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1. (WO2007003297) METHOD AND APPARATUS FOR REDUCING THE INTERFERENCES BETWEEN A WIDE BAND DEVICE AND A NARROW BAND INTERFERER
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Method and apparatus for reducing the interferences between a wide band device and a narrow band interferer.

The invention relates to the wireless communication systems, and more particularly to the processing of interferences within different wireless communication apparatuses.
A non-limitative application of the invention is directed to devices operating according to the Ultra Wide Band (UWB) standard based on OFDM (Orthogonal Frequency-Division Multiplexing), called MBOA (Multiband OFDM Alliance), which can generate interferences towards a WIMAX device which is a fix wireless device (Worldwide Interoperability for Microwave Access). Such a WIMAX device operates for example with a band width of 20 MHz at a central frequency of 3 ,5 GHz, whereas the frequency band of the MBOA system lies between 3 , 1 and 5,0 GHz.
Wireless personal area networks based on OFDM and UWB technologies like the MBOA standard will directly interfere to narrowband interferer which are close to such wide band devices. At present, no specific interference mitigation techniques are implemented in the UWB standard based on OFDM (MBOA).
Orthogonal frequency-Division Multiplexing (OFDM) is a method of digital modulation in which a signal is split into several narrowband channels (sub-carriers) at different frequencies. In order to avoid in-band spectral interference, WO 2005/006698 (INTEL) proposes to puncture, i.e. remove, selected sub-carriers. More precisely, this puncturing is made, taking into account channel knowledge, after the OFDM modulation in the transmitter, whereas a depuncturing is performed in the receiver before the OFDM demodulator. Because of the puncturing of some sub-carriers, the size of the encoded block of data which will be convert into OFDM symbols, has to be reduced. Consequently, not only the software of the MAC ("Medium Access Control") entity of the UWB device must be modified to take into account this size reduction of the data block, but the receiver needs to know the actual used puncturing scheme, for example through the transfer of control information from the transmitting device to receiving device, leading to an interruption of the transmission of the useful data between the transmitting device and the receiving device.
The invention intends to solve this problem.
An aim of the invention is to minimise the interference to an in-band victim device without needing any modification in the control layer, for example the MAC layer, of the wide band device, and without needing any additional communication overhead on the air.
Another aim of the invention is to propose a solution which permits a communication between devices implementing the invention and devices not implementing the invention.
According to an aspect of the invention, it is thus proposed a method for reducing the interferences between a main device, for example a UWB MBOA device, adapted to transmit information on sub-carriers having frequencies belonging to a main band of frequencies and at least one auxiliary device, for example a WIMAX device, adapted to emit and/or receive information within an auxiliary band of frequencies, said auxiliary band being narrower than said main band and included within said main band. The information transmitted on said sub-carriers by said man device are issued from symbols obtained by a mapping of a punctured scheme of bits according to a modulation mapping scheme.
According to this aspect of the invention, said method comprises a main interference reduction mode for reducing the interference generated by said main device towards said auxiliary device. Said main interference reduction mode is performed within said main device and includes :
- detecting an emission from and/or reception performed by said auxiliary device,
- determining from said detection step a group of at least one sub-carrier having frequencies interfering with said auxiliary band of frequencies, - determining the bits of said punctured stream which correspond to the information carried by said interfering sub-carriers of said group, and
- processing said determined bits such that said processed bits are mapped into a reference symbol having an amplitude equal or close to zero.
Thus, after OFDM modulation of such a reference symbol, the corresponding sub-carrier is not or almost not modulated. In other words, no energy or almost no energy is transmitted on this sub-carrier so that the interference will be minimised if not eliminated because this interfering sub-carriers have been notched out or almost notched out.
However, there is no modification of the size of the data block and no modification in the software of the MAC layer. In fact, the sub-carrier notching according to this aspect of the invention leads to a loss of transmitted information. In other words, on the receiving device point of view, the receiver will consider that he does not receive any information or that he receives a high level of noise. Accordingly, after OFDM demodulation and demapping, the corresponding soft bits will have a very low reliability leading to a appropriate correction during the decoding step.
Further there is no need to inform the receiving terminal. Thus the method according to this aspect of the invention can be considered as being a blind or seamless method of sub-carrier notching.
As an example, a 20 MHz narrow band carrier which can be the width of the auxiliary band of the auxiliary device (for example the WIMAX device) corresponds to only 1 ,3 % of the used UWB spectrum of a MBOA based device and corresponds for example to an interfering sub-carrier group of 5 or 7 sub-carriers. And this leads to a small amount of lost transmitted information which does not affect the performance of the device.
More generally, the larger the width of the auxiliary band of the auxiliary device is, the more the number of interfering sub-carriers to be notched out is important and the more the consequence on the communication performance is important. Accordingly, the man skilled in the art will be able to decide whether or not the invention can be applied for a given narrowband interferer depending on the desired communication performance.
However, narrow band interferers having band width smaller than 5 to 10 % of the main band width (the band width of the main device) are perfectly compatible with this aspect of the invention.
Said reference symbol is preferably chosen within a group of several reference symbols having respectively different amplitudes, each amplitude being equal or close to zero. For example, this reference symbol or neutral symbol can be chosen among a set of for example four values. The corresponding sub-carriers could then be controlled in their transmit power. The lowest value of the reference symbol would completely notch out the carrier whereas higher values would only attenuate the related sub-carriers. By doing so, some part of the cancelled information could still be transmitted and thus a slide improvement of the communication performance could be reached. Further, choosing a reference symbol having a value close to zero but not equal to zero would render the implementation of the radio frequency stage of the apparatus easier than with a reference symbol having a zero value.
According to an embodiment of the invention, the processing step of said determined bits comprises associating a control indication to each determined bit and bits associated with said control indication are mapped into said reference symbol.
For example, said processing step comprises associating a control bit to each bit of said punctured stream, said control bit having a first logical value corresponding to said control indication or a second logical value. The bits associated with control bits having said second logical value are mapped into their corresponding symbols in accordance with said modulation mapping scheme, whereas the bits associated with control bits having said first logical value are mapped into said reference symbol.

Whereas the wide band device generates interference towards the narrow band interferer, there is also an in-band interference generated by the narrowband interferer in the wide band device even if it is less important. According to another embodiment of the invention, it is thus possible to minimise also such interferences generated by the narrowband interferer towards the wide band device.
More precisely, according to such an embodiment, in which said main device is also adapted to receive information carried by said sub-carriers and to perform a reception processing including determining received symbols from the received information and demapping said received symbol for providing a punctured stream of soft bits (each soft bit having a sign representative of the estimation of the logical value of the corresponding bit and a magnitude representative of the confidence in said estimation), said method further comprises an auxiliary interference reduction mode for reducing the interference generated by said auxiliary device (the narrow band device) toward said main device. Said auxiliary interference reduction mode is performed within said main device and includes replacing the soft bits corresponding to the information received on said interfering sub-carriers by neutral soft bits having a magnitude equal to zero.
Thus, such a neutral soft bit will be considered having a very low reliability which will be taken into account into the decoding step. The interference coming from the auxiliary device is thus minimised.
According to an embodiment of the invention, the detecting step of the main interference reduction mode comprises analysing a channel step information and detecting the operation of said at lest one auxiliary device from said channel state information. Such channel state information can be delivered for example by a channel estimator generally incorporated in the wireless apparatus.
However, the detecting step preferably further comprises checking said operation detection by using a set of stored interference information respectively associated to a set of several different auxiliary devices.

In other words, in order to optimise the notching process according to the invention, the spectral properties of the potential victim device (the auxiliary device) can be taken into account in the definition process of the bits to be mapped into the reference symbol. Usually, only a limited amount of possible devices can be assumed as victim devices in the corresponding transmission band of the main device. These devices (e.g. WIMAX devices) are well defined and thus the band width and the potential carrier frequencies in use are well known. By using this information, it is much easier to define the sub-carriers to be notched out based on the channel state information. By using this a posteriori knowledge, notching groups can be predefined and easily set up. For example, a sub-carrier group of 5 or 7 sub-carriers can be defined for a WIMAX device with a band width of 20 MHz. The requirements on the frequency domain channel state information can thus be relaxed.
The main interference reduction mode advantageously comprises regularly checking the operation of said auxiliary device and if said auxiliary device is no more detectable, the main interference reduction mode concerning said no more detectable auxiliary device is stopped.
According to a variant of the invention, the main device and said at least one auxiliary device are all together incorporated within a single wireless communication apparatus. Thus, with such an embodiment, it is possible to have the simultaneous operation of two different air interfaces within a single wireless apparatus, for example a single mobile terminal, while the mutual interferences are minimised if not eliminated.
With such a collocation variant, an indication of said group of at least one sub-carrier having frequency interfering with said auxiliary band of frequencies of said auxiliary device, is advantageously stored within said apparatus and said detecting step of the main interference reduction mode comprises advantageously receiving from said auxiliary device an auxiliary control information representative of the operation or of the non-operation of said auxiliary device such that said main interference reduction mode is performed only during the operation of said auxiliary device.
Several different auxiliary devices may be respectively adapted to emit and/or receive information within several different auxiliary bands of frequency, each auxiliary band being narrower than said main band and included within said main band. In such a case, said main interference reduction mode may be performed for at least some of said several different auxiliary devices.
Another possibility exists according to the invention for mitigating the interferences between the main wide band device and the narrow band interferer. More precisely, according to an embodiment of the invention, the method comprises an additional interference reduction mode for reducing the interference between said main device and said at least on auxiliary device. Said additional interference reduction mode is performed within said main device and includes :
- detecting an emission from and/or a reception performed by said at least one auxiliary device,
- determining from said detection step a group of at least one sub-carrier having frequencies interfering with said auxiliary band of frequencies, and
shifting at least a part of said main band of frequencies including said group with a chosen frequency shift.
Of course, the man skilled in the art will adapt said frequency shift such that, after shifting, the shifted part remains within the limits of said main band while being compatible with the non-shifted part of the main band of frequencies.
The frequency shift is for example at least equal to the width of the frequency band of said at least one auxiliary device.
When the main band of frequencies is subdivided into several different mutually spaced sub-bands, the shifting step comprises shifting at least the sub-band which contains at least a part of said group of interfering sub-carriers.

As for the notching variant of the invention, said detecting step of the additional interference reduction mode (the shifting variant) comprises for example analysing a channel state information and detecting the operation of said at least one auxiliary device from said channel state information, and preferably checking said operation detection by using a set of stored interference information respectively associated to a set of several different auxiliary devices.
Said additional interference reduction mode may also comprise regularly checking the operation of said auxiliary device and if said auxiliary device is no more detectable, said additional interference reduction mode concerning said no more detectable auxiliary device is stopped.
When said at least one auxiliary device and said main device are all together incorporated within a single wireless communication apparatus, the detecting step of the additional interference reduction mode comprises advantageously, as for the main interference reduction mode, the reception from said auxiliary device of an additional control information representative of the operation or of the non-operation of said auxiliary device such that said additional interference reduction mode is performed only during the operation of said auxiliary device.

Depending on the location of the auxiliary frequency band within the main band of frequencies, either the main interference reduction mode (notching mode) or the additional interference reduction mode (shifting mode) can be selected.
It is also possible that both main interference reduction mode and additional interference reduction mode are performed for a same auxiliary device. For example, a shifting of a part (for example a sub-band) of the main band of frequencies can be performed to eliminate the interferences carried by some sub-carriers whereas the notching option is performed for the remaining interfering sub-carriers which are still within said main band of frequency after the shifting step.
It is also possible that main interference reduction mode and additional interference reduction mode be respectively performed for different auxiliary devices.

The main device can belong to a multi-carrier based Ultra Wide Band Communication system, for example but not exclusively, an OFDM based Ultra Wide Band Communication system.
Said at least one auxiliary device may belong to a fix wireless system (FWA, fixed wireless access) like a WIMAX system. However, it is also possible that such an auxiliary device belongs to a mobile radio system defined by a mobile radio standard like for example

UMTS, GSM, CDMA, EDGE, beyond IMT-2000 systems, or to a fixed satellite system (FSS), if the frequency band of the mobile radio system or the satellite system is located within the main frequency band of the main device.
According to another aspect of the invention, it is also proposed a wireless communication apparatus comprising a main device having a main transmission chain including :
- puncturing means for delivering a punctured stream of bits,

- mapping means for delivering symbols from said punctured stream of bits in accordance with a modulation mapping scheme,
a transmission stage for transmitting information issued from said symbols on sub-carriers having frequencies belonging to a main band of frequencies.
Said main device further includes main reduction interference means for reducing the interferences generated by said main device toward at least one auxiliary device adapted to emit and/or receive information within auxiliary band of frequencies, said auxiliary band being narrower than said main band and included within said main band.
Said main interference reduction means includes :
main detection means for detecting an emission from and/or a reception performed by said auxiliary device,
a main control unit connected to the main detection means for determining a group of at least one sub-carrier having frequency interfering with said auxiliary band of frequencies and determining the bits of said punctured stream which correspond to the information carried by said interfering sub-carriers of said group, and
- a main processing unit for processing said determined bits such that said mapping means are adapted to map said processed bits into a reference symbol having an amplitude equal or close to zero.
According to an embodiment of the invention, said main processing unit is adapted to associate a control indication to each determined bits, and said mapping means are adapted to map the bits associated with said control indication into said reference symbol.
According to an embodiment of the invention, said main processing unit is adapted to associate a control bit to each bit of said punctured stream, said control bit having a first logical value corresponding to said control indication, or a second logical value, and the mapping means are adapted to map the bits associated with said control bits having said second logical value into their corresponding symbols in accordance with said modulation scheme.
According to an embodiment of the invention, said main device further comprises a reception chain including
- a receiving stage for receiving information carried by said sub-carriers and delivering received symbols from said received information,
- demapping means for demapping the received symbols according to said modulation scheme and delivering a punctured stream of soft bits, each soft bit having a sign representative of the estimation of logical value of the corresponding bit and a magnitude representative of the confidence in said estimation.
Said main device further comprises auxiliary interference reduction means for reducing the interference generated by said auxiliary device towards said main device, said auxiliary interference reduction means including an auxiliary processing unit for replacing the soft bits corresponding to the information received on said interfering sub-carriers by neutral soft bits having a magnitude equal to zero.
According to an embodiment of the invention, the apparatus further comprises a channel estimation unit adapted to deliver a channel state information and said main detection means comprises main analysing means for analysing said channel state information and detecting the operation of said at least one auxiliary device from said channel state information.
The apparatus may further comprise main memory means for storing a set of interference information respectively associated to a set of several different auxiliary devices, and main checking means for checking said operation detection by using said stored set of interference information.
The apparatus may also further comprise a main management unit adapted to manage the operation of said main interference reduction means and said main interference reduction means are further adapted to regularly check the operation of said auxiliary device and if said auxiliary device is no more detectable said main management unit is adapted to stop the interference reduction concerning said no more detectable auxiliary device.
The apparatus may incorporate said main device and said at least one auxiliary device all together.
In such a case, the apparatus may further comprise a main management unit adapted to manage the operation of said main interference reduction means and auxiliary memory means for storing an indication of said group of at least one sub-carrier having frequencies interfering with said auxiliary band of frequencies of said auxiliary device. And said auxiliary device comprises auxiliary control means for delivering an auxiliary control information representative of the operation or of the non operation of said auxiliary device such that said main management unit is adapted to allow the operation of said main interference reduction means only during the operation of said auxiliary device.

According to an embodiment of the invention, several different auxiliary devices are respectively adapted to emit and/or receive information within several different auxiliary bands of frequencies, each auxiliary band being narrower than said main band and included within said main band, and said main interference reduction means are adapted to reduce the interference generated by said main device towards at least some of said several different auxiliary devices.
According to another variant of the invention, the apparatus further comprises additional interference reduction means for reducing the interference between said main device and said at least one auxiliary device, said additional interference reduction means including
- additional detecting means for detecting an emission from and/or a reception performed by said at least one auxiliary device,
- an additional control unit connected to said additional detecting means for determining a group of at least one sub- carrier having frequencies interfering with said auxiliary band of frequencies, and for shifting at least a part of said main band of frequencies including said group, with a chosen frequency shift.
When the main band of frequencies is subdivided into several different mutually spaced sub-bands, the additional control unit is adapted to shift at least the sub-band which contains at least a part of said group of interfering sub-carriers.
According to an embodiment of the invention, the apparatus further comprises a channel estimation unit adapted to deliver a channel state information, and said additional detection means comprises additional analysing means for analysing said channel state information and detecting the operation of said at least one auxiliary device from said channel state information. Additional memory means may be provided for storing a set of interference information respectively associated to a set of several different auxiliary devices, and additional checking means may check said operation detection by using said stored set of interference information. An additional management unit may be provided for managing the operation of said additional interference reduction means. Said additional interference reduction means may be further adapted to regularly check the operation of said auxiliary device and if said auxiliary device is no more detectable said additional management unit is adapted to stop the interference reduction concerning said no more detectable auxiliary device.
When said main device and said at least one auxiliary device are all together incorporated within a single wireless communication apparatus, the apparatus comprises, according to an embodiment of the invention, an additional management unit adapted to manage the operation of said additional interference reduction means and additional memory means for storing an indication of said group of at least one sub-carrier having frequencies interfering with said auxiliary band of frequencies of said auxiliary device. Said auxiliary device comprises auxiliary control means for delivering an auxiliary control information representative of the operation or of the non operation of said auxiliary device such that said additional management unit is adapted to allow the operation of said main interference reduction means only during the operation of said auxiliary device.
Both said main interference reduction means and additional interference reduction means may be adapted to perform their respective interference reduction for a same auxiliary device or for different auxiliary devices, respectively. Both main and additional detecting means may be identical as well as both main and additional control units.
Other advantages and features of the invention will appear on examining the detailed description of embodiments, these being in no way limiting, and of the appended drawings in which :
- figure 1 illustrates diagrammatically the internal protocol structure of a wireless communication apparatus according to an embodiment of the invention, - figure 2 illustrates a first embodiment of a method according to the invention,
figure 3 illustrates more in details but still diagrammatically an internal structure of a wireless communication apparatus according to the invention,
figures 4-7 illustrate diagrammatically flow charts related to an embodiment of a method according to the invention,
figure 8 illustrates diagrammatically another part of an internal structure of an embodiment of a wireless communication apparatus according to the invention,
figure 9 illustrates a flow chart related to another embodiment of a method according to the invention,
figure 10 illustrates diagrammatically another embodiment of a wireless communication apparatus according to the invention,
- figure 1 1 illustrates another embodiment of a method according to the invention,
figure 12 illustrates diagrammatically another embodiment of an internal structure of an embodiment of a wireless communication apparatus according to the invention, and
figures 13 and 14 illustrate other flow charts related to another embodiment of a method according to the invention. Figure 1 discloses an example of a wireless communication apparatus WAP belonging to a non-coordinated communication system such as a WLAN ("Wireless Local Area Network") or a WPAN

("Wireless Personal Area Network").
Such a wireless apparatus WAP belongs for example to an

OFDM based Ultra Wide Band Communication system. However, the invention is not limited to such an example and can apply more generally to generalised multi-carrier (GMC) systems in which the carriers are not necessarily orthogonal.
WPAN MAC protocols have a distributed nature where there is no central coordinator terminal or base station to assign the medium access. There, in contrast to a mobile radio terminal, a WPAN transceiver has much higher flexibility to allocate the transmission slot and formats. The allocation of the communication resources is a distributed process. The allocation to a specific time slot in the super frame can be modified from one superframe to the next. The controlling entity is the WPAN-MAC layer of the communicating terminals. The allocation is based on the requested data rate and the type of service to be transmitted. Furthermore, the available resources are taken into account in the allocation process. The MAC layer requests a reservation for a specific time slot or a number of time slots based on these constraints. These constraints can be split into local constraints, like the data rate to be transmitted or received and network wide constraints like the already existing slot reservation.
An example of distributed WPAN-MAC is MBOA MAC.
The proposed MBOA MAC standard draft is based on a UWB technology and is planed to be used in the frequency band between 3 , 1 and 10,7 GHz. First implementations using the standard work in the frequency range between 3, 1 GHz and 5,0 GHz.
The wireless apparatus WAP comprises a main device MDVC including an OFDM based UWB communication interface MCINT connected between the UWB application block MBLC and the air channel.
This communication interface MCINT comprises an UWB MAC layer clocked by a clock signal MCLK and connected to the PHY layer and to the UWB application block MBLC.
For further details concerning the MAC layer and the PHY layer of the communication interface MCINT, the man skilled in the art may refer to MBOA PHY layer Technical Specification, Version 1.0, January 2005, and to MBOA MAC layer Technical Specification, Version 0v7, October 2004.
The MAC layer manages in particular the emission/reception of the UWB data stream and is incorporated by software in a control processor.
In figure 2 it can be seen that the main band of frequencies used for the operation (transmission and/or reception) of the main device MDVC lies between 3, 1 GHz and 4,9 GHz. Further, the main frequency band is subdivided into three sub-bands SB l , SB2, SB3 , called hopping sub-bands, which are mutually spaced. More precisely, there is a guard interval of 100 MHz between the lower limit (3 , 1 GHz) of the main frequency band and the beginning of the first sub-band SB l as well as between the end of the third sub-band SB3 and the upper limit (4,9 GHz) of the main frequency band.
Further, two adjacent sub-bands are spaced by a guard interval of 50 MHz.
The allocation of the sub-bands during the transmission is made according to a predetermined hopping sequence.
In the upper part of figure 2, a narrow band device (auxiliary device) XDVC is assumed to operate in an auxiliary band of frequencies included within the second sub-band SB2. This auxiliary band of frequencies has a width of 20 MHz.
Compared to a UWB device based on techniques like MBOA standard, such a device XDVC is considered as being a narrowband device.
According to an aspect of the invention, which will be described more in details thereafter, based on the control of the transmission chain of the UWB main device MDVC, the frequencies used by the narrowband device are not used for the transmission of the

UWB signal. The corresponding sub-carriers in hopping sub-band 2 are not used, i.e. are notched out so that the interferences generated by the main UWB device MDVC toward the auxiliary device XDVC are greatly reduced if not eliminated.
Since the narrowband device only uses a very small portion of the UWB spectrum for its transmission, the sub-carrier notching can be done without a severe influence to the communication performance of the UWB device MDVC.
In order to reduce these interferences by using such a notching process, the main device MDVC of the wireless communication apparatus WAP comprises main interference reduction means MIFRM cooperating with the transmission chain TXCH of the main device (figure 3).
In a conventional manner, the transmission chain TXCH comprises an outer transmission block OUTX including an encoder CC, for example a convolutional encoder, receiving data from source coding means and delivering a bits stream to puncturing means PM which delivers a punctured bits stream.
The other conventional means of the transmission chain TXCH are interleaving means, ILM, followed by mapping means MPM which map the bits into symbols according to a modulation mapping scheme depending on the kind of used modulation, for example a BPSK modulation or more generally a QAM modulation. The symbols are then delivered to an OFDM modulator OFM which performs IFFT processing in order to associate each symbol to a sub-carrier and to form OFDM symbols. Each sub-carrier is modulated in accordance with the value of the corresponding symbol.
The OFDM symbols are then processed in a conventional radio frequency stage RF before being transmitted on air through antenna ANT.
The mapping means MPM as well as the OFDM modulator OFM belong to an inner transmission block INTX of the transmission stage.

The operation of the main interference reduction means MIFRM which are depicted in figure 3 will be now described with reference to this figure 3, figure 4 which depicts the main interference reduction mode MIRM and also to figures 5-7.
A conventional channel estimation unit CHST delivers a channel state information in the frequency domain. For example, this channel state information is an impulse response of the channel and contains for example, energy peaks at some frequencies. Main detection means DTM comprises main analysing means AM for analysing said channel state information and detecting the operation of the auxiliary device XDVC (step 40 in figure 4).
Although it is not compulsory, it is preferable that the eventual operation of the WIMAX device detected by the analysing step 51 of the channel state information (figure 5) be checked (step 52, figure 5) by mean checking means MCKM connected to main memory means MM.
These main memory means MM contain a set of stored interference information, in particular the interference information related to the auxiliary device XDVC.
As a matter of fact, only a limited amount of possible devices can be assumed as victim devices in the corresponding main transmission band of the main device. These auxiliary devices are well defined and thus a band width and the potential carrier frequencies in use are well known. These information are stored in the main memory means.
Using this a posteriori knowledge notching groups can be predefined and easily set up.
A main control unit MCU connected to the main detection means, is able to determine a group of interference sub-carriers, for example from the analysing of the channel state information. And, these interfering sub-carriers can be validated by the result of the checking operation performed by main checking means MCKM in accordance with the content of the main memory means MM.
More precisely, for example, if the group of interference sub-carriers determined by the main control unit MCU by using the information given by the main detection means DTM, corresponds to pre-stored interfering frequencies, thus, there is a high probability that the information given by the main detection means actually corresponds to a well-defined auxiliary device, and not, for example, to noise on the air channel.
The main control unit MCU will then determine the bits of the punctured stream of bits which correspond to the information carried by said interfering sub-carriers of said group.
As a matter of fact, the symbol mappings on the sub-carriers and the interleaver structure is a fixed value parameter in the standard for a given transmission mode. Thus, it can be stored as a fixed value and needs not to be recalculated. In other words, there is a one-to-one mapping (one-to-one correspondence) between a bit of the punctured bits stream and a sub-carrier in the OFDM symbol.
Thus, the determined bits corresponding to the interfering sub-carriers to be notched out, are processed in a main process unit MPU connected to the main control unit MCU and also connected between the main puncturing means PM and the interleaving means ILM.
More precisely, the processing step 43 , (performed after the determining step 42) comprises associating a control bit cbt having a first logical value (for example value 1 ) to each determined bit and associating a control bit cbt having a second logical value (for example 0 value) to each other bits (steps 70 et 71 , figure 7).
After interleaving, the bits are mapped into symbols in accordance with the chosen modulation. The bits which are associated with a control bit having the second logical value are mapped into their corresponding symbols according to the modulation mapping scheme (step 73 , figure 7).
The bits determined during the determining step 42, which are associated with the control bit having the first logical value, are mapped into a reference symbol (step 44, figure 4 and step 73 , figure 7).
This reference symbol has an amplitude equal or close to zero.

After OFDM modulation, each sub-carrier is modulated in accordance with the value of the corresponding symbol. Thus, if the reference symbol has an amplitude equal or close to zero, no information or almost no information will be transmitted by this sub-carrier. In other words, the energy associated with this sub-carrier will be nul or almost nul. Thus, this sub-carrier is in fact notched out and no interference occurs between the main device and the auxiliary device.
Instead of using only one reference symbol, it is possible to choose a reference symbol into a set of possible reference symbols, for example four reference symbols. The corresponding sub-carriers could then be controlled in their transmit power. The lowest value would completely notch out the carrier whereas the higher values would only attenuate the related sub-carrier. By doing so, some part of the cancelled information can be transmitted and thus a slight improvement of the communication performance could be reached. For example, the highest value of the reference symbol could be some percent (for example up to 2%) of the smallest amplitude of the normal symbols (the conventional symbols corresponding to the chosen modulation).
In order, in particular, to improve the operation of the main device, it is preferable that the operation of the auxiliary device XDVC be regularly checked (step 61 , figure 6). If the auxiliary device is no more detectable (step 62) then, the main interference reduction mode is stopped (step 63).
In this respect, the wireless communication apparatus WAP further comprises a main management unit MMU adapted to manage the operation of the main interference reduction means MIFRM and to stop eventually their operation.
The main interference reduction means MIFRM may be for example implemented in the PHY layer of the main device. The main management unit MMU may also be implemented in the PHY layer although it would be also possible that this main management unit be implemented by software in the MAC layer.
Generally speaking, the main control unit, the main checking means, the detection means and the main processing unit of the main interference reduction means may be realised by software within a control processor and/or by hardware.
With this aspect of the invention, the block sizes of the bit stream to be handled are constant with and without the processing step 43. Thus, no major changes are needed in the following processing unit (interleaver, mapper and OFDM modulator).
Further, no interaction in the transmission of the useful data is necessary to inform the receiver and no change in the MAC layer protocol is needed.
The MBOA standard needs only small changes in the physical layer PHY.

Devices using this aspect of the invention can communicate with devices not using this aspect of the invention. Thus a smooth introduction of the method according to this aspect of the invention with a backward compatibility can be supported.
The method according to this aspect of the invention can easily be combined with other mitigation techniques like power control and adaptive sub-carrier loading.
Only the UWB device that is interfering with the victim device can operate in the notching mode. For example, in a WIMAX system the home equipment is the only WIMAX device which can see the interference from a UWB device in the home. The uplink receiver at the base station is to far away from the UWB device to see any interference generated by the device. Thus it is not needed to notch out the corresponding sub-carriers in the complete UWB piconet but only at the device closest to the potential victim receiver. The communication performance of all other devices is not influenced at all.
As depicted in figure 8, the main device MDVC of the wireless communication apparatus WAP further comprises a reception chain RXCH including a receiving stage for receiving information carried by the sub-carriers and delivering received symbols from said received information. The receiving stage includes in particular a radio frequency stage RF connected to the antenna ANT followed by a OFDM demodulator DOFM (FFT processing).
The reception chain contains also demapping means DMPM for demapping the received symbols according to the modulation scheme and delivering a punctured stream of soft bits to deinterleaver means DILM.
A soft bit, for example a Log-Likelihood Ratio LLR, well-known by the man skilled in the art, has a sign representative of the estimation of the logical value (0 or 1 ) of the corresponding bit and a magnitude representative of the confidence in said estimation. Thus, a soft bit, which is coded on several hard bits may have theoretically a value comprised between -∞ and +∞. And, the higher the magnitude is, the higher the confidence in the estimation is.
The main device further comprises auxiliary interference reduction means AUXIFRM for reducing the interference generated by the auxiliary device towards the main device.
The auxiliary interference reduction means AUXIFRM includes, as depicted in figure 8, an auxiliary processing unit XCU for replacing the soft bits corresponding to the information received on said interfering sub-carriers by neural soft bits having a magnitude equal to zero.
This operation is more detailed in figure 9 which depicts he main steps of the auxiliary interference reduction mode XIRM.
More precisely, after receiving information carried by interfering sub-carriers (step 90) an OFDM demodulation 91 is performed. The received symbols are then demapped (step 92) and the corresponding soft bits are replaced by neutral soft bits 93.
Thus, after depuncturing in depuncturing means DPM, the bits are decoded in a decoder DCC. And, the neutral soft bits are considered as being noise or information with a very low reliability. Thus, these data are corrected in the decoding process. Accordingly, the interferences generated by the auxiliary device are minimised if not eliminated.
As illustrated in figure 10, it is possible that the wireless communication apparatus WAP incorporates both main device MDVC and auxiliary device XDVC.
In such a case, the MAC layer of the auxiliary device XDVC is able to deliver to the main management unit contained in the MAC layer of the main device MDVC an auxiliary control information XCLI representative of the operation or of the non-operation of the auxiliary device such that said main management unit is adapted to allow the operation of the main interference reduction means only during the operation of said auxiliary device.
Further, it is no more necessary to analyse the channel state information. As a matter of fact, the group of interfering sub-carriers is well known for this auxiliary device and pre-stored in the main memory means of the main device.
Such an implementation of the invention will allow for the simultaneous operation of for example a WIMAX or a mobile radio and WPAN UWB air interface in a single mobile terminal. The mutual interference will be minimised if not eliminated. The overall WPAN network will not be influenced by the frequency domain coordinated transmission and reception of the co-located WPAN device. The coordinated transmission and reception of the slave WPAN air interface might lead to a reduction of the maximum reachable data rate and/or the reliability of the link. Thus might lead to a reduction in reach of the link.
Another solution exists for reducing the interferences generated between the main device and the auxiliary device. This other solution, based on a frequency shifting, will now explain more in details with reference to figures 1 1 to 14.
More precisely, in the example depicted in figure 1 1 , the interference reduction is controlled by changing the carrier frequencies of the hopping sub-bands by moving the two lower bands slightly low in the frequency domain.
As a matter of fact, the narrowband interferer XDVC lies here near the end of the second sub-band SB2. Thus, by shifting the sub-band SB l with a shift of 100 MHz towards the low frequencies and by shifting sub-band SB2 with a shift of 150 MHz towards the low frequencies, the narrowband interferer XDVC lies now between sub-band SB2 and sub-band SB3.
Of course, the man skilled in the art will choose the frequency shift by taking into account the guard intervals of the MBOA hopping sub-bands.
As illustrated in figure 12, in order to perform this controlled frequency shift, the main device MDVC of the wireless communication apparatus WAP comprises additional interference reduction means ADIFRM for reducing the interference between the main device and auxiliary device. It can be noted that according to this variant of the invention, the frequency shifting permits to minimise, if not eliminate, the interference generated by the main device MDVC towards the auxiliary device XDVC but also the interference generated by the auxiliary device XDVC towards the main device MDVC.
As for the main interference reduction means, the additional interference reduction means ADIFRM includes additional detecting means ADTM for detecting an emission from and/or reception performed by the auxiliary device. An additional control unit ADCU is provided for determining the group of the interfering sub-carriers, and for shifting at least a part of said main band of frequencies including said group of interfering sub-carriers, with a chosen frequency shift.
And this frequency shifting is obtained for example by controlling the transposition frequency of the mixers contained in the radio frequency stage RF.
The additional interference reduction mode ADIRM, performed by the additional interference reduction means ADIFRM is depicted diagrammatically on figures 13 and 14. More precisely, after having detected the operation of the WIMAX device (step 130), the interfering sub-carriers are determined (step 131 ) and the frequencies band is shifted (step 132), for example by a sub-band shifting 140

(figure 14).
Of course it is necessary to indicate this frequency shift to all the devices of the UWB network which are in communication with said main device. This is performed for example by sending control information to these devices. This control information can be sent for example by the MAC layer of the main device through control channels.
Further, as for the main interference reduction means, the additional interference reduction means ADIFRM comprises also additional analysing means ADAM for analysing the channel state information delivered by the channel estimator, additional checking means ADCKM for checking the eventual detection of the operation of the auxiliary device by using information about the interferers, pre-stored in additional memory ADMM.

Further, an additional memory management unit ADMU manages the operation of the additional interference reduction means ADIFRM and in particular stops the operation thereof when the auxiliary device is no more detectable.
In a preferred embodiment, both main and additional detection means are identical as well as both main and additional control units and both main and additional management units.
The sub-band shifting does not reduce the available resources on the air. The data rate needs not to be reduced. Thus no loss of communication performance accurse.
Of course, both main interference reduction mode (notching mode) and additional interference reduction mode (shifting mode) can be performed for a same auxiliary device. This is the case in particular when the narrowband interferer is far enough from the end of a sub-band so that a sole frequency shifting is not enough for eliminating all the interfering sub-carriers. In such a case, the remaining interfering sub-carriers can be notched out by using the main interference reduction mode.
Although the invention has been described with an auxiliary device being a WIMAX device, such an auxiliary device could belong to a mobile radio system defined by a mobile radio standard, like for the example GSM, UMTS, CDMA, EDGE or future beyond IMT-2000 systems under development. An auxiliary device could be a fixed satellite service (FSS) device or a general fixed wireless access device (FWA)..
For an UMTS mobile radio device collocated with an UWB main device, the auxiliary control means which delivers the indication of the operation of the UMTS device can be incorporated in or connected to the well-known L2 and L3 entities of the UMTS device (This is valid for the collocation in general. The UWB device could be collocated with a Wimax terminal, a satellite terminal or another mobile radio terminal.)