Patent Application
20080025251
This application claims priority under 35 U.S.C. §119 to an application filed in the Korean Intellectual Property Office on Jan. 6, 2006 and assigned Serial No. 2006-1864, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates generally to an apparatus and method of providing a relay service in a cellular communication system, and in particular, to an apparatus and method of supporting independent channel estimation of a relay link when a direct link and the relay link are distinguished through a frequency multiplexing in a Broadband Wireless Access (BWA) communication system.
Herein, the direct link refers to a link between a base station and a mobile station and the relay link refers to a link between a relay station and a mobile station.
2. Description of the Related Art
In the fourth generation (4G) communication system, extensive research is being conducted to provide users with various Quality of Service (QoS) at a data rate of over 100 Mbps. Specific research is focusing on the high rate service to the guarantee mobility and the QoS in Broadband Wireless Access (BWA) communication systems such as Local Area Networks (LAN) and Metropolitan Area Networks (MAN). Representative systems of the BWA communication system include the Institute of Electrical and Electronics Engineers (IEEE) 802.16 communication system.
One of the most important requirements of the 4G communication system is a self-configurable wireless network configuration. The self-configurable wireless network refers to a wireless network which can provide mobile communication services by configuring the wireless network in an autonomous and distributive manner without control of a central system. Generally, in the 4G communication system, cells of a very small radius are installed to enable a high-speed communication and accommodate more traffic. In this case, it is anticipated that the centralized design using the current wireless network design scheme is impossible. Accordingly, while being controlled and deployed in the distributive manner, the 4G communication system should be able to actively cope with environmental change such as joining of a new base station. To respond to this, the self-configurable wireless network is required in the 4G communication system.
In practice, to implement the self-configurable wireless network required for the 4G communication system, a technique applied to an ad-hoc network needs to be adopted to the wireless communication system. A representative case of this adoption is a multihop relay cellular network, where the multihop relay scheme of the ad-hoc network is applied to the cellular network including a fixed base station.
In a general cellular communication system, since signals are transmitted and received between a fixed base station and a mobile station through a direct link, a highly reliable wireless communication link can be easily established between the base station and the mobile station. However, since the position of the base station is fixed, the wireless network configuration suffers low flexibility. As a result, it is hard to provide efficient communication services under a radio environment experiencing severe change of traffic distribution or traffic requirements.
To overcome those shortcomings, a multihop relay data delivery scheme can be applied to the general cellular wireless communication system using a fixed or mobile relay station or a general mobile station. The multihop relay wireless communication system is able to reconfigure the network by promptly handling the communication environment change and far more efficiently utilize the entire wireless network. For instance, the multihop relay wireless communication system can expand a cell service coverage area and increase the overall system capacity. When a channel status between the base station and the mobile station is poor, a multihop relay path is established by way of a relay station by interposing the relay station between the base station and the mobile station. The radio channel with a better channel status can be provided to the mobile station. In addition, in a cell boundary region with the poor channel status from the base station, the multihop relay scheme can provide the high-speed data channel and expand the cell service coverage area.
As shown in
If an MS is located in the cell boundary of the BS 100 or in a shadow area where shielding, for example caused by buildings, is extreme, the MS communicates with the BS 100 via the RS 130. As such, by adopting the multihop relay scheme in the cell boundary area in the poor channel status, the high-speed data channel can be provided and the cell service coverage can be expanded.
As discussed above, in a future time, the BWA communication system can utilize the relay service for the service coverage expansion and the capacity increase of the serving cell. The RS and the BS can share the same frequency band within the serving cell which supports the relay service, and should use the same subchannel allocation scheme in the Orthogonal Frequency Division Multiplexing (OFDM) symbol structure to avoid interference. The subchannel, which is provided to support the multiple access scheme of Orthogonal Frequency Division Multiple Access (OFDMA), is largely divided to a diversity subcarrier allocation, an adjacent subcarrier allocation, and a hybrid subcarrier allocation, based on the allocation scheme.
The diversity subcarrier allocation first allocates zero subcarriers and pilot subcarriers in the OFDM symbol and utilizes as data subcarriers by grouping the remaining subcarriers as subchannels.
The adjacent subcarrier allocation configures one subchannel by grouping adjacent subcarriers and allocates data subcarriers and pilot subcarriers at certain positions within one subchannel.
The hybrid subcarrier allocation groups adjacent subcarriers in the entire frequency band by a certain unit and configures a subchannel by taking a certain number of units to acquire the diversity gain. In the unit, the data subcarrier and the pilot subcarrier are allocated to fixed positions.
Since an IEEE 802.16 system, which is one of the BWA communication systems, supports a Point to Multi-Point (PMP) mode, the subcarrier allocation scheme is defined for each link. In general, the DL employs the subcarrier allocation schemes of PUSC, FUSC, OFUSC, TUSC1, TUSC2, PUSC-Adjacent Subcarrier Allocation (ASCA), and the UL employs PUSC and OPUSC. AMC is used in both the DL and the UL.
In the multihop relay cellular system as discussed above, the MS, in order to communicate with not only the BS but also the RS in some cases, needs to distinguish an BS-MS link (or the direct link) from an RS-MS link (or the relay link) by distributing resources provided from an air interface. For instance, the MS can distinguish the direct link from the relay link by performing frequency division multiplexing on the entire frequency band. Additionally, the multiple access of the OFDMA can be considered for a plurality of RSs.
To execute the frequency division multiplexing on the direct link and the relay link within one frequency band as shown in
When a plurality of RSs establishing a relay link are allocated the different subchannels to implement the multiple access by virtue of the OFDMA, the data subcarriers do not collide but the pilot subcarriers may collide according to the subcarrier allocation scheme. Upon the collision of the pilots, the MS estimates the summation of the channels. Thus, the actual data channel does not match the estimated channel, to thus greatly degrade the system performance.
As discussed above, when the direct link and the relay link are distinguished using the frequency multiplexing scheme, what is demanded is a method which can satisfy the independent channel estimation for the relay link without increasing the pilot overhead.
An aspect of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an aspect of the present invention is to provide a communication apparatus and method for supporting independent channel estimation for a relay link when a direct link and the relay link are distinguished using a frequency multiplexing in a multihop relay BWA communication system.
Another aspect of the present invention is to provide an apparatus and method for allocating a common pilot to a direct link and a dedicated pilot to a relay link when the direct link and the relay link are distinguished using a frequency multiplexing in a multihop relay BWA communication system.
Yet another aspect of the present invention is to provide an apparatus and method of applying a plurality of subcarrier allocation schemes to one OFDM symbol in a multihop relay BWA communication system.
Still another aspect of the present invention is to provide an apparatus and method of reducing a pilot overhead when a direct link and a relay link are distinguished using a frequency multiplexing in a multihop relay BWA communication system.
A further aspect of the present invention is to provide an apparatus and method of independently applying subcarrier allocation schemes to a direct link and a relay link in a multihop relay BWA communication system.
The above aspects are achieved by providing a communication method in a BWA communication system, which includes dividing an entire frequency band to a plurality of bands to support a plurality of links; determining subcarrier allocation schemes for the respective divided bands, the determination being made independently from one another; and communicating by the plurality of the links using the determined subcarrier allocation schemes.
According to another aspect of the present invention, a communication method of a base station (BS) in a multihop relay BWA communication system includes dividing an entire frequency band to a direct link area and a relay link area based on a transmission overhead of a direct link and a transmission overhead of a relay link; determining subcarrier allocation schemes for the respective divided areas, the determination being made independently from one another; and sending a signal by applying the determined subcarrier allocation scheme to the direct link area.
According to yet another aspect of the present invention, a communication method of a relay station (RS) in a BWA communication system where a direct link and a relay link are distinguished through a frequency multiplexing, includes receiving from a BS a control information message; acquiring a subcarrier allocation scheme of the relay link from the received control information message; and communicating by applying the acquired subcarrier allocation scheme to a relay link area.
According to a further aspect of the present invention, a communication method of an RS in a BWA communication system where a direct link and a relay link are distinguished through frequency multiplexing, includes determining a channel status of a band which is allocated to a relay link in an entire frequency band; and determining a subcarrier allocation scheme for the relay link band based on the channel status.
According to still another aspect of the present invention, a communication apparatus in a multihop relay BWA communication system, includes a BS for communicating by applying a common pilot based subcarrier allocation scheme to a band allocated to a direct link of an entire frequency band; and an RS for communicating by applying a dedicated pilot based subcarrier allocation scheme to a band allocated to a relay link of the entire frequency band.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:
Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.
The present invention suggests a method of satisfying the requirement for a dedicated pilot signal or pilot required in a relay link and reducing pilot overhead in a direct link when the direct link and the relay link are distinguished using a frequency multiplexing in a multihop relay BWA communication system.
The OFDM or OFDMA communication system is exemplified herein as a multihop relay BWA communication system, but not limited to this system. The present invention is applicable to general multi-carrier communication systems.
In the multihop relay BWA communication system, an RS may be a fixed or mobile node, a specific system installed by a provider, or a general subscriber station. A certain node having the above feature can be selected as the RS through an RS capability negotiation procedure with a BS according to a predefined criterion for the cell area expansion or the cell capacity increase of the BS.
The following description exemplifies subchannel allocation schemes suggested by IEEE 802.16. As discussed earlier, the diversity subcarrier allocation schemes include DL FUSC, DL OFUSC, DL PUSC, etc., the adjacent subcarrier allocation schemes include AMC, etc., and the hybrid subcarrier allocation schemes include UL PUSC, UL OPUSC, etc. Of these schemes, UL PUSC, OPUSC, and AMC are the subcarrier allocation schemes using the dedicated pilot based permutation.
When the direct link and the relay link are distinguished using the frequency multiplexing scheme as shown in
As shown in
Referring to
The controller 600 applies the common pilot based subcarrier allocation scheme to the direct link area and the dedicated pilot based subcarrier allocation scheme to the relay link area. Control information (frequency division information, resource allocation information, subcarrier allocation scheme, etc.), which is generated through this scheduling, is provided to the control channel constructor 602. Control information relating to the relay link of the L-th frame should be transmitted through a control channel of a prior channel of the L-th frame. Also, the controller 600 controls burst generation at the burst constructor 604 depending on the scheduling result.
At the transmission time of the L-th frame, the control channel constructor 602 constructs and outputs a control channel (e.g., MAP channel) transmitted in a prior interval of the L-th frame under the control of the controller 600. The burst constructor 604 constructs and outputs user data provided from an upper layer as a burst, which is a transmission unit, under the control of the controller 600.
The MUX 606 multiplexes the control channel burst from the control channel constructor 602 and the data bursts from the burst constructor 604 based on a predefined rule.
The coder 608 codes the information bit string from the MUX 606 at a corresponding coding rate and outputs coded data (coded bits or symbols). When the number of information bits is k and the coding rate is R, the number of the output symbols is k/R. The coder 608 can be a convolutional encoder, a turbo encoder, a Low Density Parity Check (LDPC) encoder, etc.
The modulator 610 outputs complex symbols by mapping the symbols fed from the coder 608 to signal points according to a corresponding modulation scheme (modulation level). For example, the modulation schemes include a Binary Phase Shift Keying (BPSK) which maps one bit (s=1) to one signal point (complex symbol), a Quadrature Phase Shift Keying (QPSK) which maps two bits (s=2) to one complex symbol, a 8-ary Phase Shift Keying (8PSK) which maps three bits (s=3) to one complex symbol, a 16-ary Quadrature Amplitude Modulation (16 QAM) which maps four bits (s=4) to one complex symbol, and a 64 QAM which maps six bits (s=6) to one complex symbol.
The subchannel allocator 612 maps the complex symbols fed from the modulator 610 to the subchannel based on burst information provided from the MAC layer, and outputs the subchannel-mapped complex symbols to corresponding memory addresses of the subframe buffer 614 corresponding to the actual direct link subframe size. In doing so, as the BS-MS direct link uses the common pilot based subcarrier allocation scheme, the symbols from the modulator 610 are mapped to the subchannel according to the common pilot based subcarrier allocation scheme.
The subframe buffer 614 is a buffer which maps the subchannel-mapped complex symbols to the actual physical subcarriers, that is, a buffer which arranges the subchannel-mapped complex symbols in accordance with the actual transmission order. The subframe buffer 614 sequentially outputs the complex symbols, which are buffered based on the time synchronization, by the OFDM symbol.
The OFDM modulator 616 transforms the complex symbols fed from the subframe buffer 614 into time domain sample data through Inverse Fast Fourier Transformation (IFFT), and outputs OFDMA symbols by duplicating and appending a rear portion of the sample data to the front of the sample data.
The DAC 618 converts the sample data of the OFDM modulator 616 to an analog signal. The RF processor 620 includes a filter and a front end unit. The RF processor 620 RF-processes the signal output from the DAC 618 to a transmittable form and sends it via a transmission (Tx) antenna in the radio channel.
The control channel transmitted from the BS is a broadcast channel. Every MS and RS in the cell coverage area receives and analyzes the control channel. The RSs recognize the relay link subcarrier allocation scheme of the L-th frame by analyzing the control channel received from the BS, and send the data to be transmitted to the MS by mapping the data to the subchannel according to the recognized subcarrier allocation scheme. The subcarrier allocation scheme of the relay link, which is informed to the RS by the BS, is the subcarrier allocation scheme which can utilize the independent pilot from the BS. The structure of the RS which sends a signal is the same as that of the BS as shown in
According to the present invention, the RSs communicating with the BS attempt multiple access through subchannel division, and the BS informs the RS of the resources allocated to the RS and the subcarrier allocation scheme through the scheduling relating to the relay link. The RSs utilize the dedicated pilot based subcarrier allocation scheme for the relay link.
Alternatively, if the resources (area) for the relay link are fixed and the RSs attempt multiple access according to a spatial multiplexing scheme, the RSs can determine the subcarrier allocation scheme by themselves by measuring the MS channel status. In this case, since the RSs establishing the relay link transmit signals in different spaces, the common pilot based subcarrier allocation scheme can be used for the relay link.
In case where the frequency resources for the relay link are fixed and the RSs attempt multiple access according to a time multiplexing scheme, the BS can merely inform the RSs of the time resource information and the RSs can determine the subcarrier allocation schemes by themselves by measuring the MS channel status. In this case, the RSs can adopt the common pilot based subcarrier allocation scheme.
Referring to
After determining the link transmission overhead required by the direct link and the relay link, in step 705 the BS divides all of the frequency bands to areas depending on the link transmission overhead. In step 707, the BS determines channel status of the direct link area and channel status of the relay link area. The channel status of the direct link area can be determined using the channel information (BS-MS channel information) reported from the MSs, and the channel status of the relay link area can be determined using the channel information reported from the RSs (RS-MS channel information).
After determining the link channel status, in step 709 the BS determines subcarrier allocation schemes for the direct link area and the relay link area, based on the channel status. By doing so, the substantial resource scheduling is carried out. The subcarrier allocation scheme applied to the direct link area is the common pilot based subcarrier allocation scheme, and the subcarrier allocation scheme applied to the relay link area is the common pilot or dedicated pilot based subcarrier allocation scheme. The direct link area and the relay link area can be subdivided into a plurality of zones depending on the scheduling. The BS determines which zone is used by each RS and which area (burst) is allocated within the corresponding zone.
After scheduling of the L-th frame, in step 711 the BS broadcasts control information (frequency allocation information, resource allocation information of each RS, subcarrier allocation scheme information, etc.) relating to the relay link of the L-th frame on the control channel of the prior frame of the L-th frame.
Next, in step 713 the BS determines if transmission for the L-th frame is required. When the transmission for the L-th frame is required, in step 715 the BS constructs a direct link subframe according to the scheduling result of the L-th frame. By doing so, the direct link subframe is constructed using the common pilot based subcarrier allocation scheme.
In step 717, the BS transmits the constructed direct link subframe in the time interval of the L-th frame. Since the RSs have received the scheduling result of the L-th frame prior to the L-th frame, the signal is carried in the time interval of the L-th frame using the subcarrier allocation scheme designated by the BS. At this time, the RSs send signals using the common pilot or dedicated pilot based subcarrier allocation scheme in accordance with the multiple access scheme.
Referring to
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Besides the frame structures of
As shown in
As set forth above, when the direct link and the relay link are distinguished through the frequency multiplexing in the multihop relay BWA communication system, the present invention enables independent channel estimation from the relay link by adopting the dedicated pilot based permutation scheme or the common pilot based permutation scheme with small FFT size for the relay link. Additionally, by adopting the common pilot based permutation scheme for the direct link, the pilot overhead for the entire frame can be optimized.
While the invention has been shown and described with reference to certain preferred embodiments thereof, additional variations and modifications in that embodiment may occur to those skilled in the art once they learn of the basic inventive concepts. For instance, while the entire frequency band is divided into two areas to support the direct link and the relay link according to the present invention, the frequency band can be divided to a greater number of areas to support a greater number of links having different characteristics and the subcarrier allocation schemes can be independently applied to the respective divided bands. The claims should not be read as limited to the described embodiments, and all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-1864 | Jan 2006 | KR | national |
