System _3_8
US 20080146159A1
(19) United States
(12) Patent Application Publication (10) Pub. No.: US 2008/0146159 A1
(43) Pub. Date:
Faltman et al.
(54)
FM TRANSMISSION SYSTEM AND METHOD
(76) Inventors:
(57)
(SE)
An RF transmission system comprises an RF transmitter
receiving a base band media signal and generating a broadcast
signal on a broadcast frequency. The broadcast frequency
may be one of a plurality of transmission frequencies Within
a frequency band. A radio data control module periodically
performs an interference detection measurement to determine
Whether an interfering signal from a remote transmitter exists
at the broadcast frequency. An open frequency is selected if an
interfering signal from a remote transmitter exists at the
broadcast frequency. The open frequency may be one of the
Correspondence Address:
(21) App1.No.:
11/609,954
(22) Filed:
Dec. 13, 2006
ABSTRACT
plurality of transmission frequencies Wherein RF interference
is Within predetermined acceptance criteria. The RF transmis
Publication Classi?cation
Int. Cl.
H04B 1 7/00
US. Cl. ................................................... .. 455/6711
Irina Faltman, Lund (SE); Bengt
Stefan Gustavsson, Helsingborg
WARREN A. SKLAR (SOER)
RENNER, OTTO, BOISSELLE & SKLAR, LLP
1621 EUCLID AVENUE, 19TH FLOOR
CLEVELAND, OH 44115
(51)
(52)
Jun. 19, 2008
sion system transmits an identi?cation of the open frequency
on the broadcast frequency and, folloWing such transmission,
sWitches the broadcast frequency to such open frequency.
(2006.01)
360/
Radio / Audio
System _3_8_
V
S
10
W28
RF Transmiter 1
RF Receiver 135
L
‘17
526
18
29
30
Radio Data Control 20
FM 101.5
Media Application §_2_
Patent Application Publication
Jun. 19, 2008 Sheet 1 0f 2
36
US 2008/0146159 A1
Radio / AUCHO
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System i3
i
10
18\A|————~——|~28
RF Transmiter Q
RF Receiver 15
l 17
29
30
11
Radio Data Control 2Q
18
26
FM 101.5
Media Application §_2_
Figure 1
( Start )
ID Open Frequency
Incremental Tune of Spectrum
42
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Measure Interference
,c/46
1
iv
Display Open Frequency
N
l
Transmit RDS Signal of
Alternate Frequency
iv
N
Commence Broadcast on Open
Frequency as In-Use Frequency
Timer Loop
Figure 2
~52
N
Patent Application Publication
Jun. 19, 2008 Sheet 2 0f 2
US 2008/0146159 A1
66
67
Signal
Strength
68
l
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Frequenfcy Band
Figure 3
RF Receiver 14 i
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50ms
50ms
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RF Transmitterg
Time
Figure 4
72
Media
Signal
> Time
V
US 2008/0146159 A1
FM TRANSMISSION SYSTEM AND METHOD
Jun. 19, 2008
clear (e.g. unused) frequency in an environment Wherein
channel usage across the spectrum is subject to change.
TECHNICAL FIELD OF THE INVENTION
SUMMARY
[0001] The present invention relates to PM transmission
system and, in particular, to an FM transmission system
Which maintains its media transmission on an open frequency
Without user intervention.
DESCRIPTION OF THE RELATED ART
[0002]
A radio data system standard has been developed for
[0009] A ?rst aspect of the present invention comprises an
RF transmission system comprising an RF transmitter receiv
ing a base band media signal and generating a broadcast
signal on a broadcast frequency. The broadcast frequency
may be a one of a plurality of transmission frequencies Within
a frequency band.
[0010]
A radio data control module: i) periodically per
forms an interference detection measurement to determine
the transmission of data in conj unction With an FM broadcast.
In more detail, digital data is QPSK modulated to generate a
57 kHZ sub carrier. The sub carrier is then mixed With the base
band media signal such that the base band media signal com
Whether an interfering signal at the broadcast frequency
exceeds threshold criteria, ii) selects an open frequency if an
prises the traditional FM components (mono audio signal,
stereo difference signal, and pilot tone) plus the 57 kHZ sub
transmit an identi?cation of the open frequency on the broad
carrier. Such base band media signal is then “mixed up” to
carrier frequency for modulation of the broadcast signal.
[0003] Standard encoding commands and data ?elds of the
Radio Data System (RDS) standard are used for transmitting
the broadcast frequency to such open frequency. The open
frequency may be one of the plurality of transmission fre
quencies Wherein RF interference is Within predetermined
radio station call letters, music type identi?er, etc to an FM
predetermined threshold.
radio. An FM radio Which is also capable of implementing
RDS may receive and display such data to the user.
[0004] An additional feature of the radio data system is the
Alternate Frequency command. A broadcasting station may
use the Alternate Frequency command to identify a list of
other frequencies that the station uses in adjacent transmitter
areas. A RDS enabled radio Will re-tune itself to a one of the
listed frequencies When the signal degrades.
[0005]
In a separate ?eld of art, FM transmission systems
are a common technology for enabling a user to output audio
from a portable device through any FM radio system. I more
detail, such an FM transmission system may be coupled to the
portable device, receive audio media output from the portable
device, and transmit the audio media as an FM stereo signal
on an unused frequency for reception by the FM radio system.
A common application for such FM transmission systems is
output of audio data from a portable device (such as an ipod or
mobile telephone) through an automobile’s stereo system
because feW automobiles include an auxiliary input port for
the automobiles stereo system.
[0006]
Some FM transmission systems broadcast on only a
single frequency knoWn to be unused by FM radio stations. In
more sophisticated FM transmission systems the user may
select the transmission frequency. In more detail, the user
may utiliZe the automobile’s stereo system to select an
unused frequency by sequentially tuning the FM radio to each
of multiple frequencies Within the band and listing for the
frequency that yields a minimum signal. The user Would the
manually tune the car radio and the FM transmitter to such
unused frequency.
[0007] A problem exists in that a frequency that may be an
unused frequency in one geographic area may be a frequency
used by a radio station in another geographic area. Therefore,
as the automobile moves, interference from remote broad
casting systems Will degrade the signal betWeen the FM trans
mitter and the automobile ’s radio.
[0008] What is needed is a system and method for imple
menting an FM transmission system Which does not suffer the
disadvantages of the above described systems. In more detail
What is needed is a system and method for implementing an
FM transmission system Which maintains its broadcast on a
interfering signal from a remote transmitter exists at the
broadcast frequency, and iii) drives the RF transmitter to
cast frequency and, folloWing such transmission, to sWitch
acceptance criteria such as having ambient energy beloW a
[0011] The radio data control module may drive the RF
transmitter to transmit an identi?cation of the open frequency
on the broadcast frequency by mixing, onto the base band
media signal, a digital indication of an alternate frequency
command and a digital indication of the open frequency. In
more detail, the alternate frequency command may be the
Radio Data System Alternate Frequency command Which, in
accordance With the Radio Data System standard, is mixed
onto the base band media signal using a 57 kHZ sub carrier.
[0012] In one sub embodiment, the interference detection
measurement may comprise a measurement of RF signal
strength at the broadcast frequency during an increment of
time during Which the RF transmitter discontinues transmis
sion. The increment of time during Which the RF transmitter
discontinues transmission may be one of a plurality of peri
odic increments on the order of 50 ms or may be during a time
increment When the signal meets predetermined null criteria
(such as White noise betWeen songs).
[0013] In another sub embodiment, the interference detec
tion measurement may comprise receiving an RF signal at the
broadcast frequency and the presence of an interfering signal
may be determined by determining a difference betWeen the
received RF signal and the broadcast signal of the RF trans
mitter.
[0014] The radio data control module may perform the
interference detection by driving operation of an RF receiver.
In more detail, the RF receiver may receive a tuning fre
quency identi?cation signal from the radio data control mod
ule. The tuning frequency identi?cation signal indicates an
identi?ed frequency. The identi?ed frequency may be one of
the frequencies Within the frequency band. The RF receiver
receives the RF signal at the identi?ed frequency and provides
an indication of the received signal to the radio data control
module.
[0015] In one aspect, the indication of the received signal
may be an indication of RF signal strength and/or ambient
energy at the broadcast frequency. In another aspect, the
indication of the received signal may be the RF signal or a
recovered base band signal.
[0016]
Selecting an open frequency comprises determining
RF interference at each of a plurality of transmission frequen
US 2008/0146159 A1
cies Within the frequency band by providing a sequence of
frequency identi?cation signals to the RF receiver; and per
Jun. 19, 2008
such frequencies. The acceptance criteria may be criteria for
combination of a hardWare circuit and a processor executing
code, or other combinations of the above knoWn to those
skilled in the art.
[0027] In the draWings, each element With a reference num
determining the frequency With the loWest strength receive
ber is similar to other elements With the same reference num
forming an interference detection measurement at each of
signal.
ber independent of any letter designation folloWing the ref
[0017] To the accomplishment of the foregoing and related
ends, the invention, then, comprises the features hereinafter
fully described and particularly pointed out in the claims. The
folloWing description and the annexed draWings set forth in
erence number. In the text, a reference number With a speci?c
letter designation folloWing the reference number refers to the
speci?c element With the number and letter designation and a
reference number Without a speci?c letter designation refers
detail certain illustrative embodiments of the invention.
These embodiments are indicative, hoWever, of but a feW of
the various Ways in Which the principles of the invention may
to all elements With the same reference number independent
be employed. Other objects, advantages and novel features of
the invention Will become apparent from the folloWing
[0028] With reference to FIG. 1, an exemplary portable
device 10 comprises an RF transmission system 11 coupled to
a media application 32.
detailed description of the invention When considered in con
junction With the draWings.
[0018] It should be emphasiZed that the term “comprises/
comprising” When used in this speci?cation is taken to
specify the presence of stated features, integers, steps or
components but does not preclude the presence or addition of
one or more other features, integers, steps, components or
groups thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019]
FIG. 1 is a diagram representing an exemplary por
table device Which may includes an RF transmission system
in accordance With one embodiment of the present invention;
[0020]
FIG. 2 is a How chart representing exemplary opera
tion of an RF transmission system in accordance With one
embodiment of the present invention;
[0021] FIG. 3 is a graph representing an exemplary
embodiment of determining interference on a frequency
Within a frequency band in accordance With one embodiment
of the present invention;
[0022] FIG. 4 is a graph representing an exemplary
embodiment of determining a clear channel in accordance
With one embodiment of the present invention;
[0023] FIG. 5 is a graph representing an alternative
embodiment of determining a clear channel in accordance
With one embodiment of the present invention; and
[0024] FIG. 6 is a graph representing an exemplary
of any letter designation folloWing the reference number in
the draWings.
[0029]
In the exemplary embodiment, the media applica
tion 32 may be any combination of hardWare, ?rmWare, and
softWare Which generates audio media. Examples include: i)
an MP3 player Which generates audio media representative of
stored audio media; and i) a telephone application Which
generates audio media representative of a telephone conver
sation.
[0030] The RF transmission system 11 receives a media
signal 18 from the media application 32 and broadcasts a
carrier signal 36 representing the media signal 18 at a broad
cast frequency. A radio a radio/audio system 38, such as an
automobile’s traditional stereo system or a home FM radio/
audio system, is tuned to the broadcast frequency, receives the
carrier signal, and outputs the audio media through its speak
ers.
[0031] It is recogniZed that the clearest reception at the FM
radio/audio system 38 is obtained When the broadcast fre
quency is a clear channel meaning that there is minimal
interference from other remote broadcasting systems.
[0032] To maintain the broadcast frequency on a clear
channel, the RF transmission system 11 periodically per
forms an interference detection measurement to determine
Whether an interfering signal at the broadcast frequency
exceeds a threshold criteria. The threshold criteria may be RF
signal strength and/ or ambient RF energy exceeding a prede
termined criteria.
embodiment for determining interference on a broadcast fre
quency in accordance With one embodiment of the present
invention.
[0033] If an interfering signal exceeds the threshold crite
ria, the RF transmission system 11: i) determines interference
DETAILED DESCRIPTION OF EMBODIMENTS
digital assistants (PDAs), smart phones or the like.
[0026] Many of the elements discussed in this speci?cation,
quency being a one of the plurality of alternate frequencies
Wherein interference is Within predetermined acceptance cri
teria; iii) broadcasts an indication of the open frequency on
the then current broadcast frequency; and iv) transitions the
broadcast frequency from the then current broadcast fre
quency to the open frequency such that the open frequency
become the neW broadcast frequency.
[0034] The broadcast of an indication of the open fre
quency on the then current broadcast frequency may be by
Way of generating a sub carrier (at 57 kHZ) Which includes a
Whether referred to as a “system” a “module” a “circuit” or
Radio Data System (RDS) standard Alternate Frequency
similar, may be implemented in hardWare circuit(s), a proces
Command and a digital indication of the open frequency for
mixing With the base band media signal 18. As such, the RDS
Alternate Frequency Command and the digital indication of
the open frequency are, in accordance With the RDS standard,
“mixed-up” to the carrier frequency for broadcast in conjunc
tion With the media. After the Alternate Frequency Command
at each of a plurality of alternate frequencies Within the FM
frequency band; ii) selects an open frequency, the open fre
[0025]
The term “electronic equipment” as referred to
herein includes portable radio communication equipment.
The term “portable radio communication equipment”, also
referred to herein as a “mobile radio terminal” or “portable
device”, includes all equipment such as mobile phones, pag
ers, communicators, e.g., electronic organiZers, personal
sor executing softWare code, or a combination of a hardWare
circuit and a processor executing code. As such, the term
circuit as used throughout this speci?cation is intended to
encompass a hardWare circuit (Whether discrete elements or
an integrated circuit block), a processor executing code, or a
US 2008/0146159 A1
Jun. 19, 2008
is broadcast, the RF transmission system 11 transitions the
broadcast frequency to the open frequency.
[0035] After the RF transmission system 11 transitions to
[0042] Returning to FIG. 1, if interference beyond an
acceptable threshold of interference is detected, the radio data
the broadcast frequency (the original broadcast frequency) to
plurality of alternate frequencies Within the frequency band;
the open frequency (as the neW broadcast frequency), the
radio/audio system 38 Will detects that the signal is no longer
available on the original broadcast frequency and Will retune
of the plurality of alternate frequencies Wherein interference
to the neW broadcast frequency.
[0036]
To implement such functionality, the RF transmis
sion system may comprise an RF transmitter 12, an RF
receiver 14, and a radio data control module 20. In general,
the RF transmitter 12 broadcasts the carrier signal 36 repre
senting the media signal 18 at the broadcast frequency. To
maintain the broadcast frequency 17 on a clear channel, the
radio data control module 20 periodically performs an inter
ference detection measurement to determine Whether an
interfering signal at the broadcast frequency exceeds the
threshold criteria.
[0037] In more detail, the radio data control module 20 may
provide an indication of a tuning frequency 29 to the RF
receiver 14. The RF receiver 14 tunes to the indicated tuning
frequency 29 for purposes of measuring broadcast signal
strength and/or ambient RF energy as a measurement of inter
ference. Turning brie?y to FIG. 4, measurement of broadcast
signal strength and/or ambient RF energy at the broadcast
frequency may be performed during periodic intervals 74a,
74b (on the order of 50 ms) When the RF transmitter 12
discontinues the broadcast signal 36.
[0038] If the RF energy exceeds a predetermined threshold,
interference beyond an acceptable threshold is concluded to
exist. The measurement of broadcast signal strength and/or
ambient RF energy may be performed by the RF receiver 14
and an indication thereof is provided to the radio data control
module Which determines Whether the such measurement of
interference exceeds the predetermined threshold.
[0039] As an alternative to discontinuing the broadcast sig
nal at periodic intervals 74a, 74b, With reference to FIG. 5,
discontinuation of the broadcast signal (and measurement of
RF energy at the broadcast frequency) may be performed
during an increment of time during Which the media signal 18
(FIG. 1) is null 72 (eg is beloW a null threshold such as being
the White noise signal betWeen songs or otherpauses in useful
media). Again, the measurement of broadcast signal strength
control module 20: i) determines interference at each of a
ii) selects an open frequency, the open frequency being a one
is Within predetermined acceptance criteria; iii) provides the
Alternate Frequency command on a sub carrier 27 for mixing
With the media signal 18 for driving the RF transmitter 12 to
broadcast an indication of the open frequency on the then
current broadcast frequency; and iv) provides an indication of
the open frequency 17 to the RF transmitter 12 to transition
the broadcast frequency from the then current broadcast fre
quency to the open frequency such that the open frequency
become the neW broadcast frequency.
[0043] Turning to FIG. 2 a How chart representing exem
plary operation of the radio data control module 20 is shoWn.
Referring to FIG. 2 in conjunction With FIG. 1, step 42 rep
resents identifying an open frequency. An exemplary process
for identifying an open frequency includes incrementing the
indication of the tuning frequency 29 provided to the RF
receiver 14 to each of a plurality of frequencies Within the FM
band (step 44) and, for each of such plurality of frequencies,
determining Whether interference is Within predetermined
acceptance criteria (step 46). The identi?ed open frequency
may be one of the plurality of frequencies Where the interfer
ence is Within the predetermined acceptance criteria.
[0044] Referring brie?y to FIG. 3, a graph representing an
exemplary method for determining Whether interference 67,
at each of a plurality of frequencies 68, is Within acceptable
criteria. The horiZontal axis represents the plurality of fre
quencies 68 Within the FM band. The vertical axis represents
signal strength or ambient energy at the frequency. The open
frequency 70 may be selected by determining the frequency
Within the frequency band With the Weakest interfering signal
67 Which may be loWest signal strength or loWest ambient
energy. Again, to enable measurement of interference Without
distortion from energy of the RF transmitter 12, the measure
ment of interference may be obtained during periodic inter
vals 74a, 74b When the broadcast signal is discontinued as
discussed With respect to FIG. 4.
[0045] Returning to FIG. 2 in conjunction With FIG. 1, step
48 represents displaying an indication of the open frequency
on a display 34. It should be appreciated that upon initial start
up of the system, the radio/audio system 38 may not be tuned
and/ or ambient RF energy may be performed by the RF
receiver 14 and an indication thereof is provided to the radio
data control module Which determines Whether the such mea
surement of interference exceeds the predetermined thresh
old.
to the broadcast frequency 17. As such, displaying the indi
cation of the open frequency on the display 34 enables the
[0040]
frequency.
To determine Whether the media signal 18 is null,
the radio data control module 20 may monitor the media
signal 18 or may monitor the broadcast signal 36 via the RF
user to initially tune the radio/audio system 38 to the open
[0046]
Step 50 represents generating the RDS signal 26
receiver 14 and, When the media signal is null, signal the RF
(including the Alternate Frequency command and a digital
indication of the open frequency) for mixing With the base
transmitter 12 to discontinue transmission of the broadcast
signal for an interval of time for performance of the interfer
band media signal 18 for on the then in use broadcast fre
quency.
ence detection measurement.
[0047]
[0041] Referring to FIG. 6, an alternative system for deter
mining Whether interference exists at the broadcast frequency
is represented. A comparison betWeen a received signal 75 (at
the broadcast frequency) With the knoWn broadcast signal 76
(a signal knoWn to have been broadcast by the RF transmitter
open frequency 17 to the RF transmitter 12 to transition the
broadcast frequency from the then current broadcast fre
quency to the open frequency such that the open frequency
become the neW broadcast frequency.
12) is performed. When the discrepancy betWeen the signals
(represented by the shaded area) exceeds a predetermined
odically measures interference at the broadcast frequency to
determine Whether an interfering signal from a remote trans
mitter exists at the broadcast frequency. Step 54 represents a
time loop to effect such periodic measurement and decision
threshold, interference beyond an acceptable threshold is
concluded to exists.
[0048]
Step 52 represents providing the indication of the
As discussed, the radio data control module 20 peri
US 2008/0146159 A1
box 56 represents determining Whether an interfering signal
exceeds acceptable criteria. If an interfering signal exceed
acceptable criteria, steps 42 though 52 are repeated to transi
tion the broadcast to an open frequency.
[0049] It should be appreciated that the systems and meth
ods of the present invention provide a convenient system for
selecting amongst multiple services that may be provided by
a remote service provider system and selection amongst mul
tiple transport options for initiating use of the selected ser
vice.
[0050] Although the invention has been shoWn and
described With respect to certain preferred embodiments, it is
obvious that equivalents and modi?cations Will occur to oth
ers skilled in the art upon the reading and understanding of the
speci?cation. For example, FIG. 1 represents the RF trans
mission system 11 as an integrated component of the portable
device 10. Alternatively, it is envisioned that the RF transmis
sion system 11 may be implemented in a module Which
couples to the portable device via an external port or a Wire
less connection such as Bluetooth . Further, the display 34
(for displaying an indication of the broadcast frequency) may
also be an integrated component of the portable device or the
module of the RF transmission system 11. The present inven
tion includes all such equivalents and modi?cations, and is
limited only by the scope of the folloWing claims.
1. An RF transmission system comprising:
an RF transmitter receiving a base band media signal and
generating a broadcast signal on a broadcast frequency,
the broadcast frequency being a one of a plurality of
transmission frequencies Within a frequency band;
a radio data control module:
periodically performing an interference detection mea
surement to determine Whether an interfering signal at
the broadcast frequency exceeds a threshold criteria,
and
selecting an open frequency if an interfering signal at the
broadcast frequency exceeds the threshold criteria,
the open frequency being one of the plurality of trans
mission frequencies Wherein RF interference is
Within predetermined acceptance criteria; and
driving the RF transmitter to transmit an identi?cation of
the open frequency on the broadcast frequency and,
folloWing such transmission, to sWitch the broadcast
frequency to such open frequency.
2. The RF transmission system of claim 1, Wherein the
radio data control module drives the RF transmitter to trans
mit an identi?cation of the open frequency on the broadcast
frequency by mixing, onto the base band media signal, a
digital indication of an alternate frequency command and a
digital indication of the open frequency.
3. The RF transmission system of claim 2, Wherein the
interference detection measurement comprises a measure
ment of RF signal strength at the broadcast frequency during
an increment of time during Which the RF transmitter discon
tinues transmission.
4. The RF transmission system of claim 3, Wherein the
increment of time occurs When the media signal meets pre
determined null criteria.
5. The RF transmission system of claim 2, Wherein the
interference detection measurement comprises receiving an
RF signal at the broadcast frequency and the presence of an
Jun. 19, 2008
6. The RF transmission system of claim 1:
further comprising an RF receiver:
receiving a tuning frequency identi?cation signal from
the radio data control module, the tuning frequency
identi?cation signal indicates an identi?ed frequency,
the identi?ed frequency being a one of the frequencies
Within the frequency band;
receiving an RF signal on the identi?ed frequency;
providing an indication of the received RF signal to the
radio data control module; and
selecting an open frequency comprises determining RF
interference at each of a plurality of transmission
frequencies Within the frequency band by:
providing a sequence of frequency identi?cation signals
to the RF receiver;
receiving an indication of the received RF signal at each
of the sequence of identi?ed frequencies; and
the acceptance criteria is the frequency With the Weakest
interfering signal.
7. The RF transmission system of claim 6, Wherein the
radio data control module drives the RF transmitter to trans
mit an identi?cation of the open frequency on the broadcast
frequency by mixing, onto the base band media signal, a
digital indication of an alternate frequency command and a
digital indication of the open frequency.
8. The RF transmission system of claim 7, Wherein the
interference detection measurement comprises a measure
ment of RF signal strength at the broadcast frequency during
an increment of time during Which the RF transmitter discon
tinues transmission.
9. The RF transmission system of claim 8, Wherein the
increment of time occurs When the media signal meets pre
determined null criteria.
10. The RF transmission system of claim 7, Wherein the
interference detection measurement comprises receiving an
RF signal at the broadcast frequency and the presence of an
interfering signal is determined by determining a difference
betWeen the received RF signal and the broadcast signal of the
RF transmitter.
11. An RF transmission system comprising:
an RF transmitter receiving a base band media signal and
generating a broadcast signal on a broadcast frequency,
the broadcast frequency being a one of a plurality of
transmission frequency Within a frequency band;
a radio data control module:
determining RF interference at each of a plurality of
transmission frequencies Within the frequency band;
selecting an open frequency, the open frequency being
one of the plurality of transmission frequencies
Wherein RF interference is Within predetermined
acceptance criteria; and
driving the RF transmitter to transmit an identi?cation of
the open frequency on the broadcast frequency and,
folloWing such transmission, to sWitch the broadcast
frequency to such open frequency.
12. The RF transmission system of claim 11, Wherein the
radio data control module drives the RF transmitter to trans
mit an identi?cation of the open frequency on the broadcast
interfering signal is determined by determining a difference
frequency by mixing, onto the base band media signal, a
betWeen the received RF signal and the broadcast signal of the
digital indication of an alternate frequency command and a
RF transmitter.
digital indication of the open frequency.
US 2008/0146159 A1
13. The RF transmission system of claim 12, wherein:
the radio data control module:
periodically performs an interference detection mea
surement to determine Whether an interfering signal at
the broadcast frequency exceeds a threshold criteria,
and selects a second open frequency upon determin
ing that an interfering signal exceeds the threshold
criteria, the second open frequency being one of the
plurality of transmission frequencies Wherein RF
interference is Within the predetermined acceptance
criteria; and
drives the RF transmitter to transmit an identi?cation of
the second open frequency on the broadcast fre
quency and, folloWing such transmission, to sWitch
the broadcast frequency to such second open fre
quency.
14. The RF transmission system of claim 13, Wherein the
interference detection measurement comprises a measure
ment of RF signal strength at the broadcast frequency during
an increment of time during Which the RF transmitter discon
tinues transmission.
15. The RF transmission system of claim 14, Wherein the
increment of time occurs When the media signal meets pre
determined null criteria.
16. The RF transmission system of claim 13, Wherein the
interference detection measurement comprises receiving an
RF signal at the broadcast frequency and the presence of an
interfering signal is determined by detecting a difference
betWeen the received RF signal and the broadcast signal of the
RF transmitter.
17. A portable device comprising:
a media application generating an audio media signal;
an RF transmitter receiving the audio media signal and
generating a broadcast signal on a broadcast frequency,
the broadcast frequency being a one of a plurality of
transmission frequencies Within a frequency band;
a radio data control module:
periodically performing an interference detection mea
surement to determine Whether an interfering signal at
the broadcast frequency exceeds a threshold criteria,
selecting an open frequency if an interfering signal at the
broadcast frequency exceeds the threshold criteria,
the open frequency being one of the plurality of trans
mission frequencies Wherein RF interference is
Within predetermined acceptance criteria; and
driving the RF transmitter to transmit an identi?cation of
the open frequency on the broadcast frequency and,
folloWing such transmission, to sWitch the broadcast
frequency to such open frequency.
18. The portable device of claim 17, Wherein the radio data
control module drives the RF transmitter to transmit an iden
ti?cation of the open frequency on the broadcast frequency by
mixing, onto the base band media signal, a digital indication
Jun. 19, 2008
signal strength at the broadcast frequency during an incre
ment of time during Which the RF transmitter discontinues
transmission.
20. The portable device of claim 19, Wherein the increment
of time occurs When the media signal meets predetermined
null criteria.
21. The portable device of claim 18, Wherein the interfer
ence detection measurement comprises receiving an RF sig
nal at the broadcast frequency and the presence of an inter
fering signal is determined by determining a difference
betWeen the received RF signal and the broadcast signal of the
RF transmitter.
22. The portable device of claim 17:
further comprising an RF receiver:
receiving a tuning frequency identi?cation signal from
the radio data control module, the tuning frequency
identi?cation signal indicates an identi?ed frequency,
the identi?ed frequency being a one of the frequencies
Within the frequency band;
receiving an RF signal on the identi?ed frequency;
providing an indication of the received RF signal to the
radio data control module; and
selecting an open frequency comprises determining RF
interference at each of a plurality of transmission
frequencies Within the frequency band by:
providing a sequence of frequency identi?cation signals
to the RF receiver;
receiving an indication of the received RF signal at each
of the sequence of identi?ed frequencies; and
the acceptance criteria is the frequency With the Weakest
interfering signal.
23. The portable device of claim 22, Wherein the radio data
control module drives the RF transmitter to transmit an iden
ti?cation of the open frequency on the broadcast frequency by
mixing, onto the base band media signal, a digital indication
of an alternate frequency command and a digital indication of
the open frequency.
24. The portable device of claim 23, Wherein the interfer
ence detection measurement comprises a measurement of RF
signal strength at the broadcast frequency during an incre
ment of time during Which the RF transmitter discontinues
transmission.
25. The portable device of claim 24, Wherein the increment
of time occurs When the media signal meets predetermined
null criteria.
26. The portable device of claim 23, Wherein the interfer
ence detection measurement comprises receiving an RF sig
nal at the broadcast frequency and the presence of an inter
fering signal is determined by determining a difference
of an alternate frequency command and a digital indication of
betWeen the received RF signal and the broadcast signal of the
the open frequency.
19. The portable device of claim 18, Wherein the interfer
RF transmitter.
ence detection measurement comprises a measurement of RF
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