Patent Grant
8265551
The present invention relates to a relay station, mobile station and relay transmission method in mobile communication systems.
In recent years, with the multimediatization of information in mobile communication systems, transmitting high capacity data such as still images and movies in addition to speech data has become popular. To realize the transmission of high capacity data, a technology in which a high-frequency radio band is used to provide a high transmission rate is studied actively.
However, when a high-frequency radio band is used, although a high transmission rate can be expected in a short distance, attenuation due to transmission distance becomes greater as the distance increases. Accordingly, when the mobile communication system employing a high-frequency radio band is operated, the coverage area of a radio communication base station apparatus (hereinafter “base station”) becomes small, which requires that a larger number of base stations be set up in order to prevent the service area from reducing. Since the set-up of base stations involves large costs, a technology is strongly demanded for realizing communication services which employ a high-frequency radio band and preventing an increase in the number of base stations.
To meet this demand, to expand the coverage area of the base stations, relay transmission technologies are investigated in which a radio communication relay station apparatus (hereinafter “relay station”) is set up between a radio communication mobile station apparatus (hereinafter “mobile station”) and a base station, and in which communication between the mobile station and the base station is carried out via the relay station.
Meanwhile, in future mobile communication systems, combining various radio access technologies (RATs) such as W-CDMA (Wideband Code Division Multiple Access), LTE (long-term evolution), WLAN (Wireless LAN), and WiMAX (Worldwide Interoperability for Microwave Access) and overlapping a plurality of RAT coverage areas in the service area of mobile communication will be taken into consideration. Then, in these mobile communication systems, a mobile station needs to detect in which RAT coverage area the mobile station is currently located and what communication service the mobile station is enjoyable. For example, when part of an LTE coverage area includes a WLAN coverage area, a mobile station located in the WLAN coverage area does not enjoy a WLAN communication service unless the mobile station detects that the mobile station is located in the WLAN coverage area, and the mobile station enjoys an LTE communication service only.
Then, conventionally, Non-Patent Document 1 discloses a technique of detecting in which RAT coverage area the mobile stations are located by reporting another RAT's information (e.g. WLAN) to the mobile stations from a RAT's base station (e.g. LTE) based on location information of the mobile stations.
However, with the above conventional technique, a control channel for reporting information about other RATs to the mobile stations is necessary. For example, when part of an LTE coverage area includes a WLAN coverage area, according to the above conventional technique, an LTE base station needs to report to mobile stations RAT information about WLAN (i.e. the information including RAT types and coverage area information about WLAN) using an LTE control channel. For this reason, according to the above conventional technique, a control channel of large capacity is necessary to report RAT information. The number of mixed RATs is expected to further increase in the future, and therefore there is a fear that the amount of RAT information and the frequency of reporting RAT information increase become tight or insufficient control channel capacity.
It is therefore an object of the present invention to provide a relay station, mobile station and relay transmission method that make a control channel for reporting RAT information unnecessary and prevent control channel capacity from becoming tight or insufficient in a mobile communication system in which a plurality of RATs mix.
The relay station of the present invention adopts a configuration including: a receiving section that receives a signal from a base station employing a first radio access technique and covering a first coverage area; an addition section that adds one of a frequency offset, a time offset and a power offset to the signal; and a transmitting section that transmits to a mobile station the signal with the offset, in a third coverage area that is identical to a second coverage area, part or entirety of which includes the first coverage area, and which is covered by a host station employing a second radio access technique different from the first radio access technique.
The mobile station of the present invention adopts a configuration including: a receiving section that receives, in a first coverage area, a signal transmitted by a base station employing a first radio access technique and covering a first coverage area, and that receives a signal relayed by a relay station in a third coverage area that is identical to a second coverage area, part or entirety of which includes the first coverage area, and which is covered by a host station employing a second radio access technique different from the first radio access technique; and a detection section that detects whether or not the mobile station is located in the second coverage area, based on which one of a frequency offset, a time offset and a power offset is added to the received signal.
The relay transmission method of the present invention includes steps of: adding one of a frequency offset, a time offset and a power offset to a signal received from a base station, employing a first radio access technique and covering a first coverage area; and transmitting the signal with one offset to a mobile station in a third coverage area that is identical to a second coverage area, part or entirety of which includes the first coverage area, and which is covered by a host station employing a second radio access technique different from the first radio access technique.
According to the present invention, in the mobile communication system in which a plurality of RATs mix, it is possible to make a control channel for reporting RAT information unnecessary and prevent control channel capacity from becoming tight or insufficient.
Now, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
LTE base station 10, which covers coverage area 11, transmits a signal in this coverage area 11. This signal is received by LTE relay station 30 and mobile station 40. LTE relay station 30 covers identical coverage area 31 to coverage area 21, which WLAN host station 20 has, and relays, in coverage area 31, the signal received from LTE base station 10 to mobile station 40. That is, LTE relay station 30 relays a signal of LTE in WLAN coverage area 21 only. Therefore, mobile station 40 directly receives a signal transmitted by LTE base station 10 in coverage area 11, and receives a signal relayed by LTE relay station 30 in coverage area 31 (i.e. coverage area 21).
To make coverage area 31 and coverage area 21 identical, it is preferable to position LTE relay station 30 in an identical place to WLAN host station 20.
Further, LTE relay station 30 adds, to the relay signal, information to show that mobile station 40 receiving the relay signal from LTE relay station 30, is located in WLAN coverage area 21. To be more specific, LTE relay station 30 adds either a frequency offset, a time offset or a power offset, as the above information to the signal received from LTE base station 10, and transmits the signal with the offset to mobile station 40, located in coverage area 31 (that is, coverage area 21). This process of adding an offset is performed in a lower layer than layer 1.
That is, mobile station 40 can decide whether or not the mobile station 40 is located in WLAN coverage area 21 based on which one of the above offsets is added to a received signal. Consequently, mobile station 40 can enjoy a WLAN communication service when mobile station 40 is located in coverage area 21 within coverage area 11.
With the present embodiment, a case will be described where a frequency offset is added to a signal subject to relay.
With the present embodiment, as shown in
When LTE relay station 30 receives the signal from LTE base station 10 and relays the signal to mobile station 40, LTE relay station 30 adds frequency offset Δf to the signal from LTE base station 10, to shift the center frequency to fR. The magnitude of Δf varies between RATs covering an identical coverage area to coverage area 31 of LTE relay station 30. For example, if coverage area 31 of LTE relay station 30 is identical to WLAN coverage area 21 as shown in
Mobile station 40 decides in which RAT coverage area mobile station 40 is located based on whether or not frequency offset Δf is added to the received signal.
Mobile station 40, located in the overlapping part of LTE coverage area 11 and another RAT coverage area, receives both the signal having center frequency fC and transmitted by LTE base station 10 and the signal having center frequency fR and relayed by LTE relay station 30. Accordingly, mobile station 40, located in overlapping part of LTE coverage area 11 and another RAT coverage area, can detect frequency offset Δf=|fR−fC| added by LTE relay station 30. For example, as shown in
On the other hand, mobile station 40, located outside the above overlapping part in LTE coverage area 11, receives only the signal having center frequency fC and transmitted by LTE base station 10. Accordingly, mobile station 40, located outside the above overlapping part in LTE coverage area 11, cannot detect frequency offset Δf having the ranges shown in
Next, an optimal value of frequency offset Δf will be explained.
In LTE, when the maximum downlink carrier frequency is 2690 MHz and the maximum moving speed of a mobile station is 350 km/h, the maximum frequency error due to crystal error in the mobile station upon detecting a coverage area (i.e. upon acquiring initial synchronization) is estimated, for example, ±5 ppm. This maximum frequency error refers to an error in the initial status of the crystal provided in the mobile station, that is, an error before performing synchronization acquisition. Accordingly, the maximum Doppler shift due to fading is 872 Hz and the maximum frequency error due to crystal error is 13450 Hz. Accordingly, the maximum frequency error ferror
Next, the configuration of LTE relay station 30 according to the present embodiment will be described.
In LTE relay station 30 shown in
Offset determination section 303, which has the table shown in
Frequency offset addition section 304 adds Δf determined in offset determination section 303 to the signal received as input from radio receiving section 302, and outputs the signal with the frequency offset to radio transmitting section 305.
Radio transmitting section 305 performs transmitting processing including D/A conversion and up-conversion on the signal with the frequency offset, and relays the resulting signal from antenna 301 to mobile station 40.
Next, the configuration of mobile station 40 according to the present embodiment will be described.
In mobile station 40 shown in
Frequency error detection section 404 detects a frequency error ferror of the received signal=(Doppler shift due to fading+the frequency error due to crystal error) and outputs the detected frequency error to frequency error compensation section 403 and frequency offset detection section 405.
Frequency error compensation section 403 compensates for the frequency error ferror of the received signal and outputs the signal after the frequency error compensation to demodulation section 407 and frequency offset compensation section 408.
Demodulation section 407 demodulates the signal after frequency error compensation and outputs the demodulated signal to diversity combination section 410.
Frequency offset detection section 405 detects frequency offset Δf=|fR−fC| with the received signal. The detected Δf is inputted to RAT detection section 406 and frequency offset compensation section 408.
Frequency offset compensation section 408 further compensates for the frequency offset Δf with the signal after frequency error compensation and outputs the signal after frequency offset compensation, to demodulation section 409.
Demodulation section 409 demodulates the signal after the frequency error compensation and the frequency offset compensation, and outputs the demodulated signal to diversity combination section 410.
Diversity combination section 410 diversity-combines the signal received as input from demodulation section 407 and the signal received as input from demodulation section 409 and outputs a combined signal.
RAT detection section 406, which has the table shown in
With the present embodiment, a case will be described where a time offset is added to a signal subject to relay.
With the present embodiment, as shown in
When LTE relay station 30 receives the signal from LTE base station 10 and relays the signal to mobile station 40, LTE relay station 30 adds time offset ΔT to the signal from LTE base station 10, to generate a signal having a peak at time t1. The magnitude of ΔT varies between RATs covering an identical coverage area to coverage area 31 of LTE relay station 30. For example, if coverage area 31 of LTE relay station 30 is identical to WLAN coverage area 21 as shown in
Mobile station 40 decides in which RAT coverage area mobile station 40 is located based on whether or not time offset ΔT is added to the received signal.
Mobile station 40, which is located in overlapping part of LTE coverage area 11 and another RAT coverage area, receives both the signal having a peak at time t0 and transmitted by LTE base station 10 and the signal having a peak at time t1 and relayed by LTE relay station 30. Accordingly, mobile station 40, which is located in overlapping part of LTE coverage area 11 and another RAT coverage area, can detect time offset ΔT=|t1−t0| added by LTE relay station 30. For example, as shown in
On the other hand, mobile station 40, located outside the above overlapping part in LTE coverage area 11, receives only the signal having a peak at time t0 and transmitted by LTE base station 10. Accordingly, mobile station 40, located outside the above overlapping part in LTE coverage area 11, cannot detect time offset ΔT having the ranges shown in
In LTE, usually, a guard interval Tguard is set based on several tens to hundreds of samples, taking into consideration of the maximum delay time of a multipath Tdelay
Next, the configuration of LTE relay station 30 according to the present embodiment will be described.
In LTE relay station 30 shown in
Time offset addition section 307 adds ΔT determined in offset determination section 306 to the signal received as input from radio receiving section 302, and outputs the signal with the time offset to radio transmitting section 305.
Next, the configuration of mobile station 40 according to the present embodiment will be described.
In mobile station 40 shown in
Time error detection section 412 detects time error of the received signal by the channel and outputs the detected time error to time error compensation section 411 and time offset detection section 413.
Time error compensation section 411 compensates for the time error of the received signal by the channel and outputs the signal after the time error compensation, to demodulation section 415 and time offset compensation section 416.
Demodulation section 415 demodulates the signal after time error compensation and outputs the demodulated signal to diversity combination section 410.
Time offset detection section 413 detects time offset ΔT=|t1−t0| with the received signal. The detected ΔT is inputted to RAT detection section 414 and time offset compensation section 416.
Time offset compensation section 416 further compensates for the time offset ΔT with the signal after time error compensation and outputs the signal after time offset compensation, to demodulation section 417.
Demodulation section 417 demodulates the signal after time error compensation and time offset compensation and outputs the demodulated signal to diversity combination section 410.
Diversity combination section 410 diversity-combines the signal received as input from demodulation section 415 and the signal received as input from demodulation section 417 and outputs a combined signal.
RAT detection section 414, which has the table shown in
With the present embodiment, cases will be described where a power offset is added to a signal subject to relay.
With the present embodiment, as shown in
When LTE relay station 30 receives a signal from LTE base station 10 and relays the signal to mobile station 40, LTE relay station 30 adds power offset ΔP to part of the signal from LTE base station 10, to generate a signal having power P0 and P1. The magnitude of ΔP varies between RATs covering an identical coverage area to coverage area 31 of LTE relay station 30. For example, if coverage area 31 of LTE relay station 30 is identical to WLAN coverage area 21 as shown in
Mobile station 40 detects in which RAT coverage area mobile station 40 is located based on whether or not power offset ΔP is added to the received signal.
Mobile station 40, located in the overlapping part of LTE coverage area 11 and another RAT coverage area, receives both the signal having power P0 and transmitted by LTE base station 10 and the signal having power P0 and P1 and relayed by LTE relay station 30. Accordingly, mobile station 40, located in overlapping part of LTE coverage area 11 and another RAT coverage area, can detect power offset ΔP=|P1−P0| added by LTE relay station 30. For example, as shown in
On the other hand, mobile station 40, located outside the above overlapping part in LTE coverage area 11, receives only the signal having power P0 and transmitted by LTE base station 10. Accordingly, mobile station 40, located outside the above overlapping part in LTE coverage area 11, cannot detect power offset ΔP having the ranges shown in
In LTE, received dynamic range Ptotal is usually set by adding a margin to dynamic range Pfading estimated using fading fluctuations. That is, to make detection easier, it is preferable that the value of power offset ΔP is added by LTE relay station 30, meets the condition ΔP≦Ptotal−Pfading.
Next, the configuration of LTE relay station 30 according to the present embodiment will be described.
In LTE relay station 30 shown in
Power offset addition section 309 adds ΔP determined in offset determination section 308 to part of the signal received as input from radio receiving section 302, and outputs the signal with the power offset to radio transmitting section 305.
Next, the configuration of mobile station 40 according to the present embodiment will be described.
In mobile station 40 shown in
Demodulation section 420 demodulates the received signal and outputs the demodulated signal to diversity combination section 410.
Power offset detection section 418 detects power offset ΔP=|P1−P0| with the received signal. The detected ΔP is inputted to RAT detection section 419 and power offset compensation section 421.
Power offset compensation section 421 compensates for the power offset ΔP with the received signal and outputs the signal after power offset compensation, to demodulation section 422.
Demodulation section 422 demodulates the signal after power offset compensation and outputs the demodulated signal to diversity combination section 410.
Diversity combination section 410 diversity-combines the signal received as input from demodulation section 420 and the signal received as input from demodulation section 422 and outputs a combined signal.
RAT detection section 419, which has the table shown in
Embodiments 1 to 3 of the present invention have been explained.
In this way, according to Embodiments 1 to 3, the relay station of a wideband communication system including LTE covers an identical coverage area to a coverage area of a narrowband communication system including WLAN and WiMAX. Then, the relay station of a wideband communication system adds either a frequency offset, a time offset or a power offset as information showing that the mobile station, which receives a relay signal from the relay station, is located in the coverage area of a narrowband communication system, to a signal received from the base station of the wideband communication system, and relays the resulting signal. Therefore, according to Embodiments 1 to 3, in a mobile communication system where a plurality of RATs mix, it is possible make a control channel for reporting RAT information unnecessary and it is possible to prevent capacity of a control channel from becoming tight or insufficient.
Further, according to Embodiments 1 to 3, the mobile station can detect the coverage area of a narrowband communication system using a relay signal in a wideband communication system, and therefore, when the mobile station detects the coverage area of each RAT, the mobile station does not need to communicate using a control channel or narrowband communication system. That is, according to Embodiments 1 to 3, the mobile station can detect the coverage area of a narrowband communication system without switching to communication using a control channel or switching to communication using the narrowband communication system. Therefore, according to Embodiments 1 to 3, the mobile station can reduce power consumed by a process of detecting the coverage area of a narrowband communication system. Further, the mobile station can shorten the time it takes to detect the coverage area of a narrowband communication system.
Further, according to Embodiments 1 to 3, in the mobile station, it is possible to diversity-combine a signal received directly from the base station of a wideband communication system and a relay signal from the relay station of the wideband communication system, so that it is possible to provide diversity effect. Therefore, according to Embodiments 1 to 3, it is possible to improve reception performance of the mobile station.
In the above Embodiments 1 to 3, LTE base station 10 reports to mobile station 40 using a broadcast channel in advance what information mobile station 40, which has detected the coverage area of a narrowband communication system, needs to report to LTE base station 10. Information requested to report to LTE base station 10 when mobile station 40 detects the coverage area of a narrowband system include mobile station ID, RAT detection result and a communication status of mobile station 40.
When mobile station 40 detects the coverage area of a narrowband communication system using a relay signal in a wideband communication system, mobile station 40 reports information requested in advance from. LTE base station 10, to LTE base station 10.
By this means, necessary information is sequentially reported to LTE base station 10 from mobile station 40 located in the coverage area of a narrowband communication system, so that it is possible to control traffic using not only coverage area information of a wideband communication system but also coverage area information of a narrowband communication system. For example, when mobile station 40 communicating in a wideband communication system with heavy traffic is located in the coverage area of a narrowband communication system with low traffic, LTE base station 10 performs handover of mobile station 40 to the narrowband communication system. Consequently, according to the present embodiment, LTE base station 10 can disperse traffic in the wideband communication system and the narrowband communication system, and optimally control the overall traffic in the coverage area of LTE base station 10. Further, in mobile station 40, it is not necessary to switch a carrier frequency or measure the power of a narrowband communication system until mobile station 40 receives a handover command to a narrowband communication system from LTE base station 10, so that it is possible to reduce the processing loads in mobile station 40.
Further, as described above, according to Embodiments 1 to 3, in mobile station 40, it is possible to reduce the time it takes to detect the coverage area of a narrowband communication system, so that, according to the present embodiment, mobile station 40 can report information quickly to LTE base station 10, and consequently, following the traffic control in LTE base station 10 improves.
Embodiments of the present invention have been explained.
The present invention may be implemented by combining the above embodiments.
Further, although cases have been explained above with the embodiments where one example of RATs of wideband communication systems is LTE and one example of RATs of narrowband communication systems is WLAN and WiMAX, the present invention does not limit the RAT of a wideband communication system to LTE. For example, other RATs of wideband communication systems include W-CDMA, LTE-Advanced or communication systems after LTE-Advanced. Further, the present invention does not limit RATs of narrowband communication systems to WLAN and WiMAX. For example, other RATs of narrowband communication systems include LTE, LTE-Advanced or communication systems after LTE-Advanced, which are used as hotspots.
Further, although cases have been explained with the above embodiments where part of the coverage area of a wideband communication system includes the entire coverage area of a narrowband communication system and the part of the coverage area of the wideband communication system overlaps the entire coverage area of the narrowband communication system, the present invention may be implemented as described above in cases where part of the coverage area of a wideband communication system includes part of the coverage area of a narrowband communication system and the part of the coverage area of the wideband communication system overlaps the part of the coverage area of the narrowband communication system.
Further, a base station apparatus may be referred to as a “Node B” and a mobile station apparatus may be referred to as a “UE.” Furthermore, the relay station according to the embodiments is referred to as “repeater,” “simple base station,” “cluster head,” and so on.
Further, although cases have been described with the above embodiment as examples where the present invention is configured by hardware, the present invention can also be realized by software.
Each function block employed in the description of each of the aforementioned embodiments may typically be implemented as an LSI constituted by an integrated circuit. These may be individual chips or partially or totally contained on a single chip. These may be individual chips or partially or totally contained on a single chip.
“LSI” is adopted here but this may also be referred to as “IC,” “system LSI,” “super LSI,” or “ultra LSI” depending on differing extents of integration. Further, the method of circuit integration is not limited to LSIs, and implementation using dedicated circuitry or general purpose processors is also possible. After LSI manufacture, utilization of a programmable FPGA (Field Programmable Gate Array) or a reconfigurable processor where connections and settings of circuit cells within an LSI can be reconfigured is also possible.
Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. Application of biotechnology is also possible.
The disclosures of Japanese Patent Application No. 2007-188572, filed on Jul. 19, 2007, and Japanese Patent Application No. 2007-330837, filed on Dec. 21, 2007, including the specifications, drawings and abstracts, are incorporated herein by reference in their entirety.
The present invention is applicable to, for example, communication systems (for example, multihop systems) in which radio communication apparatuses including mobile stations and base stations carry out radio communication via relay stations.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-188572 | Jul 2007 | JP | national |
| 2007-330837 | Dec 2007 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2008/001935 | 7/18/2008 | WO | 00 | 1/14/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/011135 | 1/22/2009 | WO | A |
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| Number | Date | Country | |
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| 20100197223 A1 | Aug 2010 | US |
