WO2007005814A1

WO2007005814A1 - A time of arrival estimation mechanism

Info

Publication number: WO2007005814A1
Application number: PCT/US2006/025955
Authority: WO
Inventors: Stuart A. Golden; Jong-Kae Fwu; Steven S. Batemen
Original assignee: Intel Corporation
Priority date: 2005-06-30
Filing date: 2006-06-29
Publication date: 2007-01-11
Also published as: US20070018891A1; US7271764B2

Abstract

According to one embodiment, a method is disclosed. The method includes receiving data at a first wireless radio device that has been transmitted from the first wireless radio device, receiving time stamp information from- a second first wireless radio device and estimating time of arrival (TOA) information based upon the data and the time stamp information.

Description

A TIME OF ARRIVAL ESTIMATION MECHANISM

FIELD OF THE INVENTION

[0001] The present invention relates to mobile wireless communication;

more particularly, the present invention relates to estimating a direct path (DP)

distance within a multi-path environment between two mobile devices.

BACKGROUND

[0002] Within a communication system, a mobile communications device

may be located using a Global Positioning System (GPS) receiver that takes

positions and times from multiple satellites to accurately measure and determine

distances. The mobile communications device compares its time with the time

broadcast by at least three satellites whose positions are known and calculates its

own position on the earth. However, the GPS system depends on expensive

atomic clocks in the GPS transmitters to generate the precision measurements.

Therefore, it is often impracticable to implement a satellite based GPS system to

provide accurate positioning measurements in various environments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The invention is illustrated by way of example and not limitation in

the figures of the accompanying drawings, in which like references indicate

similar elements, and in which:

[0004] Figure 1 illustrates a mobile wireless communications device

operating in a network with other mobile devices in accordance with the present

invention;

[0005] Figure 2 illustrates one embodiment of a two-ray multi-path model;

[0006] Figure 3 is a flow diagram that illustrates one embodiment of a

time of arrival (TOA) estimation mechanism;

[0007] Figure 4 is a flow diagram that illustrates one embodiment for time

TOA/multi-path estimation;

[0008] Figure 5 is a diagram of noise power used in determining the

number of paths for channel signals using residual error techniques;

[0009] Figures 6A and 6B is a diagram illustrating multi-path symmetry;

[0010] Figures 7-10 illustrate signals being transmitted and received by

two communication devices; and

[0011] Figure 11 is a diagram illustrating one embodiment for determining

wireless location. DETAILED DESCRIPTION

[0012] A mechanism for time of arrival (TOA) estimation is described. In

the following detailed description of the present invention numerous specific

details are set forth in order to provide a thorough understanding of the present

invention. However, it will be apparent to one skilled in the art that the present

invention may be practiced without these specific details. In other instances,

well-known structures and devices are shown in block diagram form, rather than

in detail, in order to avoid obscuring the present invention.

[0013] Reference in the 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 invention. The appearances of the phrase "in one

embodiment" in various places in the specification are not necessarily all

referring to the same embodiment.

[0014] Figure 1 illustrates one embodiment of a mobile wireless

communications device 10 operating with other mobile devices. As shown in

Figure 1, the communication network may be a communication system with base

stations to service multiple users within a coverage region. The multiple mobile

devices may share a base station and employ a multiple access scheme such as a

Code Division Multiple Access (CDMA) scheme. Wireless communications device 10 is shown communicating with base stations 30 and 40 and other mobile

devices 20 in the network.

[0015] Embodiments may include packet exchanges between users of

communication devices and access points in a Wireless Local Area Network

(WLAN). For example, one or more mobile stations or an access point may

operate in compliance with a wireless network standard such as ANSI/IEEE Std.

802.11, 1999 Edition, although this is not a limitation of the present invention. As

used herein, the term "802.11" refers to any past, present, or future IEEE 802.11

standard, or extension thereto, including, but not limited to, the 1999 edition.

Embodiments may be adapted to communicate in accordance with one or more

protocols contemplated by various IEEE 802.16 standards for fixed or mobile

wireless metropolitan area networks (WMANs). (WiMax Worldwide

Interoperability for Microwave Access is not really part of the standard name,

it's a certification for products that are compliant with 802.16 standards.) Note

that the type of communication network and the type of multiple accesses

employed by devices that emit RF signal energy are provided as examples only,

and the various embodiments of the present invention are not limited to the

embodiment shown in the figure.

[0016] Wireless communications device 10 includes a receiver 12 to receive

a modulated signal from one or more antennas. The received modulated signal may be frequency down-converted, filtered, then converted to a baseband,

digital signal. The frequency conversion may include Intermediate Frequency

(IF) signals, but it should be noted that in an alternative embodiment the

modulated RF signals may be directly down-converted without the use of IF

mixers. The scope of the claims is intended to cover either embodiment of the

receiver. The down converted signals may be converted to digital values by

Analog-to-Digital Converters (ADCs).

[0017] Wireless communications device 10 further includes a transmitter

14 having a Digital-to- Analog Converter (DAC) that converts a digital value

generated by the processor to an analog signal. The analog signal may be

modulated, up-converted to RF frequencies and amplified using a power

amplifier (with or without feedback control) to control the output power of the

analog signal being transmitted from the antenna(s).

[0018] Although shown in a wireless communications device 10,

embodiments of the present invention may be used in a variety of applications.

It should be pointed out that the timing acquisition embodiments are not limited

to wireless communication devices and include wire-line communication devices.

The present invention may be incorporated into microcontrollers, general-

purpose microprocessors, Digital Signal Processors (DSPs), Reduced Instruction-

Set Computing (RISC), Complex Instruction-Set Computing (CISC), among other electronic components. In particular, the present invention may be used in smart

phones, communicators and Personal Digital Assistants (PDAs), medical or

biotech equipment, automotive safety and protective equipment, and automotive

products. However, it should be understood that the scope of the present

invention is not limited to these examples.

[0019] Wireless communication systems typically operate over a channel

that has more than one path from transmitter to the receiver. Such a channel is

frequently referred to as a multi-path channel. These signals travel through

various paths that may be caused by reflections from buildings, objects, or

refraction. At the receiver end, these various signals are received with different

attenuations and time delays associated with its travel path.

[0020] Figure 2 is a simple two-ray multi-path model, which illustrates the

concept of a multi-path environment. In Figure 2, one signal is received via a

Direct Path (DP), and another signal is received by way of a reflected path

(indirect path). The direct DP signal can be interfered destructively by the

indirect path signal. As a result, the multi-path environment introduces

significant challenges for many wireless communications systems, which require

reliable processing/estimation of the transmit/receive signals.

[0021] In a multi-path system, the receiver receives signals from different

paths with different attenuations and delays and is expressed by: M y(0 = ∑4*('-*i) + w(0, i=l

where s(t) denotes a reference transmit ranging signal and y(t) the received

signal at the receiver. M denotes the number of paths, A₁ and τ. denote

attenuation and delay associated with the i-th path, respectively. Here, w(t) is the

composite noise due to the impairment of the transmit/receiver, and channel.

The DP signal is the first signal such that T₁. is the smallest since the DP signal

takes the most direct path. However, the multi-path estimation algorithm above

may classify noise as possible signal as well. For example, if T₁ is the shortest

delay and A₁ is very small, the algorithm may have overestimated the true

number of paths and essentially attempts to fit the signal to the residual noise.

[0022] According to one embodiment, TOA techniques are implemented

to determine the DP signal (τ_βp ) in order to compute the direct path distance

between the transmitter and receiver. The distance and TOA relationship is

given by τ_DP = Dlc, where D and c are the distance and the velocity of

propagation, respectively. In such an embodiment, the DP distance within a

multi-path environment is estimated when only one device (e.g., the receiver) has

received data packets and the other side (e.g., the transmitter) has received time

stamps only.

[0023] Figure 3 is a flow diagram that illustrates one embodiment of computing a DP distance between a transmitter and receiver. The process to

perform the computation includes a process 310 to provide a TO A/multi-path

estimation to a received packet data. Process 310 stores the estimated parameters

(e.g., number of path, TOA of each path) for future calculations.

[0024] A process 320 is included to provide TO A/Multi-Path

Reconstruction. For a two way ranging system, signals that travel from a first

transceiver to a second transceiver have some similar properties as the signal

travel from the second transceiver to the first transceiver (e.g., power

attenuation, air travel time, etc). Thus, process 320 applies the symmetric

property between the forward and reverse multi-path link to time-stamp

information in order to re-construct the multi-path profile parameters for the

other transceiver.

[0025] Range computation is provided at process 330 by utilizing the

multi-path profiling information from processes 310 and 320 to compute the

distance between the transceivers. Wireless location is provided at process 340

so that the location of the wireless radio unit can be determined with ranging to a

number of different radios. In some embodiments, the process described herein

or portions thereof may be performed by a mobile station, a processor, or an

electronic system. The processes are not limited by the particular type of

apparatus, software element, or system performing the method. The various actions may be performed in the order presented, or may be performed in a

different order and in some embodiments, some actions listed in Figure 3 may be

omitted.

TOA/Multi-Path Estimation

[0026] Figure 4 is a flow diagram illustrating one embodiment of a process

for providing TOA/Multi-path estimation. The process to provide TOA/Multi-

path estimation includes a process 410 to provide frequency offset compensation;

a process 420 that decomposes the received signal into components associated

with various paths and provides parameter estimation by multi-path

decomposition; and a process 430 to determine the number of paths in the

received signal. According to one embodiment, an initial timing acquisition

process may be performed prior to process 410. Initial timing acquisition is

based on signals communicated between two RF devices such as two mobile

devices, two base stations, one mobile device and one base station, or in general,

any two wireless communication units having a transmitter and a receiver.

Frequency Offset Compensation [0027] In process 410 a frequency offset compensation value is calculated

to correct the frequency offset between a received signal and a reference signal, e.g., a signal from a remote modem. Signals are sensitive to carrier frequency

offset between the transmitter and the receiver local oscillators, which may cause

self interference, for example, between the subchannels, e.g., modulated

subcarriers in an OFDM modulation format. Carrier frequency offset between

transmitter and receiver local oscillators may be estimated and compensated at

the receiver.

[0028] Let yn be the discrete sampled received data and S_n be the reference

data at discrete time n. The relationship between the received signal and the

reference signal may be represented as:

where A₁ is the signal amplitude, % i is the delay taken to the nearest sample, ω is

the frequency offset between the received signal and the reference signal, and en

is the noise sampled at time n.

[0029] To estimate the frequency offset, the following least-square cost

function is minimized:

2 (A,ώ) = min(^_{) βJ}) |||y» - As_n X eκρ(jωn) || ,

where (A,ώ) represent "estimated values" for amplitude and frequency offset. The cross-product Zn = yn Sn* can be defined. Note that the value for Zn does not

have to be recomputed for each hypothesized frequency value that is used.

[0030] The estimated amplitude is given by:

∑ \sn\² and the estimated frequency offset may be obtained by a searching algorithm

using:

ώ = arg min/ω £ I yn 1² - \A \² 2__i \sn \².

The estimated frequency offset is then applied to the received signal for

frequency offset correction.

Parameter Estimation by Multi-path Decomposition [0031] Once the frequency offset is compensated, the multi-path signals

are estimated (both DP and indirect path) and specific properties in the signals

are observed to select the DP signal. Further, the process estimates the dominant

multi-path component sequentially to achieve a fast solution. The process of

estimating the multi-path profile for TOA estimation is not limited to the

proposed multi-path decomposition method. It will be understood other

approaches can also be used with the TOA estimation mechanism, such as

optimal multi-path join-estimation. [0032] The decomposition process 420 sequentially estimates multi-paths

based on the energy ratio of the signal component and the noise component

(ESNR). With the ESNR generated for each of the multi-path signals, the

decomposition process arranges the signal components from the strongest ESNR

to the weakest ESNR. Since a low ESNR may result in poor estimation

performance, the decomposition executed in process 420 accounts for low ESNR

issues in accordance with the present invention. Accordingly, the attenuated

receive signals obstructed by objects and/or the non-LOS signal energy/power

that is substantially greater than that of the LOS signal is accounted for in process

420.

[0033] In the decomposition algorithm, y. (t) represents the signal used for

estimating the i-th path component. During the decomposition process for the i-

th path, the strongest signal y_t(t) is estimated and removed from the residual

signals. The estimation problem is formulated by an iterative process with first

letting r(t) = y(t), then

(A . f )= min(A . f . ) J \\ r (t) -Ai s (t-τ i ) \\ , t

The final estimate becomes:

Z(ω) = r(ω)* S*(ω)

∑ I S ⁽ω) l² Where τ ,^■ = arg minlτ ∑ I r( _ω) 1² - I Ai 1² ^ I S(ω) 1². Again, note that Z(ω) is ω ω only computed once per minimization. Note that the iteration is repeated with: r(t) = r(t) -A * s(t -f > ).

[0034] The decomposition associated with process 420 may be generalized

to an M-path example without a specific signal strength relationship between

paths. The determination of the number of paths M, and the selection of the DP

signal is illustrated in preparation for the final estimation of TOA for the DP

signal. Let A1>A2>A3 ..., and by way of example, assume that the DP signal is

the third strongest signal, i.e., y_L0S (0 =

.

[0035] In this example the DP signal has a smaller ESNR than either of the

two other indirect paths. The mechanism for selecting the number of paths M

and the DP signal is described later, but assume that these parameters are

known. The decomposition algorithm first estimates the strongest signal

component ^₁ (t) = i4_j5(t- T₁) and stores the information. The value ^₁(O is

removed from y(t) and the remaining signal becomes residual error

KO ⁼ y(t)~ 9ι(t)- After separating the y_{(t) from the received signal y(t), the

second strongest signal component y_z(t) is then estimated from r(t). The same

procedure is repeated for the i-th path until i = M. The time-of-arrival

information τ_ws is obtained from y_ωs(t) = A_wss(t-i_L0S), where LOS = 3 in this example.

[0036] Figure 5 illustrates a residual signal/noise power plot for several

path components. The Y-axis represents the residual signal/noise power and the

X-axis represents the estimated delay τ_t associated with an i-th path. During the

decomposition process, the ESNR is estimated for each of the component signals

and the strongest signal y,(0 at a time is determined and removed from the

residual error. Note that the residual signal/noise decreases as the number of

paths increases. In the example illustrated in Figure 5, the first component 502 is

shown as the strongest path among the M-path signals, second component 504

the next strongest path, followed by third component 506.

[0037] As previously stated, the decomposition associated with process

420 sequentially estimates multi-paths based on ESNR. As shown in Figure 5,

first component 502 has the strongest ESNR and in accordance with the

decomposition algorithm is selected for removal. Following the removal of first

component 502, the residual noise of the remaining components is significantly

lower. Note that the residual noise of the remaining components is about 2OdB

lower after removing the first path signal.

[0038] Process 420 continues by sequentially estimating the remaining

multi-paths based on ESNR. In this example, the second component 504 is the

remaining multi-path signal having the strongest ESNR. This second path signal (second component 504) is then removed and the residual noise of the remaining

components further drops by a few dB. As shown in the figure, the third

component 506 is the component selected from the remaining components as

having the strongest ESNR. After removing the third component 506, the

residual noise of the remaining components drops an additional few dB.

Number of Paths Determination [0039] Now returning to Figure 4 and continuing with process 430, the

number of paths in the received signal that affect the residual signal is

determined. Continuing with the example, the residual noise power for the

remaining components is relatively flat which shows that there is no clear effect

on removing any other multi-path component on the residual signal. Thus, a

threshold in the residual noise power or a residual change limit may be used to

determine the number of paths in the received signal. In the above example,

three paths have been shown to affect the final residual noise power. Selecting

additional components and removing them would not significantly reduce the

residual signal, and therefore, the number of effective multi-path is determined

to be three, i.e., M=3.

Multi-Path Reconstruction

[0040] Referring back to Figure 3 and continuing with process 320, TO A/multi-path reconstruction is performed after multi-path estimation has

been completed. Whenever a wireless radio transmits wireless signals, the

signals can be thought of as a bundle of individual light rays which are traveling

in all directions. Each individual light ray of the bundle follows the law of

reflection. Not all the rays will reach the receiver. The top figure of Figure 6A

illustrates an example of a three paths scenario (DP, multi-path 1, and multi-path

2) between transmitter-A and receiver-B. The signal transmitted from

transmitter-A will travel in all directions and only three paths will reach the

receiver-B following the law of reflection. AU other paths do not reach receiver B

or are completely attenuated before reach receiver B.

[0041] When the transmitter and receiver are reversed (e.g., the

transmitter becomes the receiver and the receiver becomes the transmitter as

shown in Figure 6B), the reverse will happen, such that the rays from the new

transmitter-B will travel in all directions, with only some of the rays reaching the

new receiver-A. Based on the law of reflection (e.g., the angle of incidence is

equal to the angle of reflection), the rays that will reach the new receiver will

follow the same paths (although in the reverse direction) as the previous

example. Thus, the signal transmitted from transmitter-B will travel in all

directions and only three paths will reach the receiver-A following the law of

reflection. All other paths doe not reach receiver A, or are completely attenuated before reaching receiver A.

[0042] Based on this description it can be concluded that the multi-path

profile (the paths/ray-traces, etc.) from point-A to point-B is the same as from

point-B to point-A (from the multi-path observed by point-A and B). Therefore,

the number of paths from point A and point B are the same as from point B and

point A, the paths/ray-traces from point A and point B are the same as from

point B and point A, the delay (traveling time) of each path from point A and

point B is the same as from point B and point A, and the relative delay between

paths from point A and point B are the same as from point B and point A.

[0043] If the multi-path profile from point A to point B and some basic

information from point B to point A (such as a time-stamp associated with the

strongest path) are known, the multi-path profile (from point B to point A) can be

reconstructed using the multi-path symmetry property. Consequently, time

stamp information is implemented to reconstruct the multi-path information.

[0044] According to one embodiment, the time stamp information is the

time at which the strongest path is received. In a further embodiment, the time

stamp information is generated by recording a time-stamp of a packet

transmitted from a device. Particularly, the receiver 12 is turned on during

transmission of the packet, while turning off low-noise amplifiers. The low-noise

amplifiers may be turned off because the signal is strong without the amplifiers [0045] The multi-path reconstruction process can be generalized to M-path

scenario without specific signal strength relationship between paths. An

example with a specific signal strength relationship can be used to explain the

process. In this example, A₁ > A₂ > A₃₅T₁ > τ₂ > τ₃ , where the DP signal is the third

strongest signal, e.g., y_L0S (t) = A₃S^ -T₃) . Further, the DP signal is smaller than

two other non-DP paths. The selection of the number of path M, and the DP

signal is critical for the final estimation of TOA for the DP signal. The selection of

M and DP signal is performed according to the multi-path estimation process 310

described above.

[0046] The multi-path profiling information that was computed from the

previous stage includes: (a) the number of paths M; (b) the DP signal among the

M paths is known (e.g., DP=3); and (c) signal strength relationship and TOA

associated with each path, e.g., A_x > A₂ > A₃ ,X₁ > T₂ > T₃. The basic concept is to

use the relative time offset information between the strongest path and the DP

path from one unit to reconstruct the same information for the other unit using

the available time-stamp associated with the strongest path.

[0047] According to one embodiment, the multi-path estimation process

includes applying the multi-path estimation process, or other multi-path

estimation algorithms, to the wireless data received by the first radio unit (point

A to B) and estimating the multi-path profile information for each path (i.e., A_x , A₂ , A₃ , τ, , τ₂ , τ₃ ). Subsequently, the TOA difference between the strongest

path and the DP path (e.g., Δτ = T₁ -τ₃ ) is estimated.

[0048] Assuming the TOA difference between the strongest and DP paths

are the same (e.g.,) based on the multi-path symmetric property. Given that the

time stamp associated with the strongest path at the second radio unit (point B to

A) is known (e.g., Ti .), the TOA for the DP path becomes τ₃ = Ti - Δτ . Once the

information associated with the DP for both wireless radio units becomes

available (τ₃ and τs ), the range between the two wireless radio units can be

computed, as will be explained in process 330 below.

[0049] Note that the above example only illustrates re-constructing the

path information using multi-path symmetry property. The information

calculated using the TOA technique will be used for ranging/location application.

Other multi-path profile information can be re-constructed for different

applications if needed. Further, the multi-path reconstruction using symmetry

property can apply to other multi-path estimation algorithms and is not limited

to the TOA/multi-path estimation process discussed above. Some examples

include forward and reverse link in the wireless communication multi-input

multi-output (MIMO) and smart antenna applications.

Range Computation [0050] Referring back to Figure 3 and continuing with process 330,

distance is computed using the estimated delay between two links (forward and

reverse links). The basic relationship between the distance and the delay are

described based on the example described below. In this example, a first wireless

radio unit (Unit #1) transmits a packet to a second wireless radio unit (Unit #2) at

time t=0, Figure 7. Subsequently, Unit #2 responses to the Unit#l packet at time

t=D. Thus, the distance between Unit #1 and Unit #2 (e.g., J₁₂ ) is to be estimated

using the previous multi-path decomposition example.

[0051] First, Unit #1 receives its own transmit packet immediately (e.g.,

t_j = 0 ) and the response packet from Unit #2 at a time D (Figure 8) after a delay

associated the propagation path (distance) between the Unit #1 to Unit #2

t₃ = D + ¹Y ( Figure 9). Since the self-received packet has very low noise and

without multi-path, no multi-path decomposition process needs to be performed,

J₁ = 0. A multi-path decomposition is applied to the response packet from

Unit#2, and the time associated with the DP path is recorded, e.g.,

t = D + i2/ = x = τ

[0052] Next, Unit #2 receives Unit #l's transmit packet after a delay

(*₄ ⁼ _/ ) associated the propagation path (distance), Figure 10. Unit #2

received its own packet with no delay (t₂ = D). The self-received packet for Unit #2 does not have multi-path so the self-received time-stamp t₂ = D . The remote

received time-stamp is estimated from the strongest pathτi and is sent back to

Unit#l or the location server. Note that the only information sent back is the

time-stamp. Without sending the wireless data packet, multi-path reconstruction

can be performed.

[0053] Based on the multi-path symmetric property described in the

previous example, the TOA for the DP path at unit #2 is t₄ = ⁿ/ =X3 = ti -Δτ .

Given t_vt₂,t₃, and t_A , the distance d_n between unit#l and unit #2 can be

computed by (I_n = (Jn₁ -Tn₁)Il, where,

Once the n\ and In₂ values are known, the two unknowns D and d_n can be solved

(c is the speed of radio wave and is known).

Wireless Location

[0054] Referring back to Figure 3 and continuing with process 340,

wireless location information is estimated using three or more different range

measurements. According to one embodiment, a mobile user performs two-way

ranging at each access point (AP)/base one at a time. The position is calculated

after two-way ranging using a triangulation approach which minimizes the mean square error criterion. Figure 11 is a diagram illustrating one embodiment for

determining wireless location.

[0055] Referring to Figure 11, a mobile unit is at location (x, y) while

AP/BS #1-3 are at locations (xl, yl), (x2, y2) and (x3, y3), respectively. Estimated

range data for each AP/BS is represented by d_lm , d_lm , d_3m . From the known AP/BS

location, and estimated range data, the mobile's position (x, y) can be determined

by solving the triangulation equations:

VU-^)² +(y- y₃)² = ^ 33m.

[0056] The above-described mechanism enables a mobile to use its own

algorithm to estimate multi-path information using TOA techniques without the

involvement of access points. Consequently, the client may estimate its range

from the access point using the estimations, or simply estimate its location. Note

that instead of computing the location at the client/mobile side, for different

applications or usage models the location may also be computed at the AP/base-

station side or at the network server using a similar triangular method.

[0057] Whereas many alterations and modifications of the present

invention will no doubt become apparent to a person of ordinary skill in the art

after having read the foregoing description, it is to be understood that any particular embodiment shown and described by way of illustration is in no way

intended to be considered limiting. Therefore, references to details of various

embodiments are not intended to limit the scope of the claims, which in

themselves recite only those features regarded as essential to the invention.

Claims

CLAIMSWhat is claimed is:

1. A method comprising:

receiving data at a first wireless radio device that has been transmitted

from the first wireless radio device;

receiving time stamp information from a second first wireless radio

device; and

estimating time of arrival (TOA) information based upon the data and the

time stamp information.

2. The method of claim 1 further comprising performing a decomposition

process on the received data to determine multi-paths between the first wireless

radio device and the second wireless radio device.

3. The method of claim 2 further comprising reconstructing the multi-path

profile between the first wireless radio device and the second wireless radio

device.

4. The method of claim 3 wherein the multi-path profile is reconstructed

using the time stamp information received from the second wireless radio device.

5. The method of claim 4 wherein the time stamp information is generated at

the second wireless radio device by:

activating a receiver at the second wireless radio device during a signal

transmission; and

deactivating one more amplifiers at the second wireless radio device.

6. The method of claim 4 wherein the multi-path profile is further

reconstructed using a symmetry property between the first wireless radio device

and the second wireless radio device.

7. The method of claim 3 further comprising estimating a range between the

first wireless radio device and the second wireless radio device.

8. The method of claim 7 further comprising estimating the location of the

first wireless radio device using the range estimation.

9. The method of claim 2 wherein the decomposition process comprises:

performing frequency compensation;

performing parameter estimation; and

determining a number of paths.

10. A wireless communication device comprising:

a transmitter to transmit data to a base station; a receiver to receive at least a portion of the transmitted data ad to receive

time stamp information from the base station; and

a processor coupled to the transmitter and receiver to estimate time of

arrival (TOA) information based upon the received data and the time stamp

information.

11. The device of claim 9 wherein the processor performs a decomposition

process on the received data to determine multiple paths between the device and

the base station.

12. The device of claim 11 wherein the processor reconstructs the multi-path

profile between the device and the base station using the time stamp information

received from the base station and symmetry properties between device and the

base station.

13. The device of claim 12 wherein the processor estimates a range between

the device and the base station.

14. The device of claim 13 wherein the processor estimates the location of the

device using the range estimation.

15. An article of manufacture including one or more computer readable

media that embody a program of instructions, wherein the program of

instructions, when executed by a processing unit, results in the process of:

receiving data at a first wireless radio device that has been transmitted

from the first wireless radio device;

receiving time stamp information from a second first wireless radio

device; and

estimating time of arrival (TOA) information based upon the data and the

time stamp information.

16. The article of manufacture of claim 15 wherein the program of

instructions, when executed by a processing unit, further causes performing a

decomposition process on the received data to determine multi-paths between

the first wireless radio device and the second wireless radio device.

17. The article of manufacture of claim 16 wherein the program of

instructions, when executed by a processing unit, further causes reconstructing

the multi-path profile between the first wireless radio device and the second

wireless radio device using the time stamp information received from the base

station and symmetry properties between device and the base station.

18. The article of manufacture of claim 17 wherein the program of

instructions, when executed by a processing unit, further causes estimating a

range between the first wireless radio device and the second wireless radio

device.

19. The article of manufacture of claim 18 wherein the program of

instructions, when executed by a processing unit, further causes estimating the

location of the first wireless radio device using the range estimation.

20. A wireless communication device comprising:

a transmitter to transmit data to a base station;

a receiver to receive at least a portion of the transmitted data and to

receive time stamp information from the base station;

a processor coupled to the transmitter and receiver to estimate time of

arrival (TOA) information based upon the received data and the time stamp

information; and

at least one dipole antenna coupled to the transceiver to radiate the data in

the form of electromagnetic waves.

21. The device of claim 20 wherein the processor performs a decomposition

process on the received data to determine multiple paths between the device and

the base station.

22. The device of claim 21 wherein the processor reconstructs the multi-path

received from the base station and symmetry properties between device and the

base station.