FIELD OFTHE INVENTION
The present invention relates to a method, a network access node and a computer
program product.
BACKGROUND
In a wireless telecommunications network, it is desirable to be able to identify the
location of, for example, user equipment in order to enable operators †o provide
location and presence-based services to users. The effectiveness of these services
increases with the accuracy with which it is possible to determine the location of the
user equipment.
Although techniques exist which attempt to accurately locate network nodes within the
wireless telecommunications network, they each have shortcomings. Accordingly, it is
desired to provide a n improved technique for determining the location of network
nodes within the wireless telecommunications network.
SUMMARY
According to a first aspect, there is provided a method of estimating a distance
between a t least one network access node and a network node of a wireless
communications network, comprising: measuring total path losses between the at least
one network access node and the network node on a t least two different frequencies;
determining frequency-dependent path losses of transmissions by the a t least one
network access node on the a t least two different frequencies; and estimating a
distance between the network node and the at least one network access node using
the total path losses and the frequency-dependent path losses on the at least two
different frequencies.
The first aspect recognises that a problem with existing techniques for estimating a
network node location is that they all have limitations, particularly in indoor
environments. For example, the satellite signals in a GPS system are usually insufficient
to provide a location estimate in an indoor environment. Cell identification methods
are possible, but their accuracy is limited by the cell size and many cells may need to
be deployed to provide highly accurate location information which is expensive and
leads to a high increase in mobility signalling. Cellular triangulation techniques
exploiting timing differences of received signals from multiple base stations have
accuracy limited to several tens of metres and small cells indoors cannot be used due
to insufficient timing differences resulting from the short distances. Power-based finger
printing using power measurements from multiple base stations cannot be used for
accurate location estimation without a database of power measurements existing for
all locations in the building which enables measurements made by the network node to
b e matched to the most likely location; although this can lead to accurate location
estimation, the creation of such a database is a time-consuming and expensive
process which needs to be performed whenever the environment changes.
The first aspect also recognises that it is difficult to estimate the distance to a network
node based on transmissions received because those transmissions will be subjected to
losses caused by obstructions (such a s walls or other physical objects) and interference
between the network nodes. However, the first aspect recognises that the losses
caused by those obstructions or interference are typically frequency-dependent. In
other words, the path losses caused by obstructions or other interference are typically
frequency-dependent, whereas the path loss in free space is frequency-independent.
That is to say, the path loss experienced in free space at different frequencies will
typically be the same, whereas the path loss through obstructions a t different
frequencies will vary. By measuring the total path losses between network nodes on
different frequencies and using frequency-dependent path losses determined for those
frequencies, it is possible to estimate the distance between network nodes. This
effectively removes the effects of the frequency-dependent path losses for the different
frequencies in order to estimate the distance between network nodes. In other words,
by measuring the total path loss a t different frequencies and using the frequencydependent
path losses which are determined a t those frequencies, it is possible to
effectively cancel the frequency-dependent path losses and estimate the distance
between network nodes. Given that network nodes are typically already configured to
enable transmissions to occur on different frequencies, no additional hardware is
required and the existing infrastructure can be utilised to provide accurate location
estimation using this approach.
Accordingly, a method of estimating a distance between network nodes may b e
provided. The method may comprise measuring the total path losses between network
nodes on at least two different frequencies. The frequency-dependent path losses of
transmissions made by a network node on the different frequencies may then be
determined. A distance may then be estimated between the network nodes using the
total path losses and the frequency-dependent path losses on the different
frequencies.
Measurement reports may be sent back to the originating network node to enable the
path loss between the network nodes to be established on the different frequencies.
In one embodiment, the frequency-dependent path losses are determined from a
difference in the total path losses on each different frequency between the at least
one network access node and the network node. Accordingly, the frequencydependent
path losses may be calculated from the difference between the path
losses on the different frequencies.
In one embodiment, the frequency-dependent path losses are determined from
transmissions on each different frequency between at least two network access nodes.
For example, the frequency-dependent path losses may be determined based on pilot
signals transmitted between network nodes.
In one embodiment, the frequency-dependent path losses are determined from
transmissions on each different frequency between at least three network access
nodes. By determining the frequency-dependent path losses between at least three
network nodes, the frequency-dependent path losses within a region bounded by the
at least three network nodes may be determined.
In one embodiment, the frequency-dependent path losses are determined from
transmissions on each different frequency and a distance between network access
nodes. Accordingly, the frequency-dependent path losses may be determined using
the transmissions and the distance between network nodes. It will be appreciated that
the location of or distance between many static network nodes may be readily
determined. Likewise, it may be possible to perform such measurements based on
requiring a mobile network node to operate at a pre-defined location to determine the
path losses.
In one embodiment, the method comprises determining a n average frequencydependent
path loss on each different frequency between network access nodes.
Accordingly, an average frequency-dependent path loss on each frequency may be
determined for a particular region.
In one embodiment, the frequency-dependent path losses at each different frequency
are determined using an effective frequency-dependent attenuation between the
network access nodes.
In one embodiment, the effective frequency-dependent attenuation is determined
using a path loss measured a t each different frequency between the network access
nodes and a distance between the network access nodes.
In one embodiment, the method comprises determining a n average effective
frequency-dependent attenuation on each different frequency between the network
access nodes.
In one embodiment, the frequency-dependent path losses are determined from
predetermined frequency-dependent path losses approximated for different
deployment environments. Accordingly, rather than determining the frequencydependent
path losses based on actual transmissions between network nodes, the
frequency-dependent path losses may be approximated based on knowledge of the
environment in which the network nodes are deployed. For example, a set of
approximated frequency-dependent path losses may be derived and then utilised
when required. The set may, for example, include frequency-dependent path losses for
typical office configurations, one of which may be selected based on knowledge of
the physical characteristics of the environment that the network nodes are to be
deployed.
In one embodiment, the distance is estimated from a corrected path loss determined
by removing the frequency-dependent path losses from the total path losses on each
different frequency. Accordingly, the distance may be determined from a standard
path loss model which uses a corrected path loss which cancels the frequencydependent
path losses on each frequency.
In one embodiment, the distance is estimated using the total path loss, a transmission
power and the average effective frequency-dependent attenuation o n each different
frequency.
In one embodiment, the distance is estimated in accordance with
F . -d + L (lin) -F d - L (lin) F , d + (lin) -F, -d - L (Iin)
=0; i=l,2,3
L (lin) -F , d L (lin) F d
In one embodiment, the method comprises estimating a distance between the
network node and each of the network access nodes. It will be appreciated that by
increasing the number of network nodes to which the distance is estimated, location
estimation can be improved.
According to a second aspect, there is provided a network node operable to
estimating a distance between at least one network access node and a network node
of a wireless communications network, comprising: measurement logic operable to
measure total path losses between the at least one network access node and the
network node on at least two different frequencies; determining logic operable to
determine frequency-dependent path losses of transmissions by the at least one
network access node on the at least two different frequencies; and estimating logic
operable to estimate a distance between the network node and the at least one
network access node using the total path losses and the frequency-dependent path
losses on the at least two different frequencies.
In one embodiment, the frequency-dependent path losses are determined from a
difference in the total path losses on each different frequency between the at least
one network access node and the network node.
In one embodiment, the frequency-dependent path losses are determined from
transmissions on each different frequency between at least two network access nodes.
In one embodiment, the frequency-dependent path losses are determined from
transmissions on each different frequency between at least three network access
nodes.
In one embodiment, the frequency-dependent path losses are determined from
transmissions on each different frequency and a distance between network access
nodes.
In one embodiment, the determining logic is operable to determine an average
frequency-dependent path loss on each different frequency between network access
nodes.
In one embodiment, the frequency-dependent path losses at each different frequency
are determined using an effective frequency-dependent attenuation between the
network access nodes.
In one embodiment, the effective frequency-dependent attenuation is determined
using a path loss measured a t each different frequency between the network access
nodes and a distance between the network access nodes.
In one embodiment, the determining logic is operable to determine an average
effective frequency-dependent attenuation on each different frequency between the
network access nodes.
In one embodiment, the frequency-dependent path losses are determined from
predetermined frequency-dependent path losses approximated for different
deployment environments.
In one embodiment, the distance is estimated from a corrected path loss determined
by removing the frequency-dependent path losses from the total path losses on each
different frequency.
In one embodiment, the distance is estimated using the total path loss, a transmission
power and the average effective frequency-dependent attenuation on each different
frequency.
In one embodiment, the distance is estimated in accordance with
F d +L ( i) · , d - L (lin) F d +L (lin) F, -d - L (lin)
=0; #= 1,2,3
L (lin)
'
-F d L (lin) F -d
In one embodiment, the estimating logic is operable to estimate a distance between
the network node and each of the network access nodes.
According to a third aspect, there is provided a computer program product operable,
when executed on a computer, to perform the method of the first aspect.
Further particular and preferred aspects are set out in the accompanying independent
and dependent claims. Features of the dependent claims may be combined with
features of the independent claims as appropriate, and in combinations other than
those explicitly set out in the claims.
Where a n apparatus feature is described as being operable to provide a function, it will
be appreciated that this includes a n apparatus feature which provides that function or
which is adapted or configured to provide that function.
BRIEF DESCRIPTION O FTHE DRAWINGS
Embodiments of the present invention will now be described further, with reference to
the accompanying drawings, in which:
Figure 1 illustrates a method for estimating the distance between network nodes
according to one embodiment;
Figure 2 illustrates a n example deployment of three different base stations or other
network nodes operating in a n environment where the user equipment is expected to
operate; and
Figure 3 illustrates the base station arrangement of Figure 2, but with the inclusion of
user equipment whose location is to be determined.
DESCRIPTION OFTHE EMBODIMENTS
Overview
The losses between a network access node such as, for example, a base station and
another network node such as, for example, user equipment are estimated. These
estimates may b e made by a n operator based on a n assessment of the deployment
environment or by measurements made by network nodes. For example, network
nodes may perform path-loss measurements Lpi and LP2 at a t least two different
frequencies, f and (for example, f could be set to 900 MHz (the GSM spectrum) and
f2 could be set to 1.9 or 2.6 GHz (the LTE spectrum)) . To enable the two path-loss
measurements to b e made, the base station transmits pilot signals in each frequency
bands. Since the signal attenuation in free space is frequency independent, but the
transmission loss caused by walls or other obstacles is frequency dependent, the path
loss for both frequencies caused by the walls Lw and Lw2 can b e calculated based on
the difference in the path loss measurements because the attenuation properties
through different materials a t different frequencies are known or can be derived, a s will
be explained in more detail below.
Once the wall losses Lw and Lw2 are known, the distance between the base station and
the user equipment can be estimated based on the corrected path loss LPC = LP - Lw .
This removes the wall effects, which makes received power-based indoor distance
measurements problematic where a measurement database would otherwise b e
required to identify locations due to the effects of walls. By using the corrected path
loss, the distance between the base station and the user equipment can be accurately
estimated using the corrected path loss LPC and a path loss equation such as, for
example, the free space path loss equation. Using this approach, the location of user
equipment can b e calculated using known triangulation methods when the distance
to a t least three base stations is determined.
Figure 1 illustrates principles of a method for estimating the distance between network
nodes. In this example, the network nodes are a base station and user equipment. The
base station transmits two pilots on two different frequencies f i and f2. The connected
user equipment send measurement reports detailing received power measurements of
the pilot signals. The measurement reports are used to calculate the path loss for the
links between the base station and the user equipment. The path loss can readily be
determined by subtracting the received power measurements reported by the user
equipment from the known transmission power. In this example, the path loss consists of
a free-space path loss over the distance d , a s well as a n additional wall loss Lw. The
free-space path loss is independent of frequency and so is equal for measurements on
both frequencies. However, the wall loss is heavily frequency-dependent (lower
frequencies are attenuated less than higher frequencies). This difference in attenuation
is apparent from the difference in the two path loss measurements LPI and LP2, and can
be used to estimate the wall losses Lwi and Lw2.
Considering a path loss model given by Equation (1) below:
L dB) = PL + \ y log 0(d) Equation (1)
PLo is a known parameter and it represents the path loss a t a reference distance
(usually 1 metre), d is the distance between the user equipment and the base station
and y is a path loss exponent. The path loss exponent, y, consists of two parts; the
frequency-independent part (free-space path loss exponent, yo = 2) and a frequencydependent
part (environment path loss exponent, ye) .
The path loss exponent can b e expressed as:
Y = Y o + Y Equation (2)
In light of Equation (2), Equation ( 1 ) can now be written (in the log scale) as:
Lp {dB) = PL + \ y o \og (d) + l \og (d) Equation (3)
Hence, it can b e seen that given the path loss a t the reference distance PLo, the free
space path loss exponent yo and the environment path loss exponent ye (each of which
may be pre-programmed or derived from measurements made by deployed network
nodes, a s will be explained in more detail below), the distance d between network
nodes can be derived from the path loss measurement L .
In order to improve accuracy in deriving the estimated distance, the network may
perform measurements to estimate the losses due to the walls or other obstructions. For
example, loss estimation can be performed automatically using three different base
stations or other network nodes operating in the environment where the user
equipment is expected to operate, as shown schematically in Figure 2.
Wall loss estimation
The estimation is performed by measuring the path losses between each pair of the
three base stations a t at least two different frequencies, f i and , a s will now be
explained in more detail.
Using knowledge of the distance between base stations (i.e., d i , d 2 and d3) . Equation
(3) enables the cy f :
where: L i (dB) is the path loss between any two base stations a t frequency fi and di is
the distance between base stations.
As the example in Figure 2 uses three different base stations, e, is calculated using
Equation (4) for each pair of the three base stations a t frequency f , resulting in three
values for y i{ . A similar evaluation is performed for e .
Equation (3) can be written on the linear scale as:
p
p (/ «)= -^-= F-d '*r-=F d ° -d ' , where =10 Equation (5)
P and Pr stand for the transmitted and received powers, respectively.
From Equation (5) it can be seen that the loss solely due to free space is given by f . ,
while the effect of the environment is given by the factor, d,. . The loss entirely induced
by the environment (excluding free space) is given by:
P P P(d - -l)
AL ( lin) - - Equation (6)
Fd ° Fd >d Fd"d -
This loss can be assumed to originate from the absorption losses of "effective" walls with
a n "effective" thickness, d , equal to the distance between respective base stations.
The power loss of the signal propagating through such an effective wall at the
frequency f is given by:
= R,L - P, 2 ' "' ; ' =1,2,3 Equation (7)
where Ptti is the power transmitted by the base station at the frequency f , F is the
"effective" attenuation constant of the "effective" wall with a thickness di (the distance
between each pair of base stations) a t the frequency f .
By equating Equation (7) with the loss entirely induced by the environment given by
Equation (6) (and recognizing that Pl f and of (7) correspond to Pt and d of (6) ) one
obtains the "effective" attenuation constant of the "effective" wall as a function of the
path loss exponent, ., . at a frequency of f :
F.f d d " + \ - d " fi
n ; / =1,2,3 Equation (8)
By recognising that Equation (8) is evaluated three times (once for each pair of the
three different base stations) a t a specific frequency, the effective attenuation
constant may be averaged
f, = + + 3 l ) Equation (9)
Here, a represents the average effective wall attenuation for the environment shown
in Figure 2 at the frequency f . A similar expression can be written for the average
effective wall attenuation a t the frequency . Now that an average effective wall
attenuation and 2 a t two different frequencies has been calculated, the
calibration has been completed. In particular, a s will be explained in more detail
below, average effective wall attenuations a t the two different frequencies which
represent derived frequency-dependent path losses may be utilised to determine the
distance of a network node, such as user equipment, from any base station by using
measured path losses of transmissions received from that network node on a t least two
different frequencies.
Location Estimation
Figure 3 shows the base station arrangement of Figure 2 , but with the inclusion of user
equipment whose location is to be determined. The path loss shown in Equation (5) a t
the two frequencies f and f2can b e written as:
Equation (10)
In Equation (10), the terms Plf> ( 1- 2 ,*') and , (l-e *' ) represent the powers
absorbed by the walls and are obtained from Equation (7) b y replacing the distance
d . with a parameter This parameter ki represents the unknown "thickness" of a n
obstructed wall with attenuation constants f fiand ^at frequencies f and f2
resp ec tive ly diue represents the distances from the user equipment to the i-th base
station. The introduction of parameter ki a s a n unknown thickness of a fictitious wall is
justified a s long a s the rate o f change o f the average attenuation constant with
frequency does not vary significantly from the rate o f change of the attenuation
constant for a particular pair o f base stations with frequency, i.e.:
;'= , 2,3 (Equation 11)
By eliminating ki from the system of equation given by Equation ( 0), one obtains the
expression from which the distances diUE are found:
F -d + L (lin) F i -d —L (/in) F , -d + L (lin) F -d - L (lin)
=0; /=1,2,3
(lin) -F . dn L (lin) F -d
Equation 12)
Which ultimately leads to the estimated distances diUE from the three base stations as
depicted in Figure 3 .
Example Operation
Assume that it is required to determine the radial distance diuE between the user
equipment and the base station BS 1 of Figure 3 . The distance between base stations
are d i = 100 metres, d 2 = 75 metres and d 3 = 50 metres. Isotropic antennas are used a t
both the transmit and receive ends.
The path losses a t the reference distance PLo and PLof2 need to b e determined. These
may be determined a t a distance of 1 metre from each base station and are
dependent o n the parameters of the antennas used in the user equipment and base
station. They can b e either measured or, provided that the parameters of the antennas
are known, calculated. The general expression for this term is known as Friis free-space
link equation and is given by:
\ 6p
( « ) = 10 log,, (Equation 13)
G,G,A2
which for the case of isotropic antennas (Gr = G t = 1) for transmit and receive which
simplifies to:
PL (dB)=2Q \og (Equation )
At the frequencies f of 900 MHz and of 1900 MHz, the path loss a t the reference
distance PLoifi (dB) is 3 1.526 d B and PLOF2 is 38.01 dB.
From Equation (4) , the path loss exponents e i and e 2 can be calculated from the
measured path loss over the distance di, d 2 and d 3 using the path losses a t the
reference distance PLo mentioned above and the distance between base stations. This
leads to the values of e = 2.4 and e 2 = 2.6. Alternatively, these values may be
estimated based o n the characteristics of the environment such as the number of walls,
the wall types and their density.
Now that the values of the path loss exponents are known, the values of the
attenuation constants are calculated from Equation (8) for each pair of the three base
stations a t each frequency. In this example, = 3.5734x1 0- ,0and = 8.9899x1 0- .
Now the distance diue from the user equipment to base station BS 1 may be estimated.
The measured path losses between base station BS1 and the user equipment are 55.5
d B and 64 d B a t f and f2 respectively. Using Equation (12), diuE is calculated as:
d=7.6m Equation (15)
From Equation (7) , the losses due to the walls may be calculated as:
Lw = 6.2577 dB and Lw = 8.3737 dB Equation ( 1 6 )
As a n additional verification, it can b e seen that the distance estimate is robust for
different wall losses between the base station and the user equipment. To demonstrate
this, assume that the attenuation due to the walls between the user equipment and
base station BS1 is two times greater than the values given in Equation (15) (i.e., Lw. =
12.5154 d Band L , 2 = 16.7474 dB). As a result, the measured path losses are now
6 .6577 d Band 72.3737 d B a t f and respectively. The measured attenuation
between base stations remains the same so that the attenuation constants n=
3.5734x1 ' and = 8.9899X 10-".
The recalculated distance is now:
d=7.6m Equation ( 17)
The calculated distances given by Equations (15) and (17) are the same, which shows
that it is possible to accurately estimate the distance independently of the wall losses.
Through approaches mentioned above, it can be seen that it is possible to accurately
determine the location of user equipment with respect to base stations. Using
triangulation techniques where the distance to a t least three network nodes of know
locations is performed, highly accurate location estimation of user equipment or other
network nodes is possible. With such accurate location estimation it is possible to
provide many location-based applications and services to users, such as:
1. A guided tour o n a smart-phone in a public building - e.g. Museum or Art
Gallery. The smart phone application uses location information provided by the femto
based service to customise information (audio/visual) presented to the user.
2. A shopper in a supermarket may b e awarded a discount coupon o n a n item.
Provided with accurate location information by the femto based service, a n
application on a smart phone could direct/guide the person to the location of the
item.
3. Finding the location of a colleague in a n enterprise environment - e.g. which
meeting room are they in. Provided with accurate location information from the femto
base service, a smart phone application could display the colleague's location.
4. Meeting attendees - useful for automatically generating a list of who attended
a meeting. A meeting organiser requests list of people in meeting room a t a particular
time. By continually recording the location of phones, the femto based service can list
who was a t the location a t a particular time.
5. Social/professional networking. Provided with location/presence information b y
a femto based service, a n application could automatically request a link to the profile
of people present a t a n event (conference, pub, house party etc.).
The above examples are just a few of a large number of possibilities of location and
presence-based services. One requirement that all of these services have in common is
that they require accurate location estimation of mobile phones. Current existing
methods are either do not provide sufficient accuracy or are too expensive to deploy.
The technique mentioned above provides for accurate location estimation which
allows measuring and compensating for wall losses between the base stations and the
user equipment and thereby enables received power based location estimation
without the need for expensive calibration for each building.
Enhancements
In network nodes, the quality of the different receivers/antennas for different
frequencies may be different, resulting in different losses. This can lead to errors in the
path-loss estimation. This problem can be prevented by auto-calibrating the
calculation. This can be done by performing measurements for a known location of
the network node (e.g. when entering the building) where there are no walls. In this
case the path-loss estimate should be equivalent for the two frequencies. Any
difference can be stored for the particular mobile and taken into account in the
calculations above to correct for the measurement error.
The same approach can be used when the wall losses at a specific location are known
for the two frequencies. This correction value is required at all points where the
distance to the network node is estimated. Therefore the base station that performs the
calibration needs to transmit the correction value to all distance measurement points
(e.g. other base stations, or a central entity that collects all measurements for the
location estimation).
This approach provides a cost effective and accurate method to estimate the distance
of a mobile to a base station in indoor environments. This enables many location and
presence based services and overcomes or alleviates problems existing solutions have
due to lack of accuracy indoors or due to expense for accurate indoor positioning.
A person of skill in the art would readily recognise that steps of various above-described
methods can be performed by programmed computers. Herein, some embodiments
are also intended to cover program storage devices, e.g., digital data storage media,
which are machine or computer readable and encode machine-executable or
computer-executable programs of instructions, wherein said instructions perform some
or all of the steps of said above-described methods. The program storage devices may
be, e.g., digital memories, magnetic storage media such as a magnetic disks and
magnetic tapes, hard drives, or optically readable digital data storage media. The
embodiments are also intended to cover computers programmed to perform said
steps of the above-described methods.
The functions of the various elements shown in the Figures, including any functional
blocks labelled a s "processors" or "logic", may be provided through the use of
dedicated hardware a s well a s hardware capable of executing software in association
with appropriate software. When provided by a processor, the functions may be
provided by a single dedicated processor, by a single shared processor, or by a
plurality of individual processors, some of which may be shared. Moreover, explicit use
of the term "processor" or "controller" or "logic" should not be construed to refer
exclusively to hardware capable of executing software, and may implicitly include,
without limitation, digital signal processor (DSP) hardware, network processor,
application specific integrated circuit (ASIC), field programmable gate array (FPGA),
read only memory (ROM) for storing software, random access memory (RAM), and non
volatile storage. Other hardware, conventional and/or custom, may also be included.
Similarly, any switches shown in the Figures are conceptual only. Their function may be
carried out through the operation of program logic, through dedicated logic, through
the interaction of program control and dedicated logic, or even manually, the
particular technique being selectable by the implementer as more specifically
understood from the context.
It should be appreciated by those skilled in the art that any block diagrams herein
represent conceptual views of illustrative circuitry embodying the principles of the
invention. Similarly, it will be appreciated that any flow charts, flow diagrams, state
transition diagrams, pseudo code, and the like represent various processes which may
be substantially represented in computer readable medium and so executed by a
computer or processor, whether or not such computer or processor is explicitly shown.
The description and drawings merely illustrate the principles of the invention. It will thus
be appreciated that those skilled in the art will be able to devise various arrangements
that, although not explicitly described or shown herein, embody the principles of the
invention and are included within its spirit and scope. Furthermore, all examples recited
herein are principally intended expressly to be only for pedagogical purposes to aid the
reader in understanding the principles of the invention and the concepts contributed
by the inventor(s) to furthering the art, and are to be construed a s being without
limitation to such specifically recited examples and conditions. Moreover, all statements
herein reciting principles, aspects, and embodiments of the invention, a s well as
specific examples thereof, are intended to encompass equivalents thereof.

CLAIMS
1. A method of estimating a distance between at least one network access node
and a network node of a wireless communications network, comprising:
measuring total path losses between said at least one network access node
and said network node on at least two different frequencies;
determining frequency-dependent path losses of transmissions by said a t least
one network access node on said a t least two different frequencies; and
estimating a distance between said network node and said a t least one
network access node using said total path losses and said frequency-dependent path
losses on said at least two different frequencies.
2. The method of claim 1, wherein said frequency-dependent path losses are
determined from a difference in said total path losses on each different frequency
between said at least one network access node and said network node.
3. The method of claim 1 or 2, wherein said frequency-dependent path losses are
determined from transmissions on each different frequency between a t least two
network access nodes.
4. The method of any preceding claim, wherein said frequency-dependent path
losses are determined from transmissions on each different frequency between at least
three network access nodes.
5. The method of any preceding claim, wherein said frequency-dependent path
losses are determined from transmissions on each different frequency and a distance
between network access nodes.
6. The method of any preceding claim, comprising determining a n average
frequency-dependent path loss on each different frequency between network access
nodes.
7. The method of any preceding claim, wherein said frequency-dependent path
losses at each different frequency are determined using a n effective frequencydependent
attenuation between said network access nodes.
8. The method of claim 7, wherein said effective frequency-dependent
attenuation is determined using a path loss measured at each different frequency
between said network access nodes and a distance between said network access
nodes.
9. The method of any preceding claim, comprising determining an average
effective frequency-dependent attenuation on each different frequency between said
network access nodes.
10. The method of any preceding claim, wherein said frequency-dependent path
losses are determined from predetermined frequency-dependent path losses
approximated for different deployment environments.
11. The method of any preceding claim, wherein said distance is estimated from a
corrected path loss determined by removing said frequency-dependent path losses
from said total path losses on each different frequency.
2. The method of any preceding claim, wherein said distance is estimated using
said total path loss, a transmission power and said average effective frequencydependent
attenuation on each different frequency.
13. The method of any preceding claim, comprising estimating a distance between
said network node and each of said network access nodes.
1 . A network node operable to estimating a distance between at least one
network access node and a network node of a wireless communications network,
comprising:
measurement logic operable to measure total path losses between the at least
one network access node and the network node on at least two different frequencies;
determining logic operable to determine frequency-dependent path losses of
transmissions by the at least one network access node on the at least two different
frequencies; and
estimating logic operable to estimate a distance between the network node
and the at least one network access node using the total path losses and the
frequency-dependent path losses on the at least two different frequencies.
15. A computer program product operable, when executed on a computer, to
perform the method steps of any one of claims 1 to 13.