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Telecommunications

Patent Issued for Apparatus and Method for Assigning Subchannels in an OFDMA Communication System

2012 AUG 1 (VerticalNews) -- By a News Reporter-Staff News Editor at Telecommunications Weekly -- A patent by the inventors Hwang, In-Seok (Seoul, KR); Yoon, Soon-Young (Seongnam-si, KR); Sung, Sang-Hoon (Suwon-si, KR); Cho, Jae-Hee (Seoul, KR); Huh, Hoon (Seongnam-si, KR), filed on January 30, 2009, was cleared and issued on July 24, 2012, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8223704 is assigned to Samsung Electronics Co., Ltd (KR).

The following quote was obtained by the news editors from the background information supplied by the inventors: "The present invention relates generally to a communication system supporting an Orthogonal Frequency Division Multiple Access (OFDMA) scheme (hereinafter referred to as an 'OFDMA communication system'), and in particular, to an apparatus and method for adaptively assigning subchannels.

"The fourth generation (4G) mobile communication system is in the process of being standardized to provide efficient interworking and integrated service between a wired communication network and a wireless communication network, beyond the simple wireless communication service that the previous-generation mobile communication systems provided. Accordingly, the technology required for transmitting a large volume of data at a same level available in the wired communication network must be developed for the new wireless communication network.

"In this context, many studies are being conducted on using an Orthogonal Frequency Division Multiplexing (OFDM) scheme as a scheme for high-speed data transmission over wired/wireless channels in the 4G mobile communication system. The OFDM scheme, which transmits data using multiple carriers, is a special type of a Multiple Carrier Modulation (MCM) scheme in which a serial symbol sequence is converted into parallel symbol sequences and the parallel symbol sequences are modulated with a plurality of mutually orthogonal subcarriers (or subcarrier channels) before being transmitted.

"The first MCM systems appeared in the late 1950's for military high frequency (HF) radio communication, and the OFDM scheme for overlapping orthogonal subcarriers was initially developed in the 1970's. In view of orthogonal modulation between multiple carriers, the OFDM scheme has limitations in its actual implementation. In 1971, Weinstein, et al. proposed that OFDM modulation/demodulation can be efficiently performed using Discrete Fourier Transform (DFT), which was a driving force behind the development of the OFDM scheme. Also, the introduction of a guard interval and a cyclic prefix as the guard interval further mitigates the adverse effects of multipath propagation and delay spread on the systems. As a result, the OFDM scheme has been widely used for digital data communication technologies such as digital audio broadcasting (DAB), digital TV broadcasting, wireless local area network (WLAN), and wireless asynchronous transfer mode (WATM).

"Although the hardware complexity was an obstacle to widespread implementation of the OFDM scheme, recent advances in digital signal processing technology including fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) have enabled the OFDM scheme to be implemented in a less complex manner.

"The OFDM scheme, similar to an existing Frequency Division Multiplexing (FDM) scheme, boasts of an optimum transmission efficiency in high-speed data transmission because it can transmit data on subcarriers, while being able to maintain orthogonality among them. The optimum transmission efficiency is further attributed to good frequency use efficiency and robustness against multipath fading in the OFDM scheme. More specifically, overlapping frequency spectrums lead to efficient frequency use and robustness against frequency selective fading and multipath fading. The OFDM scheme reduces the effects of intersymbol interference (ISI) by use of guard intervals and enables the design of a simple equalizer hardware structure. Furthermore, because the OFDM scheme is robust against impulse noise, it is increasingly popular in communication systems.

"The OFDMA scheme is a Multiple Access scheme based on the OFDM scheme. In the OFDMA scheme, subcarriers in one OFDM symbol are distributed to a plurality of users, or subscriber stations. A communication system using the OFDMA scheme includes an IEEE 802.16a communication system and an IEEE 802.16e communication system. The IEEE 802.16a communication system is a fixed-Broadband Wireless Access (BWA) communication system using the OFDMA scheme. The IEEE 802.16e communication system is a system that provides for the mobility of subscriber stations in the IEEE 802.16a communication system. Currently, the IEEE 802.16a communication system and the IEEE 802.16e communication system both use 2048-point IFFT and 1702 subcarriers. The IEEE 802.16a communication system and the IEEE 802.16e communication system use 166 subcarriers from among the 1702 subcarriers as pilot subcarriers, and use the remaining 1536 subcarriers, not including the 166 subcarriers, as data subcarriers.

"The 1536 data subcarriers are divided into 32 subchannels, each having 48 data subcarriers. The subchannels are assigned to a plurality of users according to system conditions. The term 'subchannel' refers to a channel comprised of a plurality of subcarriers. Herein, each subchannel is comprised of 48 subcarriers. The OFDMA communication system distributes all subcarriers, particularly, data subcarriers used over the entire frequency band, thereby acquiring a frequency diversity gain.

"A frequency hopping (hereinafter referred to as 'FH') scheme is a scheme of changing subcarriers assigned to a specific subscriber station, and an FH-OFDM scheme is a scheme that combines the FH scheme and the OFDM scheme. A system employing the FH-OFDM scheme (hereinafter referred to as an 'FH-OFDM system') uses the FH scheme in hopping frequency bands of the subcarriers assigned to the subscriber stations. Therefore, the FH-OFDM system also distributes all of the subcarriers, particularly, data subcarriers used over the entire frequency band, thereby acquiring a frequency diversity gain.

"The IEEE 802.16a communication system and the IEEE 802.16e communication system divide a broadband of, for example, 10 MHz into subchannels only in a frequency domain. As indicated above, the IEEE 802.16a communication system and the IEEE 802.16e communication system use a 2048-point IFFT and use 1702 subcarriers per OFDM symbol. When subchannels are assigned using Reed Solomon (RS) sequences, which secures an excellent inter-subchannel collision characteristic in a multi-cell environment, it is possible to identify about 40 cells (e.g., 41*40=1640). For example, when a Reed Solomon sequence defined in a Galois Field Q is used, the number of available subcarriers is defined as Q (Q-1). When about 1600 subcarriers are used as in the 802.16a/e system, 41 is selected from among 37, 41, and 43 which are prime numbers near to 40, so that a system using 1640 subcarriers is generated. However, the 802.16a/e system uses 48 for the number subcarriers per subchannel and thus has an inferior property in collision between subchannels. The Galois Field will be described later in detail.

"However, in order to facilitate network design along with the development of communication systems, it is necessary to increase the number of identifiable cells up to 100. The OFDMA scheme has limitations in generating subchannels only in a frequency domain in terms of the number of identifiable cells.

"Further, a Flash-OFDM scheme using a narrowband of 1.25 MHz uses 128-point IFFT, and defines 113 hopping sequences that hop different subcarriers for one period comprised of 113 OFDM symbols, as a basic resource assignment unit. A communication system supporting the Flash-OFDM scheme (hereinafter referred to as a 'Flash-OFDM communication system') defines different hopping frequencies for 113 cells in designing networks, thereby making it possible to identify 113 different cells. However, the Flash-OFDM scheme, being a narrowband-only scheme, cannot contribute to the required capacity increase."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "It is, therefore, an object of the present invention to provide a subcarrier assignment apparatus and method in an OFDMA communication system.

"It is another object of the present invention to provide a time-frequency 2-dimensional subcarrier assignment apparatus and method in an OFDMA communication system.

"It is further another object of the present invention to provide a subcarrier assignment apparatus and method for identifying base stations in an OFDMA communication system.

"It is yet another object of the present invention to provide a subcarrier assignment apparatus and method for minimizing collisions between subchannels used in neighbor base stations in an OFDMA communication system.

"It is yet another object of the present invention to provide a subcarrier assignment apparatus and method for acquiring diversity gain in an OFDMA communication system.

"In accordance with an object of the invention, a method of assigning subchannels of a transmitter in a communication system is provided. The method includes: dividing an entire frequency band into m subcarrier groups; mapping each of the m subcarrier groups to a subcarrier group index, wherein a subchannel includes n subcarriers selected from each of the m subcarrier groups corresponding to a subcarrier group index sequence, determining that a first data is needed to transmit in a first timing point; and assigning a first subchannel in the first timing point using a first subcarrier group index sequence. The first subcarrier group index sequence is different from a second subcarrier group index sequence used for assigning a second subchannel in a second timing point, and the first subcarrier group index sequence is generated by interleaving corresponding to: .PI.(k)=(a*.beta.+k)mod(Q-1) for .beta.=0, . . . , Q-2, where .PI.(k) represents an interleaving formula, .beta. represents a subchannel index of the first subchannel, k represents locations of the subcarriers included in the first subchannel, a represents an integer, and (Q-1) represents a number of subcarriers in each subchannel.

"In accordance with another object of the invention, a method of receiving data of a receiver in a communication system is provided. The method includes: dividing an entire frequency band into m subcarrier groups; mapping each of the m subcarrier groups to a subcarrier group index, wherein a subchannel includes n subcarriers selected from each of the m subcarrier groups corresponding to a subcarrier group index sequence; and receiving data using a first subchannel. The first subchannel is assigned in a first timing point using a first subcarrier group index sequence by a transmitter, when the transmitter determines that a first data is to be transmit in the first timing point, the first subcarrier group index sequence being different from a second subcarrier group index sequence used for assigning a second subchannel in a second timing point by the transmitter. The first subcarrier group index sequence is generated by interleaving corresponding to: .PI.(k)=(a*.beta.+k)mod(Q-1) for .beta.=0, . . . , Q-2, where .PI.(k) represents an interleaving formula, .beta. represents a subchannel index of the first subchannel, k represents locations of the subcarriers included in the first subchannel, a represents an integer, and (Q-1) represents a number of subcarriers in each subchannel.

"In accordance with another object of the invention, an apparatus for assigning subchannels in a communication system is provided. The apparatus includes: a subchannel assigner for assigning a first subchannel in a first timing point using a first subcarrier group index sequence when a transmitter determines that a first data is to be transmitted in the first timing point. An entire frequency band is divided into m subcarrier groups, each of the m subcarrier groups is mapped to a subcarrier group index, a subchannel includes n subcarriers selected from each of the m subcarrier groups corresponding to a subcarrier group index sequence. The first subcarrier group index sequence is different from a second subcarrier group index sequence used for assigning a second subchannel in a second timing point, and the first subcarrier group index sequence is generated by interleaving corresponding to: .PI.(k)=(a*.beta.+k)mod(Q-1) for .beta.=0, . . . , Q-2, where .PI.(k) represents an interleaving formula, .beta. represents a subchannel index of the first subchannel, k represents locations of the subcarriers included in the first subchannel, a represents an integer, and (Q-1) represents a number of subcarriers in each subchannel.

"In accordance with another object of the invention, an apparatus for receiving data in a communication system is provided. The apparatus includes: a receiver for receiving a data using a first subchannel. When an entire frequency band is divided into m subcarrier groups, each of the m subcarrier groups is mapped to a subcarrier group index, a subchannel includes n subcarriers selected from each of the m subcarrier groups corresponding to a subcarrier group index sequence. The first subchannel is assigned in a first timing point using a first subcarrier group index sequence by a transmitter when the transmitter determines that a first data is to be transmit in the first timing point, the first subcarrier group index sequence is different from a second subcarrier group index sequence used for assigning a second subchannel in a second timing point by the transmitter, and the first subcarrier group index sequence is generated by interleaving corresponding to: .PI.(k)=(a*.beta.+k)mod(Q-1) for .beta.=0, . . . , Q-2, where .PI.(k) represents an interleaving formula, .beta. represents a subchannel index of the first subchannel, k represents locations of the subcarriers included in the first subchannel, a represents an integer, and (Q-1) represents a number of subcarriers in each subchannel.

"In accordance with another object of the invention, a method of assigning subchannels by a transmitter in a wireless communication system is provided. The method includes: generating subcarrier groups by classifying subcarriers; interleaving at least one of the subcarrier group corresponding to a predetermined interleaving formula; constituting a subchannel using the interleaved subcarrier group; and assigning the constituted subchannel for transmission. The predetermined interleaving formula is expressed as: .PI.(k)=(a*.beta.+k)mod(Q-1) for .beta.=0, . . . , Q-2, where .beta. represents a subchannel index, k represents locations of the subcarriers included in .beta. subchannel, a represents an integer, and (Q-1) represents a number of subcarriers in each subchannel.

"In accordance with another object of the invention, an apparatus for assigning subchannels in a wireless communication system is provided. The apparatus includes: a subchannel assigning means for generating subcarrier groups by classifying subcarriers, constituting a subchannel using at least one interleaved subcarrier group; and assigning the constituted subchannel for transmission; and an interleaving means for interleaving at least one subcarrier group among the generated subcarrier groups corresponding to a predetermined interleaving formula. The predetermined interleaving formula is expressed as: .PI.(k)=(a*.beta.+k)mod(Q-1) for .beta.=0, . . . , Q-2, where .beta. represents a subchannel index, k represents locations of the subcarriers included in .beta. subchannel, a represents an integer, and (Q-1) represents a number of subcarriers in each subchannel."

URL and more information on this patent, see: Hwang, In-Seok; Yoon, Soon-Young; Sung, Sang-Hoon; Cho, Jae-Hee; Huh, Hoon. Apparatus and Method for Assigning Subchannels in an OFDMA Communication System. U.S. Patent Number 8223704, filed January 30, 2009, and issued July 24, 2012. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=44&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=2154&f=G&l=50&co1=AND&d=PTXT&s1=20120717.PD.&OS=ISD/20120717&RS=ISD/20120717

Keywords for this news article include: Internet, Broadband, Data Transmission, Local Area Network, Wireless Technology, Wireless Communication, Digital Signal Processing, Samsung Electronics Co. Ltd.