U.S. patent application number 12/905285 was filed with the patent office on 2011-02-03 for method for reception of long range signals in bluetooth.
Invention is credited to Albert Chen, Wen-Tso Huang, Kuang-Ping Ma.
Application Number | 20110026578 12/905285 |
Document ID | / |
Family ID | 38712551 |
Filed Date | 2011-02-03 |
United States Patent
Application |
20110026578 |
Kind Code |
A1 |
Chen; Albert ; et
al. |
February 3, 2011 |
METHOD FOR RECEPTION OF LONG RANGE SIGNALS IN BLUETOOTH
Abstract
The invention of a method for reception of long transmission
range Bluetooth signals impaired by multipath are disclosed. The
new reception method proposed allows to increase the transmission
range for data transmission in Bluetooth. The invention proposes
the use of a new FDE adapted to SC transmission without a GI or CP.
The proposed FDE very successfully mitigates ISI while being very
implemention-friendly.
Inventors: |
Chen; Albert; (Hsinchu,
TW) ; Ma; Kuang-Ping; (Hsinchu, TW) ; Huang;
Wen-Tso; (Hsinchu, TW) |
Correspondence
Address: |
Muncy, Geissler, Olds & Lowe, PLLC
4000 Legato Road, Suite 310
FAIRFAX
VA
22033
US
|
Family ID: |
38712551 |
Appl. No.: |
12/905285 |
Filed: |
October 15, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11435948 |
May 18, 2006 |
|
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12905285 |
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Current U.S.
Class: |
375/232 ;
455/41.2 |
Current CPC
Class: |
H04L 25/03159 20130101;
H04L 2025/03624 20130101; H04L 2025/03522 20130101; H04W 84/18
20130101; H04W 52/281 20130101 |
Class at
Publication: |
375/232 ;
455/41.2 |
International
Class: |
H03H 7/30 20060101
H03H007/30; H04B 7/00 20060101 H04B007/00 |
Claims
1. A method for reception of long-range signals in Bluetooth for
all transmission modes on power class 1, power class 2 and power
class 3, the method comprising: receiving Bluetooth signals; and
processing said Bluetooth signals with linear frequency-domain
equalization (FDE) in single carrier (SC) system using a Fourier
Transform.
2. The method for reception of long-range signals in Bluetooth
according to claim 1, wherein said Fourier Transform is a Discrete
Fourier Transform (DFT) deduced from a Fast Fourier Transform
(FFT).
3. The method for reception of long-range signals in Bluetooth
according to claim 2, wherein said Fast Fourier Transform (FFT) is
overlap-add-technique FFT or overlap-save-technique FFT.
4. The method for reception of long-range signals in Bluetooth
according to claim 1, wherein said Fourier Transform is an Inverse
Discrete Fourier Transform deduced from an Inverse Fast Fourier
Transform (IFFT).
5. The method for reception of long-range signals in Bluetooth
according to claim 4, wherein said Inverse Fast Fourier Transform
(IFFT) is overlap-add-technique IFFT or overlap-save-technique
IFFT.
6. The method for reception of long-range signals in Bluetooth
according to claim 1, further comprising executing an estimate of
the transmit data after receiving said Bluetooth signals.
7. The method for reception of long-range signals in Bluetooth
according to claim 6, wherein said estimate of the transmit data is
obtained using Matched Filter (MF) criterion.
8. The method for reception of long-range signals in Bluetooth
according to claim 6, wherein said estimate of the transmit data is
obtained using Zero Forcing (ZF) criterion.
9. The method for reception of long-range signals in Bluetooth
according to claim 6, wherein said estimate of the transmit data is
obtained using Minimum Mean Square Error (MMSE) criterion.
10. The method for reception of long-range signals in Bluetooth
according to claim 9, wherein said minimum mean square error (MMSE)
is obtained from {circumflex over
(d)}.sub.MMSE=F.sup.-1{H.sub.invF(r)} and H.sub.inv is obtained
from H inv = ( F { h ^ } ) * ( F { h ^ } ) * F { h ^ } + .sigma. 2
##EQU00013##
11. The method for reception of long-range signals in Bluetooth
according to claim 10, wherein said F and F.sup.-1 size is 8 or
16.
12. The method for reception of long-range signals in Bluetooth
according to claim 9, wherein said minimum mean square error (MMSE)
comprises: using FFT on estimated channel impulse response h
yielding H; conjugating complex operation on H; multiplying of H
with conj(H); adding of HH* with .sigma..sup.2; dividing of H* by
HH*+.sigma..sup.2; multiplying with phasors 1 j k M ; ##EQU00014##
and circulating circular convolution with sin x x .
##EQU00015##
13. The method for reception of long-range signals in Bluetooth
according to claim 1, wherein said transmission modes comprises 1
Mbps transmission mode (GFSK), 2 Mbps transmission mode (DPSK), and
3 Mbps transmission mode (DPSK).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of co-pending application
Ser. No. 11/435,948, filed on May 18, 2006, and for which priority
is claimed under 35 U.S.C. 120, the entire contents of all of which
are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for reception of
Bluetooth signals, and more especially, to a method for reception
of long-range signals in Bluetooth.
[0004] 2. Background of the Related Art
[0005] The Bluetooth standard distinguishes devices by their
so-called power class {[IEEE 802.15.1], [BT SIG 1.2], [BT SIG
EDR]}. For each power class, a maximum output power (Pmax), a
nominal output power and a minimum output power is specified as
shown in Table 1.
TABLE-US-00001 TABLE 1 Maximum Nominal Minimum Power Output Output
Output Class Power (Pmax) Power Power Power Control 1 100 mW N/A 1
mW (0 dB) Pmin <+4 dBm (20 dBm) to Pmax Optional: Pmin.sup.2 to
Pmax 2 2.5 mW 1 mW 0.25 mW (-6 Optional: (4 dBm) (0 dBm) dBm)
Pmin.sup.2 to Pmax 3 1 mW N/A N/A Optional: (0 dBm) Pmin.sup.2 to
Pmax
[0006] The Bluetooth technology is intended to implement wireless
personal area networks (WPAN). Therefore, the typical range of
Bluetooth devices is expected to be limited to about 10 meters.
Bluetooth devices according to power class 1, however, are capable
to transmit over a range significantly larger than the so-called
personal operating space (POS) of about 10 meters.
[0007] [IEEE 802.15.1]: the IEEE Std 802.15.1-IEEE Standard for
Information technology Telecommunications and information exchange
between systems Local and metropolitan area networks Specific
requirements-Part 15.1: Wireless Medium Access Control (MAC) and
Physical Layer (PHY) Specifications for Wireless Personal Area
Networks (WPANs), 14 Jun. 2002.
[0008] [BT SIG 1.2]: Bluetooth SIG Specification of the Bluetooth
System, Version 1.2, 5 Nov. 2003.
[0009] [BT SIG EDR]: Bluetooth SIG Specification of the Bluetooth
System with EDR, Version 2.0, 4 Nov. 2004.
Sensitivity Performance in Bluetooth
[0010] In [BT SIG EDR], a reference sensitivity level of -70 dBm is
given for an uncoded bit error rate (BER) of 0.0001 (0.01%). In
FIG. 1 and FIG. 2, the uncoded BER versus SNR is shown for
PI/4-DQPSK and D8PSK, respectively. For PI/4-DQPSK, about 14 dB SNR
are needed to achieve an uncoded BER of 0.01%. For D8PSK, about 20
dB SNR are needed to achieve an uncoded BER of 0.01%. Additional
SNR margin is needed to accommodate fixed-point implementation
losses as well as losses introduced by radio front end impairments
and non-ideal time and frequency synchronization. Therefore, about
25 dB SNR are assumed to achieve an uncoded BER of 0.01%.
Path Loss in Bluetooth
[0011] The signal power received by a Bluetooth device depending on
the signal power transmitted by another Bluetooth device is given
by Equation 1:
P.sub.RX=P.sub.TX-L.sub.Path-L.sub.Fade+G.sub.TX+G.sub.RX (1)
with [0012] P.sub.RX: received signal power [0013] P.sub.TX:
transmitted signal power [0014] L.sub.Path: path loss [0015]
L.sub.Fade: fade margin [0016] G.sub.TX: received antenna gain
[0017] G.sub.RX: transmit antenna gain The following assumptions
are applied in Equation 2 and Equation 3:
[0017] G.sub.TX=G.sub.RX=0 dBi (2)
L.sub.Fade=8 dB (3)
[0018] Therefore, based on Equation 1 and Equation 2, the path loss
is given by Equation 4:
L.sub.Path=P.sub.TX-P.sub.RX-8 dB (4)
The transmitted signal power under consideration (maximum signal
power) is in Equation 5:
P.sub.TXP.sub.TX,max=20 dBm (Power class 1 device) (5)
The received signal power under consideration (minimum signal
power) is given by Equation 6:
P.sub.RXP.sub.RX,min=N.sub.Floor+W+SNR.sub.RX+NF.sub.RX (6)
with [0019] P.sub.Tx,max: maximum transmit power [0020]
P.sub.RX,min: minimum received power [0021] N.sub.Floor: noise
floor due to thermal noise [0022] W: noise bandwidth [0023]
SNR.sub.RX: signal-to-noise-ratio required for BER=0.0001 for D8PSK
[0024] NF.sub.Rx: receiver noise figure
[0025] The noise floor due to thermal noise amounts to -174 dBm per
Hz signal bandwidth. The signal bandwidth for Bluetooth technology
equals 1 MHz. The receiver noise figure is assumed to be 20 dB.
[0026] The minimum signal power can now be computed by Equation
7:
P RX , min = - 174 dBm / Hz + 1 MHz + 25 dB + 20 dB = - 114 dBm +
45 dB = - 69 dBm ( 7 ) ##EQU00001##
[0027] The maximum path loss based on maximum transmit signal power
and minimum received signal power and fade margin based on Equation
4 is now given by Equation 8:
L Path , max = P TX , max - P RX , min - 8 dB = 20 dB + 69 dB - 8
dB = 81 dB ( 8 ) ##EQU00002##
[0028] It follows that the maximum path loss for a Bluetooth device
of power class 1 equals 81 dB. For power class 2 and power class 3,
the maximum path loss amounts to 73 dB and 69 dB, respectively.
On Transmission Range in Bluetooth
[0029] The path loss depending on the transmission range for
line-of-sight (LOS) conditions in a Bluetooth network is given by
Equation 9:
L Path = 20 log ( 4 .PI. .lamda. R ) ( 9 ) ##EQU00003##
or by Equation 10 approximately
L.sub.Path=40+20 log(R) (10)
with [0030] R: transmission range in [meters] [0031] .lamda.:
wavelength of transmission signal
[0032] The path loss depending on the transmission range for
non-line-of-sight (NLOS) conditions in a Bluetooth network is given
by Equation 11.
L Path = 36 log ( 4 .PI. .lamda. R ) - 46.7 dB ( 11 )
##EQU00004##
or Equation 12 approximately
L.sub.Path=25.3+36 log(R) (12)
[0033] Equation 9, by Equation 10, Equation 11 and Equation 12 are
visualized in FIG. 3. It follows that for a maximum pathloss of 81
dB, a maximum transmission range R.sub.max of 113 meters (in large
office) is achieved (LOS conditions) using a power class 1 device
while ensuring reliable communication. For power class 2 and power
class 3, 18 meters (in small office) and 11 meters (POS) are
achieved, respectively.
On Multipath Propagation in Bluetooth
[0034] In Bluetooth, the symbol rate equals 1 Msps while the symbol
duration T.sub.symbol equals 1 .mu.s (1000 ns). According the radio
propagation theory, a radio frequency signal propagates 300 m in 1
.mu.s (3e8 meters per second). The maximum echo delay (1st versus
2nd echo) based on the maximum transmission range is given by
Equation 13:
D max = T Symbol 300 m R max = 1 s 300 m 113 m = 377 ns ( 13 )
##EQU00005##
It follows that for a maximum transmission range R.sub.max of 113
meters a maximum echo delay of 377 ns is obtained.
[0035] For power class 2 and power class 3, 60 ns and 37 ns are
obtained, respectively.
[0036] Multipath propagation results in inter-symbol interference
(ISI). The amount of ISI introduced depends on the number and power
of all echo paths following the first arriving path.
[0037] Using the result from Equation 13, one gets a maximum ISI
percentage shown in Equation 14:
ISI max = D max T Symbol = 377 ns 1 s = 37.7 % ( 14 )
##EQU00006##
[0038] For power class 2 and power class 3, 6% and 3.7% are
obtained, respectively.
[0039] The ISI is modelled as an echo path having a relative power
(with regards to the first arriving path) equal to ISI.sub.max.
With that assumption, a worst-case multipath channel profile with a
1st (obstructed) path @ 0 dB w/ delay of 0 samples and a 2nd path
(echo) @10*log.sub.10(0.377)=-4.24 dB w/ delay of 1 sample (1
.mu.s).
[0040] The 2-path multipath propagation model for Bluetooth long
transmission range applications is shown in FIG. 4. A large office
scenario for Bluetooth long transmission range applications is
shown in FIG. 5.
Impact of Multipath Propagation on Bluetooth Demodulation
Performance
[0041] In FIG. 6, FIG. 7, FIG. 8, and FIG. 9, the simulated impact
of multipath propagation on Bluetooth EDR demodulation performance
is shown.
[0042] For the 2-path multipath propagation model, the power of the
second path is varied relative to the first arriving path. For the
exponential multipath propagation model, the RMS delay spread is
varied.
[0043] In FIG. 6, one can see that even for Pi/4-DQPSK and a very
small second path such as -15 dB (10 log.sub.10(0.0313)), there is
a degradation exceeding 3 dB already. For path larger than -9 dB
(10 log.sub.10(0.125)), successful demodulation is no longer
possible independent of the SNR.
[0044] In FIG. 7, one can see that even for D8PSK and a very small
second path such as -15 dB (10 log.sub.10(0.0313)), there is a
degradation exceeding 12 dB (!) already. For path larger than -15
dB, successful demodulation is no longer possible independent of
the SNR.
[0045] In FIG. 8, one can see that for Pi/4-DQPSK and an RMS delay
spread >250 ns, there is a degradation exceeding 3 dB.
[0046] In FIG. 9, one can see that for D8PSK and an RMS delay
spread >200 ns, there is a degradation exceeding 3 dB.
[0047] It was also shown that even for very moderate multipath
propagation, no reliable data transmission using Bluetooth
technology is possible. That is due to the inter-symbol
interference (ISI) introduced by multipath propagation. Current
(state-of-the-art) Bluetooth receivers are not capable of
mitigating the unfavorable impact of ISI on the data demodulation
in Bluetooth.
[0048] It is concluded that with current (state-of-the-art)
Bluetooth receivers, no reliable data transmission is possible with
regards to transmission ranges provided the transmission power of
power class 1 devices.
SUMMARY OF THE INVENTION
[0049] In order to solve the problems mentioned above, the present
invention provides a method for reception of long-range signals in
Bluetooth. The present invention processes Bluetooth signals with
linear minimum mean square error (MMSE) frequency-domain
equalization (FDE) in single carrier (SC) system using a Fourier
Transform and provides long transmission range Bluetooth service
with reliable data transmission.
[0050] The present invention improves the performance of Bluetooth
service based on power class 2 and 3 devices in multipath
environment.
[0051] The present invention provides FFT/IFFT-based MMSE SC FDE
receiving mode for all Bluetooth transmission modes for
low-complexity and high-performance
[0052] The present invention is used in multi-standard devices in
efficient implementation by reuse of the FFT/IFFT circuitry
[0053] To achieve the purpose mentioned above, one embodiment of
the present invention provides a method for reception of long-range
signals in Bluetooth is for all transmission modes on power class
1, power class 2 and power class 3, the method comprising:
receiving Bluetooth signals; and processing signals with linear
frequency-domain equalization (FDE) in single carrier (SC) system
using a Fourier Transform.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] The file of this patent contains at least one drawing
executed in color. Copies of this patent with color drawing(s) will
be provided by the Patent and Trademark Office upon request.
[0055] The foregoing aspects and many of the accompanying
advantages of this invention will becomes more readily appreciated
as the same becomes better understood by reference to the following
detailed description, when taken in conjunction with the
accompanying drawings, wherein:
[0056] FIG. 1 illustrating BER versus SNR for PI/4-DQPSK in
AWGN;
[0057] FIG. 2 illustrating BER versus SNR for D8PSK in AWGN;
[0058] FIG. 3 illustrating the pathloss versus transmission range
in a Bluetooth network;
[0059] FIG. 4 illustrating 2-path multipath propagation model for
Bluetooth long transmission range applications;
[0060] FIG. 5 illustrating the scenario of multipath propagation in
large office;
[0061] FIG. 6 illustrating the BER performance for Pi/4-DQPSK in
2-Path multipath;
[0062] FIG. 7 illustrating the BER performance for D8PSK in 2-path
multipath;
[0063] FIG. 8 illustrating the BER performance for Pi/4-DQPSK in
exponential multipath;
[0064] FIG. 9 illustrating the BER performance for D8PSK in
exponential multipath;
[0065] FIG. 10 illustrating the processing flow of h yielding
H.sub.inv in SC linear MMSE BLE according to one embodiment of the
present invention;
[0066] FIG. 11 illustrating h of exponential channel (left) and
corresponding h.sub.inv using M=64 (right);
[0067] FIG. 12 illustrating the Pole-Zero Diagrams of h of
exponential channel (left) and corresponding h.sub.inv using M=64
(right);
[0068] FIG. 13 illustrating the constellation diagrams for
noiseless QPSK before equalization (left) and after equalization
(right);
[0069] FIG. 14 illustrating the constellation diagrams for
noiseless QPSK before equalization (left) and after equalization
(right);
[0070] FIG. 15 illustrating the performance of Pi/4-DQPSK and FDE
in 2-path multipath (varying N);
[0071] FIG. 16 illustrating the performance of D8PSK and FDE in
2-path multipath (N=64);
[0072] FIG. 17 illustrating the performance of D8PSK and FDE in
2-path multipath (varying N);
[0073] FIGS. 18A, 18B and 18C illustrating the functional block
diagram of Bluetooth transmitter;
[0074] FIG. 19 illustrating the functional block diagram of radio
channel model for Bluetooth transmission: introduction of multipath
fading and additive White Gaussian Noise (AWGN); and
[0075] FIGS. 20A and 20B illustrating the functional Block Diagram
of Bluetooth Receiver according to one embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0076] As an invention, the use of equalization is proposed for
Bluetooth data communication.
[0077] While ISI mitigation by equalization is well-known in
state-of-the-art digital wireless communications engineering, this
invention proposes the use of a new FDE adapted to SC transmission
without a GI or CP. The proposed FDE very successfully mitigates
ISI while being very implemention-friendly.
[0078] The resulting performance of long transmission range
Bluetooth service based on power class 1 devices using BlueWARP
technology is beyond state-of-the-art Bluetooth service based on
power class 1 devices.
[0079] In the following, a generalized system model is introduced.
The model is similar to the one proposed in [Klein].
[0080] At the transmit side, a block (vector) d of data of length N
is formed in Equation 15:
d=(d.sub.1,d.sub.2 . . . d.sub.N).sup.T (15)
[0081] Any coding, modulation or spreading is assumed to be
included in d already. The data block is transmit through a channel
characterized by its impulse response h in Equation 16:
h=(h.sub.1,h.sub.2 . . . h.sub.w).sup.T (16)
[0082] The convolution of d and h is expressed in matrix notation
using the matrix H in Equation 17:
H=(H.sub.i,v), i=1 . . . N+W-1, v=1 . . . N (17)
with Equation 18:
H i , v = { h i - v + 1 1 .ltoreq. i - v + 1 .ltoreq. W 0 else ( 18
) ##EQU00007##
[0083] The received signal r is given by Equation 19:
r = ( r 1 , r 2 r N + W - 1 ) T = H d + n ( 19 ) ##EQU00008##
where n denotes an additive white Gaussian noise sequence with zero
mean and covariance matrix R.sub.nn.
[0084] Using (block) linear equalization technique for SC systems,
an estimate of the transmit data is obtained using one of the
following criteria. Equation 20: Matched Filter (MF) Criterion
{circumflex over (d)}.sub.MF=H.sup.Hr (20)
Equation 21: Zeros Forcing (ZF) Criterion
[0085] {circumflex over (d)}.sub.ZF=(H.sup.HH).sup.-1H.sup.Hr
(21)
Equation 22: Minimum Mean Square Error (MMSE) Criterion
[0086] {circumflex over
(d)}.sub.MMSE=(H.sup.HH+.sigma..sup.2).sup.-1H.sup.Hr (22)
[0087] Typically, the MMSE criterion yields superior results.
Therefore, only the MMSE criterion is pursued. Nevertheless, all
newly proposed receiver architectures are applicable as well to MF
or ZF equalization.
Single Carrier Linear MMSE Frequency-Domain Equalization using FFT
without Guard Period
[0088] In order to avoid complex receiver processing tasks such as
Cholesky decomposition for solving Equation 22, the (block) linear
MMSE equalization for SC systems can be performed efficiently in
frequency domain expressed in Equation 23 and Equation 24:
d ^ MMSE = F - 1 { H inv F ( r ) } ( 23 ) H inv = ( F { h ^ } ) * (
F { h ^ } ) * F { h ^ } + .sigma. 2 ( 24 ) ##EQU00009##
where F denotes the Discrete Fourier Transform (DFT), F.sup.-1
denotes the Inverse Discrete Fourier Transform (IDFT). h refers to
an estimated channel impulse response. The h is obtained by a
separate processing step typically called channel estimation.
H.sub.inv represents the frequency response of the propagation
channel being inverted using the MMSE criterion. Its time-domain
equivalent is given by h.sub.inv.
[0089] For actual implementations, DFT and IDFT are realized by
Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform
(IFFT), respectively.
[0090] H.sub.inv in Equation 23 can be interpreted as the frequency
response of a transversal linear equalizer filter which time
(impulse) response has to be convolved with the received signal r.
The filter can be categorized as an IIR filter. Therefore, the
filter length is infinite. However, a length can be defined which
contains most of the large coefficients and neglects small
coefficients. The length of this approximated equalizer filter is
denoted by L.sub.eq.
[0091] The length of the received data blocks varies significantly
depending on packet type and service. A fixed-length FFT/IFFT
implementation based on the maximum data block length N of all
packet types and services to be integrated in the receiver
architecture would not be efficient. Also, N can be rather large
(>2 13) which would require to implement a very large FFT (>8
k). However, it is well-known that convolution (e.g. filtering)
operations for continuous data streams or long blocks of data can
be implemented efficiently using overlap-add-technique (OAT) FFT or
overlap-save-technique (OST) FFT algorithms. The further
description focuses on OAT FFT.
[0092] As suggested in [Falconer], FDE for SC systems requires a GI
to be inserted at the transmitter. The following method, however,
allows to apply FFT-based FDE as well for systems without GI.
[0093] An M-point FFT (M=8, 16, 32, 64) is assumed. For every
M-point FFT/IFFT based convolution operation, a length M-L.sub.eq
output data block is generated. The start index within the data
block is advanced by M-L.sub.eq samples per FFT-IFFT operation.
[0094] The single FFTs/IFFTs overlap by L.sub.eq samples.
Therefore, L.sub.eq<M/2 must hold. For such short FFT/IFFT
sizes, the approximated equalizer filter must be limited which can
be accomplished either by circular convolution with a rectangular
window transformed into frequency domain RW (see equation 26) or by
multiplication with a rectangular window rw in time domain (see
equation 25). The latter approach requires one additional
frequency-time and time-frequency conversion.
The extended versions of Equation 23 are given below:
d ^ MMSE = F - 1 { F { F - 1 { ( F { h ^ } ) * ( F { h ^ } ) * F {
h ^ } + .sigma. 2 } rw } F ( r ) } ( 25 ) d ^ MMSE = F - 1 { ( ( F
{ h ^ } ) * ( F { h ^ } ) * F { h ^ } + .sigma. 2 RW ) F ( r ) } (
26 ) ##EQU00010##
denotes circular convolution.
[0095] Also, h.sub.inv must be shifted into the correct position.
Performing this operation in frequency domain corresponds to
rotating H.sub.inv with phasors having an angle increasing with
every sample of H.sub.inv
[0096] In FIG. 10, the entire processing flow of h yielding
H.sub.inv is depicted:
[0097] S01: FFT on estimated channel impulse response
[0098] S02: conjugate complex operation on H
[0099] S03: Multiplication of H with conj(H)
[0100] SO4: Addition of HH* with .sigma..sup.2
[0101] S05: Division of H* by HH*+.sigma..sup.2
[0102] S06: Multiplication with phasors
1 j k M ##EQU00011##
[0103] S07: Circular convolution with
sin x x ##EQU00012##
SC Linear MMSE FDE
[0104] In FIG. 11, h of a noiseless exponential multipath channel
without fading (upper subplot) and with fading (lower subplot) is
shown. The channel parameter RMS delay spread s was set to s=150
ns. In addition, one can see the corresponding h.sub.inv which was
obtained by converting H.sub.inv from Equation 24 back to time
domain.
[0105] In order to apply OAT for equalization, h.sub.inv has to be
shortened to the overlap length M/2. This shortened h.sub.inv is
constructed using the last quarter of samples of h.sub.inv and
appending the first quarter of samples of h.sub.inv to it.
[0106] In FIG. 12, one can see the impact of the
minimum-phase/non-minimum phase character of the non-fading/fading
exponential channel on the pole-zero diagrams of h and
h.sub.inv.
[0107] FIG. 13, visualizes the successful outcome of the described
equalization process by comparing noiseless QPSK constellations
before and after SC linear MMSE FDE. In non-faded multipath
conditions, the equalized constellation appears again to be
perfect. In multipath fading conditions, however, some noise-like
interference remains.
Bluetooth Demodulation Performance in Multipath Propagation using
SC Linear MMSE FDE
[0108] In FIG. 14, FIG. 15, FIG. 16 and FIG. 17, the Bluetooth EDR
demodulation performance using SC linear MMSE FDE is demonstrated.
In addition, the simulated impact of multipath propagation on
Bluetooth EDR demodulation performance is shown.
[0109] For the 2-path multipath propagation model, the power of the
second path is varied relative to the first arriving path.
[0110] In FIG. 14, one can see that for Pi/4-DQPSK and severe
multipath conditions (second path as high as -3 dB (10
log.sub.10(0.5)), the degradation in demodulation performance is
limited to 3 dB. The FFT size Mapplied equals 64.
[0111] In FIG. 15, one can see that for Pi/4-DQPSK and a strong
second path (-6 dB), M=128 and M=32 perform as well as M=64. Even
M=16 performs within 1 dB of the optimum performance (M=128). Very
small FFT sizes (M<16) cause servere degradation in equalization
(and therefore demodulation) performance.
[0112] In FIG. 16, one can see that for D8PSK and severe multipath
conditions (second path as high as -3 dB (10 log.sub.10(0.5)), the
degradation in demodulation performance is limited to 3 dB. The FFT
size Mapplied equals 64.
[0113] In FIG. 17, one can see that for D8PSK and a strong second
path (-6 dB), M=128 and M=32 perform as well as M=64. Even M=16
performs within 2 dB of the optimum performance (M=128). Very small
FFT sizes (M<16) cause severe degradation in equalization (and
therefore demodulation) performance.
[0114] It was shown that for Bluetooth SC linear MMSE FDE can be
used to efficiently mitigate severe ISI introduced by multipath
propagation (second path as high as -3 dB (10 log.sub.10(0.5)). In
addition, it was demonstrated that using FFT sizes as small as M=16
still allow for equalization (and therefore demodulation)
performance within 2 dB of the optimum performance using M=128.
Integration with a Bluetooth Receiver
[0115] In this section, it is described how to integrate the SC
linear MMSE FDE into a Bluetooth receiver. The integration is
described on a conceptual system level.
[0116] The SC linear MMSE FDE is assumed to be used for EDR only.
However, it can also be used for Basic Rate without
modifications.
[0117] In FIG. 18A, FIG. 18B and FIG. 18C, a (simplified)
functional block diagram of a Bluetooth transmitter according to
[BT SIG EDR] is shown: [0118] FIG. 18A [0119] The packet header and
the packet data (payload) undergo bitstream processing as described
in Volume 2 Core System Package, Part B Baseband Specification,
Chapter 7: Bitstream Processing (encryption is not shown). [0120]
Bitstream-processed packet header and access code are multiplexed
as described in Volume 2 Core System Package, Part B Baseband
Specification, Chapter 6: Packets. [0121] Bitstream-processed and
multiplexed packet header and access code are GFSK modulated as
described in Volume 2 Core System Package, Part A Radio
Specification, Chapter 3: Transmitter Characteristics. [0122] FIG.
18B [0123] Bitstream-processed packet data (payload) is switched
between either Basic Rate or EDR processing: [0124] Basic Rate:
Bitstream-processed packet data (payload) is GFSK modulated [0125]
EDR: Sync sequence and trailer are multiplexed with
bitstream-processed packet data (payload) [0126] EDR: Multiplexed
sync sequence/trailer//bitstream-processed packet data (payload) is
switched between Pi/4-DQPSK modulation or D8PSK modulation [0127]
EDR: Multiplexed and modulated sync
sequence/trailer//bitstream-processed packet data (payload) is
multiplexed with guard [0128] EDR: guard and multiplexed and
modulated sync sequence/trailer//bitstream-processed packet data
(payload) is filtered upsampled (US) with root-raised-cosine (RRC)
filter as described in Volume 2 Core System Package, Part A Radio
Specification, Chapter 3: Transmitter Characteristics [0129] FIG.
18C [0130] Processed access code, packet header and packet data
(payload) is multiplexed forming a complete transmit packet
[0131] In FIG. 19, a functional block diagram of the radio channel
model used for Bluetooth transmission is depicted. It introduces
multipath fading according to the model described in prior art.
Also, it introduces Additive White Gaussian Noise (AWGN).
[0132] In FIG. 20A and FIG. 20B, a (simplified) functional block
diagram of a Bluetooth receiver is shown: [0133] FIG. 20A [0134] A
de-multiplxer 101 demultiplexing packet header and packet data
(payload) (access code-related processing is not shown) [0135]
Packet data (payload) is switched by a switch 102 between either
Basic Rate or EDR processing: [0136] Basic Rate: packet data
(payload) is processed by a FFT-based equalizer 105, and then
demodulated by a GFSK demodulator 108. [0137] Basic Rate: optional
equalization of packet header using SC linear MMSE FDE (estimation
of channel impulse response not shown). [0138] Basic Rate: GFSK
demodulation of packet header by a GFSK demodulator 107. [0139]
EDR: Packet data (payload) is filtered downsampled (DS) with
root-raised-cosine (RRC) filter 103 (guard, sync sequence and
trailer processing is not shown). [0140] EDR: filtered packet data
(payload) is switched by a switch 104 between Pi/4-DQPSK
demodulation or D8PSK demodulation. [0141] EDR: equalization of
packet data (payload) using SC linear MMSE FDE (estimation of
channel impulse response not shown) [0142] EDR: Pi/4-DQPSK
demodulation or 8-DPSK demodulation of packet data (payload) by a
Pi/4-DQPSK demodulator 109 or an 8-DPSK demodulator 110. [0143]
FIG. 20B [0144] EDR: reverse bitstream-processing on packet data
(payload)
[0145] The key in the description of the (simplified) processing
flow in a Bluetooth receiver applying BlueWARP technology is the
positioning of SC linear MMSE FDE directly before Pi/4-DQPSK
demodulation or D8PSK demodulation.
[0146] Accordingly, one of features of the present invention is to
provide a method for reception of long-range signals in Bluetooth.
The method has outstanding performance of long transmission range
Bluetooth service based on power class 1 devices and performance
improvement of Bluetooth service based on power class 2 and 3
devices in multipath environment.
[0147] Accordingly, the Low-complexity/high-performance
FFT/IFFT-based MMSE SC FDE receiver architecture is used for all
Bluetooth transmission modes and has highly efficient
implementation by reuse of the FFT/IFFT circuitry in the context of
multi-standard devices,
[0148] Although the present invention has been explained in
relation to its preferred embodiment, it is to be understood that
other modifications and variation can be made without departing the
spirit and scope of the invention as hereafter claimed.
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