METHOD AND APPARATUS FOR DETERMINING AN OPERATING CONDITION IN A COMMUNICATIONS SYSTEM
A communication system environment estimation apparatus and method. In one embodiment, an environment estimation apparatus according to the teachings of the present invention includes a plurality of antenna elements and a receiver coupled to receive uplink signals from the plurality of antenna elements. The apparatus also includes a signal processor coupled to receive the uplink signals to select an estimation of an environment responsive to the uplink signals received from the plurality of antenna elements.
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This application is a division of and claims the benefit of priority to U.S. application Ser. No. 09/668,664, filed on Sep. 22, 2000, the disclosure of which is incorporated herein by reference in its entirety for all purposes.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates generally to communications systems and, more specifically, the present invention relates to wireless communications systems employing antenna arrays.
2. Background Information
Antenna arrays may be used in communications systems that transmit and/or receive radio frequency signals. Antenna arrays typically include a number of antennas that are spatially separated and may be employed in a number of different wireless applications including radio communications systems, cellular systems, television broadcasting, point to point systems, paging systems, medical applications or the like.
The use of antenna arrays in such systems often provide antenna performance improvements over the use of a single element antenna. These antenna performance improvements may include for received signals improved signal to noise ratio and interference rejection. Antenna performance improvements for transmitted signals may include improved directionality and hence less power towards other co-channel users, security and reduced transmit power requirements. Antenna arrays may be used for signal reception only, for signal transmission or for both signal reception and transmission.
A typical application of antenna array systems is in a wireless communication system. Examples include a cellular communication system and a wireless local loop system. Such wireless communications systems typically include one or more communications stations, generally called based stations, each communicating with its subscriber units, also called remote terminals and handsets. In cellular systems, the remote terminal is typically mobile, while in wireless local loop systems, the remote unit is typically in a fixed location.
The antenna array is typically at the base station, but may also be employed at a user terminal. Communication from the remote terminal to the base station is typically called the uplink and communication from the base station to the remote terminal is typically called the downlink. In time division duplex (TDD) systems, uplink and downlink communications with a particular remote terminal occur at the same frequency, but at different time slots. In frequency division duplex (FDD) systems, uplink and downlink communications with a particular remote terminal occur at different frequencies and may or may not occur at the same time.
Since different frequencies are used in the uplink and downlink communication channels in FDD, the behavior of the signals in the uplink and downlink communication channels between the base station and remote terminal are different. The differences are more apparent as the channels have more multipath components. In a multipath environment, scattering and/or reflections caused by, for example, buildings or the like result in amplitude and phase changes and/or multipath components in the communication signals. Multipath components behave differently for different frequencies and a communication signal arriving at an antenna array changes with the frequency. Accordingly, the performance of a wireless communications system is impacted by the presence of scatterers in the environment.
Another factor that impacts wireless communication system performance is the presence of multiple remote terminals utilizing the same frequency or channel at the same time in the environment. As the number of separate sources or remote terminals utilizing the same frequency increases, the amount of interference in the communications channel also increases.
SUMMARY OF THE INVENTIONAn environment estimation apparatus and method are disclosed. In one embodiment, an environment estimation apparatus includes a plurality of antenna elements and a receiver coupled to receive uplink signals from the plurality of antenna elements. The apparatus also includes a signal processor coupled to receive the uplink signals to select an estimation of an environment responsive to the uplink signals received from the plurality of antenna elements. Additional features and benefits of the present invention will become apparent from the detailed description, figures and claims set forth below.
The present invention is illustrated by way of example and not limitation in the accompanying figures.
In one aspect of the present invention, methods and apparatuses for determining an operating condition or environment of a communications system are disclosed. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one having ordinary skill in the art that the specific detail need not be employed to practice the present invention. In other instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present invention.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.
In one aspect of the present invention, a base station in a wireless communication system is provided with the ability to estimate an environment or condition in which the wireless communication system is operating. In one embodiment, the base station includes an antenna array having a plurality of antenna elements. Uplink communication signals are received by the antenna elements in the antenna array and processing is performed on the uplink communication signals to estimate whether the base station is operating in a low clutter or high clutter environment. In addition, processing is performed in one embodiment on the uplink communication signals when in a high clutter environment to estimate whether the base station is operating in a low interference or high interference environment.
To illustrate,
In the depicted embodiment, a receiver 109 is coupled to receive uplink communication signals 117 from the antenna elements 105 and 107 of antenna array 103. In one embodiment, signal processor 111 is coupled to receiver 109 to receive the uplink communication signals 117. In one embodiment, storage 113 is coupled to receiver 109 to store the uplink communication signals 117 received by receiver 109 and signal processor 111 is coupled to storage 113 to receive the stored communication signals. In one embodiment, storage 113 is a machine-readable medium on which software instructions that may be executed by signal processor 111 are stored.
As shown in the embodiment illustrated in
To illustrate,
As illustrated in
Referring back to
As illustrated in
In one embodiment, base station 301 receives uplink communication signals 317 through antenna array 303. Base station 301 processes the uplink signals 317 and generates an environment estimate 315, which in
As illustrated in
In one embodiment, base station 401 receives uplink communication signals 417 through antenna array 403. Base station 401 processes the uplink signals 417 and generates an environment estimate 415, which in
In one embodiment, block 505 shows that an uplink spatial signature is then estimated. As is known to those skilled in the art, rZs provides an estimate of the uplink signature, ât. For illustration purposes, assume that rZs is equal to the uplink spatial signature where rZs is [ZHS]M×1, a correlation vector of Z and s. Z represents a matrix representing the received uplink signal, s represents a reference signal, M is the number of elements in then antenna array and H represents a Hermitian transpose. In one example, assume that uplink communication signals include equal strength angle of arrival (AOA) components with AOA1=90° and AOA2=0°. It is assumed further that the antenna array includes two antenna elements such that M=2 with inter-element spacing of λ/2. Accordingly, the estimated uplink spatial signature ât is as follows:
ât=a(AOA1)+a(AOA2) (Eq. 1)
ât=ejβdcos(AOA
where β=2π/λ, d=λ/2, λ=c/f, c=speed of light and f=carrier frequency. Using the above relationships, the estimated uplink spatial signature may be calculated for this particular example as follows:
ât=ej(2π/λ)(λ/2)cos(90°)[0:1]+ej(2π/λ)(λ/2)cos(0°)[0:1] (Eq. 3)
ât=[1 1]+[1 −1] (Eq. 4)
ât=[2 0] (Eq. 5)
Continuing with the flow diagram 501 of
âg=ejβdcos(θ
In one embodiment, well-known techniques may be utilized to estimate the dominant AOA. Known AOA estimation techniques that may be utilized in accordance with the teachings of the present invention include the Delay and Sum method, Capon's method, Multiple Signal Classification (MUSIC) and Estimation of Signal Parameters via Rotational Invariance Techniques (ESPRIT).
The Delay and Sum method is also referred to as a classical beamformer method or Fourier method. The beamformer uses a weight, w, which is the spatial signatures for any given angle, θ. Thus, w=a(θ). The output power of the beamformer is calculated for each azimuthal angle. The AOA corresponding to the largest output power is declared as the source AOA. This known technique produces broad beams.
Capon's known method forms a beam in the look angle, θ, but it also tries to null uncorrelated interference. This is achieved by minimizing the output power subject to the constraint that a beam is formed in the direction of the look angle such that
minwE[y(k)]2=minwwHRZZw (Eq. 7)
subject to
wHa(θ)=1 (Eq. 8)
where y is the output, w is the weight vector, H represents a Hermitian transpose and RZZ is the input correlation matrix. The output power spectrum as a function of AOA is given by
PCapon(θ)=1/(aHRZZa(θ)). (Eq. 9)
The known MUSIC technique is a high resolution algorithm that exploits the Eigen structure of the input covariance matrix. MUSIC is a signal parameter estimation algorithm that estimates the number of incident signals, their AOAs, their strengths and the cross correlations between the incident signals. The Eigen vectors of the covariance matrix belong to either of the two orthogonal subspaces: signal subspace or noise subspace. The steering vector corresponding to the AOA of the signals lie in the signal subspace and hence orthogonal to the noise subspace. By searching through all possible array steering vectors that are perpendicular to the space spanned by the Eigen vectors of the noise subspace, the AOAs are estimated.
The known ESPRIT technique is another subspace technique that reduces the computation and storage requirements for MUSIC. ESPRIT does not require an exhaustive search or precise calibration. ESPRIT derives its advantages by utilizing array elements that have a structure that can be decomposed into two equal sized identical subarrays with corresponding elements of the two subarrays being displaced from one another by a fixed translational, not rotational, distance.
Once the dominant AOA θd is estimated, the geometric uplink spatial signal âg may be calculated using the estimated dominant AOA θd with Equation 6 above. In one embodiment, the dominant AOA θd corresponds to the AOA with the highest power. Continuing with the example described above with a dominant AOA θd assumed to be 90°:
âg=ej(2π/λ)(λ/2)cos(90°)[0:1] (Eq. 10)
âg=[1 1] (Eq. 11)
Continuing with the flow diagram 501 of
To illustrate, continuing with the example described above with ât=[2 0] and âg=[1 1], the correlation ρ is equal to the normalized dot product between ât and âg. Accordingly,
ρ=(âtHâg)/(∥âtH∥ ∥âg∥) (Eq. 12)
ρ=0.7071 (Eq. 13)
Assuming that ρ=0.7071 is greater than the low clutter threshold, than a low clutter threshold environment is selected. It is appreciated that the low clutter threshold is determined in one embodiment based on a number of factors including the number of antenna elements M in the antenna array.
ρij=<ZiHZj>/(∥ZiH∥ ∥Zj∥) (Eq. 14)
where i and j represent specific antenna elements in the antenna array and i≠j. In one embodiment, correlations are calculated for all pairs of uplink signals.
Continuing with the flow diagram 601 of
RZZ=ZZH (Eq. 15)
Continuing with the flow diagram 701 of
In this simple example, M=3 antennas and the Eigen values for RZZ=[1 1 0].
In one embodiment, after the Eigen values for RZZ are determined, the source order may be determined using well-known techniques including for example Sequential Hypothesis (SH), Minimum Descriptive Length (MDL), Akaike Information Criteria (AIC) or the like. As is known to those skilled in the art, all these techniques estimate then source order or number of sources by minimizing a log-likelihood function, where the likelihood function is the ratio of geometric mean to arithmetic mean of the Eigen values of the input correlation matrix.
Continuing with the flow diagram 701 of
After the uplink communication signals are received, a received signal strength indication (RSSI) of the uplink communications signals is then measured. The RSSI includes the components of S, N and I, where S represents the desired signal, N represents noise and I represents interference. If the RSSI is greater than an RSSI threshold, as shown in block 803, block 804 shows that in one embodiment, the signal to noise ratio is then calculated from the uplink communication signals. When a signal S is not being transmitted and/or received, the noise N can then be measured from the uplink communication signals. The signal to noise ratio is calculated using the following relationship:
signal to noise ratio=RSSI/N (Eq. 17)
After the signal to noise ratio is calculated, block 805 shows that an expected bit error rate (BER) can then be determined in accordance with the teachings of the present invention. In one embodiment, the expected BER is determined based on values predicted in advance that may for example be stored in look-up tables or the like. In particular, for a given signal to noise ratio, an expected BER can be determined. In another embodiment, the expected BER is a function of the signal to noise ratio and can therefore be derived from the signal to noise ratio.
Continuing with flow chart 801 of
In the foregoing detailed description, including what is described in the Abstract, the method and apparatus of the present invention have been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the present invention. The present specification and figures are accordingly to be regarded as illustrative rather than restrictive. The description and abstract are not intended to be exhaustive or to limit the present invention to the precise forms disclosed.
The terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with the established doctrines of claim interpretation.
Claims
1. A method of characterizing an environment, comprising:
- receiving uplink signals from a plurality of antenna array elements;
- calculating pairwise correlations of the uplink signals received by the plurality of antenna array elements;
- calculating an average of absolute values of said pairwise correlations of the uplink signals received by the plurality of antenna array elements; and
- selecting a high clutter environment estimation if the average of the absolute values of said pairwise correlations of the uplink signals received by the plurality of antenna array elements is less than a high clutter threshold.
2. The method of claim 1 wherein calculating said pairwise correlations of the uplink signals received by the plurality of antenna array elements comprises calculating a normalized dot product for said pairwise correlations of the uplink signals received by the plurality of antenna array elements.
3. A method of characterizing an environment, comprising:
- receiving uplink signals from a plurality of antenna array elements;
- calculating a correlation matrix from the uplink signals received by the plurality of antenna array elements;
- estimating a source order from the correlation matrix; and
- selecting a high interference environment estimation if the estimated source order is greater than a high interference threshold.
4. The method of claim 3 wherein estimating the source order in response to the correlation matrix comprises:
- calculating Eigen values of the correlation matrix; and
- performing a sequential hypothesis technique on the Eigen values to estimate the source order.
5. The method of claim 3 wherein estimating the source order in response to the correlation matrix comprises:
- calculating Eigen values of the correlation matrix; and
- performing an Akaike Information Criteria technique on the Eigen values to estimate the source order.
6. The method of claim 3 wherein estimating the source order in response to the correlation matrix comprises:
- calculating Eigen values of the correlation matrix; and
- performing a minimum descriptive length technique on the Eigen values to estimate the source order.
7. A method of characterizing an environment, comprising:
- receiving uplink signals from a plurality of antenna array elements;
- calculating a signal to noise ratio in response to the uplink signals received from the plurality of antenna array elements;
- measuring a bit error rate (BER) in response the uplink signals received from the plurality of antenna array elements;
- determining an expected BER in response to the signal to noise ratio; and
- selecting a high interference environment estimation if the measured BER is a BER threshold amount greater than the expected BER.
8. The method of claim 7 wherein calculating the signal to noise ratio in response to the uplink signals received from the plurality of antenna array elements comprises:
- measuring a received signal strength indication (RSSI) in response to the uplink signals received from the plurality of antenna array elements; and
- measuring noise included in the uplink signals received from the plurality of antenna array elements.
9. The method of claim 8 further comprising selecting the high interference environment estimation if the measured BER is a BER threshold amount greater than the expected BER and the RSSI is greater than a RSSI threshold value.
Type: Application
Filed: Nov 25, 2008
Publication Date: Mar 19, 2009
Applicant: INTEL CORPORATION (Santa Clara, CA)
Inventor: Paul Petrus (Santa Clara, CA)
Application Number: 12/323,378
International Classification: H04B 1/06 (20060101);