Patent Application
20100008284
The present invention relates to a multi-hop relay system, and more particularly, to a method of relaying a data burst in a relay station, which demodulates a received signal without decoding, and then modulates and transmits the demodulated signal within a single frame, and a system using the method.
This work was supported by the IT R&D program of MIC/IITA[2006-S-011-01, Development of relay/mesh communication system for multi-hop WiBro].
The Institute of Electrical and Electronics Engineers (IEEE) 802.16e working group (WG) is in the process of standardizing mobile multi-hop relay (MMR), and is actively participating in research into frame structures. In an MMR network, a relay station (RS) newly introduced between a base station (BS) and a mobile station (MS) of a conventional wireless broadband (WiBro) system transmits a signal between the BS and the MS. The MMR network has a BS-to-RS link and an RS-to-MS link. The WG aims to provide a simpler and cheaper RS than a BS, expand the cell radius of an MS, and improve the service transmission speed of the MS in a shadow region.
Since noise is amplified when a radio frequency (RF) input signal is amplified and transmitted as disclosed in Korean Patent Publication No. 2004-0037588, the RS in the conventional WiBro system cannot completely remove noise by using noise removal means. Accordingly, the RS in the conventional WiBro system is considered as a repeater.
Also, Korean Patent Publication No. 2003-0055915 discloses an RS using an interference cancellation system (ICS). In the RS, when transmitting and receiving antennas are not sufficiently separated from each other, such as in a WiBro system, a signal may be fed back from the transmitting antenna and received through the receiving antenna. Thus, a correction device is located between the transmitting and receiving antennas to offset the fed-back signal by a signal having a magnitude equal to and a phase opposite to those of the fed-back signal, thereby avoiding interference. The RS using the ICS can prevent amplification of noise, but cannot correct noise in an input signal. That is, errors included in the input signal accumulate as channel noise in the RS.
The present invention provides a method of relaying a data burst in a relay station (RS), which can reduce relay latency and efficiently use resources by demodulating a received data burst by using a direct relay zone without decoding, and then modulating and transmitting the demodulated data burst within one frame, and a system and a frame structure using the method.
According to an aspect of the present invention, there is provided a method of relaying a data burst in a relay station of a multi-hop relay system comprising a base station, the relay station, and a mobile station, the method comprising: requesting the base station to assign a direct relay zone in a frame in which a demodulation and forwarding scheme that demodulates, and then modulates and transmits a data burst is applied; and receiving an acknowledgement to the request from the base station.
According to another aspect of the present invention, there is provided a multi-hop relay system comprising a relay system relaying a data burst between a base station and a mobile station, wherein the relay station requests the base station to assign a direct relay zone in a frame using a demodulation and forwarding scheme, which demodulates, and then modulates and transmits a data burst, and receives an acknowledgement to the request from the base station.
According to another aspect of the present invention, there is provided a computer-readable recording medium having embodied thereon a program for executing a method of relaying a data burst in a relay station of a multi-hop relay system comprising a base station, the relay station, and a mobile station, wherein the method comprises: requesting the base station to assign a direct relay zone in a frame in which a demodulation and forwarding scheme that demodulates, and then modulates and transmits a data burst is applied; and receiving an acknowledgement to the request from the base station.
According to another aspect of the present invention, there is provided a computer-readable recording medium having embodied thereon a frame structure of a relay station comprising a downlink sub-frame and an uplink sub-frame in a multi-hop relay system comprising a base station, the relay station, and a mobile station, wherein the frame structure of the relay station comprises: a first direct relay zone located in the downlink sub-frame and using a demodulation and forwarding scheme that demodulates, and then modulates and transmits a data burst; and a second direct relay zone located in the uplink sub-frame and using the demodulation and forwarding scheme.
According to the present invention, since a relay station (RS) demodulates a received signal without decoding, and then directly modulates and transmits the demodulated signal within one frame, relay latency can be prevented and resources can be managed efficiently.
According to an aspect of the present invention, there is provided a method of relaying a data burst in a relay station of a multi-hop relay system comprising a base station, the relay station, and a mobile station, the method comprising: requesting the base station to assign a direct relay zone in a frame using a demodulation and forwarding scheme that demodulates, and then modulates and transmits a data burst; and receiving an acknowledgement to the request from the base station.
According to another aspect of the present invention, there is provided a multi-hop relay system comprising a relay system relaying a data burst between a base station and a mobile station, wherein the relay station requests the base station to assign a direct relay zone in a frame using a demodulation and forwarding scheme, which demodulates, and then modulates and transmits a data burst, and receives an acknowledgement to the request from the base station.
According to another aspect of the present invention, there is provided a computer-readable recording medium having embodied thereon a program for executing a method of relaying a data burst in a relay station of a multi-hop relay system comprising a base station, the relay station, and a mobile station, wherein the method comprises: requesting the base station to assign a direct relay zone in a frame by using a demodulation and forwarding scheme that demodulates, and then modulates and transmits a data burst; and receiving an acknowledgement to the request from the base station.
According to another aspect of the present invention, there is provided a computer-readable recording medium having embodied thereon a frame structure of a relay station comprising a downlink sub-frame and an uplink sub-frame in a multi-hop relay system comprising a base station, the relay station, and a mobile station, wherein the frame structure of the relay station comprises: a first direct relay zone located in the downlink sub-frame and using a demodulation and forwarding scheme that demodulates, and then modulates and transmits a data burst; and a second direct relay zone located in the uplink sub-frame and using the demodulation and forwarding scheme.
The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.
Referring to
The DL sub-frame 110 in which data is transmitted from a base station (BS) to a mobile station (MS) includes a preamble 112, an MAP 114, and a broadcast data and user data zone 116, and is 27 symbols long. The UL sub-frame 120 in which data is transmitted from the MS to the BS includes a control channel 122 and a user data zone 124, and is 15 symbols long.
The MS of a physical (PHY) layer receiving a frame from the BS demodulates and decodes user data existing in the DL sub-frame, and transmits user data having a length that is shorter than a predetermined limit to a media access control (MAC) layer within a current frame time and user data having a length that is greater than the predetermined limit to the MAC layer after one frame time. When preparation of data for the UL sub-frame is completed by using the data transmitted to the MAC layer, the MS of the PHY layer encodes and modulates the prepared data and then transmits the encoded and modulated data to the BS.
A relay station (RS) relaying a signal between the BS and the MS in the MMR system regenerates a signal received from the BS and sends the regenerated signal to the MS in downlink transmission, and regenerates a signal received from the MS and sends the regenerated signal to the BS in uplink transmission.
Since a wireless broadband (WiBro) system adopts a TDD communication scheme, when one RS is added between the BS and the MS, one downlink is divided into two downlinks. That is, a downlink is divided into BS-to-RS and RS-to-MS links. Of course, there is also a link between the BS and the MS without passing through the RS, that is, a BS-to-MS link. Hence, the MMR system has a topology including at least three links.
When the MMR system has the topology including at least three links, the domain occupied by each of the three links in one frame is divided on a time axis. When one link is divided into two links in the MMR system, that is, when one RS is added between the BS and the MS, the number of hops is 2, and when two RSs are added between the BS and the MS, the number of hops is 3. Accordingly, when multiple hops are formed by adding several RSs, communication can be made with an MS beyond the cell radius of the BS by extending coverage. However, the time division of one frame according to the number of hops has a disadvantage in that, since timedomain should be added to the frame as the number of hops increases, resources allocated in each timedomain are reduced. However, the time division of one frame according to the number of hops has an advantage in that frame latency does not occur as the number of hops increases.
Referring to
In the operation of a modem, a received signal is demodulated for every symbol. That is, a fast Fourier transform (FFT) operation and demapping are repeatedly performed for every symbol. Accordingly, demodulation latency corresponds to one symbol. Demodulated data is input to a channel decoder. Since channel decoding is performed for every user data burst, channel decoding latency may be several symbols. Hence, gap zones are proportional to the number of bursts processed by the RS. Accordingly, each GAP zone is at least 1 symbol long, and is increased and defined by each symbol.
Accordingly, the BS-to-RS zone 200 of the frame of
The present embodiment demodulates a signal without channel decoding, and then modulates and generates a signal. Bursts in the normal zone 220 of the BS-to-RS zone 200 and the normal zone 230 of the MS-to-RS zone 210, requiring channel decoding, are allocated to the normal zone 228 of the RS-to-MS zone 204 and the normal zone 238 of the RS-to-BS zone 214, which are farther away from the gap zone 224, and bursts in the direct zone 222 of the BS-to-RS zone 200 and the direct zone 232 of the MS-to-RS zone 210, which are only demodulated and modulated, are allocated to the direct zone 226 of the RS-to-MS zone 204 and the direct zone 236 of the RS-to-BS zone 214, which are closer to the gap zone 224. Accordingly, the bursts which are only demodulated are first modulated and transmitted through a demodulation and forwarding scheme, and then the decoded bursts are encoded, modulated, and transmitted through a decoding and forwarding scheme.
When an RS is located between a BS and an MS in the symmetric complex frame structure according to the present embodiment, latency does not occur irrespective of the number of RSs and any signal can be transmitted within one frame. However, as the number of hops increases, resources allotted to each timeslot decrease. A throughput enhancement CTH according to the number of hops is shown below.
where Thop denotes the number of hops and is equal to or greater than 2, C denotes a maximum transmission capacity when there is no RS, and mr denotes modulation orders (quadrature phase shift keying (QPSK)=1, 16 quadrature amplitude modulation (QAM)=2, and 64 QAM=3).
It is assumed the gap zone 224 required due to modem latency in the RS is located between the BS-to-RS zone 200 and the RS-to-MS zone 204, only a capacity increases as the modulation order mr increases, and resources of the BS-to-MS link are allocated in the gap zone 224. In the case of 2 hops, the throughput enhancement CTH increases by as much as 30% with respect to the maximum transmission capacity C. In the case of 3 hops, an increase in the throughput is little.
The present embodiment uses either one of the decoding and forwarding scheme and the demodulation and forwarding scheme according to the channel state of the MS. Accordingly, in the case of the symmetric complex frame structure of
where NGAP denotes the number of symbols in each GAP zone, and NSym denotes the number of total symbols.
In order to apply Equation 2 to a downlink, when a maximum throughput is calculated assuming that the number of symbols in each gap zone is 2 and the number of total symbols is 25, the throughput enhancement CTH increases by as much as 50% in the case of 2 hops and there is little increase in the throughput enhancement CTH in the case of 3 hops.
Referring to
Each of the UL and DL sub-frames includes a direct relay zone in which a received data burst is demodulated without decoding or encoding, and then modulated and transmitted. The direct relay zone in each of the UL and DL sub-frames comprises direct receiving zones 241 and 246, direct transmitting zones 243 and 248, and gap zones 244 and 249 located between the direct receiving zones and the direct transmitting zones. The direct receiving zone 241 of the DL sub-frame is located in the access zone 240, and the direct transmitting zone 243 of the DL sub-frame is located in the optional transparent zone 242. The direct receiving zone 246 of the UL sub-frame is located in the UL access zone 245 and the direct transmitting zone 248 of the UL sub-frame is located in the UL relay zone 247.
For example, the RS receiving a frame from the BS or its superordinate RS demodulates a data burst of the direct receiving zone 241 of the DL sub-frame of the frame without decoding, modulates the demodulated data burst, allocates the modulated data burst to the direct transmitting zone 243 of the optional transparent zone 242, and transmits the allocated data burst to the MS or its subordinate RS. Likewise, the RS receiving a frame from the MS or its subordinate RS demodulates a data burst of the direct receiving zone 246 of the UL sub-frame of the frame without decoding, modulates the demodulated data burst, allocates the modulated data burst to the direct transmitting zone 248 of the UL sub-frame, and transmits the allocated data burst to the BS or its predominant RS. That is, the RS uses a demodulation and forwarding scheme that demodulates a signal of a direct relay zone without decoding, modulates the demodulated signal, and transmits the modulated signal.
In order to define a direct relay zone of a frame according to the present embodiment, information regarding: (a) a symbol offset for a position where a direct relay zone of the DL sub-frame starts, (b) a symbol offset for a position where a direct relay zone of the UL sub-frame starts, (c) the number of OFDMA symbols of the direct relay zone of the DL sub-frame, and (d) the number of OFDMA symbols of the direct relay zone of the UL sub-frame, is necessary. Such information is one example of what is necessary for defining the direct relay zone in the frame. There are many other methods of defining the direct relay zone shown in
Referring to
For the purpose of direct relaying, in operation S260, the RS sends a direct relay request message to the BS 250. That is, the RS 252 requests the BS 25 to acknowledge the request using the frame structure of
The direct relay zone of the frame is configured using a frame configuration description message including information regarding the arrangement of the direct relay zone in the frame. In operation S264, the BS 250 broadcasts the frame configuration description message. The frame configuration description message can be broadcast at any time before the RS 250 directly relays data. For example, the frame configuration description message may be received when a network is configured, at a predetermined interval, or while the direct relay response message is sent. One example of the frame configuration description message may be an RS-configuration description (CD) message defined in IEEE 802.16j.
Examples of information included in the frame configuration description message for describing the arrangement of the direct relay zone in the frame include:
(a) the existence of a direct relay zone indicating whether a direct relay zone exists in each of a DL sub-frame and a UL sub-frame;
(b) an offset for a direct receiving zone indicating an OFDMA symbol offset for a position where a direct receiving zone starts in each of the DL sub-frame and the UL sub-frame;
(c) the number of OFDMA symbols in the direct receiving zone, indicating the number of OFDM symbols which the RS should demodulate and modulate in the direct relay zone, in each of the DL sub-frame and the UL sub-frame.
(d) an offset for a direct transmitting zone indicating an OFDMA symbol offset for a position where a direct transmitting zone starts in each of the DL sub-frame and the UL sub-frame; and
(e) the number of OFMD symbols in the direct transmitting zone, indicating the number of OFDM symbols which the RS should demodulate and modulate in the direct relay zone, in each of the DL sub-frame and the UL sub-frame.
Here, a forward error correction (FEC) block size of a data burst in a relay link between the BS and the RS should be the same as that of a data burst of an access link between the RS and the MS.
Referring to
The RS 320 uses a decoding and forwarding scheme or a demodulation and forwarding scheme to regenerate a modem signal. In the decoding and forwarding scheme, the RS 320 demodulates and decodes received data and corrects errors, and then re-encodes, modulates, and transmits the data to the MS. In the demodulation and forwarding scheme, the RS only demodulates received data, and then modulates and transmits the data to the MS.
The decoding and forwarding scheme can be used in a poor environment where the MS 325 exists outside a cell area 340 of the BS 300 and a channel state is poor, whereas the demodulation and forwarding scheme can be used when the received and transmitted signal strength of the RS 320 is sufficiently higher than that of the MS 332 and a channel state is good. Of course, there may be a link where the MS 334 and the BS 300 directly communicate with each other without the RS because a channel state is very good.
When comparing the application example of
Referring to
In a decoding and forwarding scheme, the RS 410 decodes a signal, and then re-encodes, modulates, and transmits the signal to the MS 420. Accordingly, since latency may be lengthened in the RS, data bursts using the decoding and forwarding scheme are allocated to normal zones 220, 228, 230, and 238 of a frame as shown in
The decoding and forwarding scheme channel decodes and encodes, and then modulates and transmits a signal to the MS, and the demodulation and forwarding scheme maintains a code rate and changes only a modulation method to regenerate a signal, thereby reducing the size of resources allocated to the regenerated signal.
Referring to
When 48 information bits are encoded at a code rate of ½ in the BS 500, 96 bits are obtained. When the 96 bits are modulated, since 2 bits are mapped to one symbol, 48 symbols are obtained in total. In order to regenerate a signal using a demodulation and forwarding scheme, the RS 502 receiving the 48 symbols demodulates the 48 symbols using QPSK and modulates the demodulated 48 symbols using 16 QAM. The symbols demodulated using QPSK become 96 bits. When the 96 bits are mapped again using 16 QAM, since 4 bits become one symbol, 24 symbols are obtained in total. The RS 502 transmits the 24 symbols to the MS 504. The MS 504 receiving the 24 symbols demodulates the symbols using 16 QAM to obtain the original 96 bits, decodes the 96 bits again, corrects error, and obtains 48-bit data. At this time, a code rate for the 48 information bits should not be changed and only a modulation order should be changed.
Accordingly, channel coding parameters according to the present embodiment are defined so that the same code rate can be used for information bits although modulation orders are different in order to use the demodulation and forwarding scheme. That is, channel coding parameters supporting a non-hybrid automatic repeat request (HARQ) of a conventional WiBro system are shown in
Referring to
For example, in
Referring to
In order to use a modulation and coding set (MCS) of the BS-to-RS link and an MCS of the RS-to-MS link in a different manner, in the decoding and forwarding scheme, a signal is generated by changing a modulation order and a code rate.
In the demodulation and forwarding scheme, the BS should satisfy the following slot boundary condition so as to change only a modulation order and generate a signal.
nA·mA−nR·mR (3)
Slot boundary condition:
where nA denotes the number of slots allocated in a UL access zone, nB denotes the number of slots allocated in a UL relay zone, mA denotes modulation orders (QPSK=2, 16 QAM=4, and 64 QAM=6) in the UL access zone, and mB denotes modulation orders (QPSK=2, 16 QAM=4, and 64 QAM=6) in the UL access zone.
Accordingly, in order to use all MCSs supported by the conventional MS in the demodulation and forwarding scheme, MCSs (16 QAM ⅔, ⅚ and 64 QAM ⅔, ⅚) are added in the MR-BS as shown in the extended MCS of
The extended channel coding parameters also include all parameters related to a channel encoding method. For example, parameters required by a convolution turbo code (CTC) interleaver are varied according to code block sizes. The extended channel coding parameters according to the present embodiments also include parameters not only in a non-HARA mode but also in a HARQ mode.
The present invention may be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memories (ROMs), random-access memories (RAMs), CD-ROMs, magnetic tapes, floppy disks, and optical data storage devices. The computer readable recording medium can be dispersively installed in a computer system connected to a network, and stored and executed as a computer readable code in a distributed computing environment.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0099946 | Oct 2006 | KR | national |
| 10-2007-0091152 | Sep 2007 | KR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2007/005016 | 10/12/2007 | WO | 00 | 4/13/2009 |
