MXPA06011246A - Mitigation of wireless transmit/receive unit (wtru) to wtru interference using multiple antennas or beams - Google Patents

Abstract

Multiple antenna elements of a WTRU are used to form an adaptive antenna beam pattern for receiving signals in the downlink direction. The WTRU utilizes the formed antenna beam to form a transmission antenna beam for transmitting signals in the uplink direction. In an alternate embodiment, the multiple antenna elements are used to form a plurality of fixed, predetermined antenna beams. The WTRU then selects and switches to the one of the predetermined beams that yields the best downlink reception signals. The WTRU utilizes the selected beam pattern to transmit signals in the uplink direction. In an alternate embodiment, the WTRU receives spectral arrangement information and utilizing this information to avoid transmitting in the direction of spectrally adjacent WTRUs.

Description

Figure 1. Figure 1 shows a WTRU 102 that transmits in an omni-directional way. The WTRU 104 has an omni-directional receiving beam 112. When the two WTRUs are physically and spectrally close, the WTRU 104 experiences significant levels of interference and performance degradation. The interference radius 110 of the interfering WTRU 102 is 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 10. The degradation of performance experienced by the WTRU 104 reduces the relationship between signal and interference (SIR) and, therefore, the relationship between signal and interference plus noise of signals 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 interference WTRU to WTRU (mobile station (MS) -MS). As described above, WTRUs using omni-directional antennas lack the technology to preferentially control the 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, MITIGATION OF WTRU INTERMEDIATE TRANSMISSION / WIRELESS (WTRU) UNIT FOR INTERFERENCE USING MULTIPLE ANTENNAS OR MAKES FIELD OF THE INVENTION The present invention relates to a wireless communication system. More particularly, the present invention relates to mitigating a wireless transmit / receive unit (WTRU) for WTRU interference in a wireless communication system.

BACKGROUND 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 such antennas is significantly wasting WTRU resources since most of the power of a WTRU is used to transmit and receive in directions that differ from the intended one. More significantly, this wasted energy is experienced as noise-like interference by nearby WTRUs. Such interference is especially momentary in cases where the uplink frequency (UL) of a WTRU is either the same or close to the downlink frequency (DL) of another WTRU. This concept is illustrated in only the base stations have been equipped with components and technology to maximize the antenna gain in a convenient direction, simultaneously limiting the reception of signals in the directions of interfering devices. Accordingly, it is convenient to have a WTRU that can maximize the antenna gain in a convenient direction and / or selectively receive signals from a convenient address to minimize the MS-MS interference.

THE INVENTION 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. A similar control is applied to a transmission 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 selects and switches to one of the predetermined beams that reduces the interference from nearby WTRUs. The same beam pattern is used when a transmission is made to reduce interference to nearby WTRUs.

In an alternative embodiment, a WTRU comprises an array of antennas 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 transmission directions of any high energy source (and, therefore, nearby) and transmits on its antennas to avoid a transmission in the direction of the high energy sources.

BRIEF DESCRIPTION OF THE DRAWINGS 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 the accompanying drawings, wherein: Figure 1 shows a wireless transmission / reception unit (WTRU) that transmits in an omni-directional way and interferes with a nearby WTRU; Figure 2 illustrates a part of the receiver of a WTRU comprising an arrangement of adaptive antennas; Figure 3 illustrates a WTRU using an array of adaptive antennas; Figure 4 illustrates two WTRUs in a state of reciprocal interference, one with another; Figure 5 illustrates an arrangement of switched beam antennas with their predetermined beams formed; Figure 6 illustrates a WTRU using an array of switched beam antennas; and Figure 7 illustrates two WTRUs in an asymmetric interference state with each other.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES Next, the expression "wireless transmit / receive unit" (WTRU) includes, but is not limited to, a user equipment, a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referenced below, the expression "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 to WTRU interference, the technology disclosed herein is also applicable to base station to base station interference scenarios. For example, the levels of access point (AP) interference 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 the beams below are first described in two dimensions, some of the beams may be elevated, with different azimuths. In a first preferred embodiment, adaptive antennas, i.e., an array 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 have approximately omni-directional antenna patterns (see Figure 1)), adaptive antenna arrays are able to generate antenna patterns that are dynamically adjusted in real time to adapt to current radio conditions. When used in a WTRU, an antenna array continuously monitors its radio frequency (RF) environment and, in particular, monitors signals received from a serving base station, 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 each antenna element are multiplied. These antenna weights serve to form the WTRU beam pattern. Since the antenna array is constantly monitored for radio changes, the unit of. signal processing continuously recalculates the antenna weights to optimize the antenna pattern of WTRU. The antenna weights are calculated either: 1) to maximize the signal-to-noise ratio (SNR) or the signal-to-noise ratio plus interference (SNIR); or 2) to minimize the interference signals received; or 3) to minimize the interference received while retaining the signal levels received at an acceptable constant. Next, these three optimization alternatives will be referred to together as "the three optimization alternatives". A mode of a part of the WTRU receiver described above is shown in Figure 2. Elements 202?, 2022 and 202N of antenna in Figure 2 are arranged in a linear configuration to form an array of antennas 208. It should be understood that a linear, circular, planar, and any other antenna arrangement of 2 or 3 antenna arrangements can be used. dimensions to form an array of antennas. The signals received in the array of antennas 208 depend on the location of the antennas 202l7 2022 and 202N and of the adaptive complex weights Wi, w and wN '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 wlf w2 and WN can be used to achieve the three optimization alternatives discussed above. For example, sets of appropriately quantized weights can be tested one after the other until finding an appropriate set. A signal processor 220 sends the determined antenna weights, Wi, W2 and WN, to a signal weighting unit 230. In the signal weighting unit 230, originally received signals 203 ?, 2032 and 203N are combined with calculated weights Wx, W and WN respectively, and then combined to form a single weighted signal 231. The use of adaptable antennas in this way allows the WTRUs to form directional beam patterns to achieve any of the three optimization alternatives discussed above. By creating such directional beam patterns, adaptive antennas also create nullities. The nullities are merely low gain antenna directions. Figure 3 illustrates this concept. A WTRU 302 is shown with an antenna array 310 that directs a beam pattern 320 to a base station 330. The antenna arrangement 310 also directs the nullities 321, approximately towards the WTRU 304 ', a close source of interference WTRU to WTRU (MS-MS). In this example, the null 321 beams have the effect of "nullifying" or minimizing the interference caused by signals transmitted in the uplink (UL) address from the WTRU 304.

In a second preferred embodiment, an array of adaptive antennas is used to select antenna weights to achieve one of the three optimization alternatives discussed above. The WTRU then uses antenna weights derived from the weights selected to transmit to a base station. It is important to note that the derived transmission weights are chosen in such a way that the essential shape and location of the beam created for the receiver is preserved. As an example, the derived transmission antenna weights could be the same as the selected antenna weights for received signals. The transmission with derived antenna weights as described above is particularly useful when a transmitting WTRU is in a state of reciprocal interference with a near WTRU. The WTRUs are described in a state of reciprocal interference when, for example, the UL frequency of a first WTRU is close to or the same as the DL frequency of a second WTRU and the DL frequency of the first WTRU is close to or is the same as 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 one another. The frequency of UL ". Fl of the WTRU 404 is very close to the frequency of DL fl1 of the WTRU 402. Similarly, the frequency of UL f3 of the WTRU 402 is very close to the frequency of DL f3 'of the WTRU 404. Therefore, the WTRUs 402 and 404 are in a state of reciprocal interference with one another, where both WTRUs experience MS-MS interference when the other is transmitting In communication systems using time division duplex ( TDD), the WTRUs transmit and receive signals on the same frequency.In the absence of alignment, such WTRUs could experience reciprocal interference, for example, if two TDT WTRUs are assigned different frequencies or time slots and their respective frequencies are close or their synchronizations 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 according to the present method use antenna weights to optimize the signal quality of convenient signals, according to one of the three optimization alternatives defined above. However, in the present embodiment, the WTRUs derive antenna weights from the received antenna weights selected to transmit in the UL direction. By using such derived antenna weights to form directional transmission beams, the energy directed towards neighboring WTRUs will be reduced, which serves to prevent nearby WTRUs from experiencing MS-MS interference. In a third embodiment, a switched beam / switched antenna (SBSA) arrangement is used in a WTRU receiver to protect against interference from the near WTRU (s). An SBSA forms, either multiple predetermined beams, a subset of which is selected to be used at any given time, or forms a bundle of beams from a larger set of predetermined beam positions. It should be noted that one of these beam patterns formed can be an omni-directional beam pattern. An example of these predetermined beam patterns is illustrated in the. Figure 5. The switched beam / switched antenna arrangement 510 is shown with its twelve predetermined antenna beams 520 and 522. The beam 520 is highlighted to illustrate that it is the beam that provides the highest signal quality, perhaps pointing in the direction of a base station (not shown). It should be understood that Figure 5 is only intended to serve as an example of the SBSA concept. The SBSA systems according to the present embodiment can have as few as two predetermined antenna beams, which possibly include one that has an omni-directional response. The smaller the number of antenna beams formed by an SBSA, the wider the beam should be. The beam width and the number of beams are often determined by a type of device 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 to: 1) maximize the signal-to-noise ratio plus interference (SNIR) of the received signal; or 2) minimize the 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 can be an omni-directional beam. The continued reduction of interference energy received from nearby WTRUs is preserved by frequently switching between predetermined beam patterns in response to the signal environment of the WTRU. This concept is illustrated in Figure 6. The antenna array 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. Accordingly, it has reduced the gain to a nearby WTRU 604. The use of switched beam antennas in the manner described above allows the WTRUs to be selected 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 added advantage to such an implementation is that it minimizes both in-band interference and out-band interference, at the same time. In a fourth preferred embodiment, an array of switched-beam antennas in a WTRU is used to minimize 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 frequency of the second WTRU. UL frequency of the first WTRU (see Figure 4). In the absence of proper alignment, the WTRUs in a TDD communication system could experience,. in addition, 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 Close WTRUs, or minimize the energy received from nearby WTRUs while maintaining a sufficient convenient signal level. However, in the present embodiment, the WTRU uses the same antenna beam selected to transmit in the UL direction. Since the selected beam minimizes the interference energy from unwanted sources, the transmission on this same beam will minimize the transmission of unwanted energy to nearby sources. Accordingly, by means of transmission in the selected beam direction, interference to nearby WTRUs is minimized. In a fifth embodiment, an array of smart antennas in a WTRU is used to minimize the MS-MS interference experienced by the neighboring WTRUs, particularly when the WTRUs are in an asymmetric interference state. Next, the term "smart antenna" is used to describe either an adaptive antenna array, or a switched beam / switched antenna system. For the purposes of the present embodiment, the WTRUs are in an asymmetric interference state when a first WTRU interferes with the reception of DL from a second spectrally adjacent WTRU. However, the UL transmissions of the second WTRU no. they interfere with the reception of DL from the first WTRU. This concept is illustrated in Figure 7. A communication system 700 is shown where a WTRU 702 TDD has a UL frequency of f1. A WTRU 704, an FDD device, is shown with a DL reception frequency spectrally adjacent to that of the WTRU 702. As a result, the TDD device 702 interferes with DL reception of the spectrally adjacent FDD device 704. However, it is The interference is asymmetric since the UL transmit frequency f3 of the device 704 FDD is spectrally distant from the DL fl frequency of the 702 TDD device. It should be noted that since the WTRU 702 is a TDD device, its UL frequency and DL frequency are the same. As illustrated in Figure 7, WTRUs, such as the 702 TDD device, may interfere asymmetrically with nearby WTRUs without knowing that such interference is occurring. Lack of knowledge is caused because the reception frequency of the interfering WTRU is spectrally distant from the UL frequency of the impaired WTRU. The present modality proposes to minimize such asymmetric interference by providing additional information to interfering WTRUs. A WTRU in asymmetric interference, (such as the WTRU 702 TDD of Figure 7), is notified regarding the spectral arrangement in its signal environment. In particular, it is notified regarding 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 a UL direction implies that a WTRU is probably close and may be interfered with. The interfering WTRU then adjusts its UL transmit address using, for example, any of the modes described herein, to minimize interference with the neighboring WTRU (s). Alternatively, instead of notifying an interfering WTRU of 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 modalities are analyzed in terms of separate components, it should be understood that they can be in a signal integrated circuit (IC), such as a specific application integrated circuit (ASIC), multiple ICs, discrete components or a combination of discrete components and the ICs. Similarly, although the features and elements of the present invention are described in the preferred embodiments, in particular combinations, each characteristic or element may be used alone (without the other characteristics and elements of the preferred embodiments) or in various combinations with or without other features and elements of the present invention.

Claims (32)

1. CLAIMS 1. Wireless transmit / receive unit (WTRU) for mitigating WTRU to WTRU interference in a wireless communication system, characterized in that the WTRU comprises: means for measuring the signal quality of received signals; means for calculating antenna weights based on quality measurements; means for forming an antenna beam directed to receive downlink (DL) signals based on the calculated antenna weights, the calculated antenna weights are calculated to minimize the energy received in at least one near WTRU; means for deriving transmission antenna weights from the calculated antenna weights; and means for forming a directed antenna beam to transmit uplink (UL) signals based on the derived transmission antenna weights.
2. 2. WTRU according to claim 1, characterized in that the derived antenna weights for the transmission of signals are the same as the antenna weights calculated to receive signals.
3. 3. WTRU according to claim 1, further characterized in that it comprises means for dynamically adapting the transmission and reception antenna beams formed to current radio conditions.
4. 4. WTRU according to claim 1, characterized in that the antenna weights calculated to receive signals optimize the signal-to-noise ratio (SNR) or the signal to noise ratio plus interference (SNIR).
5. 5. WTRU according to claim 1, characterized in that the antenna weights calculated to receive signals minimize the received interference.
6. 6. WTRU according to claim 1, characterized in that the antenna weights calculated to receive signals minimize the received interference, while maintaining a constant received signal level.
7. 7. WTRU according to claim 1, further characterized in that it comprises means for directing nulities in directions that differ from that of the beam formed to receive signals.
8. 8. Method for mitigating WTRU to WTRU interference in a wireless communication system, the method is characterized in that it comprises: (a) measuring the signal quality of received signals; (b) calculate antenna weights based on quality measurements, the antenna weights are calculated to minimize the energy received in at least one nearby WTRU; (c) forming a directed antenna beam to receive downlink (DL) signals based on the calculated antenna weights; (d) deriving transmission antenna weights from the calculated antenna weights; and (e) forming an antenna beam directed to transmit uplink (UL) signals based on the derived transmission antenna weights.
9. Method according to claim 8, characterized in that the antenna weights derived in step (d) are equal to the antenna weights calculated in step (b).
10. Method according to claim 8, further characterized in that it comprises dynamically adapting the transmitting and receiving antenna beams formed to current radio conditions.
11. Method according to claim 8, characterized in that the antenna weights of step (b) are calculated to optimize the signal-to-noise ratio (SNR) or the signal-to-noise ratio plus interference (SNIR).
12. Method according to claim 8, characterized in that the antenna weights of step (b) are calculated to minimize the interference received.
13. Method according to claim 8, characterized in that the antenna weights of step (b) are calculated to minimize the interference received while maintaining a constant received signal level.
14. Method according to claim 8, further characterized by comprising, directing nulities in directions that differ from that of the beam formed to receive signals.
15. 15. WTRU for mitigating WTRU to WTRU interference in a wireless communication system, WTRU characterized in that it comprises: means for forming a plurality of predetermined fixed antenna beam patterns; means for selecting one of the predetermined beam patterns, the selected predetermined beam patterns are selected to minimize the energy received in at least one nearby WTRU; means for switching to the selected beam pattern; means for receiving DL signals in the selected antenna beam pattern; and means for transmitting UL signals using the same pattern as the selected antenna beam pattern.
16. 16. WTRU according to claim 15, characterized in that the plurality of predetermined beam patterns comprises at least two beam patterns, one of which is omni-directional.
17. 17. WTRU according to claim 15, further characterized in that it comprises a means for switching in an adaptive manner between the plurality of beam patterns.
18. 18. WTRU according to claim 15, characterized in that the selected beam pattern optimizes the signal-to-noise ratio (SNR) or the signal-to-noise ratio plus interference (SNIR).
19. 19. WTRU according to claim 15, characterized in that the selected beam pattern minimizes the energy received from nearby WTRUs.
20. 20. WTRU according to claim 15, characterized in that the selected beam pattern minimizes the energy received from nearby WTRUs while preserving a predetermined signal level.
21. 21. WTRU according to claim 15, further characterized in that it comprises means for reducing the antenna gain in directions differing from that of the beam selected to receive signals.
22. 22. Method for mitigating WTRU to WTRU interference in a wireless communication system, the method is characterized in that it comprises: (a) forming a plurality of fixed predetermined antenna beam patterns; (b) selecting one of the predetermined beam patterns, the selected predetermined beam patterns are selected to minimize the energy received in at least one nearby WTRU; (c) switch to the selected beam pattern; (d) receiving DL signals in the selected antenna beam pattern; and (e) transmitting UL signals using the same antenna beam pattern as the selected antenna beam pattern.
23. 23. Method according to claim 22, characterized in that step (a) further comprises forming at least two predetermined beam patterns, one of which is omni-directional.
24. 24. Method according to claim 22, characterized in that it also comprises commutating adaptively between the plurality of beam patterns.
25. 25. Method according to claim 22, characterized in that step (b) further comprises selecting a beam pattern that optimizes the signal-to-noise ratio (SNR) or the signal-to-noise ratio plus interference (SNIR).
26. Method according to claim 22, characterized in that step (b) further comprises selecting a beam pattern that minimizes the energy received from nearby WTRUs.
27. 27. Method according to claim 22, characterized in that step (b) further comprises selecting a beam pattern that minimizes the energy received from nearby WTRUs while preserving a predetermined signal level.
28. 28. WTRU according to claim 22, further characterized in that it comprises reducing the antenna gain in directions differing from that of the beam pattern selected to receive signals.
29. 29. WTRU to mitigate interference in a wireless communication system, the WTRU is characterized by including: an array of antennas; means for receiving spectral arrangement information; means for locating spectrally adjacent WTRUs; and means for transmitting on the array of antennas to minimize the energy received in the spectrally adjacent WTRUs.
30. 30. WTRU to mitigate interference in a wireless communication system, the WTRU is characterized in that it comprises: an array of antennas; means for scanning transmission frequencies in search of high energy sources; means for determining directions of transmission of high energy sources; and means for transmitting on the array of antennas to avoid a transmission in the direction of the high energy sources and to minimize the energy received in at least one nearby WTRU.
31. 31. Method, to mitigate interference in a wireless communication system, the method is characterized in that it comprises: (a) providing a WTRU with an array of antennas; (b) receive spectral arrangement information; (c) locating WTRUs spectrally adjacent; and (d) transmitting on one of the antennas to minimize the energy received in spectrally adjacent WTRUs.
32. 32. Method for mitigating interference in a wireless communication system, the method is characterized in that it comprises: (a) providing a WTRU with an array of antennas; (b) scanning transmission frequencies in search of high energy sources; (c) determine directions of transmission of high energy sources; and (d) transmitting on the array of antennas to avoid a transmission in the direction of the high energy sources by minimizing the received energy in at least one nearby WTRU.