Spectrum sharing between wireless systems

Spectrum sharing between wireless systems

Field of the Invention

The present invention relates to digital communications and, in particular, to handling interferences while transmitting and receiving signals in wireless communications systems.

Background of the Invention

As known in the art, a primary consideration in any digital communications system is the channel bandwidth and channel separation required to transmit information. Therefore, digital systems are typically designed to utilize channel bandwidth as efficiently as possible. For example, in systems utilizing frequency division multiplexing, maximum spectral efficiency is obtained by spacing frequency channels very close to one another in an available spectrum.

Minimum carrier spacing is limited in practice, however, by adjacent channel interference. Adjacent channel interference is defined as the interference resulting when carrier frequencies are spaced close enough to one another that information signals received from number of carriers overlap in the frequency spectrum. In practice, the minimum allowable carrier spacing is a function of the bandwidths of the information signals, the practical limitations associated with receiver filtering, and the signal modulation and coding schemes used. Number of design improvement providing increased suppression of adjacent channel interference have been suggested to increase system capacity, relax coding and modulation design requirements, or improve signal quality.

In conventional systems, adjacent channel interference is suppressed in a number of ways. For example, in certain cellular radio systems, adjacent channel interference is avoided through channel allocation schemes in which channels immediately adjacent to one another in frequency are assigned to different spacial cells. Consequently, physical separation reduces mutual interference between adjacent channels. In other communications systems (e.g., satellite and land mobile radio systems), however, suppression of adjacent channel interference by physical separation of adjacent channels may not be possible.

By an alternative conventional approach, during demodulation of a given carrier signal, a bandpass filter centered at an adjacent carrier is used to extract an adjacent channel signal (ACS) at the adjacent carrier. The extracted signal is then used to estimate the adjacent channel signal envelope and carrier and to coherently detect the adjacent channel signal. The detected adjacent channel signal is then waveform shaped, and the estimated adjacent channel carrier and envelope are impressed on the resulting signal. Ideally, the described process provides a reconstructed adjacent channel signal at its carrier frequency. The reconstructed signal can then be passed through a bandpass filter centered at the carrier of interest and subtracted from the received signal to remove the adjacent channel interference.

Such an approach has several limitations, however. For example, analog signal processing using filters and mixers adds undesirable cost and size to a radio receiver, and since the analog components vary with the manufacturing process, Such receivers provide a relatively unpredictable range of performance. Additionally, subtracting a signal at radio frequency requires highly accurate carrier reconstruction and time alignment, as an error as small as half a cycle at radio frequency can cause the adjacent channel signal to double rather than diminish. Furthermore, such use of the adjacent channel carrier (phase and frequency) and envelope (amplitude) implicitly assumes that the radio channels are not dispersive. However, in many practical wireless systems (e.g., D-AMPS and GSM), the symbol rate is sufficiently high that the radio transmission medium must be modeled to include time dispersion which gives rise to signal echoes. Thus, the proposed technique is not always practical for use in many present day applications.

According to another conventional approach, demodulation parameters such as linear or decision feedback equalization filter coefficients are adapted to minimize noise and adjacent channel interference together. Alternatively, spectrally efficient continuous phase modulation (GPM) techniques can be used to reduce the effects of adjacent channel interference.

US 6108517 discloses methods and apparatus for receiving adjacent channel signals wherein adjacent channel interference effects are minimized through joint demodulation of the adjacent channel signals. A channel associated with each signal and each corresponding frequency band is estimated and used to form joint branch metrics for joint sequence estimation. Thus, a baseband processor receives baseband samples corresponding to a certain carrier frequency, and then jointly demodulates at least two information streams corresponding to different carrier frequencies in dependence upon the received baseband samples.

US 5710797 describes a single transducer digital communication receiver which is capable of extracting the data bits of at least one desired signal in the presence of interfering signals of similar type, so as to provide a system in which overlapping transmissions are tolerated and allowed. This publication describes a specific frequency plan, which includes an appropriate digital demodulator that extracts the data bits of the desired signal(s) in the presence of closely spaced signals. The disclosure enables reduced channel spacing in digital communication systems and thereby increases the system capacity (i.e. the number of users per bandwidth unit) without incurring any significant loss in system performance (e.g. power margins, BER, and channel availability). It also allows a reduced power margin that is required to maintain a pre-specified performance level without sacrificing system capacity.

The disclosure of the references mentioned herein throughout the present specification are hereby incorporated by reference.

As noted above, however, minimizing or avoiding adjacent channel interference using the above described systems provides relatively minor improvement with respect to spectral efficiency, and. current suppression mechanisms are inadequate for broad applications. Thus, there is a need for improved methods and apparatus for significantly reducing the impact of adjacent channel interference.

Summary of the Invention

It is an object of the present invention to provide a method and apparatus to minimize interferences created when a number of systems are using the same or adjacent frequency channels.

It is another object of the present invention to provide a method and an apparatus to ensure a pre determined required quality of service in unlicensed band wireless networks.

Other objects of the invention will become apparent as the description of the invention proceeds.

In accordance with an embodiment of the present invention there is provided a method for minimizing interferences in wireless networks comprising at least one base station and a plurality of subscriber terminals, wherein interferences are experienced in the wireless network resulting from the operation of at least one further base station or one further subscriber terminal, belonging to a different network. The method enables allocating time slots for operating at frequencies that are thus affected, and comprises:

providing one or more first subscriber terminal out of the plurality of subscriber terminals and wherein transmissions to the one or more first subscriber terminal are not subjected to these interferences;

providing one or more second subscriber terminal out of the plurality of subscriber terminals and wherein transmissions to the one or more second subscriber terminal are subjected to these interferences;

dividing a time slot allocated for transmission along an interfered channel that experiences interferences from substantially adjacent frequency channels or from a channel operating at a substantially the same frequency as the interfered channel or from both sources, into at least two time sub-frames. One or more of the at least two time sub-frames is reserved for transmitting radio signals to the one or more first subscriber terminal and at least one other time sub-frame of the at least two sub-frames is reserved for transmitting radio signals to the one or more second subscriber terminal; and transmitting a radio frame comprising signals being at frequencies which correspond to the frequencies in which communication is carried between the at least one base station and the plurality of subscriber terminals.

By another embodiment of the invention, the method further comprising:

providing one or more third subscriber terminal out of the plurality of subscriber terminals and wherein transmissions from the one or more third subscriber terminal are not subjected to such interferences;

providing one or more forth subscriber terminal out of the plurality of subscriber terminals and wherein transmissions from the one or more forth subscriber terminal are subjected to these interferences;

dividing a time slot allocated to reception of transmissions along said interfered channel, into at least two time sub-frames, wherein one or more of the at least two time sub-frames is reserved for receiving radio signals from the one or more third subscriber terminal and wherein at least another time sub-frame of the at least two time sub-frames is reserved for receiving radio signals from the one or more forth subscriber terminal; and transmitting radio transmissions towards the at least one base station from the one or more third subscriber terminal and from the one or more forth subscriber terminal, at the respective time sub-frame associated with each of said subscriber terminals.

As will be appreciated by those skilled in the art, it could be that a subscriber terminal which does not experience any interferences in the reception of the transmissions from the at least one base station will not experience any interferences also while transmitting towards that at least one base station, in which case the one or more first subscriber terminal is in fact equal to the one or more third subscriber terminal.

Similarly, a subscriber terminal which does experience interferences in the reception of the transmissions from the at least one base station, might also experience interferences while transmitting towards that at least one base station, in which case the one or more second subscriber terminal is in fact equal to the one or more forth subscriber terminal.

According to another embodiment of the invention, the method further comprises incorporating at least one marking signal indicating a frame beginning or a frame end or both.

In accordance with another embodiment of the invention, the method provided further comprises transmitting and/or receiving a plurality of radio frames, each comprising signals associated with different channels, and wherein the step of dividing a time slot allocated for transmission and/or receiving signals along an interfered channel is carried at each frame for a different interfered channel. Preferably, the step of dividing a time slot allocated for transmission and/or receiving signals along an interfered channel is carried at each frame for a different channel, at a predefined order, and repeats itself every cycle of pre-defined number of frames.

In accordance with yet another embodiment of the invention, the method further comprising associating at least one control signal and/or at least one control message with at least one additional channel comprised in the frame in order to dynamically affect the duration of one or more of the at least two time sub-frames associated with the at least one of the additional channels.

Ί

Preferably, the at least one control signal is used to dynamically affect one or more of the two time subframes associated with the one or more of additional channels. More preferably, the at least one control signal is used to dynamically affect one or both of the time sub-frames associated with the one or both of the channels that are operative at a frequency adjacent to that of the interfered channel.

By yet another preferred embodiment, the at least one control signal is generated based on a load of traffic to be transmitted by the at least one base station to the one or more second subscriber terminal, or on that of the further base station belonging to the other network, or on the load of traffic to be transmitted by the one or more forth subscriber terminal towards the least one base station.

According to another preferred embodiment of the invention, a control message and/or a control signal is transmitted by the subscriber terminal (second or forth), preferably in response to its traffic load thereat.

In accordance with still another embodiment of the invention, there is provided a method which comprises establishing one or more time periods for transmissions that will not cause interferences to the at least one further base station or the one further subscriber terminal, belonging to a different network, for use in one or more time sub-frames, wherein the one or more time sub-frames are used for transmitting radio signals from the base station or from one or more of the subscriber terminals.

According to another aspect of the invention, there is provided a method for use in a wireless link extending between one base station and one subscriber terminal, wherein the wireless link experiencing interferences resulting from the operation of at least one further base station or one further subscriber terminal, belonging to a different network and operative at a frequency that is substantially the same frequency as that in which the wireless link is operative (co-channel) . The method of allocating time slots for eliminating these interferences during transmission comprises:

dividing a time slot allocated for transmission into at least two time sub-frames, wherein a first time subframe out of the at least two time sub-frames is reserved for transmitting radio signals to the one subscriber terminal and wherein a second time sub-frame out of the at least two sub-frames is reserved for use by the different network; and transmitting a radio signal from the one base station to the one subscriber terminal during the first time sub-frame.

Alternatively, or in addition, a similar method is provided for the time slots that are used for transmission from the subscriber terminal to the base station'located at the other end of the wireless link.

According to yet another aspect of the invention, there is provided an access point, e.g. a base station, adapted to operate in a wireless network and comprising: an interface operative to allow communication between said base station and a communication network associated therewith;

at least one radio transceiver operative at at least one frequency and capable of transmitting communication traffic towards a plurality of subscriber terminals and receive communication traffic therefrom;

at least one processor adapted to:

determine existence of interferences caused by radio transmissions at a substantially the same or substantially adjacent frequency occurring during transmission to or reception from said plurality of subscriber terminals;

establish which of the channels carrying traffic to or from said base station experience such interferences;

divide at least one of the time slots allocated for transmission along the channels that experience interferences, into at least two time sub-frames, wherein at least one of the at least two time subframes is reserved for transmitting radio signals to at least a first subscriber terminal out of the plurality of subscriber terminals and wherein at least one other time sub-frame of said at least two time sub-frames is reserved for transmitting radio signals to at least a second subscriber terminal out of the plurality of subscriber terminals, and wherein communication with the second subscriber is subjected to these interferences.

By yet another embodiment, there is provided an access point that is adapted to operate in a wireless network and comprising:

an interface operative to allow communication between the access point and a communication network associated therewith;

at least one radio transceiver operative at at least one frequency and adapted to transmit communication traffic towards a plurality of subscriber terminals and receive communication traffic therefrom;

at least one processor adapted to:

determine existence of interferences caused by radio transmissions at a substantially the same or substantially adjacent frequency occurring during transmission to or reception from said plurality of subscriber terminals;

establish which of the channels carrying traffic to or from the access point experiencing such interferences;

divide at least one of the time slots allocated for reception of traffic along the channels that experience interferences, into at least two time sub-frames, wherein at least one of the at least two time sub-frames is reserved for receiving radio signals from at least a first subscriber terminal out of said plurality of subscriber terminals and wherein at least one other time sub-frame of the at least two time sub-frames is reserved for receiving radio signals from at least a second subscriber terminal out of the plurality of subscriber terminals, and wherein communication with the second subscriber is subjected to these interferences. Preferably, the at least one processor is further adapted to incorporate at least one marking signal indicating a frame beginning or a frame end or both.

By still another embodiment, the at least one processor is further adapted to associate at least one control signal with at least one additional channel comprised in that radio frame in order to dynamically affect the duration of the at least one time sub-frames associated with the at least one of the channels.

Preferably, the at least one control signal is used to dynamically affect the at least one time sub-frame associated with one or both additional channels that are operative at a frequency adjacent to that of the interfered channel.

In accordance with ' another embodiment of the invention, the at least one radio transceiver is adapted to transmit and receive a plurality of radio frames, each comprising signals being at different frequencies, and wherein the at least one processor is adapted to divide at each frame a time slot allocated for transmission and/or receiving signals along an interfered channel being at a different interfered frequency (channel) than the preceding frame. Preferably, the at least one processor is adapted to select an interfered channel and divide the time slots thereof as explained above at a predefined order of channels, and more preferably, that selection of channels is repeated every cycle of predefined number of frames.

According to yet another aspect of the invention, there is provided a subscriber terminal adapted to operate in a wireless network and comprising:

an interface operative to allow communication between the subscriber terminal and at least one access point (e.g. a base station);

at least one radio transceiver operative at at least one frequency and adapted to transmit communication traffic towards the at least one access point and receive communication traffic therefrom;

at least one processor adapted to:

determine existence of interferences caused by radio transmissions at a substantially the same or substantially adjacent frequency occurring during transmission to or reception from the at least one access point;

establish which of the channels carrying traffic to or from the subscriber terminal experience such interferences (in case there are more than one channel associated with that subscriber terminal);

notifying the at least access point associated with that channel of the interferences detected;

wherein the at least one radio transceiver is adapted to receive radio transmissions within a time sub-frame allocated by the at least one access point for transmitting radio transmissions to subscriber terminals that experience interferences in their communication with the at least access point station, and wherein the at least one radio transceiver is further adapted to transmit radio transmissions within a time sub-frame allocated by said at least one access point for receiving radio transmissions from subscriber terminals that experience interferences in their communication with said at least one access point.

Preferably, the at least one processor of the subscriber terminal is further adapted to incorporate at least one marking signal indicating a frame beginning or a frame end or both.

By another embodiment of the invention, the at least one processor of the subscriber terminal is further adapted to associate at least one control signal with at least one additional channel comprised in the radio frame in order to dynamically affect the duration of the at least one time sub-frame associated with the at least one additional channel. More preferably, the at least one control signal is used to dynamically affect the at least one time sub-frames associated with one or both additional channels that are operative at a frequency adjacent to that of the interfered channel.

Brief description of the Drawings

FIG. 1A - presents a schematic illustration of a radio network;

FIG. IB - presents a schematic illustration of an Access Point in accordance with the present invention;

FIG. 1C - presents a schematic illustration of a subscriber terminal in accordance with the present invention;

FIG. 2A - illustrates a two radio networks setup, overlaid and not co-located wherein interference problems are solved in accordance with the present invention;

FIG. 2B - illustrates a three radio networks partially overlaid with indoor interferences, wherein interference problems are solved in accordance with the present invention;

Fig. 3 presents a schematic time domain MAC frames, composed in accordance with the present invention;

Fig. 4 illustrates a downlink Tx composed to avoid interferences;

Fig. 5 exemplifies a downlink Tx arrangement for number of frames N=4, which experiences strong co-channel interferences;

Fig. 6 illustrates an uplink Tx example arrangement for N=3; and

Fig. 7 presents a schematic time domain MAC frame composed in accordance with another embodiment of the present invention.

Detailed Description of the Invention

A better understanding of the present invention is obtained when the following non-limiting detailed description is considered in conjunction with the following drawings in which:

Fig. 1A describes a part of radio network constructed in accordance with an embodiment of the present invention. A schematic illustration of that part of the radio network 2 is provided in Fig. 1A which comprises an AP (access point, e.g. a base station) 4 being in a wireless communication with a number of subscriber terminals, 6, 6' and 6.

Fig. IB illustrates an exploded view of access point 4, which comprises in this present example, among others, an interface 12 operative to allow the connectivity of access point 4 to the feeding transmission network, and radio transceiver 14 which allows transmitting ,and receiving radio transmissions from each of the subscriber terminals connected to this access point. Access point 4 further comprises a processor 16 operative to measure and evaluate the interferences in the transmission received resulting from any one of a number of reasons, such as a subscriber terminal is too close to another base station wherein a channel at an adjacent frequency is used, a subscriber terminal is located at the proximity of the edge of the relevant cell, and the same channel frequency is used at the neighboring cell, etc. Similarly, a subscriber terminal, (6 as shown in Fig. 1C) comprises an interface 22 operative to allow its connection to the user equipment and/or to the terminal equipment, a radio transceiver 24 which is operative to transmit and receive radio transmissions to and from access point 4, and processor 26 operative to measure and evaluate the interferences in the radio transmissions received.

As explained above, there could be a number of reasons why such interferences occur. Some examples of layouts which may lead to the creation of such interferences are illustrated in Figs. 2A and 2B.

Fig. 2A illustrates two base stations 30 and 34, each belonging to a different radio network, where they are overlaid and not co-located. Subscriber terminals 32 and 32׳, which belong to the network serviced by base station 30 are located close to base station 34, and therefore might be affected by the transmission to and from that base station, when the transmissions are at frequencies adjacent to those used by terminals 32 and 32׳, respectively.

Fig. 2B presents a schematic illustration of a somewhat more complicated scenario of three radio networks partially overlaid. In addition to the base stations and terminals shown in Fig. 2A, there are also terminals 36 and 36׳ connected to base station 34', and a wireless Local Access Network (LAN) 36.

In order to overcome such interferences by one of the embodiments of the present invention, let us consider an example of a base station that operates in a 3 time frames cycles (referred to as MAC״ Frames - Media Access Control Frames), where each such time frame comprises a time period (DL Tx) for it to transmit downlink (i.e. towards the subscribers) and a time period (Rx) for receiving the subscribers' transmissions. According to the present invention embodiment demonstrated in Fig. 3, each the two time periods DL Tx and Rx is further divided into two time sub periods. Let us now consider the first frame in the cycle where DL Tx is divided into two time sub periods. In the first one, for the duration designated as Bl, the base station will transmit to those subscribers' terminals operating at frequency F3 and which do not experience interferences from others. In the other time sub period, designated as C, the base station will transmit to those subscribers' terminals operating at frequency F3 but which do experience interferences

<img file="IL160832A_D0001.tif" />

from others. The underlying idea of this embodiment of the invention is that during time slot C there will be no interferences from others for the reasons that will be explained further on. Similarly, the Rx period of that first frame, is divided into two time sub-periods. In the first one, for the duration designated as El, the base station will receive transmissions from the subscribers' terminals operating at frequency F3 and which do not experience interferences from others. In the other time sub-period, designated as F, the base station will receive transmissions from those subscribers' terminals operating at frequency F3 but which do experience interferences from others. Thus, when interferences are detected at a subscriber's terminal, it will initiate a process whereby an appropriate slot be found within time sub-period F during which it will transmit its radio transmission towards the base station with no interferences.

However, as can be appreciated by those skilled in the art, it would be rather impractical to use time sub periods having a fixed length, and it would be highly preferred to have them varying so as to cater to the instantaneous needs arising, e.g. traffic loads at the downlink or uplink directions, overall traffic to and from the terminals experiencing interferences, etc.

According to an embodiment of the invention, in order to achieve adaptation to time varying traffic loads, the length of one or more of the time sub-frames at each of the adjacent frequency channels is controlled. Consequently, in case where there are quite a few subscribers' terminals that suffer from such co-channel and/or adjacent channel(s) interferences, the time subframe at one or both of the adjacent channels where the base stations transmit at F2 and/or F4 to channels that experience no interference shall be shortened, so that those terminals that had suffered from interferences shall have an appropriate longer time slot to transmit at.

As may be seen from Fig, 3, not all of the frames should be handled in the manner/ described above. In the example shown in this Fig., in frame No. 2 there is only one time slot for the base station to transmit, and one time slot to receive from the terminals associated with the base station, so preferably, the terminals' which experience interferences will not transmit to nor receive from the base station any radio transmissions. Similarly, these terminals are not operative in frame 3 (in which there is more time allocated to the terminals transmitting in the uplink direction). In the consecutive frame (No. 4) again there is a division to time subframes of frame No. 1 (but possibly at different time lengths) . Thus, in every 15 msec (if each of the frames is 5 msec long) cycle, the terminals with the interferences will be operative during one third of the frames.

One of the essential conditions to successfully carry out this embodiment of the invention, is that all channels will be synchronized to ensure that all respective time frames of the different channels shall start together, as otherwise there is a very little chance to obtain the desired effect, i.e. that the adjacent channel will stop transmitting when the transmissions are sent to the terminals suffering from interferences. In order to achieve such synchronization, it would be preferred to incorporate an indication marking the beginning of a frame or the end of a frame or both. As would be appreciated by those skilled in the art, such an indication may be either incorporated in

<img file="IL160832A_D0002.tif" />

each of the frames or only in some of the frames, e.g. a first frame in a cycle or in any other pre-defined period of time.

Another example is shown in Fig. 4. In this example, again there is a 4 frames cycle, but in this example 6 channels Fl to F6 are used. During frame 1, both F3 and F6 will control the length of the time sub-frames of their adjacent channels. F3 will control the duration of F2 and F4 time sub-frames, while F6 will control the length of F5 time sub-frames. In this way, all the terminals which communicate with the base station using channels at F3 or F6 frequency and are effected by interferences will have a time sub-frame within frame 1 to receive transmissions without interferences (F_3T! and F_6TI, respectively) and to transmit without interferences (F_3r!) if required.

At shown in this example, at the second time frame, a similar process is carried out, but with the difference that the control of the length of the time sub-frames of their adjacent channels is now made by channels F2 and F5. F2 will control the duration of Fl and F3 time subframes, while F5 will control the length of F4 and F6 time sub-frames. In this way, all the terminals which communicate with the base station using channels at F2 or F5 frequency and are effected by interferences will have a time sub-frame within frame 2 to receive transmissions without interferences (F_2T! and F_5Ti, respectively) and to transmit without interferences if required (not in this example).

Moving on to frame 3, a similar situation is illustrated wherein the control of the length of the time sub-frames of their adjacent channels is now made by channels Fl and F4. Fl will control the duration of F2 time sub-frames, while F4 will control the length of F3 and F5 time sub-frames. In this way, all the terminals which communicate with the base station using channels at Fl or F4 frequency and are effected by interferences will have a time sub-frame within frame 2 to receive transmissions without interferences (F_1TI and F_4T!, respectively) and to transmit without interferences if required (not in this example) . When this time frame is completed, the 3 frames cycle illustrated in Fig. 4 is completed and frame 4 presented, is in fact a repetition of frame 1 of the next frame. Alternatively, a 4 frames cycle could be decided upon. In this case frames 1 and 4 are used as shown in this Fig. and such a cycle could be used for example when there is a higher traffic load that is associated with terminals that transmit and received in the F3 and F6 channels.

In the above examples, the illustrated cycle's MAC frames are of equal length (duration). However, as will be appreciated by those skilled in the art, there could be a number of allowed MAC frame durations. Preferably, the actual value (or any other suitable division policy) will be decided by operators of the neighboring base stations, who will co-ordinate this parameter between themselves .

As was explained above, in order to achieve the required results, the activities along the various channels to and by the neighboring operators should be synchronized. For example, a MAC frame may start synchronization by using a GPS marking signal, at the beginning of the Tx activity. In order to notify what kind of sync is used, the base station will, at regular intervals, insert SYNC_MARKING SIGNALS before the frame start. In this example, o The access point (base station in our example) using GPS for sync will insert SYNC_MARKING SIGNALS type 1;

o The AP (Access Point) that synchronize its frame after another AP will insert SYNC_MARKING SIGNALS type 2;

The AP free-running will insert SYNC_MARKING SIGNALS type 3; and o More than one SYNC_MARKING SIGNAL shall be available, in order to differentiate between Access Points using the same frequency.

The division of the time slot between Tx/Rx may be:

Programmed by operators, after co-ordination, and changed only by the appropriate management system; and/or

Dynamically changed.

As was previously explained, it is highly desired to achieve a good spectrum utilization efficiency to use channels at adjacent frequencies (which cause the problems that the present invention seeks to solve). For optimal sharing, a limited number of channel widths shall be defined. In addition, a guard channel may be needed, particularly when having different channel spacing between systems occupying adjacent spectrum.

Typically, a cycle of N MAC frames is defined. N may be equal to 3, but if the interference level is high, N preferably equal to 4 or higher, should be used.

In an example where there is only one adjacent channel associated with another system, and no co-channel interferences are experienced, N=1 could suffice.

In order to summarize the above, the following slots were defined in Fig. 3 for a system using a channel at Fe frequency, using a rotating wheel period of 3 MAC frames:

slots Al, A2, A3, each lasting for the DL MAC frame duration;

slots Bl, B2, B3, each lasting for a duration of the transmissions which do not experience interferences. The duration of slots Bl, B2, B3 may be limited to a minimum value;

slot C, defined during Al MAC Frame, and starting after Bl, when no adjacent channel, which introduces interference, is operating;

In each of the slots, when using IEEE 802.16 MAC protocol, the corresponding down-link and up-link MAP, scheduling the traffic, will be transmitted (same principle as used for AAS - Advanced Antenna Systems);

In every slot, the transmission may be carried out while using a different level of power;

The SYNC_MARKING SIGNAL, defined above, is transmitted in the MAC Frame containing the slot C.

The designations of the various time slots defined above in connection with Fig. 3 will be used hereinafter for the description of the rest of the figures, and unless specified otherwise, will have the same meaning, mutates mutandis, of those referred to in connection with Fig. 3.

Down-link adjacent channel interference

As explained above, Fig. 4 presents a preferred way of handling adjacent channel interferences.

A neighborhood AP, that hears in-band other system ST (Subscriber Terminal) to AU transmission, and NOT working in an adjacent channel to that system, will operate only in the slots A2, A3. This will leave for the neighborhood system min. 66% of bandwidth. An example is an IEEE 802.11 type AP operating in the near vicinity of an indoor of an IEEE 802.16 type of subscriber terminal. The 802.16 type terminal will request its AP to schedule downlink and up-link transmission only during Al slots. In this way, both 802.16 and 801.11 type of systems will be able to work properly, and if required, guarantee pre-defined quality of service.

In the case where the interference is caused by an AP working on a adjacent frequency, there may be a number of subscribers, located in its vicinity, that hear the adjacent channel relatively loud. The AP working on Fn (F3 in the example) has to transmit to these subscribers in a slot, when the other AP is silent. The mechanism provided for slots Bl on F_n, B2 on F_n+1, B3 on Fn-! and C, allow to separate the transmission to interference affected users from those not affected and eliminate the adjacent channel interference:

Slot C is used for ST affected by interference

The transmission duration on adjacent frequencies can be controlled by the system e.g. by controlling the transmission duration of the systems working on adjacent frequencies during Bl; for the other MAC frames, the system will schedule transmission only to subscriber terminals not affected by interference.

The actual control procedure can preferably take one of the two following forms:

o The AU using the slot C, hops on the adjacent channel frequency and sends one signal requesting for lower transmission time or another signal allowing for higher transmission time (these signals are noted *♦ in Fig. 4) .

o The AU instructs an ST to send the appropriate control signal in the reserved slot.

o If communication is done between interoperable systems, MAC messages may be used.

Preferably, for every MAC frame, there will be an operators' agreed limit on the minimum time guaranteed for transmission on Bl, B2, B3 slots, for every frequency. For example, if this time is 50% of a downlink frame, a system will be able to use (50%+50% +100%) / 3 = 67% of the time resource. The operation without interference could be limited to 50% / 3 = 17%.

Down-link co-channel interference

Even in FDD or TDD, with synchronized Tx/Rx periods, there could be BS to ST (Subscriber Terminal) co-channel interference, when two operators use the same frequency in adjacent geographical areas.

A BS operator may decide to use only half of the slot C, and leave to the other base station the other half; based on radio measurements the other AU will detect the interference free period.

Through operators' coordination process, an agreement may be reached for using N=4 and to distribute the use of MAC Frames between the operators. The new MAC frame arrangement is shown in Fig. 5. The SYNC_MARKING SIGNAL will be inserted only by one of the systems working on the same frequency.

The co-channel interference can be controlled for example in MAC Frame 3, system 2 may insert signals at F3 to be decoded by system 1. System 1 may also control system 3 in frames where the synchronization marking signal is not inserted.

Up-link adjacent channel interference

The up-link interference is determined by temporary transmission of STs belonging to the other systems, and located in the AP vicinity or transmitting with high power. Fig. 6 illustrates an example of an arrangement wherein N=3.

Next, two possible interference avoidance scenarios will be exemplified:

By the first scenario, a voluntary up-link transmission policy is established, in which interfering stations' transmissions will be scheduled in a way that will not affect the AP up-link traffic.

The neighbor APs should schedule the transmission of those STs in Rx slots, in which the victim AP will not schedule receive activity. Lets use Fig. 2A for discussion. The station 32 is located in the vicinity of AP 34, being interfered by 34 and also causing interference thereat. AP 30, with which ST 32 is associated, is aware of the situation, and shall schedule the transmission of 32 in a slot in which AP 30 does not expect receiving traffic.

By the second scenario, interference-free receive slots (slot F in Fig. 6) will be established. No traffic will be allowed on the up-link adjacent channels, during these slots.

The AP will have control on the duration of transmission, for the adjacent frequencies, using the same signaling procedure as for down-link, in the same MAC frame. Power control may be additionally used.

Uplink co-channel interference

A BS may decide to use only half of the slot F, and leave to the other base station the other half; based on radio measurements the other AU will detect the interference free period. Through operators' coordination process, the operators may agree between themselves on using N=4 and distribute the use of MAC Frames.

Signaling procedure o Signaling procedures may use MAC messages, FYI signaling or a combination of both.

MAC Messages have the usage limited to interoperable systems;

PHY (Physical Layer) only signals, carrying same information as MAC messages, will preferably be designed such that they:

are tolerant to combining over the air, when coming from different sources; and

- have more general applicability, by not being technology specific.

o Message content:

For interference control, there are 8 messages:

- Restrain downlink transmission, use TIME_STEP_1

- Restrain downlink transmission, use TIME_STEP_2

- Restrain up-link transmission, use TIME_STEP_1

- Restrain up-link transmission, use TIME_STEP_2

- Increase downlink transmission, use TIME_STEP_1 Increase downlink transmission, use TIME_STEP_2 Increase up-link transmission, use TIME_STEP_1 Increase up-link transmission, use TIME_STEP_2

TIME STEP_1 may be 2% of MAC Frame duration, and TIME_STEP_2 may be 5% of the MAC Frame duration. STEP_2 may be necessary when a user transmitting during interference free period has much data to transmit, o PHY signaling

Timing:

Signal to be send at the end of MAC FRAME

Signal duration: 1 symbol time, when using OFDM256 FFT

PHY signaling, using a multi-carrier scheme, may be used.

Transmission is done by inserting energy in message specific bins.

• Reception is based by recognition of energy and decision regarding the transmitted message and its correctness.

The reception process should be tolerant to power that may be injected due to interference

Design tolerant to collisions

Separate down-link and up-link control directions

Procedure:

The most narrow channel (for example: between 10MHz and 20MHz, the narrowest channel is 10MHz) is spit into N subbands, numbered from 1 to N; an example for N=32 is given in Table 2.

The part of the channel used for signaling shall preferably be selected so that it will be compliant with the spectrum mask of the widest channel (in previous described situation, 20MHz).

Every message will preferably also include check bins for confirmation purposes.

As shown in Table 1, by dividing the proper signal band region (s) to the right number of bins, (in this example 12) all 8 above defined messages and their respective check bins can be transferred.

Table 1 - Bin allocation per sub-band

<td> Bin Number</td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td><td> 9</td><td> 10</td><td> 11</td><td> 12</td>

<td> Sub-band Number</td><td> 5</td><td> 7</td><td> 9</td><td> 11</td><td> 13</td><td> 15</td><td> 17</td><td> 19</td><td> 21</td><td> 23</td><td> 25</td><td> 27</td>

Table 2 - Example of message coding

<td> Bin 12</td><td rowspan="2"> UL bin Check</td><td> DO</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td> o</td>

<td> Bin 11</td><td> DI</td><td></td><td></td><td> &gt;&gt;</td><td></td><td></td><td></td><td> &gt;&gt;</td><td></td>

<td> Bin 10</td><td rowspan="2"> DL Bin Check</td><td> DO</td><td></td><td> &gt;&gt;</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td> Bin 9</td><td> DI</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td> Bin 8</td><td colspan="2"> STEP2 UL</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td> Bin 7</td><td colspan="2"> STEP1 UL</td><td></td><td></td><td> &gt;&gt;</td><td></td><td></td><td></td><td></td><td></td>

<td> Bin 6</td><td colspan="2"> STEP2 DL</td><td></td><td></td><td></td><td></td><td></td><td> &gt;&gt;</td><td></td><td></td>

<td> Bin 5</td><td colspan="2"> STEP1 DL</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td> Bin 4</td><td colspan="2"> Increase UL</td><td></td><td></td><td></td><td></td><td></td><td></td><td> &gt;&gt;</td><td></td>

<td> Bin 3</td><td colspan="2"> Increase DL</td><td></td><td></td><td></td><td></td><td></td><td> &gt;&gt;</td><td></td><td></td>

<td> Bin 2</td><td colspan="2"> Decrease UL</td><td></td><td></td><td></td><td> &gt;&gt;</td><td></td><td></td><td></td><td></td>

<td> Bin 1</td><td colspan="2"> Decrease DL</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td> Message</td><td colspan="2"></td><td> Restrain downlink transmission, use TIME STEP 1</td><td> Restrain downlink transmission, use TIME STEP 2</td><td> Restrain up-link transmission, use TIME STEP 1</td><td> Restrain up-link transmission, use TIME STEP 2</td><td> Increase downlink transmission, use TIME STEP 1</td><td> Increase downlink transmission, use TIME STEP 2</td><td> Increase up-link transmission, use TIME STEP 1</td><td> Increase up-link transmission, use TIME STEP 2</td>

o SYNC-MARKING SIGNAL signals

The SYNC_MARKING SIGNALS group should be selected so that it will allow Access Points operating at the same frequency, to use different signals.

Following Table 3 shows a possible bin allocation for different SYNC_MARKING SIGNALS.

Table 3 - An example of bin allocation per SYNC_MARKING

SIGNALS

<td> Sub-band number</td><td> 6</td><td> 8</td><td> 10</td><td> 12</td><td> 14</td><td> 18</td><td> 20</td><td> 22</td><td> 24</td><td> 26</td>

<td rowspan="3"> SYNC_MARKING SIGNAL Type 1</td><td> Y</td><td></td><td></td><td> y</td><td> y</td><td></td><td></td><td></td><td> y</td><td></td>

<td></td><td> y</td><td></td><td></td><td> y</td><td> y</td><td></td><td></td><td></td><td> y</td>

<td> Y</td><td></td><td> Y</td><td></td><td></td><td> y</td><td> y</td><td></td><td></td><td></td>

<td rowspan="3"> SYNC_MARKING SIGNAL Type 2</td><td></td><td> y</td><td></td><td> y</td><td></td><td></td><td> y</td><td> Y</td><td></td><td></td>

<td></td><td></td><td> Y</td><td></td><td> y</td><td></td><td></td><td> Y</td><td> y</td><td></td>

<td></td><td></td><td></td><td> y</td><td></td><td> y</td><td></td><td></td><td> y</td><td> y</td>

<td rowspan="3"> SYNC_MARKING SIGNAL Type 3</td><td> Y</td><td></td><td></td><td></td><td> y</td><td></td><td> y</td><td></td><td></td><td> y</td>

<td></td><td> y</td><td> Y</td><td></td><td></td><td> y</td><td></td><td> Y</td><td></td><td></td>

<td></td><td></td><td> Y</td><td> y</td><td></td><td></td><td> y</td><td></td><td> y</td><td></td>

Example: Start-up operation

At the first system, the Access Point will start its operation by going through the following steps:

Making clear channel assessments

Trying to find a number of free consecutive channels, suitable for its operation, adjacent to systems using the same channel spacing as his own

Analyzing other systems in the area. If other systems are found, then:

• If the Access Point does not have GPS sync., searching for the system having highest sync, status (highest: GPS, medium: free running, lowest: synchronized) • Determining the number of A slots in the MAC Frame rotating wheel, for example: N=3, N=4, etc.

• Determining the slots of type Al (SYNC_MARKING SIGNAL) • Calculating, according to channel shift, the relative position of its Al slot.

For the first installed system in a geographical area, the Subscriber Terminal will start its operation by going through the following steps:

o Searching for MAC Frame start and trying to receive the required information regarding the UL MAP in the B_n slots o If possible, trying to make the network entry first in El, E2, E3 slots.

According to another embodiment of the present invention, a similar process may be carried for each of the MAC Frames, as demonstrated in Fig. 7. Time allocation:

i. During the downlink Tx period

a. Each Access Point shall have two different transmission periods. The first transmission period will start at the beginning of the MAC frame. The point in time for the second transmission period to start will be selected in a way to avoid overlapping in time with any adjacent channels transmissions. The start of the second transmission period and the end of both transmission periods shall be marked, in order to allow other Access Points to evaluate the length of the interference-free reservated duration.

ii. During the downlink receive period:

a. Each Access Point shall have two different reception periods, where the first period will start at the beginning of the MAC Frame.

b. The Access Point shall use marking signals, indicating the end of both

i. Each Access Point will have two different Receive periods, where the first period shall start at the beginning of the MAC frame;

ii. The Access Point will use marking signals, to mark the end and start of both reservation periods. As will be appreciated by those skilled in the art, a time gap between the marking signals and the actual up-link transmission is likely to occur, due to Rx/Tx transition times.

iii. Before the END_OF_MAC_FRAME, 7 slots are reserved, for:

1. sending periodically and/or occasionally the SYNC_MARKING SIGNAL described before;

2. Sending messages to control the start and the end of Tx and Rx transmission or reception periods;

a. two messages may be sent with the same PHY signal, as described before;

b. An AP may receive messages from systems working on upper and lower adjacent frequencies; if these messages request contradictory actions, the Access Point will determine the appropriate course of action to be taken,

- Signaling procedure

a. Same signaling procedure, as described before, may be used.

- Co-channel interference

In this case, every AP will try to create different interference-free periods. The number of control slots should be increased by three, to allow the second AP to create its own interference free periods.

It is to be understood that the above description only includes some embodiments of the invention and serves for its illustration. Numerous other ways of managing various types of compressed signals in telecommunication networks may be devised by a person skilled in the art without departing from the scope of the invention, and are thus encompassed by the present invention.