U.S. patent application number 12/498912 was filed with the patent office on 2010-09-09 for multi-channel radio frequency front end circuit with full transmit and receive diversity for multi-path mitigation.
Invention is credited to Oleksandr Gorbachov.
Application Number | 20100225414 12/498912 |
Document ID | / |
Family ID | 42677718 |
Filed Date | 2010-09-09 |
United States Patent
Application |
20100225414 |
Kind Code |
A1 |
Gorbachov; Oleksandr |
September 9, 2010 |
MULTI-CHANNEL RADIO FREQUENCY FRONT END CIRCUIT WITH FULL TRANSMIT
AND RECEIVE DIVERSITY FOR MULTI-PATH MITIGATION
Abstract
A front end circuit for coupling a plurality of antennas to a
multi-channel time domain duplex RF transceiver is disclosed. The
front end circuit has a first transmit port, a first receive chain
primary port, a first receive chain secondary ports, and a first
antenna port connectable to a first one of the plurality of
antennas. The front end circuit also has a second transmit port, a
second receive chain primary port, and a second receive chain
secondary port connectable to a second one of the plurality of
antennas. A first switch has terminals connected to the first
transmit port, the first receive chain primary port, and the second
receive chain secondary port, as well as a common terminal that is
connected to the first antenna port. Additionally, the front end
circuit has a second switch that has terminals connected to the
second transmit port, the second receive chain primary port and the
first receive chain secondary port, and a common terminal connected
to the second antenna port.
Inventors: |
Gorbachov; Oleksandr;
(Irvine, CA) |
Correspondence
Address: |
STETINA BRUNDA GARRED & BRUCKER
75 ENTERPRISE, SUITE 250
ALISO VIEJO
CA
92656
US
|
Family ID: |
42677718 |
Appl. No.: |
12/498912 |
Filed: |
July 7, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12470960 |
May 22, 2009 |
|
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|
12498912 |
|
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|
61156954 |
Mar 3, 2009 |
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Current U.S.
Class: |
333/101 |
Current CPC
Class: |
H04B 1/48 20130101; H04B
7/0817 20130101; H04B 7/0602 20130101 |
Class at
Publication: |
333/101 |
International
Class: |
H01P 1/10 20060101
H01P001/10 |
Claims
1. A front end circuit for coupling a plurality of antennas to a
multi-channel radio frequency (RF) transceiver, the front end
circuit comprising: first and second transmit chains; first and
second power dividers; first and second receive chains each
including a first split and a second split interconnected to a
common by a respective one of the first and second power dividers;
an antenna switch circuit connectable to a first and a second one
of the plurality of antennas; a first network selectively
connecting the antenna switch circuit to the first transmit chain
and the first receive chain; and a second network selectively
connecting the antenna switch circuit to the second transmit chain
and the second receive chain.
2. The front end circuit of claim 1, wherein the antenna switch
circuit has a first port connectable to the first antenna, a second
port connectable to the second antenna, a third port connectable to
the first network, and a fourth port connectable to the second
network.
3. The front end circuit of claim 2, wherein: the first port and
the second port define antenna-side ports; the third port and the
fourth port define circuit-side ports; the antenna switch circuit
selectively connects pairings of the antenna-side ports to the
circuit-side ports.
4. The front end circuit of claim 3, wherein the antenna switch
circuit is a double-pole, double-throw switch.
5. The front end circuit of claim 2, wherein in a first operational
mode of the antenna switch circuit, the first port is connected to
the third port and the second port is connected to the fourth
port.
6. The front end circuit of claim 2, wherein in a second
operational mode of the antenna switch circuit, the first port is
connected to the fourth port and the second port is connected to
third port.
7. The front end circuit of claim 1, wherein the RF transceiver has
a first transmit line, a first primary receive line, a first
secondary receive line, a second transmit line, a second primary
receive line, and a second secondary receive line.
8. The front end circuit of claim 7, wherein: the first transmit
chain is connectable to a first transmit line; and the second
transmit chain is connectable to the second transmit line.
9. The front end circuit of claim 7, wherein: the first split of
the first receive chain is connectable to the first primary receive
line; and the second split of the second receive chain is
connectable to the second secondary receive line.
10. The front end circuit of claim 7, wherein: the first split of
the second receive chain is connectable to the second primary
receive line; and the second split of the second receive chain is
connectable to the first secondary receive line.
11. The front end circuit of claim 7, wherein: the first transmit
line, the first primary receive line, and the first secondary
receive line are associated with a first transceiver channel having
a first operating frequency; and the second transmit line, the
second primary receive line, and the second secondary receive line
are associated with a second transceiver channel having a second
operating frequency different from the first operating
frequency.
12. The front end circuit of claim 1, wherein the first network and
the second network are a single-pole, double throw switch with a
common terminal, a first terminal, and a second terminal, the
common terminals being connectable to the respective one of the
antennas, the first terminals being connectable to the respective
one of the transmit chains, and the second terminals being
connectable to the respective one of the receive chains.
13. The front end circuit of claim 1, further comprising: a first
band-pass filter coupled to the first antenna; and a second
band-pass filter coupled to the second antenna.
14. The front end circuit of claim 13, wherein: the first band-pass
filter is connected to the third port of the antenna switch circuit
and the first network; and the second band-pass filter is connected
to the fourth port of the antenna switch circuit and the second
network.
15. The front end circuit of claim 13, wherein: the first band-pass
filter is connected to the first port of the antenna switch circuit
and the first antenna; and the second band-pass filter is connected
to the second port of the antenna switch circuit and the second
antenna.
16. The front end circuit of claim 1, wherein the transceiver
complies with the Wireless Access for Vehicle Environments (WAVE)
standard and includes a control channel corresponding to a one of
the channels and a service channel corresponding to another one of
the channels.
17. An RF front end circuit for coupling antennas to a transceiver
having a first operational channel and a second operational
channel, each of the first and second operational channels
including a transmit line, a first receive line and a second
receive line, the front end circuit comprising: a first antenna
chain and a second antenna chain each having: a transmit mode
connecting the transmit line to a one of the antennas; a first
receive mode connecting a one of the receive lines of one of the
operational channels to the one of the antennas; a second receive
mode connecting a one of the receive lines of a different one of
the operational channels to the one of the antennas; and a third
receive mode connecting the one of the receive lines of the one of
the operational channels and the one of the receive lines of the
different one of the operational channels to the one of the
antennas; wherein the transmit mode of one antenna chain is
simultaneously active with the second receive mode of the other
antenna chain.
18. The front end circuit of claim 17, wherein the transmit mode of
the first antenna chain is exclusive of the transmit mode of the
second antenna chain.
19. The front end circuit of claim 17, wherein: the transmit mode
of the first antenna chain is exclusive of the receive modes of the
first antenna chain; and the transmit mode of the second antenna
chain is exclusive of the receive modes of the second antenna
chain.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/470,960 filed May 22, 2009, entitled MULTI-CHANNEL RADIO
FREQUENCY FRONT END CIRCUIT which relates to and claims the benefit
of U.S. Provisional Application No. 61/156,954, filed Mar. 3, 2009
and entitled DUAL-CHANNEL (DUAL FREQUENCY) HIGH-SENSITIVITY RF
FRONT-END ARCHITECTURES FOR WAVE AND OTHER TDD APPLICATIONS, each
of which are wholly incorporated by reference herein.
STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT
[0002] Not Applicable
BACKGROUND
[0003] 1. Technical Field
[0004] The present invention relates generally to radio frequency
(RF) signal circuitry, and more particularly, to
multi-channel/frequency front-end integrated circuits for time
domain duplex communications.
[0005] 2. Related Art
[0006] Due to population growth and increased mobilization, modern
metropolitan areas suffer from substantial congestion that result
in decreased productivity, wear to transportation infrastructure,
increased fuel consumption, increased risk of bodily harm by
accidents, and so forth. A number of systems currently in
development under the umbrella term of intelligent transportation
systems, or ITS, contemplate the application of information
technology to solve such transportation-related problems. These
applications include onboard navigation systems that have real-time
traffic update capabilities and map update capabilities, as well as
signal control systems that request data from passing vehicles to
determine and regulate traffic flow. Additionally, some
applications contemplate one vehicle being able to communicate with
another for collision avoidance and the like.
[0007] A variety of networking standards for intelligent
transportation systems have been proposed that consider the
specific needs and environmental limitations. One readily available
networking modality is the cellular telephone network such as
Global System for Mobile Communications (GSM), Wideband
Code-Division Multiple Access (W-CDMA), and the like. Another
networking modality current in development is Wireless Access in
Vehicular Environments (WAVE), which is based off the Institute of
Electrical and Electronics Engineers (IEEE) 802.11 wireless local
area network (WLAN) standards. Specifically, the WAVE standard is
referred to as IEEE 802.11p, and a number of car-to-car and
car-to-infrastructure applications are being developed with the
standard. As WAVE is an 802.11 variant, transceivers therefor are
functionally compatible with standard WLAN systems. However,
whereas 802.11b/g WLAN utilizes the 2.4-2.5 GHz
Industrial-Scientific-Medical (ISM) band and 802.11a WLAN utilizes
the 4.9-5.85 GHz band, WAVE utilizes the 5.9 GHz band.
[0008] Generally, WLAN systems transmit and receive signals on a
single channel of frequency. In order to share the single channel,
the transmit and the receive signals are time-domain duplexed. That
is, for a predetermined period of time, the transmitter generates a
burst signal, and for another predetermined period of time, the
other transmitter generates another burst signal to be detected by
the receiver. It is understood that the transmit signals and the
receive signals do not overlap in the time domain. Where the
receiver detects errors in the burst signal via checksums and other
well-known techniques, the other transmitter may be directed to
retry. Errors may be caused in part by increased noise from the
surrounding environment, obstacles, and so forth. If there are a
substantial number of retry attempts, data throughput is
decreased.
[0009] One pertinent feature of WAVE is the use of at least two
channels at different operating frequencies, one of which is
designated a control channel and another that is designated a
public safety channel. The control channel is understood to operate
at a fixed frequency, and is dedicated for vehicle control data.
The public safety channel(s) are understood to be dedicated for
safety data to indicate events such as emergency brake activation,
left and right turn signal activation, lane changes, etc. Other
channels may be utilized for map downloads, traffic updates,
Internet connections, and other general-purpose data transfers.
WAVE systems encompass vehicle-mounted transceivers, also referred
to as on-board units (OBUs), as well as stationary transceivers
placed alongside the road, also referred to as road-side units
(RSUs).
[0010] For the public safety and control channels, it is desirable
to have highly sensitive signal detection. Even minor transmission
delays that result from the above-mentioned retry attempts may have
dire consequences for the lives of vehicle occupants due to the
speed at which they are travelling and the criticality of the
transmitted information.
[0011] Signal reception problems in WAVE systems are commonly
attributable to multi-path propagation phenomena, where a single
signal reaches the antenna via two or more different paths. At the
RF signal level, destructive interference and phase shifts may
occur. Multipath propagation may be caused by reflection from
mountains, tall buildings, and other such structures. For example,
when a car is moving with high speed in crowded environments, the
signal between the on-board unit and the road side unit may reflect
off nearby buildings, bridges, and other cars. The substantially
weakened signal may not be recoverable by the respective
receives.
[0012] One approach to solve this problem is understood to employ
two antennas that are physically separated from each other. The
probability that the RF signals reaching both of the antennas with
different phases is known to be miniscule, so the dual-antenna
configuration is understood to exploit this low probability. In
further detail, this approach involves two receive chains, each
connected to a separate antenna. This configuration is known as
receive antenna diversity. The receiver may select the signal of
higher power as the proper signal to be decoded and further
processed. Other, more sophisticated techniques such as power
combining, maximum likelihood, and so forth for signal extraction
are also known in the art. Receive and transmit antenna diversity
is particularly useful for deployment on on-board units, as some
road side units may be screened by opposite surfaces of the
vehicle.
[0013] As indicated above, WAVE implementations operate on two
distinct channels. Thus, in order to additionally implement antenna
diversity, connections to four separate antennas may be necessary.
This implementation, however, is expensive and the cables to the
antennas may be difficult to manage, in addition to being
undesirable as having to mount so many antennas to the external
surface of the vehicle.
[0014] Accordingly, there is a need in the art for multi-channel or
frequency front-end integrated circuits for time domain duplex
communications systems such as WAVE.
BRIEF SUMMARY
[0015] In accordance with one embodiment of the present invention,
a front end circuit for coupling antennas to a multi-channel time
domain duplex radio frequency (RF) transceiver is contemplated. The
front end circuit may include a first channel module that
selectively connects a first transmit line, a first primary receive
line, and a first secondary receive line of the transceiver to the
antennas. Additionally, the front end circuit may include a second
channel module that selectively connects a second transmit line, a
second primary receive line, and a second secondary receive line of
the transceiver to the antennas. The first channel module and the
second channel module may have independently controllable shared
switching elements.
[0016] According to another embodiment of the present invention,
there is provided a front end circuit for coupling a plurality of
antennas to a multi-channel time domain duplex RF transceiver. The
front end circuit may include a first transmit port, a first
receive chain primary port, a first receive chain secondary ports,
and a first antenna port connectable to a first one of the
plurality of antennas. Further, the front end circuit may include a
second transmit port, a second receive chain primary port, and a
second receive chain secondary port. The front end circuit may also
include a second antenna port connectable to a second one of the
plurality of antennas. There may further be a first switch that has
terminals connected to the first transmit port, the first receive
chain primary port, and the second receive chain secondary port.
The first switch may also have a common terminal that is connected
to the first antenna port. Additionally, there may be a second
switch that has terminals connected to the second transmit port,
the second receive chain primary port and the first receive chain
secondary port. The first switch may include a common terminal
connected to the second antenna port.
[0017] In yet another embodiment of the present invention, an RF
front end circuit for coupling a pair of antennas to a transceiver
with a first operational channel and a second operational channel
is contemplated. Each operational channel may have a corresponding
transmit line, primary receive line, and secondary receive line.
The front end circuit may include a plurality of switching elements
that has a first switching mode connecting a first one of the
transmit lines to a first one of the antennas. The switching
elements may further have a second switching mode connecting a
second one of the transmit lines to a second one of the antennas.
Additionally, the switching elements may have a third switching
mode connecting a first one of the primary receive lines to the
first one of the antennas and a first one of the secondary receive
lines to the second one of the antennas. The switching elements may
have a fourth switching mode connecting a second one of the primary
receive lines to the first one of the antennas and a second one of
secondary receive lines to the second one of the antennas.
[0018] The present invention will be best understood by reference
to the following detailed description when read in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] These and other features and advantages of the various
embodiments disclosed herein will be better understood with respect
to the following description and drawings, in which:
[0020] FIG. 1 is a block diagram illustrating a multi-channel radio
frequency (RF) transceiver front end circuit in accordance with
various embodiments of the present invention in the context of an
exemplary IEEE 802.11p Wireless Access in Vehicle Environments
(WAVE) data communications system;
[0021] FIG. 2 is a block diagram of a conventional RF receiver
architecture;
[0022] FIG. 3 is a graph illustrating the frequency range for
different channels in a WAVE data communications system;
[0023] FIG. 4 is a graph illustrating the power spectral density of
different transmit classes in a WAVE system;
[0024] FIG. 5 is a graph showing the power spectral characteristics
of dual-channel systems;
[0025] FIG. 6 is a graph of intermediate frequency (IF) signals and
noise superimposed over IF filter responses;
[0026] FIG. 7 is a schematic diagram of a first embodiment of the
multi-channel RF transceiver front end circuit;
[0027] FIG. 8 is an exemplary timing diagram showing one
contemplated operational sequence of the first embodiment of the
multi-channel RF transceiver front end circuit shown in FIG. 7;
[0028] FIG. 9 is a schematic diagram of a second embodiment of the
multi-channel RF transceiver front end circuit with full receive
diversity and connected to a first antenna and a second
antenna;
[0029] FIG. 10 is an exemplary timing diagram showing one
contemplated operational sequence of the second embodiment of the
multi-channel RF transceiver front end circuit shown in FIG. 9;
[0030] FIG. 11 is another exemplary timing diagram showing an
operational sequence of the second embodiment of the multi-channel
RF transceiver front end circuit shown in FIG. 9;
[0031] FIG. 12 is third exemplary timing diagram showing a
different operational sequence of the second embodiment of the
multi-channel RF transceiver shown in FIG. 9;
[0032] FIG. 13 is a schematic diagram of a third embodiment of the
multi-channel RF transceiver front end circuit with full receive
diversity comprised of a first module and a second module that each
have a power splitter and an antenna switching/matching
network;
[0033] FIG. 14 is a detailed schematic diagram of one circuit that
may be implement the first module and the second module of the
multi-channel RF transceiver front end circuit in accordance with
another embodiment of the present invention;
[0034] FIG. 15 is a schematic diagram of a fourth embodiment of the
multi-channel RF transceiver front end circuit including a double
pole, double throw switch to select between the first antenna and
the second antenna; and
[0035] FIG. 16 is an exemplary timing diagram showing one
operational sequence of the fourth embodiment of the multi-channel
RF transceiver front end circuit shown in FIG. 13.
[0036] Common reference numerals are used throughout the drawings
and the detailed description to indicate the same elements.
DETAILED DESCRIPTION
[0037] The detailed description set forth below in connection with
the appended drawings is intended as a description of the presently
preferred embodiment of the invention, and is not intended to
represent the only form in which the present invention may be
developed or utilized. The description sets forth the functions of
the invention in connection with the illustrated embodiment. It is
to be understood, however, that the same or equivalent functions
may be accomplished by different embodiments that are also intended
to be encompassed within the scope of the invention. It is further
understood that the use of relational terms such as first and
second and the like are used solely to distinguish one from another
entity without necessarily requiring or implying any actual such
relationship or order between such entities.
[0038] Referring now to the block diagram of FIG. 1, an exemplary
dual channel communications system 21 includes a local node 22 and
a remote node 24 that transmit and receive signals of encoded data
to/from each other. By way of example only and not of limitation,
the dual channel communications system 21 conforms to the IEEE
802.11p Wireless Access in Vehicular Environments (WAVE) standard,
and all radio transmissions 26 between the local node 22 and the
remote node 24 are understood to be in conformity therewith. As
briefly mentioned above, the nodes transmit and receive data over
the same communications medium, that is, the designated radio
frequency (RF) channel, via time domain duplexing. It will be that
while the present disclosure references the WAVE system
specifically when considering various embodiments, any other dual
channel, time domain duplex systems that have stringent sensitivity
and data throughput specifications such as Evolved EDGE (Enhanced
Data Rates for GSM Evolution) may be readily substituted.
[0039] The local node 22 may be, for example, a vehicle, while the
remote node 24 may be another vehicle or a stationary unit
installed along the road or other transportation infrastructure. In
the local node 22, the components therein are referred to as an
on-board unit, while stationary units may be referred to as
road-side units. Regardless of the specific designation, the local
node 22 and the remote node 24 both include a transceiver 28 that
has a first channel module 30a and a second channel module 30b. In
particular, the first channel module 30a is understood to include
an RF receiver and an RF transmitter operating on one channel, and
the second channel module 30b likewise has an RF receiver and an RF
transmitter operating on another channel. The first channel module
30a and the second channel module 30b may be selectively tuned to
the operating frequency of the specified channel. A microprocessor
32 may provide the data to be transmitted from the local node 22 to
the remote node 24 and vice versa, as well as decode the data
received by the local node 22 from the remote 24 and vice versa for
further processing, among other functions.
[0040] Because the transceiver 28 generally does not generate
sufficient power or have sufficient sensitivity necessary for
reliable communications, additional conditioning of transmitted and
received RF signals is necessary. In this regard, the local node 22
and the remote node 24 include a front end module 33, which is
understood to encompass any circuitry between the transceiver 28
and the antenna 36. The front end module 33 includes a power
amplifier to increasing transmission power, and/or a low noise
amplifier for increased reception sensitivity. As will be described
in further detail, various filter circuits such as band pass
filters may also be included to provide clean transmission signals
to the antenna 36, and/or to protect the reception circuitry.
[0041] Referring to FIG. 2, a low intermediate frequency (IF)
receiver architecture 34 may be utilized in the transceivers 28.
The electromagnetic RF signal is converted to electrical current by
an antenna 36. The signal is passed through an RF band-select or
band-pass filter 38 that covers a wide frequency band to encompass
all possible operational frequencies of the applicable standard.
The band pass filter 38 is understood to reject signals reaching
the antenna 36 that may be from unwanted sources that are outside
the operating frequency band. The filtered signal is then amplified
by a low noise amplifier 39 that increases the power of the signal
to a level sufficient for a mixer 40. A local oscillator 42
generates a signal that is used to down-convert the received signal
to an IF signal, and is passed to an image reject filter 44 to
accept only a signal within a predefined frequency band. The signal
may be passed through a low pass filter 46 to further reject
out-of-band signals and mixing products. Thereafter, a variable
gain amplifier 48 amplifies the resulting signal, and is converted
to a digital signal with an analog-to-digital converter (ADC) 50.
The digital signal is provided to baseband circuitry for further
processing. The receiver 34 is one example of a channel-select
filter, and any other architecture may be substituted. For example,
a zero-IF receiver architecture may be utilized, where the RF
signal is down-converted to a baseband signal in single or multiple
steps.
[0042] As best illustrated in FIG. 3, under the WAVE standard,
numerous channels or frequency ranges around 5.9 GHz for the RF
signal are defined. Each of the channels overlaps in various
degrees with neighboring channels, and some channels have wider
frequency ranges than others. A control channel (Ch.sub.--178) is
spaced as far apart as possible from the two public safety channels
(Ch.sub.--172 and Ch.sub.--184) to minimize noise. The remaining
channels are utilized for a variety of other services as discussed
above. Despite the minimal frequency separation between two
different channels, typically on the order of 20 MHz, one
embodiment of the present invention contemplates independent
operation of transceivers at the two frequencies. The graph of FIG.
4 shows the power spectral density (in dBr), that is, the
distribution of instantaneous power across different frequency
offsets, of different WAVE transmission classes in a 10 MHz
channel. It is understood that 5 MHz, as well as 20 MHz channels
have similar spectrum masks as shown.
[0043] With reference to the graph of FIG. 5, the spectral
characteristics of dual-channel transmissions received by the
transceiver 28 and the filtering objectives of the RF receiver
architecture 34 will be considered. Specifically, the graph
illustrates the case where both antennas are transmitting at
alternate channels. A first plot 52 represents the signal of a
selected channel at the first antenna 36a, a second plot 54
represents the signal of the alternate channel at the second
antenna 36b, and a third plot 56 represents the signal of the
alternate channel at the first antenna 36a. A channel low-end
frequency 58 and a channel high-end frequency 60 defining a channel
bandwidth 62, and encompasses that portion of the selected signal
that has a greater power than a predefined threshold value. A
channel middle frequency 64 represents the frequency at which peak
power is outputted. A fourth plot 66 depicts an exemplary filter
response where the frequency offset between adjacent channels is
minimal, thus making the rejection of the alternate channel
difficult. A fifth plot 68 is an alternative exemplary filter
response that sufficiently rejects the alternate channel. As shown
in the fourth plot 66 and the fifth plot 68, diplexer-type
rejection characteristics may be useful to cut wide-band noise from
the alternate channel. Even with filtering the alternate channel as
set forth above, some level of noise from the alternate channel may
remain as depicted in a noise region 70. The various plots above
show that the spectrum shoulders from one transmit channel fall
within the central frequency region of the other channel. If the
other channel is in the receive mode, then noise from the
transmitting channel is understood to degrade the noise floor.
[0044] The graph of FIG. 6 illustrates the spectral characteristics
of the intermediate frequency signal after processing by the image
reject filter 44 and the low pass filter 46 of the RF receiver
architecture 34 depicted in FIG. 2. A first plot 72 is
representative of the useful signal for the selected channel, and a
second plot 74 is representative of the signal for the rejected,
alternate channel. A third plot 76 shows an exemplary response of
the channel-select intermediate frequency (IF) filter, that is, the
image reject filter 44 and the low pass filter 46. The
channel-select IF filter has a pass-band bandwidth generally
corresponding to the channel bandwidth 62. Notwithstanding the
filter, wideband noise from the alternate channel may remain within
the frequency range of the selected channel, as depicted by a
fourth plot 78. However, it is understood that as the physical
distance between the first antenna 36a and the second antenna 36b
is increased, the noise level may decrease as shown in a fifth plot
80.
[0045] Having considered the various operational parameters of
simultaneous operation, dual-channel time-domain duplex
communications systems such as WAVE, further details regarding the
various embodiments of the front end module 33 will be described.
The schematic diagram of FIG. 7 illustrates a first embodiment of
the front end module 33a. As discussed above, the front end module
33 is connectable to the transceiver 28 that includes the first
channel module 30a for one operational frequency or channel, and
the second channel module 30b for the other operational frequency
or channel. According to various embodiments, each of the first and
second channel modules 30a, 30b includes a transmit line, a primary
receive line, and a secondary receive line. The primary receive
line and the secondary receive line are understood to be
connectable to the two spatially separated antennas 36 for
multipath mitigation purposes. This configuration is also referred
to as antenna diversity. Along these lines, the front end module
33a includes a first antenna port 94 connectable to the first
antenna 36a and a second antenna port 96 connectable to the second
antenna 36b.
[0046] The front end module 33a also includes various ports
corresponding to the inputs and outputs of the transceiver 28. In
particular, the front end module 33a includes a first transmit port
(TXA) 82 that is tied to the transmit line of the first channel
module 30a, and a second transmit port (TXB) 84 that is tied to the
transmit line of the second channel module 30b. Additionally, the
front end module 33a includes a first primary receive port (RXA-1)
86 and a first secondary receive port (RXA-2) 88 that are tied to
the primary receive line and the secondary receive line,
respectively, of the first channel module 30a. The front end module
33a also includes a second primary receive port (RXB-1) 90 and a
second secondary receive port (RXB-2) 92 tied to the primary
receive line and the secondary receive line, respectively, of the
second channel module 30b.
[0047] At the basic level, the front end module 33a includes a
first power amplifier 98, a second power amplifier 100, a first
single pole, triple throw (SP3T) switch 102, a second single pole,
triple throw (SP3T) switch 104, a first band-pass filter 106, and a
second band-pass filter 108. The first and second SP3T switches
102, 104 are understood to selectively set the front end module 33a
to one of a transmit mode and two receive modes.
[0048] With further particularity, the first SP3T switch 102 is
understood to have a first terminal 102a that is connected to the
first power amplifier 98, with the input thereof being tied to the
first transmit port 82. Similarly, the second SP3T switch 102 has a
first terminal 104a that is connected to the second power amplifier
100 with its input tied to the second transmit port 84. The first
SP3T switch 104 also has a common terminal 102d that is tied to the
first band-pass filter 106, which in turn is tied to the first
antenna port 94. The second SP3T switch 104 likewise has a common
terminal 104d tied to the second band pass filter 108, which in
turn is tied to the second antenna port 96. In the transmit mode
for either or both of the channels, the respective one of the
common terminals 102d, 104d are connected to the corresponding
first terminals 102a, 104a. It is expressly contemplated that the
two channels are independent of one another, and signals of the
same frequency band can be transmitted simultaneously with only a
small influence on each other. Along these lines, packet width and
duty cycles may differ between the two channels.
[0049] In the receive mode of the first channel, the first SP3T
switch 102 connects the common terminal 102d thereof to a second
terminal 102b, thereby passing the signal from the first antenna
36a to the first primary receive port 86 over the first band pass
filter 106. Additionally, the second SP3T switch 104 connects its
common terminal 104d to a third terminal 104c. This ties the second
antenna 36b to the first secondary receive port 88 over the second
band pass filter 108.
[0050] With respect to the receive mode of the second channel, the
second SP3T switch 104 connects the common terminal 104d to a
second terminal 104b, while the first SP3T switch 102 connects its
common terminal 102d to a third terminal 102c that is tied to the
second secondary receive port 92. Additionally, the second terminal
104b of the second SP3T switch 104 is tied to the first secondary
receive port 90. The signal received through the first antenna 36a
is thus filtered by the first band-pass filter 106 and passed to
the second secondary receive port 92, and the signal received
through the second antenna 36 is filtered by the second band pass
filter 108 and passed to the first secondary receive port 90. The
two channels in the receive modes are also understood to be
independent of each other, that is, there is no time-based
synchronization.
[0051] The first band pass filter 106 and the second band pass
filter 108 are contemplated to have identical configurations, with
low insertion loss within the operating frequency band, that is,
less than 2 dB at the 4.9 GHz to 5.9 GHz WAVE operational
frequencies, and high rejection outside of the operating frequency
band. It is envisioned that the operational frequency band
corresponds to WAVE and WLAN, such that simultaneous operation of
both systems is possible, and the transceiver is capable of
operating over both communication protocols with the same front end
circuit. The identical configuration of the first band pass filter
106 and the second band pass filter 108 aid in size and cost
reductions.
[0052] A number of approaches to isolating one signal chain from
the other are envisioned according to various embodiments of the
present invention. In particular, the first SP3T switch 102 and the
second SP3T switch 104 are understood to have at least a 20 dB
isolation between the first terminals 102a, 104a, respectively, and
the third terminals 102c, 104c, respectively, so that one
transmitting channel does not interfere with receiving signals of
the alternate channel. Additionally, isolation between the first
antenna 36a and the second antenna 36b is also maximized, e.g.,
greater than 40 dB, by greater spatial separation and optimization
of directivity and polarization properties. In the WAVE
communications system 21, the first antenna 36a and the second
antenna 36b may be mounted on opposing sides of the vehicle such as
side minors, for example.
[0053] As briefly mentioned above, in the first receive mode, the
first antenna 36a is connected to the first primary receive port
86, and the second antenna 36b is connected to the first secondary
receive port 88. The connections in the first SP3T switch 102 and
the second SP3T switch 104 are made in dedicated time frames, and
there is understood to be no signal on the first transmit port 82
or the second transmit port 84. This configuration is understood to
provide receiver diversity for the first channel, and the
sensitivity of the receivers in the first channel module 30a of the
transceiver 28 is maximized.
[0054] Relatedly, it is also contemplated that the first antenna
36a is connected to the second secondary receive port 92, and the
second antenna 36b is connected to the second primary receive port
90. Again, the connections in the first SP3T switch 102 and the
second SP3T switch 104 are made in dedicated time frames, and there
is no signal on the first transmit port 82 or the second transmit
port 84. In this configuration, receiver diversity for the second
channel is provided, and the sensitivity of the receivers in the
second channel module 30b is maximized.
[0055] As also indicated above, however, the first antenna 36a may
be connected to the first primary receive port 86 independently of
the second antenna 36b being connected to the first secondary
receive port 88. The first antenna 36a may also be connected to the
second secondary receive port 92 independently of the second
antenna 36b being connected to the second primary receive port 90.
If the transmit chain for a given channel is active instead, that
is, there is a signal on one of the transmit ports 82, 84 being
amplified by a corresponding one of the power amplifiers 98, 100
and connected to one of the antennas 36, then one of the receive
chains of the alternate channel is, by definition, not active.
Accordingly, the sensitivity of the receiver for either the first
channel module 30a or the second channel module 30b of the
transceiver 28 is reduced.
[0056] When transmit chains for channels are active, that is, when
the first transmit port 82 is connected to the first antenna 36a
and the second transmit port 84 is connected to the second antenna
36b, the receive chains for both channels are inactive and the
antennas are disconnected from the receive ports. Thus, the
receiver components of the transceiver 28 are protected from large
signal leakage.
[0057] FIG. 8 best illustrates an exemplary operational sequence of
the first embodiment of the front end module 33a, includes a plot
of signals on the first transmit port 82, the second transmit port
84, the first primary receive port 86, the first secondary receive
port 88, the second primary receive port 90, and the second
secondary receive port 92. For the sake of convenience, the plots
of the signals on the various ports are designated by the
corresponding reference numbers thereof. Furthermore, by way of
example only and not of limitation, the first channel, that is,
those signals on the first transmit port 82, the first primary
receive port 86, and the first secondary receive port 88 are
associated with the control channel under the WAVE standard.
Additionally, the second channel, that is, those signals on the
second transmit port 84, the second primary receive port 90, and
the second secondary receive port 92 are associated with the
service channel.
[0058] The dotted lines in the timing diagram represent segments of
time where signal reception is allowed and disallowed based upon
the status of the first transmit port 82 and the second transmit
port 84. Actual signal reception is indeterminate, and may vary
during actual use. The timing diagram shows that in the interval
t/, the first transmit port 82 is active, while the first primary
receive port 86 and the second secondary receive port 92 are
inactive. In the time interval t2, the first secondary receive port
90 and the second primary receive port 88 are inactive. Between
activating the first transmit port 82 and the second transmit port
84, the first secondary receive port 88 and the second primary
receive port 90 have a period of reduced sensitivity 110.
[0059] As discussed above, in a time period 112 and 113 where both
the first transmit port 82 and the second transmit port 84 are
active, all receive ports are inactive. Furthermore, in time period
between deactivating the primary transmit port 82 while the
secondary transmit port 84 is active, and deactivating the second
transmit port 84, the first primary receive port 86 and the second
secondary receive port 92 have a period of reduced sensitivity 111.
This is understood to be caused by power leakage from the second
transmit port 84.
[0060] In a time period 114 where both the primary transmit port 82
and the second transmit port 84 are inactive, it is possible for
the first receive ports 86, 88 or the second receive ports 90, 92
to be activated. It is understood, however, that the first primary
receive port 86 and the second secondary receive port 92 cannot be
simultaneously activated, and that the second primary receive port
90 and the first secondary receive port 88 likewise cannot be
simultaneously activated.
[0061] FIG. 9 is a schematic diagram of a second embodiment of the
front end module 33b. As will be detailed further below, this
embodiment contemplates a longer allowable time frame for the
receiver 34 in order to increase data throughput. As in the first
embodiment discussed above, the front end module 33b includes the
first antenna port 94 that is connectable to the first antenna 36a
and the second antenna port 96 connectable to the second antenna
36b. Furthermore, the front end module 33b includes the first
transmit port 82 that is tied to the transmit line of the first
channel module 30a, and the second transmit port 84 that is tied to
the transmit line of the second channel module 30b. Additionally,
there is the first primary receive port 86 and the first secondary
receive port 88 that are tied to the primary receive line and the
secondary receive line, respectively, of the first channel module
30a. The front end module 33b also includes the second primary
receive port 90 and the second secondary receive port 92 tied to
the primary receive line and the secondary receive line,
respectively, of the second channel module 30b.
[0062] Generally, the second embodiment of the front end module 33b
includes many of the same components as the first embodiment 33a.
Amongst the shared components include the first power amplifier 98,
the second power amplifier 100, the first band pass filter 106, and
the second band pass filter 108. Additionally, the front end module
33b includes first stage low noise amplifiers 116a-b, second stage
low noise amplifiers 118a-d, a first single pole, double throw
switch 120, a second single pole double throw switch 122, a first
power splitter 124, and a second power splitter 126. The functional
details of the additional components as relating to the front end
module 33b will be described more fully below.
[0063] The front end module 33b may be broadly segregated into two
equal sub-blocks, with one being related to the first channel, and
the other being related to the second channel. Each sub-block is
understood to have one transmit mode and three receive modes. In
this regard, the first SPDT switch 120 and the second SPDT switch
122 generally select between the transmit mode and the receive
modes.
[0064] As shown in FIG. 9, the first transmit port 82 is connected
to an input of the first power amplifier 98. The output of the
first power amplifier 98, in turn, is connected to a first terminal
120a of the first SPDT switch 120. A second terminal 120b of the
first SPDT switch 120 is connected to the receive ports including
the first primary receive port 86 and the second secondary receive
port 92, as will be described in further detail below. A common
terminal 120c of the first SPDT switch 120 is connected to the
first band pass filter 106, then to the first antenna port 94, and
the first antenna 36a. The second transmit port 84 is connected to
an input of the second power amplifier 100. The output of the
second power amplifier 100 is connected to a first terminal 122a of
the second SPDT switch 122. A second terminal 122b of the second
SPDT switch 122 is connected to the receive ports, that is, the
first secondary receive port 88 and the second primary receive port
90. Similarly, a common terminal 122c of the second SPDT switch 122
is connected to the second band pass filter 108, which itself is
connected to the second antenna port 96 and the second antenna
36b.
[0065] In the transmit mode of the first channel, the first power
amplifier 98 is activated, and the first SPDT switch 120 connects
the first terminal 120a to the common terminal 120c. The signal is
amplified by the first power amplifier 98 and passes through the
first band pass filter 106 to the first antenna port 94 and to
first antenna 36a, from which the signal is broadcast. Furthermore,
in the transmit mode of the second channel, the second power
amplifier 100 is activated, and the second SPDT switch 122 connects
the first terminal 122a to the common terminal 122c. The signal
from the transceiver 28 on the second transmit port 84 is amplified
by the second power amplifier 100, conditioned by the second band
pass filter 108, and passed to the second antenna port 96.
[0066] In the first receive mode of the first channel, the first
SPDT switch 120 connects the common terminal 120c to the second
terminal 120b. The received signal from the first antenna 36a
passes through the first band pass filter 106, and then to the
first stage low noise amplifier 116a via the first SPDT switch 120.
The output of the first stage low noise amplifier 116a is connected
to a common port 124c of the first power splitter 124, and in
accordance with one embodiment, the amplified signal is evenly
split between a first split port 124a and a second split port 124b
of the first power splitter 124. The signal on the first split port
124a is amplified by the second stage low noise amplifier 118a, the
output of which is connected to the first primary receive port 86.
In the first receive mode, only the low noise amplifier 118a is
activated, so despite the signal being split and passed to the low
noise amplifier 118b, it is not amplified and passed to the second
secondary receive port 92.
[0067] In the second receive mode of the first channel, again, the
received signal from the first antenna 36a passes through the first
band pass filter 106 to the first stage low noise amplifier 116a
via the first SPDT switch 120, which has connected the common
terminal 120c to the second terminal 120b. The amplified signal
from the first stage low noise amplifier 116a is passed to the
first power splitter 124, which evenly splits the signal between
the first split port 124a and the second split port 124b. Because
only the low noise amplifier 118b is activated in this mode, even
though a signal is present on the first split port 124a, it is not
amplified and passed to the first primary receive port 86.
[0068] In the third receive mode of the first channel, the received
signal from the first antenna 36a is passed to the common port 124c
of the first power splitter 124 over the first band pass filter
106, the first SPDT switch 120, and the first stage low noise
amplifier 116a. As indicated above, the amplified signal is split
evenly between the first split port 124a and the second split port
124b. Both of the low noise amplifiers 118a, 118b are activated,
thereby passing the received signal to both the first primary
receive port 86 and the second secondary receive port 92.
[0069] It is contemplated that the first channel and the second
channel sub-blocks function identically, although each sub-block is
controlled and operated independently. Thus, in the first receive
mode of the second channel, the second SPDT switch 122 connects the
common terminal 122c to the second terminal 122b. The received
signal from the second antenna 36b passes through the second band
pass filter 108, and then to the first stage low noise amplifier
116b via the second SPDT switch 122. The output of the first stage
low noise amplifier 116b is connected to a common port 126c of the
second power splitter 126. The amplified signal is evenly split
between a first split port 126a and a second split port 126b. The
signal on the first split port 126a is amplified by the second
stage low noise amplifier 118d, the output of which is connected to
the first secondary receive port 90. In the first receive mode,
only the low noise amplifier 118d is activated, so although the
signal is split and passed to the low noise amplifier 118d, it is
not amplified and passed to the second primary receive port 88.
[0070] In the second receive mode of the second channel, the
received signal from the second antenna 36b passes through the
second band pass filter 108 to the first stage low noise amplifier
116b via the second SPDT switch 122, which has connected the common
terminal 122c to the second terminal 122b. The amplified signal
from the first stage low noise amplifier 116b is passed to the
second power splitter 126, which evenly splits the signal between
the first split port 126a and the second split port 126b. Because
only the low noise amplifier 118c is activated in this mode, even
though a signal is present on the first split port 126a, it is not
amplified and passed to the first secondary receive port 90.
[0071] In the third receive mode of the second channel, the
received signal from the second antenna 36b is passed to the common
port 126c of the second power splitter 126 over the second band
pass filter 108, the second SPDT switch 122, and the first stage
low noise amplifier 116b, as in the first and second receive modes
discussed previously. As indicated above, the amplified signal is
split evenly between the first split port 126a and the second split
port 126b. Both of the low noise amplifiers 118c, 118d are
activated, thereby passing the received signal to both the first
secondary receive port 88 and the second primary receive port
90.
[0072] As with the first embodiment 33a, the second embodiment of
the front end module 33b contemplates the first band pass filter
106 and the second band pass filter 108 having identical
configurations with low insertion loss within the operating
frequency band (less than 2 dB at 4.9 GHz to 5.9 GHz WAVE
operational frequencies), and high rejection outside of the
operating frequency band. As indicated above, the operational
frequency band corresponds to WAVE and WLAN, such that simultaneous
operation of both systems is possible, and the transceiver is
capable of operating over both communication protocols with the
same front end circuit. Along these lines, the various approaches
to isolating one signal chain from the others are likewise the same
as with the first embodiment 33a discussed above.
[0073] One variation of the first power divider 124 and the second
power divider 126 utilized in the second embodiment of the front
end module 33b is disclosed in Applicant's co-pending patent
application U.S. patent application Ser. No. 12/467,049 filed May
15, 2009 entitled RADIO FREQUENCY POWER DIVIDER AND COMBINER
CIRCUIT, which is expressly incorporated by reference in its
entirety herein. Generally, the power dividers 124, 126 are
configured to have a minimal power loss from the common port 124c,
126c to the first split ports 124a, 126a, and to the second split
ports 124b, 126b, respectively. One embodiment contemplates a loss
of less than 0.5 dB. Additionally, isolation between the first
split ports 124a, 126a, and the second split ports 124b, 126b,
respectively, is maximized when the common ports 124c, 126c is
matched in the operating frequency range. As mentioned above, the
power split between the first split port 124a and the second split
port 124b, as well as the first split port 126a and the second
split port 126b are even, and is approximately 3 dB less than the
power applied at the common ports 124c, 126c, respectively. Along
these lines, the impedance values at the common ports 124c, 126c
are understood to be half that at the first split ports 124a, 126a,
and the second split ports 124b, 126b. Although the patent
application mentioned above discloses a specific power splitter
circuit, any other type such as Wilkinson dividers, lumped-element
based dividers, coupled inductor based dividers, and so forth may
be readily substituted by those having ordinary skill in the
art.
[0074] With the first channel sub-block and the second channel
sub-block are in the first receive mode and thus receiving the same
channel, the signal received on the first antenna 36a is passed to
the first primary receive port 86, and the signal received on the
second antenna 36b is passed to the first secondary receive port
88. Receiver diversity for the first channel is thus provided, and
the sensitivity of the receiver in the first channel is
maximized.
[0075] When the first channel sub-block and the second channel
sub-block are in the second receive mode, the signal received on
the first antenna 36a is passed to the second secondary receive
port 92, and the signal received on the second antenna 36b is
passed to the second primary receive port 90. Receiver diversity
for the second channel is likewise provided with the sensitivity of
the receiver in the second channel is maximized.
[0076] As indicated above, the first channel sub-block and the
second channel sub-block may operate independently with respect to
one another. That is, the first antenna 36a may be connected to the
first primary receive port 86 independently of the second antenna
36b being connected to the first secondary receive port 88. Along
these lines, the first antenna 36a may also be connected to the
second secondary receive port 92 independently of the second
antenna 36b being connected to the second primary receive port 90.
In those instances where there is no receive antenna diversity, it
is understood that the overall sensitivity of the receiver 34 is
reduced.
[0077] When the first transmit port 82 is connected to the first
antenna 36a over the first SPDT switch 120, and second transmit
port 84 is connected to the second antenna 36b over the second SPDT
switch 122, the receive chains for the first channel sub-block and
the second channel sub-block are inactive and disconnected from the
respective antennas 36. The receiver components are therefore
protected from large signal leakage.
[0078] With reference to FIG. 10, one possible operational sequence
of the second embodiment of the front end module 33b is
illustrated. In further detail, it is contemplated that the
activation of the first primary receive port 86 is exclusive of the
activation of the first transmit port 82 during time period t1.
However, since the activation of the first secondary receive port
88 is independent of the first transmit port 82, the two can be
activated simultaneously. The activation of the second primary
receive port 90 is exclusive of the activation of the second
transmit port 84 during the time period t2. The activation of the
second secondary receive port 92 is also independent of the second
transmit port 84, and the two can likewise be activated
simultaneously.
[0079] During a time period 128 in which the first transmit port 82
is activated and the second transmit port 84 is not activated, the
first secondary receive port 88 and the second primary receive port
90 have a period of reduced sensitivity 130, as there is no antenna
diversity and transmit signal leakage to the receiver. Along these
lines, during a time period 132 when the second transmit port 84 is
activated but the first transmit port 82 is not, the first primary
receive port 86 and the second secondary receive port 92 also have
a period of reduced sensitivity 134. In either of the periods of
reduced sensitivity 130, 134, receiver training purposes such as
original gain setting, phase lock loop (PLL) frequency setting and
so forth may be completed.
[0080] When neither the first transmit port 82 nor the second
transmit port 84 are active as in time period 136, all of the
receive ports, that is, the first primary receive port 86, the
first secondary receive port 88, the second primary receive port
90, and the second secondary receive port 92, may be simultaneously
activated. Accordingly, full antenna diversity for both the control
channel and the service channel is contemplated.
[0081] In accordance with one aspect of the present invention, the
actual impact of the reduced sensitivity periods may be further
reduced by better isolating the first antenna 36a from the second
antenna 36b. The power level at the antennas is understood to be
approximately 20 dbm in the 10 MHz channel bandwidth for a class-C
transmitter and a -50 dBr rejection at an offset above 15 MHz from
the signal edge. In this case, the channel power spectrum density
at the antenna 36 while transmitting is -50 dBm/Hz, and the power
spectrum density at an offset above 15 MHz is -100 dBm/Hz.
Considering a noise figure of 3 dB for the first stage low noise
amplifier 116a-b, the second stage low noise amplifier 118a-d, the
SPDT switch 120,122 and a loss of 2 dB attributable to the band
pass filters 106, 108, the noise floor at the antenna inside a
channel band and at close frequency offsets is -169 dBm/Hz.
Accordingly, with the power spectrum density at an offset above 15
MHz being -100 dBm/Hz, the isolation between the two antennas 36 is
69 dB for an overall receiver sensitivity decreased by 3 dB. With
an isolation of 76 dB, the overall receiver sensitivity is may be
reduced by 1 dB.
[0082] The reduction in receiver sensitivity is understood to be
only for the period when one channel is transmitting and the other
channel is receiving, as described above. With time domain duplex
communications systems such as WLAN and WAVE that employ short
burst intervals, the probability of overlap may be greatly reduced,
particularly if the two channels are operating independently. The
probability p1 of the first transmit port 82 being active is given
by t1/T1, and the probability p2 of the second transmit port 84
being active is given by t2/T2. Further, the probability p that the
two active state overlap is p1*p2, or (t1 x t2)/(T1 x T2).
Therefore, with re-transmission of lost data, overall impact on
data throughput may be minimal.
[0083] In WAVE applications that involve the control and public
safety channels, even a minimal reduction in data throughput may
not be acceptable because of the criticality of the information and
the potentially grave safety consequences. The timing diagram of
FIG. 11 shows another possible operational sequence of the second
embodiment of the front end module 33b, in which the control
channel is given priority in transmission and reception. The
activation of the first transmit port 82, which is dedicated to the
control channel, is fully independent. The first secondary receive
port 88 and the second primary receive port 90 both have a period
137 of reduced sensitivity 138. The time period 137 is understood
to be between the rising edge of the activation of the first
transmit port 82, and the rising edge of the activation of the
second transmit port 84. Furthermore, the first primary receive
port 86 and the first secondary receive port 88 remain activated
between the successive activations of the first transmit port 82,
referenced as time period 140.
[0084] The activation of the second transmit port 84 is permitted
only when the first transmit port 82 is activated, for example, a
time period 142 that ends with the deactivation of the first
transmit port 82. Because the probability of overlapping
activations of the first transmit port 82 and the second transmit
port 84, the transmit throughput of the service channel is
understood to be low in comparison to the transmit throughput of
the control channel. However, the second primary receive port 90
and the second secondary receive port 92 are likely to be
simultaneously active with the first primary receive port 86 and
the first secondary receive port 88. Accordingly, the reception
throughput of the service channel is high and thus suitable for
downloading data.
[0085] The timing diagram of FIG. 12 shows yet another possible
operational sequence of the second embodiment of the front end
module 33b. In this example, the control channel is given priority
in transmission and full diversity in reception. While the first
transmit port 82 is activated, no reception of the first channel
occurs, and the first primary receive port 86 and the first
secondary receive port 88 are deactivated. It is possible for the
second transmit port 84 to be activated during this time period,
and the second primary receive port 90 may be activated, albeit
with a period of reduced sensitivity 142. Additionally, the second
secondary receive port 92 is deactivated. In this regard, the
timing of the second secondary receive port 92 is coupled with the
timing of the first transmit port 82.
[0086] A time frame t2 is dedicated for receiving the control
channel, and the first primary receive port 86 and the first
secondary receive port 88 are activated. During this time, the
second transmit port 84 is deactivated, as is the second primary
receive port 90. However, it is possible for the second secondary
receive port 92 to be activated, allowing reception of the service
channel. The second transmit port 84 may be activated once the
first primary receive port 86 and the first secondary receive port
88 are deactivated. As such, the timing of the second primary
receive port 88 is coupled with the timing of the second transmit
port 84.
[0087] The schematic diagram of FIG. 13 illustrates a specific
implementation of the second embodiment of the front end module 33b
shown in FIG. 9, and is comprised of two identical front end
integrated circuits 144a, 144b. According to various embodiments,
the integrated circuits may each be fabricated on a single die, or
the entire front end module 33b may be fabricated on a single
die.
[0088] Each integrated circuit 144 includes four transmit/receive
ports as described above, including a transmit port, two receive
ports, and an antenna port. In further detail, the first integrated
circuit 144a includes the first transmit port 82, the first primary
receive port 86, and the second secondary receive port 92. The
first transmit port 82 is connected to the first power amplifier
98, while the first primary receive port 86 is connected to the
second stage low noise amplifier 118a and the second secondary
receive port 92 is connected to the second stage low noise
amplifier 118b. The second integrated circuit 144b includes the
second transmit port 84 connected to the second power amplifier
100. Moreover, the second integrated circuit 144b includes the
first secondary receive port 88 connected to the second stage low
noise amplifier 118c, as well as the second primary receive port 84
connected to the second stage low noise amplifier 118d.
[0089] Additionally, each integrated circuit 144 includes four
control ports for the activation of the power amplifier, the two
second stage low noise amplifiers, and the first stage low noise
amplifier. The first integrated circuit 144a has a low noise
amplifier control line 148 that enables the second stage low noise
amplifier 118a, and another low noise amplifier control line 150
that enables the second stage low noise amplifier 118b. A power
amplifier control line 152 enables the first power amplifier 98,
and a low noise amplifier control line 154 enables the first stage
low noise amplifier 116a. Similarly, the second integrated circuit
144b has a low noise amplifier control line 156 that enables the
second stage low noise amplifier 118c, in addition to a low noise
amplifier control line 158 that enables the second stage low noise
amplifier 118d. There is also a power amplifier control line 160
that enables the second power amplifier 100, in addition to a low
noise amplifier control line 162 that enables the first stage low
noise amplifier 116b.
[0090] As explained more fully above, the second embodiment of the
front end module 33b contemplates one transmit mode and three
receive modes. In the first transmit mode, one or both of the power
amplifier control lines 152, 160 are enabled, activating the power
amplifiers 98, 100. In the first receive mode, the low noise
amplifier control line 148 is enabled to activate the second stage
low noise amplifier 118a, and the low noise amplifier control line
156 is enabled to activate the second stage low noise amplifier
118c. Additionally, the low noise amplifier control line 154 and
the low noise amplifier control line 162 are enabled to activate
both of the first stage low noise amplifiers 116a-b. In the second
receive mode, the low noise amplifier control line 150 is enabled
to activate the second stage low noise amplifier 118b, and the low
noise amplifier control line 158 is enabled to activate the second
stage low noise amplifier 118d. Again, the low noise amplifier
control line 154 and the low noise amplifier control line 162 are
both enabled to activate both of the first stage low noise
amplifiers 116a-b. In the third receive mode, all of the low noise
amplifier control lines 148, 150, 154, 156, 158, and 162 are
activated for simultaneously reception.
[0091] The functionality of the various components of the front end
integrated circuit 144 are understood to be identical to those
described above in relation to the front end module 33b, including
the second stage low noise amplifiers 118a-d, the power splitters
124, 126, the power amplifier 98, and the first stage low noise
amplifiers 116a-b. Instead of the SPDT switches 120, 122 previously
considered, however, a matching and switching networks 164, 166 may
be substituted. The matching and switching networks 164, 166
include common terminals 164c, 166c, respectively, which are
understood to correspond generally to the common terminals 120c,
122c of the SPDT switches. Further, the matching and switching
networks 164, 166 also include first terminals 164a, 166a that
correspond to the first terminals 120a, 122a of the SPDT switches,
as well as second terminals 164b, 166b that correspond to the
second terminals 120b, 122b of the SPDT switches. In this regard,
it will be recognized that the SPDT switches 120, 122 are
interchangeable with the matching and switching networks 164, 166,
respectively.
[0092] One embodiment of the matching and switching circuits 164,
166 is disclosed in Applicant's co-pending patent application U.S.
patent application Ser. No. 12/412,226 filed Mar. 26, 2009 entitled
RADIO FREQUENCY TRANSCEIVER FRONT END CIRCUIT, which is expressly
incorporated by reference in its entirety herein. Generally, the
matching and switching circuits 164, 166 are configured to pass the
signal from the antenna connection 146 to the power splitters 124,
126 when the first stage low noise amplifiers 116a-b are activated
and the power amplifiers 98, 100 are deactivated. Additionally, the
signal from the transmit ports 82, 84 are passed to the antenna
connection 146 when the power amplifiers 98, 100 are activated and
the first stage low noise amplifiers 116a-b are deactivated.
[0093] The antenna connections 146a, 146b are tied to the common
terminals 164c, 166c of the respective one of the first and second
front end integrated circuits 144a, 144b. It is contemplated that
the first and second band pass filters 106, 108 are external to the
front end integrated circuits 144a, 144b, and are connected to the
signal chain from the antenna connections 146a, 146b. One port of
the first band pass filter 106 is connected to the first antenna
36a, and one port of the second band pass filter 108 is connected
to the second antenna 36b.
[0094] With reference to the schematic diagram of FIG. 14, further
details regarding one implementation of the front end integrated
circuit 144 will be described. Although the general components will
be referenced in terms of the first front end integrated circuit
144a, it will be appreciated by those having ordinary skill in the
art they are equally applicable to the second front end integrated
circuit 144b. It is contemplated that the front end integrated
circuit 144 represents a basic building block of the front end
module 33.
[0095] The front end integrated circuit 144 is generally defined by
a transmit block 200, a first receive block 202, and a second
receive block 204. The various subparts thereof are understood to
correspond to the aforementioned power amplifier 98, the first
stage low noise amplifier 116a, the second stage low noise
amplifiers 118a, 118b, and the matching and switching network 164,
as will be detailed more fully below. The transmit block 200
includes the first transmit port 82, and the first receive block
202 includes the first primary receive port 86. Additionally, the
second receive block 204 includes the second secondary receive port
92 The front end integrated circuit 144 also includes the first
antenna connection 146 associated with each of the transmit block
200, the first receive block 202, and the second receive block 204.
There is also an antenna matching block 208 that generally
correspond to the matching and switching networks 164, and
accordingly share various components of the transmit block 200, the
first receive block 202, and the second receive block 204.
[0096] In further detail, the transmit block 200 has a single-stage
power amplifier with a transistor Q1 in a common emitter
configuration. It is understood that multi-stage amplifiers may
also be utilized for higher gain applications, and those having
ordinary skill in the art will recognize the appropriate
modifications to the basic configuration presented herein for such
multi-stage amplifiers. In some embodiments, it is contemplated
that the transistor Q1 has a bipolar junction structure, though in
some embodiments, they may have a field-effect structure (MOSFET,
MESFET, and the like). In this regard, while the present disclosure
variously references bases, collectors, and emitters of bipolar
junction transistors, it is to be understood that such elements
directly correspond to the gates, drains, and sources of field
effect transistors.
[0097] The first power amplifier 98 includes circuitry for matching
the input of the front end integrated circuit 144 to the 50-Ohm
output impedance of the transceiver 28 at the operating frequency,
as is common in most RF systems. The components of a power
amplifier input matching network 210 include capacitors C1 and C3,
as well as inductors L1 and L2, which match the first transmit port
82 to a base 212 of the transistor Q1 while it is being turned on
and off in the operating frequency range. The capacitor C1 is tied
to the first transmit port 82, the capacitor C3, and the inductors
L1 and L2. The inductor L2 is tied to the base 212, and the
capacitor C3 is tied to ground. The power amplifier input matching
network 210 may be variously configured according to different
gain, linearity, and wideband operation requirements.
[0098] Tied to the inductor L1 is an adjustable voltage source V1
that sets the bias point of the transistor Q1 of the first power
amplifier 98 through a resistor R1. The bias conditions, in
conjunction with the size or geometry of the transistor Q1, are
chosen to maximize the operating power level at the antenna 36
during transmission. Additionally, an RF decoupling capacitor C2
having a sufficiently high capacitance is connected to the voltage
source V1. These components are understood to comprise one
embodiment of a transmit control circuit 216 that is coupled to the
first power amplifier control line 152. A variable voltage may be
generated intermittently by the transceiver 28 on the first power
amplifier control line 152 and thus the transistor Q1, that is, the
first power amplifier 98 is activated and deactivated. The transmit
control circuit 216 is not intended to be limited to voltage supply
circuits as considered above, and any other suitable supply such as
a current minor architecture may be readily substituted.
[0099] The transmit block 200, and specifically the collector 214
of the transistor Q1, is connected to the antenna matching block
208 that generally corresponds to the first matching and switch
network 164. The antenna matching block 208 is defined by a power
amplifier output matching segment 218 that includes inductors L3,
L4, L5 and L6, as well as capacitors C4 and C6. The power amplifier
output matching segment 218 impedance matches the transistor Q1 to
the antenna 36 at the predefined operating frequency when active.
The collector 214 of the transistor Q1 is connected to the inductor
L3, which in turn is connected to capacitors C4, C6, and the
inductor L4. The values of the capacitor C4 and the inductor L5
connected in series thereto and to ground are selected to provide a
series resonance at the second harmonic of the predefined operating
frequency. A voltage source V2 is connected to the inductor L4, and
provides biasing to the collector 214 of the transistor Q1. It is
contemplated that the voltage source V2 is provided by battery or
other appropriate device independent of the other control lines
referenced herein. Similar to the voltage source V1, an RF
decoupling capacitor C5 is connected between the voltage source V2
and ground.
[0100] In accordance with various embodiments, the inductor L6 has
an electrostatic discharge function. The resistive component of the
inductor L6 is contemplated to have a value less than 5 Ohm to
provide a direct current (DC) pass from the antenna connection 146
to ground in case a high voltage is accidentally applied.
Accordingly, the need for electronic discharge clamp circuitry that
degrades signal transmission performance, as is typical in silicon
substrate-based semiconductor devices, is eliminated.
[0101] The power amplifier output matching segment 218 is
configured in a way that the resistive part of the impedance at the
collector 214 of the transistor Q1 is equal or below the resistive
component of an output impedance or transistor load impedance
required for the activated transistor Q1 that corresponds to a
predetermined 1 dB compression point (P1 dB) at a specific bias
voltage. In this regard, the power amplifier output matching
segment 218 is loaded at the antenna side by a predefined load
(typically 50 Ohms) while the first receive block 202, including a
first stage low noise amplifier input matching segment 220, is
disconnected.
[0102] The first stage low noise amplifier input matching segment
220 is comprised of a capacitor C9 and an inductor L10 that are
exclusive thereto. The first stage low noise amplifier input
matching segment 220 is combined with the inductors L3, L4, L5 and
L6 and capacitors C4 and C6, which are shared with the power
amplifier output matching segment 218, to impedance match the first
stage low noise amplifier 116a to the antenna 36 while active. The
capacitor C9 and the inductor L10 are connected in series to the
collector 214 of the transistor Q1 and a base 226 of a shared low
noise amplifier transistor Q2.
[0103] A number of factors are applicable to the optimal
configuration of the first stage low noise amplifier input matching
segment 220. In particular, the size or geometry of the shared low
noise amplifier transistor Q2 is selected such that the resistive
component of an input impedance of an activated shared low noise
amplifier transistor Q2 is substantially similar to the resistive
component of an output impedance required for the activated
transistor Q1 of the power amplifier 98. The values of the
capacitor C9 and the inductor L10 are selected to reach a minimal
noise figure (NF) between the antenna 36 and the output of the
first stage low noise amplifier 116a, as well as a minimal input
return loss for an activated shared low noise amplifier transistor
Q2 and a deactivated transistor Q1 of the power amplifier 98. A
suitable NF, according to one embodiment, may be less than 3 dB.
The input return loss is understood to be measured from the antenna
36, and includes the receive chain of the antenna matching block
208, i.e., the shared power amplifier output matching segment 218
and the low noise amplifier input matching segment 220. One
embodiment contemplates an input return loss of less than -10
dB.
[0104] The capacitor C9 and the inductor L10 are selected to
correspond to a substantially minimized voltage swing at the base
226 of the transistor Q2. When the first power amplifier 98 is on,
an optimized configuration minimizes the voltage being applied to
the first stage low noise amplifier 116a to prevent the transistor
Q2 from conducting while the base-emitter resistance decreases,
thereby degrading the transmitted RF signal.
[0105] Generally, the smallest value of the capacitor C9 is
understood to result in the minimum voltage amplitude at the
base-emitter junction of the transistor Q2 when the transistor Q1
is on and the transistor Q2 is off, thus increasing its
reliability. Additionally, linearity of the power amplifier 98 is
achieved at higher transmit power levels. Avoiding a resonance
frequency of the low noise amplifier input matching segment 220
close to the predefined operating frequency also decreases voltage
swing at the base-emitter junction of the deactivated transistor
Q2, so in one exemplary configuration, the resonance frequency is
set to be at least a few hundred MHz higher.
[0106] As indicated above, the antenna matching block 208 is
connected to the first receive block 202, which includes the first
stage low noise amplifier 116a and other associated circuitry. The
first receive block 202 and the second receive block 204 together
define the first stage low noise amplifier first 116a. The
transistor Q2 is associated with the first stage low noise
amplifier 116a, and is also in a common-emitter configuration.
Additionally connected to the emitter 227 of the shared low noise
amplifier transistor Q2 is an optional degeneration inductor L9
that is tied to ground. In some cases, the base-emitter impedance
of the shared low noise amplifier transistor Q2 may be better
matched to the antenna 36.
[0107] An adjustable voltage source V4 is also connected to the
base 226 of the shared low noise amplifier transistor Q2 for
activating and setting its bias point. As previously noted, a
variable voltage may be generated intermittently by the transceiver
28 on the low noise amplifier control line 154 and so the first
stage low noise amplifier 116a is activated and deactivated
thereby. The voltage is provided through a resistive divider 230
that includes a resistor R3 connected to the adjustable voltage
source V4 and a resistor R2 connected to ground and the resistor
R3. The junction between the resistor R2 and the resistor R3 is
tied to the base 226 of the shared low noise amplifier transistor
Q2. The resistive divider 230 is configured to have a sufficient
resistance to prevent shunting of the impedance at the base 226 of
the transistor Q2, that is, the base-emitter resistance of the
activated shared low noise amplifier transistor Q2 is less than
that of the resistive divider 230. An RF decoupling capacitor C10
is also connected to the voltage source V4. These components are
understood to comprise one embodiment of a first stage receive
control circuit 232. As with the transmit control circuit 216, the
first stage receive control circuit 232 is not intended to be
limited to a voltage supply as above, and other configurations such
as a current minor are also suitable. A voltage source V3 biases
the collector 228 of the shared low noise amplifier transistor Q2,
and there is included an RF decoupling capacitor C8. The collector
228 is coupled to the inductor L8 and a capacitor C11, which are
understood to be an inter-stage matching circuit.
[0108] The first stage low noise amplifier 116a is connected to the
second low noise amplifier stage 118a and a second low noise
amplifier stage 118b over the power divider 124. In further detail,
the power divider 124 includes the common port 124c connected to
the first stage low noise amplifier 116a, specifically, through the
capacitor C11. Additionally, the power divider 124 includes the
first split port 124a and the second split port 124b. The values of
the inductor L8 and the capacitor C11 are selected such that there
is a substantially resistive impedance in the predefined operating
frequency at the common port 124c. Furthermore, the resistive
impedance at the common port 124c is selected to minimize the
resistive part of the impedance at the collector 228 of the shared
low noise amplifier transistor Q2, thereby increasing 1 dB gain
compression to sustain large blocking RF signals.
[0109] The second stage low noise amplifier stage 118a includes the
transistor Q3 that is in a common-emitter configuration. The
collector 236 is tied to a bias voltage source V6 through an
inductor L13, which is part of a second stage low noise amplifier
output matching circuit 238a in combination with the capacitor C7
and the inductor L7. The second stage low noise amplifier output
matching circuit 238a is connected to the first primary receive
port 86 and impedance matches the transistor Q3 thereto.
Additionally, the RF decoupling capacitor C15 is tied to the
voltage source V6. A first receive control circuit 240a includes
the adjustable voltage source V5 that is connected to the low noise
amplifier control line 118a to provide a suitable voltage to settle
the bias point of the transistor Q3. The second stage receive
control circuit 240a is comprised of the resistor R4 and the
inductor L12, as well as the RF decoupling capacitor C14.
[0110] The second stage low noise amplifier 118a is further
comprised of an input matching circuit 242a that is connected to
the first split port 124a of the power divider 124. More
particularly, the matching circuit 242a is comprised of capacitors
C12 and C13, and inductors L11 and L12 to match the impedance at
the first split port 124a and the impedance of the base-emitter
junction of the transistor Q3 when activated. As indicated above, a
high isolation between the first split port 124a and the second
split port 124b is understood to minimize the influence of the
transistor Q4.
[0111] The second stage low noise amplifier 118b is based on the
transistor Q4, also in a common-emitter configuration. The
collector 246 of the transistor Q4 is tied to a bias voltage source
V8 through the inductor L17, and together with the capacitor C19
and the inductor L14, define the second stage low noise amplifier
output matching circuit 238b that is connected to the second
secondary receive port 92. The bias voltage source V8 is also
connected to the RF decoupling capacitor C20. A second stage
receive control circuit 240b includes the adjustable voltage source
V7 that is connected to low noise amplifier control line 150 to
settle the bias point of the transistor Q4. The second stage
receive control circuit 240b also includes the RF decoupling
capacitor C18.
[0112] The second stage low noise amplifier 118b is further
comprised of an input matching circuit 242b connected to the second
split port 124b of the power divider 124. The matching circuit 242b
is comprised of capacitors C16, C17 and inductors L15 and L16 to
match the impedance at the second split port 124b and the impedance
of the base-emitter junction of the transistor Q4 when activated.
Again, the high isolation between the second split port 124b and
the first split port 124a is understood to minimize the influence
of the transistor Q3.
[0113] The various operational states of the front end integrated
circuit 144 will now be considered in light of the foregoing
features, particularly in relation to the transmit modes and the
receive modes of the front end module 33. In the transmit mode, the
transistor Q1 is activated with an appropriate enable signal being
applied to the transmit control circuit 216 from the power
amplifier control line 152. The transistors Q2, Q3, and Q4 are off.
The signal at the transmit port 82 is amplified by the transistor
Q1 and transmitted via the antenna 36.
[0114] In the first receive mode, the first stage low noise
amplifier transistor Q2 and the transistor Q3 are activated, with
an appropriate voltage applied to the first stage receive control
circuit 232 and the second stage receive control circuit 240a. The
transistors Q1, and Q4 are off, and the signal received by the
antenna 36 is amplified by the first stage low noise amplifier 116a
(transistors Q2) and the second stage low noise amplifier 118a
(transistor Q3) and passed to the first primary receive port
86.
[0115] In the second receive mode, again, the first stage low noise
amplifier transistor Q2 is activated, with an appropriate voltage
being applied to the first stage receive control circuit 232
through the low noise amplifier control line 154. Furthermore, the
second stage low noise amplifier transistor Q4 is activated by a
voltage applied to the second stage control circuit 240b by the low
noise amplifier control line 150. The transistors Q1 and Q3 are
off, and the signal received by the antenna 36 is amplified by the
first stage low noise amplifier 116a (transistor Q2) and the second
stage low noise amplifier 118b (transistor Q4).
[0116] In the third receive mode, the first stage low noise
amplifier transistor Q2 is activated with the appropriate voltage
applied to the first stage receive control circuit 232 through the
low noise amplifier control line 154. The second stage low noise
amplifier transistors Q3 and Q4 are both activated by voltages
applied to the second stage control circuits 240a, 240b by the low
noise amplifier control lines 148, 150, respectively. The
transistor Q1 is off, and the signal received by the antenna 36 is
amplified by the first stage low noise amplifier 116a (transistor
Q2), the second stage low noise amplifier 118a (transistor Q3) and
the second stage low noise amplifier 118b (transistor Q4).
[0117] With reference to FIG. 15, a third embodiment of the front
end module 33c contemplates the addition of a dual pole, dual throw
(DPDT) switch for full transmit and receive diversity. As in the
second embodiment 33b considered above, the front end module 33c
includes the antenna port 94 that is connectable to the first
antenna 36a and the second antenna port 96 connectable to the
second antenna 36b. Furthermore, the front end module 33c includes
the first transmit port 82 that is tied to the transmit line of the
first channel module 30a, and the second transmit port 84 that is
tied to the transmit line of the second channel module 30b.
Additionally, there is the first primary receive port 86 and the
first secondary receive port 88 that are tied to the primary
receive line and the secondary receive line, respectively, of the
first channel module 30a. The front end module 33b also includes
the second primary receive port 90 and the second secondary receive
port 92 tied to the primary receive line and the secondary receive
line, respectively, of the second channel module 30b.
[0118] The third embodiment of the front end module 33c includes
many of the same components as the second embodiment 33b. Amongst
the shared components include the first power amplifier 98, the
second power amplifier 100, the first band pass filter 106, the
second band pass filter 108, the first stage low noise amplifiers
116a-b, the second stage low noise amplifiers 118a-d, the first
SPDT switch 120, the second SPDT switch 122, the first power
splitter 124, and the second power splitter 126. Thus, the
functionality of such components both individually and in relation
to one another is understood to be the same. One additional
component included in the third embodiment 33c is, as mentioned
above, the DPDT switch 250, and further details will be
described.
[0119] The DPDT switch 250 has a first port 250a connected to the
first antenna port 94, a second port 250b connected to the first
band pass filter 106, a third port 250c connected to the second
band pass filter 108, and a fourth port 250d connected to the
second antenna port 96. It is contemplated that the isolation
between any one of the ports of the DPDT switch 250 is maximized,
and is at least greater than 20 dB.
[0120] In operation, the DPDT switch 250 has a first state in which
the first port 250a is connected to the second port 250b, and the
fourth port 250d is connected to the third port 250c. There is also
a second state in which the first port 250a is connected to the
third port 250c, and the fourth port 250d is connected to the
second port 250b. Thus, the first transmit port 82 and the second
transmit port 84 can be selectively connected to either of the
first or second antennas 36a, 36b. It will be appreciated that this
is suitable for situations where one of the antennas 36 suffers
from multi-path phenomena or is shadowed by obstacles in the
transmit mode. Receive antenna diversity is understood to continue
to function as described above.
[0121] FIG. 16 shows an operational sequence of the third
embodiment of the front end module 33c. It is contemplated that the
activation of the first primary receive port 86 is exclusive of the
activation of the first transmit port 82 during time period t1.
However, since the activation of the first secondary receive port
88 is independent of the first transmit port 82, the two can be
activated simultaneously. The activation of the second primary
receive port 90 is exclusive of the activation of the second
transmit port 84 during the time period t2. The activation of the
second secondary receive port 92 is also independent of the second
transmit port 84, and the two can likewise be activated
simultaneously.
[0122] During a time period 252 in which the first transmit port 82
is activated and the second transmit port 84 is not activated, the
first secondary receive port 88 and the second primary receive port
90 have a period of reduced sensitivity 254, as there is no antenna
diversity. Additionally, the period of reduced sensitivity 254 may
be the result of leakage of the transmitted signal. Along these
lines, during a time period 256 when the second transmit port 84 is
activated but the first transmit port 82 is not, the first primary
receive port 86 and the second secondary receive port 92 also have
a period of reduced sensitivity 258. In either of the periods of
reduced sensitivity 254, 258, receiver training purposes such as
original gain setting, phase lock loop (PLL) frequency setting and
so forth may be completed.
[0123] When neither the first transmit port 82 nor the second
transmit port 84 are active as in time period 260, all of the
receive ports, that is, the first primary receive port 86, the
first secondary receive port 88, the first secondary receive port
90, and the second secondary receive port 92, may be simultaneously
activated. Accordingly, full antenna diversity for both the control
channel and the service channel is possible.
[0124] The particulars shown herein are by way of example and for
purposes of illustrative discussion of the embodiments of the
present invention only and are presented in the cause of providing
what is believed to be the most useful and readily understood
description of the principles and conceptual aspects of the present
invention. In this regard, no attempt is made to show details of
the present invention with more particularity than is necessary for
the fundamental understanding of the present invention, the
description taken with the drawings making apparent to those
skilled in the art how the several forms of the present invention
may be embodied in practice.
* * * * *