Optimization of Hybrid ARQ for IP Packet Transmission

Wireless Personal Communications16: 203–219, 2001.© 2001Kluwer Academic Publishers. Printed in the Netherlands.

Optimization of Hybrid ARQ for IP Packet Transmission

ANAND R. PRASADGenista Corporation, Aoyama Nozue Bld. 301 2-11-10 Kita Aoyama Tokyo 107-0061, JapanE-mail: [email protected]

Abstract. This paper presents, optimizes, and analyzes the performance of a novel hybrid Selective Repeat/MultiCopy (SR/MC) Automatic Repeat Request (ARQ) scheme for transmitting fragmented Internet Protocol (IP)packets. The ARQ scheme works in the SR mode until the last IP packet fragment is transmitted. If a fragment isnegatively acknowledged after the last fragment is transmitted, then the system goes into the MC mode. In the MCmode, multiple copies of the erroneous fragment are transmitted. After the IP fragments are received without error,the system returns to the SR mode. The optimization of the ARQ is done in terms of two parameters: fragment sizeand the optimum number of packets to be transmitted in the MC mode,M . Optimum values for both parametersare calculated for Bit Error Rate (BER), throughput, IP packet size, and delay. The fragment size is also calculatedfor actual data throughput for a given IP packet size, both with and without Forward Error Correction (FEC). Then,the performance of the proposed scheme is evaluated in terms of BER and IP packet size with the optimumM

and fragment size. Performance results are obtained with and without Bose Chaudhuri Hocquenghem (BCH) errorcorrection codes under Additive White Gaussian Noise (AWGN) as well as Flat Rayleigh Fading channels. TheARQ scheme gives optimum performance forM equal to 10 fragments and fragment size of 75 bytes. Under theAWGN channel, a throughput of 0.9 is achieved for any IP packet size and at higher BER conditions compared tothe Selective Repeat+ Stutter Scheme 2 (SR+ ST 2). An 8 dB improvement is achieved under the flat Rayleighfading channel using BCH(63, 51, 2) for a throughput of 0.9.

Keywords: wireless IP, automatic repeat request, wireless LANs

1. Introduction

The past decade has seen major changes in the types of communication services providedfor the users and in the infrastructure. Besides the present-day telephony, Internet access,client-server applications with remote servers, video on demand, and interactive multimediaare just a few examples. At the same time, the restriction on the mobility of terminals hasbrought about rapid development in the field of Radio Local Area Networks (also referredto as cableless or wireless LANs) [1–3]. Radio LANs not only decrease wiring complexityand increase mobility, but also provide increased flexibility and ease of installation. Thiscreates a new type of access technology. Although this new access technology fulfills severalpractical requirements (increased mobility, flexibility, etc.), several technical problems stillremain unsolved.

In order to fulfill such service requirements, point-to-point communication is used as thenetwork architecture in this paper. The system is used as an Internet browser most of the timeand whenever required for E-mail, games, etc. Since the main purpose of this system is toaccess Internet, an efficient scheme for IP packet transmission in a wireless medium is themajor requirement.

Since we are talking about a wireless system, characteristics of the radio channel mustbe taken into account. Radio channel characteristics vary with the location of the user and,

204 Anand R. Prasad

because of user mobility, they vary in time. The number of propagation mechanisms hindersmobile radio links, viz. multipath fading, shadowing, and attenuation mechanisms on thepropagation path between transmitter and receiver. This means that classical system analysisconducted via AWGN channels may not be applicable. Thus, performance analysis must bedone via radio channels with shadowing and multipath fading to get a realistic view of theperformance. Rayleigh fading is a special case of multipath scattering where the power of theline of sight signal is negligible compared to the reflected signal power. This channel modelis often used for the worst-case analysis of a wireless system and is used in this paper to testthe performance of the proposed ARQ scheme.

To combat the high degree of error caused by the wireless transmission of data, a robusterror control scheme is a necessity. Basically, error control schemes can be divided into twocategories: ARQ schemes and Forward Error Correction (FEC) schemes. ARQ schemes areoften used for reliable data transmission. This is because FEC schemes require too manyparity bits for perfect data transmission. There are several known ARQ schemes [4, 5]: Go-back-N, Stop and Wait, and Selective Repeat are the most basic ones. In an ARQ scheme,correctly received fragments are Acknowledged (ACK) and fragments received with errorare Negatively Acknowledged (NACK). NACKed fragments are then retransmitted. In short,ARQ is an error detection with a retransmission scheme. As the purpose of our system iswireless IP packet transmission, the efficiency of the system depends on the ARQ scheme.

IP packets can vary in size between 40 bytes and a maximum of 1500 bytes. Wirelesstransmission of such large packets can cause many errors, thus bringing forward the needfor fragmentation. However, it must be kept in mind that increasing the number of fragmentsmeans increasing the overhead, which in turn leads to increased memory management. There-fore, optimal fragment size is required to give high throughput, to use the channel efficiently,and to have low memory management.

An efficient ARQ scheme for IP packet transmission was presented in [6] and [7]. Thescheme works in the Selective Repeat (SR) mode until all of the fragments are transmitted. Ifa NACK is received after the last fragment is transmitted, the system goes into the MC mode.In [6] and [7], the performance of the unoptimized hybrid ARQ was analyzed. In this paper,the hybrid ARQ scheme is optimized in terms of fragment size and the number of copiesof fragments,M, transmitted in the MC mode. First, the optimum value forM is calculatedfor a given IP packet size, fragment size, and throughput. The optimum value ofM is alsocalculated against the throughput for a given BER, IP packet size, and fragment size. Theperformance of the ARQ scheme is then evaluated in terms of BER and IP packet size forthe optimized values ofM and fragment size. AWGN as well as flat Rayleigh fading channelare used to study the performance of the proposed scheme. The results, in terms of BER andEb/N0, of a Direct Sequence Spread Spectrum (DS-SS) system using QPSK modulation arealso used to analyze the performance of the ARQ under flat Rayleigh fading channel. All ofthe results are then compared with that of Selective Repeat+ Stutter Scheme 2 (SR+ST 2)scheme [8, 9], and conventional Go-Back-N (GBN). Performance results are obtained withand without BCH(n, k, t) error correction codes.

SR+ ST 2, used for comparison with the proposed protocol, works in the SR mode forthe first NACK of a fragment and goes into the MC mode if a second NACK is received forthe same fragment. This scheme performs better than GBN, but the performance degradesrapidly as the channel condition deteriorates. This is because the scheme changes to the MCmode after a second NACK is received for a fragment, which can frequently happen with badchannel conditions. The proposed scheme makes use of the knowledge of IP packet size and

Optimization of Hybrid ARQ for IP Packet Transmission205

Figure 1. System model.

the number of fragments before transmission. Knowing the number of fragments, efficient useof the SR scheme can be made until the last fragment is transmitted. If there are erroneousfragments even after transmitting the last fragment, the ARQ can make use of the MC mode.Thus, it increases the throughput and thereby efficiently uses the scarce wireless channel.

The system considered in this paper is described in Section 2, while the proposed ARQscheme is discussed in detail together with the SR+ST 2 scheme in Section 3. Throughputanalysis is done in Section 4. The optimization method is discussed in Section 5 and Section 6presents and explains the numerical results. Conclusions and future work are finally sketchedin Section 7.

2. System Description

This section first describes the system architecture considered for the performance analysis ofthe proposed scheme. Then, the channel model and simulation model used are discussed.

2.1. SYSTEM ARCHITECTURE

In this paper, we consider a point-to-point network architecture. The system is used mainly asan Internet browser and whenever required for E-mail, games, etc. The system we consideredis shown in Figure 1: there is one Base Station (BS) to which several Personal Stations (PS)can communicate. PSs cannot communicate with each other. The BS is connected to a wiredLAN so that users can access Internet through the BS. The connection between the PS andthe BS is wireless. The user can also move (slow mobile) with the PS while the PS is stillcommunicating with the BS.

Since the main function of the system is to communicate with Internet, an efficient trans-mission of Internet Protocol (IP) packets is required. IP packets can vary in size from 40 bytesto a maximum of 1500 bytes; since wireless transmission of such large packets can causemany errors, fragmentation is required. It must be kept in mind that increasing the number offragments will mean increasing the overhead, which will require severe memory managementin the practical applications. Therefore, an optimal fragment size is required that gives highthroughput and thus uses the channel efficiently. In Figure 2, the fragmentation of an IP packetand the associated overhead are given.

206 Anand R. Prasad

Figure 2. IP packet fragmentation.

2.2. CHANNEL MODEL

Choosing the appropriate channel model is necessary for the realistic performance analysis ofa communication system. A classical AWGN channel is considered first in this paper for theperformance analysis of the proposed scheme. In contrast to the AWGN channel with errorsrandomly distributed in time, burst errors are experienced in wireless channels. A typicalwireless channel allows relatively reliable communication during certain periods interruptedby periods of poor communication. The latter is called fading. Since wireless communicationis being discussed in this paper, the influence of the wireless medium on the efficiency of theARQ scheme must also be considered.

Shadowing and multipath fading can characterize fading in wireless networks. Shadowingis caused by the presence of obstacles between the transmitter and the receiver. Multipathfading occurs because the received signal is a superposition of a large number of reflectedsignals. Rayleigh fading is a special case of multipath fading in which the power of the lineof sight signal is small or negligible compared to the reflected signal power. Rayleigh fadingcan thus be used for the worst-case analysis of a wireless system.

As the system model used in this paper is concerned with wireless communication allowingslow mobility, a good idea of the performance of the proposed scheme can be achieved bytesting the system under flat Rayleigh fading channel. Both the AWGN and flat Rayleighfading channels are used in this paper to test the performance of the proposed ARQ.

2.3. SIMULATION MODEL

The simulation model and simulation parameters used in this paper are presented in Fig-ure 3 and Table 1, respectively. IP packet fragments were first BCH-coded and thenQPSK-modulated.

The QPSK-modulated signal was then spread spectrum (SS)-modulated before beingpassed through the flat Rayleigh fading and AWGN channel. The signal thus received wasthen demodulated and decoded. The result in terms of BER for a given Signal-to-Noise ratio,bb/N0, was acquired as output. The results generated from the simulation model, in terms ofBER andEb/N0, were then used to generate numerical results for the proposed ARQ scheme.In Figure 4, the output of the simulation model is plotted with and without BCH(63,51,2); acomparison with the theoretical result without BCH is also given.


Figure 3. Simulation model.

Table 1. Simulation parameters.

FEC BCH(63,51,2)

Modulation QPSK

Chip rate 1 Mcps

Bit rate 181.81 kbps

Symbol rate 90.9 ksps

fD 10 Hz

Figure 4. BER performance of the assumed radio channel.

208 Anand R. Prasad

Figure 5. IP fragment transmission without error.

3. Description of Proposed ARQ Scheme

A detailed explanation of the proposed ARQ scheme is given in this section [6, 7]. Acomparison between the SR+ ST 2 scheme and the proposed scheme is also shown.

The proposed ARQ works as follows: (1) the IP packet received by the transmitter isfragmented in equal sizes; (2) the fragments are then BCH-encoded for error correction; (3)the system remains in the SR mode until the last fragment is transmitted; (4) an erroneous orlost fragment is negatively acknowledged; and (5) if there are erroneous fragments after thelast fragment is transmitted, the system goes into the MC mode, whereM copies of erroneousor lost fragments are transmitted. The cycle of transmittingM copies of erroneous fragmentsis continued until all of the fragments are received without error. The system then returns tothe SR mode.

The transmission of IP fragments without error is shown in Figure 5. The IP packet bufferdecreases as the fragments are transmitted and ACKed by the receiver when received correctly.In Figure 6, an example of the proposed ARQ transmission with error and change in modeis given. This example is for an IP packet divided into 10 equal fragments. From Figure 6,we can see that the system remains in the SR mode until the last fragment is transmitted.Fragments 2 and 6 are not received correctly in the SR mode, so the system goes into the MCmode when a NACK for fragment 2 is received after the last fragment is transmitted. In theMC mode,M copies (in this exampleM = 3) of each erroneous fragment (fragments 2 and6) are transmitted. The cycle of retransmission is continued until an ACK for all fragments isreceived. The system then returns to the SR mode.

The SR+ ST 2 scheme stays in the SR mode for the first retransmission and then goes intothe MC mode. In the MC mode, multiple copies of the NACKed fragment are retransmitteduntil an ACK is received for the fragment. The system then returns to the SR mode if no moresecond NACKs have been received in the mean time. An example of this scheme is given inFigure 7 with Round Trip Delay (RTD)= 4. Fragments 2 and 3 are received with error; theyare retransmitted once in the SR mode; the system goes into the MC mode when they areNACKed again. Fragment 2 was first transmitted continuously until an ACK was received,


Figure 6. Mode change due to error.

Figure 7. Example of SR+ ST 2.

then fragment 3 was transmitted. Once an ACK is received for fragment 3, the system goesback to the SR mode.

4. Numerical Analysis

4.1. THROUGHPUTANALYSIS

Throughput analysis of the proposed ARQ scheme is presented in this section.For throughput calculations under the AWGN channel, the fragment error rate (FER) for

the case without BCH can be written as

P =m∑x=1

(m

x

)px(1− p)m−x = 1− (1− p)m , (1)

210 Anand R. Prasad

whereP is the FER,x is the number of erroneous bits,m is the number of bits in the fragment,andp is the BER.

While for BCH(n, k, t), the FER is

P = 1−(

t∑x=0

(n

x

)px(1− p)n−x

)mk

, (2)

where we use the knowledge that BCH(n, k, t) divides the fragment into blocks ofk bits andaddsn− k bits to each block. Thesen− k bits can correctt bit error.

The throughput of any packet transfer scheme in simple terms is the ratio of the numberof fragments to be transmitted to the number of fragments actually transmitted. Using thisknowledge, the throughput of the proposed ARQ scheme is

S = N

NSR+NMC, (3)

whereS denotes the throughput,N is the number of fragments to be transmitted,NSR isthe number of fragments transmitted in the SR mode, andNMC is the number of fragmentstransmitted in the MC mode.

In the SR mode,N fragments plus the fragments with error must be transmitted. Consid-eringi erroneous fragments in the SR mode, the total number of fragments transmitted underthis mode can be given as

NSR=N∑i=0

(N

i

)P i(1− P)N−i ((N − i)+ i 1

1− P . (4)

N − i fragments are transmitted without error andi erroneous fragments are repeated11−P

times, whereP is the frame error probability.If, after the last fragment is transmitted, there are fragments with error, then the system

goes into the MC mode. Suppose that there arej fragments with error after the last fragmentis transmitted. The system then goes into the MC mode. This is the 0th cycle of the MC mode.The probability ofj erroneous fragments at the 0th cycle can be given as

P 0(j) =(N

j

)(P

11−P)j (

1− P 11−P)N−j

, (5)

whereP 0(j) is the probability ofj errors in the 0th cycle. In the next cycle,i out of thejfragments will have error. Thus, the probability ofi erroneous fragments out ofj can be givenas

P s+1(i) =N∑j=i

qjiPs(j) (6)

for the cycles + 1, whereqji gives the probability that there arei fragments out of previousj fragments with error.qji can be given as

qji =

((1− P)M)j ; i = 0,1≤ j ≤ N(j

i

)(PM)i(1− PM)j−i; 1≤ i ≤ j ≤ N

0; otherwise

, (7)


whereM is the number of repetitions of erroneous fragments under the MC mode. Thus, thenumber of fragments transmitted during thes + 1 cycle is iM. The number of fragmentstransmitted in the MC mode is the sum of the number of fragments transmitted from cycle 1onwards. This can be given as

NMC =∞∑s=1

N∑i=1

N∑j=i

P s(j)iM

. (8)

Substituting Equations (8) and (4) in Equation (3), we get

S = N

N∑i=0

(N

i

)P i(1− P)N−i

((N − i)+ i 1

1− P)+∞∑s=1

N∑i=1

N∑j=i

P s(j)iM

(9)

which is the expression of the throughput of the proposed ARQ scheme.

4.2. DATA THROUGHPUTANALYSIS

Since IP packets can be as big as 1500 bytes, we must fragment them before transmission inorder to get better performance. Although a smaller fragment size will give better results, itwill also require much more overhead. Therefore, we must calculate the optimum fragmentsize. Optimum fragment size can be calculated in terms of actual data throughput,SD. SDis the ratio of fragment size,FS , (actual data) and ARQ fragment size, which consists ofoverhead,O, andFS . In the following, the overhead,O, is the fragment number.O will varyfor different protocols; it will usually be twice theO calculated here plus some constant value.SD for transmission without FEC is given as

SD = Fs

FS +O =FS

FS + log2

⌈IPSFS

⌉ , (10)

where IPS stands for IP packet size. For transmission with BCH(n, k), we can writeSD as

SD = FS

FS +O =FS

FS +⌈FS

n

⌉k + log2

⌈IPSFS

⌉ . (11)

4.3. DELAY ANALYSIS

In this study, we require the delay calculation in order to obtain the optimum fragment size.The normalized delay,d, is the sum of number of fragments transmitted in the SR and MCmodes

d = NSR+NMC . (12)

5. Optimization Method

In order to optimize the performance of the proposed ARQ, two parameters (IP fragment sizeand the number of copies transmitted in the MC mode,M) must be optimized. The criteria

212 Anand R. Prasad

Figure 8. M against BER forS = 0.9, IP packet size 750 bytes, and fragment size 78 bytes.

used for optimization are BER, throughput, delay, and IP packet size. A parameter must beoptimized for the varying values of the criteria and all other parameters; i.e., the optimizationprocedure is iterative. The pseudo code for this optimization process is given as follows.

Optimize(A){For(BER= 0 to 10−5){

For(S = 0 to 1){For(d = 0 to 100){

For(B = a to z){CalculateA;Find optimum value ofA for given BER, S, d andB;

}}

}}

}

If A isM, thenB stands for fragment size and varies from 1 (a) to IP packet size (b). IfA

is fragment size, thenB stands forM and varies between 0 and 100. Calculations were donefor varying values of all the criteria for both parameters. In this paper, just enough results toprove the optimized value are presented.

6. Numerical Results

The numerical results of the proposed ARQ scheme are given in this section. The throughput iscalculated using Equation (9). The results for the AWGN channel are presented first, followedby the results for the fading channel.


Figure 9. M againstS for BER= 10−3, IP packet size 750 bytes, and fragment size 78 bytes.

6.1. AWGN CHANNEL

This section gives the results for the proposed ARQ scheme under the AWGN channel. Beforewe begin with the throughput results, we have to optimize the ARQ. Optimizing the ARQmeans finding the optimum values forM and the IP fragment size.

Under the AWGN channel,M can be calculated for a fixedS or a fixed BER. These resultsare given as Figure 8 and Figure 9, respectively, for an IP packet size of 750 bytes and afragment size of 78 bytes. Both figures confirm thatM = 10 is the optimum value. Similarresults were obtained for varying IP packet size,S, BER, and fragment size.

Knowing the optimum value forM, we must find the optimum fragment size for the pro-posed ARQ. The optimum fragment size will be the one that gives a maximum throughputand a minimum delay. Since a small fragment size means a large overhead, one must alsocalculate the ratio of the actual data and overhead against the packet size.

The result for fragment size and normalized delay is given in Figure 10 for a varying IPpacket size and BER= 10−3. We can see from this result that a fragment size of 75 bytes givesthe least delay. Similarly, the result for throughput against fragment size is given in Figure 11for a varying IP packet size and BER= 10−3. The throughput for the varying IP packet size isthe same until a fragment size of 75 bytes. Similar results as in Figure 10 and Figure 11 havebeen obtained for other values of BER andM.

The optimum fragment size was also found using Equations (10) and (11) in terms ofactual data throughput and fragment size transmitted without FEC and with BCH(63, 51) fora varying IP packet size. In Figure 12, the result is given for a IP packet size of 1500 bytes.Once again, a fragment size around 75 bytes was found to be the optimum value.

Now that we know the optimum value forM andFS , we can calculate the throughputSusing Equation (9). The proposed scheme is compared with the GBN and SR+ ST 2 scheme.

214 Anand R. Prasad

Figure 10. Normalized delay against fragment size for a varying IP packet size and a BER of 10−3.

In Figure 13, the result is given forM = 5, a fragment size of 75 bytes, and an IP packet sizeof 250 and 1500 bytes. The result is compared with SR+ ST 2 and GBN.

As expected, we see that the performance of the proposed scheme is better for the smallerIP packet size. We also observe that even forM = 5, the proposed scheme outperforms GBNand SR+ ST 2 for high BER.

In Figure 14, the proposed scheme is once again compared with GBN and SR+ ST 2 for afragment size of 75 bytes, an IP packet size of 1500 bytes, andM = 5 and 10. Once again, wesee that the proposed scheme outperforms GBN and SR+ ST 2. However, we also observethat the performance forM = 10 is better than forM = 5 obtained above.

6.2. FADING CHANNEL

In order to calculate throughput under a fading channel, the results generated by the simulationmodel given in Section 2.3 are used. In Figure 15, the results are given for throughput againstEb/N0 for the proposed ARQ with BCH(63,51), theoretical and without BCH. The result ofthe proposed ARQ is compared with that of SR+ ST 2 and GBN for a fragment size of75 bytes, an IP packet size of 1500 bytes, andM = 5 and 10 in Figure 16. The channelconsidered is a flat fading channel with a Doppler frequency,fD, of 10 Hz.

Similar to the AWGN channel results, we can see that the proposed scheme outperformsSR+ST 2 and GBN. For a throughput of 0.9, there is an improvement of 8 dB when comparedto SR+ ST 2 with BCH(63,51,2).

7. Conclusions

The hybrid Selective Repeat(SR)/Multicopy(MC) ARQ scheme is optimized in this paper.Performance of the optimized ARQ is then measured in terms of throughput,Eb/N0, and


Figure 11. Throughput against fragment size for a varying IP packet size and a BER of 10−3.

Figure 12. Data throughput against fragment size for an IP packet size of 1500 bytes with BCH(63,51) and withoutFEC.

216 Anand R. Prasad

Figure 13. Throughput against BER under the AWGN channel for SR/MC (proposed) scheme withM = 5, GBN,and SR− ST 2 with a fragment size of 75 bytes and an IP packet of 250 and 1500 bytes.

Figure 14. Throughput against BER under the AWGN channel for SR/MC (proposed) scheme withM = 5 and10, GBN, and SR− ST 2 with a fragment size of 75 bytes and an IP packet size of 1500 bytes.


Figure 15. Throughput againstEb/N0 for the proposed scheme under a flat fading channel.

Figure 16. Throughput againstEb/N0 comparison of proposed scheme, SR+ ST 2, and GBN under a flat fadingchannel.

BER. Numerical results of the proposed scheme are also compared with that of the SR+ ST 2scheme and the conventional Go-Back-N scheme (GBN). The results show that the proposedscheme outperforms both the SR+ ST 2 scheme and the GBN under the AWGN and flatRayleigh fading channels.

The proposed scheme gives optimum performance for a fragment size of 75 bytes and thenumber of copies in the Multi-Copy modeM = 10. A fragment size of 75 bytes is large,

218 Anand R. Prasad

which requires less overhead and thus less memory management, making the transmitter andreceiver structure simpler.

The proposed ARQ scheme gives a throughput higher than 0.9 for any IP packet size formuch higher BER when compared with SR+ ST 2.

Knowing the above, we can say that the proposed scheme gives very good performanceand can be used very efficiently for IP packet transmission. Since the simulation model usedis very practical, we can conclude that the proposed scheme will work very efficiently for anywireless communications systems.

Although the proposed ARQ scheme was only studied for IP packet transmission, it maywell be used elsewhere, e.g., wireless ATM.

References

1. R. Fantacci and M. Scardi, “Performance Evaluation of Preemptive Polling Schemes and ARQ Techniquesfor Indoor Wireless Networks”,IEEE Trans. on Vehicular Technology, Vol. 45, No. 2, pp. 248–257, 1996.

2. S. Kumar and D.R. Vaman, “An Access Protocol for Supporting Multiple Classes of Service in a LocalWireless Environment”,IEEE Trans. on Vehicular Technology, Vol. 45, No. 2, pp. 288–302, 1996.

3. A.R. Prasad, “Asynchronous Transfer Mode Based Mobile Broadband Transmission”, inProc. IEEE ThirdSymposium on Communication and Vehicular Technology in Benelux, Eindhoven, The Netherlands, 25–26October 1995, pp. 143–148.

4. J. Walrand,Communication Networks: A First Course. Richard D. Irwin, Inc. and Aksen Associates, Inc.:Boston, 1991.

5. M. Schwartz,Telecommunication Networks: Protocols, Modeling and Analysis, Addison Wesley: California,1987.

6. A.R. Prasad, Y. Shinohara and K. Seki, “Performance of Hybrid ARQ for IP Packet Transmission on FadingChannel”,IEEE Trans. on Vehicular Technology, Vol. 48, No. 3, pp. 900–910, 1999.

7. A.R. Prasad and K. Seki, “Hybrid ARQ for IP Packet Transmission”, inICUPC’97, 12–16 October 1997, pp.531–535.

8. H. Tanaka, “"A Performance of Selective-Repeat ARQ with Cyclical Multicopy Retransmission”,IEICETransactions on Fundamentals of Electronics, Communications and Computer Sciences, Vol. E79-A, No. 9,pp. 1386–1391, 1996.

9. M.J. Miller and S. Lin, “The Analysis of Some Selective Repeat ARQ Schemes with Finite Receiver Buffer”,IEEE Trans. on Comm., Vol. COM-29, No. 9, pp. 1307–1315, 1981.


Anand Raghawa Prasadreceived his M.Sc. degree in Electrical Engineering from DelftUniversity of Technology, Delft, The Netherlands, in 1996 in the field of “Self Similarity ofATM Network Traffic”. From 1996 to November 1998, he worked as a Research Engineerand later as a Project Leader at the Uniden Corporation, Tokyo, Japan. From December 1998to September 2000 he worked as a Systems Architect for Wireless LANs at Lucent Technolo-gies, Nieuwegein, The Netherlands. Since October 2000 he has been working as a TechnicalDirector at Genista Corporation, Tokyo, Japan. He will complete his Ph.D. by the end of2000 at the Norwegian University of Science and Technology, Trondheim, Norway, under thesupervision of Prof. Dr. Steinar Andresen. The tentative title of his thesis is IP-based WirelessLANs: Protocols, Security and Deployment. He holds and has applied for several patents. Hehas published several papers in journals, international conferences, and a chapter in a book.His research interests lie in the fields of security and QoS for wireless technologies, fixed andmobile internet access, and software radio.

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Optimization of Hybrid ARQ for IP Packet Transmission