at “http://www.comsoc.org/pubs/net/ntwrk/authors.html.”

Important Dates:Submission Deadline: June 10, 2005Reviews Completed: September 30, 2005Final Manuscripts Due: November 30, 2005Publication of Special Issue: 1st Quarter, 2006

Guest Editors:John Apostolopoulos Marco Conti Archan MisraHP Labs IIT-CNR IBM Research1501 Page Mill Road MS 1181Via G. Moruzzi, 119 Skyline DrivePalo Alto, CA, 94306, USA 56124 Pisa Italy Hawthorne, NY 10533, USA.japos@hpl.hp.com marco.conti@iit.cnr.it archan@us.ibm.com

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