Mitigation of wireless transmit/receive unit (wtru) to wtru interference using multiple antennas or beams

The present invention relates to a wireless communication system. More particularly, the present invention relates to mitigating a wireless transmission / reception unit (WTRU) for WTRU interference in a wireless communication system.

Conventional wireless transmission / reception units (WTRUs) typically comprise a single omni-directional antenna that transmits and receives in the same way in all directions. However, using these antennas significantly wastes resources from WTRU since most of the energy of a WTRU is used to transmit and receive Go in directions that differ from the intended one. More significantly, this wasted energy is experienced as interference similar to noise by nearby WTRUs. Such interference is especially momentary in cases where the uplink frequency (UL) of one WTRU is either the same or close to the downlink frequency (DL) of another WTRU. This concept is illustrated in Figure 1.

Figure 1 shows a WTRU 102 that transmits omni-directionally. The WTRU 104 has an omnidirectional reception beam 112. When the two WTRUs are physically and spectrally close, the WTRU 104 exhibits significant levels of interference and performance degradation. The interference radius 110 of the interfering WTRU 102 is

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determined by its own transmission level, the sensitivity of the receiving WTRU 104, the antenna pattern of the WTRU 104, and the level of the convenient signal of the WTRU 104. The degradation of perfor The experience experienced by WTRU 104 reduces the relationship between signal and interference (SIR) and, therefore, the relationship between signal and interference plus signal noise received by it. If significant enough, the interference 120 caused by the WTRU 102 can lead to reduced data rates, loss of connection, and / or poor signal quality. This phenomenon is known as WTRU interference to WTRU (mobile station (MS) -MS).

As described above, WTRUs that use omni-directional antennas lack technology to preferentially control antenna gain to minimize the transmission of unwanted signals to nearby WTRUs. Similarly, the use of such antennas prevents WTRUs from rejecting interfering signals emitted from unwanted sources that include other nearby WTRUs. Typically, only base stations have been equipped with components and technology to maximize the gain of antenna in a convenient direction, simultaneously limiting the reception of signals in the addresses of interfering devices.

According to Elio, it is convenient to have a WTRU that

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You can maximize antenna gain in a convenient direction and / or selectively receive signals from a convenient address to minimize MS-MS interference.

The present invention relates to a method and apparatus for mitigating a wireless transmission / reception unit (WTRU) interference to WTRU in a wireless communication system. The multiple antenna elements of a WTRU are used to control the reception gain of the WTRU antenna. Similar control is applied to a transmitting antenna to reduce emissions to nearby WTRUs.

In an alternative embodiment, the multiple antenna elements are used to form a plurality of predetermined fixed antenna beams. Then the WTRU will Read and switch to one of the default beams that reduces interference from nearby WTRUs. The same beam pattern is used when a transmission is made to reduce the interference caused to nearby WTRUs.

In an alternative embodiment, a WTRU comprises an antenna system and receives spectral arrangement information. Using this spectral information, the. WTRU performs a transmission to avoid spectrally adjacent WTRUs. Alternatively, the WTRU scans transmission frequencies for high energy sources. The WTRU then determines the addresses of /

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transmission of any high energy source (and, therefore, close) and transmits on its antennas in order to avoid a transmission in the direction of high energy sources.

A more detailed understanding of the invention can be obtained from the following description, given by way of example and to be understood together with c on the accompanying drawings, where:

Figure 1 shows a wireless transmission / reception unit (WTRU) that transmits omnidirectionally and interferes with a nearby WTRU;

Figure 2 illustrates a part of the receiver of a WTRU comprising an adaptive antenna system;

Figure 3 illustrates a WTRU using an adaptive antenna system;

Figure 4 illustrates two WTRUs in a state of reciprocal interference with each other;

Figure 5 illustrates a system of switched beam antennas with their predetermined beams formed;

Figure 6 illustrates a WTRU using a system of switched beam antennas; and Figure 7 illustrates two WTRUs in a state of asymmetric interference with each other.

Next, the expression wireless transmission / reception unit (WTRU) includes, but is not limited to

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elio, a user equipment, a mobile station, a subscriber unit or fixed or mobile, a pager, or any other type of device capable of operating in a wireless environment. When reference is made below, the term "base station" includes, but is not limited to, a Node B, a site controller, an access point or any other type of interface device in a wireless environment.

Although the following embodiments are described in terms of WTRU interference to WTRU, the technology disclosed herein is also applicable to interference scenarios from base station to base station. For example, the levels of interference from access point (AP) to AP, where the downlink of a first AP interferes with the uplink of a second AP, can be mitigated using the technology disclosed herein.

Additionally, although you make them below they are described first in two dimensions, some of. the beams can be elevated, with a different zimuts.

In a first preferred embodiment, adaptable antennas, that is, a system of adaptive antennas, are employed in a WTRU receiver to protect against interference from a nearby WTRU. Unlike the unique antennas used by conventional WTRUs, (which

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they have approximately omni-directional antenna patterns (see Figure 1)), adaptive antenna systems are capable of generating antenna patterns that are dynamically adjusted in real time to adapt to current radio conditions. When used in a WTRU, an antenna system continuously monitors its radio frequency (RF) environment and, in particular, monitors signals received from a base station in service and any interference received.

A signal processing unit, also in the present WTRU, is used to calculate antenna weights by which the signals received in ca are multiplied It gives antenna element. These antenna weights serve to form the WTRU beam pattern. Since the antenna system constantly monitors radio changes, the signal processing unit continually recalculates the antenna weights to optimize the WTRU antenna pattern. The antenna weights are calculated either: 1) to maximize the relationship between signal and noise (SNR) or the relationship between signal and noise plus interference (SNIR); or 2) to minimize the interference signals received; or 3) to minimize the interference received while maintaining the received signal levels in an acceptable constant. Next, reference will be made to these three optimization alternatives jointly as the three

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Optimization alternatives An embodiment of a part of the WTRU receiver described above is shown in Figure 2.

The antenna elements 202_lz 202_z and 202_N in Figure 2 they are arranged in a linear configuration to form an antenna system 208. It should be understood that a linear, circular, planar, or other 2 or 3 dimensional antenna arrangement can be used to form an antenna system . The signals received in the antenna system 208 depend on the location of the antennas 202_lz 202_z and 202_N and of the adaptive weights w w_lf w₂ and w_N applied to the received signals. Alternatively, adaptive delays and gain combinations could be used instead of these complex weights. Any method to adjust these weights w_lz w₂ and w_N can be used to reach the three alternatives Optimization vases discussed above. For example, sets of suitably quantified weights can be tested one after another until a suitable set is found. A signal processor 220 sends the determined antenna weights, w_lz . w₂ and w_N, to a signal weighting unit 230. In the signal weighting unit 230 the signals originally received 203_lz 203₂ and 203_N are combined with calculated weights w_lz w₂ and w_N respectively, and then

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combine to form a unique weighted signal 231.

The use of adaptable antennas in this way allows WTRUs to form directional beam patterns to achieve any of the three optimization alternatives discussed above. When creating such patterns It is directional beam, adaptable antennas also create nullities. Nullities are merely low gain antenna directions. Figure 3 illustrates this concept. A WTRU 302 is shown with an antenna system 310 that directs a beam pattern 320 towards a base station 330. The antenna system 310 also directs the annulments 321, approximately toward WTRU 304, a nearby source of WTRU interference to WTRU (MS-MS). In this example, null beams 321 have the effect of canceling or minimizing interference caused by signals transmitted in the uplink (UL) direction from WTRU 304.

In a second preferred embodiment, an adaptive antenna system is used to select antenna weights in order to achieve one of the three optimization alternatives discussed above. The WTRU then uses antenna weights derived from the selected weights to transmit to a base station . It is important to note that the derived transmission weights are chosen in order to preserve the essential shape and location of the beam created for the

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receiver. As an example, the derived transmit antenna weights could be the same as the selected antenna weights for received signals.

Transmission with antenna weights derived from such a horn as described above is particularly useful when a transmitting WTRU is in a state of reciprocal interference with a nearby WTRU. WTRUs are described in a state of reciprocal interference when, for example, the UL frequency of a first WTRU is near or is the same as the DL frequency of a second WTRU and the DL frequency of the first WTRU is near or is the same than the UL frequency of the second WTRU. For illustrative purposes, Figure 4 shows two WTRUs, 402 and 404, in a state of reciprocal interference with each other. UL frequency fl of the WTRU 404 is very close to the DL fl 'frequency of the WTRU 402. Similarly, the UL f3 frequency of the WTRU 402 is very close to the DL f3' frequency of the WTRU 404. Therefore, WTRUs 402 and 404 are in a state of reciprocal interference with each other, where both WTRUs experience MS-MS interference when the other is transmitting.

In communication systems that use time division duplex (TDD), WTRUs transmit and receive signals on the same frequency. In the absence of alignment, such WTRUs may experience interference

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reciprocal. For example, if two TDD WTRUs are assigned different frequencies or time slots and their respective frequencies are close or their timings are not properly aligned, or both, these WTRUs may experience reciprocal interference.

In the same manner as described above in the first preferred embodiment, the WTRUs s in accordance with the present embodiment use antenna weights to optimize the signal quality of suitable signals, in accordance with one of the three optimization alternatives defined above. However, in the present embodiment, the WTRUs derive antenna weights from the receiving antenna weights selected to transmit in the UL direction. By using such derived antenna weights to form directional transmission beams, the energy directed towards the neighboring WTRUs will be reduced, which serves to prevent nearby WTRUs from experiencing MSMS interference.

In a third embodiment, a switched beam / switched antenna (SBSA) system is used in a WTRU receiver to protect against nearby WTRU interference (s). An SBSA forms, either multiple default beams, a subset of which is selected to be used at any given time, or

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well, it forms a set of beams from a larger set of predetermined beam positions. It should be noted that one of these formed beam patterns can be an omni-directional beam pattern. An example of these predetermined beam patterns is illustrated in Figure 5. The switched beam / switched antenna system 510 is shown with its twelve predetermined beams 520 and 522. Beam 520 is highlighted to illustrate that it is the beam that provides the highest signal quality, which perhaps points in the direction of a base station (not shown).

It should be understood that Figure 5 is intended only to serve as an example of the SBSA concept. SBSA systems according to the present embodiment may have as few as two predetermined antenna beams, possibly including one that has an omni-directional response. The smaller the number of antenna beams formed by an SBSA, the wider it should be cad to do. Beam width and number of beams are often determined by a device type and size considerations.

In accordance with the present embodiment, the signals are measured in each of the predetermined beams of WTRUs. One of these beams is then selected so as to: 1) maximize the relationship between signal and noise plus interference (SNIR) of the received signal; or 2) minimize the

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energy received from nearby WTRUs; or 3) minimize the energy received from nearby WTRUs while maintaining a sufficient convenient signal level. A switching function then switches to the selected of these fixed beam patterns to receive convenient signals in the downlink direction. In some cases, the selected beam may be an omni-directional beam. Continuous reduction of interference energy received from nearby WTRUs is preserved by switching frequently between predefined beam patterns rolled in response to the WTRU signal environment. This concept is illustrated in Figure 6.

The antenna system 610 of the WTRU 602 has formed multiple predetermined beams 620 and 622. The beam 622 is highlighted to illustrate that it is active and directed towards a base station 630. According to it, it has reduced the gain towards a nearby WTRU 604 .

The use of switched beam antennas in the manner described above allows WTRUs to select from a plurality of predetermined antenna beams. By selecting one of these beams, the interference received from nearby WTRUs is reduced, as shown in Figure 6. An advantage added to such an implementation is that it minimizes both the interference in the band and the out-of-band interference, at the same time.

In a fourth preferred embodiment, it is used

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a system of beam antennas switched on a WTRU to minimize The MS-MS interference experienced by a nearby WTRU, particularly if the WTRUs are in a state of reciprocal interference. As described above, the WTRUs are in reciprocal interference when, for example, the DL frequency of a first WTRU is close to the UL frequency of a second WTRU while the DL frequency of the second WTRU is close to the UL frequency of the first WTRU (see Figure 4). In the absence of proper alignment, WTRUs in a TDD communication system could also experience reciprocal interference.

In the same manner as described above in the third preferred embodiment, a WTRU selectively switches between a plurality of predetermined fixed antenna beams to maximize the SNIR, minimize the energy received from nearby WTRUs, or minimize the energy received from nearby WTRUs while maintaining a sufficient convenient signal level. However, in In the present embodiment, the WTRU uses the same antenna beam selected to transmit in the UL direction. Since he does. selected minimizes interference energy from unwanted sources, transmission over this same beam will minimize the transmission of unwanted energy to nearby sources. According to elio, by means of transmission in the

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selected beam direction, interference to nearby WTRUs is minimized.

In a fifth embodiment, an intelligent antenna system is used in a WTRU to minimize the MS-MS interference experienced by nearby WTRU (s), particularly when the WTRUs are in an asymmetric interference state. Next, the term intelligent antenna is used to describe either an adaptive antenna system, or a switched beam / switched antenna system. For the purposes of the present embodiment, the WTRUs are in an interference state to asymmetric when a first WTRU interferes with the DL reception of a second adjacent WTRU. However, the UL transmissions of the second WTRU do not interfere with the DL reception of the first WTRU. This concept is illustrated in Figure 7.

A communication system 700 is shown where a WTRU

TDD 7 02 has a UL frequency of fi. A WTRU 704, an FDD device, is shown with a reception frequency DL spectrably adjacent to that of the WTRU 702. As a result, the TDD device 702 interferes with the DL reception of the adjacent FDD device 704. However, this interference is asymmetric since the UL f3 transmission frequency of the FDD 704 device is spectrably distant from the DL fi frequency of the

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TDD 702 device. It should be noted that since the WTRU 702 is a TDD device, its UL frequency and its DL frequency are the same.

Such a horn is illustrated in Figure 7, WTRUs, As the TDD 702 device, they can interfere asymmetrically with nearby WTRUs without knowing that such interference is occurring. The lack of knowledge is caused because the frequency of reception of the interfering WTRU is spectrally distant from the UL frequency of the damaged WTRU. The present embodiment proposes to minimize said asymmetric interference by providing additional information to interfering WTRUs. A WTRU in asymmetric interference, (such as WTRU TDD 702 of Figure 7), is notified of the spectral arrangement in its signal environment. In particular, it is notified with respect to the UL frequencies of WTRUs whose DL frequencies are adjacent to their UL frequency. This information alerts the interfering WTRU to the existence of other WTRUs to which it may possibly cause interference. The interfering WTRU then scans those UL frequencies to determine the actual locations of these WTRUs. The Interfering WTRU can determine the locations of these WTRUs, for example, by looking for high energy signals. An energy level high enough in an UL direction implies that a WTRU is probably close and may be

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interfered The interfering WTRU then adjusts, according to it, its UL transmission address using, for example, any of the embodiments described herein, so as to minimize interference with nearby WTRU (s).

Alternatively, instead of notifying an interfering WTRU regarding a spectral arrangement in its signal environment and thus limiting the search for WTRUs, the WTRU can scan all possible frequencies. Although the components of the various embodiments are analyzed in terms of separate components, it should be understood that they may be in a signal integrated circuit (IC), such as a specific application integrated circuit ifica (ASIC), multiple ICs, discrete components or a combination of discrete components and IC (s).

Similarly, although the features and elements of the present invention are described in the preferred embodiments, in particular combinations, each feature or element can be used alone (without the other features and elements of the preferred embodiments). ) or in various combinations with or without other features and elements of the present invention.