HK1109272B - Wtru and method for mitigating wtru to wtru interference in wireless communications - 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

WTRU and method for mitigating WTRU-to-WTRU interference in wireless communications

Technical Field

The present invention relates to wireless communication systems. More particularly, the present invention relates to mitigating interference to wireless transmit/receive units (WTRUs) in wireless communication systems.

Background

A conventional wireless transmit/receive unit (WTRU) typically includes a single omni-directional antenna that transmits and receives equally in all directions. However, since most of the energy of the wtru is used for transmission and reception in directions other than the desired direction, resources of the wtru are significantly wasted using this property. More significantly, the wasted energy experiences noise-like interference from nearby wtrus. Such interference is particularly noticeable in cases where the Uplink (UL) frequency of one wtru is the same as or close to the Downlink (DL) frequency of another wtru. This concept is depicted in fig. 1.

Fig. 1 shows a wtru 102 for transmitting in all directions. The wtru 104 has an omni-directional receive beam 112. When the two wtrus are in physical and spectral proximity, 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 (pattern) of the wtru 104 and the desired signal level of the wtru 104. The performance degradation experienced by wtru 104 reduces the signal-to-interference ratio (SIR) and the signal-to-interference-plus-noise ratio of its received signal. If significant enough, the interference 120 generated by the wtru 102 may result in reduced data rates, connection loss, and/or poor signal quality. This phenomenon is referred to as wtru-to-wtru (mobile station (MS) -mobile station) interference.

As described above, a wireless transmit/receive unit using an omni-directional antenna lacks a technique for preferentially controlling antenna gain to minimize transmission of undesired signals to nearby wireless transmit/receive units. Likewise, the use of such an antenna avoids the wtru rejecting interference with signals transmitted from undesired sources including other nearby wtrus. Typically, only base stations are equipped with components and techniques for maximizing antenna gain in a desired direction while limiting reception of signals in the direction of interfering devices.

Accordingly, it is desirable to have a wireless transmit/receive unit that can maximize antenna gain in a desired direction and/or selectively receive signals from the desired direction to minimize MS-MS interference.

Disclosure of Invention

The present invention relates to a method and apparatus for mitigating WTRU-to-WTRU interference in a wireless communication system. A plurality of antenna elements of a wtru are used to control the receive gain of the antenna of the wtru. Similar control is applied to the transmit antennas to reduce transmission toward nearby wtrus.

In an alternative embodiment, a plurality of antenna elements are used to form a plurality of fixed predetermined antenna beams. The wtru then selects and switches to one of the predetermined beams for reducing interference from nearby wtrus. The same beam pattern is used when transmitting to reduce interference generated to nearby wtrus.

In an alternate embodiment, the wtru includes an antenna array and receives the spectral arrangement information. By using the spectrum information, the wtru transmits to avoid spectrally adjacent wtrus. Alternatively, the wtru scans the transmission frequency while searching for a high energy source. The wtru then determines the direction of transmission of any high energy (and nearby) source and transmits on its antenna to avoid transmitting in the direction of the high energy source.

Drawings

The invention may be understood in more detail by means of the following examples and the accompanying drawings, in which:

fig. 1 shows a wtru configured to transmit in all directions and interfere with nearby wtrus;

fig. 2 depicts a receiver portion of a wireless transmit/receive unit including an adaptive antenna array;

fig. 3 depicts a wireless transmit/receive unit utilizing an adaptive antenna array;

fig. 4 depicts two wtrus in a mutual interference state with each other;

fig. 5 depicts a switched beam antenna array with a formed predetermined beam;

fig. 6 depicts a wireless transmit/receive unit utilizing a switched beam antenna array; and

fig. 7 depicts two-goose wtrus in an asymmetric interference state with each other.

Detailed Description

Hereinafter, the term "wireless transmit/receive unit" includes, but is not limited to, user equipment, mobile stations, fixed or mobile subscriber units, pagers, or any other type of component that may operate in a wireless environment. When referred to hereafter, the term "base station" includes but is not limited to a node-B, a site controller, an access point, or any other type of interfacing device in a wireless environment.

Although the following embodiments describe wtru-to-wtru interference, the techniques disclosed herein may also be applied to a base station-to-base station interference scenario. For example, an access point-to-access point interference level where a downlink of a first Access Point (AP) interferes with an uplink of a second access point may be mitigated by using the techniques disclosed herein.

Furthermore, although beams are described below primarily in two dimensions, some beams with different azimuth angles may also be boosted.

In a first preferred embodiment, adaptive antennas, i.e. adaptive antenna arrays, are employed in receivers of wtrus to protect against interference from nearby wtrus. Unlike a single antenna used by conventional wtrus, which have approximately an omni-directional antenna pattern (see fig. 1), adaptive antenna arrays can produce antenna patterns that are dynamically adjusted in real time to accommodate current radio conditions. The antenna array used in the wtru continuously monitors its Radio Frequency (RF) environment and, in particular, monitors signals received from the serving base station and any received interference.

A signal processing unit, also located within the present wtru, is used to calculate the antenna weights by which the signals received in each antenna element are multiplied. These antenna weights are used to form the beam pattern of the wtru. Since the antenna array constantly monitors radio changes, the signal processing unit continuously recalculates antenna weights to optimize the antenna pattern of the wtru. Antenna weights are calculated to: 1) maximizing a signal-to-noise ratio (SNR) or a signal-to-noise-plus-interference ratio (SNIR); or 2) minimizing the received interference signal; or 3) minimize received interference while maintaining the received signal level at an acceptable constant. Hereinafter, these three optimization alternatives will be collectively referred to as "these three optimization alternatives". An embodiment of the receiver portion of the above described wtru is shown in fig. 2.

Antenna element 202 in fig. 2₁，202₂And 202_NArranged in a linear configuration to form antenna array 208. It should be appreciated that linear, circular, planar, and any other 2 or 3 dimensional antenna arrangement may be used to form the antenna array. The signal received in antenna array 208 depends on antenna element 202₁、202₂And 202_NAnd adaptive complex weights w applied to the received signal₁、w₂And w_N. Alternatively, adaptive delay and gain combinations may be used instead of these complex weights. For adjusting these weights w₁、w₂And w_NAny of the methods described above may be used to achieve the three optimization alternatives described above. For example, appropriately quantized groups of weights may be tried one after another until an appropriate group is found. The signal processor 220 transmits the determined antenna weights w₁、w₂And w_NTo the signal weighting unit 230. In the signal weighting unit 230, the signal 230 that is initially received₁、230₂And 230_NAre respectively associated with the calculated weight w₁、w₂And w_NAre combined and then combined to form a single weighted signal 231.

The use of adaptive antennas in this manner allows the wtru to form a directional beam pattern to achieve any of the three optimization alternatives described above. When creating a directional beam pattern, the adaptive antenna also creates a null. The null is only the direction of low antenna gain. Fig. 3 depicts this concept. The wtru 302 is shown with an antenna array 310 for directing a beam pattern 320 towards a base station 330. Antenna array 310 also directs null 321 approximately toward wtru 304, i.e., a nearby source of wtru-to-wtru (MS-MS) interference. In this example, null beam 321 has the effect of "making no signal" or minimizing interference caused by signals transmitted in the uplink direction from wtru 304.

In a second preferred embodiment, an adaptive antenna array is used to select antenna weights to achieve one of the three optimization alternatives described above. The wtru then transmits to the base station using the antenna weights derived from the selected weights. It is important to note that the derived transmission weights are chosen such that the significant position and shape of the beam created for the receiver is preserved. For example, the derived transmit antenna weights may be the same as the antenna weights selected for receiving the signal.

The above-described transmission with derived antenna weights is particularly useful when the transmitting wtru is in a mutual interference state with nearby wtrus. For example, wtrus are described as being in a mutual interference state when the uplink frequency of a first wtru is close to or the same as the downlink frequency of a second wtru and the downlink frequency of the first wtru is close to or the same as the uplink frequency of the second wtru. To illustrate, fig. 4 shows two wtrus 402 and 404 in mutual interference with each other. The UL frequency f1 of WTRU 404 is very close to the DL frequency f 1' of WTRU 402. Likewise, the uplink frequency f3 of the wtru 402 is very close to the DL frequency f3' of the wtru 404. Therefore, WTRUs 402 and 404 are in a mutual interference state with each other, where both WTRUs experience MS-MS interference when the other WTRU is transmitting.

In a communication system using Time Division Duplex (TDD), wtrus all transmit and receive signals at the same frequency. Such wtrus may experience mutual interference when there is a lack of alignment. For example, two time division duplex wtrus may experience mutual interference if they are assigned different time slots or frequencies and their respective frequencies are close together or their timing is not properly aligned, or both.

In the same manner as described in the above-described first preferred embodiment, the wireless transmission/reception unit according to the present embodiment uses the antenna weights to optimize the signal quality of the desired signal according to one of the above-described three optimization alternatives. However, in the present embodiment, the wtru derives antenna weights from the selected receive antenna weights to transmit in the uplink direction. By using such derived antenna weights to form directional transmission beams, the energy directed to neighboring wtrus will be reduced to protect nearby wtrus from experiencing MS-MS interference.

In a third preferred embodiment, a switched beam/switched antenna array (SBSA) is employed in a wtru receiver to protect against interference from nearby wtrus. Switched beam/switched antenna arrays either form a plurality of predetermined beams, a subset of which is selected for use at any given time, or the SBSA forms a larger set of beams from a predetermined beam location. It should be noted that one of these formed beam patterns may be an omni-directional beam pattern. Examples of these predetermined beam patterns are depicted in fig. 5. The switched beam/switched antenna array 510 is shown with its twelve predetermined antenna beams 520 and 522. The beam 520 is emphasised as the beam that provides the highest signal quality, possibly pointing in the direction of the base station (not shown).

It should be appreciated that fig. 5 is intended only to be provided as an example of a switched beam/switched antenna array concept. A switched beam/switched antenna array system according to the present embodiment may have as few as two predetermined antenna beams, possibly including one with an omni-directional response. The smaller the number of antenna beams formed by the switched beam/switched antenna array, the wider each beam will need to be. The beam width and number of beams are typically determined by device type and size considerations.

According to the present embodiment, signals are measured in predetermined beams of each wtru. One of the beams is then selected to: 1) maximizing a signal-to-noise-plus-interference ratio (SNIR) of the received signal; or 2) minimizing the energy received from nearby wtrus; or 3) minimize the energy received from nearby wtrus while maintaining a sufficiently desired signal level. The switching function then switches to a selected one of the fixed beam patterns to receive the desired signal in the downlink direction. In some examples, the selected beam may be an omni-directional beam. The continuous reduction in interference energy received from nearby wtrus is maintained by frequently switching between predetermined beam patterns in response to the wtru's signal environment. This concept is depicted in fig. 6.

Antenna array 610 of wtru 602 has formed a plurality of predetermined beams 620 and 622. Beam 622 is emphasised as being active and directed towards base station 630. Thus, it has reduced the gain towards the nearby wtru 604.

The use of switched beam antennas in the manner described above allows the wtru to select from a plurality of predetermined antenna beams. When one of these beams is selected, the interference received from nearby wtrus is reduced as shown in fig. 6. An additional advantage of this embodiment is that it minimizes both in-band and out-of-band interference.

In a fourth preferred embodiment, a switched beam antenna array is used in a wtru to minimize MS-MS interference experienced by nearby wtrus, particularly if the wtrus are in a mutual interference state. As described above, for example, when the downlink frequency of the first wtru is close to the uplink frequency of the second wtru and the downlink frequency of the second wtru is close to the uplink frequency of the first wtru, the wtrus are in mutual interference (see fig. 4). Without proper alignment, wireless transmit/receive units in a time division duplex communication system may also experience mutual interference.

In the same manner as described above for the third preferred embodiment, the wtru may be selectively switched between a plurality of predetermined fixed antenna beams to maximize the signal-to-noise-plus-interference ratio, minimize the energy received from nearby wtrus, or minimize the energy received from nearby wtrus while maintaining a sufficiently desired signal level. However, in this embodiment, the wtru transmits in the uplink direction using the same selected antenna beam. Because the selected beam minimizes interference energy from undesired sources, transmissions on the same beam will minimize transmission of undesired energy toward nearby sources. Thus, by transmitting in the selected beam direction, interference towards nearby wtrus is minimized.

In a fifth preferred embodiment, a smart antenna array is used in a wtru to minimize MS-MS interference experienced by nearby wtrus, particularly when the wtru is in an asymmetric interference state. Hereinafter, the phrase "smart antenna" is used to describe an adaptive antenna array or a switched beam/switched antenna array. For this embodiment, the wtru is in an asymmetric interference state when the first wtru interferes with downlink reception by a second wtru in close spectral proximity. However, uplink transmissions of the second wtru do not interfere with downlink reception of the first wtru. This concept is depicted in fig. 7.

A communication system 700 is shown in which a time division duplex wtru 702 has an uplink frequency of f 1. The wtru 704, i.e. the FDD device, is shown to have a downlink reception frequency that is spectrally adjacent to the frequency of the wtru 702. As a result, the time division duplex device 702 interferes with downlink reception by spectrally adjacent FDD devices 704. However, this interference is asymmetric because the uplink transmission frequency f3 of FDD device 704 is spectrally separated from the downlink frequency f1 of time division duplex device 702. It should be noted that since wtru 702 is a time division duplex device, its uplink and downlink frequencies are the same.

As depicted in fig. 7, a wireless transmit/receive unit, such as a time division duplex device 702, may asymmetrically interfere with nearby wireless transmit/receive units without being aware that the interference is occurring. This unconsciousness is caused by the receiving frequency of the interfering wtru being spectrally distant from the uplink frequency of the victim wtru. The present embodiment proposes to minimize this asymmetric interference by providing additional information to the interfering wtru. An asymmetrically interfering wtru, such as the tdd wtru 702 of fig. 7, is informed of the spectral arrangement located in its signal environment. In particular, it is informed of the uplink frequency of the wtru whose downlink frequency is adjacent to its uplink frequency. The information alerts the interfering WTRU to the presence of other WTRUs to which the interfering WTRU may interfere. The interfering wtrus then scan the uplink frequencies to determine the actual locations of the wtrus. For example, interfering wtrus may determine the location of the wtrus by searching for high energy signals. A sufficiently high energy level in the uplink direction means that the wireless transmit/receive unit may be nearby and may be interfered with. Thus, the interfering wtru then minimizes the interference to nearby wtrus by adjusting its uplink transmission direction using, for example, any of the embodiments described herein.

Alternatively, rather than informing interfering wtrus about the spectral arrangement in their signal environment and thus limiting the wtru search, the wtrus may scan all possible frequencies. While components of various embodiments are discussed as separate components, it should be appreciated that they may reside on a signal Integrated Circuit (IC), such as an Application Specific Integrated Circuit (ASIC), a plurality of ICs, discrete components, or a combination of discrete components and ICs.

Similarly, although 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.

Claims (14)

1. A wtru for mitigating wtru-to-wtru interference in wireless communications, the wtru comprising:

a signal processing unit configured to measure a signal quality of the received signal and to calculate antenna weights based on the quality measurement;

an antenna array configured to form a steered antenna beam to receive a downlink signal based on calculated antenna weights calculated to minimize energy received at least one neighboring wtru;

the signal processing unit is further configured to derive transmit antenna weights from the calculated antenna weights; and

the antenna array is further configured to form a steered antenna beam to transmit the uplink signal based on the derived transmit antenna weights.

2. The wtru of claim 1 wherein the antenna weights derived for transmitting signals are the same as the antenna weights calculated for receiving signals.

3. The wtru of claim 1, wherein the antenna array is further configured to dynamically adapt the formed receive and transmit antenna beams to current radio conditions.

4. The wtru of claim 1 wherein antenna weights calculated for received signals are used to optimize signal-to-noise or signal-to-noise-plus-interference ratios.

5. The wtru of claim 1 wherein antenna weights calculated for received signals are used to minimize received interference.

6. The wtru of claim 1 wherein the antenna weights calculated for the received signals are used to minimize received interference while maintaining a fixed received signal level.

7. The wireless transmit/receive unit of claim 1, wherein the antenna array is further configured to steer nulls in directions other than the direction of the beam formed to receive signals.

8. A method for mitigating wtru-to-wtru interference in wireless communications, the method comprising:

measuring a signal quality of the received signal;

calculating antenna weights based on the quality measurements, the antenna weights calculated to minimize energy received at the at least one neighboring wtru;

forming a steered antenna beam to receive the downlink signal based on the calculated antenna weights;

deriving transmit antenna weights from the calculated antenna weights; and

forming a steered antenna beam to transmit the uplink signal based on the derived transmit antenna weights.

9. The method of claim 8, wherein the derived antenna weights are equal to the calculated antenna weights.

10. The method of claim 8, further comprising dynamically adapting the formed receive and transmit antenna beams to current radio conditions.

11. The method of claim 8, wherein the calculated antenna weights are calculated to optimize a signal-to-noise ratio or a signal-to-noise-plus-interference ratio.

12. The method of claim 8, wherein the computed antenna weights are computed to minimize received interference.

13. The method of claim 8, wherein the calculated antenna weights are calculated to minimize received interference while maintaining a fixed received signal level.

14. The method of claim 8, further comprising steering nulls in directions other than beams formed for receiving signals.