Abstract:
The invention relates to a conversion of a pulse modulated signal to a radio frequency signal enabling use of applications and protocols designed for wireless optical links on radio frequency channels. The method comprises receiving the pulse modulated input signal, decoding the received pulse modulated input signal into a decoded data bit-stream, encoding the decoded data bit-stream into a recoded data bit-stream, under use of the recoded data bit-stream modulating a radio frequency signal, and transmitting the modulated radio frequency signal. In the receiver path a received radio frequency signal is converted to a pulse modulated output signal by the steps of demodulating the received radio frequency signal into a demodulated data bit-stream, decoding the demodulated data bit-stream into a received data bit-stream, encoding the received data bit-stream into a pulse modulated output signal, and forwarding the pulse modulated output signal.

Description:
FIELD OF INVENTION 
     The present invention relates to a method and apparatus for converting a pulse modulated signal to a radio frequency signal which enable the use of applications and MAC (medium access control) protocols designed for wireless optical links on radio frequency (RF) channels. In particular, the use of various applications and MAC protocols designed for the IrDA® wireless infrared channel (IrDA is a trademark of Infrared Data Association) on the ultra-wideband (UWB) radio frequency (RF) channel is provided. 
     BACKGROUND 
     The UWB-RF channel has recently become available in the USA (e.g., in the frequency range 3.1 GHz-10.6 GHz allocated for indoor as well as outdoor use). European and Japanese authorities are preparing similar rules to enable commercial marketing and use of UWB-RF devices. 
     Short-range wireless technologies in the wireless local area network (WLAN) space as well as the wireless personal and body area network spaces (WPAN/WBAN) continue to proliferate rapidly. In particular, wireless links based on infrared (IR or Ir) light emission have experienced an enormous growth in the recent past owing to ease of use and low cost. The Infrared Data Association (IrDA) has projected a total shipment of 1.3 Billion units by the year 2003, with over 250 Million IrDA devices installed in mobile phones and personal digital assistants (PDAs). This high adoption rate reflects the presence of a large number of IrDA applications in the marketplace and a sizable investment by the industry and users alike. On the other hand, radio-based short-range wireless devices such as Bluetooth™ (Bluetooth is a trademark owned by Bluetooth SIG, Inc.) are also deployed at a rapid pace, thereby reducing the relative size of the IrDA-based market segment rather quickly. This will influence the IR-based industry which is looking for alternate ways to leverage their investments and continue their business. 
     Two dominant technologies in the short-range wireless space—Bluetooth and IrDA —were specifically designed for replacing short-range wired communication links. Bluetooth is based on an RF technology offering less than 1 Mb/s of user data rate and IrDA offers a number of data rates, e.g., SIR (115 Kb/s), FIR (4 Mb/s), and VFIR (16 Mb/s). IrDA uses optical-IR transmission which requires line of sight (LOS) between transmitter and receiver. IrDA and Bluetooth technologies are also used for consumer-based applications within the single office/home office (SOHO) environment. Each has its own strengths and weaknesses with respect to link range, data rates, required regulation and costs. 
     While some of these technologies&#39; intended uses and applications overlap, each of the two systems offer all of the hardware and software layers that constitute a set of communication protocols. IrDA is an established and well proven point-to-point, narrow-angle, data-transmission standard that operates at bit rates between 9600 b/s and 16 Mb/s over distances of 0-1 m (mostly 20 cm). It has a wide range of supported hardware and software platforms and is well introduced in the market place. Though IrDA&#39;s benefits seem to abound, the technology has its disadvantages. For many applications, its limited range and pointing angle is rather inconvenient and its optical signals fail to penetrate walls or propagate around obstructions (IrDA was not designed to rely on diffused optical signal propagation). Additionally, IrDA devices must be nearly stationary to achieve synchronization with other IrDA devices (narrow optical beam). Where IrDA fails to be user friendly, radio-based systems offer advantages, such as non-line-of-sight (NLOS) transmission through walls and other obstructions. However, many RF-based systems, such as Bluetooth, are regulated differently in various countries worldwide and thus suffer non-trivial insertion into the markets. 
     The two main markets for short-range wireless devices are the portable and desktop computing and handheld markets. Due to architectural and range constraints, the level of adoption of IrDA in the desktop space has been relatively low. Current desktop designs in the marketplace are more appropriate for placing the desktop in a cabinet or on the floor. However, such a usage scenario is not favorable for point-and-shoot optical link applications as offered by IrDA. 
     The disadvantages of optical-IR communication links and the investments from the manufacturers and the user community in IrDA-based technology and applications could both be leveraged and maintained into the future by replacing or enhancing the optical transceiver of the IrDA system (i.e., part of the PHY layer) with a suitable radio-based transceiver. 
     Given the recent introduction of a license-free spectrum band between 3.1 GHz and 10.6 GHz (USA/FCC) for UWB radio devices, a new and inherently compatible radio technology has become available to design and implement such radio-based systems. As a result, the many applications and protocol stacks, including medium access control protocols, originally conceived for wireless optical links should be useable on the UWB radio channel. 
     It would be advantageous if the two types of communication systems could be brought together to make use of the wireless optical system and the radio channel. Owing to the different transmission media used (optical and radio frequency, respectively) as well as because of legacy considerations, these different wireless communication systems have traditionally also been designed with different medium access control (MAC) mechanisms; in addition, their positioning in the market place have been different in general, although their applications do overlap in certain areas (e.g., PDA data base synchronization with PC data base). 
     SUMMARY AND ADVANTAGES OF THE INVENTION 
     In accordance with the present invention there is provided a method for converting a pulse modulated input signal to a radio frequency signal. The radio frequency signal can be a pulsed radio frequency signal, as it is used in connection with ultra-wideband (UWB) radio frequency (RF) signals. The method comprises the steps of receiving the pulse modulated input signal; decoding the received pulse modulated input signal into a decoded data bit-stream; encoding the decoded data bit-stream into a recoded data bit-stream; modulating a radio frequency signal with the recoded data bit-stream; and transmitting the modulated radio frequency signal. 
     The method further allows a conversion of a received radio frequency signal to a pulse modulated output signal by the steps of demodulating the received radio frequency signal into a demodulated data bit-stream; decoding the demodulated data bit-stream into a received data bit-stream; encoding the received data bit-stream into a pulse modulated output signal; and forwarding the pulse modulated output signal. 
     It is also possible to directly modulate the radio frequency signal under use of the decoded data bit-stream which would reduce circuitry. 
     Moreover, it is also possible to directly modulate the radio frequency signal under use of the received pulse modulated input signal by polarity modulation, also referred to as 180° phase modulation. This would even more simplify the circuitry. 
     The pulse modulated input signal can be received from an optical controller thereby a developed optical signal specification can be used. 
     The radio frequency signal can be amplified. This allows a broader broadcast range thereby reaching devices further away from a transmit place. 
     The pulse modulated input signal can be based on the IrDA specification and the radio frequency signal comprises an ultra-wideband (UWB) signal. Also possible is that the pulse modulated output signal is adapted to the IrDA specification and the received radio frequency signal bases on an ultra-wideband (UWB) signal specification. 
     The pulse modulated input signal can be an optical signal that is converted to an electrical signal for charging a battery used to operate a transverter. This allows supporting the power supply (battery) of a mobile device. IrDA protocols in combination with UWB-RF transverters can potentially be implemented such that the required battery power is lower than that of conventional optical IrDA devices. The reason is that UWB devices emit only micro-watt RF power levels while optical devices emit up to the milliwatt level and beyond. 
     In another aspect of the invention there is provided a transverter for converting a pulse modulated input signal to a radio frequency signal. This apparatus comprises a signal decoder unit for decoding the pulse modulated input signal into a decoded data bit-stream; a data encoder unit for encoding the decoded data bit-stream into a recoded data bit-stream; and a radio frequency modulator which under use of the recoded data bit-stream modulates a radio frequency signal. 
     The transverter for further converting a received radio frequency signal to a pulse modulated output signal comprises a demodulator unit for demodulating the received radio frequency signal into a demodulated data bit-stream; a data decoder unit for decoding the demodulated data bit-stream into a received data bit-stream; and a signal encoder unit for encoding the received data bit-stream into the second pulse modulated signal. 
     The transverter for converting a pulse modulated input signal to a radio frequency signal and converting a received radio frequency signal to a pulse modulated output signal can be implemented as a transceiver. It is also possible to use the means for converting a received radio frequency signal to a pulse modulated output signal as described above within a single device that is a receiver. 
     The transverter can comprise an optical transceiver and an optical window which attenuates an optical signal received and/or sent by the optical transceiver. This would allow an easy close spatial coupling without further modifications. 
     The transverter can be part of a mobile device, e.g., an electronic watch, using the IrDA protocol specification. 
     In general, the method and apparatus allow the use of the existing large base of applications and optical or IrDA protocol stack (medium access control) through suitable conversion circuits on future based wireless links, particularly those based on license-free UWB radio links. 
     Further, the use of IrDA devices can be expanded to non-directional (non-line-of-sight) communication links while maintaining the security advantages of optical IrDA communication, since UWB radio signals are inherently difficult to detect (very low power spectral density, e.g., less than 75 nW/MHz according to the FCC&#39;s specifications). 
     The total system development costs and thus user expenses can be kept low because there is no need for a new development of a communication specification or entirely new standard. The UWB-RF mode can be integrated into the existing standard. 
     The UWB-RF mode added to IrDA allows users to connect to other devices over link distances significantly beyond IrDA&#39;s fundamental 1 m limit, and also to establish links across a wall (which optical signals cannot penetrate) and around obstacles. 
     UWB-RF mode added to IrDA allows users to transmit at the same time to a number of different clients (one-to-many broadcast), instead of using the one-to-one infrared narrow beam that is typical for IrDA. In such applications and with transmitting devices equipped with both optical and radio ports, it would be possible to transmit either simultaneously or alternately through the optical port and/or the radio port, thereby extending the covering area of the transmission. 
     The advanced infrared (AIr) system developed at the IBM Zurich Research Laboratory is a proposed optical IrDA standard for indoor multipoint-to-multipoint connectivity. The distance and data rate are variable ranging from 250 kb/s over 8 m to 4 Mb/s over 4 m. It is designed for cordless connections to multiple peripherals and meeting room collaboration applications. The AIr link protocol, medium access control as well as part of the physical layer functions (e.g., encoding and decoding) are well suited for UWB-RF devices; the variable data rate feature of AIr based on repetition coding is particularly advantageous for the UWB-RF channel. 
     UWB-RF transverters can also be applied to extend the use of wired standard connections, such as Ethernet or Universal Serial Bus (USB). 
    
    
     
       SHORT DESCRIPTION OF FIGURES 
       Preferred embodiments of the invention are described in detail below, by way of example only, with reference to the following schematic drawings. 
         FIG. 1  shows prior art of a wireless optical communication device comprising an application and protocol stack—also referred to as optical (infrared) controller—and an optical transceiver that is part of the physical layer. 
         FIG. 2   a  shows a prior art electrical interface connection between an optical (infrared) controller and two optical transceivers. 
         FIG. 2   b  shows an alternate prior art electrical interface connection between an optical (infrared) controller and one optical transceiver. 
         FIG. 3   a  shows a table with signaling rate and pulse duration specifications of a prior art wireless optical communication system; the particular table describes IrDA&#39;s wireless infrared system. 
         FIG. 3   b  shows an example of pulse modulated waveforms for a prior art wireless optical communication system (IrDA) for certain signaling rates according to the table shown in  FIG. 3   a.    
         FIG. 4  shows a wireless radio frequency (RF) communication device comprising an optical (infrared) controller, an electrical interface connection, and a [ultra-wideband (UWB)] radio frequency (RF) transverter. 
         FIG. 5   a  shows a prior art electrical interface connection between an optical (infrared) controller and a prior art optical transceiver as well as a wireless [ultra-wideband (UWB)] radio frequency (RF) transverter. 
         FIG. 5   b  shows an alternate prior art electrical interface connection between an optical (infrared) controller and the wireless [ultra-wideband (UWB)] radio frequency (RF) transverter. 
         FIG. 6   a  shows a prior art line-of-sight (LOS) wireless optical link configuration between two optical interface ports. 
         FIG. 6   b  shows a line-of-sight (LOS) wireless link configuration between two radio frequency (RF) interface ports according to the current invention. 
         FIG. 6   c  shows a non-line-of-sight (NLOS) wireless link configuration between two radio frequency (RF) interface ports according to the current invention. 
         FIG. 6   d  shows a simultaneous non-line-of-sight (NLOS) and line-of-sight (LOS) wireless link configuration between two radio frequency (RF) interface ports. 
         FIG. 7  shows an ultra-wideband (UWB) radio frequency (RF) transverter comprising a data converter that includes an electrical transmitted signal (ETS) decoder and an electrical received signal (ERS) encoder using a single filter for transmitter (TX) and receiver (RX). 
         FIG. 8  shows another ultra-wideband (UWB) radio frequency (RF) transverter comprising a data converter that includes an electrical transmitted signal (ETS) decoder and an electrical received signal (ERS) encoder using two separate filters for transmitter (TX) and receiver (RX), respectively. 
         FIG. 9   a  shows yet another ultra-wideband (UWB) radio frequency (RF) transverter comprising a data converter that includes an electrical transmitted IrDA (IRTX/SWDAT) pulse decoder and an electrical received IrDA (IRRX/SRDAT) pulse restorer using a single filter for transmitter (TX) and receiver (RX). 
         FIG. 9   b  shows an illustration of signal E at the output of an UWB-RF power amplifier. 
         FIG. 10  shows an illustration of typical transmitter signals A-E indicated in  FIGS. 7 and 9   a.    
         FIG. 11  shows an illustration of typical receiver signals F-J indicated in  FIG. 7 . 
         FIG. 12   a  shows an alternate embodiment of the ultra-wideband (UWB) radio frequency (RF) transverter comprising a data converter that includes an optical transmitted signal (OTS) receiver and decoder and an optical received signal (ORS) encoder and transmitter. 
         FIG. 12   b  shows an illustration of an apparatus of a wireless converter based on the ultra-wideband (UWB) radio frequency (RF) transverter that connects through an optical interface port (e.g., IrDA compliant) with a host platform that comprises an optical transceiver, a controller executing the optical link protocol, and a host (or client) application that makes use of the link provided by the wireless converter. 
         FIG. 13   a  shows an illustration of the IrDA protocol stack and its native communication modes (optical): Sub-SIR, SIR, FIR, and VFIR. 
         FIG. 13   b  shows an illustration of the IrDA protocol stack, its native optical communication modes (Sub-SIR, SIR, FIR, and VFIR), and an additional radio mode enabled by an UWB-RF transverter. 
     
    
    
     The drawings are provided for illustrative purposes only and do not necessarily represent practical examples of the present invention to scale. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIGS. 1 to 3  illustrate the prior art IrDA system based on optical narrow-beam communication over distances of up to one meter. In particular,  FIG. 1  shows that the physical layer system can be separated into two parts, a first part called ENDEC (encoder/decoder)  11  that belongs to the protocol stack within an optical (infrared) controller  1 , and a second part called optical transceiver  2 . The same reference numbers are used within the description to denote the same parts or alike.  FIG. 2   a  indicates a prior art electrical interface connection  3  between the optical (infrared) controller  1  and two optical transceivers  2 , and  FIG. 2   b  shows an alternate prior art electrical interface connection  3  between the optical (Infrared) controller  1  and one optical transceiver  2 . The table in  FIG. 3   a  shows signaling rate and pulse duration specifications of a prior art wireless optical communication system; the particular table describes IrDA&#39;s wireless infrared system.  FIG. 3   b  shows various modulation modes and associated signals as specified by the IrDA standard; specifically, the pulse-like signals that are typical for optical communication can be noticed. The pulse-like optical modulation signal features can be directly used in an advantageous manner when converting these signals to similar pulsed UWB-RF signals. 
       FIG. 4  shows how the system illustrated by  FIGS. 1 to 3  can be converted into a wireless radio frequency (RF) communication device comprising the optical controller  1  and a wireless [ultra-wideband (UWB)] RF transverter  4  connected by the electrical interface connection  3 . The wireless [ultra-wideband (UWB)] RF transverter  4  is also referred to as [UWB] RF or RF transverter  4 . The concept introduced with reference to  FIG. 4  is further illustrated in  FIG. 5   a , by means of the electrical interface connection  3  between the optical (infrared) controller  1  and the optical transceiver  2  as well as the wireless [ultra-wideband (UWB)] RF transverter  4 .  FIG. 5   b  shoes an alternate embodiment with the electrical interface connection  3  between the optical (infrared) controller  1  and the wireless [ultra-wideband (UWB)] RF transverter  4 . 
       FIG. 6  illustrates some of the usage advantages. In particular,  FIG. 6   a  shows a prior art line-of-sight (LOS) wireless optical link configuration between two optical interface ports, for example, IrDA compliant (narrow-beam) optical ports. The same mode can be implemented with LOS wireless radio link configurations between two RF interface ports as illustrated in  FIG. 6   b ; the advantage in this case is that the RF signal&#39;s beam is essentially omni-directional, such that exact pointing of the devices is not necessary, as would be the case with an optical link.  FIG. 6   c  shows a non-line-of-sight (NLOS) radio link configuration between two RF interface ports, while  FIG. 6   d  illustrates a simultaneous NLOS and LOS radio link configuration between two RF interface ports. 
       FIG. 7  illustrates a preferred general architecture of the [ultra-wideband (UWB)] RF transverter  4  comprising a data converter  41  that includes here an electrical transmitted signal (ETS) decoder  42 , also referred to as signal decoder unit  42 , and an electrical received signal (ERS) encoder  43 , also referred to as signal encoder unit  43 , using a single filter  55  for transmission and reception. The output of the ETS decoder  42  feeds the transmitter path of the RF transverter  4 , comprising the functions of a data encoder unit  51 , followed by an [UWB] RF generator and modulator  52  that is also regarded as a radio frequency modulator  52 , and a [UWB] RF power amplifier  53 . The generic notion of a “power amplifier” is used although it is understood that specific UWB-RF signals are very low-power signals by their very definition. The amplifier&#39;s  53  output is fed to a transmit/receive (TX/RX) switch  54  that feeds the signal to the single filter  55 ; the latter is connected to an antenna  56  for emission of an RF signal. The data encoder unit  51  receives the decoded data stream from the ETS decoder  42  and introduces a new modulation signal that is suited for transmission over the RF channel. Similarly, the receiver path of the [UWB] RF transverter  4  operates in the reverse order, where the TX/RX switch  54  delivers a received radio frequency signal F to an RF low noise/variable gain circuit  57  for amplification and amplitude level adjustment. The output of this circuit  57  is fed to a demodulator unit  58  which in general extracts the baseband signal from the RF signal G applied to its input. The demodulator unit  58  feeds the data decoder  59 , which in turn delivers the decoded data to the ERS encoder  43 . The functional block called transverter controller  60  coordinates, receives and outputs all necessary control and timing (clock) signals interfacing to the various functions of the transverter  4 . The electrical interface signals ETS, ETC, ERC, and ERS, as indicated at the inputs and outputs of the transverter  4 , respectively, are understood to be part of a general electrical interface connection  3 ; for example, these signals connect to the optical (infrared) controller  1  which is either an IrDA compliant controller, an Air compliant controller, or an IRGATE compliant controller. 
     Signals A to J are indicated in  FIG. 7  and will be shown in more detail with reference to  FIGS. 9   b  to  11  and described below. 
     In operation the [UWB] RF transverter  4  converts a pulse modulated input signal A, also labeled as ETS, to a radio frequency signal D or E which is also contemplated as modulated radio frequency signal D or amplified modulated radio frequency signal E, respectively. For that, the ETS decoder  42  decodes the received pulse modulated input signal A into a decoded data bit-stream B. Then, the data encoder unit  51  encodes the decoded data bit-stream B into a recoded data bit-stream C. The radio frequency modulator  52  modulates under use of the recoded data bit-stream C the radio frequency signal D which can be amplified by the [UWB] RF power amplifier  53  to the amplified modulated radio frequency signal E. The amplified modulated radio frequency signal E is finally sent via the transmit/receive (TX/RX) switch  54  and the single filter  55  to the antenna  56 . 
     In the receive path, the [UWB] RF transverter  4  converts a received radio frequency signal F, G to a restored or pulse modulated output signal J. The received radio frequency signal F, G is received via the antenna  56 , the single filter  55 , and the transmit/receive (TX/RX) switch  54 . As mentioned above, the received radio frequency signal F is feed to the RF low noise/variable gain circuit  57  for amplification and amplitude level adjustment. This circuit  57  outputs the RF signal G which is fed to the demodulator unit  58  for demodulating the RF signal G into a demodulated data bit-stream H. The data decoder unit  59  decodes then the demodulated data bit-stream H into a received data bit-stream I. Finally, the signal encoder unit  43  encodes the received data bit-stream I into the pulse modulated output signal J which then can be forwarded as ERS signal on the electrical interface connection  3 . 
       FIG. 8  illustrates an alternate general architecture of the [ultra-wideband (UWB)] RF transverter  4  as was described above. The difference in this embodiment is that two separate filters  551 ,  552  for transmission (TX) and reception (RX) are being used. Such an arrangement may be advantageous, for example, when there is a need to apply different design criteria to the transmitter and receiver paths of the RF transverter  4 . Typically, the TX filter  551  may need to be optimized jointly with the antenna characteristics for the proper shaping of the emitted signal spectrum according to regulatory requirements. On the other hand, the RX filter  552  is usually used to match the input characteristics of the RF low noise/variable gain circuit  57  to minimize the receiver&#39;s noise figure and thus to optimize the system&#39;s error rate performance. Alternatively, different TX and RX filters could be used because transmit and receive signals are designed to use different RF bands. 
     In the context of this disclosure, it is assumed that the transverter  4 , for example as shown in  FIG. 9  and described below emits and receives signals as specified in the FCC&#39;s First Report and Order document, ET Docket 98-153, FCC 02-8, adopted on Feb. 14, 2002, and released on Apr. 22, 2002; therein, it is defined that UWB radio devices are devices generating signals with a fractional emission bandwidth of 0.2 (i.e., 20%) below 2.5 GHz or an absolute minimum bandwidth of 500 MHz above 2.5 GHz, whichever applies. This and other related assumptions are only exemplary for the definition of UWB radio devices; in the future, similar definitions for UWB radio devices may be introduced by other regulatory bodies, e.g., in Europe or Asia, or existing definitions and specifications may be modified in the future. 
       FIG. 9   a  shows an example of a specific UWB-RF transverter  4  comprising the data converter  41  that here includes an electrical transmitted IrDA (IRTX/SWDAT) pulse decoder  44  and an electrical received IrDA (IRRX/SRDAT) pulse restorer  45 . The output of the pulse detector  44  feeds directly the transmitter path of the UWB-RF transverter  4  comprising the functions of an UWB pulse generator and modulator  521  and the UWB-RF power amplifier  53 . The latter&#39;s output is fed to the TX/RX switch  54  that feeds the signal to filter  55  whose output is connected to the antenna  56 . The data encoder unit  51  previously shown in  FIG. 7 , for example, is not used in this scheme, since the detected pulses received from the output of pulse detector  44  are directly used to control an UWB pulse generator/modulator  521 , also referred to as modified radio frequency modulator  521 . This generator/modulator  521  can modulate the radio frequency signal, e.g., by binary polarity modulation or more general multilevel modulation. Similarly, the receiver path of the UWB-RF transverter  4  operates in the reverse order, where the TX/RX switch  54  delivers the received signal to an RF low noise/variable gain amplifier  57  for received signal amplification and amplitude adjustment. The output of this circuit is fed to the demodulator unit  58  which extracts the baseband signal from the RF signal applied to its input; typically, the demodulator unit  58  can be implemented as a simple envelope detector or a more efficient direct RF-pulse detector. 
     It has been shown, that efficient direct pulse detectors can be implemented by making use of the specific properties of nonlinear circuit elements, such as tunnel diodes. Similarly, nonlinear circuit elements can be used to generate UWB-RF signals. A pulse-driven method applied to UWB is shown in “Cellonics™ UWB, The Future of Wireless Now, A White Paper”, (MWP-01), by Cellonics Inc Pte Ltd, page 11 (Cellonics™ is a trademark of Cellonics Inc). 
     The demodulator unit  58  in  FIG. 9   a  feeds directly a pulse restorer  45 . The functional block called transverter controller  60  coordinates, receives and outputs all necessary control and timing (clock) signals interfacing to the various functions of the RF transverter  4 . The latter interfaces directly to the IrDA compliant electrical interface connection  3 , as shown in  FIG. 2 . For illustration,  FIG. 9   b  indicates the typical shape of signal E at the output of the UWB-RF power amplifier  53 . Here, T s  is the slot or symbol interval, T P  is the (effective) pulse width—whose inverse value indicates approximately the resulting spectral bandwidth B of the signal—and T c  represents approximately one period of the spectrum&#39;s center frequency f c . 
       FIG. 10  illustrates typical signal forms, A to E, at the different transmitter positions within the RF transverter  4  shown in  FIG. 7 . In particular, this illustration indicates that T s , the slot or symbol interval as determined by the IrDA system, is typically large enough to avoid inter-pulse interference (IPI), even if multipath propagation is present. Specifically,  FIG. 10  illustrates IrDA&#39;s FIR mode offering 4 Mb/s data rate with four-slot pulse position modulation (4 PPM, see also  FIG. 3   a ) using T s =125 ns. The pulse modulated input signal A in the example of  FIG. 10  is a 4-PPM IrDA signal (FIR mode) which the ETS decoder  42  decodes into the decoded data bit-stream B according to the IrDA specifications. The data encoder  51  maps the decoded data bit-stream B into the recoded data bit-stream C, for example, by means of the simple rate ⅔ parity check code indicated in  FIG. 10 . Note that this simple code serves for the purpose of illustration and is not necessarily a preferred encoding method. The recoded data bit-stream C is sent to the [UWB] RF generator &amp; modulator  52  whose output provides, for example, a polarity-modulated radio frequency signal D, E. It should noted that the respective polarity assignment of bit “ 0 ” and bit “ 1 ” in the radio frequency signal D, E indicated in  FIG. 10  is only a matter of definition and can thus be exchanged. 
       FIG. 11  illustrates typical signal forms, F to I, at the different receiver positions within the RF transverter  4  shown in  FIG. 7 . Generally, the receiver inverts the different signal path functions introduced by the transmitter. Thus, the received radio frequency signal F, after being amplified by the RF low noise/variable gain amplifier  57  to an amplified received radio frequency signal G, is fed to the demodulator  58  whose output provides the demodulated data bit-stream H. The following data decoder  59  maps the demodulated data bit-stream H to the received data bit-stream I, which is further translated by the ERS encoder  43  into the pulse modulated output signal J; in this example of  FIG. 11 , the signal form J adheres to IrDA&#39;s FIR specification (4-PPM providing a data rate of 4 Mb/s). 
     The waveforms shown in  FIGS. 10 and 11  are examples for the case of IrDA-FIR mode (4 Mb/s). When the IrDA protocol uses lower data rates (cf. e.g.,  FIG. 3 ), then T s , the slot or symbol interval as determined by the IrDA system, is longer. In this case, it is proposed to transmit suitable short sequences of pulses within the longer slot interval; this added redundancy will offer advantages in the areas of detection capability and synchronization of the received pulse sequences. For example the sequence “10010110111” could be transmitted for every optical pulse, where a “1” indicates transmission of a single [UWB] RF pulse and a “0” indicates the absence of such a pulse. 
     A further use and embodiment of the [ultra-wideband (UWB)] radio frequency (RF) transverter  4  is shown in  FIG. 12   a , where the interface to the optical system is through its native optical interface port, here considered part of the data converter  41 . Thus, the latter includes an optical transmitted signal (OTS) receiver and decoder  46  and an optical received signal (ORS) encoder and transmitter  47 . Otherwise, this system is similar to the system described with reference to  FIG. 7 . An apparatus containing this [ultra-wideband (UWB)] radio frequency (RF) transverter  4  is illustrated in  FIG. 12   b . A wireless converter  7  is based on the [ultra-wideband (UWB)] radio frequency (RF) transverter  4  that connects through an optical interface port (e.g., IrDA compliant) with a host platform  6 , for example an IBM “ThinkPad” laptop computer (ThinkPad is a trademark of International Business Machines Corporation in the United States, other countries, or both) or a PDA, comprising an optical transceiver  8 , a controller executing the optical link protocol  62 , and a host [or client] application  61 . The wireless converter  7  and the host platform  6  are equipped with a suitable matching docking system  71 ,  72  to mechanically connect and secure the relative position of the two units, as well as to block the optical signals used for the optical interface consisting of standard IrDA transceivers  8 . The (semi-) transparent windows  91 ,  92 —also denoted optical windows  91 ,  92 —in front of the optically active elements of the IrDA transceivers can be made of different materials. For example, the converter&#39;s transparent window  92  can be of material with relatively high optical signal attenuation, such that the optical receiver does not have to operate in the saturation mode, which would be the case because of the short optical link distance without such additional attenuation. 
       FIG. 13   a  shows the IrDA communication modes (optical): Sub-SIR, SIR, FIR, and VFIR and  FIG. 13   b  illustrates how the IrDA system could be extended by adding an UWB-RF based mode with the UWB-RF transverter  4 . Besides the benefits already listed above, such a system has the added advantage that the requirement for accurately aiming of the communicating devices—as is the case for optical IrDA links—can be avoided, such that handicapped persons could benefit. 
     Additional features can be built into UWB-RF transverters that will help to implement accurate positioning and location tracking applications. Because of their large bandwidth, UWB signals are inherently suited for this type of application. 
     For the application shown in  FIG. 12   b , the necessary DC (direct current) power to drive the RF transverter  4  may be supplied by rechargeable batteries contained in the unit or the host platform  6  may provide the power. Alternatively, energy derived from the optical signal may be converter to an electrical signal that is suited for charging, at least in part, the battery on board of the RF transverter  4 . 
     Any disclosed embodiment may be combined with one or several of the other embodiments shown and/or described. This is also possible for one or more features of the embodiments.