Abstract:
The present invention relates to ad hoc mobile devices and to ad-hoc networks. 
     An embodiment of the invention relates to an ad hoc mobile device capable of transmitting and receiving data in an ad-hoc network, comprising a receiver capable of receiving and decoding an encoded signal which is transmitted over a physical transmission channel, wherein said receiver is able to handle at least two different code structures; a transmitter capable of generating and transmitting an encoded signal, wherein said transmitter is able to handle at least two different code structures; and a control unit which is connected to said receiver and said transmitter, said control unit being able to change the code structure currently used by the receiver and the transmitter.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to ad hoc mobile devices and ad-hoc networks. 
         [0002]    Ad hoc networks are self-configuring networks of mobile devices connected by wireless links. Each mobile device is free to move independently in any direction, and will therefore change its links to other devices frequently. 
         [0003]    The data transmission in today&#39;s ad-hoc networks is strongly limited by interference. 
       OBJECTIVE OF THE PRESENT INVENTION 
       [0004]    An objective of the present invention is to provide an ad hoc mobile device which is capable of reducing negative effects of interfering signals on ongoing communication. 
         [0005]    A further objective of the present invention is to provide an ad hoc network which is capable of reducing negative effects of interfering signals on ongoing communication. 
         [0006]    A further objective of the present invention is to provide a method of handling a data connection between a first and a second ad hoc mobile device in an ad hoc network in order to reduce negative effects of interfering signals on ongoing communication. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    An embodiment of the invention relates to an ad hoc mobile device capable of transmitting and receiving data in an ad-hoc network, comprising a receiver capable of receiving and decoding an encoded signal which is transmitted over a physical transmission channel, wherein said receiver is able to handle at least two different code structures; a transmitter capable of generating and transmitting an encoded signal, wherein said transmitter is able to handle at least two different code structures; and a control unit which is connected to said receiver and said transmitter, said control unit being able to change the code structures currently used by the receiver and the transmitter. 
         [0008]    Preferably, the device is configured to agree with another ad hoc mobile device on a code structure to be used for further communication. Such an agreement may be found by exchanging code structure information via data and/or control data packets. 
         [0009]    The device may be configured to establish a data connection with another ad hoc mobile device based on a predefined default code structure, and to switch from the default code structure to a different code structure thereafter to transmit or receive an encoded signal to/from the other ad hoc mobile device based on said different code structure. 
         [0010]    Further, the device is preferably configured to select the different code structure and to signal the selected code structure to the other ad hoc mobile device for the subsequent data transfer. 
         [0011]    The device may be further configured to receive a control signal that defines said different code structure, from the other ad hoc mobile device, and to switch its receiver to said different code structure for further data reception. 
         [0012]    The device may be configured to change the code structure by carrying out one or more of the following steps: selecting a code polynomial out of a plurality of predefined code polynomials; selecting a turbo-interleaver or a turbo-deinterleaver out of a plurality of predefined turbo-interleavers or turbo-deinterleavers; selecting a channel-interleaver or a channel-deinterleaver out of a plurality of predefined channel-interleavers or channel-deinterleavers; selecting a channel class out of a plurality of predefined channel classes; selecting a scrambling rule out of a plurality of predefined scrambling rules; and/or selecting a permutation for symbol mapping to subcarriers. 
         [0013]    Preferably, the receiver comprises a decoder capable of handling the at least two different code structures. The transmitter preferably comprises an encoder capable of handling the at least two different code structures. The control unit is preferably connected to the encoder and the decoder to change the code structure currently used by the encoder and/or the decoder. 
         [0014]    The ad hoc mobile device may be capable of communicating based on a RTS/CTS scheme. Preferably, the device is capable of sending a Clear-To-Send(CTS) Request to another ad hoc mobile device after receiving a Request-To-Send(RTS)-signal from said other ad hoc mobile device, said Request To Send(RTS)-signal being sent based on a default code structure and containing information defining a different code structure for further data transfer. 
         [0015]    A further embodiment of the present invention relates to an ad-hoc network comprising at least two ad hoc mobile devices as described above. 
         [0016]    Preferably said at least two ad hoc mobile devices communicate with each other based on a code structure previously agreed on. 
         [0017]    A further embodiment of the present invention relates to a method of handling a data connection between a first and a second ad hoc mobile device, the method comprising the steps of: establishing a data connection between said first and said second ad hoc mobile device based on a predefined default code structure; agreeing on a different code structure; and switching said first and said second ad hoc mobile device from the default code structure to a different code structure to transmit or receive a decoded signal based on said different code structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    In order that the manner in which the above-recited and other advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended figures and tables. Understanding that these figures and tables depict only typical embodiments of the invention and are therefore not to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail by the use of the accompanying drawings in which 
           [0019]      FIG. 1  shows an exemplary embodiment of a first ad-hoc mobile device and a second ad-hoc mobile device; 
           [0020]      FIGS. 2-4  show log-likelihood ratio density distributions of a QPSK signal embedded in QPSK interference and Gaussian noise having different receive power ratios; and 
           [0021]      FIG. 5-6  show the first and second ad-hoc mobile device during communication in RTS/CTS mode in an exemplary fashion. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    The preferred embodiments of the present invention will be best understood by reference to the drawings, wherein identical or comparable parts are designated by the same reference signs throughout. 
         [0023]    It will be readily understood that the present invention, as generally described herein, could vary in a wide range. Thus, the following more detailed description of the exemplary embodiments of the present invention, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention. 
         [0024]      FIG. 1  shows an exemplary embodiment of a first ad hoc mobile device  10  which transmits and receives data to/from a second ad-hoc mobile device  20  over a physical transmission channel  25 . The first device  10  inter alia comprises an antenna  30 , a receiver  35 , and a transmitter  40 . 
         [0025]    The receiver  35  is configured to receive and decode an encoded and modulated bitstream contained in the incoming signal IS, which is received over the physical transmission channel  25 . To this end, the receiver  35  comprises a down-converter unit  45  for down-conversion and digitization. The down-converter unit  45  is configured to down-convert and digitize the incoming signal IS and to provide an incoming baseband complex symbol stream BS. 
         [0026]    The receiver  35  further comprises a channel estimator  61  which provides estimated channel samples P 1 . The estimated channel samples P 1  describe channel distortions imposed to the encoded and modulated bitstream by the physical transmission channel  25 . Channel estimators are known in the art (e.g. “OFDM and MC-CDMA for Broadband Multi-User Communications, WLANs and Broadcasting,” L. Hanzo, M. Munster, B. Choi and T. Keller, Wiley—IEEE Press, September 2003). 
         [0027]    An equalizer  62  of the receiver  35  equalizes the baseband complex symbol stream BS and provides a first equalized symbol stream P 2 . The equalizer  62  provides the equalized symbol stream P 2  by calculating a deconvolution between the estimated channel samples P 1  generated by the channel estimator  61 , and the baseband complex symbol stream. BS. 
         [0028]    A demapper  63  of the receiver  35  processes the equalized symbol stream P 2  and provides a log-likelihood ratio (LLR) stream P 3 . 
         [0029]    A decoder  64  of the receiver  35  comprises a soft-input-soft-output decoder unit  64   a  and a converter unit  64   b . The soft-input-soft-output decoder unit  64   a  processes the log-likelihood ratio stream P 3  and provides a decoded log-likelihood ratio stream P 4 . 
         [0030]    The decoded log-likelihood ratio stream P 4  is converted to a bitstream IBS by the converter unit  64   b  of decoder  64 . As such, the bitstream IBS comprises the data bits transmitted by the encoded and modulated bitstream and contained in the incoming signal IS. 
         [0031]    The transmitter  40  of the first device  10  comprises an encoding unit  70 , and an up-converter unit  80  for digital/analog-conversion and up-conversion. 
         [0032]    The transmitter  40  is configured to process an outgoing data bitstream DS and to generate an encoded and modulated bitstream TS for transmission over the physical transmission channel  25 . The encoded and modulated bitstream TS is sent to the second device  20 . To this end, the encoding unit  70  comprises an encoder  71  and a mapper  72 , which both encode the data bitstream DS and generate an encoded outgoing baseband complex symbol stream EDS. The outgoing baseband complex symbol stream EDS is digital/analog-converted and up-converted by the up-converter unit  80  in order to generate the transmission signal TS. The transmission signal TS is transmitted via the antenna  30  to the second ad hoc mobile device  20 . 
         [0033]    The receiver  35  and the transmitter  40  are both able to handle a plurality of different code structures. As can be seen in  FIG. 1 , the soft-input-soft-output decoder  64   a  and the encoder  71  are connected to a control unit  90  which is able to change the code structure currently applied by the soft-input-soft-output decoder  64   a  and/or the encoder  71 . To this end, the control unit  90  may transmit a code structure selection signal CSSS to the soft-input-soft-output decoder  64   a  and/or the encoder  71 . 
         [0034]    In order to determine a code structure for communication, the control unit  90  evaluates the incoming bitstream IBS and/or the outgoing data bitstream DS, depending on the communication status and communication scheme. If the control unit  90  determines that a new code structure needs to be selected, its code structure selection unit  91  preferably selects the appropriate code structure by selecting a code polynomial out of a plurality of predefined code polynomials, by selecting a turbo-interleaver or a turbo-deinterleaver out of a plurality of predefined turbo-interleavers or turbo-deinterleavers, by selecting a channel-interleaver or a channel-deinterleaver out of a plurality of predefined channel-interleavers or channel-deinterleavers, by selecting a channel class out of a plurality of predefined channel classes, by selecting a scrambling process and/or permutation process for subcarrier mapping. 
         [0035]    Preferably, the control unit  90  agrees with each ad hoc mobile device, which communicates with the device  10 , on an individual code structure for their individual communication. The use of individual code structures randomizes the interference and avoids amplification of interference during decoding. This will be explained in further detail below: 
         [0036]    Most decoders like decoder  64  in  FIG. 1  show an amplification behavior which is approximately linear. As such, a log-likelihood ratio (LLR) vector component caused by interference with the same code structure will be amplified with the coding gain of the decoder, i.e. in the same manner and to the same extent as the “wanted” signal. In other terms, the interfering signal will be treated like the wanted signal and will be amplified with the coding gain. Thus, the signal-to-interference-ratio (SIR) will remain unchanged, and—depending on the current SIR-value—proper decoding of the wanted signal might be impaired. 
         [0037]    In contrast thereto, if the code structures are randomized over the channels (and over the pairs of ad hoc mobile devices), it is more likely that interfering channels will significantly differ in their code structure from the code structure of the wanted signal. Thus, the LLR vector components caused by interference will not be amplified with the coding gain of the decoder, or at least not to the same extent. Thus, the signal-to-interference-ratio (SIR) will increase during decoding, and proper decoding of the wanted signal will be more likely. It is even possible to enable proper decoding in cases where the SIR-value before decoding (after mapping) is smaller than one (below zero measured in dB).  FIGS. 2-4  show an example where the step of decoding increases the SIR-value from below 0 dB before decoding to a value much higher than 0 dB after decoding. 
         [0038]      FIG. 2  shows the log-likelihood-ratio (LLR) density distribution of a QPSK signal having a SIR-value of −1.7 dB and a SNR (signal-noise-ratio) of 10 dB after demapping. The log-likelihood-ratio (LLR) density distribution as shown in  FIG. 2  corresponds to signal P 3  in  FIG. 1  which is generated by demapper  63 . In  FIG. 3 , reference sign S 3  refers to the wanted signal, reference sign S 2  refers to the interference (interfering) signal, reference sign S 4  refers to noise, and reference sign S 1  refers to the joint signal. 
         [0039]    If the interfering signal S 2  uses the same code structure as the wanted QPSK signal S 3 , the decoder  64  will fail to generate a properly decoded signal as the interfering signal S 2  experiences the same decoder gain as the wanted signal S 3 . Thus, the SIR-value remains at approximately −1.7 dB and decoding will not be possible. This is shown in  FIG. 3  in an exemplary fashion.  FIG. 3  shows the log-likelihood-ratio (LLR) density distribution after decoding by the soft-input-soft-output decoder  64   a . The log-likelihood-ratio (LLR) density distribution of  FIG. 3  is contained in signal P 4  of  FIG. 1 . 
         [0040]    However, if the interfering signal S 2  uses a code structure differing from the one of the wanted QPSK signal S 3 , the decoder  64  will be able to generate a properly decoded signal since the interfering signal S 2  will not be amplified at all, or at least much less than the wanted signal S 3 . Thus, the SIR-value will significantly increase during decoding, and a properly decoded signal may be generated. This is shown in  FIG. 4  in an exemplary fashion. Again, the log-likelihood-ratio (LLR) density distribution is shown after decoding. 
         [0041]    The devices  10  and  20  as shown in  FIG. 1  may operate in various different modes. For further explanation, it is assumed in an exemplary fashion that both devices  10  and  20  use a RTS/CTS-mode (RTS/CTS: Request-To-Send/Clear-To-Send). In this case, the communication may be carried out as explained with reference to  FIGS. 5 and 6 . 
         [0042]      FIG. 5  shows the device  10  according to  FIG. 1 , after the device  20  has sent a RTS (Request-To-Send) signal to the device  10 . At this stage, both devices  10  and  20  have not yet agreed on a specific code structure. Thus, the device  20  sends the RTS-signal based on a predefined default code structure. 
         [0043]    The device  10  and its control unit  90  receive the RTS-signal. The control unit  90  analyzes the RTS-signal, and selects a code structure on a random basis using its code structure selection unit  91 . The randomly selected code structure is designated by reference numeral CS in  FIG. 5 . 
         [0044]    The code structure CS is preferably selected individually for each transceiver pair (ad hoc mobile device pair). For communication with other devices than the second device  20 , the first device  10  preferably chooses different code structures. As a result, an individual code structure is used for each link, and gain amplification of interfering signals at the decoder stage is avoided or at least reduced. 
         [0045]    After selecting the code structure CS, a code structure signal unit  92  of the control unit  90  generates a modified CTS-signal CTS′ which includes the usual CTS-information “clear to send” and additionally a code structure indication which identifies the selected code structure CS. 
         [0046]    The transmitter  40  sends the modified CTS-signal CTS′ to the second device  20  using the predefined default code structure. 
         [0047]    As the control unit  90  of the device  10  expects the second device  20  to transmit at least one further data signal based on the code structure CS, it sends a corresponding code structure selection signal CS′ to the soft-input-soft-output decoder  64   a  in order to switch the soft-input-soft-output decoder  64   a  into a decoding mode that allows decoding based on the selected code structure CS. 
         [0048]    For the exemplary embodiment discussed herein, it is assumed that the second device  20  might be identical or at least similar to the device  10 . As such, the description of the first device  10  applies to the second device  20  mutatis mutandis. Therefore, in  FIG. 6 , the same reference numerals have been used to visualize the internal components of the second device  20 . 
         [0049]      FIG. 6  shows the second device  20  during communication with the first device  10  in further detail after the modified CTS-signal CTS′ has been sent from the first device  10  to the second device  20 . 
         [0050]    The control unit  90  of the second device  20  identifies the “clear-to-send”-information contained in the modified CTS-signal CTS′, and the additionally indication of the selected code structure CS. Then, the control unit  90  sends a code structure selection signal CS′ indicating the selected code structure CS to its decoder  71  in order to switch it to the respective code structure CS. From that point on, the decoder  71  will use the respective code structure CS for encoding further data D during communication with the first device  10 . The encoded data D(CS) are transmitted towards the first device  10 . 
         [0051]    In the manner described above, each pair of ad hoc mobile devices and each channel may use its individual code structure. In case of interference, the interfering signal will have no, or at least no significant, correlation with the wanted signal and the interfering signal will not experience decoding gain. 
       REFERENCE SIGNS 
       [0000]    
       
           10  first ad hoc mobile device 
           20  second ad-hoc mobile device 
           25  physical transmission channel 
           30  antenna 
           35  receiver 
           40  transmitter 
           45  down-converter unit 
           61  channel estimator 
           62  equalizer 
           63  demapper 
           64  decoder 
           64   a  soft-input-soft-output decoder unit 
           64   b  converter unit 
           70  encoding unit 
           80  up-converter unit 
           90  control unit 
           91  structure selection unit 
           92  code structure signal unit 
         BS baseband complex symbol stream 
         CS code structure 
         CS′ code structure selection signal 
         CSSS code structure selection signal 
         CTS′ modified CTS-signal 
         D data 
         D(CS) encoded data 
         DS outgoing data bitstream 
         EDS outgoing baseband complex symbol stream 
         IS incoming joint signal 
         P 1  estimated channel samples 
         P 2  equalized symbol stream 
         P 3  log-likelihood ratio stream 
         P 4  decoded log-likelihood ratio stream 
         RTS RTS-signal 
         S 1  joint signal 
         S 2  interference (interfering) signal 
         S 3  wanted signal 
         S 4  noise 
         TS transmission signal (encoded and modulated bitstream)