7
WIRELESS INFRARED COMMUNICATIONS WITH EDGE POSITIOM MoDU LATION FOR THOMAS LUFTNER, DANUBE INTEGRATED CIRCUIT ENGINEERING MARIO HUEMER, UNIVERSITY OF APPLIED SCIENCES OF UPPER AUSTRIA R. WEIGEL, UNIVERSITY OF ERLANGEN-NUREMBERG JOSEF HAUSNER, INFINEON TECHNOLOGIES CHRISTIAN KROPL AND R. HAGELAUER, UNIVERSITY OF LINZ The authors present o new modulation scheme that offers on increased bandwidth efficiency compared to the previous approaches, and an attractive power efficiency. Since the technique can be optimized to the characteristics of the wireless infrared channel, it also maintains low bit error rates. ABSTRACT Driven by the Infrared Data Association, wireless infrared communication has become a very popular and widely used method for short- range data transmission between mobile devices like laptops, PDAs, and mobile phones. Espe- cially in ad hoc connection applications, lrDA excels over radio-based solutions like Bluetooth or cable-based solutions likc USB, due to the point-and-shoot characteristic of infrared com- munication. Quality and speed of infrarcd com- munications are mainly limited by the bandwidth of infrared transceivers. Therefore, it is impor- tant to use a modulation technique with high bandwidth efficiency, while simultaneously main- taining a low hit error rate and high powcr effi- ciency. Consequently, the IrDA has continuously improved the modulation techniques of its stan- dards by introducing return to zero inverted (RZI) for the serial infrarcd (SIR) mode, 4- PPM for the fast infrared mode, and HHH(1,13) for the latest very fast infrared mode [l]. This article presents a new modulation scheme called edge position modulation (EPM) with RLL cod- ing, which offers increased bandwidth efficiency over the previous methods and attractive power efficiency. Since the novel modulation technique can be optimized to the characteristics of the wireless infrared channel, it also maintains low bit error rates. INTRODUCTION In recent years mobile digital devices such as personal digital assistants (PDAs), mohile phones, digital cameras, and laptops have pene- trated the consumer market. All thcse devices require a powerful short rangc communication method for data exchangc among each other, connections with printers, or local area network (LAN) access. Basically, the communication methods can he based on cable connections, radio links, or infrared links. Since each has its individual strengths and weaknesses, each has found its way into various products. Data exchange via cables is a well established method; universal serial bus (USB) has become a widely used standard interface. USB excels due to its high baud rates up to 480 Mhis, hut suffers from its limitcd mobility duc to cable connection [2]. Therefore, USB is best for applications that require stable high-performance. connections for transmission of high data volumes, where mobili- ty is not very important. An example application would be the connection of a vidcoconferencing camera to your laptop. However, mobility is a big advantage for radio-based short-range communication methods such as Bluetooth, which have appeared recently in many mobile devices. Bluetooth can transmit data through solid nonmetal objects and sup- ports a nominal link range of 10 cm-IO m at a moderate baud rate up to 721 kbis [3]. Because of the nature of radio, Bluetooth is a point-to- multipoint communication system, which sup- ports connections of two devices as well as ad hoc networking between several devices. But in order to prcvcnt unauthorized access, Bluetooth requires sophisticated authentication and encryp- tion mcchanisms, which hamper fast connection establishment. Therefore, Bluetooth is best for applications that rcquire stable point-to-point or point-to-multipoint connections for data exchangc at moderate speeds, where mobility is the key requircment. An example application would he the transmission of audio data from your mobilc phone to your headset. Contrary to USB and Bluetooth, infrared transmission based on the Infrared Data Associ- ation (IrDA) standard enables fast simple con- ncction establishment due to its point-and-shoot Characteristic. Together with high baud rates up to 16 Mhis, this makes lrDA transmission per- IEEE Wireless Communications - April 2003 153h-IZR4/03/$17.00 D 2003 IEEE 15

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Page 1: Wireless infrared communications with edge position modulation for mobile devices

WIRELESS INFRARED COMMUNICATIONS WITH EDGE POSITIOM MoDU LATION FOR

THOMAS LUFTNER, DANUBE INTEGRATED CIRCUIT ENGINEERING

MARIO HUEMER, UNIVERSITY OF APPLIED SCIENCES OF UPPER AUSTRIA R. WEIGEL, UNIVERSITY OF ERLANGEN-NUREMBERG

JOSEF HAUSNER, INFINEON TECHNOLOGIES

CHRISTIAN KROPL AND R. HAGELAUER, UNIVERSITY OF LINZ

The authors present o new modulation scheme that offers on increased bandwidth efficiency compared to the previous approaches, and an attractive power efficiency. Since the technique can be optimized to the characteristics of the wireless infrared channel, it also maintains low bit error rates.

ABSTRACT Driven by the Infrared Data Associat ion,

wireless infrared communication has become a very popular and widely used method for short- range data transmission between mobile devices like laptops, PDAs, and mobile phones. Espe- cially in ad hoc connection applications, l rDA excels over radio-based solutions like Bluetooth or cable-based solutions likc USB, due to the point-and-shoot characteristic of infrared com- munication. Quality and speed of infrarcd com- munications are mainly limited by the bandwidth of infrared transceivers. Therefore, it is impor- tant to use a modulation technique with high bandwidth efficiency, while simultaneously main- taining a low hit error rate and high powcr effi- ciency. Consequently, the IrDA has continuously improved the modulation techniques of its stan- dards by introducing return t o zero inverted ( R Z I ) f o r the serial infrarcd (SIR) mode, 4- PPM for the fast infrared mode, and HHH(1,13) for the latest very fast infrared mode [l]. This article presents a new modulation scheme called edge position modulation (EPM) with RLL cod- ing, which offers increased bandwidth efficiency over the previous methods and attractive power efficiency. Since the novel modulation technique can be optimized t o the characteristics of the wireless infrared channel, i t also maintains low bit error rates.

INTRODUCTION In recent years mobile digital devices such as personal digital assistants (PDAs) , mohile phones, digital cameras, and laptops have pene- trated the consumer market. All thcse devices require a powerful short rangc communication method for data exchangc among each o ther , connections with printers, or local area network (LAN) access. Basically, the communication

methods can h e based on cable connections, radio links, o r infrared links. Since each has its individual strengths and weaknesses, each has found its way into various products.

Data exchange via cables is a well established method; universal serial bus (USB) has become a widely used standard interface. USB excels due to its high baud rates up to 480 Mhis, hut suffers from its limitcd mobility duc to cable connection [2]. Therefore, USB is best for applications that require stable high-performance. connections for transmission of high data volumes, where mobili- ty is not very important. An example application would be the connection of a vidcoconferencing camera to your laptop.

However , mobility is a big advantage for radio-based short-range communication methods such as Bluetooth, which have appeared recently in many mobile devices. Bluetooth can transmit data through solid nonmetal objects and sup- ports a nominal link range of 10 cm-IO m a t a moderate baud rate up to 721 kbis [3]. Because of the nature of radio, Bluetooth is a point-to- multipoint communication system, which sup- ports connections of two devices as well as ad hoc networking between several devices. But in order to prcvcnt unauthorized access, Bluetooth requires sophisticated authentication and encryp- tion mcchanisms, which hamper fast connection establishment. Therefore, Bluetooth is best for applications that rcquire stable point-to-point or point- to-mult ipoint connec t ions for d a t a exchangc at moderate speeds, where mobility is the key requircment. A n example application would h e the transmission of audio data from your mobilc phone to your headset.

Contrary to USB a n d Bluetooth, infrared transmission based on the Infrared Data Associ- ation (IrDA) standard enables fast simple con- ncction establishment due to its point-and-shoot Characteristic. Together with high baud rates up to 16 Mhis, this makes l rDA transmission per-

IEEE Wireless Communications - April 2003 153h-IZR4/03/$17.00 D 2003 IEEE 15

Page 2: Wireless infrared communications with edge position modulation for mobile devices

I I LED

PD Preamplifier Binaly slicer

, I W Figure 1 . Mujur cumpottents of the wireless inpared chunnel.

fectly suited to applications that require high- performancc ad hoc point-to-point connections. Examples would he the download of pictures from your digital camera to your laptop or pay- ing for your meal in your company's cafeteria with your mobile phone via an IrDA port.

In order to provide competitive baud rates, thc IrDA has continuously improved thc modu- lation techniques of its standards by introducing return- to-zero inverted (RZI) for t he serial infrared (SIR) modc, 4-pulse position modula- tion (4-PPM) for the fast infrared (FJR) mode, and HHH(1,13)' for the latest very fast infrared (VFIR) mode [ I ] . This article prescnts a new modulation scheme called edge position modula- tion (EPM) with run-length-limited (RLL) cod- ing, which is a f u r t h e r development of t h e previous techniques.

In order to build up a common understand- ing, we present t h e hasic components of t he physical layer of a n IrDA transmission system and the corresponding wireless infrared channel. The characteristics of the wireless infrared chan- nel determine the requirements for modulation t echn iques for re l iahle t ransmission. T h e s e

I HHHi.7 an nhhreviarion of the names Hin, Has- "er, andHeisr, t h e d a d opers of the code.

X I 0-5 Signals

1.25 1.255 1.26 1.265 1.27 1.275 1.28 1.285 1.29

Time (I) xio-5

W Figure 2. Signals in the receiver path: U ) photocurrent d t h DC content of the ambient noise; b) high-puss filtered signal; c) low-pass filtered signal.

requirements are then presented together with definitions of bandwidth efficiency and power efficiency, which are major criteria for the quali- ty of the different modulation techniques. We classify different typcs of pulse-position-based modulation schemes in terms of transmission reliability, handwidth cfficiency, and power effi- ciency. W e introduce the novel EPM technique. Finally, in the conclusion we give a summary of

es of the different modulation tech- niques presented in this article.

WIRELESS INFRARED TRANSMISSION SYSTEM OVERVIEW

In general, transmission systems consist of sever- al abstraction layers with different responsibilities [4]. For example, the data link layer is rcsponsi- ble for transmitting data packets consisting of sevcral bytes between two (point-to-point) or more (point-to-multipoint) devices in an error- free way. Therefore, the data link layer has to perform framing of data packets, error detection, and, optionally, error correction. (For the data link layer specified by the l rDA see [5]. ) For the transmission of single bits over a physical chan- nel, the data link layer uses thc underlying physi- cal layer. Thc physical layer has to convert the hits into signals that can be transmitted reliahly over the channel. For wireless infrared transmis- sion systems based on IrDA this conversion is performed in two steps: modulation and optical intensity (i.e., optical power) modulation. At the receiver the bitstream is retrieved hy consecutive processes, direct detection and demodulation, the counterparts of intcnsity modulation and modu- lation. T h e infrared link between the optical modulator and the detector must he line-of-sight (LOS) according to the IrDA standard.

Modulation and demodulation are usually pcrformed by digital signal proccssing, while intensity modulation and direct detection a re obviously analog tasks that have to be performed o n a n ex t r a componcn t called an in f r a red transceiver. From the modulationldcmodulation point of view, the wireless infrared channel con- sists of intensity modulation, t he optical link, and direct detection. Figure 1 shows a typical wireless infrared channel with the major required components of the transmitter and receiver.

An LED transforms the electrical binary sig- nal from the modulator into infrared radiation, whereby the radiant intensity should have the same wavcform as the clectrical signal. Note that I rDA only uses binary-level modulation (i.e., LED on and off) . However, t he pulses on the optical link are slightly distorted due to the low- pass characteristics of the LED. . ' The optical LOS link can be considered non- frequency-selective, hut significant path loss is introduced proportional to the square of dis- tance hetween the transmitter and the receiver. Additionally, t he detected radiant flux at the receiver depends on the effective detector area. Furthermore, the optical link usually induces ambient radiation from the sun, incandescent lamps, or fluorescent lamps. This ambient radia- tion can be seen as an additive white Gaussian noise process with a very high DC content.

16 IEEE Wirelesi Communications - April 2003

Page 3: Wireless infrared communications with edge position modulation for mobile devices

A photodiode (PD) converts the detectcd rad ian t flux to electrical current. D u e to the low-pass characteristic of the P D and nonlinear signal clipping, the signal is further distorted. Significant pulse extensions can occur especial- ly under near field conditions [i.e., thc distancc between transmitter and receiver is less than I cm) [61. Pulse cxtension is a major challenge to the modulation techniques, as we will see later. Because of the detected ambicnt irradiation, the P D also induces ambient noise currcnt. Consequently, a high-pass filter has to suppress the DC contcnt of this amhient noise current. The high-pass-filtered signal f rom the P D is amplified by a preamplifier with au tomat ic gain control (AGC), which balances the large dynamic signal amplitude variations that occur through distance variations between receiver and transmitter. In order to reduce the induced amplifier noise, the signal is finally low-pass- filtered.

The effects on the wireless infrared channcl- pointed out above arc presented in Fig. 2, which shows simulation results of a n optical link between a standard transmitter and a standard receiver a t 16 Mh/s (VFIR) as specified in the lrDA physical layer specification [I]. Signal 2.a shows the simulated photocurrent with the ambi- ent noise current. The D C content of the ambi- ent noise is suppressed by a high-pass filter; the result is represented by signal 2.b in the figure. Here it is important to note that the data signal from the modulator should have a constant D C content, because otherwise the high-pass filter would distort the signal with the effect of phase jitter after the binary hard decision. Thus, it is advantageous to have an almost constant duty cycle of the da ta signal f rom the modulator. After low-pass filtering signal 2.c is ready for binary hard decision.

Figure 3 shows the binary hard decision pro- cess. The digital output (signal 3.a) is obtained by comparing the analog input [signal 3.h) to a threshold voltage, which can optionally be adapt- ed to the detected signal power.

As stated above, the receiver has to deal with very large dynamic signal amplitude variations. Therefore, the preamplifier has to adjust the ampli- tude of its output to a constant value by means of AGC; furthermore, the threshold voltage can be adapted to the detectcd signal power. Howcver, since infrared transceiven are low-wst devices, thc accuracy of these adaptations is usually very poor, which results in phase jitter aftcr the binary hard decision. Further phase jitter is introduced due t o intersymbol interference if the gap between two pulses is too short, as indicated in Fig. 3.

GENERAL CHARACTERISTICS OF

INFRARED COMMUNICATION MODULATION TECHNIQUES FOR

As stated above, modulation is the process that converts a bitstream into an electrical waveform that can be reliahly transmitted ovcr the wirelcss infrared channel. Along with its reliability, thc quality of a modulation code depends on band- width efficiency and power efficiency. In this sec- tion we discuss these threc characteristics in

I I i 2.21 2.22 2.23 2.24 2.25 2 .26 2.27

Time (5) ~10-5

Figure 3. Binary hard decision: a) digital output; b) analog input.

order to derive evaluation criteria for the modu- lation techniques presented later.

TRANSMISSION REllABlliN The reliability of the transmission depends on the capability of the modulation technique to adapt the signal to thc wirclcss infrared channel in a way that allows demodulation at the receiv- c r with a low hit error rate. Therefore, the mod- ulation technique should avoid:

Intcrsymbol interference, which can result in phase jitter after the binary hard decision

* Multiple consecutive high chips, since the resulting infrarcd signal would be distorted by the high-pass filter in the receiver - Even two consecutive high chips, since at the receiver it is hard to distinguish between such a double pulse or an extended single pulse

* Strong variations of the D C content of the data signal, because the high-pass filter would distort the signal with the effect of phase jitter after thc binary hard decision

* A long absence of a 0 to 1 transit ion, since there should he a t least one 0 to 1 transition within 16 transmission chips for an adequate sample clock recovery with a digital phase locked loop (DPLL) in the receiver In addition, the demodulation process must

be able to dea l with unwanted effects of the wireless infrared channel, which are independent of the modulation technique, such as: * Phase jitter due to variations of the detccted

signal power * Pulse extensions

BANDWIDTH EFFICIENCY The achievable hit rate of an infrared communi- cation is mainly limited by the bandwidth of the infrared transceivcrs. Therefore, it is important to use a modulation tcchnique with high band-

IEEE Wirzlcss Communicatiuns * April 2003 17

Page 4: Wireless infrared communications with edge position modulation for mobile devices

width efficiency qo, which we define as the ratio between the achievehle bit rate Rbjr and band- width B of the infrarcd transceiver:

Following from this, thc bandwidth efficiency q~ can he derived as the ratio betwecn the pulse duration T,iS, and bit duration T,,&

......... ..............

-8 -6 4 -2 0 2 4 6 8

Time ( 5 ) x104

Figure 4. Eye diagram of IWRZI with U time window of Tbit

x10-6

I i I I , I Time (SI x10-8

-8 -6 4 -2 0 2 4 6 8

Figure 5. Eye diagram of 4-PPM with a time window of Trymbol.

POWER EFFICIENCY Mobile dcvices are usually battery-powered; thcrefore, power efficiency is very important for our type of application. Wc dcfine power effi- ciency q p as the ratio betwecn the energy per infrared pulse E,,.ise and the required avcrage cnergy per hit Ebb:

Following from this, power efficiency q p can be derived as the ratio betwccn bandwidth efficien- cy qo and the average duty cycle aveDC of thc modulated signal.

PULSE-POSITION-BASED MODULATION TECHNIQUES

In this section we present several pulse-position- based modulation techniques currently used in the various wireless infrared transmission sys- tems for mobile devices. We evaluate them in terms of transmission reliability, bandwidth effi- cicncy q ~ , and power efficicncy qp.

NON-RETURN-TO-ZERO (INVERTED) The simplest form of modulation is NRZ(I), also known as on-off keying (OOK). Here l(0) repre- sents a pulse with a duration equal to the hit duration, and O(1) represents the absence of a pulsc. NRZ(1) has very attractive bandwidth effi- ciency, q~ = 1, and powcr efficicncy, qr = 2. However, this modulation scheme allows multi- ple consecutive pulses, which would be sup- pressed by the high-pass filter of the receiver. Therefore, NRZ(I) is not feasible for our appli- cations in terms of rcliability.

RETURN TO ZERO (INVERTED) To avoid long high signals the nlm-RZ(1) modu- lation technique (wifh n < m) has been intro- duced f o r wireless infrared appl icat ions. In RZ(I) l(0) represents a pulse with a duration of nlm ' Tbi,, and 0(1) the absence of a pulse. The bandwidth efficicncy of RZ(I ) is given by qa = nim, and with qp = 2 it hes the same power effi- ciency as NRZ(1). I rDA uses 3116-RZI for hit rates up to 115.2 khis and 114-RZI for 576 kbis and 1.152 Mhis bit rates [l]. Therefore, we show in Fig. 4 how 114-RZI deals with the wireless infrared channel. The eye diagram indicates that R Z ( I ) provides good transmission reliability because there is enough space hetween two con- secutive pulses so that there is no intersymbol intcrference even when extended pulscs occur.

On the other hand, 3116-RZI and 114-RZI have very poor bandwidth efficiencies qs of 0.19 and 0.25, respectively. Furthermore, RZ(1) do not support sample clock recovery at the receiver, hccause i t allows a long low signal without any 0 to 1 transition that could he used for synchroniza- tion. 'Therefore, hit stuffing is necessary for RZI, which further decreases the bandwidth efficiency, sincc the enforced pulses carry no information.

18 IEEE Wireless Communications - April 2003

Page 5: Wireless infrared communications with edge position modulation for mobile devices

hl PULSE POSITION MODULATION In order to overcome the shortcomings of RZ(I) N-PPM has been introduced into many wireless optical applications [ 7 ] . With N-PPM informa- tion is transmitted by varying the position of a pulse within a symbol. PPM allows one pulse to he set in one of the N possible positions; thus, it is called N-PPM. Since a pulse can be set in one of N possible positions, N diffcrcnt messages can he sent within one symbol, allowing logz(N) bits of data to be encoded per symbol.

l r D A uses 4-PPM for its 4 Mbis FIR mode, while in the physical layer IR PHY of the IEEE 802.1 1 s tandard [SI 4-PPM is foreseen for 2 Mbis operation and 16-PPM for 1 Mbis. While 4-PPM has improvcd bandwidth efficiency 9s = 0.5, qp = 2), 16-PPM has very good power effi- ciency (qa = 0.25, q p = 4).

Figure 5 shows the eye diagram of 4-PPM, where it can h e seen that slight intersymbol interference occurs when there is only one low chip between the pulses of two consecutive sym- bols. But t he big drawback of PPM is that it allows double pulses on the symbol borders, which are hard to distinguish from extended sin- gle pulses at the demodulation process.

HHH(I,l3) For i ts latest 16 Mh/s VFIR s tandard , I r D A introduced the HHH' (1,13) code [ I , 61 with the improved bandwidth efficiency of 0.67. Basically, the HHH(1,13) is an RLL(d = I , k = 13) code, where d and k are the minimum and maximum number of 0s between 1s after the encoder. With the parametcr d = 1 this code guarantees that t he re a rc n o legal double pulses as they can occur with the PPM codes. With the HHH(I,13) code double pulses can only occur due to pulse extension (e.g., under near-field conditions), so the second pulsc can always be suppressed. The pa rame te r k = 13 guarantees enough 0 t o 1 transitions for reliable clock recovery.

HHH(1,13) has not only good bandwidth efficiency qo of 0.67, hut also attractive power efficiency q[lp of 2.6, since the average duty cycle is only 0.258. Unfortunately, HHH(1,13) has la rge duty cycle variations tha t result in a n increased phase jitter due to the high-pass char- acterist ic of the wireless in f ra red channel . Therefore, a scrambling mechanism is used in V F I R in o r d e r t o reduce the occurrence of ex t reme changes between the minimum a n d maximum duty cycles.

The eye diagram in Fig. 6 shows a scrambled HHH(I ,13 ) signal after the wireless infrared channel. I t can be seen that the varying duty cycle and intersymbol interference still result in phase j i t ter that can lead to significant pulse deviations after the binary hard decision. How- ever, most of these distortions of the infrared transceiver can he repaired by the single-chip correction mechanism described above.

EDGE POSITION h!ODULATlON I n general, the modulation schemes described above are all pulse-position-based; that is, the time is divided into discrete time slots with a length equal to or longer than the pulse length;

I x10-6 I 3 1 1 I ir

5 . . :

4 -3 -2 -1 0 1 2 3 4 Time (5) x10-8

I H Figure 6. Eye diagram of HHH(I,13).

XI 0-6

I ' I 5

4

3

2

1

0

-1

-2

-3

4

2.21 2.22 2.23 2.24 2.25 2.26 2.27

l ime ( 5 ) ~ 1 0 - 5

I

H Figure 7. EPM signals afrer the wireless iczfrared channel: a) digital signal afrer binary hard decision, b ) analog signal before binary hard decision.

depending on the information to bc transmitted, there is or is not a pulse within such a time slot.

An alternative way is the edge-position-based modulation scheme: the time is divided into dis- crete time slots of duration greater than the rise time and the jitter of the rising edge of the puls- es after hinary hard decision; depending on the information to be transmitted, there is o r is not a rising edge of a pulse within such a time slot.

Usually the rise t ime and j i t t c r a r e much smaller than the pulse length, so thc time slots of

IEEE Wireless Communications - April 2003 19

Page 6: Wireless infrared communications with edge position modulation for mobile devices

2.5

2

1.5

1

IY 0.5

0

-0.5

-1

m c .- - 2

113 rate Pulse RU(5.12) generation encoder

1 Demodulation I

X l rr€

i Wireless infrared

channel I '

I I

_n_17_n_ 4 Pulse

113 rate m - RLL(5.12) generation encoder

A T _n_17_n_

4 Pulse 113 rate m -

RLL(5.12) generation encoder

T

Recovered clock

DPLL

Figure 8. Modulation and demodulation components of EPM.

EPM can be smaller than the time slots of pulse- position-based modulation. For our type of appli- cation the rise time and the jitter of the rising edge of the pulses after the hinary hard decision can he assumed to be less than one third of the pulse duration. Thus, with EPM more informa- tion can he transmitted within a certain time, since there are more possibilities to arrange puls- es than in PPM schemes, as indicated in Fig. 7.

In order to avoid intersymbol interfcrence a coding Scheme is necessary which guarantees that after a pulse there is a long enough gap before the next pulse begins, so the rising edge of the next pulsc is not disturbed by the previous one. The required gap duration strongly depends

-3 -2 -1 0 1 2 3 Time (I) x10-8

I Figure 9. "Eye diagram" of EPM with 113-rate RLL(5,lZ) with a time window of 513 . Tpu~re

on the components of the receiver, but measure- ments of currently available transceivers and the channel simulations above showed that a gap duration 1.5 times t h e pulse duration is a rea- sonable and even conservative value.

A feasible coding scheme for iiur purpose is the li3-rate RLL(5,lZ) code developed by Adler [9]. By applying this code we can produce a time slot duration Ttlmcrcoi = 0.4167 . T,,,,, and a min- imum gap duration T,,,,,, = 1.5 . T,,,I,,, while providing enough 0-to-1 transitions for efficient clock recovery. The input of the. RLL encoder is the bitstrcam to be transmitted, and the outputs arc the positions where the pulses should start.

For demodulation at the receiver the incom- ing binary pulses are sampled with the frequency Lo,ni,ie = llT,in,~s~o,, whereby the phase is recov- ered by means of a DPLL from the input signal. On the occurrence of a rising edge, a 1 is dcliv- ered to the RLL decoder; otherwise, it gets a 0. After edge detection the RLL decoder can final- ly recover the transmitted information. Figure 8 gives an overview of the complete modulation and demodulation process of EPM. This figure also shows the relation between the hit duration Tbil and pulse duration T,,,,lsr, so the bandwidth efficiency can be derived as 78 = 0.8. With an average duty cycle of 0.29, EPM also has very attractive power cfficicncy qp of 2.76.

The duty cycle variations and intersymbol intcrfcrence of EPM with 1/3-rate RLL(5,12) are very small, resulting in low phase jitter, as can he seen in the eye diagram of EPM in Fig. 9. There- fore, EPM also provides the required transmis- sion reliability.

CONCLUSION In this article we investigate various modulation techniques that are appropriate for mobile short- range point-to-point low-cost infrared data inter- connection applications. Furthermore, we introduce the novel edge position modulation

20 IEEE Wireless Communications * April 20U3

Page 7: Wireless infrared communications with edge position modulation for mobile devices

m Table 1. Overview of the bandwrdth ejjicrency andpower efficiency cif the drffeerenr modulation techniques

with run-length-limited coding, which is a further devclopment of existing methods. The evalua- tion criteria of the modulation techniques are transmission reliability, bandwidth efficiency, and power efficiency.

Transmission reliability mainly depends on the capability of the modulation technique to adapt the signal to the wireless infrared channcl in a way that a l l o w s demodulation at the receiv- er with a low bit error rate. We reveal the diffi- culties of thc different methods and show that E P M can guarantee reliahle transmission, since it can easily b e optimized f o r t he wireless infrared channel.

The achievable hit rate of infrared communi- cation is mainly limitcd by the bandwidth of the infrared transceivers; thus, bandwidth efficiency is a major criterion of modulation techniques. We show that EPM offers significantly increased handwidth efficiency over existing methods, while maintaining attractivc power efficiency. For example, if we use EPM in combination with a VFIR transceiver that has a specified band- width of 24 MHz, we could achieve a bit rate of 19.2 Mbis in contrary to HHH(1,13), which only allows a bit rate of I6 Mbis. Table 1 provides an overview of the bandwidth and power efficien- cies of the various modulation techniques.

REFfREHCES Ill IrDA. Serial Infrared Physical Layer Specification. v. 1.4.

(21 USB Implementers Forum. Inc.. Universal Serial Bus

131 Bluetooth, Specification of the Bluetooth System (vol. 1,

[41 A. S. Tanenbaum. Compufer Networks. 3rd ed.. Prentice Hall, 2000.

151 l rD4 Senal Infrared Link Access Protocol (IrtAP), Y. 1.1, June 1996.

[61 W. HiR. M. Harsner, and N. Heire, "IrDA-VFIR (16 Mblr): Modulation Code and System Design," IEEE Perr. Com- mu".. Feb. 2001. pp. 58-71.

I71 I. Millar et al . , "The lrDA Standards for High-speed Infrared Communicationi,'' Hewleff-Packard J.. Article 2, Feb. 1998.

(81 B. O'Hara and A. Petrick. 802.11 Handbook: A Design- er's Companion, lEEE Pres, 1999.

191 R. L. Adler. U. K. Brayton. and B. P. Kitchens. "A Rate 1/3 (5.12) RLL Code,:'IBM T s h . Disclosure Bull., vol. 27, no. 8, Jan. 1985.

May 2001

Specification. rev. 2.0, 2000.

core) , v. 1 .o B. 1999.

BlOGRAPHlfS THOMAS LUFTNER 1thomas.lueftnerQinfineoncom) received his Dip1.-lng. degree in mechatronlcs from the Johanner Kepler University of Linz. Austria, in 2000. During his study he focused on communications engineering and microelec- tronics. He wrote his diploma thesis for lnfinean techno lo^ gier, and since 2000 he has been w i th IrDA member

Danube Integrated Circuit Engineering (DICE). Linz. Austria. where he has worked on the development of a fast infrared mntroller for bareband ICs of cellular phones. Since 2002 he.har also been a lecturer a t the University of Applied Sci- ences of Upper Austria. Hagenberg.

CHRISTIAN KROPL ([email protected]) received a Diplama degree in mechatronicr from Johanner Kepler Uni- versity of h r , Austria. H~ wrote hi: diploma thesis a t lrDA member Danube integrated Circuit Engineering. Linz. AUI- tria. under the rupervirion of Thomas Luftner. The thesis deals wi th the modeling and simulation of a wireless infrared communication System for low-power applications.

Manlo HUEMER Lmario.huemer@fhhagenberg) received a Dip1.-lng. degree in mechatronicr and a Dr.techn. (Ph.D.1 degree from Johanner Kepler University. Linz, Austria. in 1996 and 1999. respectively. From 1997 to 2000 he war an assistant profesror at the lnztitute for Communications and Information Engineering a t the University of Linz. From 2000 to 2002 he war with lnfineon Technologies Austria Research and Development Center for wire lei^ products. Since 2002. he ha$ held the position of Professor of com- munications and information engineering a t the University of Applied Sciences of Upper Austria.

ROBERT WEIGEL [F] ([email protected]~technik.Uni-erlangende) received Dr.4ng. and Dr.-lng.habi1. degrees. both in electri- cal engineering and computer science. from Munich Uni- versity of Technology, Germany. in 1989 and 1992, rerpectively. From 1982 to 1988 he was a research engi- neer. from 1988 to 1994 a senior research engineer. and from 1994 to 1996 a proferror of RF Circuits and Systems at Munich University of Technology. In winter 1994-1995 he was a guest proferror of SAW technology a t Vienna University of Technology, Austria. Since 1996 he has been director of the Institute for Communications and Informa- tion Engineering a t the University of Linz. In August 1999. he co-founded DICE ~ Danube Integrated Circuit Engineer- ing, Linz. an lnfineon Technologies Development Center devoted to the design of mobile radio circuits and systems. In 2000. he was appointed a proferror for RF engineering a t Tongji University, Shanghai, China. In 2002 he moved to Erlangen. Germany. to take the directorship of the Institute for Electronics Engineering at the University o f Erlangen- Nuremberg. He has been engaged in rerearch and develop- ment on microwave theory and techniques. integrated optics, high-temperature superconductivity. SAW technolo- gy. and digital and microwave communication systems.

RICHARD HAGEMUER ([email protected]) received his Ing. lgradu- ate) degree i n electrical engineering from the Fach- hol-hrchule Nuremberg, Germany. in 1977. and his Dip1.-lng. degree in 1981 from the University of Eilangen- Nuremberg. Germany. From 1981 to 1984 he was a mem- ber of scientific s taf f a t the Institute of Electronicr a t the University of Erlangen~Nuremberg. From 1984 to 1993 he war head of the Application Specific IC Department at Fraunhofer-Gerellrchaft. Institute of Integrated Circuits (FhG-118). Erlangen. From 1989 t o 1993 he war project leader at FhG-118 of the national research project "Circuit Design of Key Components far ADC$ Based on Hetero-FET and MESFET." Since 1993 he has been a full profesror of complex digital systems at Johanner Kepler University. Linz. Aust r ia Since October 1997 he has been head of the Rerearch Institute for Integrated Circuits a t the university. and since 2000 dean of the Faculty of Natural Sciences and Engineering. His research interests include mixed signal design, high-speed ADC, and wireless communications.

JOSEF HAUINER Uoref.haurnerQinfineon.com) studied electri- cal engineering a t Technical University Munich. where he received his Dip1.-lng. and Dr.-lng. degree in 1986 and 1991. respectively. both in the field Of microwave tethnol- ogy as a research arristant at the InStitute for High Fre- quency Technology. Afterward, he started his industrial career with Siemens AG. working on high-speed access syr~ terns on digital subscriber lines (HDSL). After five years. he took a position developing the next-generation DSL tech- nology (SDSL. SHDSL) within Siemens Semiconductor where he has significantly contributed to international rtandardr in SDSL transmission. Since 1999. he is within the Wireless Group of lnfineon Technologies. He is rerpoq- rible for Infineon's wireless strategy and concept engineer- ing . He has ruccersfully managed numerous projects covering communications ICs. including complete system- on-chip designs for cellular radio.

Transmission reliability mainly depends on

the capability of the modulation technique

to adapt the signal to the wireless

infrared channel in a way that allows

demodulation a t the receiver with a low

bit error rate. The authors showed that EPM can guarantee

a reliable transmission, since

it can easily be optimized for the wireless infrared

channel.

IEEE Wirclcss Communications April 2003 21