EP2178153A1

EP2178153A1 - Network element for a multiband mobile coomunications system

Info

Publication number: EP2178153A1
Application number: EP08290987A
Authority: EP
Inventors: Andreas Pascht; Thomas Bitzer; Ralf Matz
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2008-10-20
Filing date: 2008-10-20
Publication date: 2010-04-21

Abstract

The invention relates to a network element for a multiband mobile communications system, the network element comprising: a first set of transmission filters and a second set of reception filters, each filter having a stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is designed for maximum reflection at the output port in the stop bands; a first set of quarter-wavelength transmission lines connecting the first set of transmission filters with a first connection point and a second set of quarter-wavelength transmission lines connecting the second set of reception filters with a second connection point. The network element further comprises: a first circulator with a first, a second and a third port, wherein the first port is coupled to the first connection point, and the third port is coupled to a first termination; a second circulator with a forth, a fifth and a sixth port, wherein the forth port is coupled to the second port of the first circulator, and the fifth port coupled to an antenna; a third circulator with a seventh, an eight and a ninth port, wherein the seventh port is coupled to the sixth port of the second circulator, the eight port is coupled to the second connection point and the ninth port coupled to a second termination.

Description

Technical field

The invention relates to a network element for a mobile communications system, to a method of multiplexing in a mobile communications system.

Background and related art

A number of digital mobile telephone standards are currently deployed worldwide. These standards include the European GSM and UMTS, and in the USA the CDMA standard. Due to the increasing demand for mobile telephone services, many of these standards are deployed together, and further deployments of new standards, currently being drafted or in deployment trials, are foreseeable. These new standards include the Long Term Evolution (LTE) and the IEEE 802.16.
The European Telecommunications Standards Institute (ETSI) has developed the so called third generation mobile environment known as the Universal Mobile Telecommunication System (UMTS) which is in operation since 2002. UMTS operates in the 2 GHz frequency band and offers data transmission rates of up to 2 Mbits/sec, specially with the new enhancements of High Speed Downlink Access (HSDPA), compared to a rate of 9.6 Kbits/sec offered by the GSM standard.
In the transition from second generation standards to third or forth generation standards, both second and third generation standards currently coexist and will continue to do so. Therefore, multiband communication systems, that include two or more frequency bands belonging to the two or more communication standards will continue coexisting in parallel and working together to provide coverage and services to the mobile stations.

Summary of the Invention

The invention relates to a network element for a multiband mobile communications system, the network element comprising: a first set of transmission filters and a second set of reception filters, each filter having a stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is designed for maximum reflection at the output port in the stop bands; a first set of quarter-wavelength transmission lines connecting the first set of transmission filters with a first connection point and a second set of quarter-wavelength transmission lines connecting the second set of reception filters with a second connection point. The network element further comprises: a first circulator with a first, a second and a third port, wherein the first port is coupled to the first connection point, and the third port is coupled to a first termination; a second circulator with a forth, a fifth and a sixth port, wherein the forth port is coupled to the second port of the first circulator, and the fifth port coupled to an antenna; a third circulator with a seventh, an eight and a ninth port, wherein the seventh port is coupled to the sixth port of the second circulator, the eight port is coupled to the second connection point and the ninth port coupled to a second termination.
The term 'quarter wavelength' as expressed herein refers to the wavelength of the corresponding centre frequency of the filter. The quarter wavelength is different for each filter and therefore the transmission lines have different lengths.
The embodiments allow the simultaneous transmission and reception of wireless signals in a mobile communications system, that can be applied for frequency division duplex (FDD) or to time division duplex (TDD) modes. The band pass of each of the transmission and reception filters has a pass band around the center frequency of each band. The output port of the filters in the pass band shows no reflection and in the stop band all the energy of the wave is reflected back. Further, by using the set of transmission and reception filters, and the quarter wavelength transmission lines and the use of the circulators, several received and transmitted paths are connected in parallel to one broadband antenna, reducing the number of components in a multiplexer topology. The arrangement shown in the network element 100 isolates the output ports of the filters and reduces the necessary amount of components.
In an embodiment, the filters are designed for no reflection in the pass bands at the output ports, wherein the output ports of the filters are designed as short circuit connections in the stop bands, wherein the quarter-wavelength transmission lines are designed for transforming the short circuit connection into an open circuit connection at the first and the second connection point. In a further embodiment, the mobile communication system is a Time Division Duplex or a Frequency Division Duplex system.
In another aspect, the invention relates to a network element for a time division duplex multiband mobile communications system, the network element comprising:

a set of filters, each filter having stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is designed for maximum reflection at the output port in the stop bands;
a set of circulators, each circulator with a first, a second and a third port, wherein the first port is adapted for transmitting a first signal, the second port is connected to the input port of the filter, the third port is adapted for receiving a second signal;
a set quarter-wavelength transmission lines, each transmission line connecting the filter with a connection point, the connection port coupled to an antenna.

In an embodiment, the filters are designed for no reflection in the pass bands at the output ports, wherein the output ports of the filters are designed as short connections in the stop bands, wherein the quarter-wavelength transmission line are designed for transforming the short connection in an open connection at the connection point.
In a further embodiment, the mobile communication system is a Time Division Duplex system.
The network element of any of the preceding embodiments, the output impedances of all filters in the stop bands are open circuits with a phase of zero or short circuits with a phase of 180°.
The network element of any of the preceding embodiments, where for the first set and second set, if the input port is marked as port 1 and the output port is marked as port 2 describing scattering parameters (S-parameters), the scattering parameter S₂₁ has a maximum magnitude in the pass bands and a minimum magnitude in the stop bands.
The network element of any of the preceding embodiments, where for the first set and second set, if the input port is marked as port 1 and the output port is marked as port 2 describing scattering parameters (S-parameters), the scattering parameter S₂₂ has a minimum magnitude in the pass bands and a maximum magnitude in the stop bands.
In another aspect, the invention relates to a method for multiplexing in a network element of a multiband communications system, the method comprising:

filtering a first set of signals within a set of frequency bands through a first set of transmission filters, each filter having a stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is designed for maximum reflection at the output port in the stop bands;
transforming the first set of filtered signals from the output ports of the transmission filters to a first connection point via a set of quarter-wavelength transmission lines;
transferring the first set of filtered signals from the first connection point to a first circulator with a first, a second and a third port, wherein the first port is coupled to the first connection point, and the third port is coupled to a first termination;
transferring the first set of filtered signals to an antenna through a second circulator with a forth, a fifth and a sixth port, wherein the forth port is coupled to the second port of the first circulator, and the fifth port coupled to the antenna.

In a further embodiment, the method for multiplexing further comprises:

receiving a second set of signals by the antenna;
transferring the second set of signals from the antenna to the second circulator;
transferring the second set of signals from the sixth port of the second circulator to a third circulator with a seventh, eight and ninth port, wherein the seventh port is coupled to the sixth port of the second circulator, the eight port is coupled to a second connection point and the ninth port coupled to a second termination;
filtering the second set of signals within a second set of frequency bands through a second set of reception filters from the second connection point via the set of quarter-wavelength transmission lines, wherein the set of quarter-wavelength transmission lines connect the first set of transmission filters with a first connection point and connect the second set of transmission filters with a second connection point.

In another aspect, the invention relates to a method for multiplexing in a network element of a time division duplex multiband mobile communications system, the method comprising:

transferring a set of signals to a set of circulators, each circulator having a first, a second and a third port; wherein the first port is adapted for transmitting a first signal, the third port adapted for receiving a second signal;
filtering the set of signals within a set of frequency bands from the second port through a set of filters, each filter having a stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is adapted for maximum reflection at the output port in the stop bands, wherein the second port is coupled to the input port of the filter;
transferring the set of filtered signals to a connection point from the output ports of the set of filters via the set of quarter-wavelength transmission lines.
transmitting the set of filtered signals from an antenna connected to the connection point.

In a further embodiment, the method further comprises:

receiving a second set of signals by the antenna;
distributing the second set of signals from the connection point to the set of filters via the set of quarter-wavelength transmission lines;
filtering the set of signals with the set of filters;
distributing the filtered set of signals to the set of circulators.

In another aspect, the invention relates to a mobile communication system for multiplexing and demultiplexing, the mobile communication system being operable to perform in accordance with any one of the preceding embodiments.

Brief description of the drawings

In the following preferred embodiments of the invention will be described in greater detail by way of example only making reference to the drawings in which:

Figure 1: shows an embodiment of a network element for a mobile communications system with common antenna,
Figure 2: shows an example of the quarter wavelength transmission lines in the network element,
Figure 3: shows a graphic of the transmission behaviors of the different filters connected in parallel,
Figure 4: shows an embodiment of the network element with common antenna,
Figure 5: shows an embodiment of a method of multiplexing in a mobile communications system.

Detailed description

Fig. 1 shows a network element 100 for a mobile communications system comprising a first set of transmission filters 101 and a second set of reception filters 102, each of the transmission and the reception filters having a stop band, a pass band around a center frequency, an input port, an output port. Each of the filters is designed for maximum reflection at the output port in the stop bands. The network element 100 further comprises a first set of quarter wavelength transmission lines 103 for coupling the output ports of the transmission filters with a first connection point 104 and also for connecting the output ports of the set of reception filters with a second connection point 122.
The network element further comprises a first circulator 106 with a first port 107, a second port 108 and a third port 109. The first port is coupled to the first connection point 104, the third port 109 is coupled to a first termination 110. The network element 100 further comprises a second circulator 111 with the fourth port 112, a fifth port 113, and a sixth port 114. The fourth port 112 is coupled to the second port 108 of the first circulator 106, and the fifth port 113 is coupled to an antenna 115.
The network element 100 further comprises a third circulator 116 with a seventh port 117, an eighth port 118 and a ninth port 119. The seventh port 117 is coupled to the sixth port 114 of the second circulator, the eighth port 118 is coupled to the second connection point 122 and the ninth port 119 is coupled to a second termination 120. The second connection point 122 is coupled to a second set of quarter wavelength transmission lines 121 which are connected to the second set of reception filters 102.
The network element 100 represented in fig. 1 acts as a multiplexer that combines several frequency bands available for a mobile communication system in systems such as time-division duplex (TDD) and frequency-division duplex (FDD). By using the set of transmission and reception filters, and the quarter wavelength transmission lines and the use of the circulators, several received and transmitted paths are connected in parallel to one broadband antenna, reducing the number of components in a multiplexer topology. The arrangement shown in the network element 100 isolates the output ports of the filters and reduces the necessary amount of components.
The multiplexer arrangement allows the simultaneous transmission and reception of wireless signals in a mobile communications system, that can be applied for frequency division duplex (FDD) or to time division duplex (TDD) modes. In this example, four different frequency bands are used for transmission and four frequency bands are used for reception of signals with different carrier frequencies. The band pass of each of the transmission and reception filters has a pass band around the center frequency of each band. The output port of the filters in the pass band shows no reflection and in the stop band all the energy of the wave is reflected back. The output port of the filter are perceived in the stop band either as an open circuit, where the phase of the output reflection factor is 0, or as a short circuit, where the phase of the output reflection factor is 180 degrees.
The output ports of the filters may act as a short circuit in the stop band of the filter. In this case, the quarter wavelength transmission lines transform the short circuit into an open connection at the connection points 104 and 122.
Fig. 2 shows an example of the connection principle of the quarter wavelength transmission lines between the filters and the connection points. The network element 200 comprises four transmission filters 202-205 connected to a common connection point 206 that is further connected to an antenna not shown in the figure. In general, any number of filters could be connected in the described way.
If a signal is transmitted at the carrier frequency 1 through the first filter 202 the pass band of the first filter 202 is centered around the same carrier frequency. At this frequency, the other filters 203-205 are operated in the stop bands and the output ports of these three filters 203-205 act as a short circuit connection. The quarter wavelength transmission lines transform this short circuit connection to an open circuit connection at the connection point 206. Therefore, the transmitted signal from the first filter only sees open connections and the only path that it may take is the path leading to the antenna. As a result the different paths are decoupled from each other and there is no interference between them.
Fig. 3 shows a graphic with the transmission behavior of the four filters shown in figs. 1 and 2 in the four frequency bands.
The graphic 300 shows the four frequency bands 301-304 with the high decoupling between the different filter transmission curves. This allows the transmission and reception within the network element to operate with a very low mutual interference, due to the use of the quarter wavelength transmission lines and the arrangement of the circulators.
Fig. 4 shows a network element 400 comprising four filters 401-404, coupled to four circulators 405-408 and a common antenna 409 connected through a connection point 410. The four filter 401-404 are also coupled to the connection point 410 via a set of quarter-wavelength transmission lines 411.
The network element 400 comprises an arrangement of transmission and reception paths that share the same set of filters and the antenna in the case of a time-division duplex operation, where the frequency bands for the transmission and the reception are the same. Using the circulators 405-408, the transmit and the reception paths of each frequency band can be separated which allows to use only one filter per frequency band. This leads to half the number of required filters compared to the embodiment of figs. 1 and 2. Each filter of the set of filters 401-404 has the characteristics of stop band, a pass band around the carrier frequency of the transmitted or received signal, an input port that is coupled to the circulator, an output port that is connected to the connection point and the antenna and each filter is designed for a maximum reflection at the output port in the stop band.
The filters are designed for no reflection in their pass band at the output ports and the output ports of the filters are designed as short circuit connections in the stop bands. The quarter wavelength transmission lines transform the short circuit connection at the output port of the filters into an open circuit connection at the connection point.
As a result, when one of the filters passes a transmit signal to the common connection point and then to the antenna, the rest of the filters do not influence that signal path because they are operated in short circuit mode at that according frequency which is transformed into an open circuit at the connection point by the quarter wavelength transmission line. The same applies in the backward direction when receiving a signal from the common antenna: If the received signal consists of signal parts on frequencies within the various pass bands of the filters, then each signal part perceives only one filter at the connection point. This is due to the fact that at that according frequency only one of the filters is matched to the connection point whereas all other filters are operated in short circuit mode which is transformed to an open circuit at the connection point.
Fig. 5 shows a method 500 for multiplexing in a network element of a multiband communications system. The method comprises: In a first step 501, filtering a first set of signals within a set of frequency bands through a first set of transmission filters, each filter having a stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is designed for maximum reflection at the output port in the stop bands.
In a second step 502, transforming the first set of filtered signals from the output ports of the transmission filters to a first connection point via a set of quarter-wavelength transmission lines. In a third step 503, transferring the first set of filtered signals from the first connection point to a first circulator with a first, a second and a third port, wherein the first port is coupled to the first connection point, and the third port is coupled to a first termination. In a fourth step 504, transferring the first set of filtered signals to an antenna through a second circulator with a forth, a fifth and a sixth port, wherein the forth port is coupled to the second port of the first circulator, and the fifth port coupled to the antenna.

List of reference numerals

100	Network element
101	First set of transmission filters
102	Second set of reception filters
103	'First set of quarter wavelength transmission line
104	First common connection point
106	First circulator
107	First port
108	Second port
109	Third port
110	First termination
111	Second circulator
112	Fourth port
113	Fifth port
114	Sixth port
115	Common antenna
116	Third circulator
117	Seventh port
118	Eighth port
119	Ninth port
120	Second termination
121	Second set of quarter wavelength transmission line
122	Second connection point
200	Set of filters
202	First filter
203	Second filter
204	Third filter
205	Fourth filter
206	Common connection point
300	Transmission graphics
301	Transmission behavior of first filter
302	Transmission behavior of second filter
303	Transmission behavior of third filter
304	Transmission behavior of forth filter
400	Network element
401	First filter
402	Second filter
403	Third filter
404	Fourth filter
405	First circulator
406	Second circulator
407	Third circulator
408	Fourth circulator
409	Common antenna
410	Connection point
500	flowchart
501	First step
502	Second step
503	Third step
504	Forth step

Claims

A network element for a multiband mobile communications system, the network element comprising:
- a first set of quarter-wavelength transmission lines (103) connecting said first set of transmission filters (101) with a first connection point (104) and a second set of quarter-wavelength transmission lines (121) connecting said second set of reception filters (102) with a second connection point (122);

- a first circulator (106) with a first (107), a second (108) and a third port (109), wherein said first port (107) is coupled to said first connection point (104), and said third port (109) is coupled to a first termination (110);

- a second circulator (111) with a forth (112), a fifth (113) and a sixth port (114), wherein said forth port (112) is coupled to said second port (108) of said first circulator (106), and said fifth port (113) coupled to an antenna (115);

- a third circulator (116) with a seventh (117), an eight (118) and a ninth port (119), wherein said seventh port (117) is coupled to said sixth port (114) of said second circulator (111), said eight port (118) is coupled to said second connection point (122) and said ninth port (119) coupled to a second termination (120).
The network element of claim 1, wherein said filters are designed for no reflection in said pass bands at said output ports, wherein said output ports of said filters are designed as short circuit connections in said stop bands, wherein said quarter-wavelength transmission lines are designed for transforming said short circuit connection into an open circuit connection at said first and said second connection point.
The network element of claim 1 or claim 2, wherein said mobile communication system is a Time Division Duplex or a Frequency Division Duplex system.
A network element (400) for a time division duplex multiband mobile communications system, the network element comprising:
- a set of filters (401,402,403,404), each filter having stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is designed for maximum reflection at said output port in said stop bands;

- a set of circulators (405, 406, 407, 408), each circulator with a first, a second and a third port, wherein said first port is adapted for transmitting a first signal, said second port is connected to said input port of said filter, said third port is adapted for receiving a second signal;

- a set quarter-wavelength transmission lines (411), each transmission line connecting each filter with a connection point (410), said connection port (410) coupled to an antenna (409).
The network element of claim 4, wherein said filters are designed for no reflection in said pass bands at said output ports, wherein said output ports of said filters are designed as short connections in said stop bands, wherein said quarter-wavelength transmission line are designed for transforming said short connection in an open connection at said connection point.
The network element of claim 4 or 5, wherein said mobile communication system is a Time Division Duplex system.
The network element of any of the preceding claims, wherein the output impedances of all filters in said stop bands are open circuits with a phase of zero or short circuits with a phase of 180°.
The network element of any of the preceding claims, wherein if said input ports are marked as port 1 and said output ports are marked as port 2 describing scattering parameters of said first and said second set of filters, the scattering parameter S₂₁ has a maximum magnitude in said pass bands and a minimum magnitude in said stop bands.
The network element of any of the preceding claims, wherein if said input ports are marked as port 1 and said output ports are marked as port 2 describing scattering parameters of said first and said second set of filters, the scattering parameter S₂₂ has a minimum magnitude in said pass bands and a maximum magnitude in said stop bands.
A method (500) for multiplexing in a network element of a multiband communications system, the method comprising:
- filtering (501) a first set of signals within a set of frequency bands through a first set of transmission filters, each filter having a stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is designed for maximum reflection at said output port in said stop bands;

- transforming (502) said first set of filtered signals from said output ports of said transmission filters to a first connection point via a set of quarter-wavelength transmission lines;

- transferring (503) said first set of filtered signals from said first connection point to a first circulator with a first, a second and a third port, wherein said first port is coupled to said first connection point, and said third port is coupled to a first termination;

- transferring (504) said first set of filtered signals to an antenna through a second circulator with a forth, a fifth and a sixth port, wherein said forth port is coupled to said second port of said first circulator, and said fifth port coupled to said antenna.
The method for multiplexing in a network element of claim 10 further comprising:
- receiving a second set of signals by said antenna;

- transferring said second set of signals from said antenna to said second circulator;

- transferring said second set of signals from said sixth port of said second circulator to a third circulator with a seventh, eight and ninth port, wherein said seventh port is coupled to said sixth port of said second circulator, said eight port is coupled to a second connection point and said ninth port coupled to a second termination;

- filtering said second set of signals within a second set of frequency bands through a second set of reception filters from said second connection point via said set of quarter-wavelength transmission lines, wherein said set of quarter-wavelength transmission lines connect said first set of transmission filters with a first connection point and connect said second set of transmission filters with a second connection point.
A method for multiplexing in a network element of a time division duplex multiband mobile communications system, the method comprising:
- transferring a set of signals to a set of circulators, each circulator having a first, a second and a third port; wherein said first port is adapted for transmitting a first signal, said third port adapted for receiving a second signal;

- filtering said set of signals within a set of frequency bands from said second port through a set of filters, each filter having a stop band, a pass band around a carrier frequency, an input port, an output port, wherein each filter is adapted for maximum reflection at said output port in said stop bands, wherein said second port is coupled to said input port of said filter;

- transferring said set of filtered signals to a connection point from said output ports of said set of filters via said set of quarter-wavelength transmission lines.

- transmitting said set of filtered signals from an antenna connected to said connection point.
The method of claim 12, the method further comprising:
- receiving a second set of signals by said antenna;

- distributing said second set of signals from said connection point to said set of filters via said set of quarter-wavelength transmission lines;

- filtering said set of signals with said set of filters;

- distributing said filtered set of signals to said set of circulators.
A mobile communication system for multiplexing and demultiplexing, the mobile communication system being operable to perform in accordance with any one of the preceding claims 10 to 13.